DEVELOPMENT OF PILOT PLANT FOR BIO-ETHANOL PROCESSING

Abstract

The paper outlines achievements obtained in developing a pilot bio-ethanol plant at theDepartment of Chemical and Mining Engineering (CME), University of Dar es Salaam. Thepilot plant consists of: 30 L inoculums tank; 1,700 L fermenter; 1,500 L/day distillationcolumn; and ancillary equipment. The prototype is a platform intended to be used fortechnology demonstration and research by graduate and undergraduate students studyingthe production of bio-ethanol using traditional and non-traditional raw materials like coffeemash, cashew fruit, and sisal inulin. The equipment has been developed using locallyavailable engineering resources and the distillation column with 18 sieve tray measures 0.5m diameter 7 m high operates at atmospheric pressure. The condenser is cooled by 15 o Cchilled water from utility lines and the reboiler is powered by 63 kW boiler installed atCME. Although the system includes biological, chemical and mechanical engineeringdetails, only the important design issues are presented. A MATLAB code was developed forestimating the number of theoretical plates using the Mc Cabe-Thiele method. The water-ethanol vapour liquid equilibrium VLE data was obtained using relative volatilitiesestimated by Antoine equations for vapour pressure. The process design was done usingvarious simulation packages and custom programs like Microsoft Excel for mass balance,Microsoft Visio for process and instrumentation (P&I) diagram AutoCAD software formechanical engineering drawings. After performing hydraulic leak tests, the prototype wastested using blackstrap molasses 80 o brix which was prepared for fermentation usingdilution and inoculums formulations developed in Microsoft Excel for water dilution, yeastand nutrients like (NH 4 ) 2 SO 4, KH 2 PO 4, MgCl 2. A batch mash boiling test conducted on thecolumn showed that the response of tray temperatures exhibited first-order delay behaviorwith an average lag of 17 minutes and a delay of 50 -65 minutes depending on tray distancefrom the reboiler. Due to lack of feedback control equipment specifically on-linecomposition analyzers and suitable actuators, continuous control of ethanol compositioncould not be undertaken. It is planned to procure pertinent control hardware during thenext phase of the project. However the batch test gave initial ethanol purity of 80% whichdecreased as the ethanol content in the still was continuously depleted.