Evolution of Syngas from Co-Gasification of Polyethylene and Woodchips

Abstract

Gasification of polyethylene (PE) and woodchips (WC) mixtures have been investigated in a semibatch reactor, using high temperature steam as the gasifying agent. The reactor temperature was maintained at 900 o C. The ratio of PE to WC was varied from 0% to 100% in 20% intervals. Characteristics of syngas were evaluated based on the yield of syngas, hydrogen, energy, total hydrocarbons and apparent thermal efficiency of the process. Results show that properties of syngas evolved during gasification of PE-WC blends cannot be determined from the weighted average syngas properties obtained from separate gasification of WC and PE. Superior results in terms of syngas yield, hydrogen yield, total hydrocarbons yield, energy yield and apparent thermal efficiency from PE-WC blends were obtained as compared to expected weighed average yields from the individual components. The results obtained support synergistic interaction between PE and WC during high temperature steam gasification of these mixtures. These results also reveal the importance of mixing two or more compounds on the performance of stream gasification of wastes. I. Introduction Greater use of renewable energy sources is of pinnacle importance especially with the limited reserves of fossil fuels. It is expected that future energy use will have increased utilization of different alternative sources of energy available to us, including biomass, municipal solid wastes, industrial wastes, agricultural wastes and other low grade fuels. These energy sources and wastes provide unique challenges for energy utilization since the energy yield and gas composition from gasification or pyrolysis of these materials is strongly impacted by the feed mixture composition. Development of sustainable renewable energy technologies for their use in current and new power plants is of greater importance now than ever before due to several reasons. Some of these reasons include energy security and availability, independency from foreign oils and reduction of greenhouse gas emissions to provide cleaner environment for better health and plant, and animal life. These reasons dictate the development of alternative and sustainable energy technologies. Gasification provides part of the solution towards dependable renewable energy source. Gasification is a robust solution to solve the growing problem of landfills, since energy can be fully extracted and the waste is destructed with minimum residue and with the properly developed process the remaining residue is non-leachable. Gasification systems may run on single or multiple sources of feedstock. However, in many cases the gasification systems often encounter the problem of unsteady source of biomass feed throughout the year so that the biomass composition cannot be taken as fixed. During off-season for a given biomass, another feedstock has to be mixed with the feedstock in order to maintain a steady supply of feedstock to the gasifier for seeking the desired output power from the gasification power plant. On the other hand, a gasification system might be designed to run on solid wastes, which consists of a mixture of different carbonaceous materials. However, the composition of the waste can change both temporally and spatially so that one must examine in detail the role of various input, design and operational parameters on the gasifier performance. Much attention has been given to evaluate the behavior of various kinds of single component materials under gasification or pyrolysis conditions. 1-5 Examining the characteristics and kinetics of single component samples provides basic information on the behavior of different samples for use as feedstock in gasification systems. This then helps in the better design of gasifiers for improved performance and controlled syngas composition of defined and higher heating value. However, the data obtained from single component experiments may result in some misleading information about the actual syngas properties and the process kinetics. The fate of multi-components as feed stock to the gasifier might be much different than the expected fate of single components. The misleading information might arise from the assumption that the syngas characteristics resulting from gasifying a mixture of