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CN-121993784-A - Circulating fluidized bed flue gas recirculation system and circulating method thereof

CN121993784ACN 121993784 ACN121993784 ACN 121993784ACN-121993784-A

Abstract

The invention provides a circulating fluidized bed flue gas recirculation system and a circulating method thereof, which relate to the technical field of boiler flue gas treatment and comprise a waste heat exchanger, a recirculation fan and a flow distributor, wherein an outlet of a second pipeline is sequentially connected with a dense phase region and a dilute phase region, two branch pipelines of the dense phase region are sequentially communicated with an electric proportion adjusting baffle, a fan heater, a primary fan and a preheater, the preheater is connected with an air chamber, an arc-shaped guide plate is arranged in the air chamber along the length direction, an abrasion-resistant composite hood is arranged on an air distribution plate of a furnace from the air chamber, the dilute phase region is connected with the dilute phase region of the furnace, a stop valve is arranged on an outlet pipeline of the dilute phase region, a third pipeline and a flue gas bypass, the problem that denitration efficiency and flue gas temperature adjusting effect are poor under low-load working conditions is solved, the direct dilution of flue gas injected into the dilute phase region to achieve high Wen Ouyang concentration, meanwhile, the generation of reducing components is supplemented, and the technical effect of ultralow emission requirements is met.

Inventors

  • TANG GUOAN
  • ZHOU XIAOMING
  • TANG XIUNENG
  • HE JIANLE
  • WANG WENYU
  • LIANG XIUJIN
  • HU ZHIYONG
  • Yang Haoyin
  • CHEN JUNHUA
  • Lv Buchu

Assignees

  • 华电电力科学研究院有限公司

Dates

Publication Date
20260508
Application Date
20260331

Claims (10)

