Case Studies
Waste heat utilisation in a deep frying facility
Processes in the food industry often involve the use of large quantities of heat. Along with the cooling needed to cool the products, the high internal heat load induced by this high heat usage creates a considerable cooling demand in production rooms and this requirement can only be partially met by fresh air supply even during transition periods. If the use of heat in production is combined with suitable waste heat streams, an absorption chiller can often cover the base load of the cooling demand economically.
In the illustrated case, the use of YAZAKI's model WFC 30 absorption chiller was studied in a deep-frying factory. In four production lines working in 15-shift-per week operation about 15 t/h of material are first steamed in steam-heated ovens and then deep fried.
The heat needed to drive the cooling unit is drawn from the approx. 5,800-m³/h flue gas of the afterburning of the deep fryer's exhaust air. The hot combustion gas is first used to heat thermal oil and then leaves the unit at a temperature of 250 °C. With the aid of a heat exchanger, it is possible to transfer an average of 220 kW to a hot water system during the production shifts (cf. Figure 1).
- Figure 1: Ordered annual load duration curve of the waste heat supply and cooling demand for room cooling
As the case of application makes it possible to select a high drive temperature (95 °C) and a low cooling outlet temperature (27 °C), and as it provides a sufficient quantity of waste heat, the WFC 30 installation can be configured to deliver about 30% over its nominal useful cooling capacity (cf. Figure 2).
- Figure 2: Nominal operating points and achievable cooling capacity at a cooling water input of 27 °C as a function of heating water input temperature.
The high heat input of approx. 800 W/m2 in the steaming and deep frying hall creates a considerable cooling demand for the room air. A thermal building simulation was used to estimate a cooling demand of about 5,000 h/yr with a peak load of 780 kW (cf. annual load duration curve in Figure 1). Thanks to the high coincidence level of waste heat generation and cooling demand, the YAZAKI WFC 30 makes it possible to cover about 48% of the cooling demand with waste heat. The peak of the remaining cooling demand is cut by 136 kW.
The case studied shows that YAZAKI absorption chillers offer an attractive option for the utilisation of existing waste heat potentials. A total investment of €78,000 yields an annual operating cost advantage of €14,000 and thereby amortises itself in 6.7 years (5% interest). In addition to the financial benefit, the avoided electrical demand represents a reduction in production-related CO2 emissions of about 86 tons.
Analysis by Perpendo GmbH für Energietechnik und Verfahrenstechnik, Aachen
