Smokeless fuel production from wood and polyethylene mixtures

Substitution of fossil fuels by renewable energy sources in meeting energy needs is looked upon as an option for preventing global warming threat. To utilise biomass energy, extensive studies have been undertaken on the development of wood pelleting technology. In some countries, wood pellets are already commercialised and utilisation in power plants as well as for residential heating has increased significantly during the recent yearsOn the other hand, plastics form an important part of today?s life. This results in plastic wastes come into sight extensively. However, because only about one third of the waste plastics can be recovered by recycling operations, vision pollution as well as ecological pollution related to waste plastics has increased inevitably with the ever-increasing consumption trend. Waste disposal methods such as land filling are not sustainable owing to very low biological decomposition rates of plastics in nature. Thus, options of reclaiming or disposing of waste plastics by the means other than recycling must also be considered.Pyrolysis of various type of polyethylene has also been investigated under different conditions. These studies reveal that liquid pyrolsis products obtained in high conversion ratios contain wide spectrum of paraffinic, olefinic and aromatic hydrocarbons and composed mainly of aliphatic hydrocarbons.Although a vast number of studies have been devoted to the conversion of both biomass and plastics into liquid fuels, there is not much work handling volatile matter removal levels for the objective of increasing solid product yields. It is known that the factors such as temperature, particle size, heating rate and retention time of primary pyrolysis products in the system are effective on the amounts of solid, liquid and gaseous products here.In this study, co-pyrolysis and co-combustion of high-density polyethylene (WHDPE), low-density polyethylene (WLDPE), among municipal plastic wastes, and raw high-density polyethylene (RHDPE) and pine wood powder, chosen as biomass, were investigated. The effects of different pyrolysis parameters (heating rate, final temperature, sweeping rate, mixing ratio, grain size, number of pellets, etc.) on the yields of products formed from the pyrolysis in fixed bed of pellets prepared from the mixtures of these materials in predetermined proportions were determined. In addition, volatiles and char combustion rates and times of the pellets were measured.In the co-pyrolysis of pellets containing WHDPE and pinewood in equal proportions, maximum solid yield was obtained at 1oC/min heating rate and under 10 ml/min nitrogen sweeping flow for 500oC final temperature. It was determined that the highest liquid product yield obtained at 5oC/min heating rate and 700oC final temperature without nitrogen sweeping (0 ml/min). In addition, solid product yield decreased and liquid product yield increased with increasing WHDPE contents. It was observed that the solid product yield didn?t change considerably in the experiments conducted for studying the effects of size of blended materials or number of pellets being pyrolised at the same run. In the co-pyrolysis of pellets containing WLDPE or RHDPE and pinewood in equal proportions, solid product yields were not different compared the yields obtained from WHDPE-pinewood pellets.It was observed that volatiles and char combustion times decreased with initial temperature of furnace when pellets containing WHDPE and pine wood in equal proportions burn. The rates found by using time-dependent mass values of burning pellets have shown that volatiles combustion rates increased with initial temperature, whereas carbon combustion rates increased with starting temperature up to 800oC and decreased again at 900oC.Key Words: Pyrolysis, Combustion, Wood, High-Density Polyethylene, Low-Density Polyethylene