In 2020, Swinton Technology and Analytic AS delivered a complete measurement system for the Golar Viking FSRU conversion. The delivery consisted of three major measurement components: the feed LNG sampling system, export gas meter run and the measurement supervisory. The complete system is designed with high-quality components providing low maintenance requirements, a high degree of operability and advanced diagnostics, which will be of great importance to both the measurement technician and the Hydrocarbon Accountants.
About Analytic
Analytic AS’s expertise and core business is delivering turn-key laboratory and measurement solutions. Analytic offer high-quality systems for fiscal metering instrumentation, and also operational and engineering support. From available well data, Analytic design and deliver the complete analysis and allocation chain, all the way from the production process through to the accounts system. In addition, Analytic deliver SOP manuals, measurement, and laboratory management systems and both general and tailor-made training.
With more than 25 years of extensive experience in operating fiscal systems and laboratories within the international oil and gas industry, our competent technical experts provide service, support and guidance on all systems and analytical test instruments; both for on-line and laboratory applications.
The FSRU’s Supervisory
The primary purpose of the TruST Metering Supervisory Computer is to provide redundant calculation and recording of high accuracy values for mass, volume and energy into secured registers and reports for custody transfer purposes. For this project, TruST was also performing all the flow of computer tasks. We used the ST103A (ST’s high accuracy I/O module) for pulses and a HART device which was connected to via Modbus TCP/IP.
All calculations are done to the latest versions of recognised international standards. TruST monitors and control the feed LNG sampling and the export gas measurement systems. It provides the graphical user interface, report generation, monitoring, alarms, archiving of data and Condition Based Monitoring (CBM) of the complete metering system. A detailed and thorough CBM system, which is easy to use for the metering technician, reduces the time needed for diagnosing the current state of the system and verifying the quality of the recorded data.
The following displays give examples of CBM implementation within TruST.
For the gas chromatographs, the supervisory collects a baseline measurement to which the measurements are compared resulting in the below graphic representation.
Figure 1: Gas Chromatograph Calibration Display
A dashboard is used to display the CBM status of all flow meters and Gas Chromatographs, using a traffic light indication of severity:
Figure 2: Example TruST CBM Dashboard
More detailed diagnostics are also available for individual flow meters and instruments:
Figure 3: Ultrasonic Meter (USM) Diagnostics
The Gas Flow Measurement Skid
Figure 4: Export Gas Measurement Skid
The export gas meter run includes two high-quality 8-path Ultrasonic meters, pressure and temperature transmitters and pressure reduction probe for the gas takeoff to the Gas Chromatograph. All instruments are mounted on a skid. The configuration of the package is customised to fit the requirements, hence can be delivered without a skid.
The 8-path USM is approved according to OIML class 0,5. As a result, the flow conditioner can be eliminated, and only a 5D upstream length is required. This solution saves footprint, weight, and cost.
The 8-path meter combines reflection paths with direct paths, which results in a detailed flow profile recognition with superb noise immunity. Due to this unique patented path configuration, the device offers the lowest uncertainty possible with comprehensive diagnostics capabilities. The reflective paths with their sophisticated diagnostics ensure that the meter quickly identifies swirl, fouling, or liquids inside the meter. The direct paths provide enhanced robustness for higher valve noise immunity and CO2 rich applications.
A pressure reduction probe is fitted which directly takes down the pressure at the process temperature inside the pipe, eliminating the risk of condensation in the sample lines.
The LNG Gas Sampling System
Figure 5: LNG Sampling System
The gas sampling system consists of two in-line sample probes with individual vaporisers, one vacuum pump, three receivers and a manual sampling point. This automatic LNG sampling system will be controlled from the TruST Metering Supervisory Computer which shows the delivered system.
Proper operation of the vaporiser is vital for providing 100% LNG flashing to ensure representative sampling and reliable measurements from the Gas Chromatograph. This can be a challenge for a system when the pressure in the mainline is low. For this reason the vacuum pump is installed, securing adequate flow through the vaporiser and the rest of the system.
The system meets the requirements of the referenced international standards: The system meets the requirements of the referenced international standards:
- ISO 10715 Natural gas – Sampling Guidelines
- ISO 8943 - Refrigerated light hydrocarbon fluids -- Sampling of liquefied natural gas - Continuous and intermittent methods
- GIIGNL – LNG Custody Transfer Handbook
The Gas Chromatograph System
The Gas Chromatograph is specially designed for natural gas energy measurements. This analyser uses chromatography components based on the latest Micro-Electro-Mechanical Systems (MEMS) and capillary column technique that provides accurate and highly consistent analysis results. The device features a compact, explosion-proof design that includes analytical hardware, stream selection and required electronics for standalone operation.
The Gas Chromatograph has a very low consumption of carrier gas, giving reduced OPEX due to longer maintenance intervals and reduced cost for purchasing gas. As an example, one 50-litre gas bottle will typically last for up to 2 years. The Encal 3000 weighs 30 kilos which makes it relatively easy to integrate into a process system with limited available space. The cabinet is designed to withstand the specified blast load.
Figure 6: Gas Chromatograph Enclosure. Compact design, low carrier gas consumption.
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