A system and method for directly mineralizing flue gas carbon dioxide using gypsum

Abstract

The present invention relates to a system and method for directly mineralizing flue gas carbon dioxide by using gypsum. The absorption tower can sequentially achieve the processes of cooling, decarbonization, and escape ammonia capture of desulfurized flue gas. Among them, a slurry area is arranged at the bottom of the lower cooling section and is connected in a cycle to the upper ammonium bicarbonate spraying layer, which can achieve the capture of the waste heat of the desulfurized flue gas and provide heat for the low-temperature concentration crystallization of ammonium sulfate slurry. A ammonium bicarbonate holding layer is arranged at the bottom of the middle decarbonization section and forms a cycle with the ammonium bicarbonate spraying layer. By supplementing ammonia through the pipeline of the ammonium bicarbonate spraying layer, continuous decarbonization reaction of the cooled flue gas can be achieved, and at the same time, the separation of the lower cooling section and the middle decarbonization section areas can be realized. In the upper ammonia removal section, a gypsum spraying layer, a demister, and a process water spraying layer are sequentially arranged along the height direction. The gypsum holding layer and the gypsum spraying layer form a cycle spraying to achieve the continuous capture process of escape ammonia. The structure of this system is simple, the design is reasonable, the cost of flue gas decarbonization and utilization is low, and at the same time, continuous online treatment of large flue gas volume can be realized.

Description

Technical Field

[0001] The present invention belongs to the field of purification of air pollutants, and relates to a system and method for directly mineralizing flue gas carbon dioxide by using gypsum. Background Art

[0002] The problem of global warming affects the development of the entire human race. CO2 is the main cause of global warming. Any large-scale control of CO2 emissions to address global warming must focus on the capture of CO2 from large combustion equipment.

[0003] Currently, the main technology for carbon dioxide removal from flue gas of coal-fired power units is carbon capture, utilization and storage (CCUS). It uses organic amines as absorbents to react with CO2 in the flue gas to form water-soluble salts, and then heats the absorbent solution to release and capture CO2, while regenerating the absorbent solution. This technology has problems such as high energy consumption, low economic benefits, and secondary pollution. Most of the captured carbon dioxide is used for geological sequestration and enhanced oil recovery, which has the problem of secondary leakage. Therefore, there is an urgent need to develop high-efficiency and low-cost flue gas carbon dioxide removal and resource utilization technologies.

[0004] Currently, ammonia water (NH3) and gypsum (CaSO4) are used to react with CO2 in the flue gas to produce ammonium sulfate, that is, chemical fertilizer, and calcium carbonate, CO2 + 2NH3 + CaSO4·2H2O → (NH4)2SO4 + CaCO3↓ + 2H2O, thereby realizing flue gas carbon dioxide removal and its mineralization.

[0005] The technology of directly mineralizing flue gas CO2 with gypsum to co-produce ammonium sulfate and calcium carbonate has always been a research hotspot. For example, Chinese Patent CN100551494C discloses a method and system for removing carbon dioxide from power plant flue gas by the ammonia method. The end product of this method is ammonium bicarbonate chemical fertilizer, and there are problems of a large amount of decomposition during the evaporation and crystallization of ammonium bisulfate slurry. Chinese Patent Document CN102303874B discloses a method for converting phosphogypsum to ammonium sulfate by a polycrystalline method. The gypsum slurry of this method comes from the slurry of the phosphoric acid system and requires a pretreatment and purification process to obtain pure reactants. In summary, none of these patents involve the development of carbon capture and utilization process technologies coupled with wet flue gas desulfurization systems, nor the research on the process technology of internal circulation in the absorption tower. Summary of the Invention

[0006] Aiming at the problems of high cost and inability to be applied on a large scale in the existing technology during mineralization and carbon dioxide removal, the present invention provides a system and method for directly mineralizing flue gas carbon dioxide by using gypsum.

