Coal hydrogenation method. Solid fuel hydrogenation Bituminous coal hydrogenation

Hydrogenation coal processing is the most versatile direct liquefaction method. Theoretical basis the effects of hydrogen on organic compounds under pressure were developed at the beginning of the 20th century. Academician V.N. Ipatiev. The first extensive studies on the application of hydrogenation processes to coal processing were carried out by German scientists in the 1910-1920s. In the period 1920-1940s. in Germany, a number of industrial enterprises were created based on this technology. In the 1930-1950s. pilot and industrial installations for the direct liquefaction of coal by the hydrogenation method were built in the USSR, England, the USA, and some other countries.

As a result of hydrogenation processing, the organic mass of coal is dissolved and saturated with hydrogen to a degree depending on the purpose of the target products. The production of commercial motor fuels is ensured by processing the liquid products obtained at the first (liquid-phase) stage using vapor-phase hydrogenation methods.

During the liquid-phase hydrogenation of coal in the temperature range of 300-500 ° C, the complex matrix of coal is destroyed, accompanied by the rupture of chemical bonds and the formation of active free radicals. The latter, being stabilized by hydrogen, form molecules of a smaller size than the initial macromolecules. Recombination of free radicals also leads to the formation of high molecular weight compounds. The hydrogen required to stabilize the radicals is partly provided through the use of hydrogen donor solvents. These are compounds that, interacting with coal, are dehydrogenated at high temperatures, the atomic hydrogen released in this process is added to the products of coal destruction. The hydrogen donor solvent is also a pasting agent. To be in the liquid phase of the hydrogenation process, it must have a boiling point above 260 ° C. Condensed aromatic compounds, primarily tetralin, have good hydrogen-donor properties. Higher-boiling compounds of this group (naphthalene and cresol) are less active, but when they are mixed with tetralin, a synergistic effect arises: a mixture of equal parts of tetralin and cresol has a higher donor ability than each separately.

In practice, it is not individual substances that are most widely used as hydrogen donor solvents, but distillate fractions of coal liquefaction products with a high content of condensed aromatic compounds. Harmful impurities in solvents are polar compounds, for example phenols, as well as asphaltenes, the content of which should not exceed 10-15%. To maintain the donor properties, the circulating solvent is hydrogenated. With the help of a solvent, it is usually possible to "transfer" to coal no more than 1.5% (mass.) Of hydrogen. An increase in the conversion depth of the organic mass of coal is achieved by introducing gaseous molecular hydrogen directly into the reactor.

On the basis of numerous studies, it has been established that coal of low stages of metamorphism is preferable for hydrogenation processing into liquid products.

Table 3.5. Characteristics of brown coals of the Kansk-Achinsky and bituminous coals of the Kuznetsk basins

Field, region

Kansk-Achinsk basin

Field

Bara »Danish
Itatskoe
Berezovskoe
Irsha-Borodinskoe
Nazarovskoe
Abanskoe
Uryupinskoe
	Kuznetsky
Leninist
Erunakovsky
Tersinsky
Plotnikovsky

ma and brown_coals with exponent reflectivity vitrinite L ° = 0.35-0.95 and the content of inert petrographic microcomponents is not higher than 15% (wt.). These coals must contain 65-86 wt% carbon, more than 5 wt% hydrogen, and at least 30 wt% volatiles based on organic matter. The ash content in them should not exceed 10% (mass.), Since high ash content negatively affects the material balance of the process and complicates the operation of the equipment. In our country, these requirements are best met by brown coals of the Kansko-Achinsky and hard coals of the Kuznetsk basins (Table 3.5).

The suitability of coals for the production of liquid fuels by hydrogenation can be estimated from the data of the elemental composition. I. B. Rapoport found that the yield of liquid hydrogenation products, calculated on the organic mass of coal, decreases with an increase in the mass ratio of carbon to hydrogen in its composition and reaches a minimum value (72%) at C: H = 16. Statistical analysis of the composition and ability to liquefy American coals made it possible to establish with a correlation of 0.86 the following linear dependence of the yield of liquid products [C? f,% (mass.)] from the content [% (mass.)] (in the original demineralized carbon of hydrogen and organic sulfur:

A linear dependence of a slightly different type with a correlation of 0.85 was obtained in the study of Australian coals:

Brown coals are easily liquefied, but they, as a rule, contain a lot of oxygen (up to 30% for OMC), the removal of which requires a significant consumption of hydrogen. At the same time, the content of nitrogen in them, which also requires hydrogen to be removed, is lower than in coal.

Porosity and solvent wettability are important physical characteristics. The degree of liquefaction of coals is significantly affected by the mineral impurities and trace elements contained in them. By exerting a physical and catalytic effect in liquefaction processes, they violate the direct relationship between the yield of liquid products and the composition of the organic part of coal.

The main parameters affecting the degree of coal liquefaction and the properties of the products obtained during liquid-phase hydrogenation are the temperature and pressure at which the process is carried out. The optimum temperature regime for liquid-phase hydrogenation is in the range of 380-430 ° C and for each specific coal lies in its narrow range. At temperatures above 460 ° C, there is a sharp increase in gas formation and the formation of cyclic structures. With increasing process pressure, the rate of coal liquefaction increases.

There are two known methods for the implementation of liquid-phase hydro-genation processing of coals in order to obtain synthetic motor fuels - thermal dissolution and catalytic hydrogenation.

Thermal dissolution is a mild form of chemical transformation of coal. When interacting with a hydrogen donor solvent, part of the organic matter of coal goes into solution and after separation of the solid residue is usually a high-boiling coal extract, freed from minerals, sulfur-, oxygen- and nitrogen-containing compounds and other undesirable impurities. Hydrogen gas can be supplied to the solution to increase the conversion of the coal. Depending on the type of initial coal, solvent and process conditions, the thermal dissolution method can be used to obtain products for various purposes.

For the first time, the technology of thermal dissolution of coal was proposed by A. Pott and H. Brochet in the 1920s. By the beginning of the 1940s, a plant with a capacity of 26.6 thousand tons per year of extract operated on the basis of this technology in Germany.

In this installation, a paste consisting of one part of crushed coal and two parts of a solvent was heated in a tube furnace to 430 ° C under a pressure of 10-15 MPa. Liquid products were separated from the dissolved coal and its mineral part by filtration at a temperature of 150 ° C and a pressure of 0.8 MPa. The solvent used was a mixture of tstralin, cresol and medium oil of liquid-phase hydrogenation of coal tar pitch. The yield of the extract with a softening temperature of 220 ° C and a content of 0.15-0.20% (wt.) Of ash was about 75% (wt.) Of the organic matter of coal. The extract was used mainly as a raw material for the production of high quality electrode coke.

Since the 1960s, in a number of countries, new generation processes based on thermal dissolution of coal have been developed and implemented in pilot and demonstration installations. According to their intended purpose, they can be divided into two types: 1) processes in which only primary solid or liquid products under normal conditions are obtained, usually intended for combustion in power plant furnaces, and 2) processes involving the processing of primary products into more qualified (first of all, in motor) fuels using secondary processes of thermal processing, hydrogenation and upgrading.

The SRC (Solvent Refined Coab) coal extraction process developed in the USA in the basic version SRC-I is carried out at a reactor temperature of 425-470 ° C, a pressure of 7-10 MPa, and a residence time in the reaction zone of “30 min. The main product of the process is coal extract, purified from sulfur, which solidifies at a temperature of 150-200 ° C.

In a modified version of the SRC-II process, the diagram of which is shown in Fig. 3.2, by increasing the pressure to 14 MPa and increasing the residence time of the coal paste in the reaction zone, liquid fuel of a wide fractional composition is obtained as the main target product. The original coal, after crushing and drying, is mixed with hot coal slurry. The resulting paste together with hydrogen is passed through a fired heater and then sent to the reactor. The required temperature and partial pressure of hydrogen is maintained by supplying cold hydrogen to several points of the reactor. The reaction products are first separated in gas separators. Gas separated from liquid products, containing mainly (I stage) hydrogen and gaseous hydrocarbons with an admixture of hydrogen sulfide and carbon dioxide, after cooling to 38 ° C is sent to the acid gas purification system. At the cryogenic unit, gaseous C 3 -C4 hydrocarbons and purified hydrogen are released (it is returned to the process). The remaining methane fraction after methanation of the carbon monoxide contained in it is fed into the fuel network. Liquid pro

Rice. 3.2. Diagram of the process of thermal dissolution of BIS-I coal:

1 - mixer for making pasta; 2 - oven for heating the paste; 3 - reactor; 4 - block of gas separators; 5 - absorber of acid gases; 6 - cryogenic gas separation; 7 - unit for cleaning fuel gas; 8 - separation of gaseous hydrocarbons; 9-unit for purification of synthetic gas and hydrogen evolution; 10 - unit for obtaining sulfur; II - reactor for gasification of the residue; 12 - atmospheric column; 13 - vacuum column;

