Oily Water Separator

I would think that condensation would be the major contributor to water in the tanks.

Diesel has no vapour pressure which would displace the moisture laden air in a petrol tank.

During warmer periods such as daytime with the sun shining on the tank, the diesel expands and forces some air out of the tank, when the tank cools again, air and attendant moisture is drawn into the tank and water then condenses on the cooler walls.

Pre-contaminated fuel is another possibility to guard against.

For these reasons, I would expect a water separator to be a requisite.

Having the fuel pickup somewhat above the bottom of the tank along with a bottom mounted drain - either manual or automatic - to remove existing water is another useful protection.

Noted. However, my main concern is about treating oily water before discharging into the environment. As mention based on my experience oily water separator is a requisite for HFO fired power plant/marine operations but is it necessary for diesel power plants.

The main question is, "What is the source of the water that you are discharging?" and "where are you dumping it to?"

If that water contacts and flushes oil from whatever the source, then you need to put in the right equipment to meet your discharge permit limits. An easy visual clue is that if the water has a sheen, then you should consider treating it. It also depends on where you discharge to. If dumping down the drain to a municipal treatment plant, then they can tell you what their limits are for oil content. If dumping in the swamp behind the plant then you need to be careful to meet your discharge permit. If dumping to your own cooling pool, then you need to be sure that nobody will notice and complain and meet any pollution standards for the area. Diesel and motor oil cleanup in soil is a real pain in the rear.

Oily water separator? Most tanks I've dealt with have a "PetCock" at the lowest point in the tank that you open up and stroke it a couple times to remove the water/ condensate from the tank. And that should be in your daily operation manual. And if not, it should be implemented ASAP.

Working on Turbofan jet engines, I don't recall dealing with any "oily water" separators. Bottom line is "PM" preventive maintenance.

You shouldn't need one, a proper drainage system in case of leak through into the tank, and condensation accumulation is standard though....

..."A lack of routine maintenance is the most common reason that free water enters a diesel fuel storage tanks. Because diesel fuel and water will separate, it is important to have your storage tank drained routinely to prevent this water from contaminating your fuel. In addition, a tank’s integrity should be inspected and, when necessary, repaired to ensure that no water is able to infiltrate. All aboveground storage tanks should be properly sealed to prevent contamination from rainwater."...

http://www.tanksdirect.com/blog/storage-tanks-2/diesel-fuel-storage-tanks-must-be-kept-free-from-water-contamination/

I work at a combined cycle power plant. Only some bigger than yours. We did have an oil water separator tank, since sump drains, and pits were being pumped to wastewater measurement and discharge area.

Oil films are forbidden by our permit, so we had to pay close attention, and if there was an "event" not handled by the OWS, we could by-pass its discharge to a holding basin, and use oil absorber pads floating on that water.

The problem most likely arising will be operator error in judgment of when to "float off" the oil layer to collection for disposal. Too often, and one ends up paying for water disposal in the name of waste oil, and not often enough, one ends up surging the wastewater system with oil. There is no ideal system out there I am aware of.

I have seen advertisements for filter cartridges that just remove oil from water, and pass the water through. I think the cartridges are yellow from being pre-treated with an oleophilic material. For a plant of your capacity, with anticipated flows in the low range (even storm water run off), you can remediate the situation considerably by the use of oil absorber pads where any oily leakage is noted or likely, changing these out on a schedule, or when they start to become saturated with oil.

Place oil absorbing pigs around all plant drains. If you have a run-off collection system, you perhaps could consider use of the special filter elements. Use search term "oil absorbing filter cartridges", and possibilities will open up.

"oil water separator" search term also yields good results.

The units are reciprocating engines with no water consumption. The layout is a simple one with no pits or sumps.

There are drains around the perimeter of the engine house for storm water catchment. My concern is the oil film that would form from any minor leaks. Does this warrant an oily water separator?

Minor leaks from where to where?

Some information seems to always go begging in these discussions.

If your system is really as described, then get some oil absorbent pads, and use them frequently, and change them often, and pay to have them disposed of, like the rest of "us".

