Transformation objective
Low nitrogen combustion combined with SNCR denitrification achieves ultra-low emissions, with a flue gas nitrogen oxide concentration of no more than 50mg/Nm3 at the boiler environmental protection detection point (the oxygen content of flue gas at the environmental protection detection point is no more than 8%, the oxygen content of flue gas after the boiler superheater is no more than 4%, the amount of coal gas burned is no more than 25% of the total fuel heat, and the amount of coal sludge burned is no less than 45% of the total fuel heat). Pure low nitrogen combustion (cutting off ammonia water) achieves denitrification in the furnace, and the concentration of nitrogen oxides in the flue gas at the boiler environmental protection detection point is not more than 250mg/Nm3 (the oxygen content in the flue gas at the environmental protection detection point is not more than 8%, the oxygen content in the flue gas after the boiler superheater is not more than 4%, the amount of coal gas burned is not more than 25% of the total fuel heat, and the amount of coal slurry burned is not less than 45% of the total fuel heat). Observational indicators (not used as engineering acceptance criteria): Compared before and after the renovation, the annual urea consumption savings are about 40%.
1. Implement multi-stage staged combustion technology for secondary air in the central region
The height between the secondary air outlet and the air distribution plate has a significant impact on denitrification, so it needs to be modified. For boilers with unsatisfactory denitrification effects, the central air patent generalized air distribution is adopted, and high gradient multi-stage graded air supply is carried out in the furnace hall. Install two-stage central secondary air on the boiler wall. It is necessary to open several holes in the front and rear walls of the furnace, and the specific quantity needs to be determined after considering the comprehensive influence of the rigid beam of the boiler on site, the horizontal, vertical and inclined support structure of the boiler body, the anti-wear structure inside the furnace, the boiler steel frame and support. The holes are evenly distributed on the front and rear walls.
The specific aperture of the opening should be determined by referring to the original design of the secondary air aperture and calculating the wind speed and volume. Generally, one opening needs to cut multiple water-cooled wall pipes (if the fin width is appropriate, water-cooled wall pipes can also be omitted). The specific elevation of the openings in the middle of the furnace should be determined by considering various factors such as the boiler steel beams and supports, the rigid beams and vertical supports of the water-cooled wall, and the anti-wear structures inside the furnace (such as anti-wear beams and spraying areas). Consider two-stage central secondary air, which takes into account the staged combustion of blue carbon exhaust gas. Weld guide flat steel (T-shaped fins) on the water-cooled wall fins around the opening to enhance heat absorption. Materials and Construction: Removal of insulation and protective skin, opening of furnace walls (cutting 2 water-cooled wall pipes or cutting fins for each opening), heat-resistant steel nozzles, large and small heads, pipes, elbows, production of sealing boxes (comb shaped plates, etc.), pouring of refractory materials, restoration of insulation and protective skin.
Due to the fact that the current lower secondary air duct is close to the boiling bed material layer with high pressure, that is, the lower secondary air back pressure is high and difficult to penetrate the boiling bed material layer, it does not enhance combustion nor improve the degree of coal particle burnout. Instead, being too close to the bed material layer makes it difficult to control the generation of nitrogen oxides in the lower part of the furnace due to oxygen enrichment; The current circulating fluidized bed boiler has dozens of secondary air ducts densely arranged on the 2-3 layers, which cannot achieve staged combustion and reduce the generation of nitrogen oxides. The emission concentration of nitrogen oxides in the flue gas is difficult to meet environmental standards.
According to the current atmospheric environmental protection policy, boilers must stop operating if their flue gas emissions do not meet the standards. Therefore, it is necessary to improve the wind distribution to achieve staged combustion, significantly reduce the nitrogen oxides emitted from boiler flue gas, and promote a middle wind furnace in circulating fluidized bed boilers. Patent No. ZL2013208604918
Invention content: The purpose of this utility model is to provide a middle air furnace of a circulating fluidized bed boiler. The middle air and the multi-layered secondary air at the lower part of the furnace are separated by a certain distance in the height direction, realizing layered air supply and layered combustion, that is, staged combustion, which can reduce the concentration of nitrogen oxides emitted from boiler flue gas and meet environmental protection standards. The central wind is the wind that transports oxygen to the furnace and also plays a role in combustion. The utility model provides a circulating fluidized bed boiler with a central wind furnace, which has the following technical features:
Introducing a portion of the original total air volume of the existing fluidized bed boiler into the middle of the boiler through pipes and dampers is called boiler middle air.
The middle air of the boiler can be drawn from the secondary air box of the boiler, and all middle air branch pipes are connected to the secondary air box through air doors.
The middle air of the boiler can be drawn from the main primary air box of the boiler, and all middle air branch pipes are connected to the middle primary air box through air doors.
Set up a central air box to connect the central air duct to the boiler main air duct through a primary air outlet.
There are about 15 air branch pipes in the middle of the boiler, corresponding to about 15 openings on the furnace wall. The air in the middle of the boiler enters the furnace through the opening in the middle of the furnace wall, which can enhance combustion and improve the degree of coal particle burnout, as well as reduce the concentration of nitrogen oxides in the boiler flue gas.
