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U.S. Department of Energy
Washington, DC. USA

Operating your boiler with an optimum amount of excess air will minimize heat loss up the stack and improve combustion efficiency. Combustion efficiency is a measure of how effectively the heat content of a fuel is transferred into usable heat. The stack temperature and flue gas Oxygen (or Carbon Dioxide) concentrations are primary indicators of combustion efficiency.

Natural Resources and Office of Energy Efficiency
Typically, reducing O2 in the flue gas by 1 percent- for example, from 5 percent to 4 percent- increases boiler efficiency by about 2.5 percent.

Controlling excess air is the most important tool for managing the energy efficiency and atmospheric emissions of a boiler system.

As graph shows, the effect of air temperature on excess air in the flue gas can be dramatic.


Principle of Combustion Air Trim (CAT) Control System:

In today's scenario of higher fuel cost, no one can afford the luxury of wasting any kind of fuel. In Boilers, Hot Air Generators, Thermic Fluid Heaters etc. maximum wastage of fuel is in dry flue gases so the optimization in combustion of all types of fuel is very important.

Dharam International offers CAT Control System which uses a special rugged Zirconium Oxide Sensor (ZrO2). This Sensors has faster speed of response and is ideal for online Oxygen measurement in combustion process. It has greater measuring accuracy, durability and longer working life.

The system consist of the in-situ Oxygen measuring probe which detects the partial pressure directly in the flue gas ducting. The signal is sent to the intelligent control circuit which regulates the primary and secondary air by using Variable Frequency Drive (VFD).

The maximum optimization of ID/FD draft fans by using CAT Control System ensures perfect combustion of fuel which will reduce NOx and CO emissions to great extent. The fuel and electrical savings are also substantial.

Taken together, air/fuel cross-limiting, excess air regulation, oxygen trim and total heat control can provide excellent control and fuel efficiency for all types of combustion systems.

The complete system consist of Zirconium Oxide Sensor (ZrO2), Intelligent Control Circuit, Variable Frequency Drive, Stack Temperature Indicator, Controller and alarms.