Multi-level framework for optimal operation of gasifier system utilising crop residues from small and medium-scale farms

Abstract

Lack of techno-economic framework for optimal gasification and the identification of critical parameters for optimal operations is one of the major challenges restricting the gasification of crop residues. This study aims to develop an optimal techno-economic framework for the gasification of crop residues from clustered small/medium-scale farms. The developed model was applied to a case study in Adiembra, a farming community for a 10-kW gasifier engine system. Eight scenarios of individual feedstock and their blends were considered. The results revealed specific fuel consumption ranging from 1.79 – 3.53 kg/kWh. The economic analysis showed marginal profitability except for rice husk and straw which are not profitable. At the current grid electricity price, the minimum level of subsidies required to ensure the financial viability of the feedstocks is within the range of 30 – 70 % of the investment cost based on the various feedstock scenarios considered. The study revealed individual feedstocks with the best technical and economic prospects for optimal gasification to be cocoa pod husk, maize stalk and husk, maize cobs, rice straw and rice husk in the order of best to worst. The use of feedstock blends generally improved the overall syngas characteristics and financial viability. A total number of farms ranging between 107 – 532 are required to be clustered within a radius of 0.74 – 2.12 km with a cluster radius greater than 3.91 km not being financially viable. The fraction of each feedstock type in the blends were optimised with corresponding increase in syngas generation within the range of 9 – 35 % and decrease in the required number of farms within the range of 30 – 57 %. The outcome of the study demonstrates that sustainable gasification of crop residues for minigrid electricity generation requires co-gasification of various residue types, valorisation of by-products and increase in the current feed-in-tariff rate in Ghana.