Study On The Characteristics Of Clean Briquette Prepared By Semi-coke From Bituminous Coal Pyrolysis

Coal plays an important role in China's energy structure.In recent years,with the increasing demand for ultra-low emission of coal burning pollution and the further improvement of atmospheric environment,the pollution caused by civil coal burning has been paid more and more attention.The development of clean briquette with low pollution emission is one of the effective methods to reduce the pollution caused by civil coal burning.In this paper,the semi-coke prepared by the pyrolysis of bituminous coal is used as raw material.The molding process,combustion characteristics and NO_x pollutant release characteristics of the briquette prepared by semi-coke are systematically studied.Semi-coke was prepared by rapid pyrolysis at 400?800?from Shenmu bituminous coal in Yulin.The influence of pyrolysis conditions on the physical and chemical properties of semi-coke was studied systematically,semi-coke suitable for molding and its pyrolysis conditions were obtained.The results show that with the increase of the final temperature of pyrolysis,the yield,volatile content,sulfur content and surface oxygen containing functional group content of semi-coke decrease gradually,the aromatization degree increases,the specific surface area and pore volume of semi coke decrease first and then increase.With the increase of pyrolysis residence time,the volatile content of semi-coke gradually decrease,and tend to be stable at certain residence time.The volatile content,sulfur content and calorific value of 700?-5 min and 800?-3 min semi-coke meet the national standard for briquette preparation.Briquette was prepared by cold pressing with binder using 700?-5 min and 800?-3min semi-coke as raw materials.The experimental study further found that there is an optimal forming pressure of 10 k N for semi-coke forming,and the best moisture content is 17%.The mixture of 3%pre-gelatinized starch and 7%sodium silicate as a composite binder reduces the amount of single binder,and at the same time,the briquette cold compressive strength is stronger.The pre-gelatinized starch is attached to the semi-coke surface as floccules,and sodium silicate is embedded between the semi-coke particles as needle and sheet structures.Through the test of briquette combustion performance,it is known that binder has an important influence on the combustion performance of briquette.The comprehensive combustion coefficient of briquette increases and the combustion activation energy decreases,mainly because the pre gelatinized starch combustion promotes the combustion of briquette.The existence of Na inorganic catalytic component in sodium silicate binder promotes the combustion of briquette,improves the combustion characteristics of briquette;composite binder integrates the influence of the two binders on the combustion characteristics of briquette,and further improves the combustion characteristics of briquette compared with the two binders alone.On the other hand,binder has an important effect on the formation of NO_x in briquette.The nitrogen content of pre-gelatinized starch binder is lower than that of semi-coke,and a large amount of oxygen is consumed in the early combustion stage to form a weak reducing atmosphere,which reduces the release of NO_x from briquette.The addition of sodium silicate reduces the formation of NO_x in briquette,the compound binder significantly reduces the formation of NO_xin briquette.