Siemens LMV 5 Series, Technical Instructions, Page: 174 / 374

Technical Instructions LMV Series
Document No. LV5 ‐ 1000
Section 6 Page 2 SCC Inc.
Introduction
The LMV52.240 and the LMV52.440 both have O
2
(oxygen) trim and O
2
alarm (previously called
“monitor”) capability. In addition, the LMV52.440 offers advanced features such as temperature
compensated light ‐ off and more dynamic O
2
trim capabilities. In general, the LMV52.440 is
recommended for more difficult applications such as low and ultra ‐ low NOx burners where the burner
stability band is much smaller than a traditional nozzle mixing burner. Some features in the LMV52.440
were specifically designed for ultra ‐ low NOx mesh burners.
The O
2
trim functions by using an in ‐ situ O
2
sensor installed in the boiler stack, and then adjusting
actuators and / or VSD to maintain a % O
2
setpoint. Only air ‐ related (air influenced) actuators are
adjusted, thus the O
2
trim does not adjust the firing rate (fuel ‐ related load). Only the air rate (air ‐ related
load) is adjusted.
Each Ratio Control Curve Point that is entered (see Section 4) will have a corresponding O
2
trim setpoint,
rich limit (O
2
alarm) and lean limit (O
2
max value). The exception to this rule is that O
2
trim cannot be
performed on Point 1. If 10 points are entered on the Ratio Control Curve, there will be 9 trim points
and 10 rich limit (O
2
alarm) points. Having 10 points on the Ratio Control Curve is recommended.
As is the case with advanced systems such as O
2
trim, the fundamental systems that lie underneath the
advanced system must be in place and working correctly to enable the advanced system to work
correctly. For example, if the gas pressure supply is not repeatable upstream of the firing rate control
valve (fundamental system), then the O
2
trim (advanced system) is likely to deactivate. The
fundamental systems on the burner / boiler that must be working correctly are outlined in detail in the
Pre ‐ Requisites listed in Section 4. The Pre ‐ Requisites for LMV52 systems with O
2
trim must be met
before O
2
trim commissioning is attempted.
If the Pre ‐ Requisites are satisfied, then reliable operation of the O
2
trim depends on correct parameter
settings for the application and correct commissioning of the O
2
trim. This section will outline the basics
behind how the O
2
trim system operates, and will outline the typical commissioning procedure for a
traditional nozzle mixing burner (standard emissions) and a pre ‐ mix mesh burner (low or ultra ‐ low NOx).
Nozzle mixing burners that use a high percentage of FGR to achieve low NOx typically behave in a way
that is similar to a pre ‐ mix mesh burner, so the commissioning procedure for these types of burners is
similar to a pre ‐ mix mesh burner.
O
2
Trim (O
2
Control) Fundamentals
By definition, an O
2
trim (O
2
control) system monitors the level of O
2
in the exhaust gases of the boiler
and adjusts the fuel or air flow to maintain an O
2
setpoint. The LMV52 accomplishes this task by reading
the %O
2
(wet basis) with an in ‐ situ O
2
sensor and by adjusting the angular position of air flow influencing
actuators. If the burner is equipped with a VSD (variable speed drive) for the blower, the O
2
trim can
also adjust the blower speed to influence the burner airflow.
HOME