News | August 13, 2001

Photoacoustic monitor Helps BASF Manage Ethylene Oxide Levels

BASF Corp.'s Geismar Louisiana Facility needed to monitor ethylene oxide levels from 19 remote sampling points around the plant to ensure compliance with the OSHA 8 hour TWA exposure limit of 1 ppmv and check for leaks and process upsets.

The Solution
A sampling and measurement system comprised of an Innova Air Tech Instruments Model 1312 Photoacoustic Multigas Monitor and CBISS Intelligent Sampling System was selected for the application. The monitor, based on infrared photoacoustic spectroscopy, offered several advantages over other analytical techniques, including:

  • Sample each point rapidly (40-50 second average).
  • Compensate for interference from other gasses including moisture.
  • Extremely stable, thus requiring infrequent calibrations.

The system is housed in a NEMA enclosure and installed in an air-conditioned pressurized analyzer building. A heater inside the enclosure prevents water condensation during periods of high ambient temperature and humidity. A member filter placed between the sampler and the monitor prevents liquids being pulled inside the monitor. Sample lines from the system to the remote sampling points are 0.25-inch Nylon tubing and vary in length from a few feet to up to 500 feet.

Flow is generated through all of the sample lines simultaneously with an aspirator, ensuring that new, fresh gas samples will be introduced to the monitor. The flow rate in each line is regulated with a rotameter (range 0-5000 cc/min), which allows for balancing of the individual flows to the sampler. Internal valves in the sampler are used to isolate one sample line at a time from the aspirator fro sampling by the monitor.

Initially the Model 1312's internal pump was used to pull gas samples from each isolated line for analysis. However, it was discovered after the initial instillation that large pressure drops in the longer sample lines was causing "low air flow" errors to occur in the 1312. To correct this problem a duel diaphragm pump was placed between the sampler and the analyzer to provide at least 3 lpm bypass flow to the monitor.

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