Integration of ethanol production with a sugar factory producing maximum cogeneration

摘要

Cogeneration (meaning generation of electrical power for export to consumers outside the factory) has come in greater demand in recent years, due to more favourable prices for electrical energy of biomass origin. The paper shows the most important characteristics of a factory redesigned for producing maximum cogeneration, i.e. low process steam demand, high pressure steam boilers, condensing and partly back-pressure turbines and wholly electrified drives. The case examined also refers to a factory where approximately 50% of the total sugars recovered from the entering cane are sent to the annexed ethanol distillery. In order to increase the cogeneration potential of the sugar factory, it is worthwhile examining possibilities to reduce the steam consumption in the distillation process. When employing intermediate pressure steam and multiple vapour usage in the distillation plant, the steam consumption there can be reduced to approximately 43% of conventional schemes widely in use. This way less exhaust steam is required in the combined plant, increasing the available high-pressure steam to the condensing turbines. The combined effect of redesigning the cane sugar factory for maximum cogeneration coupled with an energy efficient distillery allows the cogeneration to rise from currently 12.8 kWh/t to 82.6 kWh/t cane. The result is a financially attractive proposition, especially in cases where significant amounts of power can be sold during the cane crop at reasonable prices like in Brasil, Guatemala, Mauritius and more recently India.