The Migration And Catalytic Characteristics Of Potassium During Co-pyrolysis/Gasification Of Coal And Biomass

Recently,a number of researchers have found synergy in co-processing of coal and biomass,in particular co-gasification.A large number of studies have found that the intinsic alkali metals in biomass have a good catalytic effect during co-gasification of coal and biomass.In this paper,we studied the migration of potassium and its catalytic performance during co-pyrolysis/gasification of coal and biomass.Four kinds of biomass feedstocks and two coal samples were selected as raw materials,including Chinese redwood(CR),soybean stalk(SS),orange peel(OP),and peanut shells(PS),a lignite and a bituminous coal.Firstly,the migration amounts of potassium during co-pyrolysis/gasification were determined.The results indicated that about 20 % of potassium migrated from biomass to the surface of coal char during co-pyrolysis/gasification at 900?.A handful of potassium releaseed from the blended chars during the early stages of gasification,while the content of alkali that retained in blended chars is nearly invariable with the increase of gasification time.A large amount of alkali content fixed in blended chars that obtained after gasification at 850? and 900?,while it has hardly any at 850?.We can draw a conclusion that the temperature plays an important role in potassium migration.The co-pyrolysis/gasification of coal and biomass were studied using a congruent-mass thermogravimetry analysis(TGA)method.Results revealed that the potassium,which transfer from biomass to the surface of coal char during co-pyrolysis,has no catalytic effect on coal-char pyrolysis and gasification.While the potassium that from biomass ash played a catalytic role in promoting gasification reactivity of coal char.The high alkali content in biomass ash corresponded to an extraordinary catalytic.The co-gasification of soybean stalk and lignite at 850? may be a better choice in the temperature range of 800-900?.Soybean stalk(SS)that washed by deionized water and hydrochloric acid solution were used as raw materials.Aiming to study catalysis of water-soluble potassium and acid-soluble potassium during co-gasification.We observed that the water-soluble alkali transfer from soybean stalk to the surface of lignite char during co-gasification by making direct comparisons between Potassium was observed in the BSE elemental mappings of lignite char obtained by co-gasification of lignite with original soybean stalk(SS),but disperared in the mappings of lignite chars obtained by co-gasification of lignite with water-washed and acid-washed soybean stalks There was no synergy observation during co-gasificationof lignite with either water-or acid-wased soybean stalks,.The results show that the water-soluble potassium has a significant contribution to gasification of coal-char.Lignite(HM),soybean stalk(SS),and water-washed soybean stalk were selected as raw materials in the study of decomposition of tar during co-pyrolysis/gasification in a fixed bed reactor.The results showed that potassium played an important role in promoting tar decomposition.There is an uncertanty with weighted average method in calculation of tar.