Hydrocarbon gas. Use of plant hydrocarbon gases
In the post-Soviet space, the term “LPG” usually evokes an association with propane-butane and its use as fuel for autonomous gasification systems of facilities. However, in reality liquefied petroleum gas- this is a much wider range of hydrocarbons, which, in addition to propane and butane, includes methane, ethylene, isobutane and their mixtures.
LPG terminology
In world practice, liquefied propane-butane is usually called petroleum gas (LPG), since these hydrocarbons are by-products in the oil refining process. In Russia, it is also customary to include light hydrocarbon raw materials, such as butylene and propylene fractions, in the CIS. Liquid natural gas has a separate classification. It is abbreviated as LNG or liquefied methane, since the basis of natural gas is CH4.
Despite this division, in state documentation and standardization one name is mainly used - “Liquefied hydrocarbon gases”, which includes both CIS and LNG. Although, taking into account the development of the industry for the production and marketing of liquefied natural gas, it is possible that in the near future separate standards will be developed for the storage, transportation and operation of LNG.
In general, based on the analysis of the chemical composition, it is correct to include all products with a hydrocarbon base as LPG, ranging from synthetic liquid fuel, ethylene, isobutane and ending with the popular mixture of propane and butane. By the way, you can read why these components are mixed.
Properties and abilities of liquefied propane, butane and methane
The main difference between LPG and other types of fuel is the ability to quickly change its state from liquid to gaseous and back under certain external conditions. These conditions include ambient temperature, internal pressure in the tank and volume of the substance. For example, butane liquefies at a pressure of 1.6 MPa if the air temperature is 20 ºС. At the same time, its boiling point is only -1 ºС, so in severe frost it will remain liquid, even if the cylinder valve is opened.
Propane has a higher energy content than butane. Its boiling point is -42 ºС, so even in harsh climatic conditions it retains the ability to rapidly form gases.
Methane has an even lower boiling point. It turns into a liquid state at -160 ºС. For domestic purposes, LNG is practically not used, but for import or transportation over long distances, the ability of natural gas to liquefy at a certain temperature and pressure is of significant importance.
transportation by tanker
Any liquefied petroleum gas has a high expansion coefficient. So, a filled 50-liter cylinder contains 21 kg of liquid propane-butane. When all the “liquid” evaporates, 11 cubic meters of gaseous substance are formed, which is equivalent to 240 Mcal. Therefore, this type of fuel is considered one of the most efficient and cost-effective for autonomous heating systems. You can read more about this.
When operating hydrocarbon gases, it is necessary to take into account their slow diffusion into the atmosphere, as well as the low flammability and explosiveness limits when in contact with air. Therefore, you need to be able to handle such substances correctly, taking into account their properties and special safety requirements.
Properties table
Liquefied petroleum gas - why it is better than other types of fuel
The industry for using LPG is quite wide, which is due to its thermophysical characteristics and operational advantages compared to other types of fuel.
- Transportation.
The main problem of delivering conventional gas to populated areas is the need to lay a gas pipeline, the length of which can reach several thousand kilometers. To transport liquefied propane-butane, the construction of complex communications is not required. For this purpose, ordinary cylinders or other containers are used, which are transported by road, rail or sea transport over any distance. Considering the high energy efficiency of this product (with one SPB cylinder you can cook food for a family for a month), the benefits are obvious.
- Produced Resources.
The purposes of using liquefied hydrocarbons are similar to the purposes of using main gas. These include: gasification of private facilities and settlements, production of electricity through gas generators, operation of vehicle engines, production of chemical products.
- High calorific value.
Liquid propane, butane and methane are very quickly converted into a gaseous substance, the combustion of which releases a large amount of heat. For butane - 10.8 Mcal/kg, for propane - 10.9 Mcal/kg, for methane - 11.9 Mcal/kg. The efficiency of thermal equipment that runs on LPG is significantly higher than the efficiency of devices that use solid fuel materials as raw materials.
- Easy to adjust.
The supply of raw materials to the consumer can be regulated both manually and automatically. For this purpose, there is a whole range of devices responsible for the regulation and safety of liquefied gas operation.
- High octane number.
SPB has an octane rating of 120, which makes it a more efficient feedstock for internal combustion engines than gasoline. When using propane-butane as a motor fuel, the overhaul period for the engine increases and the consumption of lubricants is reduced.
- Reducing costs during gasification of populated areas.
Very often, LPG is used to eliminate peak load on main gas distribution systems. Moreover, it is more profitable to install an autonomous gasification system for a remote settlement than to build a network of pipelines. Compared to laying network gas, specific capital investments are reduced by 2-3 times. By the way, more information can be found here, in the section on autonomous gasification of private facilities.
Summing up the article, we can conclude that liquefied hydrocarbons have a wide range of useful properties, which has made them a fairly popular product in many areas of industry. For domestic needs, propane-butane is an indispensable raw material, since it allows you to cook food and heat homes even in the most remote areas. Moreover, ordering its delivery is not at all difficult. Just follow this link and select the product you need.
USE OF PLANT HYDROCARBONS GASES. FUEL AND COMPLEX PROFILE PLANTS
CHAPTER VIII
USE AND PROCESSING OF PLANT HYDROCARBONS GASES
CHARACTERISTICS OF GASES
All processes of destructive processing of petroleum raw materials are accompanied by the formation of hydrocarbon gases. The yield of these gases averages 5-20% of the raw material. During deep processing, a modern oil refinery with a capacity of 12 million tons of oil per year produces approximately 1 million tons (i.e., over 8% by weight) of gaseous hydrocarbons. In this regard, pyrolysis occupies a special place among destructive processes, where gas rich in light olefins is the target product. In this case, after extracting ethylene, propylene and butylene-butadiene fraction, a saturated part of the gas also remains, which during the pyrolysis of gases is mainly recycled, and during the pyrolysis of gasoline and other liquid raw materials it leaves the gas fractionation unit.
Gas yields during the main catalytic processes of processing petroleum feedstock are very significant: catalytic reforming produces 10-20% (wt.) of gas from the feedstock (including 1 to 2% hydrogen); with catalytic cracking, the gas yield is 12-15% (wt). In table 39 gives the approximate composition of gases formed during the main oil refining processes.
For processes occurring under hydrogen pressure (reforming, isomerization, hydrocracking, hydrotreating), the composition of gases is relatively simple and, like natural and associated gases, is characterized by the absence of unsaturated hydrocarbons. At the same time, all thermal and some catalytic processes produce gases of a more complex composition, with a higher or lower content of unsaturated hydrocarbons. The concentration of unsaturated hydrocarbons depends to some extent on the composition of the raw material, but is mainly determined by the severity of the regime, and for catalytic cracking, by the catalyst used. For example, continuous coking of tar under normal conditions (530-
540 °C) produces gas with “30% (mass) of unsaturated hydrocarbons, and raising the temperature to 600 °C increases the amount of unsaturated hydrocarbons to almost 50%. The transition of catalytic cracking units to zeolite-containing catalysts caused a decrease in the overall gas yield.
In addition to the content of unsaturated hydrocarbons, factory gases are also characterized by the concentration of the “fatty” part - the C 3 -C4 fraction. The most valuable hydrocarbons of this fraction are iso-butane and butylenes, which are the raw materials for catalytic alkylation (production of the high-octane component of automobile and aviation gasolines). Of least interest is the “dry” part of the gas - hydrogen, methane and the Cr fraction (ethane + ethylene). The hydrogen and ethylene contained in dry gas are valuable, but hydrogen is extracted only from reforming gas, since it is formed there in significant quantities and is separated in a high-pressure gas separator at the reformer itself (the rest of the gas contains only traces of hydrogen). The gases of the remaining processes, when mixed before purification and gas fractionation, contain hydrogen in a relatively small concentration.
Table 39. Composition of hydrocarbon gases during main oil refining processes
Gas composition, % (wt.)
Components | Thermal cracking under pressure | Slow motion coking |
continuous fluidized bed coking |
catalytic cracking of vacuum gas oil |
catalytic reforming of benzene^ |
heavy hydrocracking 1 | distillate raw materials e j |
||
tar® |
» ? I R th " 0JG.& § | on amorphous catalyst | ||||||
Hydrogen | ||||||||
Methane | ||||||||
Ethylene | ||||||||
Ethane | ||||||||
Propylene | ||||||||
Propane | ||||||||
n-Butylene | ||||||||
"n-Butane | ||||||||
Isobutane | 15, $ | |||||||
Isobutylene | ||||||||
Sum of unlimited |
a Data from A. N. Tarasov. ^Data by A.F. Krasyukov. in Data 3. I. Syunyaeva. d Data from V. N. Erkia. d Generalized data. e Data from S.P. Rogov.
centration. During deep oil refining, the yield of dry gases reaches 3-4.5% (mass), and their composition is approximately the following (% mass, per gas):
Hydrogen.....3.0-3.5 Ethane......“30
Methane......26-27 Propane + propylene. . 8.0-8.5
Ethylene........27-28 Fraction C*. . . . "5
Of course, the composition of dry gas at different plants varies depending on the profile of the plant and the ratio between the capacities of individual processes. The complexity of the technology for separating ethylene and hydrogen forces us to abandon this for now, and dry gas is usually used at the plant as a process fuel. However, it is possible that preliminary separation of the most valuable components from dry gas will be provided. M, Based on the relative concentration of the dry and fatty parts of the gas, thermal cracking gas under pressure H and coking gas, where the content of fractions up to and including Cr B is 35-60% (wt.), can be considered “dry”. On the contrary, catalytic cracking gases contain 60-75% C3-C4 hydrocarbons (see Table 39) - these are “fat” gases.
The resources of refinery gases are naturally related to the depth of oil refining at the refinery; During deep processing, rational use of gas is of especially great economic importance. The direction of processing of gas fractions is determined by the profile of the plant, especially taking into account the fact that the plant is usually a petrochemical complex in which oil refining processes are combined with the preparation of monomers for petrochemical synthesis or are accompanied by the petrochemical processes themselves (production of polypropylene, additives I
Some gas components are used directly by hydrocarbons at the plant: “dry” gas is usually a process fuel, hydrogen-containing reforming gas is necessary for hydronic processes (hydrotreating, hydrocracking). If hydrocracking units are included in the plant layout, the need for hydrogen cannot be satisfied by reforming alone, so part of the dry gas (usually methane and ethane) is subjected to conversion B to produce hydrogen. AND
Essential for the use of refinery gases is the complete selection of the most valuable components from their potential content, i.e., the efficient operation of gas separation plants. Most modern refineries have two gas separation units: for saturated gases and for unsaturated gases. Ш The joint separation of these gases is irrational, since the unsaturated components are more valuable, and they are easier to select with the greatest completeness from more concentrated mixtures. Gas diagrams
Table 40. Some physical constants of gaseous hydrocarbons
Hydrocarbon |
T. kip. at 760 mm Hg. Art., °С |
DENSITY |
Density of liquefied gas,* kg/m3 |
Critical temperature, |
pressure, |
569.9 (-103.4 °C) | |||||
Propylene | 609.5 (-47 °C) | ||||
Isobutylene |
626.8 (-6.8 °C) | ||||
a-Butylene |
|||||
zuigas-.r-Butylene |
|||||
cis-|3-Butylene | |||||
Isobutane | |||||
Acetylene | 615.4 (-80.3 °C) | ||||
Butadiene |
* The temperature at which the density of the liquefied liquid is determined is indicated in parentheses.
the separation of saturated and unsaturated gases may be similar or slightly different (depending on the profile of the plant, i.e., on the specific volume of both gases).
