Techno-economic feasibility study of hemicellulose extraction from softwood saw dust
Islam, Md Hujjatul (2017)
Islam, Md Hujjatul
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The main objective of this thesis is to study the feasibility of hemicellulose extraction from sawdust integrated into the wood pellet production process. Extraction process design and simulation was carried out using Aspen Plus simulation tool. The operating parameters for extraction were selected such a way that only high molecular weight hemicelluloses are obtained. In order to accomplish this, extraction time of 20 minutes and temperature 160 °C were considered. Solid to liquid ratio was considered 1:7 in order to avoid any problem in the circulation of the sawdust and water mixture. Pinch analysis was done in order to optimize the process for maximum energy recovery. It was found that around 66 MW (in large scale operation) of energy can be recovered and use for heating of reactor feed and drying of sawdust. The conversion and yield of hemicellulose from sawdust were obtained 9.3% and 8.89% respectively. The product was 80% hemicellulose and 20% water. The economic evaluation was done in order to study the feasibility of the extraction process. Small and large scale operation was considered for evaluation. The small scale production capacity was 1.5 ton / h and the large scale capacity was 9.3 ton/h. The return on investment for small scale and large scale operation was 32.8% and 44.9% respectively. The payout time for small scale is 2.67 years and for large scale is 2.02 years. Moreover, the Internal Rate of Return (IRR) was found 32% for small scale and 41% for large scale. It is considered safe to invest in a project that has IRR higher than 25%. Sensitivity analysis shows that variation of product price and production rate have high degrees of risk for investing in the project. Finally, it can be summarized that extraction of hemicellulose by autohydrolysis from sawdust before pelleting is technically and economically feasible except the fluctuation of product price and production rate.