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D. Berghout
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The design and analysis of an integrated heat supply system for large industrial potato fryers
Utilizing a steam heat pump cycle with frying vapor as primary heat source
Industrial potato frying processes require large amounts of thermal energy, with the dominant share used for moisture evaporation from the product. This energy leaves the system as hot frying vapor and is typically rejected to the environment, while process heat is supplied by fossil-fired steam boilers. Recovering and upgrading this latent heat therefore represents a major opportunity to reduce external energy demand and improve the sustainability of industrial frying operations. This thesis investigates the feasibility of recovering frying vapor heat and returning it to the fryer as high-pressure steam using a closed-loop mechanical vapor recompression (MVR) system with water as the working fluid.
A structured methodology was applied, combining literature review, steady-state thermodynamic modelling, equipment sizing, and dynamic simulation. First, the energy distribution of the frying process was analysed, showing that evaporation-related heat dominates the total thermal demand and that the recoverable heat potential depends strongly on the vapor dew point. Based on this analysis, a complete system configuration was developed consisting of a vertical shell-and-tube condenser, a flash tank, and a three-stage water-injected screw compressor. The heat exchangers were sized to ensure sufficient heat-transfer capacity, reliable condensate drainage, acceptable pressure drops, and robustness against fouling. The flash tank was designed to accommodate the large specific volume of low-pressure vapor while providing adequate thermal and mass buffering. Water injection in the compressor limits discharge temperatures and enables high pressure ratios under near-saturated compression conditions.
For a representative industrial fryer with a heat load of 8161 kW and a vapor dew point of 87.5 °C, the reference configuration recovers approximately 4045 kW of latent heat from the frying vapor. After compression, 6572 kW of useful heat is returned to the fryer, with the remaining 1589 kW supplied externally. Under these conditions, the system achieves an MVR coefficient of performance of 2.63, demonstrating that a substantial fraction of the process heat demand can be met through internal heat recovery. Sensitivity analysis shows that vapor dew point, flash tank temperature, and condenser temperature approach strongly affect system performance, with vapor dew point being particularly critical: a decrease from 90 to 85 °C reduces recoverable heat by nearly 1 MW.
An improved configuration incorporating an additional vapor compression heat pump allows further cooling of the condensate and recovery of additional low-grade heat, enabling full coverage of the fryer heat demand without external steam. The resulting temperature levels are suitable for ammonia (R717) as a natural refrigerant. Finally, a dynamic model was developed to assess operability under realistic production disturbances. Simulations show that combined feed-forward and feedback control significantly improves transient performance, ensuring stable operation and consistent product quality. ...
A structured methodology was applied, combining literature review, steady-state thermodynamic modelling, equipment sizing, and dynamic simulation. First, the energy distribution of the frying process was analysed, showing that evaporation-related heat dominates the total thermal demand and that the recoverable heat potential depends strongly on the vapor dew point. Based on this analysis, a complete system configuration was developed consisting of a vertical shell-and-tube condenser, a flash tank, and a three-stage water-injected screw compressor. The heat exchangers were sized to ensure sufficient heat-transfer capacity, reliable condensate drainage, acceptable pressure drops, and robustness against fouling. The flash tank was designed to accommodate the large specific volume of low-pressure vapor while providing adequate thermal and mass buffering. Water injection in the compressor limits discharge temperatures and enables high pressure ratios under near-saturated compression conditions.
For a representative industrial fryer with a heat load of 8161 kW and a vapor dew point of 87.5 °C, the reference configuration recovers approximately 4045 kW of latent heat from the frying vapor. After compression, 6572 kW of useful heat is returned to the fryer, with the remaining 1589 kW supplied externally. Under these conditions, the system achieves an MVR coefficient of performance of 2.63, demonstrating that a substantial fraction of the process heat demand can be met through internal heat recovery. Sensitivity analysis shows that vapor dew point, flash tank temperature, and condenser temperature approach strongly affect system performance, with vapor dew point being particularly critical: a decrease from 90 to 85 °C reduces recoverable heat by nearly 1 MW.
An improved configuration incorporating an additional vapor compression heat pump allows further cooling of the condensate and recovery of additional low-grade heat, enabling full coverage of the fryer heat demand without external steam. The resulting temperature levels are suitable for ammonia (R717) as a natural refrigerant. Finally, a dynamic model was developed to assess operability under realistic production disturbances. Simulations show that combined feed-forward and feedback control significantly improves transient performance, ensuring stable operation and consistent product quality. ...
