Passive Gas Dehydration Design – PDS Unit for Pipeline-Quality Natural Gas
As part of a passive gas dehydration design assignment, we completed the full detailed engineering design of a modular, skid-mounted passive gas dehydration unit, coordinating several engineering disciplines.
Operating at a design pressure of 100 barg in an ATEX-classified environment, the system is designed to reduce the water dew point of produced natural gas to the level required for pipeline sale, while supporting safe and predictable operation.
Industry
Oil and Gas – Upstream and Midstream
Our Primary Role
Passive gas dehydration design in a lead engineering role
Project Involvement
Full multidisciplinary detailed engineering design
Project Background
Natural gas produced from dry gas reservoirs contains water vapour. The presence of water creates operational risks: under unfavourable conditions, it may condense, promote corrosion and lead to the formation of gas hydrates, potentially causing pipeline blockages.
Natural gas intended for pipeline sale must therefore remain within the applicable water dew point limits.
The assignment involved the design of a modular, skid-mounted PDS unit. The passive gas dehydration system conditions the water dew point of the produced natural gas so that the outlet “dry” gas achieves pipeline-quality specifications.
The client intended to deploy an established technology, already proven during trial operation, at additional gas fields. Chess Energy was engaged as the lead engineering designer for the investment.
The term “passive” refers to the dehydration method. The unit’s dehydration towers use a solid-bed process in which the desiccant comes into direct contact with the gas, absorbs the water and gradually forms a brine solution. This solution is drained and the solid material is replenished periodically.
This solution does not require continuous, energy-intensive regeneration, which may offer advantages from both an operational and maintenance perspective.
Key Engineering Requirements of Passive Gas Dehydration Design
For a unit of this kind, the engineering challenge is twofold: the system must simultaneously achieve the required product quality and meet safe operating requirements while handling hazardous media at significant pressure in an explosive ATEX environment.
Product Quality
If the gas does not achieve the required level of dryness, its sale may be restricted or prevented.
Reducing the water dew point of natural gas was therefore one of the primary objectives of the process design. The unit had to be sized to maintain the specified water dew point throughout the expected operating range. Process sizing was carried out using simulation based on the actual gas composition.
Safe Operation
For a system operating at a design pressure of 100 barg and handling hazardous media, pressure containment, safety relief, drainage, depressurisation and explosion protection cannot be left to operational procedures alone. These requirements must be resolved during the engineering design phase.
Each item of equipment within the unit is equipped with an individual safety valve and a manual depressurisation option.
Modular Configuration
The unit consists of two separately transportable and movable skids that are connected at the installation site.
This configuration places additional demands on the design. The piping, pipe supports and connection points must be engineered to withstand transportation while also allowing the system to be commissioned efficiently following installation.
What Specific Engineering Activities Did We Perform?
Engineering Design
The passive gas dehydration design was delivered as a lead engineering assignment. The complete detailed engineering package was developed as a coordinated and technically consistent multidisciplinary design covering process and mechanical engineering, industrial architecture for process facilities, primary instrumentation and electrical power supply.
Our process and mechanical engineering activities included:
- developing the process configuration and the Piping and Instrumentation Diagram (P&ID),
- performing process sizing calculations, including piping and flare-line diameters and safety valves, based on fluid-flow simulation,
- performing the mechanical strength calculations of pressurised piping in accordance with the applicable standards in force,
- defining the safety, drainage and depressurisation systems,
- specifying the requirements for fabrication, installation, welding, surface protection and insulation, together with the pressure-testing procedures.
During the engineering process, we applied both European standards and regulatory frameworks, including EN standards and the Pressure Equipment Directive (PED), as well as international standards such as ASME where appropriate for the relevant component. We also drew on experience gained during previous projects.
The documentation was approved by a responsible designer holding the required GO gas-industry engineering authorisation and was also subjected to an independent internal design review.
What Did We Learn from the Project?
The project clearly demonstrates that the result of careful passive gas dehydration design is often invisible: the unit simply performs as intended, and the gas remains suitable for sale.
The added value lies in the details: accurate sizing, consideration of extreme operating conditions, the timely integration of safety requirements and the coordination of several engineering disciplines into a single, consistent design.
The project also confirmed that transferring a proven technology to a new location is not simply a matter of copying an existing design. Local conditions, connection points and operating parameters must be reassessed in every case.
Careful engineering design performed under the appropriate professional authorisations can help ensure that a unit continues to achieve its target performance under varying inlet conditions while maintaining predictable operation.
Let’s Discuss Your Project
Are you planning a process unit or system where product quality and safe operation are equally critical, whether in an explosive environment or involving pressurised media?
Let’s discuss how multidisciplinary engineering design, from concept development through to detailed engineering, can support the reliable and safe achievement of your investment objectives.
