Sunday, May 9, 2010

Hay for oil spill is no plan

By Donald Sensing

This video is making the rounds as the common-sense solution to the massive oil spill in the Gulf of Mexico.

As most engineers know, "Everyone has a brilliant idea that will not work." And this is one of them, although we must commend these two gentlemen for trying.

Hay absorbs water just as readily as oil. There are EPA-approved products that absorb only oil, even in water, for example HTP. But for this discussion we'll assume hay will absorb only the oil.

The area of the spill now exceeds 6,000 sq. miles and more than 11 million gallons of oil are in the sea (link).

That means that the weight of the oil in the water is just over 40,000 tons (7.29 lbs/gallon).

Let's assume it takes only 2 ounces of hay per sq. ft. of oil, which seems reasonable, requiring one pound of hay per eight sq. ft.

Six thousand sq. miles of oil is 172,232,755,200 square feet. That will require 21,529,094,400 pounds of hay to absorb. Note that these are billions figures. That amount of hay is 10,764,547 tons.

So you're going to transport almost eleven million tons of hay to sea to absorb 40,000 tons of oil.

Then, after the hay has absorbed the oil, the oil is still in the water. Only instead of having to deal with (a mere) 40,000 tons of oil alone, you've got to scoop up 10,804,619 tons of oil-sodden hay.

I admire these men's earnestness, but this is not a plan.

Let's do the cube, too. A bale of hay is compacted by a hay baling machine and can weigh between 60-130 pounds, depending on the machine's settings. Let's use the high figure. This hay bale measures 48 inches by 18 by 18, giving a volume of 15,552 cubic inches, or 9 cubic feet.

So: the volume of cargo capacity to transport the hay to the spill is 1,490,475,766 cubic feet. For planning purposes, cargo vessels use 100 cubic feet of volume to equal one metric ton of weight. Confusingly, this measure mixes English and metric systems and also uses the word "ton" to refer to the 100 cubic feet. In merchant-vessel terminology, a metric ton, or tonne, is referred to as a deadweight tonne (DWT) and equals 1,000 kilograms, hence one metric ton. ("Tonne" means 1,000 KG so "metric tonne" is redundant; in the US the term, "metric ton" is usually used instead of "tonne.")

It takes 11.11 bales of hay to fill 100 cubic feet, and the bales do not weigh a tonne, they weigh 1,444.44 pounds, or 655 kg. In other words, any vessel carrying hay would "cube out" before it would "weight out" - it would run out of space for the hay before it met its weight limit.

To carry all 165,608,418 bales of hay for the job would require 14,904,758 tons of volume (14,904,758 units of 100 cubic feet). A single modern Handymax bulk-cargo vessel has a capacity of about 55,000 DWT, but would cube out with hay at 4,950,000 bales. Hence, transporting 165.6 million hay bales to the spill area would require 33 Handymax ships. That's a tiny fraction of the number of Handymax ships in the world, of course, and certainly well within the harbor capacity of Gulf ports to handle. So simply carrying the hay to the spill appears to pose little logistic problem, but recovering it from the sea is an enormous problem since cargo vessels are entirely unequipped to do so. So what is these gentlemen's plan to do that?

We always must remember to think the problem all the way through. I mean no disrespect to these two gentlemen, truly, but they did not do so.


Well, there's always the hair of the dog!

There are some ways to use hay to fight oil spills, just not of this magnitude.

Fla. Dept. of Environmental Protection says hay will create more problems than it solves

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Doug said...

I'm sure your math is fine, but you obviously don't understand what they're proposing and why. Watch the video again. First of all, and this won't affect your math but it is an important point, the hay doesn't "absorb" the oil. The oil clings to the hay. Obviously the weight is the same either way though.
Second of all, this is a solution to the cleanup problem once the spill comes to shore. It is already coming to shore, but it will be much easier to clean up oily hay than liquid oil.

Anonymous said...

Thanks for revealing some of the math and logistics. However,the point these two guys were making was to simply let wave action and tidal flows bring the floating hay ashore where cleanup would be less costly and the contaminated hay could be burned. Sounds better than trying to clean or dispose of oil contaminated sand. Am I missing something here?

Donald Sensing said...

Yes, I think both previous commenters are missing something, mainly that there are many more efficient and effective oil absorbents and dispersants than hay that are also more efficient to transport.

Anon also assumes that all the hay will wash ashore, which is simply an unsupportable assumption. One of the worries about the spill is that it may get carried across the Atlantic by the Gulf stream. The last thing we needs is 40K tns of oil clinging to millions of tons of hay floating across the ocean toward Europe.