[0007] The present invention is realized through the following technical solutions:

[0008] A system for directly mineralizing flue gas carbon dioxide by using gypsum, characterized in that it includes an absorption tower, an ammonium sulfate crystal generation device, and a calcium carbonate generation device;

[0009] The calcium carbonate generating device includes a crystallization tank and a gypsum slurry tank;

[0010] The absorption tower includes a lower cooling section, a middle decarbonization section, and an upper deammoniation section arranged in sequence from bottom to top;

[0011] At the bottom of the lower cooling section, there is a slurry area, at the top, there is an ammonium sulfate spray layer, and on the side wall, there is a desulfurized flue gas inlet. The slurry area is located below the desulfurized flue gas inlet, and on the side wall of the slurry area, there are a slurry reflux port, a slurry circulation outlet, and a slurry output port arranged from high to low in sequence; The slurry circulation outlet is connected to the input end of the ammonium sulfate spray layer through an ammonium sulfate circulation pump;

[0012] The input end of the ammonium sulfate crystal generating device is connected to the slurry output port, and the output end is connected to the slurry reflux port;

[0013] At the bottom of the middle decarbonization section, there is an ammonium bicarbonate holding layer, at the top, there is an ammonium bicarbonate spray layer. On one side of the ammonium bicarbonate holding layer, there are an ammonium bicarbonate circulation outlet and an ammonium bicarbonate outlet. The ammonium bicarbonate circulation outlet is connected to the input end of the ammonium bicarbonate spray layer through an ammonium bicarbonate circulation pump; The ammonium bicarbonate outlet is connected to the ammonium bicarbonate inlet of the crystallization tank; On the other side of the ammonium bicarbonate holding layer, there is an ammonia water inlet;

[0014] At the bottom of the upper deammoniation section, there is a gypsum holding layer, and along the height direction at the top, there are a gypsum spray layer, a demister, and a process water spray layer arranged in sequence; On one side of the gypsum holding layer, there is a gypsum circulation outlet, and the gypsum circulation outlet is connected to the gypsum spray layer through a gypsum slurry tank.

[0015] Furthermore, the ammonium sulfate crystal generating device includes an ammonium sulfate discharge pump, an ammonium sulfate cyclone, and a centrifuge;

[0016] The top outlet of the ammonium sulfate cyclone is connected to the slurry reflux port of the absorption tower, the side cut inlet is connected to the slurry output port of the absorption tower, and the bottom outlet is connected to the side cut inlet of the centrifuge;

[0017] The liquid phase outlet of the centrifuge is connected to the slurry reflux port of the absorption tower, and the solid phase outlet outputs ammonium sulfate crystals.

[0018] Furthermore, the calcium carbonate generating device further includes a calcium carbonate cyclone;

[0019] The crystallization tank is provided with a gypsum inlet and a crystallization discharge port, and the gypsum inlet is connected to the gypsum outlet of the gypsum slurry tank;

[0020] The top outlet of the calcium carbonate cyclone is sequentially connected to an evaporation deammoniator and a vacuum belt filter, and the bottom outlet is connected to the gypsum inlet of the crystallization tank;

[0021] The crystallization discharge port of the crystallization tank is connected to the side cut inlet of the calcium carbonate cyclone.

[0022] Furthermore, a stirrer is installed at the top of the crystallization tank.

[0023] Furthermore, the filtrate outlet of the vacuum belt filter is connected to the slurry tank at the bottom of the absorption tower via a filtrate pump.

[0024] Furthermore, heat exchange coiled pipes are arranged inside the ammonia evaporation eliminator.

[0025] Furthermore, the heat exchange coiled pipes are connected to hot flue gas or hot steam.

[0026] Furthermore, an ammonia gas outlet is arranged at the top of the ammonia evaporation eliminator and is connected to the input end of the ammonium bicarbonate spraying layer.

[0027] A method for directly mineralizing flue gas carbon dioxide with gypsum, characterized by comprising the following steps:

[0028] The desulfurized flue gas enters from the inlet of the absorption tower and countercurrently contacts and exchanges heat with the circulating sprayed ammonium sulfate solution in the lower cooling section to realize the evaporation and concentration of the ammonium sulfate solution;

[0029] The desulfurized flue gas is cooled to 20°C - 30°C and enters the middle carbon dioxide removal section of the absorption tower. The ammonia tank continuously supplies ammonia to the middle carbon dioxide removal section to form a circulating spray of ammonia-containing absorption liquid, which countercurrently contacts and reacts with the low-temperature flue gas to remove CO2, and the desulfurized flue gas is decarbonated to form decarbonated flue gas;

[0030] The decarbonated flue gas enters the upper ammonia removal section and countercurrently contacts the circulating sprayed gypsum solution to remove the escaped ammonia in the decarbonated flue gas. The flue gas sequentially passes through the demister and the process water spraying layer to achieve clean emission.

