Problem
More and more, companies operating air pollution control
equipment today realize that the initial capital cost of an
oxidizer system can be rapidly eclipsed by continued operating
expenses if careful attention is not periodically given to the
system.
Action
Below are ten tips to ensure your oxidizer is operating at peak
performance. The first five tips focus on parameters end-users
should know about their oxidizer systems, while the last five
address energy reduction projects to be considered.
Solution
1. Know how much your Oxidizer is supposed to be costing
you to operate.
It is surprising how many facilities cannot answer the following
two questions.
- How much is operating our oxidizer expected to cost?
- How close is our oxidizer operating to that expected
value?
The "out of site, out of mind" approach is entirely too
prevalent these days when it comes to air pollution control
equipment. While that speaks highly for the reliability of systems
installed today, it also hints at a blind spot around the
day-to-day operating cost of oxidizer systems. With relatively
minimal inputs, oxidizer vendors can run a performance model for
you and give you the expected operating cost range for your
oxidizer system.
2. Pay attention to the Percentages.
After 5 years of operation, a Regenerative Thermal Oxidizer
(RTO) originally designed for 95% TER (Thermal Energy Recovery) may
have slipped to 93% TER. This might not sound like a big deal, and
this may go unnoticed by even the most attentive maintenance
department. However, an average sized RTO (25,000 SCFM) operating
for a full year at 93% TER verses 95% TER could cost upwards of an
additional $65,000.00 a year! Percentage points do count over the
course of a year. Get to know the critical parameters to watch as
your system ages.
3. Know your VOC loads - especially the amplitude and
duration of peaks.
Often it is peak VOC (Volatile Organic Compound) loads that
determine your oxidizer design, but average VOC loads that
determine your oxidizer operating cost. When an oxidizer is
specified, designed and installed, often times it is the
anticipated VOC loading peaks that dictate the amount of heat
recovery incorporated. Typically, estimates for a future "worst
case scenario" are made to ensure a conservative approach is taken.
After a couple years of operation, it may be time to examine
whether the design was too conservative and the peak solvent usage
is much lower than originally estimated. Operating an oxidizer
designed to handle a theoretical peak loading may be costing you
much more than necessary for your actual day-to-day production
loading.
4. Know what oxidizer system would be specified for your
process today.
Finding out exactly what would be
specified to treat your process exhaust today is a valuable
exercise - especially if your existing equipment is in need of
significant repairs or upgrades. Knowing what would be specified in
today's energy conscious market can serve to illuminate cost
effective upgrades to your existing equipment.
For instance - 5 to 10 years ago an RTO with 90% heat recovery
may have been specified to treat your process exhaust. Today,
oxidizer vendors may prescribe an RTO with 95 or 96% heat recovery
and a hot gas bypass damper to deal with high VOC loading periods.
If your existing oxidizer system is due for repairs, one can also
determine whether it would be cost effective to upgrade to today's
standards at the same time.
Alternatively, it may be a completely different oxidation
technology specified today. With today's control schemes, RTOs have
expanded their applicability greatly over past years, while also
dropping significantly in initial capital cost. Knowing exactly
what would be specified today can save you from sinking too much
money into an outdated oxidizer system.
5. Know what grant money is available to
you
Energy reduction upgrades to existing equipment will have an
associated initial capital cost. This can be significantly reduced
with grant money from local utility companies. Across the country,
money has been earmarked for the specific purpose of funding energy
reduction projects. Know what grant money is available to you, whom
to contact, when and how to apply. The main intent of these
programs is to take upgrade projects that you (or your management)
may be on the fence about and contribute the funds necessary to
make them very attractive.
6. Concentrate High Volume Low VOC Airstreams prior to
Oxidizer
If a significant portion of the air entering your oxidizer is at
or near ambient temperature with low levels of VOC loading, a VOC
concentrator may be applicable for reducing the heat input required
by your oxidizer system.
As a result of recent regulations, many facilities around the
country have been forced to improve localized VOC capture as well
as prove high destruction efficiency in their oxidizer system. In
many cases this has lead to the installation of additional capture
hoods or enclosures and increased the amount of air to be treated
by a particular oxidizer system. A concentrator can take exhaust
air at or near ambient temperatures and concentrate it so that what
is actually sent over to the oxidizer system is reduced by a factor
of 8 to 15 times. This greatly reduced airflow is typically
fuel-rich with VOCs and much less of an operating cost burden on
the oxidizer system.
7. Focus on Combustion Air
Combustion air, both in your oxidizer system or in your process
burners, is often overlooked as a potential area for operating cost
savings. Next to main oxidizer system fans, the smaller combustion
fan supplying high-pressure air across the oxidizer burner can seem
insignificant. However, these smaller fans, more often than not,
are supplying fresh air at outdoor temperatures directly into the
oxidation chamber where it must be heated to full oxidation chamber
temperature. At a temperature difference usually over 1400 F, it
does not take much airflow over the course of a year to add up to
significant operating cost dollars.
Making sure burners are tuned properly and not firing on excess
combustion air can make a big difference. With RTOs, there is the
additional opportunity to install a flameless fuel injection system
where combustion air is not needed at all. Finally, even with a
perfectly tuned burner, combustion air can be preheated using a
heat exchanger or a blend with stack air.
8. Improve Primary Heat Recovery
Oxidizers are typically designed with some form of internal heat
recovery. Usually the hot purified gases leaving the combustion
chamber are used to pre-heat the incoming solvent laden airstream.
This is referred to as the Primary Heat Recovery of an oxidizer
system. Projects that improve the primary heat recovery of an
oxidizer system often offer the quickest payback because they
provide additional heat recovery at all times the oxidizer is in
service. For recuperative thermal and catalytic units this
typically consists of adding additional passes to the internal
air-to-air heat exchanger. For RTOs and RCOs this would be handled
with increasing or changing the type of ceramic heat recovery media
or changing the control scheme that dictates how often beds are
switched from inlet to outlet.
9. Consider Secondary Heat Recovery
If improving primary heat recovery is not cost effective - or
oxidizer operating conditions do not allow it - secondary heat
recovery may be the best option for conserving the heat input to an
oxidizer system. Heat exchangers can be added to the exhaust stack
of an existing oxidizer to capture excess stack heat in air, water,
or even steam. There is a wide variety of low back-pressure designs
that can be added to an oxidizer's stack without requiring a
replacement of the oxidizer system fan.
Payback for these projects is greatly improved if the captured
heat can be used back in the exhaust generating process itself,
because again - it is assumed that the process is operating at all
times the oxidizer is operating. For example: fresh air is passed
through a secondary heat exchanger in an oxidizer exhaust stack and
supplied back as base loading for the oven zones the oxidizer is
treating. Every time the oxidizer is on the oven zones require
heat, so this heat recovery project pays back all year long. If the
same fresh air was supplied back to the plant as tempered makeup
air, this may only provide payback during the heating season.
Following this logic, in the past comfort heat applications may
have been ignored. But considering today's unstable and rising fuel
costs, coupled with the energy recovery grants available to
facilities, these projects deserve attention.
10. Properly Maintain Existing Systems
Finally, no matter how well an overall system is designed, it
cannot continue to operate at a high efficiency level without
proper maintenance. A handful of small inefficiencies in system
operation can lead to large operating cost bill over the course of
a year. At today's energy prices, regular calibration of feedback
instruments and control loops can pay for itself many times
over.
All too often production facilities take the "No News is Good
News" approach to their air pollution control equipment when they
really should be chasing the benefits of "Company Stays Green and
Saves Green" headlines instead.