Implementation Analysis of Bagasse Power Plants Considering Technology Options on Sugarcane Cultivars and Power Plants

The power systems of the remote islands lying south of Kyushu Island in Japan consist of mutually isolated microgrids, and the islands location places them at a disadvantage in terms of thermal power generation cost and the security of fossil resources. However, many of the islands have power plants in cane sugar mills that have the potential to provide excess electricity and heat. Connecting the mills with the main power grid of the island may reduce the cost of power generation and enhance the security, but this has not been carried out because the sugar production period is short and the amount of surplus bagasse is limited. Replacing the current sugarcane cultivar with one that is more fibrous and produces a higher yield per farmland area may extend the sugar production period and increase bagasse supply. This transition, however, would involve a retrofitting design of the power plant in the mills, which are designed to optimize only the production of sugar. In this paper, an implementation analysis of bagasse power plants connected with the main grid of the island was conducted that takes into account the technological options for sugarcane cultivars and the power plants in sugar mills. First, a simulator that can estimate the mass and energy balance of a cane sugar mill for the type of the cultivar and power plant was developed based on a previous simulator. Three options were considered: Case A, the current cultivar and the power plant are used, and surplus electricity is sold only in the period of sugar production; Case B1, a high-yielding cultivar is chosen, the back-pressure steam turbine used to generate electricity is replaced by a condensing-extraction steam turbine, and surplus electricity is sold only in the period of sugar production; and Case B2, the cultivar and the turbine are as in Case B1 and electricity is sold during sugar production and at other times by using surplus bagasse stored from the sugar production period. Using the developed simulator, the three cases were compared in terms of the amount of raw sugar, molasses and bagasse produced, the energy balance in the period of sugar production, the potential sale of electricity, and the maximum proportion of power generated from fossil fuels that is replaceable by power from bagasse. For all target islands, the period and the scale of selling electricity can be expanded with the increase in raw sugar production in Cases B1 and B2. In Minami Daito Island, at most 9.48% of power from fossil fuels can be replaced with that from bagasse. Effective utilization of surplus heat, mixed combustion of bagasse with other regional biomass, and savings in the energy demand of the cane sugar mills may further enhance the positive effects of introducing bagasse power generation.