Refrigeration

Ensuring Reduced Down Time and Profitability

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This included the defrosting of the evaporators in a freezer, which was normally done using water defrost to melt the ice formed over the evaporator coils. Using water defrost, the plant was following typical process below for defrosting the hardener. This process typically took around one and half hours’ time.

When they decided to opt for the hot gas defrosting of both the hardener and one of the IQF, they tried using a readily available solution in the market- Solenoid Controls and Valves-for one of their freezers (Hardener).

Vibrations – A Nuisance and a Cost Factor

The system design of hot gas defrost comprised of a single stage gas powered Solenoid valve in the wet suction line and a conventional back pressure control valve in the condensate return line. The liquid and hot gas line comprised of a conventional individual component design. All the stop valves used were locally made and of the old flanged type design.

With the current installation design, they faced difficulties in maintaining a constant back pressure for defrosting. The variation in pressure was 100 to 180 psig. Due to the large variation in the pressure

between the evaporators and wet suction line, the opening of single stage solenoid valve in the wet suction after defrosts created severe and dangerous vibrations in the system.

To limit the vibrations, reduction of the inlet hot gas pressure and defrost back pressure setting, was required, which led to a poor defrosting performance. To manage this situation the company approached Danfoss with requirements such as reduced energy bills, reduced water consumption for defrost and reduced labor work.

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