1 - dried powdered coal; II - hydrogen; III - coal suspension; IV - process fuel; V is sulfur; VI - oxygen; VII - water vapor; VIII - inert residue; IX - the remainder of the mineral part of the coal; X - liquid product after gas separation; LU - fuel gas; HC - ethane; XIII - propane; XIV - butanes; XV - gasoline fraction for refining and reforming; XVI - middle distillate for refining; XVII -

heavy distillate ducts from gas separators enter the atmospheric column, where they are separated into gasoline fraction (28-193 ° C), middle distillate (193-216 ° C) and heavy distillate (216-482 ° C). The coal suspension formed at the first stage of separation in gas separators is divided into two streams: one is fed to the displacement with the initial coal, the other - to the vacuum column. From the top of the vacuum column, part of the liquid distillate contained in the suspension is discharged into the atmospheric column, and the remainder from the bottom goes to obtain synthesis gas used for hydrogen production or as fuel,

Calculated for dry ash-free bituminous coal, the yield of products in the EIS-C process at a hydrogen consumption of 4.4% (wt.) Is [% (wt.)]:

The process of thermal dissolution of coal EDS ("Exxon Donor Solvent") is intended for the production of synthetic oil with its subsequent processing into motor fuels. This technology mixes coal with a hot hydrogen donor solvent after crushing and drying. As the latter, a fraction 200-430 ° C of the liquid product of the process is used, which is preliminarily hydrogenated in an apparatus with a fixed layer of Co-Mo catalyst. The mixture is fed into an ascending flow reactor together with gaseous hydrogen, where thermal dissolution of coal occurs at a temperature of 430-480 ° C and a pressure of 14-17 MPa. The resulting products are separated (in a gas separator and vacuum rectification) into gases and fractions boiling up to 540 ° C and a residue> 540 ° C, which also contains unreacted coal and ash. Product yields, conversion rates and other process indicators depend on the type of coal being processed. The yield and composition of liquid products are also influenced by the recirculation of the residue. For example, for. different technological design of the process (without recirculation of the residue-I and with the recirculation of the residue - II), the yield of fractions is: [% (wt.)]:

Depending on the type of raw material, the yield of liquid products on dry and ash-free coal with complete recirculation of the residue can vary from 42 to 51% (wt.), And the yield of Ci-C 3 gases from 11 to 21% (wt.). All the resulting fractions must be hydrotreated to remove sulfur and nitrogen. The content of hetero compounds increases with an increase in the boiling point of the fractions.

Two variants of the EDS process flow diagram are proposed, differing in the methods of hydrogen and fuel gas production. In the first variant, hydrogen is obtained by steam reforming of light gases that make up the products of the process, and fuel gas is obtained by processing the residue of vacuum distillation of the liquid product of the process in a coking unit with coke gasification (Flexicoking), which simultaneously produces an additional amount of light liquid products. The thermal efficiency of this process is about 56%.

The second option provides maximum flexibility in the product range. About half of the vacuum residue is processed at the Flexicoking unit to obtain liquid products and fuel gas, and hydrogen is produced from the remaining amount. Thus, light hydrocarbon gases obtained during thermal dissolution are a commercial product. The thermal efficiency of this variant reaches 63%.

On the basis of EDS technology, a demonstration plant with a capacity of 250 tons of coal per day was put into operation in the USA in 1980, capital investments in the construction of which amounted to $ 370 million. $ 1.4 billion (1982 prices).

The advantages of thermal dissolution processes include a lower operating temperature than in coal pyrolysis and the possibility of varying the quality of the resulting liquid product within a relatively wide range by changing the process parameters. At the same time, during thermal dissolution, deep conversion of coal is achieved at a high process pressure, and high-molecular compounds prevail in the composition of the resulting products. The presence of the latter is due to the fact that, even at low temperatures, the processes of recombination of the resulting free radicals begin to occur, accompanied by the formation of secondary structures of an aromatic nature, less reactive than the initial organic matter of coal. The presence of hydrogen donors and molecular hydrogen dissolved in the paste in the reaction mixture cannot sufficiently prevent these processes from proceeding. A number of difficulties arise in the industrial implementation of this method. A difficult technical problem is the separation of unreacted coal and ash from liquid products. The resulting target product is liquid under the process conditions, and under normal conditions it can be a semi-solid and even solid substance, which is difficult to transport, store and process into final products.

Catalytic hydrogenation. An increase in the degree of coal conversion, an improvement in the composition of the obtained liquid products and a decrease in the pressure of the hydrogenation process are possible with the use of catalysts. The latter promote the transfer of hydrogen from the solvent to coal and activate molecular hydrogen, converting it into atomic form.

Research in the field of direct hydrogenation of coal with the use of catalysts was initiated by German scientists F. Bergius and M. Peer in 1912. As a result of these works, in 1927, the first industrial unit for the catalytic hydrogenation of coal with a capacity of 100 thousand tons of liquid products per year was built (Bergius-Pir process). By the beginning of the 1940s, 12 enterprises of this type were already operating in Germany, which produced up to 4.2 million tons of motor fuels per year, primarily aviation gasoline. In 1935, a coal hydrogenation plant was built in England, and in the USA, work in this area was carried out on a large pilot plant in the period 1949-1953.

In the Soviet Union, research on the hydrogenation of domestic coals was begun by N.M. Karavaev and I. B. Rapoport in 1929. Later, a significant contribution to the development of these works was made by A. D. Petrov, A. V. Lozovoy, B. N. Dolgov , DI Orochko, AV Frost, VI Karzhev and a number of other Soviet scientists. In 1937, the first in our country plant for the hydrogenation processing of brown coal in the city of Kharkov was designed and put into operation. By the early 1950s, several more similar enterprises were built.

In industrial installations of those years, three- and four-stage coal processing schemes were used. At the stage of liquid-phase hydrogenation, the paste - 40% of coal and 60% of a high-boiling coal product with the addition of an iron catalyst - was exposed to gaseous hydrogen at a temperature of 450-490 ° C and a pressure of up to 70 MPa in a system of three or four reactors arranged in series. The degree of conversion of coal into liquid products and gas was 90-95% (wt.). Since economical methods of catalyst regeneration were not developed at that time, in most cases cheap low-activity catalysts based on oxides, sulfides, and iron were used. After passing through the system of reactors and a hot separator at a temperature of 440-450 ° C, the circulating hydrogen-containing gas and liquid products were removed from the top. Then, in the cold separator, the gas was separated from the liquid and, after washing, was returned to the cycle in a mixture with fresh hydrogen. The liquid product, after a two-stage pressure reduction to separate hydrocarbon gases and water, was subjected to distillation, while a fraction with a boiling point of up to 320-350 ° C and a residue (heavy oil, it was used to dilute the hydrogenation sludge before centrifugation) were isolated.

Liquid-phase hydrogenation was carried out according to two schemes: with a closed cycle (complete recirculation) in the pasting agent and with an excess of heavy oil. The first scheme was used by most of the hydrogenation plants, focused mainly on the production of gasoline and diesel fuel. When operating with an excess of heavy oil, the coal productivity of the plant increased by 1.5-2 times, but the heavy oil had to be subjected to separate hydrogenation processing into lighter-boiling products or used to obtain electrode coke.

When processing coals with a closed-pasting cycle, the yield of liquid products boiling away at temperatures up to 320 ° C was 55-61% (wt.) With a hydrogen consumption of up to 6% (wt.). These products, containing 10-15% phenols, 3-5% nitrogenous bases and 30-50% aromatic hydrocarbons, were then subjected to two-stage hydrogenation in the vapor phase on a fixed bed of hydrocracking catalysts. The total yield of gasoline with an octane number of 80-85 according to the motor method reached 35% (wt.), And with the simultaneous production of gasoline and diesel fuel, their total yield was about 45% (wt.) In the calculation of the initial coal; hydrogen was obtained by gasification of coal or char.

The sludge containing up to 25% solids was sent for processing, which was the most cumbersome and energy-intensive stage of the entire technological cycle. After dilution with the heavy fraction of the hydrogenate to a solid content of 12-16% (wt.), The sludge was centrifuged. The residue with a solid content of about 40% was processed by semi-coking in rotary drum kilns with a capacity of 10-15 t / h and light liquid coking products were mixed with the distillate fraction of the hydrogenate. The distillation of heavy oil obtained by centrifugation was returned to the cycle to prepare a paste.

The low activity of the catalyst, the difficulties in processing the sludge, and other factors made it necessary to use high pressures and large amounts of hydrogen in the process. The units had a low unit performance, were distinguished by significant energy consumption.

In various sections of the I C ° ZDany and the second generation R ° chessy in various countries, primarily in the USSR, the USA and the Federal Republic of Germany

In the development of these processes, the main focus of research has been on reducing the pressure of equipment productivity, reducing energy consumption, and improving methods for processing sludge and regenerating catalysts. To date, about 20 options have been proposed for the technological design of the processes of hydrogenation catalytic liquefaction of coal on viscous installations - from laboratory to demonstration ones with a productivity from 50 to 600 t / day for coal P.

