Prioritising options to reduce the process steam consumption of raw sugar mills

摘要

LOW WORLD sugar prices are making it increasingly difficult for raw sugar mills to remain competitive, and many milling companies are embarking on new revenue earning opportunities. In almost all new ventures, the energy from bagasse (as steam or cogenerated electricity) or the fibre itself provides an important basis for generating the additional revenue. Integral to increasing the economic viability of such projects is the need to cost-effectively reduce the steam consumed by the factory for sugar manufacture. The Sugar Research Institute has completed a comprehensive study of numerous options to reduce the process steam consumption of factories, and to determine the financial implications of the different options. Process simulation software for evaporators, pans and heaters were integrated with a basic high pressure steam model. For each process steam efficiency option, the effects on boiler load, fuel consumption, and cogeneration output could be accurately assessed for selected steam conditions at the boiler. The outputs from the integrated process model were directly linked to the financial model. For nominated input conditions, the project determined a prioritised list of technically and economically attractive options for reducing the steam consumption of the factory. The analyses were undertaken for three scenarios which include sale of export electricity, sale of surplus steam or sale of surplus bagasse. This paper describes the development of the integrated models and the results for a base case study. The results show a quintuple station is the preferred evaporator configuration for circumstances where the steam on cane is reduced from current levels of approximately 50% on cane to about 40%. To reduce the steam consumption below this level, a sextuple arrangement is preferred. A quadruple set shows inferior results for all steam on cane values. Options for steam on cane to below 30% were found to be technically feasible for cane factories, but these configurations are not likely to be economically justified.