HK1183925B - Method for power production by combustion of carbonaceous fuels and co2 capture - Google Patents

Abstract

A power plant for combustion of carbonaceous fuels with CO2 capture, comprising a pressurized fluidized bed combustion chamber (2), heat pipes (8, 8') for cooling of the combustion gas in the combustion, a direct contact cooler (15), a cleaned exhaust pipe (18) for withdrawal of the exhaust gas from the direct contact cooler (15) and introduction of the cooled exhaust gas into a CO2 absorber (19), where a lean exhaust pipe (20) is connected to the top of the absorber (19) for withdrawal of lean exhaust gas from the absorber (20), and a rich absorbent pipe (30) is connected to the bottom of the absorber (19) for withdrawal of rich absorbent and introduction of the rich absorbent into a stripping column (32) for regeneration of the absorbent to give a lean absorbent and a CO2 stream that is further treated to give clean CO2, where a water recirculation pipe (16) is connected to the bottom of the direct contact cooler (15) for withdrawal of used cooling water and connected to the top of the direct contact cooler(15) reintroduction of the cooling water at the top of the direct contact cooler, wherein a heat exchanger (17) connected to water recycle pipes (70, 70') for delivery and withdrawal, respectively, of cooling water to the heat exchanger, is provided in the recirculation pipe (16) for cooling the circulating direct contact cooler cooling water in pipe (16).

Description

For combustion and CO by carbonaceous fuels2Method for capturing and producing electric power

Technical Field

The invention relates to the removal of CO from a gas containing CO₂For example for capturing CO from exhaust gases from combustion of carbonaceous fuels₂The field of (1). More particularly, the invention relates to the treatment of CO₂Improvement in capture of CO₂Energy requirement of trapped deviceIs reduced.

Background

Due to CO in the atmosphere₂Causing CO to be released in the combustion of carbonaceous fuels, more particularly fossil fuels₂To focus on. Reduce CO₂The method of emission to the atmosphere is to capture CO from the exhaust gas of combustion of carbonaceous fuels₂And safely storing the trapped CO₂. Over the past decade or so, a number of proposals have been made for CO₂A trapping protocol.

Proposed for CO₂The techniques of trapping can be grouped into three main groups:

1.CO₂absorption: wherein CO is₂Reversible absorption from exhaust gas to leave a lean CO₂Exhaust gas, and regenerating the absorbent to provide CO which can be further treated and stored₂。

2. And (3) fuel conversion: in which a hydrocarbon fuel is converted (reformed) into hydrogen and CO₂。CO₂Separated from the hydrogen gas and safely stored, and the hydrogen gas is used as a fuel.

3. Oxygen-enriched combustion: wherein the carbonaceous fuel is combusted in the presence of oxygen that has been separated from the air. Replacement of air with oxygen leaves predominantly comprising CO₂And steam which may be separated by cooling and flashing.

WO2004/001301a (sargass) 31.12.2003 describes an apparatus for burning carbonaceous fuels at high pressure, in which the combustion gases are cooled inside a combustion chamber by steam generation in steam tubes in the combustion chamber, and CO is separated from the combustion gases by absorption/desorption₂To produce lean combustion gas and CO for storage₂And thereafter the lean combustion gas is expanded throughout the gas turbine.

WO2006/107209A (SARGASAS)12.10.2006 describes a coal fired pressurized fluidized bed combustion unit including improvements in fuel injection and exhaust gas pretreatment.

The combustion of the carbonaceous fuel at high pressure and the cooling of the pressurized combustion gases from the combustion chamber reduces the volume of the fuel gas compared to a similar amount of fuel gas at atmospheric pressure. Furthermore, the high pressure and cooling of the combustion process make it possible to achieve a sufficiently stoichiometric combustion. Sufficient stoichiometric combustion resulting in an oxygen residual amount of < 5 vol%, e.g. < 4 vol% or < 3 vol%, reduces the required mass flow of air for a particular power production. The combination of the high pressure and the reduced air mass flow significantly reduces the total volume of the exhaust gas to be treated. Furthermore, it significantly increases the CO in the fuel gas₂The concentration and partial pressure of the catalyst greatly simplify the equipment and reduce the CO capture₂The required energy.

WO2010/020684 relates to a device and method for removing or substantially reducing NOx and SOx from exhaust gas from marine diesel engines. Furthermore, fig. 6 and the corresponding description explain the addition of a CO-use in such a device₂The removed units are illustrated. A scrubber is provided for removing impurities in the gas, such as ammonia slip from the SCR unit. Furthermore, a cooler is provided for cooling the washing liquid in the washer. However, this application does not mention energy saving measures by transferring heat between the cooler and other processes in the plant.

