SNCR (selective non-catalytic reduction) denitration system and method for circulating fluidized bed boiler

Abstract

The invention belongs to the technical field of denitration of circulating fluidized bed boilers, and discloses an SNCR (selective non-catalytic reduction) denitration system and method for a circulating fluidized bed boiler. The compressed air subsystem is used for supplying compressed air; the denitration raw material subsystem comprises a denitration reducing agent module and a denitration additive module; the denitration reducing agent module is used for supplying a denitration reducing agent, and the denitration additive module is used for supplying a denitration additive; the denitration reducing agent is an ammonia water solution with a preset concentration, and the denitration additive is an ethanol solution with a preset concentration; the raw material distribution and injection subsystem is used for injecting a denitration reducing agent or a mixed solution of the denitration reducing agent and a denitration additive to a preset area of the circulating fluidized bed boiler by using compressed air; according to the invention, ethanol is introduced as a denitration additive, so that the temperature required by denitration reaction is reduced, the lower limit of a conventional SNCR denitration temperature window is expanded from 850 DEG C to 650 DEG C, and the SNCR denitration efficiency is improved by more than 30%.

Description

Technical Field

[0001] The invention belongs to the technical field of circulating fluidized bed boiler denitration, and in particular relates to an SNCR denitration system and method for a circulating fluidized bed boiler. Background Art

[0002] The flue gas produced by coal combustion contains smoke, sulfur dioxide (SO2), nitrogen oxides (NO x ) and other atmospheric pollutants. Environmental pollution caused by coal-based electricity generation is an important factor restricting the development of the power industry. Clean coal technology uses a variety of advanced technologies to reduce environmental pollution generated during coal utilization to a minimum, such as circulating fluidized bed (CFB) combustion technology. The basis of CFB combustion technology is the fluidization principle. As an environmentally friendly combustion equipment, circulating fluidized bed boilers use low temperature, low oxygen and air staging to achieve low nitrogen combustion, NO x The amount of NO generated is lower than that of pulverized coal boilers; according to the difference in coal types and changes in combustion conditions, NO x The emission value is generally between 150-300mg / m 3 between.

[0003] SNCR denitrification technology is a denitrification method that uses a reducing agent (mostly 5% dilute ammonia or 10% urea solution) to reduce NO in flue gas to nitrogen (N2) and water (H2O) in the absence of a catalyst. The high-efficiency temperature range of the reducing agent is called the temperature window, and the optimal temperature window is generally 850-1100℃. CFB boilers using SNCR denitrification technology can generally achieve a denitrification efficiency of 60%-80%. CFB boilers using low-nitrogen combustion technology can generally reduce NO x The original emission concentration is controlled at 200mg / m 3 Below, further use of SNCR denitrification can achieve 50mg / m 3 Ultra-low emission requirements.

[0004] In recent years, based on the requirements of deep peak regulation in the thermal power industry, not only has the load of boilers changed more frequently, but the proportion of low-load operation periods has also increased significantly; when CFB boilers are operated under low-load conditions, the temperature of the reaction area deviates from the denitrification temperature window, resulting in a significant decrease in SNCR denitrification efficiency, and the injected reductant forms a large amount of escaped ammonia without participating in the denitrification reaction; secondly, CFB boilers have strong fuel adaptability and can be mixed with a large proportion of unconventional solid fuels such as biomass, urban sludge, garbage-derived fuels, and solid waste. Mixing or burning unconventional solid fuels can achieve resource utilization of waste while disposing of solid waste. Unconventional fuels generally have low content of combustible substances such as C and H, high content of moisture and ash, and low heat release during combustion, while the heat capacity of the flue gas components generated by combustion is large, resulting in a combustion temperature lower than that of coal-fired conditions; therefore, under the deep peak regulation conditions of conventional coal-fired CFB boilers, most CFB boilers that mix / burn unconventional solid fuels have low furnace outlet temperatures, generally in the range of 700-750°C, and cannot achieve efficient denitrification. Summary of the invention

[0005] In view of the technical problems existing in the prior art, the present invention provides a SNCR denitrification system and method for a circulating fluidized bed boiler to solve the technical problem that when the CFB boiler is deeply peak-shaving or burning unconventional solid fuels, the temperature in the denitrification reaction area deviates from the denitrification temperature window, resulting in low SNCR denitrification efficiency and inability to achieve efficient denitrification.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention provides a SNCR denitration system for a circulating fluidized bed boiler, comprising a compressed air subsystem, a denitration raw material subsystem, and a raw material distribution and injection subsystem;

[0008] The compressed air subsystem is used to supply compressed air to the raw material distribution and injection subsystem;

[0009] The denitration raw material subsystem includes a denitration reducing agent module and a denitration additive module; the denitration reducing agent module is used to supply the denitration reducing agent to the raw material distribution and injection subsystem, and the denitration additive module is used to supply the denitration additive to the raw material distribution and injection subsystem; wherein the denitration reducing agent is an ammonia solution of a preset concentration, and the denitration additive is an ethanol solution of a preset concentration;

[0010] The raw material distribution and injection subsystem is used to use compressed air as atomizing air and cooling air to inject the denitration reducing agent or a mixed solution of the denitration reducing agent and the denitration additive into a preset area of ​​the circulating fluidized bed boiler.

