Pie City increases quality of product by merging into one facility

By Kevin Walter, mechanical engineer, Lutz Refrigeration

With an objective to produce pies with the same quality and consistency, pie manufacturer, Pie City, merged their Gauteng production facilities into one.

As the old facilities were to be closed, about 40% of the cooling and freezing equipment was moved to the new site in the East Rand. Graham Berman Refrigeration installed the balance of the equipment at the new facility.

The factory receives raw products in the form of fresh meat and flour. With the help of mixers and capdans, frozen pies come off the production line in a variety of shapes and sizes. The client sought to produce 7 000 pies per hour.

The project commenced in July 2018 and was completed in November 2018. The project entailed taking occupation of a factory in the east of Johannesburg which was an empty shell with office infrastructure only. By the middle of October all cold rooms, pie production plant and supporting systems were in place and pies were flying off the conveyer to stores around the country. This was critical as the lease for the old factory had been cancelled and production had to continue to supply all the stores around town.


Images by Ntsako Khosa

System operation

The spiral freezer is cooled by a Multiplex Refrigeration plant with five Large GEA compressors being cooled by an Evapco water-cooled condenser. The Multiplex mechanics and electrics were designed and assembled by Lutz Refrigeration with a design very similar to an ammonia system design with the distinction, however, of low-charge direct expansion freon gas to the stainless-steel cooling coil. The cooling system can provide up 230kW of cooling in a -34°C room. The advantage for pie city in going with such a large freon system, was a much easier set-up in term of regulation, lower capital cost, lower maintenance cost and with the water-cooled design, energy usage was brought in line with ammonia efficiency.

The Blast freezer runs as low as -35°C, but in operation it was found that the best setting was closer to -30°C to trim energy usage, allowing an entire compressor to switch off. At these temperatures, the plant cycles between three and four compressors out of five. This also keeps the compressors running more comfortably within their design envelope at suction pressures of -38°C and discharge of 35°C, equating to a coefficient of performance of 1.5. For every 1kW electricity used, there is effectively 1.5kW cooling – equivalent to a comparative water-cooled ammonia system at these temperatures.

This blast spiral freezer can draw up to as much as 150kVA when running flat out. However, being a multiplex design, it runs hard when switched on for the first 15 minutes to get the room on temperature, then starts to unload to a point where it cycles between three and four compressors for the rest of the day, the Carel control system alternates between the compressors to keep run hours equal across the units.

Manufacturer line

The pie manufacture line came in from Switzerland. This line is absolutely state of the art with fitted with VSD and PLCs. The system can produce 8 000 pies per hour on certain lines out of a footprint area of roughly 150m². The only manufacturing process not handled by the automated pie line machine is the cooking of the fillings which still happens via good old-fashioned love and care with the chefs mixing up ingredients in automatic cookers and cooking batches and mixing them by hand.

The pies flow off the automated pie line directly into the spiral freezer and out to the packing area, where a team of packers slot the pies into boxes and straight into holding freezers and delivery trucks.

System impact

The difference in power draw on this system from a traditional simplex design would be roughly 30% in terms of electrical kW/hrs used. This is achieved entirely by allowing the plant to unload in order to match cooling requirements and hence keep condensing pressures as low as 35°C and below. Additionally, the use of a multiplex design eases pressure from the electricity grid by preventing on/off spikes all day.

The majority of freon cooling systems on spirals employ a number of simplex units (up to four on larger units), while this plant has one large multiplex. To make an analogy, this would be like comparing many small bakkies to one large truck. The energy savings are intuitive even to a layman.

Officially kicking things off

A celebratory ribbon cutting event was held where all major stakeholders from clients to contractors and suppliers were all invited for a tour of the entire plant shortly after it was commissioned. Pie City staff thanked all contractors for their extra effort – working Saturdays and even Sundays to ensure that the critical deadline was met. All plant on site is inspected monthly by the original suppliers with Service Level Agreements in place. In terms of refrigeration the requirement for maintenance is actually very low with inspection of gas levels, pipes line, expansion valves and cleaning the cooling tower being carried out monthly. Touch wood, the spiral freezer cooling plant has had less than two hours downtime in more than 12 months since commissioning.

Prof list

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