Inside and outside coal-fired integrated association circulating power generation system and electricity-generating method
Technical field
The present invention relates to a kind of handle and organically combine based on the inside and outside coal combustion technology and the integrated combined cycle of coal partial gasification, and the effective new-generation system and method for separating carbon dioxide.
Background technology
System and technology related to the present invention mainly comprises at present: the CO of combined circular coal-burning power generating system, coal generating system
2Isolation technics and high initial temperature vapor recycle etc., the state of development and the feature of technology is as follows separately for it.
1, combined circular coal-burning power generating system (CFCC)
At present, combined circular coal-burning power generating system mainly comprises: the association circulating power generation system (PGFBCC) of integrated gasification combined cycle for power generation system (IGCC), pressurized fluidized bed combined circular coal-burning power generating system (PFBCC) and the fluidized bed combustion of coal partial gasification etc.
(1) in the IGCC system, coal produces synthetic gas (the existing airflow bed gasification furnaces of using through gasification more, its efficiency of carbon con version is generally all more than 95%), through the gas-fired rear drive gas turbine power generation of purified treatment, utilize high-temperature exhaust air in waste heat boiler, to produce the steam drive steam turbine power generation.In order to prepare coal gas, also be provided with air separation equipment (be used to make oxygen air feed usefulness, be called for short air separation plant) among the IGCC of employing entrained flow gasification technology; Also be useful on the dedusting and the desulphurization plant of gas purification among the IGCC.IGCC is a kind of technology that oil crisis began one's study and developed period the seventies in last century.Owing to develop a collection of high performance gas-turbine engine the nineties in last century in the world, adopt the IGCC net efficiency of about 1300 ℃ (FA level) gas turbines of initial temperature can reach 43%~45% (LHV), on thermal performance, can compete mutually, thereby make the IGCC technology stride into the commercial trial period with traditional coal fired power generation unit.Big capacity (more than the 200MW grade) the IGCC unit that has moved in the world at present has many, as the Wabash River power plant of the Buggenum power plant of Holland, Hispanic Puertollano power plant and the U.S. and the unit of Tampa power plant.
IGCC is the waste heat boiler type combined cycle generation mode that replaces natural gas with coal gas, different is to have certain loss (the product bit-loss that comprises energy loss and energy) in coal gasification and gas purification process, and the auxiliary power consumption rate is higher, thereby the thermal efficiency that makes IGCC is lower than the thermal efficiency that burns the natural gas combined cycle, but than steam single cycle (Rankine cycle) efficient height.IGCC is to carry out in the coal gas of high pressure, high concentration, low discharge to the processing of pollutant, thus good purification, and also disposal cost is low.The exhaust gas desulfurization rate of IGCC can reach more than 98%, and can obtain salable byproduct elementary sulfur or sulfuric acid.The shortcoming of IGCC is: because coal gasifying process (generally adopting entrained flow gasification) adopts the gasification furnace of high temperature, gasification temperature can reach 1500 ℃, so the size of gasification furnace is big, cost is very high; Simultaneously the impurity in the coal is in molten condition, is mixed in the coal gas, make the waste heat boiler manufacture process requirement height that reclaims the coal gas of high temperature sensible heat, involve great expense; So the cost of IGCC unit is than higher.In addition, also have equipment such as air separation plant and gas purification, system complex among the IGCC.
(2) PFBCC belongs to pressurized boiler type combined cycle, and coal is in the pressurized fluidised-bed boiler internal combustion, and feedwater is heated into steam is used for steam turbine power generation on the one hand, is used for gas turbine power generation after the high-temperature flue gas process dedusting that burning forms on the other hand.Fluidized bed temperature generally is no more than 900 ℃ (for preventing the coking in coal seam), and the initial temperature of gas turbine is restricted; But the initial temperature of steam turbine is not subjected to the restriction of combustion gas turbine delivery temperature, and can take subcritical pressure boiler.The net efficiency of PFBCC has only below 40% at present.Carry out calcium injection and desulfurization in fluidized-bed combustion boiler, desulfuration efficiency can reach about 90%~95%.The PFBCC technology is at first to be begun one's study by Britain coal utilization research institute (CURI) in 1969, and what finish the commercial scale exploitation the earliest is ABB AB.In Sweden, the U.S. etc. built up several PFBCC demonstration power stations after the eighties last century, comprises the 15MW demonstration unit of China Jia Wang power plant.
The PFBCC system is based on steam turbine power generation, and initial temperature of gas turbine is not high, makes the raising of efficient be restricted, and its thermal performance is a little less than the thermal performance of IGCC system under the current techniques condition.Because the fume high-temperature purification techniques is not obtained substantive breakthroughs, dust in flue gas and alkali metal do not solve as yet to combustion gas turbine harm problem at all, therefore can only adopt low initial temperature gas turbine, and can not adopt advanced in performance modern gas turbines, thereby limited the raising of PFBCC system effectiveness.The desulfuration efficiency of PFBCC is on the low side relatively, and environmental-protecting performance is poorer than the environmental-protecting performance of IGCC.But the PFBCC system does not have coal gasifying process and system, does not have air separation unit yet, and system is simple relatively, and the unit cost is low.Thermal performance, environmental-protecting performance and the property safe and reliable to operation of PFBCC system are still waiting to improve and improve at present, so technical development is slow.
(3) the PGFBCC system has used for reference the comprehensive advantage of PFBCC system and IGCC system: adopt coal partial gasification technology to provide coal gas for (overhead) combustion chamber, can adopt the gas turbine of high initial temperature, advanced feature; The semicoke of discharging from coal (part) gasification furnace bottom burns fluidized-bed combustion boiler, and the steam (the steam turbine initial temperature is not subjected to the restriction of combustion gas turbine delivery temperature) that can produce high parameter is used for steam turbine power generation; In coal (part) gasification furnace and semicoke boiler, add desulfurizing agent simultaneously and carry out desulfuration in furnace, do not need complicated gas cleaning system; The coal partial gasification is gasifying agent with the air, does not need air separation unit.Therefore, under present technical conditions, the PGFBCC system is dominant than IGCC technology aspect equipment investment, and its generating efficiency and IGCC are suitable substantially.
