A urea-to-ammonia denitrification system

Abstract

The utility model relates to the field of environmental protection, and discloses a urea-ammonia denitration system, including a urea hydrolysis unit, an ammonia-air mixing unit, and an SCR catalytic unit; an ammonia spraying unit is arranged in the SCR catalytic unit; the ammonia spraying unit is connected to the ammonia-air mixing unit, the ammonia-air mixing unit includes a diffusion tube, an ammonia gas input pipe located in the diffusion tube, and the ammonia gas input pipe is connected to the urea hydrolysis unit; one end of the diffusion tube is connected to a hot air input pipe; the other end of the diffusion tube is connected to the ammonia spraying unit; a heat exchanger is arranged inside the outlet side of the SCR catalytic unit; one end of the heat exchanger is connected to a blast module; the air blown in by the blast module is transported to the hot air input pipe after absorbing heat through the heat exchanger; a heating fan is also connected to the hot air input pipe. The system adopts urea hydrolysis method to produce ammonia, and adopts dual heat sources for heating, which can deal with the problem of crystallization caused by changes in ammonia gas flow.

Description

Technical Field

[0001] The utility model relates to the technical field of environmental protection equipment, in particular to a urea ammonia denitrification system. Background Art

[0002] CN220878384U discloses a device for urea hydrolysis to produce ammonia and to precisely control ammonia spraying in different zones, including an ammonia production system and an ammonia spraying system connected thereto. Its structural characteristics are that the ammonia production system includes a urea dissolution tank, a urea dissolution pump, a urea solution storage tank, a urea solution delivery pump and a urea hydrolysis reactor connected in sequence, and the catalyst tank is connected to the urea hydrolysis reactor via a catalyst pump. The ammonia spraying system includes a regulating and metering module, an ammonia air mixer, an SCR inlet flue and an SCR reactor connected in sequence, and the air is connected to the air intake side of the ammonia air mixer via a dilution fan and a dilution air heater, and an ammonia spraying grid, a flue guide plate and an SCR rectifying grid are arranged in the SCR inlet flue in sequence according to the direction of flue gas flow. The ammonia-containing product gas produced by the urea hydrolysis reactor is input into the regulating and metering module.

[0003] When urea is used to produce ammonia, the air temperature in the ammonia-air mixer needs to be controlled to be sufficient to prevent the low-temperature reverse reaction of ammonia gas, air and carbon dioxide from forming urea crystals after contact.

[0004] In the prior art, the heat source of the ammonia-air mixer comes from the hot air provided by the hot air blower; when the amount of ammonia increases, the heat provided by the hot air blower decreases, and the crystallization problem is inevitable. Utility Model Content

[0005] The purpose of the utility model is to solve the above-mentioned problem and provide a urea-to-ammonia denitrification system, which adopts urea hydrolysis to produce ammonia and adopts dual heat sources for heating, and can cope with the problem of crystallization caused by changes in ammonia flow.

[0006] In order to achieve the above purpose, the utility model provides the following technical solutions:

[0007] A urea-to-ammonia denitration system comprises a urea hydrolysis unit, an ammonia-air mixing unit and an SCR catalytic unit; an ammonia spraying unit is arranged in the SCR catalytic unit; the ammonia spraying unit is connected to the ammonia-air mixing unit, and is characterized in that the ammonia-air mixing unit comprises a diffusion tube and an ammonia gas input pipe located in the diffusion tube, and the ammonia gas input pipe is connected to the urea hydrolysis unit; one end of the diffusion tube is connected to a hot air input pipe; the other end of the diffusion tube is connected to the ammonia spraying unit; a heat exchanger is arranged inside the outlet side of the SCR catalytic unit; one end of the heat exchanger is connected to a blower module; the air blown in by the blower module is transported to the hot air input pipe after absorbing heat through the heat exchanger; a heating fan is also connected to the hot air input pipe.

[0008] Compared with the prior art, the beneficial effects of the utility model are:

[0009] The utility model adopts a urea hydrolysis method to prepare ammonia and adopts dual heat sources for heating, so as to cope with the problem of crystallization caused by the change of ammonia flow rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a schematic structural diagram of Example 1;

[0011] Figure 2 is a schematic structural diagram of the SCR catalytic unit of Example 1;

[0012] Figure 3 is a schematic structural diagram of the ammonia-air mixing unit of Example 1;

[0013] Figure 4 is a stereogram of the ammonia gas inlet pipe and the conical head of Example 1;

[0014] Figure 5 It is an axial cross-sectional view of the ammonia inlet pipe and the conical head of Example 1. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of them. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0016] Example 1

[0017] refer to Figures 1 to 5 A urea-to-ammonia denitration system comprises a urea hydrolysis unit 1, an ammonia-air mixing unit 2, and an SCR catalytic unit 3; an ammonia injection unit 4 is arranged in the SCR catalytic unit 3; the ammonia injection unit 4 is connected to the ammonia-air mixing unit 2, the ammonia-air mixing unit 2 comprises a diffusion tube 21, an ammonia gas input pipe 22 located in the diffusion tube 21, and the ammonia gas input pipe 22 is connected to the urea hydrolysis unit 1; one end of the diffusion tube 21 is connected to a hot air input pipe 23; the other end of the diffusion tube 21 is connected to the ammonia injection unit 4; a heat exchanger 5 is arranged inside the outlet side of the SCR catalytic unit 3; one end of the heat exchanger 5 is connected to a blast module 51; the air blown in by the blast module 51 is transported to the hot air input pipe 23 after absorbing heat through the heat exchanger 5; the hot air input pipe 23 is also connected to a heating fan 24.

