System for eliminating ammonia escape during SCR (selective catalytic reduction) denitration of coal-fired boiler

Abstract

The utility model discloses a system for eliminating escape of SCR (selective catalytic reduction) denitration ammonia of a coal-fired boiler, which comprises an ammonia gas preparation system and an SCR reactor, and the ammonia gas preparation system is connected with the SCR reactor through an ammonia gas conveying pipeline; an inlet flue of the SCR reactor is connected with a boiler economizer flue gas system; an ammonia gas adsorption device is arranged in an outlet flue of the SCR reactor, the ammonia gas adsorption device is a box-type adsorbent bed, an adsorbent is contained in the ammonia gas adsorption device, and the bottom of the ammonia gas adsorption device is connected with an adsorbent output pipeline; the other end of the adsorbent output pipeline is connected with the adsorbent desorption tower, the adsorbent output end of the adsorbent desorption tower is connected with the ammonia gas adsorption device through a desorbed adsorbent pipeline, and the ammonia gas output end of the adsorbent desorption tower is connected with the ammonia gas conveying pipeline through a desorbed ammonia gas pipeline. According to the scheme, excessive ammonia gas is adsorbed in the adsorbent, the problems of ammonia escape during SCR denitration and the like are thoroughly solved, the ammonia gas is reused after desorption, and resources and denitration operation cost are saved.

Description

Technical Field

[0001] The utility model belongs to the technical field of coal-fired boiler flue gas treatment, and in particular relates to a system for eliminating SCR denitration ammonia escape of a coal-fired boiler. Background Art

[0002] As atmospheric environmental problems become increasingly severe, domestic thermal power generation groups have put forward slogans such as "ultra-clean emissions", "near-zero emissions", "ultra-low emissions", and "green power generation". According to the power industry standards and national environmental protection standards, under the situation of ultra-low NOx emissions, the operating efficiency of the flue gas denitrification system of domestic coal-fired power plants is close to the critical value of SCR technology. In order to stably meet the ultra-low emission requirements, the unit operation generally adopts excessive ammonia injection to solve the problem of line operation and meet the emission standards, but it will lead to the following problems:

[0003] (1) Large amounts of ammonia injection lead to large ammonia escape, wasting denitrification absorbent resources and costs;

[0004] (2) Excessive ammonia will react with SO3 to form ammonium bisulfate, which will form a viscous substance below 280°C, blocking subsequent flue gas system equipment such as air preheaters, increasing the power consumption of the induced draft fan, and in severe cases, causing abnormal shutdown;

[0005] (3) The plates and wires of the electrostatic precipitator are covered with dust, which affects the dust removal efficiency;

[0006] (4) The high ammonia content in coal ash affects the comprehensive utilization of coal ash.

[0007] In order to solve the above problems, there are currently two main solutions in China:

[0008] The first is the SCR inlet and outlet flue flow field optimization technology: optimizing the flue flow field allows the flue gas entering the SCR to fully contact with ammonia, making the denitrification reaction more thorough and reducing the excess ammonia injection coefficient.

[0009] The second is precise ammonia injection technology: by accurately measuring the NOx concentration of flue gas before and after the SCR reaction, the ammonia injection grid is controlled in different areas, and the ammonia concentration of the outlet emission index is accurately controlled to reduce excessive ammonia injection.

[0010] Both of them reduce the amount of ammonia injection as much as possible while meeting environmental protection requirements by precisely controlling and changing the reaction flow field, thereby reducing the excess coefficient of ammonia and reducing ammonia escape; however, ammonia escape will still exist and the problem of ammonia escape cannot be completely solved. Utility Model Content

[0011] The technical problem to be solved by the utility model is to provide a system for eliminating ammonia escape from SCR denitration of coal-fired boilers, completely solve the problem of ammonia escape, and achieve the reuse of excess ammonia while meeting ultra-low emission standards and avoiding pollution and blockage, thereby avoiding waste of resources.