PGFBCC still is in key technology exploitation and tackling key problem stage, and there are two kinds of citation forms in its system: the PGFBCC system of PFBC and the PGFBCC system of AFBC.The PGFBCC of PFBC is also referred to as second generation PFBCC system (English name: Second-generation PFBCC, or Topping cycle, or Hybrid cycle) is on the basis of PFBCC, increases the overhead combustion chamber of a pyrolysis oven (or partial gasification stove) and gas turbine.Coal at first carries out Pintsch process or partial gasification in pyrolysis oven or partial gasification stove, the coal gas that produces is delivered to the flue gas that comes out from pressurized fluidised-bed boiler with heating in the overhead combustion chamber, make its temperature bring up to 1300 ℃ of grades from about 850 ℃, thereby can use high performance gas turbine, overall system efficiency is improved.The PGFBCC system of AFBC comprises the ABGC electricity generation system of Britain Mitsubishi Babcock company exploitation etc., the difference of the PGFBCC system of it and PFBC is: the required oxygen of The normal pressure fluidized bed boiler combustion is supplied with by the exhaust or the pressure fan of combustion gas turbine, and the required oxygen of PFBC boiler is supplied with by the air of gas turbine blower outlet.The fluid-bed combustion boiler of PGFBCC system both can add hot water and steam working medium, also can the heating high-pressure air, the former the Btu utilization of coal-char combustion in vapor recycle, and the latter is circulated the Btu utilization of coal-char combustion in combustion gas, the latter is more favourable to the efficient that improves system, but the technical difficulty of the gas of high temperature-gas heat exchanger and manufacturing cost are all bigger.
At present, the PGFBCC system preponderates than IGCC system aspect investment, but it also has certain technological difficulties and defective: to the PGFBCC system of PFBC, the high temperature purification technology of coal gas and (fluidized-bed combustion boiler) flue gas does not also thoroughly solve, adopt dry method (as ceramic filter) dedusting 850 ℃ of temperature grades, its dedusting precision can not satisfy the requirement of advanced gas turbine, also can't remove the alkali metal harmful to gas turbine; Gas-turbine combustion chamber and Fuel Control System need redesign or transform, to adapt to the requirement of high temperature refrigerant and high-temperature fuel.The PGFBCC systems technology of AFBC is simple relatively, but efficient does not have significantly to improve than IGCC, and as under the condition that adopts identical gas turbine, the efficient of ABGC system and the efficient of IGCC are suitable substantially.The PGFBCC system depends on the in-furnace calcium spraying desulfurization, and desulfuration efficiency has only about 90%~95%, when the sulfur content of coal surpasses 2%, can not satisfy environmental requirement to the sulphur emissions of atmosphere, so the environmental-protecting performance of PGFBCC system is good not as IGCC.
The Vision 21 PGM electricity generation systems that U.S. Foster Wheeler company proposes also belong to combined circular coal-burning power generating system, adopt the gas turbine of a new generation, vapor recycle adopts supercritical parameter, and organically combines with fuel cell power generation, produces cleaning liquid fluid fuel and chemical products simultaneously; Aspect low pollution, in the in-furnace calcium spraying desulfurization, coal gas and flue gas are carried out smart desulfurization, and utilize SCR technology to remove NO in the flue gas
xThereby realize that net power station efficiency is more than 60% and to the zero release of pollutant of environment.
Combined circular coal-burning power generating system also comprises The normal pressure fluidized bed combined circular coal-burning power generating system (AFBCC) in addition, it and above-mentioned PFBCC system class are seemingly, just adopt the The normal pressure fluidized bed boiler and add hot-air, the air of high temperature enters gas turbine power generation, and the flue gas that burning produces is used for the feedwater of heating steam circulation.The thermal efficiency of this system will be lower than the thermal efficiency of PFBCC system.Its advantage is that the clean air working medium of employing can be avoided the corrosion to combustion gas turbine.But layout air hose heating surface is had any problem in fluidized-bed combustion boiler.The research and the technological development of present this electricity generation system are few.
2, the CO of coal generating system
2Isolation technics
A large amount of dischargings of carbon dioxide cause that the problem of global warming comes into one's own day by day, are to cause CO in the atmosphere as a large amount of consumption of main primary energy coal
2The basic reason that balance is destroyed.Important one of mode of utilizing of coal is generating, how to reduce electricity generation system CO
2Emission level more and more comes into one's own.Raise the efficiency the CO that can correspondingly reduce the unit generated energy
2Discharge capacity, but it is little to reducing the greenhouse gas emission effect significantly.Therefore, exploitation is at coal conversion, combustion process and separation of C O from tail gas
2It is its key technology.
According to U.S. Argonne National Laboratory, the research report of USDOE national energy technique center and the documents such as research paper of Paolo Chiesa in 1999 in 2000, separation of C O in the present coal generating system
2Technology can reduce 5 classes: separate in smoke evacuation (1), and promptly steam generating system and the IGCC system afterbody in routine adds separation of C O in the smoke evacuation
2Measure.Because CO in the smoke evacuation
2By nitrogen dilution, make CO
2Concentration becomes, and amount very low, that need handle is very big, is accompanied by a large amount of energy consumptions, causes the reduction significantly (about 12 percentage points) of system effectiveness, is infeasible from Technological Economy analysis.Its improvement way is the half-closed gas turbine cycle scheme of oxygen or air burning, promptly compressor inlet recirculation is guided in the exhaust of part turbine, makes CO in the exhaust
2Concentration increases, and reduces treating capacity, reduces corresponding power consumption, but only improve system effectiveness 0.5-0.8 percentage point.(2) before burning, fuel gas is handled and separated.In the IGCC system, the main combustible gas component of the synthetic gas that coal gasification produces is CO and H
2, CO gas is converted into CO by conversion reaction
2And hydrogen, pass through physical absorption system more cheaply again CO
2Separate, remaining major part is desirable hydrogen-enriched fuel gas.Owing to separate and CO absorption
2Be to carry out in not by the synthetic gas of nitrogen dilution, corresponding energy consumption just reduces many, compares with preceding a kind of approach, and system's net efficiency has obvious improvement.(3) polygenerations systeme of overhead chemical process.Synthetic gas has utilized most of carbonaceous component by the overhead chemical process earlier, then the ideal fuels of unreacted logistics (hydrogen-enriched fuel gas) as dynamical system.Polygenerations systeme adopts the energy consumption that has once reduced chemical process by flow process, makes the CO of the dynamical system that uses hydrogen-rich fuel simultaneously
2Discharging greatly reduces.(4) the multiple thermodynamic cycle combination of the directed different component that shifts of synthetic gas.It is CO, H that coal gasification produces the synthetic gas main component
2And CO
2, carbonaceous component and the directed transfer of hydrogen component, offer the circulation system of two pure oxygen burnings respectively, then combustion product is respectively CO
2And H
2O just can the convenient processing of low energy consumption.This separation of C O
2Method simple, but the system effectiveness decline scope is also bigger.(5) by the thermodynamic cycle innovative measure.As O
2/ CO
2The circulatory system had increased air separation plant before coal combustion, enter the O of boiler
2Purity is very high, CO in the flue gas that the burning back produces
2Concentration also very high (can reach more than 90%) therefore reclaims CO at the flow process afterbody
2Shi Buzai needs separator.O
2Purity is high more, the CO of recovery
2Purity is high more, CO
2The energy consumption of liquefaction is more little, but the power consumption of air separation plant is also high more, and optimizing the oxygen purity that calculates the best is 97.5%.This method is than separating, reclaim CO in the smoke evacuation
2The energy consumption of method is little, causes that the amplitude of efficient reduction is low relatively.For another example, the traditional flame combustion of applied chemistry chain reaction replacement also is to control CO by the circulation new and innovative ways
2Discharging.Also have, in recent years the high initial temperature vapor recycle of Ti Chuing, the effectively CO of segregated combustion generation
2, will introduce this circulation below.