[0011] Further, the raw material distribution and injection subsystem includes a first additive switch valve, a second additive switch valve, a first distribution mixer, a second distribution mixer, a first injector and a second injector;

[0012] The inlet of the first additive switch valve and the inlet of the second additive switch valve are both connected to the outlet of the deNOx additive module, the outlet of the first additive switch valve is connected to the first liquid inlet end of the first distribution mixer, and the outlet of the second additive switch valve is connected to the first liquid inlet end of the second distribution mixer; the second liquid inlet end of the first distribution mixer and the second liquid inlet end of the second distribution mixer are both connected to the outlet of the deNOx reductant module; the first inlet of the first injector and the first inlet of the second injector are both connected to the outlet of the compressed air subsystem; the liquid outlet end of the first distribution mixer is connected to the second inlet of the first injector, and the liquid outlet end of the second distribution mixer is connected to the second inlet of the second injector.

[0013] Furthermore, both the first injector and the second injector are gas-liquid dual-fluid injectors.

[0014] Furthermore, the first ejector is arranged in the furnace of the circulating fluidized bed boiler or at the inlet flue of the high-temperature separator; the second ejector is arranged in the tail flue of the circulating fluidized bed boiler and placed between the high-temperature superheater and the low-temperature superheater of the circulating fluidized bed boiler.

[0015] Furthermore, the compressed air subsystem includes an air compressor and an air storage tank; the outlet of the air compressor is connected to the inlet of the air storage tank, and the outlet of the air storage tank is connected to the first inlet of the first injector and the first inlet of the second injector.

[0016] Furthermore, the denitration reducing agent module includes an ammonia water storage tank, an ammonia water delivery pump, an ammonia water dilution mixer, a dilution water tank and a dilution water pump;

[0017] The ammonia water storage tank stores raw ammonia water, and the outlet of the ammonia water storage tank is connected to the inlet of the ammonia water delivery pump; the dilution water tank stores demineralized water, and the outlet of the dilution water tank is connected to the inlet of the dilution water pump; the outlet of the ammonia water delivery pump is connected to the first liquid inlet end of the ammonia water dilution mixer;

[0018] The dilution water tank stores desalted water, the outlet of the dilution water tank is connected to the inlet of the dilution water pump, the outlet of the dilution water pump is connected to the second liquid inlet end of the ammonia dilution mixer, and the liquid outlet end of the ammonia dilution mixer is connected to the second liquid inlet end of the first distribution mixer and the second liquid inlet end of the second distribution mixer.

[0019] Furthermore, the denitrification additive module includes an ethanol storage tank and an ethanol delivery pump, wherein ethanol is stored in the ethanol storage tank, an outlet of the ethanol storage tank is connected to an inlet of the ethanol delivery pump, and an outlet of the ethanol delivery pump is connected to both an inlet of the first additive switch valve and an inlet of the second additive switch valve.

[0020] Furthermore, the molar ratio of ethanol to ammonia in the mixed solution of the denitration reducing agent and the denitration additive is 0.1-0.8.

[0021] The present invention also provides an SNCR denitration method for a circulating fluidized bed boiler, using the SNCR denitration system for a circulating fluidized bed boiler;

[0022] Wherein, the SNCR denitrification method for a circulating fluidized bed boiler comprises:

[0023] Spray denitrification reducing agent or a mixed solution of denitrification reducing agent and denitrification additive into the preset area of ​​the circulating fluidized bed boiler to remove NO in the flue gas x .

[0024] Furthermore, the process of spraying the denitration reducing agent or the mixed solution of the denitration reducing agent and the denitration additive into the preset area of ​​the circulating fluidized bed boiler is as follows:

[0025] When the flue gas temperature in the preset area of ​​the circulating fluidized bed boiler is 650-750℃, a mixed solution of denitrification reducing agent and denitrification additive is sprayed to remove NO in the flue gas. x ;

[0026] When the flue gas temperature in the preset area of ​​the circulating fluidized bed boiler exceeds 750℃, the denitrification reducing agent is injected to remove NO in the flue gas. x .

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The SNCR denitration system and method for a circulating fluidized bed boiler provided by the present invention introduces a denitration additive module to supply an ethanol solution of a preset concentration as a denitration additive to a raw material distribution and injection subsystem, so that a denitration reducing agent or a mixed solution of a denitration reducing agent and a denitration additive is sprayed to a preset area of ​​the circulating fluidized bed boiler by using the raw material distribution and injection subsystem; by introducing ethanol as a denitration additive, free radicals such as H and OH generated by the dehydrogenation reaction of ethanol itself promote the denitration reaction, and CO generated by the incomplete oxidation reaction also has a certain promoting effect on denitration, thereby reducing the temperature required for the denitration reaction, achieving the expansion of the lower limit of the conventional SNCR denitration temperature window from 850°C to 650°C, and being able to improve the SNCR denitration efficiency by more than 30%, effectively covering coal-fired CFB boiler units participating in deep peak regulation, and CFB boilers that burn unconventional solid fuels such as biomass and solid waste; the system structure of the present invention is simple, and can be easily switched between a low-temperature SNCR denitration mode and a conventional SNCR denitration mode, and can achieve a better denitration effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 This is a structural block diagram of the SNCR denitration system for a circulating fluidized bed boiler provided in Example 1.

