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Generator Soot on Yacht Hulls...

Discussion in 'Generators' started by YachtForums, Jun 4, 2014.

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  1. Marmot

    Marmot Senior Member

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    I used to sail on steam powered containerships. The "station wagon effect" at high speeds would produce black "sootdrifts" on the aft deck that were several inches deep where the wind deposited it. Kind of funny (not for the owner) but we once had a Taiwan trawler yacht as deck cargo from Kaoshiung to Seattle and after a week of high speed running and strong winds the tarps covering the thing were in shreds and every part of it was covered with a layer of ultrafine soot an inch deep inside and out. Somebody is probably still trying to figure out why he keeps finding soot in the strangest places.

    Back on topic though ... dry stack generator exhausts are prone to problems of all sorts. As everyone knows, generator exhaust is nearly always cool, too cool for the most part. For every pound of fuel burned in the engine, nearly a pound of water is produced. In a long run up a dry stack the water vapor in the exhaust will condense and coat the pipe walls. That makes a wonderful surface for soot to collect until it reaches the point where gas flow or vibration causes a sheet of it to break off and land on Mrs. Owner's suntan oiled belly. This is not part of the yacht life she expected and some poor engineer is in for an earful.

    I am glad you added external cleaning and filtering. Even a Tier IV 500kW generator will discharge more than 1/2 a pound (240gm) of particulates each day and much of that is going to collect in the piping long enough to make an impression the Mrs. won't soon forget.

    If drystacks really were, life would be much better but they are not dry, they don't get hot enough and stay hot long enough to stop acting like little hydrocarbon condensers where carbon, hydrated hydrocarbons, sulphates, and vapor phase aromatics have a reunion before leaving for more sunny locations or sharing Mrs. Owner's beach towel.
  2. HTMO9

    HTMO9 Senior Member

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    Dry exhaust stacks

    Marmot, I am 100 % with you on your chemical analysis of the combustion process of diesel engines and their exhaust products. On small diesel gensets, especially the variable speed / inverter type and DC gensets, the dry exhaust stack to the mast is not the best idea at all. I am talking about 300 / 500 KVA and above and with a DE setup in mind. In this field, the dry stack is much more feasable. But in my opinion, only with external aft treatment. The absolute aerosol free gaseous exhaust without any soot or micro dust will never happen.

    The problem is even bigger on our large commercial low speed 2-strokes and with the use of HFO. The external exhaust gas cleaning machinery is meanwhile taking more space in the engine room than the engine itself. The problem we have is finding and maintaining the optimum balance between highest possible EGT and keeping the NOx down according to the rules. But this amount of space is normally not available on a yacht.

    My point was mostly about minimizing soot on "her" towel by optimizing the exhaust stack design in order to make the "briquettes" hopefully come down to deck level far behind the yacht. And I know, this does not help with the boat on anker at calm winds.

    What do think is the best solution for a typical sized yacht with two big bangers (Cat 3516 or MTU 16V4000) on conventional shaft and wheel and 3 to 4 gensets with 350 to 400 KVA plus emergency genset as far as type and design of the exhaust system are concerned?
  3. Marmot

    Marmot Senior Member

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    I have been hoping someone would ask that question! :D

    Actually I think Jorge Lang is probably the best qualified to answer but I can provide very good advice on what to install just downstream of the turbocharger.

    Unfortunately I am fully occupied with a project for the next few hours and honestly can't take time to write but I will be happy to respond (while remaining within the bounds of forum rules) as soon as I can.
  4. YachtForums

    YachtForums Administrator

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    I think your expertise in this area warrants an exception. Besides, I'm linking this thread off an upcoming feature story on SeaClean.
  5. Marmot

    Marmot Senior Member

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    Thank you Carl, that is a rare honor and I will try to not abuse your confidence.

    Like I wrote earlier, Jorge Lang is the subject matter expert on main engine exhausts for that size of high speed diesels.

    As far as the generator exhausts are concerned, my area of expertise covers causes and solutions for excessive emissions but for the system beyond the emissions control components, I defer to Jorge and his firm.

    Having spent most of my working life manipulating the conversion of the energy in liquid hydrocarbons to rotational work via reciprocating and turbine internal and external combustion engines, I take a rather nuanced view of the process and its side effects. Since my role in the process was to make sure the guy who paid for the fuel got the greatest return for each BTU it could produce, tweaking the process was part of the job. One important indicator of success was the condition of the exhaust, its temperature, pressure, oxygen content, and visible emissions.