BergiusN-? Pipya, FRG On the basis of the previously used R U Pira process with the use of a non-regenerable iron catalyst, the so-called "new German technology" of coal hydrogenation has been developed. Unlike the old process, a circulating middle distillate is used to make a paste (instead of a centrifugal drain). Liquid products are separated from the solid residue by? -Vacuum distillation (instead of centrifugation) and the sludge is subjected to gasification to obtain hydrogen. In Bottrop (Germany) on the basis of this new

Among the processes of catalytic hydrogenation of coal developed abroad, one of the most prepared for industrial implementation is the H-Coal process (USA). According to this technology, liquid-phase hydrogenation is carried out using a fluidized bed of an active fine-dispersed Co-Mo catalyst according to the scheme shown in Fig. 3.3.

Dry crushed coal is mixed with the recycle hydrogenation product to form a paste with a content of 35-50% (wt.) Coal, which is then injected with compressed hydrogen. The resulting mixture is heated and fed under a distribution grid to a fluidized bed reactor. The process is carried out at a temperature of 425-480 ° C and a pressure of about 20 MPa. Reaction products and unconverted coal are continuously withdrawn from the reactor at the top, and spent catalyst at the bottom. Constant Cyvod and catalyst regeneration ensure the maintenance of its high activity.

Vapors removed from the reactor, after condensation, are separated into hydrogen, hydrocarbon gases and light distillate. The gases are sent to purification, and hydrogen is recycled. Liquid products from the top of the reactor enter a separator, in which a fraction is separated, which is then subjected to distillation to obtain light and heavy distillates. Gasoline and diesel fractions are obtained from the first. The residual product discharged from the bottom of the separator is divided in hydrocyclones into two streams: low and high solids content.

The first stream is used as a pasting agent, and the second is treated with a precipitator, and the separated sludge containing up to 50% of solid particles is gasified to produce hydrogen. The liquid product remaining after the separation of the sludge is subjected to vacuum distillation to obtain a heavy distillate and a residue used as boiler fuel.

The yield of target products in the "H-Coa1" process reaches 51.4% (wt.) For the organic mass of coal, including gasoline fraction (28-200 ° C) -25.2% (wt.), Middle distillate (200 -260 ° C) - 12.9% (wt.) And heavy distillate - 13.3% (wt.). The hydrogen consumption for liquid-phase hydrogenation is 4.7% (wt.). The process has been tested on a pilot plant with a coal capacity of 600 tons per day.

In our country, the Institute of Fossil Fuels (IGI), together with the institutes Grozgiproneftekhim and VNIIneftemash in the 1970s, carried out a wide range of research in the field of hydrogenation processing of coal in liquid

Rice. 3.3. Scheme of the process of hydrogenation liquefaction of coal "H-Coa1":

1 stage of coal preparation; 2 - heater; 3 - reactor with a fluidized bed of catalyst; 4 - capacitor; 5 - hydrogen extraction unit; 6 - high-speed separator; 7 - atmospheric column; 8 - hydrocyclois; 9 - separator; 10 - vacuum column; 1 - coal; II - hydrogen; III - recycle heavy distillate;. IV - paste; V - hydrogenate level; VI - the level of the fluidized catalyst; VII - regenerated catalyst; VIII - vapor-gas phase; IX - condensed phase; X - spent catalyst; XI - liquid; XII - resins; XIII - gaseous hydrocarbons, ammonia and hydrogen sulfide for separation and production of sulfur; XIV - light distillate for refining; XV - heavy distillate; XVI - non-reacted liquid residue for hydrogen production; XVII-heavy distillate for upgrading; XVIII -

residual fuel fuels. The result of the research was a new technological process (IPG process), in which, thanks to the use of a regenerated active catalyst and inhibiting additives, the use of improved sludge processing technology and a number of other technological solutions, it was possible to "reduce the pressure to 10 MPa while ensuring a high yield of liquid hydrogenation products. Reducing the process pressure. significantly reduced specific capital and operating costs and allowed the use of high-performance reactors with a capacity of 250-500 m 3, which are already used in the oil refining industry.

According to the IPG technology, coal is preliminarily crushed by crushing to a particle size of 5-13 mm, subjected to high-speed drying in vortex chambers to a residual moisture content of 1.5% (mass), then it is crushed again by vibration grinding to a particle size of less than 100 microns.

A catalyst of 0.2% Mo n 1.0% Fe (III) is applied to the crushed coal. This combination makes it possible to achieve the degree of conversion of the organic mass of coal up to 83%. The maximum activity of the catalyst is provided when it is applied from solution to dried coal. The joint vibratory grinding of coal and catalyst salts is also effective, since this opens the micropores of the structure of the organic mass of coal and ensures complete and uniform deposition of the catalyst on the surface of the coal.

In addition to the catalyst, inhibitors such as quinoline, anthracene and other compounds can be introduced into the reaction zone, which stabilize free radicals and activate the destruction of the organic part of the coal due to the release of atomic hydrogen during their decomposition. The introduction of 1-5% of such additives provides an increase in the degree of coal conversion and the yield of liquid products by 10-15%.

Coal with a catalyst deposited on it enters the paste preparation system. Coal distillate with a boiling point of 300-400 ° C is used as a pasting agent, which is pre-hydrogenated under a pressure of 10 MPa at a separate stage. For the normal conduct of the process, the paste is prepared with an equal ratio of coal and solvent; with a higher coal content, the transport of the paste in the system becomes difficult due to its high viscosity. Coal-oil paste, into which gaseous hydrogen is introduced, is preheated in a tubular furnace and enters the system of hollow unheated reactors with a space velocity of 1.0-1.5 h -1. During the residence time of the paste in the reactor (30-60 min), coal hydrogenation reactions take place with the formation of hydrocarbon gases (% -C4, ammonia, hydrogen sulfide and carbon oxides [up to 10% (wt.)], Water and liquid products. with the release of heat, cold hydrogen-containing gas is supplied to the reactors to control the temperature; it also serves as a stirring agent.

The products of the hydrogenation reactions from the reactor are sent to a hot separator. From the top of the separator, a steam-gas flow containing gases and light liquid products is discharged, and from the bottom - sludge consisting of liquid products boiling above 300-325 ° C, unreacted coal, ash and catalyst.

The total solids content of this sludge is 10-15% (w / w). The vapor-gas stream is cooled and separated into a liquid part and a hydrocarbon gas containing 75-80% (vol.) Hydrogen, C1-C4 hydrocarbons, ammonia, hydrogen sulfide and carbon oxides. After separation of other gases by the method of pressure swing adsorption, hydrogen is returned to the process. Hydrocarbon gas is used to produce hydrogen in the amount of 50-60% of its consumption in the process. The rest of the required hydrogen is obtained in a separate unit by gasification of coal or residues from sludge processing.

Table 3.6. Characterization of liquid products of various coal hydrogenation processes in comparison with oil

Sludge processing - one of the most technically difficult stages of the process - in the IPG scheme is carried out in two stages. In the first, the sludge is filtered to a residual solids content of about 30% (wt.), And in the second, it is subjected to vacuum distillation until the content of the resulting residue is 50-70% (wt.) Of solids. This residual product is burned in a cyclone furnace with liquid bottom ash removal. In the process of combustion, molybdenum by 97-98% passes into the gas phase (1M02O3) and is deposited on ash, from which it is then extracted by hydrometallurgical methods for reuse... The heat released during combustion can be used to generate 2.5-2.8 thousand kWh of electricity, or 11 tons of steam per each ton of sludge residue.

Liquid products of hydrogenation processing of coal differ from ordinary oil in elemental composition and lower hydrogen content, as well as in the presence of significant amounts of nitrogen- and oxygen-containing compounds and alkenes (Table 3.6). Therefore, in order to obtain commercial motor fuels, they must necessarily undergo secondary gas-phase hydrogenation processing.

In the scheme of the IPG process, hydrotreating of a wide distillate of liquid-phase coal hydrogenation with a boiling point of up to 400 ° C is carried out at a pressure of 10 MPa sequentially in two temperature zones of the reactor in order to avoid the occurrence of undesirable polymerization reactions leading to the formation of high-boiling compounds. In the first zone at 230-250 ° С

Part of the alkenes that are most prone to polymerization is hydrogenated. Then, at a temperature of 400 ° C, the bulk of the alkenes and partially aromatic compounds are hydrogenated; the destruction of sulfur-, oxygen- and nitrogen-containing compounds also occurs. Hydrotreating is carried out in the presence of aluminum-mocobalt-molybdenum catalysts, which are widely used in oil refining. However, in some cases, due to the high ¦ content of heteroatomic compounds in coal distillates, these catalysts are insufficiently effective or are quickly poisoned. Therefore, new stable catalysts are required.

