DESCRIPTION OF HEAT PUMP ASSISTED STARCH DRYING PROCESS:
The starch is dried in a continuous process. Drying air is preheated by a water-to-air heat exchanger from a heat recovery cycle with water as heat transfer fluid. After this initial preheating, the water also serves as source for the evaporator of the heat pump system. The inlet temperature is then at approx. 70°C. At the condenser side, high temperature heat is released to the drying agent via an intermediate water circuit and a water-to-air heat exchanger. The heat supply temperature of the heat pump is up to 160°C and is measured at the outlet of the condenser in the intermediate water circuit.
DESCRIPTION OF HEAT PUMP DEMONSTRATOR
The DryFiciency heat pump demonstrator placed in a container outside the starch plant has a heating capacity of approx. 400 kW, which is about 10% of the starch dryer’s heat demand. The heat supply temperatures ranges from 110 to 160°C. The demonstrator shall decrease the end energy consumption by 2,200 MWh/a, and shall lead to a reduction in CO₂ emissions of 500 t/a.
The heat pump is realized as twin-cycle configuration with two refrigerant cycles. This configuration is more efficient when dealing with a wide operating range. It also offers advantages in terms of start-up behavior and approval due to the lower refrigerant charge per circuit.
Innovative components are applied in the heat pump prototype including a modified semi-hermetic screw compressor by Bitzer and a novel lubricant developed by FUCHS. OpteonMZTM supplied by Chemours is used as refrigerant. The Bitzer screw compressor is based on the company’s proven HS series, which was adapted to fit the requirements of high-temperature applications up to 160°C. It has a two-shaft rotary displacement design with high efficiency profile geometry. It is optimized for parallel operation with up to six compressor units, allows optimal capacity adjustment and has minimal energy requirements under full and part load. The compressor is further equipped with a high efficiency suction gas cooled motor and a high efficiency rotor profile.
The DryFiciency heat pump demonstrator started its trial operation in early 2020. Extensive monitoring of the operation is carried out to evaluate efficiency and other important process parameters, as well as stability of refrigerant and lubricant when exposed to high temperatures, in the upcoming months.
If you want to know more about the DryFiciency heat pump technology, please contact the project coordinator.