Ammonia-based system and method for carbon capture and co-production of ammonium fertilizer from flue gas of coal-fired power plants

Abstract

The present invention discloses a system and method for capturing carbon from flue gas of a coal-fired power plant and producing ammonium fertilizer in conjunction with an ammonia process. After desulfurization, the flue gas passes through the saturation zone, absorption zone, and ammonia washing zone of the desulfurization system in sequence, and passes through a primary ammonia washing spray layer and a secondary ammonia washing spray layer, and finally the clean flue gas is discharged into the atmosphere. After sodium hydroxide, sodium carbonate, and a flocculant are added to the desulfurization wastewater, the obtained clear liquid is pumped into the primary ammonia washing spray layer through a clear liquid delivery pump to spray and absorb the escaped ammonia. After reaching the pH upper limit, it enters the slurry tank of the absorption zone. After the pH of the slurry tank of the absorption zone reaches the upper limit, it enters the saturation zone. After the saturated zone slurry passes through a cyclone and a centrifuge for solid-liquid separation, the clear liquid returns to the saturation zone again. After the saturated zone slurry passes through a cyclone and a centrifuge for two separations, solid ammonium bicarbonate is obtained. The present invention can synergistically treat part of the desulfurization wastewater and carbon dioxide in the flue gas after desulfurization. The ammonium bicarbonate fertilizer produced can be used to produce ammonium fertilizer or compound fertilizer, and has high economic value.

Description

Technical Field

[0001] The present invention relates to the field of carbon dioxide capture, and more specifically, to a system and method for capturing carbon dioxide from flue gas of a coal-fired power plant and co-producing ammonium fertilizer based on an ammonia process. Background Art

[0002] Existing CO2 capture and utilization methods primarily directly utilize CO2 for dry ice, refrigeration, beverages, and other applications. However, due to insufficient market demand, the cost of purification and pressurization exceeds the revenue generated by selling the CO2. Traditional MEA processes suffer from degradation, corrosion, and high regeneration energy consumption, severely impacting their application. MEA is lost during the process due to oxidation, thermal degradation, irreversible reactions, and evaporation. Furthermore, MEA has strict limits on SO2 concentration in flue gas (no more than 10 ppm), making it difficult for existing flue gas desulfurization (FGD) to meet these ultra-low SO2 concentration requirements. These issues contribute to high initial investment and operating costs for MEA processes. Therefore, further research and application of CO2 capture are urgently needed to achieve acceptable and low-cost capture of flue gas CO2.

[0003] In view of the characteristics of flue gas from coal-fired power plants, the goal of the new absorbent is not high removal efficiency, but low absorbent cost and regeneration energy consumption. The by-products produced should be products with a large market and utilization value.

[0004] Regarding absorbent sources, ammonia is a major chemical product, and the production capacity and demand for synthetic ammonia are enormous. Ammonia is readily available, with synthetic ammonia plants, coal chemical plants, petrochemical companies, and other enterprises of varying sizes near nearly every power plant selling ammonia. Regarding absorbent applications in power plants, ammonia or liquid ammonia is used as a reducing agent in selective catalytic reduction (SCR) denitrification and as an absorbent in ammonia-based flue gas desulfurization (FGD). Some power plants have ammonia storage systems. Regarding price, ammonia is only one-sixth the price of MEA. Regarding ammonia's decarbonization absorption capacity, research has shown that its absorption capacity for removing CO2 from power plant flue gas is three times that of MEA. Regarding the treatment of decarbonization products, the byproduct of the ammonia decarbonization circulating slurry, after liquid-solid separation, is NH4HCO3, a widely used nitrogen fertilizer in agriculture with high economic value. In summary, ammonia offers significant advantages as a decarbonization absorbent and co-production of ammonium fertilizer.

[0005] CN220554641U discloses a device for controlling ammonia escape by capturing carbon from low-sulfur flue gas and producing nitrogen fertilizer. The device comprises an ammonia desulfurization zone, an ammonia decarbonization zone, an ammonia washing zone, and an acid addition system. The ammonia desulfurization zone, the ammonia decarbonization zone, and the ammonia washing zone are sequentially connected, the ammonia desulfurization zone and the ammonia washing zone are connected via a liquid phase pipeline, and the acid addition system is connected to the ammonia washing zone. To address the ammonia escape problem, the process system passes the desulfurization circulating fluid from the ammonia desulfurization process system into the decarbonization system to wash ammonia. However, this requires the use of an ammonia desulfurization system in conjunction with it. However, ammonia desulfurization systems are rarely used in China, making this system less widely applicable.

