A system for combined denitration of circulating fluidized bed boiler under full load condition

Abstract

This utility model discloses a system for combined denitrification under full-load conditions in a circulating fluidized bed boiler, comprising a wide-temperature-range SNCR denitrification module and a flue gas circulation module. The injectors in the wide-temperature-range SNCR denitrification module are arranged in the inlet flue of the high-temperature separator, the inlet flue of the high-temperature superheater, or the boiler furnace. The flue gas circulation module includes a flue gas circulation header and flue gas circulation branch pipes arranged along the flue gas flow direction. The flue gas circulation header connects to the flue gas circulation branch pipes, which are connected to the air preheater via a primary air fan. The inlet of the flue gas circulation header connects to the outlet of the induced draft fan. This utility model extends the lower limit of the conventional 800~1050℃ temperature window to 650℃. It uses ethanol as a low-temperature additive, resulting in relatively low denitrification costs and convenient ethanol addition and removal. Compared with existing SCR denitrification technology, the system is simpler and more economical. It does not require boiler modification, nor does it require additional denitrification reactors and catalysts, making the system relatively simple and facilitating switching between low-temperature denitrification mode and conventional denitrification mode.

Description

Technical Field

[0001] This utility model belongs to the field of environmental protection technology for circulating fluidized bed boilers, specifically relating to a system for combined denitrification under full load conditions of circulating fluidized bed boilers. Background Technology

[0002] Clean coal technology employs various advanced technologies to minimize environmental pollution generated during coal utilization. Among the existing clean coal technologies, purification technologies during coal combustion, such as circulating fluidized bed (CFB) combustion technology, currently possess the advantages of strong adaptability to different coal types and low pollutant generation.

[0003] my country began research and development of CFB boilers in the 1980s, gradually establishing a complete theoretical system for CFB boiler design. Due to their excellent fuel adaptability, ability to co-fire unconventional fuels such as biomass and solid waste, and low pollutant emissions, CFB boilers have been widely applied in my country's power, chemical, and paper industries. Among these, the power industry has the most mature application of CFB boiler technology and has formed a relatively complete industry standard system. It has largely solved problems such as long-term stable operation and efficient control of pollutants under wide loads. Currently, my country has more than 3,000 CFB boilers, including over 400 large-capacity CFB boilers with a capacity of 410 t / h or higher, mainly used in the power industry. Smaller-capacity CFB boilers are widely distributed in the chemical and paper industries. The 700MW ultra-supercritical CFB boiler unit of Yunnan Energy Investment Group's Honghe Power Plant was connected to the grid on March 21, 2025, achieving a plant thermal efficiency of 46.34%, which is of profound significance for promoting the development of new coal-fired power. In the thermal power industry, CFB boiler units account for about 10% of the installed capacity of coal-fired power plants. They have advantages in burning petroleum coke, biomass, and solid waste, and play a supplementary role to pulverized coal boilers.

[0004] CFB boilers, as an environmentally friendly combustion device, achieve low-NOx combustion through low temperature, low oxygen, and air staging. x The generation rate is lower than that of pulverized coal boilers. Depending on the type of coal and changes in combustion conditions, NO... x Emission values ​​are generally between 150 and 300 mg / m³ 3 Between. Before the implementation of the new air pollutant emission standards for thermal power plants in 2011, most CFB boiler units could meet the NOx emission standards without using flue gas denitrification. xEmission limits are required. Relevant industry policies require that pollution prevention and control in thermal power plants should follow and promote a technical approach that combines source control and end-of-pipe treatment; the selection of pollution prevention and control technologies should be tailored to the specific coal type, furnace type, and local conditions, while taking into account the principles of advanced technology, economic rationality, and ease of maintenance. Air pollution prevention and control in coal-fired power plants should take achieving emission standards as a basic requirement and fully implement ultra-low emissions as the goal. Ultra-low emissions from coal-fired power plants include particulate matter, SO2, and NO. x Emission concentrations not exceeding 10, 35, and 50 mg / m³ respectively 3 (Standard conditions, dry basis, 6% O2; unless otherwise specified, all pollutant concentrations below refer to these conditions). Currently, most coal-fired CFB boilers use low-NOx combustion + SNCR denitrification technology to achieve NO... x Ultra-low emissions.

[0005] SNCR denitrification technology is a denitrification method that uses a reducing agent (often 5% dilute ammonia or 10% urea solution in engineering) to reduce NO in flue gas to nitrogen (N2) and water (H2O) in the absence of a catalyst. Using dilute ammonia as the reducing agent, the main chemical reaction is shown in equation (1): (1) Using urea as a reducing agent, the main chemical reaction formulas are shown in formulas 2-4: (2) (3) (4) The optimal temperature range for the reducing agent to react efficiently is called the temperature window. The optimal temperature range is generally 800-1050℃. CFB boilers using SNCR denitrification technology can generally achieve a denitrification efficiency of 60%-80%. CFB boilers using low-NOx combustion technology can generally reduce NO... x The original emission concentration was controlled at 200 mg / m³. 3 The following further demonstrates that SNCR denitrification can achieve 50 mg / m³. 3 The ultra-low emission requirements.

[0006] SCR denitrification technology involves injecting dilute ammonia or other suitable reducing agents into the flue gas upstream of the catalyst, utilizing the catalyst to remove NO from the flue gas. x The reduction to N2 and H2O generally occurs at temperatures between 300-420℃. This technology is widely used in pulverized coal boilers but less so in CFB boilers. This is mainly due to the following reasons: (1) CFB boiler NO x The original emission values ​​are relatively low, and the technical strategy of "low-NOx combustion + SNCR denitrification" can generally meet the NOx requirements. x(1) The requirements for ultra-low emissions; (2) SCR reactors require a large space, and most old units are difficult to retrofit due to site limitations; (3) CaSO4 generated by in-furnace desulfurization in CFB boilers will cause catalyst deactivation. New units generally reserve space for the installation of SCR catalysts. Retrofitting most in-service units is costly.