Adopt that a kind of mode separation of C O no matter be
2, all to consume extra energy, make the decrease in efficiency of system.So separation of C O
2The key of technology is to reduce the energy consumption of separating with processing procedure as far as possible, to improve the net efficiency of system.
3, high initial temperature vapor recycle.
This circulation is main working medium with water vapour, add pure oxygen to the combustion chamber, adopt the internal combustion mode, can reach and the same high intake air temperature of gas turbine cycle (being the technology that gas turbine has been adopted in the design of steam turbine), thereby keep high cycle efficieny (suitable) with the efficient of the combustion and steam combined cycle of equal initial temperature; Fuel (can be natural gas, synthetic gas or liquid fuel) burns in water vapour with pure oxygen, does not have NO
xEmission problem; Owing to have only water vapour and CO in the gas that obtains after the burning
2, CO in turbine exhaust condensation process
2Automatically separated.When this circulation was used for coal generating system, the process system of its preparation clean gas and coal gasification, the gas purification process system of IGCC were identical, equally also need air separation unit.This electricity generation system requires coal is gasified totally, so have shortcomings such as coal gasification and gas purification equipment manufacturing cost height, gas heat recovery system energy grade lose greatly, system complex, all do not breaking through present IGCC electricity generation system level aspect efficient and the investment two.
This loop concept was put forward by Japanese scholar and Austrian scholar with nineteen ninety-five respectively at 1994 the earliest, and the latter is named as " Graz " circulation (with the naming of this university).Had other scholars that this circulation is studied afterwards again, and as Italy and the scholar of Britain in this respect research recently new development was arranged, the exhaust that utilizes high-temperature turbine is to CH
4Reform, thereby can further improve cycle efficieny; And the recycle scheme of three kinds of different high steam production processes carried out sunykatuib analysis, compared the performance quality of different recycle schemes.
But up to the present, the research of high initial temperature vapor recycle aspect also only is confined to the notion of circulation itself and simple thermodynamic cycle.Although to being that the cycle characteristics of fuel is studied with the synthetic gas, but still the employing coal is gasified totally, gaseous fuel carries out the internal combustion mode and adds hot water and steam working medium, also be the simple connected mode of coal gasifying process and high initial temperature vapor recycle, and coal gasification course and circulation combination do not inquired into from system height.Therefore to be used for the coal be that the potentiality of electricity generation system of fuel also fully do not excavate in this circulation.
Summary of the invention
The objective of the invention is in order to overcome the Rankine cycle of the most employing of present coal fired power generation device steam, generating efficiency is not high, the problem of environmental pollution is more serious, and the clean coal power generation technology of developing (as IGCC generation technology and PFBCC generation technology) though performance improve to some extent, but there are problems such as investment cost height, technical difficulty is big, the efficient raising is limited, and consider control CO
2The great environmental problem of discharging; And a kind of inside and outside coal-fired integrated association circulating power generation system is provided.
The objective of the invention is to improve greatly the efficient of coal generating system.The present invention proposes the novel integrated combined cycle of high initial temperature high pressure ratio, and the circulation initial temperature can reach the initial temperature level of modern gas turbines; Adopt coal partial gasification technology and external combustion, the internal combustion mode that combines simultaneously, in circulation, do not adopt compressor to promote the pressure of working medium, thereby saved working medium compression wasted work; The work done working medium main component of turbine is a water vapour, and pressure at expulsion can be very low, reaches vacuum state, circulation pressure ratio height.
Another object of the present invention is that low energy consumption ground reclaims CO
2Adopt coal gas in the water vapour atmosphere, to carry out theoretical combustion system, have only water vapour and CO in the combustion product with pure oxygen
2, in the process that turbine exhaust heat release is condensed, CO
2Automatically separated, avoided the shortcoming of a large amount of additional energies of consumption that conventional isolation technics brings.
A further object of the present invention is to reduce the cost of clean coal power generation technology significantly.Adopt coal partial gasification mode, compare with pursuing the nearly absolutely conventional gasification furnace of efficiency of carbon con version, technical difficulty descends greatly, and the cost of gasification furnace also reduces significantly; The gas temperature of partial gasification outlet of still is low relatively, it is few to contain slag, and the cost of the waste heat boiler that reclaims gas heat also is reduced; There is not compressor equipment in the system; Adopt in-furnace calcium spraying desulfurization and the mode that dry desulfurization in the coal gas combines, need not the conventional wet desulphurization equipment that adopts system complex, involves great expense.