[0006] CN116272329B discloses a deamination device suitable for ammonia-based carbon capture and its application. The deamination slurry tank is connected to a first bubbling unit and a second bubbling unit, each of which is equipped with a forced oxidation blower. The second bubbling unit is located at the top of the organic amine decarbonization device and is equipped with a deamination absorbent. The first bubbling unit absorbs SO2 to form sulfurous acid, which is forcibly oxidized to sulfuric acid in the deamination slurry tank. The sulfuric acid is then used to capture escaping ammonia gas. This system requires a large amount of energy for forced oxidation, and the product ammonium sulfate may be mixed with volatile organic amines, making it difficult to reuse. Summary of the Invention

[0007] The present invention discloses a system and method for capturing carbon dioxide from flue gas of coal-fired power plants and co-producing ammonium fertilizer based on an ammonia process. The system can be used in an integrated process route for capturing and utilizing carbon dioxide, and can collaboratively treat part of the desulfurization wastewater and CO2 in the flue gas after desulfurization. The generated ammonium bicarbonate fertilizer can be used to produce ammonium fertilizer or compound fertilizer, and has high economic value.

[0008] The designed ammonia-based coal-fired power plant flue gas carbon capture and co-production of ammonium fertilizer system can couple the treatment of CO2, Mg in desulfurization wastewater and flue gas. 2+ Most of the escaped ammonia can be suppressed, and the water volume in the decarbonization system can be kept balanced.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] Ammonia-based flue gas carbon capture and co-production of ammonium fertilizer system for coal-fired power plants, including a desulfurization wastewater treatment system, a decarbonization system, and a dehydration system;

[0011] The decarbonization system includes a decarbonization tower;

[0012] The top exhaust port of the decarbonization tower is connected to the flue gas duct of the branch after decarbonization;

[0013] The decarbonization tower is equipped with a secondary ammonia washing spray layer, a secondary ammonia washing slurry divider, a primary ammonia washing spray layer, a primary ammonia washing slurry divider, an absorption zone spray layer, an absorption zone slurry divider and a saturation zone spray layer from top to bottom. The absorption zone is located above the absorption zone slurry divider. The bottom of the decarbonization tower is the saturation zone.

[0014] The decarbonization system is further provided with an ammonia washing area, which includes a secondary ammonia washing process water tank and a primary ammonia washing slurry tank;

[0015] The secondary ammonia washing spray layer, the secondary ammonia washing slurry divider and the secondary ammonia washing process water tank form a circulation through the secondary ammonia washing slurry circulation pump; the secondary ammonia washing process water tank is connected to the process water tank;

[0016] The first-level ammonia washing spray layer, the first-level ammonia washing slurry divider and the first-level ammonia washing slurry tank form a circulation through the first-level ammonia washing circulation pump; the desulfurization wastewater treatment system is connected to the first-level ammonia washing spray layer; the low-temperature flue gas concentrated acid slurry tank is connected to the first-level ammonia washing spray layer through the concentrated acid slurry delivery pump;

[0017] The absorption zone spray layer, the absorption zone slurry divider and the absorption zone slurry tank form a circulation through the absorption zone slurry circulation pump; the absorption zone slurry tank is connected to the concentrated ammonia solution replenishment tank;

[0018] The saturated zone spray layer and the saturated zone form a circulation through the saturated zone slurry circulation pump;

[0019] The flue gas duct of the post-desulfurization branch is connected below the spray layer of the saturated zone;

[0020] The saturated zone is also connected to the dewatering system through a saturated slurry discharge pump.

[0021] The desulfurization wastewater treatment system comprises a desulfurization wastewater tank, a heavy metal precipitation tank, a calcium precipitation tank, a colloid precipitation tank and a sedimentation tank connected in sequence;

[0022] The heavy metal precipitation tank is equipped with a sodium hydroxide delivery pipeline and a heavy metal precipitation discharge pipeline;

[0023] The calcium precipitation tank is equipped with a sodium carbonate delivery pipeline and a precipitated calcium discharge pipeline;

[0024] The colloid sedimentation tank is equipped with a flocculant delivery pipeline and a precipitated colloid discharge pipeline;

[0025] The sedimentation tank is connected to the clear liquid tank, and the clear liquid tank is connected to the first-level ammonia washing spray layer of the decarbonization tower through a clear liquid delivery pump.

