Carbon dioxide capture with ammonia with flue gas desulfurization systems, and methods

Abstract

A method includes a flue gas desulfurization step of removing sulfur oxides from the flue gas using an ammonia-based desulfurization scrubber. A further step includes treating the desulfurized flue gas by a carbon dioxide capture unit utilizing ammonia to remove carbon dioxide from the desulfurized flue gas. The desulfurization step includes recycling the desulfurized flue gas as an oxidant towards the desulfurization scrubber. A system for flue gas desulfurization and carbon dioxide removal is also disclosed herein.

Description

[0001] manual Technical Field

[0002] The present disclosure relates to flue gas treatment. In particular, embodiments disclosed herein relate to a carbon capture and storage system (CCS system for short) and a desulfurization system using ammonia for flue gas pretreatment. Background Art

[0003] Most of the energy used in the world is still generated by the combustion of fossil fuels containing carbon and hydrogen, such as coal, oil, and natural gas. In addition to carbon and hydrogen, these fuels also contain oxygen, moisture, and pollutants such as ash, sulfur (usually in the form of sulfur oxides, known as SO x ), nitrogen compounds (usually in the form of nitrogen oxides, known as NO x ), chlorine, mercury and other trace elements.

[0004] Recognition of the damaging effects of pollutants released into the atmosphere during combustion has triggered the implementation of increasingly stringent limits on emissions from power plants, refineries, and other industrial processes. For operators of such facilities, pressure is increasing to achieve near-zero emissions of pollutants.

[0005] In the combustion of fuels (such as coal, oil, peat, waste, biofuels, natural gas, etc.) for the production of electricity or for the production of materials such as cement, steel, glass, steam, heating media and hydrogen, hot flue gas streams are generated. Hot flue gases contain, among other pollutants, large amounts of carbon dioxide (CO2), which is responsible for the so-called greenhouse effect and the associated increase in global temperatures; and sulfur oxides (SO x ). If released into the atmosphere, sulfur oxides can cause acid rain.

[0006] Many systems and processes have been developed to reduce pollutant emissions. These systems and processes include, but are not limited to, desulfurization systems, particulate filters, and the use of one or more sorbents that absorb pollutants from flue gases. Examples of sorbents include, but are not limited to, activated carbon, ammonia, limestone, etc.

[0007] Ammonia has been shown to be effective in removing carbon dioxide from flue gases. In one specific application, the absorption and removal of carbon dioxide from a flue gas stream with ammonia is performed at sub-ambient temperatures. These systems are based on the so-called chilled ammonia process (abbreviated CAP, a specific ammonia-utilizing process for CCS). Other systems utilizing ammonia, such as the so-called mixed salt process (MSP), or amine mixtures containing ammonia are known in the art to capture and remove carbon dioxide from flue gases before the carbon dioxide-depleted flue gases are discharged into the atmosphere.

[0008] Carbon dioxide capture is not without its drawbacks. Known carbon capture systems are bulky, expensive and energy intensive, resulting in reduced carbon dioxide emissions to the environment at the cost of reduced thermodynamic efficiency of the power generation cycle or other industrial CO2 emitting processes.

[0009] Efforts are currently underway to reduce the cost of carbon capture and storage systems both in terms of CAPEX and thermodynamic efficiency reduction.

[0010] The efficiency of the carbon capture process can be increased if the carbon dioxide concentration in the flue gas is increased. Higher concentrations of carbon dioxide also involve a reduction in the total volume flue gas flow rate to be treated, which has a positive impact in reducing the costs of CCS.

[0011] It would also be beneficial to remove pollutants, such as sulfur oxides, from the flue gas before it is conveyed to a carbon dioxide capture unit. However, sulfate oxide scrubbing upstream of the carbon dioxide capture process has some disadvantages. In particular, the need to add oxygen to the flue gas stream adversely affects the efficiency of the carbon dioxide capture process downstream of the desulfurization scrubber.

[0012] Methods and systems that alleviate or address the above-mentioned disadvantages would be welcomed in the art. Summary of the invention

[0013] According to one aspect, disclosed herein is a method for post-combustion carbon dioxide capture using ammonia, which improves the overall efficiency of the flue gas treatment process. The method according to the present disclosure includes the steps of desulfurizing a flue gas stream in a desulfurization scrubber system and removing sulfur oxides from the flue gas stream. The method further includes the step of treating the desulfurized flue gas by a carbon dioxide capture unit using ammonia to remove carbon dioxide from the desulfurized flue gas. In order to improve the efficiency of the carbon dioxide removal process, according to the embodiments disclosed herein, the desulfurization step includes recycling the desulfurized flue gas as an oxidant through the desulfurization scrubber.

