SNCR (selective non-catalytic reduction) and SCR (selective catalytic reduction) collaborative denitration ultralow emission system for coal-fired boiler

Abstract

The utility model relates to an SNCR (selective non-catalytic reduction) and SCR (selective catalytic reduction) collaborative denitration ultra-low emission system for a coal-fired boiler. The system comprises an SNCR denitration unit, a primary economizer, an airflow uniform distribution device, an SCR denitration unit and a secondary economizer, the SNCR denitration unit consists of an ammonia water / urea solution tank, a delivery pump and a spray gun; and the SCR denitration unit comprises an SCR layer. The system disclosed by the utility model is simple and reasonable in structure, reliable in operation, low in investment and operation cost, long in service life and free of secondary pollution, and the NOx-containing flue gas of the coal-fired boiler can be efficiently denitrated and purified.

Description

Technical Field

[0001] The utility model relates to the technical field of flue gas purification, and in particular to a system for realizing ultra-low emission by using SNCR and SCR coordinated denitration of a coal-fired boiler. Background Art

[0002] Coal-fired boilers are boilers that use coal as fuel. Coal burns in the furnace to release heat, heating the heat medium water or other organic heat carriers (such as thermal oil, etc.) to a certain temperature (or pressure). Coal-fired boilers are divided into coal-fired water boilers (supplying water), coal-fired hot water boilers (for heating and bathing), coal-fired steam boilers (for supplying steam), coal-fired thermal oil boilers (for steaming and drying), etc. according to their uses.

[0003] my country's energy structure is mainly coal-based. Large-scale and widespread industrial coal-fired boilers consume a lot of coal and are also the main source of coal smoke pollution in my country. As the requirements for energy conservation and environmental protection increase year by year, how to further promote energy conservation and emission reduction while promoting the healthy and steady development of the industry and ensuring the safe operation of industrial coal-fired boilers has become a new topic and severe challenge facing the development of the industrial boiler industry.

[0004] Previously, according to the emission standards for coal-fired boilers (under the condition of 9% oxygen content, NOx emission concentration ≤ 200mg / Nm 3 ), coal-fired boilers generally use the SNCR process for in-furnace denitrification, which can basically meet emission requirements. However, with the implementation of ultra-low emission standards (under the condition of 6% baseline oxygen content, NOx≤50mg / Nm 3 ), the traditional in-furnace SNCR denitrification technology can no longer meet the requirements of emission standards.

[0005] In the process of renovating existing coal-fired boilers, many companies hope to make use of the original SNCR denitrification system as much as possible and carry out renovation on this basis to save investment and cost.

[0006] Based on the above situation, it is urgent to develop a system and method for ultra-low emission of SNCR and SCR coordinated denitrification of coal-fired boilers to achieve upgrading and transformation of the flue gas denitrification process of coal-fired boilers. Summary of the invention

[0007] The utility model provides a SNCR and SCR coordinated denitrification ultra-low emission system for coal-fired boilers, which has a simple and reasonable structure, can realize efficient denitrification and purification of NOx-containing flue gas from coal-fired boilers, and has reliable operation, low investment and operation costs, long service life, and no secondary pollution.

[0008] In order to achieve the above purpose, the utility model adopts the following technical solutions:

[0009] A system for ultra-low emission SNCR and SCR coordinated denitrification of a coal-fired boiler comprises a SNCR denitrification unit, a primary economizer, an airflow distribution device, an SCR denitrification unit and a secondary economizer; the SNCR denitrification unit consists of an ammonia / urea solution tank, a delivery pump and a spray gun, the ammonia / urea solution tank and the delivery pump are arranged outside the coal-fired boiler, the spray gun is arranged in the furnace of the coal-fired boiler near the flue gas outlet, the ammonia / urea solution tank is connected to the spray gun through a delivery pipeline, and a delivery pump is arranged on the delivery pipeline; the SCR denitrification unit comprises an SCR layer; the primary economizer, the airflow distribution device, the SCR layer and the secondary economizer are arranged in the flue of the coal-fired boiler in sequence along the flue gas flow direction.

[0010] Furthermore, the spray gun is arranged in a high temperature zone of 850-1050°C in the coal-fired boiler, and multiple spray guns are arranged on the flue gas flow section. The spray gun adopts a rear end atomizing spray gun, and a compressed air inlet is arranged on the conveying pipeline close to the spray gun to connect the compressed air pipeline.

