The Applications of Ammonia-Water Absorption-Compression High-Temperature Heat Pumps in European Food Industry

1 The Applications of Ammonia-Water Absorption-Compression High-Temperature Heat Pumps in European Food Industry Shuai Ren, Marcel Ulrich Ahrens, Armin Hafner Norwegian University of Science and Technology - NTNU, Department of Energy and Process Engineering, Trondheim, Norway, [email protected] Keywords: High-temperature heat pump, ENOUGH project, ammonia-water mixture, food industry, GHG emissions reduction Abstract Food systems are globally responsible for around 21-37% of total greenhouse gas (GHG) emissions. The ENOUGH project, funded by the EU Green Deal initiative project aims to contribute to the climateneutral food business by mitigating climate change, reducing energy use, and increasing energy efficiency in processing, distribution, conservation, and food preparation. There is a large amount of waste heat available in the food supply processes and a particular focus of NTNU within the ENOUGH project is to integrate the thermal processes in the food supply chain to utilize the waste heat and maximize the energy efficiency in the cooling, heating, and freezing processes. The high-temperature heat pumps (HTHPs) which can combine both heating and cooling processes have been applied in many industrial processes for waste heat recovery and heat supply. In the food supply chain, a large amount of fossil fuels is consumed for hot water and steam generation, which gives rise to both economic and environmental concerns. Previous studies showed that heat sink temperatures up to 100°C-150°C are realizable with industrial HTHPs (Arpagaus et al., 2018; Jensen et al., 2015) so that the HTHPs are deemed as a promising replacement to the steam boilers owing to their high energy efficiency and sustainability. The HTHPs using natural refrigerants as working fluid such as ammonia and water has gained particular interest from researchers in recent years due to their low global warming potential (GWP) and known environmental impacts (Ahrens, Loth, et al., 2021; Jensen et al., 2015; Mateu-Royo et al., 2021). The ammonia-water absorption-compression high-temperature heat pump (ACHP) in NTNU is designed based on the Osenbrück cycle aiming to achieve high-temperature lifts and do have gliding heat rejection temperatures, as shown in Figure 1. It combines the technologies of an absorption and vapor compression heat pump with a mixture of ammonia and water as the working fluid. Heat is extracted and released at non-constant temperature glides and the necessary compression ratio is lower compared to conventional vapor compression heat pumps. High heat sink temperatures up to 150°C can be achieved with comparatively high COPs. In addition, the capacity can be controlled by changing the overall composition of the working fluid mixture, which ensures high system flexibility and adaptability. 2 These properties make the ACHP system interesting for the use in various sectors with high temperature heat demands in the food supply chain, such as meat processing, fish processing as well as in dairies. Figure 1: Simplified representation of a combined absorption-compression heat pump cycle In meat processing, refrigeration systems are utilized to cool down refrigerated chambers for meat storage, rapid cooling tunnels and building rooms (Iten et al., 2021), while the steam boilers which are accountable for the most intensive thermal energy consumption, are applied to the hot processes such as scalding, smoking, cooking, sterilization and pasteurization. The heat required in these hot processes are all in the range of 60°C-160°C which is within the working domains of the ACHPs (Jensen et al., 2015). Bergamini et al. (2019) evaluated the performance of three HTHP cycles with four different natural refrigerants for boiler substitution. Compared with natural gas boilers, the HTHPs exhibit good performance in delivering heat up to 180°C, especially for the cycles with R717 (ammonia) and R718 (water) as refrigerants. In dairy production, the processes such as drying, pasteurization, sterilization, UHT treatment and cleaning in place (CIP) are the major consumers of hot water and steam (Ramirez et al., 2006). The fully integrated dairy energy system with ACHPs is capable of providing all temperature levels of heating and cooling demands and obtaining significant energy savings compared to conventional dairy systems. The achievable waste heat recovery rate is up to 95% and the achievable GHG emissions reduction is up to 23.2%-91.7% by employing ACHPs with natural refrigerants (Ahrens, Foslie, et al., 2021). An integrated energy system combining the cold processes and hot processes with the ACHPs can recover the waste heat from the refrigeration systems ae well as the medium temperature processes and provide high temperature heat supply for the hot water and steam consumers in the food plant, such as smoking, scalding, drying, pasteurization, sterilization, cleaning, steaming & cooking and ultra-high temperature (UHT) treatment, as shown in Figure 2. The ACHP test rig in NTNU can provide a flexible experimental system for the investigation and optimization of the operating parameters, conditions and components for the ACHP applications in different food processes. It serves as a starting point for further research by combining theoretical approaches, possible solutions, and experimental results. 3 In the frame of ENOUGH, the applicability of the ACHP to the food supply chain will be investigated and its performance will be optimized. The system modelling and experimental validations will be conducted at NTNU. The integration of the ACHP between sectors of the food chain will be analyzed and the replicable approach will be discussed. The feasibility, reliability, and performance of the ACHP in the applied field will be demonstrated to various stakeholders. Figure 2: Possible applications of ACHP in food processes References Ahrens, M. U., Foslie, S. S., Moen, O. M., Bantle, M., & Eikevik, T. M. (2021). Integrated high temperature heat pumps and thermal storage tanks for combined heating and cooling in the industry. Applied Thermal Engineering, 189, 116731. Ahrens, M. U., Loth, M., Tolstorebrov, I., Hafner, A., Kabelac, S., Wang, R., & Eikevik, T. M. (2021). Identification of Existing Challenges and Future Trends for the Utilization of Ammonia-Water Absorption–Compression Heat Pumps at High Temperature Operation. Applied Sciences, 11(10), 4635. Arpagaus, C., Bless, F., Uhlmann, M., Schiffmann, J., & Bertsch, S. S. 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