RU2364737C1 - Method of multipurpose solid fuel use at combined cycle power plants with cogeneration of power and secondary end products in form of liquid and solid fuels with improved consumer properties - Google Patents

Abstract

FIELD: heating systems, fuel.

SUBSTANCE: proposed invention refers to environmentally sound multipurpose method of low-grade high reactivity coals (brown and bituminous coals with high volatile content) use at environmentally sound combined cycle power plants with high thermal effectiveness. The method involves complex multi-stage processing of solid fuels using fluidised bed technology, which is integrated into steam gas plant thermal cycle.

EFFECT: providing the highest fuel use efficiency, adaptability to changes in market situation, and high technical and economic properties of the complex.

3 cl, 2 dwg

Description

The invention relates to a method for environmentally friendly integrated use of low-grade high-reactive coals (brown and stone with a high yield of volatile) in environmentally friendly power plants of a combined cycle with high thermal efficiency by a multi-stage processing process, including high-speed pyrolysis of coal with the release of resins and gasification of semi-coke, and can be used in energy for the joint production of energy and by-products in the form of ennobled firmly Go, liquid boiler and high-purity synthetic motor fuels.

There is a method of in-cycle thermal processing of brown coal by thermocontact coking by pyrolysis with a solid heat carrier under low pressure to produce heat and electric energy in a combined cycle plant and a by-product in the form of activated carbon from semi-coke (RF patent No. RU 2211927).

The disadvantages of this method are:

- The process of pyrolysis and gasification of semicoke at a pressure close to atmospheric, which increases the size and cost of the installation and complicates effective integration with the combined cycle.

- The difficulty of achieving uniform mixing of coal with a solid bulk coolant for large industrial plants.

- A large number and length of technological connections for the transfer of bulk material (semi-coke, hot fluid) from unit to unit, which complicates operation and reduces the reliability of the system.

- Production of only one by-product - activated carbon, the market capacity for which may be limited, which determines the unit capacity and the need for such plants.

Closest to the method proposed in this invention is a known method of using high sulfur ash fuels in combined cycle plants (CCGT), which consists in the fact that all consumed CCGT fuel is gasified by partial oxidation at temperatures from 1000 to 1500 ° C under pressure of compressed hot air, part of which is taken after the CCGT high-pressure compressor. The resulting low-calorie gas is cooled using energy to generate water vapor, which serves as the working fluid of the steam turbine at a combined cycle power plant, then it is cleaned of solid particles and sulfur compounds and the purified gas is burned in combined-cycle plants (V.M. Maslennikov, S.A. Khrimtianovich et al.: author USSR certificate No. 263064, IPC C10B, Int. C1. F23C, England patents No. 1104075, USA No. 3287902 .. dated 11.29.1966, FRG No. 1285088 of 01.25.1965, France No. 1427256, Japan No. 916736 - prototype) .

This method has been widely recognized in the world under the name “Intra-cycle gasification technology” in the domestic technical literature and integrated gasification combined cycle (IGCC) in the foreign and has entered the commercial implementation stage in a number of Western countries. The disadvantage of this method is that the organic mass of fuel is completely converted to low-calorie gas, without extraction of by-products, and the obtained purified gas with a sufficiently high content of hydrogen and carbon monoxide is used only for the production of electricity, although it could be used for the catalytic synthesis of valuable products. In addition, despite the possibility of achieving high efficiency and high environmental standards, as international experience shows, the payback period for investments in the production of electricity alone is relatively long, due to the complexity and high capital intensity of gasification and gas purification equipment.

The present invention solves the indicated technical problem, providing, together with the production of energy, the possibility of obtaining by-product products with high market potential and thereby a significant improvement in technical and economic indicators and flexibility to changes in market conditions.