[0031] Furthermore, in the crystallization tank of the calcium carbonate generating device, the nitrogen-sulfur molar ratio of the ammonium bicarbonate solution to the desulfurized gypsum slurry is 2 - 2.5, and a large amount of calcium carbonate and gypsum are produced in the slurry at the bottom, and are pumped into the calcium carbonate hydrocyclone by the crystallization discharge pump;

[0032] The bottom slurry rich in gypsum in the calcium carbonate hydrocyclone is pumped back into the crystallization tank by the gypsum reflux pump for continuous reaction. The slurry at the top of the calcium carbonate hydrocyclone is discharged to the ammonia evaporation eliminator, and the ammonia gas in the liquid phase is removed, and then enters the vacuum belt filter to filter out solid calcium carbonate. The ammonium sulfate filtrate is pumped back to the slurry tank at the bottom of the absorption tower by the filtrate pump;

[0033] The slurry at the bottom of the absorption tower enters the ammonium sulfate hydrocyclone and centrifuge through the ammonium sulfate discharge pump to separate ammonium sulfate crystals. The slurry in the ammonium sulfate hydrocyclone flows back to the bottom of the absorption tower to continue heat absorption and concentration crystallization.

[0034] Compared with the prior art, the present invention has the following beneficial technical effects:

[0035] The present invention relates to a system for directly mineralizing flue gas carbon dioxide using gypsum. By arranging a lower cooling section, a middle decarbonization section, and an upper ammonia removal section in the absorption tower, the system can successively achieve the processes of cooling, decarbonization, and escape ammonia capture of desulfurized flue gas. Among them, a slurry area is arranged at the bottom of the lower cooling section and is connected in a cycle to the upper ammonium bicarbonate spraying layer, which can capture the waste heat of the desulfurized flue gas and provide heat for concentrating ammonium sulfate crystals. A ammonium bicarbonate holding layer is arranged at the bottom of the middle decarbonization section and forms a cycle with the ammonium bicarbonate spraying layer, which can achieve continuous decarbonization reaction of the cooled flue gas and at the same time separate the lower cooling section and the middle decarbonization section. The upper ammonia removal section is successively provided with a gypsum spraying layer, a demister, and a process water spraying layer along the height direction. The gypsum holding layer and the gypsum spraying layer form a cyclic spraying to achieve continuous capture of escape ammonia. The system has a simple structure, reasonable design, low cost of flue gas decarbonization and utilization, and can simultaneously achieve continuous online treatment of large flue gas volumes.

[0036] Furthermore, the calcium carbonate generation device in the present invention is successively connected to a crystallization tank, a calcium carbonate hydrocyclone, and an evaporation ammonia removal device. The crystallization tank can collect and stir the ammonium bicarbonate solution generated in the middle decarbonization section and the gypsum slurry generated in the upper ammonia removal section, and discharge them into the calcium carbonate hydrocyclone. The calcium carbonate hydrocyclone rotates at a high speed to divert the gypsum slurry back to the crystallization tank to continue participating in the reaction, saving costs and improving utilization efficiency. The calcium carbonate is diverted to the evaporation ammonia removal device to obtain solid calcium carbonate and filtrate, and the filtrate is diverted to the slurry pool in the lower cooling section for recycling.

[0037] Furthermore, the ammonium sulfate crystal generation device is connected to the slurry pool in the cooling section. Through the ammonium sulfate hydrocyclone and centrifuge, and with the cooperation of the waste heat of the desulfurized flue gas, low-temperature evaporation crystallization of ammonium sulfate can be achieved. Ammonium sulfate is mainly used as a fertilizer and is suitable for various soils and crops. At the same time, it can also be used in textiles, leather, medicine, etc. The system is reasonably designed and can reduce production costs.

[0038] The present invention also relates to a method for directly mineralizing flue gas carbon dioxide using gypsum. The desulfurized flue gas releases heat in the lower cooling section of the absorption tower, and at the same time, the ammonium sulfate spraying layer continuously sprays the desulfurized flue gas, causing the desulfurized flue gas to continuously release heat. The ammonium sulfate crystal generation device uses the desulfurized flue gas to evaporate the ammonium sulfate solution to form ammonium sulfate crystals. The desulfurized flue gas undergoes a decarbonization reaction in the middle decarbonization section to form decarbonized flue gas, solving the problem of carbon dioxide emissions. The upper ammonia removal section removes the escape ammonia in the decarbonized flue gas through continuous spraying of gypsum solution, achieving clean emission of the flue gas. This method can be applied on a large scale, with low production costs and high decarbonization efficiency.