The characteristics of the initial distillate of brown coal hydrogenation using the IPG technology and the products of its hydrotreatment are given in table. 3.7. Primary distillate products of liquid-phase coal hydrogenation are unstable. During storage, they change color and form insoluble precipitates, which are caused by the presence of

Table 3.7. Characteristics and yield of distillate of liquid-phase hydrogenation of brown coal and products of its hydrotreatment

	Hydrogenation distillate	Distillate hydrotreating products
Index		sum ap-th	and. room -180 ° C
Density, kg / m 3 Content,
nitrogenous bases
Iodine number, Group hydrocarbon composition, paraffins and naphthenes aromatic hydrocarbons Fractional composition, ° С: 50% (vol.) C. C. Elemental composition, Initial distillate yield,% (mass.)			86.01 13,98 0,01

composition in trace amounts of nitrogen-containing non-basic compounds such as pyrrole. These compounds may not be completely removed during hydrotreating, and to obtain sufficiently stable products in general scheme process, it is recommended to include adsorptive and extractive denitrogenation of a wide hydrogenation distillate or its fractions.

Fraction and. Since - 180 ° C of the hydrotreated distillate has an octane number of 66 (motor method) and is characterized by an increased content of actual resins and nitrogenous compounds. To obtain a component of high-octane motor gasoline, its deep hydrotreating and subsequent reforming are required. The diesel fraction, due to the high content of aromatic hydrocarbons, has a relatively low cetane number. A fraction with a boiling point of 300-400 ° C, a part of which is used as a component of a pasting agent, can serve as a raw material for hydrocracking to obtain gasoline and diesel fractions. The material balance of the hydrogenation of brown coal in the Kansk-Achinsk basin according to two versions of the IPG technology is presented below (in the numerator I option - processing of sludge to a solid content of 70%, in the denominator II option - the same, 50%):

~ Received

Taken [% (mass.)] [% (Mass.)]

including:		Diesel fuel
		Boiler fuel
Catalyst		Gas for production
Inhibitor
Hydrogen (co		Hydrogen sulfide
		Carbon dioxide

As you can see, with the complete processing of coal, 45-55% (mass.) Of motor fuels and chemical products are obtained.

Jet fuel of the TS-1 type can also be obtained from the products of coal liquefaction by the IPG method. For this purpose, the fraction 120-230 ° C separated from the total distillate of liquid-phase hydrogenation after "dephenolization" must go through three successive stages: low-temperature hydrogenation (6 MPa, 230 ° C, wide-pore aluminum-nickel-molybdenum catalyst), hydrotreating (6 MPa, 380 ° C and the same catalyst) and hydrogenation of aromatic hydrocarbons (6 MPa, 290 ° C, industrial palladium-aluminum catalyst). The third stage is necessary if the hydrotreated fraction 120-230 ° С contains more than 22%

Rice. 3.4. Scheme of the production of motor fuels by hydrogenation of coal using the IGI technology - Grozgipro-neftekhim:

1-coal preparation; 2 - coal liquefaction; 3 - hydrogen production; 4 - isolation of the solid residue; 5 6, 10 - rectification; 7 - sludge disposal unit; 8 - isolation of phenols; 9 - hydrogenation; 11 - hydrotreating and reforming; 12, 14 - hydrocracking; 13 - isomerization and hydrogenation;

1 - coal; 11 - pastor; III - catalyst; IV-hydrogen; V - gases C 4 and CO; VI - liquid products of hydrogenation; VII - Г4Нз, Нг $ and СОг; VIII - Fraction> 400 ° C; IX - solid residue; X is water; XI - feiol, cresols; XII - "faction n. K. - 180 ° C; XIII - fraction 180-300 ° C; XIV - fraction 300-400 ° C; XV - ash for the production of building materials; XVI - process steam; XVII - electricity; XVIII - gasoline; XIX - jet fuel; XX - diesel fuel

^ mass.) of aromatic hydrocarbons. But the data.

By including various sets of hydrogenated product and its fractions processing in the process flow diagram, the ratio of the produced gasoline and diesel fuel can be changed from 1: 0 to 1: 2.6. Diesel fractions can be hydrocracked to maximize gasoline production. The scheme for obtaining motor fuels according to one of the options based on the IGI technology is shown in Fig. 3.4. When organizing production according to this scheme, 3 million tons per year of motor fuels will require 19.7 million tons per year of brown coal from the Kansk-Achinsk basin, including 9 million tons for hydrogenation, 3 million tons for gasification for hydrogen production and 7.3 million tons for energy needs. At the same time, the production of the following products (in million tons per year) can be ensured: gasoline - 1.45, diesel fuel - 1.62, liquefied gases - 0.65, ammonia - 0.07 and sulfur - 0.066. Thermal K. and. such production is 55%.

In foreign processes of coal hydrogenation, it is also planned to use various options for upgrading and recycling liquid products. For example, in the project of a complex for processing 30 thousand tons of US bituminous coal based on the BIS-I process, it is envisaged to subject all liquid hydrogenation products to hydrocracking with a conversion rate of about 50%. The resulting gasoline fraction after additional hydrotreating should go to reforming to obtain a component of motor gasoline with an octane rating of 100 (research method). In general, the complex is supposed to receive the following products (thousand tons per day): motor gasoline - 2.78, middle distillates - 8.27, heavy boiler fuel- 4.75, liquefied gases - 0.64 and sulfur - 0.12. Capital expenditures for the construction of the complex are estimated at $ 5.7 billion (in 1982 prices). The annual operating costs when the capacity is loaded by 90% will be (in million dollars): the cost of coal - 420, energy costs - 101, catalysts and chemicals - 77, operating materials - 114, personnel (1,900 people) - 79.

As the available estimates show, the reduced costs for the production of motor fuels from coal by the hydrogenation method according to the technologies developed to date are several times higher than the costs of obtaining them from petroleum feedstock with the average cost of extracting the latter. However, the cost difference can be reduced when compared to fuels produced from oil produced, for example, using expensive enhanced oil recovery methods or on deep sea shelves.

The ongoing research and development work in the field of hydrogenation coal processing in many countries is aimed at improving the technological and instrumental design of processes, developing new catalysts and additives, and increasing the energy efficiency of all stages. These searches can provide a reduction in the unit costs of obtaining motor fuels from coal. The combination of the processes of hydrogenation and gasification of coal in a single stream without complicating stages of separation of liquefaction products and without loss of energy spent on heating the raw material should be considered promising.

Coal gasification and synthesis of hydrocarbon fuels

When obtaining motor fuels from coal by means of its indirect liquefaction, the first stage is gasification.

Solid fuel gasification is a thermal process during which the organic part of the fuel in the presence of oxidants (air or technical oxygen, water vapor) is converted into a mixture of combustible gases.

Already at the beginning of the 19th century, gas obtained by distilling coal was used to illuminate streets in major cities around the world. Initially, it was obtained in the process of coking, but by the middle of the century, on an industrial scale, residue-free gasification of coke and coal was carried out in cyclic, and then in continuously operating gas generators. At the beginning of this century, coal gasification was widespread in many countries of the world, primarily for the production of energy gases. In the USSR, by 1958, about 2500 gas generators of various sizes and designs were in operation, which ensured the production of about 35 billion cubic meters per year of energy and process gases from solid fuels of various types. However, due to the subsequent rapid growth in the production and transportation of natural gas, the volumes of solid fuel gasification both in our country and abroad have significantly decreased.

Coal gasification is carried out at high temperatures and is a multistage heterogeneous physicochemical process. The organic mass of coal, primarily carbon, which is part of its composition, interacts with gaseous oxidants. In this case, the following primary reactions of carbon with oxygen and water vapor occur:

In addition to the indicated reaction products, during the gasification of coals in the first stage of their heating, pyro

* The heats of reactions are given at a temperature of 15 ° C and a pressure of 0.1 MPa.

Lisa. During gasification, as a rule, practically all the organic part of the coal turns into gas and, in some cases, partly into tar, and the mineral part with a small admixture of unreacted fuel forms ash or liquid slag.

Unlike hydrogenation, the requirements for feedstock for gasification processes do not have significant restrictions on the stage of metamorphism and petrographic composition, but the role of mechanical and thermal strength, sintering capacity, moisture, ash and sulfur content is very significant. A number of restrictions on these parameters are reduced after preprocessing coals - drying, oxidation, etc. The most significant indicator of the use of coals in various gasification processes is the melting point of ash residues. It determines the temperature range of the main process and the choice of the ash removal system.

The activity of solid fuels and the rate of gasification largely depend on the mineral constituents acting as catalysts. The relative catalytic effect of trace elements of fossil coals during gasification can be represented by the following series:

The main parameters characterizing individual processes of solid fuel gasification can be attributed to: the way of supplying heat to the reaction zone; a method for supplying a gasifying agent; type of gasifying agent; process temperature and pressure;

the method of formation of the mineral residue and its unloading. All these parameters are interconnected and are largely determined by the design features of the gas generators.