    For the most part, once the limits of tweaking were reached and exhaust conditions were as good as they could get for the load and hardware conditions, that was pretty much the end of story. But, after moving over to the yacht world where little if any tweaking was done, or even possible, by the engineers onboard, I saw that exhaust emissions were probably the most important factor as long as the wheels turned and the lights were on. Soot stains on the paint, oil sheens on the water, and foul smelling diesel fumes rose to the top of the things to worry about list.

    To save a lot of typing and as much as possible avoid boring members to death, an article published in Dockwalk Magazine in October of 2011 provides a fairly good overview of the what and why of the problem and the application of the "best available technology" at that time. Yacht engines have passed a lot of gas since then and the best available has become a lot better. Look for an update in DW in September.

    To cut to the chase, the best available technology today for generator emissions management that meets current and upcoming regulations for yachts with the generator sizes between about 65 and 500kW is a continuously regenerating diesel particulate filter with a catalyst that will withstand fuel sulfur content up to the international limit of 1000ppm for use within an Emissions Control Area (ECA) where most yachts operate.

    Starting in 2011, many yachts installed passive DPFs that engineers believed would regenerate (burn off the soot) at exhaust temperatures as low as 250*C. Such a low regeneration ignition temperature can only be obtained by the use of precious metal catalysts such as Platinum, Rhodium, and Palladium. The problem with precious metals is they are "poisoned" by the sulfur in diesel fuel. As long as the yacht operates in an area where fuel sulfur is limited to <15ppm (ULSD) all is well. But, if the yacht loads fuel in a port where commercial shipping is the largest consumer and the engineer does not demand ULSD, marine diesel fuel might contain more than a thousand times the sulfur needed to kill the catalyst. Additionally, high sulfur levels multiply the weight of particulate emissions produced during combustion.

    Few yacht generators consistently produce exhaust temperature high enough for long enough to assure passive filter regeneration and frequent filter cleaning is required. The best solution for yachts that have a passive (low temperature) filter already installed is to retrofit a modular heater with temperature control upstream of the filter. This will work very well until sulfur kills the catalyst then the filter should be replaced with a sulfur tolerant element.

    (caution - crass commercial message follows)

    I designed a generator exhaust treatment system that addresses all of the issues described above. I manufacture the electrical side and supply the catalyzed filters and have a licensing agreement with DeAngelo Marine Exhaust in Fort Lauderdale to fabricate and install complete SeaClean systems as well as modular retrofit solutions.

    The SeaClean system has been spectacularly successful since it was first introduced in 2012 as a retrofit solution. Since then and since discovering the reasons for failure of systems from other manufacturers, we have taken the approach of designing each installation as a "bespoke" or custom package with the specific requirements of the yacht and its type of operation driving the design process.

    If anyone is still awake and reading and has a question or comment I will be happy to respond to PMs.
  6. HTMO9

    HTMO9 Senior Member

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    Exhaust gas treatment

    Thank you very much Marmot, found the 2011 article and the associated websites. Will spread some tasks next week.
  7. Marmot

    Marmot Senior Member

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    I defer to the experts at SWRI: http://www.natbiogroup.com/docs/education/lubricity additive study results.pdf

    17)Marvel Mystery Oil
    Gas, oil and Diesel fuel additive (NOT ULSD compliant, may damage 2007 and
    newer systems)
    HFRR 678, 42 microns worse than baseline fuel.
    320:1 ratio
    10.4 oz/tank
    $3.22/tank

    18)ValvTect Diesel Guard Heavy Duty/Marine Diesel Fuel Additive
    Multi-purpose
    Cetane improver, emulsifier, alcohol free
    HFRR 696, 60 microns worse than baseline fuel
    1000:1 ratio
    3.32 oz/tank
    $2.38/tank
  8. olderboater

    olderboater Senior Member

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    Thanks. I was referring to their basic fuel but guessing there is a similarity between the additives in their fuel and their Diesel Guard.

    I guess it's also much like all fuel changes that the newer engines are all designed for it and the older engines might sometimes struggle a bit. Much like when lead was eliminated in gas. I've never used any fuel additives but I have used Valvtect Diesel Fuel on a few occasions.

