Produced Water Treatment with Deoiling Hydrocyclones - Misconceptions & Corrections (B-PWT014)
Misconception 6 : Deoilers need pumps to work properly / Deoilers don’t work with pumps
Correction 6 : Deoilers require pumps only when the available operating pressure is below a specified minimum, and operate effectively and efficiently when strict design guidelines are followed.
We saw previously that Deoilers have minimum pressure drop requirement to operate efficiently, and in some cases a maximum pressure drop limit. The minimum pressure drop requirement depends on the Deoiler liner size, but with the latest generation Deoiler this figure is around 40 psi. Below this figure a Deoiler system requires pumps.
At this point one should ask the question, “For the produced water process conditions provided, which include a low operating pressure, should a Deoiler system be chosen as the most appropriate technology?” In some instances the answer is no, so evaluate the equipment choices available carefully (seen earlier in this series), before a final decision on what’s appropriate.
The issue in using a pump with any produced water equipment, let alone a Deoiler, is the fact that many pumps will interact with what might be a quite benign produced water stream, and create a tough to separate emulsion of small oil droplets.
Now there are various low shear pumps, typically progressive cavity pumps, which do a good job in not creating this emulsion. Multistage centrifugal pumps may be applicable as well. However, in both cases the equipment can be quite large and certainly quite expensive.
For the majority of service work in the upstream oil & gas industry, single stage centrifugal pumps are the preferred choice.
Single-stage centrifugal pumps can be used if the shearing effect is minimised by following these strict design requirements;
- Single stage centrifugal pump, closed impeller type
- Pump speed at less than 1800 rpm
- Maximum suction to discharge pressure differential of 100-120 psi
- Pump operating at a constant flowrate and at 75% or greater pump curve efficiency
- Operating at a constant flowrate using a system recycle design, which allows for any turndown requirement
By following these criteria, a pumped Deoiler system can provide an effective, efficient, produced water treatment system.
Bibliography:
- Flanigan D.A., et al., Conoco Speciality Products Ltd., “Use of Low-Shear Pumps and Hydrocyclones for Improved Performance in the Clean-up of Low-Pressure Water”, SPE 19743, ATCE San Antonio, October 8-11, 1989.