According to the method of supplying heat necessary to compensate for the endothermic effect of the reaction of carbon with water vapor, gasification processes are divided into autothermal and allothermal. Autothermal processes are most widespread; in them, heat is obtained by burning part of the coal introduced into the process. In allothermic processes, heat is supplied by direct heating of coal with a circulating solid, liquid or gaseous coolant, indirect heating of the coolant through the reactor wall or by means of a heating element immersed in the reactor.

To organize the process of interaction of fuel and oxidizer in the reactor, a continuous moving bed of lumpy coal, a cocurrent flow of coal and oxidizer in the entrainment mode and a fluidized bed of fine-grained coal are used. In gas generators with a continuous bed, a downward movement of lumpy fuel and an upward movement of a stream of hot gases are organized. This principle determines the high chemical and thermal activity of the process and allows gasification of most types of coals, with the exception of sintering ones. The specific productivity of such gas generators is limited by the entrainment of fine coal fractions, which is partially compensated by an increase in pressure. Moderate temperatures in the upper part of the coal bed cause an increased methane content in the product gas [up to 10-12% (vol.)], As well as the formation of significant amounts of such by-products as resins, liquid hydrocarbons and phenols.

In gas generators with a fluidized bed, crushed coal is loaded with a particle size of 0.5-8.0 mm. The fluidization mode is supported by the supply of a gasifying agent. Good mixing in the bed provides high rates of heat and mass transfer, and practically no liquid by-products are formed during gasification. The methane content in the produced gas usually does not exceed 4% (vol.). At the same time, in processes with a fluidized bed, the entrainment of small fuel particles is high, which reduces the degree of conversion in one pass and complicates the operation of equipment for subsequent technological stages.

Pulverized coal is processed in blow-off gas generators. It is introduced into the reactor in a cocurrent flow with steam-oxygen blasting, while the temperature in the reaction zone reaches 2000 ° C. All types of coal can be processed in these gas generators. The reactions in them take place at a high speed, which ensures a high specific productivity. Product gas is practically free of methane, tar and liquid hydrocarbons. However, due to the high operating temperature, the oxygen consumption in such gas generators is higher than in gas generators with a solid or fluidized bed of fuel, and an efficient heat recovery system is required to ensure a high thermal efficiency. When operating such gas generators, it is necessary to strictly observe the feed supply regime, since due to the small amount of coal simultaneously in the reactor, any violation of the regime leads to a halt in the process.

One of the options for gasification in the entrainment mode is the use of a coal-water slurry instead of dry pulverized fuel. This facilitates the supply of fuel to the reactor and eliminates the need to use bunker systems for its loading.

Typically, the gasifying agents in gasification processes are air, oxygen and water vapor. With air-steam blowing, there is no need for an air separation unit, which makes the process cheaper, but the resulting gas is low in calories, since it is highly diluted with air nitrogen. Therefore, in gasification schemes, preference is given to steam-oxygen blast and the ratio of steam to oxygen is determined by conditions. carrying out the process. Hydrogen gasification processes use hydrogen as one of the gasifying agents to produce a high-calorific gas rich in methane.

The gasification temperature, depending on the selected technology, can vary widely - from 850 to 2000 ° C. The temperature regime is determined by the reactivity of coal, the ash melting point, and the required composition of the produced gas. In autothermal processes, the temperature in the reactor is controlled by the steam: oxygen ratio in the blast. For allothermic processes, it is limited by the maximum possible heating temperature of the coolant.

In various gasification processes, the pressure can vary from atmospheric to 10 MPa. An increase in pressure creates favorable conditions for an increase in the temperature and energy efficiency of the process, and contributes to an increase in the concentration of methane in the product gas. Gasification under pressure is preferable in cases of obtaining gas, which is then used in syntheses that are carried out at high pressures(costs for compression of synthesis gas are reduced). With increasing pressure, it is possible to increase the gasification rate and the unit capacity of the gas generators. When gasifying lumpy and coarse-grained fuel, the gasification rate is proportional to the square root of the pressure, and when gasifying fine-grained and pulverized fuel, it is proportional to the pressure.

In gas generators with liquid slag removal, the process is carried out at temperatures above the ash melting temperature (usually above 1300-1400 ° C). "Dry ash" gas generators operate at lower temperatures, and ash is removed from them in solid form.

In addition to carbon monoxide and hydrogen, the gasification gas contains compounds containing sulfur and ammonia, which are poisons for catalysts of subsequent syntheses, as well as phenols, resins and liquid hydrocarbons. These compounds are removed in a purification stage downstream of the gasifier. In industrial gasification processes, methods of physical and chemical absorption of these components are used to purify synthesis gas from sulfur compounds and carbon dioxide. Methanol, propylene carbonate, N-methylpyrrolidone, sulfolane and di-zopropanolamine, dimethyl and polyethylene glycols, ethanolamines, etc. are used as absorbers.

To ensure the optimal ratio of CO: Ng in the synthesis gas, a special

Fig. "3.5. Diagram of the coal gasification process 1 - drying and grinding of coal; 2_ - air separation; 3 - gasification; 4 - ash or slag utilization; 5 - raw gas purification; 6 - CO conversion;

I - coal; II - water vapor; III - nitrogen; IV-sour; V - ash or slag; VI - raw gas; VII - pure gas; VIII - NgB, GShz, resins; /.X - synthesis gas; X - C0 3

ny block for catalytic conversion of carbon monoxide with water vapor.

A schematic of the gasification process with the production of synthesis gas ready for further processing is shown in Fig. 3.5.

To achieve maximum thermal efficiency and. in the process, the gas generator must operate at elevated pressure, with low oxygen and water vapor consumption, and low heat losses. It is also desirable that the gasification produces a minimum amount of by-products and the process is suitable for processing various coals. However, some of these factors are mutually exclusive. For example, it is impossible to ensure a low oxygen consumption and avoid by-products. Therefore, in each specific case, it is required to choose the optimal combination of process parameters.

Currently, more than 50 types of gas generators have been developed, however, only * four of them have found industrial application: gas generators "Lurgi", "Winkler", "Koppers-Totzek" and "Texaco". The main indicators of the gasification processes carried out on the basis of these devices are given in table. 3.8.

The Lurgi process was first applied on an industrial scale in 1936 in Germany. In 1952, the second generation of gas generators of this type was created, and to date, more than 100 installations with Lurgi generators have been built in different countries. The capacity of a single apparatus increased from 8 to 75 thousand m 3 / h for dry gas.

In the Lurgi gas generators, lump coal is introduced into the reaction zone through a sealed feed hopper and gasified in a counter-current steam-oxygen mixture. The latter is fed under the grate that supports the coal layer; dry ash is discharged through the same grate. The volumetric ratio of steam: oxygen is chosen so that the temperature of the coal bed is below the melting point of the ash. Saturated water vapor is generated in the cooling jacket of the generator.

Coal entering the gasifier passes through three heating zones in succession. In the first zone - the upper part of the reaction

	Gas generator
Index Coal characteristic: type particle size, mm moisture content,% (mass) State of coal in the reactor Working pressure, MPa Maximum temperature in the gasifier, ° С Type of blast State of the ash Coal residence time in the gasifier Carbon conversion rate,% Maximum unit capacity of the gas generator: coal, t / h WMD for gas, thousand m 3 / h Consumption, t / t WMD: steam oxygen Volume ratio steam / oxygen Composition of raw gas *,% (vol.): Average ratio of Н 2: СО in gas Heat of combustion of gas (highest), MJ / m 3 Thermal efficiency of gas generator,%	All coals, except for coking coal 6-40 Stationary layer 2.0-3.0 Dry 1-3 h 99	Lignites and subbituminous 0.1-8 Pseudo liquefied layer 0.12-0.21 PAROKISI 20-40 minutes 60-90	"CorreGB- Cutting mode burly Liquid 0.5-10 s 90-96	"Texaso" coals 0.1-10 Up to 40 Water-coal suspension in the carryover mode 3.5-4.0 iy slag 1-10 s 99

torus - at a temperature of 350 ° C, it is dried with hot gases, in the middle - at a temperature of l; 600 ° C, the coal undergoes semi-coking with the formation of gases, tar and char. In the third zone, located at the base of the gas generator, at a temperature of 870 ° C, as a result Reactions of fuel with steam and oxygen produce a gas that practically does not contain methane. The gas passes the coal bed from bottom to top, while its temperature decreases, and in the colder zones of the reactor, reactions of methane formation begin to proceed. Thus, the produced product gas contains unsaturated hydrocarbons and resins, which requires obligatory gas purification and causes a high water consumption for cooling and removing unwanted components. The gas also contains an increased amount of methane [up to 8-12% (vol.)] 1.

