Study On Lees Combustion And The Emission Characteristics Of Chlorine And Potassium In Biomass Combustion

As global warming is becoming worse, people pay more attention to biomassenergy gradually. It is inevitable that biomass energy will get a rapid developmentbecause of the advantage of biomass that releases “Zero” CO2. At present, the main useof biomass domestic is the thermal conversion, and direct combustion is a verypromising developing direction. The fluidized bed combustion technology has a greatadvantage in biomass combustion, however biomass is rich in alkali metal and chlorinewhich release during combustion and bring deposition, slag bonding, agglomeration,and high temperature corrosion etcetera problems to the heating surfaces, and it willseriously affect the scale utilization of biomass. The migration characteristic ofpotassium and chlorine in the flue gas during biomass combustion in middletemperature were studied. And took the lees for example, studied the combustioncharacteristic of biomass in fluidized bed in detail.Wheat straw, rice straw and other four kinds of biomass were combusted at fivetemperatures from650℃to850℃, and all flue gas was absorbed, the ion meter andAtomic Emission Spectrometry were used to measure the chlorine and potassiumseparately, the emission characteristics of potassium and chlorine in flue gas wasobtained. The results show that wheat straw and rice straw are easy to burnout below700℃. Because of the emission of potassium during the combustion, the generatedsilicate wrapped the biomass particle, hindered the burnout of biomass, which leads tothe ash color of wheat straw, rice straw and rice husk represents as cinereous. Chlorinemainly releases as HCl during the combustion process. Expect for wheat straw, over90%chlorine of other five biomass releases as HCl. The potassium of wheat straw, cottonstalk and rice husk mainly release below800℃, while the corn stalk and other twokinds of biomass mainly release above750℃.A series of studies were carried out in a small bubbling fluidized bed on lees, theresults show that lees have excellent ignition characteristics, can catch fire withinseveral seconds when the temperature is over600℃. The lees can be fluidized well withquartz sand in fluidized bed and can burn out easily, and there is no ashes left in the bedmaterial. There is no coking phenomena when lees are fired in fluidized bed at800-900℃. Because lees are rich in nitrogen, NOx emission is very high duringcombustion process. The fluidized bed combustion technology is widely adaptable tofuels, especially for lees whose moisture content is very high, and furthermore fluidizedbed combustion can easily decrease the NOx emission, and it is an extremely promisingtechnology to fire lees.