Benzene Emissions Calculations for TEG Units by GLYCalc and HYSYS
Written by James Holoboff, Process Ecology

GRI-GLYCalc and Aspentech’s HYSYS are simulation tools frequently used to predict benzene
emissions from glycol dehydration units. GLYCalc has been the software of choice for regulatory
agencies in North America with respect to estimating benzene emissions from glycol dehydration units.

The vast majority of dehydration units use Triethylene Glycol (TEG) to remove water from natural gas; the
ability of these software tools to accurately predict benzene emissions in TEG dehydration units is
therefore of primary importance for both operators and regulatory agencies. In addition, accurate
prediction of dry gas water content is essential for the optimization of dehydration units and for the
generation of Dehydrator Engineering and Operations Sheet graphs.

GLYCalc has been successfully used in industry to calculate benzene emissions in TEG units, but there
are limitations. As for HYSYS, the Peng Robinson package has historically been the standard for
dehydration unit calculations; recently Aspentech introduced a Glycol package which notably has
interaction parameters fitted for TEG-BTEX systems.

GPA Research Report 131 (The Solubility of Selected Aromatic Hydrocarbons in Triethylene Glycol) is a
key source of equilibrium data for TEG-water-BTEX systems at typical contactor, flash tank and still
conditions.

Specifically, we have found that:

  • HYSYS-Peng Robinson, HYSYS-Glycol and GLYCalc all had a reasonable match to the BTEX
    liquid-phase concentration data from GPA RR-131 at contactor and flash tank conditions.
  • HYSYS-Peng Robinson and HYSYS-Glycol had reasonable matches to BTEX concentration data
    at regenerator conditions. Given the empirical nature of the relationship used to model the
    regenerator in GLYCalc, it is difficult to make the comparison; however, we conclude that
    GLYCalc consistently overpredicts BTEX K-values in the regenerator.
  • HYSYS predicted dry gas water content more accurately than GLYCalc. It is not uncommon for
    GLYCalc and HYSYS to give vastly different predictions; we conclude that GLYCalc frequently
    predicts dry gas water contents 50% lower than expected values. HYSYS-Glycol gave the best
    predictions here.
  • It is further noted that property packages can be modified (most notably by modifying interaction
    parameters to better represent available experimental and plant data) and selectively applied in
    HYSYS providing an opportunity to improve on the available methods.

The following figure illustrates the comparison between the RR-131 data, GLYCalc, HYSYS-PR and
HYSYS-Glycol at contactor conditions. All methods gave a reasonable match.
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Overall, GLYCalc gives reasonable predictions of benzene emissions in TEG units despite some of the
shortcut methods used in the calculations. However, it does underpredict dry gas water content so care
should be taken when calculating glycol circulation rate requirements.

As for HYSYS, the Glycol package in HYSYS 2006.5 gives excellent results. Care should be taken when
using different property packages or older versions of HYSYS.

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