WO2009/035340 relates to a CO for a power plant₂A capture unit wherein the lean absorbent recovered from the bottom of the stripper by flashing produces steam for reducing the reboiler duty. Furthermore, the steam produced can additionally be compressed and can be added as make-up water, which comes as condensate from the CO used for the steam and downstream of the stripper₂Flash tanks in separate paths. However, there is no mention or indication of using the scrubbing water from the direct contact cooler at the top of the stripper to generate steam or further heating the scrubbing water in a heat exchanger for the direct contact cooler to introduce the off-gas to improve the CO₂Energy efficiency of capture.

For CO₂Trapped byAll methods and processes are energy consuming. Accordingly, considerable effort has been devoted to developing lower energy consumption methods and processes to reduce energy losses, typically in the form of steam and cooling water at relatively low temperatures and pressures. Many ways have been taken to determine for heat integration in several process steps that the heat generated at one stage is transferred to a heat requiring process (heatdemanningprocess). The aim of these ways is to obtain a method for producing electrical energy from carbonaceous fuels and simultaneously capturing CO₂To a more energy efficient method, process and apparatus.

However, for the inclusion of CO₂There remains a great need for trapped solutions that improve the energy efficiency of power plants. It is an object of the present invention to provide an improved solution for heat integration for improved energy efficiency, i.e. to maximize the output of useful energy (as heat and/or electricity) for a given amount of chemical energy as carbonaceous fuel.

Disclosure of Invention

According to the present invention there is provided a method for combustion and CO by carbonaceous fuel₂A method of capturing produced electricity, wherein the carbonaceous fuel is combusted in a combustion chamber in the presence of an oxygen-containing gas and under pressure; wherein the combustion gas in the combustion chamber is cooled by generating steam within a heat pipe provided in the combustion chamber; wherein the exhaust gases are recovered by an exhaust gas conduit via a heat exchanger and an exhaust gas treatment unit, and a direct contact cooler is connected with a water recirculation conduit for recirculating water collected at the bottom of the direct contact cooler and reintroducing water at the top of the cooler, in which cooler the partially cooled exhaust gases are further cooled and humidified by counter-flow to water; wherein the exhaust gas is recovered from the direct contact cooler through a clean exhaust gas duct and is introduced into the CO₂Absorber in the CO₂In the absorber, a lean absorbent is introduced into an upper contact zone in the absorber to promote counter-current flow of the exhaust gas to liquid CO₂Absorbent agent for treatingProduction of rich absorbent and CO₂Lean exhaust gas, said rich absorbent being in said CO₂The absorber bottom is collected and passed from the CO through a rich absorbent conduit₂The bottom of the absorber is recovered, and the CO is recovered₂A lean exhaust gas is recovered from the top of the absorber through a lean exhaust gas conduit connected to the absorber; wherein the lean exhaust gas is scrubbed in a scrubbing section, heated in a heat exchanger, and expanded throughout the turbine to produce electrical energy before being released to the atmosphere; wherein the rich absorbent conduit is connected to introduce the rich absorbent to a stripper for regeneration of the absorbent to produce lean absorbent and CO₂A stream of the lean absorbent recovered through a lean absorbent recycle line in which the lean absorbent is pumped back to the absorber, the CO₂The stream is further treated to produce clean CO₂(ii) a Wherein said CO is₂The stream is cooled by a cooling fluid flowing through a direct contact cooler provided at the top of the stripping column; and wherein the water is collected by a collection plate provided below the direct contact cooler, and wherein a water recirculation line is arranged for recovering the collected water; wherein the cooling water of the circulating direct contact cooler in the recirculation conduit is cooled in a heat exchanger provided in the recirculation conduit, wherein the cooling water is conveyed and recovered through a water recirculation conduit connected to the heat exchanger, respectively; and wherein water recovered from the heat exchanger through a recycle line is flashed over a flash valve and a flash tank, wherein water from the flash tank is recovered through a line to recycle the water as a wash fluid in a direct contact cooler of the stripping column; and wherein the steam in the stripping tank is introduced as additional stripping steam in the stripping column through a steam line connected to said flash tank.

Drawings

FIG. 1 is a schematic diagram of a first embodiment of the present invention;

FIG. 2 is a schematic diagram of a second embodiment of the present invention;

FIG. 3 is a graph showing CO during cooling₂/H₂A plot of enthalpy change of O versus temperature;

FIG. 4 is a graph showing the change in enthalpy of the fuel gas as a function of temperature comparing an atmospheric pressure device and a pressure boosting device; and

FIG. 5 is a view showing H₂A plot of temperature of O across the lean absorbent as a function of vapor pressure.

Detailed Description

Fig. 1 is a schematic view of an apparatus according to the present invention. Carbonaceous fuel (also referred to herein as carbonaceous fuel) is introduced into the pressurized combustion chamber 2 through the fuel conduit 1 at a pressure of 5 to 50 bar (hereinafter simply referred to as bar) 1. The pressure in the combustion chamber is preferably above 10 bar, for example about 15 bar.

The fuel may be natural gas, oil, coal, biofuel or any other carbon rich fuel and it is well known to those skilled in the art that the manner of introduction and ignition of the fuel depends on the type of fuel.