In table 40 shows some physical constants of gaseous hydrocarbons. The least volatile isomers are (5-butylene and n- butane. The critical temperatures of the components of the C4 fraction lie in the range of 134-163 °C, which indicates the possibility of liquefaction of these hydrocarbons at relatively low pressures and temperatures above 30-40 °C, accessible for water cooling. For example, n-butane at 40 °C has a pressure of 0.4 MPa, and at this temperature can be easily converted into liquid (even with water cooling at the top of the butane column). On the contrary, ethylene has a critical temperature of only +9.5 °C, i.e., water cooling is unsuitable for its condensation even at much higher pressure, and special refrigerants must be used.
PREPARATION OF GASES FOR PROCESSING
General principles and technological schemes for drying hydrocarbon gases and purifying them from hydrogen sulfide are set out in part I of the course “Oil and Gas Processing Technology” in relation to natural and associated gases. Mentioned below are only those preparation methods that are typical for plant hydrocarbon gases.
Drying of factory gases is not always required. As a rule, it is used in cases where the gas is subjected to subsequent low-temperature rectification (for example, when isolating pure ethylene) or is sent directly for catalytic processing to an installation with a catalyst that is sensitive to moisture. At low rectification temperatures (up to -100 °C), water condensate will precipitate even with low gas humidity. For example, for hydrocarbon gas located at 0.MPa" with a water content of 2 g/m3, the dew point was l; 14 °C, and 1 PRI C0 G holding water 0.17 g/m 3 only -20 ° C, i.e. at temperatures below -20 ° C, the gas should have contained less than 0.17 g of moisture 1ag
1 m 3. An increase in pressure also necessitates deeper drying, since the pressure increases the dew point; for example, for the same gas, with an increase in absolute pressure from 0.7 to 3.5 MPa, the dew point increased from 14 to 39 °C, and 14 °C and 3.5 MPa, the maximum permissible moisture content was only 0.5 g/m3.
The degree of gas drying is determined not only by the possibility of water condensation, but also by the formation of hydrates. Hydrates! They are complex compounds of gas molecules with water. Hydrates of methane (CH 4 -6H 2 0), ethane (C 2 Hb-7H 2 0)) and D p are known. In appearance, the hydrates are voluminous crystalline; formations, depending on the composition, white or transparent, like ice. Hydrates are unstable and, with changes in temperature or temperature, easily decompose into gas and water.
It is characteristic that hydrates are able to form only at elevated pressures and temperatures above zero, and heavier hydrocarbons form hydrates more easily than low molecular weight ones. Thus, methane is capable of forming hydroxide at 12.5 °C and 10 MPa; ethane at the same temperature forms 1 HID p at under a pressure of only 2.5 MPa. Hydrates can exist only in the presence of excess moisture in the gas, i.e., when the partial pressure of water vapor in the gas phase is greater than the vapor pressure of the gas. Thus, the moisture content in the gas must correspond to the dew point at which in which the pressure of saturated water vapor will be less than the pressure of hydrate vapor at the ambient temperature.
Liquid moisture absorbers cannot reduce the dew point below minus 15 °C, and for reliable operation of the installation that fractionates pyrolysis gases, the dew point should not exceed minus^ gg_
minus 70 °C. Therefore, to dry pyrolysis gases, solid absorbers are used - mainly zeolites or zeolites with aluminum gel. Drying gases containing unsaturated hydrocarbons with adsorbents is complicated by the possibility of partial polymerization. tions of these components. In relation to pyrolysis gas, the preliminary separation of hydrocarbons C5 and C4, consisting partly of dienes, which polymerize most easily, is of exceptional importance. The content of 3-5% (wt.) C5 hydrocarbons in the gas leads to a rapid loss of adsorbent activity.
A necessary component of catalytic reforming installations is a unit for drying circulating hydrogen-containing gas. In ch. VI it was noted that in order to avoid deactivation of the catalyst (due to halogen leaching), the moisture content in the circulating gas is maintained within the range of (14-1.5) 10 ~ 3% (vol.).
Preliminary drying of the reforming feedstock is carried out in the stabilization column of the hydrotreating unit. Drying of the circulating gas occurs in one of two or more alternately operating adsorbers filled with acid-resistant (against HC1) zeolites. The time of continuous operation of the adsorber is 24-36 hours, after which the gas supply is switched to another adsorber, and the layer of spent zeolite is treated with hot inert gas (up to 350 °C). According to A.D. Sulimov, adsorbers for gas drying can be turned on only during the period when the reforming unit is brought into operation, as well as during catalyst regeneration.
As a rule, before sending factory gases for separation, they are purified. The purpose of purification is most often the removal of sulfur compounds, represented in petroleum gases mainly by hydrogen sulfide. The presence of hydrogen sulfide in gas is unacceptable due to: 1) the corrosive and toxic properties of hydrogen sulfide and 2) the poisonous effect on many catalysts. Since when processing sulfurous raw materials the concentration of hydrogen sulfide in the gas can be very significant, it is necessary not only to remove it from the gas, but also to use it to produce sulfur or sulfuric acid. If heavy gas components are received from a process plant in liquid form (under pressure), they are sometimes subjected only to alkali washing to remove sulfur and acid compounds. To purify hydrocarbons in the gas phase, aqueous solutions of ethanolamines, phenolates and other reagents are used. The most common cleaning methods are ethanolamines:
H 2 N-C 2 H 4 OH HN(C 2 H 4 OH) 2 N(C 2 H 4 OH) 3
monoethaiolamine diethanolamine triethanolamine
Gas purification with ethanolamines is a typical example of a circular sorption process (Fig. 101). In processes of this type, hydrogen sulfide is absorbed from the gas by a reagent solution in one apparatus and released from the solution as a result of its stripping in another apparatus. The reagent thus regenerated is returned to absorb hydrogen sulfide. Gas purification occurs by chemisorption of hydrogen sulfide with a 15-30% aqueous solution of ethanolamine. Sometimes a mixture of ethanolamine and ethanol is used or the gas is treated sequentially with these solvents. For example, in catalytic reforming installations of an older type (35-5), where hydrotreating of raw materials was carried out using ETS at TST, purification of the circulating gas with mono ethanolamine was provided, followed by washing with water and drying of DIE titanium.
lenglycol. T^xno^LO giche Purified CepoSodopol What is the factory cleaning scheme?
Rice. 101. Technological scheme for gas purification with a two-stage supply of monoethanolamine:
1 - absorber; 2 - absorbent refrigerators; 3 - pumps; 4 - heat exchangers; 5 - hydrogen sulfide refrigerator; 6 - desorber; 7 - monk.
gases, in principle, is not 0 different from that for natural gas.
Of the other amines, methyldiethanol^min^N-methylpyrrolidone ((cyclic amine) is used; pos^L0diy is recommended for ras 30Bj containing, in addition to hydrogen sulfide, a significant amount of carbon dioxide.
The main devices for purifying gases with liquid reagents are a plate-type or packed-type absorber and a stripping column (de-sorber). The absorber is made of carbon steel; it contains 10-20 plates or a nozzle made of Raschig rings. We also manufacture distillation columns for stripping hydrogen sulfide! yut ta. rail or attachment.
The heat required for steaming is introduced through an external boiler, usually heated with water steam. An important parameter is the temperature of the bottom of the desorber. Thus, for monoethanolamine, a steaming temperature of no more than 125 °C is recommended, since with increasing temperature the rate of application of this reagent rapidly increases. Due to the high temperature at the bottom of the stripping column and in the boiler, hydrogen sulfide corrosion is observed, so the tubes of the boiler are made of stainless steel (Art. 18-8); The lower part of the column also has a corresponding lining.
SEPARATION OF GAS INTO COMPONENTS
The composition of factory gases presented in table. 39 (p. 275), is typical for the entire gas (balance quantity) F obtained in a given process, i.e., it means that ) g etI . The zine fraction does not contain gaseous components - gasoline is stable. Practically separating the gas from the gas! NZ ina can be carried out in one or several stages.
For example, during catalytic reforming and hydrogenation processes, hydrogen-containing gas is separated in a high-pressure gas separator. The concentration of hydrogen in it is determined by the pressure and separation temperature: the higher the pressure and the lower the temperature, the greater the solubility of the hydrocarbon part of the gas in the catalyst and the “drier” (easier) the gas separated from the catalyst.
In the high-pressure gas separator, located according to the catalytic reforming installation diagram directly behind the heat exchangers and condensers, the pressure is almost the same as in the reactor block, for example 3 MPa; this ensures separation of the gas with 70-80% (vol.) hydrogen, and most of the hydrocarbon components remain dissolved in the catalyst. The compositions of the gas and liquid phases will be determined by the equilibrium relationships inherent in a given combination of temperature and pressure. In the next gas separator, due to the pressure drop, part of the hydrocarbon gas is released from the catalyst, but the heaviest part of it remains (mainly) in the catalyst, which must be stabilized. A similar picture is observed in hydrogenation plants.
In the catalytic cracking process, which occurs at a pressure close to atmospheric, the low pressure in the gas separator forces the use of a compressor, which receives gas. However, in this case, although the gas separator mode favors the separation of heavy components, the latter will partially remain in gasoline, and its stabilization will be required. At the same time, the gas leaving the gas separator captures the light fractions of gasoline, which must then be extracted from it.
Many of the modern schemes combine gas separation into components and gasoline stabilization.
For clear separation of gaseous hydrocarbons, rectification or a combination of rectification and absorption is required. The latter is necessary if there is a lot of “dry” part in the gas, especially methane. In this case, it is advisable to first separate the “dry” part by absorption, followed by separation of the remaining gas by rectification. With moderate methane content, the absorption unit can be excluded from the circuit. In Fig. 102 shows a diagram of this type, intended for the separation of limiting gases: wet gas and unstable head fraction from atmospheric distillation plants, as well as catalytic reforming gases.
All gaseous components (reformed hydrocarbon gas, straight gas) are compressed by a compressor TsK-1) followed by cooling in a water refrigerator XK-1 and ammonia refrigerator XK-2 up to 4 hours C. To liquefied gas in the collection S-4 unstable liquid stabilization distillates from AT and reforming units are added and the entire flow is directed to the deethanizer column K-1-
Column K-1 operates in the mode of incomplete condensation of the main product - methane-ethane fraction. Ammonia refrigeration
Rice. 102. Technological diagram of a gas fractionation unit (GFU):
TsK-1- gas compressor; XK-1- water refrigerator; ХК-2, ХК-3- ammonia refrigerators; ХК-4, ХК-5, ХК-6 - air coolers; S-1, S-2, S-3, S-4- separators-collectors of liquid gas; K-1 - deethanizer; K" 2 - debutanizer; K-3 - propane column; K-4 - isobutane column; E-1, E-2, E-3, E-4 - irrigation tanks; N-1, N-2- pumps.
Nick XK-3 cools the head strap to 0°C; At the same time, condensate (the heavier part of the dry gas - ethane) circulates in the form of irrigation, and the balance amount of dry gas leaves the top of the tank E-1. De-ethanized column residue K-1 enters the column for further separation K-2. Column K-2 serves to separate the propane-butane fraction from hydrocarbons Cs and higher. Column head strap K-2 after condensation and cooling, it partially serves as reflux for this column; the rest of the condensate enters the propane column K-3, where the propane fraction is separated. In the column K-4 division occurs n- and iso: butane.
