Graded absorption ammonia method-based decarburization apparatus and method

Abstract

Disclosed is a graded absorption ammonia method-based decarburization method. Carbon dioxide in gas is removed by using an absorption circulating liquid containing an ammonium salt, and ammonia escape is controlled while efficient decarburization is achieved by means of graded solution component control and reaction condition control. The graded solution component control comprises concentration gradient control of ammonium carbonate, ammonium bicarbonate, ammonium carbamate, ammonia water, or a combination thereof, and is represented by the molar ratio of total ammonium to total CO2. The reaction condition control comprises temperature control, pH control and pressure control. Flue gas enters a decarburization tower, graded absorption is used, and concentration control, temperature control and multi-point ammonia addition are performed, thereby improving decarburization efficiency, saving the decarburization operation cost, and controlling ammonia escape.

Description

A device and method for decarbonization by graded absorption ammonia Technical Field

[0001] The present invention belongs to the technical field of environmental protection, and in particular relates to a device and method for decarbonization by a graded absorption ammonia method. Background Art

[0002] Climate change is a problem that affects all of human development. CO2 is a major contributor to climate change, and industrial gases produced by chemical production activities contain large amounts of CO2. Anyone seeking to control CO2 emissions on a large scale and address climate change must focus on developing efficient CO2 capture technologies.

[0003] The chemical absorption method using ammonia water as the absorption liquid has the characteristics of strong absorption capacity, low corrosiveness, low regeneration energy consumption, low replenishment cost, is not easily degraded by other components in the flue gas, and can remove multiple acidic gas pollutants at the same time. It has been widely studied by scholars at home and abroad.

[0004] Patent application CN108144428A proposes a staged, multi-point ammonia addition process, primarily divided into a pre-wash section, an absorption section, and a fine particulate matter control section. Each of these sections features several spray layers. The pre-wash section cools the flue gas while concentrating the pre-wash circulating wash liquid. The absorption section absorbs and removes sulfur dioxide from the flue gas, controlling ammonia escape and aerosol formation in each section. Similarly, this method lacks control over CO2 removal from industrial gases.

[0005] Patent CN101524621B provides a flue gas decarbonization system with graded absorption and regeneration, which consists of an absorption system, a regeneration system and a heat exchange system. It has lower energy consumption than traditional technologies. However, this system is only applicable to systems using ethanolamine as a desulfurizer. Energy saving is achieved by controlling the return of multi-stage regeneration liquid to the absorption system.

[0006] Patent application CN200880122376.2 discloses a multi-stage CO2 removal system and method for treating flue gas streams. Using an absorber vessel, the flue gas stream is contacted with an ionic solution containing ammonia at a low temperature of 0-20°C. The solution in the first absorption stage has a higher temperature and a lower ammonia-to-carbon ratio than the solution in the third absorption stage. By maintaining a lower temperature and a lower temperature in the third stage, ammonia slip can be reduced. However, the higher ammonia-to-carbon ratio in the third stage increases ammonia slip. This process still suffers from low decarbonization efficiency, high energy consumption, and significant ammonia slip.

[0007] Summary of the Invention

[0008] A method for decarbonization by graded absorption ammonia is disclosed, which uses an absorption circulating liquid containing ammonium salt to remove carbon dioxide from the gas. By controlling the composition of the graded solution and the reaction conditions, efficient decarbonization is achieved while controlling ammonia escape.

[0009] At 10-30°C and one atmosphere of pressure, the main products of the reaction of CO2 and ammonia are ammonium carbamate and ammonium carbonate. This reaction is reversible.

[0010] Overall chemical reaction formula:

[0011] In the actual reaction process, there are many intermediate reactions, and the general process is as follows:

[0012] Ammonium carbamate hydrolysis:

[0013] NH3 and H2O react:

[0014] The ammonium bicarbonate produced by hydrolysis reacts with ammonia water to form ammonium carbonate:

[0015] Ammonium carbonate absorbs carbon dioxide to form ammonium bicarbonate:

[0016] The above reactions demonstrate the complex chemical reactions between carbon dioxide and ammonia, many of which are reversible and result in complex solution compositions. Improving the efficiency of the CO2-ammonia reaction while minimizing ammonia escape requires rational, graded solution composition control and reaction condition control.

[0017] Graded solution composition control includes concentration gradient control of ammonium carbonate, ammonium bicarbonate, ammonium carbamate, ammonia, or a combination thereof, characterized by the total ammonia to total CO2 molar ratio.

