Effect of bioethanol conversion efficiency and ratio of rice paddy area to flatland on energy consumption and CO2 emission of rice straw transport process in Japan

• We examined the energy consumption and CO2 emissions of rice straw transport.
• Predictive models for the energy consumption and CO2 emissions were constructed.
• A bioethanol plant should be constructed in an area with a high rice paddy ratio.

In Japan, rice straw is recognised as the most promising biomass for bioethanol production based on the amount and availability. This study examined the energy consumption and the CO2 emissions of the rice straw transport process. Specifically, we investigated the effects of the ethanol conversion efficiency (ε) and the ratio of the rice paddy area to flatland (γ) on the CO2 emission and energy consumption of the rice straw transport process. The energy consumption and the CO2 emissions (ε: 0.60–1.0; γ: 0.050–0.20) were determined to be 0.17–0.37 MJ L−1 and 0.012–0.025 kg L−1, respectively. The predicting model for the energy consumption and the CO2 emissions of the rice straw transport process was constructed, and the energy consumption and the CO2 emissions were proportional to the ethanol conversion efficiency raised to the −1.5 power and γ raised to the −0.5 power. These results showed that the lower γ, the higher the energy consumption of the rice straw transport process. Furthermore, the energy consumption of the rice straw transport process increased at large-scale plants because of the higher value of average transportation distance.