Air or an oxygen-containing gas is introduced into the compressor 4 through the intake 3. The compressor 4 is driven by an electric motor 5 or a gas turbine 6 via a common shaft 25 which will be described further below. The skilled person will understand that: compressor 4 may represent one or more compressors or compressor platforms connected in series, optionally with an intercooler between individual compressors or between compressor steps. Parallel compressors may be used for very large systems.

Air and an oxygen-containing gas are introduced from the compressor 4 through a compressed air duct 7 to the combustion chamber 2 as a source of oxygen for combustion in the combustion chamber. The air and fuel introduced to the combustion chamber are controlled to produce a residual oxygen content in the exhaust gas of less than 5 vol%, for example less than 4 vol% or less than 3 vol%. Low residual oxygenThe content results in high CO₂Content of fuel gas. Thus, when air is used and the residual oxygen is as indicated above, the CO in the exhaust gas₂The content is about 8% to about 18% by volume.

Inside the combustion chamber, heat pipes 8, 8 'are arranged to cool the combustion gases by generating steam and superheated steam inside the heat pipes 8, 8', respectively. The combustion gases are cooled by the heat pipes 8, 8' so that the exhaust temperature of the exhaust gases is 300 to 900 ℃.

The internal arrangement in the combustion chamber may be different depending on the desired fuel. When coal is used as fuel, air is introduced to create a fluidized bed of fuel for combustion and heat pipes 8, 8' are arranged in the fluidized bed. When using oil or gas as fuel, two or more stages (stages) of oil or gas burners, respectively, are arranged in the combustion chamber, and heat pipes 8, 8' are arranged between the stages to cool the combustion gases between each stage. The skilled person will appreciate that it is also possible to use a combination of the above fuels or other carbon rich fuels.

The above references WO2004001301 and WO2006107209 describe embodiments of arrangements for different fuels.

The exhaust gas is recovered from the combustion chamber through an exhaust gas conduit 9 and cooled in a heat exchanger 10 to a temperature between 250 and 450 ℃.

Downstream of the heat exchanger 10 one or more units for exhaust gas pretreatment are arranged. Preferably, a filter unit 11 is arranged immediately downstream of the heat exchanger 10 to remove particles from the fuel gas. For exhaust gases with a low particle content, for example exhaust gases from the combustion of oil or gas as fuel, the filter unit can be omitted. However, a filtration unit is necessary when using coal because of the particles produced by the coal, which may be detrimental to the downstream steps of the gas treatment unit.

The combustion of carbonaceous fuels in the presence of air produces NOx. In addition to its environmental impact, NOx also does not favor CO₂And (4) trapping. Therefore, a Selective Catalytic Reduction (SCR) unit 12 is arranged downstream of the heat exchanger 10 and the optional filter unit 11. According to known techniques, urea or NH₃The SCR unit is introduced and reacts with NOx over the catalyst to remove NOx. The temperature in the SCR unit is preferably between 250 and 450 ℃. The preferred operating temperature for the SCR unit is about 350 ℃.

Downstream of the SCR unit one or more heat exchangers and a scrubbing unit are arranged. The first heat exchanger 13 is a fuel gas cooling unit for cooling the exhaust gas to below 250 ℃. The second illustrated unit 14 may be a parallel scrubber (co-currentscrubber). Depending on the gas composition and operating conditions, scrubbers may also be used for cooling of the gas.

Downstream of the cooling units 13, 14, a counter-current scrubber or a direct contact cooler is arranged. Cooling water is introduced into the cooler 15 above the contact zone 15' through a recirculation conduit 16 and is brought in counter-current flow to the exhaust gases which are introduced into the cooler 15 below the contact zone. The water is collected at the bottom of the cooler 15, cooled in a heat exchanger 17 and circulated through a recirculation conduit 16.

Since the purpose of units 11, 12, 13, 14 and 15 is to produce exhaust gas for carbon dioxide capture, they may be collectively referred to as pretreatment units.

Cooled off-gas is recovered from the cooler 15 via a clean off-gas line 18 and introduced into the lower part of the absorption tower 19, where it is brought in counter-current flow with the absorbent into one or more contact zones 19 ', 19 "' within the absorber. Absorbent (a fluid that traps CO₂And may be subsequently enhanced by applying CO in the gas phase relative to the CO immediately above the surface of the fluid₂CO with a lower partial pressure₂Partial pressure regeneration) introduces absorbent through lean absorbent line 35 into the absorber above the upper contact zone.

Absorbing CO in waste gas by absorbent in absorber₂To be produced through rich absorbent line 30Loaded CO recovered at the bottom of the absorber₂Or rich in CO₂The absorbent of (1). The lean exhaust gas is recovered via a lean exhaust gas line 20 from which more than 80%, more preferably more than 95% of the CO in the exhaust gas introduced into the absorber is removed₂。

The pressure in the absorber is slightly lower than the pressure in the combustion chamber, for example 0.5 to 1 bar lower than the pressure in the combustion chamber, which corresponds to a pressure in the absorber of 4.0 to 49.5 bar.