[0018] Reaction condition control includes temperature control, pH control, and pressure control.

[0019] The cooled flue gas contacts the ammonium carbonate generating liquid and the decarbonization absorption liquid in sequence to achieve the coordinated control of ammonium carbonate generation, ammonium carbonate crystallization, carbon dioxide absorption and ammonia escape.

[0020] The ammonium carbonate generating solution is provided with at least one stage of gas-liquid contact, the molar ratio of total ammonia to total CO2 in the solution is 1-3, preferably 1-2, the total ammonia includes ammonia and ammonium radicals; the total CO2 includes free CO2 and carbonized CO2;

[0021] The decarbonization absorption circulating liquid is provided with at least two stages of gas-liquid contact. The molar ratio of total ammonia to total CO2 in the first-stage solution is 1.2-4, preferably 1.4-3.5, more preferably 1.6-3, and most preferably 1.8-2.5. The molar ratio of total ammonia to total CO2 in the solution between the first and last stages is 1.5-4.5, preferably 1.8-4, more preferably 2-3.5. The molar ratio of total ammonia to total CO2 in the last-stage solution is 1-3, preferably 1.2-2.8, more preferably 1.5-2.5, and most preferably 1.6-2.

[0022] The gas-liquid contact form of the ammonium bicarbonate generating liquid is preferably a spray type, a packing type, or a bubbling type, and the gas-liquid contact form of the decarbonization absorption liquid is preferably a spray type or a packing type.

[0023] Temperature control reduces the temperature of the solution through a cold source, and the solution contacts the flue gas to reduce the flue gas temperature. The cold source can be a refrigeration machine to obtain chilled water, and the chilled water cools the solution through a heat exchanger or a coil. The temperature of the ammonium carbonate generation liquid is controlled at 10-30°C, preferably 12-28°C, preferably 15-25°C, and most preferably 16-22°C. The temperature of the first-stage decarbonization absorption liquid is higher than the temperature of the ammonium carbonate generation liquid. The high solution temperature is conducive to reducing the investment in cooling equipment. The temperature of the decarbonization absorption liquid between the first and last stages is usually higher than the temperature of the first-stage decarbonization absorption liquid and the last-stage decarbonization absorption liquid. The temperature of the last-stage decarbonization absorption liquid is lower than the temperature of the ammonium carbonate generation liquid, which can control ammonia escape. Preferably, the temperature of the ammonium carbonate generation circulating liquid is controlled at 15 to 25°C, the temperature of the first-stage decarbonization absorption circulating liquid is higher than the temperature of the ammonium carbonate generation circulating liquid, and the temperature of the last-stage decarbonization absorption circulating liquid is lower than the temperature of the ammonium carbonate generation circulating liquid.

[0024] pH control is achieved by adding ammonia or by solution replacement between stages.

[0025] Ammonia is mainly added to the decarbonization absorption liquid, and can be added separately from multiple stages of the decarbonization absorption liquid. No ammonia is added to the ammonium carbonate generating liquid or a small amount of ammonia is added, and the amount of ammonia added to the decarbonization absorption liquid in the last stage is lower than that in the previous stage or no ammonia is added. Preferably, ammonia is added to the first and second stage decarbonization absorption circulating liquids and the amount of ammonia added to the second stage decarbonization absorption circulating liquid accounts for 80-50wt% of the total ammonia added, preferably 75-55wt%, more preferably 72-57wt%, and most preferably 60-65wt%. No ammonia is added to the last stage decarbonization absorption circulating liquid and the ammonium carbonate generating circulating liquid. Adding ammonia at multiple stages is beneficial to the control of solution composition and the adjustment of solution pH value, and the amount of ammonia escape is controlled while ensuring the decarbonization absorption efficiency. No ammonia is added to the ammonium carbonate generating liquid or a small amount of ammonia is added to ensure the production of ammonium bicarbonate. The amount of ammonia added to the decarbonization absorption liquid in the last stage is lower than that in the previous stage or no ammonia is added, which can effectively control ammonia escape.

[0026] Solution replacement is achieved by transferring the solution from one stage to the next via overflow pipes or pumps, allowing for control of solution composition and pH. The pH of the ammonium bicarbonate solution is lower than that of the decarbonation absorption solution, and the ammonium bicarbonate content is higher than that of the decarbonation absorption solution.

[0027] The pH value of the decarbonization absorption liquid is ≥8.0, preferably ≥8.2, more preferably ≥8.5, and most preferably ≥9.0.

