Combustion Technology (Pty) Ltd
|Combustion||Perfect Combustion||Incomplete Combustion|
|Efficiency Types||Testing||O2 versus CO2|
|Three T's of Combustion||NOx||Draft|
|Flue Gas Test Procedures||Acceptable Test Results||Accurate Testing|
|Savings Potential||Training Centre|
All process and space heating systems are engineered and designed by the manufacturers to operate with very specific ranges of excess combustion air, carbon monoxide, draft, and stack temperature readings. Unless combustion analysis readings are within these parameters, Steady State Efficiency readings are false and will not reflect actual consumption.
For example, an underfired boiler with a low stack temperature may provide SSE readings that suggest efficient, economical operation. In actuality, all boilers and forced air systems are designed to operate most efficiently at their full firing rate. Underfired burners may cause excessively low stack temperatures which could result in condensation damage and potential flue gas spillage due to loss of stack draft.
Additionally, continual low fire (or underfired) operation of many power burners causes the flame to burn closer to the burner head, exposing it to higher than design temperatures and cause warpage or burn off.
Looking at the flame color, shape and stability have been used as rules of thumb for many years but eyeballing will not allow you to truly optimize the safety, efficiency, full service life and environmental compliance of your equipment.
Many commercial boilers and high
efficiency residential heating systems do not even have an observation port to see the
flame. Even when an observation door is
available, simply opening the door to view the flame changes all the actual operating
conditions and characteristics of the combustion process.
Just as doctors make use of the most
sophisticated instrumentation possible when diagnosing their patients, the best way to
make sure that equipment you are responsible for is operating safely, and at maximum
efficiency, is by using combustion instrumentation.
Traditional, chemical or Orsat type instrumentation will give you information that is comparable in accuracy to electronic instrumentation, but electronic instruments have several very important advantages.
Many electronic instruments measure on
a continuous basis, like a movie or video camera. Traditional
instruments are more like a still camera, which takes only one picture at time. With traditional instrumentation (the still
camera) you might miss the most important picture because your camera is only capable of
taking one picture at a time.
Because most electronic instruments draw flue gas samples on a continuous basis, like a video camera, you can see all of the information that will help to evaluate the operating condition of heating equipment throughout the entire cycle of operation from start up to shut down, including transient changes along the way. Electronic instruments will also do sampling and efficiency calculations rapidly and automatically.
Some models will store and/or print
out complete reports of test results or transfer the stored data to a computer while
adding time and date information to the data collected.
This provides hard
copy documentation that the burner was operating safely and efficiently when you left the
job. Undoubtedly, combustion testing will
identify additional service work required. The
print out can help the customer understand the nature of additional costs.
Over time, it also establishes a history of burner performance and may provide an early indication of a failing component.
A printed readout left with the
customer serves as a seasonal reminder to have the burner combustion tested and also lets
the customer know they have hired a company which has invested in the training and test
instruments to insure safe, reliable and efficient burner operation.
To initiate the combustion process,
oxygen in the combustion air and the fuel mix and are ignited to produce heat. During the combustion process, carbon dioxide (CO2)
is produced in predictable quantities based on oxygen measurements and fuel types.
While the traditional, wet chemical type instrumentation determined the percentage of CO2 in a flue gas sample, electronic instrumentation measures the amount of oxygen (O2) remaining after the combustion process. Again, this is predictable depending on the design of the equipment. For those used to thinking in terms of CO2, many electronic instruments provide a calculated CO2 reading based upon the fuel and the O2 percentage in the flue gases as measured by the instrument.
Also, keep in mind that O2, CO2 and excess air are simply different ways of conveying exactly the same information.
The air we breathe is 20.9% oxygen. As more oxygen is used to burn the fuel in the
combustion process, more CO2 is produced and diluted by excess air. Flue gas oxygen and carbon dioxide measurements
are therefore inversely proportional. That
is, as oxygen readings decrease, carbon dioxide readings increase.
Heating equipment is becoming more and
more efficient, in part due to increased control over the amount of combustion air. In addition, residential and commercial structures
are being built with much tighter envelopes in an effort to reduce fuel consumption. As a consequence, critical factors such as a
sufficient combustion air supply, draft, etc. can be very easily affected by such
influences as building pressure imbalances or improper fuel pressure.