Visualization and control of the ammonia refrigeration plant at Americold in Dublin

September 27, 2022 | Reliance SCADA

Americold is a US company based in Atlanta, Georgia. It is a world leader in temperature-controlled warehousing and logistics. The company has 249 facilities around the world.

There is one in Dublin, Ireland. It is a new two-stage ammonia refrigeration plant designed and installed for Americold cold stores.

The ammonia system at the Dublin plant has three temperature levels:

The –41°C surge drum (surge vessel), which serves the blast freezers
The –34°C surge drum, which serves the freezer rooms
The –9°C surge drum, which serves the cooler rooms

Various technological systems were installed at the plant by the GEA company. They are:

2 x LLT Grasso WB-6A screw compressor package (LLT = low low temperature)
2 x LT Grasso V 1100 reciprocating compressor package (LT = low temperature)
2 x HT Grasso SB-2A screw compressor package (HT = high temperature)
2 x Thermofin air-cooled condenser with water spray
1 x Thermofin dry-air–cooled glycol cooler
12 x NH₃ cooler in the freezer rooms
7 x NH₃ cooler in the expedition area
4 x NH₃ cooler in the cooler rooms
1 x LLT surge drum package with 4 liquid NH₃ pumps
1 x LT surge drum package with 2 liquid NH₃ pumps
1 x HT surge drum package with 2 liquid NH₃ pumps
1 x ekonomizer vessel
1 x Hansen air AUTO-PURGER
1 x PHE (plate heat exchanger) for heating up the underfloor heating circuit with the heat from the oil cooling circuit
2 x pump (duty/standby) for the oil-cooling glycol circuit
2 x pump (duty/standby) for the underfloor heating circuit

Control system

In 2022, the Dutch company Chiron-tec B.V. implemented a system for the control and monitoring of all the above equipment.

The system consists of three Siemens SIMATIC S7-1500 PLCs (with 1,128 IO signals) and the Reliance SCADA/HMI system.

The refrigeration system in detail

The ammonia refrigeration system is served by six single-stage GEA Grasso compressor packages configured into a two-stage plant.

All the GEA Grasso packages – two WB-6A single-stage screw compressor packages for the LLT side, two V 1100 single-stage reciprocating compressor packages for the LT side, and two SB-3A screw compressor packages for the HT side – are arranged in a duty/duty configuration.

The compressors at the LLT side suck "dry" ammonia vapor from the LLT surge vessel, compress it, and discharge the superheated vapor into the HT surge vessel via a bubble pipe.

The compressors at the LT side suck "dry" ammonia vapor from the LT surge vessel, compress it, and discharge the superheated vapor into the HT surge vessel via a bubble pipe. The high-temperature superheated vapor then boils the liquid ammonia in the HT vessel producing vapor at a high temperature.

The compressors at the HT side suck "dry" ammonia vapor from the HT surge vessel, compress it, and discharge the superheated vapor to the roof-mounted air-cooled condensers.

The condensers draw in ammonia gas and reject the heat. By removing the heat, the gas condenses to a liquid and maintains a pressure within the HT side of the refrigeration system. The liquid is then drained into the high-pressure float valves that expand it to the economizer vessel.

The economizer supplies the liquid to the HT surge vessel via a motorized expansion valve. This valve is controlled by a level transmitter fitted to the economizer vessel.

The HT surge drum also supplies the liquid to the LT and LLT surge vessels via motorized expansion valves controlled by level transmitters fitted to the LT and LLT surge vessels.

Liquid ammonia within the HT, LT, and LLT surge vessels is pumped to the roof-mounted valve stations and coolers using ammonia pumps (duty/standby) fitted underneath the drums.

The liquid refrigerant evaporates within the coolers and removes the heat from the room. Finally, a mix of liquid and vapor returns to the surge vessel.

The plant control software is designed to be as energy efficient as possible. For instance, the installation is equipped with a lot of reporting functions to see how much energy is used for each cycle of a blast freezer.