Investigation of co-combustion characteristics of pulverized coal with miscanthus floridulus biochar

In the context of the current world energy crisis, global warming and increasing carbon dioxide emission, alternative fuels for replacing traditional fossil fuel such as coal and petroleum have been studied and developed worldwide [1]. Bioenergy production has been proposed as an alternative energy source and it is produced from organic material such as wood, grass, agricultural residues, animal waste and so on. From the perspective of the use for combustion, biomass can be considered as a carbon neutral fuel since it is able to fix carbon dioxide when it grows. The carbon cycle is much shorter when compared to fossil fuels so it may be treated as zero carbon emissions. Nowadays, two direct combustion techniques concerning biomass are noteworthy. The first one is to use only biomass as fuel for industrial furnaces, and the other is co-firing of biomass with fossil fuels. Unfortunately, raw material of biomass is relatively difficult to be handled and utilized because of its high moisture content, low grindability and low bulk and energy density [2]. In addition, direct combustion of biomass always brings the smoke problem, particulate matters and lower temperature as compared with coal. Various thermochemical conversion technologies such as thermal pyrolysis may be used to transform raw biomass into biofuels or biochar and improve combustion properties. Biochar is the main product of torrefection process, which is a mild pyrolysis process and carried out in the temperature range of 200-300 C in the oxygen-free condition [3]. After torrefaction, it makes the solid fuel easier to store and increases its heating value. Miscanthus floridulus is a kind of C4 perennial grass and possesses high lignin content when compared to woody biomass [4]. Originating from Asia and Africa, miscanthus is one of the hardly and drought-tolerant plants that is widely available and easy to grow around the world. It is crucial to have complete database of the thermochemical characteristics of fuels when investigating its combustion behavior. In this study, we focus on the fuel properties of pulverized coal and miscanthus floridulus biochar mixtures and its combustion phenomenon at different blending ratios. Thermogravimetric analysis (TGA) was employed to observe the thermal behavior of the fuel. Furthermore, the fuel was pelletized in a cylindrical die under controlled conditions and its combustion process was examined by using a laboratory scale free-drop furnace.