[0026] The dehydration system comprises a saturated slurry box, a cyclone, a centrifuge and an ammonium bicarbonate storage bin which are connected in sequence.

[0027] The absorption zone, saturation zone and ammonia washing zone of the decarbonization system are all equipped with pH online monitoring devices, and the absorption zone and saturation zone are equipped with density online monitoring devices.

[0028] The ammonia-based flue gas carbon capture and co-production ammonium fertilizer system provided by the present invention has the function of simultaneously treating CO2 from thermal power plants and desulfurization wastewater to produce ammonium bicarbonate fertilizer with added value. After heavy metals, calcium ions and colloids are precipitated in the desulfurization wastewater, it is used to enter the first-level ammonia spray layer in the ammonia washing area to absorb ammonia; the saturated solid-liquid mixed ammonium bicarbonate slurry in the saturated area passes through a cyclone and a centrifuge for two-stage solid-liquid separation to produce ammonium bicarbonate fertilizer; the amount of ammonia water to be supplied and the timing of supply are determined according to pH and density; the first-level ammonia spray layer and the second-level ammonia spray layer in the ammonia washing area are respectively added with the clear liquid after desulfurization wastewater treatment and process water for circulating spray washing ammonia. Sodium hydroxide is added to the desulfurization wastewater to precipitate heavy metals, calcium oxalate is added to precipitate calcium, and flocculants are added to precipitate colloids to obtain a slurry mainly containing Mg. 2+ 、SO4 2- 、Cl - of clear liquid.

[0029] Furthermore, for power plants equipped with a low-temperature flue gas concentration desulfurization wastewater system, low-temperature flue gas concentration slurry can be introduced into the decarbonization system, and the escaped ammonia can be recovered by spraying through the first-level ammonia washing spray layer.

[0030] The present invention provides a method for capturing carbon from flue gas of coal-fired power plants and co-producing ammonium fertilizer based on the ammonia process, which includes three processing routes: gas, liquid, and solid:

[0031] 1. Gas processing route;

[0032] The desulfurized flue gas generated by industrial combustion is drawn into the branch flue gas duct by the induced draft fan and enters the decarbonization system. The flue gas contains carbon dioxide, water vapor and a small amount of impurity particles. The decarbonization system is divided into three functional areas, and the flue gas passes through the following areas in sequence:

[0033] (1) Saturated zone: In the saturated zone, the flue gas is directly contacted and absorbed by the spray slurry, the temperature is reduced, and a small amount of CO2 in the flue gas is initially captured.

[0034] (2) Absorption zone: The flue gas absorbed by the saturated zone slurry spray enters the absorption zone. In the absorption zone, most of the CO2 in the flue gas is efficiently absorbed by the absorption liquid.

[0035] (3) Ammonia washing area: After passing through the absorption area, the flue gas enters the ammonia washing area, and the spray layer captures the ammonia escaping from the flue gas. Secondary ammonia washing spray layer: The secondary spray layer further improves the absorption efficiency and ensures that the emission concentration of ammonia in the flue gas meets the standard.

[0036] The flue gas after multi-stage absorption is discharged through the exhaust pipe, and the ammonia concentration of the flue gas is controlled to be lower than 3ppm.

[0037] 2. Liquid handling routes;

[0038] (1) Pretreatment of wastewater: The wastewater generated during the desulfurization process is pretreated with chemical agents, including the addition of sodium hydroxide and sodium carbonate to adjust the pH value of the wastewater. Flocculants are added to precipitate and separate suspended particles and impurities in the wastewater to obtain clear liquid and flocs.

