18 May 2017
Heat is an important energy source for the chemical industry to drive their processes. Waste heat recovery and re-use therefor provides attractive energy saving and cost saving opportunities. However, in batch processes the availability of waste heat and the demand for heat are shifted in time and storage of thermal energy is needed to overcome this mismatch.
This study looks into the feasibility of a collective waste heat recovery system for a series of batch reactors. An exothermal reaction is carried out in these reactors and the surplus heat is in the current configuration removed by cooling water. In the studied configuration for waste heat recovery, the heat from the batch reactors is collected in a thermal storage system, which is used as heat source for a heat pump system. This heat pump can lift the temperature of the waste heat to the level that it can be fed to the on-site steam supply system.
A dynamic model is developed that incorporates the waste heat supply from the reactors, the thermal storage system and the heat pump. The model is used to study the impacts of thermal storage capacity and heat pump capacity on the waste heat recovery potential and amount of steam produced by the heat pump. The thermal storage system levels out the fluctuations in heat supply, enabling a more constant operation of the heat pump and a reduction in need for any backup steam supply. The analysis indicates that the heat storage system can be economically feasible, achieving pay back times of less than 5 years. The price of electricity is an important factor on the economic analysis.