[0028] Pressure control is achieved by installing control valves or liquid seals in the ammonia decarbonization system. Installing control valves or liquid seals on the gas pipeline after the decarbonization absorption zone or after the ammonia escape control system can maintain system pressure as needed.

[0029] The ammonia decarbonization device maintains normal pressure ± 50kPa, preferably normal pressure ± 40kPa, more preferably normal pressure ± 30kPa, and most preferably normal pressure ± 25kPa.

[0030] A device for decarbonization by a graded absorption ammonia method comprises a decarbonization system, an ammonia escape control system, an ammonium bicarbonate treatment system, an ammonia supply system, and a cooling system.

[0031] The decarbonization system adopts zoning control, including the ammonium carbonate generation area and the decarbonization absorption area. The ammonium carbonate generation area is equipped with at least one stage of gas-liquid contactor, and the decarbonization absorption area is equipped with at least two stages of gas-liquid contactors. Equipment / components that only allow gas to pass through are installed between each area and each level.

[0032] One or more layers of demisters are installed after the last stage of the decarbonization absorption zone, and the remaining layers may be equipped with one or more layers of demisters as needed. The demisters may be of the baffle, ridge, filler, wire mesh type, or a combination thereof.

[0033] The ammonia escape control system adopts a multi-stage washing cycle and at least one layer of acid solution washing is set.

[0034] The cooling system is used to reduce the temperature of the ammonium carbonate generation circulating fluid and the decarbonization absorption circulating fluid.

[0035] The ammonium bicarbonate treatment system includes ammonium bicarbonate crystallization equipment and solid-liquid separation equipment.

[0036] The CO2 content in the process gas before decarburization is 6-50v%; preferably 8-40v%; more preferably 10-30v%.

[0037] The CO2 content in the gas after the fractional absorption ammonia treatment of the present invention is 0-10v%; preferably 0-8v%; preferably 0-6v%.

[0038] Clean flue gas SO2≤10mg / Nm 3 , preferably ≤5mg / Nm 3 , better ≤2mg / Nm 3 .

[0039] The net flue gas ammonia escape is ≤20ppm, preferably 15ppm, more preferably 10ppm.

[0040] The CO2 removal efficiency is ≥60%, preferably ≥70%, and more preferably ≥80%.

[0041] The present invention also relates to the following embodiments:

[0042] 1. A method for decarbonization by graded absorption ammonia, characterized in that carbon dioxide in the gas is removed by using an absorption circulating liquid containing ammonium salt, and efficient decarbonization is achieved while controlling ammonia escape by controlling the composition of the graded solution and the reaction conditions.

[0043] 2. The method of embodiment 1, wherein the graded solution composition control is characterized by the total ammonia to total CO2 molar ratio, and the solution composition includes ammonium carbonate, ammonium bicarbonate, ammonium carbamate, ammonia, or a combination thereof.

[0044] 3. As described in Embodiment 1, the reaction condition control includes temperature control, pH control, and pressure control.

[0045] 4. As described in the method of embodiment 2, the flue gas after cooling is sequentially contacted with the ammonium bicarbonate generation circulating liquid and the decarbonization absorption circulating liquid to achieve the coordinated control of ammonium bicarbonate generation, ammonium bicarbonate crystallization, carbon dioxide absorption, and ammonia escape, wherein

[0046] The ammonium bicarbonate generating liquid is provided with at least one stage of gas-liquid contact, and the molar ratio of total ammonia to total CO2 in the solution is 1-3, preferably 1-2, wherein the total ammonia includes ammonia and ammonium radicals; the total CO2 includes free CO2 and carbonized CO2;

[0047] The decarbonization absorption liquid is provided with at least two stages of gas-liquid contact, the molar ratio of total ammonia to total CO2 in the first-stage solution is 1.2-4, preferably 1.4-3.5, more preferably 1.6-3, and most preferably 1.8-2.5, the molar ratio of total ammonia to total CO2 in the solution between the first and last stages is 1.5-4.5, preferably 1.8-4, more preferably 2-3.5, and the molar ratio of total ammonia to total CO2 in the last-stage solution is 1-3, preferably 1.2-2.8, more preferably 1.5-2.5, and most preferably 1.6-2.

[0048] 5. As described in the method of embodiment 4, the gas-liquid contact form of the ammonium bicarbonate generating liquid can be a spray type, a packing type, or a bubbling type, and the gas-liquid contact form of the decarbonization absorption liquid can be a spray type or a packing type.