High pressure and high CO of exhaust gas introduced to absorber₂The combination of the contents allows to reduce the volume of the absorber and the volume of the circulating absorbent, while obtaining high efficiency of CO₂Trapping becomes possible.

The absorbent used in the absorber is preferably a hot aqueous potassium carbonate solution. Preferably, the absorbent comprises 15 to 35 wt% K dissolved in water₂CO₃。

The absorption of CO in a hot potassium carbonate system is based on the following overall reversible reaction₂：

Lean exhaust gas is recovered at the top of the absorber 19 through a lean exhaust gas line and introduced into a scrubbing section 21 where it is brought in countercurrent to a contact section 21' in a scrubbing section 21 where it is contacted with scrubbing water. The washing water is collected at the bottom of the washing section through the washing water circulation line 22 and reintroduced into the washing section above the contact section 21'. Scrubbed lean exhaust gas is recovered from the top of the scrubbing section through treated exhaust gas conduit 23.

The gas in the treated waste line 23 is introduced into the heat exchanger 10, where the treated exhaust gas is heated by the hot untreated exhaust gas leaving the combustion chamber 2 in the heat exchanger 10.

Thus, the heated and treated exhaust gas is then introduced to the gas turbine 6, where the gas is expanded to produce electrical energy in the generator 24. The expanded gas is recovered through an expanded exhaust gas conduit 26 and cooled in a heat exchanger 27 before being released to the atmosphere through an exhaust gas outlet 28.

The compressor 4 and the gas turbine 6 may be arranged on a common shaft 25 such that the compressor 4 is at least partially operated by rotational energy from the gas turbine 6. At present, however, it is preferred that the compressor be operated by the electric motor 5 and that the gas turbine operate the generator 24 to produce electrical power. The separation of the compressor 4 and the gas turbine 6 results in greater flexibility in the operation of the plant.

Fat absorbent, i.e. loaded with CO₂Is collected at the bottom of absorber 19 and is recovered therefrom via rich absorbent conduit 30. The fat absorbent in line 30 is flashed to a pressure slightly above 1 bar absolute (barabsolute), for example 1.2 bar absolute, hereinafter referred to simply as bara, over a flash valve 31 before being introduced into a stripper 32. In line 30 (not shown in fig. 1), there may be a flash tank or an extraction unit for removing undesired explosive components, such as oxygen, drawn into the absorbent from the fuel gas.

One or more contacting sections 32 ', 32 "' are disposed in stripping column 32. The rich absorbent is introduced above the upper contacting portion of the stripper and in counter-current to the steam introduced below the lowest contacting portion. Due to low pressure and CO in the stripper₂Diluting, CO in the stripper₂The low partial pressure of (A) causes the equilibrium in the above reaction (1) to shift to the left, and CO₂Is released from the absorbent.

Lean absorbent is collected at the bottom of stripper 32 and recovered through lean absorbent conduit 33. Lean absorbent conduit 33 is split into two conduits: a first lean absorbent reboiler conduit 34, the first lean absorbent reboiler conduit 34 being heated in a reboiler 36 to produce vaporization from a liquid introduced as stripping gas into the stripping column through a steam line 37; and a lean absorbent recycle line 35, where the lean absorbent is pumped back to the absorber 19 in the lean absorbent recycle line 35. A pump 38 and a cooler 39 are provided in line 35 to pump in and cool the absorbent, respectively, and thus increase the pressure of the absorbent before it is introduced into the absorber.

By CO₂The recovery line 40 collects CO at the top of the stripper₂And steam. A desorber direct contact cooler 66 is disposed above the contact zones 32 ', 32 ", 32'", and a rich absorbent is introduced to the stripper 32 via conduit 30 to cool the vapor (vapour) and CO exiting the upper contact zone₂Above the point of the gas mixture. The cooling fluid is introduced above the direct contact cooler section and allowed to flow through the direct contact cooler section 66. A collector plate (collector plate)65 is disposed below the direct cooler contact to allow water vapor to pass upwardly through the stripper column 32 and prevent cooling fluid from flowing into the contact zones 32 ', 32 "'. The fluid collected at the collection plate 65 is recovered through the water circulation pipe 70 and utilized as described below.

The moisture in line 40 is cooled in cooler 41 and introduced to flash tank 42. The liquid formed by cooling in the cooler 41 is collected at the bottom of the flash drum 42 via a liquid return line 43 and introduced into the stripping column 32. Alternatively, not shown in FIG. 1, the liquid may be routed to the top of the absorber tower 19. A liquid balance conduit 44 may be provided for adding liquid to conduit 43 or removing liquid from conduit 43 to balance the amount of water circulated.

