5.0 Challenges faced by the
Critical Power Engineer
The Critical Power Engineer is faced
with significant air compliance
challenges due to the regulatory
environment. These challenges are
compounded if the site location is not
fully finalized when the initial design is
done. A change in air shed location
could have a significant change in the
results of the AERMOD simulation. A
change in emissions mitigation
requirements could then have a
significant impact on the physical
space required for the various after-
treatment devices.
Until recently after-treatment was done
using separate devices for each
emissions function. For example Figure
6 shows a separate silencer and SCR
system in the exhaust stream of a large
generator used in a Data Center. As
can be seen in Figure 6, the physical
space required for the devices and the
complex piping and expansion joints
required between them makes for a
large and overly complex system.
Some vendors are offering exhaust
after-treatment systems that combine
all required functions in a single
“cube”. These multi-function systems
can contain any combination of SCR,
silencing, oxidation catalyst and
particulate filters in the same cube.
This makes installation much easier and
allows the Critical Power Engineer to
design a system which meets the
regulatory requirements of any air shed
in the US. The cube is typically installed
above the engine. As a result it does
not take up much more space than a
conventional silencer. An example of
such a system is shown in Figure 6.
6.0 Summary
The regulatory requirements for
obtaining an air permit for large scale
critical power facilities using stationary
diesel engines is continuing to become
more complex. It is important for
Critical Power Engineers to understand
the overall regulatory framework and
build enough flexibility into their
design to ensure that the requirements
for an air permit can be met.
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7X24 MAGAZINE FALL 2014
Figure 5
Separate SCR and Silencer in a Data Center: Traditional Approach
Figure 6
Example of a Multi-Function Exhaust System in a Single Cube
Bob Stelzer is the Chief Technical Officer for Safety Power Inc. He can reached at
