Numerical simulation of low nitrogen combustion in CFB boiler based on post-combustion technology
Severe environmental protection policies have put forward higher requirements for coal combustion power generation.As a mature clean coal power generation technology,the circulating fluidized bed(CFB)boiler has broad research prospects.CFB post-combustion technology is a new type of fluidized bed out-of-stock technology that has been applied to 75 t/h CFB coal slime boilers and achieved ultra-low NOx emissions.Exploring the feasibility and effectiveness of post-combustion technology in larger-scale CFB boilers has become the focus of future research.In this study,a numerical model of the flow and combustion of a 150 t/h CFB boiler in full-loop was established using the method of computational particle fluid dynamics(CPFD).The availability of the model was verified by comparing it with industrial data.The effects of excess air ratio in CFB,primary air ratio,and ratio of upper and lower secondary air on furnace combustion and NOx emissions were studied after the addition of post-combustion technology.The results showed that there was a typical core-circulation structure in the furnace.On the one hand,oxygen-poor combustion inhibited NOx generation,and on the other hand,the high CO concentration zone caused by combustion was also conducive to NOx reduction.After the use of post-combustion technology,the reduction atmosphere of the furnace increased,and the NOx emission reduced from 174.6 mg/m3 to 114.2 mg/m3.Combined with the air stage,optimizing the primary air ratio and the ratio of upper and lower secondary air,CO emission increased from 3.4×10-5 in the basic working condition to 7.1×10-5,the combustion efficiency was slightly reduced,and NOx emission was further reduced.Under optimal working conditions,NO,emission decreased from 174.6 mg/m3 to 76.3 mg/m3,NOx emission decreased by 56.3％,and the furnace temperature distribution was uniform.The research results can provide valuable theoretical insights for the application of post-combustion technology in CFB boilers and provide support for its practical application.
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