[0014] The desulfurized flue gas contains sufficient residual oxygen to oxidize the dissolved ionic SO2 removed by reactions in the desulfurization scrubber, which increases the affinity of ionic sulfur to the liquid phase.

[0015] In summary, sulfur oxides are removed from flue gases based on the following reactions:

[0016]

[0017] Where x = 1 or 2

[0018] The ammonium sulfate (NH4)2SO4 produced by the desulfurization process is used as a valuable product from the desulfurization process, for example as a fertilizer. The oxygen required to complete the oxidation process is provided by the recycled desulfurized flue gas. Compared with the desulfurization process of the current technology, the method disclosed herein reduces the total flow rate of the carbon dioxide capture process flowing through the downstream of the desulfurization process. In addition, the molar concentration of carbon dioxide is increased. Both of these factors improve the efficiency of the carbon dioxide capture process, making the carbon dioxide capture process more economically convenient and reducing the energy required to run the process.

[0019] In some embodiments, the carbon dioxide capture unit utilizing ammonia is a chilled ammonia process unit. However, other CCS systems utilizing ammonia may be used, such as a mixed salt process.

[0020] The desulfurized flue gas recycled towards the desulfurized scrubber as oxygen source can be recycled from the outlet of the desulfurized scrubber and / or from a carbon dioxide capture unit downstream of the desulfurized scrubber. In this second case, the recycled desulfurized flue gas has been cooled and conditioned in the carbon dioxide capture unit before recycling.

[0021] According to another aspect, a carbon capture system utilizing ammonia for treating post-combustion gases is disclosed herein. The system includes a desulfurization scrubber, such as an ammonia-based desulfurization scrubber, comprising a flue gas inlet, an oxidant feed conduit, and a desulfurized flue gas outlet. The system further includes a carbon dioxide capture section or unit utilizing ammonia.

[0022] In the embodiments disclosed herein, the oxidant feed conduit is adapted to receive desulfurized flue gas and recycle the desulfurized flue gas to the desulfurization scrubber, where the recycled desulfurized flue gas is used as an oxidant, ie, as an oxygen source for the desulfurization scrubbing process.

[0023] A desulfurized flue gas recirculation line may be provided to recirculate the desulfurized flue gas to the desulfurized scrubber. For example, the recirculation line may be fluidly connected to an oxidant injector of the desulfurized scrubber. The desulfurized flue gas recirculation line may be fluidly connected to a desulfurized flue gas outlet of the desulfurized scrubber and / or to a carbon dioxide capture unit.

[0024] Further features and embodiments of the method and system according to the present disclosure are described below with reference to the accompanying drawings and are set out in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Reference will now be made briefly to the accompanying drawings, in which:

[0026] Figure 1 is a functional block diagram of a combined flue gas desulfurization and carbon capture system utilizing ammonia; and

[0027] Figure 2 is available in Figure 1 Schematic diagram of an embodiment of a desulfurization scrubber used in a system. DETAILED DESCRIPTION

[0028] First reference Figure 1 , a functional block diagram of a system 1 for flue gas treatment is shown. Flue gas, such as combustion gas from a gas turbine, a steam generator of a steam turbine, a burner, an industrial CO2 emission source, etc., is delivered to an ammonia-based desulfurization process 5 at 3. The desulfurization process 5 includes an ammonia-based desulfurization scrubber. An embodiment of a desulfurization scrubber for use in combination with a CCS system will be described below.

[0029] The desulfurized flue gas flows from the flue gas desulfurization process 5 to the ammonia-based carbon dioxide capture unit 9 via line 7. Ammonium sulfate is collected at 10. After the carbon dioxide has been partially or completely removed from the flue gas, the treated flue gas is discharged to the atmosphere at 11. The carbon dioxide is transported to further refining steps, liquefaction processes, storage facilities, etc. at 13. Condensed moisture from the ammonia-based carbon dioxide capture unit 9 can be collected at 15 and can be used as water make-up in the desulfurization process 5 or in the carbon dioxide capture unit 9. Ammonium sulfate from the ammonia-based carbon dioxide capture unit 9 can be transported via line 17 and integrated with the ammonium sulfate produced from the ammonia-based desulfurization process 5. Box 19 schematically represents an ammonia storage tank, which provides (see line 18) ammonia make-up to the ammonia-based desulfurization process 5 and the ammonia-based carbon dioxide capture unit 9 as needed.

