Study On SNCR And SCR Combined Denitrification Technology For Flue Gas Of Coal-fired Fluidized Bed Boiler

With the increasing attention of the society to environmental protection,the pollutant discharge requirements of coal-fired power plants are increasingly strict.In2014,China formulated and released the ultra-low emission standard for coal-fired power plants,requiring coal-fired power plants to meet the ultra-low emission requirement before 2020,in which the NOx emission concentration limit is50mg/Nm~3.The existing denitration unit of circulating fluidized bed boiler has been unable to meet the requirements of the new standard,which needs to be improved.Selective catalytic reduction(SCR)denitration device can be added on the basis of the original selective non-catalytic reduction(SNCR)denitration device,and the SNCR-SCR combined denitration process can be upgraded.However,there are two schemes for adding SCR denitration device.One is the built-in SCR with SCR device installed in the boiler,and the other is the external SCR with SCR device added outside the boiler.Combined with the cases of denitrification renovation of circulating fluidized bed boilers in Nantong and Yangzhou thermal power plants,this paper studies and analyzes the two renovation process schemes.Firstly,according to the field conditions and working conditions,the transformation scheme of the boiler economizer is determined,and the position and equipment selection of the new SCR system are defined.Secondly,CFD flow field was used to calculate and optimize the flow field in the external SCR reactor,and the optimal structure and position of the guide plate were determined.Finally,the operation effect and technical economy before and after the transformation of the two technical routes are analyzed and compared in detail.The results show that it is feasible to upgrade the flue gas denitration unit of circulating fluidized bed boiler to SNCR-SCR combined denitration unit,and the denitration unit upgraded by the two schemes can meet the requirements of the ultra-low emission standard for NOx emission index.Because the built-in SCR denitration device has no independent ammonia injection system,and the external SCR denitration device is equipped with an independent ammonia injection system,so the external SCR operation mode is more flexible.When the original NOx emission concentration is not high,the SCR denitration device can be run independently,which is more economical.The denitration efficiency of SNCR+external SCR denitration device is higher than that of SNCR+internal SCR denitration device,and the reducing agent utilization ratio of the former is also higher than that of the latter.Through the statistics and analysis of the operating cost,the SNCR+external SCR denitration device is lower.Through the detailed introduction of two engineering cases and technical and economic comparison,it provides reference and reference for the denitration transformation of similar boilers in the future.