[0039] (2) Recycling of ammonia washing liquid. The pre-treated clear liquid is sent to the primary ammonia washing spray layer of the ammonia washing area to capture the remaining escaped ammonia in the flue gas. When the pH of the ammonia washing liquid in the secondary ammonia washing area reaches the upper limit, it is transported to the primary ammonia washing area. The ammonia washing liquid in the primary ammonia washing area is sent to the secondary ammonia washing spray layer of the ammonia washing area to capture the escaped ammonia in the flue gas for the first time. When the pH of the ammonia washing liquid in the primary ammonia washing area reaches the upper limit, it is transported to the slurry tank in the absorption area and mixed with ammonia water for CO2 absorption reaction. Furthermore, after a period of operation, the slurry density in the saturated area is lower than 1050kg / m 3 When the water content of the system is high, the ammonia washing process water tank is required to absorb the saturated ammonia washing liquid and concentrate it through reverse osmosis. The 15% concentrated ammonium bicarbonate solution can be passed into the absorption area slurry tank to obtain low-concentration clear liquid.

[0040] (3) Cascade utilization of decarbonized slurry. The slurry in the absorption zone absorbs CO2 for the first time, playing the main role in CO2 absorption. When the pH of the slurry in the absorption zone slurry tank reaches the upper limit, the slurry is transferred to the saturation zone. The main components of the slurry in the absorption zone are ammonia water, ammonium carbonate, etc. In the saturation zone, the slurry absorbs CO2 for the first time to improve the absorption efficiency. The main components of the slurry in the absorption zone are ammonium bicarbonate, ammonium carbonate, etc.

[0041] (4) Solid-liquid separation of liquid. The slurry in the saturated zone is separated through a two-stage solid-liquid separation process. The cyclone separation separates the ammonium bicarbonate solid particles from the slurry to obtain a portion of low-concentration slurry. The centrifuge separation centrifuges the liquid after cyclone separation at high speed to further separate the liquid and the ammonium bicarbonate solid particles to obtain a low-concentration slurry and concentrated solid matter.

[0042] (5) Recirculation of low-concentration slurry: the separated low-concentration slurry is transported back to the saturated slurry tank for recycling.

[0043] 3. Solids handling routes;

[0044] (1) The formation of by-product ammonium bicarbonate. The concentrated solid obtained by solid-liquid separation is mainly composed of ammonium bicarbonate.

[0045] (2) Processing and utilization of by-products: After further dehydration and drying, the solid matter is packaged and made into ammonium bicarbonate by-product, which can be directly used as agricultural fertilizer or other industrial purposes.

[0046] Furthermore, the pH value of the low-temperature flue gas concentrated slurry is controlled to be in the range of 2-3; the pH value of the desulfurization wastewater in the heavy metal precipitation tank of the desulfurization wastewater treatment system is controlled to be in the range of 8-9, preferably, the pH is optimal at 8.4; the pH value of the slurry in the saturated zone of the decarbonization system is controlled to be in the range of 8-8.5, preferably, the pH value is optimal at 8.3, and the slurry density of the saturated zone of the decarbonization system is 1100-1120 kg / m 3 , preferably, the slurry density is controlled to 1103kg / m 3 The optimal pH range is 9.5-10 in the decarbonization system's absorption zone. The pH of the ammonia wash liquid in the primary ammonia wash slurry tank in the ammonia wash zone is controlled between 10-10.5, and the pH of the ammonia wash liquid in the secondary ammonia wash process tank in the ammonia wash zone is controlled between 8-9. After the pH of the secondary ammonia wash process tank reaches the upper limit, the clear liquid enters the primary ammonia wash process tank. After the pH of the primary process tank reaches the upper limit, the clear liquid enters the absorption zone slurry tank. After the slurry in the absorption zone slurry tank reaches saturation, it enters the saturation slurry tank.

[0047] The present invention calculates the concentration of ammonium bicarbonate in the solution based on the control relationship between the measured density and the ammonium bicarbonate saturation. Combined with the monitored pH value, a balance equation can be established to calculate the effective ammonia concentration in the absorption zone. The reference value C is introduced and there is a positive correlation with the CO2 absorption efficiency, that is, a one-to-one correspondence. Substituting it into the formula:

[0048] C=738.58[NH3] 2 +11.32[NH3],

[0049] [NH3] represents the effective ammonia concentration;

[0050] C is solved, and the C value of the absorption slurry is adjusted by adding concentrated ammonia water in the concentrated ammonia water replenishment tank (30) to maintain the decarbonization system efficiency above 80%.

[0051] The proposed method, which utilizes carbon capture byproducts as fertilizer, is one of the most viable byproduct utilization options currently available, linking carbon emission reduction with ecological regulation. NH4HCO3 recycling not only offsets operating expenses but also significantly reduces operating costs through process simplification. Replacing existing NH4HCO3 production also improves the environment and reduces energy consumption.

