Hydrogenation of coal reaction. Destructive hydrogenation of coal

To obtain valuable chemical compounds from coal, heat treatment processes (semi-coking, coking) or heat treatment in the presence of hydrogen under pressure (hydrogenation) are used.

The thermal decomposition of coal is accompanied by the formation of coke, tar and gases (mainly methane). Resins from the semi-coking of hard coals mainly contain aromatic compounds. Resins from the semi-coking of brown coals, along with aromatic compounds, also contain a significant amount of saturated cycloalkanes and alkanes. Coke is the target product of semi-coking. During the thermal processing of coal in the presence of hydrogen, it is possible to almost completely convert the organic mass of coal into liquid and gaseous hydrocarbons.

Thus, hydrogenation of coals can be used to produce not only motor and aviation fuels, but also basic petrochemical raw materials.

Hydrogenation liquefaction of coal is a complex process that includes, on the one hand, the disaggregation of the structure of the organic mass of coal with the breaking of the least strong valence bonds under the influence of temperature, and on the other, the hydrogenation of broken and unsaturated bonds. The use of hydrogen is necessary both to increase the H:C ratio in products due to direct hydrogenation, and to stabilize the destruction products of eliminated macromolecules.

The implementation of the process of hydrogenation of coal under relatively low pressure - up to 10 MPa - is possible using a hydrogen paste-forming donor of petroleum or coal origin and the use of effective catalysts.

One of the main problems in coal liquefaction is the optimization of the process of hydrogen transfer from paste-forming donors to the coal substance. There is an optimal degree of hydrogen saturation of donor molecules. The paste agent should contain 1-2% more hydrogen than in coal liquefaction products. The introduction of various types of substituents into the structure of donors affects both thermodynamic and kinetic characteristics. The transfer of hydrogen from donors to carriers - molecules of aromatic compounds - occurs stepwise according to the free radical mechanism.

At low pressure (up to 10 MPa), the use of donors allows coal to add no more than 1.5% hydrogen, and for deep liquefaction of coal (90% or more) it is necessary to add up to 3% hydrogen, which can be done by introducing it from the gas phase.

A molybdenum catalyst, used in combination with iron and other elements, significantly intensifies the process, increases the depth of coal liquefaction and reduces the molecular weight of the products.

The main primary products of coal hydrogenation are hydrogenation product and sludge containing ~ 15% solid products (ash, unconverted coal, catalyst). Gaseous hydrogenation products containing C1-C4 hydrocarbons, ammonia, hydrogen sulfide, carbon oxides mixed with hydrogen are sent for purification using the short-cycle adsorption method, and gas with 80-85% hydrogen content is returned to the process.

When the hydrogenate condenses, water is separated, which contains dissolved ammonia, hydrogen sulfide and phenols (a mixture of mono- and polyhydric).

Below is a schematic diagram of the chemical processing of coal (diagram 2.3).

The water condensate contains 12-14 g/l of phenols of the following composition (in% (wt.):

To obtain phenols, aromatic hydrocarbons and olefins, a scheme has been developed for the chemical processing of coal liquefaction products, which includes: distillation to isolate the bp fraction. up to 513 K; isolation and processing of crude phenols; Hydrotreating of the dephenolized broad fraction with bp. up to 698 K; distillation of the hydrotreated product into fractions with bp. up to 333, 333-453, 453-573 and 573-673 K; hydrocracking of middle fractions in order to increase the yield of gasoline fractions; catalytic reforming of fractions with bp. up to 453 K; extraction of aromatic hydrocarbons; pyrolysis of raffinate gasoline.

When processing brown coal from the Borodino deposit of the Kansko-Achinsk coal basin, in terms of the dry weight of coal, the following compounds can be obtained (in wt.%):

In addition, 14.9% C1-C2 hydrocarbon gases can be isolated; 13.4% - liquefied hydrocarbon gases C 3 -C 4, as well as 0.7% ammonia and 1.6% hydrogen sulfide.

Coal reserves in nature 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 contains half of the world's coal reserves.

Coal is a complex mixture of organic substances that were formed as a result of the decomposition of wood and plant debris over millions of years. Coal processing occurs in three main directions: coking, hydrogenation and incomplete combustion.

Coking of coal is carried out in coke ovens, which are chambers in the upper part of which there are holes for loading coal (Fig. 5). The chambers are separated from each other by heating walls. They burn gas that is preheated in regenerators 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 - Diagram of a separate element of a coke oven

The temperature in the chambers is 1000–1200°C. At this temperature, without access to air, coal undergoes complex chemical transformations, as a result of which coke and volatile products are formed. Coking of hard coal is a periodic process: after unloading the coke, 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 and ammonia water condense. Ammonia, benzene, hydrogen, methane, carbon monoxide (II), nitrogen, ethylene and other substances remain uncondensed. By passing these gases through a solution of sulfuric acid, ammonia is released in the form of ammonium sulfate. Ammonium sulfate is used as a nitrogen fertilizer. Benzene is absorbed into the solvent and then distilled from the solution. After separation from ammonia and benzene, coke oven gas is used as fuel or as a chemical raw material. Coal tar is formed in small quantities (up to 3%). But given the scale of coke production, coal tar is considered as a raw material for the industrial production of a number of organic substances. Benzene and its derivatives, naphthalene, phenol and other aromatic compounds are obtained from coal tar. The main products obtained from coal coking are presented in the diagram (Fig. 6).

If you remove products boiling at 350°C from the resin, what remains is a solid mass - pitch. It is used for the production 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 produces a mixture of liquid hydrocarbons, which can be used as motor fuel. The advantage of this method is the possibility of hydrogenating low-grade, cheap brown coal, the reserves of which are huge in our country.

