A recreational products company bought a three year-old manufacturing facility with an existing Regenerative Thermal Oxidizer (RTO) for the production of their outboard engines. 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 utilizing the existing RTO to control their emissions. However, the paint exhaust produced 80,000 SCFM (128,400 Nm3/hr), an impossible challenge for the existing RTO, which had been designed and built to control only 17,000 SCFM (27,285 Nm3/hr). Looking towards the future, the company wanted an air pollution control system capable of managing future expansion.
Anguil’s engineering team demonstrated a solution that allowed the company to utilize the 17,000 SCFM (27,285 Nm3/hr) RTO that came with the building. By placing two 40,000 SCFM (64,200 Nm3/hr) Rotor Concentrators upstream from the RTO, the company could cost-effectively expand their operation and still achieve regulatory compliance.
This outboard engine manufacturing plant had multiple paint spray booths and ovens producing 80,000 SCFM (128,400 Nm3/hr) 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 VOC emissions concentrator/oxidizer technology, reducing the 80,000 SCFM (128,400 Nm3/hr) paint line exhaust to 8,000 SCFM (12,840 Nm3/hr), 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 VOC emissions 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 the 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 re-insulation 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