2. Adjusting the inclination angle of the original secondary air outlet and implementing a diversion platform
The uneven distribution of oxygen in the furnace is solved by using patented technology of secondary air inlet guide platform to address the oxygen deficiency in the center of the boiler. Patent number ZL2011200922059.
Circulating fluidized bed boilers commonly suffer from oxygen deficiency in the center of the furnace, with severe uneven distribution of oxygen in the furnace, which is not conducive to denitrification. The high oxygen area near the secondary air inlet produces a large amount of nitrate. Under the premise of Plan 1 (i.e. when the dense phase zone is already low in oxygen), the patented technology of secondary air outlet guide platform is used to solve the problems of oxygen enrichment on the furnace wall, uneven oxygen distribution in the furnace, and central oxygen deficiency (causing local high nitrate content problems). Secondary air outlet guide platforms are implemented for 6-8 original secondary air outlets, which are made of refractory and wear-resistant materials. Simultaneously adjusting the angle of the original secondary air duct, patent number ZL2015207063444, a secondary air direction deflection device for fluidized bed boilers; Do not allow the secondary wind to spray towards the material layer at a steep angle to reduce the oxygen content in the material layer. During the operation of a circulating fluidized bed boiler, a large flow of wall sticking ash flow is generated from top to bottom, which closely adheres to the surface of the water-cooled wall tube bank and flushes the surface of the water-cooled wall tube bank. The secondary air jet must pass through the wall sticking ash flow before it can be injected into the furnace to play its role; The wall sticking ash flow, like a waterfall, has a large momentum and blocks the secondary air jet, weakening its penetration and reducing the oxygen content in the core area of the furnace, thus reducing the degree of coal particle burnout and energy waste. The phenomenon is that the carbon content and nitrate content in the ash discharge of circulating fluidized bed boilers are still high, which is a common but intolerable problem for enterprises. The present invention patent number ZL2011200922059 is a guiding platform for the upper part of the secondary air nozzle of a fluidized bed. Its function is to change the direction of the wall attached ash flow at the upper part of the secondary air nozzle, so that the wall attached ash flow no longer flushes the secondary air jet. This relatively improves the penetration of the secondary air jet, increases the oxygen content in the core area of the furnace, thereby enhancing the degree of coal particle burnout, greatly reducing the carbon content in boiler fly ash, and reducing energy waste. The prominent features of the upper guide platform of the fluidized bed secondary air nozzle are:
1. Use a sloping surface to split the vertical downward ash flow into two streams.
The length of the diversion platform (in the horizontal direction) is much greater than the thickness of the wall attached ash flow layer.
3. The end of the diversion platform is slightly higher than the root to prevent the inertia of a small amount of wall sticking ash flow from causing a new ash curtain to affect the penetration of the secondary air jet.
4. The width of the diversion platform is greater than that of the secondary air nozzle to prevent the formation of a new ash curtain caused by a small amount of wall sticking ash flow, which affects the penetration of the secondary air jet.
5. The construction of the diversion platform can be formed by welding high-quality heat-resistant and wear-resistant alloy steel, or by forming heat-resistant and wear-resistant plastic. It is recommended to use heat-resistant and wear-resistant plastic.
Materials and Construction: Removal of refractory materials on the upper part of the secondary air outlet, production and welding of dowels, and formation of refractory and wear-resistant materials for the guide platform.
Catalytic combustion of 3-layer fly ash
The catalytic combustion technology of material layer fly ash achieves fly ash recirculation, which will appropriately affect the circulation rate. During implementation, patented technology is used to comprehensively utilize the fly ash from the lower part of the economizer, preheater, and dust collector according to the site conditions, which is significantly beneficial for denitrification. Experimental results have shown that fly ash returning to the material layer has a catalytic effect and can effectively reduce NOx.
The gas powder transmitter is precision manufactured using the principle of Venturi contraction expansion injection suction and vacuum extraction. It has a DN100 three-way structure and is made of all stainless steel (304 or 316) with good wear resistance. It is suitable for using 9-60KPa wind to create a vacuum chamber to suction powdered substances. After mixing with the powder, the gas is pressurized through a diffusion tube and then transported by a DN100 pipeline to a container that is horizontally 30-100 meters and vertically 12 meters away (container back pressure 2-3KPa). Suitable for power plants to continuously send fly ash into boilers for fly ash recirculation.
4. Implement uniform implantation of returned materials
Uniform implantation of returned materials can reduce the production of nitrate. Need to adjust the direction of material return. Uniform bed placement of returned materials can reduce the unevenness of bed temperature and decrease the production of nitrate in the furnace. The patented technology of dense phase flow guide platform in circulating fluidized bed boiler is used to adjust the direction of returned materials. Returning materials to the back wall will cause some of the returned materials to be discharged with the slag discharge, resulting in a relatively smaller circulation rate. Uniform bed placement of returned materials can increase the circulation rate, reducing the amount of returned materials discharged with the slag discharge. Materials and Installation: Fire resistant and wear-resistant plastic construction near the return port. A refractory pouring platform with a small inclination angle on the upper surface is set up near the furnace wall at the return port of the circulating fluidized bed boiler's dense phase zone diversion platform, allowing the return material to perform an approximate flat throwing motion after leaving the return port. The purpose is to prevent a large amount of return material from washing the air cap, effectively avoiding or slowing down the wear and dust leakage of the air cap. It can reduce significant economic losses.
