Problem
A recreational products company bought a three year-old
manufacturing facility with an existing regenerative thermal
oxidizer (RTO) for the production of their outboard engine. They
required emission control equipment to manage the volatile organic
compounds (VOCs) emitted by the solvents used in the engine
painting processes. The company wanted to minimize overall costs by
using the existing RTO to control their emissions. However, the
paint exhaust produced 80,000 SCFM, an impossible challenge for the
existing RTO, which had been designed and built to control only
17,000 SCFM. Looking towards the future, the company wanted
pollution control equipment that would be capable of managing
future expansion.
Action
Anguil's engineering team demonstrated a solution that allowed
the company to utilize the 17,000 SCFM RTO that came with the
building. By placing two 40,000 SCFM Rotor Concentrators upstream
from the RTO, the company could cost-effectively expand their
operation and still achieve regulatory compliance.
Solution
This outboard engine manufacturing plant, had multiple spray
booths and ovens producing 80,000 SCFM of exhaust air.
Controlling the higher temperature oven exhaust alone would
preclude the use of technologies such as VOC adsorption.
However, the combined booth and oven exhaust allowed ANGUIL to use
its integrated concentrator/oxidizer technology, reducing the
80,000 SCFM paint line exhaust to 8,000 SCFM, thus incorporating
the existing RTO.
This reduction was made possible when
spray booth and oven exhausts were directed to the concentrator
system. The VOCs from these sources are adsorbed onto zeolite
that is impregnated onto a honeycomb substrate as the air passes
through the substrate. These adsorbed VOCs are then desorbed
off the concentrator wheel in an airflow that is one-tenth the
process flow rate-resulting in a VOC concentration approximately 10
times higher than the process stream. Since the desorption
air must still be controlled by an oxidizer to meet regulatory
requirements, this smaller flow rate reduces the capital cost of
the oxidizer. With the concentration of VOCs leaving the
concentrator subsequently much higher than the original process,
the operating cost of the oxidizer is also significantly
reduced.
One advantage of the RTO is its low operating cost. Vertical
beds of ceramic media alternately store and release 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 oxidation further elevates the process air
temperature to the point where the RTO is self-sustaining with no
auxiliary fuel usage. The use of supplemental fuel injection (SFI)
also reduces the point of self-sustained operation to a lower
process inlet concentration. Operation with SFI minimizes
combustion air introduction into the chamber, which further reduces
operating fuel usage.
Many integrated concentrator/oxidizer systems employ the excess
heat from the oxidizer as a source of desorption energy at the
concentrator wheel. Since the RTO can be so fuel efficient,
the oxidizer outlet temperature is low, limiting the use of heat
recovery from the oxidizer. Because the RTO was an existing
unit and the customer wanted to maintain high energy efficiency, a
dedicated heat source was installed to desorb the VOCs from the
concentrator wheel.
The RTO used at this facility was an existing unit that
experienced several operating problems. To minimize overall
cost of the emission control for the paint system, Anguil provided
mechanical and electrical modifications to allow its integration
with the concentrator. The resulting benefits of the
concentrator/RTO integration included:
- Additional process flow capacity: low concentrator desorption
flow allowed for additional process lines to be integrated with
existing RTO
- Automated and integrated control system design: including
compliance with insurance/safety requirements and remote telemetry
for easy system monitoring
- Prolonged equipment life: oxidizer reinsulation eliminated hot
spots
- Enhanced VOC destruction: valve repair minimized leakage, while
the control valve captured/oxidized the VOC "spike" typical of
two-chamber RTO installations
- Reduced operating costs and NOx emissions: Supplemental fuel
injection (SFI) reduces the auxiliary fuel requirement and greatly
reduces the NOx output from the RTO