The Study Of Gasification Characteristics Of Pyrolyzed Coal Char In Staged Conversion Polygeneration System

At present,most of the coal consumed is still used through a single way.For the purpose of obtaining liquid fuel and electricity,coal staged conversion polygeneration technology achieve efficient utilization of coal sources according to different composition and reaction properties,it may solves source and energy problem effectively.Based on the coal staged conversion,the coal pyrolysis-gasification-combustion staged conversion utilization polygeneration technology was proposed to establish the staged conversion polygeneration system together with heat,electricity,methanol and fuel oil.The simulation and relevant experimental research were also carried out.Firstly,the process simulation of the coal pyrolysis-gasification-combustion staged conversion utilization polygeneration system(CPGC)was established by Aspen Plus software.For evaluating the feasibility of the polygeneration system,thermodynamic performance and economic indexes,i.e.,system efficiency,total capital investiments,internal of return(IRR),discounted payback period(DPP)of the coal pyrolysis-gasification staged conversion utilization polygeneration system(CPG)were also calculated and compared.The simulation results show that the system efficiency of the CPGC system is 47.02%LHV,which is higher than the CPG system.It indicates that the CPGC system has certain feasibility.Secondly,the experiment tables of multi atmosphere pyrolysis and multiple mixed atmosphere TGA were established.The effect of pyrolysis atmosphere on coal char characteristics and gasification reactivity was studied.The coal was pyrolyzed in a tube furnace under different atmosphere,respectively.The Raman spectroscopy and N2 adsorption methods were adopted to characterize the physical properties of the produced char samples.The results show that the char prepared in CO2 atmosphere has more disordered carbon structures and a higher specific surface area,while the chars prepared in CO,CH4 and H2 have higher degree of graphite carbon structures and a lower specific surface area.The TGA experimental results show that the gasification reaction rate of char samples prepared in CO2 atmosphere is highest,while the CO,H2 and CH4 atmospheres are obviously lower than the Ar atmosphere.These may caused by char-CO2 gasification,disproportionation reaction of CO,the thermal cracking of CH4 and char-H2 deoxygenated and condensation.Then,the effect of specific surface area on the reaction mechanisms of coal char gasification was conducted in the mixture of H2O and CO2 or in the mixture of H2O,CO2,H2 and CO.The coal chars with different specific area were obtained through different heating rates.Results indicate that the Langmuir-Hinshelwood(L-H)model based on separate active sites assumption is more accurate for the big specific surface area coal char,while the L-H model based on common active sites assumption is more accurate for the small specific surface area coal char.Because the big char could provide more active sites,the competition for the active sites between the H2O and CO2 may weakened.Finally,the effect of mineral on the reaction mechanisms of coal char gasification was studied in the mixture of H2O and CO2 or in the mixture of H2O,CO2,H2 and CO.The demineralized char was obtained by acid washing,the Na salt char was obtained by solution impregnation method.The results show that neither the L-H model based on separate active sites assumption nor the L-H model based on common active sites assumption are suitable for the gasification rate of demineralized char.The L-H model based on separate active sites assumption is close to the gasification rate of the Na salt char.The removal of minerals can reduce the catalytic effect of coal char,there is a fierce competition for the active sites between H2O and CO2.The alkali metal salt has a catalytic effect on coal char gasification,it can provide more active sites for the gasification reaction to weaken the competition between the H2O and CO2.