By CO₂A recovery line 45 recovers the gas phase in the flash tank 42 and compresses it through a compressor 47 and cools it in a heat exchanger 48 to produce a CO pass through before it is further processed₂Compressed dry CO exiting the exit line 46₂。

The cooling fluid collected at the collecting plate 65 and recovered through the pipe 70 is introduced into the above-described heat exchanger 17 to cool the circulating cooling water in the circulating pipe 16. A pump 71 may preferably be arranged in the line 71 to circulate the water. As described below, heat is recovered from heat exchanger 17 via conduit 70A hot fluid and introducing the heated fluid to the above-identified heat exchanger 48 to be compressed CO in the heat exchanger 48₂And the steam is further heated. The further heated fluid is then recovered from the heat exchanger 48 through water line 72, flashed on flash valve 73, and the flashed fluid is then introduced into flash tank 74 to produce water that collects at the bottom of the flash tank 74 and steam that collects at the top of the flash tank 74 and is recovered through steam line 77. In the vapor conduit 77 there is arranged a compressor 75 followed by an optional trim cooler 66. The steam in steam conduit 77 is then introduced as stripping steam to stripping column 32 via line 37. Not shown in fig. 1, the fluid in line 70 may be routed directly to flash valve 73, or may be heated in a cryogenic energy source that is additional or different from heat exchangers 17 and 48. Examples of such heat sources are the scrubber 14, the compressor 4, the hot and cold gas auto-regulator, or residual heat in the lines 26 and/or 28. More heat reduces the power requirements of the compressor 75 and may increase the thermal efficiency of the overall system.

Liquid from flash drum 74 is recovered via line 78 and introduced via conduit 43 as wash liquid to the stripper direct contact cooler. Therefore, a pump 79 is preferably arranged in line 78 to provide sufficient pressure.

Cooling water for the combustion chamber is introduced from the water pipe 50 to the heat pipe 8. The steam generated in the heat pipe 8 is recovered through a steam pipe 51 and expanded throughout a high pressure steam turbine 52. Steam from the high pressure turbine section is introduced to the steam reheater 8' via line 53 and the resulting steam is recovered via steam conduit 54. The superheated steam in the conduit 54 is expanded in the intermediate and low pressure parts of the steam turbine 55. The fully expanded steam is recovered from the steam turbine section 55 through an expansion steam line 56 and cooled in a cooler 57 to produce water which is stored in a water collection tank 58. The water collected in the tank 58 is recovered through line 50 via a heat exchanger 27 where it is heated by the purified exhaust gas before being reintroduced into the heat pipe 8 in the heat exchanger 27.

Preferably, the first and second steam turbine sections 52, 55 are arranged on a common shaft 80 together with an electrical generator 81 for generating electrical energy. Steam cycles and optimization of steam cycles are known to those skilled in the art.

The partially expanded steam is recovered from the second intermediate pressure steam turbine section 55 through a partially expanded steam conduit 59. The partially expanded steam in the conduit 59 is introduced into a humidity conditioner where it is cooled by a water spray introduced from a water conduit 61. Cooled steam is recovered from the humidifier 60 through a reboiler steam line 62 and used for indirect heating of the lean absorbent in the reboiler 36 to produce steam from the lean absorbent. Water resulting from the condensation of steam introduced into reboiler 36 via conduit 62 is recovered via condensate line 63 and introduced into drum 58.

The skilled person will understand that: references to contacts in this specification, for example contacts 15 ', 15 "', 19" ', 21 "', 32" ', are contacts that preferably include structured and/or unstructured packaging material to increase the internal surface area, and thus the contact area between the liquid and gas in the contact.

Fig. 2 shows an embodiment of the invention which is more energy efficient than the embodiment described with reference to fig. 1. The only difference in the embodiment of fig. 2 compared to the embodiment of fig. 1 is the flashing of the lean absorbent, which will be described below. While flashing of lean absorbent is known per se as a way to increase energy efficiency, its combination with the thermal conversion features described with reference to fig. 1 is not known.

The portion of the lean absorbent leaving the stripper is introduced to a flash valve 90 via line 33 returning to the absorber 19 and subsequently released to a flash tank 91. The vapor phase in the flash tank 91 is recovered through a vapor line 92 and is compressed by a vapor compressor 93 to thereby heat the vapor. The compressed and heated steam is then introduced to the stripper column as stripping gas via compressed steam line 94. The liquid phase collected at the bottom of flash drum 92 is recovered from the bottom of flash drum 92 and pumped by pump 95 into lean absorbent line 35. In this embodiment, the cooler 39 is not used.

Example 1

Absorption of the above-mentioned CO according to reaction formula 1)₂：

The equilibrium of the equations is given according to equation 2):

(2)K_eq＝(HCO₃ ^-)²/[(CO₃ ^2-)PCO₂]

defining the saturation of the absorbent according to equation 3):

(3) s 2x # mole (KHCO)₃) /[ # moles/K₂CO₃) +2X # mole (KHCO)₃)]。

In the operation of the absorption/desorption unit, the target saturation is: for lean absorbents, s is 0.30 (minimum 0.1) because of the higher degree of K₂CO₃Regeneration requires additional energy and is generally for the above-mentioned CO₂The process is not essential; and for rich absorbents, s is 0.60 (max 0.7) because of the higher concentration of KHCO₃Resulting in higher absorber loading but may also result in an undesirable increase in crystallization temperature.