Purpose of the present invention can realize by following measure:
A kind of inside and outside coal-fired integrated association circulating power generation system, this system comprises coal gasifier A, waste heat boiler B, combustion chamber H, high-temperature gas turbine I, regenerator J, cryogenic gas turbine K, semicoke boiler R, high-pressure steam turbine V; Wherein the raw gas of coal gasifier A generation links to each other with waste heat boiler B, and the semicoke that coal gasifier A discharges then links to each other with semicoke boiler R; Waste heat boiler B utilizes the raw gas of coal gasifier A that the feedwater heating from regenerator J is produced high steam, and the coal gas after the heat exchange enters combustion chamber H among the waste heat boiler B; The feedwater of its low temperature heating surface of heating behind the coal-char combustion that semicoke boiler R discharges coal gasifier A, the feedwater of the low temperature heating surface heating of semicoke boiler R be with after the feedwater through regenerator J heating mixes, generation high steam after further being heated by semicoke boiler R again; The high steam that semicoke boiler R produces mixes the back with the high steam that waste heat boiler B produces and links to each other with high-pressure steam turbine V; The steam discharge of high-pressure steam turbine V enters combustion chamber H after regenerator J heating, and heats the gas that the back forms tool circulation initial temperature by the cooling coal gas of coal gasifier A in the H of combustion chamber, and this gas links to each other with high-temperature gas turbine I; Gas after the high-temperature gas turbine I work done enters cryogenic gas turbine K work done after regenerator J carries out heat exchange.
This system also comprises dry-method dust-removal device C, hydrolyzer D, dry-method desulfurization device E, washer F; Coal gas after waste heat boiler B cooling is isolated the carbon containing grit, through hydrolyzer D the COS in the coal gas is converted into H through dry-method dust-removal device C
2S, through dry-method desulfurization device E desulfurization, after washer F washing, enter combustion chamber H.
The carbon containing grit that described dry dust removal equipment C separates enters semicoke boiler R with the semicoke of coal gasifier A.
Also comprise air separation unit T in this system, the oxygen that air separation unit T produces links to each other with combustion chamber H with coal gasifier A.
This system also comprises condenser L, multistage cold CO
2Compressor M, refrigeration machine N; The exhaust of cryogenic gas turbine K links to each other with condenser L, and the incondensable gas of discharging from condenser L enters multistage cold CO
2Compressor M and through refrigeration machine N further cooling obtain liquid CO
2
This system also comprises condensate pump O, condensate water heater P and feed pump Q; The condensate water of condenser L links to each other with condensate water heater P through condensate pump O, enters condensate water heater P heat-setting water by bleeding of cryogenic gas turbine K, and the condensate water after the heating enters systemic circulation again after feed pump Q supercharging.
Drawing gas of described high-pressure steam turbine V links to each other with coal gasifier A.
Purpose of the present invention also can realize by following measure:
A kind of inside and outside coal-fired integrated combined cycle generation method comprises the steps: that (1) coal, water vapour, desulfurizing agent and oxygen enter coal gasifier A, obtains raw gas at coal gasifier A top, obtains semicoke in its bottom; (2) raw gas enters waste heat boiler B, makes it change high steam into to the feedwater heating from regenerator J; (3) the semicoke air that is admitted to semicoke boiler R and pressure fan S outlet carries out combustion reaction the feedwater heating is obtained high steam; Boiler slag removal is discharged from the bottom, smoke exhaust system; Pressure fan S sends into semicoke boiler R after supercharging air; Air enters air separation unit T, produces oxygen, obtains byproducts such as nitrogen simultaneously, and oxygen is sent into coal gasifier A and combustion chamber H respectively after by compressor U supercharging; (4) enter high-pressure steam turbine V work done generating after the high steam that step (2) and step (3) are obtained mixes; (5) raw gas after the cooling enters combustion chamber H the steam discharge by the high-pressure steam turbine V of regenerator J heating is heated to the circulation initial temperature; (6) admixture of gas with circulation initial temperature enters high-temperature gas turbine I work done generating; (7) exhaust of high-temperature gas turbine I enters regenerator J to the feedwater heating; Send into waste heat boiler B and semicoke boiler R respectively after feedwater is heated to different temperature in regenerator J; (8) gas enters cryogenic gas turbine K work done generating after the heat release cooling in regenerator J.
Raw gas after the described cooling enters dry dust removal equipment C, and isolated carbon containing grit is admitted to semicoke boiler R, and the coal gas after the dedusting passes through hydrolyzer D, dry-method desulfurization device E and washer F successively, and the clean gas that obtains enters combustion chamber H.
Described inside and outside coal-fired integrated combined cycle generation method comprises the steps: that also (1) cryogenic gas turbine K exhaust enters condenser L, and hydrophobic being cooled of turbine exhaust and condensate water heater obtains condensate water in condenser L; And from condenser L, extract incondensable gas out; (2) incondensable gas enters multistage cold CO
2Compressor M carries out the gas compression; Gas-liquid mixture after the supercharging further cools off by refrigeration machine N, reclaims liquid CO
2, remaining admixture of gas row is to atmosphere.
Described condensate water is after condensate pump O supercharging, unnecessary part is discharged system, major part enters condensate water heater P as cycle fluid and heats up, and the feedwater after feed pump Q supercharging is divided into three the tunnel: remove regenerator J, washer F water, semicoke boiler R low temperature heating surface; Feedwater through regenerator J heating mixes with the feedwater of heating through semicoke boiler R low temperature heating surface, further heating changes steam into and reaches the high-pressure steam turbine initial temperature in semicoke boiler R, then with vapor mixing from waste heat boiler B, enter high-pressure steam turbine V work done, the turbine coal gasifier A that draws gas is used for coal gasification.
The present invention has following advantage compared to existing technology:
1, the present invention by the system integration based on the inside and outside coal combustion technology of coal partial gasification, novel thermodynamic cycle and separation of C O
2Process organically combines, and has realized the high efficiency of electricity generation system, the superior feature of environmental protection and good and economic.
2, the present invention adopts internal combustion and external combustion is combined, is main working medium, has the advanced person of high gentle low pressure at expulsion just, a novel integrated combined cycle with water vapour.
3, the new thermodynamic cycle that proposes of the present invention method that adopts external combustion and internal combustion to combine heats with the external combustion mode in the low-temperature zone of thermodynamic cycle endothermic process (in the semicoke boiler water be heated, vaporization and overheated), utilizes the energy of the semicoke that the coal partial gasification obtains; Heat with the internal combustion mode in high temperature section (water vapour further heats up in the combustion chamber), utilize the energy of the coal gas (after purified treatment) that the coal partial gasification obtains.Because adopt the internal combustion mode, the circulation initial temperature can reach the initial temperature level of modern gas turbines; Utilize the heat of external combustion process that water under high pressure is changed into high steam, thereby saved the compressor that promotes power pressure in the Brayton cycle, saved the compression wasted work; Coal gas carries out the theory burning with pure oxygen in the water vapour atmosphere in the combustion chamber, has only water vapour and CO in the combustion product
2(content is relatively very low), the turbine exhaust can reach vacuum state, has made full use of the low advantage of Rankine cycle sink temperature.Therefore new circulation can reach the very high thermal efficiency.In the process that turbine exhaust heat release is condensed, CO
2Automatically separated, avoided the system complex that conventional isolation technics brings, the shortcoming that equipment manufacturing cost rises and consumes a large amount of additional energies, can low energy consumption separation of C O
2Therefore newly circulate in thermal performance and separate greenhouse gases two aspects and all have brand-new characteristics.