[0018] In actual application, high-temperature flue gas is input from the inlet side of the SCR catalytic unit 3, and passes through the ammonia injection unit 4, where ammonia and high-temperature flue gas are mixed; the ammonia injection unit 4 is selected as an ammonia injection grid; the ammonia of the ammonia injection unit 4 comes from the ammonia-air mixing unit 2, and the ammonia-air mixing unit 2 uses two heat sources, the heating fan 24 and the heat exchanger 5, to supply hot air; in general process, the heat exchanger 5 provides heat, because the exhaust gas after catalysis of the SCR catalytic unit 3 is relatively high when it encounters heat, but the characteristic of the heat exchanger 5 is that it cannot change the flow rate significantly, and the air temperature will drop rapidly after the flow rate increases. In order to make up for this defect, the heating fan 24 is introduced. Once the ammonia flow rate increases, the power of the air blowing module 51 of the heat exchanger 5 remains basically unchanged, and the heating fan 24 is started. Under some working conditions with a small ammonia flow rate, the heating fan 24 will be started separately and the heat exchanger 5 will be disabled.

[0019] In a specific application scenario, it is necessary to flexibly switch the use of the heat exchanger 5 and the heating fan 24 according to the disclosure.

[0020] Preferably, the urea hydrolysis unit 1 comprises a urea hydrolyzer 11, a urea solution inlet pipe 12 connected to the urea hydrolyzer 11, a catalyst solution inlet pipe 13, and a waste liquid discharge pipe 14; a discharge port 15 is provided at the top of the urea hydrolyzer 1, and a steam-water separator 16 is provided in the discharge port 15; the discharge port 15 is connected to an ammonia inlet pipe 22. The urea hydrolysis unit 1 also comprises a urea tank 17; the urea solution inlet pipe 12 pumps the solution in the urea tank 17 into the urea hydrolyzer 11 through a pump; the waste liquid discharge pipe 14 is connected to the urea tank 17. In addition, a steam supply pipe 18 is also included; the steam supply pipe 18 is used to provide heat for the urea hydrolyzer 11.

[0021] The urea solution is provided by the urea tank 17, and the urea tank 17 dissolves urea through water; in the normal production process, the urea solution is continuously pumped into the urea hydrolyzer 11 by a pump, and the steam supply pipe 18 heats the solution in the urea hydrolyzer 11 through the shell and tube heat exchanger 5; preferably, the steam supply pipe 18 is also connected to the waste liquid discharge pipe 14, and the dissolution of urea is promoted by inputting water vapor into the urea tank 17;

[0022] More preferably, an ammonia reflux pipe 19 is further included, one end of which is connected to the ammonia input pipe 22 and the other end of which is connected to the urea tank 17 and extends to the lower part of the urea tank 17 .

[0023] In some emergency conditions, it is necessary to greatly reduce the supply of ammonia. In this case, the ammonia reflux pipe 19 is opened to allow the ammonia to flow back to the urea tank 17 to react with water and carbon dioxide in the gas to generate urea.

[0024] In this embodiment, a safety discharge pipe 10 is further provided on the top of the urea hydrolyzer 11, and a safety valve is provided on the safety discharge pipe 10; the safety valve is connected to the ammonia reflux pipe 19. This is a conventional safety setting, and no further explanation is given for this.

[0025] In order to improve the ammonia-air mixing effect, the middle part of the diffuser 21 is a throat 211; the outlet of the ammonia gas inlet pipe 22 is located near the throat 211; the throat 211 is provided with a plurality of guide plates 212 with the same inclination direction. The guide plates 212 are arranged at the throat 211. Since the inner diameter of the throat 211 is significantly smaller than the diameter of other positions of the diffuser 21, the flow velocity is significantly increased, and the guide plates 212 can improve the ammonia-air mixing effect.

[0026] As a further optimization of this embodiment, the output end of the ammonia inlet pipe 22 coincides with the axis of the diffusion pipe 21, and a conical head 213 is provided at the outlet position of the ammonia inlet pipe 22, and the tip of the conical head 213 extends to the inside of the ammonia inlet pipe 22; there is a gap 214 between the conical head 213 and the inner wall of the ammonia inlet pipe 22, the axial section of the conical head 213 is an equilateral triangle, and the diameter of the thick end of the conical head 213 is L1; the outer diameter of the ammonia inlet pipe 22 is L2; ​​the depth of the tip of the conical head 213 extending to the inside of the ammonia inlet pipe 22 is L3; the ratio of L1 to L2 is 170-175:105-110; the ratio of L3 to L1 is 30-35:170-175, the inner diameter of the ammonia inlet pipe 22 is L4; the ratio of L4 to L2 is 85-90:105-110. Preferably, L1 is 172 mm, L2 is 109 mm, L3 is 33.7 mm, and L4 is 89 mm.