The outstanding technical features of the dense phase flow guide platform in circulating fluidized bed boilers include: 1 Set up a refractory pouring table with a small inclination angle on the upper surface near the furnace wall at the return port. 2. After the return material leaves the return port, perform an approximate flat throwing motion to prevent a large amount of return material from washing the air cap. 3. The angle between the surface of the refractory pouring table at the return port and the horizontal plane is between 10 ° -18 °. 4. Improve the trapezoidal refractory pouring platform at the junction of the wind cap and furnace wall to have a sloping upper surface. Make the bed material flow along the slope to form an internal circulation, effectively preventing material accumulation. The angle between the surface of the refractory pouring table and the horizontal plane is between 30 ° and 45 °.
5. Implement uniform scattering of coal into the furnace
Uniform scattering of coal into the furnace can reduce the production of nitrate in the furnace. Using patented jet nozzle technology to adjust the direction of coal spraying air jet and air box. Using a gas jet at the coal chute to evenly scatter the incoming coal into the material layer can reduce the concentration of HCN in the flame and thus decrease the amount of rapid NOx generation.
ZL2015207063459， A tubular nozzle group for coal feeding port of fluidized bed boiler;
Introduction to the patented technology used: The coal feeding port of a circulating fluidized bed boiler in a power plant is generally located at the lower part of the furnace (about 1.2 meters from the bottom of the bed), and the coal enters the bed material at the lower part of the furnace through the coal feeding pipeline and then burns. The angle between the coal feeding pipeline and the horizontal direction is generally around 60 °. This steep angle causes the coal to concentrate in the bed material and form a pile, which is not conducive to rapid combustion. It also leads to uneven distribution of the burned ash in the flue gas. The burned ash is subjected to the pressure of the flue gas in the furnace and tends towards the furnace wall (water-cooled wall) where the coal feeding port is located, further causing high concentration of ash to wash and wear the water-cooled wall on that side. In severe cases, wear and leakage may occur, and the machine may be shut down for maintenance, seriously affecting normal production. The current circulating fluidized bed boiler has poor blowing and coal spreading effects on the coal feeding pipeline and coal feeding port, and coal accumulation in the material layer often occurs due to the lack of air chambers and nozzles for coal spreading, resulting in weak strength. The commonly used method now is to form an arc-shaped air outlet at the coal feeding port to enhance blowing, but the effect is not good. The coal spreading wind, due to its inability to play a role in coal spreading, causes coarse coal gangue particles to collide with the refractory and wear-resistant materials inside the coal feeding furnace for a long time, causing them to fall off. After the refractory and wear-resistant materials fall off, the water-cooled wall is exposed, and the exposed water-cooled wall tubes are soon worn and leaked by the coal gangue particles. After the leakage, the furnace needs to be shut down for maintenance.
Therefore, it is necessary to set up a nozzle below the coal feeding port to form a strong arc-shaped jet to blow and scatter the incoming coal, preventing a large amount of coal from accumulating in the material layer near the furnace wall, further preventing uneven distribution of ash residue in the flue gas after coal combustion, and preventing the water-cooled wall from being eroded and worn by high concentration ash residue.
The utility model invention patent discloses a tubular nozzle group for a coal feeding port of a fluidized bed boiler, which comprises a coal feeding pipeline, a raw coal spreading air duct, a furnace wall, a coal feeding port, a raw arc-shaped coal spreading air outlet, a tubular nozzle, a coal spreading air box, a material layer, and a tubular nozzle group. The feature is that a tubular nozzle is set below the coal feeding port, and 8 tubular nozzles form a tubular nozzle group. The tubular nozzle group is rectangular in shape, and the tubular nozzle group is built into the coal spreading air box. The volume of the coal spreading air box is several times that of the raw coal spreading air duct.
Installation and construction method: 1) Expand the original coal spreading air duct volume of the existing fluidized bed boiler into a new coal spreading air box, with the volume of the coal spreading air box being several times that of the original coal spreading air duct. The flow velocity of high velocity coal blowing air in a larger coal blowing box will decrease, and the static pressure of the coal blowing air will increase. This will increase the pressure difference on both sides of the tubular nozzle, thereby enhancing the gas jet. 2) Install tube nozzles below the original rectangular coal feeding port of the existing fluidized bed boiler, modify the coal feeding port, and adjust the size of the rectangular coal feeding port. The diameter of the tubular nozzle is 28-42mm, the wall thickness is 5mm, and the material is made of heat-resistant and wear-resistant steel 0Cr25Ni20. For boilers that do not have a lower coal spreading vent, add a lower coal spreading vent. 3) 6-8 tubular jet nozzles form a tubular nozzle group. 4) The tubular jet nozzle group is rectangular in shape, with the lower 8 tubular jet nozzles spraying in a direction 200mm beyond the longitudinal centerline of the air distribution plate. The tubular nozzle group forms a strong rectangular jet below the rectangular coal feeding port to blow and scatter the incoming coal, preventing a large amount of coal from accumulating in the material layer near the furnace wall. 5) The tubular jet nozzle group is built into the coal spraying box. 6) The jet nozzle is connected and welded to the bellows shell with broken steel plates. 7) The gaps between the jet nozzles are filled and welded with broken steel plates to prevent air leakage.