4, system of the present invention adopts coal partial gasification technology, and temperature is lower in the gasification furnace, and the harmful substance in the coal is not melted, and the harmful components in the coal gas are low, and are less demanding to follow-up gas purification process; The sensible heat that reclaims coal gas is effective to heat the water vapour working medium of end circulation, does not require the high temperature coal gas purification technology that adopts; Add desulfurizing agent to gasification furnace simultaneously, removed the sulphur more than 90% in the coal, the load of coal gas desulfurization alleviates greatly, can adopt dry desulfurizing process to carry out smart desulfurization.Gas cleaning system of the present invention comprises coal gas dry-method dedusting, hydrolysis, dry desulfurization and washing four parts: utilize at the ceramic filter of 200 ℃ of temperature grade maturations and isolate unreacted carbon granules and flying dust in the coal gas; By hydrolytic process the COS in the coal gas is converted into H
2S; Adopt dry desulfurizing process that coal gas is carried out smart desulfurization; Utilize washing that the trace impurity in the coal gas is eliminated at last, obtain clean gas and be used for the combustion chamber.Compare with the gas cleaning system of conventional IGCC, the characteristics of native system are: the simple relatively dry desulfurizing process of adopting process system; Simultaneously dedusting being divided into two-stage and two-stage is separated-dry method dust reclaims the carbon containing ash content in the coal gas, and wet dedusting comprises that the impurity that dry desulfurization produces eliminates to residual impurity in the coal gas.
5, the present invention separates the CO that gas-fired generates by the circulation innovation
2, combustion process is oxidant with the pure oxygen, the NO of generation
xSeldom, therefore has better environmental-protecting performance than IGCC system.
6, process system of the present invention obtains simplification, technical difficulty reduces, thereby effectively reduces the cost of clean coal power generation unit.Coal partial gasification temperature levels is low, technical difficulty is little, and the size of gasification furnace reduces greatly, and can adopt cheap fluidized-bed gasification furnace; Harmful components content such as the slag in the raw gas are low, the gas temperature of gasification furnace outlet is low, and are low to the material requirement of waste heat boiler, reduced the manufacturing cost of waste heat boiler; The dry desulfurizing process system is simple, equipment is few, cost is low relatively; Promote power pressure and finish, saved expensive compressor equipment by feed pump; The top circulation is adopted identical main working medium with end circulation, does not need the waste heat boiler equipment of conventional combined cycle; The circulation feed temperature is low, does not establish complicated feedwater back heating system and equipment.When the present invention makes the clean coal power generation system reach efficient and environmental protection,, the economy of electricity generation system will be improved significantly by reducing cost.
7, system of the present invention does not establish compressor, and the problem of compressor surge in the time of can avoiding conventional gas turbine variable load operation helps improving the operational flexibility and the security reliability of unit.
8, air separation unit is produced a large amount of nitrogen, even is produced argon gas as byproduct, thereby bring extra returns producing coal gasification, gas-fired with in the oxygen in the system of the present invention, improves the economy of electricity generation system.
9, electricity generation system of the present invention is a fuel with coal (comprising colm) not only, and can adopt other fuel, as petroleum coke, residual oil, living beings, municipal refuse etc., has good fuel tolerance.
Description of drawings
Fig. 1 is the T-s figure of integrated combined cycle of the present invention.
Fig. 2 is the T-s figure of ABGC thermodynamic cycle.
Fig. 3 is inside and outside coal-fired integrated association circulating power generation system flow chart (the semicoke boiler is oxidant with the air) of the present invention.
Fig. 4 is inside and outside coal-fired integrated association circulating power generation system flow chart (the semicoke boiler is oxidant with oxygen) of the present invention.
Concrete embodiment
The T-s figure of new circulation of the present invention sees Fig. 1 (point among the figure is corresponding with the logistics sequence number of Fig. 3).Endothermic process is divided into two sections: 24-38 heats (comprising that coal-char combustion is to the heating to water vapour of the heating of water vapour and coal gas of high temperature) for the external combustion mode, and 18-17 heats for the internal combustion mode; The work done process is divided into three sections: 38-23 is a high-pressure steam turbine, and 17-20 is high-temperature gas turbine (water vapour and CO
2Mixed working fluid), 21-26 is cryogenic gas turbine (water vapour and CO
2Mixed working fluid); Exothermic process is 26-27; The temperature rise of feedwater pressurization is low, is 27 points, 36 points on figure; Process 27-36,36-24,23-18 are respectively the heating of feedwater backheat (thermal source is bled for the cryogenic gas turbine), feed-water preheating and middle pressure steam backheat heating process (thermal source of latter two process is the exhaust of high-temperature gas turbine).The pressurization that in new circulation, does not have gas.
New circulation can be thought the integrated combined cycle that two circulations organically combine: prolong line segment 26-21 intersection section 23-18 in 18 ' point, the diagrammatic representation in the line segment left side steam Rankine cycle of heat again-end circulation, the diagrammatic representation on line segment right side have the gas Brayton cycle-top circulation of backheat (the backheat temperature rise is very little); 18 '-21 expression " virtual turbine " work done processes, 21-18 ' expression " virtual compressor " compression process.
