Liquids streams recovered during gas processing normally require fractionation/distillation prior to being delivered to market. Fractionation at a gas plant typically consists of a Stabilizer Tower to fractionate the liquids separated in the Inlet Separators to produce condensate and a Deethanizer, if the gas plant has refrigeration capacity, to produce natural gas liquids (NGLs)—a mixture of propane, butane and condensate. NGLs can be further fractionated into specification propane, field grade butane, LPG (mix of propane and butane), normal & iso-butane, and condensate. In sour gas plants, fractionation of water containing hydrogen sulphide is often carried out in Sour Water Strippers to remove the hydrogen sulphide. Gas Liquids Engineering Ltd. (GLE) has designed a number of distillation/fractionation projects which include:
- Stabilizers – Designed to meet condensate and conventional oil TVP, RVP, and condensate and oil blend specifications
- Deethanizers – Designed with partial reflux, conventional refrigeration based condensers as well as knockback condensers or non-refluxed reboiled absorbers with kettle style/thermosyphon/once-through, and forced circulation type reboilers.
- Demethanizers – Side reboilers, bottoms trim reboilers and overhead vapour management
- Depropanizers – Partial and total condensers
- Debutanizers – Total condensers using air cooled or refrigerant cooled condensers
- Butane Splitters – Multi-stage, total condensers, high reflux options, and feed forward control systems
- Frac Oil Towers – C6+ product based fractionation
- Sour Water Strippers – Heated or cool gas blow through and traditional reboiled sour water stripper
While some fractionation systems are relatively simplistic, others require extensive process engineering and development. In designing fractionation systems, the design variables listed below are all considered and assessed to maximize robustness, flexibility, cost effectiveness and performance of the fractionation system.
- Stage efficiencies – Infinite stages/minimum reflux initiatives to reduce stages
- Turndown Requirements and future needs
- Control systems – Fundamental to the success of fractionation / distillation
- Tower internals – Trays (sieve/ballast/valve), random packing, and structured packing. Each have different impacts on fractionation performance.
- Utility minimization and ease of operation