Below are the main operating parameters of the columns of the described HFC and the number of trays in the columns:
Installations for gas fractionation by rectification are characterized by some features. The need for complete or partial condensation of the overhead stream forces distillation to be carried out under pressure, which is higher, the lighter the overhead stream. However, increased pressure makes separation difficult. For example, for a binary mixture of propane + isobutane, the relative volatility a at 100 °C and 2 MPa is equal to 1.7, and at the same temperature, but at 1 MPa it is already a = 1.9, i.e., separation is easier.
The subsequent use of gas components requires their fairly clear separation and high selection from the potential, which is why HFC columns contain a large number of trays. It is known that the permissible vapor velocity in the columns is a function of the difference in the densities of the hot reflux flowing from the plate and the vapors rising in the same section. Since increasing the pressure to 1-2 MPa increases the vapor density by 10-20 times (against separation conditions at atmospheric pressure), the permissible vapor velocities in HFC columns do not exceed 0.20-0.25 m/s.
The described HFC scheme is of little use if the gas is rich in methane, which is typical, for example, of thermal cracking and coking gases. In this case, in the reflux tank of the first column (de-ethanizer), due to the high partial pressure of methane, it is not possible to achieve even partial condensation of the gas. The column operates only as an evaporator, and the gas fractionation scheme must include a unit for preliminary absorption separation of the methane-ethane fraction, i.e., separate the gas using an absorption-distillation scheme (AGFU).
The use of conventional absorption is not effective enough, since absorption alone cannot achieve clear separation, and if a dry gas is selected at 100% of its potential content in the gas mixture, it will inevitably take with it a certain amount of heavier components. If we make sure that the C3 fraction is completely absent from the dry gas, part of the dry gas will leave along with the saturated absorbent and, when the latter is stripped, will end up in the C3-C4 fractions.
The most widely used device at present is called a fractionating absorber and combines the processes of absorption of the C3 fraction and desorption of dry gas (therefore, the fractionating absorber is sometimes called an absorber-desorber). The fractionating absorber is a combination column; the upper part receives cold absorbent, and the lower part receives heat. Wet gas is supplied to the middle part of the apparatus (Fig. 103). Typically, the apparatus has 40-50 plates, distributed approximately equally between the absorption and desorption sections. As a result, many
stepwise contact of gas and liquid phases in the upper h part of the apparatus, the heaviest part of the gas is absorbed; Flowing down, the saturated absorbent meets increasingly hot vapors desorbed from the liquid flowing into the lower part of the column. As a result, the top of the fractionating absorber leaves
dry gas containing Ci-C 2 hydrocarbons, and C 3 -3-C 4 hydrocarbons are removed from below along with the lean a&bsorbent.
Rice. 103. Fractionating absorber (deethanizer):
I - column; 2, 4 - absorbent refrigerators; 3 - pumps; 5 - boiling
The pressure in the fractionating absorber is usually maintained at 1.2 to 2.0 MPa, although in some cases it reaches 3 MPa. As the pressure increases, the absorption of gas components increases, but it should be borne in mind that an increase in pressure within the range of 1.2-2 MPa contributes little to the absorption of propane, and at the same time, the non-additional absorption of ethane (hydrocarbon equilibrium constants) increases significantly Cu-Cr decreases with increasing pressure to a greater extent than for C3-C hydrocarbons 4).
Below is a diagram of a unit for joint gas separation and catalytic cracking of gasoline, operated at one of the plants (Fig. 104). The main devices are a gas-fractionation absorber 3, stabilization column 8, propane column 11 w butane column 14.
Wet gas from the gas separator through the top of the drop separator / enters the cleaning unit A monueta-nolamine and then supplied by compressors to a gas fractionating absorber 3; Unstable gasoline is pumped there as irrigation from the bottom of the tank 2, as well as (slightly above the gas input) condensate formed as a result of compression of the wet gas, and liquid from the drop separator /.
The main absorbent supplied to the top of the absorber 3, serves unstable gasoline from a container 2\ In addition, stable gasoline is supplied (several plates higher) to absorb the carryover of unstable gasoline. The absorber has a system
three circulation irrigations to remove absorption heat; circulating streams are cooled in water coolers 4 and return to the plate above. Dry gas passes through a gas separator 5, where a certain amount of condensate is separated” and goes into the gas network of the plant.
Dry gas
1 - drop eliminator; 2, 10 - containers; 3 - gas fractionating absorber; 4 - circulating irrigation refrigerators; 5 - gas separator; 6 - tubular furnace (reboiler); 7 - heat exchangers; 8 - stabilizer; 9 - refrigerator-condensers; 11 - propane column; /2-. refrigerators; 13 - reboilers; 14 - butane column; A - monoethanol gas purification unit with amine; B - compressor; IN - unit for cleaning and drying the stabilization distillation; G- unit for alkalizing stable gasoline.
Deethanized gasoline with absorbed fractions C 3 -C4 is heated in heat exchanger 7 and fed into the stabilization column 8, the purpose of which is the debutanization of gasoline. Bake 6 (two-section) is a reboiler for columns 3 to 8. Stable gasoline passes through heat exchanger 7, gives off heat to unstable gasoline and the feedstock of the propane column, and is cooled in the refrigerator 12 and goes to the block G alkalization. The stabilization distillate (head) is condensed in the refrigerator-condenser 9 and from the container 10 partially pumped out to irrigate the column 8\ the balance amount of the distillate is sent sequentially for purification with monoethanolamine and alkali solution and for drying with diethylene glycol. Then the distillate, consisting mainly of fractions C3-C4, is sent to the column AND to separate the propane-propylene fraction, which is removed from the installation from the top of this column after condensation and cooling.
Remaining from the column 11 flows into the column 14, where a similar separation of the butane-butylene fraction occurs from the heavier residue (mainly the C5 fraction), which through the refrigerator 12 joins the stream of stable gasoline. In view of
Table 41. Characteristics of devices and technological mode of the gas fractionation plant
Absorber3 Column8 ColumnJ1 Column14
Indicators
Diameter, mm
Distance between plates, mm Pressure, MPa Temperature, °C
power supply section
Irrigation frequency
Note. Each column has 60 double-flow valve trays.
that the temperature of the bottom of the columns And and 14 relatively small (Table 41), they are heated by steam reboilers 13.
The described installation has a design capacity of 417 thousand tons per year, including 257 thousand tons of unstable gasoline and 160 thousand tons of wet gas. During operation, the productivity of the installation exceeded the design one. The purity of the propane-propylene fraction is 96%, butane-butylene 97%; selection from potential 82 and 95%, respectively; dry gas contained only 0.3% of the C4 fraction and almost 90% consisted of fractions up to C2 (inclusive).
Typically, in a rectification unit for unsaturated gases, the separation of fractions C 3 and C 4 is practiced without their subsequent separation into the saturated and unsaturated part. If the refinery provides for the polymerization of propylene or its use as a component of alkylation feedstock, the propane accompanying propylene does not have a harmful effect on these processes. Since propylene reacts completely, propane is then easily separated from the products. The same can be said about n- Bhutan. If the plant has a catalytic cracking unit, it is usually accompanied by an alkylation unit for isobutane with olefins; The ballast fraction in this process is n-butane, which is then separated from the catalyzate.
USE OF GAS COMPONENTS
Dry gas, propane-propylene and butane-butylene fractions leave the AGFU units of the unsaturated gas separation unit. Typical plant gases from unsaturated hydrocarbons contain only olefins: ethylene, propylene, butylenes. Hydrocarbons of higher unsaturation - acetylene, butadiene - are contained only in pyrolysis gases, and appear in thermal cracking gases only with a significant tightening of the regime.
By polymerizing gaseous olefins, a wide variety of products can be obtained - from light gasoline fractions to high molecular weight polymers, the molecular weight of which reaches two to three million.
In the 1930s, the process of selective catalytic polymerization of butylenes was widely used for the subsequent hydrogenation of the dimer (iso-CgHie) and thus obtaining technical isooctane, a component of aviation gasoline. This process subsequently lost its importance, as it was replaced by the catalytic alkylation of isobutane, contained in large quantities in catalytic cracking gases, with butylenes. Later, a process was introduced to produce polymer gasoline based on propylene, which was less scarce. Phosphoric acid supported on quartz is used as a catalyst. Polymerization is carried out at 220-230 °C, 6.5-7.0 MPa and a volumetric feed rate of raw materials from 1.7 to 2.9 h -1. Co-polymerization of propylenes and butylenes or butylenes and amylenes is also used.
Saturated hydrocarbons contained in the polymerization feed naturally do not react, but have a beneficial effect on the thermal balance of the reactor, preventing the reaction from proceeding too deeply, accompanied by the formation of heavier polymers. The heat of polymerization is “1550 kJ (370 kcal) per 1 kg of propylene. The polymer obtained from the butylene fraction (dimer) has the maximum octane number - about 90; gasoline - a product of propylene polymerization - has an octane number of approximately
10 below (80-82 by motor method). In terms of the chemical composition, polymer-gasoline, naturally, consists almost entirely of olefins, which determines its low chemical stability during storage and low acceptability to ethyl liquid; with the addition of 3 ml of TES, the octane number of polymer-gasoline increases by only 3-4 units.
The petrochemical industry's great demand for propylene forced it to abandon the use of this olefin for the production of polymer gasoline.
CATALYTIC ALKYLATION OF ISOBUTANE WITH OLEFINS
The essence of the process. The alkylation process involves the addition of an olefin to paraffin to form the corresponding hydrocarbon of a higher molecular weight. From the point of view of the molecular structure, the resulting alkyl paraffin can be considered as the original paraffin, in which one hydrogen atom is replaced by an alkyl group. However, the main reaction is accompanied by a number of side reactions, resulting in the formation of a more or less complex hydrocarbon mixture.
Various modifications of the alkylation process have been implemented in the petroleum refining industry. The most common installations are for the alkylation of isobutane with olefins (mainly butylenes) to produce a wide gasoline fraction - alkylate. Alkylate, consisting almost entirely of isoparaffins, has a high octane number (90-95 according to the motor method) and is used as a component of automobile and aviation gasoline. For some time, the product of benzene alkylation with propylene, isopropyl benzene (cumene), was also widely used as a high-octane component of aviation gasoline. Due to the continuous reduction in the production of aviation fuel for carburetor engines, cumene has lost its importance as a fuel component, but is used as an intermediate in the production of phenol and acetone. In the years
During World War II, another high-octane component, neohexane (2,2-dimethylbutane), was produced (in limited quantities) by thermal alkylation of isobutane with ethylene.
In 1932, V.N. Ipatiev showed the possibility of interaction of isobutane, previously considered an “inert” hydrocarbon, with olefins. AlCl was used as a catalyst. This reaction, then developed using other catalysts - sulfuric acid and later hydrogen fluoride - was quickly introduced into industry. The first industrial sulfuric acid alkylation units were put into operation in the late 30s, and hydrofluoric alkylation units in 1942. The target product at first was exclusively a component of high-octane aviation gasoline, and only in the post-war years did alkylation begin to be used to improve the motor qualities of commercial motor gasoline.
