Reliable conveyance of aggressive starch solution
Generally, the paper industry has to deal less with viscous than with corrosive or aggressive media. Even the starch solution, used for gluing paper, is likewise aggressive. It prevents paint or ink from spreading in the capillaries of the actual hydrophilic material. However, the starch must gelatinase for the desired affect and is therefore transported at 80 °C.
The heat alone poses a problem for many materials. In addition, however, the starch sticks to seals, acts corrosively – which is further promoted by the heat – and attacks sealing surfaces from conventional materials within a few months. Add to this that pulsation and especially cavitation must be avoided to allow the precise metering and uniform application of the starch solution.
Task
A large paper plant wanted to replace its outdated pumps by modern technology. Facing the challenge of having to move larger capacities of roughly 80 m³/h in a tight space, the use of a strong but compact rotary lobe pump was recommended. This pump works with two rotors engaging with each other but moving in opposite directions thus creating large chambers between rotors and housing. This permits high delivery volumes and prevents clogging even with sticky media like starch.
A TORNADO® rotary lobe pump of the XLB series for larger quantities with three-vane rotary lobes was used here in favour of rather gentle and low-pulsation flow. Two of these run in normal operation, the third serves as a back-up unit during cleaning or maintenance of the other pumps. In this manner, continuous feeding of the coating system could be realised.
Solution
The material used for the rotors was ethylene propylene diene monomer (EPDM) rubber which is very resistant both to the thermal and chemical effects of the hot starch. For the same reasons, the housing was lined with stainless steel.
To prevent sticking of the shaft seals, special mechanical seals were used to securely seal the medium.
In addition, the TORNADO® is designed for easy maintenance. The pump cover can be removed in an axial direction which opens up free access to the entire interior of the pump. Cleaning work or maintenance tasks can thus be carried out quite conveniently. Also, the rotary lobes can be removed simply and independently of each other or new ones inserted. This makes for very brief downtimes.