[0031] Among them, 1 air compressor, 2 air storage tank, 3 pressure reducing valve, 4 gas flow meter; 5 raw ammonia pipeline interface, 6 ammonia storage tank, 7 ammonia delivery pump, 8 ammonia flow meter, 9 ammonia regulating valve, 10 ammonia dilution mixer; 11 desalted water pipeline interface, 12 dilution water tank, 13 dilution water pump, 14 dilution water flow meter, 15 dilution water regulating valve; 16 ethanol storage tank, 17 ethanol delivery pump, 18 ethanol flow meter, 19 ethanol regulating valve; 20 first reducing agent flow meter, 21 first reducing agent regulating valve , 22 second reducing agent flowmeter, 23 second reducing agent regulating valve; 24 first additive switching valve, 25 second additive switching valve; 26 first distribution mixer, 27 second distribution mixer; 28 first injector, 29 second injector; 30 first thermometer, 31 second thermometer; 100 furnace, 200 high-temperature separator inlet flue, 300 high-temperature separator; 400 tail flue, 500 high-temperature superheater, 600 low-temperature superheater, 700 economizer, 800 air preheater. DETAILED DESCRIPTION

[0032] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the technical solutions in the embodiments of this application will be described clearly and completely in combination with the drawings in the embodiments of this application; obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0033] Example 1

[0034] As attached Figure 1 As shown, this embodiment 1 provides an SNCR denitration system for a circulating fluidized bed boiler, including a compressed air subsystem, a denitration raw material subsystem and a raw material distribution and injection subsystem; the compressed air subsystem is used to supply compressed air to the raw material distribution and injection subsystem; the denitration raw material subsystem includes a denitration reductant module and a denitration additive module; the denitration reductant module is used to supply the denitration reductant to the raw material distribution and injection subsystem, and the denitration additive module is used to supply the denitration additive to the raw material distribution and injection subsystem; wherein the denitration reductant is an ammonia solution of a preset concentration, and the denitration additive is an ethanol solution of a preset concentration; the raw material distribution and injection subsystem is used to use compressed air as atomizing wind and cooling wind to spray the denitration reductant or a mixed solution of the denitration reductant and the denitration additive into a preset area of ​​the circulating fluidized bed boiler.

[0035] In this embodiment 1, the compressed air subsystem includes an air compressor 1, an air tank 2, a pressure reducing valve 3 and a gas flow meter 4; the outlet of the air compressor 1 is connected to the inlet of the air tank 2, the outlet of the air tank 2 is connected to the inlet of the pressure reducing valve 3, and the outlet of the pressure reducing valve 3 is connected to the inlet of the gas flow meter 4; preferably, the pressure reducing valve 3 adopts a self-operated pressure reducing valve; the outlet of the gas flow meter 4 is divided into two paths, one of which is connected to the first inlet of the first injector 28 in the raw material distribution and injection subsystem, and the other is connected to the first inlet of the second injector 29 in the raw material distribution and injection subsystem.

[0036] It should be noted that the compressed air subsystem produces and supplies the atomizing air and cooling air required by the first injector 28 and the second injector 29. The first injector 28 and the second injector 29 both adopt a gas-liquid dual-fluid structure. During their hot operation, they require 0.3-0.5MPa of compressed air as atomizing air and cooling air to achieve uniform mixing of the reducing agent or the mixed solution of the reducing agent and the additive with the flue gas, promote the denitrification chemical reaction, reduce the temperature of the injector, and prevent high-temperature damage; the number of injectors is arranged according to the boiler flue gas volume, and the amount of atomizing air and cooling air required for each injector is certain. The total amount of compressed air required by the injector can be summarized to control the amount of compressed air produced in the air compressor 1; the gas storage tank 2 plays a role in pressure stabilization and flow buffering; the pressure reducing valve 3 is used to adjust the compressed air pressure to control the pipeline pressure within the design range; the gas flowmeter 4 is used to monitor the gas flow of the compressed air and serve as a parameter for adjusting the gas output of the air compressor 1.

[0037] The working process of the compressed air subsystem is specifically as follows:

[0038] The compressed air with preset pressure and flow requirements is produced by air compressor 1 and enters into air storage tank 2; air storage tank 2 buffers the gas to achieve stable pressure and flow of the outlet compressed air; further, pressure reducing valve 3 is used to adjust the compressed air pressure to within the design range of 0.3-0.5MPa to obtain the compressed air with the pressure and flow required for the hot operation of the ejector; gas flow meter 4 monitors the pipeline gas flow and adjusts the gas output of air compressor 1 in time.

[0039] In this embodiment 1, the denitrification reducing agent module includes an ammonia water storage tank 6, an ammonia water delivery pump 7, an ammonia water flow meter 8, an ammonia water regulating valve 9, an ammonia water dilution mixer 10, a dilution water tank 12, a dilution water pump 13, a dilution water flow meter 14 and a dilution water regulating valve 15.

