Development of a Model to Predict Benzene Emissions from Glycol Dehydrators with Condensation Tanks

Process Ecology Inc.

September 14, 2020

Executive Summary

The oil and gas industry uses glycol dehydrators at many facilities to remove moisture from natural gas streams. The glycol used in these processes also absorbs other components from the gas stream and some of these components are released to the atmosphere during the glycol regeneration process. Benzene, a known carcinogen, is one of these components and there are regulations in place that limit the allowable benzene emissions from glycol dehydrators. One method for reducing benzene emissions from the glycol regeneration vapour stream is to pass the vapour through a condenser tank or some other form of condenser equipment such as a chiller. These condenser devices are allowed by regulations as a control method to reduce benzene emissions as long as the condensing efficiency is measured directly in the field. This efficiency measurement is a costly and dangerous activity as it involves work at height and increased chance of exposure to benzene. There is a need for a simulation method to allow the upstream oil and gas industry and regulators to establish the benzene removal efficiency for these condenser devices without the need for field measurement.

The objective of the project is to develop a software tool (or “Application”) which can be used to estimate benzene emissions as a function of various inputs provided by the user, such as the regeneration still vapour composition and conditions, condenser/tank characteristics, and
ambient conditions.

The first report, submitted December 31, 2012, described the work done to develop the thermodynamic, heat transfer and ambient mathematical models required for the Application.

The report was updated and reissued at later dates. This report summarizes the development
work and presents conclusions regarding its application. In summary:

  • A survey of Total Capture Tests was completed and compared to simulation models.
  • A review of monitoring methods was done in anticipation of potential “enhanced” onsite monitoring to supplement Total Capture Test results.
  • A thermodynamic model was developed to predict vapour-liquid-liquid equilibrium of water-hydrocarbon mixtures.
  • A heat transfer model was developed for the standard TankSafe brand condenser as well as for a typical above-ground tank.
  • An online Application was developed, integrating the thermodynamic and heat transfer models. This Application allows the user to input data related to their facility and predict the benzene emissions reduction performance there.
  • An ambient condition “model” was developed to allow for prediction of year-round temperatures and wind speeds in Western Canadian locations. The ambient model was incorporated in the online Application.
  • The model was compared and validated to Total Capture tests, as well as multiple field studies. These tests and studies showed that the Condenser Application reliably estimates vent temperatures and benzene emissions reductions in condensers.
  • The online Application was made available to PTAC, where it resides at https://condenser.ptac.org.

Full Report

Best Management Practices

# 09-9210-50 / 13-AU-ARPC-04 / 15-ARPC-01 / 17-ARPC-16