Estimation of the potential of rice straw for ethanol production and the optimum facility size for different regions in Vietnam

To explore the potential for economical ethanol production from rice straw in Vietnam, this study estimated the rice straw density that is available for ethanol production, delivery cost of the rice straw, and determined the optimal facility size for different regions. The amount of rice straw annually generated is nearly 50 dry Mt year−1. The rice straw available for ethanol production in regions 1, 2, 3, 4, 5, and 6 was estimated to be 69, 6.8, 14, 3.9, 12, and 108 dry t km−2, respectively. The delivery cost of rice straw varied from 20.5 to 65.4 $ dry t−1, with a transportation distance of 0 to 120 km. Regions 1 and 6 were estimated to be optimal locations for ethanol production, with optimally-sized facilities of 112.5 and 195 ML year−1, respectively. The feedstock supply radius was 50 and 48 km for regions 1 and 6, respectively, with a total cost of feedstock and fixed cost of ethanol of 0.244 $ L−1 and 0.224 $ L−1, respectively. These results represented for the case study at present time. Naturally, the optimal plant size is sensitive to the changes of various conditions. Thus, an equation for the calculation of the optimal feedstock supply radius was developed with the involvement of various factors.