Experimental Study On Co-combustion Characteristics Of Pingshuo Coal And Biomass

Due to the global environmental concerns over excessive fossil fuel usage, the newand clean energy has been searched to substitute for fossil resources. Compared withpetroleum and natural gas, which are in deeper and deeper shortages, the amount of coaldeposit is abundant. Coal, as a traditional fossil fuel, will still be a major energy sourcein the foreseeable future throughout the world, especially in China.Pingshuo coal is a typical thermal coal in China, which characteristically has ahigh content of sulfur and chlorine. Because of the great amount of SOx, NOxand CO2emission during the direct combustion of coal, it is highly important to develop moreeffective, efficient technology to clean utilize coal.As we know, biomass is one of the most important renewable energy resources,and its application becomes more and more significant for climate protection. Comparedwith other renewable energy resources, biomass is abundant in annual production, witha geographically widespread distribution in the world. The application of biomass asenergy source can lead to a zero net CO2emission in a very short life cycle period, sincecarbon in the form of CO2and energy are fixed by photosynthesis during biomassgrowth. Consequently, the co-utilization of biomass in the existing coal-fired plants isvery appealing nowadays.Thus, the co-combustion experiments of Pingshuo coal&biomass were conductedagainst the background. Then it can be found that biomass plays an important roleduring their co-pyrolysis and co-combustion process. Besides, its high thermochemicalreactivity and high volatile matter yield facilitate the conversion and upgrading of thefuel mixture.The characteristics and utilization ways of biomass were firstly summarized andthe current and future developments of biomass fuel conversion technologies wereanalyzed in the paper. Then, the significance, main approaches and research status ofcoal/biomass co-combustion and co-pyrolysis were introduced in detail. Therefore, it ishighly significant to do this work.It is well-known that pyrolysis is the first conversion step during coal and biomasscombustion and gasification processes. The pyrolysis plays a key role in clean coalutilization because of its effects on the resulted char characteristics and processproperties. Therefore, the co-pyrolysis and co-combustion processes of Pingshuocoal/biomass are the focuses of this research. The pyrolysis behaviors of Pingshuo coal and biomass had been investigated using a thermo-gravimetric analyzer and moreattention was paid to the pyrolysis characteristics and kinetic parameters of their blends.Moreover, the comparison between the experimental and the calculated DTG curvesshows that the co-pyrolysis process is not the simple sum of the pyrolysis weight lossrate of Pingshuo coal and the biomass. At last, the activation energy and the frequencyfactor of the co-pyrolysis were calculated by Coats-Redfern method and the first-orderreaction model. The results show that the activation energy and the frequency factorchange with the mixture ratio of the biomass and the regularity was consistent with theabove-mentioned conclusions. Therefore, it can be deduced that there exist synergeticeffects between the biomass and Pingshuo coal during their co-pyrolysis process.The combustion behaviors of Pingshuo coal and biomass mixed char wereinvestigated using TG analyzer. The effects of different pyrolysis conditions on thecombustion characteristics of Pingshuo coal char, as well as the addition ratio ofbiomass were analyzed. The ignition temperature and the burnout temperature of themixed char are lower than those of Pingshuo coal char. The ignition temperature and theburnout temperature of the mixed chars decrease with the increase of biomass mixtureratio. Thus, the ignition performance and the burnout performance of the mixed charincrease compared with those of Pingshuo coal char. Furthermore, the maximumcombustion rate of the mixed char increases and the corresponding temperaturedecreases with the increase of the biomass mixture ratio. Moreover, compared withother chars (except biomass char) employed in the research, the combustion rate of themixed char with the biomass blending ratio of70wt%is the highest. In addition, theignition performance, the burnout performance, the ignition characteristic index and thecombustion characteristic index are also better than those of other chars. This resultsuggests that the addition of the biomass can facilitate the combustion process, andthere is an optimal blending proportion during the whole combustion process.On the basis of the results of the thermo-gravimetric experiments, the combustionkinetic parameters of Pingshuo coal and biomass mixed char has been calculated withgood correlation using Coats-Redfern method and a first-order reaction model. It can beobviously seen that the activation energy of biomass char is lower than that of Pingshuocoal char and the biomass char has a higher reactivity. In addition, along with thechange of the biomass mixture ratio, the activation energy and the frequency factor ofthe mixed char vary regularly. The activation energy of the mixed char lies between that of biomass char and Pingshuo coal char. The larger the mixture ratio of the biomass is,the lower the activation energy of the mixed char is. It can be concluded that theaddition of the biomass can facilitate the burning process of the mixed char.