Figure 6 - Main products obtained from coal coking

Incomplete combustion of coal produces carbon (II) monoxide. Using a catalyst (nickel, cobalt) at normal or elevated pressure, it is possible to produce gasoline containing saturated and unsaturated hydrocarbons from hydrogen and carbon monoxide (II):

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

D.I. Mendeleev proposed a progressive method of converting coal into gaseous fuel by gasifying it directly at its location (underground). Currently, work on underground gasification of coal is being carried out in our country and abroad.

Hydrogenation coal processing is the most universal method of direct liquefaction. The theoretical basis for the effect of hydrogen on organic compounds under pressure was developed at the beginning of the 20th century. Academician V.N. Ipatiev. The first extensive research on the application of hydrogenation processes to coal processing was carried out by German scientists in the 1910-1920s. During the period 1920-1940s. A number of industrial enterprises based on this technology were created in Germany. In the 1930-1950s. experienced and industrial installations for the direct liquefaction of coal by hydrogenation 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 it is 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 liquid-phase hydrogenation of coals in the temperature range of 300-500°C, the complex matrix of coal is destroyed, accompanied by the breaking of chemical bonds and the formation of active free radicals. The latter, stabilized by hydrogen, form molecules smaller than the original macromolecules. Recombination of free radicals also leads to the formation of high molecular weight compounds. The hydrogen required to stabilize radicals is partially provided through the use of hydrogen donor solvents. These are compounds that, interacting with coal, when high temperatures are dehydrogenated, and the atomic hydrogen released joins the products of coal destruction. The hydrogen donor solvent is also a paste former. 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-donating properties. Higher boiling compounds of this group (naphthalene and cresol) are less active, but when they are mixed with tetralin, a synergistic effect occurs: a mixture of equal parts of tetralin and cresol has a higher donor capacity than each individually.

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

Based on numerous studies, it has been established that for hydrogenation processing into liquid products, coals of low stages of metamorphosis are preferable.

Table 3.5. Characteristics of brown coals of the Kansk-Achinsk basin and hard coals of the Kuznetsk basin

Kansk-Achinsk basin

Field

ma and brown coals with vitrinite reflectivity index L° = 0.35-0.95 and the content of inert petrographic microcomponents not higher than 15% (wt.). These coals must contain 65-86% (wt.) carbon, more than 5% (wt.) hydrogen and at least 30% (wt.) volatile substances based on organic mass. 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 from the Kan-Achinsk basin and hard coals from the Kuznetsk basin (Table 3.5).

The suitability of coals for the production of liquid fuels by hydrogenation can be assessed from elemental composition data. I. B. Rapoport found that the yield of liquid hydrogenation products per organic mass of coal decreases with increasing 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? l, % (wt.)] from the content [% (wt.)] (in the original demineralized carbon of hydrogen and organic sulfur:

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

Brown coals are easily liquefied, but they usually contain a lot of oxygen (up to 30% at OMU), the removal of which requires a significant consumption of hydrogen. At the same time, their nitrogen content, which also requires hydrogen to remove, is lower than in hard coals.

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

The main parameters influencing 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 optimal temperature regime for liquid-phase hydrogenation is in the range of 380-430°C and for each specific coal lies in its own narrow range. At temperatures above 460°C there is a sharp increase in gas formation and the formation of cyclic structures. As the process pressure increases, the rate of coal liquefaction increases.

There are two known methods for carrying out liquid-phase hydrogenation 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, it usually represents a high-boiling extract of coal, freed from minerals, sulfur-, oxygen- and nitrogen-containing compounds and other undesirable impurities. To increase the degree of coal conversion, hydrogen gas can be supplied to the solution. Depending on the type of source coal, solvent and process conditions, products for various purposes can be obtained by thermal dissolution.

The technology for thermal dissolution of coal was first proposed by A. Pott and H. Brochet in the 1920s. By the early 1940s, an installation with a capacity of 26.6 thousand tons of extract per year was operating in Germany based on this technology.

In this installation, a paste consisting of one part of crushed coal and two parts of 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. A mixture of tstralin, cresol and medium oil of liquid-phase hydrogenation of coal tar pitch was used as a solvent. The yield of the extract with a softening point of 220 °C and a content of 0.15-0.20% (wt.) 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, new generation processes based on thermal dissolution of coal have been developed and implemented in pilot and demonstration plants in a number of countries. By intended purpose they can be divided into two types: 1) processes in which only primary solid or liquid products under normal conditions are obtained, intended, as a rule, for combustion in power plant furnaces, and 2) processes involving the processing of primary products into more qualified (firstly turn into motor fuels through secondary processes of thermal processing, hydrogenation and refining.

The extraction purification process for coal SRC (Solvent Refined Coab) developed in the USA in the basic version SRC-I is carried out at a temperature in the reactor 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 grinding and drying, is mixed with a hot coal suspension. The resulting paste, along with hydrogen, is passed through a fired heater and then sent to the reactor. The required temperature and partial pressure of hydrogen are maintained by supplying cold hydrogen to several points in the reactor. The reaction products are first separated in gas separators. The gas separated from liquid products, containing predominantly (stage I) hydrogen and gaseous hydrocarbons with an admixture of hydrogen sulfide and carbon dioxide, after cooling to 38°C, is sent to the acid gas removal system. In a cryogenic installation, gaseous hydrocarbons C 3 -C4 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 supplied to the fuel network. Liquid pro-

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

1 - mixer for preparing pasta; 2 - oven for heating pasta; 3 - reactor; 4 - gas separator block; 5 - acid gas absorber; 6 - cryogenic gas separation; 7 - fuel gas purification unit; 8 - separation of gaseous hydrocarbons; 9-unit for purification of synthetic gas and hydrogen separation; 10 - sulfur production block; II - residue gasification reactor; 12 - atmospheric column; 13 - vacuum column;