[0049] 5. As described in the method of embodiment 4, the pH value of the ammonium carbonate generating liquid is lower than that of the decarbonization absorption liquid, and the ammonium bicarbonate content is greater than that of the decarbonization absorption liquid.

[0050] 6. As described in the method of embodiment 4, the pH value of the decarbonization absorption liquid is greater than 8.0, preferably ≥8.2, more preferably ≥8.5, and most preferably ≥9.0.

[0051] 7. As described in the method of embodiment 4, ammonia is mainly added to the decarbonization absorption liquid, no ammonia is added or less ammonia is added to the bicarbonate ammonium generation liquid, and the amount of ammonia added to the decarbonization absorption liquid in the last stage is lower than that in the previous stage or no ammonia is added.

[0052] 8. As described in Embodiment 7, ammonia is added from the decarbonization absorption liquid at multiple stages.

[0053] 9. As described in the method of embodiment 3, the temperature of the ammonium carbonate generating liquid is 10-30°C, preferably 12-28°C, preferably 15-25°C, and most preferably 16-22°C. The temperature of the first-stage decarbonization absorption liquid is higher than the temperature of the ammonium carbonate generating liquid, and the temperature of the last-stage decarbonization absorption liquid is lower than the temperature of the ammonium carbonate generating liquid.

[0054] 10. As described in Embodiment 4, the ammonia decarbonization device maintains normal pressure ± 50 kPa, preferably normal pressure ± 40 kPa, more preferably normal pressure ± 30 kPa, and most preferably normal pressure ± 25 kPa.

[0055] 11. The method according to embodiment 1, characterized in that the clean flue gas SO2 ≤ 10 mg / Nm 3 , preferably ≤5mg / Nm 3 , more preferably less than 2 mg / Nm 3 .

[0056] 12. The method according to embodiment 1, wherein the net flue gas ammonia escape is ≤20 ppm, preferably 15 ppm, and more preferably 10 ppm.

[0057] 13. The method according to embodiment 1 is characterized in that the CO2 removal efficiency is ≥60%, preferably ≥80%.

[0058] 14. A device for graded absorption ammonia decarbonization, characterized by comprising a decarbonization system, an ammonia escape control system, an ammonium bicarbonate treatment system, an ammonia supply system, and a cooling system.

[0059] 15. In the device as described in Implementation Option 14, the decarbonization system adopts zoning control, including a urea generation zone and a decarbonization absorption zone, wherein the urea generation zone is provided with at least one level of gas-liquid contact, and the decarbonization absorption zone is provided with at least two levels of gas-liquid contact, and equipment / components that only allow gas to pass through are provided between each zone and each level.

[0060] 16. As described in Embodiment 14, the device has one or more layers of demisters after the last stage of the decarbonization absorption zone, and the remaining layers may be provided with no demisters or one or more layers as needed. The demisters may be in the form of baffles, ridges, fillers, wire mesh, or a combination thereof.

[0061] 17. In the device as described in Embodiment 14, the ammonia escape control system adopts multi-stage washing cycle control, and at least one layer of acidic solution washing is provided.

[0062] 18. In the apparatus as described in Embodiment 14, a cooling system is used to reduce the temperature of the ammonium carbonate production liquid and the decarbonization absorption liquid.

[0063] 19. In the apparatus as described in Embodiment 14, the ammonium bicarbonate treatment system includes an ammonium bicarbonate crystallization device and a solid-liquid separation device.

[0064] 20. As described in the method of embodiment 3, the flue gas is contacted with the ammonium bicarbonate generating liquid and the decarbonization absorption liquid in sequence to achieve the coordinated control of ammonium bicarbonate generation, ammonium bicarbonate crystallization, carbon dioxide absorption, and ammonia escape, wherein

[0065] Temperature control reduces the temperature of ammonium bicarbonate generating liquid and decarbonization absorption liquid through the cold source. The ammonium bicarbonate generating liquid and decarbonization absorption liquid come into contact with the flue gas to reduce the flue gas temperature.

[0066] pH control is achieved by adding ammonia or replacing the solution between stages.

[0067] Pressure control is achieved by installing a control valve or liquid seal in the ammonia decarbonization system. No pressure control device is required during atmospheric pressure operation. 21. In the method of embodiment 1, the CO2 content of the process gas before decarbonization is 6-50% by volume; preferably 8-40% by volume; more preferably 10-30% by volume; and the CO2 content of the gas after decarbonization is 0-10% by volume; preferably 0-8% by volume; and more preferably 0-6% by volume.

