| Coal-fired power plants constitute a dominant proportion of power supply in China which is around 75%of the entire demand.China is bestowed with abundant coal resources out of which 55%belong to the low-rank coals(LRCs)reserves.Rising energy demand has brought LRCs,such as sub-bituminous and lignite coals,into mainstream focus owing to their abundance and low cost.However,their large-scale utilization is narrow down due to low calorific value,high moisture and oxygen contents.Moreover,inherently found toxic elements in the coal such as selenium(Se),the most toxic and environmentally-sensitive element,has posed serious threats for human health and environment.Coal combustion may release enormous amount of Se as the process involves complex physical and chemical reactions..On contrary,use of biomass for fuel purpose is comparatively cleaner than coal and is considered a prime carbon resource that can be directly transformed into fuel.Global reliance on biomass to yield energy has significantly enhanced.In this context,the present research work has used two-pronged approach in which hydrothermal treatment(HTT)of coal at 200-300 ? and torrefaction(at 300 ?)of biomass(for co-combustion with coal)were synergistically applied to remove/reduce Se element and upgrade Huainan(HN)coal.A series of experiments was carried out,including hydrothermal treatment of coal and biomass torrefication,characterizations using several techniques(TGA,SEM,TEM,TEM-EDS,XRD,FTIR,XPS,Ramman spectroscopy,Elemental Analyzer and measurement of Se through AFS.A total of 37 samples including 1 biomass,1 torrefied heated at 300 ? for 30 min with heating rate of 10 ?/min,10 blend samples of both biomass and torrefied with coal(10:90,20:80,30:70,40:60,50:50),7 raw coal and 18 hydrothermally treated(at 200 ?,250,300 ?)coal samples were prepared.Influence of thermal pretreatment on fuel properties and retention-emission behavior of Se during co-combustion and hydrothermal treatment of coal was examined;i.e.(?)co-combustion of biomass and torrefied with coal for fuel property improvement and retention-emission of Selenium;(?)hydrothermal dewatering of low-rank coals;influence on the properties and combustion characteristics of the solid products;(?)effect of hydrothermal treatment on surface chemistry and structural characteristics of low-rank coal in relation to Selenium removal and transformation.Finding pertaining to hydrothermal treatment revealed that it is promising technique for up-gradation of LRCs particularly the inherent moisture and oxygen content decreased significantly while fixed carbon content and calorific value increased.Characterization of Huainan coal has provided used evidence for conversion of LRCs near to high-rank coals(HRCs).The upgraded coals had higher ignition and burnout temperatures,while their combustion was shifted and delayed towards higher temperature zone.Prominent changes were found in coal structure,composition,rank,and combustion characteristics at hydrothermal temperature of 300 ?.In addition,the Se content was marginally decreased with increased hydrothermal treatment temperature(HTT).The removal proportion of Se was significant and increased up to 50.7%with increased HTT temperature(300 ?).Similarly,an improved ignition behavior and thermal reactivity of coal through the addition of a suitable proportion of biomass and torrefied was observed during co-combustion.In blend samples,Se emission decreased when the ratio of both biomass and torrefied increased.Higher reduction(48%)in the total Se volatilization was found for torrefied/coal than the individual coal sample,which is an indication that torrefied material has the best potential of selenium retention. |
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