Pump and heat exchanger combine in soft candy production
Pumping cooked syrup through a scraped surface heat exchanger in the production of soft candy demands a pumping solution that ensures a smooth product flow at all times.
When one of the world's leading confectionery manufacturers approached AxFlow for the provision of fluid handling solution for this application in its soft candy production plant in the Czech Republic, AxFlow's engineers came up with a design which combined a Waukesha Cherry Burrell Universal I Series pump pump with a Waukesha scraped surface heat exchanger (SSHE).
For applications where the fluids are of a viscous nature, scraped surface heat exchangers present a quick and efficient manner for transferring heat into and out of the fluid. For confectionary processing applications they also have the benefit of retaining the product structure. These heat exchangers use blades to continuously scrape the inside surface of the cooling chamber. This action protects highly viscous fluids from sticking to the cooling surface and from a full crystallisation of the product since it is exposed to the low temperature in a slow and controlled way. To provide the desired level of effectiveness, the product being handled needs to be pumped at a constant pressure to achieve a constant liquid flow.
AxFlow's Daniel Rukavicka takes up the story: "The customer had an idea of the production requirements and called upon the joint experience of AxFlow and WCB to design a fluid handling system dedicated to cooling sugar mass from +125ºC down to +70ºC, where the product viscosity was in the region of 145,000cPs. We also had to split the cooling procedure into two stages. In the second stage the liquid starts to form small crystals, which is necessary for the final product. However, on the other stage, if the liquid is cooled too quickly, or if it drops below the minimum temperature, the whole product is damaged by fast crystallisation and is useless for the final product."
In order to feed the SSHE with cooked syrup (a blend of sugar, glucose syrup, water and fat boiled starches) with a viscosity of 855cPs and density of 1.36kg/l at +125ºC, the pump needed to provide a flow rate of 900kg/h at a discharge pressure of 10-12 bar. The WCB Universal I specified for the duty offered the necessary differential pressure and was fitted with a double mechanical seal and jacketed front cover.
The Waukesha Cherry-Burrell Universal series rotary piston pump has a well-established place within many sectors of food processing particularly where the pumped medium has a high viscosity or contains solids or particles. Using an operating principle known as the external circumferential piston (ECP), the arc-shaped rotary pistons travel in annular-shaped cylinders machined in the pump body. Because the rotors of the Universal Series ECP pump produce a scooping action, they do not squeeze and compact the medium being pumped. The ECP's long sealing path reduces slippage and produces a smooth product flow without destructive pulses or pressure peaks, and without the need for valves or complex parts.
The Waukesha Universal ECP pump combines a very gentle, pulse-free pumping action with the high suction capacity necessary for allowing the thick mix to be drawn into the pump without any separation of the ingredients. The low shear action of the pump guarantees that all ingredients arrive at the depositing line in pristine condition every time.
"Our customer has enjoyed good experience with this type of pump," reports Daniel Rukavicka, "having used one of the same size running on a similar application for over three years. Feed back from our customer has been positive, with the final product achieving good market success. Because the whole system was designed with a reserve capacity our customer is in a position where they can increase production volume if necessary."