Many large-scale thermal water heating furnaces recover the heat from the flue gases by means of a condensing scrubber. In this type of system, the flue gases are saturated with moisture and the partially-cooled, wet flue gas is then passed through a condensing scrubber. A condensing scrubber is also technically a heat-exchanger, of the direct-contact type. There are a number of advantages of this type of system compared with more conventional plate or tube condensors:
The heat exchanger is also a very good flue gas cleaner. It is very good at removing most pollutant gases. It is near perfect at rmoving particles larger than about PM5. For particles less than PM1 or so, efficiency is not good for any system, but a condensing scrubber is only surpassed by bag houses or electrostatic precipitators.
The condensing scrubber heat exchanger is cheaper than non-contact heat exchangers.
The condensing heat exchanger captures the latent heat of condensation, just as a condensing gas water heater does. The resulting flue gases are cool yet creosote build-up is not a problem, as the creosote has been removed at the scrubber.
There are of course disadvantages. The corrosion potential is horrendous if suitable material is not used. Since the nasties are all collected in the cooling water, the water may require treatment before disposal.
Although this type of system appears to be gaining popularity for large-scale systems, over several decades at least, I have never heard of it being used for domestic systems. I wonder why. It seems as if many of the advantages claimed for large-scale systems could well apply to very small scale systems as well. Simplicity of construction would appear to be just as relevant on the small scale. A much cleaner flue output is also not to be sneezed at.
I found one paper in which a very simple bubbler type wet scrubber was used as the condensor-scrubber for a 17kw diesel burner(1). I can't see any reason why this would not work for a wood gasifier, but that may well be because I just don't know enough.
Anyone got any comments or thoughts?
(1) Design of scrubbers for condensing boilers, F Haase and H Koehne, Progress in Energy and Combustion Science Vol 25 (1999), pp305-337
The heat exchanger is also a very good flue gas cleaner. It is very good at removing most pollutant gases. It is near perfect at rmoving particles larger than about PM5. For particles less than PM1 or so, efficiency is not good for any system, but a condensing scrubber is only surpassed by bag houses or electrostatic precipitators.
The condensing scrubber heat exchanger is cheaper than non-contact heat exchangers.
The condensing heat exchanger captures the latent heat of condensation, just as a condensing gas water heater does. The resulting flue gases are cool yet creosote build-up is not a problem, as the creosote has been removed at the scrubber.
There are of course disadvantages. The corrosion potential is horrendous if suitable material is not used. Since the nasties are all collected in the cooling water, the water may require treatment before disposal.
Although this type of system appears to be gaining popularity for large-scale systems, over several decades at least, I have never heard of it being used for domestic systems. I wonder why. It seems as if many of the advantages claimed for large-scale systems could well apply to very small scale systems as well. Simplicity of construction would appear to be just as relevant on the small scale. A much cleaner flue output is also not to be sneezed at.
I found one paper in which a very simple bubbler type wet scrubber was used as the condensor-scrubber for a 17kw diesel burner(1). I can't see any reason why this would not work for a wood gasifier, but that may well be because I just don't know enough.
Anyone got any comments or thoughts?
(1) Design of scrubbers for condensing boilers, F Haase and H Koehne, Progress in Energy and Combustion Science Vol 25 (1999), pp305-337