Initial study on solar process heat for South African sugar mills

Abstract

Solar thermal (ST) systems for the South African (SA) sugar industry could reduce coal consumption in the boilers and partly replace bagasse (pressed sugar cane fibres) as a heating fuel. Based on the heat and mass balance of a representative sugar mill, the most promising solar heat integration points were identified and preranked according to their potential energetic and economic benefits. The identified opportunities for solar process heat (SPH) are the generation of live steam and exhaust steam, the pre-heating of boiler feed water, the drying of bagasse and raw sugar, and the heating of clear juice. Without additional thermal storage, ST systems can supply between 12 and 27 % of the heat demand of these processes. The estimated levelized costs of heat (LCOH) for the SPH systems range from 2.57 Eurocent/kWh (0.42 ZAR/kWh) for solar drying of raw sugar during the crushing season (CS) to 4.57 Eurocent/kWh (0.75 ZAR/kWh) for all-year solar live steam generation. This study assumes that SPH has to compete with coal, which is the cheapest energy source in SA, to replace bagasse. Using current coal prices and past price increase rates, the estimated achievable internal rate of return (IRR) for solar live steam generation is 4.6 % if the steam can be used during the whole year, e.g. for electricity export. The highest IRR of 9.1 % is expected for sugar drying during the crushing season.