[0068] 22. The method according to embodiment 1 is characterized in that the gas is process gas after ammonia desulfurization. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 is an embodiment

[0070] Process gas 1, ammonium carbonate production zone 2, ammonium carbonate production zone circulation pump 3, ammonium carbonate production zone heat exchanger 4, ammonia 5, decarbonization absorption zone 6, first-stage decarbonization absorption zone 7, liquid collector 8, second-stage decarbonization absorption zone 9, liquid collector 10, third-stage decarbonization absorption zone 11, first-stage decarbonization absorption zone circulation pump 12, first-stage decarbonization absorption zone heat exchanger 13, second-stage decarbonization absorption zone circulation pump 14, second-stage decarbonization absorption zone heat exchanger 15, third-stage decarbonization absorption zone circulation pump 16, third-stage decarbonization absorption zone heat exchanger 17, ammonia escape control system 18, ammonia escape control system water wash zone 19, liquid collector 20, ammonia escape control system acid wash zone 21, ammonia escape control system water wash zone circulation pump 22, desulfurization circulating liquid return 23, circulating liquid from ammonia desulfurization system 24, flue gas emission 25, ammonium bicarbonate discharge pump 26, crystallizer 27, solid-liquid separation equipment 28, packaging machine 29, solid ammonium bicarbonate 30 DETAILED DESCRIPTION

[0071] The gas to be treated in the method of the present invention is any suitable gas, preferably the process gas after ammonia desulfurization.

[0072] The CO2 content in the gas is significantly reduced by the fractional ammonia absorption method of the present invention. Specifically, the CO2 content in the process gas before decarbonization is 6-50v%, preferably 8-40v%, and more preferably 10-30v%.

[0073] The CO2 content in the gas after the fractional absorption ammonia treatment of the present invention is 0-10v%; preferably 0-8v%; preferably 0-6v%.

[0074] The method for decarbonization by graded absorption of ammonia protected by the present invention is preferably carried out in a device for decarbonization by graded absorption of ammonia defined in the present invention.

[0075] The beneficial effects of the present invention are mainly reflected in the decarbonization efficiency, ammonia escape, and ammonium bicarbonate fertilizer (abbreviated as ammonium carbonate) production. The decarbonization efficiency achieved by the method according to the present invention is at least 60%, preferably at least 70%, and more preferably at least 80%. After decarbonization, ammonia escape is smaller (between 800-5000ppm), which can reduce the load of the ammonia escape control system, thereby reducing investment costs and operating expenses. Ammonia escape after passing through the ammonia escape control system is ≤20ppm, preferably 15ppm, and more preferably 10ppm. The solid content of ammonium carbonate in the ammonium carbonate generation zone is greater than 2wt%, preferably greater than 5wt%, and more preferably greater than 8wt%. At the same time, the decarbonization device can partially absorb the pollutant SO2 to obtain a lower SO2 concentration, less than 10mg / Nm 3 , preferably less than 5 mg / Nm 3 , more preferably less than 2 mg / Nm 3 .

[0076] Decarburization efficiency = (Q1*w1-Q2*w2) / (Q1*w1)*100%

[0077] Q1 is the dry flue gas flow rate at the decarbonization device inlet under standard conditions, m 3 / h;

[0078] w1 is the volume fraction of carbon dioxide in the flue gas at the inlet of the decarbonization device measured by the instrument, %;

[0079] Q2 is the dry flue gas flow rate at the outlet of the decarbonization device under standard conditions, m 3 / h;

[0080] w1 is the volume fraction of carbon dioxide in the flue gas at the outlet of the decarbonization device measured by the instrument, %.

[0081] The method for testing the SO2 content in the gas in the present invention is HJ 629-2011 Stationary pollution source waste gas. Determination of sulfur dioxide. Non-dispersive infrared absorption method;

[0082] The CO2 content test method is HJ 870-2017 Determination of carbon dioxide in waste gas from stationary pollution sources - Non-dispersive infrared absorption method;

[0083] The NH3 content test method is HJ 533-2009 Determination of ammonia in ambient air and exhaust gas - Nessler's reagent spectrophotometry.

[0084] The present invention provides the following Example 1 and Comparative Examples 1 and 2 to further illustrate the beneficial technical and economic effects of the method and apparatus for graded absorption ammonia decarbonization of the present invention.

