Energy conservation in ice slurry applications

Significant improvements in coefficient of performance (COP) can be made when the evaporating temperature of a vapour compression cycle is raised. Producing the ice slurries used in cooling applications and ice pigging by crushing blocks of ice made from pure water and mixing the particles with a solution of freezing point depressant (FPD) later enables higher evaporator temperatures than if the solution itself is frozen in a scraped surface ice maker. Predictions of the possible improvements to COP can be made in CoolPack, a refrigeration cycle simulation program, over a range of evaporator temperatures. A series of experiments designed to verify these predictions were carried out where the operating conditions of a scraped surface ice maker were altered by retrofitting compressor speed control to a scraped surface ice maker. Following verification of the CoolPack results, further experiments were conducted that evaluated the energy required for two stage comminution of large ice blocks into fine particles. Two theoretical slurry production systems were then compared: mixing crushed ice with an FPD solution and a scraped surface ice maker with FPD solution feedstock. Although energy conservation was shown with comminution the proposed method introduces a number of challenges that require careful consideration. ► Producing ice slurries from crushed ice can improve efficiency of secondary refrigerant loops. ► Compressor speed control on existing scraped surface ice makers is used to investigate if improvements in COP can be made. ► Vapour compression cycle analysis is carried out to quantify savings possible by raising evaporator temperature. ► A full energy audit is conducted to compare production from crushed ice versus conventional scraped surface ice makers.