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

Heavy distillate products from gas separators enter the atmospheric column, where they are separated into a 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 supplied for displacement with the original coal, the other is fed into a 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 is used to produce synthesis gas used for the production of hydrogen or as fuel,

Based on dry deashed bituminous coal, the yield of products in the EIS-C process at a hydrogen consumption of 4.4% (wt.) is [% (wt.)]:

The EDS (“Exxon Donor Solvent”) process of thermal dissolution of coal is intended for the production of synthetic oil and its subsequent processing into motor fuels. According to this technology, coal, after grinding and drying, is mixed with a hot hydrogen donor solvent. As the latter, a fraction of 200-430°C of the liquid product of the process is used, previously hydrogenated in an apparatus with a stationary layer of Co-Mo catalyst. The mixture is fed into a flow reactor with an upward flow along with hydrogen gas, where thermal dissolution of the 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 by vacuum rectification) into gases and fractions that boil away at temperatures up to 540 °C and a residue >540 °C, which also contains unreacted coal and ash. The yield of products, the degree of conversion and other process indicators depend on the type of coal being processed. The yield and composition of liquid products is also affected by residue recycling. For example, at. different technological design of the process (without recycling of residue-I and with recycling of 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 recycling of the residue can vary from 42 to 51% (wt.), and the yield of Ci-C 3 gases can vary from 11 to 21% (wt.). All resulting fractions must be hydrotreated to remove sulfur and nitrogen. The content of heterocompounds increases with increasing boiling point of the fractions.

Two options for the EDS process flowsheet are proposed, differing in the methods of producing hydrogen and fuel gas. In the first option, hydrogen is obtained by steam reforming of light gases included in the process products, and fuel gas is obtained by processing the residue of vacuum distillation of the liquid product of the process in a coking plant 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 product range. About half of the vacuum residue is processed at the Flexicoking installation to produce liquid products and fuel gas, and the remaining amount is used to produce hydrogen. Thus, light hydrocarbon gases obtained by thermal dissolution are a commercial product. The thermal efficiency of this option reaches 63%.

Based on EDS technology, a demonstration plant with a capacity of 250 tons of coal per day was put into operation in the USA in 1980, the capital investment in the construction of which amounted to $370 million. A design for an industrial enterprise with a capacity of 23 thousand tons of coal per day was developed, the cost of which is estimated at 1.4 billion dollars (in 1982 prices).

The advantages of thermal dissolution processes include a lower operating temperature than in the pyrolysis of coals and the possibility of varying the quality of the resulting liquid product over a relatively wide range by changing the process parameters. At the same time, during thermal dissolution, deep conversion of coal is achieved at high process pressure and high-molecular compounds predominate in the composition of the resulting products. The presence of the latter is due to the fact that even at low temperatures, recombination processes of the resulting free radicals begin to occur, accompanied by the formation of secondary structures of an aromatic nature, less reactive than the original organic matter of coal. The presence of hydrogen donors and molecular hydrogen dissolved in the paste in the reaction mixture cannot sufficiently prevent the occurrence of these processes. 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 process conditions, but under normal conditions it can be a semi-solid or even solid substance, which is difficult to transport, store and process into final products.

Catalytic hydrogenation. Increasing the degree of coal conversion, improving the composition of the resulting liquid products and reducing the pressure of the hydrogenation process is possible with the use of catalysts. The latter facilitate the transfer of hydrogen from the solvent to the carbon and activate molecular hydrogen, converting it into atomic form.

Research in the field of direct hydrogenation processing of coal using catalysts was started by German scientists F. Bergius and M. Peer in 1912. As a result of these works, in 1927, the first industrial installation for the catalytic hydrogenation of coal with a capacity of 100 thousand tons per year of liquid products was built (Bergius-Pier process). By the beginning of the 1940s, there were already 12 enterprises of this type 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 at a large pilot plant in the period 1949-1953.

In the Soviet Union, research on the hydrogenation of domestic coals was started by N. M. Karavaev and I. B. Rapoport in 1929. Later, significant contributions to the development of these works were made by A. D. Petrov, A. V. Lozovoy, B. N. Dolgov , D.I. Orochko, A.V. Frost, V.I. Karzhev and a number of other Soviet scientists. In 1937, the first plant in our country for the hydrogenation processing of brown coal was designed and put into operation in Kharkov. 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% coal and 60% high-boiling coal product with the addition of an iron catalyst - was exposed to hydrogen gas at a temperature of 450-490 ° C and a pressure of up to 70 MPa in a system of three or four reactors in series. The degree of conversion of coal into liquid products and gas was 90-95% (mass.). Since economical methods for regenerating catalysts had not been developed at that time, in most cases cheap, low-activity catalysts based on iron oxides and sulfides were used. After passing through the reactor system and hot separator at a temperature of 440-450 °C, the circulating hydrogen-containing gas and liquid products were removed from above. The gas was then separated from the liquid in a cold separator and, after washing, returned to the cycle mixed with fresh hydrogen. The liquid product, after a two-stage pressure reduction to separate hydrocarbon gases and water, was subjected to distillation, and a fraction with an end boiling point of 320-350 °C and the 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 (full recirculation) through the paste former and with an excess of heavy oil. The first scheme was used by the majority of hydrogenation plants, focused primarily on the production of gasoline and diesel fuel. When working with an excess of heavy oil, the productivity of the installation for coal 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 produce electrode coke.

When processing coals with a cycle closed by the paste former, 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 vapor phase hydrogenation on a stationary bed of hydrocracking catalysts. The total yield of gasoline with an octane number of 80-85 using the motor method reached 35% (wt.), and with the simultaneous production of gasoline and diesel fuel, their total yield was about 45% (wt.) based on the initial coal; Hydrogen was obtained by gasification of coal or semi-coke.