[0012] According to the technical scheme of the utility model, the utility model provides a system for eliminating ammonia escape from SCR denitration of a coal-fired boiler, including an ammonia preparation system and an SCR reactor, wherein the ammonia preparation system is connected to the SCR reactor through an ammonia delivery pipeline; the inlet flue of the SCR reactor is connected to the flue gas system of the boiler economizer; an ammonia adsorption device is arranged in the outlet flue of the SCR reactor, the ammonia adsorption device is a box-type adsorbent bed, the ammonia adsorption device contains adsorbent, and the bottom of the ammonia adsorption device is connected to an adsorbent output pipeline; the other end of the adsorbent output pipeline is connected to an adsorbent desorption tower, the adsorbent output end of the adsorbent desorption tower is connected to the ammonia adsorption device through a post-desorption adsorbent pipeline, and the ammonia output end of the adsorbent desorption tower is connected to the ammonia delivery pipeline through a post-desorption ammonia pipeline.

[0013] Furthermore, an adsorption device baffle door is provided at the bottom of the ammonia adsorption device, and an adsorption device bin pump is provided in the adsorbent output pipeline; a desorption tower baffle door is provided at the adsorbent output end of the adsorbent desorption tower, and a desorption tower bin pump is provided in the adsorbent pipeline after desorption; the adsorption device bin pump and the desorption tower bin pump are both connected to a compressed air system.

[0014] Furthermore, the adsorbent desorption tower is also connected to a hot air input pipeline, and an electric heater is arranged in the hot air input pipeline.

[0015] Furthermore, the hot air input duct is connected to the hot air delivery duct at the upstream side of the electric heater.

[0016] Furthermore, there are two adsorbent desorption towers, which are arranged in parallel for alternate use.

[0017] Furthermore, the outlet flue is arranged horizontally; and the adsorbent pipeline after desorption is connected to the top of the ammonia adsorption device.

[0018] Furthermore, an ammonia escape meter is provided at the downstream side of the ammonia adsorption device in the outlet flue.

[0019] Furthermore, the inlet flue is connected to the economizer of the coal-fired boiler system, and the outlet flue is connected to the air preheater of the coal-fired boiler system.

[0020] Furthermore, the SCR reactor includes an ammonia injection grid and a flue gas rectifier which are arranged in sequence from the inlet flue to the outlet flue; and the connection position of the ammonia delivery pipeline to the SCR reactor corresponds to the ammonia injection grid.

[0021] Furthermore, the adsorbent is in the form of particles made from a modified form of molecular sieve or MOFs material.

[0022] Compared with the prior art, the beneficial technical effects of the utility model are as follows:

[0023] The utility model proposes a solution to ammonia escape from SCR denitration of coal-fired boilers in thermal power plants. An ammonia adsorption device is added to the horizontal flue between the SCR outlet and the air preheater inlet to adsorb excess ammonia in the adsorbent. The flue gas after entering the air preheater contains no ammonia, which completely solves the problems of ammonia escape from SCR denitration and subsequent flue blockage caused by ammonia bisulfate. Traditional technical solutions can only reduce ammonia escape but cannot eliminate it; and the precise ammonia injection technology it adopts is based on precise measurement, and the requirements for instruments in this solution are relatively low. In addition, the excess ammonia in this solution can be reused after desorption, saving resources and denitration operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram according to an embodiment of the utility model.

[0025] Description of reference numerals in the accompanying drawings:

[0026] 1. Ammonia preparation system; 2. SCR reactor; 3. Inlet flue; 4. Outlet flue; 5. Ammonia adsorption device; 6. Adsorbent output pipeline; 7. Adsorbent desorption tower; 8. Adsorbent pipeline after desorption; 9. Ammonia pipeline after desorption; 10. Ammonia delivery pipeline; 11. Adsorption device baffle door; 12. Adsorption device silo pump; 13. Desorption tower baffle door; 14. Desorption tower silo pump; 15. Compressed air system; 16. Hot air input pipeline; 17. Electric heater; 18. Primary hot air delivery pipeline; 19. Economizer; 20. Air preheater; 21. Ammonia injection grid; 22. Flue gas rectifier. DETAILED DESCRIPTION

[0027] The utility model provides a system for eliminating ammonia escape from SCR denitration of a coal-fired boiler. An ammonia escape absorption device is arranged at the outlet flue of the SCR reactor to completely eliminate ammonia escape from the SCR denitration. The absorbed ammonia is desorbed and returned to the ammonia injection system for repeated utilization, thereby achieving the goal of meeting ultra-low emission standards, avoiding pollution and blockage, and avoiding waste of resources.