In the industrial alkylation process, it is easier and cheaper to obtain a high-octane component of gasoline than in the previously used process of catalytic polymerization of butylenes followed by hydrogenation of the dimer into isooctane. Replacing the selective polymerization of butylenes with catalytic alkylation of isobutane with butylenes provided the following advantages:
1) producing gasoline rich in isooctane in one stage instead of the two-stage process of polymerization - hydrogenation;
2) half the consumption of valuable olefins to obtain the same amount of high-octane component;
3) no hydrogen consumption for hydrogenation;
4) more complete involvement of olefins contained in plant gases; in alkylation, the olefins react completely, while in polymerization, the less active olefin (for example, n-butylene in the polymerization of a mixture of butylenes) remains partially unreacted.
However, catalytic alkylation of isobutane began to develop rapidly only as a result of the widespread introduction of catalytic cracking units. Catalytic cracking gas, rich in isobutane, provided alkylation units with one of the raw material components, and gases from thermal processes had to be used to produce olefins.
Main factors of the process. Only sulfuric acid and liquid hydrogen fluoride are used as industrial alkylation catalysts. The choice of these substances is due to their good selectivity, ease of handling of the liquid catalyst, relative cheapness, and long operating cycles of the plants due to the possibility of regeneration or continuous replenishment of the catalyst activity.
Only iso-structure paraffins containing an active tertiary hydrocarbon atom can be subjected to catalytic alkylation in the presence of sulfuric acid or hydrogen fluoride. In this case, the alkylation of isobutane with ethylene is difficult, apparently due to the stability of the resulting intermediate compounds - ethers. Alkylation with propylene and especially butylenes proceeds quite deeply. The acid concentration is decisive. Thus, for alkylation of isobutane with butylenes, 96-98% sulfuric acid can be used, but for alkylation with propylene, only 98-100% acid is used.
It is characteristic that as a result of the main reaction of addition of isobutane to the olefin, simultaneous structural isomerization occurs, which indicates the highest probability of a carbonium-ion chain mechanism. Along with the main alkylation reaction, in which 1 mole of isobutane is consumed by 1 mole of olefin, side reactions occur.
1. Hydrogen transfer, or self-alkylation. Thus, the interaction of isobutane with propylene partially proceeds in the following direction:
2iso-C 4 H 10 -j- C 3 H e -> iso-C 8 H 18 -j- C 3 H 8
This reaction is undesirable, as it causes increased consumption of isoparaffin and the formation of low-value propane.
2. Destructive alkylation. The primary alkylation products are cleaved, and the resulting olefin (different from the original) reacts again with the original paraffin, for example:
2"zo-C 4 H 10 + SdN, -> iso- C 5 H 12 + iso- S to H 14
3. Polymerization. Acid catalysts cause polymerization of olefins, therefore, an unfavorable regime for alkylation - low concentration of isoparaffin, insufficient catalyst activity and elevated temperature - causes the appearance of polymers in the composition of alkylation products.
During the alkylation process, gradual deactivation of the catalyst occurs - a drop in the acid concentration and its darkening, caused by the interaction of the acid with unsaturated hydrocarbons and moisture. Moisture may be contained in the raw material, and is also formed as a result of side reactions of olefins with. acid:
SlN 2P + H a S0 4< - ¦ ? - С Л Н 2Л _2 + 2Н 2 0 -t- so 2
As the acid concentration decreases, the target alkylation reaction is weakened and the proportion of polymerized olefins increases. The required acid concentration in the reaction zone is maintained by partially or completely replacing the spent acid with fresh acid.
The alkylation reaction proceeds with a positive thermal effect (“960 kJ, or 230 kcal per 1 kg of alkylate). To maintain the isothermal regime, the generated heat must be continuously removed from the reaction zone.
Thermodynamically, alkylation is a low temperature reaction. Temperature limits for industrial sulfuric acid alkydation are from 0 to 10 °C; alkylation in the presence of hydrogen fluoride is carried out at a slightly higher temperature - approximately 25-30 ° C. This difference is explained by the fact that at temperatures above 10-15°C, sulfuric acid begins to intensively oxidize hydrocarbons.
Lowering the temperature, although it slows down alkylation, increases its selectivity towards the formation of the primary alkylation product, and therefore the quality of the resulting alkylate improves. A decrease in temperature by 10-11 °C causes an increase in the octane number of the alkylate by approximately 1. An excessive decrease in temperature is limited by the solidification temperature of the acid catalyst, as well as by an increase in the viscosity of the catalyst and, therefore, the difficulty of dispersing it in the reaction mixture. The ability to carry out the reaction at a higher temperature is one of the advantages of hydrogen fluoride, as it simplifies the system for removing heat from the reaction mixture.
The pressure in the reactor is chosen so that all or most of the hydrocarbon feedstock is in the liquid phase. The pressure in industrial reactors averages 0.3-1.2 MPa.
The catalysts used cause the polymerization of olefins, so it is necessary that the concentration of olefins in the reaction mixture be significantly lower than required by the stoichiometric reaction equation. For this purpose, it is practiced
Table 42. Indicators and product yield in the production of alkylate - a component of motor gasoline
Data from O. Iverson and L. Shmerling
* Yield of depentanized total alkylate.
adding raw materials with a stream of isobutane continuously circulating in the system. The molar ratio of isobutane: olefin in the hydrocarbon mixture supplied for alkylation is usually (4-=-10) : 1; the most commonly used dilution is six or seven times. With an excess of isobutane, the quality of the alkylate increases and not only polymerization, but also side reactions of dealkylation are suppressed. Since the selectivity of the process increases with a large ratio of isobutane, the consumption of olefins per unit amount of isobutane is reduced. Increasing the isobutane:olefin ratio above 10:1 is ineffective. It should be taken into account that with an increased ratio of isobutane, operating costs for its circulation and cooling increase, and it is also necessary to increase the size of the main apparatus.
The intensity of mixing of the hydrocarbon phase and the catalyst is of great importance, due to the fact that their mutual solubility is very low. Obviously, the reaction occurs in the catalyst phase and at the phase boundary between isobutane dissolved in the catalyst and the olefin component of the feedstock. In the absence or deficiency of isobutane, contact of the olefin with the acid causes polymerization of the olefins. Intensive stirring also promotes the separation of the formed alkylate from the catalyst. The desire to increase the concentration of isobutane at the point of injection of the mixture led to the development of special mixing and circulation devices that make it possible to increase the concentration
the ratio of isobutane and olefin in the incoming mixture is up to 100: lH or more. From the data in table. 42 it can be seen that the ratio between I30 -H butane and olefin in the initial feed mixture should be close to theoretical. The highest octane number of alky-I lat is observed with butylene raw materials. I
The concept of reaction duration is conditional for this process, since, in accordance with the above, the reaction may not occur in the entire volume of the catalyst. The space velocity shock indicator usually taken as a basis and its reciprocal value are also relative. ConditionalThe duration of the reaction. IN
The volume of the catalyst should be taken as the volume of acid B dispersed in the reactor, since the rest of it, falling into the settling zone or not forming an emulsion and3 (due to not sufficiently intense mixing, will actually not catalyze alkylation. However, it is impossible to take into account this volume, and in this case the conditional space velocity is expressed by the volumetric amount of olefins supplied per hour per unit volume of catalyst.The space velocity largely depends on the intensity of mixing of the reaction mass, especially at the points where olefins are introduced. Insufficient mass exchange causes local overheating of the reaction mixture and a decrease in the quality of the alkylate.The average volumetric flow rate of olefins for sulfuric acid alkylation is 0.1-0.6 h -1.
The completeness of the reaction is ensured by a long stay of the hydrocarbon phase in the reactor of 5-10 minutes for fluorohydrogen alkylation and 20-30 minutes for sulfuric acid alkylation. In this case, the volume ratio of catalytic converter and hydrocarbon is taken equal to 1: 1 (this was established based on the presence in the reactor of a homogeneous emulsion of hydrocarbons in acid). An increase in the relative volume of acid does not harm the process! su, but increases the viscosity of the mixture and, accordingly, energy consumption! gies for stirring; a decrease in the proportion of acid leads to increased ! the formation of its emulsion in a hydrocarbon, leading to a deterioration in the Quality of the first alkylate and an increase in catalyst consumption. Ratio acid: hydrocarbon varies somewhat depending on the con- ? acid concentration, its density, raw material quality, reactor type \ etc. The above 1:1 ratio is average. I Industrial installations for sulfuric acid alkylation. In the oil refining industry, the most common process is sulfuric acid alkylation. Depending on the design of the reactor and the waste separation system, several options for the technological scheme of the installation are possible. It was noted above that the alkylation reaction proceeds with significant positive thermal effect.The generated heat is removed in two ways: 1) cooling the reaction mixture through the heat exchange surface; 2) cooling the mixture by partial evaporation. Accordingly, there are two types of reactors.
In Fig. 105 and 106 show sketches of the first type of reactors, the so-called contactors.
In Fig. 105 shows a vertical contactor (total height “11.7 m, internal diameter “2 m”) of an older type, designed for low throughput. The reaction mixture is cooled with ammonia or propane circulating through double tubes.
Hmdoagent1
Cool agent
Products
reactions
Acid
Raw materials
Rice. 105. Vertical contactor:
I- frame; 2 - cylindrical casing; 3 - tube bundle; 4-propeller pump.
Having exited through the open ends of the internal tubes, the liquefied gas passes into the outer annular gap and, evaporating, exits the system. Heat removal is controlled by changing the pressure in the cooling system. The reaction mixture is stirred with a propeller pump; The drive is an electric motor or a steam turbine. The working volume of the reactor is divided by a cylindrical partition; a mixture of hydrocarbons and acid, driven by a propeller pump, continuously circulates in the apparatus, rising along the annular section and descending through the inner cylinder, where heat is removed from it through the surface of the cooling tubes. To regulate the upward flow, vertical ribs are welded to the cylindrical partition.
In the horizontal contactor (Fig. 106), the input of raw materials and catalyst is carried out more successfully; they immediately enter the zone of the most intense mixing. Next, the mixture is pumped through the annular space and, at the opposite end of the apparatus, turns into the inner cylinder. The horizontal position of the device is arranged
Eliminates the need for gear transmission to the drive and facilitates maintenance of the contactor. Extremely intense circulation occurs in the apparatus; its multiplicity reaches 200 m 3 per minute in large installations. With such a circulation rate, the incoming mixture is almost instantly mixed with the emulsion filling the reactor. The ratio of isobutane: olefin at the point of entry of the feed stream reaches 500:1 or more. Horizon-
Rice. 106. Horizontal contactor:
1 - tube bundle; 2, 5 - circulation pipe; 3 - frame; 4 - propeller mixer:
6 - guide blades; 7 - turbine.
Steel contactors are structurally simpler. They also differ in that the reaction product stream is used as a coolant. Their capacity is larger than that of vertical devices, but it can only be increased to certain limits, since the use of very large contactors worsens the quality of mixing; Therefore, they prefer to install at least three or four contactors.
The power supply system of the devices is of great importance. Experience in operating sulfuric acid alkylation plants has shown that it is advisable to feed circulating isobutane and catalyst into the contactor in series, and it is better to feed the initial hydrocarbon mixture (isobutane and olefins) in parallel, distributing it into flows according to the number of contactors. In this case, the relative proportion of olefins in the reaction mixture decreases, which makes it possible to increase the selectivity of the process, reduce the consumption of sulfuric acid and improve the quality of the alkylate.
