Coal-fired boiler SCR denitration ultra-low emission device

Abstract

The utility model belongs to the technical field of flue gas denitration purification, and particularly relates to a coal-fired boiler SCR denitration ultra-low emission device which comprises an SCR layer, a first-stage economizer, a gas flow uniform distribution device, a second-stage economizer and an ammonia water / urea solution tank, and is characterized in that the ammonia water / urea solution tank is communicated with a pyrolysis gasification device; the pyrolysis and gasification device is connected with an ammonia spraying grid through an air duct, the ammonia spraying grid is arranged in a flue behind the first-stage economizer, the pyrolysis and gasification device is sequentially connected with heat exchange equipment I and heat exchange equipment II through pipelines, and the heat exchange equipment II is arranged in a flue behind the second-stage economizer or a flue behind the SCR layer; and the pyrolysis gasification device is communicated with a compressed air pipe. The NOx-containing flue gas purification device can efficiently purify NOx-containing flue gas, and is reliable in operation, low in investment and operation cost, long in service life and free of secondary pollution.

Description

Technical Field

[0001] The utility model belongs to the technical field of flue gas denitrification and purification, and particularly relates to an SCR denitrification ultra-low emission device for coal-fired boilers. Background Technique

[0002] With the continuous advancement of the ultra-low emission transformation work of coal-fired boilers, many coal-fired boiler enterprises have completed the relevant transformation work. For the NOx ultra-low emission technology, most enterprises adopt the SNCR and SCR collaborative denitrification technology. In other words, the ammonia gas that is not reacted in the front-end SNCR is used as the ammonia source for the back-end SCR reaction. However, this collaborative technology has the problem of excessive ammonia injection in the front end. If not well controlled, it is very easy to cause corrosion and damage to the boiler heating surface. In the most serious cases, each boiler enterprise needs to repair or even replace the boiler heating surface during each outage period, bringing additional economic costs to the boiler enterprises.

[0003] The Chinese utility model patent with the application number 202410407090.X discloses a system for ultra-low emission of SNCR and SCR collaborative denitrification of coal-fired boilers. The system includes an SNCR denitrification unit, a primary economizer, an air distribution device, an SCR denitrification unit, and a secondary economizer; the SNCR denitrification unit consists of an ammonia water / urea solution tank, a transfer pump, and a spray gun; the SCR denitrification unit includes an SCR layer. The system can achieve efficient denitrification and purification of flue gas containing NOx in coal-fired boilers, with low investment and operating costs. However, this solution has the problem of being unable to accurately control the ammonia injection volume. Excessive ammonia injection will cause serious boiler corrosion and the phenomenon of excessive ammonia in the chimney exhaust outlet; too little ammonia injection cannot meet the NOx emission limit requirements.

[0004] The Chinese patent with the application number 201520222895.3 discloses a two-stage desulfurization and SCR denitrification device for coal-fired boiler flue gas, including a coal-fired boiler, an electric air inlet valve, a reaction tower, a bag filter, a main fan, a desulfurization tower, a dehumidification and purification tower, a heat pipe heat exchanger, an SCR reactor, an ammonia vaporizer, and a chimney. The coal-fired boiler is sequentially connected to the electric air inlet valve, the reaction tower, the bag filter, the main fan, the desulfurization tower, the dehumidification and purification tower, the heat pipe heat exchanger, the SCR reactor, the ammonia vaporizer, and the chimney. A bypass pipeline is connected between the coal-fired boiler and the inlet of the electric air inlet valve, and the bypass pipeline is connected to the inlet of the chimney. A bypass valve is provided on the bypass pipeline. The outlet of the electric air inlet valve is connected to the gas inlet of the reaction tower. A conical ash collecting tank is connected below the gas inlet of the reaction tower, and the conical ash collecting tank is connected to an electric ash discharge valve. This solution has the disadvantages of being too complex, occupying a large area, having high investment, and being difficult to control in actual operation.

[0005] Therefore, there is a need for further optimization of the SCR denitrification ultra-low emission of coal-fired boilers in the prior art. Especially for the upgrade and transformation of the denitrification process in the coal-fired boiler industry, further optimization and improvement are required. Content of the Utility Model

[0006] The purpose of the present utility model is to provide a SCR denitration ultra-low emission device for a coal-fired boiler, overcoming the deficiencies of the prior art, using a pyrolysis gasification device to obtain ammonia gas rapidly gasified, entering the flue through an ammonia injection grid, realizing the efficient purification of NOx-containing flue gas, and having reliable operation, low investment and operation costs, long service life, and no secondary pollution.

