What “Efficiency Testing” Means in Boilers PDF Print E-mail
Written by D. R. Wulfinghoff   
Wednesday, 09 June 2010 09:13
Article Index
What “Efficiency Testing” Means in Boilers
How to Do a Combustion Efficiency Test
The Logic of Combustion Efficiency Tests
Assumptions of Combustion Efficiency Testing
Why the Oxygen Test is Better than the Carbon Dioxide Test
All Pages

What “Efficiency Testing” Means in Boilers

Efficiency is defined as the ratio of the useful output energy produced by a system to the raw energy input into the system. In principle, it is possible to test the overall efficiency of a boiler plant. You could do this by measuring the energy content of the steam or hot water that is exported by the boiler plant and the total quantity of energy that is input to the boiler plant, including fuel for the boilers and other energy for the auxiliary equipment.

In actual boiler plants, such a comprehensive test is impractical. Measuring steam or hot water energy with reasonable accuracy, say within one percent, is possible only under laboratory conditions. Field measurements of flow are vulnerable to error, even if they are done by expensive consultants. Measuring input energy is also subject to error. You would have to analyze the energy content of your fuels, make corrections for ambient conditions, and create very stable test conditions. This is not possible under realistic conditions.

Fortunately, you don’t need to measure the total efficiency of a boiler plant if your objective is to tune up the plant’s efficiency, rather than running a testing laboratory. You can use an easy procedure, called a “combustion efficiency” test, to measure the aspects of boiler efficiency that cause most losses in normal operation. The “combustion efficiency” test determines how completely the fuel is burned, and how effectively the heat of the combustion products is transferred to the steam or water.

The efficiency of the other boiler plant components, such as pumps, fans, and motors, tends to remain constant, so you don’t need to test their efficiency on a continuing basis.
Limitations of the Combustion Efficiency Test
The combustion efficiency test is your primary tool for monitoring boiler efficiency. You can achieve accuracy in the range of one percent of efficiency if you do the testing carefully and use equipment of good quality. However, be sure that you understand what the test is telling you. The combustion efficiency test does not account for:


• standby losses. You perform a combustion efficiency test when the boiler is operating under a steady load. Therefore, the combustion efficiency test does not reveal standby losses, which occur between firing intervals. You cannot measure standby losses directly. You have to estimate them from the type of boiler and the firing schedule.
• heat loss from the surface of the boiler to the surrounding space. As a practical matter, you cannot measure this loss. Typical estimates state that the loss from surface radiation is about two percent of the boiler’s full load energy consumption.
• blowdown loss. The amount of energy wasted by blowdown varies over a wide range.
• soot blower steam. The amount of steam used by soot blowers is a variable that depends on the type of fuel and the judgement of the staff.
• auxiliary equipment energy consumption. The combustion efficiency test does not account for the energy use by auxiliary equipment, such as burners, fans, and fuel pumps.

While the combustion efficiency test does not give the overall efficiency of the boiler plant, it is by far the easiest method of tracking moment-to-moment, day-to- day, and season-to-season variations of boiler efficiency. Combustion efficiency testing tells you how far boiler efficiency drifts away from the best efficiency that you can achieve when the boiler is fully tuned up.



 

Comments  

 
0 #1 Justin Park 2011-11-02 12:44
Dear sir or Madam,

I had a device to increase gas combustion efficiency.

I am looking for a 3rd party test lab to verify the performance. Would you recommend 2 to 3 test labs.

Thanks,
All is well for you
Quote
 

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