3 replies to this topic

[pmunishankar]

Dear practiecing engineers,

I am working on a project handling waste water in upstream oil and gas project. Here is the situation I am into.

We have got 3 phase separator that separates oil and gas from water. The separated water is passed through Induced Gas Floatation (IGF) unit and then to walnut shell filters. The product is clear water and it is used for other purposes. The waste stream generated in IGF and back wash water from filters is collected in waste water tank. This water needs to transported to wells located about 20+ KM for disposal. We are required to design this system.

The properties of combined waste stream (IGF + Back wash) is attached.
My question here is which type of pump is suitable for this service and why?
Flow rate: 24 m³/ hr; Discharge pressure: 150 psig
When I roughly estimated the specific speed, it is coming out to be 383 (English Units for 3000 rpm) recommending me to go for radial centrifugal pump possibly with gear box. The other question coming to me is why centrifugal why not rotary or positive displacement? Which type of pumps are normally used for waste / saline water transport?

Please send me any supporting papers so that I can convince my peers.

Thanks a lot,
Muni Shankar

Attached Files

•  Specification.pdf   7.3KB   43 downloads

Edited by pmunishankar, 11 February 2012 - 05:43 AM.

[ankur2061]

munishankar,

What is the unit for oil and grease in your specification? I am assuming it is 8,767 ppm by volume. How come your IGF unit is producing effluent water with so much oil & grease and TSS?

I have serious doubts that you can release waste water with so much oil and grease to disposal wells. The H2S content of 0.1 mg/l also is high.

Normally transport of waste water with oil and grease is done with low shear centrifugal pumps in many installations. These pumps run at low speeds of 750 rpm. The idea of using low shear centrifugal pumps is to prevent shearing and thus formation of water-oil emulsion which is detrimental when further treatment and disposal is required. Low speed postive displacement pump such as progressive cavity pumps which prevent shearing are also acceptable. What finally becomes important in the selection is the CAPEX and OPEX
of the pump. You will have to do this analysis to arrive at the most economic option for your application.

Hope this helps.

Regards,
Ankur.

[pmunishankar]

Dear Ankur,

Thanks for your reply.
yah, you are right. Oil & grease content is 8767 ppm by volume.

I just want to clarify the questions raise by you.
How come your IGF unit is producing effluent water with so much oil & grease and TSS?
The original design was that IGF waste is collected in a tank that separates the oily water to recyle back the 3 Phase separator. The scheme now is modified not to recycle but to dispose it off.

As there is no downstream further treatment, I think centrifugal pumps doesnt pose any problem with respect to oil - water emulsion shear your are mentioning. While I am calculating the specific speed to find the suitability of centrifugal pumps, it is requiring to choose rpm of pump to be more than 3000. If I consider 3000 rpm, specific speed is lower than 500 (English units). Attached my preliminary calculations.

Please Advise...

Thanks and Regards,
Muni Shankar

Attached Files

•  Pump Specifications.pdf   802.19KB   51 downloads

Edited by pmunishankar, 12 February 2012 - 12:47 AM.

[ankur2061]

munishankar,

As a process engineer I don't select a pump based on suction specific speed, I only provide the process data in terms of liquid properties (specific gravity, viscosity), NPSHa, Total Differential Head, Discharge Pressure and MOC of wetted parts. The vendor / manufacurer proposes a model based on the process and mechanical data (mechanical seal, cooling plan, quench plan, specific speed limitations). The suitability of the model propsed by the vendor is reviewed both by the process engineer and the mechanical rotating engineer against the process and mechanical data.

I have never done specific speed calculations and would not be able to advise on selection of pump based on suction specific speed. That I would leave it for the vendor to advise or a mechanical rotating engineer to check.

Hope this helps

Regards,
Ankur.