- A leading Australian natural gas producer engaged PSA Engineering to design and commission a new fire and gas safety system for the power generation facility at a major water treatment plant servicing its Queensland onshore gas reserves.
- The new safety system would replace the existing non-compliant system and be required to meet a far more stringent standard set by OLF, the Norwegian Oil and Gas Association.
- Full lifecycle functional safety engineering solution
- Functional safety documentation
- Safety Instrumented Systems (SIS) hardware and software design
- Detailed Factory Acceptance Testing (FAT)
- Electrical systems
- Hazardous area commissioning
- PSA Engineering designed and commissioned the new fire and gas SIS system, achieving the high safety performance target set by the standard OLF-070.
- Our detailed FAT testing delivered seamless system integration with no changes made onsite during the commissioning phase.
- The new system is compliant with IEC 61511 SIL 2 design Fire and Gas Safety Instrument System regulations.
Gas power generation SIL 2 fire and gas SIS
Ensuring the safety of people and assets is a key driver for the oil and gas industry, and international standards play a vital role in developing best practices across the sector.
As the operator of a coal seam gas project, our client required a significant upgrade to their fire and gas installations to meet their commitment to OLF-070, a stringent international standard set by the Norwegian Oil and Gas Association, not typically undertaken in Australia.
The CSG water treatment plant is powered by seven gas generators, each housed within an individual enclosure with multiple SIL 2 certified fire and gas sensors to monitor for fire and gas events. The key driver for the project was to replace a non-compliant SIL 2 fire and gas system with one that complied.
“With a treatment capacity of more than 90,000 cubic metres per day, reducing safety risks was a critical consideration for the water treatment plant.” John Teahan | Lead I&E engineer | PSA Engineering.
The PSA Engineering team, led by John Teahan, designed and commissioned the new fire and gas SIS system for the power generation facility, achieving the high safety performance target set by the standard.
CSG water treatment plants
Coal seam gas (CSG) is primarily methane; it forms in the coal seam and is held in place by groundwater pressure. Pumping the water to the surface releases the pore pressure, allowing the gas to be extracted and collected.
The by-product groundwater is high in sodium and contains impurities, making it unsuitable for consumption or irrigation. After extraction, the water is pumped through a network of pipes and storage ponds to the water treatment plant where it is processed so local landholders, industry and councils can safely use it.
The water treatment plant’s power generation facility is fuelled by methane from the gas fields.
Methane is a non-toxic, odourless gas that is highly flammable and explosive. The fire and gas safety system is designed to detect any loss of gas and immediately shutdown the facility and alert workers so they can follow emergency procedures.
Working in partnership
The first step in delivering the new fire and gas SIS system was producing the functional safety lifecycle documentation, detailing the safety procedure requirements specific to the project.
During this intensive phase, we worked closely with the client and their internal safety auditor to adhere to quality management standards set out by the IEC 61511 SIL 2 design Fire and Gas Safety Instrument System regulations.
This documentation phase, a crucial step in all process safety projects, also laid the foundations for a productive working relationship between the PSA Engineering and our client. As Lead I&E engineer John Teahan points out, this was the first time working together for both teams, and the expectations were high.
“There was heavy scrutiny at the beginning of the project,” says John, “and rightly so. The system we designed is critical to the safety of people and assets… but once the client saw how we worked, they became comfortable. That process helped us gain their trust and helped us deliver the best possible outcome.”
Functional safety solution
The new fire and gas SIS is designed to meet SIL 2 as per OLF-070 standard. To achieve this PSA Engineering selected hardware and software solutions that could be integrated into the existing plant systems, meeting both technical and logistical requirements.
As independent providers, we are vendor agnostic, which allows us to select the technology best suited to the requirements of the project.
The hardware selected included flame detectors, gas detectors, interposing relays, beacons and sirens. The Rockwell AADvance fault tolerant control system was selected as the fire and gas safety programmable logic controller (PLC).
The system provides a fully independent shutdown path to the gas generator units, isolation of fuel gas valves and associated electrical systems. This ensures a quick and effective emergency shutdown procedure in the event of a fire or gas incident. The system also immediately triggers the effected generator’s beacon and siren system plus the Plant Wide Emergency Siren, giving personnel who may be in the area maximum time to evacuate.
