Estimation of CO2 Reduction Potential and Cost of Solid Biomass Fuel Production Process Integrated with a Waste Gasification and Direct Melting System

In recent years, the introduction of a gasification and direct melting system (GDMS) has been promoted for carbon recycle and energy recovery from carbonaceous waste, and for extending the life of the final landfill. However, CO2 emissions by the use of coal coke is a problem. In this study, the production process of solid biomass fuels (SBFs) derived from biomass residue (i.e., sawdust briquette (SB), rice straw briquette (RSB), and biocoke made from a mixture of agricultural residues (MIXBIC)) was integrated with the waste GDMS to reduce CO2 emission from coal coke. The heat for drying of SBFs is supplied by the exhaust heat from the GDMS to reduce kerosene usage. The CO2 reduction potential and economics of the SBF production process were evaluated. We found the CO2 emissions from coal coke can be reduced by 95.9-90.5, 95.6-90.9, and 78.2-69.7% at transport distances of 0-200 km by using SB, RSB, and MIXBIC, respectively. When the transport distance of the biomass residue was 50 km, the net total annualized costs of the proposed SBF production process were -0.043 +/- 0.029, 0.138 +/- 0.025, and 1.05 +/- 0.37 MUSD/year, in the cases of SB, RSB, and MIXBIC, respectively, when the payback time was 10 years. In the case of SB, the CO2 reduction costs were negative value when the transport distance was shorter than 75-200 km (average 133 km), indicating the capital costs can be recovered within 10 years. In the case of RSB, CO2 reduction costs can be recovered in areas where the rice straw procurement cost is low. In the case of MIXBIC, reduction of the capital costs of the molding machine was critical to reducing the annualized cost. The calculated CO2 reduction costs at 0-200 km in the cases of SB, RSB, and MIXBIC were -26(+10) to 12(+/- 15), 45(+/- 8.8)-79(+/- 12), and 471(+/- 171)-630(+/- 207) USD/t of CO2, respectively.