6. Improvement of separator efficiency and return feeder transformation
The selection of pressure and temperature for the return air of the material feeder is not conducive to denitrification, and it needs to be adjusted. If necessary, the gas supply system and the air distribution plate of the material feeder should be modified. Improper circulation ratio is not conducive to denitrification, and it needs to be adjusted by modifying the separator to improve efficiency; Use fire-resistant and wear-resistant materials to form a horizontal flue at the rear and gradually shrink. Due to the low flue gas velocity at the inlet of the separator, increasing the thickness of the wear-resistant material layer at the inlet of the separator and reducing the inlet area can increase the inlet flue gas velocity. After the addition of the convex platform contraction in this renovation, the flow velocity of the flue gas entering the separator inlet has increased to 26-30m/s, and the efficiency is expected to be further improved. After the reduction of the inlet cross-section of the separator, the amount of return material will be greatly increased. During the transformation, the return air velocity of the material feeder will be optimized according to the actual required air volume to ensure that the loose air volume is small while ensuring fluidization, in order to prevent reverse flow from affecting the efficiency of the separator. The adjustability of the return air is good to ensure smooth return of material. Set the nozzle group to adjust the circulation ratio.
7-layer low oxygen combustion adjustment and renovation
Circulating fluidized bed boilers commonly suffer from the problem of high nitrate content in oxygen enriched combustion of the material layer. The main reason for preventing coking is to use a high primary air rate and a large angle of downward inclination of the secondary air. A high oxygen content in the material layer will have a negative impact on denitrification in the furnace, and it is necessary to optimize and adjust it locally. In implementation, patented technology is used to adjust the oxygen content in the primary air on both sides of the boiler with water and gas. Low oxygen combustion in the material layer can achieve low nitrate combustion, which can significantly reduce the amount of nitrate produced during combustion. When the bed temperature is already high (close to 980 ℃), adjust the circulating ash amount to make the decrease in bed temperature not significant. When it is necessary to increase the primary air to lower the bed temperature, it is necessary to forcibly reduce the oxygen content of the material layer. Increasing the air does not increase the oxygen content! Realize low-temperature and low oxygen combustion. Install nozzles in the primary air duct of the boiler, using industrial water, well water, and circulating water to reduce the oxygen content of the primary air, suppress bed temperature, and appropriately increase the secondary air rate while ensuring fluidization efficiency, creating conditions for reasonable air classification of the secondary air.
This plan also includes flue gas recirculation, and the flue gas recirculation system can be used normally for 6 months every year.
Low oxygen combustion in the material layer can effectively reduce nitrogen oxides, which can only be reliably achieved on the basis of secondary air nozzle modification. The reason for this is that the circulating fluidized bed is inherently oxygen deficient at the center, and the addition of water vapor will exacerbate this situation. Therefore, it is necessary to undergo secondary air modification (diversion platform and tilt angle modification) to ensure the uniformity of oxygen content in the furnace. Due to the lack of secondary air modification, some projects directly added flue gas recirculation, which resulted in extremely harsh combustion conditions, with CO emissions reaching 10000ppm or higher. However, adding a material layer low oxygen combustion system to the CFB boiler after secondary air transformation can not only improve combustion, but also make the entire combustion uniform in the height and horizontal direction of the furnace.
Install guide plates on the 8 fins (welded with T-shaped fins in the middle)
For phenomena such as high bed temperature and high nitrate content, it is necessary to adjust the heat absorption in the middle of the furnace (while considering the reduction of heat absorption in the water-cooled wall caused by the secondary air bend or refractory material cover in the middle), and also appropriately reduce the bed temperature. Adopting the patented technology of welding guide plates (flat steel perpendicular to the fins) on the water-cooled wall fins in the middle, i.e. T-shaped fins. When the bed temperature is already high (close to 960 ℃), it is necessary to weld guide plates on the water-cooled fins in the middle of the four walls to enhance the heat absorption of the upper part of the furnace, which can affect the decrease in bed temperature. Weld a guide plate 2-3 meters high onto the water-cooled wall fins, using 0Cr25Ni20 flat steel, 6 * 35, double-sided spot welded.