  1. 1. The circulating fluidized bed flue gas recirculation system comprises a furnace (1), wherein the furnace (1) is sequentially provided with a first pipeline (2), an induced draft fan (3) and a chimney (4) along the flue gas flowing direction, the outlet of the induced draft fan (3) is communicated with a flue gas bypass (6) through a second pipeline (5), the flue gas bypass (6) is connected into the first pipeline (2) as shutdown protection, a third pipeline (7) is further connected onto the second pipeline (5) as hot secondary air, The outlet of the second pipeline (5) is sequentially connected with a waste heat exchanger (8), a recirculation fan (9) and a flow distributor (10), and two outlets of the flow distributor (10) are respectively a dense-phase area outlet pipeline (11) and a dilute-phase area outlet pipeline (12); The dense-phase area outlet pipeline (11) is provided with two branch pipelines (13), each branch pipeline (13) is sequentially communicated with an electric proportion adjusting baffle (14), a fan heater (15), a primary fan (16) and a preheater (17), the preheater (17) is connected with an air chamber (18), an arc-shaped guide plate (19) is arranged in the air chamber (18) along the length direction, and an abrasion-resistant composite hood (20) is arranged on an air distribution plate from the air chamber (18) to the hearth (1); The dilute phase zone outlet pipeline (12) is connected to the dilute phase zone of the hearth (1), and stop valves are arranged on the dilute phase zone outlet pipeline (12), the third pipeline (7) and the flue gas bypass (6).
  2. 2. The recirculation system of claim 1, wherein the fluid is a liquid, The waste heat exchanger (8) is a finned tube type flue gas air heat exchanger and is used for preheating primary air by utilizing waste heat of recycled flue gas.
  3. 3. The recirculation system of claim 1, wherein the fluid is a liquid, The distance between the arc-shaped guide plates (19) in the air chamber (18) is 2-3 m, and the air chamber (18) is divided into 3-4 independent fluidization areas; The access point of the dilute phase region outlet pipeline (12) is positioned at a position 6-8 m away from the air distribution plate in the hearth (1), and the temperature in the hearth (1) is 850-950 ℃.
  4. 4. The recirculation system of claim 1, wherein the fluid is a liquid, The recirculation fan (9) is connected with an inert gas storage tank (21).
  5. 5. A method of recirculating flue gas in a circulating fluidized bed, characterized in that the method uses a recirculation system according to any one of claims 1-4, comprising the steps of: Step 1, under the low-load working condition, extracting part of flue gas from an outlet of the induced draft fan (3) of the boiler, and introducing the part of flue gas into the second pipeline (5); Step 2, after the flue gas in the second pipeline (5) is preheated by the waste heat exchanger (8), the flue gas pressurized by the recirculation fan (9) is distributed to the dense-phase zone outlet pipeline (11) by 60% -70% through the flow distributor (10), and is distributed to the dilute-phase zone outlet pipeline (12) by 30% -40%; step 3, mixing the flue gas of the dense-phase zone outlet pipeline (11) with primary air after the proportion is controlled by the electric proportion adjusting baffle (14), and sending the mixture into the air chamber (18) after the mixture is heated by the fan heater (15), the primary air fan (16) and the preheater (17) in sequence; Step 4, the mixed gas in the air chamber (18) flows through the arc-shaped guide plate (19) for partition flow guiding, and is uniformly injected into a dense-phase region of the hearth through the wear-resistant composite hood (20); step 5, directly injecting the flue gas of the dilute phase region outlet pipeline (12) into a high-temperature core region of the dilute phase region of the hearth (1) after the flue gas is regulated by a stop valve; And 6, closing an outlet pipeline (12) of the dilute phase region when the system is stopped, and opening a secondary hot air reflux pipeline of the flue gas bypass (6) and the third pipeline (7) to prevent condensate corrosion.
  6. 6. A recycling method according to claim 5, characterized in that, In the step 2, the calculation formula of the distribution of the recycled smoke of the dense-phase zone outlet pipeline (11) and the dilute-phase zone outlet pipeline (12) is as follows: (1); (2); Wherein, the Is the flow rate of the dense phase zone; Is the flow rate of a dilute phase zone; is the total circulating smoke flow; the proportion of smoke in the dense phase area; is the proportion of flue gas in the dilute phase region.
  7. 7. A recycling method according to claim 5, characterized in that, The waste heat recovery amount of the waste heat exchanger (8) in the step 2 is as follows: (3); Wherein, the The specific heat is fixed for the flue gas; The specific heat is fixed for the air pressure, Is the quality of the flue gas, In order to be of air quality, Is the temperature reduction value of the flue gas, The temperature of the air is raised.
  8. 8. A recycling method according to claim 5, characterized in that, In the step 3, the adjustment precision of the electric proportional adjustment baffle (14) is +/-1 degrees, and the calculation formula of primary air in the electric proportional adjustment baffle (14) is as follows: (4); Wherein, the For the air quantity required by theoretical combustion, The primary air excess coefficient is less than or equal to 1.05.
  9. 9. A recycling method according to claim 5, characterized in that, In the step 4, the wear-resistant composite hood (20) is made of silicon carbide chromium alloy, and a calculation formula of small hole wind speed of the wear-resistant composite hood (20) is as follows; (5); Wherein, the N is the number of wind caps of a single boiler; the radius of the single hole is 5mm; the flow coefficient was 0.85.
  10. 10. A recycling method according to claim 5, characterized in that, The specific steps of the step 6 include: step 6.1, closing a stop valve on the dilute phase zone outlet pipeline (12) to stop the injection of the dilute phase zone flue gas; And 6.2, opening a stop valve on the flue gas bypass (6), closing a valve of the second pipeline (5), and opening a stop valve on the third pipeline (7) to lead secondary hot air into the second pipeline (5) so as to prevent flue gas condensate from corroding the pipeline and equipment.

