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CN-122006445-A - Optimized flue gas denitration system of circulating fluidized bed boiler

CN122006445ACN 122006445 ACN122006445 ACN 122006445ACN-122006445-A

Abstract

The invention provides an optimized flue gas denitration system of a circulating fluidized bed boiler, which belongs to the technical field of flue gas denitration and comprises a boiler, a cyclone separator group, a preheater, a dust remover, an induced draft fan, a chimney, a material returning device, an air chamber, a jet system and a flue gas recirculation device, wherein the cyclone separator group comprises a plurality of cyclone separators, the jet system comprises a static mixer, a first spray gun group and a second spray gun group, and the flue gas recirculation device comprises a recirculation fan and a primary fan. The invention meets the ultra-low emission requirement by SNCR dynamic zone injection, smoke recirculation load-changing self-adaption and coal-denitration advanced linkage based on the difference between the inlet and the outlet of the cyclone separator, and solves the problem of NOx fluctuation under load and coal changing.

Inventors

  • LUO HUI
  • GUAN XIAOXIAO
  • ZHU XIANG
  • FANG PAN
  • SUN QIAN
  • GONG JIALONG
  • LI WENZHEN
  • YANG WEI

Assignees

  • 武汉龙净环保工程有限公司

Dates

Publication Date
20260512
Application Date
20260130
Priority Date
20251215

Claims (10)

  1. 1. An optimized circulating fluidized bed boiler flue gas denitration system comprises a boiler (110), a cyclone separator group (120) connected with the boiler (110), a preheater (130) connected with the cyclone separator group (120), a dust remover (140) connected with the preheater (130), an induced draft fan (150) connected with the dust remover (140), a chimney (160) connected with the induced draft fan (150), a material returning device (170) connected with the boiler (110) and the cyclone separator group (120), and an air chamber (180) arranged at an inlet of the boiler (110), and is characterized by further comprising an injection system (200) and a flue gas recirculation device (300), wherein the cyclone separator group (120) comprises a plurality of cyclone separators (121); The injection system (200) comprises a static mixer (210), a first spray gun group (220) and a second spray gun group (230), wherein the static mixer (210) is connected with dilution water and reducing agent, the first spray gun group (220) is arranged at the inlet of a cyclone separator (121), the first spray gun group (220) is connected with the static mixer (210), the first spray gun group (220) comprises a plurality of narrow-angle atomizing spray heads (221), the second spray gun group (230) is arranged at the outlet of the cyclone separator (121), the second spray gun group (230) is connected with the static mixer (210), and the second spray gun group (230) comprises a plurality of wide-angle atomizing spray heads (231); The flue gas recirculation device (300) comprises a recirculation fan (310) and a primary fan (320), wherein one end of the recirculation fan (310) is connected with a flue between an outlet of the induced draft fan (150) and an outlet of the cyclone separator (121), the other end of the recirculation fan is connected with an inlet of the primary fan (320), an inlet of the primary fan (320) is connected with air, and an outlet of the primary fan is connected with the preheater (130).
  2. 2. The optimized circulating fluidized bed boiler flue gas denitration system of claim 1, wherein the spray angle of the narrow-angle spray nozzle (221) is 30 degrees, the spray particle size is controlled to be 50-80 μm, the spray angle of the wide-angle spray nozzle (231) is 60 degrees, and the spray particle size is controlled to be 80-120 μm.
  3. 3. An optimised circulating fluidised bed boiler flue gas denitrification system according to claim 2, wherein the first lance set (220) is connected to the static mixer (210) by a first distribution line (240), the first distribution line (240) pressure being set at 0.8-1.0MPa; The second spray gun group (230) is connected with the static mixer (210) through a second distribution pipeline (250), and the pressure of the second distribution pipeline (250) is set to be 0.6-0.8MPa.
  4. 4. An optimized circulating fluidized bed boiler flue gas denitration system according to claim 3, wherein 50% of narrow angle atomizer heads (221) and wide angle atomizer heads (231) are applied when in low load operation, 75% of narrow angle atomizer heads (221) and wide angle atomizer heads (231) are applied when in medium load operation, and all narrow angle atomizer heads (221) and wide angle atomizer heads (231) are applied when in full load operation.
  5. 5. An optimised circulating fluidised bed boiler flue gas denitrification system according to claim 4, characterised in that there are 4 cyclones (121), each cyclone (121) being provided with 6 narrow angle atomising heads (221) and 4 wide angle atomising heads (231).
  6. 6. An optimised circulating fluidised bed boiler flue gas denitrification system according to claim 5, wherein the concentration of urea solution in the static mixer (210) is increased to 15% when the concentration of NOx in the flue gas is >300mg/m3 and the concentration of urea solution in the static mixer (210) is decreased to 10% when the concentration of NOx in the flue gas is <150mg/m 3.
  7. 7. An optimized circulating fluidized bed boiler flue gas denitration system according to claim 1, wherein the number of the primary fans (320) is 2, the recirculation fans (310) are connected with the pressure transmitter (311) and the temperature sensor (312) and then are connected with one primary fan (320) through a main pipeline (330) and then are connected with the other primary fan (320) through a bypass pipeline (340), the main pipeline (330) is provided with a flue gas flow meter (350) and a main electric regulating valve (331), and the bypass pipeline (340) is provided with the flue gas flow meter (350) and a bypass electric regulating valve (341).
  8. 8. The flue gas denitration system of an optimized circulating fluidized bed boiler as set forth in claim 7, wherein the circulation amount of the recirculation fan (310) is automatically increased to 18-20% when the bed temperature is >950 ℃, the circulation amount of the recirculation fan (310) is decreased to 10-12% when the bed temperature is <850 ℃, and the circulation amount of the recirculation fan (310) is additionally increased by 2-3% when the coal nitrogen content is > 1.5%; when the circulation volume of the recirculation fan (310) is increased by more than 5%, the urea injection volume is reduced by 3-4% in advance by the injection system (200), and when the power grid voltage fluctuates by +/-10%, the frequency converter of the recirculation fan (310) is automatically switched to a voltage stabilizing mode.
  9. 9. An optimised circulating fluidised bed boiler flue gas denitrification system according to claim 8, wherein the plenum (180) is connected to the preheater (130) by a flue gas bleed branch (370); The inlet of the boiler (110) adopts high-temperature flue gas in the air chamber (180) at high load, the air chamber (180) introduces low-temperature flue gas in the preheater (130) at low load, and the preheater (130) regulates the temperature of the flue gas, so that the temperature of air entering the air chamber (180) is regulated at 150-200 ℃.
  10. 10. An optimised circulating fluidised bed boiler flue gas denitrification system according to claim 9, wherein the flue gas recirculation means (300) further comprises a venturi mixing nozzle (360), the venturi mixing nozzle (360) comprises a first inlet (361), a second inlet (362), a mixing outlet (363) and a scaling structure (364), the first inlet (361) is connected with air, the second inlet (362) is connected with a main circuit electric regulating valve (331) and a bypass electric regulating valve (341), the mixing outlet (363) is connected with a primary fan (320), the scaling structure (364) comprises a shrink tube (3641), a throat nozzle (3642) and a expansion tube (3643) which are connected in sequence, the first inlet (361) and the second inlet (362) are connected with the shrink tube (3641) inlet, the mixing outlet (363) is connected with the primary fan (320), and the inner wall of the throat nozzle (3642) is provided with arc-shaped turbulence teeth (3644).