[0007] To achieve the above purpose, the present utility model is realized through the following technical solutions:

[0008] A SCR denitration ultra-low emission device for a coal-fired boiler includes an SCR layer, a primary economizer, an air distribution device, a secondary economizer, and an ammonia water / urea solution tank. The ammonia water / urea solution tank is arranged outside the coal-fired boiler. The primary economizer, the air distribution device, the SCR layer, and the secondary economizer are sequentially arranged in the flue of the coal-fired boiler along the flue gas flow direction. The primary economizer is arranged in the high-temperature section of the flue, with the inlet connected to the boiler water inlet end and the outlet connected to the inlet of the secondary economizer. The secondary economizer is arranged in the low-temperature section of the flue, with the inlet connected to the outlet of the primary economizer and the outlet connected to the boiler water outlet end. The ammonia water / urea solution tank is connected to a pyrolysis gasification device, the pyrolysis gasification device is connected to an ammonia injection grid through a duct, the ammonia injection grid is arranged in the flue behind the primary economizer, the pyrolysis gasification device is sequentially connected to a first heat exchange device and a second heat exchange device through pipelines, and the second heat exchange device is arranged in the flue behind the secondary economizer or in the flue behind the SCR layer; a compressed air pipe is connected to the pyrolysis gasification device.

[0009] Further, the first heat exchange device is a heater or an air preheater. Further, the second heat exchange device is an air preheater.

[0010] Further, a 20-hole and / or 13-hole honeycomb high-dust catalyst layer is laid on the SCR layer.

[0011] Further, a shock wave sootblowing device or a sound wave sootblowing device is arranged on the SCR layer.

[0012] Further, both the first heat exchange device and the second heat exchange device adopt an indirect heat exchange structure.

[0013] Further, the heater is an electric heater or a steam heater.

[0014] Further, the ammonia injection grid is of a modular structure.

[0015] Compared with the prior art, the beneficial effects of the present utility model are as follows:

[0016] 1) Using the ammonia distillation process to provide ammonia for SCR denitration can ensure the long-term stable and reliable operation of the whole system; it has no impact on the boiler heating surface and extends the service life of the heating surface;

[0017] 2) The use of a primary economizer and a secondary economizer with high thermal efficiency can make full use of the heat of flue gas temperature to increase the feed water temperature of the boiler and meet the heating demand;

[0018] 3) The use of an air distribution device with a perforated plate or grid plate structure can ensure the full mixing of flue gas and ammonia, increase the denitration efficiency, and reduce ammonia escape;

[0019] 4) The use of a medium-temperature and high-dust catalyst can effectively ensure the denitration efficiency, prevent blockage, and save replacement costs;

[0020] 5) The use of high-efficiency soot blowing methods such as shock waves and sound waves can ensure the cleanliness of the catalyst surface for a long time, increase the specific surface area, and improve the denitration efficiency;

[0021] 6) The use of electric heating or steam as the heat source of the heater can improve the evaporation efficiency and ensure the stable output of ammonia;

[0022] 7) The use of an efficient ammonia evaporation method can effectively reduce ammonia escape, save ammonia consumption, and reduce operating costs;

[0023] 8) The use of a modular ammonia injection grid is convenient for transportation and installation; the ammonia injection amount of each module can be adjusted separately to effectively reduce ammonia escape; the mixing device can further improve the uniformity of ammonia injection. Description of the Drawings

[0024] Figure 1 is a schematic structural diagram of the first embodiment of the present invention;

[0025] Figure 2 is a schematic structural diagram of the second embodiment of the present invention.

[0026] In the figure: 1 - coal-fired boiler, 2 - primary economizer, 3 - air distribution device, 4 - SCR layer, 5 - secondary economizer, 6 - heat exchange device one, 7 - heat exchange device two, 8 - pyrolysis gasification device, 9 - ammonia injection grid, 10 - flue, 11 - air duct. Detailed Embodiments

[0027] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with specific embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention.

[0028] To more clearly illustrate the specific embodiments of the present utility model or the technical solutions in the prior art, the following will briefly introduce the specific examples required for the description of the specific embodiments or the prior art. Obviously, the specific examples described below are some embodiments of the present utility model. For those of ordinary skill in the art, without creative efforts, other specific examples can be obtained based on these specific examples.