    Much like the exhausts. I know nothing about the science. I do know if the boat is covered with soot, however.
  9. Capt Bill11

    Capt Bill11 Senior Member

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    I noticed you have a data logger with your system. Have you thought of increasing the number of data points it logs to cover other things like engine functions and electrical loads, etc.?
  10. Marmot

    Marmot Senior Member

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    Yes.

    Most of the installations we are doing now are on engines with electronic controls that incorporate some degree of performance datalogging anyway so our doing so would be redundant and add to the system cost as well as "intrude" on the existing engine databus. I would prefer to keep our system at arms length from the engine and power management system in order to eliminate any potential conflicts with those systems.

    Though, if we can join the PMS conversation it would allow us to incorporate some control features that are not possible with a stand alone (or maybe better described as stand-off) system that is comparitively dumb but very dependable.

    Logging of generator output is simple and can be added to an existing SeaClean at small additional cost to the owner but that information is probably already available to him elsewhere. It is a good datapoint for us to fine tune the control system and we are working on adding scope to the range of data logged and possibly incorporate some remote access features.

    We are building a generator test cell that will allow us to develop and test those features in a controlled environment. It should be online in a couple of months.
  11. Capt J

    Capt J Senior Member

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    We didn't have a noise issue on one Megayacht I worked on with dry exhaust. However, cleaning the soot off of that level was a royal pain. It seemed like it would just adhere itself to everything like epoxy.
  12. karo1776

    karo1776 Senior Member

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    Way too complicated...

    Its been over 50 years ago but my Scottish Grandfather, the retired Merchant Master, had this all figured out. In the Scot way... cheap and simple... to fix up a "buggered gob... "

    His boat, about the size of Sultana, had the generator soot problem. But there was a short maybe 40mm or a little less piece of pretty heavy pipe that stuck out of the hull for the generator exhaust, right about waterline, I guess it stuck out maybe 40mm in diameter or a little less.

    The fix was the old fashioned flexible corrugated radiator hose with a couple hose clamps. About a 1/3 of a meter long. I remember changing it one time for him. Solved the problem... and he paid no never mind to the thing underway... I do remember it flopping around a bit. Being a kid I thought it was the way things were done.

    Problem Solved... cost in 1959 all of "two bob bit." End of Story... !
  13. Marmot

    Marmot Senior Member

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    Yeah, and on steamboats we just turned 90 degrees to the wind and blew tubes.
  14. karo1776

    karo1776 Senior Member

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    Yes... he actually started his career on coal fired steam ship as officer of the deck... !

    When I was in the USN I remember visiting him on leave once... and one of his old buddies (one I suppose of a an uncountable number) was visiting to... talking about his days in the British Navy on a Destroyer... or something... after I mentioned I had been assigned on a Destroyer Escort for a couple months for a summer training cruise. The old boy piped right up about his WW1 (one not two) days on the coal fired destroyer escort or whatever it was... but they got sunk... and he was one of the few survivors... Of course, "Ed" my grandfather got to rubbing it in that in two wars "his ship" never took a hit... but many did.

    Sadly he died long time ago. As my grandmother said... he drunk his guts out by time he was thirty... and had too many women and sea stories to tell... !

    But that is more grizzled gormless faff for another time... late and me duvet is calling my name!
    Last edited: Aug 23, 2014
  15. Capt J

    Capt J Senior Member

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    But if there is no soot on the hull from the generator, what does a deckhand have to do when sitting on anchor? I've found that having the generator exhaust most underwater helps considerably as well. I also have seen where the generator exhausts into one of the main exhausts further upstream of the exit and that helps a lot.
  16. HTMO9

    HTMO9 Senior Member

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    A well known Dutch (sail) boat yard advertises their custom designed exhaust gas treatment system with the attribute, it will pass the the white handkerchief test even after years :D.

    At my sailboat, the outlets are under the stern overhang and even with a dark blue hull, regular cleaning has still to be done. But as a true blow boater, the use of the main engine is reduced to the minimum possible anyhow. But for docking under sail in Palma, one would need a sailboat like Maltese Falcon. It is really amazing, what can be done with this type of rig.
  17. Capt Bill11

    Capt Bill11 Senior Member

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    Yes I was thinking of just more data point logging and not much if any controlling. Logging say load data might make for interesting reading to see how your vessel is really using it's A/C power and when.
  18. Marmot

    Marmot Senior Member

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    Yes, that is a good idea.

    Most larger boats already have trend monitoring features on their power management systems but that may not be available on smaller boats in an easily accessible form.