[0040] The inlet of the ammonia water storage tank 6 is connected to the original ammonia water pipeline interface 5, and the outlet of the ammonia water storage tank 6 is connected to the inlet of the ammonia water delivery pump 7; the outlet of the ammonia water delivery pump 7 is connected to the inlet of the ammonia water flowmeter 8, and the outlet of the ammonia water flowmeter 8 is connected to the inlet of the ammonia water regulating valve 9, and the outlet of the ammonia water regulating valve 9 is connected to the first liquid inlet end of the ammonia water diluted mixed gas 10.

[0041] The inlet of the dilution water tank 12 is connected to the desalted water pipeline interface 11, and the outlet of the dilution water tank 12 is connected to the inlet of the dilution water pump 13; the outlet of the dilution water pump 13 is connected to the inlet of the dilution water flowmeter 14, and the outlet of the dilution water flowmeter 14 is connected to the inlet of the dilution water regulating valve 15, and the outlet of the dilution water regulating valve 15 is connected to the second liquid inlet end of the ammonia dilution mixer 10.

[0042] The liquid outlet end of the ammonia dilution mixer 10 is divided into two paths; wherein the first path is connected to the second liquid inlet end of the first distribution mixer 26 in the raw material distribution and injection subsystem, and the second path is connected to the second liquid inlet end of the second distribution mixer 27 in the raw material distribution and injection subsystem.

[0043] The operation process of the denitration reducing agent module is as follows:

[0044] The concentration of 15% to 20% is connected to the original ammonia pipeline interface 5 by a tank truck or pipeline and transported to the ammonia storage tank 6. The outlet of the ammonia storage tank 6 is connected to the ammonia delivery pump 7, the ammonia flow meter 8 and the ammonia regulating valve 9 in sequence. x Ammonia water is transported according to the removal amount, denitration ammonia nitrogen ratio and other parameters; desalted water is used as dilution water for the denitration reducing agent and is transported to the dilution water tank 12 through the desalted water pipeline interface 11; the outlet of the dilution water tank 12 is connected to the dilution water pump 13, the dilution water flow meter 14 and the dilution water regulating valve 15 in sequence to transport the dilution water according to the concentration requirement of the denitration reducing agent after dilution; ammonia water and dilution water are connected to the ammonia water dilution mixer 10 through their respective delivery pipelines for mixing and dilution to obtain an ammonia solution of preset concentration.

[0045] In this embodiment 1, the denitrification additive module includes an ethanol storage tank 16, an ethanol delivery pump 17, an ethanol flowmeter 18 and an ethanol regulating valve 19; ethanol is stored in the ethanol storage tank 16, the outlet of the ethanol storage tank 16 is connected to the inlet of the ethanol delivery pump 17, the outlet of the ethanol delivery pump 17 is connected to the inlet of the ethanol flowmeter 18, and the outlet of the ethanol flowmeter 18 is connected to the inlet of the ethanol regulating valve 19; the outlet of the ethanol regulating valve 19 is arranged in two ways, one of which is connected to the inlet of the first additive switch valve 24 in the raw material distribution and injection subsystem, and the other is connected to the inlet of the second additive switch valve 25 in the raw material distribution and injection subsystem.

[0046] The denitration additive module, when working, uses the ethanol storage tank 16 to store ethanol with a concentration of more than 90%, and the outlet of the ethanol storage tank 16 is connected to the ethanol delivery pump 17, the ethanol flow meter 18 and the ethanol regulating valve 19 in sequence, and delivers ethanol according to the requirements of the flue gas temperature and the alcohol-ammonia ratio in the denitration reducing agent injection area. It should be noted that the volume of the ammonia water storage tank 6 and the dilution water tank 12 is designed according to the boiler rated load continuous operation for 72 hours, and the volume of the ethanol storage tank 16 can be designed according to the boiler 72 hours low-temperature denitration period; 15% to 20% mass concentration of ammonia water is used and further diluted to 5% mass concentration as the denitration reducing agent, and the denitration additive used is ethanol with a mass concentration of more than 90%.

[0047] Specifically, the standard flue gas volume and NO are calculated and measured based on the boiler fuel quantity, combustion temperature and other conditions. xcontent, the maximum molar ratio of ammonia to NO (ammonia nitrogen ratio, NSR) of the designed SNCR denitrification reducing agent is 3, the consumption of pure ammonia is calculated, and the consumption of 20% ammonia water is further calculated. The volume of the ammonia water storage tank 6 is determined according to the 20% ammonia water consumption when the boiler is running at full load for 72 hours; the mass concentration of ammonia water injected into the flue gas is generally 5%, and the consumption of dilution water is calculated based on this, and the volume of the dilution water tank 12 is determined according to the dilution water consumption when the boiler is running at full load for 72 hours; according to the low-load operation time requirement of the boiler below 40% load per day, the consumption of ethanol is determined in combination with the low-load boiler flue gas volume, flue gas temperature, alcohol-ammonia ratio and other conditions, and the volume of the ethanol storage tank 16 is determined according to the 72-hour ethanol operation time and consumption of the boiler.

[0048] In this embodiment 1, the raw material distribution and injection subsystem includes a first reductant flowmeter 20, a first reductant regulating valve 21, a second reductant flowmeter 22, a second reductant regulating valve 23, a first additive switching valve 24, a second additive switching valve 25, a first distribution mixer 26, a second distribution mixer 27, a first injector 28, a second injector 29, a first thermometer 30 and a second thermometer 31.