[0030] The ammonia-utilizing carbon dioxide capture unit 9 may be based on the Chilled Ammonia Process (CAP), the Mixed Salt Process (MSP) or any other ammonia-utilizing process suitable for removing carbon dioxide from desulfurized flue gases.

[0031] In order to better understand the present invention, Figure 2 A more detailed representation of an embodiment of an ammonia-based desulfurization scrubber 20 for an ammonia-based desulfurization process 5 is shown in FIG. A person skilled in the art will appreciate that Figure 2 One of several possible layouts for a desulfurization scrubber using ammonium salts is shown, and other embodiments are possible.

[0032] In some embodiments, the desulfurization scrubber 20 may include a flue gas quench section 21 and an absorber section 23. The flue gas quench section 21 includes a flue gas quench duct 25 fluidly coupled to a flue gas inlet 27 through which superheated flue gas enters the quench duct 25.

[0033] Flue gas quenching is achieved by an ammonium sulfate solution distributed via a quench distributor 31. The ammonium sulfate solution is circulated by a main circulation pump 33 and sprayed into the flue gas through a nozzle grid 35. Water contained in the ammonium sulfate solution sprayed in the flue gas quenching duct 25 evaporates from the ammonium sulfate solution quenching the flue gas until the adiabatic saturation temperature is reached. In this way, the residual flue gas heat is used to concentrate the ammonium sulfate solution, and the internal filling material of the absorption tower section 23 is protected from the high-temperature flue gas.

[0034] The flue gas quenching section 21 further comprises a sump 37 in which the concentrated ammonium sulfate solution leaving the quenching duct is collected by gravity. A mixing device 39 (e.g., an impeller type mixing device) is arranged in the sump 37 to maintain a uniform temperature and concentration of the solution collected in the sump 37 and to further suspend possible precipitates.

[0035] The desulfurization scrubber 20 includes an oxidant feed conduit 40 to feed the oxidant to the scrubber.

[0036] In some embodiments, the first oxidant injector 41 is fluidly coupled to the oxidant feed conduit 40 and is disposed at the bottom of the storage tank 37. Figure 2 In the embodiment of the present invention, the oxidant feed conduit 40 and the first oxidant injector 41 are fluidly connected to the desulfurized flue gas outlet 43 of the desulfurized scrubber 20 through the desulfurized flue gas recirculation line 47. The desulfurized flue gas outlet 43 is arranged at the top of the absorption tower section 23. The oxidant fan 45 can be arranged along the desulfurized flue gas recirculation line 47, which fluidly connects the desulfurized flue gas outlet 43 with the first oxidant injector 41.

[0037] In some embodiments, the desulfurized flue gas recycle line 47 may be fluidly coupled (see Figure 1 The desulfurization scrubber 20 is connected to the desulfurization scrubber 20 by a pipeline 47X to the intermediate section of the carbon dioxide capture unit 9. If convenient, as a supplement or alternative to using the desulfurized flue gas directly from the outlet of the desulfurization scrubber 20, a portion of the partially cooled desulfurized flue gas (containing CO2) can also be provided to the desulfurization scrubber 20 as an oxidation source via the pipeline 47X.

[0038] Thus, according to the present disclosure, the oxidation reaction in the sump 37 is achieved by utilizing oxygen contained in the desulfurized flue gas delivered at the top of the absorber section 23 and / or from the carbon dioxide capture unit 9, rather than adding ambient air to the desulfurization process.

[0039] The flue gas quenching duct 25 delivers the quenched and water-saturated flue gas to the absorber section 23, between the primary oxidation tank 51 arranged at the bottom of the absorber section 23 and the structured packing 53 of the absorber section 23. In some embodiments, the primary oxidation tank 51 at the bottom of the absorber section 23 is separated from the storage tank 37 by a partition wall 55, which maintains a higher concentration of ammonium sulfate material in the storage tank 37 and is beneficial for the downstream dehydration step.

[0040] The flue gases leaving the quench duct enter the absorption tower section 23 above the dividing wall 55 .

[0041] The high concentration ammonium sulfate solution is gradually removed from the storage tank 37 by a suction pump 59 and further dehydrated and dried to produce dry ammonium sulfate.

[0042] The ammonium sulfate saturation is controlled by adjusting the amount of solution supplied to the quench distributor 31. Feeding the remaining solution to the quench distributor 31 reduces the ammonium sulfate concentration in the product overflowing from the storage tank 37 to the primary oxidation pond 51.

