Properties analysis of pellets fuel from sewage sludge and biomass for renewable energy

Abstract

Renewable energy policies have driven the wood pellet and biofuel market over the last decades worldwide. Therefore, the pelletization of industrial waste and agricultural waste is beneficial for storage, logistics, and also for application as biofuel. The objective is to study the thermal properties, fuel pellet durability, exhaust gas composition from the combustion of fuel pellets, and the economic return of fuel pellet usage from sewage sludge and biomass (rice straw and sawdust). The results showed that the fuel pellets extruded from wastewater sludge consisted mainly of water. Therefore, they have a calorific value (12.56 MJ/kg) and durability lower than the two biomass pellets (89.0%). However, it is still in the range of fuel properties that can use as fuel and can store for the long term. Moreover, the flue gas composition from the pellet combustion was analyzed. The result indicated that the gas composition of the pellets fuel from wastewater sludge was similar to that of the two biomass pellets fuel and was within the standard value. Still, the SO₂ value was slightly higher than the benchmark. In considering the economic cost, it was found that the use of pellets from wastewater sludge was the most cost-effective, with a total cost savings of 15,657.80 baht/year, a total cost savings rate of 59.58%, NPV 48,328.03 baht, IRR 31.19%, B/C 144.64% and a payback period of 3.00 years. Therefore, utilizing sewage sludge for waste to energy is an excellent process to manage this waste because it can reduce waste disposal costs and also use as an environmentally friendly alternative fuel.