[0052] The beneficial effects of the present invention are embodied in:

[0053] (1) The CO2 removal efficiency can be stably controlled to above 80%;

[0054] (2) The ammonia emission concentration in the flue gas at the outlet of the decarbonization system can be controlled within 3ppm;

[0055] (3) It can collaboratively treat desulfurization wastewater, with a treatment capacity of up to 3t / h;

[0056] (4) No wastewater is generated during the operation of the decarbonization system;

[0057] (5) The system is highly practical and can be used for ultra-low carbon emission reduction layout of thermal power plants under various circumstances. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 Schematic diagram of the system structure of the present invention;

[0059] Legend: 1-decarbonization tower, 2-desulfurization wastewater tank, 3-sodium hydroxide delivery pipeline, 4-heavy metal precipitation tank, 5-heavy metal precipitation discharge pipeline, 6-sodium carbonate delivery pipeline, 7-calcium precipitation tank, 8-precipitated calcium discharge pipeline, 9-flocculant delivery pipeline, 10-colloid precipitation tank, 11-precipitated colloid discharge pipeline, 12-sedimentation tank, 13-clear liquid tank, 14-clear liquid delivery pump, 15-low-temperature flue gas concentrated acid slurry tank, 16-concentrated acid slurry delivery pump, 17-post-desulfurization branch flue gas duct, 18-secondary ammonia washing spray layer, 19-secondary ammonia washing slurry splitter, 20-primary ammonia washing spray layer, 2 1-first-stage ammonia washing slurry divider, 22-absorption zone spray layer, 23-absorption zone slurry divider, 24-saturation zone spray layer, 25-saturation zone, 26-second-stage ammonia washing process water tank, 27-process water tank, 28-first-stage ammonia washing slurry tank, 29-absorption zone slurry tank, 30-concentrated ammonia water replenishment tank, 31-second-stage ammonia washing slurry circulation pump, 32-first-stage ammonia washing circulation pump, 33-absorption zone slurry circulation pump, 34-saturation zone slurry circulation pump, 35-saturated slurry discharge pump, 36-saturated slurry tank, 37-cyclone, 38-centrifuge, 39-ammonium bicarbonate storage tank, 40-branch flue gas duct after decarbonization.

[0060] Figure 2 2 is a graph of the outlet escaped ammonia concentration under different MgCl2 concentration conditions of the embodiment. DETAILED DESCRIPTION

[0061] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other similar device diagrams can be obtained based on the drawings without inventive work. The situations in which the circulation pump, slurry supply pump, and the number and installation position of the spray layers are simply adjusted are all protected by this patent.

[0062] Example 1:

[0063] like Figure 1As shown, the desulfurization wastewater generated by the desulfurization system, the outlet pipeline of the desulfurization wastewater tank 2 is connected to the water inlet of the heavy metal precipitation tank 4, the heavy metal precipitation tank 4 is provided with a sodium hydroxide delivery pipeline 3 and a heavy metal precipitation discharge pipeline 5, the outlet pipeline of the heavy metal precipitation tank 4 is connected to the water inlet of the calcium precipitation tank 7, the calcium precipitation tank 7 is provided with a sodium carbonate delivery pipeline 6 and a precipitated calcium discharge pipeline 8, the outlet pipeline of the calcium precipitation tank 7 is connected to the water inlet of the colloid precipitation tank 10, the colloid precipitation tank 10 is provided with a flocculant delivery pipeline 9 and a precipitated colloid discharge pipeline 11, the outlet pipeline of the colloid precipitation tank 10 is connected to the water inlet of the sedimentation tank 12, the outlet pipeline of the sedimentation tank 12 is connected to the water inlet pipeline of the clear liquid tank 13, the outlet pipeline of the clear water tank 13 is connected to the first-level ammonia washing spray layer 20, and a clear liquid delivery pump 14 is provided in the pipeline. The outlet pipeline of the low-temperature flue gas concentrated acidic slurry tank 15 is connected to the first-level ammonia washing spray layer 20, and a concentrated acidic slurry delivery pump 16 is provided in the pipeline.

