Study On Pollutant Emission Characteristics Of Biomass Pellet Fuels Combustion By A Simulated Industrial Boiler

With the rapid development of social economy,the human face threats,such as energy shortage and serious pollution.The key to solve this problem is to research the sustainable alternative energy,and biomass energy is a renewable and clean energy with broad application prospects.Biomass energy utilization technology in China is still in its infancy,existing some problems such as backward technology,lack of emission standards and other issues.The aim of this study is to research the combustion characteristics and emission characteristics of NOX,SO2,particulate matter and HCl of biomass pellet fuels in the combustion process.This is important for the promotion and application of biomass energy and formulation of pollutant emission standards for biomass combustion.In this study,three kinds of fuels,such as pine sawdust,mixed wood and corn straw,were used to study the pollutant emission characteristics by a simulated industrial boilers.Study on combustion characteristics by thermogravimetric analysis and tube furnace experiment was carried out.The effects of conditions such as fuel type,combustion temperature(700??800??900??1000?)and air flow(3L/min?4L/min ? 5L/min)on the concentration of conventional and feature pollutants were investigated by using a tubular furnace to simulate industrial boilers.And then dynamic models were established.Through above methods,the emission characteristics of the pollutants in the tail gas from the biomass pellet fuel combustion were grasped.The result shows:(1)Study on combustion characteristics of biomass fuels.Pyrolysis of the three kinds of biomass fuels is divided into three stages: preheat drying,volatiles precipitation combustion and coke combustion,and the second stage is the mostimportant part.In this part,the TG curve has the maximum change and the peak of the corresponding position of DTG curve.In the late combustion of pine and corn fuel,coke precipitation need to absorb a certain amount of heat to the outside,but it is not needed for mixed wood fuels.Three kinds of fuels with high volatile content can show a better combustion performance.However,the pine sawdust is better than the other two fuels because of its best stability,highest burning rate and lowest igniting and burning temperature.Combustion temperature,air flow and other factors on the combustion characteristics of pellet fuels have impact on it.In the same air flow condition,the higher the temperature,the narrow the concentration peak,and the shorter the time required to reach the peak.When the fuel is in incomplete combustion state,CO emission concentration will be significantly increased.(2)Study on characteristics of conventional air pollutant emission.The amount of NOX production and concentration changes are the results of jiont action of the fuel type,air flow,combustion temperature and other factors.NOX and SO2 are produced in the volatile combustion stage mainly,and their amounts have a certain relationship with N and S content of itself.SO2 will be released with small amount in incomplete combustion or moderate temperature conditions(800~900?).NOX emissions situation is relatively complex: the increase of CO emissions resulted in a decrease of NOX concentration when the temperature is maintained at 800?.And also decreased with the increase of air flow volume.The amount of particulate matter emitted by biomass combustion is much less than that of coal,and the emission load increases with the rise of temperature and intake air.(3)Study on emission characteristics of characteristic air pollutants(HCl).The turbidimetric method is an effective for determination of trace chlorine in tail gas from biomass pellet fuels combustion.After 1g biomass burning HCl can be released 0.2 to1.2 mg,there is a certain relationship with the chlorine content to the biomass itself.Of course,it also related to the physical properties of the fuel.The amount of HCl increased with the aggrandize of air flow and temperature,but high temperature also causes K to be directly appear in gaseous form(KCl),and resulting in decrease of hydrogen chloride emissions.(4)Study on reactic kinetics of biomass pellet fuel combustion.The Coats-Redfern integral method was used to kinetic analysis,and selected the appropriate reaction mechanism function,to study the reactic kinetics at differenttemperature stages.The combustion reaction series of different fuels is not immutable,and the reaction series is different at different reaction stages.In the process of biomass pellet fuels combustion,the activation energy of combustion reaction of biomass pellet fuel decreased first and then increased with the advance of reaction.This is consistent with the mechanism of the precipitation combustion reaction of the main combustible components such as volatiles and coke.(5)The optimal combustion conditions.Temperature control at 800 ?,the air flow control within 4~5 L/min can reduce the emissions of NOX,SO2,particulate matter and HCl.Under this condition,the conversion rate of fuel N was the lowest,which was 13.0%,4.6% and 11.8%,respectively,in the pine sawdust,mixed wood and corn straw.