[0007] A 300MW CFB boiler uses urea as a reducing agent, and the boiler operates at 90% NO load. x Original emissions value: 213.5 mg / m³ 3 As the ammonia-to-nitrogen ratio (NSR) increased from 1.45 to 2.08, the denitrification efficiency also increased, reaching a maximum of 82.96% at 2.08. However, as the NSR further increased to 2.48, the denitrification efficiency decreased. This indicates that SNCR denitrification technology can achieve relatively ideal denitrification efficiency when applied to CFB boilers. It also shows that under certain conditions, there is a threshold for NSR; a higher NSR does not necessarily mean higher denitrification efficiency, and excessive injection of reducing agent can increase ammonia slip.

[0008] When NH3 in flue gas encounters SO3, it produces (NH4)2SO4 or (NH4)HSO4. (NH4)HSO4 has a dew point of 147℃ and accumulates on surfaces in liquid form or disperses as droplets in the flue gas. Liquid (NH4)HSO4 is a highly viscous substance; it can adhere to fly ash in the flue gas, causing blockages in air preheaters and posing a risk of corrosion.

[0009] In recent years, due to the requirements of deep peak shaving in the thermal power industry, boiler load changes have become more frequent, and the proportion of low-load operation has increased significantly. When CFB boilers operate under low-load conditions, the temperature in the reaction zone deviates from the denitrification temperature window, leading to a significant decrease in SNCR denitrification efficiency. The injected reducing agent forms a large amount of escaped ammonia without participating in the denitrification reaction. Under deep peak shaving conditions, CFB boiler NO x There is currently no universally applicable solution for the effective control of emissions and the corrosion problem of air preheaters, and related technologies need further research.

[0010] CFB boilers are highly adaptable to various fuels, capable of co-firing large proportions of unconventional solid fuels such as biomass, municipal sludge, waste-derived fuels, and solid waste. Co-firing or burning unconventional solid fuels simultaneously treats solid waste and achieves resource utilization. Unconventional fuels generally have lower C and H content and higher moisture and ash content, resulting in less heat release during combustion, while the flue gas produced has a high heat capacity, causing combustion temperatures lower than those under coal-fired conditions. Therefore, in deep peak-shaving operations of conventional coal-fired CFB boilers, CFB boilers co-firing / burning unconventional solid fuels often suffer from low furnace outlet temperatures, typically in the range of 600-800℃, hindering efficient denitrification.

[0011] If the lower limit of the temperature window for SNCR denitrification can be extended to achieve full-load NO in CFB boilers x Ultra-low emissions can address the aforementioned issues to some extent and reduce the environmental burden on power generation companies. NOx emissions from coal-fired boilers under medium and high load conditions... x Ultra-low emission technology is relatively mature, and in recent years, the NO2 emissions from coal-fired boilers at full load have been increasing. x Research and patents on ultra-low emissions are mostly concentrated in the field of low-temperature denitrification.

[0012] Chinese patent CN1883767A discloses a method for direct dry denitrification of flue gas using ethanol at medium temperature. It describes a method that utilizes ethanol to chemically react with NO and O2 in flue gas at temperatures ranging from 750 to 1100°C to produce N2, H2O, and CO2, thereby achieving dry denitrification. Because the ethanol is injected into the medium-temperature flue gas region and reacts directly and rapidly with NO to generate N2, there is no need for a separate denitrification reactor, denitrification byproduct separation device, or catalyst. This technology does not use conventional denitrification reducing agents such as ammonia or urea; instead, it uses ethanol to broaden the range of reducing agents. The denitrification system is similar to a conventional SNCR system and is simpler than the SCR process. However, the application temperature range is still above 750°C, making it unsuitable for deep peak shaving applications in coal-fired CFB boilers or CFB boilers using unconventional solid fuels.

[0013] Chinese patent application CN03125332.6 discloses a dry flue gas purification process and system for simultaneous desulfurization and denitrification. The described flue gas denitrification process uses hydrogen peroxide or methanol as an additive, which is injected into flue gas at a temperature of 350-700℃. NO in the flue gas reacts chemically with the hydrogen peroxide or methanol to generate NO2. Ammonia or urea is then used as a denitrification agent, injected into the desulfurized flue gas to carry out the denitrification reaction, generating ammonium nitrate. This patent expands the lower limit of the SNCR denitrification temperature window, but requires the addition of a denitrification reaction tower and a denitrification byproduct separation device in the lower temperature region after desulfurization. This increases the resistance of the unit's flue gas system, significantly increases the initial investment and operating costs of the denitrification system, and makes the environmental protection equipment more complex.

[0014] In summary, due to the recent emergence of technologies such as deep peak shaving and unconventional solid fuel blending in the thermal power industry, the problems encountered during the application of these technologies are still in the exploratory and continuous improvement stage. There are few reports on research and patents related to systems and methods for denitrification under full load conditions in CFB boilers. Utility Model Content

[0015] To address the problems existing in the prior art, this utility model discloses a system for combined denitrification under full-load conditions in a circulating fluidized bed boiler, comprising a wide-temperature-range SNCR denitrification module and a flue gas recirculation module. The wide-temperature-range SNCR denitrification module uses ammonia as the denitrification reducing agent and ethanol as the low-temperature denitrification additive; it has two modes: low-temperature denitrification and conventional denitrification. In the denitrification reaction zone, when the flue gas temperature is 650~750℃, the low-temperature denitrification mode is used. Ethanol is added at a molar ratio of 0.1~0.5 to ammonia (hereinafter referred to as the "ethanol-ammonia ratio"), and a mixed solution is injected to remove NO from the flue gas. x In this temperature range, the efficiency of NO removal can be improved by 30% to 40% compared to conventional SNCR denitrification. When the flue gas temperature is above 750℃, the low-temperature denitrification mode is switched off and replaced with conventional denitrification mode. Conventional boiler operating parameter adjustments cannot effectively reduce the oxygen volume fraction in the furnace, and the wide-temperature-range SNCR denitrification module cannot remove NO from the flue gas. x When emissions are controlled below the limit, the flue gas recirculation module can generally be put into operation to reduce NO emissions. x Emissions reduced by 30~50 mg / m³ 3 NO can be achieved through the above method. x Ultra-low emissions under full load conditions.

