Techno-Economic Investigations on the Small-Scale Production of Ethanol from Egyptian Rice Straw

Ligno-cellulosic biomass represents a major source of pollution worldwide as it is utilized as a source of fuel in rural stoves which are of very low efficiency or disposed of by direct/open burning. Efforts are being conducted worldwide to utilize lignocellulosic biomass for the production of ethanol, bio-oil or other sources of fuel that could replace the depleting fossil fuels. Most of the studies and early stage applications are directed towards the production of ethanol in large scale facilities of capacities around 15 - 100 Mm(3)/y. Taking into consideration the high transport costs especially in rural communities where ligno-cellulosic biomass is generated, it seems appropriate to investigate the techno-economics of production of ethanol on a relatively small-scale (about 2,800-4,000 t/y). Such units could be established close to the source of generation of ligno-cellulosic biomass without the need of transport to a centralized facility. In this work, techno-economic studies for the production of ethanol from rice straw for the proposed scale have been conducted. Technology aspects are first presented for the 40 ton/day rice straw process comprising the various processing stages. These include shredding to appropriate particle size, alkaline pretreatment stage followed by washing with water and acid to neutralization, enzymatic hydrolysis (saccharification) simultaneous with fermentation (SSF) using Saccharomyces Cerevisiae. The produced ethanol is then concentrated to over 99 % through azeotropic distillation. Preliminary design of the wastewater treatment plant is also provided. ASPEN PLUS from ASPENTECH for simulation has been used for conducting the material & energy balance and preliminary design of the processing units. Techno-economic studies have been conducted taking into consideration the conditions prevailing in our area. Capital investments, annual production costs and financial analysis has been conducted using ASPEN ICARUS. The capital costs have been estimated to be about LE 6-10 million for various proposed scenarios. The corresponding annual operating costs ranged between LE 1-1.5 million respectively. The Internal Rate of Return (IRR), has been estimated for several anticipated selling price for the produced ethanol ranging from 0.4 to 0.6 cents/l. It has been concluded that the proposed process could be feasible when the selling price is about 0.5 cents/L.