[0049] The inlet of the first additive switch valve 24 and the inlet of the second additive switch valve 25 are both connected to the outlet of the denitrification additive module, and are used for the supply or cutoff of ethanol to realize the regional control of the denitrification additive; specifically, the inlet of the first additive switch valve 24 is connected to the first outlet of the ethanol regulating valve 19, and the inlet of the second additive switch valve 24 is connected to the second outlet of the ethanol regulating valve 19; the outlet of the first additive switch valve 24 is connected to the first liquid inlet end of the first distribution mixer 26, and the outlet of the second additive switch valve 25 is connected to the first liquid inlet end of the second distribution mixer 27.

[0050] The second liquid inlet end of the first distribution mixer 26 and the second liquid inlet end of the second distribution mixer 27 are both connected to the outlet of the denitration reductant module; specifically, the second liquid inlet end of the first distribution mixer 26 is connected to the first liquid outlet end of the ammonia dilution mixer 10, and the second liquid inlet end of the second distribution mixer 27 is connected to the second liquid outlet end of the ammonia dilution mixed gas 10; the first reductant flowmeter 20 and the first reductant regulating valve 21 are sequentially arranged between the second liquid inlet end of the first distribution mixer 26 and the first liquid outlet end of the ammonia dilution mixer 10; the second reductant flowmeter 22 and the second reductant regulating valve 23 are sequentially arranged between the second liquid inlet end of the second distribution mixer 27 and the second liquid outlet end of the ammonia dilution mixer 10, for denitration reductant flow control.

[0051] The first inlet of the first injector 28 and the first inlet of the second injector 29 are both connected to the outlet of the compressed air subsystem; specifically, the first inlet of the first injector 28 is connected to the first outlet of the gas flow meter 4, and the first inlet of the second injector 29 is connected to the second outlet of the gas flow meter 4; the liquid outlet end of the first distribution mixer 26 is connected to the second inlet of the first injector 28, and the liquid outlet end of the second distribution mixer 27 is connected to the second inlet of the second injector 29.

[0052] The first ejector 28 and the second ejector 29 are both gas-liquid dual-fluid ejectors, which can be used according to different boiler load conditions, flue gas temperature, NO x The content and denitrification efficiency require the number of gas-liquid dual-fluid injectors to be arranged; among them, the arrangement positions of the gas-liquid dual-fluid injectors are selected from the furnace 100, the high-temperature separator inlet flue 200, and the outlet flue area of ​​the high-temperature superheater 300; it should be noted that the working environment of the gas-liquid dual-fluid injector is a high-temperature environment, and the use of compressed air as cooling wind can reduce the working temperature of the injector, extend its service life, and facilitate the diffusion of the denitrification reducing agent in the flue gas, improve the mass transfer effect, and optimize the denitrification reaction efficiency.

[0053] Specifically, the first injector 28 is arranged at the furnace 100 of the circulating fluidized bed boiler or the inlet flue 200 of the high-temperature separator; the second injector 29 is arranged in the tail flue 400 of the circulating fluidized bed boiler and placed between the high-temperature superheater 500 and the low-temperature superheater 600 of the circulating fluidized bed boiler; the first thermometer 30 is arranged on the side of the first injector 28 to collect the flue gas temperature in the area around the first injector 28; the second thermometer 31 is arranged on the side of the second injector 29 to collect the flue gas temperature in the area around the second injector 29. Ethanol and denitrification reducing agent are both introduced into the distribution mixer, mixed according to the set alcohol-ammonia ratio, and then sprayed into the flue gas at 650-750°C to achieve NO in the flue gas. x removal; thermometers are set in different injection areas to monitor whether the regional flue gas temperature meets the requirements of the low-temperature denitrification temperature range. When the flue gas temperature is higher than 750℃ or lower than 650℃, the SNCR denitrification system should cut off the addition of ethanol.

[0054] In this embodiment 1, diluted ammonia water is directly used as a denitrification reducing agent in the area where the boiler flue gas temperature is above 750°C to remove NO in the flue gas. x , in the low-temperature flue gas temperature range of 650-750℃; due to the deviation from the high-efficiency denitrification temperature window of 850-1100℃ for conventional SNCR denitrification, ammonia water without additives cannot effectively remove NO in flue gas. x; At this time, using ethanol as a denitrification additive can increase the SNCR denitrification efficiency by more than 30%, and can expand the lower limit of the temperature window range of SNCR denitrification to 650°C; It should also be noted that the ejector can be arranged in different temperature zones according to the boiler flue gas flow process in the furnace 100, the high-temperature separator inlet flue 200, and between the high-temperature superheater 500 and the low-temperature superheater 600 in the tail flue 400; However, the ash concentration in the high-temperature separator 300 area is high, and the temperatures of the economizer 700 and the air preheater 800 after the low-temperature superheater 600 are generally lower than 650°C, and it is not suitable to set an ejector.