Improvement and renovation of existing SNCR efficiency
Conduct a comprehensive inspection of the atomization situation of the existing SNCR nozzles, analyze the spray gun distribution points, confirm the uniformity of ammonia water in the flue, and confirm the adaptability of the flue gas temperature zone to denitrification (found temperature zone). The method of using a spray gun to spray ammonia or urea into the flue gas in the furnace, abbreviated as SNCR, can achieve a denitrification efficiency of 60&-80%. This method requires the flue gas temperature to be between 1100 ℃ and 850 ℃. Multiple denitrification spray guns of the current circulating fluidized bed boiler in power plants are installed in the horizontal flue at the furnace outlet. The denitration spray gun is installed in the horizontal flue at the furnace outlet, which has significant drawbacks. The denitration method of spraying ammonia water or urea inside the furnace requires a flue gas temperature of 1100 ℃ -850 ℃. The current circulating fluidized bed boiler has low denitration efficiency and even fails to meet the denitration standards when the flue gas temperature in the horizontal flue at the furnace outlet is below 850 ℃ under low load during operation. According to the current atmospheric environmental protection policy, if the NOx emissions from boiler flue gas do not meet the standard, the boiler must stop operating. Therefore, it is necessary to improve the arrangement of denitrification spray guns in circulating fluidized bed boilers to enhance denitrification efficiency, significantly reduce the nitrate in the flue gas emitted by the boiler, and design and implement a denitrification spray gun arrangement system for circulating fluidized bed boilers. The method to improve denitrification efficiency is to install denitrification spray guns in the middle of the boiler furnace. The temperature of the flue gas in the middle of the boiler furnace is between 980 ℃ and 850 ℃, which meets the requirements of the denitrification method of spraying ammonia water or urea inside the furnace. The height from the middle of the furnace to the outlet of the furnace is 15 meters, which allows sufficient reaction space and time for the ammonia water or urea sprayed into the furnace.
Patent number: ZL2016210579231， A denitrification spray gun arrangement system for circulating fluidized bed boilers.
summary of the invention
The purpose of this utility model is to provide a denitrification spray gun arrangement system for circulating fluidized bed boilers. A denitrification spray gun arrangement system for circulating fluidized bed boilers, comprising a boiler furnace, a horizontal flue, a denitrification spray gun, a screen heating surface, a rear wall, a front wall, and an arc-shaped atomizing airflow. Its feature is that multiple inclined denitrification spray guns are arranged on the front and rear walls in the middle of the boiler furnace. 2. Multiple denitrification spray guns arranged on the front and rear walls are all in the same horizontal plane. 3. The multiple denitrification spray guns arranged on the front and back walls form a hedge, and the centerlines of the two denitrification spray guns in the hedge are compared. 4. Each denitrification spray gun is tilted downwards, and the angle between the denitrification spray gun and the horizontal plane is not greater than 30 °. 5. The airflow at the outlet of the denitrification spray gun forms an arc-shaped atomized airflow under the action of the rising flue gas in the furnace. 6. Multiple denitrification spray guns arranged on the front and back walls form opposing streams, and the arc-shaped atomization airflow of every two opposing denitrification spray guns forms a W atomization airflow. 7. The tilted denitrification spray gun extends 150mm into the furnace. 8. The front 150mm section of the denitrification spray gun is made of wear-resistant material with a thickness of 0.5mm, and the denitrification spray gun is made of Cr25Ni20 heat-resistant and wear-resistant steel. 9. Multiple denitrification spray guns arranged on the front and rear walls in the middle of the boiler furnace should avoid the screen heating surface. The utility model arranges a denitrification spray gun in the middle of the boiler furnace, and the temperature of the flue gas in the middle of the boiler furnace is between 980 ℃ and 850 ℃, which meets the requirements of the denitrification method of spraying ammonia water or urea inside the furnace. The height from the middle of the furnace to the outlet of the furnace is 15 meters, which provides sufficient reaction space and time for the ammonia water or urea sprayed into the furnace. Four on each front and rear wall, with secondary air vents arranged on each wall.
Low nitrogen combustion of 10 orchid carbon exhaust gases
Add 12-20 sets of blue carbon tail gas burners on the front and rear walls of the boiler. Realize staged combustion. The combustion air is introduced from the primary air (with flue gas recirculation). It is necessary to make holes on the water-cooled wall in the middle of the boiler, and cut 2 pipes for each hole.
11 Operation optimization adjustment
The long-term habit of deviating from the optimized values of some main operating parameters will have a negative impact on denitrification in the furnace, which is mainly adjusted by the owner in accordance with technical requirements
★ Optimize and adjust the primary wind rate; Excessive deviation of the primary air flow rate is not conducive to denitrification and needs to be optimized and adjusted based on ensuring the particle size of the coal entering the furnace. If necessary, the owner may install a separate fine screening machine.
★ Optimize and adjust the secondary air ratio.
★ Optimize and adjust bed temperature. The deviation of bed temperature is too large, and increasing the primary air to adjust the bed temperature is extremely detrimental to denitrification. Optimization adjustment is necessary. Adopt warm air fluidization technology for adiabatic separators, adjust the circulation ratio to correct bed temperature deviation, and modify the return feeder to adjust the circulation ratio.
