We've spent a lot of effort this past year to do better in winter with HAWSEPIPER's Afloat Global HQ and Detention Center. Living without running water every time the temperature went under 20 degrees was a good motivator, as was having water in our fuel, which stalled our pump engines. We've made great improvements on both those things.
What we haven't done is make heavy fuel oil any less viscous at cold temperatures, and so we're still struggling, just like every other heavy fuel bunker tanker operating in single-digit temperatures.
Heavy Fuel Oil, or #6 oil, is a glossy black, tarry oil, very thick and viscous (resistant to flow). It's like molasses, but more so. It needs to be heated up over 100 degrees to flow at a slow rate, and over 120 to flow moderately well. Generally, we like getting the stuff at about 130 degrees, but 120 is about the average. Wintertime, unless you have the capability of heating the product on board (we don't), you lose +/- 10 degrees a day, and the cold steel surfaces will collect a skin of congealed oil that won't flow, so no matter what we do, our retained bottoms (the sludge on the bottom of the tank that we can't pump) grows thicker by somewhere from our summer bottoms of about 1/4 inch to 1/2 inch+. Regardless, we try to keep it to a minimum by begging for hot product and also rolling and trimming the barge as heavily as possible to get the stuff to drain down. Generally, over the course of a few jobs, we can get heavy bottoms back to a reasonable 1/4" or 3/8" if we get a good shot of 130+ degree oil here and there.
So, that's one headache we deal with. We got extra heat-trace tape laid onto our potable water system, and between that and running a block heater on our water pump, we seem to have solved the problem of frozen piping. Taking a shower does wonders for morale.
Water contamination in diesel fuel is a pretty common problem, and we got ice dams last year at several places in our cargo pumps' fuel systems. We solved this by draining and scrubbing down the surfaces of our fuel tank and improving our procedures for thieving and draining off water bottoms in our fuel before they get far from the tank. So far so good there. We're also trying to stay on top of moisture getting into our air system, as well. We rely on compressed air-starting for our cargo pump engines, and have had issues of water vapor freezing up our starters, which means injecting antifreeze into the air line behind the starters and blasting it into the starter, a crude and really dirty, messy solution that cuts the life of the starter down considerably. Hopefully we've avoided that, too, this year.
So, with those things seen to, we've still got problems here. It's the damn oil.
There is heavy fuel oil, and there is heavy fuel oil. We move several grades of fuel oil, separated by sulfur content (environmental regulations, as sulfur is a great lubricant additive and also bad for the environment) and viscosity of the oil. Ship's engines and boilers want certain viscosity fuels to run properly, and this varies with brand and age of the engine, newer engines being more versatile generally but also more sensitive.
Most ship engines can run on heavy oil or lighter oils like diesel. Both fuels have advantages. heavy oil (HFO for short) being much less expensive. Diesel being more clean-burning and energy-dense, but expensive, which is an issue when fuel consumption is measured in tons per hour (a large container ship can burn several thousand tons of fuel oil in a single voyage).
Generally, we sell fuel oil at 380, 500 and 700 centistoke density. Centistoke is a measure of viscosity (it's 1cm X 1 gram^-1 movement at a standard temperature and pressure, I believe, but let's just call it a measurement of resistance to flow), so the lower the number the better it flows at a given temperature. The higher the number, the less it wants to flow, but the cheaper it is, too. New, larger ships do tend to like the 700cst fuel for economic reasons.
Now, below a certain temperature (the Pour Point), gravity alone won't cause a heavy fuel oil to flow. It's like upending a bottle of honey after keeping it in the fridge, but again, more so. You need pressure to move the oil (squeeze the bottle), and pressure is an issue. We have limits as to how much pressure we're willing to crank up to before stuff starts blowing up. We'll hit our max safe pressure with our cargo pumps pretty often even in summer when pumping HFO to a ship, and that number is quite high.
We discovered this year that 700cst fuel will set up like a glue at low temperatures, and resist flow to the point that things lock up. We're moving more 700 fuel because the East Coast is getting more super-sized ships now that the panama canal expansion is done AND now that so many ports have been dredged and had some low-lying bridges replaced or raised up. So this is new territory.
Well, if it cools down, it turns into a plastic-like substance, turns out.
|Looking inside a fuel hose|
|reaching in and tugging on the fuel column at full strength resulted in this.|
So that's not nice at all. A bunch of us are dealing with that. 380 or 500cst fuel, at high pressure, will get pushed slowly, like a tootsie roll through a garden hose. Eventually, the warmer liquid fuel oil will start flowing, and dissolve the chunky stuff once it breaks through at some point in a column. Well, the 700 stuff is better than a cork in a wine bottle, turns out.
Although working conditions here on the HQ have been pretty miserable with this deep-ass cold and the usual winter miseries of hydraulics and valves not wanting to work right etc etc, the plugged line issue is a new one for us, but thankfully, we've been able to keep the fuel going. Our plugged lines were in places where we could swap out hoses. We're in good shape for the shape we're in.
Word is that we'll be almost at 32 degrees one day next week, although that's well below the pour point for HFO, hopefully between us and our less-lucky peers, we might be able to fix any cold-related issues at that point. We haven't missed any work so far, and hopefully won't have to in the future, too, but it certainly has been challenging.
That is damned impressive. Impressively annoying as well to you, it appears.
I had no idea at all that fuel oils could be that viscid. I served aboard two oil-burners (CV-67 & CV-59), but never set foot in the engineering spaces, as I was an avionics tech.
Hope it gets better for you, but the forecast indicates otherwise.
We have similar issues up north working SAGD. The oil cools so low it won't pump. We solve it by blending in agents that lower the viscosity... but have to be removed at the other end of the pipeline.
The other thing we do with some of our tanks us recirc. We constantly pump through our hoses and truck out station back into our bitumen tanks. That way the fluid never sets up in the lines. We also use electric heat trace on some lines.
You could try pumping some of your tank contents through the hoses and back into your tank to keep the hose contents moving and non-frozen. Though unless you have a tank heater your going to accelerate the loss of heat from the tank.
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