Effect of bagasse drying on thermal energy storage utilizing zeolite water vapor ad/desorption at a sugar mill

Recently, polygeneration in the sugarcane industry, which produces not only raw sugar but also other products (ethanol and electricity), has been attracting attention for green economy via the utilization of local natural resources. We focus on “heat” as a polygeneration method for the sugarcane industry. This study describes a thermal energy storage and transport system that can eliminate the spatio-temporal mismatch between the heat source, the sugar mill, and the fossil fuel consumption. The polygeneration system connects the thermal energy storage system with the sugar mill plant, such that the additional power generated by drying sugarcane bagasse, a fuel with a high moisture content, is used as the auxiliary power for thermal energy storage. Here, assuming the bagasse drying process at a sugar mill, we studied the bagasse drying rate, the bagasse drying in the bagasse elevator, simulations of a sugar mill with bagasse drying, and the thermal energy storage system utilizing the water vapor ad/desorption cycle of zeolite; a sugar mill in Tanegashima, Japan, was used as an example. A fixed-bed test packed with sugarcane bagasse was conducted, and a numerical model was developed for simulating the temperature distribution and the evolution of the outlet vapor pressure in the fixed-bed reactor. Subsequently, the bagasse drying process using a covered bagasse elevator was numerically simulated, and a moisture reduction of 2% was expected. This result was incorporated into the process simulation, to evaluate the relationship between additional power generation and temperature as well as the flow rate of unused heat for thermal energy storage. Finally, this relationship was incorporated into the numerical design of a heat-charging device, to evaluate the effect of bagasse drying on the thermal energy storage system. The coefficient of performance (COP) of the heat-charging system with bagasse drying was 1.6 times higher than that without bagasse drying.