★ Optimize and adjust the oxygen content of flue gas. Control the oxygen content of flue gas and make correct judgments, taking into account the desulfurization inside the furnace.
★ Optimize and adjust bed pressure. Adjust the material layer appropriately and adjust its impact on bed temperature and NOx emissions.
★ Optimize and adjust the loop ratio; Adjust the circulation rate by running or taking ash adding measures to affect the bed temperature. Observe the changes in NOx in the flue gas during the above adjustments, identify the impact of each parameter on NOx in the flue gas, and then develop operating parameters that are beneficial for denitrification.
Attachment Patent Technical Support
ZL 2011200718979， Upper guide platform of fluidized bed secondary air nozzle;
ZL2013208604918， A middle wind furnace of a circulating fluidized bed boiler;
ZL2016209239099， A multi gap air supply device for circulating fluidized bed boilers;
ZL2017206666566， A gas powder sending device;
ZL2011200922059， Circulating fluidized bed boiler dense phase zone diversion platform;
ZL2015207063459， A tubular nozzle group for coal feeding port of fluidized bed boiler;
ZL2015207063444， A secondary wind direction deflection device for fluidized bed boilers;
ZL200720089314.9， Vertical water-cooled wall anti-wear groove of circulating fluidized bed boiler; ZL2011200815790， Primary air furnace on fluidized bed boiler bed;
ZL2011203222195， A cage type drum steel ball crusher;
ZL2016201007483， A screening spiral conveying device;
ZL2016201336175， A screening crusher;
ZL2011200815841， Comb shaped fins used for fluidized bed boiler tube banks;
ZL2007200923036， Circulating fluidized bed boiler with P and E fins;
ZL2016204148661， A low NOx combustion system for circulating fluidized bed boilers;
ZL201110100247.7， A steam heating method for bed materials of a fluidized bed boiler (invention);
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Case analysis:
Two 330MW 1178t/h CFB circulating fluidized bed boilers in Shanxi Youyu Power Plant were retrofitted for low nitrogen combustion (with technical support from Zhang Quansheng and 45 patents). When the load reached 245MW, the pure low nitrogen combustion flue gas nitrogen oxide concentration was 41mg/Nm3, easily achieving ultra-low emissions without urea denitrification! Industry insiders are welcome to investigate.
After 3-4 months of implementing SNCR denitrification in the steam and water workshop of Inner Mongolia Dalate New Energy Group Company's power plant, serious ash accumulation in the economizer developed into ash blockage. The boiler burns inferior bituminous coal. In March 2015, Zhang Quansheng, a former CFB expert from China Electric Power Union, was invited to the site to solve problems, conduct technical diagnosis, give lectures and exchanges, and come up with solutions; One boiler was renovated in April, and by September, all three boilers had been renovated, adjusted, and debugged; The ammonia water consumption for SNCR denitrification of 3 CFB boilers is equal to zero!
Three 240t/h CFB boilers in Yunnan Xuanwei Phosphorus Power Company's power plant were retrofitted with central wind power in 2009, but without SNCR system, the NOx in the flue gas naturally remained below 180mg/Nm3! At that time, Zhang Quan was in charge of the power plant as the assistant general manager of the Phosphorus Power Company.
The 130t/h medium temperature separation differential bed CFB boiler of Jingfu Coal Chemical Company Thermal Power Plant in Fugu County, Shaanxi Province has been successfully retrofitted for low nitrogen combustion. The converted concentration of nitrogen oxides in the flue gas is 60mg/Nm3 at full load without the use of ammonia water! The local environmental standard for flue gas nitrogen oxide concentration is 100mg/Nm3, which easily achieves the standard emission of ammonia free flue gas denitrification. A small amount of ammonia water can meet the ultra-low emission standard of less than 50mg. (Before the renovation, coal slurry accounted for 30%, boiler load was 132t/h, ammonia water volume was 0m3/h (ammonia water was cut off), high bed temperature was 968, flue gas oxygen content was 4.51/8.43 (after low temperature/chimney), and flue gas nitrogen oxide concentration was as high as 300/366mg/Nm3 (measured value/converted). After the renovation, cutting off ammonia water saved more than 2 million yuan in annual ammonia water procurement costs)!
Annex CFB flue gas denitrification ultra-low emission or ultra-low ammonia consumption transformation technology characteristics
Deep low nitrogen combustion technology (DLNC) in the furnace, emphasizing deep low nitrogen combustion denitrification in the furnace; The depth of deep denitrification in the furnace is manifested in the classification of secondary air depth, lower primary air rate, deep layer low oxygen combustion technology, and deep layer fly ash catalytic combustion technology; It is also manifested in the pursuit of maximizing the denitrification efficiency inside the furnace (60-70% related to bed temperature), but not deliberately pursuing the maximization of denitrification efficiency inside the furnace. This is to take into account the flue gas temperature and oxygen content required for normal denitrification of the SNCR system. DLNC+SNCR efficiency improvement is necessary to ensure ultra-low emissions of flue gas denitrification in CFB boilers.
