Twin Tower TSA Gas Dehydration Unit

Continuous Dehydration on a Swing Cycle

The SorbiTech Twin Tower TSA Dehydration Unit dries natural gas to a guaranteed water dew point on a continuous temperature swing adsorption cycle. Two molecular sieve adsorbers run 180 degrees out of phase: while one vessel is on adsorption at line pressure and temperature, the other is in the regeneration sequence of heating, soaking, and cooling. The unit therefore delivers dry gas without interruption, and a third vessel can be added for sour service or for half cycles longer than 24 hours.

The duty is set by inlet conditions and the contracted outlet dew point, which typically falls between minus 10 °C for sales gas and minus 70 °C for upstream of a cryogenic unit. The package is engineered by SorbiTech and is delivered with a single SorbiTech performance guarantee covering the molecular sieve and the equipment together.

Vessel Construction and Internals

The adsorber vessels are stamped to ASME VIII Division 1 or to PED 2014/68/EU, with 316L stainless internals on every wetted surface in contact with the sieve. The pressure shell is carbon steel with a corrosion allowance set by the inlet hydrogen sulphide level and the project life.

Internal distributors are sized for uniform face velocity to avoid channelling at the wall, which is the most common cause of premature breakthrough. A ceramic ball support and a wire mesh hold down keep the bed in place during pressurisation, and an inlet basket prevents the molecular sieve from contacting any liquid carryover that escapes the upstream coalescer.

The Regeneration Loop

A side stream of dry product gas is heated in a direct fired or electric heater to 250 to 320 °C, passed through the off line vessel in counter flow to remove the adsorbed water, then cooled in an air cooler or shell and tube exchanger and returned to the inlet header. The vent stream from the heating stage is condensed to recover water, which is metered to monitor cycle performance.

The cooler returns the regenerated vessel to within 10 °C of adsorption temperature before switchover, so the first hour of the next adsorption cycle is not consumed by residual heat.

Scope of Supply

A complete package engineered by SorbiTech and supplied by SorbiTech includes:

• Twin or triple adsorber vessels to ASME VIII Div.1 or PED, with 316L internals
• Inlet filter coalescer to keep free liquids off the bed
• Regeneration gas heater and air or water cooled exchanger, ATEX or IECEx rated
• Switching valve manifold, fully welded or flanged to specification
• Media charge of SorbiTech 3A molecular sieve to ISO 9001:2015, loaded under nitrogen
• PLC or DCS sequence control with outlet dew point monitoring and trend logging

Design Data and Sour Service

Capacity from 0.5 to 200 MMSCFD, inlet up to 120 barg, inlet temperature minus 20 to plus 60 °C. Outlet water dew point set per contract from minus 10 °C down to below minus 70 °C. Built to NACE MR0175 and ISO 15156 for sour service in the presence of hydrogen sulphide and carbon dioxide, with hardness controlled welds and post weld heat treatment as required.

Where It Fits in the Treatment Train

The unit covers the duty described under natural gas dehydration, sitting between an upstream inlet separator or gas sweetening unit and a downstream sales gas meter, NGL recovery train, or cryogenic gas plant. For a cryogenic feed the dew point requirement tightens and the bed is sized accordingly.

Sequence Control and Operator Interface

SorbiTech runs the adsorption, switchover, depressurisation, heating, soaking, cooling, and pressurisation steps on a deterministic time base, with override on outlet dew point. A typical PLC architecture is Allen Bradley CompactLogix or Siemens S7-1500 with a hot standby option for critical service, integrated with the plant DCS over Modbus TCP, Profinet, or OPC UA.

The operator interface presents the cycle position, the outlet dew point, the regeneration outlet water rate, and the trend of each vessel temperature against the design curve. Drift on any of those signals is flagged as a maintenance event before it reaches a process trip.

Spare Parts and Lifecycle Support

A typical TSA unit requires planned spare parts for the switching valves, the heater elements, the cooler fan or pump, the inlet coalescer cartridges, and the bed support ceramic balls. SorbiTech holds the recommended two year spares list in stock at the regional service centre and the bed replacement charge of SorbiTech 3A media in a separate inventory reserved against the contracted change out window.

Delivery and Performance Guarantee

Delivered turnkey by SorbiTech or fabricated to client drawings, with civil, mechanical, and electrical scope included where the project requires it. Because the media and the equipment both sit inside the SorbiTech Group, one performance guarantee covers the complete dehydration system from inlet flange to outlet dew point. Long term lifecycle contracts cover media changeouts, valve overhauls, and controls firmware updates inside a single shutdown window. The SorbiTech twin tower TSA package carries natural gas dehydration in the oil & gas sector with 3A, 4A, or 13X media.