Marine Gen Set-Heat recovery

[RJ]

A neighbor approached me last week wondering if I was interested in a older diesel Kohler Marine genset that he was no longer interested in. It does need some TLC but nothing I can't handle. Normally I never think twice about marine sets usually the word marine = $$$, however having a brother that just recently lost power for nearly two weeks in an ice storm. Then I remembered being in New England during the ice storm 10 years ago and loosing power for nearly a month. These extended run times got the old noggin thinking about the law of thirds and how much energy is being tossed out the door.

Now a marine setup already has the heat exchanger and water cooled exhaust manifold all in place. It wouldn't be very hard to plumb this into an existing hot water and heat system. I was doing some reading about heat recovery at this link:

http://listerengine.com/smf/index.php?topic=2705.0

Soot buildup seems to be the issue as you cool the exhaust from the engine. Not knowing very much about marine sets and how this is handled in any marine application that uses water cooled whether it be propulsion or making electricity. I was hoping someone might be able to shed some light on this for me before I jump into something that might be doomed from the get-go. Pulling the heat from a water cooled engine is pretty simple enough it's the exhaust portion that poses the problems.

-RJ

[RJ]

Thanks for the reply.

I have seen several exhaust manifolds for marine use. From that used on a ski boat to pretty large diesel units. I don't ever recall anyway to clean them. I know Kohler also has some industrial duty sets that use water cooled manifolds:

http://www.kohlerpower.com/onlinecatalog/pdf/g5202.pdf

Have they developed a way to keep them clean and soot free?


As to your unit, it would appear that indeed the acid produced is removing some of the copper. Long term that might concern me as well. Do you have to load the 20/2 pretty well to get a good amount of heat or is the exhaust temp pretty steady regardless of load.

-RJ

[Quinnf]

Marine gensets of the type you describe are usually fresh water cooled through two coolant circuits.  Fresh water/coolant circulates through the block and head and usually through a water jacketed exhaust manifold (though sometimes the exhaust manifold is raw-water cooled).  The warmed water then passes through a water/water heat exhanger and dumps its heat to raw water supplied by a pump belted off the crankshaft.  Once the raw water passes through the heat exchanger, it then proceeds to an exhaust elbow connected to the end of the exhaust manifold.  From that point on, the temperature of the exhaust is reduced to the point where flexible rubber steam hose can be used to route the exhaust through a muffler, and then overboard. 

Trouble comes in when you pass the exhaust gasses directly through a heat exchanger that is designed for liquids.  Any sulfur in the exhaust will combine with water vapor in the exhaust to form sulfuric acid which eats away at the copper in the bronze alloy, producing blue/greenish copper sulfate.  Marine heat exchangers are usually protected from galvanic corrosion by the use of a sacrificial zinc electrode attached somewhere inside the raw water side fo the heat exchanger.  Unfortunately, however, little or no protection is afforded the heat exchanger when passsing exhaust gas through it.

Cast iron is a better choice than bronze for your application.

Quinn

[Petersbpus]

Quinn is 100% accurate in his description of a marine system.
If you wish to convert the marine unit to stationary use,
remove the wet elbow and dry stack it, There will be either pipe threads or a flange mount
remove the heat exchanger and raw water pump from the cooling system and add a radiator. The engine will have it's own circulation pump already there.
Because of the jacketed\cooled exhaust manifold the heat load is greater on the cooling system, so size the radiator larger rather than smaller and monitor it.
you may need a change of thermostat because it would be set up to be cooled (Exchanged) by raw water at 70 to 90 degrees F not air.

As far as soot in the exhaust manifold, it is full size inside just like a dry manifold and I have never heard of this as an issue, It must just build up and flake off into the exhaust stream.
condensation in that area would also not come into play because it is transferring heat to 165+ degree coolant not ambient air or water.

For the acid problems with tube exhaust heat exchangers, how bout some baking soda\water solution injection\addition now and then just before the exchanger.??
Would that not flush the soot also??

If I am missing the point and you want to recover all the heat from the exhaust you could recirculate the "raw" water from a tank and recover additional heat from that exhaust water tank with yet another exchanger and pump.(closed loop into the house or shop for radiant heat,
BUT
As I pointed out before the mounted raw to coolant exchanger is sized to be supplied with water at less than 90 degrees F.
You would have to at least double the exchange surface (just a guess) Hook up another in parallel. to keep the engine cool.

Bob P.

[Stan]

Just don't go drinking green water, especially after you've been sniffing black exhaust!   
Stan

[tiger]

I once worked on a Kohler 20 kw marine unit, It was a joy. 1200rpm with a 4cylinder Herculies diesel and a 6 pole gen head. we installed it on a 65 ft ex army T boat of all steel construction. loaded up burned under 2 gal per hour.If your find is anything like the above, snap it up! It was very quiet, you could not hear it standing beside the boat on the dock!
tiger sends

[RJ]

Thank you all for the posts. I only wish the unit was a 6 pole 1200 rpm unit. It's a 1800 RPM screamer    I'm pretty sure it's a Kohler model 12.5 CCO. It does have a raw water pump and setup just like Quinn and Bob mentioned. It has a raw water pump that runs into a heat exchanger. The engine coolant is on a different loop. Since this setup has all the heat exchangers built in I thought it would make a great canidate for a heat recovery unit. I could plumb my furnace loop and boiler right into the raw water setup pretty easily. I would setup a electric radiator that would turn on and open a valve when there was no call for the heat in the house and depending on weather it's warm outside or cold have the setup either pushing the hot air out or pulling cool air into the garage/barn to warm it up.

My big concern not knowing a lot about these units is the soot and acid that I keep hearing people talk about. I still don't fully understand why this isn't a problem with these units.

[Petersbpus]

The only marine 1200 RPM Gensets I am aware of are much older GM sets, I know of two boats that have them, both are from the 80's. From what they have told me they are not replaceable today.
An 1800 rpm multi- cylinder unit is not very loud, certainly not a screamer.
Silence the exhaust and the  intake
Water muffled exhaust is very quite,
If the unit has the factory intake silencer, on small marine older units it is normaly just that, a sliencer not a filter at all.


The last travel trailor I owned, had a gas water heater that consisted of about a 2" diameter U shaped pipe that ran into and back out of the tank. The flame simply blew thru this pipe, I know that pipe was aluminum so corrosion may be an issue, I don't think it would, with that short of a run and not over cooling the exhaust, not that much surface area
maybe better materials are available for bigger bucks, BUT
you could run your dry exhaust thru one of those or other gas water heater and use the heated water  ( or coolant) to circulate for space heating.
Just run a pipe tap into the end of the pipe and install a nipple. Welding would be better, just purchase  aluminum pipe couplers and have them welded into place.
I would bet someone on this forum has done this already.

 

[Petersbpus]

Here is a video of test run of my 11.5 Onan marine unit after refurbishment. It has been sold.


http://www.youtube.com/watch?v=zbssy25CfSw&NR=1