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% (mass), the sludge was subjected to centrifugation. The residue with a solid content of about 40% was processed by semi-coking in drum rotary kilns with a capacity of 10-15 t/h and light liquid coking products were mixed with the distillate fraction of the hydrogenation product. The distillation of heavy oil obtained during centrifugation was returned to the cycle to prepare the paste.

The low activity of the catalyst, difficulties in sludge processing, and other factors necessitated the use of high pressures and large quantities hydrogen. The installations had low unit productivity and were characterized by significant energy intensity

In various countries I S ° ZDan n R ° chess of the second generation in various countries and primarily in the USSR, USA and Germany

During the development of these processes, the main focus of researchers was on reducing the pressure of equipment productivity, reducing energy efficiency, 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 direct hydrogenation catalytic liquefaction of coal in elm personal installations - from laboratory to demonstration ones with a productivity of 50 to 600 tons/day of coal.

BergiusN-?Pipä Germany On the basis of the previously used R U Peer process using a non-regenerable iron catalyst, the so-called “new German technology” of coal hydrogenation was developed. Unlike the old process, a circulating middle distillate is used to produce the paste (instead of the overflow produced by centrifugation). Liquid products are separated from the solid by residual vacuum distillation (instead of centrifugation) and the sludge is subjected to gasification to produce hydrogen. In the renullation, it was possible to reduce the operating pressure from 70 to 30 MPa, increasing the specific productivity of coal, the degree of conversion and thermal efficiency. 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-Coa1 process (USA). According to this technology, liquid-phase hydrogenation is carried out using a fluidized layer of an active finely dispersed Co-Mo catalyst according to the scheme shown in Fig. 3.3.

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

The vapors removed from the reactor, after condensation, are separated into hydrogen, hydrocarbon gases and light distillate. Gases are sent for purification, and hydrogen is sent for recycling. 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. From the first, gasoline and diesel fractions are obtained. The residual product removed from the bottom of the separator is divided into two streams in hydrocyclones: with a low and high solids content.

The first stream is used as a paste former, and the second is treated with a precipitant and the released sludge containing up to 50% solid particles is gasified to produce hydrogen. The liquid product remaining after sludge separation 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.) based on the organic mass of coal, including the gasoline fraction (28-200°C) - 25.2% (wt.), middle distillate (200 -260°C) - 12.9% (wt.) and heavy distillate - 13.3% (wt.). Hydrogen consumption for liquid-phase hydrogenation is 4.7% (mass.). The process was tested on a pilot plant with a coal capacity of 600 tons per day.

In our country, the Institute of Combustible Fossils (IGI), together with the Grozgiproneftekhim and VNIIneftemash institutes, carried out a wide range of research in the field of hydrogenation processing of coal into liquids in the 1970s.

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

1st 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 - hydrocycloi; 9 - separator; 10 - vacuum column; 1 - coal; II - hydrogen; III - recirculating heavy distillate;. IV - paste; V - hydrogenation level; VI - fluidized catalyst level; 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 - unreacted liquid residue for hydrogen production; XVII-heavy distillate for refining; XVIII -

residual fuel. The result of the research was a new technological process(IGI process), in which, thanks to the use of a regenerated active catalyst and inhibitory 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 costs and made it possible to use high-performance reactors with a capacity of 250-500 m 3, which are already used in the oil refining industry. The IGI process is being tested at large pilot plants.

According to the IGI technology, coal is pre-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 crushed a second time by vibration grinding to a particle size of less than 100 microns.

A catalyst of 0.2% Mon and 1.0% Fe(III) is applied to the crushed coal. This combination makes it possible to achieve a degree of conversion of the organic mass of coal up to 83%. Maximum activity of the catalyst is ensured when it is applied from solution to dried coal. Combined vibration 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 application of the catalyst to 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 coal due to the release of atomic hydrogen during their decomposition. The introduction of 1-5% of such additives ensures an increase in the degree of coal conversion and the yield of liquid products by 10-15%.

Coal with a catalyst applied to it enters the paste preparation system. Coal distillate with a boiling point of 300-400°C is used as a paste former, which is preliminarily hydrogenated under a pressure of 10 MPa in a separate stage. For normal operation 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 is difficult due to its high viscosity. The coal-oil paste, into which hydrogen gas is introduced, is preheated in a tubular furnace and enters a system of hollow unheated reactors at a volumetric velocity of 1.0-1.5 h -1 . During the residence time of the paste in the reactor (30-60 minutes), coal hydrogenation reactions occur with the formation of hydrocarbon gases (%-C4, ammonia, hydrogen sulfide and carbon oxides [up to 10% (wt.)], water and liquid products. As the process proceeds with the release of heat, cold hydrogen-containing gas is supplied to the reactors to regulate the temperature; it also serves as a mixing agent;

The products of hydrogenation reactions from the reactor are sent to a hot separator. From the top of the separator, a steam-gas stream containing gases and light liquid products is removed, 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% by weight. The vapor-gas stream is cooled and divided into a liquid part and hydrocarbon gas containing 75-80% (vol.) hydrogen, C1-C4 hydrocarbons, ammonia, hydrogen sulfide and carbon oxides. After separation of other gases by short-cycle adsorption, hydrogen is returned to the process. Hydrocarbon gas is used to produce hydrogen in an amount of 50-60% of its consumption in the process. The rest of the required hydrogen is produced in a separate installation by gasification of coal or residues from sludge processing.

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

Sludge processing, one of the most difficult stages of the process from a technical point of view, is carried out in two stages in the IGI scheme. At the first, the sludge is filtered to a residual solids content of about 30% (wt.), and at the second, it is subjected to vacuum distillation until the resulting residue contains 50-70% (wt.) solids. This residual product is burned in a cyclone furnace with liquid slag removal. During the combustion process, 97-98% of molybdenum goes into the gas phase (1M02O3) and is deposited on ash, from which it is then extracted using hydrometallurgy 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 ton of sludge residue.