Obviously, the wasted work of " virtual compressor " compression process is less than the wasted work of desired compression process, and therefore the efficient of pushing up circulation 21-18 '-17-20-21 is more much higher than the single-cycle efficient of conventional combustion gas; To end circulation 27-38-23-18 '-26-27, similar substantially with the steam Rankine cycle of routine, but also have any different: 1. owing to added fuel and oxygen in circulating combustion chamber, top, the working medium flow of cryogenic gas turbine work done (21-26) is greater than the working medium flow of endothermic process, and the turbine work done increases; 2. circulating exhaust heat in top is used for the end cyclic steam heat (20 '-23 ' heating 23-18 ') and feed-water preheating (23 '-21 heating 36-24) and directly work done (21-26) again, be different from the simple heat transfer process of conventional combined cycle, the sensible heat loss of not discharging fume; 3. contain certain incondensable gas CO in the exhaust of cryogenic gas turbine
2, condenser pressure is higher than the back pressure of conventional Rankine cycle under the chilling temperature that equates.Numerical computations shows that preceding two factors occupy an leading position, and bottom circulating efficiency of the present invention is higher than conventional Rankine cycle efficient.Therefore equal heat than the ratio of total circulation caloric receptivity (the combustion process working medium caloric receptivity with) condition under, the efficient of new circulation will be higher than the efficient of the conventional combined cycle of interior external combustion combination.
ABGC is the conventional combined cycle of typical interior external combustion combination, and its T-s figure sees Fig. 2, can think the combination of conventional Brayton cycle (1-2-3-4-1) and Rankine cycle (5-7-8-9-10-5).To new circulation and ABGC, when the heat ratio that adopt to equate, the circulation initial temperature is got equal numerical value, the condensing pressure of new circulation a little more than ABGC at the bottom of the back pressure of circulation, other restrictive condition of system such as the crushing of parts, heat transfer temperature difference etc. are all got equal value.Certain specific operation is carried out analog computation (to be compared with embodiment, do not consider loss, the system oxygen wasted work of fuel conversion process, the crushing of parts etc., only calculate the efficient of thermodynamic cycle itself), the result shows: the top cycle efficieny of new circulation is significantly higher than the top cycle efficieny of ABGC, exceed 13.20 percentage points, the bottom circulating efficiency of new circulation is higher 2.68 percentage points than the bottom circulating efficiency of ABGC, and therefore the efficient of new circulation is than the efficient high 5.73 percentage points (result of calculation is listed table 1 in) of ABGC.
The thermal efficiency comparative unit of new circulation of table 1 and ABGC circulation: %
| New circulation | ????ABGC |
Top cycle efficieny η
t | ????52.68 | ????39.48 |
Bottom circulating efficiency η
b | ????44.08 | ????41.40 |
Heat compares γ
t | ????48.23 | ????48.23 |
Gross efficiency η
b+γ
t·η
t(1-η
b)
| ???58.29 | ????52.56 |
New cycle efficieny of the present invention is suitable with the waste heat boiler type combined cycle efficiency of equal initial temperature, but the latter adopts the internal combustion mode, can only use gas and liquid fuel, and separation of C O automatically
2, consider separation of C O
2After efficient will descend, be lower than thermal efficiency of cycle of the present invention.
The concrete structure of the embodiment of electricity generation system of the present invention is please referring to Fig. 3, and system of the present invention comprises coal gasification subsystem, power cycle subsystem and CO
2Reclaim subsystem three parts.In this system: the A-coal gasifier; The B-waste heat boiler; The C-dry-method dust-removal device; The D-hydrolyzer; The E-dry-method desulfurization device; The F-washer; The G-sewage disposal device; The H-combustion chamber; I-high-temperature gas turbine; The J-regenerator; K-cryogenic gas turbine; The L-condenser; Multistage cold CO of M-
2Compressor; The N-refrigeration machine; The O-condensate pump; P-condensate water heater; The Q-feed pump; R-semicoke boiler; The S-pressure fan; The T-air separation unit; The cold oxygen compressor of U-one inter-stage; The V-high-pressure steam turbine.
Present embodiment provides a kind of inside and outside coal-fired integrated association circulating power generation system, and this system comprises coal gasifier A, waste heat boiler B, combustion chamber H, high-temperature gas turbine I, regenerator J, cryogenic gas turbine K, semicoke boiler R, high-pressure steam turbine V; Wherein the raw gas of coal gasifier A generation links to each other with waste heat boiler B, and the semicoke of coal gasifier A then links to each other with semicoke boiler R; Waste heat boiler B utilizes the raw gas of coal gasifier A that the feedwater heating from regenerator J is produced high steam, and the coal gas after the waste heat boiler B cooling is isolated the carbon containing grit, through hydrolyzer D the COS in the coal gas is converted into H through dry-method dust-removal device C
2S, through dry-method desulfurization device E desulfurization, after washer F washing, enter combustion chamber H.The carbon containing grit that described dry dust removal equipment C separates enters semicoke boiler R with the semicoke that coal gasifier A discharges.Semicoke boiler R is with the feedwater of semicoke and its low temperature heating surface of carbon containing grit burning back heating of coal gasifier A discharge, the feedwater of the low temperature heating surface of semicoke boiler R heating is further heated generation high steam afterwards by semicoke boiler R again with after feedwater through regenerator J heating mixes; The high steam that semicoke boiler R produces mixes the back with the high steam that waste heat boiler B produces and links to each other with high-pressure steam turbine V; The steam discharge of high-pressure steam turbine V enters combustion chamber H after regenerator J heating, and heats the gas that the back forms tool circulation initial temperature by clean gas in the H of combustion chamber, and this gas links to each other with high-temperature gas turbine I; Gas after the high-temperature gas turbine I work done enters cryogenic gas turbine K work done after regenerator J carries out heat exchange.Wherein the exhaust of cryogenic gas turbine K links to each other with condenser L, and the incondensable gas of discharging from condenser L enters multistage cold CO
2Compressor M and through refrigeration machine N further cooling obtain liquid CO
2The condensate water of condenser L links to each other with condensate water heater P through condensate pump O, enters condensate water heater P heat-setting water by bleeding of cryogenic gas turbine K, and the condensate water after the heating enters systemic circulation again after the feed pump supercharging.
Also comprise air separation unit T in this system, the oxygen that air separation unit T produces links to each other with combustion chamber H with coal gasifier A.