[0028] See also Figure 1The utility model discloses a system for eliminating ammonia escape in SCR denitration of a coal-fired boiler according to an embodiment of the present invention, comprising an ammonia preparation system 1 and an SCR reactor 2. The ammonia preparation system 1 is connected to the SCR reactor 2 through an ammonia delivery pipeline 10, thereby providing the required ammonia as a denitration absorbent to the SCR reactor 2. The inlet flue 3 of the SCR reactor 2 is connected to the flue gas system of the boiler economizer (a structure in the existing coal-fired boiler system, located at the flue gas output side of the coal-fired boiler), so that the raw flue gas to be denitrated generated by the coal-fired boiler enters the SCR reactor 2.

[0029] An ammonia adsorption device 5 is provided in the outlet flue 4 of the SCR reactor 2. The ammonia adsorption device 5 is a box-type adsorbent bed fixedly arranged in the flue, and the flue gas side resistance is about 200Pa. The ammonia adsorption device 5 contains adsorbent, and the bottom of the ammonia adsorption device 5 is connected to an adsorbent output pipeline 6. The other end of the adsorbent output pipeline 6 is connected to an adsorbent desorption tower 7. The adsorbent output end of the adsorbent desorption tower 7 is connected to the ammonia adsorption device 5 through a post-desorption adsorbent pipeline 8. The ammonia output end of the adsorbent desorption tower 7 is connected to the ammonia adsorption device 5 through a post-desorption ammonia pipeline 9. The ammonia output end of the adsorbent desorption tower 7 is connected to the ammonia delivery pipeline 10, thereby realizing the collection and reuse of excess ammonia. An anti-backflow valve is provided on the post-desorption ammonia pipeline 9 to prevent ammonia from the ammonia preparation system 1 from backflowing into the adsorbent desorption tower 7.

[0030] More specifically, an adsorption device baffle door 11 is provided at the bottom of the ammonia adsorption device 5, and an adsorption device bin pump 12 is provided in the adsorbent output pipeline 6. A desorption tower baffle door 13 is provided at the adsorbent output end of the adsorbent desorption tower 7, and a desorption tower bin pump 14 is provided in the adsorbent pipeline 8 after desorption. The adsorption device bin pump 12 and the desorption tower bin pump 14 are both connected to a compressed air system 15. In this solution, the adsorbent is pneumatically conveyed by a bin pump, which has a simple and stable structure and is easy and fast to control. In other feasible embodiments, the adsorbent is conveyed by other means such as a conveyor belt.

[0031] The adsorbent is preferably in the form of a granular modified form of a molecular sieve or MOFs material. In terms of structure, the adsorbent adopts a granular structure, which is easier to transport and is particularly suitable for pneumatic conveying by a silo pump. In terms of materials, the modified form of the molecular sieve or MOFs material is further preferably a MCM-41 deep modified composite material that selectively adsorbs ammonia. The adsorbent of this material can have a good ammonia adsorption effect at 280°C to 430°C corresponding to the high-temperature flue gas of the boiler SCR, and has a good desorption effect under the conditions of reduced pressure and increased temperature.

[0032] The adsorbent desorption tower 7 is constructed separately outside the SCR flue system. The adsorbent has an adsorption capacity at about 300°C to 400°C, for example. After adsorbing a certain amount of ammonia, it needs to be desorbed and the adsorbed ammonia is released. The desorption method is, for example, to introduce sufficient hot air to provide heat to the adsorbent. The adsorbent desorption tower 7 is connected to a hot air input pipe 16, and an electric heater 17 is provided in the hot air input pipe 16, so that high-temperature gas is introduced into the adsorbent desorption tower 7 during the desorption operation. More specifically, for example, the hot air input pipe 16 is connected to a primary hot air delivery pipe 18 on the upstream side of the electric heater 17. In other words, a primary hot air is taken from a pipeline drawn out from the coal-fired boiler system as hot air for desorption. The heating temperature of the electric heater 17 is set to about 480°C, for example, to heat the input primary hot air to ensure that there is enough heat entering the adsorbent desorption tower 7.