[0029] Generally, the components of the embodiments of the present utility model described and shown in the specific examples here can be arranged and designed in countless different configurations. Therefore, the following detailed description of the embodiments of the present utility model provided in the specific examples is not intended to limit the scope of the present utility model to be protected, but merely represents the selected embodiments of the present utility model.

[0030] See Figure 1 , which is a schematic structural diagram of the first embodiment of an SCR denitration ultra-low emission device for a coal-fired boiler of the present utility model, including an SCR layer 4, a primary economizer 2, an air distribution device 3, a secondary economizer 5, and a pyrolysis gasification device 8. The ammonia water / urea solution tank is arranged outside the coal-fired boiler 1. The primary economizer 2, the air distribution device 3, the SCR layer 4, and the secondary economizer 5 are sequentially arranged in the flue 10 of the coal-fired boiler 1 along the flue gas flow direction. The primary economizer 2 is arranged in the high-temperature section of the flue, with the inlet connected to the boiler water inlet end and the outlet connected to the inlet of the secondary economizer 5. The secondary economizer 5 is arranged in the low-temperature section of the flue, with the inlet connected to the outlet of the primary economizer 2 and the outlet connected to the boiler water outlet end. The ammonia water / urea solution tank (not shown in the figure) is connected to the pyrolysis gasification device 8. The pyrolysis gasification device 8 is connected to the ammonia injection grid 9 through a duct 11. The ammonia injection grid 9 is arranged in the flue behind the primary economizer 2. The pyrolysis gasification device 8 is sequentially connected to a first heat exchange device 6 and a second heat exchange device 7 through pipelines. The second heat exchange device 7 is arranged in the flue behind the secondary economizer 5. The pyrolysis gasification device 8 is connected to a compressed air pipe.

[0031] The first heat exchange device 6 is a heater, and the heater can be an electric heater or a steam heater. The second heat exchange device 7 is an air preheater. A 20-hole and / or 13-hole honeycomb high-dust catalyst layer is laid on the SCR layer 4. A shock wave sootblowing device or a sound wave sootblowing device is arranged on the SCR layer 4. Both the first heat exchange device 6 and the second heat exchange device 7 adopt an indirect heat exchange structure.

[0032] The ammonia injection grid 9 is a modular structure, and each module is provided with an adjustment unit, an injection unit, and a mixing unit.

[0033] When the SCR denitration ultra-low emission device of a coal-fired boiler 1 of the present utility model works, first, the outdoor air is heated to the target gasification temperature after two-stage heat exchange, and then acts on the ammonia water / urea solution to obtain ammonia gas. The specific operation steps are as follows:

[0034] 1) The NOx-containing flue gas discharged from the coal-fired boiler exchanges heat with the boiler feed water in the primary economizer, raising the temperature of the boiler feed water to 40 - 50°C, while the flue gas temperature drops to 320 - 380°C. The NOx-containing flue gas after temperature reduction and the ammonia gas entering the flue through the ammonia injection grid 9 are fully mixed under the action of the air distribution device 3. When the pyrolysis gasification device 8 uses ammonia water as the ammonia source, the flow rate of the ammonia water evaporator is 2.7 - 3.0 m / s, the evaporation temperature is 280 - 290°C, and the residence time is 2.1 - 2.3 s. When using urea as the ammonia source, the flow rate of the urea pyrolyzer is 0.9 - 1.2 m / s, the pyrolysis temperature is 550 - 600°C, and the residence time is 7 - 9 s.

[0035] 2) The fully mixed NOx-containing flue gas and ammonia gas complete the denitrification reaction under the action of the catalyst on the SCR layer. The number of layers of the SCR layer 4 is adjusted according to the initial NOx concentration, with at least 2 layers provided. When the pressure difference between the inlet and outlet of the SCR layer ≥ 1000 Pa, the soot cleaning device is started to clean the SCR layer to ensure the denitrification efficiency.

[0036] 3) The flue gas after denitrification exchanges heat with the boiler feed water again in the secondary economizer 5 and is then transported to the external pipe network for heat supply utilization.