A similar change in the reactor power supply system at one of the alkylation units at the Grozny plant reduced* acid consumption by 35%. Sometimes, with such a scheme for operating contactors, additional parallel supply of acid is practiced. For example, in a system of four contactors, circulating isobutane passes in series, the original hydrocarbon
the flow is divided into four parallel ones, and the acid, having passed through the first and second reactors, is separated from the hydrocarbon phase in the settling tank and returned to the first reactor. Likewise, the third reactor receives acid from the settling tank serving the third and fourth reactors.
In reactors alkylated- By The intensity of stirring the reaction mixture is of great importance. Decrease E 91 temperature increases octa-~
13 p i Sh P id Temperature°?
Rice. 107. The effect of temperature on the octane number of an alkylate.
new alkylate number<§ 30
(Fig. 107). However, it has been shown that for a given number J 89 rpm (320-380 per minute), the temperature should not be lower than 10-11°C, since with a further decrease in temperature, the viscosity of the reaction emulsion increases so much that a greater number of stirrer revolutions is required. Thus, the reaction temperature and the stirrer speed must be in an optimal combination - in particular, for vertical contactors, 8 ° C is recommended - and 500-520 rpm with a contact time of 8-10 min *.
Modern high-power plants are best suited to a cascade reactor (Fig. 108). This is a reactor of the second type, where the mixture is cooled due to its partial evaporation. A cascade reactor is a horizontal cylindrical apparatus with several displacement sections equipped with stirrers and a two-section settling zone. Circulating isobutane and sulfuric acid enter the first mixing section; the feedstock - a mixture of isobutane and olefins - is evenly distributed across all sections, due to which a significant excess of isobutane is provided in each zone. The diagram of the mixing section is shown in Fig. 109. Above the mixers there are coils for introducing raw materials and vertical perforated pipes for circulation of the emulsion. The direction of emulsion flow can be seen in Fig. 109.
The accepted pressure regime in the reactor is as follows: in the first mixing section 0.15-0.20 MPa, pressure drop across each section 0.01-0.02 MPa; The average olefin flow rate is approximately 0.3 h-1. In the last two sections, the acid is separated from the hydrocarbon layer. The temperature and pressure in the reactor ensure partial evaporation of the hydrocarbon phase, mainly the lightest component - isobutane. Having evaporated
The resulting gas is sucked off by a compressor and, after cooling and condensation, is returned to the reaction zone. The released heat of reaction is removed due to the heat of evaporation of isobutane. The temperature in the reactor is maintained at a given level automatically.
A cascade reactor can have from three to six mixing sections. There are installations with a reactor in which there are six mixing sections (three on each side) and one settling zone located in the middle part of the apparatus. At one of the largest sulfuric acid alkylation plants with a capacity of up to 950 m 3 of alkylate per day, two
Rice. 108. Horizontal cascade type reactors: A- five-section; b- double;
1 , 2, 3, 4, 5 - sections; b - acid settling zone; 7 - alkylate withdrawal zone; 8 - capacity of Nzobutane.
5-stage reactor with a diameter of 3.5 m and a length of 22 m.
The presence of cascade reactors operating on the “auto-cooling” principle simplifies and reduces the cost of alkylation plants, as it allows one to eliminate the need for refrigerant (ammonia, propane). A comparison of the specific consumption of sulfuric acid in reactors of the described designs indicates the advantages of a cascade reactor; for a vertical contactor this flow rate is achieved
Rice. 109. Mixing section of the cascade reactor:
1, 2 - reactor sections; 3 - stirrer; 4 - circulation pipes.
200-250 kg per 1 ton of alkylate, in cascade 60-100 kg/t. The octane number of the target product (light alkylate) in the first case is 90-91 (by the motor method), in the second it is 92-95. However, cascade reactors have some disadvantages: the sections are interconnected, and a violation of the regime in one of them can lead to a breakdown in the operation of the apparatus as a whole; As the emulsion moves, the concentration of isobutane decreases.
The schematic flow diagram of the sulfuric acid alkylation plant is shown in Fig. 110. This scheme is characterized by a complex separation unit consisting of four distillation columns: propane, isobutane,
butane and secondary alkylate distillation columns. The initial hydrocarbon mixture is cooled by evaporating butane in a refrigerator and enters in five parallel streams into the mixing sections of the reactor; circulating isobutane and sulfuric acid are also supplied to the first section. Sulfuric acid leaves the settling zone of the reactor (for circulation or discharge) To a hydrocarbon mixture that is neutralized with alkali and washed with water.
Part of the hydrocarbons evaporated in the reactor is supplied to the compressor through the droplet breaker. 2, which feeds it through the refrigerator into a container and a propane column 3. This column serves to separate and remove propane from the system to prevent its gradual accumulation in the system. The remainder of the propane column - isobutane - is partially circulated through the feed cooler and compressor intake 2, and partially joins the general flow of circulating isobutane. Main hydrocarbon stream from settling tank 5 sent to the isobutane column 6 for separation of recirculating isobutane. The head of this column - isobutane - is returned to the first mixture -
Original
carbonsZorods
"4 p Yu
Etc.-^Heavy
alkylate
Alkali+baud
Rice. 110. Technological scheme for sulfuric acid alkylation of nzobutane with olefins:
1 - reactor; 2 - compressor; 3 - propane column; 4 - irrigation tanks; 5 - settling tank; 6 - isobutane column; 7 - butane column; 8 - secondary distillation column; 9 - coalescing apparatus; 10 - separator.
body section of the reactor. If there is some excess of fresh isobutane in the feedstock, its removal is provided. The remainder of the iso-butane column goes for further separation into butane column 7, and the remainder of the butane column goes into the column 8 for alkylate distillation. From the top of this column, vapors of the target fraction (light alkylate) leave, and from the bottom - heavy alkylate, boiling above 150-170 ° C and usually used as a component of kerosene.
In table 43 presents data on the distillation columns of a large alkylation plant and their operating mode. For clear separation of products, the columns are equipped with steam reboilers and, as can be seen from the table, have a significant number of plates. Instead of a circulating isobutane stream, the isobutane column strip can be depropanized. The advantage of such a system is a slightly higher concentration of propane in the feedstock of the propane column, which facilitates the release of propane.
In many modern sulfuric acid alkylation plants, the hydrocarbon stream leaving the reactor is purified with bauxite and only then neutralized with alkali and washed with water. This purification is necessary to separate the esters formed under the action of the catalyst. When treated with alkali, only part of the acidic products is neutralized, and the most persistent of the esters either decompose when heated and cause gradual sludge formation in the distillation system and corrosion, or end up in the commercial alkylate and reduce its anti-knock properties.
To remove these harmful impurities, the hydrocarbon stream after the reactor is directed sequentially into a coalescing apparatus filled with glass wool and into one or two columns filled with bauxite. The purpose of the coalescing apparatus is to remove the smallest droplets of acid contained in the hydrocarbon stream. Bauxite columns operate alternately: from 500 to 1500 m of alkylate can be passed through 1 kg of bauxite (depending on the degree of its contamination with ethers), after which the hydrocarbon stream is switched to the second column. The removal of traces of sulfuric acid and esters by bauxite is based on the selective adsorption of these polar compounds. The attrition of bauxite is judged by the beginning of desorption - the release of neutral esters containing sulfur along with the alkylate. Contaminated bauxite is blown with water vapor and washed
Table 43. Dimensions and technological parameters of distillation columns in a sulfuric acid alkylation plant
Data from V. P. Sukhanov
water and dried by passing hydrocarbon gas through it. The hydrocarbon stream purified by bauxite is subjected to alkaline and water washing. Due to the introduction of bauxite purification into the alkylation scheme, the continuous operation of the installation increases and exceeds 8 months.
The intensity of mixing the emulsion in the reactor has a decisive influence on the formation of esters; At high stirring intensity, the esters decompose. Analysis of the operation of industrial installations showed that the minimum content of esters in the total alkylate was observed at a sulfuric acid concentration of 89-92% (wt.) (Fig. 111). The presence of a minimum is explained by the fact that at a higher acid concentration, its interaction with olefins increases, i.e., the formation of esters is also activated. At excessively low acid concentrations, its selectivity as an alkylation catalyst decreases, and esters leave with the alkylation products.
96 94 92 90 88 8$
Concentration H2S0 4.% (wt.)
Rice. 111. Dependence of the content of esters in the total alkylate on the concentration of sulfuric acid:
1 - alkylation of isobutane with butylene; 2 - alkylated isobutane with propylene.
The purity and absence of moisture in the alkylation feedstock are of great importance. It was shown that by reducing the moisture content of the raw material from 0.03 to 0.001% (wt.), it is possible to reduce the consumption of sulfuric acid by 16 kg (per 1 ton of alkylate). The combination of settling tanks placed on the flow of cooled raw materials in front of the reactors with adsorption removal of moisture should provide a significant economic effect.
As a result of side reactions, the alkylate, as a rule, contains more or less heavy fractions - boiling above 170 ° C, i.e. above the end boiling point of commercial gasoline. In this regard, a secondary alkylate distillation column is required. The yield of heavy alkylate under normal conditions does not exceed 5%. The concentration of isobutane in the reaction zone is of decisive importance. Since the reaction outcome is determined by the composition of the reactor effluent, it is important that a high concentration of isobutane is maintained in this effluent.
The presence of inert diluents (n-butane and propane) deteriorate the quality of the alkylate, and the purity of the isobutane used for circulation plays a very important role. Thus, with all other operating parameters being equal, an increase in the concentration of isobutane in
the hydrocarbon stream coming from the reactor from 40 to 70% (vol.) caused an increase in the octane number of the total alkylate from 90 to 92.8; Moreover, in the first case, the difference between the octane numbers of the total and light alkylate was 0.9, and in the second it was only 0.3, which indicates that the yield of the light alkylate was approaching 100%.
The disadvantage of sulfuric acid alkylation is the rather significant consumption of sulfuric acid due to its dilution by reaction byproducts. The lowest acid consumption is observed if pure butylenes are used as olefin feedstock; When using propylene, acid consumption increases approximately threefold. As shown above, acid consumption is also related to the intensity of stirring of the reaction mixture and to temperature, an increase in which increases the degree of dilution of the acid. Acid consumption also increases if the raw material contains impurities such as sulfur compounds and moisture. Catalyst costs can be reduced by using spent acid for other purposes (for example, for purifying oils and other petroleum products), as well as by regenerating it.
Industrial installations of hydrofluoric alkylation. At foreign plants, alkylation units with hydrogen fluoride as a catalyst are quite widespread. Liquid hydrogen fluoride is more active than sulfuric acid and, due to its volatility (boiling point 20 °C), is easier to regenerate. Another advantage of this catalyst is its lower density (? 1.0 versus 1.84 for sulfuric acid). This facilitates the formation of an emulsion of the catalyst with the hydrocarbon phase in the reactor and even eliminates the need for mechanical stirring. The concentration of the catalyst used is 90%, and it has a relatively small effect on the yield and quality of the alkylate. However, the catalyst regeneration system is quite complex.
