Thermochemical Storage of Heat from a Combined Heat and Power Plant: a System Approach

Description Thermal energy storage systems have been identified as a promising solution to reduce energy consumption by reducing the mismatch between heat demand and heat supply. Compared to other thermal energy storage systems, thermochemical storage (TCM) has some main advantages: it has a potential higher energy density and thermal energy can be stored for a long period without substantial heat losses. TCM makes use of a reversible reaction A(s) + B(g)  C(s) + heat to release or store thermal energy, depending on the direction of the reaction. Mostly agent B is steam and A is a salt which is hydrated, for instance magnesium sulfate. Energy density and temperature window, in which the reversible reaction is feasible, depend on the salt used. To dehydrate the salt to its original state (and absorbing heat), excess heat, in the form of solar heat, waste heat of an industrial process or heat from a combined heat and power plant (CHP) can be used and thus stored in the TCM. When a heat demand appears, steam is injected in the TCM, which reacts with the salt, resulting in a hydration process and the release of heat. In most cases the salt is loaded on a porous matrix material, to improve mass transfer of steam, heat conduction and overall heat transfer. A major concern is melting of the salt, caused by high temperatures and high steam concentrations, which leads to loss of dispersion of the salt in the matrix structure. In a previous master thesis, TCM has mainly been studied in the residential sector for seasonal storage of solar energy. Applying TCM to the industrial sector introduces other challenges and maybe even more benefits since different time scales and temperature levels are encountered. For example in the case of combined heat and power (CHP) plants, the use of TCM based thermal energy storage could extend the potential of CHP to cases with a heat demand that is less constant. In this master thesis, TCM integrated in an industrial CHP system will be approached from a system point of view, hereby mainly focusing on the TCM. Firstly, TCM materials that are suitable for integration in a CHP will be selected, based on multiple criteria like operational temperature window, heat storage density, power density and resistance to deterioration. Secondly, a simple dynamic model of a TCM reactor will be