Liquid products of hydrogenation processing of coals differ from conventional oil in their elemental composition and lower hydrogen content, as well as the presence of significant quantities 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 IGI process scheme, hydrotreating of a wide distillate of liquid-phase hydrogenation of coal with a boiling point of up to 400 °C is carried out under 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°C

The part of alkenes most prone to polymerization is hydrogenated. Then, at a temperature of 400°C, the bulk of alkenes and partially aromatic compounds are hydrogenated; sulfur-, oxygen- and nitrogen-containing compounds are also destroyed. Hydrotreating is carried out in the presence of aluminum-cobalt-molybdenum catalysts, widely used in oil refining. However, in a number of cases, due to the high content of heteroatomic compounds in coal distillates, these catalysts are not effective enough or are quickly poisoned. Therefore, new stable catalysts are required.

The characteristics of the initial distillate of brown coal hydrogenation using IHI technology and its hydrotreating products are given in Table. 3.7. Primary distillate products of liquid-phase hydrogenation of coal are unstable. During storage, they change color and form insoluble precipitates, which is caused by the substances present in them.

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

composition in trace quantities of nitrogen-containing compounds of a non-basic nature such as pyrrole. These compounds may not be completely removed by hydrotreating, and to obtain sufficiently stable products, it is recommended that adsorption and extractive denitrogenation of the broad hydrogenation distillate or its fractions be included in the overall process design.

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

~ Received

Taken [% (wt.)] [% (wt.)]

As you can see, with 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 using the IGI method. To do this, the 120-230 °C fraction isolated 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 aluminum palladium sulfide catalyst). The third stage is necessary if the hydrotreated fraction 120-230°C contains more than 22%

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

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

1 - coal; 11 - paste former; III - catalyst; IV-hydrogen; V - gases C 4 and CO; VI - liquid hydrogenation products; VII - G4Hz, Ng$ and COg; VIII - Fraction >400 °C; IX - solid residue; X - 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

^wt.) aromatic hydrocarbons. But to the data.

By including in the technological scheme various sets of processes for processing hydrogenation product and its fractions in the IGI process, it is possible to change the ratio of the resulting gasoline and diesel fuel - from 1: 0 to 1: 2.6. To maximize gasoline production, diesel fractions can be hydrocracked. The scheme for producing motor fuels according to one of the options based on IGI technology is shown in Fig. 3.4. When organizing the production of 3 million tons of motor fuels per year according to this scheme, 19.7 million tons per year of brown coal from the Kansk-Achinsk basin will be required, 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 c.i. of such production is 55%.

In foreign coal hydrogenation processes, it is also planned to use various options for upgrading and recycling liquid products. For example, the project of a processing complex based on the BIS-I process for 30 thousand tons per day of US bituminous coals provides for all liquid hydrogenation products to be subjected to hydrocracking with a conversion rate of about 50%. The resulting gasoline fraction after additional hydrotreating must be reformed to obtain a component of motor gasoline with an octane number of 100 (research method). In general, the complex is expected to produce 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 costs for the construction of the complex are estimated at $5.7 billion (in 1982 prices). Annual operating costs at 90% capacity utilization will be (in million dollars): cost of coal - 420, energy costs - 101, catalysts and chemicals - 77, operating materials - 114, personnel costs (1900 people) - 79.

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

Research and development work in the field of hydrogenation processing of coal, ongoing 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 reduce the unit costs of producing motor fuels from coal. A combination of the processes of hydrogenation and gasification of coal in a single stream without the complicating stages of separation of liquefaction products and without the loss of energy spent on heating the raw materials should be considered promising.

Coal gasification and synthesis of hydrocarbon fuels

When producing motor fuels from coal by indirect liquefaction, the first stage is gasification.

Gasification of solid fuel is a thermal process during which the organic part of the fuel in the presence of oxidizing agents (air or industrial 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 during the coking process, but by the middle of the century, residue-free gasification of coke and coal was carried out on an industrial scale in cyclic and then in continuously operating gas generators. At the beginning of this century, coal gasification was widespread in many countries around the world, primarily for the production of energy gases. By 1958, about 2,500 gas generators were operating in the USSR various sizes and structures that ensured the production of about 35 billion m3 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 gasification of solid fuels both in our country and abroad have decreased significantly.

Coal gasification is carried out at high temperatures and is a multi-stage heterogeneous physicochemical process. The organic mass of coal, primarily the carbon included in its composition, interacts with gaseous oxidizing agents. 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, pyrolysis products are formed in the first stage of their heating.

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

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

Unlike hydrogenation, the requirements for raw materials 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, moisture content, ash and sulfur is very significant. A number of restrictions on these parameters are reduced after pre-treatment coals - drying, oxidation, etc. The most significant indicator of the use of coals in certain gasification processes is the melting point of ash residues. It determines the temperature range of the main process and the choice of slag removal system.

The activity of solid fuels and the rate of gasification largely depend on the mineral components that act 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 gasification of solid fuels may include: the method of supplying heat to the reaction zone; method of supplying the gasifying agent; type of gasifying agent; process temperature and pressure;

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

Based on 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 allothermic. 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 using a heating element immersed in the reactor.

To organize the process of interaction between fuel and oxidizer in the reactor, a continuous moving layer of coarse coal, a cocurrent flow of coal and oxidizer in entrainment mode, and a fluidized layer of fine-grained coal are used. In gas generators with a continuous layer, a downward movement of lump fuel and an upward movement of a flow of hot gases are organized. This principle determines the high chemical and thermal activity of the process and makes it possible to gasify most types of coals, with the exception of caking 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 layer cause an increased methane content in the product gas [up to 10-12% (vol.)], as well as the formation of significant quantities of by-products such as tars, liquid hydrocarbons and phenols.