[0037] See Figure 2 , which is the structural schematic diagram of the second embodiment of the SCR denitrification ultra-low emission device for a coal-fired boiler of the present utility model, including an SCR layer 4, a primary economizer 2, an air distribution device 3, a secondary economizer 5, and a pyrolysis gasification device 8. The ammonia water / urea solution tank is arranged outside the coal-fired boiler 1. The primary economizer 2, the air distribution device 3, the SCR layer 4, and the secondary economizer 5 are sequentially arranged in the flue of the coal-fired boiler 1 along the flue gas flow direction. The primary economizer 2 is arranged in the high-temperature section of the flue, with the inlet connected to the boiler feed water end and the outlet connected to the inlet of the secondary economizer 5. The secondary economizer 5 is arranged in the low-temperature section of the flue, with the inlet connected to the outlet of the primary economizer 2 and the outlet connected to the boiler water outlet end. The ammonia water / urea solution tank (not shown in the figure) is connected to the pyrolysis gasification device 8. The pyrolysis gasification device 8 is connected to the ammonia injection grid 9 through a wind duct. The ammonia injection grid 9 is arranged in the flue behind the primary economizer 2. The pyrolysis gasification device 8 is sequentially connected to a heat exchange device one 6 and a heat exchange device two 7 through pipelines. The heat exchange device two 7 is arranged in the flue behind the SCR layer 4. The pyrolysis gasification device 8 is connected to a compressed air pipe.

[0038] The heat exchange device one 6 is an air preheater. The heat exchange device two 7 is also an air preheater. A 20-hole and / or 13-hole honeycomb high-dust catalyst layer is laid on the SCR layer 4. A shock wave soot cleaning device or a sonic soot cleaning device is arranged on the SCR layer 4. Both the heat exchange device one 6 and the heat exchange device two 7 adopt an indirect heat exchange structure.

[0039] The method of the utility model can not only effectively achieve the ultra-low emission of flue gas containing NOx, but also has low investment and operation costs, is low-carbon and environmentally friendly, has a long service life, and does not cause secondary pollution.

[0040] Although the embodiments of the present utility model have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principle and spirit of the present utility model. The scope of the present utility model is defined by the appended claims and their equivalents.

Claims

1. A coal-fired boiler SCR denitrification ultra-low emission device, comprising an SCR layer, a primary economizer, an airflow distribution device, a secondary economizer and an ammonia / urea solution tank, wherein the ammonia / urea solution tank is arranged outside the coal-fired boiler, the primary economizer, the airflow distribution device, the SCR layer and the secondary economizer are arranged in sequence in the flue of the coal-fired boiler along the flue gas flow direction, the primary economizer is arranged in the high-temperature section of the flue, the inlet is connected to the water inlet end of the boiler, and the outlet is connected to the inlet of the secondary economizer; the secondary economizer is arranged in the low-temperature section of the flue, the inlet is connected to the outlet of the primary economizer, and the outlet is connected to the water outlet end of the boiler; it is characterized in that The ammonia / urea solution tank is connected to the pyrolysis gasification device, the pyrolysis gasification device is connected to the ammonia injection grid through an air duct, the ammonia injection grid is arranged in the rear flue of the first-level economizer, the pyrolysis gasification device is connected to the heat exchange device 1 and the heat exchange device 2 in sequence through pipelines, the heat exchange device 2 is arranged in the rear flue of the second-level economizer or in the rear flue of the SCR layer; the pyrolysis gasification device is connected to a compressed air pipe.

2. The SCR denitration ultra-low emission device for a coal-fired boiler according to claim 1 is characterized in that: The first heat exchange device is a heater or an air preheater.

3. The SCR denitration ultra-low emission device for a coal-fired boiler according to claim 1 is characterized in that: The second heat exchange device is an air preheater.

4. The SCR denitration ultra-low emission device for a coal-fired boiler according to claim 1 is characterized in that: The SCR layer is provided with a 20-hole and / or 13-hole honeycomb high-dust catalyst layer.

5. The SCR denitration ultra-low emission device for a coal-fired boiler according to claim 1 is characterized in that: A shock wave cleaning device or a sonic wave cleaning device is arranged on the SCR layer.

6. The SCR denitration ultra-low emission device for a coal-fired boiler according to claim 1, characterized in that: The heat exchange device 1 and the heat exchange device 2 both adopt an indirect heat exchange structure.

7. The SCR denitration ultra-low emission device for a coal-fired boiler according to claim 2 is characterized in that: The heater is an electric heater or a steam heater.

8. The SCR denitration ultra-low emission device for a coal-fired boiler according to claim 1, characterized in that: The ammonia injection grid is a modular structure.

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