[0039] Further, in the calcium carbonate production device, the ammonium carbamate solution generated after decarbonization in the middle decarbonization section and the gypsum slurry in the gypsum slurry tank are simultaneously introduced into the crystallization tank, and stirred to react to generate calcium carbonate and gypsum. The gypsum and calcium carbonate solution are separated by a calcium carbonate cyclone, and the calcium carbonate filter cake and ammonium sulfate filtrate are filtered out. The ammonium sulfate filtrate re-enters the bottom of the absorption tower to achieve recycling, solving the problem of carbon dioxide emissions. At the same time, the precipitated calcium carbonate filter cake can be reused for wet flue gas desulfurization to achieve calcium circulation in the desulfurization system. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 FIG. is a schematic diagram of a system for directly mineralizing flue gas carbon dioxide with gypsum in a specific embodiment of the present invention;

[0041] Figure 2 FIG. is a schematic diagram showing the absorption effect of gypsum slurry on ammonia slip under simulated flue gas conditions in a specific embodiment of the present invention.

[0042] In the figure: process water spray layer 1, demister 2, gypsum spray layer 3, absorption tower 4, ammonium carbamate spray layer 5, ammonium sulfate spray layer 6, centrifuge 7, ammonium sulfate cyclone 8, ammonium sulfate discharge pump 9, ammonium sulfate circulation pump 10, ammonium carbamate circulation pump 11, crystallization tank 12, crystallization discharge pump 13, gypsum reflux pump 14, filtration pump 15, stirrer 16, gypsum circulation pump 17, gypsum slurry tank 18, gypsum slurry discharge pump 19, calcium carbonate cyclone 20, ammonia evaporation device 21, vacuum belt filter 22, heat exchange coil 23, lower cooling section 24, middle decarbonization section 25, upper deammoniation section 26, ammonium sulfate crystal production device 27, ammonia tank 28, ammonia supply pump 29, calcium carbonate production device 30. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] The following further describes the present invention in detail with reference to specific embodiments, which are explanations of the present invention rather than limitations.

[0044] A system for directly mineralizing flue gas carbon dioxide with gypsum according to the present invention, as Figure 1As shown in the figure, it includes an absorption tower 4, an ammonium sulfate crystal generation device 27, and a calcium carbonate generation device 30; the absorption tower 4 includes a lower cooling section 24, a middle decarbonization section 25, and an upper deammoniation section 26 arranged in reverse order along the height. Among them, a slurry area is provided at the bottom of the lower cooling section 24, an ammonium sulfate spray layer 6 is provided at the top, a desulfurized flue gas inlet is provided on the side wall, the slurry area is located below the desulfurized flue gas inlet, and a slurry return port, a slurry circulation outlet, and a slurry output port are sequentially arranged on the side wall of the slurry area from high to low; the input end of the ammonium sulfate crystal generation device 27 is connected to the slurry output port, and the output end is connected to the slurry return port. The slurry return port is the highest in the height direction and is used to connect and recover the uncrystallized ammonium sulfate solution in the ammonium sulfate crystal generation device 27; an ammonium sulfate circulation pump 10 is provided at the slurry circulation outlet and is connected to the input end of the ammonium sulfate spray layer 6 to realize the circulating spraying process of ammonium sulfate.

[0045] A carbon ammonium holding liquid layer is provided at the bottom of the middle decarbonization section 25, a carbon ammonium spray layer 5 is provided at the top, a carbon ammonium circulation outlet is provided on one side of the carbon ammonium holding liquid layer, a carbon ammonium circulation pump 11 is provided at the carbon ammonium circulation outlet and is connected to the input end of the carbon ammonium spray layer 5 to realize the circulating spraying process of carbon ammonium; and a carbon ammonium outlet is provided on one side of the side wall of the middle decarbonization section 25 and is connected to the carbon ammonium input end of the calcium carbonate generation device 30; ammonia in the absorption liquid is supplemented through an ammonia supply pump 29 to the inlet pipeline of the carbon ammonium spray layer 5. The mass concentration of the carbon ammonium solution in the ammonia-containing absorption liquid is 5%-20%, and it reacts with carbon dioxide in the desulfurized flue gas at a temperature between 20°C and 30°C to generate ammonium carbonate solution. The reaction formula is:

[0046] 2NH3 + CO2 + H2O → (NH4)2CO3

[0047] (NH4)2CO3 + CO2 + H2O → NH4HCO3

[0048] NH4HCO3 + NH3 → (NH4)2CO3

[0049] A gypsum holding liquid layer is provided at the bottom of the upper deammoniation section 26, and a gypsum spray layer 3, a demister 2, and a process water spray layer 1 are sequentially arranged at the top along the height direction; a gypsum circulation outlet is provided on one side of the gypsum holding liquid layer. Specifically, the calcium carbonate generation device 30 includes a crystallization tank 12 and a gypsum slurry tank 18. The gypsum circulation outlet is sequentially connected to the gypsum slurry tank 18 and a gypsum circulation pump 17 and returns to the gypsum spray layer 3 to form a gypsum circulation system, and at the same time, it can capture the escaping ammonia contained in the decarbonized flue gas; among them, the gypsum holding liquid layer separates the upper deammoniation section 26 and the middle decarbonization section 25 to form two separate areas.

[0050] Among them, the structures of the ammonium bicarbonate liquid-holding layer and the gypsum liquid-holding layer are the same, both including a liquid-holding tank and a liquid-guiding tank. The liquid-holding tanks are arranged at intervals to form a flue gas flow channel for the entry of flue gas. The liquid-guiding tank is arranged upside down above the flue gas flow channel, and its side wall extends into the adjacent liquid-holding tank. All the liquid-holding tanks are interconnected to facilitate the confluence and circulation of the collected spray liquid.

[0051] The ammonium sulfate crystal generation device 27 includes an ammonium sulfate discharge pump 9, an ammonium sulfate cyclone 8, and a centrifuge 7; the liquid phase outlet of the ammonium sulfate cyclone 8 is connected to the slurry return port of the bottom cooling section 24, and the solid phase outlet is connected to the side cut-in port of the centrifuge 7. The side cut-in port is connected to the slurry output port of the absorption tower 4 through the ammonium sulfate discharge pump 9; the centrifuge 7 includes a liquid phase outlet for mainly outputting ammonium sulfate solution at the top and a solid phase outlet for mainly outputting ammonium sulfate crystals. The liquid phase outlet is connected to the slurry return port of the absorption tower 4; among them, the top outlet of the ammonium sulfate cyclone 8 and the ammonium sulfate solution outlet of the centrifuge 7 converge into the same pipeline and are connected to the slurry return port of the bottom cooling section; the series connection of the ammonium sulfate cyclone 8 and the centrifuge 7 can achieve the matching separation method of the centrifuge cyclone, reducing costs and improving production efficiency.

[0052] The calcium carbonate generation device 30 includes a crystallization tank 12, a gypsum slurry tank 18, and a calcium carbonate cyclone 20; among them, the top of the crystallization tank 12 is provided with an ammonium bicarbonate inlet and a gypsum inlet, and the bottom is provided with a crystallization discharge port. The ammonium bicarbonate inlet is connected to the ammonium bicarbonate outlet of the middle decarbonization section 25, and the gypsum inlet is connected to the gypsum outlet of the gypsum slurry tank 18. And a gypsum slurry discharge pump 19 is provided at the gypsum outlet of the gypsum slurry tank 18. Among them, a stirrer 16 is arranged inside the gypsum slurry tank 18. During use, the stirrer 16 rotates to drive the internal gypsum slurry and ammonium bicarbonate solution to react fully; the crystallization discharge port is connected to the side cut-in port of the calcium carbonate cyclone 20 through the crystallization discharge pump 13; the top outlet of the calcium carbonate cyclone 20 is successively connected to an ammonia evaporation eliminator 21 and a vacuum belt filter 22, and the bottom outlet is provided with a gypsum reflux pump 14 and is connected to the gypsum inlet of the crystallization tank 12.

[0053] Among them, a filtrate outlet is provided at the bottom of the vacuum belt filter 22, and a filtrate pump 15 is provided at the filtrate outlet and connected back to the slurry pool at the bottom of the absorption tower 4. The main component of the filtrate is ammonium sulfate solution, which is recycled to the slurry pool of the bottom cooling section 24 through the filtration pump 15; the inside of the ammonia evaporation eliminator 21 includes a heat exchange coil 23, and the heat source used includes hot flue gas or hot steam; an ammonia gas outlet is provided at the top of the ammonia evaporation eliminator 21 and connected to the input end of the ammonium bicarbonate spray layer 5 of the middle decarbonization section 25, and is cyclically added to the absorption liquid in the middle decarbonization section 25 to participate in the reaction, improving the utilization rate and reducing costs.

