Resource and technology assessment of cocoa pod husk for cogeneration

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Agriculture contributes 35.4% of foreign exchange earnings while employing about 60% of the country’s workforce. Cocoa and palm nut are the major tree crops under production in the country. Cocoa production contributes about 13% of agricultural GDP ( Current production, 2003/2004 cocoa season, stands at about 730,000 metric tons of dry cocoa beans. In extracting the cocoa beans, a lot of waste is produced in the form of the husk which can be a good source of energy for the generation of electricity. Currently, it is burnt to produce ash for soap making while the energy generated is not utilized for any activity. The objective of this project focused on the resource and technology of co-generating electrical and thermal energy from cocoa pod husk. The methodology used and the results achieved are presented and discussed. Four cogeneration technologies are considered and the assessment of cocoa pod husk availability is based on the quantity of cocoa beans produced and geographical distribution of cocoa farms, crop harvesting seasons, delivery cost and alternative uses. In the economic evaluation, the application for industrial and household purposes at the scale of 500 kW and 600 kW, respectively were assumed. Sensitivity analysis was carried out with respect to investment, fuel, grid electricity cost and discount rate on investment. It was realized that the investment cost is the main factor affecting the viability of the project. Also, discounted payback period of 12.1 years with 13.3% return on investment for the industrial application has been realized. The cost of energy generated using cocoa pod for rural electrification was found to be 0.067 $/kWh but reduces to 0.05 8 $/kWh at a discount rate of 6%. This competes well with the unit cost of 0.065 $/kWh and 0.094 $/kWh for the first 300 units of grid electricity for residential and commercial users, respectively. Cocoa production in the country is expected to continue in an increasing trend for the next 30 years, hence there will be enough cocoa pod waste to sustain the plant throughout its life time. Cogeneration of electric and thermal energy from cocoa pod husk is, therefore, a very competitive source of generating energy to supplement the Akosombo hydro and Takoradi thermal power plants.
A thesis submitted to the College of Engineering in partial fulfilment of the requirements for the award of Master of Science in Mechanical engineering, 2005