Principle of operation
The principle of operation for drying in conventional dryers can be divided in two parts. The first step concerns fresh outdoor air that is being brought inside the dryer and heated. Secondly, the air is circulated over the wet product. During circulation it picks up moisture from the wet product due to which its humidity increases and its temperature decreases. The energy contained in this humid air flow may make it a useful heat source. Standard procedure is to exhaust this used air or dehumidify it. Most of the humid and cold air is recirculated when the innovative heat pump is applied. The air is cooled below condensation point and thus dehumidified at the evaporator of the heat pump. The pressure and temperature of the refrigerant are increased with the use of a compressor. This energy is released into the dryer air, at the condenser site. Due to the application of a heat pump large energy savings can be obtained. Furthermore, the drying process is less influenced by outdoor air conditions. A more stable drying process increases the quality of the French fries.
The heat pump uses Ammonia as its refrigerant. This is a natural refrigerant with which high efficiencies can be obtained. Another advantage is the fact that considerable knowledge about this refrigerant is present in the food industry: Ammonia is very commonly applied there.
Two reciprocating compressors are used; a Grasso 45 HP and a Grasso 65 HP. These compressors have a continuous capacity control. Their COP in this process depends on the drying conditions and varies between 5 to 8.
The heat pump dryer is designed as an ammonia pump system. In the engine room, compressors, separator and pumps are situated. Evaporators are situated on the roof and connect the ducting for exhaust and fresh air with each other. Condensers are installed inside the dryer.
The heat pump is designed to condensate 1.500 kg of water per hour. If this quota is reached an annual energy saving of 800.000 Nm³ of natural gas is obtained. The payback time is than 4 years. This particular project has a shorter payback time since financial support is given by the so called SBIR program of AgentschapNL (the Dutch government).