Conserving resources through heat recovery

Frozen food products generate growing sales worldwide every year. The market in Germany is also continuing to develop positively, as the latest figures from the German Frozen Food Institute (dti) show: Managing Director Sabine Eichner expects sales to grow by 3.5 per cent to over four million tonnes for all of 2023. For total sales, the dti is forecasting growth of 15.3 per cent to 21.38 billion euros. "Despite the positive forecast, the market trend in the frozen food sector must be viewed from a differentiated perspective," says Eichner. There were different developments within the individual product groups: Frozen baked goods, meat, fish, vegetables, ready meals and snacks were more or less down until the middle of the year compared to the previous year. However, potato products, fruit, cheese, alternatives for vegetarian/vegan diets and pizza held up well in the frozen food segment and in some cases even increased in sales.

According to calculations by the dti for sales in food retail and frozen-food home delivery services, the market will stagnate in 2023. The reasons for the pause in growth in this segment include the sharp rise in energy prices. This makes it all the more important for companies in the sector to invest in energy-efficient process technologies, such as those presented at Anuga FoodTec. This is because a large number of process steps in frozen food production require refrigeration, e.g. freezing of ready meals or freeze-drying of soups and sauces. Cooling during production and transport can also quickly constitute a decisive factor in the cost structure for manufacturers and become a price driver. Furthermore, in times of advancing climate change and the energy transition, it is increasingly important for producers to utilise energy as resource-efficiently and sustainably as possible.

One of the companies at Anuga FoodTec that specialises in refrigeration technology is GEA. In addition to the entire refrigeration system, the machine manufacturer also supplies a suitable heat recovery system. In view of the growing interest in ecological sustainability, food producers are increasingly looking at this option. GEA identifies the processes in which waste heat can be recovered and utilised for other processes. A broad portfolio of heat pumps is available for various applications that require both heating and cooling. As the heart of every system, the compressor technology used plays a decisive role. Modern reciprocating compressors such as the V series are specially designed for the high final compression pressure in a heat pump. They offer condensation temperatures which, depending on the design, are just as suitable for operation with low-temperature hot water as for the provision of process heat of up to 95 degrees Celsius.

GEA relies on ammonia as a natural refrigerant for both heat pumps and refrigeration systems. Both technologies work according to the same physical circulation principle of the Carnot process, in which a refrigerant circulates in a closed system. The principle: The liquid refrigerant vaporises at low pressure and absorbs heat from the environment or a system to be cooled via a heat exchanger. If the vaporised refrigerant is then compressed, it releases heat back into a heating circuit. This enables heat pumps to be used to replace both old refrigeration systems and boilers at the same time. This is not just interesting for frozen food manufacturers. That's because almost every company in the food industry has one or more refrigeration systems in operation. These have often been in use for many years and have not been replaced. In addition: If the product range changes, the production processes also change. As the demand for cooling and heating increases, so does the need for energy-efficient and climate-friendly concepts.

If food producers want to operate refrigeration and heating systems efficiently and sustainably, they must continuously adapt them. A project that GEA has realised for Wipasz, one of the largest poultry processors in Poland, shows what a solution of this kind can look like. With a capacity of up to 14,500 chickens per hour, the cutting area is very spacious. The poultry must be cooled quickly to four degrees Celsius immediately after being slaughtered and then kept at this temperature and low humidity throughout the cutting and packaging process until it is further chilled or frozen for distribution. To achieve the ambient temperatures required for a low meat temperature, GEA installed a total of 5.3 megawatts of cooling capacity for five plate freezers, five batch freezing tunnels, two cold stores and 64 air coolers. The system is equipped with Grasso V1800 reciprocating compressors for air conditioning the plant, a Grasso SP1 screw compressor for the primary cooling process of the poultry and a Grasso SP2 screw compressor for freezing and generating heat for water and air conditioning.

In addition, GEA installed eight ventilation systems to ventilate the production rooms and four more to air-condition the office building. All of them are supplied with cooling from the central ammonia plant and the heat recovered from this is used for heating. Wipasz was also provided with two heat recovery systems that cover the entire hot water and heating requirements, including the offices and communal areas. As the production rooms must be dry, the company has a high heating requirement. The total heat requirement, including all office buildings and technical areas, is 3.9 megawatts. The customised 65 HP heat pump is an important component of the factory's waste heat recovery system and generates higher temperatures of up to 55 degrees Celsius.

However, the concept of heat recovery not only shows its strengths in refrigeration technology. Wherever compressors are used and compressed air is required in the process, food producers can save energy - from pneumatic conveying to packaging. Owing to thermodynamics, the generation of compressed air is automatically associated with a large amount of thermal energy. For example, the thermal energy from the clean exhaust air can be used to directly heat neighbouring office areas or production areas. Using screw compressors with exhaust air ducts, compressor manufacturer Kaeser ensures that waste heat can be utilised, for example to heat rooms with the heated cooling air.

However, the greatest waste heat potential lies dormant in the pressurised gas flow itself. A large part of the electrical energy is bound there in the form of heat. To utilise this energy source, compressed air specialists, including Aerzen at Anuga FoodTec, provide shell and tube heat exchangers that can be used to support heating systems and heat water. The basis for any waste heat utilisation is the determination of the available heat quantity. This depends on the usable temperature difference, the mass or volume flow, the time availability and the specific heat capacity of the heat transfer medium. By adapting the heat recovery solutions to the respective application, the electrical energy used for compressed-air generation can be recovered to a large extent and the overall efficiency of compressed-air generation can be increased.