Research On Combustion And NO_x Release Characteristics During Blended Coals Combustion In A 330MW Pulverized Coal Boiler

In order to reduce the cost of burning coal,the economical coals were co-fired with in a 330 MW pulverized coal boiler designed for Dakuang coal from Jingyuan County.The qualities of unstability and high sulfur of the economical coals lead to the combustion instability in the furnace and the SO₂ concentration in the flue gas being not consonant with environmental requirements.The blending options need choosing to ensure that the boiler unit operates safely,environmentally and economically.In this paper,the research on combustion and NO_x release characteristics during typical coals and blended coals combustion was done by means of a constant-temperature TG test rig.The results show that: under the high temperature of 1500 ? and in air atmosphere,the burn out time of blended coals depends on hard-to-burn coals for a phenomenon called “tacking” of the free burning coals Besides,the curves of NO_x generation showed bimodal pattern in the main,and both the peaks of the blended coal below those of the either coal.Furthermore,the calculated NO_x cumulative emissions of the blended coal is smaller than that of the either coal.It follows that co-firing can reduce the NO_x emissions.The test of choosing the optimal blending options of Ning coal,Dakuang coal and Shichang coal has been taken in a 330 MW coal-fired boiler.In the test,how blending ways,blending options and operation modes affect unburned carbon levels in the ash and NO_x emissions is the subject.The results show that the unburned carbon levels in the ash will remain unchanged,and the NO_x emissions will be lower under the out-furnace coal blending method than under the in-furnace coal blending method for Ning coal co-firing with the Shichang coal of 50%.It is easier for Shichang coal to reduce both of the unburned carbon levels in the ash and NO_x emissions mixing with Dakuang coal than Ning coal.Besides,in the range of 25⁵0%,along with the Ning coal blending ratio increasing,the unburned carbon levels in the ash increase.In the range of 50⁶0%,the unburned carbon levels in the ash decrease.Not only the blending options but also operation modes can influence the NO_x emissions.As the oxygen concentration increases,the NO_x emissions increase all the time.With the increasement of generation load,the NO_x emissions increase first and then decrease.The lower the operational burners locate,the less NO_x emissions.The more the ventilation door of OFA opens by,the less NO_x emissions.In order to assess the economy of serveral blending options,an economic evaluation index was put forward,including the costs of coals,desulfurizer,the agent for de-NO_x,auxiliary power.The computational results show that the electric distribution cost will drop with the increasement of Shichang coal blending radio which is not greater than 50%.Eventually,the best blending option is:Dakuang coal: Ning coal: Shichang coal=1:1:1,in consideration of the safety,the environment,the economy.