The gasification process using the Lurgi method is distinguished by a high degree of carbon conversion, reaching 99%. The thermal efficiency of the gas generator is 75-85%. The advantage of the "Lurgi" process is also that it is carried out at an increased pressure, which significantly increases the unit productivity of the gas generator and allows to reduce the cost of gas compression when using it in further syntheses.

The Winkler process is the first commercial coal gasification process. The maximum unit capacity of operating gas generators of this type is currently 33 thousand m 3 of gas per hour. The process is based on the processing of coal in a fluidized bed at atmospheric pressure. The temperature in the bed is maintained at 30-50 ° C below the softening temperature of ash, which is removed from the reactor in a dry form.

The "Winkler" gas generator is an apparatus lined with refractory material from the inside, a fluidized bed is created by blowing a steam-oxygen mixture through crushed coal. Coarser particles of coal are gasified directly in the bed, and small particles are carried out. it and gasified at a temperature of 1000-1100 ° C in the upper part of the reactor, where the gasifying agent is additionally fed. Due to the intense heat and mass transfer in the reactor, the resulting gas is not contaminated with pyrolysis products and contains little methane. About 30% of the ash is removed from the bottom of the reactor in a dry form using a screw conveyor, the rest is carried out by the gas flow and captured in a cyclone and scrubbers.

The Winkler process provides high productivity, the ability to process a variety of coals and control the composition of the final products. However, in this process, the losses of unreacted * coal are large - up to 25-30% (mass.) Removed from the reactor, which leads to heat losses and a decrease in the energy efficiency of the process. The fluidized bed is highly sensitive to changes in the process mode, and low pressure limits the productivity of gas generators.

The representative of the processes of gasification of pulverized fuel in the entrainment mode is the process "Corregv-T ^ hec". The first industrial gas generator of this type with a capacity of 4 thousand m 3 per hour of synthesis gas was created in 1952; modern gas generators have a gas capacity of 36-50 thousand m 3 / h.

The gas generator is a water-cooled conical apparatus. It is equipped with two or four burners located opposite each other and is lined with heat-resistant material from the inside. High turbulization of the reagents, achieved by supplying counter flows of the fuel mixture from opposite sides of the chamber, ensures the occurrence of reactions at high speeds and an improvement in the composition of the produced gas.

Coal is preliminarily crushed to particles with a size of no more than 0.1 mm and dried to a residual moisture content of no more than 8% (wt.). Coal dust from the bunkers is fed to the burners by the flow of part of the oxygen required for the process. The rest of the oxygen is saturated with water vapor, heated and injected directly into the chamber. Superheated steam is introduced into the reactor through the tubular jacket, which creates a curtain that protects the walls of the reactor from high temperatures. At temperatures of gases in the combustion zone up to 2000 ° C, the carbon of the fuel almost completely reacts in 1 s. Hot generator gas is cooled in a waste heat boiler to 300 ° C and "washed" with water in a scrubber to a dust content of less than 10 mg / m 3. Sulfur contained in coal is 90% converted to hydrogen sulfide and 10% to carbon sulfide. The slag is removed in liquid form and then granulated.

Due to the high temperature of the process, any type of coal can be used for gasification, including caking, and the resulting gas is poor in methane and does not contain condensable hydrocarbons, which facilitates its subsequent “purification”. The disadvantages of the process include low pressure and increased oxygen consumption.

The Texaso process is based on the gasification of a coal-water slurry in a vertical lined gas generator operating at pressures up to 4 MPa. It has been tested in pilot plants, and a number of large commercial gas generators are currently under construction. The Texaso process does not require pre-drying of coal, and the suspension form of the raw material simplifies the design of the feed unit. The disadvantages of the process include increased consumption of fuel and oxygen, which is due to the supply of additional heat for the evaporation of water.

The work carried out at present to improve autothermal processes is mainly aimed at increasing the gasification pressure, increasing the unit capacity and thermal efficiency. e. reactors, the maximum reduction in the formation of by-products. In autothermal gasification processes, up to 30% of coal is consumed not for the formation of gas, but for obtaining the necessary heat. This negatively affects the economics of the processes, especially when the cost of coal mining is high. Therefore, considerable attention is paid to recent times development of schemes for allothermic gasification of solid fuel using heat obtained from metal melts or from high-temperature nuclear reactors.

Melt processes are a variant of coal gasification in the entrainment mode. In them, coal and a gasifying agent are fed to the surface of molten metals, slags or salts, which play the role of heat carriers. The most promising process is with molten iron, since it is possible to use the free capacities of oxygen converters in ferrous metallurgy available in a number of countries. In this process, a hollow converter-apparatus lined with refractory material with a bath of molten (temperature 1400-1600 ° C) iron serves as a gas generator. Coal dust mixed with oxygen and water vapor is fed from the top of the apparatus perpendicular to the surface of the melt at high speed. This flow, as it were, blows off the sludge formed on the surface of the melt and mixes the melt, increasing the surface of its contact with coal. Due to the high temperature, gasification takes place very quickly. The degree of carbon conversion reaches 98%, and thermal efficiency. etc. is 75-80%. It is believed that iron also plays the role of a gasification catalyst. When lime is added to the melt, the latter reacts with the sulfur of the coal, forming calcium sulfide, which is continuously removed along with the slag. As a result, it is possible to free the synthesis gas from the sulfur contained in the coal by 95% - The synthesis gas obtained in the process with the melt contains 67% (vol.) CO and 28% (vol.) H 2. Iron losses to be replenished amount to 5-15 g / m 3 of gas.

A promising large-scale and relatively inexpensive source of high-grade heat for gasification of solid fuels can be a high-temperature gas-cooled nuclear reactor, which is currently under development and pilot testing. The reactor provides the supply of high-grade heat (950 ° C) for the coal gasification process. Heat from the intermediate helium loop will be transferred to the steam gasification reactor directly to coal, which, under the influence of steam, will turn into synthesis gas. With gasification using the thermal energy of a high-temperature nuclear reactor, the need for coal for the production of an amount of synthesis gas equal to that of autothermal processes will decrease by 30-50%, while the environmental cleanliness of the process will increase.

A wide range of hydrocarbons and oxygen-containing compounds can be obtained from synthesis gas, depending on the process conditions and the catalyst used. On an industrial scale, synthesis gas is currently used to produce products such as methanol, liquid hydrocarbons, etc.

Back in 1925, F. Fischer and H. Tropsch carried out the synthesis of aliphatic hydrocarbons from CO and H 2, which was named after them. The synthesis was carried out on iron and cobalt catalysts at atmospheric pressure and a temperature of 250-300 ° C. In research and industrial practice, modifications of cobalt and iron catalysts, fused, sintered, cemented and deposited on kieselgut, kaolin and other supports with various structural (A1 2 0z, V2O5, SiO2) and chemical (CuO, CaO, ZnO, K2O) promoters. "In the presence of iron catalysts, the formation of olefins and oxygen-containing compounds increases. Cobalt catalysts promote the formation of predominantly alkanes of normal structure, largely high molecular weight.

The design of the reactors used has a significant effect on the parameters of the Fischer - Tropsch synthesis process and the composition of the resulting products. In apparatuses with a fixed catalyst bed, operating at low temperatures, mainly aliphatic hydrocarbons are obtained. In fluidized bed reactors, where reactions are carried out at higher temperatures, a significant amount of olefins and oxygenates are present in the products.

The first industrial plants for the Fischer-Tropsch synthesis were put into operation in the mid-1930s in Germany and England. By 1943, the total capacity of the created installations for the production of motor fuels by this method exceeded 750 thousand tons per year. Most of them used a fixed bed of cobalt catalyst. A pilot plant with a fluidized bed of an iron catalyst with a capacity of 365 thousand tons per year of hydrocarbon products was operated in 1948-1953. in the USA. A domestic pilot plant for the Fischer-Tropsch synthesis has been in operation in Dzerzhinsk since 1937 for a number of years. Since 1952, the production of hydrocarbons from synthesis gas has been operating in the city of Novocherkassk, where synthesis is carried out in reactors with a fixed bed of cobalt catalyst, and the target products are liquid hydrocarbon solvents, raw materials for detergents and other chemical products.

In 1954-1957. An industrial enterprise was built for the processing of coal into liquid motor fuels 5ABOO-1 in South Africa with a capacity of 230 thousand tons per year of liquid products. Later, two more similar enterprises were created in the same place - BABO-P (1981) and BABO-SH (1983), with a nominal capacity of 2200 thousand tons per year of liquid products each.

