Evaporation increases capacity for drying cheese
A novel use of evaporation using heat exchanger technology from HRS Heat Exchangers has increased drying capacity for a major European processor of cheese products.
The client takes out-of-specification cheese products from production sites across Europe and converts them into high-quality protein for use in pet food and animal feed. The cheese is pasteurised and then dried to produce a powdered additive.
When the client wanted to increase production capacity, its first thought was to install an additional dryer; an expensive and energy-intensive solution. However, as the capacity of the dryer is determined by the amount of water it can remove per hour, another way to increase overall throughput would be to reduce the water content of the cheese products before drying, so that a larger volume could be dried at one time.
The Design Process
The client approached HRS because of its established expertise in evaporation and concentration technology. The first step was to determine if the existing dryer would cope with a more concentrated cheese solution. HRS supplied a trial evaporation system which the client used to analyse 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, and so HRS designed an appropriate evaporation system to sit between the existing pasteuriser 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, but as water is removed it becomes more solid and concentrated, with less heat transfer. In order to provide adequate processing, 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, requiring a smaller evaporator, smaller ancillaries and less energy 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 build-up 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 200 mbar, meaning that the water in the cheese solution boils off at 60°C.
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 3.6 tonnes of cheese product per hour, increasing the total solid concentration from 34 to 45%, and increasing dryer capacity by a similar amount.