Description

Circulating fluidized bed flue gas recirculation system and circulating method thereof Technical Field The invention relates to the technical field of boiler flue gas treatment, in particular to a circulating fluidized bed flue gas recirculation system and a circulating method thereof. Background The circulating fluidized bed boiler has become the main stream combustion equipment of coal burning thermoelectric because of advantages of wide fuel adaptability, high combustion efficiency, low original emission of pollutants, etc. The flue gas recirculation technology is widely applied to ultralow emission modification and energy-saving optimization of a circulating fluidized bed boiler as a means for regulating and controlling the combustion atmosphere in the boiler, reducing the generation of nitrogen oxides (NO x) and improving the low-load operation stability of the boiler. The prior art discloses a China patent with publication number CN120926434A, which discloses a low-load flue gas recirculation system for a circulating fluidized bed boiler, and mainly comprises a hearth, an induced draft fan, a recirculation fan, a connecting pipeline, an air chamber, a conventional carbon steel hood and a preheating and heat exchange auxiliary equipment set. The flue gas circulation path is that after the flue gas at the outlet of the induced draft fan is led out through a pipeline, the flue gas is pressurized by a recirculation fan and is concentrated and injected into the bottom of a dense-phase region of the hearth only through an air chamber, an air distribution plate and a conventional hood, the mixing proportion of the recirculation flue gas and primary air is regulated only by the flow of the fan, an independent flue gas waste heat recovery device is not configured in the system, a fluidization homogenization diversion structure is not arranged in the air chamber, and equipment shutdown anti-corrosion protection is realized only through a flue gas bypass and secondary hot air reflux. Therefore, in the prior art, the injection point of the recycled flue gas is single and is only concentrated in the dense-phase region of the hearth, an independent injection channel is not arranged in the dilute-phase region of the NO x generating core, the reducing atmosphere of the high-temperature core region cannot be accurately reinforced, and the denitration efficiency and the flue gas temperature regulation and control effect are poor under the low-load working condition. Disclosure of Invention The invention aims to provide a circulating fluidized bed flue gas recirculation system and a circulating fluidized bed flue gas recirculation method, which are used for solving the technical problems of poor denitration efficiency and poor flue gas temperature regulation effect under a low-load working condition in the prior art. The invention provides a circulating fluidized bed flue gas recirculation system, which comprises a hearth, wherein the hearth is sequentially provided with a first pipeline, an induced draft fan and a chimney along the flue gas flowing direction, an outlet of the induced draft fan is communicated with a flue gas bypass through a second pipeline, the flue gas bypass is connected into the first pipeline as shutdown protection, and a third pipeline is connected onto the second pipeline as hot secondary air; The outlet of the second pipeline is sequentially connected with a waste heat exchanger, a recirculation fan and a flow distributor, and the two outlets of the flow distributor are respectively a dense-phase area outlet pipeline and a dilute-phase area outlet pipeline; the dense-phase area outlet pipeline is provided with two branch pipelines, each branch pipeline is sequentially communicated with an electric proportion adjusting baffle, a warm air blower, a primary fan and a preheater, the preheater is connected with an air chamber, an arc-shaped guide plate is arranged in the air chamber along the length direction, and a wear-resistant composite hood is arranged on an air distribution plate from the air chamber to a hearth; the dilute phase zone outlet pipeline is connected to the dilute phase zone of the hearth, and the dilute phase zone outlet pipeline, the third pipeline and the flue gas bypass are all provided with stop valves. Further, the waste heat exchanger is a fin-tube type flue gas air heat exchanger and is used for preheating primary air by utilizing waste heat of recycled flue gas. Further, the distance between the arc-shaped guide plates in the air chamber is 2-3 m, and the air chamber is divided into 3-4 independent fluidization areas; the access point of the dilute phase region outlet pipeline is positioned at a position 6-8 m away from the air distribution plate in the hearth, and the temperature in the hearth is 850-950 ℃. Further, an inert gas storage tank is connected to the recirculation fan. The invention provides a circulating fluidized bed flue gas recirculation method, which uses