[0016] No boiler modification or additional denitrification reactor is required. In most cases, simply adding a low-temperature denitrification additive ethanol supply and mixing device to the existing SNCR denitrification system can achieve the effect of extending the lower limit of SNCR denitrification temperature. Under low boiler load or deep peak-shaving conditions, the flue gas recirculation module can operate in conjunction with the wide-temperature-range SNCR denitrification module, or it can operate independently to achieve NO reduction, depending on the boiler's denitrification requirements. x Emissions meet standards.

[0017] To achieve the above objectives, the present invention adopts the following technical solution: a system for combined denitrification under full load conditions of a circulating fluidized bed boiler, comprising a wide temperature range SNCR denitrification module and a flue gas circulation module, wherein the ejector in the wide temperature range SNCR denitrification module is arranged in the inlet flue of the high temperature separator, the inlet flue of the high temperature superheater, or the boiler furnace. The flue gas recirculation module includes a flue gas recirculation main pipe and flue gas recirculation branch pipes arranged along the flue gas flow direction. The flue gas recirculation main pipe is connected to the flue gas recirculation branch pipes, and the flue gas recirculation branch pipes are connected to the air preheater via a primary air fan. The inlet of the flue gas recirculation main pipe is connected to the outlet of the induced draft fan.

[0018] Furthermore, along the flue gas flow direction, the main flue gas circulation pipe is equipped with a main pipe electric switch valve, a main pipe reducer, and a flue gas circulation fan. The branch flue gas circulation pipes are equipped with branch pipe reducers, branch flue gas flow meters, branch regulating valves, and branch electric switch valves. The outlet of the branch electric switch valve is connected to the inlet of the primary air fan. The flue gas circulation fan is a variable frequency fan.

[0019] Furthermore, the injector inlet is connected to a compressed air pipeline and an ammonia-ethanol mixer.

[0020] Furthermore, a self-regulating pressure reducing valve and a gas flow meter are installed along the air flow direction on the compressed air pipeline. The compressed air to the injector is divided into two paths: one path serves as atomizing air to atomize the process liquid; the other path serves as cooling air to cool the injector and reduce its temperature.

[0021] Furthermore, the inlet of the ammonia-ethanol mixer is connected to an ethanol supply device, which includes an ethanol storage tank, an ethanol transfer pump, an ethanol flow meter, an ethanol regulating valve, and an ethanol switching valve connected in sequence. The outlet of the ethanol switching valve is connected to the ammonia-ethanol mixer.

[0022] Furthermore, the inlet of the ammonia-ethanol mixer is connected to an ammonia dilution mixer, which is connected to an ammonia supply device and a dilution water supply device. The ammonia supply device includes an ammonia storage tank, an ammonia delivery pump, an ammonia flow meter, and an ammonia regulating valve connected in sequence. The dilution water supply device includes a dilution water tank, a dilution water pump, a dilution water flow meter, and a dilution water regulating valve connected in sequence. The ammonia regulating valve and the dilution water regulating valve are connected to the ammonia dilution mixer.

[0023] Furthermore, the ammonia storage tank volume is designed based on the boiler's rated load for continuous operation for 72 hours; the dilution water storage tank is designed to meet the boiler's rated load for continuous operation for no less than 24 hours; and the ethanol storage tank volume is designed based on the boiler's 72-hour low-temperature denitrification consumption.

[0024] Furthermore, the injector adopts a gas-liquid dual-fluid injector, and the injector structure adopts a multi-point or matrix type.

[0025] Furthermore, a thermometer is installed above the injector to monitor the temperature of the flue gas in the area.

[0026] Furthermore, the number of flue gas recirculation branch pipes is set to one, two, or more, depending on the number of primary air fans in the boiler.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects: This invention presents a system for combined denitrification under full-load operation of CFB boiler units participating in deep peak shaving. The system uses ammonia as a denitrification reducing agent and ethanol as a low-temperature SNCR denitrification additive, extending the lower limit of the conventional SNCR denitrification temperature window from 800℃ to 650℃. This covers most coal-fired CFB boiler units participating in deep peak shaving, as well as CFB boilers co-firing biomass, solid waste, and other unconventional solid fuels. No boiler modification is required, and no additional denitrification reactor or catalyst is needed. The system is relatively simple, with convenient switching between low-temperature and conventional denitrification modes, achieving good denitrification results. It is suitable for most CFB boilers operating at full load. x In ultra-low emission applications, under low boiler load or deep peak-shaving conditions, the flue gas recirculation module can operate in conjunction with a wide-temperature-range SNCR denitrification module, depending on the boiler's denitrification requirements. Under certain conditions, it can also operate independently to achieve NO reduction. x Achieves emission standards; compared to general CFB boiler air staging and other low-NOx combustion technologies, it adds effective means to regulate oxygen volume fraction and bed temperature in the dense phase zone, resulting in superior low-NOx combustion performance. It can meet the full-load NOx emission standards of most coal-fired circulating fluidized bed boilers participating in deep peak shaving. x Ultra-low emission requirements.