[0033] In a preferred embodiment, Figure 1 As shown, there are two adsorbent desorption towers 7, and the two adsorbent desorption towers 7 are arranged in parallel for alternate use; in other words, the two adsorbent desorption towers 7 are connected in parallel, and the corresponding delivery pipelines, warehouse pumps, etc. are also two sets, and there are valves for controlling the on-off, so that the two adsorbent desorption towers 7 are controlled in one use and one standby. More specifically, for example, when the adsorbent of the ammonia adsorption device 5 is input into the left set of adsorbent desorption towers 7 system for desorption, the adsorbent after desorption is already in the adsorbent desorption tower 7 on the right side, and its pipeline system is connected and the adsorbent is input into the ammonia adsorption device 5; vice versa, such alternating use enables the ammonia adsorption device 5 to work continuously.

[0034] More specifically, the outlet flue 4 is a horizontally arranged flue, the desorbed adsorbent pipeline 8 is connected to the top of the ammonia adsorption device 5 (that is, above the outlet flue 4), and the adsorbent output pipeline 6 (and the adsorption device baffle door 11) is located at the bottom of the ammonia adsorption device 5 (that is, below the outlet flue 4), so that gravity can be used to transport the adsorbent at this position and ensure that the adsorption effect is sufficient.

[0035] The inlet flue 3 is connected to the economizer 19 of the coal-fired boiler system, and the outlet flue 4 is connected to the subsequent flue gas system of the coal-fired boiler system, such as the air preheater 20. The SCR reactor 2 includes an ammonia injection grid 21 and a flue gas rectifier 22 arranged in sequence from the inlet flue 3 to the outlet flue 4. The connection position of the ammonia delivery pipeline 10 to the SCR reactor 2 corresponds to the ammonia injection grid 21, for example, the ammonia delivery pipeline 10 is connected to the nozzle structure on the ammonia injection grid 21 to uniformly inject ammonia. The economizer 19 pipeline at the ammonia injection grid 21 transports flue gas from bottom to top.

[0036] The main working process of the preferred embodiment of this scheme is as follows. The flue gas from the economizer and the ammonia from the ammonia preparation system react in the SCR reactor under the action of the catalyst. After the reaction, the excess ammonia is discharged along with the flue gas through the SCR outlet flue. An ammonia adsorption device is set on the horizontal flue of the SCR outlet (the ammonia adsorption device is a fixed box-type adsorbent bed with a flue gas side resistance of about 200Pa). The excess ammonia in the flue gas is adsorbed in the adsorption device, and the flue gas after the ammonia is removed enters the subsequent flue gas system.

[0037] Further preferably, the outlet flue 4 is equipped with an ammonia escape meter (not shown in the figure) on the downstream side of the ammonia adsorption device 5, and preferably the ammonia escape meter is controlled in linkage with the adsorption device bin pump 12 and the desorption tower baffle door 13. As the system runs, ammonia is continuously adsorbed in the ammonia adsorption device 5, and the ammonia escape meter begins to count ammonia. The interlocked adsorption device bin pump 12 opens the desorption tower baffle door 13 under the adsorbent, and the adsorption device bin pump 12 is started to send the adsorbent full of ammonia to the adsorbent desorption tower 7 through the adsorbent output pipeline 6. After the adsorbent desorption tower 7 is positioned at the set position, the desorption tower baffle door 13 under the ammonia adsorption device 5 is closed, and the adsorbent desorption tower baffle door and bin pump that have completed desorption are opened, and the desorbed adsorbent is sent to the ammonia adsorption device 5 for reciprocating circulation; the desorbed ammonia enters the SCR original ammonia delivery pipeline 10 through the post-desorption adsorbent pipeline 8 for reuse. This solution can achieve more automated control.

[0038] In summary, this scheme proposes a solution for ammonia escape in high-temperature SCR denitrification of coal-fired boilers in thermal power plants. An ammonia adsorption device is added to the horizontal flue between the SCR outlet and the air preheater inlet, and all excess ammonia is adsorbed in the adsorbent. There is no ammonia in the flue gas entering the air preheater and subsequent flue gas, which completely solves the problems of ammonia escape from SCR denitrification, blockage of subsequent flue gas system equipment caused by ammonium bisulfate, and dust wrapping in the dust collector. Traditional technical solutions can only reduce ammonia escape but cannot eliminate it; and the precise ammonia injection technology it adopts is based on precise measurement, and this scheme has relatively low requirements for instruments. In addition, the excess ammonia in this scheme can be reused after desorption, saving resources and denitrification operating costs. This scheme can also be further set up on the basis of flue flow field and precise ammonia injection.

