Study On The Technology Of Low-NO_x Emission For The 600MW Down-fired Boiler With Swirl Burner

Low-NOx combustion technology which was operated in early domestic thermal power plant is relatively leg behind the trend,especially for the down-fired boiler whose NOx has higher emissions that is generally up to 1000 mg / m3 or more and has severe impact on the environment,meanwhile the old technology goes far away from the current emission standards.So the study of low-NOx retrofit of down-fired boiler is practically significant.This dissertation is taking NOx emission of down-fired boiler of 600 MW unit of one power plant as my research target.NOx emission concentration is 1300mg/m3 before retrofit.Based on extensive literature survey and conventional engineering practice,I analyzed why NOx of down-fired boiler in this plant is higher and meanwhile made a plan of increasing OFA nozzles,changing new style central ring concentrated swirl burner,offsetting exhaust nozzel which classify stage air into two,adding refractory belts to solve the problem.This dissertation established the numerical simulation model.The numerical simulation calculation is matching well with the test result before boiler retrofit,so it verified the correctness of the model.Then it analyzed the speed field,temperature field,oxygen distribution,CO distribution and NOx distribution of 600 MW down-fired boiler retrofit design through numerical simulation,and result in the generation characteristics of nitrogen oxides on 600 MW down-fired boiler.The results of numerical simulation show that the low-NOx combustion retrofit scheme can effectively reduce the NOX emission.Based on 600 MW down-fired boiler combustion adjustment test,it is concluded that the operation oxygen,damper opening of OFA windbox,NOX port closing numbers,stage air damper opening,burner core air damper opening,unit load,pulverizer numbers effect on NOx emission,CO emission,fly ash fuel and heat efficiency of boiler.It is concluded the best operation parameter of 600 MW down-fired boiler under the condition of emissions priority.Under the reduction operation priority,boiler NOX emissions could be controlled to a minimum of 563.34mg/m3.In order to control the efficiency of boiler not lower than before the retrofit,NOX emissions can be controlled within 741.54 mg/m3.After retrofit,the boiler NOX emissions significantly reduced and stable-combustion feature enhanced and increased the adaptability of coal.