[0064] A post-desulfurization branch flue gas duct 17 is provided at the bottom of the decarbonization tower 1, and a post-decarbonization branch flue gas duct 40 is provided at the top of the decarbonization tower 1. Below the bottom opening of the decarbonization tower 1 is a saturated zone. The external circulation pipeline of the saturated zone 25 is connected to the saturated zone spray layer 24, and a saturated zone slurry circulation pump 34 is installed in the pipeline.

[0065] An absorption zone slurry divider 23 is installed above the saturation zone spray layer 24. The absorption zone slurry divider 23 is connected to the inlet of the absorption zone slurry tank 29. The outlet pipeline of the absorption zone slurry tank 29 is connected to the absorption zone spray layer 22. An absorption zone slurry circulation pump 33 is installed in the pipeline. The outlet of the concentrated ammonia solution replenishment tank 30 is connected to the inlet of the absorption zone slurry tank 29 via a pipeline.

[0066] A first-level ammonia washing slurry divider 21 is provided on the upper part of the absorption zone spray layer 22. The first-level ammonia washing slurry divider 21 is connected to the inlet of the first-level ammonia washing slurry tank 28. The outlet pipeline of the first-level ammonia washing slurry tank 28 is connected to the first-level ammonia washing spray layer 20. A first-level ammonia washing circulation pump 32 is installed in the pipeline.

[0067] A secondary ammonia wash slurry divider 19 is provided above the primary ammonia wash spray layer 20. The secondary ammonia wash slurry divider 19 is connected to the inlet of the secondary ammonia wash process water tank 26. The outlet pipeline of the secondary ammonia wash process water tank 26 is connected to the secondary ammonia wash spray layer 18. A secondary ammonia wash slurry circulation pump 31 is installed in the pipeline. The outlet of the process water tank 27 is connected to the inlet of the secondary ammonia wash process water tank 26 via a pipeline.

[0068] The outlet of the saturated zone 25 is connected to the inlet of the saturated slurry tank 36, a saturated slurry discharge pump 35 is installed in the pipeline, the outlet of the saturated slurry tank 36 is connected to the inlet of the cyclone 37, the bottom flow outlet of the cyclone 37 is connected to the inlet of the centrifuge 38, and the outlet of the centrifuge 38 is connected to the inlet of the ammonium bicarbonate storage tank 39.

[0069] Example 2:

[0070] The present invention provides a method for capturing carbon from flue gas of coal-fired power plants and co-producing ammonium fertilizer based on the ammonia process, which includes three processing routes: gas, liquid, and solid:

[0071] The gas treatment route includes: the flue gas undergoes multi-stage absorption in the saturation zone, absorption zone and ammonia washing zone of the decarbonization system to remove part of the CO2 and escaped ammonia, and the concentration of the emitted ammonia is controlled below 3ppm; the slurry pH in the saturation zone 25 of the decarbonization system is 8-8.5, the slurry pH in the absorption zone is 9.5-10, the pH in the first-level ammonia washing slurry tank 28 of the ammonia washing zone is 10-10.5, and the pH in the second-level ammonia washing process water tank 26 is 8-9.

[0072] The liquid treatment route includes: in the desulfurization wastewater treatment system, the wastewater undergoes pretreatment, recycling of ammonia washing liquid, cascade utilization of decarbonization slurry and solid-liquid separation to ensure that the desulfurization wastewater and ammonia washing liquid are treated and recycled; the pretreatment step of the desulfurization wastewater includes adding sodium hydroxide and sodium carbonate to adjust the pH value, and adding flocculants to remove suspended particles and impurities to obtain clear liquid and flocs, and the clear liquid is used for recycling of ammonia washing liquid.

[0073] The solid processing route includes: obtaining ammonium bicarbonate solid by-product through solid-liquid separation in a dehydration system, and forming ammonium bicarbonate fertilizer that can be used in agriculture or industry after dehydration and drying.

[0074] The present invention calculates the concentration of ammonium bicarbonate in the solution based on the control relationship between the measured density and the ammonium bicarbonate saturation. Combined with the monitored pH value, a balance equation can be established to calculate the effective ammonia concentration in the absorption zone. The reference value C is introduced and there is a positive correlation with the CO2 absorption efficiency, that is, a one-to-one correspondence. Substituting it into the formula:

[0075] C=738.58[NH3] 2 +11.32[NH3]

[0076] [NH3] represents the effective ammonia concentration;

[0077] C is solved, and the C value of the absorption slurry is adjusted by adding concentrated ammonia water in the concentrated ammonia water replenishment tank (30) to maintain the decarbonization system efficiency above 80%.

