Energy Efficiency and Life Cycle Assessment with System Dynamics of Electricity Production from Rice Straw Using a Combined Gasification and Internal Combustion Engine

Abstract

This study assessed the environmental performance and energy efficiency of electricity generation from rice straw using a combined gasification and internal combustion engine (G/ICE). A life cycle assessment (LCA) was performed to consider the conversion to electricity of rice straw, the production of which was based on the Philippine farming practice. Rice straw is treated as a milled rice coproduct and assumes an environmental burden which is allocated by mass. The results of an impact assessment for climate change was used directly in a system dynamic model to plot the accumulated greenhouse gas emissions from the system and compare with various cases in order to perform sensitivity analyses. At a productivity of 334 kWh/t, the global warming potential (GWP) of the system is equal to 0.642 kg CO2-eq/MJ, which is 27% lower than the GWP of rice straw on-site burning. Mitigating biogenic methane emissions from flooded rice fields could reduce the GWP of the system by 34%, while zero net carbon emissions can be achieved at 2.78 kg CO2/kg of milled rice carbon sequestration. Other sources of greenhouse gas (GHG) emissions are the use of fossil fuels and production of chemicals for agricultural use. The use of agricultural machinery and transport lorries has the highest impact on eutrophication potential and human toxicity, while the application of pesticides and fertilizers has the highest impact on ecotoxicity. The biomass energy ratio (BER) and net energy ratio (NER) of the system is 0.065 and 1.64, respectively. The BER and NER can be improved at a higher engine efficiency from 22% to 50%. The use of electricity produced by the G/ICE system to supply farm and plant operations could reduce the environmental impact and efficiency of the process.