[0055] Denitrification principle and working process:

[0056] The SNCR denitration system for a circulating fluidized bed boiler described in Example 1, when in use, sprays a denitration reducing agent or a mixed solution of a denitration reducing agent and a denitration additive into a preset area of ​​the circulating fluidized bed boiler to remove NO in the flue gas. x Specifically, ammonia water is used as a denitrification reducing agent, and ethanol is used as a low-temperature denitrification additive. In the flue gas temperature range of 650-750°C, the amount of ethanol added is determined according to the molar ratio of ethanol to ammonia of 0.1-0.8, and the mixed solution is sprayed to achieve NO in the flue gas. x Removal: In the area where the flue gas temperature is above 750℃, no ethanol is added, and only ammonia water is used as a denitrification reducing agent to remove NO in the flue gas. x .

[0057] Among them, the principle of using ethanol as a denitrification additive is as follows:

[0058] Ethanol itself undergoes a dehydrogenation reaction to generate free radicals such as H and OH, which promote the denitrification reaction through the following reaction process (1)-(5); wherein the reaction process (1)-(5) is as follows:

[0059]

[0060] At the same time, the CO produced by the incomplete oxidation reaction of ethanol also promotes denitrification to a certain extent, thereby reducing the temperature required for the denitrification reaction.

[0061] Using the SNCR denitration system for a circulating fluidized bed boiler described in Example 1, an SNCR denitration test was carried out on a kW-level CFB test bench. The results showed that at 650-750°C, as the temperature increased, the SNCR denitration efficiency without additives and with ammonia water as a denitration reducing agent increased from about 6% to about 40%; when ethanol was added at 650°C, as the alcohol-ammonia ratio increased from 0.1 to 0.8, the SNCR denitration efficiency could be increased by 20%-40%; wherein the alcohol-ammonia ratio is the molar ratio of ethanol to ammonia; as the flue gas temperature increased, the effect of the ethanol additive decreased, and when the flue gas temperature was 750°C, the denitration efficiency was increased by a maximum of about 10%; further increasing the flue gas temperature, the addition of additives would inhibit the progress of the SNCR denitration reaction and reduce the denitration efficiency.

[0062] Based on the above principles and test results, for coal-fired CFB boilers participating in deep peak load regulation, when the flue gas temperature in the preset area of ​​the circulating fluidized bed boiler is 650-750℃, a mixed solution of denitrification reducing agent and denitrification additive is sprayed to remove NO in the flue gas. x ; Wherein, the molar ratio of ethanol to ammonia in the mixed solution of the denitrification reducing agent and the denitrification additive is 0.1-0.8; when the flue gas temperature in the preset area of ​​the circulating fluidized bed boiler exceeds 750°C, the denitrification reducing agent is sprayed to remove NO in the flue gas x .

[0063] In this embodiment 1, the compressed air subsystem is used to prepare and supply compressed air, the denitration raw material subsystem is used to prepare and supply denitration reducing agent and denitration additive, and the raw material distribution and injection subsystem is used for the distribution and injection of denitration reducing agent and denitration additive; because the boiler is under a load condition of 40% or more, the flue gas temperature in the high-temperature separator inlet flue 200 is 750-920°C, the first-stage heating surface arranged in the tail flue 400 is a high-temperature superheater 500, and the second-stage heating surface is a low-temperature superheater 60 0, the flue gas temperature between the two-stage heating surface is about 600-720℃; accordingly, it is preferred to arrange the first injector 28 in the high-temperature separator inlet flue 200 area, and arrange the second injector 29 between the high-temperature superheater 500 and the low-temperature superheater 600; after the denitrification additive is transported to the raw material distribution and injection subsystem, it is divided into different branches according to the injector layout area, and each branch is provided with an additive switch valve and a distribution mixer, which are mixed with the diluted ammonia water and then sprayed into the flue gas to realize the zoning control of ethanol.

[0064] When the boiler is under load of 40% or more, the ejector arranged in the 200 area of ​​the high-temperature separator inlet flue can be put into operation. At this time, the flue gas temperature in this area is above 750℃, and the conventional SNCR denitrification mode should be adopted to stop the supply of ethanol; it can also be operated according to NO xEmission situation, and the injector arranged between the high-temperature superheater 500 and the low-temperature superheater 600 is put into operation at the same time. The low-temperature SNCR denitrification mode should be adopted here, and ethanol should be added to improve the denitrification efficiency. The two-stage combination can reduce the consumption of single-stage injection ammonia water to a certain extent, improve the denitrification efficiency, reduce ammonia escape, and reduce dust accumulation and corrosion in the air preheater 800 area.

[0065] When the boiler is operating at a load of less than 40%, and under the condition of stable combustion of the boiler, the flue gas temperature in the high-temperature separator inlet flue 200 area is generally between 680 and 750°C. At this time, the ejector in this area is put into operation, and the low-temperature SNCR denitrification mode is adopted, and ethanol is added; at the same time, the flue gas temperature between the high-temperature superheater 500 and the low-temperature superheater 600 is lower than 600°C, and the ejector in this area should be shut down.

[0066] Compared with conventional SNCR denitration methods and systems, the SNCR denitration system described in Example 1 adds ethanol, a low-temperature SNCR denitration additive, which can expand the lower limit of the denitration temperature window to 650°C, meeting the NO requirements of most coal-fired CFB boilers involved in deep peak regulation. x Ultra-low emission requirements; compared with SCR denitrification, it has the characteristics of simple system, no need to modify the boiler body, no need to add denitrification reactor, etc., and has better economy.

