CO2 trans-critical installation — a processing plant first

By John Ackermann

A deep commitment to producing delicatessen products that are of the highest quality, safe to eat, and have the least impact on the environment, swayed the decision towards CO2 refrigeration for the new BM Food Manufacturers plant in Montague Gardens.

BM006At the heart of the system: two low-temperature, three medium-temperature, and two parallel semi-hermetic
Frascold compressors, all fitted with VFDs.

To meet an increase in the demand for their popular range of Mediterranean Delicacies branded products, BM Food Manufacturers opted to completely revamp their 18-year-old plant in Montague Gardens, Cape Town.

The interior of the 1 200m2 building, with its simplex R22 refrigeration units, was totally gutted. The new plant needed to meet EU standards, be energy efficient, and have minimal impact on the environment. In the processing of ready-to-eat soups and prepared meals, the refrigeration plant consumes the largest portion of power.

As the long-standing refrigeration contractor to BM Food Manufacturers, Richard Drinkrow of Mainstream Refrigeration was asked to design a plant that would meet all the requirements and place Mediterranean ahead of future market trends. A plant with a refrigerant that would not be threatened by international environmental agreements was a key consideration. Of all the refrigerants available, natural refrigerants in the form of CO2 and ammonia with a global warming potential of 1 and 0, have the least impact on the environment and no likelihood of being phased out by environmental laws or agreements.

“BM Foods is excited about our new CO2 plant, not only to improve product quality and production, but also because of its very low impact on the environment. All future refrigeration plants on our sites will be CO2.”

Based on experience and emerging international trends, Drinkrow recommended CO2. “Because of the high pressures and piping standards, we expected the capital outlay to be much higher than a conventional plant with synthetic refrigerants. Although marginally higher, the CO2 plant had the benefit of a higher efficiency, virtually zero direct global warming, and a high production volume of hot water. The high-pressure, high-temperature CO2 from the compressors, pass through a plate heat exchanger and heats cooled water to between 40 and 45°C,” says Drinkrow.

Constant hot water cuts production time

“Large volumes of hot water are needed for hand washing, cleaning, and the making of soups. With a constant supply of hot water, the production time of soup has been halved. Hand washing, hygiene, and productivity is better than ever, and all our instant gas and electrical water heaters have been removed. The high power bill for heating water has been vastly reduced,” says Costas Vayanos, CEO of BM Food Manufacturers.

The Mediterranean Delicacies plant in Montague Gardens has three refrigeration circuits housed in different buildings. The office and admin block have a R22-charged system for the storage of finished product and the manufacturing of dips and meze.

The seafood plant, installed in 2006, is charged with R404A, which had been a viable refrigerant at the time.

The new CO2 plant has a trans-critical booster pack with parallel compressors. The pack manufactured in the Ottery workshop of Mainstream Refrigeration has seven Frascold semi-hermetic compressors, all fitted with variable frequency drives (VFDs) for capacity control. Three compressors operate on the medium temperature (MT) circuit (-7°C), two on the low temperature circuit (-32°C), and two provide parallel compression on the MT. The MT circuit maintains the temperature (0–4°C) in five cold rooms, three double-blast chiller tunnels, and a blast chiller.

“Until we commissioned the CO2 plant, our production was limited by our refrigeration capacity and availability of hot water. With the new plant, this has been reversed and our production capacity now lags our cooling capacity.”

The LT circuit has a blast freezer that can also operate as -25°C cold room.

The discharge from the MT compressors is piped to a plate heat exchanger fed with water from three air-cooled (piped in parallel) finned coolers connected to the municipal water mains. The horizontal coil coolers each have four EC fans, which are speed controlled and/or cycled to maintain required system pressures. Water from the CO2 plate heat exchanger feeds a 1 000-litre tank as a buffer for a constant supply of water at 40–45°C to the many hand-washing points, production cookers, and for plant cleaning.

All evaporator coils are direct expansion (DX) with copper tubing and aluminium fins and fitted with AC fan motors.

In-house skills training

“Since doing our first CO2 plant in 2009, we have come a long way in the design and installation of CO2 systems,” explains Drinkrow. “To become familiar, we installed our own training system in our workshop and developed as we became more confident with the high pressures and the unique condensing requirements. Our in-house training has proved invaluable to provide technicians with the required skills and confidence. With each new plant that we have installed, we have tried new innovations to improve efficiency and reduce energy usage. The BM plant, being our first industrial plant, compared with our previous plants mainly in the retail sector, required a greater focus on the recovery of heat for hot water production and water treatment to prevent possible scaling.”

The flash gas from the top of the CO2 receiver is piped to the suction of the two parallel compressors to improve the coefficient of performance (COP) of the plant and prevent any flash gas at the inlet to the DX coils, which are all fitted with electronic expansion valves.

Innovative water treatment

The large volumes of hot water used requires make-up from the municipal mains, and scaling in the plate heat exchanger (CO2/water) was of prime concern. To prevent scaling, an electronic ‘descaler’ was installed on the outside of the water feed to the heat exchanger. The operation of the device is based on creating a magnetic field, which assists in the ionisation of the water. “For some unknown reason, since commissioning the CO2 plant, the scaling in the water feed to a steam generation plant elsewhere on the site has reduced significantly,” says Drinkrow.

With the low ambient temperature in winter, the plant is often just idling and has excess capacity. The plant was designed to handle the required duty when the ambient is above 38°C, as can occur in the summer months in Cape Town.

“Until we commissioned the CO2 plant, our production was limited by our refrigeration capacity and availability of hot water. With the new plant, this has been reversed and our production capacity now lags our cooling capacity. We also are confident that the CO2 plant will cope on the days when temperatures in Cape Town are above 38°C in summer,” says Vayanos.

BM Food Manufacturers has two manufacturing facilities, one in Johannesburg with a staff of 250 and one in Cape Town with a staff of 280. The business was started by Vayanos’s uncle, who is now 87. Vayanos joined the company as the accountant and later took over the reigns as CEO when his uncle retired.

“Our refrigeration plant has undergone a massive shift from having many simplex units to the high-capacity, environmentally friendly CO2 plant. Before commissioning the CO2 plant, there would be a noticeable rise in the air temperature of the blast chillers as we pushed in trolleys of warm product that still had to be cooled. With the CO2 plant, the air temperature follows virtually a straight line. The quicker the warm product is cooled, the longer the shelf life,” says Vayanos.

BM Food Manufacturers supply to retailers, food service, and fast-food outlets across the entire market. As far as possible, ingredients are sourced locally and only those that cannot be sourced from South Africa or that are in short supply, are imported. “Quality of ingredients are of utmost importance, as they impact on the reputation of our brand name.”

Reduced carbon footprint

“The CO2 plant is another step towards our drive in saving the natural resources of our planet for future generations,” says Vayanos. At the 18 000m2 site in Montague Gardens, rainwater is harvested for the washing of vehicles, large areas of the extensive roof space are fitted with solar panels for power generation, and all recyclable materials are hand sorted and sent to a recycling plant in Philippi, where methane gas is produced and used for power generation.

“BM Foods is excited about our new CO2 plant, not only to improve product quality and production, but also because of its very low impact on the environment. All future refrigeration plants on our sites will be CO2,” concludes Vayanos.


Click here to read the October 2018 issue of Cold Link Africa



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