There are different ways to make an effective blending:

• Inline dosing pumps, pumping through a static mixer or into a mixing tank.
• Batch-dosing into mixing tanks on weight cells.
• Inline dosing through a mass-flow meter, letting the flow meter control the speed of the positive displacement pump.

As many of the additives have a high viscosity, the pumps used have to be able to handle the viscosity and at the same time be able to create a high vacuum (having a low NPSHr value) to overcome the pipe friction on the suction side of the pump.
Rotan pumps have been used for many years for this application, and as they have fine NPSHr values they are able to handle high viscosities. Further the capacity variation is very low if you change pressure and/or viscosity. Thus the pumps are easy to control and in some applications they are used as batch dosing units as they repeat the dosed amount within ±2 per cent, pumping through the same pipe system at a constant viscosity.

The end user expects maintenance free pump service in 7–8 years in oil blending applications, therefore the initial pump selection is much important. The speed of the pump, the NPSH value, taken the viscosity range in consideration when pumping the different base oils and additives, are crucial.

Picture is one of Prista Oil’s blending plants in Romania. Prista Oil is one of the leading oil-blending producers in the Balkan countries, Turkey and Ukraine.