Tank Cleaning for Biofuel Conversions

With the rapid introduction of ethanol in the Southeastern United States, there needs to be an understanding of some of the issues related to this new product. To be sure, biofuels, whether they be ethanol or biodiesel need extra care and attention.
The following are several issues that we are seeing relating to E-10 gasoline.

• Phase Separation
• Tank contamination caused by detergent action of ethanol

Let’s look first at phase separation:
Normal gasoline has a small amount of water in it. As more water enters a tank, it will simply settle on the bottom of the tank because water is heavier, and gas will hold very little water. However, ethanol attaches itself to water. So a fuel such as E-10 will absorb water as it enters the tank. If too much water enters the tank, eventually the ethanol in the gas becomes so saturated with water it becomes too heavy and gravity pulls the water and ethanol downward to the bottom of the tank. It falls in the form of droplets through the base gas to the bottom of the tank like rain. It is estimated that this process takes from 15 to 24 hours on average, but it may take longer. Does phase separation happen often? No, because you constantly rotate your stock and the moisture remains suspended as it is delivered through your system. The saturation point will not be met unless a fairly large amount of water enters your tank.

The big question, of course, is how much water is too much? There is no set amount. I have read where ethanol can hold 1/2% water and probably be ok. Maybe a little bit more, even. That would mean 25 gals of water in 5,000 gals of E-10. As long as this water stays suspended, you will simply sell the fuel and it will go through the system, burn in the engines and do just fine.
The risk is what happens if you take on some more water when your ethanol/fuel is already holding its limit of water? The risk, of course, is phase separation.

Also, something to be aware of, warmer ethanol/fuel will hold more water than cooler fuel. If you already have a fairly high concentration of water in your E-10 and then lower the temperature (by adding some cold fuel) this can trigger a phase separation. (Fuel sitting in a tanker over night during the winter can easily be 20 degrees cooler than the fuel in your underground tank.)

This, of course, all leads to the obvious conclusion that we should take all reasonable steps to prevent water from entering the tank in the first place. As we clean tanks for conversion, probably a third of them contain what would be an unacceptable amount of water for E-10 storage. Later in this writing I will mention some of the things we see in the field that invite a water problem, but next let’s first explore what to do if you experience a phase separation. You have two traditional options.

• Remove all the contents of the tank.
• Remove the water/ethanol from the tank bottom, purge the lines, and then boost the octane up to the desired level.

We at Atlantic Clean Fuel use the 2nd option. On a typical phase separation involving an E-10 mixture, you can assume approximately 10% of the tank’s content will be sitting on the bottom as water/ethanol waste. This must be completely removed and disposed of. Using a vacuum system, the waste is removed from the entire length of the tank.

Atlantic Clean Fuel has equipment very well suited for this job. Using our extended vacuum system, we can reach all lengths of the tank bottom. It takes about twice as much time to do a phase separation cleanup as it does for a regular tank cleaning and this does not include purging the lines. Typically, the line purging is done by the customer’s service department. Our charges for a phase separation cleaning are approximately the cost of cleaning two tanks. Also, provisions must be made in advance for the disposal of the waste. Atlantic Clean Fuel may be able to handle the removal and disposal; this depends on the location of the site and amount of waste. There is extra cost involved if we do the removal. Another option is we can leave drums filled with the waste at the site for removal by the customer or the customer can provide a small tank truck to carry the waste.

By computing 10% of the contents of the tank, you can pretty much estimate the amount of waste that will have to be removed and disposed of. Disposition of the waste should be determined and agreed upon between the customer and Atlantic Clean Fuel before the cleaning begins.

The second issue to be aware of: Tank contamination due to the cleaning action of the ethanol along the tank sides and bottom.

Rust and dirt that has accumulated over the years will loosen up and settle on the tank floor due to the cleaning action of ethanol. Extra dirty tanks, usually tanks that contained water over a period of time, often will create enough build up of matter that frequent filter changing will become necessary. When filters need changing often, every month or so, the tank should be cleaned.

Tanks that have been converted to biofuels, ethanol or biodiesel, should be cleaned within the first year of the conversion. Tanks that were found to be extra dirty or tanks promoting filter changes should be cleaned sooner. The Steel Tank Institute as well as the Ethanol Coalition both recommend annual tank cleaning after converting to any biofuel. When you begin dispensing biofuels, we feel that some schedule of cleaning should be established. When we clean tanks for conversion, we are constantly amazed at how clean some tanks are and how filthy others are. And it isn’t always because of the station’s age. I would recommend cleaning of the filthy tanks annually and maybe every second or third year on the cleaner ones. Atlantic Clean Fuel has a “scheduled maintenance program”. A number of our customers are using this program. This is done at a reduced price. Contact us for details if you want to know more about this program.

Where does the water come from?

Water in tanks is, of course, the major concern. When we do tank cleaning, you will receive a form report filled out by our cleaning crews. The most important subject on these reports is water content. If significant water is found, 10-20 gallons or more, your maintenance people should examine the tank for problem areas. If water entered the tank before and nothing was done to prevent it from happening again, it probably will.

Here is a list of things to look for:
• Verify that all tank caps are in good repair with fresh gaskets. Gaskets are cheap and should be changed annually. Caps should “click” down nicely.
• Check the grommet around the wire entering the probe. These are often missing or in poor shape which results in an avenue for water.
• The cavities around the fill and probe must be cleaned out regularly. Sand and debris will wash into these areas filling them so there is no place for water to go.
• Water should never be allowed to rise above entry caps. This often happens when cavities fill up with sand.
Entry areas of all tanks should be checked after every rainfall and standing water removed. (Little hand-operated pumps are cheap and work great.)
• Water drainage on property should be directed away from tanks. Eves and down spouts from buildings and canopies should be kept in good working order keeping water flow away from tank covers.
• Sometimes water comes with fuel from delivery tank trucks. This is one good reason for regular sticking.
• Occasionally, tank failure will allow moisture into the tank, especially if you have a high water table.

Preventive Measures:

• Tanks with ethanol should be stuck weekly and after every rain. Use an ethanol paste to determine water density. Ethanol paste must be held in the fuel at least a minute to get a true reading. The color will tell you the water content.
Your supplier will know what to use. I will give a free tube to any customer who wants one.
• Tanks not containing ethanol should be checked for water on the bottom, sticking both probe and fill. Tanks are rarely level. (Incidentally, our new reports will show the slope of your tanks so you will know where the water is and where to check.)

In conclusion:
Tank cleaning is a fairly expensive service, but the cost of dirty tanks and phase separation is much more severe. “Out of sight, out of mind” was never so true. Now that we are in the age of biofuels, tanks will require much more attention, both by your people and outside cleaners such as us. Cleaner tanks, in the long run will save you money, because you will have less filter changes, less problems such as phase separation, happier customers, and clean tanks last longer!