The absorber is usually operated at 80 to 110 ℃ and the desorber (stripper) at 90 to 120 ℃ depending on the pressure, since K₂CO₃Higher pressure and higher concentration, the temperature in the desorber is typically 92 c at the top and 110 c at the bottom.

Feeding to a desorber for desorbing/stripping predominantly vaporous CO₂Is used to:

1. heating the absorbent;

2. heating the circulating liquid;

3. the heat of reaction, although very low for some absorbents (e.g., those hot potassium carbonate-based systems);

4. stripping steam generation (CO at the top of the desorber depending on the nature of the absorbent)₂About 0.8 to 1.2 times the mass of).

For a coal-fired power plant of the pressurized fluidized bed type, coal is fed with a SOx sorbent and typically 25% water to form a slurry that is injected into the fluidized bed of the combustor. Steam was generated in the heat pipes of the combustor at a burn rate of 275LHV Low Heating Value (LHV) and 282MW High Heating Value (HHV). Typically at about 165 bar absolute and 565 c, 86kg/s steam is produced in the pipe 8 and this steam is expanded throughout the turbine 52.

The expanded steam is reheated to about 565 c in a heat pipe 8' of 40 bar absolute and expanded throughout the steam turbine 55. Typically, about 18kg/s of steam is recovered from the steam turbine stage at various pressures and used for boiler preheating. Not shown in fig. 1 and 2 for clarity. Further, at about 4 bar absolute, steam from the steam turbine is recovered in line 59. The amount of such recovery should be minimized. Based on this, the amount of steam fully expanded throughout the steam turbine is 86kg/s minus about 18kg/s minus the flow of steam in line 59. Which corresponds to 68kg/s minus any steam in line 59. The fully expanded steam from turbine 55 is recovered via line 56 and recycled as boiler feed water into heat pipe 8, while some 12kg/s steam is partially expanded and recovered via conduit 59. The steam recovered through conduit 59 typically has a temperature of about 258 ℃ and a pressure of 4 bar absolute, but this temperature and pressure also vary depending on the steam turbine system. The steam is cooled in the humidifier 60 to produce steam at about 4 bar absolute and 144 ℃, which is introduced into the reboiler of the desorber 36 for indirect heating to produce steam in the reboiler.

Alternatively, assuming an adiabatic efficiency of 90% for the steam turbine, the 4 bar absolute and 258 ℃ steam recovered through line 59 can be expanded at about 27 ℃ to about 0.035 bar absolute such that about 0.7MJ of electrical energy is produced per kilogram of expanded gas. For a 120MW steam turbine, if the flow in line 59 is zero, the steam flow from the 4b bar absolute stage to the condenser is about 68 kg/sec. The combustion chamber produces about 24.5kg/sCO₂With about 22kg/s captured (90% captured). The latent heat required when used to operate the desorber was 3.6MJ/kg of captured CO₂About 80MW of latent heat is required. When cooled to saturation temperature at 4 bar absolute and condensed at 4 bar absolute, the heat content of the 4 bar 258 ℃ steam is about 2.4 MJ/kg. Thus, the amount of steam required from the steam turbine is about 80/2.4kg/s, or about 34 kg/s. The loss of power from the steam turbine is 34^*0.7MW or about 24 MW.

On the cold side of stripper reboiler 36, the pressure is slightly above atmospheric. Thus, the product produced from the steam extracted from the steam turbine is now, for example, 1.2 bar absolute steam at a temperature of about 110 ℃ (the boiling point of the lean absorbent at that pressure).

Under the same assumption as above, that is, 22kg/s of CO was stripped from the adsorbent₂The required energy is 3.6MJ/kgCO₂Or about 80MW latent and sensible heat. Which corresponds to about 34kg/h steam flow to the desorber bottom generated in the reboiler.

Here, about 12kg/s of the condensed heat was supplied to the above items 1) to 3). The remaining about 22kg/s was used as stripping steam for entry 4). The steam and the recovered CO₂Together exiting at the top of the desorber packaging material. This means that: the energy used for stripping is essentially CO₂Energy lost to dilution stripping steam. Mixed with 22kg/sH₂22kg/sCO of O₂Meaning that about 70 mole% of H is present₂And O. So H₂The partial pressure of O decreases from slightly above 1 bar absolute at the bottom of the desorber to about 0.7 bar absolute at the top (corresponding to a dew point of about 90 ℃ for water when the total pressure is 1.0 bar absolute). In practice, the steam is condensed to obtain CO₂And therefore the latent heat loss of the stripping steam, which is the ratio to the CO recovered as a result₂Dilution produces much greater losses associated with a drop in the partial pressure of the stripping steam. It is desirable to maintain this latent heat and supply energy only to compensate for the loss of stripping steam partial pressure.

