| Nowadays, energy shortage and environmental pollution are the two major problems that humans are facing to. Coal is still the most important primary energy of China. Polygeneration is an integrated sustainable energy system to solve the problems such as resources, energy, and environment. For this reason, Zhejiang University developed polygeneration system generating electricity, chemicals, liquid fuels and gas based on heat ash carrier. Heat ash influences the yields of gas, coke and tar. which would have an effect on the efficiency and stability of operation. In view of this, this paper launched research on coal pyrolysis characteristics loaded different metal salts (KCl, NaCl, CaCl2, MgCl2, FeCl3and NiCl2) and kinds of metal oxides (Fe2O3, Al2O3and MgO, CaO). The thermal infrared spectrometry technology (TG-FTIR), Differential Scanning Calorimetry (DSC), Pyrolysis-Gas Chromatograph/Mass Spectrometer)(Py-GC/MS) were all used to study the influences of additives and CO2on coal pyrolysis characteristics. Finally, experiments were carried out on a small fixed bed and Gas Chromatography (GC) and Gas Chromatography/Mass Spectrometry (GC-MS) were used to analyze concentration of gas and tar quantitatively.To study the effect of temperature and coal type on coal pyrolysis behavior, the pyrolysis process of four different types of coal was investigated by TG-FTIR. FTIR spectrum and kinetic analysis revealed the mechanism of the formation and variation of gas products such as CO, CO2, CH4and so on. Bituminous coal generates more CH4than lignite, while their outputs of CO, CO2are less than lignite. TG-FTIR were used to study the catalytic influences of additives and CO2on coal pyrolysis. Results indicated that the maximum mass loss rate decreased with metal additives in the primary pyrolysis stage. Kinetic analysis was taken for all samples adopting the method of Coats-Redfern. Activation energy of raw coal in the primary pyrolysis stage was lowered with doped metal additives. The yields of CH4, CO2, toluene, phenol and formic acid were decreased, but the evolution of CO was increased. The presence of metals in the coal samples have been involved in a repeated bond-forming and bond-breaking process, which greatly hindered the release of tars during pyrolysis as the tar precursors were connected to coal/char matrix and were thermally cracked, becoming a part of char. CO2reduced the yield of toluene, phenol and carbonyl-compounds but metal catalysts made changes of the formation of these species. Gasification was strongly increased by CO2gasification with the nascent char which were highly reactive species like-COO-N (N is monovalent metal). Metals doped in the coal samples have been involved in a repeated bond-forming and bond-breaking process, which resulted in highly reactive radicals accompanied by the formation of tar during high temperature phase.Py-GC/MS was used to investigate the output and distribution of tar pyrolysed at a rate of10000℃/s to different temperature (550℃,750℃C,950℃) loaded with different additives. DSC revealed the influence of various additives on heat of reaction during pyrolysis at a rate of30℃/min in N2and CO2atmosphere.Through pyrolysis experiments at different temperatures (650℃,650℃,700℃) in fixed bed. research indicated that MgCl2promotes the yield of tar nearly by60%. At650℃and700℃, metal additive boost gas yield significantly. GC-MS revealed tar components of each samples catalysed by kinds of additives. |
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