Waste water accumulation

Ciculate the tank contents via a high speed centrifuge, this will remove the solids content and oil. The gases can be separated by passing thru a heater and condenser arrangement.

Offshore Engineering&Design

Milutin:

We need much more information from you. 10,000 m[sup]3[/sup] is 63,000 barrels ... that is indeed a big amount!

(1) Does your refinery have a sour water stripper? Are all of your sour waters routed through the sour water stripper? If so, your stripper is either much too small or badly mis-operated, because 0.4 wt% H2S (4,000 ppmw, ppm by wt) is completely unbelievable for water that been through a correctly sized and operated sour water stripper.

(2) Same comment about the 10,000 mg/L of NH3. That is 10,000 ppmw which is also unbelievable if your sour waters are routed through a correctly sized and operated sour water stripper.

(3) Does your refinery route all wastewater through an API separator or corrugated plate interceptor (CPI) and a dissolved air flotation unit (DAF)? If so, then a "significant percent" of oil is also unbelievable ... it should be down in the ppm range rather than percent range.
Again, either your API, CPI and DAF are undersized or badly operated.

(4) Almost every refinery in existence has sour water stripping, API or CPI, and DAF units. Does your refinery have them? Also, following the DAF unit, does your refinery have some sort of biological treatment unit?

(4) The only other thought I have is that perhaps the analyses of that stored water should be independently checked for accuracy.





Milton Beychok
(Visit me at www.air-dispersion.com)
.

Hi chief and mbeychok,

This water is collected in tank farm, suppose that origin of water is from slops, there was no possibility to route this water to SWS, and no SWS spare capacity available.

To solve this problem we make one SWS available for processing this water. Capacity of SWS is about 15 m3/h and column has only 13trays, steam stripped. I am not sure if this SWS is capable to strip out H2S and ammonia to acceptable level.

Concentrations of H2S and NH3 are really high, we also decided to make additional tests to confirm this values but they looks correct.
It is not possible to send this water to API separator because very high pollutants concentrations.

Also high oil content is another concern, before sending to SWS it should be oil free. I am not sure if any company provide service for deoliling water with some portable high speed centrifuge or hydrocyclone?

Regards,

Milutin

Milutin:

You still haven't told us whether or not your refinery has an API/CPI separator and DAF unit. The reason I ask is that I am curious as to how your refinery got itself into this mess.

Your stripper, if designed properly, will certainly lower the H2S and NH3 content ... if the stripping steam rate is properly set. But at 15 m3/hour, it will be very slow going indeed ... and the oil will be a problem.

As for using a rented portable centrifuge, it will take a great many of them to process 10,000 m3.

Do you have a local public wastewater treatment plant that will take this water off your hands ... probably for a large fee. I think that is worth looking into that ... instead of trying to de-oil the 10,000 m3 and then steam strip the de-oiled water.

You might also look into using hydrogen peroxide, potassium permanganate or chlorine to oxidize the H2S. That might make it more palatable to a local public treament plant.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

It is really mess, it take two years to accumulate such quantity of water.

We have only API separator, outlet water from API separator is sent over the fence to another company for biological treatment.

Company for biological treatment has sharp conditions (or maybe not sharp, I don't have experience in this area)for water quality from API separator:
Oil content up to 250ppm
H2S up to 5ppm
Mercaptans up to 5ppm

So there are no way sending this polluted water to treatment, and no other company available for treating this water.

We considered treating with H2O2, but in my opinion such water should be also deoiled before oxidizing, and it should be done on separate plant, not in tank directly.


Regards,

Milutin

Milutin:

If that water has been in the tanks for quite some while, it may have formed a layer on top of the water by now. Can you tell if that is so? If there is an oil layer, can you get a vacuum hose into the top of the tak and vacuum out that oil layer? That might be helpful.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

Hi mbeychok,

Oil is actually emulsified in water and water has oil content about 2wt%.
I am not sure if it is possible to run SWS with such quantity of oil?

Regards,

Milutin

Milutin:

I would not suggest trying to strip H2S from an oil-water emulsion. It would probably foul the stripper trays or packing quite badly. Also if any of the oil is light enough to go overhead, it would probably result in your Claus sulfur plant producing black sulfur.

Have you tried emulsion-breaking chemicals in that tank?

Milton Beychok
(Visit me at www.air-dispersion.com)
.

Milutin:

Since the oil content of this wastewater stream seems to be controlling the further SWS stripping or other removal processes for ammonia and H2S, consider an initial DAF oil separation. I suggest a DAF (dispersed air flotation, as opposed to dissolved air flotation....from my hands-on experience with WEMCO systems twenty-five years ago at the largest crude through-put refinery in the world in the Carribbean), this with appropriately selected demulsifiers and solids wetting agents is a superior system and process for cleanup of oily/solids laden refinery waste water, at an affordable cost.

Any number of petroleum process chemical suppliers, such as GE Betz and Nalco, can provide the chemical requirement to satisfy your requirements.

Orenda