Numerical simulation and economic assessment of solar process heat and cooling for a Portuguese brewing factory

Abstract

A significant share of the world energy consumption is related to the industrial sector energy demand. E.g. in the European Union, about 50% of the energy consumption is for heat and cooling; of which 37% are related to the industrial sector. In order to attain the ambitious greenhouse gas and fossil fuel consumption reduction, it is crucial to advocate renewable energy technologies use in the industrial processes. Regarding the global thermal energy demand, about 60% is consumed in the temperature range of 30–250 °C; for which a possible solution consists into the use of solar thermal energy. Despite the potential of solar energy use for industrial process, nowadays the share is rather low. In this paper, a pre-feasibility study of solar energy integration into an industrial brewery process is addressed, for both heat and cooling demand. The case study is a brewery factory located north of Porto, Portugal, and the assessment carried out through numerical simulation. A typical brewery process requires heat at distinct temperatures levels, and to attain a fully integrate solar energy, temperatures of 180°C are needed. Thus, linear Fresnel reflector collectors were chosen for the solar field. Brewing cycle is constituted by several and sequential processes, i.e. a batch cycle with variable heat demand over time. Therefore, a significant amount of solar energy is dumped. Instead of using conventional thermal energy storage system, an alternative solution is proposed and assessed. In the brewing cycle, some process (e.g. fermentation) require heat at low temperatures (1°C) which can be addressed using a robust and low-cost thermal driven cooling solution, i.e. an ejector cooling cycle. Results show that the variable heat demand hinders a large-scale solar field performance, as thermal energy storage is not considered. The SF energy dumped occur on a daily basis and also in the months with high availability of solar radiation (i.e. summer). An interesting solution assessed in this work, consists in using the energy waste to drive a thermal driven cooling system in order to surpass the cooling needs of the industrial process, in this case, an ejector cooling cycle. Preliminary results show that this improvement permits to improve the useful heat ratio from 60% to 80%, and thus reducing the solar energy dumped. Nevertheless, the low cooling cycle coefficient of performance (0.25) outcome in a reduction of the whole system conversion efficiency.