1. Air combs are installed in the process exhaust behind a diffuser, which
disrupts and homogenizes the flow to assure an even temperature and eliminate
Processes that use heat
and/or solvents usually produce airborne volatile organic compounds (VOCs),
which, according to local air quality and U.S. Environmental Protection Agency
(EPA) standards, must be captured or rendered inert prior to exhaust emission
into the atmosphere. In the ceramic industry, affected processes usually
incorporate various kilns, ovens and furnaces.
As heightened awareness and sensitivity to environmental impact meets more
acute emission compliance standards and guidelines, companies throughout the
U.S. are becoming increasingly educated with respect to emissions standards and
are striving to meet compliance guidelines. The traditional bulky and expensive
VOC removal technologies usually involve thermal combustors that dilute exhaust
air to reduce its volatility to non-explosive levels, and then employ high
temperature to oxidize the compounds completely.
Two innovative energy-saving approaches can enhance performance and reduce costs
associated with VOC removal and compliance. In appropriate applications, 99.7%
or better efficiency with respect to VOC removal can be achieved.
It often does not make economic sense to replace existing
equipment. Thus, a modification called a thermal catalytic combustor retrofit
is designed for the existing system. A non-platinum, spiral fiber catalyst,
which has a high surface area and is durable and efficient, is applied to
ceramic combs of varying sizes, depending on the system type and flow rate (see
Figure 1). These combs are installed in the process exhaust behind a diffuser,
which disrupts and homogenizes the flow to assure an even temperature and
eliminate any hotspots.
Since this catalyst reacts favorably at very low temperatures, the required
temperature within the combustor is typically reduced by 30-40%, which equates
to a 50-60% reduction in the energy required to accomplish the same task.
Various safety mechanisms are also installed to assure proper temperature
range, volatility control, minimum flow rate and pressure drop.
When a new system is designed, the VOC content itself is
used, in part, to drive the reaction. Generally speaking, for every gram of VOC
per cubic meter of suspension gas in typical applications, the reaction
temperature increases by 30ºC. Thus, a system can be designed that reduces
the flow rate to one that matches the amount of VOC concentration to the
catalyst and arrives at an equilibrium, or a state that uses little or no
additional energy to maintain the reaction temperature. In many cases, the heat
source used to arrive at a desired trigger temperature can be electric (due to
the reduced flow rate), further reducing the overall cost of the system.
In many traditional approaches, the creation
creates yet another problem to be addressed.
Since the temperatures used by these new systems are quite low, however, no NOx
is formed. Many manufacturers require very high temperatures as part of their process.
In these cases, VOCs from solvents and other agents are removed as the system
heats up to the optimum range of the catalytic system prior to arriving at
higher processing temperatures, thus still providing a low-cost VOC removal
2. General schematic of the VOC removal system.
These systems feature few, if any, moving parts in nearly
all applications. A general schematic is shown in Figure 2. In situations where
black smoke, unburned carbons, dust or different solid particulates are
present, pre-filtering or other treatment of exhaust air must be accomplished
to assure proper catalyst function and longevity. A wide variety of systems is
available to match specific flow and pollution control requirements.
Savings for some customers can be substantial;
larger manufacturers can save thousands of dollars per day in energy costs. In Europe, with its higher energy prices, typical capital
investment recovery is 3-4 months. Still, it can be expected that a U.S.
application could see its capital investment recovered within the first year of
For more information regarding VOC removal technologies, contact
Catalycom-US at 1034 Emerald Bay Rd., South Lake Tahoe, CA 96150; (530)
543-1025; fax (530) 543-1026; e-mail email@example.com; or visit the website at www.catalycom-us.com.
A specially designed baffle was installed to mix
the airflow to assure an even temperature throughout the cross-section of the
ONLINE EXTRA: Success at Volkswagen
Volkswagen’s main production plant in Wolfsburg, Germany,
combines the thermal combustion of paint fumes with finish curing via heat
exchange from an afterburner installed in the painting exhaust flow. Since VW
had a great deal of capital invested in the current system, it made little
economic sense to scrap it and build a new system.
A KNV system was installed
downstream of the afterburner. One concern in this case was that, due to
limited space and pre-existing condition, the system needed to be located quite
close to the burner. A specially designed baffle was installed to mix the
airflow to assure an even temperature throughout the cross-section of the duct.
Next, two walls of ceramic aircombs, treated with the necessary catalyst for
the intended VOC content, were installed in the duct via a custom-made steel
VW was able to reduce its operating temperature at the burner from 750
to 500ºC, a 30% temperature reduction. This equated to a 43% reduction in
energy requirement and an estimated savings of €3500 (about $5400 at current
conversion rates) per day at the time of installation for this system alone.