Hybrid-heating-systems for optimized integration of low-temperature-heat and renewable energy

Abstract

The food and beverage industries are significant industrial producers of green-house gas (GHG) emissions. Reductions can be achieved by increased energy efficiency and the use of renewable energy to replace fossil fuel use. The main efficiency method within this industries is the use of low temperature heat (LTH), i.e. below 100 °C. Sources for LTH include heat recovery from process flows, heat rejection from utility operations (i.e. chillers, combined heat and power (CHP), condensing economisers), and renewable energy (i.e. solar thermal). A hybrid heating system (H2S) has been developed that can retrofit steam heater designs for the integration of LTH. Two different systems have been found, for adapting direct and indirect steam heaters, either installing an extra hot water heater or using the indirect hot water loop for the integration. In both systems the existing steam heater remains a part of the system for individual back-up. The set-up and the control algorithm of the H₂S allow installing a 37 % smaller hot water grid than a common design with one central back-up heater. Investigations using a comprehensive model of a whey separation and drying plant showed that implementing a piston engine CHP unit combined with the H₂S reduce the energy costs by 42 % and the GHG emissions by 33 %.