Condensing Economizers

Conventional economizers typically recover heat from stack gases to  preheat boiler feedwater. The temperature of the flue gas is reduced to within 50 – 75 degrees F above the incoming boiler feedwater temperature. This is well above the dewpoint of water vapor in the flue gas and consequently only the sensible heat component of the gas is recovered.

When an alternate COLD heat sink exists , such as process water or a high percentage of makeup water or air makeup units, the gas temperature can be lowered below the dew point of water vapor in the gas. For a boiler firing natural gas with 15% excess air, the dewpoint is approximately135 F

As the temperature drops below the dewpoint , water vapor begins to condense and the latent heat component, is recovered. For every cubic foot of natural gas burned, 0.10 lbs water vapor are formed. The actual amount of vapor condensed is dependent on the final gas temperature, with a resultant recovery rate of approximately 1000 Btu/ lb of condensate.

We utilize the "indirect contact" technology where the liquid is circulated inside  finned tubes and does not have "direct contact" with the combustion gases.Consequently the temperature of the liquid is not limited by the dew point of the exhaust gas, and can be heated to approximately 200 F. This configuration also eliminates contamination of the liquid by combustion products and consequently it can be utilized directly in process applications. 

Depending on the conditions, the additional sensible heat recovered plus the latent heat component combine with resultant boiler efficiencies up to 95%