[0043] In addition to the main oxidation tank 51, the absorber section 23 further includes a liquid distributor 61 that feeds the ammonium sulfate solution from the main oxidation tank 51 to a grid of spray nozzles 63 arranged above the structured packing 53 via the main circulation pump 33. A large-capacity demister 67 is arranged above the spray nozzles 63 to remove any liquid entrained in the flue gas flowing toward the top of the desulfurization tower section 23 via the packing 53.

[0044] The prepared ammonium sulfate solution is supplied to the top of the packing 53 by the main circulation pump 33 and distributed via the liquid distributor 61 and the associated spray nozzles 63 .

[0045] As the ammonium sulfate solution falls countercurrently through the rising flue gas in the packing 53, sulfate oxide species (SO x ) is absorbed into the prepared ammonium sulfate solution. The acidified ammonium sulfate solution leaves the bottom of the packing and falls into the main oxidation tank.

[0046] The main oxidation tank 51 is equipped with an oxidant injector 69 and a mixing device 71, such as an impeller type mixing device. The mixing device 71 is used to avoid local composition and temperature differences in the liquid phase. The injector 69 is fluidly connected to the oxidant feed conduit 40.

[0047] In addition, an ejector 69 is immersed in the main oxidation tank 51 and forces the oxidation of sulfite by adding an oxidant to the solution and distributes the sulfite from the ammonia tank 19 (see also Figure 1 The supplementary ammonia is used to adjust the solution pH.

[0048] An oxidant is injected into the main oxidation tank 51 by an injector 69 , and the oxidant is provided by the desulfurized flue gas recycled from the top of the tower section 23 through the recirculation line 47 and the oxidant feed conduit 40 .

[0049] As described above, in addition to or instead of the recycled desulfurized flue gas from the desulfurized flue gas outlet 43 of the desulfurized scrubber, the desulfurized flue gas can be recycled from the CCS system (carbon dioxide capture unit) upstream of the CO2 capture step (line 47X). This will provide desulfurized flue gas, which is also cooled and conditioned.

[0050] Whichever desulfurized flue gas source is used (whether the desulfurized flue gas outlet 43 or the carbon dioxide capture unit 9 ), the oxidation reactions in the main oxidation pond 51 and in the storage tank 37 are promoted by the residual oxygen contained in the recycled desulfurized flue gas delivered by the fan 45 .

[0051] Through the water replenishment pipeline 73, the water replenishment source ( Figure 2 The largest part of the make-up water is required for saturation of the flue gas. A portion of the water can be removed from the ammonium sulfate in the dehydration step and recycled. Other water sources, such as from the downstream carbon dioxide capture unit 9 ( Figure 1 ) condensate, further reducing the total make-up water requirement.

[0052] By utilizing waste heat from the flue gas and separating the absorber sump 37, the concentration of ammonium sulfate species in the circulating solution is significantly lower than that of the product. The lower ammonium sulfate concentration in the circulating solution helps force oxidation, lowers the partial pressures of ammonia and SO2 and ultimately reduces ammonia slip.

[0053] Avoiding high ammonium sulfate solution concentrations, high solution pH (above pH 5), and poor oxidation can help avoid aerosol formation.

[0054] The major reactions associated with each process step performed in the desulfurization scrubber 20 and the general locations where they occur are as follows.

[0055] The prepared ammonium sulfate solution enters the absorption tower section 23 through the liquid distributor 61 and the spray nozzle 63. The pH value of the ammonium sulfate solution is slightly less than 5, and it absorbs SO2 from the flue gas rising countercurrently through the packing 53. The SO2 is dissolved according to Equation 1

[0056]

[0057] begins to affect speciation, thereby lowering pH and forming more acidic species according to Equations 2 and 3

[0058]

[0059] The acidified ammonium sulfate solution leaves the packing at a pH of approximately 3.0 to 3.5.

[0060] In the main oxidation tank 51, ammonia and oxygen-containing desulfurized flue gas are added to adjust the pH value and thereby shift the speciation to less acidic species according to Equations 4, 5, and 6.

[0061]

[0062] Promotes the conversion of sulfite to sulfate, Equation 7:

[0063]

[0064] Ammoniated solution is provided for SO2 absorption, especially at high SO x Very effective system for absorbing SO2 at low flue gas concentrations.

[0065] Sulfite ion SO3 2- It is the ionic form of aqueous SO2, which is formed during wet flue gas desulfurization. Sulfite does not bind to solution as well as sulfate SO4 2- then closely, and correlated with increasing SO2 partial pressure and associated trends in aerosol formation.