The deep low nitrogen combustion technology (DLNC) in the furnace is mainly characterized by:
★ Secondary air depth graded combustion
★ Catalytic combustion of material layer fly ash
★ Deep layer low oxygen combustion
★ Lower primary wind rate
★ Optimize the fluidization status of materials in the furnace (provide technical support for improving the air cap and air distribution plate)
★ Improve ignition and burnout characteristics (particle size adjustment, uniform coal scattering, and uniform material return implantation technology)
★ Five major cycles (internal, external, bottom slag, fly ash, flue gas)
★ Five port renovation (hood outlet, secondary outlet, coal inlet, coal sowing outlet, return outlet)
★ Five Uniformities (primary air, secondary air, coal combustion, return material, smoke temperature)
★ Adding ash (adjusting the circulation ratio to affect the bed temperature)
★ Three elimination and two reduction (eliminating local oxygen enrichment, reducing general oxygen enrichment, eliminating local hypoxia, eliminating local high temperature, and reducing general high temperature)
★ Effective nitrogen reduction height in the reduction zone and efficient desulfurization and denitrification (SNCR) in the oxidation zone
★ Heat recirculation maintains bed temperature
★ Smoke duct air supply and water spraying (taking into account desulfurization)
The technical characteristics of DLNC flue gas denitrification ultra-low emission system are mainly manifested in:
One outstanding, two combined, three balanced, four uniform, five mouth transformation, six cycles.
1 ）. Highlight deep ultra-low nitrogen combustion technology
The difference between deep low nitrogen combustion technology and ordinary low nitrogen combustion lies in its depth and efficiency, with a denitration efficiency of about 70% in the furnace while maintaining stable combustion of the boiler.
2）. The principle of combining the two
Adhere to the combination of deep low nitrogen combustion and SNCR efficiency improvement, and deep ultra-low nitrogen combustion must be combined with SNCR efficiency improvement to achieve ultra-low emissions of flue gas denitrification. It is impossible to achieve ultra-low emissions of flue gas denitrification by working alone. It should be emphasized here that although the low bed temperature and low oxygen content correspond to low nitrogen combustion flue gas denitrification emission values, this is based on sacrificing boiler design combustion efficiency and sacrificing SNCR non reaction, ultimately failing to meet ultra-low emission requirements. The owner does not agree and finds it difficult to accept.
3）. Balancing three aspects
Deep low oxygen and low temperature combustion:
To ensure that the bed temperature meets the SNCR reaction temperature window and the SNCR can function normally; To balance the bed temperature and oxygen content to meet the combustion efficiency requirements of the boiler design; We need to take into account the impact on desulfurization and oxygenation inside the furnace.
After the low nitrogen combustion transformation, the combustion share in the upper part of the furnace will increase, and the difference between the flue gas temperature at the furnace outlet and the bed temperature will be very small, which is more conducive to achieving the temperature window and complete combustion of fly ash required by SNCR in the later stage.
At low loads, the SNCR middle spray gun is used to ensure the temperature window required by the SNCR, while the oxygen content in this temperature window area is sufficient to maximize the efficiency of the SNCR.
4）. Four uniformly fluidized ones.
Evenly scatter coal. Uniformity of material and oxygen content in flue gas. Uniform implantation of returned materials.
By achieving temperature uniformity between the material and the flue gas through four uniformities, the purpose of temperature uniformity is to eliminate the peak nitrate caused by local high temperatures and achieve an ideal low nitrogen temperature environment of 880-940 ℃. The uniform local oxygen level maintains a reducing atmosphere in the overall low nitrogen environment of the dense phase zone inside the furnace.
5）. Five port renovation of hood air outlet. Secondary air outlet. Coal inlet. Coal blowing vents. Return port.
Through the above five port renovation, local oxygen enrichment is eliminated, general oxygen enrichment is reduced, local hypoxia is eliminated, and local high temperature is eliminated.
6）. Six types of internal loops.
External circulation, bottom slag recirculation, fly ash recirculation, flue gas recirculation, heat recirculation.
Through the above six cycles, the problem of severe impact on the ultra-low emission effect of flue gas denitrification caused by excessively high or low bed temperature under high and low boiler loads can be solved.
Power Plant CFB Deep Low Nitrogen Combustion (DLNC) ----------------------------------------------------------------------
Attachment: Three major principles of NOx generation during combustion process
The mechanism of NOx generation during combustion is much more complex than SO2, and the concentration of NOx in flue gas cannot be calculated from the sulfur content of coal like SO2. Its generation is closely related to the combustion method, especially the combustion temperature and excess air coefficient. NOx is a general term for NO and NO2, and the NOx in flue gas of coal-fired power plants is mainly produced by coal combustion. Usually, the NOx generated by combustion consists of over 90% NO and less than 10% NO2. According to the mechanism of nitrogen oxide generation, it can be divided into three types: thermal type, fuel type, and rapid type NOx. Among them, rapid type NOx generates very little and can be ignored.