[0085] Example 1

[0086] After ammonia desulfurization, process gas 1 enters the ammonium bicarbonate generation zone 2. The solution is cooled by the ammonium bicarbonate generation zone circulation pump 3 and the ammonium bicarbonate generation zone heat exchanger 4, where it reacts with the flue gas to produce ammonium bicarbonate. The ammonium bicarbonate solution / slurry is pumped into a crystallizer 27 via an ammonium bicarbonate discharge pump 26, then passes through a solid-liquid separation device 28 and a packaging machine 29 to produce solid ammonium bicarbonate 30.

[0087] The gas continues to enter the decarbonization absorption zone 6, which includes, from bottom to top, the first-stage decarbonization absorption zone 7, the second-stage decarbonization absorption zone 9, and the third-stage decarbonization absorption zone 11. Each zone is separated by a liquid collector. The liquid collector adopts a tower plate and gas cap structure, allowing the gas to pass from bottom to top and collecting the circulating liquid in the upper area. In the first-stage decarbonization absorption zone 7, the circulating liquid is cooled by the first-stage decarbonization absorption zone circulation pump 12 and the first-stage decarbonization absorption zone heat exchanger 13, and contacts with the flue gas to absorb carbon dioxide. Part of the circulating liquid is removed from the carbon ammonium production zone 2. The gas enters the second-stage decarbonization absorption zone 9 through the liquid collector 8. The circulating liquid is cooled by the second-stage decarbonization absorption zone circulation pump 14 and the second-stage decarbonization absorption zone heat exchanger 15, and contacts with the flue gas to absorb carbon dioxide. Part of the circulating liquid is removed from the first-stage decarbonization absorption zone 7. Ammonia 5 is added to the first-stage decarbonization absorption zone 7 and the second-stage decarbonization absorption zone 9 through a pipeline. The gas enters the third-stage decarbonization absorption zone 11 through the liquid collector 10, and the circulating liquid is cooled by the third-stage decarbonization absorption zone circulation pump 16 and the third-stage decarbonization absorption zone heat exchanger 17, and contacts with the flue gas to absorb carbon dioxide. Part of the circulating liquid goes to the second-stage decarbonization absorption zone 9.

[0088] The gas continues to enter the ammonia escape control system 18. The ammonia escape control system includes, from bottom to top, an ammonia escape control system water washing zone 19 and an ammonia escape control system acid washing zone 21. The two zones are separated by a liquid collector. The liquid collector adopts a tower plate and gas cap structure, allowing the gas to pass from bottom to top and collecting the circulating liquid in the upper zone. In the ammonia escape control system water washing zone 19, the circulating liquid is washed by the ammonia escape control system water washing zone circulating pump 22, and contacts with the flue gas to absorb free ammonia. The gas enters the ammonia escape control system acid washing zone 21 through the liquid collector 20, adopts the circulating liquid 24 from the ammonia desulfurization system, and contacts with the flue gas to absorb free ammonia. The solution after the reaction (i.e., the desulfurization circulating liquid) 23 is returned to the desulfurization system. The flue gas after ammonia removal is discharged 25.

[0089] Temperature control uses a cooling source to lower the circulating fluid temperature. This cooling source, produced by a refrigeration unit, allows the circulating fluid to contact the flue gas, thereby reducing the flue gas temperature. This cooling source utilizes chilled water produced by a refrigeration unit, which is then passed through a plate heat exchanger to cool the circulating fluid. The circulating fluid is sprayed with the flue gas to reduce the flue gas temperature. The circulating fluid temperature for the ammonium bicarbonate generation process is controlled between 20 and 25°C, preferably 22°C. The circulating fluid temperature for the first-stage decarbonization and absorption process is higher than that for the ammonium bicarbonate generation process, while the circulating fluid temperature for the final stage decarbonization and absorption process is lower than that for the ammonium bicarbonate generation process.

[0090] pH is controlled by ammonia addition and solution replacement between stages.

[0091] Ammonia is added to the first and second stage decarbonization absorption circulating liquids and the amount of ammonia added to the second stage decarbonization absorption circulating liquid accounts for 80-50% of the total ammonia added, preferably 60%. No ammonia is added to the third stage decarbonization absorption circulating liquid and the ammonium carbonate generating circulating liquid.

[0092] The solution replacement overflows through the pipeline, transferring the circulating fluid from the previous stage to the next stage, which can control the solution composition and pH value. The pH value of the ammonium carbonate production circulating fluid is lower than that of the decarbonization absorption circulating fluid, and the ammonium bicarbonate content is greater than that of the decarbonization absorption circulating fluid.

[0093] Decarbonization absorption circulating fluid

[0094] The pH value is ≥8.0, preferably ≥8.2, more preferably ≥8.5, and most preferably ≥9.0.