[0066] As described above, the oxidation reaction is performed using oxygen from the desulfurized flue gas, which is recycled from downstream of the absorber section 23, or if convenient, from a location in the CCS system upstream of the CO2 capture step (carbon dioxide capture unit 9), rather than injected air as in the desulfurization process of the prior art. Avoiding the addition of air to the flue gas flowing through the desulfurization process 5 and the carbon capture process 9 and using the residual oxygen contained in the flue gas to promote the oxidation reaction in the pool 51 and the storage tank 37 generally improves the efficiency of the desulfurization and carbon dioxide capture processes.

[0067] In fact, according to prior art desulfurization processes, for simple air injection, the added air volume flow is expected to be about 5% of the total flue gas flow. In conventional desulfurization processes, the added air contributes to the volume of flue gas treated in the downstream CCS system. In addition, air injection reduces the CO2 concentration in the desulfurized flue gas by diluting it with unreacted air (mainly nitrogen, but also including a large amount of oxygen due to mass transfer limitations).

[0068] By avoiding the air injection otherwise applied in the current technology and recirculating the desulfurized flue gas towards the storage tank 37 and / or the main oxidation pond 51, a dual advantage is achieved:

[0069] - the total flow rate from the desulfurization process 5 through the carbon dioxide capture unit 9 is reduced, since no air flow is added;

[0070] - The carbon dioxide concentration in the stream flowing through the carbon dioxide capture unit 9 is increased, making the carbon capture process more efficient.

[0071] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be appreciated by those skilled in the art that various changes, omissions and additions may be made to the specific disclosure herein without departing from the scope of the present invention as defined in the following claims.

Claims

1. A method for removing carbon dioxide from flue gas, the method comprising the following steps: desulfurizing a flue gas stream and removing sulfur oxides from the flue gas stream in an ammonia-based desulfurization scrubber; as well as treating the sweetened flue gas through a carbon dioxide capture unit utilizing ammonia to remove carbon dioxide from the sweetened flue gas; The desulfurization step includes recycling the desulfurized flue gas as an oxidant toward the desulfurization scrubber.

2. The method according to claim 1, wherein the desulfurized flue gas is recycled from the desulfurized flue gas outlet of the desulfurized scrubber.

3. The method according to claim 1 or 2, wherein desulfurized flue gas is recycled from the carbon dioxide capture unit using ammonia.

4. The method according to claim 3, wherein the desulfurized flue gas is recycled downstream from a further cooling and conditioning step in the carbon dioxide capture unit with ammonia.

5. The method according to one or more of the preceding claims, wherein the carbon dioxide capture unit utilizing ammonia is a chilled ammonia process unit.

6. A carbon capture system utilizing ammonia for treating post-combustion flue gas, the system comprising: an ammonia-based desulfurization scrubber comprising a flue gas inlet, an oxidant feed conduit, and a desulfurized flue gas outlet; as well as an ammonia-utilizing carbon dioxide capture unit fluidly coupled to the ammonia-based desulfurization scrubber and adapted to receive desulfurized flue gas from the ammonia-based desulfurization scrubber; The oxidant feeding conduit is fluidly connected to the desulfurized flue gas recirculation pipeline and is suitable for feeding the desulfurized flue gas as an oxidant to the desulfurization scrubber.

7. The system of claim 6, wherein the oxidant feed conduit is fluidly coupled to the desulfurized flue gas outlet of the desulfurization scrubber.

8. The system of claim 6 or 7, wherein the oxidant feed conduit is fluidly coupled to the carbon dioxide capture unit utilizing ammonia.

9. The system of claim 8, wherein the oxidant feed conduit is fluidly coupled to the carbon dioxide capture unit utilizing ammonia downstream of the cooling and conditioning step.

10. The system according to one or more of claims 6 to 9, wherein the carbon dioxide capture unit with ammonia is based on a chilled ammonia process.

11. The system according to any one of claims 6 to 10, wherein the desulfurization scrubber comprises: a flue gas quench duct, the flue gas inlet being fluidly connected to the flue gas quench duct; a quench distributor adapted to distribute an ammonia salt solution into the flue gas flowing through the quench conduit; a concentrated ammonia solution collecting storage tank, the concentrated ammonia solution collecting storage tank being located at the bottom of the flue gas quenching pipe; as well as a sulfur oxide absorber section, the sulfur oxide absorber section being fluidly connected to the flue gas quench duct and the desulfurized flue gas outlet; wherein the sulfur oxide absorber section comprises an oxidation tank and a liquid distributor, the liquid distributor being adapted to distribute an ammonia salt solution into the flue gas flowing through the sulfur oxide absorber section; The oxidant feeding conduit is fluidly connected to the storage tank and the oxidation pond to feed the desulfurized flue gas into the storage tank and the oxidation pond.

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