[0067] In this embodiment 1, for the denitrification of low-temperature flue gas from CFB boilers, ammonia water is used as a denitrification reductant and ethanol is used as a low-temperature SNCR denitrification additive, and the lower limit of the conventional SNCR denitrification temperature window is expanded from 850°C to 650°C, covering most coal-fired CFB boiler units involved in deep peak regulation and CFB boilers that burn unconventional solid fuels such as biomass and solid waste; no boiler modification is required, and no additional denitrification reactor and catalyst are required. The system is relatively simple, and the low-temperature SNCR denitrification mode and the conventional SNCR denitrification mode are easy to switch, which can achieve a better denitrification effect.

[0068] Example 2

[0069] The structure and principle of the SNCR denitration system for a circulating fluidized bed boiler provided in this embodiment 2 are basically the same as those of the SNCR denitration system for a circulating fluidized bed boiler described in the above embodiment 1.

[0070] The difference is that it also includes a control subsystem, which is used to control the compressed air subsystem, the denitrification raw material subsystem and the raw material distribution and injection subsystem; specifically, the control subsystem includes a first control module, a second control module, a third control module and a fourth control module.

[0071] The input end of the first control module is connected to the output end of the gas flow meter 4, and the output end of the first control module is connected to the control end of the air compressor 1; wherein, the first control module is used to control the air compressor 1 according to the flow data of compressed air collected by the gas flow meter 4.

[0072] The input end of the second control module is connected to the output ends of the ammonia flowmeter 8 and the dilution water flowmeter 14, and the output end of the second control module is connected to the control ends of the ammonia delivery pump 6, the ammonia regulating valve 9, the dilution water pump 13 and the dilution water regulating valve 15; wherein, the second control module is used to control the ammonia delivery pump 6, the ammonia regulating valve 9, the dilution water pump 13 and the dilution water regulating valve 15 according to the ammonia flow collected by the ammonia flowmeter 8 and the dilution water flow collected by the dilution water flowmeter 14.

[0073] The input end of the third control module is connected to the output end of the ethanol flowmeter 18, and the output end of the third control module is connected to the control ends of the ethanol delivery pump 17 and the ethanol regulating valve 19; wherein, the third control module is used to control the ethanol delivery pump 17 and the ethanol regulating valve 19 according to the ethanol flow collected by the ethanol flowmeter 18.

[0074] The input end of the fourth control module is connected to the output ends of the first reductant flowmeter 20 and the second reductant flowmeter 22, and the output end of the fourth control module is connected to the control ends of the first reductant regulating valve 21 and the second reductant regulating valve 23; wherein, the fourth control module is used to control the first reductant regulating valve 21 and the second reductant regulating valve 23 according to the reductant flow collected by the first reductant flowmeter 20 and the second reductant flowmeter 22.

[0075] The input end of the fifth control module is connected to the output ends of the first thermometer 30 and the second thermometer 31, and the output end of the fifth control module is connected to the control ends of the first additive switch valve 24 and the second additive switch valve 25; wherein, the fifth control module is used to control the first additive switch valve 24 and the second additive switch valve 25 according to the temperature data collected by the first thermometer 30 and the second thermometer 31.

[0076] The SNCR denitration system and method for circulating fluidized bed boilers of the present invention adopts ammonia water as a denitration reducing agent and ethanol as a denitration additive. In the flue gas area with a flue gas temperature of 650-750°C, ethanol is added in an amount according to a molar ratio of ethanol to ammonia of 0.1-0.8, and the mixed solution is sprayed to achieve NO in the flue gas. xCompared with conventional SNCR, the denitration efficiency can be improved by at least 30%; when the flue gas temperature is above 750°C, the use of low-temperature additives will inhibit the denitration reaction of ammonia water, and the supply of low-temperature additives should be cut off. At this time, the SNCR denitration system is converted into a conventional SNCR denitration mode; the present invention does not require the modification of the boiler or the addition of a denitration reactor. In most cases, the supply and mixing device of low-temperature denitration additive ethanol can be added to the original SNCR denitration system to achieve the effect of expanding the lower limit of SNCR denitration temperature.

[0077] The above embodiment is only one of the implementation methods that can realize the technical solution of the present invention. The scope of protection claimed by the present invention is not limited only to this embodiment, but also includes changes, replacements and other implementation methods that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention.

Claims

1. A SNCR denitration system for a circulating fluidized bed boiler, characterized in that: It includes compressed air subsystem, denitrification raw material subsystem and raw material distribution and injection subsystem; The compressed air subsystem is used to supply compressed air to the raw material distribution and injection subsystem; The denitration raw material subsystem includes a denitration reducing agent module and a denitration additive module; the denitration reducing agent module is used to supply the denitration reducing agent to the raw material distribution and injection subsystem, and the denitration additive module is used to supply the denitration additive to the raw material distribution and injection subsystem; wherein the denitration reducing agent is an ammonia solution of a preset concentration, and the denitration additive is an ethanol solution of a preset concentration; The raw material distribution and injection subsystem is used to use compressed air as atomizing air and cooling air to inject the denitration reducing agent or a mixed solution of the denitration reducing agent and the denitration additive into a preset area of ​​the circulating fluidized bed boiler.