[0027] The conical head 213 has two functions. On the one hand, by extending into the interior of the ammonia inlet pipe 22, the ammonia flow rate can be gradually increased. The portion extending into the interior of the ammonia inlet pipe 22 is inclined and serves as a guide. On the other hand, the diameter of the thick end is much larger than the outer diameter of the ammonia inlet pipe 22, so that the ammonia-air mixture can flow and mix along the conical head 213 and be ejected at the edge of the conical head 213.

[0028] Preferably, the conical head 213 and the ammonia gas inlet pipe 22 are connected via a plurality of connecting plates 215; two adjacent connecting plates 215 form a gas channel, and the edge of the connecting plate 215 and the edge of the thick end of the cone are located on the same plane.

[0029] The connecting plate 215 not only connects the conical head 213 and the ammonia inlet pipe 22, but also more importantly constructs at least four evenly distributed gas channels to avoid gas chaos outside the conical head 213, facilitate ejection, and enable the ammonia-air mixture to be further fully and orderly mixed in the throat 211.

[0030] The above is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements or modifications without departing from the principle of the present invention. These improvements or modifications should also be regarded as within the protection scope of the present invention.

Claims

1. A urea-to-ammonia denitrification system, comprising a urea hydrolysis unit, an ammonia-air mixing unit, and an SCR catalytic unit; the SCR catalytic unit is provided with an ammonia injection unit; the ammonia injection unit is connected to the ammonia-air mixing unit, characterized in that: The ammonia-air mixing unit includes a diffusion tube and an ammonia input pipe located in the diffusion tube, wherein the ammonia input pipe is connected to the urea hydrolysis unit; one end of the diffusion tube is connected to a hot air input pipe; the other end of the diffusion tube is connected to an ammonia injection unit; a heat exchanger is provided inside the outlet side of the SCR catalytic unit; one end of the heat exchanger is connected to a blower module; the air blown in by the blower module is transported to the hot air input pipe after absorbing heat through the heat exchanger; the hot air input pipe is also connected to a heating fan.

2. The urea-to-ammonia denitrification system according to claim 1, characterized in that: The urea hydrolysis unit comprises a urea hydrolyzer, a urea solution input pipe connected to the urea hydrolyzer, a catalyst solution input pipe, and a waste liquid discharge pipe; a discharge port is provided on the top of the urea hydrolysis unit, a steam-water separator is provided in the discharge port; the discharge port is connected to the ammonia input pipe.

3. The urea-to-ammonia denitrification system according to claim 2, characterized in that: The urea hydrolysis unit further comprises a urea tank; the urea solution inlet pipe pumps the solution in the urea tank into the urea hydrolyzer through a pump; and the waste liquid discharge pipe is connected to the urea tank.

4. The urea-to-ammonia denitrification system according to claim 3, characterized in that: It also includes a steam supply pipe; the steam supply pipe is used to provide heat for the urea hydrolyzer; the steam supply pipe is also connected to the waste liquid discharge pipe.

5. The urea-to-ammonia denitrification system according to claim 3, characterized in that: It also includes an ammonia reflux pipe, one end of which is connected to the ammonia input pipe and the other end of which is connected to the urea tank and extends to the lower part of the urea tank.

6. The urea-to-ammonia denitrification system according to claim 5, characterized in that: A safety discharge pipe is also provided on the top of the urea hydrolyzer, and a safety valve is provided on the safety discharge pipe; the safety valve is connected to the ammonia reflux pipe.

7. The urea-to-ammonia denitrification system according to claim 1, characterized in that: The middle part of the diffusion tube is the throat; the outlet of the ammonia gas inlet pipe is located near the throat; the throat is provided with a plurality of guide plates with the same inclination direction.

8. The urea-to-ammonia denitrification system according to claim 7, characterized in that: The output end of the ammonia inlet pipe is parallel to or coincides with the axis of the diffusion pipe. A conical head is provided at the outlet of the ammonia inlet pipe, and the tip of the conical head extends into the interior of the ammonia inlet pipe. There is a gap between the conical head and the inner wall of the ammonia inlet pipe.

9. The urea-to-ammonia denitrification system according to claim 8, characterized in that: The axial section of the conical head is an equilateral triangle, the diameter of the thick end of the conical head is L1; the outer diameter of the ammonia inlet pipe is L2; ​​the depth of the tip of the conical head extending into the inside of the ammonia inlet pipe is L3; the ratio of L1 to L2 is 170-175:105-110; the ratio of L3 to L1 is 30-35:170-175, and the inner diameter of the ammonia inlet pipe is L4; the ratio of L4 to L2 is 85-90:105-110.

10. The urea-to-ammonia denitrification system according to claim 9, characterized in that: The conical head and the ammonia gas inlet pipe are connected via a plurality of connecting plates; two adjacent connecting plates form a gas channel, and the edge of the connecting plate and the edge of the thick end of the conical body are located on the same plane.

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