Study On Characteristics And Mechanism Of Co-pyrolysis Of Baiyinhua Lignite And Pine

Lignite,as a low-rank coal with high moisture and volatiles content,accounts for about40%of the total coal reserves.Its clean and efficient use is vital to energy and environmental protection.Biomass,as the fourth largest energy source after coal,oil and natural gas,plays an important role in the entire energy system and does not increase the carbon dioxide content in the atmosphere,which is carbon neutral.However,certain disadvantages including low heating value,low density and high moisture content limit its effective use.Besides,biomass is widely distributed and suffering the seasonal supply.Compared with lignite,biomass has higher H/C ratio and hydrogen content,which indicates that there may exists the synergetic effect in the co-pyrolysis of coal and biomass.Therefore,the co-pyrolysis behavior of lignite and biomass is studied.This paper focused on the effect of feeding mode,heating rate,pyrolysis temperature,and mixing ratio on production distribution of co-pyrolysis.In addition,a novel in-situ-PY-UV/EI-TOF was used to investigate the mechanism of synergy effect.The TG/DTG analysis of the separate pyrolysis of Baiyinhua lignite and pine as well as the co-pyrolysis of their blends with different blending ratios were performed on thermogravimetric analyzer.The results show that negative synergy effect is found during co-pyrolysis,especially at m_coal/m_pine=4/6 and 6/4.The effects of heating rate?0.5–20 ^oC/s?,pyrolysis temperature?450–600 ^oC?,feeding mode and blending ratio during the co-pyrolysis of Baiyinhua lignite and pine on products distribution and tar composition were investigated in an infrared heated fixed bed reactor.The results show that the products distributions suffer remarkably feed influence.It was found that when the coal layer was above the pine layer,the tar yield was 8.25 wt.%higher than other feeding modes.At the same time,the gas yield decreased significantly and the char yield decreased slightly.It is inferred that larger void space is beneficial to the volatile-volatile and volatile-char reaction when the pine layer in lower layer.To confirm this deduction,a columnar feeding mode was designed and the pine was substituted by compressed pine to reveal the importance of void space among feeding particles for volatiles reaction.When the feed blending ratio was 1:1,the highest tar yield and the maximum difference between the experimental tar yield and the calculated tar yield were obtained.The co-pyrolysis of Baiyinhua coal and pine showed the best synergy effect at 550 ^oC and with a heating rate of 10 ^oC/s.In order to investigate the synergy mechanism between lignite and pine,the in-situ-PY-UV/EI-TOF mass spectrometry was used to characterize the separately pyrolysis and co-pyrolysis primary products of Baiyinhua lignite and pine.The results show that the primary pyrolysis products of pine contain a large number of radicles,small molecule compounds and abundant aromatic compounds such as guaiacol;the primary pyrolysis products of Baiyinhua lignite contain olefins,aromatics and oxygenated compounds.The species of primary pyrolysis products of the co-pyrolysis process are consistent with those of the separate pyrolysis but the relative content of some substances has increased or decreased of different degrees,which indicates that there are interactions in the co-pyrolysis of coal and pine.However,under high vacuum conditions,the limited contact space/time weakens the secondary reaction between the primary products produced by the separate pyrolysis of coal and biomass.Combining the analysis of the primary co-pyrolysis products and the co-pyrolysis tar from fixed bed reactor with different feeding modes,it is inferred that the synergistic effect may be due to the polymerization reaction of small molecule compounds and the free radicals generated by pine pyrolysis,which can stabilize the intermediate products of coal pyrolysis.