[0011] Furthermore, the ammonia / urea solution tank, delivery pump, spray gun and delivery pipeline are all made of corrosion-resistant materials.

[0012] Furthermore, the first-stage economizer and the second-stage economizer both adopt smooth tube heat exchangers or fin tube heat exchangers.

[0013] Furthermore, the hot water inlet of the first economizer is connected to the water inlet pipe of the coal-fired boiler, the hot water outlet of the first economizer is connected to the hot water inlet of the second economizer through a pipe, and the hot water outlet of the second economizer is connected to the water supply pipe as the water outlet of the coal-fired boiler.

[0014] Furthermore, the air flow distribution device is a porous plate or a grid plate.

[0015] Furthermore, the SCR layer is arranged in a flue with a flue gas temperature in the range of 320 to 380° C., and the SCR layer is a medium-temperature catalyst layer.

[0016] Furthermore, the medium-temperature catalyst provided in the medium-temperature catalyst layer is a high-dust flue gas denitrification catalyst.

[0017] Furthermore, a dust cleaning device is provided in the flue close to the SCR layer.

[0018] Compared with the prior art, the beneficial effects of the utility model are:

[0019] 1) The use of SNCR and SCR collaborative denitrification process can ensure the long-term stable and reliable operation of the entire system; reduce the workload of the SCR layer catalyst, extend the service life of the catalyst, and reduce operating costs;

[0020] 2) Compared with the SCR denitrification process alone, the SNCR and SCR synergistic denitrification process can eliminate the complex, high-investment, and high-energy-consuming ammonia evaporation system, thereby reducing costs and increasing efficiency;

[0021] 3) The first-stage economizer and the second-stage economizer adopt smooth tubes or finned tube structures with high heat exchange efficiency to achieve efficient utilization of flue gas waste heat and meet heating needs;

[0022] 4) Use an air flow distribution device with a porous plate or grid plate structure to ensure sufficient mixing of flue gas and ammonia, so as to prepare the mixed gas for efficient reaction in the subsequent catalyst layer;

[0023] 5) When the SCR layer uses a medium-temperature catalyst, it can reduce the replacement cost while ensuring the denitration efficiency;

[0024] 6) When the SCR layer uses high-dust catalyst, it can ensure that the catalyst works stably and efficiently for a long time and is not prone to clogging;

[0025] 7) Using shock waves, sound waves and other methods to clean dust can effectively remove dust adhering to the surface of the catalyst, ensuring that the catalyst has enough specific surface area for catalytic reaction and improving denitrification efficiency;

[0026] 8) All SNCR process-related equipment is made of stainless steel to ensure long-term and stable operation of the SNCR liquid delivery system;

[0027] 9) The spray gun is set in the temperature range of 850-1050℃ in the coal-fired boiler, which can give full play to the role of SNCR denitrification, reduce the denitrification load of the subsequent SCR layer, and reduce the operating cost;

[0028] 10) The rear-end atomizing spray gun has a simple internal structure, a large diameter, and is not easy to be blocked, ensuring long-term stable and efficient operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of a system for coordinated denitration and ultra-low emission of SNCR and SCR for a coal-fired boiler described in the utility model.

[0030] In the figure: 1. Coal-fired boiler 2. Primary economizer 3. Airflow distribution device 4. SCR layer 5. Secondary economizer 6. Ammonia / urea solution tank 7. Delivery pump 8. Spray gun 9. Flue 10. Delivery pipeline DETAILED DESCRIPTION

[0031] The specific implementation of the utility model is further described below in conjunction with the accompanying drawings:

[0032] like Figure 1As shown, the SNCR and SCR coordinated denitrification ultra-low emission system of the coal-fired boiler described in the utility model includes an SNCR denitrification unit, a primary economizer 2, an airflow distribution device 3, an SCR denitrification unit and a secondary economizer 5; the SNCR denitrification unit is composed of an ammonia / urea solution tank 6, a delivery pump 7 and a spray gun 8, the ammonia / urea solution tank 6 and the delivery pump 7 are arranged outside the coal-fired boiler 1, the spray gun 8 is arranged in the furnace of the coal-fired boiler 1 near the flue gas outlet, the ammonia / urea solution tank 6 is connected to the spray gun 8 through a delivery pipe 10, and a delivery pump 7 is arranged on the delivery pipe 10; the SCR denitrification unit includes an SCR layer 4; the primary economizer 2, the airflow distribution device 3, the SCR layer 4 and the secondary economizer 5 are arranged in the flue 9 of the coal-fired boiler 1 in sequence along the flue gas flow direction.