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

In gas generators operating in entrainment mode, pulverized coal is processed. It is introduced into the reactor in a co-flow with steam-oxygen blast, while the temperature in the reaction zone reaches 2000°C. All types of coal can be processed in such gas generators. Reactions in them occur at high speed, which ensures high specific productivity. The product gas contains practically no methane, tars and liquid hydrocarbons. But due to the high operating temperature, the oxygen consumption in such gas generators is greater than in gas generators with a continuous or fluidized bed of fuel, and an effective heat recovery system is necessary to ensure high thermal efficiency. When operating such gas generators, the raw material supply regime must be strictly observed, since due to the small amount of coal simultaneously present in the reactor, any violation of the regime leads to a stop of the process.

One option for gasification in entrainment mode is the use of a water-coal suspension instead of dry pulverized fuel. This makes it easier to supply fuel to the reactor and eliminates the need to use bunker systems to load it.

Typically, air, oxygen and water vapor serve as gasifying agents in gasification processes. With steam-air blasting, there is no need to install air separation, which reduces the cost of the process, but the resulting gas is low-calorie, since it is highly diluted with nitrogen from the air. Therefore, in gasification schemes, preference is given to steam-oxygen blast and the ratio of steam to oxygen is determined by the conditions. carrying out the process. In hydrogasification processes, hydrogen is used as one of the gasifying agents, thereby producing a high-calorie gas rich in methane.

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

In various gasification processes, pressure can vary from atmospheric to 10 MPa. An increase in pressure creates favorable conditions for increasing 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 (the cost of compressing synthesis gas is reduced). With increasing pressure, it is possible to increase the rate of gasification and the unit power of gas generators. When gasifying lumpy and coarse-grained fuels, the gasification rate is proportional to the square root of the pressure, and when gasifying fine-grained and pulverized fuels, it is proportional to the pressure.

In gas generators with liquid slag removal, the process is carried out at temperatures above the melting point of the ash (usually above 1300-1400 °C). “Dry ash” gas generators operate at lower temperatures, and the 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 for subsequent synthesis, as well as phenols, resins and liquid hydrocarbons. These compounds are removed in the purification stage following the gas generator. 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 diisopropanolamine, dimethyl and polyethylene glycols, ethanolamines, etc. are used as absorbents.

To ensure the optimal CO:Hg ratio in the synthesis gas, the technological scheme usually includes special

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

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

unit for the catalytic conversion of carbon monoxide with water vapor.

A diagram of the gasification process to produce synthesis gas, ready for further processing, is shown in Fig. 3.5.

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

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

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

In Lurgi gas generators, lump coal is introduced into the reaction zone through a sealed loading hopper and gasified in the countercurrent of a steam-oxygen mixture. The latter is fed under a grate that supports a layer of coal; Dry ash is removed through the same grate. The volume-ratio of steam: oxygen is selected such that the temperature of the coal bed is lower than the melting point of the ash. Saturated water vapor is formed in the cooling jacket of the generator.

Coal entering the gas generator sequentially passes through three heating zones. In the first zone - the upper part of the reaction

torus - at a temperature of 350 ° C it is dried with hot gases, in the middle - at a temperature of l; 600 ° C, coal is subjected to semi-coking with the formation of gases, tar and semi-coke.. 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 contains virtually no methane. The gas passes the coal layer from the bottom up, while its temperature decreases, and methane formation reactions begin to occur in the colder zones of the reactor. Thus, the resulting product gas contains unsaturated hydrocarbons and resins, which requires mandatory gas purification and causes high water consumption for cooling and removal of undesirable components. The gas also contains an increased amount of methane [up to 8-12% (vol.)] 1.

The gasification process using the “Lurgi” method is characterized 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 elevated pressure, which significantly increases the unit productivity of the gas generator and reduces the cost of gas compression when used in further syntheses.

The Winkler process is the first industrial process coal gasification. 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 30-50°C below the softening temperature of the ash, which is removed from the reactor in dry form.

The Winkler gas generator is a device lined from the inside fireproof material, a fluidized bed is created by blowing a steam-oxygen mixture through crushed coal. Larger coal particles are gasified directly in the layer, and small particles are carried out. it and are gasified at a temperature of 1000-1100°C in the upper part of the reactor, where a gasifying agent is additionally supplied. Due to intensive heat and mass exchange 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 dry form using a screw conveyor, the rest is carried out by a gas flow and collected 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 there are large losses of unreacted *coal - up to 25-30% (wt.) carried out of the reactor, which leads to heat losses and a decrease in the energy efficiency of the process. The fluidized layer is highly sensitive to changes in process conditions, and low pressure limits the productivity of gas generators.

A representative of the gasification processes of pulverized fuel in the entrainment mode is the “Korregv-T^hek” process. 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 productivity of 36-50 thousand m 3 /h.

The gas generator is a conical device with water cooling. It is equipped with two or four burners located opposite each other, and is lined on the inside with heat-resistant material. High turbulence of the reagents, achieved by supplying counter flows of the fuel mixture from opposite sides of the chamber, ensures reactions occur at high speeds and improves the composition of the resulting gas.

The coal is pre-crushed to particles no larger than 0.1 mm in size and dried to a residual moisture content of no higher than 8% (mass). Coal dust from the bunkers is supplied to the burners with a flow of part of the oxygen necessary for the process. The rest of the oxygen is saturated with water vapor, heated and introduced directly into the chamber. Superheated water vapor is introduced into the reactor through a tubular jacket, which creates a curtain that protects the reactor walls from exposure to high temperatures. At gas temperatures in the combustion zone up to 2000°C, fuel carbon reacts almost completely within 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 . The sulfur contained in coal is 90% converted into hydrogen sulfide and 10% into carbon sulphide. 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 low in methane and does not contain condensable hydrocarbons, which facilitates its subsequent “cleaning”. Disadvantages of the process include low pressure and increased oxygen consumption.

