CROFT Passive Dehydration System (PDS)

CROFT Passive Dehydration System (PDS)

Posted by Cameron Croft on Jul 1st 2019

What is a Passive Dehydration System (PDS)?

The PDS, or Passive Dehydration System, is Croft’s preferred alternative to a glycol unit for the dehydration of natural gas. Dehydrating raw natural gas is necessary to remove the water and bring the gas to a point where it is within a range that meets pipeline specifications, which is usually 7 lbs/MMcf.

The PDS utilizes a patented, environmentally-friendly desiccant, enviroDRI™, to dehydrate the gas with minimal moving parts. Wet gas enters the inlet at the bottom of the vessel. The gas then flows through the enviroDRI™, and as this happens, the water is absorbed from the gas. The water and enviroDRI™ mixture then falls to the bottom of the PDS and can be drained into storage tanks on location. Since the enviroDRI™ is non-hazardous, there are no special disposal instructions.

What parts go to a Passive Dehydration System (PDS)?

It is recommended that the PDS be serviced on a 30-day schedule to ensure the system is running properly, as well as the parts. As with any system, there are parts that can wear down over time.

1. Timer Box– The timer box is a control panel that operates the activation of dump valves with duration and frequency.

2. Dump Valves–Dump valves rid the system of the enviroDRI™ mixture that is found at the bottom of the vessel after the dehydration has taken place. The dump valve is connected to a timer box that automatically releases the mixture to a holding tank.

3. Gauge Valve Sets–These valves are used when replacing a broken sight glass to isolate process fluid.

4.Sight Glass–The sight glass is located on the outside of a separator and allows you to view the liquid level.

5. Pressure Safety Valves–A pressure relief valve is set to the unit’s maximum operating pressure to ensure safety. If the pressure exceeds that value, the valve will open, keeping the pressure within the safety limits.

6. Pressure Regulators-Pressure regulators help monitor and maintain supply pressure to the dump valve and have gauges that allow for a service technician to view the pressures without disengaging the system.

7. Temperature Gauges (Not Pictured)–Temperature gauges are designed to show process temperature.

8. Thermowells (Not Pictured) –Thermowells are designed to block the process fluid and to be a connection port for temperature gauges.

9. enviroDRI (Not Pictured) – enviroDRI™ is a patented, environmentally friendly desiccant.



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