Pulp & Paper mills are very high pollution generating chemical plants and produces large amount of sludge as a result of waste water treatment. Disposal of this large quantity of sludge has always been a major concern for pulp & paper industry. Landfilling and landspreading used to be most commonly used sludge disposal method in India but stricter environmental regulation has imposed several restrictions on using these methods. Different alternative to landfilling is being investigated with the objective to reduce the volume of material that is landfilled, to recover material, such as fibers and fillers, from the waste stream for reuse, and to recover usable energy from the sludge. Air gasification is one such method which uses thermo-chemical approach to convert any biomass into bio-gas.
Although gasification has been extensively studied but not much work has been done on the fluidized bed gasification of pulp and paper mill sludge. Good quality of feedstock to gasification is very important in getting good quality of gasification product in terms of producer gas. Torrefaction has been investigated as very good method of improving the quality of feedstock. Torrefaction is a mild pyrolysis process that occurs at 200-300oC and reduces the oxygen and moisture content significantly by losing water, carbon dioxide and carbon monoxide. The proposed work puts forward an idea of integrated torrefaction and air gasification process for paper mill sludge. It is expected that under suitable combinations of torrefaction and gasification conditions, bio-gas with enhanced physical and chemical properties can be produced from pulp and paper mill sludge. The broad objective of the proposed project is to produce bio-gas of higher quality from gasification with torrefaction as pretreatment.
Torrefaction of raw sludge from pulp & paper mill will be carried out in a fixed bed reactor. This pretreatment will be done with the aim of improving the properties of sludge biomass which in turn should enhance the performance of gasification. Gasification of the raw sludge and torrefied sludge will be carried out in an air bubbling fluidized bed reactor at a temperature 650-7500C. Air gasification produces much more gas than the bio-oil and this gas is rich with carbon mono oxide and hydrogen. This gas stream could be converted into other forms of more readily usable energy or used directly for combustion fuel. The specific chemical derivatives that are produced during gasification will also be studied.