[0054] A method for directly mineralizing flue gas carbon dioxide using gypsum includes the following steps:

[0055] The desulfurized flue gas enters from the desulfurized flue gas inlet of the absorption tower 4, and countercurrently contacts and exchanges heat with the ammonium sulfate solution sprayed in circulation in the lower cooling section 24 to achieve the evaporation and concentration of the ammonium sulfate solution. Among them, when the solid content of the slurry pool in the bottom cooling section 24 is greater than 10%, the ammonium sulfate discharge pump 9 is started to carry out the evaporation and concentration process of the ammonium sulfate solution.

[0056] The desulfurized flue gas is cooled to 20°C - 30°C and enters the middle decarbonization section 25 of the absorption tower 4. The ammonia tank 28 continuously supplies ammonia to the middle decarbonization section 25 through the ammonia supply pump 29 to form a circulating spray of ammonia-containing absorption liquid, which reacts with the low-temperature flue gas in a countercurrent contact to remove CO2 and form decarbonized flue gas.

[0057] The decarbonized flue gas enters the upper deammoniation section 26 and countercurrently contacts the circulating gypsum solution sprayed to remove the escaped ammonia in the decarbonized flue gas. The flue gas passes through the demister 2 and the process water spray layer 1 in sequence to achieve net emission.

[0058] In the calcium carbonate generation device 30, the ammonium carbonate solution generated after decarbonization in the middle decarbonization section 25 and the gypsum slurry in the gypsum slurry tank 18 are simultaneously introduced into the crystallization tank 12. The nitrogen-sulfur molar ratio of the ammonium carbonate solution to the desulfurized gypsum slurry is 2 - 2.5. A large amount of calcium carbonate and gypsum are contained in the slurry at the bottom of the crystallization tank 12, and it is pumped into the side cut-in of the calcium carbonate cyclone 20 by the crystallization discharge pump 13.

[0059] The gypsum-rich bottom slurry of the calcium carbonate cyclone 20 is pumped back into the crystallization tank 12 by the gypsum reflux pump 14 for continuous reaction. The slurry at the top of the calcium carbonate cyclone 20 is discharged to the evaporation deammoniator 21, and the ammonia in the liquid phase is removed through the evaporation deammoniator 21 and enters the vacuum belt filter 22 for filtration. Solid calcium carbonate is filtered out, and the filtered ammonium sulfate filtrate is pumped back into the bottom slurry pool of the absorption tower 4 by the filtrate pump 15.

[0060] The slurry at the bottom of the absorption tower 4 enters the ammonium sulfate cyclone 8 through the ammonium sulfate discharge pump 9. A large amount of ammonium sulfate is contained in the slurry at the bottom of the cyclone and enters the centrifuge 7 to separate ammonium sulfate crystals. The slurry at the top of the ammonium sulfate cyclone 8 is refluxed to the bottom of the absorption tower 4 for continuous concentration and crystallization.

[0061] The present invention provides a specific embodiment to test the absorption effect of gypsum slurry on ammonia escape under simulated flue gas conditions in the laboratory:

[0062] The supply volume of the flue gas is set to 5 L / min, the ammonia escape amount is 50 μL / L, the absorption liquid 1 is gypsum slurry with a mass fraction of 20%, the absorption liquid 2 is pure water. This experiment is completed on a small spray tower test bench, and the spray liquid-gas ratio is between 2 - 20 L / V. The experimental results are shown in Figure 2 . The experimental results show that under the same liquid-gas ratio condition, the deammoniation effect of using gypsum slurry with a mass fraction of 20% is significantly better than that of pure water, and the ammonia escape rate can be controlled below 5 μL / L when the liquid-gas ratio is greater than 6.