Electricity-generating method flow process of the present invention is as follows:
Coal 1, water vapour 2, desulfurizing agent (lime stone, 3) and oxygen 4 enter coal gasifier A, obtain raw gas 5 at top of gasification furnace, obtain semicoke 6 in its bottom.The carbon containing grit 11 that semicoke behind the release pressure is discharged with the deduster bottom is sent into semicoke boiler R, and the air 39 that exports with pressure fan S carries out combustion reaction to the feedwater heating, and boiler slag removal 41 is discharged from the bottom, flue gas 40 discharge systems.Pressure fan 39 is sent into semicoke boiler R after air 42 superchargings.Oxygen is provided by air separation unit T, and air 43 enters air separation unit T, produces oxygen 44, obtains byproducts 45 such as nitrogen simultaneously, and oxygen is sent into coal gasifier A and combustion chamber H (homologue stream is respectively 4 and 19) respectively after by compressor U supercharging.Raw gas 5 enters waste heat boiler B, makes it change steam 9 into to feedwater 8 heating from regenerator J; Coal gas 7 after the cooling enters follow-up dry dust removal equipment C, and isolated carbon containing grit 11 is admitted to semicoke boiler R, and the coal gas 10 after the dedusting enters hydrolyzer D.COS is converted into H in hydrolyzer
2S, coal gas 12 enters dry-method desulfurization device E then; The coal gas 13 of sulfur-bearing does not enter washer F again and carries out final purification, and the water 15 of washing coal gas is from the feedwater delivery side of pump, and the water 16 that discharge the bottom is admitted to sewage disposal device G and handles, and the clean gas 14 that obtains enters combustion chamber H working medium is heated.
The steam 18 that is heated by regenerator J enters combustion chamber H, is heated to the circulation initial temperature by clean gas 14 and oxygen 19 burning liberated heats, and high-temperature gas mixture 17 enters high-temperature gas turbine I work done, and exhaust 20 enters regenerator J water vapour working medium is heated.Send into waste heat boiler B and semicoke boiler R respectively after feedwater 22 is heated to different temperature in regenerator J; The steam discharge 23 of high-pressure steam turbine V is heated back 18 and sends into combustion chamber H.Gas working medium heat release cooling back 21 in regenerator J enters cryogenic gas turbine K work done, bleeds 25 to be used for the heating of condensate water backheat, and turbine exhaust 26 enters condenser L.Turbine exhaust 26 and heater condensate 28 are recycled water cooling and obtain condensate water 27 in condenser L; From condenser L, extract out incondensable gas (29, CO
2And water vapor mixture, main component is CO
2).Above-mentioned incondensable gas enters multistage cold compressor M, and the isolated condensate water of gas compression processes is discharged system (30); Gas-liquid mixture 31 after the supercharging by refrigeration machine N further cool off (the refrigeration thermal source be compressor between cold and hot amount), reclaim liquid CO
232, remaining admixture of gas 33 rows are to atmosphere.Condensate water 27 after condensate pump O supercharging, unnecessary part 34 discharge systems, most of condensate water 35 enters bleeder heater P as cycle fluid and heats up 36, heater adopts turbine 25 heating of bleeding, the hydrophobic condenser that enters.Feedwater after feed pump Q supercharging is divided into three the tunnel: remove regenerator J22; Washer F water 15; Semicoke boiler R low temperature heating surface 37.Feedwater 24 through regenerator J heating mixes with the feedwater of heating through semicoke boiler R low temperature heating surface, further heating changes steam into and reaches high-pressure steam turbine initial temperature 38 in semicoke boiler R, mix with steam 9 then from waste heat boiler B, enter high-pressure steam turbine V work done, turbine draws gas and 2 goes gasification furnace to be used for coal gasification.
It is fuel that system embodiment of the present invention adopts coal, and the parameter of its balance condition and performance indications are referring to table 2-table 4.Relevant condition is: 900 ℃ of gasification furnace outlet temperatures; Semicoke boiler excess air coefficient 1.2; 130 ℃ of semicoke exhaust gas temperatures; Combustion chamber excessive oxygen coefficient 1.03; Combustion chambers burn efficient 99%; High-temperature gas turbine admission pressure 3.8MPa, 1300 ℃ of temperature (considering that high-temperature component cooling intake air temperature reduces by 50 ℃); 550 ℃ of high-pressure steam turbine initial steam pressure 16.5MPa, temperature; High-temperature gas turbine isentropic efficiency 90%; High-pressure steam turbine, cryogenic gas turbine isentropic efficiency 88% (cryogenic gas turbine moisture district isentropic efficiency 85%); Feed pump, condensate pump efficient 78%; 11 ℃ of the minimum heat transfer temperature differences of regenerator; 10 ℃ of the minimum heat transfer temperature differences of waste heat boiler; 4.7 ℃ of the minimum heat transfer temperature differences of condensate water heater; Condenser pressure 0.008MPa; CO
2Compressor, oxygen compressor efficient 80%; Liquid CO
25 ℃ of discharge temperatures; 15 ℃ of atmospheric pressure 0.1013MPa, temperature; Mechanical efficiency * electric efficiency 98%; Each parts crushing value is referring to table 4.
In the circulation initial temperature is that system of the present invention net efficiency has reached 45.36% (LHV) under the condition of 1300 ℃ (the turbine intake air temperature that are equivalent to FA level gas turbine), suitable with the IGCC system net efficiency that adopts FA level gas turbine; Native system can reclaim 41.21% liquid CO
2, when keeping the original purification level of IGCC, environmental-protecting performance is further improved; The present invention makes the difficulty of technology such as coal gasification reduce, simplify system again, and the investment of unit is reduced about 20%, thereby has overcome the difficult problem that the IGCC investment is big, be not easy to apply.The present invention is by the circulation innovation, coal grading is transformed (coal partial gasification, coal gas and semicoke utilize respectively) and integrated combined cycle combine, dexterously semicoke energy and coal gas energy are used with external combustion and internal combustion mode respectively, realized the cascade utilization of different quality energy, the trans-utilization and the advanced thermodynamic cycle of coal are organically combined, thereby the combination property (comprising thermal performance, environmental-protecting performance and economy) of coal generating system is significantly increased, and therefore proposition of the present invention is the breakthrough of thermodynamic cycle and the breakthrough of clean coal power generation technology.
If also send into oxygen to the semicoke boiler, make semicoke and oxygen carry out combustion reaction, then combustion product is mainly CO
2Thereby, with this part CO
2Also separate, realize the CO of total system
2Another embodiment of the present invention Fig. 4 is seen in near-zero release.Send into semicoke boiler R from the part of oxygen 39 that air separation unit T obtains, (main component is CO to the flue gas that burning produces
2, 40) and after subcooler S cooling 42, enter CO
2Compressor M.Other parts of system and connected mode and Fig. 3 are identical.Because the oxygen consumption of this system increases, the power that air separation unit is consumed rises, and reclaims CO simultaneously
2Increase the wasted work that also makes compressor and increase, so the efficient of system descends to some extent.Identical with other conditionally complete of the embodiment of Fig. 3, result of calculation shows: system's net efficiency is 41.00% (LHV), CO
2(liquid state) rate of recovery reaches 94.45%.