[0033] Furthermore, the spray gun 8 is arranged in a high temperature zone of 850-1050°C in the coal-fired boiler 1, and multiple spray guns are arranged on the flue gas flow section. The spray gun 8 adopts a rear end atomizing spray gun, and a compressed air inlet is arranged on the conveying pipeline 10 near the spray gun 8 to connect the compressed air pipeline.

[0034] Furthermore, the ammonia / urea solution tank 6, the delivery pump 7, the spray gun 8 and the delivery pipeline 10 are all made of corrosion-resistant materials.

[0035] Furthermore, the primary economizer 2 and the secondary economizer 5 both adopt smooth tube heat exchangers or fin tube heat exchangers.

[0036] Furthermore, the hot water inlet of the first-level economizer 2 is connected to the water inlet pipe of the coal-fired boiler 1, and the hot water outlet of the first-level economizer 2 is connected to the hot water inlet of the second-level economizer 5 through a pipe, and the hot water outlet of the second-level economizer 5 is connected to the water supply pipe as the water outlet of the coal-fired boiler 1.

[0037] Furthermore, the air flow distribution device 3 is a porous plate or a grid plate.

[0038] Furthermore, the SCR layer 4 is arranged in the flue 9 where the flue gas temperature is in the range of 320-380° C., and the SCR layer 4 is a medium-temperature catalyst layer.

[0039] Furthermore, the medium-temperature catalyst provided in the medium-temperature catalyst layer is a high-dust flue gas denitrification catalyst.

[0040] Furthermore, a dust cleaning device is provided in the flue 9 close to the SCR layer 4 .

[0041] The working principle of the SNCR and SCR coordinated denitrification ultra-low emission system of the coal-fired boiler described in the utility model is as follows:

[0042] 1) Ammonia / urea solution flows out of the ammonia / urea solution tank 6 under the suction of the delivery pump 7, forms a mixed gas with compressed air in the delivery pipe 10 in front of the spray gun 8, is atomized into droplets by the spray gun 8 and sprayed into the high-temperature area in the furnace of the coal-fired boiler 1, and the ammonia / urea solution is vaporized into ammonia gas, and then the SNCR denitration reaction occurs, and the NOx in the flue gas is denitrated in the first stage;

[0043] 2) The excess ammonia that does not participate in the reaction enters the flue 9 with the high-temperature flue gas, and passes through the first-stage economizer 2 to exchange heat with the boiler water, the flue gas temperature is reduced to 320-380°C, and under the action of the air flow distribution device 3, the flue gas and ammonia are fully mixed;

[0044] 3) The mixed gas of flue gas and ammonia enters SCR layer 4, where SCR denitration reaction occurs under the action of medium-temperature catalyst, and secondary denitration of NOx in flue gas is performed;

[0045] 4) The clean flue gas after two-stage denitrification is heat exchanged with boiler feed water again through the secondary economizer 5. The outlet water of the secondary economizer 5 is transported to the external pipe network as boiler outlet water for heating. The clean flue gas after heat exchange meets the emission standards;

[0046] 5) When the inlet and outlet pressure difference of the SCR layer 4 is greater than the set value, the cleaning device is started to clean the SCR layer 4.

[0047] The coal-fired boiler 1 of the utility model is provided with two-stage economizers, wherein the first-stage economizer 2 is provided at the high-temperature section of the coal-fired boiler 1, and the second-stage economizer 5 is provided at the low-temperature section of the coal-fired boiler 1. An SNCR unit is provided in the furnace of the coal-fired boiler 1 upstream of the first-stage economizer 2. SNCR is a selective non-catalytic reduction technology, which is a clean denitrification technology that does not use a catalyst and sprays an amino-containing reducing agent (such as ammonia water, urea solution, etc.) into the furnace within a temperature range of 850 to 1100°C to reduce and remove NOx in the flue gas to generate nitrogen and water.

