As containers and temporary storage, tanks to entire tank farms are the backbone of many industries, in particular in the oil and fuel sector. But these types of media are often highly viscous, making it difficult to empty or ‘strip’ all the medium out of the tanks. Residual product is normally left behind, significantly reducing the useful volume of the tank. More and more companies in these sectors are now using NOTOS® screw pumps from NETZSCH Pumpen & Systeme GmbH to maximise the profitability of their tanks.
Look behind the scenes
Tanks are ideal for storing media that is volatile, potentially hazardous or has to be protected against contamination. They are therefore commonly used for mineral oils and oil products from diesel and petrol to polyols, as well for plant-based products such as palm oil. All these materials cause problems when it comes to emptying tanks, such as when medium is pumped to the next step in the production chain. This may be because of comparatively high viscosity or a low vapour pressure.
If you use conventional centrifugal pumps, the poor intake often leaves behind residual product that then cannot be used. The wrong type of pump can also cause cavitation resulting in interruption to flow, which will lead to pump failure in the long term. The biggest challenge is to keep the bitumen hot in the pumps, so that the product can be kept at a comparatively low viscosity of 500 cSt. The NOTOS® pumps from NETZSCH have already been tried and tested on numerous occasions in real-life scenarios.
One of the world’s largest companies handling petroleum products wanted its 4NS pumps at a terminal in England to be fitted with an additional heating jacket to keep the bitumen hot in the pumps. The performance of the pumps is unaffected by the heat, as the robust units are designed for temperatures up to 300 °C. Besides the separation that is required for structural reasons between bearing and pumped medium, this is possible thanks to a range of materials from grey cast iron and chrome-nickel steel to Hastelloy alloys that are used for the pumps.
The choice of materials also contributes to pump performance, as spindles made with these materials also have almost no deflection, which allows for fine production tolerances between the dynamic and static parts, thereby reducing backflow. In combination with a pump chamber with geometry designed for optimum flow and to minimize turbulences, it is possible to achieve high rates of efficiency while still gently pumping the medium. Screw pumps are therefore being used increasingly as an alternative to centrifugal pumps, because they have lower NPSHr values and therefore significantly better intake behaviour. They also make it possible to strip out a tank completely with nothing more than the pump.