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

The work currently being carried out to improve autothermal processes is mainly aimed at increasing the gasification pressure, increasing the unit power and thermal efficiency. d. reactors, maximum reduction in the formation of by-products. In autothermal gasification processes, up to 30% of coal is spent not on gas formation, but on obtaining the necessary heat. This has a negative impact on the economics of the processes, especially when the cost of coal mining is high. Therefore, considerable attention is paid to Lately development of schemes for allothermic gasification of solid fuel using heat obtained from molten metals or from high-temperature nuclear reactors.

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

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

From synthesis gas, depending on the process conditions and the catalyst used, a wide range of hydrocarbons and oxygen-containing compounds can be obtained. 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, melted, sintered, cemented and deposited on kieselgut, kaolin and other supports with various structural (Al 2 03, V2O5, Si0 2) 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 parameters of the Fischer-Tropsch synthesis process and the composition of the resulting products are significantly influenced by the design of the reactors used. In devices with a stationary catalyst bed operating at low temperatures, mainly aliphatic hydrocarbons are produced. In fluidized bed reactors, where reactions are carried out at higher temperatures, the products contain significant amounts of olefins and oxygen-containing compounds.

The first industrial installations for Fischer-Tropsch synthesis were put into operation in the mid-1930s in Germany and England. By 1943, the total capacity of the established installations for the production of motor fuels using this method exceeded 750 thousand tons per year. Most of them used a stationary bed of cobalt catalyst. A pilot plant with a fluidized bed of iron catalyst with a capacity of 365 thousand tons per year of hydrocarbon products was operated in 1948-1953. in USA. The domestic pilot plant for 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 Novocherkassk, where synthesis is carried out in reactors with a stationary bed of cobalt catalyst, and the target products are liquid hydrocarbon solvents, raw materials for detergents and other chemical products.

In 1954-1957 was built industrial enterprise for processing coal into liquid motor fuels 5АБОБ-1 in South Africa with a capacity of 230 thousand tons per year of liquid products. Later, two more similar enterprises were created there - BABO-P (1981) and BABO-SH (1983), each with a nominal capacity of 2,200 thousand tons of liquid products per year.

At all enterprises, the gasification of high-ash (up to 30%) bituminous coal containing 1% sulfur and having a calorific value of 23 MJ/kg is carried out in gas generators "Lu" operating under pressure. The schematic technological diagram of the MILLING is shown in Fig. 3.6. Reactors of two designs are used here: with a stationary and fluidized bed of catalyst (at other plants - only reactors with a fluidized bed). In each fixed-bed reactor, the catalyst is placed in pipes (more than 2000 pieces, 12 m long and 50 mm in inner diameter). The gas passes through the pipes at a high linear speed, which ensures rapid removal of reaction heat and the creation of conditions close to isothermal along almost 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. Scheme of the ZABOI plant:

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

I - air; II - coal; III - water; IV - pitch; V - creosote; VI - benzene-toluene-cresol fraction; VII - wide gasoline fraction; VIII - phenols; IX - alcohols; ketones; XI - liquid products; XII - purified 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 - ННз; XXIII - (MVDgBO

In reactors with a fluidized bed of catalyst (diameter 2.2 m and height 36 m), synthesis is carried out at a temperature of 300-350 ° C and a pressure of 2-3 MPa, the gas flow into the reactor reaches 100 thousand m 3 / h. The reaction products enter the settling section and then into cyclones to separate the captured catalyst dust. The Hg:CO ratio in the raw synthesis gas is 2.4-2.8, the resulting liquid products are distinguished by a high content of olefins. At BABOB enterprises, alkali-promoted iron-based catalysts are used in all types of reactors; these catalysts are cheap and provide low methane yield; coal consumption to produce 1 ton of liquid products is 5.6-6.4 tons. To obtain motor fuels that meet the requirements of standards for fuels from oil, the resulting products are subjected to upgrading: gasoline fractions - purification and reforming, propylene and butenes - polymerization . Thermal efficiency complex for processing coal into motor fuels using 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, coal processing by gasification followed by the synthesis of motor fuels requires high capital and operating costs. For example, capital investments for the construction of the ZABOB-P plant amounted to about 4 billion dollars (in 1980 prices). With 8000 hours of operation, the total operating costs at this enterprise are 987 million dollars per year (in 1980 prices), including:

• Coal cost 125
• Staff content 80
• Electricity 80
• Catalysts and reagents 24
• Water 2
• 80 auxiliary materials and repairs
• Overhead 80
• Depreciation charges 520

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

Hydrogenation (hydrogenation) of solid fuel is the process of converting the organic part of the fuel into liquid products enriched with hydrogen and used as liquid fuel. The problem of hydrogenation of solid fuels arose in connection with the increased consumption of oil and the need to effectively use low-calorie and high-ash fossil coals, which present difficulties in their combustion. On an industrial scale, hydrogenation of solid fuels was first organized in the 30s of the 20th century in Germany and was developed due to the need to use heavy tarry oils with a high sulfur content for the production of motor fuels. Currently, destructive fuel dehydrogenation plants with a capacity of 200 to 1600 tons/day are operating in various countries.

Hydrogenation of solid fuel is a destructive catalytic process that occurs at a temperature of 400-560°C under a hydrogen pressure of 20 - 10 MPa. Under these conditions, intermolecular and interatomic (valence) bonds in the organic mass of the fuel are broken and reactions of destruction and depolymerization of high-molecular structures of coal occur.

The problem of hydrogenation of solid fuels arose in connection with the increased consumption of oil and the need to effectively use low-calorie and high-ash fossil coals, which present difficulties in their combustion. On an industrial scale, hydrogenation of solid fuels was first organized in the 30s of the 20th century in Germany and was developed due to the need to use heavy tarry oils with a high sulfur content for the production of motor fuels. Currently, destructive fuel dehydrogenation plants with a capacity of 200 to 1600 tons/day are operating in various countries.