[0028] Furthermore, the ammonia storage tank volume is designed according to the boiler's rated load for continuous operation for 72 hours; the dilution water storage tank is designed to meet the boiler's rated load for continuous operation for no less than 24 hours; and the ethanol storage tank volume can be designed according to the boiler's 72-hour low-temperature denitrification usage.

[0029] Furthermore, compressed air is delivered to the injector and split into two paths. One path is atomizing air, used to atomize the denitrification reducing agent liquid and promote uniform mixing of the reducing agent and flue gas, thereby accelerating the denitrification chemical reaction rate per unit time. The other path serves as cooling air, used to cool the injector and prevent damage from high temperatures. The injector structure can be either multi-point or matrix type.

[0030] Furthermore, a switching valve is installed on the ethanol supply pipeline for ethanol dosing and switching between the system's conventional denitrification mode and low-temperature denitrification mode. When the system operates in low-temperature denitrification mode, both ethanol and the denitrification reducing agent are led to the mixer, mixed according to the set alcohol-ammonia ratio, and then injected into the flue gas at 650-750℃ to remove NO from the flue gas. x The removal.

[0031] Furthermore, a thermometer is installed in the injection area to monitor whether the 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.

[0032] Furthermore, along the flue gas flow direction, the main pipe's electrically operated valve is used to switch the flue gas recirculation system on and off; the flue gas recirculation fan is used to overcome the resistance of the flue gas recirculation duct and quantitatively deliver the clean flue gas drawn from the induced draft fan outlet to the primary air fan inlet duct. Flue gas flow meters installed on the branch pipes are used to control and provide feedback on the branch pipe flue gas flow; the branch pipe regulating valves further adjust the flue gas flow based on the branch pipe flue gas flow meter readings; the branch pipe electrically operated valves are used for the isolation and connection between the flue gas recirculation system and the primary air duct.

[0033] Furthermore, depending on the type of boiler island desulfurization system, if an in-furnace limestone desulfurization process or a flue gas circulating fluidized bed desulfurization process is adopted, the flue gas circulation main pipe and flue gas circulation branch pipes should be made of carbon steel; if a limestone-gypsum wet desulfurization process is adopted, the flue gas circulation main pipe and flue gas circulation branch pipes should be made of stainless steel or carbon steel pipes with anti-corrosion treatment to improve the durability of the system.

[0034] Furthermore, the flue gas recirculation fan adopts frequency conversion regulation, which saves energy on the one hand and reduces the number of regulating dampers on the other hand, making the system more compact.

[0035] Furthermore, the flue gas recirculation system can also operate independently; when the boiler operates at low load or under deep peak-shaving conditions, the initial generation rate should not exceed 80 mg / m³. 3 At the same time, a separate flue gas recirculation system is put into operation, using deep low-NOx combustion to achieve NO reduction. x Ultra-low emissions. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the system of this utility model.

[0037] Among them, 100-boiler furnace, 101-separator inlet flue, 102-high temperature separator, 103-tail flue, 104-high temperature superheater, 105-low temperature superheater, 106-economizer, 107-air preheater, 108-desulfurization tower, 109-dust collector, 110-fan, 111-chimney, 112-primary air fan, 201-common instrument compressed air system interface, 202-self-regulating pressure reducing valve, 203-gas flow meter, 204-raw ammonia water pipeline interface, 205-ammonia water storage tank, 206-ammonia water transfer pump, 207-ammonia water flow meter, 208-ammonia water regulating valve, 209-ammonia water 210-Dilution mixer, 211-Demineralized water pipe interface, 212-Dilution water tank, 213-Dilution water pump, 214-Dilution water flow meter, 215-Dilution water regulating valve, 216-Ethanol storage tank, 217-Ethanol transfer pump, 218-Ethanol flow meter, 219-Ethanol switch valve, 220-Ammonia-ethanol mixer, 221-Thermometer, 222-Ejector, 301-Electric switch door of flue gas circulation main pipe, 302-Main pipe reducer, 303-Flue gas circulation fan, 304-Branch pipe reducer, 305-Branch pipe flue gas flow meter, 306-Branch pipe regulating valve, 307-Branch pipe electric switch door. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] The principle of ethanol as an additive for SNCR denitration: Ethanol itself undergoes a dehydrogenation reaction, producing free radicals such as H and OH, which promote the denitration reaction through multiple reactions. At the same time, the CO produced also has a certain promoting effect on denitration. The main reactions are shown in equations (5) to (10), thereby reducing the temperature required for the denitration reaction.

[0040] (5) (6) (7) (8) (9) (10) SNCR denitrification experiments conducted on a laboratory-scale CFB test bench showed that, within the range of 650–750℃, with increasing temperature, the SNCR denitrification efficiency using ammonia as the denitrification reducing agent increased from approximately 6% to about 40% without additives. Adding ethanol at 650℃ could further increase the SNCR denitrification efficiency by up to ~40%. However, the effect of ethanol additives decreased with increasing flue gas temperature, reaching a maximum improvement of approximately 10% at 750℃. Further increases in flue gas temperature, particularly with the addition of additives, inhibited the SNCR denitrification reaction, reducing the denitrification efficiency.

[0041] A 350MW CFB boiler unit participating in deep peak shaving has developed a flue gas recirculation technology route based on boiler operating conditions. When the boiler load is below 40% BMCR, the SNCR denitrification system is shut down, and the flue gas recirculation unit is put into operation to achieve NO reduction. x Ultra-low emissions. After project completion, system operation performance tests were conducted. NOx was stably controlled at approximately 28% BMCR. x Emissions are between 45 and 50 mg / m³ 3 Within a certain range, while maintaining a certain margin for regulation.