The stated technical problem is solved in that: in a method for the environmentally friendly integrated use of solid fuels, mainly low-grade high-reaction coals (brown and stone with a high yield of volatile), integrated into the heat cycle of a combined cycle power plant with the aim of co-production of low-calorie purified gas for energy generation and by-products commercial products in the form of enriched solid, liquid boiler and high-purity synthetic motor fuels, including combined-cycle gas a power plant (CCGT), crushing and drying coal, oxidizing gasification to produce a low-calorie generator gas with heat recovery from exothermic reactions in a power plant cycle, purifying gas from solid particles and sulfur compounds and using purified gas as fuel for a combined cycle power plant, some of the air after The CCGT high-pressure compressor is used for a three-stage countercurrent process of thermochemical coal processing, in which the first stage is dried and The charcoal source coal is subjected to pyrolysis due to the heat of gasification products coming from the second stage, with the formation of pyrolysis products in the form of coal tar and pyrogas vapor, which are removed from the first stage together with gasification products, followed by the release of liquid resins to produce by-products and purified energy gas for energy production at CCGT, and semicoke, which is sent for processing to the second stage by oxidative gasification with a mixture of air and combustion products from of the third stage, the resulting generator gas is sent to the first stage for pyrolysis, coal ash containing metal sulfides with carbon residues, is subjected to afterburning in the third stage using part of the air from the CCGT high-pressure compressor as an oxidizing agent, as a result of which the carbon burns out, while the sulfides metals are oxidized to environmentally friendly sulfates, cooled and removed from the cycle ash with the utilization of physical and chemical heat in the process of gasification of the second stage semicoke, to intensify the The processes of gasification and pyrolysis, as well as to increase the yield of liquid fractions at all stages of processing, use the technology of a fluidized and circulating fluidized bed, the steam-gas mixture obtained after a three-stage processing of coal containing vapors of coal tar, particles of ash and semi-coke is purified with gas cooling and condensation coal tar vapors by two-stage washing with liquid resins circulating after washing through heat exchangers - coolers with different temperature levels during washing, while The first stage in the course of the gas-vapor mixture at the higher temperature is condensed and the heavier resin fractions are recovered, together with the main part of the trapped solid particles, which are sent for use as a binder in the production of coal briquettes, and in the second stage, at a lower temperature, they are condensed and recovered lighter and cleaner fractions of coal tar, which are used as the basis for the production of liquid boiler fuels, while the heat from the condensation of the tar and cooling of the gas mixture They are combined in the steam turbine cycle of a CCGT unit.

1 and 2 are schematic diagrams explaining the essence of the proposed method for the integrated use of low-grade coal in the energy sector.

The scheme in figure 1 includes a coal preparation unit (crushing, sorting, drying) 1, a lock-bunker system for supplying crushed coal 2 to a multi-stage coal processing reactor 3, working under pressure, a lock-bunker system for removing ash 4 from the reactor, a two-stage fractional system condensation of pyrolysis resins: 5 - heavy-medium fractions with a boiling point above 320-350 C, 6 - light-medium fractions with a boiling point below 320 C, a gas purification system for sulfur compounds 7, a gas turbine unit with a cycle air compressor 8 and boo a black (booster) compressor 9, a combustion chamber 10, a gas turbine 11, an electric generator 12, a steam turbine 13, an exhaust gas heat recovery boiler 14, a briquetting unit 15, a stabilization and conditioning unit for liquid boiler fuel 16, a catalytic synthesis unit 17.

The system operates as follows:

The coal, crushed and dried to hygroscopic humidity, from the coal preparation system 1 through a lock-hopper feed system 2 enters the combined pyrolysis-gasification reactor 3. The reactor includes 3 stages in one unit: pyrolysis, gasification, afterburning. Each can be carried out in a fluidized bed or in a circulating fluidized bed. Coal from the gateway bunkers enters the pyrolysis stage, a heating and fluidizing medium in which, mainly, are gasification products of the semi-coke. Pyrolysis occurs at temperatures of 570-620 ° C (the temperature depends on the properties of a particular coal). The vapor-gas phase of the pyrolysis products is mixed with a fluidizing gas and removed from the reactor 3 into the fractional condensation system 5-6. The solid phase - semi-coke in a dense stream - at the indicated temperature completely or partially enters the gasification stage. Possibility of dosing a calcium sorbent for gas absorption to absorb sulfur is provided. The mineral part of the coal with the remnants of semicoke from gasification enters the afterburning stage, where the remaining carbon is burned in the air. As an oxidizing agent and a fluidizing medium, compressed air is used in a gas turbine compressor 8 and in a booster compressor 9, which is heated by compression to a temperature of 300-400 ° C. Combustion products, together with air, are an oxidizing agent and a fluidizing medium for a gasification stage. The ash residue from the afterburning stage is a mixture of oxides that does not contain sulfides and does not form toxic effluents during disposal in dumps. The ash is removed from the reactor through a lock-bunker system 4.

The gas-vapor mixture from the reactor is discharged through a system of cyclone separators to separate the bulk of the solid particles. The separated particles are returned to the gasification stage. The gas-vapor mixture is washed with liquid pyrolysis resin in contact condensers 5 and 6. Each of them is a scrubber with a circulation circuit, including pumps for pumping resin in the circuit, heat exchangers for cooling the resin, and irrigation devices for organizing effective direct contact of droplets with the gas-vapor mixture. The vapor-gas mixture moves from bottom to top, in contact with drops of chilled resin, moving under the influence of gravity in countercurrent. In this case, vapor condensation of the resin occurs on the surface of the droplets. At the same time, gas is purified from solid particles. In the heat exchanger of the condenser 5, heat is transferred to generate saturated steam with a pressure of about 1.2 MPa and a temperature of 320 ° C for a combined cycle steam turbine. In this case, heavy fractions of resins with TNCs condense above 320 ° C. These fractions, contaminated with ash and coke particles, are removed from the circuit to the coal briquette production unit 15, where they are used as a binder.