At all enterprises, gasification of high-ash (up to 30%) bituminous coal, containing 1% sulfur and having a combustion heat of 23 MJ / kg, is carried out in gas generators "LU ^" operating under pressure. A schematic flow diagram of BOTTOM is shown in Fig. 3.6. Here, reactors of two designs are used: with a stationary and a fluidized bed of catalyst (in other plants - only reactors with a fluidized bed). In each fixed-bed reactor, the catalyst is placed in pipes (more than 2000 pcs. 12 m long and 50 mm inner diameter). The gas passes through the pipes at a high linear velocity, which ensures rapid removal of the reaction heat and the creation of conditions close to isothermal almost along the entire length of the pipes. At an operating pressure in the reactor of 2.7 MPa and a temperature of about 230 ° C, the maximum yield of alkanes is achieved.

Rice. 3.6. ZABOI plant diagram:

1 - oxygen production; 2 - gas generators; 3 - power plant; 4 - the "Phenosolvan" process; 5 - separation; 6 - processing of resins and oils; 7 - process "Rectisol"; 8, 9 - Fischer - Tropsch synthesis reactors with a fixed and fluidized bed of catalyst, respectively; 10 - conversion; 11 - the release of oxygen-containing compounds; 12 - cleaning of paraffins; 13 - processing of liquid products; 14 - oligomerization of olefins; 15 - cryogenic separation; 16 - synthesis of ammonia;

I - air; II - coal; III - water; IV - pitch; V - creosote; VI - benzene-toluene-cr-ash fraction; VII - broad gasoline fraction; VIII - phenols; IX - alcohols; ketones; XI - liquid products; XII - refined paraffins; XIII - boiler fuel; XIV - diesel fuel; XV - gasoline; XVI - fuel gas to the city network; XVII - 0 2; XVIII - N2; XIX - gases C 3 -C 4; XX - H 2; XXI - sour bastards:

XXII - YNz; XXIII - (Ministry of Internal Affairs

In reactors with a fluidized bed of catalyst (with a diameter of 2.2 m and a height of 36 m), the synthesis is carried out at a temperature of 300-350 ° C and a pressure of 2-3 MPa, the gas flow rate into the reactor reaches 100 thousand m 3 / h. The reaction products enter the settling section and then cyclones to separate the entrained catalyst dust. The ratio NH: CO in the raw synthesis gas is 2.4-2.8, the resulting liquid products are characterized by an increased content of olefins. At the enterprises of BABOE, catalysts based on iron, promoted with alkali, are used in all types of reactors; these catalysts are cheap and provide a low methane yield; coal consumption for obtaining 1 ton of liquid products is 5.6-6.4 tons. ... Thermal efficiency complex for processing coal into motor fuels using the Fischer-Tropsch synthesis is 35-40%. The properties of gasoline and diesel fractions obtained in different types of reactors differ significantly (Table 3.9). Along with motor fuels, these plants produce ammonia, sulfur and other chemical products.

Like other liquefaction processes, gasification of coal with subsequent synthesis of motor fuels requires high capital and operating costs. For example, capital investments for the construction of the ZABO-P plant amounted to about $ 4 billion (in 1980 prices). With 8,000 hours of operation, the plant's total operating costs are $ 987 million per year (in 1980 prices), including:

• Coal cost 125
• Staff maintenance 80
• Electricity 80
• Catalysts and reagents 24
• Water 2
• 80 auxiliaries and repairs
• Overhead 80
• Depreciation deductions 520

In comparison with hydrogenation processes, the method of coal liquefaction through the Fischer - Tropsch synthesis is simpler in terms of instrumentation and operating conditions, but its thermal efficiency is about 15% lower.

COAL HYDROGENIZATION - transformation of high-molecular substances of the organic mass of coal (OMC) under hydrogen pressure into liquid and gaseous products at 400-500 ° C in the presence of various substances, organic solvents, catalysts, etc. The scientific basis for this process was developed at the beginning of the 20th century. VN Ipatiev, ND Zelinsky, F. Bergius, F. Fisher and others. In the 1930s. in some countries, notably Germany and Great Britain, were built industrial enterprises for the production of gasoline, diesel fuel, lubricating oils, paraffins, phenols, etc. from coal and coal tar. In the 1940s. the production of liquid products from coal exceeded 4 million tons / year. In the 1950s. the hydrogenation of coal was mastered on a semi-industrial scale in the USSR.

In the 1950s. rich oil fields were discovered in the USSR, the Middle East and other regions of the world. The production of synthetic liquid fuels from coal has practically ceased as its cost was 5-7 times higher than the cost of motor fuel obtained from oil. In the 70s. the price of oil has risen sharply. In addition, it became obvious that with the existing scale of oil consumption (~ 3 billion tons / year), its reserves suitable for production by economical methods will be depleted in the middle of the 21st century. The problem of involving solid fuel, mainly coal, in processing to obtain liquid oil substitute products has become urgent again.

For the hydrogenation of coal, unoxidized brown and low-metamorphosed bituminous coals are used. The content of the mineral part in them should not exceed 5-6%, the ratio C: H - 16, the yield of volatile substances should be more than 35%, the content of petrographic components of the vitrinite and liptinite group - more than 80%. High-ash coals must be pre-processed.

OMU with a C content of 70-85%, usually used for hydrogenation, is a self-associated multimer consisting of spatially structured blocks (oligomers). The blocks include macromolecules of carbon atoms, hydrogen and heteroatoms (O, N, S), which leads to an uneven distribution of electron density; therefore, donor-acceptor interaction takes place in the blocks, incl. hydrogen bonds are formed. The breaking energy of such bonds does not exceed 30 kJ / mol. There are blocks with a molecular weight of 200-300, 300-700 and 700-4000, which are soluble in heptane (oil), benzene (asphaltenes) and pyridine (asphaltenes), respectively. Within the blocks, macromolecules are linked by methylene, as well as by O-, N-, and S-containing bridges. The breaking energy of these bonds is 10-15 times greater than the breaking energy of blocks. During the hydrogenation of coal, blocks are separated first of all. The subsequent destruction of blocks requires an elevated temperature and the presence of active H2. To obtain liquid products from coal, it is necessary, along with destruction, to hydrogenate the resulting low molecular weight unsaturated compounds.

The basic technological scheme of coal hydrogenation is shown in the figure:

Figure: Schematic diagram of coal hydrogenation.

Initial operations - coal preparation.

To increase the specific surface area, coal is crushed to particles less than 0.1 mm in size, often in combination with drying. The best results are achieved with vibratory grinding and grinding in a disintegrator. In this case, the specific surface area increases by 20-30 times, the volume of transition pores by 5-10 times. Mechanochemical activation of the surface occurs, as a result of which the reactivity of coal increases (especially when grinding in a mixture with a paste-forming solvent and a catalyst). Drying plays an important role. Moisture fills the pores, preventing the penetration of reagents to the coal, is released during the process in the reaction zone, reducing the partial pressure of H2, and also increases the amount of waste water. Coals are dried to a residual moisture content of 1.5% using tubular steam dryers, vortex chambers, tube-dryers, in which hot flue gases with a minimum O2 content (0.1-0.2%) serve as a heat carrier so that the coal does not undergo oxidation ... To avoid a decrease in reactivity, the coal is not heated above 150-200 ° C.

To increase the degree of conversion of WMD into liquid products, a catalyst (from salt solutions, in the form of a powder, emulsion or suspension) in an amount of 1-5% by weight of coal is applied to coal. The more active the catalyst, the lower the pressure the coal can be hydrogenated at. The maximum catalytic activity is possessed by the compounds Mo, W, Sn, when using which the hydrogenation of coal can be carried out at a relatively low pressure - 10-14 MPa. However, their use is limited due to the difficulty of regenerating from a mixture with the remainder of the unconverted coal. Therefore, in many processes, cheap, albeit low-activity, catalysts are used (for example: red mud-waste after the separation of А12О3 from bauxite), compensating for their insufficient activity by increasing the hydrogen pressure to 30-70 MPa.

The efficiency of coal hydrogenation is largely determined by the chemical composition and properties of the paste-forming solvent, in a mixture with which (50-60% of the paste-forming agent) the coal is processed. The pasting agent should contain high-boiling fractions of the coal hydrogenation product (boiling point> 325 ° C) with a minimum content of asphaltenes to keep the coal in the liquid phase. In most variants of the hydrogenation of coal, substances with hydrogen-donating properties are added to the pasting agent to stabilize the blocks formed from the coal multimer at a relatively low temperature (200-350 ° C), when molecular hydrogen is inactive. The blocks easily split off hydrogen from donors and, due to this, do not "stick together".

The hydrogen-donating component of the pasting agent is obtained by hydrogenation of the coal hydrogenation fraction with a boiling point of 300-400 ° C. In this case, bi-, tri-, and tetracyclic aromatic hydrocarbons are partially hydrogenated to form hydroaromatic derivatives, which are capable of giving off hydrogen at higher rates than naphthenic hydrocarbons. The amount of donor in the pasting agent can be 20-50% (the composition of the pasting agent is optimized depending on the type of raw material and hydrogenation conditions). High-boiling fractions of petroleum products are also used as a donor.

