Four biomass materials, namely peach pips, pine wood, bamboo and Napier grass, and one example of chemical waste, lithium hexafluorophosphate (LiPF6), were studied. The biomass types were selected because they were easily accessible locally. The LiPF6 waste is solidified in poly(methyl methacrylate) (PMMA). Gasification of this solid is of interest to industry.
Prior to the gasification studies, TGA-FTRI analyses were conducted on the biomass samples. This was done to study their thermal behaviour under nitrogen as well as under oxygen. The results indicated that, in general, pyrolysis of biomass takes place in three stages, namely hydration, active pyrolysis, and passive pyrolysis. These stages occur at different temperatures depending on the type of biomass as well as the heating rate used. The conversion efficiency of these materials is increased under oxygen, due to the fact that combustion takes place in the presence of oxygen, either partially or fully, depending on the amount made available. TGA results obtained under nitrogen were used to compute the kinetic parameters of each biomass material.
Because their fluffy nature led to feed problems, bamboo and Napier grass were excluded from the plasma gasification experiments. Results obtained during the gasification of peach pips and pine wood indicated that conversion efficiency slightly increases with an increase in temperature. Feed rate seemed to have minimal effect on both conversion efficiency and gas concentration; the energy conversion efficiency did, however, improve.
The conversion efficiencies obtained by TGA and by the plasma system, were roughly similar. Due to the higher temperatures, ~ 1000 °C, of the plasma reactor, the gaseous products obtained were predominantly carbon monoxide and hydrogen. On the other hand, carbon dioxide predominated in the TGA-FTIR experiments. Only a slight trace of monoxide was observed. Plasma treatment of PMMA encapsulated waste LiPF6 also yielded carbon monoxide and hydrogen as main products.
The energy conversion efficiency observed for the plasma process was 30 40 %. This value is ratio of the combustion enthalpy of syngas yield and the electrical energy input into the plasma torch. The main heat loss was via the torch anode. This may be corrected by an improved thermo-mechanical design.