Oxidizer case histories in the pharmaceutical industry
The pharmaceutical industry faces unique challenges in complying with environmental pollution and emission control regulations. Three pharmaceutical process case studies are examined: fluidized bed drying, tablet coating and reaction vessels, and batch operations.
Recently, a contract drug manufacturing company faced violation of their state operating permit, costly fines, and potential Title V permit classification. To avoid penalties, a more robust abatement device had to be installed, one that met the necessary emissions standards for volatile organic compounds (VOCs).
Process case study 1: Fluidized bed drying
The solution also had to be designed to work within a range of varying exhaust volumes and high VOC loads, provide low operating cost, and include a heatrecovery solution that offered substantial return on investment. It also needed to be designed to do the following:
- Provide continuous VOC destruction across operational range
- Provide high uptime reliability
- Be fully automatic, with no operator interface required
- Be installed easily
- Provide features that help minimize maintenance
- Integrate a waste heat boiler
The process includes multiple fluidized bed granular dryers and tablet coating stations that feed the new oxidizer. Each process exhausts a high concentration of methanol, acetone, and alcohol based VOCs. The lower explosive limit (LEL, sometimes referred to as lower flammable limit) from the process is expected to be approximately 40 percent LEL. This is considered a high LEL and requires certain expertise and equipment design features to safely handle the process exhaust stream.
A catalytic oxidizer was installed and integrated with a waste heat boiler (WHB) to provide approximately 8,000 lb / hr of 90 psig steam. The integration of the WHB with the catalytic oxidizer provides substantial operating cost savings compared to operating the current stand-alone boiler (Figure 1).
The current system installed is a regenerative thermal oxidizer (RTO). This technology incorporates a ceramic heat exchange media and valves designed to provide low gas consumption and consistent VOC destruction in low solvent loading applications.
RTOs are usually designed to accept only VOC concentrations from 5 to 10 percent LEL. For an RTO to work in this application, both a hot gas bypass and large amounts of dilution air must be introduced. The RTO is based on maximizing thermal efficiency at low VOC concentrations; therefore, the design is based on heat storage and release. When excess energy (in the form of VOC concentration) is introduced, the internal temperatures change fast. In that case, the RTO would experience a high-temperature shutdown or would not be capable of meeting the VOC destruction efficiency dictated in the plant's operating permit.
In this application, the pharmaceutical plant had many processes that contribute a range of VOC loadings to the oxidizer. To provide production flexibility, the oxidizer must be designed to accept any level of exhaust volume and VOC loading on a moment's notice.