Page 139 - Boiler plant and distribution system optimization manual

124 Boiler Plant and Distribution System Optimization Manual

2. OxYGEN TRIM

Cost
Moderate to low

Potential Savings
Moderate

Description
There are many factors that can influence
and introduce errors into the air/fuel ratio such
as fuel property changes, air temperature, control
system response, fuel pressure and burner perfor-
mance (Table 10.3). An oxygen trim system can
automatically and continuously compensate for
the variables in the combustion process, insuring
that the boiler is programmed to operate at near
optimum efficiency.

Sources of Errors in Control Systems
Figure 10.19—Plus point minus point evaluation ta-
ble for conversion from natural gas to residual fuel
oil.

that you pay for natural gas after it is used and
fuel oil must be purchased and stored for many
months or years before it is used. This ties up cap-
ital which can be used for other purposes. Anoth-
er real problem is the cost of environmental com-
pliance in some regions as well as the uncertainty
of future environmental requirements for storage
tanks and underground piping.
Although the use of electricity to generate
steam would seem to be an unwise choice, the Table 10.3—The sources of errors in control systems
whole picture should be considered. Distribu- with a rough estimate of how large they could be-
come without an oxygen trim system to automatical-
tion systems can waste a very large percentage
ly compensate for some of the problems. An oxygen
of heat, especially if they are lightly loaded. It
trim system can compensate for many system errors,
may be more cost effective to use electric boilers
allowing a lower excess air level to be maintained
at those locations with only intermittent or light
on an automatic basis. However, many boiler plants
steam use, especially if long or inefficient steam have not taken full advantage of this potential and
and condensate runs are involved. are maintaining a higher than necessary set point for
excess oxygen. The O trim system can also be used
2
Advantages/Disadvantages as a tool to diagnose and control system problems.
A complete analysis could be time consum-
ing, especially if the plant would have to be re- Advantages/Disadvantages
configured to burn another type of fuel, but on Without oxygen trim, high levels of excess
the other hand going through the trouble could oxygen are necessary to compensate for many
be quite profitable. sources of errors in the combustion process; this