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Challenges

  • In most industrial or commercial heating processes, a large amount of the heat energy that is produced through fuel combustion is underutilized and wasted in the exhaust gas streams. For boilers and dryers, the typical fuel utilization efficiency is 80% (plus or minus 5%).

  • Wasting 20% of the fuel that is fired is inefficient and extremely costly. Very large quantities of this unused energy are recoverable and reusable.

PROPOSAL
  • TEMCombustion proposed to add economizers to the steam boiler water feed to increase energy recovery rate.

  • Economizer can reduce the fuel consumption of the boiler by lowering the running capacity of the boiler itself & increase the efficiency. 

An economizer captures heat from the flue gas that would typically go to waste, and utilizes it to preheat the feedwater. By doing this, an economizer is able to increase thermal efficiency by decreasing the energy required to heat the water to steam. This will typically result in a reduction of 1% in fuel cost per 10 degrees rise in feedwater temperature.

 

The economizers’ simple technology and static parts provide longevity and low maintenance, and they are available in multiple designs and configurations. Conventional economizers are cylindrical or rectangular and come in a range of sizes for both firetube and watertube boilers.

BOILER EFFICIENCY COMPARISON
Boiler with Condensing Economizer
92% to 95%
27°C to 66°C
Boiler with Standard Economizer
84% to 86%
121°C to 149°C
Boiler
78% to 83%
177°C to 179°C
Combustion Efficiency at 4% Excess Oxygen
Stack Gas Temperature

The most common are non-condensing economizers. They are heat exchanger coils‚ usually finned‚ that are located in the flue gas ducting at the exit of the boiler. Typically, a non-condensing economizer will raise the overall efficiency by 2% to 4%.

They are designed and operate to maintain the flue gas temperature above the flue gas condensing temperature to prevent corrosion of the flue gas ducting. This is particularly important for fuels containing sulphur‚ as sulphurous compounds will form in the flue gas that will both raise the overall flue gas dewpoint and when condensation occurs will lead to the formation of sulphuric acid‚ which is highly corrosive.

Boiler feed water is pumped through the heat exchanger tubes, where it absorbs heat from the hot flue gas before being pumped into the boiler.

Unical Economizers copy.jpg
OUTCOME
  • Stack gas temperature lowered from 249°C to 157°C at full-fire conditions

  • Water temp in Economizer increased from 108°C to 135°C

  • 74°C differential translates to fuel savings of 674,123 Btu/hr at full fire

  • 4% increase in boiler efficiency

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