Fiscal Metering – a useful guide
March 31, 2021
What is fiscal metering?
It sounds like a very simple question and on one level it is. It’s also quite a complex question, and while the technical authorities in most businesses will fully understand the nuances and details of that, a lot of other technical, project and operations managers may not have a full grasp of key aspects, simply because it’s often seen as quite niche as a subject within the larger oil and gas discussion.
Here at Thyson Technology, we’re committed to delivering precisely what our customers need, and that includes providing useful content to support your knowledge and understanding of the industry we all work in.
The central question contained in any discussion on fiscal metering is the critical concept of uncertainty. There is always an element of uncertainty in any meter that measures the flow of liquid or gas, from an industrial meter to the meter in your home, and that uncertainty is not only pivotal to understanding the physical transfer of a fluid from one owner or custodian, to another, (also known as ‘custody transfer’) but also an important factor in accurately determining network shrinkage (OUG, Input and Output) or loading/unloading an LNG tanker.
Fiscal metering: a definition
Fiscal metering is a metering system used commercially, that’s similar in principle to the gas meter in your home. They vary in size and in some cases, they’re so large, you can walk through them. They measure the flow of gas at custody transfer points from the seller to the new owner of the gas.
In other words, fiscal metering operates like a cash register.
Fiscal meters used in the industry are described by the regulations as Class 1 primary elements. At Thyson, we build systems using our preferred suppliers’ meters, unless a customer has a preference for a different supplier.
There are three types of primary elements we commonly use:
Accuracy and uncertainty
Flow metering is an exacting science.
Any fiscal meter system should be as accurate as possible, so the seller and buyer know the precise volume and energy/components of fluid that is traded, and therefore, an accurate value is also part of the transaction, or as close as possible to the real energy value. Uncertainty over the flow measurement is the core issue in fiscal metering and every provider of fiscal metering solution’s must understand their metering system’s uncertainty and be able to communicate this, with evidence, to the customer.
When gas from the North Sea comes onshore at St Fergus Gas Reception Terminals, for example, the gas will be processed by the producers and then sold to gas shippers who then sell the gas to the suppliers, typically of the Big Six (69% in 2019). The value of the processed gas is dependent on both accurate determination of the volume, as well as the Gas Quality/Calorific Value. The shipper uses the National Transmission System and the distribution networks to transport natural gas to their domestic and industrial customers. The Uniform Network Code (UNC) forms the basis of the commercial contract between gas transporters and shippers. Within the UNC, there are specific requirements set out for gas quality and volumetric uncertainty.
Budget uncertainty vs actual uncertainty calculations
For customers, the most important element they are concerned about is that their provider gives them the confidence to trust them, that their partner and provider knows what they’re doing, understands the issues surrounding uncertainty and discusses the imperative of using approved instruments.
In short, customers want to know, when you build a system, that you know it’s going to perform. At Thyson, we prepare a calculation based on information from our OEM generic performance data. Each piece of equipment has a level of uncertainty attributed to it. We enter the data into a specific calculation tool, referencing ISO 5168, the international standard for Procedure for Evaluation of Uncertainties. We tend to call this the budget uncertainty.
Calibrating fiscal meters
Fiscal metering solution providers like Thyson use accredited meter testing facilities to determine the uncertainty of the primary element across the applicable measurement range.
In simple terms, the accredited test site flows natural gas or measured fluid through the test meter, and compares this to a certified reference meter, validated using a prover in some cases. The ideal outcome is to have the gas flow reading the same in both instances, however there will always be a bias. The smaller the bias on a repeatable basis, the better the meter the OEM can be considered to be.
The bias will be recorded on a calibration certificate and will be applied as a correction to the installation, typically in the flow computer, although some clients prefer the correction to take place within the actual meter. The customer will normally witness each step, to provide assurance and confidence that the volumetric flow or mass uncertainty attributed into the uncertainty calculation is correct.
Once the fiscal meter system has been installed, we carry out a validation of secondary instruments, including a performance evaluation of the gas chromatograph to determine the installed uncertainty. The entire sum of uncertainties is collected and an overall fiscal metering uncertainty is calculated, again using ISO 5168, ensuring the customer has met their contractual requirements and is left with peace of mind over the entire process.
UK and international fiscal metering standards.
Thyson builds integrated metering systems, the size of which can range from 2 inches to 36 inches in diameter (DN 50 to DN 900). For each meter, there are various industry standards applied, such as IGEM/GM/4, which covers the range of meters listed previously, or more specifically, ISO 17089, for Ultrasonic Meter Installations.
The fiscal metering systems Thyson provides include condition-based monitoring, which ensures a level of self-diagnostics every second of every minute of every day, to verify that it is performing correctly. This can be viewed securely online where we implement Kelton’s Meter Manager.
It’s our role to ensure customers have complete confidence in their fiscal metering systems. Although under regular scrutiny and auditing using online diagnostics, a fit and forget approach can be taken, knowing the fiscal metering system is built to the highest standards, and will warn them of any issues. In addition, providers like Thyson will service and maintain the metering system regularly, to ensure that it continues to perform as expected.
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