Dimethyl ether production from rice straw: process modelling and simulation

Abstract

Climate change has been a worldwide concern for recently centuries, and exploitation as well as use of fossil fuels dominantly contribute towards the environmental degradation. Several types of alternative energy resources have been taken into account and evaluated in order to find out viable options for the future, and dimethyl ether (DME) is one of those that are worth serious consideration. In this research, a continuous DME production process was developed and simulated using Aspen HYSYSTM. Rice straw, the most popular type of biomass in Vietnam, was chosen to be feedstock for the fuel production. The proposed process consists of five major sections: rice straw pretreatment and gasification for synthesis gas (syngas) generation using a circulating fluidized bed gasifier (CFBG); water-gas shift reaction (WGSR) for H2/CO ratio adjustment in syngas; gas cleaning stage where H2O, H2S and CO2 are removed; DME synthesis via direct production pathway; and DME purification for separation of main product and recycling of methanol. The simulation results indicated a production capacity of approximately 2,307 kg of DME per hour and chemical energy conversion efficiency (ηDME) from biomass into DME of 75%. In addition to that finding, an investigation into the gasifier's operating parameters was conducted for the purpose of maximizing amount of DME generated. From investigation data obtained, the operating temperature of CFBG, steam to biomass (S/B) ratio, and equivalence ratio (ER) that fulfilled such an aim were concluded to be 900oC, 0.27, and 0.32, respectively. This work offers a novel option for utilization of massive availablity of agricultural residues in Vietnam by turning it into a type of promising fuel, and therefore lessen environmental burden as well as may develop Vietnam's energy market.