[0048] In the appropriate temperature range, when ammonia is used as the reducing agent, the reaction equation is: 4NH3+4NO+O2→4N2+6H2O. When urea is used as the reducing agent, the reaction equation is: NO+CO(NH2)2+1 / 2O2→2N2+CO2+H2O. The denitrification efficiency of SNCR flue gas denitrification technology is generally 30% to 80%, which is greatly affected by the structure and size of the boiler.

[0049] The utility model adopts an SCR unit as a supplementary denitration unit. SCR is a selective catalytic reduction technology. Under the action of a catalyst, the reducing agent NH3 reduces NO and NO2 to N2 at a temperature of 290 to 400°C, and almost no oxidation reaction of NH3 occurs, thereby improving the selectivity of N2 and reducing the consumption of NH3.

[0050] The SNCR and SCR coordinated denitrification ultra-low emission system and method for a coal-fired boiler described in the utility model adopts two-stage denitrification of SNCR and SCR, which can not only effectively achieve ultra-low emission of NOx flue gas containing coal-fired boilers, 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.

[0051] The above is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent substitutions or changes within the technical scope disclosed by the present invention according to the technical solution and inventive concept of the present invention, which should be covered by the protection scope of the present invention.

Claims

1. The SNCR and SCR synergistic denitrification ultra-low emission system for coal-fired boilers is characterized by: It includes a SNCR denitrification unit, a primary economizer, an airflow distribution device, an SCR denitrification unit and a secondary economizer; the SNCR denitrification unit consists of an ammonia / urea solution tank, a delivery pump and a spray gun, the ammonia / urea solution tank and the delivery pump are arranged outside the coal-fired boiler, the spray gun is arranged in the furnace of the coal-fired boiler near the flue gas outlet, the ammonia / urea solution tank is connected to the spray gun through a delivery pipeline, and a delivery pump is arranged on the delivery pipeline; the SCR denitrification unit includes an SCR layer; the primary economizer, the airflow distribution device, the SCR layer and the secondary economizer are arranged in the flue of the coal-fired boiler in sequence along the flue gas flow direction.

2. The system for ultra-low emission of SNCR and SCR coordinated denitrification of coal-fired boilers according to claim 1 is characterized in that: The spray gun is arranged in a high temperature zone of 850-1050°C in the coal-fired boiler, and multiple spray guns are arranged on the flue gas flow section. The spray gun adopts a rear-end atomizing spray gun, and a compressed air inlet is arranged on the conveying pipeline close to the spray gun to connect the compressed air pipeline.

3. The system for ultra-low emission of SNCR and SCR coordinated denitrification of coal-fired boilers according to claim 1 is characterized in that: The ammonia / urea solution tank, delivery pump, spray gun and delivery pipeline are all made of corrosion-resistant materials.

4. The system for ultra-low emission of SNCR and SCR coordinated denitrification of coal-fired boilers according to claim 1 is characterized in that: The first-stage economizer and the second-stage economizer both adopt smooth tube heat exchangers or fin tube heat exchangers.

5. The system for ultra-low emission of SNCR and SCR coordinated denitrification of coal-fired boilers according to claim 1 is characterized in that: The hot water inlet of the first economizer is connected to the water inlet pipe of the coal-fired boiler, the hot water outlet of the first economizer is connected to the hot water inlet of the second economizer through a pipe, and the hot water outlet of the second economizer is connected to the water supply pipe as the outlet of the coal-fired boiler.

6. The system for ultra-low emission of SNCR and SCR coordinated denitrification of coal-fired boilers according to claim 1 is characterized in that: The airflow uniform distribution device is a porous plate or a grid plate.

7. The system for ultra-low emission of SNCR and SCR coordinated denitrification of coal-fired boilers according to claim 1 is characterized in that: The SCR layer is arranged in a flue where the flue gas temperature is in the range of 320 to 380° C., and the SCR layer is a medium-temperature catalyst layer.

8. The system for ultra-low emission SNCR and SCR coordinated denitrification of coal-fired boilers according to claim 7 is characterized in that: The medium-temperature catalyst provided in the medium-temperature catalyst layer is a high-dust flue gas denitration catalyst.

9. The system for ultra-low emission of SNCR and SCR coordinated denitrification of coal-fired boilers according to claim 1 is characterized in that: A dust cleaning device is installed in the flue near the SCR layer.

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