moist air burning: explanations and performances

Steam pump and wet combustion: explanations and performance
By Rémi Guillet.

Steam pump

Having started in the early 1970 years of research and development on condensing furnaces (combustion products) in order to limit air flue gas condensation of fuel that was new at the time, gas natural, correspondingly increase the combustion efficiency with this type of heat generator, the energy crisis following the oil shock of 1973 had the opportunity to pursue this route to extend their scope application (in truth very small!).

Indeed, the effective condensation of the water produced during combustion in a heat generator assumes that the lowest temperature of the "cold source", or the temperature of the water entering there in the case of a boiler, is lower than the dew point temperature of the combustion gases produced (approximately 60 ° C in the case of natural gas combustion products).

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Can even be observed that the water vapor is not pure, the condensation is not isothermal and significant condensation involves a rejection of the combustion products at least 15 ° C below said dew point temperature: a constraint greatly limiting the application of condensing generators field.

So, how to expand the scope of knowledge that the water temperature in a heating loop by returning hot water boiler reaches 70 ° C? pressurization of the combustion products, separating the water vapor from other gases? Many solutions proposed by engineers and other academics involved in thermal research after the oil shock of 1973.

In my case, the proposed solution has been to increase the tension of the water vapor in the combustion products through the furnace, conducting an exchange (ultimate) enthalpy between the outgoing gases ( saturated with water vapor at the end of a first sequence of condensation in the condensing furnace or more often in the heat recovery / condenser associated with a traditional generator) and combustion air, said exchange relating to both the residual sensible heat recycled by preheating the incoming air, and the latent heat of residual condensation after an ultimate condensation of the water vapor from the outgoing gas side and recycled by evaporation of this water in the incoming air as well moistened.

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From a quantitative point of view and at this final stage of exchange, everything happens in the steam pump as if there were pumping water vapor contained in the outgoing gas recovery / condenser recycling of this vapor in the incoming air.

Correspondingly, at the end of this exchange, the sensible and latent heat released to the chimney becoming almost zero, the combustion efficiency reached its maximum or 100% (based on the gross calorific value of the fuel)

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