A gas pipeline compressor station modernization

Gas demand in southern Europe has risen by an average annual rate of 16% since 2002. As a result, a pipeline from eastern Europe experienced significant flow increases, putting extra pressure on its six compression stations as operation was extended to meet demand. The twenty-year-old compression trains were not designed for such high capacity, so reliability issues quickly arose. We responded by undertaking a comprehensive modernization of two compression stations (L and K) including the following responsibilities:

• investment design, coordination with the State-owned operating company and appropriate authorities
• delivery of the following equipment and materials:
• seven new gas turbines installed in refurbished footprints to operate with existing centrifugal compressors
• eleven automated control systems
• twelve state-of-art anti-surge valves
• one Integrated Control System(ICS)
• extensive secondary systems and equipment
• disassembly, construction, installation and pre-commissioning
• specialized training of station operators
• technical documentation and warranty service

More than meets the eye

When most people think of modernizing a compression train, they usually only consider the two main components – the turbine and the compressor. But the upgrade will put significantly different power and technological demands on the entire system. In order to achieve optimal performance, a complete assessment and/or revamping of many of the support and peripheral station components is usually required.

Gas turbine requirements

The gas turbine was unsalvagable , so we supplied a new unit following a full battery of tests and simulations to ensure smooth operation based on the upgraded station features. A 60-cm misalignment between the original installed compressor and turbine required special design accommodations for the replacement unit.

The normal production cycle for a unit of this type would have been too long for the aggressive schedule required. Therefore the manufacturing process required special attention in order to shorten the turnaround time by 30%. The new machine that included GT/CC Integrated Control as well as onboard vibration monitoring, diagnostics and axial displacement protection was certified according to international standards. Its specifications included:

• minimum partial load, continuous: 40% of rated power at 15°C
• rotating speed: 70-105%
• minimum efficiency 28%

We also refurbished four existing gas turbines with the following scope:

• new turbine combustion control
• new axial compressor IGV control system
• control system refurbishment
• control cab
• anti-surge valves
• transmitters and primary transducers
• elimination of pneumatic transducer for speed measurement
• power supply, electrical equipment and associated instrumentation cabling
• oil system refurbishment

Control system requirements

The electronic control system is an integral part of a compression train. GE’s current Integrated Control System (ICS) technology enables simultaneous monitoring and control of both the turbine and compressor to ensure immediate response for high-level functions such as load sharing and gas flow allocation across multiple units. The ICS can further control the complex list of support functions throughout the station. Items such as scrubbers, station valves, coolers and fuel skids can all be controlled by the same governor system as the turbines and compressors.

When revamping a control system, key objectives include reliable operations, flexibility to meet all possible operating conditions, compatibility with existing station equipment, and an expandable design to accommodate future upgrades and technologies.

The advanced automatic and programmable features of our ICS greatly enhance the ability to consistently meet operator needs on many levels. For example, primary functions of one station’s ICS were to control station valves, recirculation valves and coolers. Data acquisition and monitoring were also required in relation to the fuel gas block, gas filters, electrical substation, firefighting and weather stations. Since the ICS had to interface with an existing Distributed Control System (DCS) operating within a Local Area Network, we configured it in the following sub-systems:

• Station Control System (SCS)
• Emergency Station De-Pressurization System (ESDS)
• Operator Control System (OCS)

Optimal load sharing was required under all operating conditions, so a gas measuring system was also added. Other features in our ICS for this project included:

• automatic turbine control
• anti-surge control
• compressor protection
• automatic protection according to setting parameters
• automatic stabilization of the set operating mode
• emergency protection system
• programmable 14-day operating parameters
• diagnostic functions
• measurement and control of unit process parameters
• data transfer to station control system
• transmitters, primary transducers, cables
• dedicated control cab with air conditioning
• gas detection devices for all units in selected station

Conclusion

Because the project was not only broad in scope, but highly detailed in specialized disciplines, our project managers took on the responsibility of attaining special permits from local authorities wherever required. We also worked collaborativelly with the manufacturer of the four original turbines that were kept as part of the station setup. This expedited ordering and delivery of various OEM parts in addition to replacements and upgrades from our own inventory.

A phased execution plan was developed in order to finish the entire modernization and rehabilitation program in just three years. In the end, our complete installation, commissioning and start-up cycle was 40% shorter than what would normally be expected for an application of this kind.

For more information, please contact:

Gianluca Sturniolo
gianluca.sturniolo@ge.com

 

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