Steam Economizer

LKE

Total enthalpy recovery exchanger is what I call my latest project for raising the efficiency of my new SGO-5 steamer.It appears that the condesate is returning at somewhere around 95 degrees which if raised to 210 degrees would not quite use up the energy which is being lost up the chimney in sensible and latent heat. At this point my design calls for lowering the condensate temperature even further by preheating the combustion air so that a theoretical 96% efficiency could be acheived.In that configuration it would consist of a conventional coil and two direct contact exchangers plus a countercurrent coaxial coil with appropiate circulators.TEREX will be exhausted by a direct venter through the wall so ultra low final temperatures can be tolerated.
It would be of great interest to know if there is a market potential for such an effiency booster, and at what price point.Mod-con boilers seem to have a very high price point but yet are very marketable. What would the market expect in terms of return on investment?

adayton_2

Steam Economizers

suggested in the steam/hydronics "efficiency" thread sound great but I only found fairly large versions/models for commercial or huge Industrial steam plants. Are there any around for typical residential size boilers? Seems i recall one or two being somewhat tepidly available about 20 years ago but interest seemed to wane.

PS: attached is a neat article re: economizers

Alfred

ttekushan_2

lack of small economizers

Hi there.

I'm the one who keeps bringing this up. Economizers are used in large scale applications where two conditions always seem to exist: 1) Combustion draft is forced via forced induction burners (so the economizer won't change fuel/air ratios by cooling flue gasses); 2) There's someplace to put all that heat. Usually this is circulated with continuous flow to a sizeable condensate receiver to preheat boiler feed water to maintain full rated output of the boiler. Lack of thermal stress is a bonus.

The cooler the exhaust temp an economizer can achieve, the greater its energy recovery. I assume there is a magic point at which flue gas condensation can occur where heat recovery really jumps. There is one in particular whose manufacturer escapes me for the moment where exhaust gasses are diverted right through a sort of water/media bath with exit temps around 60 degrees F. I remember it looked very large and expensive. Most get their greatest results where most of the sensible heat of the return water is pretty well depleted.

For natural draft residential boilers, some sort of resevoir in the condensate return should be there to collect recovered heat. This is easy. A simple tank of some sort in series with the return, close to the Hartford connection would suffice.

But here's the tricky part. You need something to force the gasses through the economizer, perhaps something like a small externally driven turbine, to maintain the proper draft through the combustion chamber. This would have to be set up for each particular application. Today's electronic controls should easily be able to fine tune the turbine or blower speed.

And then you would have to line the chimney due to the lower exit temps.

The only way this is practical is that the controls are feedback controlled (i.e, basic combustion analysis) and are made in some large enough quantities to bring the price down to a level where the payback period is substantially shorter than the life expectancy of the basic equipment.

The manufacturers out there would have a much better handle on this. In the past, I could see it wouldn't sell enough to justify development cost. Today? Different story methinks. I think maybe the steam boiler manufacturers may have thought of this in the past. Maybe its time for them to reconsider.

-Terry

adayton_2

Economizer efficacy

may be somewhat limited with the shift toward gas fired mod-con style boilers. These already carry the benefit of very low (condensing) temperature flue gas. This leaves oil fired steam and hot water (baseboard) boilers. I should think this would still be a large enough market for the next ten to 20 years years as to be viable for an existing manufacturer and the consumer public to benefit. As for the exonomizer functional application in an residential (or small commercial) setting, since these small systems would not benefit from feed water preheating, I was thinking that it could be used to preheat DHW with perhaps a mid sized storage tank ( and xchanger as needed) . This would be a viable use for the reclaimed stack heat and effectively extend the apparent size/capacity of the DHW system. the primary DHW boiler could then be a relatively small on-demand type unit.

Alfred

adayton_2

Pay Back period

should be 3 to 5 years depending on life span and solid quality/durability of your economizer hardware solution. Expected lifetime of the unit should be 2 to 3 times that so the consumer gets gravy payback percievably for several years past initial pay back period. Maintenance recurring costs is also very important. One of the problems I found with oil fired steamers/water boilers is soot no matter how slight needs periodic removal from the flue stack chamber of the economizer. another issue is the potential requirement for a stack fan to "pull" flue gasses up the chimney because they become so cold that there no longer is a chimney effect.

food for thought.

Alfred