The application program was a two-tier design, including a human-machine interface application (HMI), allowing the control room operator to view global safety function during emergency testing or during a fire or gas event.
In addition to our client’s standard safeguards for managing the application of SIS sensor overrides, we also included additional safeguards designed to deliver a higher safety performance. These enhancements included more override features and allowed for greater operator control.
Seamless commissioning process
Time is money in the oil and gas industry, and shutdowns need to be scheduled with precision, to avoid costly delays. The seamless commissioning process of the new fire and gas SIS across all seven gas generators is working proof of our team’s expertise and commitment to providing the best outcomes for our clients.
The detailed Factory Acceptance Testing (FAT) carried out prior to installation meant that no changes were made onsite. As John Teahan points out, this is highly unusual and a fantastic result for the client.
“To meet the IEC 61511 quality standard, we had to conduct multiple tests on every component,” says John. “There were over 2500 test criteria, so we applied a very rigorous method to the testing process, and as a result, we made zero changes onsite, which is almost unheard of in the industry.”
The impressive scope of this project saw us pull over 4500 metres of cable and deliver a new fire and gas SIS system that integrated perfectly with our client’s existing systems, achieving the high safety performance target set by the strict guidelines of OLF-070.
Detailed project information
The fire and gas SIS was required to host the following functions:
- 1v2 fire detection & 1v2 20%LEL gas detection & 1v2 40%LEL gas detection located at both inlet and exit louvres within 7 No. GE Jenbacher J620 4.16 MVA gas engine enclosures
- 1v1 smoke sensor located in each generator’s local control room
- Isolate gas engine fuel gas systems, generator & aux power systems on confirmed fire, gas or smoke within the gas engine enclosures and local control room
- 1v2 20%LEL gas detection & 1v2 40%LEL gas detection for a gas condensate open trough system
- Provision of SIS monitoring & application of sensor overrides for testing purposes via HMI & hard-wired control panels in the main control room.
Key functional safety lifecycle documents:
- Functional safety management plan
- Safety requirements specification
- Cause + effects charts
- SIS functional design specification inc. hardware, application program & HMI graphics
- User defined function block specification
- SIS verification & validation plan
- FAT procedures
- SIL verification report
- SIS validation procedures
- Critical function test procedures
- Independent functional safety assessment.
Key hardware equipment:
- Flame detectors: Det-Tronics X3301 SIL 2 IEC61508 SIL 2
- Gas detectors: Simtronics GD10P IEC61508 SIL 2
- Rockwell AADvance Safety PLC. 1v2D CPU architecture to increase availability, hence SIL 3 design.
- Phoenix PSR series SIL 3 relays to interface to final elements.
Analysis of the existing system design and subsequent formal review with the end-user resulted in the following design decisions on interfacing the existing final elements to the SIS:
- Generator 11kV circuit breakers. SIS de-energise to trip (DTT) output via SIL 3 PSR relay into CB UVR circuit.
- Fuel gas train valves. SIS DTT outputs via SIL 3 PSR relays to each individual double isolation valve set. Note: Fuel gas train AS 3814 type B certified.
- 2 No. 415V CB existing shunt trips changed for UVRs. SIS DTT outputs via SIL 3 PSR relays to each 415V CB UVR.
- New beacon & siren for local activation in the event of a fire and gas event. E2S SIL 2 beacons & sirens were selected. This includes wiring a fail-safe supervision circuit to the SIS.
- The existing non-SIL complaint system path for shutdown will be retained by tie-in of h-w confirmed 20%, 40%LEL gas & flame from the SIS into the existing shutdown circuits via the existing PLC systems.
Additional safeguards have been designed into the SIS:
- For a 1v2 sensor group, overriding the second sensor is not possible within both the HMI & SIS FB, if the first sensor is in override or fault state, i.e. the global safety function is always available.
- If the second sensor of a voted group enters the fault state while the first is not available, i.e. in override or in fault, the global safety function will TRIP its final elements.
- Application of an override is a two-step process. Step 1 requires operating a master override key switch followed by Step 2, setting the sensor to its override state from within the HMI within a 15s window. Post 15s requires intentional rotation of the master override switch from off-on state.
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