In the heat exchanger of the condenser 6, the cooling medium is the feed water of the steam turbine cycle with a temperature of 120-150 ° C. Light and medium fractions of pyrolysis resins condense in it, which are removed from the circuit into the liquid boiler fuel production unit 16, where the resins are degassed and stabilized.

After the condensers, if necessary, the gas is purified from hydrogen sulfide and other sulfur compounds in the desulfurization system 7. It is most advisable to use a chemisorption process such as the Stretford process, where a solution of potash in water serves as a sorbent. Cleaning is carried out at a temperature in the absorber of about 120 ° C, at which condensation of water vapor does not occur, and as a result, liquid effluents do not form, the cleaning of which requires additional costs.

The purified gas is either supplied directly to combustion in the combustion chamber 10 of the gas turbine unit of a technical vocational school, or first to the single-pass unit for the catalytic synthesis of methanol (dimethyl ether, gasoline) 17, the spent synthesis gas after which is fed to the combustion chamber of the gas turbine 10.

The proposed method provides the effective use of physical and chemical heat of fuel and energy of excess pressure of gas flows in the cycle of a combined cycle plant.

Figure 2 presents an example implementation of the proposed method of organizing the processes of pyrolysis-gasification in a fluidized bed, in which 3 stages of the process: pyrolysis of coal, gasification of semicoke and afterburning of coke residue with the oxidation of sulfides, are arranged in a common power casing and are carried out in three fluidized beds located sequentially along the gas with a common countercurrent with respect to the coal flow.

Fluidization modes are selected optimal for each stage. Benefits of using fluidized bed technology:

- The high intensity of heat and mass transfer of particles with gas provides conditions for the organization of high-speed coal pyrolysis, approaching the conditions of thermal contact coking, and therefore, a good yield of light fractions.

- The high speed of mixing the particles along the height of the layer ensures minimal heterogeneity in composition, which favors the efficient operation of desulfurization sorbents.

- The ability to control over a wide range of residence times of the solid and gas phases in each stage.

The method is implemented as follows (figure 2):

The coal, dried to hygroscopic humidity, ground to a particle size of minus 2 mm, enters the fluidized bed of the pyrolysis stage 2 through the lock hopper 1. The fluidizing medium is the gasification products of semi-coke, coming from below through a gas distribution grid with a temperature of 1000 to 1200 ° C, containing hydrogen, carbon monoxide, nitrogen, water vapor and carbon dioxide and are practically free of oxygen. Particles of coal fall into the fluidized bed, quickly mix with the heated semi-coke and heat up at a speed of several thousand degrees per second, mainly due to collisions with hot particles. The volume of this section, the height of the fluidized bed of the velocity and the gas temperature at the inlet are selected so that the average temperature in the layer is 570-620 ° C (depends on the type of coal), the residence time of the gas-vapor mixture in the section is about 0.8-1 s , the residence time of the solid phase in the layer required for the required degree of degassing is several minutes.

In the process of rapid heating and release of pyrogas, the particles are subjected to further grinding due to an increase in pressure in the internal pores. The pyrolysis products are removed from the reactor through a particle separator 9 into a resin condensation system.

The layer height is kept constant by unloading the excess semicoke to the gasification stage through channel 3. The captured fine fraction of particles is sent to the gasification stage of the semicoke through a special PC channel.

In the gasification stage of semicoke 4, oxidative gasification of semicoke in a fluidized bed takes place. The oxidizing agent and fluidizing medium is hot air with the addition of water vapor and coke combustion products from the lower stage of the reactor. The gasification process by partial oxidation of semicoke occurs at an average fluidized bed temperature of 800-850 ° C. The amount of oxidizing agent should be about 33-36% of the stoichiometric flow rate. The result is a generator gas with a heat of combustion of about 1300 kcal / nm ³ . The height of the layer and the residence time of the particles in the fluidized bed are selected so that the degree of conversion of the organic mass of the particles into gas is at least 95%, which depends on the reactivity of the coal. Above the fluidized bed, an additional tier of air supply is arranged. When part of the generator gas is burned in it, the temperature in front of the gas distribution plate of the pyrolysis stage 2 rises to 1000-1200 ° C. In this case, a significant part of finely dispersed coke particles, carried away by the gas stream from the fluidized bed, burns out. In the steady state process, the mineral part of coal prevails in the composition of the fluidized bed material of gasification stage 4, while the coke concentration does not exceed 5-6% of the total mass of particles in the layer.

Sulfur contained in coal is converted during gasification, mainly to hydrogen sulfide, and the metals of the mineral part of coal are converted to sulfides, which, when ash is buried in ash dumps, can contaminate subsoil water with toxic compounds. Therefore, before the ash is removed from the plant, it must be subjected to oxidative processing in order to convert sulfides into harmless sulfates.

