Water coil round exhaust ... Worth the effort?

[Dyslexicbloke]

Hi folks,
I’v been a bit busy so not made much progress with the CHP but the genny is doing fine.

Anyway I just completed my new purpose built shed so her indoors will stop moaning about the thing being under the gazebo and I might finally get to pipe it up and reclaim some heat .

That brings me to the question.
My engine has a little pot exhaust, tube in tube out, not a pepper pot but only about 150mm long by 120mm diameter.

I plan to add a big expansion box when I route the exhaust out of the enclosure but will leave the pot in as it seems do a reasonable job.

Since the pot seems to heat up very quickly I was wondering about encasing it in a copper coil and hooking it into the water system ….
I don’t want to over cool the exhaust anyway, gotta watch those dew points

I would appreciate any thoughts you have ….
Subtext here is that I cant afford a ‘proper heat exchanger right now ….
The shed, pipe-work and wiring have used my entire budget for a while and I expect I will still end up dipping into the housekeeping…. More grief !!

I’l update the blog with a couple of pics when I get the engine in place

Thanks folks, looking forward to your insights.

Al

[longstroke]

Hi Al,

Yes is the short answer.

Better if you can have a stainless exhaust system and not worry about dew points.
The rule of thirds is a good approximation of energy produced by a diesel generator - 1/3 electrical output, 1/3 heat removed by the cooling system and the last 1/3 heat lost in the exhaust gasses.

So it will be easy to reclaim some of the waste exhaust heat cheaply, but as with a lot of things to do it to a higher level will cost more.

Hope this is helpful!

[jotec]

I tried copper tube but found it hard to keep it in full contact with the tube. I have 2 of these on the Lister and they work really well. 1 would probably not cost much more than the copper to make a wound HE.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=230551683325&ssPageName=STRK:MEWAX:IT#ht_500wt_714

Dick

[Dyslexicbloke]

Both helpful thanks ...
Dick, I had wondered about the issue of keeping it in contact, I tried doing it with some small tube on the old petrol genny and it didnt work at all but I think I lerned enough from that to give it a try and I have some maluable copper lying around.

That said the Stainless units would clearly be a better job ...

What is the bore of those flanges on the unit you have suggested? You have mentioned them before and they do look like a reasonably priced option.
The problem will be making some form of adaptor for them.
I dont have any way to machine heavy stuff or weld stainless so I would have to draw something up and then farm it out.

Thanks
Al

[jotec]

I can not remember the exact size of bore but I think it is about 30mm dia. I made a sheet box from mig welded steel to bolt on each end. I used 2 of the HEs on the Lister and they have done over 2500 hours. The water input is about 55c output is about 70c, input exhaust temp 210 output about 110. Have a look at the bottom of the blog if you want to see how I did it. http://www.dpks.co.uk/CHP/main.htm
If I was doing for a single HE fitting I would use 3.5 mm plate welded onto a piece of tube on each end. Stainless would be better than mild but I hope it is going to last a reasonable time. BTW you can weld stainless with a mig.

HTH
Dick

[Ivan]

Even maleable copper will become brittle after a relatively short time due to engine vibration - so make sure you've got flexible joints. You won't get enough surface area in contact with the exhaust to extract much heat.

[renewablejohn]

Simple heat exchanger I have successfully used in the past constructed of 15mm and 22mm copper tube plus 2x 22mm "T" compression joints and 2x 22mm to 15mm reduction olives.  Make "C" shape of 22mm tube using the T compression joints then file lip off reduction olives and pass 15mm tube through long side of "C" tighten up reduction olives. Job done. Connect 15mm pipe to exhaust, 22mm pipe to water and insulate. If exhust capacity greater than 15mm then use multiple pipes. 

[knighty]

for my (eventual) chp system, my rough plan is a length of 4inch pipe, with a few half inch pipes running up inside it... all welded in... a bit like the one frotter made ?


not sure how many pipes to use on the inside yet... I'll aim to have the same surface area as the exhaust... or maybe a little less to keep the speed of the exhaust gas up high and hopefully combat coaking etc...


I'm tempted to look into running thermal oil through the heat exchanger instead of water.... that way I could keep the exhaust temperature up higher and avoid a lot of the tar/coak/acid problems... but I'll have to have a think and figure out how much heat I'd be able to extract with hotter oil vs cooler water...

[jotec]

Knighty How is the progress on the CHP?
Dick

[Dyslexicbloke]

I think I'v decided not to mess about ......
I am going with one of the units Dick suggested even if it has to go down the priority list a bit due to cost ....
It not easy doing this stuff on a verry limmited budget.

Anyway I figure that some heat is better than none at all so I will concentrate on the water system first and add in the exhaust exchanger later when I can.

Thanks All, your comments were usefull in helping me come to a decsion after some more research and a great deal of thought.

Al

[knighty]

Knighty How is the progress on the CHP?
Dick

slow !

I need to build my new freezer, so I can move all the freezer parts out of the way of where I want the CHP system to go !

it's starting to move along now tho... had a wall built a couple of weeks ago, and 4 ton of steel girders should be coming next week... once I get those assembled I can call in the fridge engineers to do there stuff and they should move pretty quick !

it's hard to get anything done because we're so busy, we can't slow down production at all because we'll run out of stock

on the up side... I've had plenty of time to think it through.... from every possible angle... right now I'm thinking big thermal store, with a coil running from top to bottom for hot water.... it would be great to have a coil for the steam cleaner too... but it would have to be pressurised and I'm not sure how I could do it to run at 1000psi (then i wouldn't need to put diesel into the steam cleaner to have it hot -the pumps in them die if the incoming water is hot)

[jotec]

My advice is not to mess with high pressure steam. Any slight mistake is potentially fatal. (having said that I would like to get a steam engine running at some time in the future to generate electric -I know it is in efficient but it would be nice!)
Dick

[knighty]

I'll only be running up to 90'C

I don't know much about steam... but my father does.... the old steam boiler which used to run the boilers in the factory weighed 12 ton (empty)

a coil of pipe inside the thermal store, fed from the pressure washer and connected to a hose/lance should be ok ?

other option would be a heat exchanger... but ones rated for 1000psi are ££££.... at that price might as well stick to punting diesel in the steam cleaner... (about £20 a week)


I'll keep thinking about it.... like you say... I don't really want to mess with steam!