Recovery of exhaust gas heat

webskier

Has anybody heard of a system whereby steam boiler exhaust heat is recovered by condensation? There must be 1000's of applications where conversion to hot water is impractical .



Regards,



Mark

Polycarp

I've wondered the same thing

As far as I know, the manufacturers haven't overcome the high return water temperature problem in order to make condensing technology work for steam boilers.  But instead of pre-heating the return water, I could see a steam boiler pre-heating domestic hot water with condensing technology.  It would turn the boiler into a combi of sorts (and there aren't good aggregate efficiency ratings for combis as far as I know).  But even if the ratings wouldn't recognized it right away, it sure would save energy.

Steamhead

It's been done in other countries

Hoval and Gasmaster are two companies that have marketed higher-efficiency steamers, but as usual, American boiler manufacturers are lagging behind.



And if you'd seen the disastrous results of attempts to convert steam systems to hot-water that I have, you'd steer clear of them. We don't do these conversions, and won't work on systems that others have converted. Too much liability.

jumper

if you have space &

If you have space in your boiler room & can use low temperature heat, then a waste heat recuperator can save some money. For example you can melt snow. You also have to handle cold exhaust & make sure draft is correct. If gas prices decline while electric increases you may be sorry. It's also difficult to justify an investment that doesn't even cover your cell phone bill.

The Steam Whisperer (Formerly Boilerpro)

Yes, it's done.....

there are a number of manufacturer's marketing heat recovery units.  These units take the heat of the exhaust and preheat the intake air.  The Super Boiler here in the US uses this technology for high pressure steam .  The most effective are those using a heat transfer membrane, I believe. 

ChrisJ

vent heat

While its not quite the same I had considered installing vents around the B-vent I had installed last fall.  It seemed like having a vent opening to the "tunnel" it goes up on the first floor and than a vent near the ceiling on the second floor would cause a draft to pull heat from it.  Even though it wouldn't produce too much output I figured every little bit helps, right?



Wasn't so sure how well it would work especially with the B-vent being double wall I decided not too. I also decided I wanted to block any air flow in between floors even though it passed inspection without it.  Oddly enough all the inspector wanted to see where the steel spacers which center the vent in the space and maintain the 1 inch clearence. 

arches

maybe something like this?

Cain Energy Manager

Combustion Capacity: 200,000 - 6,400,000 BTU/hr input

Entering Gas Temps.: 350 - 700°F

Heat Sink Types: Boiler feedwater, makeup water, hot water return, hot water storage tank, condensate tank, process water, potable water



http://www.cainind.com/media/PDF/page_boiler_EM.pdf

I'm not sure if that really means 200k BTU input or for use on a 200k BTU boiler. Big difference! If the former, would only be suitable for boilers >1mn BTU (assuming 80% efficiency).

Henry

Stack economisers

There are plenty of companies that provide various stack economisers in North America. There are some that provide a S/S heat exchanger to preheat and heat water for DHW or Preheating glycol for FA systems. Then there are the high end units made by Sofame, Quickwater and several others that recoup 99% of energy via direct contact technologie. I have personaly worked on and developed some of the Sofame technology. We had run up ultra-low nox and efficiencies up 99%!