Industrial potato frying processes require large amounts of thermal energy, with the dominant share used for moisture evaporation from the product. This energy leaves the system as hot frying vapor and is typically rejected to the environment, while process heat is supplied by fossil-fired steam boilers. Recovering and upgrading this latent heat therefore represents a major opportunity to reduce external energy demand and improve the sustainability of industrial frying operations. This thesis investigates the feasibility of recovering frying vapor heat and returning it to the fryer as high-pressure steam using a closed-loop mechanical vapor recompression (MVR) system with water as the working fluid.
A structured methodology was applied, combining literature review, steady-state thermodynamic modelling, equipment sizing, and dynamic simulation. First, the energy distribution of the frying process was analysed, showing that evaporation-related heat dominates the total thermal demand and that the recoverable heat potential depends strongly on the vapor dew point. Based on this analysis, a complete system configuration was developed consisting of a vertical shell-and-tube condenser, a flash tank, and a three-stage water-injected screw compressor. The heat exchangers were sized to ensure sufficient heat-transfer capacity, reliable condensate drainage, acceptable pressure drops, and robustness against fouling. The flash tank was designed to accommodate the large specific volume of low-pressure vapor while providing adequate thermal and mass buffering. Water injection in the compressor limits discharge temperatures and enables high pressure ratios under near-saturated compression conditions.
For a representative industrial fryer with a heat load of 8161 kW and a vapor dew point of 87.5 °C, the reference configuration recovers approximately 4045 kW of latent heat from the frying vapor. After compression, 6572 kW of useful heat is returned to the fryer, with the remaining 1589 kW supplied externally. Under these conditions, the system achieves an MVR coefficient of performance of 2.63, demonstrating that a substantial fraction of the process heat demand can be met through internal heat recovery. Sensitivity analysis shows that vapor dew point, flash tank temperature, and condenser temperature approach strongly affect system performance, with vapor dew point being particularly critical: a decrease from 90 to 85 °C reduces recoverable heat by nearly 1 MW.
An improved configuration incorporating an additional vapor compression heat pump allows further cooling of the condensate and recovery of additional low-grade heat, enabling full coverage of the fryer heat demand without external steam. The resulting temperature levels are suitable for ammonia (R717) as a natural refrigerant. Finally, a dynamic model was developed to assess operability under realistic production disturbances. Simulations show that combined feed-forward and feedback control significantly improves transient performance, ensuring stable operation and consistent product quality.
A structured methodology was applied, combining literature review, steady-state thermodynamic modelling, equipment sizing, and dynamic simulation. First, the energy distribution of the frying process was analysed, showing that evaporation-related heat dominates the total thermal demand and that the recoverable heat potential depends strongly on the vapor dew point. Based on this analysis, a complete system configuration was developed consisting of a vertical shell-and-tube condenser, a flash tank, and a three-stage water-injected screw compressor. The heat exchangers were sized to ensure sufficient heat-transfer capacity, reliable condensate drainage, acceptable pressure drops, and robustness against fouling. The flash tank was designed to accommodate the large specific volume of low-pressure vapor while providing adequate thermal and mass buffering. Water injection in the compressor limits discharge temperatures and enables high pressure ratios under near-saturated compression conditions.
For a representative industrial fryer with a heat load of 8161 kW and a vapor dew point of 87.5 °C, the reference configuration recovers approximately 4045 kW of latent heat from the frying vapor. After compression, 6572 kW of useful heat is returned to the fryer, with the remaining 1589 kW supplied externally. Under these conditions, the system achieves an MVR coefficient of performance of 2.63, demonstrating that a substantial fraction of the process heat demand can be met through internal heat recovery. Sensitivity analysis shows that vapor dew point, flash tank temperature, and condenser temperature approach strongly affect system performance, with vapor dew point being particularly critical: a decrease from 90 to 85 °C reduces recoverable heat by nearly 1 MW.
An improved configuration incorporating an additional vapor compression heat pump allows further cooling of the condensate and recovery of additional low-grade heat, enabling full coverage of the fryer heat demand without external steam. The resulting temperature levels are suitable for ammonia (R717) as a natural refrigerant. Finally, a dynamic model was developed to assess operability under realistic production disturbances. Simulations show that combined feed-forward and feedback control significantly improves transient performance, ensuring stable operation and consistent product quality.