Guernsey Dairy – Replacement of Ice Thermal Storage Tank
A Baltimore Aircoil Co ice thermal storage tank had been installed at the Guernsey Dairy some 28 years ago. The ice thermal store contains a lattice of approximately 800 steel tubes immersed in 25,500 litres of water. A glycol / water solution is cooled to -7° C and is circulated through these steel tubes. Ice builds on the outside of the tubes up to a maximum thickness of 35 mm. A maximum stored cooling energy of 1,440 kW is available during the day without need for further mechanical cooling. During milk production the water in the tank is circulated around the dairy production equipment, the returning warmed water melts the ice, but the leaving chilled water temperature remains constant at 0.5°C. It is not until the vast majority of the ice has melted that the water temperature will rise. The milk production cycle allows the water temperature to rise to around 4°C, ensuring that all of the ice has melted.
2No. 320kW nominal capacity water chillers operate overnight in a run and standby mode to chill the glycol / water solution and build the ice necessary for the next morning’s production cycle. Operating the chillers in this way improves the reliability of the chilled water plant due to continuous operation of the system refrigeration compressors without stopping and starting.
The ice thermal storage tank was showing signs of serious corrosion and the decision was taken to replace the tank before there was a major leak or serious failure.
Alpha Air Conditioning Ltd has been a trusted service provider to the Guernsey Dairy for 18 years. We were proud to be given the responsibility of completing this task on time and within budget.
This was a complex project and had to be carried out without causing any interruption to milk production. The longest period of time the dairy could be without chilled water was 36 hours. There was a requirement to replace large sections of the 4” steel process water pipe work. This pipe work would need to be fabricated and welded in position. Due to the large number of welds it was quickly established it would not be possible to complete the change-over in such limited time.
Alpha Air Conditioning Ltd proposed the following solution: A 3000 litre temporary water buffer vessel was installed into the process water circuit. Alongside this, a temporary plate heat exchanger was also installed. Process water from the buffer vessel was circulated through one side of the heat exchanger with the primary chilled glycol / water mixture being circulated through the other side at a temperature of -3° C. This arrangement allowed the process water in the buffer vessel to remain at 1.5° C. This chilled water was circulated to the Dairy’s milk production equipment using the process water pumps. This successful solution allowed the Dairy to continue full production with no interruptions.
It was specified by Baltimore Aircoil Co that no inward pressure could be applied to the sides of the tank. In order to conform to this, a 1 over 2 spreader beam was required to match the positions of the lifting points. The spreader beam would ensure the new ice thermal store could be lifted safely. The old tank was removed a few day prior to the new tank being craned into position. New steel process pipe work was fabricated and welded in place, with new ABS plastic pipe work being installed on the primary cooling circuit. The new ice thermal store was then craned onto the steel support frame. The final pipe work connections were made. The system was filled, and leak tested prior to being insulated, then weather and vapour sealed with PIB lagging.
The new ice thermal storage tank was installed and commissioned by Alpha Air Conditioning Ltd with no interruption to the dairy’s milk production. The dairy engineering team contributed greatly to the project and we are grateful to them for their invaluable assistance in what was a challenging, but highly rewarding project.