[0042] Based on the above principles and experimental results, a combined denitrification implementation plan under full load conditions was developed for CFB boilers participating in deep peak shaving. (See attached document.) Figure 1 The system consists of Module I—a wide-temperature-range SNCR denitrification module and Module II—a flue gas recirculation module.

[0043] Module I includes: raw ammonia water storage and transportation device, dilution water storage and transportation device, low temperature denitrification additive storage and transportation device, compressed air transportation and regulation device, and injector.

[0044] The raw ammonia water storage and transportation device includes a raw ammonia water interface 204, an ammonia water storage tank 205, an ammonia water transfer pump 206, an ammonia water flow meter 207, and an ammonia water regulating valve 208; the dilution water storage and transportation device includes a demineralized water interface 210, a dilution water tank 211, a dilution water pump 212, a dilution water flow meter 213, and a regulating valve 214; ammonia water and dilution water are connected to a mixer 209 via their respective transportation pipelines, and further transported to an injector 222. The cryogenic additive storage and transportation device includes an ethanol storage tank 215, an ethanol transfer pump 216, an ethanol flow meter 217, and an ethanol regulating valve 218; used for the preparation and supply of denitrification reducing agents and cryogenic additives.

[0045] The compressed air delivery and regulation device includes a utility compressed air system interface 201, a self-regulating pressure reducing valve 202, and a gas flow meter 203. The compressed air from the utility compressed air system interface 201 is adjusted by the self-regulating pressure reducing valve 202 to maintain the compressed air pressure within the design range, providing the necessary pressure and flow rate of atomizing and cooling air for the hot operation of the ejector 224. The gas flow meter 203 monitors the gas flow rate in the pipeline, and the measured value serves as the basis for adjusting the air volume from the utility compressed air system interface 201. The compressed air delivery and regulation device is used for the supply and regulation of cooling and atomizing air for the ejector.

[0046] The wide-temperature-range SNCR denitrification module stores and supplies the boiler with ammonia as the SNCR denitrification reducing agent and ethanol as the low-temperature additive. Ammonia with a mass concentration of 15%~20% is used, further diluted to approximately 5% by mass, as the denitrification reducing agent. The low-temperature additive used is ethanol with a mass concentration of 50%~100%. The low-temperature denitrification additive ethanol is generally added at an alcohol-to-ammonia ratio of 0.1~0.5. Raw ammonia with a concentration of 15%~20% can be transported by tanker truck or pipeline to the raw ammonia pipeline interface 204 and then to the ammonia storage tank 205. The outlet of the ammonia storage tank 205 is sequentially connected to an ammonia transfer pump 206, an ammonia flow meter 207, an ammonia regulating valve 208, and an ammonia dilution mixer 209, based on the NO content in the boiler flue gas. x The raw ammonia solution is supplied with ammonia water to meet the removal rate and denitrification ammonia nitrogen ratio. Dilution water is supplied from demineralized water pipeline interface 210 to dilution water tank 211. The outlet of dilution water tank 211 is sequentially connected to dilution water pump 212, dilution water flow meter 213, dilution water regulating valve 214, and ammonia water dilution mixer 209, supplying dilution water according to the required concentration of the denitrification reducing agent after dilution. Raw ammonia water and dilution water are supplied to ammonia water dilution mixer 209 via their respective pipelines, and further supplied to ejector 222.

[0047] Injector 222 is the core equipment of the SNCR denitrification system. It adopts a gas-liquid dual-fluid injector and the injector structure can be multi-point or matrix to ensure the uniformity of mixing between the denitrification reducing agent and the flue gas.

[0048] The injector 222 is arranged at the inlet of the high-temperature superheater 104 in the tail flue 103 according to the boiler flue gas flow in different temperature zones. It can also be arranged at the boiler furnace 100 or the separator inlet flue 101. A thermometer 221 is installed above the injector 222 to monitor whether the flue gas temperature in the area 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.

[0049] Ethanol storage tank 215 stores ethanol as a cryogenic additive for SNCR denitrification. The outlet of ethanol storage tank 215 is sequentially connected to ethanol transfer pump 216, ethanol flow meter 217, ethanol regulating valve 218, ethanol on / off valve 219, ammonia-ethanol mixer 220, and injector 222. Ammonia-ethanol dilution mixer 209 is sequentially connected to ammonia-ethanol mixer 220 and injector 222, supplying ethanol according to the flue gas temperature and ethanol-ammonia ratio in the denitrification reducing agent injection zone. An ethanol on / off valve 219 is installed on the ethanol supply pipeline in the ethanol supply unit for adding and cutting off the cryogenic additive, thus controlling the cryogenic denitrification additive. Both ethanol and the denitrification reducing agent are led to ammonia-ethanol mixer 220, mixed according to the set ethanol-ammonia ratio, and then injected into the 650-750℃ flue gas. When the temperature in the reaction zone exceeds 750℃, the ethanol on / off valve 219 is closed to cut off the ethanol supply.

[0050] The wide-temperature-range SNCR denitrification module injects denitrification reducing agent through injector 222 to remove NO from the flue gas. x Remove. This can be done based on the flue gas temperature and NO2 under different boiler load conditions. x The required number of injectors 222 is determined by the content and denitrification efficiency. The compressed air and denitrification reducing agent supplied by the wide-temperature-range SNCR denitrification module are distributed to each injector 222 through their respective supply pipelines; the ethanol supply pipeline is equipped with an ethanol switch valve 219 for supplying or cutting off ethanol, and ethanol and denitrification reducing agent are mixed by an ammonia-ethanol mixer 220 and then supplied to the injectors 222.