Can also further improve the performance of system of the present invention by other method, as: system flow and parameter optimization; Adopt low energy consumption space division technique (separation separates the mode of combining etc. with cryogenic freezing as film); Improve the initial conditions (even adopting supercritical parameter) of end circulation and the initial conditions of top circulation by technological progress.
It is about 45% that gasification furnace carbon conversion ratio of the present invention is only required, the difficulty of coal gasification reduces greatly, and the leeway also very big (the carbon conversion ratio is lower than 90% coal gasification to be realized easily) of further improving the carbon conversion ratio.As adopting higher carbon conversion ratio, the energy that makes coal be converted into coal gas increases (energy of semicoke reduces relatively) relatively and promptly improves the heat ratio, from coal gas, isolate hydrogen then, be used for hydrogen-oxygen combined cycle generation or fuel cell power generation, promptly isolated hydrogen fuel is used for generation mode more efficiently in system, semicoke and residual gas are used for the integrated combined cycle generation mode of internal combustion, external combustion combination, and then the efficiency value of system also will increase substantially at present.Therefore system of the present invention combines with advanced person's hydrogen fuel generation technology, will become very promising advanced clean coal power generation technology.
The performance data of certain coal of table 2 (dry back)
Industrial Analysis (percentage by weight, %) | Elementary analysis (percentage by weight, %) |
Moisture 5.000 fixed carbon 34.087 fugitive constituents 49.043 ash 16.870 | Ash content 16.870 carbon 67.274 hydrogen 4.478 nitrogen 1.239 chlorine 0.030 sulphur 4.185 oxygen 5.924 |
Table 3 overall system performance data
The consumption of coal amount | 18.24(kg/s) | Gasification furnace carbon conversion ratio | 44.82% |
The heat ratio | 51.73% | Feedwater flow | 100.00(kg/s) |
High-temperature gas turbine power | 190.37(MW) | High-pressure steam turbine power | 35.79(MW) |
Cryogenic gas turbine power | 34.17(MW) | Gross horsepower | 260.33(MW) |
Water pump, blower fan wasted work rate | 2.38(MW) | Oxygen compressor wasted work rate | 9.50(MW) |
CO
2Compressor wasted work rate
| 12.00(MW) | Air separation unit wasted work rate | 17.50(MW) |
Machinery, motor loss | 4.72(MW) | Net power | 214.23(MW) |
Net efficiency | 45.36%(LHV) | CO
2The rate of recovery
| 41.21% |
*-oxygen purity 96% (percent by volume);
System oxygen power consumption rate 0.245kWh/kg oxygen;
Coal Lower heat value 25898kJ/kg.
-relevant calculation formula:
Net efficiency=net power/(Lower heat value of consumption of coal amount * coal)
CO
2The liquid CO of the rate of recovery=recovery
2The CO that/burning generates
2
Table 4 balance condition state parameter
The logistics sequence number | Pressure (MPa) | Temperature (℃) | Flow (kg/s) | The logistics sequence number | Pressure (MPa) | Temperature (℃) | Flow (kg/s) |
1 coal | 4.500 | ?15.0 | ?18.24 | 23 steam | 4.000 | ?339.3 | ?97.60 |
2 steam | 4.500 | ?354.6 | ?0.60 | 24 water | 17.000 | ?310.6 | ?64.06 |
4 oxygen | 4.500 | ?281.5 | ?3.38 | 25 steam ' | 0.080 | ?94.6 | ?11.84 |
5 coal gas | 4.500 | ?900.0 | ?14.03 | 26 steam ' | 0.008 | ?44.7 | ?114.82 |
7 coal gas | 4.400 | ?200.0 | ?14.03 | 27 water | 0.008 | ?25.0 | ?102.69 |
8 steam | 17.000 | ?190.0 | ?7.23 | 28 water ' | 0.080 | ?38.6 | ?11.84 |
9 steam | 16.500 | ?550.0 | ?7.23 | ?29CO
2′
| 0.008 | ?25.0 | ?23.97 |
10 coal gas | 4.400 | ?200.0 | ?12.86 | 30 water | 0.101 | ?25.0 | ?3.45 |
11 dust | 4.400 | ?200.0 | ?1.17 | ?31CO
2′
| 7.000 | ?25.0 | ?20.52 |
12 coal gas | 4.400 | ?202.3 | ?12.86 | 32 liquid CO
2 | 7.000 | ?5.0 | ?18.12 |
13 coal gas | 4.350 | ?202.3 | ?12.09 | 33 gases | 7.000 | ?5.0 | ?2.40 |
14 coal gas | 4.300 | ?132.6 | ?12.60 | 34 water | 1.000 | ?25.2 | ?2.69 |
15 steam | 5.000 | ?92.1 | ?1.80 | 35 water | 1.000 | ?25.2 | ?100.00 |
16 waste water | 4.300 | ?136.4 | ?1.28 | 36 water | 1.000 | ?89.9 | ?100.00 |
17 steam ' | 3.800 | ?1249.9 | ?126.66 | 37 water | 17.000 | ?90.0 | ?26.91 |
18 steam | 3.920 | ?543.7 | ?97.60 | 38 steam | 16.500 | ?550.0 | ?90.97 |
19 oxygen | 4.500 | ?281.5 | ?16.46 | 39 air | 0.104 | ?17.9 | ?88.27 |
20 steam ' | 0.106 | ?573.7 | ?126.66 | 40 flue gases | 0.101 | ?130.0 | ?94.70 |
21 steam ' | 0.101 | ?101.0 | ?126.66 | 42 air | 0.101 | ?15.0 | ?88.27 |
22 water | 17.000 | ?90.0 | ?71.29 | 44 oxygen | 0.101 | ?15.0 | ?19.84 |
*-and do not simulate the desulphurization reaction in gasification furnace and the semicoke boiler, do not comprise the data of logistics 3,6,41 in the table.
-do not simulate the internal process flow process of air separation unit, do not comprise the data of logistics 43,45 in the table.
-logistics 15 is the data behind the feed pump outlet throttling.
-" steam ' " is the mixture of steam and other incondensable gas, and main component is a steam.
-" water ' " is the mixture of water and other incondensable gas, and main component is a water.
-" CO
2' " be CO
2With the mixture of other gas, main component is CO
2