Study of the reactivity of Casamance vegetable and agricultural waste char gasification with steam and CO2

Abstract

The increasing energy demand coupled with the need to reduce greenhouse gas emissions and the threat of exhaustion of oil reserves make us consider a possible recourse to the use of biomass waste as a source of renewable energy. Nowadays, gasification is not yet economically and operationally attractive for the power industry and more research is needed to facilitate the process and improve the desirability of the gasification process. Gasification tests were conducted on five wastes char mainly of agro-sylvo-pastoral residues, in order to study the behaviors of char conversion based on experimental data. Peanut shells, palm shells, cashews nut shells, cashew wood and “kaicedrat” wood char obtained by pyrolysis at 450°C are used. The samples were gasified at three different reaction temperatures (950 to 1050°C) in a fixed bed reactor, using steam or CO2 as gasification agent and with average fraction of particle size 630 and 3000 µm. The experimental parameters, which affect the char’s reactivity, are reviewed similarly to those related to the char and its structural features and operation parameters. Gasification kinetic conversion was studied at different models: the volume reaction model (VRM) and shrinking core model (SCM) in order to interpret the char conversion data. Further, the activation energy and pre-exponential factor were determined using the Arrhenius correlation. The experimental results showed that more syngas ((CO + H2)) of high quality were obtained at 1000 to 1050°C during char gasification with steam or CO2. The present results showed that temperature has a positive effect on kinetic char conversion. In addition, the low heating values obtained as a function of temperature depend on the nature of sample. For further investigation, it can be shown that the reaction rate is dependent on the char samples. Thus comparing the five biomasses, particular importance about reactivity and lower heating value (LHV) is attached to cashew nut shells, palm shells and peanut shells.