There are three ways in which NOx is generated during the combustion process (generation mechanism):
(1) Fuel NOx
Produced by the oxidation of nitrides in fuel after thermal decomposition. Fuel type NOx refers to the NOx generated by organic nitrogen compounds in the fuel during combustion, and its amount mainly depends on the air-fuel mixture ratio. Fuel type NOx accounts for approximately 75% to 90% of the total NOx generated during combustion. For conventional coal-fired boilers, NOx is mainly generated through fuel based pathways!.
The amount of fuel type NOx produced is related to the nitrogen content of the fuel. Nitrogen in coal ranges from 0.4% to 2.9% and exists in the form of cyclic nitrogen-containing compounds such as pyridine, quinoline, indole, etc. During the coal combustion process, approximately 20-80% of nitrogen is converted into NOx, with NO accounting for 90-95%. NO2 is formed by the conversion of a portion of NO downstream of the flame zone or after emission. The NOx generated during coal combustion mainly originates from nitrogen-containing fuel type NOx in coal, accounting for about 75-90%.
The generation mechanism of fuel type NOx is very complex, and its generation and destruction process is related to the proportion of nitrogen in the fuel after thermal decomposition in the volatile matter and coke, which varies with combustion conditions such as temperature and oxygen. Nitrogen compounds are first converted into intermediate products such as cyanide (HCN), ammonia (NH3), and CN that can precipitate from the fuel along with the volatile components. This part of nitrogen is called volatile component N, and the generated NOx accounts for 60% to 80% of the fuel type NOx. The nitrogen-containing compounds remaining in the coke are called coke N. Figure 1 is a schematic diagram of the conversion of nitrogen in coal into volatile matter N and coke N.
(Reducing the air volume once to reduce the oxygen content of the material layer, while low-temperature combustion can reduce the amount of production. The bed temperature mainly depends on the adjustment of circulating ash)
According to the market buying and selling situation, purchasing coal with low nitrogen content can reduce denitrification costs, and combined with low nitrogen combustion in the furnace, it can prevent ash blockage in the economizer!.
(2) Thermal NOx
N2 in the air oxidizes at high temperatures. Thermal NOx refers to the oxidation of nitrogen in the air to form NOx at high temperatures when the furnace temperature is above 1350 ℃. When the temperature is high enough, thermal NOx can reach 20%. At temperatures below 1300 ℃, there is almost no thermal NOx.
Thermal NOx is the sum of NO and NO2 generated by N2 and O2 in the air at high temperatures during combustion. Its generation characteristic is that the generation reaction is slower than the combustion reaction, mainly generating NOx in the high-temperature zone downstream of the flame zone. The reaction equation is as follows: N2+O=NO+N （1） N+O2=NO+O （2） N+OH=NO+H （3）
Some basic combustion experiment data shows that when the temperature is<1350 ℃, fuel type NOx accounts for almost 100%; When the temperature is 1600 ℃, thermal NOx accounts for 25-30%. The generation of thermal NOx is slower than the combustion reaction, therefore, accelerating the combustion process can effectively suppress the generation of thermal NOx. (Zhang Quansheng: The fluidized bed combustion method involves the release of heat during the movement of carbon particles at a height of 20-40 meters (as evidenced by the fact that the smoke temperature does not drop much after the screen heating surface absorbs heat), making it impossible to achieve accelerated combustion. Only by controlling the operation to achieve low oxygen and low-temperature combustion can the production of nitrate be reduced.); When the bed temperature is below 1300 ℃, the circulating fluidized bed boiler has almost no thermal NOx, but the bed temperature still needs to be controlled not to exceed 930 ℃. (3) Prompt NOx
Produced by the reaction between N2 in the air and hydrocarbon ion groups (such as CH) in the fuel. Rapid NOx refers to the reaction between nitrogen in the air and hydrocarbon ion groups (CH) in the fuel during combustion to generate NOx. When hydrocarbon fuels are burned with rich fuel, NOx is rapidly generated near the reaction zone. It is the collision of hydrocarbon (CH, CH2, CH3, and C2) ion clusters generated during fuel combustion with N2 in the combustion air to produce HCN CN， Then it reacts with a large amount of O and OH generated in the flame to produce NCO, which is further oxidized to NO. In addition, when the concentration of HCN in the flame is high, there are a large number of ammonia compounds (NHi) that react rapidly with oxygen atoms to generate NO. Rapid NOx is generated by the reaction of CHi radicals and N2 molecules to form HCN, which is then oxidized through several subsequent elementary reactions. The superoxide entering the high-temperature material layer with coal can rapidly dissociate active oxygen atoms [O], By increasing the concentration of active oxygen atoms [O] in the combustion atmosphere, it can promote the oxidation reaction of CHi radicals and inhibit the reaction between CHi radicals and N2, thereby achieving the goal of reducing rapid NOx. It can be seen that superoxide can effectively suppress the generation of some NOx, thereby reducing harmful gas emissions and exhaust treatment costs in factory production processes, and forming better comprehensive benefits for users. Among these three NOx generation pathways, the proportion of rapid NOx is less than 5%; So the rapid generation of NOx is very small and can be ignored.
