Co-gasification of biomass and plastic waste in a bubbling fluidized bed reactor
Abstract
Plastics are versatile, durable, and can be manipulated to match different needs. The COVID-19 pandemic has demonstrated the importance of reducing plastic waste and is believed to be responsible for increasing the generation of plastic waste by 54,000 tons/day which was reported in 2020. Another widely available waste is biomass waste. Agriculture and agroforestry, forest and wood processing, municipal waste, and the food industry are all considered major producers of biowaste. Co-gasification is considered one of the most promising methods of chemical recycling that targets the production of syngas (hydrogen and carbon monoxide) and light hydrocarbon gases. In this study, the gasification of pure birch sawdust wood (BSD) and pure rice husk (RH) was compared with mixtures where each BSD and RH was mixed with both LDPE and HDPE in the presence of three different bed materials, namely silica sand, olivine, and red mud. It was found that mixing the biomass with LDPE and HDPE increased hydrogen gas (H2) production. The Hydrogen gas concentration in the product gas increased slightly from 10% to 12% by volume when birch sawdust (BSD) was mixed with LDPE with a ratio of 1:1, while the hydrogen gas concentration increased to 15-16% by volume when birch sawdust was mixed with HDPE with a ratio of 1:1 and olivine has been used as bed material. The lower heating value of the produced gas, which has a direct relationship with the hydrogen and light hydrocarbons concentration, increased from 2.8 to 5.7 MJ/Nm3. Red mud increased the lower heating value of the produced gas when rice husk was premixed with HDPE from 3-4 MJ/Nm3 to 5.5-6 MJ/J/Nm3, however, the main drawback of using red mud as a bed material was the occurrence of attrition which requires a precautionary measure to control the dust produced and prevent air pollution. The produced gases from the gasification processes are commonly used in internal combustion engines applications, but due to the high content of hydrogen gas (H2/CO range 2-3) in the product, it can be considered a renewable source of hydrogen by further processing the gas mixture to obtain pure hydrogen gas that is utilized in various chemical industries.