[0078] Table 1 is a comparison table of ammonium bicarbonate slurry concentration and density, which is used to calculate the ammonium bicarbonate concentration in the absorption zone slurry.

[0079] Table 1 is a comparison table of ammonium bicarbonate slurry concentration and density

[0080] concentration(%) <![CDATA[Density (kg / m 3 ).]]> 0 1 5 1.008 10 1.017 15 1.026 20 1.036 25 1.046 30 1.057 35 1.068 40 1.079 45 1.091 50 1.103

[0081] In this embodiment, the pH of the absorption zone is set to 10, the ammonium bicarbonate concentration is 10%, the absorption efficiency is 82%, and the slurry density is 1.057 kg / m 3 In order to maintain the absorption efficiency within the range of 85-90%, at this time, the effective ammonia concentration is 1.08mol / L, the C value is 891.20, and according to operating experience, the C value needs to be controlled to be greater than 2000 so that the absorption efficiency can be greater than 85%. In this case, ammonia water is added to the absorption zone until the pH is greater than 10.1. The pH value of the absorption zone can be adjusted at any time according to the amount of ammonia water added, and the real-time C value is calculated to maintain the absorption efficiency within the range of 85-90%. Figure 2 shown.

Claims

1. A system for capturing carbon dioxide from flue gas of coal-fired power plants and co-producing ammonium fertilizer based on the ammonia process, characterized by: Including desulfurization wastewater treatment system, decarbonization system and dehydration system; The decarbonization system comprises a decarbonization tower (1); The desulfurization wastewater treatment system comprises a desulfurization wastewater tank (2), a heavy metal precipitation tank (4), a calcium precipitation tank (7), a colloid precipitation tank (10), and a sedimentation tank (12) connected in sequence; the sedimentation tank (12) is connected to a clear liquid tank (13), and the clear liquid tank (13) is connected to a primary ammonia washing spray layer (20) of a decarbonization tower (1) via a clear liquid delivery pump (14); The top exhaust port of the decarbonization tower (1) is connected to the post-decarbonization branch flue gas duct (40); The decarbonization tower (1) is provided with a secondary ammonia washing spray layer (18), a secondary ammonia washing slurry separator (19), a primary ammonia washing spray layer (20), a primary ammonia washing slurry separator (21), an absorption zone spray layer (22), an absorption zone slurry separator (23), and a saturation zone spray layer (24) in order from top to bottom; the absorption zone is located above the absorption zone slurry separator (23); and the bottom of the decarbonization tower (1) is the saturation zone (25). The decarbonization system is further provided with an ammonia washing area, which includes a secondary ammonia washing process water tank (26) and a primary ammonia washing slurry tank (28); The secondary ammonia washing spray layer (18), the secondary ammonia washing slurry divider (19) and the secondary ammonia washing process water tank (26) form a circulation through the secondary ammonia washing slurry circulation pump (31); the secondary ammonia washing process water tank (26) is connected to the process water tank (27); The primary ammonia washing spray layer (20), the primary ammonia washing slurry divider (21) and the primary ammonia washing slurry tank (28) form a circulation through the primary ammonia washing circulation pump (32); the desulfurization wastewater treatment system is connected to the primary ammonia washing spray layer (20); the low-temperature flue gas concentrated acid slurry tank (15) is connected to the primary ammonia washing spray layer (20) through the concentrated acid slurry delivery pump (16); The absorption zone spray layer (22), the absorption zone slurry divider (23) and the absorption zone slurry tank (29) form a circulation through the absorption zone slurry circulation pump (33); the absorption zone slurry tank (29) is connected to the concentrated ammonia solution replenishment tank (30); The saturated zone spray layer (24) and the saturated zone (25) form a circulation through the saturated zone slurry circulation pump (34); The lower portion of the saturated zone spray layer (24) is connected to the post-desulfurization branch flue gas duct (17); The saturated zone (25) is also connected to the dewatering system via a saturated slurry discharge pump (35).

