Direct Contact Inc. (DCI) Heat Recovery Systems bring the heated exhaust/vent gas into direct contact with the contact liquid. This differs significantly from other systems that employ coils or plates to provide the heat transfer surface and keep the streams separated (indirect).

The heat transfer coefficient of DCI’s unique direct contact method (800-1000 BTU/hr-ft2-°F) is many times larger than that of the typical indirect method (approximately 10 BTU/hr-ft2-°F), providing a much more efficient method of recovering heat and allowing for a smaller unit, which can do more.

The DCI system also efficiently drops the temperature of the gas stream to below it’s condensation temperature, or Dew Point, (view graph) forcing the condensation of water vapor contained in the waste stream. This capability can generate an additional utility savings by recovering water vapor that would otherwise be lost; this has the potential to significantly lower the fresh/makeup water demands of the facility.

Condensing Economizers (Direct)

The Direct Contact Condensing Economizer contacts water with flue gas.

• Water adiabatically cools the flue gas (converting the sensible heat to latent heat)
• Water evaporates to bring the flue gas to its wet bulb temperature
• Cools the flue gas further, to below its dew point temperature and condenses water vapor
• Overall heat transfer coefficient ranges between 800-1000 BTU /hr-ft2-oF

• Directly as makeup water to the boiler or
• Indirectly to heat process fluids with heat exchangers

Condensing Economizers (Indirect)

The Indirect Contact Condensing Economizeris similar to an Economizer, transferring the captured heat through an extended surface coil.

Such a unit will:

• Lower gas temperature to below its dew point temperature
• Have a low overall heat transfer coefficient (10 BTU /hr-ft

• High first costs
• Relatively high pressure drops
• Relatively high operating costs