In Fig. 112 shows a schematic flow diagram of a hydrofluoride alkylation plant. The feedstock undergoes bauxite drying in columns 1 and enters the reactors 2. Tubular type reactors with water cooling are used, since the reaction proceeds at 20-40 °C. In some installations, the reactors are structurally combined with settling tanks. A special feature of hydrofluoride alkylation installations is the presence of a catalyst regeneration system. After settling from the main volume of HF, the alkylate enters the regenerator column 4, where the circulating isobutane is separated as a side stream. Regenerator column 4 heated below by circulating the residue through the oven 3. In this case, isobutane, propane and the catalyst are stripped from the alkylate. At. heating the residue to 200-205 °C also destroys organic fluorides formed
as by-products of the reaction. From the top of the regenerator column 4 Propane, hydrogen fluoride and some isobutane leave in the gas phase. After condensation, part of this mixture is returned to the reactors, part is fed to the column reflux 4, and the rest is sent to the propane column 6, from the top
Rice. 112. Scheme of a plant for the alkylation of isobutane with olefins in the presence of hydrogen fluoride:
1 - drainage columns; 2 - reactors; 3 - bake; 4 - regenerator column; 5 - settling tank; 6 - propane column; 7 - steam heater. .
which leaves stripped hydrogen fluoride, and from the bottom - propane
with traces of isobutane.
For a more complete recovery of the catalyst, regeneration (in a separate block) of part of the acid layer from the settling tank is also provided. Alkylate from the bottom of the column 4 after cooling, it passes through bauxite columns, where it is freed from the remainder of fluoride compounds. As a result of good regeneration, catalyst consumption does not exceed 1 kg per 1 ton of alkylate.
Due to its toxicity and significant volatility, the use of a hydrogen fluoride catalyst requires strict precautions. Continuous automatic monitoring is carried out over points of possible leakage of hydrogen fluoride: in water flows cooling reactors and condensers, in acid refrigerators, etc. The area where acid pumps and devices containing acid are located is considered dangerous, and can only be entered in special acid-resistant costumes and masks. Much attention is paid to the selection of materials and designs of equipment, equipment and pipelines. Special gasket materials made from HF-resistant substances - organofluorine plastics - are used. In areas of greatest corrosion, Monel metal is used, and the main equipment is made of carbon steel.
At US oil refineries, sulfuric acid alkylation predominates, but by the beginning of 1977, the share of hydrofluoric alkylation had already reached 40% of the total (by raw materials) versus 30.6% in 1970. The relatively faster growth in the capacity of alkylation units with hydrogen fluoride is explained by the improvement of the process design . For example, in some installations where only butylenes are used as olefins, HF and propane stripping columns are excluded from the scheme, and the stripping of the isobutane column is directly returned to the process. Installations are described where mixing of raw materials with acid is carried out in a riser (large-diameter vertical pipes connecting the outlet fittings of acid coolers with the inlet fitting of the reactor). At the same time, the reactors themselves are devoid of mixing devices, which eliminates the destruction of the apparatus from the corrosive effect of hydrogen fluoride.
Increasing alkylation feedstock resources. Alkylation feedstock resources are limited. Isobutane is found in significant concentration only in catalytic cracking and hydrocracking gases; it can also be isolated from associated gas. Butylenes are contained in gases of catalytic, thermal cracking and coking and are absent in gases obtained during hydrogenation processes.
Isobutane resources can be increased by isomerization n- butane on catalysts related to catalysts for the isomerization of C5-Sb hydrocarbons. Isomerization unit n- butane can be combined with an alkylation unit - with total%r isobutane column.
To expand olefin resources, the propylene fraction is involved in the alkylation process or subjected to dehydrogenation n- butane. However, on the one hand, an alkylate based on propylene or a mixture of it with butylenes has a lower octane number: when using only propylene - by about 5 units. On the other hand, propylene is a valuable petrochemical raw material, and the dehydrogenation of m-butane is often carried out to obtain butadiene, a raw material for the production of synthetic rubber. It is possible that the resources of C 3 -C 4 olefins will increase due to the increasing tendency towards heavier pyrolysis feedstocks and a tightening of the regime of catalytic cracking units.
USE OF HYDROGEN SULFIDE CONTAINED IN PLANT HYDROCARBONS GASES
Hydrocarbon gases from plants processing sour crude oils contain hydrogen sulfide. Part of this hydrogen sulfide is formed during thermal or thermocatalytic destruction of the most stable sulfur compounds contained in petroleum feedstock, during its thermal and catalytic cracking and coking. In this case, the sulfur contained in the raw material is distributed among the products of the process. During hydrogenation processes, a deeper destruction of sulfur compounds occurs: most of them are converted into hydrogen sulfide and concentrated in gas.
In table Figure 44 shows the approximate yield of dry gas and the content of hydrogen sulfide in it during the main destructive processes of processing petroleum feedstock. It can be seen that there is only one hydrocracking unit for high-sulfur fuel oil with a capacity of 1 million tons per year. will give from 2200 to 7700 tons of hydrogen sulfide per year.
Hydrogen sulfide produced from process plants is typically used in refineries to produce sulfur and sometimes to produce sulfuric acid. The most common industrial method for producing sulfur based on factory and natural gases is the Claus process, carried out in two stages: 2H 2 S -f 30 2 h-^ 2S0 2 + 2H a O 2H 2 S + S0 2 h = * 2/xS x+ 2H a O
The first reaction occurs without a catalyst - hydrogen sulfide is burned with a lack of air (to avoid further oxidation of S0 2 to S0 3). The volume of air entering the combustion zone must dbiTb be strictly dosed in order to ensure the required ratio of S0 2 and H 2 S for the second stage of the process. The temperature in the furnace for burning H 2 S, depending on the concentration of H 2 S and hydrocarbons in the gas, is 1100- 1300 °C. The furnace is usually a cylindrical horizontal apparatus. So, in an installation designed to produce l; 145 tons of sulfur per day, the furnace-reactor had a diameter of 3.66 m and a length of 10.7 m. Gas burners were mounted along the length of the furnace or at one of the ends. A horizontal lattice transfer wall is placed along the axis of the furnace for better gas mixing.
The formation of sulfur begins already in the first reactor. The second stage reaction takes place over a catalyst - aluminum oxide. The installation diagram is shown in Fig. 113. Hot gases from reactor furnace 1 pass through the waste heat boiler 3, Where they cool-
Table 44. Gas output and hydrogen sulfide content V during the main destructive processes of processing sulfur and high-sulfur oils
Data Ya. G. Sorkina
Gas yield for raw materials, % (wt.) | ||
Thermal cracking of 40% sulfur residue | ||
Catalytic cracking of vacuum gas oil at high | ||
sour oil |
||
Delayed coking of 28% cracked residue |
||
mixtures of oriental oils | ||
Hydrotreating of diesel fuel from sulfur | ||
Hydrocracking of fuel oil.high sulfur oil | ||
Thermal contact cracking of high-sulfur tar | ||
Arlan oil |
Note. Gas yield and HaS content are referred to “dry gas*, i.e., “excluding stabilization distillation.” "
up to approximately 450 °C, so that the sulfur remains in the gas phase (the condensation temperature of sulfur vapor is “300 °C). Next, the gas is additionally
Rice. 113. Scheme for sulfur production (Claus process):
I- furnace-reactor; 2 - blower; 3 - waste heat boiler; 4 - acid gas heater; $, 8 - reactors with catalyst; 6 - economizer; 7, 0 - scrubbers; /0 - sulfur collection; it- commercial sulfur capacity.
cooled thoroughly in a heat exchanger 4 (not lower than 340 °C), and the gas mixture enters the reactor 5, containing a catalyst.
The interaction of Hg5 and S0 2 is favored by low temperatures, therefore, the reaction is exothermic. Therefore, the catalytic part of the process, in turn, is divided into two stages (reactors 5 and 8 ). Reactor inlet temperature 5 about 340 °C, in reactor 8 about 265 °C; the temperature rise in each reactor is approximately 40 °C; the volumetric flow rate of gas supply to the catalyst is 850 h -1.
Hot gases after the reactor 5 a water economizer 6 and a scrubber 7 with a nozzle pass through, where further cooling of the gases occurs and their separation from condensed sulfur, which flows in the form of a melt from the bottom of the scrubber into the collection 10. Gases from scrubber 7 are reheated in the heater 4 and reactor 8 and scrubber pass in a similar way 9, from where liquid sulfur is also poured into a collection tank 10. Both scrubbers are sprayed with molten sulfur.
The resulting sulfur has a high degree of purity. Most of it is used to produce sulfuric acid. If for this purpose you use not sulfur as a feedstock, but directly hydrogen sulfide, it will be more expensive. In addition, sulfur is easily transported to sulfuric acid production sites, which may not coincide with refinery locations. Sulfur is also used in the rubber industry, medicine, for the production of carbon disulfide and in other sectors of the national economy.
Hydrocarbon gases
. Composition of liquefied hydrocarbon gases
LPG is understood as such individual hydrocarbons or mixtures thereof, which at normal temperatures. conditions are in a gaseous state, and with a relatively small increase in pressure without a change in temperature or a slight decrease in temperature at atmospheric pressure it turns into a liquid state.
Under normal conditions, the only saturated hydrocarbons (C n H 2 n +2) are methane, ethane, propane, and butane. At O 0 C, ethane condenses into liquid when the pressure increases to 3 MPa. Propane up to 0.47 MPa, N-butane up to 0.116 MPa, Isobutane up to 0.16 MPa. Let's consider which hydrocarbons turn into a liquid state with a relatively small decrease in temperature and atmospheric pressure; propane and butane are suitable for practical use. Along with normal saturated hydrocarbons, there are isomeric compounds that differ in the nature of the arrangement of carbon atoms, as well as in some properties. The isomer of butane is isobutane.
Structure and type of N-butane
CH 3 -CH 2 -CH 2 -CH 3
Isobutane:
In addition to the limiting ones, the composition of LPG also contains a group of unsaturated ones. Or unsaturated hydrocarbons, characterized by double or triple bonds between carbon atoms. These are ethylene, propylene, butylene (normal and isomeric). The general formula of unsaturated hydrocarbons with a double bond is C n H 2 n. Ethylene C2H4 CH2=CH2. To produce liquefied hydrocarbon gases, fatty natural gases are used, i.e. gases from oil and condensate fields containing large amounts of heavy hydrocarbons. At gas processing plants, propane-butane fraction and gas gasoline (C5H12) are released from these gases. Technical propane and butane, as well as their mixtures, are liquefied gas used to supply gas to consumers.
Technical gases differ from pure gases by containing small amounts of hydrocarbons and the presence of impurities. For technical propane, the content of C3H8 + C3H6 (propylene) d.b. Not<93%. Содержание С2Н6 +С2Н4 (этилен) не >4%. The content of C4H10+C4H8 is not >3%.
For technical butane: C4H10+C4H8 d.b. Not<93%. С3Н8 +С3Н6 не>4%. С5Н12+С5Н10 not >3%.
For a mixture of those butane and propane content: C3H8+C3H6, C4H10+C4H8 d.b. Not< 93%. С2Н6 +С2Н4 не>4%. С5Н12+С5Н10 not >3%.