The change in enthalpy due to the condensation of the stripping gas as a function of the condensation temperature is shown in figure 3. As water condenses, the partial pressure of the water vapor decreases, requiring a lower temperature for further condensation. Thus, to recover additional heat in the direct contact cooler section 66 of the stripper, the cooling water from flash tank 74 via line 78 and pump 78 needs to be made cooler. This reduces the pressure in the flash tank 74 and thus reduces the work required by the compressor 75. If less heat is recovered from the direct contact cooler section 66 and the difference is supplied by a separate heat source of higher temperature, then the temperature in the flash tank may be higher. This also results in higher pressure and less work is required by the compressor 75.

According to fig. 3, the recoverable heat in the range of 80 to 90 ℃ amounts to about 28MW, which can be recovered from the desorber direct contact cooler section 66 in the wash water recovered through conduit 70.

The thermal energy recovered in the desorber direct contact cooler 66 is an important source for obtaining heat in the process. Cooling CO recovered from desorber/stripping by direct contact cooling with water₂And/or steam. As a result of this cooling, the steam in the steam-saturated gas is condensed and thus water vapor is mixed with the desired product (CO)₂) And (5) separating.

Another important source of recoverable heat is the fuel gas direct contact cooler 15. The fuel gas enters the fuel gas direct contact cooler 15 at a temperature of about 115 to 120 ℃. Which contains water vapor from the combustion process, or hydrogen from the combustion of a portion of the gas, oil, or biofuel, or from a fuel feed system, such as coal, that can be fed to the combustor 2 as a water slurry. The water vapor saturation temperature depends on the amount and pressure of the water vapor. The fuel gas saturation temperature is about 115 c when the coal fuel is fed to the combustion chamber as a slurry and at a pressure of about 12 to 13 bar absolute. If natural gas fuel is used, the amount of water vapor will be higher and the saturation temperature will be higher. If the pressure is lower, the saturation temperature will be lower. Due to the fact that the fuel gas is at high pressure and contains a significant amount of steam, the condensation of the steam will start at a relatively high saturation temperature, generating a significant amount of recoverable high temperature energy in the form of heat. Figure 4 shows the effect of pressure on the amount of high temperature recoverable heat when the fuel gas is cooled. The curve was plotted assuming a fuel gas flow rate of 111kg/s with a fuel gas inlet temperature of 115 ℃ and a fuel gas outlet temperature of 100 ℃ and a fuel gas water content of 14.5%.

The differences between the atmospheric (conventional) system and the system according to the invention are: the water vapor in the pressurized system condenses. Even if it is H₂The amount of O vapor may be the same, with atmospheric systems having much lower H₂The partial pressure of O, and therefore, the cooling of the fuel gas does not produce condensate, resulting in greatly reduced energy recovery.

According to the invention, the fuel gas is cooled to about 100 ℃ in a condenser preferably used as a direct contact cooler, in which the fuel gas flows in countercurrent through the packaging material to the circulating water. This water captures the energy in the gas and is cooled in heat exchanger 17, which heat exchanger 17 receives the cooling water from the desorber direct contact cooler, further heating the water and supplying more energy.

The dotted curve in fig. 4 is for comparison only, showing the system for a more conventional atmospheric pressure CO₂One advantage of the capture system, at conventional atmospheric pressure CO₂In a capture system, very little useful energy (in this case capacity above 100 ℃) will be obtained from the same fuel gas.

The third source of heat energy recovery is CO₂A compressor cooler 48. The amount of useful energy in the compression cooler is lower than in the above-mentioned coolers, but the temperature in the compression cooler is higher.

Table 1 shows the CO-carrying reaction of the present invention₂The net power produced by the captured power plant as a function of the steam generated by thermal regeneration in the fuel gas direct contact cooler 15 (represented in the table by "condenser"), in the desorber direct contact cooler section 66 (represented in the table by "desorber"), and in the compressor intercooler 48 (represented in the table by "compressor").

TABLE 1

Table 1 clearly shows that the net power of the steam turbine is increased due to the improved heat recovery from the three elements of the plant and shows the most important advantages of the invention.

When 20kg/s steam is produced and compressed by the present invention and routed to the bottom of the desorber instead of the same amount of 4 bar absolute steam from the steam turbine, the net power, steam turbine output minus flash compressor power, increases by more than 10 MW.

Further increases in the steam production by flashing and compression, for example to 25kg/s, require a large increase in the flash compressor capacity and a much smaller increase in the net power. Production in excess of 25kg/s will have no or adverse effect on net steam turbine output minus flash compressor capacity.

Example 2

This example illustrates the additional effect of steam from flash tank 81 flashing as stripping gas, compressing and injecting into the regeneration column, as shown in figure 2.

