REVIEW ON RENEWABLE ENERGY SOURCES BASED ON THERMAL CONVERSION IN THE PULP AND PAPER INDUSTRY

Abstract

Pulp and paper industries have great potential and prospect for resources of renewable energy. These resources are generated from almost all stages of the pulp and paper manufacturing process. Energy-rich biomass in pulp mills includes bark, sawdust, wood waste, pins, fines, knots, black liquor, and sludge from wastewater treatment plant (WWTP). Energy-rich rejects at the paper mill includes fiber and plastics from the hydropulper unit, and sludge from WWTP. Among these biomasses, bark has the greatest quantity while hydropulper rejects has the highest calorific value. The amount of bark reaches 100-300 kg/t pulp or 60-90% of wood waste in pulp mills, while hydropulper rejects although only reach 5-10% of used paper quantity, has a heating value of 28.81 MJ/kg (air dried basis). Biomass and reject can be converted into renewable energy with a higher energy density through thermal-based conversion technologies such as hydrothermal processing, torrefaction, pyrolysis, and gasification. The renewable energy products include hydrated sludge, biomass pellets, torrefied biomass, bio-oil, and syngas. Several technologies such as gasification are already operating commercially, while several other technologies such as hydrothermal and pyrolysis are still being improved.