[0095] .

[0096] The system operates at normal pressure (the actual pressure is slightly higher than atmospheric pressure, the specific pressure is shown in the table below), and no pressure control device is set.

[0097] The solution composition and control conditions are shown in the following table:

[0098] Ammonia decarbonization uses 99.6% liquid ammonia as the absorbent. The process gas 1 parameters are shown in Table 1 below:

[0099] Table 1

[0100] The main parameters of the process gas after treatment in the decarbonization absorption zone 6 are shown in Table 2 below:

[0101] Table 2

[0102] The main parameters of the process gas after treatment in the ammonia scrubbing tower 18 are shown in the following table:

[0103] Comparative Example 1

[0104] Compared with Example 1, only the temperature control is different. The temperature control of the first and second decarbonization absorption zones is the same as that of the third zone, both set to 20°C.

[0105] Because the temperature of the first and second decarbonization absorption zones is controlled at a lower temperature, the temperature difference with the cold source is reduced. Therefore, the required heat exchange area of ​​heat exchangers 13 and 14 increases, increasing equipment investment costs. Moreover, when the ambient temperature is 20°C, the cold source of heat exchangers 13 and 15 in the first and second decarbonization absorption zones in Example 1 can be cooled by low-temperature ambient air through an air cooler to save operating costs. In Comparative Example 1, since the ambient temperature is the same as the target temperature, both set at 20°C, air coolers cannot be used for cooling, and cooling can only be achieved with chilled water, which consumes more energy.

[0106] In Comparative Example 2, compared with Example 1, the only difference is the addition of ammonia. Ammonia is added to the ammonium carbonate generation zone and the first, second and third stage decarbonization absorption zones, and the amount of ammonia added to the fourth stage is the same.

[0107] Since the ammonia addition in the ammonium bicarbonate generation zone reached 25%, no ammonium bicarbonate was generated in the solution, and no ammonium bicarbonate crystals were obtained. The addition of 25% ammonia in the third-stage decarbonization absorption zone led to a significant increase in decarbonization ammonia escape, reaching 6000ppm in the process gas after treatment in the decarbonization absorption zone 6.

[0108] From the comparison between the above embodiments of the present invention and the comparative examples, it can be seen that the method and apparatus of the present invention can achieve efficient decarbonization while controlling ammonia escape through graded solution composition control and reaction condition control, thereby achieving excellent technical and economic effects.

[0109] The above description is merely a preferred embodiment of the present invention. Those skilled in the art, once understanding the technical means of the present invention, will naturally be able to modify the present invention according to their actual needs. Therefore, all equivalent changes and modifications made within the scope of the present invention are still covered by the present invention.

Claims

1. A method for decarbonization by graded absorption ammonia, characterized in that: The carbon dioxide in the gas is removed by using an absorption circulating liquid containing ammonium salt. By controlling the composition of the solution and the reaction conditions, efficient decarbonization is achieved while controlling ammonia escape.

2. The method of claim 1 , wherein the graded solution composition control is characterized by a total ammonia to total CO2 molar ratio, and the solution composition comprises ammonium carbonate, ammonium bicarbonate, ammonium carbamate, ammonia, or a combination thereof.

3. The method of claim 1, wherein the reaction conditions are controlled including temperature control, pH control, and pressure control.

4. The method according to claim 2, wherein the flue gas after cooling is sequentially contacted with the ammonium bicarbonate generation circulating liquid and the decarbonization absorption circulating liquid to achieve the coordinated control of ammonium bicarbonate generation, ammonium bicarbonate crystallization, carbon dioxide absorption, and ammonia escape, wherein The ammonium bicarbonate generating liquid is provided with at least one stage of gas-liquid contact, and the molar ratio of total ammonia to total CO2 in the solution is 1-3, preferably 1-2, wherein the total ammonia includes ammonia and ammonium radicals; the total CO2 includes free CO2 and carbonized CO2; The decarbonization absorption liquid is provided with at least two stages of gas-liquid contact, the molar ratio of total ammonia to total CO2 in the first-stage solution is 1.2-4, preferably 1.4-3.5, more preferably 1.6-3, and most preferably 1.8-2.5, the molar ratio of total ammonia to total CO2 in the solution between the first and last stages is 1.5-4.5, preferably 1.8-4, more preferably 2-3.5, and the molar ratio of total ammonia to total CO2 in the last-stage solution is 1-3, preferably 1.2-2.8, more preferably 1.5-2.5, and most preferably 1.6-2.