[0051] The volume of ammonia storage tank should be designed according to the boiler's rated load for continuous operation for 72 hours; the volume of dilution water storage tank should generally be designed to meet the boiler's rated load for continuous operation for no less than 24 hours; the volume of ethanol storage tank can be designed according to the boiler's 72-hour low-temperature denitrification consumption.

[0052] A high-temperature superheater 104, a low-temperature superheater 105, an economizer 106, and an air preheater 107 are sequentially installed in the tail flue 103. The flue gas outlet of the air preheater 107 is sequentially connected to a desulfurization tower 108, a dust collector 109, a fan 110, and a chimney 111.

[0053] In the flue gas recirculation module: along the flue gas flow direction, the flue gas recirculation main pipe is equipped with a main pipe electric switch valve 301, a main pipe reducer 302, and a flue gas recirculation fan 303; the flue gas recirculation main pipe interface is located at the outlet of the induced draft fan 110, and the flue gas recirculation main pipe electric switch valve 301 is located on the flue gas recirculation pipeline for the commissioning and decommissioning of the flue gas recirculation system; the flue gas recirculation main pipe electric switch valve 301 is connected to the main pipe reducer 302 and the flue gas recirculation fan 303, and the flue gas recirculation fan 303 is connected to the flue gas recirculation branch pipe. Along the flue gas flow direction, the flue gas recirculation branch pipe is equipped with a branch pipe reducer 304, a branch pipe flue gas flow meter 305, a branch pipe regulating valve 306, and a branch pipe electric switch valve 307. The electrically operated switch 301 for the main flue gas recirculation pipe is used to switch the flue gas recirculation system on and off; the main pipe reducer 302 is used to connect the main pipe to the inlet of the flue gas recirculation fan 303; the flue gas recirculation fan adopts a frequency conversion regulation method, eliminating the need for a regulating valve, thus meeting airflow regulation requirements and reducing energy consumption. Two or more branch pipes are installed at the outlet of the flue gas recirculation fan 303 depending on the number of primary air fans. The size of the branch pipe reducer 304 is determined based on the outlet pipe size of the flue gas recirculation fan and the branch pipe size; the branch pipe flue gas flow meter 305 is used to monitor the branch pipe flue gas flow and adjust the opening of the branch pipe regulating valve 306 based on its feedback value to obtain the target flue gas flow; the electrically operated switch 307 for the branch pipe is used to switch the flue gas recirculation system to the inlet pipe of the primary air fan 112.

[0054] The dimensions of the flue gas recirculation main pipe and branch pipes are selected based on a flow velocity of 12~15m / s. The flue gas recirculation fan adopts frequency conversion regulation, which saves energy and reduces the number of regulating valves, making the system more compact. Depending on the type of boiler island desulfurization system, if an in-furnace limestone desulfurization process or a flue gas recirculation fluidized bed desulfurization process is used, carbon steel can be selected for the pipe material; if a limestone-gypsum wet desulfurization process is used, stainless steel or corrosion-resistant carbon steel pipes are preferable to improve the system's durability.

[0055] Circulating fluidized bed boilers can be broadly categorized by operating load: high load (≥80%), medium load (50% ≤ load rate < 80%), low load (30% ≤ load rate < 50%), and deep peak-shaving load rate < 30%. Module I includes a raw ammonia storage and transportation device, a dilution water storage and transportation device, a low-temperature denitrification additive storage and transportation device, a compressed air transportation and regulation device, and an injector. It features two modes: conventional denitrification reaction zone temperature ≥ 800℃ and low-temperature denitrification (650℃ ≤ reaction zone temperature ≤ 750℃). Ammonia is used as the denitrification reducing agent, and ethanol as the low-temperature denitrification additive. When the boiler operates under medium to high load conditions, the flue gas temperature in the denitrification reaction zone is generally between 800 and 920℃. Module I injects diluted ammonia as a reducing agent into the boiler's denitrification reaction zone to remove NO from the flue gas. xWhen the boiler operates at low load or deep peak-shaving conditions with flue gas temperatures of 650~750℃, the denitrification module adds ethanol at a molar ratio of 0.1~0.5 to ammonia, and further injects the mixed solution into the denitrification reaction zone to remove NO from the flue gas. x Effective removal.

[0056] Module II introduces the clean flue gas from the induced draft fan outlet, after it has been treated by the boiler's environmental protection facilities to meet ultra-low emission standards, into the primary air fan inlet. This is used to adjust the oxygen volume fraction and bed temperature in the dense phase zone of the furnace, aiming to reduce NO. x Generation volume. When circulating fluidized bed boilers operate at low loads and under deep peak-shaving conditions, conventional boiler operating parameter adjustment methods cannot effectively reduce the oxygen volume fraction in the furnace combustion, and the wide-temperature-range SNCR denitrification module cannot remove NO from the flue gas... x When emissions are controlled below the limits, the flue gas recirculation system is put into operation. The recirculated flue gas is added to the primary air and sent into the dense phase zone of the furnace. Since the oxygen volume fraction in the flue gas is generally between 5% and 9%, and the content of inert gases such as CO2 and N2 that do not participate in the combustion reaction is relatively high, the oxygen volume fraction in the dense phase zone can be effectively reduced. This also reduces the fuel's combustion share in this region and lowers the bed temperature. The low-oxygen, low-temperature combustion atmosphere limits NO during combustion. x The generation of [something] achieves a deep low-NOx combustion effect.

