Problem
A Mid-western outboard engine manufacturer bought a three
year-old plant for the production of its marine engines. When
finished the engines are removed from the assembly line and run for
quality control. The 25,000 SCFM of exhaust from testing contains
volatile organic compounds (VOCs) that require regulatory
compliance. Also, within this exhaust is a great deal of water
vapor and carbon monoxide (CO).
Anguil Environmental Systems, Inc. had already planned to equip
this plant with pollution control equipment for its paint
processing operation using a new Anguil rotor concentrator coupled
with a 17,000 SCFM Regenerative Thermal Oxidizer (RTO) the company
inherited with the plant at time of purchase. The engine test cell
emissions control issue however, was complicated by the water vapor
emitted with the VOCs. Control of the CO emissions was not an
objective for this application because its release was not a
concern to any local regulatory authority.
Action
After a thorough technical evaluation, Anguil engineers,
choosing from the many technologies available including the rotor
concentrator / oxidizer technology used for the painting process,
choose a new 25,000 SCFM RTO, the most cost-effective solution for
the existing conditions.
Solution
Several factors effected their decision. The presence of a large
percentage of water vapor in the process exhaust caused concern
regarding the effectiveness of the concentrator type adsorption
system. Vapor-liquid separators could be used to minimize the water
introduction into the concentrator but the low winter temperatures
would require the additional cost of heat jacketing and insulation
to prevent freezing. This increased the overall cost of the system,
especially when using stainless steel for all component parts in
contact with the process exhaust.
Another potential problem regarding the concentrator system was the
presence of small amounts of high-boiling oils that may not
adequately be desorbed off a concentrator system. The boiling point
temperatures of these oils was high enough that even the high
temperature desorption that was offered on this concentrator was
determined to be insufficient to obtain complete desorption. This
problem could have been addressed by installing a "sacrificial"
guard bed of carbon in front of the concentrator to capture the
high-boiling VOCs, but at additional cost and inconvenience. There
would be added process equipment to purchase and maintain,
replenishment of carbon in the beds on a routine basis and proper
disposal of the used material, an unattractive option.
A more suitable technology choice emerged as an RTO. Emissions from
the test cells were still a very small concentration and this
technology is cost-effective with 95% heat energy recovery or
higher. However, the existing RTO coupled to the concentrator
controlling the paint processing, did not offer the needed capacity
or the material make up to prevent corrosion.
Anguil engineers presented their analysis to the customer with all
the control options available and the optimal technology chosen for
treating the engine test cell emission was a new RTO. The
engineering study, which took into account the high quantity of
water vapor and CO emissions, determined that all ductwork between
the test cells and the RTO must be constructed of stainless steel
to prevent corrosion. The ductwork was also sloped back to the
process entry stream to minimize carryover of excessive amounts of
water to the RTO. The RTO internal insulation and inlet ductwork
were also designed to process the high amount of water vapor to
minimize erosion of the RTO insulation and corrosion potential of
the steel.
The RTO operation is very energy efficient with thermal energy
recovery of 95% or higher. The process air containing high
concentrates of VOCs passes through vertical beds of ceramic media
that alternately stores and releases heat or energy to elevate the
process air temperature. Since RTOs have such high heat recovery,
the process air can be heated to a value very close to the
combustion chamber set-point temperature. Heat released from VOC
destruction during oxidation further elevates the process air
temperature to the point where the RTO is self-sustaining with no
auxiliary fuel usage.
With this system, we elected to use supplemental fuel injection
(SFI) that reduces the point of self-sustained operation to a lower
process VOC concentration. Burners are shut during operation with
SFI minimizes introduction of combustion air into the chamber, and
further reduces operating fuel usage with a flameless design that
eliminates NOx emissions, problematic in some RTOs.
The manufacturing plant is now able to meet compliance on multiple
emission sources, while saving capitol expense utilizing equipment
inherited with their plant purchase as well as operational cost
savings on the newer more efficient RTO. An additional benefit with
selection of an RTO was to the environment. Although not require,
RTOs control the CO emissions along with VOCs from the test cells.
This facility can accommodate future expansion and stay in
compliance for many years to come.