Effect of Multi Injection Process on “Zeolite Boiler” in Thermochemical Energy Storage and Transport System of Unused Heat From Bagasse Boiler

Abstract

In the sugar mill in Tanegashima which is an isolated island in Japan, raw sugar production process produces raw sugar and bagasse simultaneously. Raw bagasse is not storable because of its perishability due to high moisture content. Actually, the bagasse boiler burns more bagasse than that is required for the sugar mill. Hence, the temperature of flue gas increases and a massive amount of unused heat at around 200 °C is exhausted during sugar mill operation period. On the other hand, many other factories in this island burn imported oil at package boilers to generate process steam up to 120 °C all year around. To resolve this spatial and seasonal mismatch, we employed thermochemical energy storage and transport system using zeolite steam adsorption and regeneration cycle. We introduced a basic design of heat release device which is called “Zeolite boiler”, that is a moving bed with indirect heat exchanger. Adsorbed steam is assumed to be generated by a package boiler. A small zeolite boiler with 20 kg/h of zeolite was designed by using a developed quasi-2D simulation code that numerically solves mass and heat conservation equations of the counter-flow reactor model. As the result of single injection from the top of chamber, the zeolite boiler could generate 4.95 kg/h of dry saturated steam at 0.2 MPa when 4.0 kg/h of steam was injected from the package boiler. Multi injection process was considered to improve the heat recovery rate. By injecting 3.0 kg/h and 1.0 kg/h of steam separately from the top and the middle of the chamber, 5.9 kg/h of steam was generated and heat recovery rate was increased by 13 points.