Steam Gasification of Excavated Waste Residue (EWR) from a Landfill Bioreactor Operated Under cold Climate Conditions

Abstract

The use of fossil fuel to generate energy has contributed to the emission of greenhouse gases, which is a leading factor in the depletion of the ozone layer. This effect of fossil fuel on the atmosphere has led to the push for a renewable source of energy with less environmental problems. Gasification of excavated landfill waste residue (EWR) is one of the promising alternatives for generating environmentally friendly energy. Steam gasification is a type of gasification method that has proven to be the most favorable method among the various methods of converting waste to energy. This method enhances the quality and heating value of the product gas. This study examines the energy potential of converting EWR into useful gases by steam gasification process. This study evaluates the effect of factors such as temperature, reaction time, and steam to feedstock ratio affecting the steam gasification process. Optimization of the gasification process and the interaction effect of these factors on the gasification products were also investigated using the response surface methodology (RSM) based on Box Behnken experimental design. Analysis of variance (ANOVA) was conducted to determine the level of confidence of the quadratic model derived from the Box Behnken method. In this study, the products obtained during the steam gasification process are hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), and tar. The optimum process condition for the steam gasification are found to be temperature 1000 C, reaction time of 45 minutes, and steam to feedstock ratio of 0.5. The ANOVA results show that temperature and reaction time has a significant influence on the steam gasification process compared to the steam to feedstock ratio. The results also show that product gas yield increases with temperature. As the gasification temperature increases from 800 0C to 1000 0C, the product gas yield increases by 230% while the tar yield reduces by 73% at a constant reaction time of 45 minutes, and steam to feedstock ratio of 0.5. In order to obtain maximum product gas output, the steam-to-feedstock ratio and the reaction time was kept within the optimum value. Finally, the results show that the lower heating value (LHV) of the product gas, the carbon gasification efficiency, and the cold gas efficiency of the steam gasification process increase as gasification temperature and reaction time increase. The LHV increases by 450% as the temperature increases from 800 C to 1000 C, reaction time from 15 to 45 minutes, and steam to feedstock ratio of 0.5. The carbon gasification efficiency and cold gas efficiency also increase by about 7% and 10% respectively under the same condition.