Natural gas processing
Download August 22, 2011

Column Specifications for a Typical Gas Plant simulation model

Many gas plants have one or more columns to provide product fractionation and purification. The 3 most common are the deethanizer, debutanizer and stabilizer as shown here (condensers and reboilers omitted for clarity).  

Creating a gas plant simulation model requires assigning specifications to the columns, such that they converge and also accurately model the operation of the plant. Good modeling specifications result in a robust model that can be used for design and troubleshooting applications.

The deethanizer is designed to take liquid from the low temperature separator (LTS) and remove ethane and lighter components from the liquid. The bottoms from the deethanizer are sent to the debutanizer where they are separated into a mixed LPG product (mostly C3s and C4s) and a stabilized condensate product (C5+ material). The stabilizer takes inlet condensate and removes C4- material in order to meet a vapour pressure specification.

Product properties that are of interest are the C2/C3 mole ratio in the LPG product and the Reid Vapour Pressure (RVP) in the stabilized condensate.

In the actual operating plant, the column specifications are usually:


  • Bottom Tray or Reboiler Temperature
  • Debutanizer:
  • Bottom Tray or Reboiler Temperature
  • Reflux Flow or Reflux Ratio
  • Stabilizer (no condenser):
  • Bottom Tray or Reboiler Temperature

For simulation purposes, the above specifications are most useful when troubleshooting an existing fractionation train. By using these specifications in a simulation, the predicted product properties can be compared against measured samples and the simulation parameters adjusted to match current behaviour.

However, when designing a new or modified fractionation train, the most useful specifications in a simulator will reflect the product properties more closely: 


  • C2 mole fraction in bottoms or C2/C3 mole ratio in bottoms, a C2/C3 mole ratio of 2% is common.
  • Debutanizer:
  • RVP in bottoms - 12 psia would be a typical maximum value.
  • Reflux Ratio - 0.5 or 1.0 is a common value.
  • Stabilizer (no condenser):
  • RVP in bottoms - 12 psia would be a typical maximum value.

When creating a new simulation for a fractionation train, it is usually easier (and good modeling practice) to start with flow rate specifications for the columns. Once each column is converged, switch the column specifications from flowrates over to matching product specifications as listed above. Gas plant fractionation column simulations are generally robust and will operate well over a fairly wide range of inlet conditions.

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By Laura Chutny, M Eng., P.Eng.

Laura brings more than 27 years of experience in process engineering and chemical engineering research. Her key strengths are in process modeling and dynamic simulation, conceptual design, air emissions estimation and emissions reduction. Laura has a diverse experience in upstream and downstream oil & gas, chemical and polymer industries. Laura began her career with Shell Canada providing engineering support at Scotford Refinery. She then spent five years in engineering companies SNC Lavalin and then Fluor Daniel Canada. Between 2000 and 2006 Laura acted as Senior Support Staff for Hyprotech/Aspentech supporting a number of software products for process modeling, optimization and estimation. She joined Process Ecology in 2008 after working as a Research Scientist with Nova Chemicals. At Process Ecology she specializes in Air Emissions Estimation, reporting and reductions as well as safety in Process Design. Laura is a Chemical Engineer from the University of Alberta and holds an M.Eng. degree from the University of Delaware. She is also a member of APEGA, APEGBC and the AIChE. When she’s not Engineering, she can be found riding her bike, knitting and never far from a good cup of coffee or a well aged single malt.



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