Figure 5 shows the vapor pressure of the lean absorbent as a function of temperature of about 100 c. The heat capacity of the lean absorbent is about 3.0 kJ/kg-K. A lean absorbent flow rate of 1000kg/s and cooling from about 112 ℃ (approximate temperature at the bottom of the desorber) to about 98.6 ℃ (approximate temperature of absorbent feed to the top of desorber), yielding about 1000 ℃^*3.0^*(112-98.6)kW＝40000kW。

For 22kg/s CO₂Yield of (3.6 MJ/kgCO)₂Total desorber heat demand in the form of latent heat in the vapor of (a), the total heat demand being about 80 MW. Thus, lean flash (leanflash) can produce about 50% of this heat.

For a latent heat of steam of about 2250kJ/kg (about 1.2 bar absolute), this corresponds to about 17.8kg/s steam. It must be compressed from about 0.75 bar absolute to 1.2 bar absolute. Assuming an adiabatic power of 80%, the compressor efficiency is about 2.0 MW.

Table 2 summarizes the effect of the flashed lean absorbent on the overall output of the steam turbine.

TABLE 2

Table 2 clearly shows the flashing of lean adsorbent over the total output from the steam turbine. In combination with the energy characteristics of example 1, the net power can be increased from 96MW to 115MW compared to 120MW without carbon capture.

The fact that the heat of reaction of equation 1) is low is advantageous for the potassium carbonate system because the corresponding exothermicity of the reaction in the absorber is low, thereby facilitating the heating of the absorbent in the absorber. The heating of the absorbent in the absorber can move the reaction to the left and thus reduce the absorption capacity of the absorbent.

Claims (2)

1. For combustion and CO by carbonaceous fuel₂A method for trapping and producing electric power, which comprises the steps of,

wherein the carbonaceous fuel is combusted in a combustion chamber (2) in the presence of an oxygen-containing gas and under pressure;

wherein the combustion gas in the combustion chamber is cooled by generating steam within a heat pipe provided in the combustion chamber;

wherein the exhaust gases are recovered from the combustion chamber by a first exhaust gas conduit (9) via a first heat exchanger (10) and an exhaust gas treatment unit (11, 12), and a first direct contact cooler (15) is connected with a first water recirculation conduit (16) for recirculating water collected at the bottom of the first direct contact cooler (15) and reintroducing water at the top of the first direct contact cooler (15), in which first direct contact cooler (15) the partially cooled exhaust gases are further cooled and humidified by counterflow to water;

wherein the exhaust gas is recovered from the first direct contact cooler (15) through a clean second exhaust gas conduit (18) and is introduced into the CO₂An absorber (19) in the CO₂In an absorber (19), a lean absorbent is introduced into the CO₂An upper contact zone (19') in the absorber (19) to promote counter-current flow of the flue gas to liquid CO₂Absorbent to produce rich absorbent and CO₂Lean exhaust gas, said rich absorbent being in said CO₂The absorber bottom is collected and is taken from the CO via a rich absorbent conduit (30)₂The CO is recovered at the bottom of the absorber (19)₂Lean exhaust gas is connected to the CO₂A lean exhaust gas line (20) of the absorber (19) from the CO₂The top of the absorber (19) is recovered;

wherein said CO is₂The lean exhaust gas is scrubbed in a scrubbing section, heated in the first heat exchanger (10) and expanded throughout the turbine to generate electrical energy before being released to the atmosphere;

wherein the rich absorbent conduit (30) is connected to introduce the rich absorbent to a stripper (32) for regeneration of the absorbent to produce lean absorbent and CO₂A stream of lean absorbent recovered through a lean absorbent recycle line (35), in which lean absorbent recycle line (35) the lean absorbent is pumped back to CO₂An absorber (19), the CO₂The stream is further treated to produce clean CO₂；

Wherein said CO is₂The stream is cooled by a cooling fluid flowing through a second direct contact cooler (66) provided at the top of the stripping column (32); and wherein collection is by means of a collection plate (65) provided below the second direct contact cooler (66)Water, and wherein a second water recirculation conduit (70) is arranged for recovering the collected water;

the method is characterized in that: cooling water of a circulating first direct contact cooler (15) in the first water recirculation conduit (16) in a second heat exchanger (17) provided in the first water recirculation conduit (16), wherein cooling water is conveyed and recovered through the second water recirculation conduit (70) and a third water recirculation conduit (70') connected to the second heat exchanger (17), respectively; and is

Wherein water recovered from the second heat exchanger (17) through the third water recycle conduit (70') is flashed over a flash valve (73) and a flash tank (74), wherein water from the flash tank (74) is recovered through a first line (78) to recycle the water as a wash fluid in a second direct contact cooler (66) of the stripping column; and is

Wherein the steam in the flash tank (74) is introduced into the stripping column as additional stripping steam through a steam line (77) connected to the flash tank (74).

2. The method of claim 1, wherein:

heating the fluid in the third water recirculation conduit (70 ') in a third heat exchanger (48) before the fluid in the third water recirculation conduit (70') is introduced to a flash valve (73) for flashing, the third heat exchanger (48) providing for cooling the compressed CO₂And steam.