Study On Combustion Characteristics And Kinetics Of Briquette

Briquette technology is an important clean coal technology?CCT?.The core of briquette technology is the binder and combustion characteristic of briquette.The reaction kinetics of briquette combustion mainly studies the quantitative relationship between the reaction rate of briquette combustion and the conditions such as temperature,conversion rate,gas phase reactant concentration,etc.The key to learn the combustion characteristic of briquette is to explore the optimum reaction conditions and characteristic parameters,which are helpful for the choice of optimum process parameters as well as the design and scale-up of reactors.In this paper,a large-scale thermal analysis experimental system is used.Experimental study and theoretical analysis are combined to investigate the effects of factors such as heating rate,oxygen concentration and molding pressure on the parameters of characteristic and kinetics of briquette combustion.The best mixture ratio of binder and additives was obtained,which gives the briquette with better strength and combustion characteristic.At the same time,the behavior of pollutant emissions during ignition and combustion process of briquette particles under different conditions was studied.The main research content is as follows:Different raw materials,such as ligninsulfonate,bentonite,starch,polyvinyl alcohol?PVA?and humic acid fertilizer,etc,are adopted to prepare binder by chemical processes,and then molded into standard briquette by cold pressing technology.The thermogravimetric analyzer was used to analyze the exothermic processes of four coal samples with different ash content at different heating rates.The combustion characteristic parameters were obtained by analyzing the TG and DTG curves of coal samples.The results show that ignition temperature of coal samples increases gradually with the increase of ash content and heating rate.At the same heating rate,the flammability index and ignition stable combustion characteristic index of coal samples decrease with the increase of ash content,which means the ignition characteristic and combustion stability of coal samples reduce.To achieve the aim of research,an experimental system of the large-scale thermal analysis was designed and built.The experimental system is mainly composed of four parts: gas supply system,reactor system,balance system and flue gas analysis system.The Coats-Redfern integration method was used to process the thermal analysis experimental data to obtain apparent activation energy of briquette combustion at different heating rates,oxygen concentrations and molding pressures.The results show that the apparent activation energy of the briquette increases compared to the pulverized one.The apparent activation energy of briquette particles decreases with the increase of heating rate and oxygen concentration,while increases at first and then decreases with the increase of molding pressure.The NO and SO₂ produced by the coal combustion are detected on-line by the flue gas analyzer.The results show that the emission of NO and SO₂ from coal combustion can be reduced by briquetting.The addition of binder can greatly improve the hardness and strength of the briquette,while with tiny effect on the NO and SO₂ emissions of the briquette combustion process.The conversion of N to NO and the emission of SO₂ from briquette combustion increase with the increase of heating rate and the increase of oxygen concentration.With the increase of molding pressure of briquette,NO emission concentration and ?NO of briquette combustion first decrease to a pointand then increase,while SO₂ emission gradually decrease.The addition of sulfur fixing agent Ca O greatly reduces the emission of SO₂ from briquette combustion.