Assessing the potential of energy saving in a traditional sugar cane mill during steady state and transient conditions-part I: base case plant model

Sugar cane mills are energy intensive industries and also have a large potential of providing surplus energy in terms of heat or power. Identification of heat and mechanical losses in sugar mills is one approach in indicating energy saving potential in sugar mills, especially in traditional mills. Such assessment of the energy flows in sugar mills needs to be done both in steady state and transient conditions (where sudden stoppages occur). In this paper, such an approach is considered where a base case plant is modeled for steady state and transient state operations. For the transient state study, a typical stoppage is chosen and three different scenarios are modeled. Heat loss calculations are done for major cogeneration units and for the amount accumulated of the surplus bagasse when the steady state operation is estimated. The results of the models show that during steady state operation, the losses related to mechanical prime movers is on the higher side as the mills and shredder are driven by steam and generate mechanical power higher than what is needed by the mills and the shredder equipment themselves. In the transient state scenarios, where fuel oil is introduced during press mill stoppage, there is steam wasted (steam that could have been used for mechanical power generation) starting from the period where the fuel oil is introduced until the power required during the stoppage is reached. The CO2 emission during the use of fuel oil is also quite significant during the stoppage.