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If boiler makeup rate is less than 35 percent, an optional heat-sink component—an air heater—is recommended. This device
pumps a portion of heat from the TMC back to the boiler via
air, managing water temperatures in applications that return and reuse a major portion of condensate from their steam systems and, thus, do not supply sufficient cold makeup water for the TMC to reach maximum effectiveness.

The deaerator/makeup tank functions as both a holding tank and a conditioning vessel
for the boiler feedwater. Hot water from the low-pressure economizer is mixed with
recovered process condensate and conditioned by exposure to a small portion of process
steam from the boiler to drive out any residual dissolved oxygen. The deaerated hot
water then flows to the high-pressure feedwater pump, which sends it on through the
high-pressure economizer and finally to the boiler. A key energy-saving factor is the
reduced steam needed to maintain temperature in the deaerator because of heat added
in the TMC and low-pressure economizer.

Testing shows TMC technology can increase fuel-to-steam energy efficiency by up to 15 percent (from a baseline of 80 percent) and the capture of moisture in flue gas by up to 40 percent, with the water used in the boiler without the need for further treatment.

Information prepared by Curt Bermel and Dan Willems, Gas Technology Institute, and Steve Rendos, Cannon Boiler Works Inc. Photographs and diagrams courtesy of Cannon Boiler Works Inc.

For Design Solutions author guidelines, call Scott Arnold, executive editor, at 216-931-9980, or write to him at scott.arnold@penton.com.