2. The system for capturing carbon dioxide from flue gas of a coal-fired power plant and co-producing ammonium fertilizer based on an ammonia process according to claim 1, characterized in that: The heavy metal precipitation tank (4) is provided with a sodium hydroxide delivery pipeline (3) and a heavy metal precipitation discharge pipeline (5); The calcium precipitation tank (7) is provided with a sodium carbonate delivery pipeline (6) and a precipitated calcium discharge pipeline (8); The colloid precipitation tank (10) is provided with a flocculant delivery pipeline (9) and a precipitated colloid discharge pipeline (11).

3. The system for capturing carbon dioxide from flue gas of a coal-fired power plant and co-producing ammonium fertilizer based on an ammonia process according to claim 1, characterized in that: The dehydration system includes a saturated slurry tank (36), a cyclone (37), a centrifuge (38) and an ammonium bicarbonate storage bin (39) which are connected in sequence.

4. The system for capturing carbon dioxide from flue gas of a coal-fired power plant and co-producing ammonium fertilizer based on an ammonia process according to claim 1, characterized in that: The absorption zone, saturation zone (25) and ammonia washing zone of the decarbonization system are all equipped with pH online monitoring devices, and the absorption zone and saturation zone (25) are equipped with density online monitoring devices.

5. A method for capturing carbon from flue gas of coal-fired power plants and co-producing ammonium fertilizer based on an ammonia process, characterized in that: The system for capturing carbon from flue gas of a coal-fired power plant and co-producing ammonium fertilizer based on an ammonia process according to any one of claims 1 to 4 is adopted, wherein the method comprises three processing routes: gas, liquid and solid: The gas treatment route includes: wherein the flue gas undergoes multi-stage absorption in the saturation zone, absorption zone and ammonia washing zone of the decarbonization system to remove CO2 and escaped ammonia; The liquid treatment route includes: in the desulfurization wastewater treatment system, wastewater undergoes pretreatment, recycling of ammonia wash liquid, cascade utilization of decarbonization slurry, and solid-liquid separation to ensure that desulfurization wastewater and ammonia wash liquid are treated and recycled; The solid processing route includes: obtaining ammonium bicarbonate solid by-product through solid-liquid separation in a dehydration system, and forming ammonium bicarbonate fertilizer that can be used in agriculture or industry after dehydration and drying.

6. The method for capturing carbon dioxide from flue gas of a coal-fired power plant and co-producing ammonium fertilizer based on an ammonia process according to claim 5, characterized in that: The pretreatment step of the desulfurization wastewater includes adding sodium hydroxide and sodium carbonate to adjust the pH value, and adding flocculants to remove suspended particles and impurities to obtain clear liquid and flocs. The clear liquid is used for the recycling of ammonia washing liquid.

7. The method for capturing carbon dioxide from flue gas of a coal-fired power plant and co-producing ammonium fertilizer based on an ammonia process according to claim 5, characterized in that: In the gas treatment route, the ammonia washing area is divided into primary and secondary ammonia washing areas to ensure that the emission concentration of ammonia is within 3ppm.

8. The method for capturing carbon dioxide from flue gas of a coal-fired power plant and co-producing ammonium fertilizer based on an ammonia process according to claim 5, characterized in that: The pH value of the slurry in each unit is controlled within the following ranges: the pH value of the slurry in the saturated zone (25) of the decarbonization system is 8-8.5, the pH value of the slurry in the absorption zone is 9.5-10, the pH value in the first-stage ammonia washing slurry tank (28) of the ammonia washing zone is 10-10.5, and the pH value in the second-stage ammonia washing process water tank (26) is 8-9.

9. The method for capturing carbon from flue gas of a coal-fired power plant and co-producing ammonium fertilizer based on an ammonia process according to claim 5, characterized in that: The concentration of ammonium bicarbonate in the solution is calculated based on the comparison relationship between the measured density and the saturation of ammonium bicarbonate. Combined with the monitored pH value, a balance equation is established and the effective ammonia concentration in the absorption zone is calculated.

10. The method for capturing carbon dioxide from flue gas of a coal-fired power plant and co-producing ammonium fertilizer based on an ammonia process according to claim 5, characterized in that: The reference value C is positively correlated with the CO2 absorption efficiency, i.e., a one-to-one correspondence. Substitute it into the formula: C=738.58[NH3] 2 +11.32[NH3] [NH3] represents the effective ammonia concentration; C is solved, and the C value of the absorption slurry is adjusted by adding concentrated ammonia water in the concentrated ammonia water replenishment tank (30) to maintain the decarbonization system efficiency above 80%.

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