Refrigeration Uses Heat Pumps, Ammonia
Eurammon’s website states: “Energy can be saved in particular by those applications that are coupled to heat recovery from industrial processes. Waste heat generated in this way can be put to profitable use in the building — a potential that was scarcely used for a long time.”
As noted by Thomas Spänich, member of the board at Eurammon, “Heat pumps operated with natural refrigerants such as ammonia (NH3) are also particularly environment-friendly. They have either no or only a negligible global warming potential. Heat pumps with natural refrigerants are already being used for cost- and energy-efficient operation. They can be planned and implemented individually depending on the requirements of the particular building and the customer’s specific needs. The market for heat pumps can therefore expect to see further strong growth in the near future.”
An example is a project that GEA Refrigeration Germany is heading up in Norway. The company developed a 2-megawatt heat pump installation for the energy provider Bio Varma Sarpsborg AS to heat water up to 82˚C for the municipal district heating network. The heat pump uses two different waste heat sources to keep energy costs as low as possible. The 1.5 megawatts of power come from recooling 45˚C warm cooling water from a refrigeration system serving the municipal waste incineration plant, with a further 3 megawatts supplied in the form of 38˚C warm water from a biological sewage plant.
The water is initially heated using the hot oil in the oil separator. Then most of the work is performed by the condenser at a condensation temperature of 82˚C maximum. The last few degrees then come from a superheater fed by 105˚C hot gas on the jacket side.
The large-sized ammonia heat pump system has been equipped with two large oil filters and an oil pump with an 18.5-kilowatt motor capable of pumping just about 900 liters per minute. GEA has also provided a 1,200-kilowatt high-voltage motor and a frequency converter for motor and oil pump. The centerpiece of the system consists of an R-series high-pressure compressor. The high-pressure side of the system had to be rated for a pressure level of 52 bar because of the high condensation temperatures. This resulted in the need for new components, pipes, and moldings to be procured and, in some cases, even specially designed.
Another ammonia-based project was undertaken in Switzerland by Fleischtrocknerei Churwalden AG, which produces organic quality meat products. Refrigeration company SSP Kälteplaner developed a sustainable heating and cooling system for the meat processing center in Landquart, using heat pumps and refrigerating machines that run on ammonia and carbon dioxide. The central aspect of heat generation and refrigeration consists of making use of the groundwater stream of the Alpine Rhine plain. Catchments and groundwater pumps take water from the groundwater stream and then return it in thermally changed state. The energy gained in this way — refrigerating or heat energy, as required — is brought to the required temperatures by refrigerating machines and heat pumps for a wide range of uses.
Heat energy of altogether around 950 kW is needed on two different temperature levels: at medium temperatures of about 60˚C as process energy among others for climatic chambers, hot process water or container washing machines; and at lower temperatures of up to 40˚C as heat energy for heating purposes, for dehumidification, for preheating hot process water, and for defrosting the cold storage rooms.
A refrigerating plant capacity of 1,200 kW is needed for maintaining temperatures around freezing point for workrooms, and also for temperatures of -8˚C in chilled storage rooms and maturing plants, as well as temperatures of -25˚C in the deep-freeze storage rooms.
A two-stage ammonia heat pump is used for heating purposes according to the different temperature levels, using groundwater at 12˚C and 8˚C. Each stage is fitted with two York/Sabroe reciprocating compressors, which are regulated in a stepless manner by frequency changers. Cassette-welded plate heat exchangers by Alfa Laval are used as evaporators and condensers. The ammonia charge in the heat pump amounts to approximately 300 kilograms. The production systems are rated for temperatures in the medium range of 60˚C.
The motor waste heat and compression heat from the compressed air and vacuum generation system is fed directly into the system, while the ammonia heat pump generates the necessary remaining energy. The ammonia heat pump also plays a supportive role at the lower temperature level of 40˚C and generates the necessary remaining energy. The “warm” groundwater basin acts as heat source.
Consistent use is made of any generated waste heat. Where possible, it is fed directly into the heat distribution system and distributed again immediately. This is used for cooling motors, including those used for generating compressed air or in the central vacuum system. Waste heat on the lower level is dissipated into the “warm” groundwater basin. This includes condensation waste heat from the refrigeration and tool cooling at the packaging machines in the framework of the cooling water circuit.
Two ammonia refrigerating machines are responsible for refrigeration and are cooled with groundwater. After cooling, the water is fed to the “warm” groundwater basin. When the need arises, the heat pump can bring the waste heat from the basin up to a higher temperature. Refrigerating energy of 0˚C and -8˚C is generated in each case by a refrigerating machine using NH3 as refrigerant and two industrial reciprocating compressors. One of the respective compressors in each case is equipped with a frequency changer. The energy is transported to the refrigeration sites using a water/glycol blend as secondary refrigerant. The recooling energy is taken from the “cold” groundwater basin. Exchanging the water from the heat pump to the refrigerating machine and vice versa achieves maximum efficiency ratios, while keeping the drive motors and refrigerant circuits as small as possible.
CO2 is used in the deep-freeze storage rooms. The refrigerant is evaporated directly with electronic expansion valves in the room chillers, before passing to the reciprocating compressor where it is liquefied to subcritical state in a cascade condenser. The waste heat from the systems is dissipated to the glycol network at a temperature of -8˚C where the heat can be put indirectly to further use.
In summer, needed cooling energy is taken from the “cold” groundwater basin and used directly for room cooling in ventilation systems, cooling ceilings or in server rooms. Apart from the pump conveying energy, no primary energy is used for air conditioning refrigeration.
In the United Kingdom, Star Refrigeration developed a heat pump solution for a Nestle chocolate factory in order to bring about significant reductions in the energy costs for refrigeration and heating applications. It replaced existing HCFC-22 packaged chillers and a central coal-operated steam generation unit that had supplied all terminal devices and systems using and dissipating hot steam during their work processes.
The new concept entailed taking waste heat from the cooling circuit and boosting it to provide process water heating up to the required temperature. Star Refrigeration’s Neatpump heat pump provides water up to a temperature of 60˚C, which is fed as preliminary heat also to processes needing higher temperatures.
In cooperation with Vilter Manufacturing Inc. (U.S.) and Cool Partners (Denmark), Star Refrigeration developed a high-pressure heat pump solution that uses ammonia with screw compressors to a temperature of 90˚C. The system extracts the waste heat at -5˚C from the glycol as the secondary refrigerant from the refrigeration process and raises this to the main heating demand at 60˚C. A gas-fired boiler is used to increase the 60˚C water temperature for a number of smaller heating demands on site.
Publication date: 11/12/2012