Description

Optimized flue gas denitration system of circulating fluidized bed boiler Technical Field The invention relates to the technical field of flue gas denitration, in particular to an optimized circulating fluidized bed boiler flue gas denitration system. Background Under the current energy structure taking coal-fired power generation as a main body, a Circulating Fluidized Bed (CFB) boiler becomes one of core equipment for power supply due to the characteristics of wide fuel adaptability and high combustion efficiency, however, a large amount of nitrogen oxides (NOx) can be generated in the combustion process of the circulating fluidized bed boiler, the NOx is one of main atmospheric pollutants, the harm to the environment and the human health is extremely serious, and along with the increasing strictness of national environmental protection standards, the requirement on the emission limit value of the NOx in the flue gas of a thermal power plant is continuously improved, so that the deep emission reduction of the NOx becomes an important subject to be solved urgently in the coal-fired power plant. In recent years, the national environmental protection policy is continuously coded, the control standard for the emission of the atmospheric pollutants of the thermal power plant is becoming severe, the emission limit value of nitrogen oxides (NOx) is being tightened, the ultra-low emission (less than or equal to 50mg/m < 3 >) becomes a hard index for the survival and development of the coal-fired unit, and in the background, the flue gas denitration system of the Circulating Fluidized Bed (CFB) coal-fired unit faces unprecedented challenges. The existing flue gas denitration device of a 2X 300MWCFB coal-fired unit adopts a selective non-catalytic reduction (SNCR) process, the design boundary of the existing flue gas denitration device definitely requires that the original concentration of boiler NOx is not higher than 300mg/m < 3 > when the SNCR system is stopped, however, in the actual operation process, the original concentration of NOx of the unit is always in the range of 250-350mg/m < 3 >, the denitration efficiency of the existing SNCR process can only be maintained at 50% -70%, and the NOx emission concentration is difficult to stably control within the ultra-low emission limit (less than or equal to 50mg/m < 3 >) even under ideal working conditions, so that the requirements of the current and future environmental protection policies can not be met. The problem is particularly prominent under the low-load working condition in the running process of the unit, the generation amount of NOx is obviously increased due to the fact that the oxygen amount of the unit running at the low-load moment is high, the existing denitration system lacks effective dynamic adjustment capability, the impact caused by the working condition change is difficult to cope with, the fluctuation of the emission concentration of NOx is large, and the exceeding risk is extremely high. Meanwhile, the conventional SNCR system has a plurality of short plates, the phenomenon of uneven ammonia spraying is common, the mixing effect of urea solution and flue gas is poor, the partial denitration reaction is insufficient, the temperature window is easy to deviate, the denitration efficiency is further reduced, the ammonia escape rate is high, the waste of reducing agent is caused, the subsequent problems of air preheater blockage, corrosion and the like can be caused, and the safe and stable operation of a unit is influenced. Therefore, the development of the technology for realizing high-efficiency denitration, adapting to working condition change and deep emission reduction under the premise of ensuring normal operation of a unit is necessary, the NOx emission concentration is further reduced to an ultralow limit value, and the stricter environmental protection requirement is met. Disclosure of Invention The invention aims to overcome the defects of the background technology and provide an optimized flue gas denitration system of a circulating fluidized bed boiler. The invention mainly solves the problems that 1) the existing SNCR denitration system is unstable in denitration efficiency under a variable load working condition, NOx emission concentration is difficult to stably control within an ultralow limit value, especially in low load operation, the original NOx generation concentration is increased due to higher unit operation oxygen content, the denitration effect is affected, 2) the quantity of spray guns, arrangement modes and the like of the existing SNCR injection system are unreasonable, so that urea solution and flue gas are insufficiently and uniformly mixed, the sufficient denitration reaction is affected, the denitration efficiency is reduced, 3) a urea solution preparation system, a flow distribution system, a control system and the like are not matched with the denitration requirement after modification, urea solution consumptio