2. Technical liquefied gases. LPG brands
The composition of liquefied gases used in gas supply is selected taking into account the climatic conditions where it is used. And it is determined by the requirements of GOST 20448 “Liquefied hydrocarbon fuel gases for municipal and domestic consumption. Technical conditions". The composition is selected so that at low temperatures in winter the vapor pressure of the mixture is sufficient for normal operation of the regulators. And at high temperatures in summer it did not exceed the maximum pressure for which cylinders and tanks for LPG are designed. According to GOST, the saturated vapor pressure of the mixture should be not less than 0.16 MPa at t=+45 0 C. If liquefied propane can be used at temperatures from -35 to +45, then butane in conditions with natural evaporation cannot be used. used at temperatures below 0, although at t >0 it has a significant advantage over propane. Therefore, by selecting the composition of liquefied gas, the desired properties can be obtained.
GOST for LPG establishes 3 brands of liquefied gas:
1) A mixture of propane and butane technical winter SPBTZ
2) A mixture of propane and butane technical summer SPBTL
) Technical butane
The division of a mixture of propane and butane into winter and summer grades is associated with external ts that determine the elasticity of us. vapors of liquefied gases located in cylinders or underground tanks.
In winter, as part of the mixture d.b. more propane and propylene, in summer their quantity may be reduced. For the same purpose, the maximum content of butane and butylene in the mixture is limited, because at low temperatures they have low vapor pressure.
Taking into account the optimal elasticity of saturated vapors, GOST provides for the content of propane and propylene in the winter grade not<75% по массе. А в летней марке и бутане техническим содержанием этих компонентов не нормируется. Сумма бутанов и бутиленов в зимней марке не нормируется, в летней не >60%, in technical butane not<60% по массе. Ограничение в составе сжиженных газов содержания лёгких компонентов (этан, этилен) связано с тем, что наличие значительного количества этих углеводородов приводит к резкому увеличению упругости паров. Например, при 35 0 C упругость насыщенных паров этана достигает 4,9 МПа. В то же время наличие незначительного количества легких компонентов в сжиженном газе повышает общее давление насыщенных паров смеси, что обеспечивает в зимнее время нормальное газоснабжение потребителей.
The presence of a significant amount of pentane is also unacceptable, because this leads to a sharp decrease in saturated vapor pressure and an increase in the dew point (the condensation temperature of pentane is about 3 0 C).
3. LPG property
There are 3 possible states of liquefied gas in which they are stored and used:
1) In the form of a liquid (liquid phase)
2) Steam (vapor phase), i.e. saturated vapors present together with liquid in a tank or cylinder.
) Gas (when the pressure in the vapor phase is lower than the saturated vapor pressure at a given temperature).
The properties of liquefied gases easily change from one state to another, making them a particularly valuable source of gas supply, because They can be transported and stored in liquid form and burned as gas. That. During transportation and storage, predominantly liquid phases are used, and during combustion, gaseous phases are used.
The elasticity of saturated gas vapors is the most important parameter by which the operating pressure in cylinders and tanks is determined. The pressure and temperature of liquefied gases strictly correspond to each other.
The elasticity of saturated LPG vapors varies proportionally to the temperature of the liquid phase and is a strictly defined value for a given temperature.
All equations relating the physical parameters of a gaseous or liquid substance include absolute pressure and temperature. And the equations for technical calculations of the strength of the walls of cylinders and tanks include excess pressure.
In its gaseous composition, LPG is 1.5-2.1 times heavier than air. In a liquid state, they are almost 2 times lighter than water.
The latent heat of vaporization is very insignificant (approximately 116 kW/kg), so the heat consumption for evaporation of liquefied gas is 0.7% of the potentially contained thermal energy. The viscosity is very low, which ensures transportation of LPG through pipelines, but at the same time favors leaks. They are characterized by low air flammability limits (2.3% for propane, 1.7% for butane).
The difference between the upper and lower limits is negligible, so when compressing them, the air-liquefied gas ratio can be used. It has low ignition temperatures compared to most flammable gases (510 0 C for propane and 490 0 C for butane). Condensation may form when the temperature drops to the dew point or when the pressure increases. Liquefied gases are characterized by a low boiling point and therefore, when evaporated during a sudden exit from a pipeline or tank into the atmosphere, they are cooled to a negative temperature. The liquid phase coming into contact with unprotected human skin can lead to frostbite. The nature of the effect resembles a burn.
Unlike most liquids, which slightly change their volume when the temperature changes, the liquid phase of LPG quite sharply increases its volume with increasing temperature (16 times more than water).
The compressibility of liquefied gases compared to other liquids is very significant. If the compressibility of water is taken as one, then the compressibility of oil is 1.56, and propane is 15. If the liquid phase occupies the entire volume of the tank, then when the temperature increases, there is nowhere for it to expand, and it begins to compress. The pressure in the tank increases. Pressure increase d.b. no more than the permissible calculated value, otherwise an accident is possible. Therefore, when filling tanks and cylinders, it is planned to leave a vapor cushion, i.e. do not fill them completely. The amount of steam cushion for underground tanks is 10%, for underground and cylinders 15%.
Liquefied gases have a higher volumetric calorific value than natural gases (approximately 3 times higher).
Liquefied gases are non-toxic, but their low flammability limits and slow diffusion into the atmosphere, combined with their lack of odor, color and taste (both in liquid and gaseous form), dictate the need for their odorization.
4. Advantages and disadvantages of LPG
As a fuel, liquefied gases have all the advantages of natural gases. In addition, for them you can additionally note:
The ability to create the necessary supply of gas in liquid form for the consumer.
2. Easy to transport
Release of the greatest amount of heat during combustion
LPG contains no corrosive substances
Availability of use in any form and under any conditions
Disadvantages of LPG:
Variability of composition and heat of combustion during natural evaporation
2. Small values of the lower limit of the ignition limit
The density of propane and butane is greater than the density of air, which in case of leaks causes accumulation of LPG in low places and creates explosive situations
Low flash point
Possibility of frostbite for service personnel in emergency situations
High coefficient of volumetric expansion
5. State diagrams of liquefied gases
To calculate processes and equipment, it is necessary to know the relationship between various LPG parameters with sufficient accuracy. This can be done using state diagrams. From them you can determine:
Vapor pressure at a given temperature
2. Pressure of superheated vapors under given conditions
Specific volume and density of liquid, vapor and gas phases; their enthalpy
Degree of dryness and humidity of vapors
Heat of vaporization
The work of compression by a compressor and the increase in temperature during compression
The effect of cooling liquid and gas when pressure is reduced (throttled)
Gas flow rate from the nozzles of gas burner devices
The phase diagram is constructed on a grid of horizontal lines of constant absolute pressure and vertical lines of constant enthalpy. The following points and lines are plotted on the diagram grid.
) Point “K” of the critical state of a given hydrocarbon in terms of critical pressure and temperature.
2) Borderline curve of PLC, passing through the point of critical condition and dividing the diagram into 3 zones:
I. Characterizes the liquid phase
II. Vapor-liquid phase. Gas phase
The LC branch characterizes the state of saturation of liquid at various pressures, and the CP branch characterizes the state of saturated vapor at these pressures.
4) Lines of constant temperature are depicted by a broken line TEML with a horizontal section EM (constant pressure and temperature during boiling of the liquid phase). Temperature isotherms above the critical point of a given hydrocarbon are depicted by T’E’ curves
) Lines of constant specific volumes (isochores)
OB - in the liquid phase region
O'B' - in the region of the vapor-liquid phase
B’B’’ - in the gas phase region
The same lines correspond to constant density
Point O on the LC boundary curve shows the specific volume of the liquid phase.
Point B’ on the control point - vapor phase located in tanks or cylinders under operating conditions
) Lines of constant entropy AD, A’D’ (adiabats). They are used to determine the parameters of hydrocarbons when they are compressed in a compressor and when they flow out of the nozzles of gas burner devices
The pressure of the liquid and vapor phase in a closed volume at a given temperature is determined by the point of intersection of the isotherm with one of the boundary curves KM or KP.
The pressure at the intersection point of M and E will be the desired one. If the isotherm does not intersect the boundary curve, this means that at a given temperature the gas will not turn into a liquid state, and its pressure can be determined if its specific volume is known, for example, the isobar at the point of intersection of the T’E’ isotherm and the B’B isochore.”
The specific volume of a saturated liquid or vapor can be determined by the temperature or pressure at the point of intersection of a given isobar or isotherm with the boundary curves of the KM liquid or KP vapor. The specific volume of a gas is determined by the pressure and temperature at the intersection point of the corresponding isobars and isotherms.
The enthalpy of the liquid vapor and gas phase is determined on the x-axis at given values of pressure and temperature at the point of intersection of isobars with boundary curves, lines of constant dryness or isotherms.
The heat of vaporization at a given pressure is determined as the difference in enthalpies at points E and M of a given isobar with common boundary curves
The degree of steam dryness X is determined by L isobar with a curve of constant steam dryness at a given enthalpy.
When calculating processes, auxiliary lines are drawn on the diagram. So, when throttling the liquid phase from P start to P end, a vertical MS line is applied (the process occurs without heat supply or removal). The temperature at the end of throttling is determined at point C. The intersection of the steam dryness curve with the Pcon isobar shows how much steam is formed during throttling. Gas compression is represented on the diagram by adiabats. The gas temperature at the end of compression is determined by the isotherm passing through point D'. The theoretical work of compression of 1 kg of gas is determined by the difference in heat content at points D’ and A’.
The actual work of compression will be somewhat greater and is determined by the formula
Adiabatic efficiency of the compression process (0.85-0.9)
6. Mixtures of gases and liquids. Recalculation of mixture composition
liquefied petroleum gas supply
The composition of liquefied gas in the liquid and vapor phases can be expressed by mass g i, volume fractions y i and molecular fractions for gases r i, for liquids X.
Where m i is mass, kg
Vi - volume, m 3
N i is the number of moles of the i-th component in the mixture.
For gas (ideal mixtures) the mole and volume fractions are equal, this follows from Avogadro’s law
Conversion of the composition of liquefied gas from one type to another is carried out as follows:
For liquid mixtures:
A) with a known mass composition of the components, the volumetric and molar composition is determined by the formulas
Where ρ i and M i are density and molar mass, respectively
B) for a given volumetric composition, mass and molar composition are found according to the formulas
C) with a known molar composition, mass and volume are determined by the formulas
D) For gas mixtures, conversion from molar to mass is carried out according to (5), and from mass to volumetric and molar according to (1) and (2).
7. Determination of properties of LPG
With a known composition of liquefied gas, the pressure of the mixture can be calculated using the formulas:
The density of a gas mixture of a given composition is determined:
Mole fraction of the i-th mixture component
Density of the i-th mixture component, kg/m 3
It is found according to the table or calculated according to Avogadro’s law:
Where is the molecular weight of the i-th component, kg/kmol
Molecular volume of the i-th component, m 3 /kmol
The average density of a liquid mixture with a known mass composition is determined by the formula:
With a known molecular composition:
,
Where is the density of the i-th component included in the liquid mixture in the liquid phase, kg/l
The density of the gas mixture at elevated pressure is found from the equation of state for real gases.
,
Where is the absolute pressure (MPa) and t-pa of the mixture.
Gas constant of the mixture, (J/kg K)
z-compressibility coefficient, taking into account the deviation of real gases from the values of ideal gases.
The gas constant of the mixture is calculated from the universal gas constant and the molecular weight of the mixture.
The compressibility coefficient is determined from the graph depending on the given parameters (pressure and temperature) of the gas.
The average critical pressure and temperature for a mixture of gases is determined by its composition.