[0057] This design is for CFB boilers participating in deep peak shaving. The wide-temperature-range SNCR denitrification module uses ammonia as the denitrification reducing agent. When the boiler operates at medium to high load conditions with flue gas temperatures above 750℃, the denitrification module injects diluted ammonia as the reducing agent into the boiler's denitrification reaction zone to remove NO from the flue gas. x When the boiler operates at a low load with a flue gas temperature of 650~750℃, the denitrification module adds ethanol at an alcohol-ammonia ratio of 0.1~0.5, and further injects the mixed solution into the denitrification reaction zone to remove NO from the flue gas. x Effective removal; conventional boiler operating parameter adjustment methods cannot effectively reduce the oxygen volume fraction in furnace combustion, and the wide-temperature-range SNCR denitrification module cannot remove NO from the flue gas. x When emissions are controlled below the limit, the flue gas recirculation module is activated to control NO during combustion. x The amount of NO generated. The above method can achieve NO production. x Ultra-low emissions under full load conditions. The wide-temperature-range SNCR denitrification module uses ammonia water with a mass concentration of 15%~20% and further diluted to a mass concentration of about 5% as the denitrification reducing agent. The low-temperature denitrification additive used is ethanol with a mass concentration of 50%~100%, and the amount of ethanol added is calculated according to the set alcohol-ammonia ratio.

[0058] In the wide-temperature-range SNCR denitrification module, the compressed air pressure from the public instrument compressed air system interface 201 should be stable. The self-regulating pressure reducing valve 202 adjusts the outlet compressed air pressure to 0.3~0.5MPa for atomization of the denitrification reducing agent liquid in the injector and for cooling and protecting the injector body. The gas flow meter 203 provides feedback values ​​for operators to monitor and adjust the compressed air flow in real time. Qualified compressed air to the injector 222 is divided into two paths: one is atomizing air, used for atomizing the denitrification reducing agent liquid and promoting uniform mixing of the reducing agent and flue gas, accelerating the denitrification chemical reaction rate per unit time; the other is cooling air, used for cooling the injector to prevent high-temperature damage.

[0059] In the denitrification reaction zone, where the flue gas temperature exceeds 800℃, the system's wide-temperature-range SNCR denitrification module operates in conventional mode to remove NO from the flue gas. x In the denitrification reaction zone, where the flue gas temperature is between 750 and 800°C, a combination of flue gas recirculation module injection and wide-temperature-range SNCR denitrification module in conventional mode can achieve high denitrification efficiency. In the low-temperature flue gas temperature range of 650–750°C, the low-temperature mode of the wide-temperature-range SNCR denitrification module can be used to achieve NO reduction. x Emissions meet standards. Under low-load or deep peak-shaving conditions, conventional boiler operating parameter adjustment methods cannot effectively reduce the oxygen volume fraction in the furnace combustion, and wide-temperature-range SNCR denitrification modules cannot remove NO from the flue gas. x When emissions are controlled below the limit, the flue gas recirculation module can be put into operation to further reduce NO emissions while maintaining stable combustion in the furnace. x Emissions reduced by 30~50 mg / m³ 3 The above method achieves NO2 operation at full load for CFB boilers. x Ultra-low emissions.

[0060] Under medium and low load and deep peak-shaving conditions, because the primary air volume cannot be lower than the critical fluidizing air volume, a significant reduction in the secondary air volume leads to a decrease in the low-NOx combustion effect of staged combustion in the furnace. x The amount of NO generated increases; simultaneously, due to the decrease in temperature in the SNCR denitrification reaction zone, conventional SNCR denitrification methods cannot meet the NO requirements. x Ultra-low emission requirements. After Module II is put into operation, it can effectively reduce the oxygen volume fraction in the dense phase region of the furnace, creating a reducing reaction atmosphere and suppressing NO. x generate.

[0061] When the flue gas temperature in the boiler denitrification reaction zone is between 750 and 800℃, both the conventional denitrification mode and the low-temperature denitrification mode of Module I are in the inefficient range. Activating the flue gas recirculation system reduces NO₂ levels. xThe amount of gas generated increases, and due to the decrease in combustion intensity in the dense phase zone and the increase in the combustion share in the transition and dilute phase zones, the temperature in the denitrification reaction zone can generally rise by about 20°C, thereby improving the efficiency of the conventional denitrification mode in Module I. Similarly, when the flue gas temperature in the boiler denitrification reaction zone is between 600 and 650°C, putting into operation the flue gas recirculation system can improve the efficiency of the low-temperature denitrification mode in Module I.

[0062] When the boiler is operating at medium or high loads of 60% or above, the flue gas temperature in the inlet flue area of ​​the high-temperature superheater 104 is 800~920℃, and the ejector 222 is arranged in this area; depending on the boiler structure and coal quality characteristics, the ejector 222 can also be arranged in the separator inlet flue 101 or the boiler furnace 100.

[0063] Based on actual measured standard state flue gas volume and NO x The content is designed with a maximum NSR of 2.5 for SNCR denitrification. The consumption of raw ammonia water is calculated. The volume of ammonia water storage tank 205 is determined according to the ammonia water consumption of the boiler at full load for 72 hours. Ammonia water transfer pump 206, ammonia water flow meter 207 and ammonia water regulating valve 208 are configured.

[0064] The mass concentration of ammonia water injected into the flue gas is generally 5%. The volume of ammonia water storage tank 211 is determined according to the dilution water consumption during 24 hours of full-load boiler operation, and a dilution water transfer pump 212, a dilution water flow meter 213, and a dilution water regulating valve 214 are configured.

[0065] The ethanol consumption is determined based on the boiler's daily low-load operation time (below 60% load) and deep peak-shaving operation time (below 30% load). The volume of the ethanol storage tank 215 is determined according to the boiler's 72-hour ethanol operation time and consumption. An ethanol transfer pump 216, an ethanol flow meter 217, an ethanol regulating valve 218, and an ethanol shut-off valve 219 are also configured.