[0063] Build a pilot system with a simulated flue gas volume of 100 m 3 / h (standard condition), the CO2 content in the flue gas is 15%, the oxygen content is 6%, and the rest is nitrogen. The flue gas inlet temperature of Absorber 4 is controlled between 50°C and 60°C, and the flue gas temperature entering the middle decarbonization section 25 of Absorber 4 is controlled between 20°C and 30°C;

[0064] The slurry pool volume of the bottom cooling section 24 of Absorber 4 is 500 L, the height of the spray layers between the upper, middle and lower sections is 1.5 m, each spray layer is arranged in a single layer, the circulation pump uses a mechanical diaphragm pump, and the slurry circulation pressure is controlled between 0.15 MPa and 0.4 MPa;

[0065] Inside the ammonia evaporation eliminator 21 is a serpentine heat exchange coil 23, and steam flows in the coil for heat exchange. The temperature of the slurry inside the ammonia evaporation eliminator 21 is controlled between 50°C and 70°C, and the evaporated ammonia gas is introduced into the inlet pipeline of the ammonium bicarbonate circulation pump 11 through a pipeline to realize the recycling of ammonia;

[0066] The concentration of the ammonia water absorption liquid in the middle decarbonization section 25 of Absorber 4 is controlled to operate between 1% and 5%. The initial mass concentration of the gypsum slurry in the upper ammonia removal section 26 of Absorber 4 is 20%. When the ammonium sulfate slurry in the bottom cooling section 24 of Absorber 4 is concentrated by the ammonium sulfate circulation pump 10 to a solid content greater than 10%, the ammonium sulfate discharge pump 9 is started;

[0067] The nitrogen-sulfur molar ratio of the ammonium bicarbonate solution and the desulfurized gypsum slurry entering the crystallization tank 12 is controlled to operate between 2 and 2.5. The stirrer 16 installed at the top of the crystallization tank 12 has a rotation speed of 130 r / min;

[0068] The final test results show that the removal rate of carbon dioxide in the desulfurized flue gas can reach 78%, the ammonia escape at the outlet of Absorber 4 is less than 5 μL / L, the purity of the obtained calcium carbonate is greater than 98%, and the purity of ammonium sulfate is greater than 99%, meeting the requirements of first-class fertilizer grade.

Claims

1. A system for directly mineralizing flue gas carbon dioxide using gypsum, characterized in that, It includes an absorption tower (4), an ammonium sulfate crystal generation device (27) and a calcium carbonate generation device (30); The calcium carbonate generation device (30) includes a crystallization tank (12), a gypsum slurry tank (18) and a calcium carbonate hydrocyclone (20); The crystallization tank (12) is provided with a gypsum inlet and a crystallization discharge outlet, and the gypsum inlet is connected to the gypsum outlet of the gypsum slurry tank (18); The top outlet of the calcium carbonate hydrocyclone (20) is sequentially connected to an ammonia evaporation and removal device (21) and a vacuum belt filter (22), and the bottom outlet is connected to the gypsum inlet of the crystallization tank (12); the filtrate outlet of the vacuum belt filter (22) is connected back to the slurry pool at the bottom of the absorption tower (4) through a filtrate pump (15); The crystallization discharge outlet of the crystallization tank (12) is connected to the side cut inlet of the calcium carbonate hydrocyclone (20); The absorption tower (4) includes a lower cooling section (24), a middle decarbonization section (25) and an upper deammoniation section (26) arranged in sequence from bottom to top; A slurry area is arranged at the bottom of the lower cooling section (24), an ammonium sulfate spray layer (6) is arranged at the top, a desulfurized flue gas inlet is arranged on the side wall, the slurry area is located below the desulfurized flue gas inlet, and a slurry reflux port, a slurry circulation outlet and a slurry output port are arranged on the side wall of the slurry area from high to low in sequence; the slurry circulation outlet is connected to the input end of the ammonium sulfate spray layer (6) through an ammonium sulfate circulation pump (10); The desulfurized flue gas is in countercurrent contact heat exchange with the circulating ammonium sulfate solution in the lower cooling section (24) to realize the evaporation and concentration of the ammonium sulfate solution; the desulfurized flue gas is cooled to 20°C - 30°C and enters the middle decarbonization section (25) of the absorption tower (4); The input end of the ammonium sulfate crystal generation device (27) is connected to the slurry output port, and the output end is connected to the slurry reflux port; A carbon ammonium holding layer is arranged at the bottom of the middle decarbonization section (25), a carbon ammonium spray layer (5) is arranged at the top, a carbon ammonium circulation outlet and a carbon ammonium outlet are arranged on one side of the carbon ammonium holding layer, the carbon ammonium circulation outlet is connected to the input end of the carbon ammonium spray layer (5) through a carbon ammonium circulation pump (11); the carbon ammonium outlet is connected to the carbon ammonium inlet of the crystallization tank (12); an ammonia water inlet is arranged on the other side of the carbon ammonium holding layer; A gypsum holding layer is arranged at the bottom of the upper deammoniation section (26), a gypsum spray layer (3), a demister (2) and a process water spray layer (1) are arranged in sequence along the height direction at the top; a gypsum circulation outlet is arranged on one side of the gypsum holding layer, and the gypsum circulation outlet is connected to the gypsum spray layer (3) through the gypsum slurry tank (18); The ammonium sulfate crystal generation device (27) includes an ammonium sulfate discharge pump (9), an ammonium sulfate hydrocyclone (8) and a centrifuge (7); The top outlet of the ammonium sulfate hydrocyclone (8) is connected to the slurry reflux port of the absorption tower (4), the side cut inlet is connected to the slurry output port of the absorption tower (4), and the bottom outlet is connected to the side cut inlet of the centrifuge (7); The liquid phase outlet of the centrifuge (7) is connected to the slurry reflux port of the absorption tower (4), and the solid phase outlet outputs ammonium sulfate crystals.

