Assessment of the implementation of alternative process technologies for rural heat and power production from cocoa pod husks

Abstract: Cocoa pod husks are generated in Côte d’Ivoire, in abundant quantities annually. The majority is left as waste to decompose at the plantations. A review of the ultimate and proximate composition of CPH resulted in the conclusion that, CPH is a high potential feedstock for both thermochemical and biochemical processes. The main focus of the study was the utilization of CPH in 10,000 tons/year power plants for generation of energy and value-added by-products. For this purpose, the feasibility of five energy conversion processes (direct combustion, gasification, pyrolysis, anaerobic digestion and hydrothermal carbonization) with CPH as feedstock, were investigated. Several indicators were used for the review and comparison of the technologies. Anaerobic digestion and hydrothermal carbonization were found to be the most suitable conversion processes. For both technologies an analysis was conducted including technical, economic, environmental and social aspects. Based on the characterization of CPH, appropriate reactors and operating conditions were chosen for the two processes. Moreover, the plants were chosen to be coupled with CHP units, for heat and power generation. After the evaluation and calculation of the main products and by-products that can be obtained, an economic analysis was conducted. Most of the electricity was assumed to be sold to grid (0.10 USD/kWh), after self-utilization, and the by-products were assumed to be sold as bio-fertilizers or soil conditioners, in both cases. The prices suggested for the by-products were estimated based on their nutrient content. For the economic analysis, total investment costs, running costs, revenues and more economic indicators were obtained and calculated. Both case study plants were found to be economically feasible (NPV>0). After comparing the NPV values, hydrothermal carbonization had higher NPV value, meaning it is more profitable. Though, there are many more barriers to overcome for hydrothermal carbonization than for anaerobic digestion. Moreover, the two case study plants can help with GHG mitigation, since 1,760 - 1,980 tCO2 eq/year can be avoided. Furthermore, several social benefits were identified. In conclution, hydrothermal carbonization and anaerobic digestion plants, utilizing CPH for energy conversion are feasible and cost viable solutions. Although, the governmental support can reduce the risks by assisting in the promotion of the by-products markets.