Page 101 - Boiler plant and distribution system optimization manual
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86 Boiler Plant and Distribution System Optimization Manual
oxygen in the combustion products and adjusts tems are that it is independent of fuel type and it
the airflow accordingly for peak combustion effi- is almost unaffected by air infiltration common in
ciency (Figure 8.13). the negative draft type of boilers.
Carbon monoxide systems must be viewed
with caution because the carbon monoxide lev-
CARBON MONOxIDE TRIM el is not always a measure of excess air. A dirty
burner, poor atomization, flame chilling, flame
Carbon monoxide (CO) trim systems are also impingement on boiler tubes and poor fuel mix-
used to excess air. Carbon monoxide trim sys- ing can also cause a rise in carbon monoxide lev-
tems, in fact offer several advantages over oxygen el.
trim systems.
In the carbon monoxide system trim system,
the amount of unburned fuel (in the form of CO) DIGITAL CONTROL
in the flue gasses is measured directly and the air
to fuel ratio control is set to actual combustion The latest developments in automatic boiler
conditions rather than pre-set oxygen levels. This control systems have been in the technology of
way the carbon monoxide trim system is contin- distributed digital control (DDC) of boilers. DDC
uously searching out the point of maximum effi- systems are based on microcomputer technology
ciency (Figure 8.14). and control the boiler by means of “software”
Other benefits of carbon monoxide trim sys- rather than fixed interconnections or “hardwired
Figure 8-13—A jackshaft control system with oxygen trip control.