The degree of conversion of OMU increases with the introduction of organic additives-compounds capable of interacting with coal and its degradation products (γ-picoline, quinoline, anthracene, etc.) into the pasting agent. The additives also temporarily stabilize reactive radicals formed during the primary destruction of coal, etc. prevent the formation of condensation by-products.

The resulting coal-oil paste mixed with a circulating hydrogen-containing gas (80-85% H2 at the inlet, 75-80% at the outlet) is heated in a heat exchange system and a tube furnace and then sent to the reactor for hydrogenation. For 1 ton of paste, 1.5-5.5 thousand m3 of gas is introduced. Part of the gas is fed into the reactor cold to cool the reaction mixture and maintain a constant temperature, since during the hydrogenation of coal 1.2-1.6 MJ is released per 1 kg of coal. With an increase in temperature, the rate of destruction of OMU increases, but at the same time the rate of hydrogenation decreases.

Hydrogenation is carried out in three or four sequentially located cylindrical hollow reactors. The duration of the hydrogenation of coal, as a rule, is determined by the volumetric flow rate of the coal-oil paste into the reaction system. This speed depends on the type of coal, paste former, catalyst, temperature and pressure of the process. The optimal space velocity is selected empirically and is usually 0.8-1.4 tons per 1 m3 of reaction volume per hour (processes with a higher space velocity are being developed).

The reaction products are separated in a separator into a steam-gas mixture and a heavy residue - sludge. From the first stream, liquid products (oil, water) and gas are separated, which, after separation of saturated hydrocarbons (C1-C4), NH3, H2S, CO2 and CO, H2O, is enriched with 95-97% H2 and returned to the process. The sludge is separated into liquid products and a solid residue. Liquid products after separation of water are subjected to distillation into a fraction with a boiling point of up to 325-400 ° C and a residue, which is returned to the process for making a paste.

Due to the complex structure of the OMU, the different reactivity of its fragments, the final liquid products contain many components, mainly mono- and bicyclic aromatic and heterocyclic compounds with impurities of paraffinic and naphthenic hydrocarbons, as well as phenols, pyridine bases, and other substances that can be isolated ...

Natural coal reserves significantly exceed oil reserves. Of the 3.5 trillion tons of fossil fuels that can be extracted from the earth's interior, 80% is coal. Our country has half of all the world's coal reserves.

Coal is a complex mixture of organic matter that has formed from the decomposition of wood and plant residues over millions of years. Coal processing is carried out in three main directions: coking, hydrogenation and incomplete combustion.

Coal coking is carried out in coke ovens, which are chambers, in the upper part of which there are holes for charging coal (Fig. 5). The chambers are separated from each other by heating walls. They burn gas, preheated in regenerators, which are located under the chambers.

1 - gas collector for condensation products; 2 - removal of volatile coking products; 3 - hatch for loading coal; 4 - coking chambers;

5 - heating walls; 6 - regenerators (heat exchangers) for heating fuel gas and air

Figure 5 - Scheme of a separate element of a coke oven

The temperature in the chambers is 1000–1200 ° С. At this temperature, without access to air, coal undergoes complex chemical transformations, as a result of which coke and volatile products are formed. Coal coking is a batch process: after the coke is unloaded, a new portion of coal is loaded into the chamber. The resulting coke is quenched with water. The cooled coke is sent to metallurgical plants, where it is used as a reducing agent in the production of pig iron. When volatile products (coke oven gas) are cooled, coal tar is condensed and ammonia water... Ammonia, benzene, hydrogen, methane, carbon monoxide (II), nitrogen, ethylene and other substances remain uncondensed. Passing these gases through a sulfuric acid solution, ammonia is released in the form of ammonium sulfate. Ammonium sulfate is used as nitrogen fertilizer. The benzene is taken up in a solvent and then distilled off from the solution. After separation from ammonia and benzene, coke oven gas is used as a fuel or as a chemical raw material. Coal tar is formed in insignificant quantities (up to 3%). But given the scale of coke production, coal tar is seen as a raw material for the industrial production of a range of organic substances. From coal tar get benzene and its derivatives, naphthalene, phenol and other aromatic compounds. The main products obtained by coking coal are shown in the diagram (Fig. 6).

If products boiling up to 350 ° C are removed from the resin, then a solid mass remains - pitch. It is used for the manufacture of varnishes (pitch varnish), which are indispensable for painting iron and wooden structures.

Hydrogenation of coal is carried out at a temperature of 400–600 ° C under a hydrogen pressure of up to 25 MPa in the presence of a catalyst. This forms a mixture of liquid hydrocarbons, which can be used as a motor fuel. The advantage of this method is the ability to hydrogenate low-grade cheap brown coal, the reserves of which are huge in our country.

Figure 6 - Main products obtained by coking coal

Incomplete combustion of coal gives carbon monoxide (II). On a catalyst (nickel, cobalt) at normal or elevated pressure from hydrogen and carbon monoxide (II), you can get gasoline containing saturated and unsaturated hydrocarbons:

nCO + (2n + 1) H 2 ® C n H 2 n +2 + nH 2 O

nCO + 2nH 2 ® C n H 2 n + nH 2 O

DI Mendeleev proposed a progressive method for converting coal into gaseous fuel by gasifying it directly at the place of occurrence (underground). Currently, in our country and abroad, work is being carried out on underground gasification of coal.

Destructive hydrogenation is carried out with the aim of obtaining light liquid fuel from solid or heavy liquid fuel - gasoline and kerosene. In terms of its chemistry, this is a very complex process, in which the splitting (destruction) of high-molecular compounds (macromolecules of coal) occurs simultaneously with the formation of simpler saturated and unsaturated hydrocarbons and fragments and the addition of hydrogen to fragments - at the site of double bonds and to aromatic hydrocarbons. Depolymerization and other processes also occur.
The addition of hydrogen (hydrogenation) is accompanied by a decrease in volume and the release of heat. Hydrogenation reactions are promoted by an increase in pressure and removal of reaction heat.
Usually, the hydrogenation of coals is carried out at a pressure of 2000-7000 ncm2 and a temperature of 380-490 ° C. To accelerate the reaction, catalysts are used - oxides and sulfides of iron, tungsten, molybdenum with various activators.
Due to the complexity of the hydrogenation process, the process of obtaining light fuel from coal - gasoline and kerosene - is carried out in two stages - in the liquid and vapor phase. Young bituminous and brown coals containing a significant amount of hydrogen are most suitable for hydrogenation. Coals are considered the best if the ratio between carbon and hydrogen is no more than 16-17. Harmful impurities are sulfur, moisture and ash. Allowable moisture content 1-2%, ash 5-6%, sulfur content should be minimal. To avoid high hydrogen consumption, oxygen-rich fuels (eg wood) are not hydrogenated.
The hydrogenation process technology is as follows. Finely crushed coal (up to 1 mm) with the required ash content is mixed with a catalyst, most often with iron oxides, dried and thoroughly ground in a pestle mill with oil, which is obtained by separating hydrogenation products. The content of coal in the paste should be 40-50%. The paste is fed into the hydrogenation unit with a pestle pump under the required pressure; fresh and circulating hydrogen is supplied there by compressors 2 and 3. The mixture is preheated in heat exchanger 4 by heat
Coming from the hydrogenation column of vapors and gases, and then in a tube furnace 5 to 440 ° C and enters the hydrogenation column 6, where due to the heat of reaction, the temperature rises to 480 °. After that, the reaction products are separated in a separator in the upper part of which vapors and gases leave, and from the lower part - sludge.
The vapor-gas mixture is cooled in a heat exchanger 4 and a water cooler 8 to 50 ° C and separated 9. After the pressure is removed, the condensate is distilled to obtain a "wide fraction" (300-350 °) and heavy oil. The wide fraction, after extracting phenols from it, enters the second stage of hydrogenation. The sludge separated in the separator 7 is separated by centrifugation into a heavy oil and a solid Istate, which is subjected to semi-coking. As a result, a heavy oil and a fraction are formed, which is added to the wide one. Ash residues are used as fuel. Heavy oils are used to make pasta. The gases separated in the separator 9, after the absorption of hydrocarbons in the scrubber 10 with oils under pressure, are returned to the process by means of the circulation pump 3.
Hydrogenation in the second stage is carried out most often in the presence of WSo at a pressure of 3000 ncm2 at 360-445 ° C. Gasoline and kerosene or diesel fuel are isolated from the obtained hydrogenation product. In the fuel obtained by hydrogenation, there are no unsaturated hydrocarbons, and sulfur is in the form of hydrogen sulfide, which can be easily removed by washing with alkali and then with water. Destructive hydrogenation is carried out in columns made of alloy steels containing chromium, nickel, and molybdenum. The wall thickness is up to 200 liters and the height is up to 18 m and the diameter is 1 m. In the columns for hydrogenation in the vapor phase, the catalyst is placed on mesh shelves.
Gasoline output can reach 50-53% for the combustible mass of coal.