[0066] Ammonia and ethanol are introduced to the ammonia-ethanol mixer 220, and after mixing, they are delivered to the injector 222. Thermometer 221 is used to monitor and provide feedback on the flue gas temperature in the denitrification reaction area. Based on the feedback value, the operator determines whether to use the conventional denitrification mode or the low-temperature denitrification mode.

[0067] When the boiler operates at 60% load or below, and under the condition of stable combustion, the flue gas temperature in the inlet area of ​​the high-temperature superheater 104 is generally 600~800℃. At this time, module I adopts the low-temperature denitrification mode, and module II is put into operation to control NO in conjunction with the adjustment of furnace oxygen volume fraction and bed temperature. x Emissions. When the boiler is under low load or deep peak shaving conditions, NO x The original emission value is not higher than 80 mg / m³ 3 At the same time, module II can also be put into operation independently to achieve NO x Ultra-low emissions.

[0068] In summary, the system for combined denitrification under full-load operation of circulating fluidized bed boilers described in this utility model, compared to conventional SNCR denitrification methods and systems, adds low-temperature SNCR denitrification additive ethanol, which can extend the lower limit of the denitrification temperature window to 650℃, meeting the NO requirements of most CFB boilers participating in deep peak shaving under full-load operation. x Ultra-low emission requirements. The added flue gas recirculation system makes denitrification methods more flexible and diverse; compared with SCR denitrification, the system is simpler and has better economic efficiency.

[0069] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A system for combined denitrification under full-load operation of a circulating fluidized bed boiler, characterized in that: It includes a wide-temperature-range SNCR denitrification module and a flue gas recirculation module. The injector (222) in the wide-temperature-range SNCR denitrification module is arranged in the inlet flue of the high-temperature separator (101), the inlet flue of the high-temperature superheater (104), or the boiler furnace (100). The flue gas recirculation module includes a flue gas recirculation main pipe and a flue gas recirculation branch pipe arranged along the flue gas flow direction. The flue gas recirculation main pipe is connected to the flue gas recirculation branch pipe, and the flue gas recirculation branch pipe is connected to the air preheater (107) via a primary air fan (112). The inlet of the flue gas recirculation main pipe is connected to the outlet of the induced draft fan (110).

2. The system for combined denitrification under full load conditions of a circulating fluidized bed boiler according to claim 1, characterized in that: Along the flue gas flow direction, the main flue gas circulation pipe is equipped with a main pipe electric switch valve (301), a main pipe reducer (302), and a flue gas circulation fan (303). The flue gas circulation branch pipe is equipped with a branch pipe reducer (304), a branch pipe flue gas flow meter (305), a branch pipe regulating valve (306), and a branch pipe electric switch valve (307). The outlet of the branch pipe electric switch valve (307) is connected to the inlet of the primary air fan (112). The flue gas circulation fan (303) is a variable frequency fan.

3. The system for combined denitrification under full load conditions of a circulating fluidized bed boiler according to claim 1, characterized in that: The inlet of the injector (222) is connected to a compressed air pipe and an ammonia-ethanol mixer (220).

4. The system for combined denitrification under full load conditions of a circulating fluidized bed boiler according to claim 3, characterized in that: A self-regulating pressure reducing valve (202) and a gas flow meter (203) are installed on the compressed air pipeline along the air flow direction. The compressed air to the injector (222) is divided into two paths. One path is used as atomizing air to atomize the process liquid; the other path is used as cooling air to cool the injector and reduce the temperature of the injector (222).

5. The system for combined denitrification under full load conditions of a circulating fluidized bed boiler according to claim 3, characterized in that: The inlet of the ammonia-ethanol mixer (220) is connected to an ethanol supply device, which includes an ethanol storage tank (215), an ethanol transfer pump (216), an ethanol flow meter (217), an ethanol regulating valve (218), and an ethanol switch valve (219) connected in sequence. The outlet of the ethanol switch valve (219) is connected to the ammonia-ethanol mixer (220).

6. The system for combined denitrification under full load conditions of a circulating fluidized bed boiler according to claim 3, characterized in that: The inlet of the ammonia-ethanol mixer (220) is connected to the ammonia dilution mixer (209). The ammonia dilution mixer (209) is connected to the ammonia supply device and the dilution water supply device. The ammonia supply device includes an ammonia storage tank (205), an ammonia transfer pump (206), an ammonia flow meter (207), and an ammonia regulating valve (208) connected in sequence. The dilution water supply device includes a dilution water tank (211), a dilution water pump (212), a dilution water flow meter (213), and a dilution water regulating valve (214) connected in sequence. The ammonia regulating valve (208) and the dilution water regulating valve (214) are connected to the ammonia dilution mixer (209).

7. The system for combined denitrification under full load conditions of a circulating fluidized bed boiler according to claim 6, characterized in that: The ammonia storage tank is designed to meet the boiler's rated load for continuous operation for 72 hours; the dilution water storage tank is designed to meet the boiler's rated load for continuous operation for no less than 24 hours; and the ethanol storage tank is designed to meet the boiler's 72-hour low-temperature denitrification requirement.

8. The system for combined denitrification under full load conditions of a circulating fluidized bed boiler according to claim 1, characterized in that: The injector (222) adopts a gas-liquid dual-fluid injector, and the injector structure adopts a multi-point or matrix type.

9. The system for combined denitrification under full load conditions of a circulating fluidized bed boiler according to claim 1, characterized in that: A thermometer (221) is installed above the injector (222) to monitor the temperature of the flue gas in the area.

10. The system for combined denitrification under full load conditions of a circulating fluidized bed boiler according to claim 1, characterized in that: The number of flue gas recirculation branch pipes is set to one, two, or more, depending on the number of primary air fans in the boiler.

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