2. The SNCR denitration system for a circulating fluidized bed boiler according to claim 1, characterized in that: The raw material distribution and injection subsystem includes a first additive switch valve (24), a second additive switch valve (25), a first distribution mixer (26), a second distribution mixer (27), a first injector (28) and a second injector (29); The inlet of the first additive switch valve (24) and the inlet of the second additive switch valve (25) are both connected to the outlet of the denitration additive module, the outlet of the first additive switch valve (24) is connected to the first liquid inlet end of the first distribution mixer (26), and the outlet of the second additive switch valve (25) is connected to the first liquid inlet end of the second distribution mixer (27); the second liquid inlet end of the first distribution mixer (26) and the second liquid inlet end of the second distribution mixer (27) are both connected to the outlet of the denitration reductant module; the first inlet of the first injector (28) and the first inlet of the second injector (29) are both connected to the outlet of the compressed air subsystem; the liquid outlet end of the first distribution mixer (26) is connected to the second inlet of the first injector (28), and the liquid outlet end of the second distribution mixer (27) is connected to the second inlet of the second injector (29).

3. The SNCR denitration system for a circulating fluidized bed boiler according to claim 2, characterized in that: The first injector (28) and the second injector (29) are both gas-liquid dual-fluid injectors.

4. The SNCR denitration system for a circulating fluidized bed boiler according to claim 2, characterized in that: The first ejector (28) is arranged at the furnace (100) of the circulating fluidized bed boiler or the inlet flue (200) of the high-temperature separator; the second ejector (29) is arranged in the tail flue (400) of the circulating fluidized bed boiler and is placed between the high-temperature superheater (500) and the low-temperature superheater (600) of the circulating fluidized bed boiler.

5. The SNCR denitration system for a circulating fluidized bed boiler according to claim 2, characterized in that: The compressed air subsystem comprises an air compressor (1) and an air storage tank (2); the outlet of the air compressor (1) is connected to the inlet of the air storage tank (2), and the outlet of the air storage tank (2) is connected to the first inlet of the first ejector (28) and the first inlet of the second ejector (29).

6. The SNCR denitration system for a circulating fluidized bed boiler according to claim 2, characterized in that: The denitration reducing agent module comprises an ammonia water storage tank (6), an ammonia water delivery pump (7), an ammonia water dilution mixer (10), a dilution water tank (12) and a dilution water pump (13); The ammonia water storage tank (6) stores raw ammonia water, and the outlet of the ammonia water storage tank (6) is connected to the inlet of the ammonia water delivery pump (7); the dilution water tank (12) stores demineralized water, and the outlet of the dilution water tank (12) is connected to the inlet of the dilution water pump (13); the outlet of the ammonia water delivery pump (7) is connected to the first liquid inlet end of the ammonia water dilution mixer (10); The dilution water tank (12) stores desalted water, the outlet of the dilution water tank (12) is connected to the inlet of the dilution water pump (13), the outlet of the dilution water pump (13) is connected to the second liquid inlet end of the ammonia dilution mixer (10), and the liquid outlet end of the ammonia dilution mixer (10) is connected to the second liquid inlet end of the first distribution mixer (26) and the second liquid inlet end of the second distribution mixer (27).

7. The SNCR denitration system for a circulating fluidized bed boiler according to claim 2, characterized in that: The denitration additive module comprises an ethanol storage tank (16) and an ethanol delivery pump (17), wherein ethanol is stored in the ethanol storage tank (16), an outlet of the ethanol storage tank (16) is connected to an inlet of the ethanol delivery pump (17), and an outlet of the ethanol delivery pump (17) is connected to an inlet of the first additive switch valve (24) and an inlet of the second additive switch valve (25).

8. The SNCR denitration system for a circulating fluidized bed boiler according to claim 1, characterized in that: The molar ratio of ethanol to ammonia in the mixed solution of the denitration reducing agent and the denitration additive is 0.1-0.

8.

9. A SNCR denitration method for a circulating fluidized bed boiler, characterized in that: Utilizing the SNCR denitration system for a circulating fluidized bed boiler as described in any one of claims 1 to 8; Wherein, the SNCR denitrification method for a circulating fluidized bed boiler comprises: Spray denitrification reducing agent or a mixed solution of denitrification reducing agent and denitrification additive into the preset area of ​​the circulating fluidized bed boiler to remove NO in the flue gas x .

10. The SNCR denitration method for a circulating fluidized bed boiler according to claim 9, characterized in that: The process of spraying a denitration reducing agent or a mixed solution of a denitration reducing agent and a denitration additive into a preset area of ​​a circulating fluidized bed boiler is as follows: When the flue gas temperature in the preset area of ​​the circulating fluidized bed boiler is 650-750℃, a mixed solution of denitrification reducing agent and denitrification additive is sprayed to remove NO in the flue gas. x ; When the flue gas temperature in the preset area of ​​the circulating fluidized bed boiler exceeds 750℃, the denitrification reducing agent is injected to remove NO in the flue gas. x .

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