Hydrogenation of solid fuel is a destructive catalytic process occurring at a temperature of 400-560°C under hydrogen pressure 20 -

10 MPa. Under these conditions, intermolecular and interatomic (valence) bonds in the organic mass of the fuel are broken and the following reactions occur:

destruction and depolymerization of high molecular structures of coal

(C)n + pH2 → CnH2n;

hydrogenation of the resulting alkenes;

destruction of higher alkanes followed by hydrogenation of alkenes and the formation of alkanes of lower molecular weight

CnH2n+2 → CmH2m+2 + CрH2p + H2 → CрH2p+2;

hydrogenation of condensed aromatic systems followed by ring cleavage and dealkylation

opening of five-membered rings with the formation of isoalkanes and others.

Since the hydrogenation process occurs in an excess of hydrogen, the polymerization and polycondensation reactions of primary destruction products are suppressed and at a sufficiently high hydrogen/carbon ratio, compaction products are almost not formed.

Simultaneously with the hydrogenation of carbon compounds, hydrogenation reactions of compounds containing sulfur, oxygen and nitrogen proceed according to reactions similar to the hydrotreating reactions of petroleum products (Chapter VII).

The hydrogenation process is catalytic. Contact masses based on molybdenum, nickel or iron compounds with various activators are used as catalysts, for example:

MoO3 + NiS + CaO + BaO + Al2O3.

catalyst activator carrier

By changing the process parameters (temperature, pressure, contact time) and the composition of the catalyst, the hydrogenation process can be directed towards obtaining products of a given composition. The yield of liquid and gaseous products of hydrogenation of solid fuel depends significantly on the content of volatile substances in it, that is, on the degree of its carbonization. Coals with a high degree of carbonization (anthracite, lean coals) cannot be used as raw material for hydrogenation. Suitable fuels for this purpose are brown coals or hard coals with a hydrogen/carbon ratio of not less than 0.06 and an ash content of not more than 0.13 wt. dollars

The hydrogenation process of solid fuels can be carried out in the liquid or vapor phase. Of the numerous technological schemes for liquid-phase hydrogenation, the most economical is the cyclic scheme. It differs from others in lower hydrogen consumption, lower temperature and pressure of the process and allows full use of all components of the processed raw materials. A schematic diagram of such a hydrogenation plant is shown in Fig. 1.8.

As a result of hydrogenation of all types of solid fuels, a liquid product containing isoalkanes and naphthenes is formed, used as a feedstock for catalytic reforming and hydrocracking, as well as boiler fuel and gas.

Figure 1.8. Cyclic scheme of liquid-phase hydrogenation of fuel: 1 - raw material preparation apparatus; 2 - paste pump; 3 - hydrogenation reactor; 4 - centrifuge; 5, 6 - distillation units; 1 - neutralizer; 8 - hydrotreating reactor

Destructive hydrogenation is carried out with the aim of producing light liquid fuel - gasoline and kerosene - from solid or heavy liquid fuels. In terms of its chemistry, this is a very complex process in which simultaneous splitting (destruction) of high-molecular compounds (coal macromolecules) occurs with the formation of simpler saturated and unsaturated hydrocarbons and fragments and the addition of hydrogen to the 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. The occurrence of hydrogenation reactions is facilitated by an increase in pressure and removal of reaction heat.
Typically, hydrogenation of coals is carried out at a pressure of 2000-7000 nsm2 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 producing light fuels - gasoline and kerosene - from coal is carried out in two stages - in the liquid and vapor phase. Young hard and brown coals containing a significant amount of hydrogen are most suitable for hydrogenation. The best coals are those whose ratio between carbon and hydrogen is no more than 16-17. Harmful impurities include sulfur, moisture and ash. The permissible moisture content is 1-2%, ash 5-6%, sulfur content should be minimal. To avoid high consumption of hydrogen, fuels rich in oxygen (for example, wood) are not hydrogenated.
The technology of the hydrogenation process is as follows. Finely ground coal (up to 1 mm) with the required ash content is mixed with a catalyst, most often iron oxides, dried and thoroughly ground in a pestle mill with oil, which is obtained by separating the hydrogenation products. The coal content in the paste should be 40-50%. The paste is fed into the hydrogenation unit with a pestle pump at the required pressure; fresh and circulating hydrogen is supplied there by compressors 2 and 3. The mixture is preheated in heat exchanger 4 due to heat
The vapors and gases coming from the hydrogenation column and then in the tubular furnace 5 reach 440°C and enter the hydrogenation column 6, where due to the heat of the reaction the temperature rises to 480°. After this, the reaction products are separated in a separator from the upper part of which vapors and gases leave, and from the lower part - sludge.
The vapor-gas mixture is cooled in heat exchanger 4 and water cooler 8 to 50° C and separated 9. After removing the pressure, the condensate is distilled, obtaining a “wide fraction” (300-350°) and heavy oil. The wide fraction, after phenols are extracted from it, enters the second stage of hydrogenation. The sludge separated in separator 7 is separated by centrifugation into heavy oil and solid residue, which is subjected to semi-coking. As a result, a heavy oil and a fraction are formed, which is added to the broad oil. 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 by oils under pressure, are returned to the process using a circulation pump 3.
Hydrogenation in the second stage is most often carried out in the presence of WSo under a pressure of 3000 nsm2 at 360-445 ° C. Gasoline and kerosene or diesel fuel are isolated from the resulting hydrogenation product. There are no unsaturated hydrocarbons in the fuel obtained by hydrogenation, and sulfur is in the form of hydrogen sulfide, which is 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.l and the height is up to 18 m and the diameter is 1 m. In columns for hydrogenation in the vapor phase, the catalyst is placed on mesh shelves.
The gasoline yield can reach 50-53% of the combustible mass of coal.