Global Dessert Supplier,
Bishop Stortford

The client

The client, well-known for their little ramekins of delicious chocolate puddings, have over the years grown from supplying a local supermarket to where it is now – a worldwide phenomenon.

The brief

The client’s facility at Bishop Stortford underwent modification from a frozen food distribution centre to a process factory. To support the facility to operate as a process factory, the inclusion of a spiral system whilst maintaining 50% of the existing freezer area was required.

The original freezer store was operating from four existing compressors based on the functioning condition of -35oC to maintain a temperature of -28oC. As the new store temperature requirement was -25oC, the current compressors were retro-fitted to enable them to operate at a higher suction pressure to increase efficiency – functioning at -32oC. JD Industrial designed a spiral refrigeration package using ammonia as the primary refrigerant to support the retrofit.

The solution

Spiral Refrigeration Package (Ammonia)

  • ABB 110kW – 280 frame size motor to allow one of the existing Sabroe TSMC 116l compressors (operating at 1750rpm) to gain the required duty at the lower operating conditions required. This is sized to allow the compressor to turn down to 1000 rpm whilst maintaining the required cooling
  • ABB ACS 800-07 Cabinet build drive – Sized at 110 kW to match the absorbed power of the above compressor.
  • Surge drum package – Sized for 270 kW of cooling capacity based on evaporation temperature of -40 °C, in conjunction with duty/standby liquid pumps, modulating fill control valves, oil pot, high level cut out and dual filter arrangement. To gain the required capacity, one of the two compressors attached to the spiral surge vessel has been retro-fitted with a new motor and VSD drive. This will allow the drive speed to be increased to 1800 rpm – increasing the duty from 122 kW to 149.5 kW, therefore requiring both compressors to be at 100% operating the spiral freezer to provide 271.5 kW.
  • BAC CXVE207-0809-20L evaporative condenser – Sized to accommodate the compressor total heat rejection of the compressor plant, design conditions at 33°C condensing pressure and 21 oC wet bulb temperature – 957 kw. The condenser includes:
  • Two 7.5 kW fans
  • 4 kW spray pump
  • 6 kW electrical heaters within the sump
  • The condenser fans are controlled via two ABB panel mounted VSD’s.
  • Ammonia to water HX – For preheating water supplies to boilers or process equipment, based on de-superheating the ammonia vapour and providing the heating effect of the water of 114 kW. This takes the main water feed from +15 °C to +34.8 °C at a flow rate of 5³/hr.
  • Liquid receiver
  • Ammonia valve station
  • Automatic emergency isolation valves – In the HP, LP pumped and intermediate liquid lines
  • Two extract fan hoods – To the existing valve stations including strip curtains from the hoods to the installed drip trays.
  • NH3 gas detection monitoring and ventilation system comprising:
  • Two single speed zone 2 ventilation fans rated to provide normal ventilation requirements for temperature control and emergency ventilation at a minimum of 15 air changes per hour.
  • 16-point TQ ammonia detection system with the required head detectors.
  • Ammonia valves, pipework and controls

Energy Saving Features

A number of additional energy saving measures were employed within the design to support optimum efficiency at all heat load and ambient conditions. These include:

  • Floating suction pressure on the cold store
  • Floating discharge pressure control in relation to optimal ambient wet temperature

Electrical / Software

  • Control panels – Serving all refrigeration equipment.
  • Field wire – Installed to all refrigeration equipment
  • SCADA & automation system – The central automation system controls of all four compressors, vessels and condensers. The Profibus network is the main network protocol design for data transfer between the common controls processor and the client’s network for SCADA interaction. Communication signals to the common controls HMI (KTP600) via Profibus have also been incorporated into the design.
  • Remote Access – Enabled for the industrial PC that was provided by JDI. The client and JDI will be able to remotely monitor and control the system via the graphics interface software.
  • Automation fault dial out – Remote dial out via standard speech was installed within the ventilation panel. This has the ability of text message format from the SCADA.
  • Siemens central PLC node – With Profibus DP communications protocol only. The model of automation system will be Siemens ET200s with one KTP600 Siemens HMI.

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