What are your local code requirements? At this point, we have no idea where in this world you live in. Give us a location where you're at and we might be able to assist you. This is a world forum.

Two things are required for condensation of water vapour to occur and a drastic change in temperature.

At 30⁰C and 100% humidity an empty 760 litre fuel tank could hold 23 grams of water or thereabout and at 10⁰C about 13 grams of water.

One would expect to see sweating on the outside of the fuel tank, if it was also going to take place on the inside of the tank.......in my 13 years at sea, and 45 years of teaching marine engineering, I have never seen a fuel tank sweating......during my teaching career, I used to take students on several different types of ships, we even had our own vessel, a large sea going tug......we also had fuel tanks and fuel systems on static/running engine set ups in the workshop, (these were only small fuel tanks), even a vessel refuelling set-up.......never saw anything that even looked like condensation.......even with engines that have high fuel returns, e.g. GM, Cummins, the fuel tanks got quite warm and even with ambient temperatures of 0⁰C - -3 or -4⁰C, (mind you haven't seen those temperatures for many a year) some mornings in winter, up to 45⁰C+ in summer...........still no condensation.

The only time I guess, that you may see sweating, is in extremely cold waters and the cold night temperatures warm up fairly quickly - I must admit I have never been in that situation......as I said I guess it may occur then.

It is a problem that is grossly overrated, unfortunately, by many so-called experts. Generally water-in-fuel comes from other sources through generally poorly designed or poorly maintained fuel systems and storage/filling facilities.......particularly filling and venting points. How good is your supplier? Do you know the set up he has? does he maintain it well?, etc. Another problem that can occur is if a person refuels from drums - how are the drums stored, if they are just standing up, unprotected from the elements, you will get water into the drums.

Case in point, sumps of engines, high temperature oil, low ambient air temperatures.......how often do you see corrosion in rocker covers.......I have seen it twice, and in both cases water entered the oil through a cooling system fault, e.g "o" ring failure on cylinder liner/block. If condensation does not occur in the sumps of engines, where we get drastic changes in temperature, if condensation does not occur under these conditions, how on earth will it occur in fuel tanks. Oil testing for water, carbon content, etc was always carried out at least 2 times a week when continually at sea.....if ever water was detected it was always a cooling system leak.....

I apologise, if I seem a bit pedantic in my views, but, this is/was a pet aversion of mine..............blaming water in fuel on condensation........to my way of thinking, its an "out," because its "just too difficult" to find the real reason for the problem.

3 x 1.1 MW is a decent size.

Depends on some things (including, but not limited to); your location, your acceptable level of risk/repercussion, your level of environmental responsibility.

If discharging any waste liquid to ground or sewer, there will be some acceptable level dictated by your relevant environmental protection agency (if they exist where you are). In Queensland, Australia, I believe the acceptable level of hydrocarbons is 30ppm.

We utilise a waste buffer tank that is plumbed to all gen-set canopies. All runoff from engine leaks, engine wash downs, canopy leaks etc is captured. Its then run through a VGS (vertical gravity separator) in a polish mode. Waste oil is skimmed off the top (as well as sludge off the bottom) in the VGS and deposited in a waste holding tank for appropriate disposal off-site. Polished water is discharged to sewer after a sample is tested. Note: Discharging to sewer above acceptable levels can have considerable negative effects on bacteria and microbes at the local waste treatment facility. They don’t like that at all!

The other benefit of the waste buffer tank is when you have a serious coolant leak, it is all captured…though this does incur a considerably larger cost of disposal, as it cannot be separated out.

Our bunds utilise hydrocarbon filters in a canister arrangement. Chances of spills is minimal, but it does happen. The bigger ones are usually when a tank is overfilled by the fuel delivery contractor and expansion takes place in the middle of the day…..fun times. Where a sheen is evident, bund fluid (mostly rain water) is diverted through the filters prior to discharge to ground.

I could supply some links, but im not up on forum policy at the moment, so if you require more info, just let me know.