Vertical Centrifugal Immersion Pumps for Effluent Transfer

Process Background and Issues Faced

A dye house was having issues with their current Vertical Immersion sump pump used for the circulation of effluent within their facility.

The pump they were using was suffering from severe corrosion which was frequently having to have parts replaced, and maintained. This was mainly due to the chemical compatibility of the effluent, which was wastewater from the dyeing process containing mixtures of acids from wool washing and dye transfer producing 200M³H at 10M head.

The main component was diluted Formic Acid which is used as a neutralizing agent and ph adjustor. This was diluted within a 5000L tank creating a low PH3 corrosive effluent mix with wool particles up to 5mm in length. Coupled with a fluid temperature of 50°C, which at times rose to 90°C it created the ideal conditions for certain metals to corrode quickly.

Existing Pump Evaluation, New Selection and Material Specification

Firstly, we had to ascertain what materials were used in the existing unit and whether these were suited to the process, then understand if another design would be better suited.

Due to the high temperatures a submersible pump was ruled out as this design uses the surrounding liquid to cool the motor. As the fluid reaches temperatures of 90°C this made it unsuitable for a unit to be completely submerged.

Another possible solution was a self priming pump, however due to the high temperatures there was a possibility of cavitation. This is due to the liquid temperature being close to boiling point meaning there would be an associated low NPSH, likely to result in issues such as accelerated wear, and heavy vibration. To read more about the advantages and disadvantages of Submersible Vs Immersion Vs Self Priming Pumps read here.

Given the high operating temperature it was clear another vertical immersion pump was the most appropriate solution, with a column length of 2.5M making the complete unit over 3.6M in length.

Vertical Immersion Design and Why they are used 

Vertical Immersion Pumps are ideal in applications where fluids are corrosive, contain solid particles or where fluids are being pumped at high temperatures. This is because the motor is located outside of the fluid, leaving only the mechanical parts to work within the fluid.

Units can be built to up to 4M long as shafts are given extra support through the utilisation of additional bearings, ensuring the shaft does not whip and freely rotates. However care must be taken to ensure corrosive or solid laden liquids do not cause damage to the bearings located in the column.

As the pump head is immersed in the liquid it also means that applications with a Low NPSH can be accommodated as the unit does not have to prime. Various materials were evaluated to assess compatibility with the liquid, and prevent chemical attack such as having the unit manufactured in duplex, to having parts in Stainless Steel, or coated with chemical resistant coatings to reduce corrosion.

The client opted for the unit to be constructed with a AISI 316 Stainless Steel impeller, the casing in Ductile Iron and Column in steel with epoxy coating. As our designs are completely configurable individual parts can be manufactured to specified materials to suit the required process. They chose this as an acceptable specification which would closely fit their scheduled maintenance routine. The unit was manufactured and supplied within 12 working weeks, and due to its size delivered via a dedicated courier.