Research On Low NO_x Combustion Technology Based On Tertiary Rich/lean Streams Seperation

The environmental pollution produced by NOx emission from coal-fired power plant becomes more and more serious with the rapid development of economy.The NOx emission control technology becomes more and more important for reducing air pollution and has been researched and developed well recently.The normal approach is low NOx burner combined with SOFA nozzle technology.But this approach is not appropriate when burning low volatiles coal with hot air pulverized-coal transport system and storage bunker.In these cases,normal Low NOx combustion system retrofitting cannot meet the requirements of NOx emission control limit.Based on the stereo-staged low NOx combustion technology,a new proposal combined with separating the tertiary air into rich and lean streams is introduced and studied.This approach has been applied and verified on a 135 MW tangentially fired boiler.The main results of this application were as follows:(1)Main hot test results before retrofitting: The NOx emission was1456mg/Nm3 when the tertiary air rate was more than 53% with the recycling damper opening of 50%).Therefore,it was unable to meet the technical agreement requirements through the normal low NOx combustion retrofitting.It requires technical breakthroughs.(2)Based on the experimental results before retrofitting and sufficient evaluation,we proposed a new combustion system which combine stereo-staged low NOx combustion technology and tertiary air separation technology together.The tertiary air separator has been investigated by the numerical simulation to meet the operation requirements.(3)Main hot test results after retrofitting: The separation efficiency of tertiary air separator is as follows.At normal operating conditions,the tertiary air flow ratio of rich/lean streams is 47.69:52.31,and the powder quantity ratio of rich/lean streams is 84.35:15.65.This test results agreed well with numerical simulation results.After retrofitting by Low NOx combustion technology combined with separating the tertiary air into rich and lean streams,at boiler load of 100%,75%,and 50% BMCR,the measured values of NOx emission were 539.7mg/Nm3,533.3mg/Nm3 and 500mg/Nm3 respectively,less than the requirement of550mg/Nm3.The NOx emission can be further reduced by 120mg/Nm3 when the rich/lean tertiary air separation system is on operation,comparing with normal Low NOx combustion arrangement.