For this, as well as for a more complete use of carbon fuel, the bulk material from the gasification stage 4 through the overload channel 5 is poured into the lower part of the fluidized bed of afterburning 6. Hot (about 400 ° С) air entering through the gas distribution plate serves as an oxidizing agent and fluidizing medium. The oxidized ash is discharged through the ash discharge channel 7, into which air and steam are supplied countercurrently. The amount of air and steam is selected so that the final burnout of coke and cooling of the ash occurs in a dense stream. The combustion products of coke, mixed with air, move upward and through the gas distribution plate of the fluidized bed 4 enter the fluidized bed of gasification of semicoke.

All channels for loading bulk materials: PC, 3, 5, 7, should have a level of dense phase, which serves as a water seal, preventing the breakthrough of gas through the channel. The height of the specified level is adjusted so that the weight of the solid phase column is sufficient to overcome the differential pressure of gas between the respective plates or other gas distribution devices, providing continuous flow of bulk material. The distance between the layers in height should be selected taking into account this requirement.

Overload channels in the high-temperature zone should be insulated, if necessary equipped with cooling devices.

The advantages of this proposal are that:

- The addition of coal briquetting and catalytic synthesis of liquid hydrocarbon blocks provides the possibility of producing a wide range of marketable products together with energy: liquid boiler fuels based on light fractions of coal tar, domestic and industrial coal briquettes suitable for long-distance transportation, and synthetic motor fuels, resulting in technical and economic indicators and flexibility to fluctuations in market conditions are significantly increased.

- The combination of a number of stages (pyrolysis, gasification, afterburning of residues) in one unit with a common power building eliminates long technological communications for transferring the bulk phase between units and reduces heat loss to the environment. In this case, the solid phase moves from the pyrolysis stage to the subsequent stages of semicoke gasification and afterburning of residual carbon from top to bottom, and the vapor-gas phase counter-flow from bottom to top, providing the required modes of fluidization, partial oxidation and rapid heating of coal particles for pyrolysis. As a result, maximum fuel efficiency can be achieved.

Claims (3)

1. A method of environmentally friendly integrated use of solid fuels, mainly low-grade high-reaction coals (brown and stone with a high yield of volatile), integrated into the heat cycle of a combined cycle gas turbine plant with the aim of co-production of low-calorie purified gas to generate energy and commercial by-products in the form of refined solid, liquid boiler and high-purity synthetic motor fuels, including a combined cycle power plant (PTU), coal crushing and drying oxidizing gasification to produce a low-calorie generator gas with heat recovery from exothermic reactions in a power plant cycle, purifying gas from solid particles and sulfur compounds and using purified gas as fuel for a combined cycle power plant, characterized in that part of the air after the high-pressure compressor is used for a three-stage countercurrent process of thermochemical coal processing, in which, in the first stage, the dried and ground raw coal is tested they produce pyrolysis due to the heat of gasification products coming from the second stage, with the formation of pyrolysis products in the form of coal tar and pyrogas vapor, which are removed from the first stage together with gasification products, followed by the release of liquid resins to produce by-products and purified energy gas for energy production in vocational schools, and semi-coke, which is sent for processing to the second stage by oxidizing gasification with a mixture of air and combustion products coming from the third stage, the generated generator gas is sent to the first stage for pyrolysis, coal ash containing metal sulfides with carbon residues is subjected to afterburning in the third stage using part of the air from the high-pressure compressor as an oxidizing agent, as a result of which the carbon burns out, while metal sulfides are oxidized to environmentally friendly sulfates, ash is cooled and removed from the cycle with the utilization of physical and chemical heat in the process of gasification of the second stage semicoke. 2. The method according to claim 1, characterized in that in order to intensify the processes of gasification and pyrolysis, as well as to increase the yield of liquid fractions in all stages of processing using the technology of fluidized and circulating fluidized bed. 3. The method according to claim 1, characterized in that the cleaning of the vapor-gas mixture obtained after a three-stage processing of coal containing a pair of coal tar, ash particles and semi-coke is carried out with gas cooling and condensation of the coal tar vapor by a two-stage washing with liquid resins circulating after washing through heat exchangers - coolers with various temperature levels during washing, while in the first stage along the gas-vapor mixture at a higher temperature, the heavier resin fractions are condensed and extracted together with the new part of the captured solid particles, which are sent for use as a binder in the production of coal briquettes, and in the second stage, at a lower temperature, lighter and cleaner fractions of coal resins are condensed and recovered, which are used as the basis for the production of liquid boiler fuels, while the heat from condensation of the resins and cooling of the gas-vapor mixture is utilized in the steam turbine cycle of the vocational school.

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