A novel use of evaporation using heat exchanger technology from HRS Heat Exchangers, Hertfordshire, England, increased drying capacity for a major European processor of cheese products. The company takes out-of-specification cheese offerings from production sites across Europe and converts them into high-quality protein for use in pet food and animal feed. The cheese is pasteurized and then dried to produce a powdered additive.

When the processor wanted to increase production capacity, its first thought was to install an additional dryer — an expensive and energy-intensive solution. However, because the capacity of the dryer is determined by the amount of water it can remove per hour, another way to increase overall throughput is to reduce the water content of the cheese products before drying so a larger volume can be dried at one time.

Creating an evaporation system

The client approached HRS because of its established expertise in evaporation and concentration technology. The first step was to determine if the existing dryer could cope with a more concentrated cheese solution.

HRS supplied a trial evaporation system, which the client used to analyze all aspects of the revised production system, the properties of the materials and the potential results. The trial unit proved that the concept was feasible, so HRS designed an appropriate evaporation system to sit between the existing pasteurizer and dryer.

The trials and material analyses also showed how the physical and thermal properties of the cheese change as it is heated and the water is removed. At the beginning of the process, the product is fairly liquid with good thermal transfer characteristics. As water is removed, it becomes more solid and concentrated with less heat transfer. To provide adequate processing, it was determined that a continuous treatment process would have to be designed around the “worst case” thermal characteristics at the end of the process.

It was, therefore, decided to adopt a batch treatment approach, as overall this required a smaller heat-transfer surface, less equipment and less energy — necessitating a smaller evaporator and smaller ancillaries to run. The batch system, which employs two tanks — one of which is filled while the other is being treated — is also simpler to design and operate. Employing a two-tank system with full automation also results in a continuous operational process.

Heated cheese is a high-fouling, extremely viscous material. Therefore, an evaporator based on the HRS Unicus Series of reciprocating scraped-surface heat exchangers was supplied to prevent the buildup of cheese and burnt-on cheese residue on the tube walls of the heat exchanger. To reduce energy requirements and improve operational efficiency, the evaporator operates at a vacuum of around 2.9 psi, meaning that the water in the cheese solution boils off at 140 degrees Fahrenheit.

HRS supplied two complete skid-mounted systems, each of which comprised the Unicus evaporator, two tanks, pumps, controls and connections. Each skid-mounted system can process 3.96 tons of cheese product per hour, increasing the total solid concentration from 34% to 45% and increasing dryer capacity by a similar percentage.