Claims

1. A system for eliminating SCR denitrification ammonia escape from coal-fired boilers, characterized in that: The invention comprises an ammonia preparation system (1) and an SCR reactor (2), wherein the ammonia preparation system (1) is connected to the SCR reactor (2) via an ammonia delivery pipeline (10); an inlet flue (3) of the SCR reactor (2) is connected to a boiler economizer flue gas system; An ammonia adsorption device (5) is provided in the outlet flue (4) of the SCR reactor (2), wherein the ammonia adsorption device (5) is a box-type adsorbent bed, wherein the ammonia adsorption device (5) contains an adsorbent, and the bottom of the ammonia adsorption device (5) is connected to an adsorbent output pipeline (6); The other end of the adsorbent output pipeline (6) is connected to an adsorbent desorption tower (7), the adsorbent output end of the adsorbent desorption tower (7) is connected to the ammonia adsorption device (5) via a post-desorption adsorbent pipeline (8), and the ammonia output end of the adsorbent desorption tower (7) is connected to the ammonia delivery pipeline (10) via a post-desorption ammonia pipeline (9).

2. The system for eliminating SCR denitrification ammonia escape in coal-fired boilers according to claim 1 is characterized in that: An adsorption device baffle door (11) is provided at the bottom of the ammonia adsorption device (5), and an adsorption device silo pump (12) is provided in the adsorbent output pipeline (6); A desorption tower baffle door (13) is provided at the adsorbent output end of the adsorbent desorption tower (7), and a desorption tower bin pump (14) is provided in the post-desorption adsorbent pipeline (8); The adsorption device bin pump (12) and the desorption tower bin pump (14) are both connected to a compressed air system (15).

3. The system for eliminating SCR denitrification ammonia escape in coal-fired boilers according to claim 1 is characterized in that: The adsorbent desorption tower (7) is also connected to a hot air input pipeline (16), and an electric heater (17) is provided in the hot air input pipeline (16).

4. The system for eliminating SCR denitration ammonia escape in coal-fired boilers according to claim 3 is characterized in that: The hot air input pipe (16) is connected to a primary hot air delivery pipe (18) on the upstream side of the electric heater (17).

5. The system for eliminating SCR denitration ammonia escape in coal-fired boilers according to claim 1 is characterized in that: There are two adsorbent desorption towers (7), and the two adsorbent desorption towers (7) are arranged in parallel for alternate use.

6. The system for eliminating SCR denitration ammonia escape in coal-fired boilers according to claim 1 is characterized in that: The outlet flue (4) is arranged horizontally; the post-desorption adsorbent pipeline (8) is connected to the top of the ammonia adsorption device (5).

7. The system for eliminating SCR denitration ammonia escape in coal-fired boilers according to claim 1 is characterized in that: The outlet flue (4) is provided with an ammonia escape meter on the downstream side of the ammonia adsorption device (5).

8. The system for eliminating SCR denitration ammonia escape in coal-fired boilers according to any one of claims 1 to 7, characterized in that: The inlet flue (3) is connected to the economizer (19) of the coal-fired boiler system, and the outlet flue (4) is connected to the air preheater (20) of the coal-fired boiler system.

9. The system for eliminating SCR denitration ammonia escape in coal-fired boilers according to any one of claims 1 to 7, characterized in that: The SCR reactor (2) comprises an ammonia injection grid (21) and a flue gas rectifier (22) which are arranged in sequence from the inlet flue (3) to the outlet flue (4); the ammonia delivery pipeline (10) corresponds to the ammonia injection grid (21) at a connection position of the SCR reactor (2).

10. The system for eliminating SCR denitration ammonia escape in coal-fired boilers according to any one of claims 1 to 7, characterized in that: The adsorbent is in the form of particles made from a modified form of molecular sieve or MOFs material.

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