Volume of gas obtained during evaporation of the LPG mixture, m.b. found by the formula:
Mass of the i-th mixture component, kg
Molecular mass of the i-th component of the mixture, kg/kmol
V Mi - molecular volume of the i-th component
To calculate the lowest volumetric combustion temperature of an LPG mixture, the following relationship is used
Lower volumetric heat of combustion of the i-th component, kJ/m 3
Lowest mass combustion temperature
The flammability limits of LPG mixtures that do not contain ballast impurities are determined:
L cm - lower or upper limit of ignition of a gas mixture.
Lower or upper flammability limit of the i-th component.
. LPG overflow schemes. LPG movement due to level differences
There are a number of methods for moving liquefied gas from railway or tank trucks to stationary containers. And vice versa, filling transport containers and cylinders from stationary storage facilities. The properties of LPG, being boiling liquids, with low density and vaporization temperature, determine the specificity of the method of circuits and equipment for moving.
LPG is moved:
due to the difference in levels
compression of gases
by heating or cooling
using a compressor
using a pump
mutual displacement of liquid
Due to the difference in levels
The use of hydrostatic pressure is used when filling underground tanks from railway and road tankers, as well as when filling LPG into cylinders, if the terrain allows. To drain tanks into a tank, it is necessary to combine their vapor and liquid phases.
In communicating vessels, the liquid is established at the same level, so the liquid phase will flow into the lower reservoir.
To create a sufficient drain rate, at the same temperature and pressure, in the tank and reservoir it is necessary that, due to hydrostatic pressure, a pressure difference of at least 0.7-0.1 is created.
The minimum required hydrostatic head under these conditions will be 14-20 meters of liquid.
In winter, the tank has a lower temperature than the reservoir, i.e. P of gas in the tank will be less than in the reservoir.
Therefore, to drain, the level difference must compensate for this pressure difference
,
Where is the gas pressure in the tank, Pa
Gas pressure in the tank
Density of the liquid phase of LPG, kg/m 3
In summer, at the initial moment of drainage, it is possible to locate the tanks below the reservoir. But here the temperature in the tank will be influenced by the hotter liquid from the tank, and the pressure drop will drop to approximately 0. The drainage will stop. Therefore, in summer, when draining, the vapor phases of the tank truck and the tank do not need to be connected.
"+" method:
Simplicity of the circuit
2. Lack of mechanical units
Reliable operation of all components
The circuit is ready for operation at any time, regardless of the presence of an external energy source
"-" method:
Inability to use terrain with mountainous terrain.
2. Long process duration.
Large losses of gas when sending it back in the form of vapors in drained tanks.
9. Gas filling stations
GNS are the basis for supplying systems with gases and supplying consumers with liquefied gases coming from gas-gasoline plants.
The following are performed on the GNS. works:
· -reception of liquefied gases from the supplier
· -compressor drain gases to their storage facilities
· - storage of LPG in above-ground, underground or isothermal tanks, in cylinders or underground voids.
· - draining unevaporated residues from the cylinder and compressed air. gas from cylinders with a number of malfunctions
· -compressed oil spill gas into cylinders, mobile tanks and tank trucks
· -reception of empty and delivery of filled cylinders
· - transportation of compressed air. gases through the internal pipeline network
· -repair of cylinders and their re-examination
Maintenance and repair of equipment at the station
In some cases, the GNS produces:
· -refueling of vehicles running on liquefied gas. gas from a petrol pump
· -mixing of gas vapors with air or low-calorie gases
· - delivery of compressed vapors. gas of gas-air and gas mixtures in the mountains. distribution systems
To perform these operations, the GNS has the following. divisions and workshops:
· -discharge overpass of a railway line or tr-input with disconnecting devices
· - LPG storage base, consisting of above-ground or underground tanks operating under pressure, isothermal. tanks
· - pumping and compression shop for draining LPG from railway tanks into storage facilities and supplying it for filling
· -workshop for filling cylinders and draining unevaporated heavy residues from them
· - warehouse for a daily supply of empty and filled cylinders
· -columns for filling tank trucks
· -communications of liquid and vapor phases, connecting all sections of the gas pumping station and ensuring their movement.
Depending on the volume of storage facilities and the method of installation of tanks, these distances range from 40 to 300 m.
Literature
1. Abramochkin E.G.: Modern optics of Gaussian beams. - M.: FIZMATLIT, 2010
2. Alekseev G.V.: Optimization in stationary problems of heat and mass transfer and magnetic hydrodynamics. - M.: Scientific world, 2010
Amusya M.Ya.: Photon absorption, electron scattering, vacancy decay. - St. Petersburg: Science, 2010
Antonov V.F.: Physics and biophysics. - M.: GEOTAR-Media, 2010
Bankov S.E.: Electromagnetic crystals. - M.: FIZMATLIT, 2010
Barabanov A.L.: Symmetries and spin-angle correlations in reactions and decays. - M.: FIZMATLIT, 2010
Belokon A.V.: Mathematical modeling of irreversible polarization processes. - M.: FIZMATLIT, 2010
Boboshina S.B.: General physics course. - M.: Bustard, 2010
Breuer H.-P: Theory of open quantum systems. - Izhevsk: Institute of Computer Research, 2010
Vinogradov E.A.: Thermally stimulated electromagnetic fields of solid bodies. - M.: FIZMATLIT, 2010
Virchenko Yu.P.: Random sets with Markov refinements in one-dimensional immersion space. - Belgorod: BelSU, 2010
G.P. Berman et al.; lane from English E.V. Bondareva; under scientific ed. S.V. Kapelnitsky: Magnetic resonance force microscopy and single-spin measurements. - Izhevsk: Izhevsk Institute of Computer Research, 2010
Golenishchev-Kutuzov A.V.: Photonic and phononic crystals. - M.: FIZMATLIT, 2010
Dyachkov P.N.: Electronic properties and applications of nanotubes. - M.: BINOM. Knowledge Laboratory, 2010
Features of the use of liquefied petroleum gas (LPG) in the form of a mixture of propane with butane and its component liquefied natural gas (LNG) methane in automotive gas equipment.
There are two gas compositions widely used for automobiles: propane and methane. Which one is better, cheaper, more technologically advanced and more reliable? Let's figure it out so that after reading there is no doubt.
Equipment for methane is used in only 25% of cars; the remaining 75% of cars are equipped with propane. At the same time, methane is often installed on commercial vehicles, where the choice is made not by the driver, but by the organization that owns the vehicle. Let's look at the reasons for this ratio in the LPG market.
An autoblogger examines the features of propane and methane in a fifteen-minute video: which is better for a car, the main difference
Features of propane-butane (CIS)
Propane is a carbon gas, a by-product of oil production. It is odorless, transparent and harmless to humans. Odorants are also added to it so that in case of leaks it can be smelled. Chemical formula - C 3 H 8.
At gas stations we see the inscription “propane-butane”. Butane is also a carbon gas that is released under similar conditions. It is mixed with propane in order to achieve the desired octane number. Moreover, at different times of the year the compositions change: in winter there is more propane, and in summer there is butane.
It is stored in cylinders in a car in liquefied form. That is, it is liquid, not gaseous - it “flops” in the cylinder. Also a big advantage is the working pressure, which is only 14 atmospheres. It requires containers made of lighter metal and the walls of the cylinder are much thinner. Nowadays, toroidal cylinders in the shape of a donut, which are placed in place of the spare tire, are most widespread. In this case, the cylinder does not take up space in the trunk, but you have to sacrifice a spare tire.
With average equipment, when fully refueled, you can travel 650...850 kilometers, which is four times more than your opponent.
Propane consumption is 11...13 liters per 100 km on an average car with a 1.6 liter engine on the 4th generation of LPG.
The equipment costs twice as much. In our experience, nine out of ten gas installation companies specialize in propane.
Lots of gas stations. Another big plus is that there are tens of times more gas stations using propane.
Engine power loss is lower, about 5...10%.
Propane benefits:
- Cheap equipment.
- There are a lot of companies that service and install.
- Low pressure.
- Stored in liquefied form.
- Lightweight and compact equipment, can be installed in the spare tire slot.
- More mileage.
- Less power loss of about 5...10%.
Cons of propane:
- Propane is about 3 rubles per liter more expensive than methane. Propap costs 17 rubles versus 14 per liter of methane.
- More explosive than methane. If the cylinder is damaged, it does not evaporate so quickly into the atmosphere.
Propane, although it costs a little more, has a lot of advantages and the prevalence of refills.
Compatibility of LPG and LNG with the latest generations of gas equipment
And finally, about another disadvantage of methane - incompatibility with the fifth and sixth generations of gas equipment. Propane can work with these generations, but methane cannot and most likely cannot.
In the 5th and 6th generations, gas is supplied liquid to the fuel injection system and is similar to gasoline. Propane is stored in cylinders in liquid form, and methane in gaseous form. Therefore, the installation of methane is only possible up to the 4th generation of equipment. The latest generations provide consumption approximately equal to gasoline consumption. In this case, virtually no power is lost. The engine can be started immediately on gas even at sub-zero temperatures.
- - [A.S. Goldberg. English-Russian energy dictionary. 2006] Topics: energy in general EN hydrocarbon gases ...
Facility using liquefied petroleum gases- (LPG), an industrial and municipal production facility that provides storage and (or) sale of LPG, transportation of LPG through gas pipelines to the consumer, as well as its use as fuel in hazardous... ... Official terminology
facility using liquefied and hydrocarbon gases (LPG)- An industrial and municipal production facility that provides storage and (or) sale of LPG, transportation of LPG through gas pipelines to the consumer, as well as its use as fuel in hazardous production... ... Technical Translator's Guide
liquefied hydrocarbon gases- LPG Liquefied hydrocarbon mixtures of propane, propylene, butanes and butenes with admixtures of hydrocarbon and non-hydrocarbon components, obtained by processing natural gas and oil, used as motor fuel, for municipal... ... Technical Translator's Guide
liquefied hydrocarbon gases- 32 liquefied hydrocarbon gases; LPG: Liquefied hydrocarbon mixtures of propane, propylene, butanes and butenes with admixtures of hydrocarbon and non-hydrocarbon components, obtained by processing natural gas and oil, used as... ... Dictionary-reference book of terms of normative and technical documentation
Liquefied petroleum gases- The “LPG” request is redirected here; see also other meanings. Household 45 kg LPG cylinders in New Zealand Liquefied petroleum gases (LPG) (English ... Wikipedia
re-evaporate liquefied hydrocarbon gases- - Topics oil and gas industry EN regasify ... Technical Translator's Guide
Natural gases- (classification) occur and manifest themselves in different ways. geol. and geochemical conditions, very diverse in chemical comp. and physical properties. The classifications of G. p. are known: Vernadsky (1912, 1934), Sokolov (1930), Khlopin and Cherepennikov (1935), Belousov... ... Geological encyclopedia
Associated petroleum gases- hydrocarbon gases accompanying oil and released from it during separation. The amount of gases (in m3) per 1 ton of extracted oil (the so-called gas factor) depends on the conditions of formation and occurrence of oil fields and can... ... Great Soviet Encyclopedia
ASSOCIATED PETROLEUM GASES- hydrocarbon gases accompanying oil and released during its production in gas and oil fields. These gases are dissolved in oil and are released from it due to a decrease in pressure when the oil rises to the surface of the earth. IN… … Chemical encyclopedia