In September 1998, the EPA propagated a ruling in 40 CFR and imposed stringent standards to reduce emissions of hazardous air pollutants (HAPs) from the manufacturing of pharmaceutical products in the US. This ruling affected approximately 100 facilities, including a pharmaceutical company in upstate New York. This company was determined to stay below the acceptable MACT levels and finally contracted a consultant to develop a compliance plan.
Figure 1. Regenerative thermal oxidizers
The design included a primary and backup system, each comprising two 35,000-SCFM caustic scrubber systems and two 35,000-SCFM regenerative thermal oxidizers (RTOs) (Figure 1). The RTOs were designed to process emissions such as acetone, methylene chloride, alcohol, methanol, ethanol, isopropyl, and mineral spirits, and were designed to attain more than 99% destruction efficiency. The scrubbers were specifically designed to process treated gases and to attain 99.5% reduction of the HCI resulting from the oxidation process. Following the design phase, both technologies were selected to oxidize the HAPs and volatile organic compounds (VOCs), and to remove the ensuing HCI emissions from the oxidizer’s outlet. After receiving the specification package, engineers at Anguil Environmental Systems started to design the system within the specification limits.
The specification package included a number of parameters, such as process producing emissions - multiple (~60) sources including reactor vents and conservation vents, RTOs, purification chamber outer skin, ceramic media support grid, outlet plenum, bed/plenum/hopper, butterfly valves (bed inlet, outlet and purge), and acid gas scrubber quench.
The oxidizers were designed first, wherein each oxidizer included three insulated steel chambers that were filled with high-temperature ceramic energy recovery media. The engineering staff at Anguil Environmental Systems specified that each RTO would process approximately 35,000 SCFM of VOC/HAP-laden air, providing 99.5% destruction efficiency. Each oxidizer would use two burners to sustain its oxidation temperature set-point and provide uniform temperature distribution within the combustion chamber for maximum destruction of VOC/HAP compounds.
Below the energy recovery chambers, inlet and outlet diverter valves and the related air duct plenum passages were located. This setup would enable the process airflow to be diverted in and out of the heat recovery chambers. One duct would serve as an inlet to the energy recovery chamber, while the other would act as an outlet from the chambers to the acid gas scrubber. Another smaller duct would direct the heated purge air to the chambers.
Each chamber includes a purge valve, which would control the flow of purge air within the chamber. A Programmable Logic Controller (PLC) would control the directional mode and purging and alter the airflow direction at regular intervals to improve the efficiency of the system. The usual flow directions in the RTO would be changed every 90 seconds.
In operation, solvent-laden air would flow into the oxidizer through an energy recovery chamber, where the structured ceramic heat-transfer media would quickly preheat this air before introducing it into the oxidation chamber. Subsequent to the oxidation purification reaction, the exit energy-recovery chamber would be heated by the hot outgoing gas.
The flow direction of the solvent-laden air would be changed at regular intervals to sustain optimum heat recovery efficiency by the diverter valves on demand from the PLC control system. The energy recovery chamber, which served as an inlet, would be purged for a cycle before serving as an outlet. This ensures that all the air that flowed into a bed would be treated as much as possible.
Process Air Flow
Two 35,000-SCFM systems provide redundancy while processing airflows from 6,500 SCFM to 35,000 SCFM, and each RTO/scrubber train work in tandem with or independent of each other. The systems can be returned down to 5,850 SCFM; in case the airflow to an RTO/scrubber is below this level, a pressure control loop is used to open the fresh air damper to sustain the minimum system airflow.
Destruction Efficiency Design
A residence time of 2 seconds at 1650°F was recommended to attain an average destruction efficiency of 99.5%%, but actual compliance test data showed a destruction efficiency of more than 99.9%. To ensure high destruction efficiencies, additional steps were taken to reduce the air, which was not completely treated when the airflow changed direction. For 99.5% destruction efficiency, the system was designed with three chambers. One chamber would serve as an inlet and the second as an outlet, while the third one was being purged. The purge air would be heated to reduce the possibility of HCI gas water vapor condensation and the ensuing corrosion potential. The three-chamber design also helped in reducing any inlet and outlet bypass during valve cycling.
The acid gas scrubber was capable of processing the highest exhaust capacity of the RTO exhaust, providing 99.5% HCI removal. About 50% of the HCI was scrubbed in the scrubber quench. After exiting the horizontal quench, the air flowed into the bottom of a countercurrent packed tower scrubber. Caustic and water solution was sprayed on the top of the tower and the solution absorbed the remaining acid gases as the air moved up the column. The air then moved via a mist eliminator to remove entrained water prior to exiting the scrubber column.
Anguil Environmental Systems, who worked closely with the customer and the consultant throughout the bid process, was commissioned to install the systems. The systems exceeded the customer's goal of 99.5% destruction efficiency and ensured compliance with the EPA's pharmaceutical MACT.
About Anguil Environmental Systems
Anguil Environmental Systems is a global provider of industrial air pollution control and energy recovery systems. The thermal and catalytic oxidizers supplied and manufactured by Anguil are used to destroy Volatile Organic Compounds (VOCs) and Hazardous Air Pollutants (HAPs) that are by-products of various manufacturing processes. When released into the atmosphere, these carcinogens are known to cause respiratory ailments, heart conditions, birth defects, nervous system damage and cancer in humans and animals.
In addition to their harmful effects on plants and trees, when left untreated, VOCs and HAPs degrade in the presence of sunlight and contribute to low-lying ozone or smog. Anguil differentiates itself from the competition by offering various vapor combustion technologies used for the destruction of these pollutants. This ensures an unbiased equipment selection for each application based on the destruction requirements, efficiency needs and process parameters. Anguil not only designs, manufacturers, services and installs Regenerative Thermal Oxidizers (RTOs) but also direct-fired, catalytic and thermal recuperative systems. In addition, Anguil offers a wide variety of heat recovery and energy conservation technologies. Their energy recovery systems help manufacturers achieve greater energy efficiency, lower operating costs and reduce greenhouse gas emissions through the utilization of waste heat. The recovered energy is often used in process and comfort heating applications or converted into electricity.
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