Thermal gasification of densified sludge/wastepaper fuels has been shown to be technically feasible for the co-disposal of sludge and source-separated wastepaper. The performance and economic feasibility of a downdraft packed-bed gasifier system fueled with densified sludge/wastepaper and wastepaper fuels has been evaluated.
To assess the performance of the gasifier, a series of gasifier runs were conducted at various air input rates with the use of various densified fuels. In eight of the runs, a densified fuel consisting of 20 percent lagoon-dried sludge and 80 percent recycled wastepaper was used; in five runs, densified wastepaper cubes were used. Gaseous and particulate emissions resulting from the combustion of producer gas were measured. Char, a by-product of the gasification process, was evaluated as a substitute for powdered activated carbon. The performance of a small dual-fuel diesel engine combusting producer gas generated from the gasification of densified wastepaper was also demonstrated.
The cost of sludge disposal in sludge-wastepaper gasification system, using wood chips as an auxiliary fuel, was found to be competitive with the cost of sludge disposal by landfilling if the electricity generated by the gasification system can be sold at a cost of $0.12/kWh，$0.09/kWh， and $0.085/kWh for communities sizes of 10,000, 30,000, and 50,000 persons, respectively. The economic feasibility of sludge/wastepaper gasification is highly sensitive to the cost of wood chips, the solids content of the dewatered sludge, the percentage of wastepaper collected, and the resale cost of electricity.
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