2. The system for directly mineralizing flue gas carbon dioxide using gypsum according to claim 1, wherein, A stirrer (16) is installed at the top of the crystallization tank (12).

3. The system for directly mineralizing flue gas carbon dioxide using gypsum according to claim 1, wherein A heat exchange coil (23) is arranged in the ammonia evaporation and removal device (21).

4. The system for directly mineralizing flue gas carbon dioxide using gypsum according to claim 3, characterized in that, The heat exchange coil (23) is connected to hot flue gas or hot steam.

5. The system for directly mineralizing flue gas carbon dioxide using gypsum according to claim 1, characterized in that, An ammonia outlet is provided at the top of the evaporation ammonia eliminator (21) and is connected to the input end of the ammonium bicarbonate spray layer (5).

6. A method for directly mineralizing carbon dioxide in flue gas using gypsum, characterized in that, Based on any one of the systems for directly mineralizing flue gas carbon dioxide using gypsum described in claims 1-5, the following steps are included: The desulfurized flue gas enters from the inlet of the absorption tower (4) and countercurrently contacts and exchanges heat with the circulating ammonium sulfate solution sprayed in the lower cooling section (24) to achieve evaporation and concentration of the ammonium sulfate solution; The desulfurized flue gas is cooled to 20°C - 30°C and enters the middle decarbonization section (25) of the absorption tower (4). Ammonia is continuously supplied from the ammonia tank (28) to the middle decarbonization section (25) to form a circulating spray of ammonia-containing absorbent liquid, which countercurrently contacts and reacts with the low-temperature flue gas to remove CO2, and the desulfurized flue gas is decarbonized to form decarbonized flue gas; The decarbonized flue gas enters the upper ammonia removal section (26) and countercurrently contacts the circulating gypsum solution sprayed to remove the escaped ammonia in the decarbonized flue gas. The flue gas passes through the demister (2) and the process water spray layer (1) in sequence to achieve clean emission.

7. The method for directly mineralizing flue gas carbon dioxide using gypsum according to claim 6, wherein, In the crystallization tank (12) of the calcium carbonate generating device (30), the nitrogen-sulfur molar ratio of the ammonium bicarbonate solution to the desulfurized gypsum slurry is 2 - 2.5, and a large amount of calcium carbonate and gypsum are produced in the bottom slurry, which is pumped into the calcium carbonate cyclone (20) by the crystallization discharge pump (13); The bottom slurry rich in gypsum in the calcium carbonate cyclone (20) is pumped back to the crystallization tank (12) by the gypsum reflux pump (14) to continue the reaction. The slurry at the top of the calcium carbonate cyclone (20) is discharged to the evaporation ammonia eliminator (21), and the ammonia in the liquid phase is removed and enters the vacuum belt filter (22) to filter out solid calcium carbonate. The ammonium sulfate filtrate is pumped back to the bottom slurry tank of the absorption tower (4) by the filtrate pump (15); The slurry at the bottom of the absorption tower (4) enters the ammonium sulfate cyclone (8) and the centrifuge (7) through the ammonium sulfate discharge pump (9) to separate ammonium sulfate crystals. The slurry in the ammonium sulfate cyclone (8) flows back to the bottom of the absorption tower (4) to continue heat absorption and concentration crystallization.

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