Another Question about my Co-Gen system

[Dune]

So I more or less decided to make a simple pipe within a pipe heat exchanger for my diesel generator motor. The design would be 2'' copper pipe inside 3'' copper pipe, the 2'' pipe being the full ten feet, with threaded male adapters welded to each end to acomodate the transition from steel to copper and back again. The 2'' asembly would then be slid into a three inch pipe, with tees fitted at each end, and extend past the tees, meaning that the 3'' would be aproximately 8.5 feet long, before adding the tees. Where the 2'' passes through the tees, I would then weld 2" i.dx 3'' o.d. covers, which brings up my question.
The question is of the plumbing scheme of the engine itself. It seems that the most practical way, is to send the engine coolant through the exhaust exchanger, after it exits the engine, as oposed to a seperate circuit, which would also need a seperate pump. I need to figure this out before I can build the exhaust heat exchanger, to be able to size the three inch tees properly. Thankyou for any input.

 

[Gooserider]

I would be somewhat concerned about several issues...

1. Remember that you are doing the co-gen thing as a bonus, always keep in mind that your primary function is to cool the engine, and you should NEVER compromise the engine cooling to optimize the cogen output, as that risks harm to the engine....

2. Cooling the exhaust will obviously add heat to the coolant, I would be worried about the risk of overheating the coolant (and thus the engine) unless you are absolutely certain that the system you are heating will ALWAYS be able to sink the extra BTUS, in addition to adequately cooling the engine itself...

3. You will get optimal heat recovery from your exhaust cooler if you plumb it for a "counter flow" hookup (which means the input needs to be on the side farthest from the engine) and if your coolant input temperature is as low as possible...

Therefore I would think you'd be better off to have the second pump (can you run it off the engine somehow?) running just the exhaust coolant circuit... It might make sense to do a split manifold though so that you have a common heat exchanger on the output side, but two loops going to and from it...

Gooserider

 

[Dune]

Thanks Goose. I am definitely with you on the counterflow thing. I have a Modine heater I am putting in the garage as a btu dump. My primary heat exchanger (engine coolant/hydronic fluid) is huge, about four times what I need. This would all be great if I had massive water storage, I could probably run the engine every other or second day.

 

[pybyr]

What about doing a "Garn-like" exhaust HX-- big tank, with long pipes through it lengthwise, making several passes. Put flanges or unions on the "u-turns" you'd need on the ends, so that you could take them off and brush out the HX tubes.

 

[deerefanatic]

Here's a good idea...... What kind of motor is it? If it's a common motor like a 6bt cummins, get a marine manifold, as they are water cooled and seem to suck a LOT of heat out of the exhaust......

 

[Dune]

Here's a good idea...... What kind of motor is it? If it's a common motor like a 6bt cummins, get a marine manifold, as they are water cooled and seem to suck a LOT of heat out of the exhaust......

Yeah, I wish. It is a Continental Red Seal Diesel. Never seen one in a boat, and I've been doing marine engineering for over thirty years. I have built water cooled exhaust manifolds before, but I don't have the time to get that involved on this project. There is so much to do as is that I have to simplify it as much as possible.
Great idea though, thanks.