5. The method according to claim 4, wherein the gas-liquid contact form of the ammonium bicarbonate generating solution can be a spray type, a filler type, or a bubbling type, and the gas-liquid contact form of the decarbonization absorbing liquid can be a spray type or a filler type.

6. The method according to claim 4, wherein the pH value of the decarbonization absorption liquid is greater than 8.0, preferably ≥8.2, more preferably ≥8.5, and most preferably ≥9.

0.

7. The method as claimed in claim 4, wherein ammonia is mainly added to the decarbonization absorption liquid, no ammonia is added or less ammonia is added to the ammonium carbonate generating liquid, and the amount of ammonia added to the decarbonization absorption liquid in the last stage is lower than that in the previous stage or no ammonia is added.

8. The method according to claim 7, wherein ammonia is added from the decarbonization absorption liquid at multiple stages.

9. The method as claimed in claim 3, wherein the temperature of the ammonium carbonate generating liquid is 10-30°C, preferably 12-28°C, preferably 15-25°C, and most preferably 16-22°C, the temperature of the first-stage decarbonization absorption liquid is higher than the temperature of the ammonium carbonate generating liquid, and the temperature of the last-stage decarbonization absorption liquid is lower than the temperature of the ammonium carbonate generating liquid.

10. The method according to claim 4, wherein the ammonia decarbonization device maintains normal pressure ± 50 kPa, preferably normal pressure ± 40 kPa, more preferably normal pressure ± 30 kPa, and most preferably normal pressure ± 25 kPa.

11. The method according to claim 1, wherein Clean flue gas SO2≤10mg / Nm 3 , preferably ≤5mg / Nm 3 , more preferably less than 2 mg / Nm 3 .

12. The method according to claim 1, wherein The net flue gas ammonia escape is ≤20ppm, preferably 15ppm, more preferably 10ppm.

13. The method according to claim 1, wherein The CO2 removal efficiency is ≥60%, preferably ≥80%.

14. A device for decarbonization by graded absorption ammonia method, characterized in that: It includes decarbonization system, ammonia escape control system, ammonium bicarbonate treatment system, ammonia supply system and cooling system.

15. The device as described in claim 14, wherein the decarbonization system adopts zoning control, including a bicarbonate ammonium generation zone and a decarbonization absorption zone, wherein the bicarbonate ammonium generation zone is provided with at least one level of gas-liquid contact, and the decarbonization absorption zone is provided with at least two levels of gas-liquid contact, and equipment / components that only allow gas to pass through are provided between each zone and each level.

16. The device as described in claim 14, wherein one or more layers of demisters are provided after the last stage of the decarbonization absorption zone, and the remaining layers are not provided with demisters, or are provided with one or more layers of demisters as needed, and the demisters are selected from baffles, ridges, fillers and wire mesh types, or a combination thereof.

17. The device according to claim 14, wherein the ammonia escape control system adopts multi-stage washing cycle control, and at least one layer of acidic solution washing is provided.

18. The device as claimed in claim 14, wherein the cooling system is used to reduce the temperature of the ammonium carbonate production liquid and the decarbonization absorption liquid.

19. The device according to claim 14, wherein the ammonium bicarbonate processing system comprises an ammonium bicarbonate crystallization device and a solid-liquid separation device.

20. The method according to claim 3, wherein the flue gas is sequentially contacted with ammonium bicarbonate generating liquid and decarbonization absorption liquid to achieve coordinated control of ammonium bicarbonate generation, ammonium bicarbonate crystallization, carbon dioxide absorption, and ammonia escape, wherein Temperature control reduces the temperature of ammonium bicarbonate generating liquid and decarbonization absorption liquid through the cold source. The ammonium bicarbonate generating liquid and decarbonization absorption liquid come into contact with the flue gas to reduce the flue gas temperature. pH control is achieved by adding ammonia or replacing the solution between stages. Pressure control is achieved by setting a control valve or liquid seal in the ammonia decarbonization system. No pressure control device is provided during normal pressure operation.

21. The method of claim 1, wherein the CO2 content in the process gas before decarburization is 6-50v%; preferably 8-40v%; more preferably 10-30v%; and the CO2 content in the gas after treatment is 0-10v%; preferably 0-8v%; preferably 0-6v%.

22. The method of claim 1, wherein This gas is the process gas after ammonia desulfurization.

23. The method of claim 4, wherein the pH value of the ammonium carbonate generating solution is lower than that of the decarbonization absorption solution, and the ammonium bicarbonate content is greater than that of the decarbonization absorption solution.