By means of its next-generation technologies, Sick helped to revamp a plant for the fiscal measurement of natural gas. This also allowed to optimize measurement accuracy, ensuring a constant monitoring of performances
by Luca Basaglia
The intense cold in winter reminds us that natural gas is a fundamental resource with a central role in our country’s energy system. For this reason revamping plants and infrastructures dedicated to its transportation and distribution becomes strategic. Sick’s fiscal flow rate measurement technology for gaseous fluids using ultrasound sensors is a solution which increasingly arouses the interest of the natural gas sector. Solutions for the fiscal measurement of natural gas include the supply of single components or of integrated solutions depending on the client’s needs.
A concrete example is provided by the partnership with Società Gasdotti Italia (SGI), for the revamping project of the fiscal measurement plant of the natural gas interconnection point in Castel Di Ieri, near l’Aquila. SGI is an important operator for the transportation of natural gas through a network of high pressure pipelines roughly 1,550 km long.
Technological innovation of measurement plants
The interconnection point in Castel di Ieri at Avezzano is one of the input points of the SGI network which allows transportation of natural gas in different areas of such central Italian regions as Abruzzo, Marche and Lazio.
Natural gas is derived from the main branch of the SRG pipeline, and is input into the Regulation and Measurement cabin in Castel di Ieri at an altitude of about 1,00 metres. Here natural gas is initially filtered, then fiscally measured, and afterwards regulated in terms of pressure and flow, as regards the amount of gas which SGI’s dispatch service manages in order to satisfy civil and industrial users downstream. SGI’s main requirement was increasing the capacity of the measurement and regulation plant from a delivered flow (Qero) of 150,000 Sm3/h to 350,000Sm3/h, considerably increasing the performances of the plant itself. Regarding the measurement part, conventional mechanical solutions (turbine meters) have been replaced with ultrasonic measurement solutions. Meters installed allow a superior measurement capacity in the case of low flow rates, going from a Qmin/Qmax ratio of 1:20 (the typical capacity of a turbine meter) to a Qmin/Qmax ratio of 1:185 (capability
of Sick’s ultrasound meters).
The commissioning deadlines have been respected
An important challenge for the project was meeting deadlines. Everything was done in a short time, from the initial phases of design and construction of the measurement skid to the test and gauging of the measuring lines, and from the transportation of the measurement skid, which was assembled at an altitude of 1,000 m, to the commissioning test of the measurement system. The deadlines for the commissioning of the natural gas measurement plant were peremptorily respected. The SGI interconnection point at Castel di Ieri, which underwent revamping, is made up by a measurement system with 2 independent lines with a bypass. The measurement chain is made up for each line by a Flow Computer, a temperature transmitter, a pressure transmitter and the primary ultrasound measurement element.
The possibility of measuring gas autonomously for weeks
The Sick measurement system can count on a primary measurement element, Flowsic600-XT Forte. Besides ensuring a high level of accuracy in compliance with the latest OIML R137 2012 standards, the tool is equipped with PowerIn Technology™, an integrated battery back-up system which allows the fully autonomous measurement of gas in case of a power cut for up to three weeks. Besides, thanks to a continuous automated correction of the Reynolds number and of the geometry of the meter’s body, the integrated temperature and pressure sensor system helps provide an accurate measurement in all working conditions of the plant’s operation. The transfer of results, from gauging to the application on the field, is carried out without the implication of additional uncertainties due to the effect of pressure and temperature changes. Measurement lines (upstream/downstream pipes and ultrasound meters) have been gauged under high pressure in Germany at one of the main acknowledged gauging institutes, recognised at European and global level and ISO IEC 17025 certified. The total non-compensated volumes (Vm) measured by the Flowsic600-XT Forte are transmitted using a high-frequency (HF) impulse signal of the utmost precision to the Flow Computer (Electronic Volume Converter, EVC). The latter receives the information regarding pressure and temperature from two transmitters, then carries out the automatic conversion of the volumes of natural gas in basic condition volumes (Vb), brought back to the reference thermodynamic conditions.
Higher accuracy and measurement capacity
The performances of the measurement system are constantly controlled by the diagnostics of the Flowsic600-XT, which monitors the progressive decay and the functioning of the components of the instrument, measuring and analysing one or more related factors (SNR, AGC, Error Rate, Flow Profile). Information on the state of the meter’s functioning and, therefore, on the flow measurement is transferred by the flow meter to the flow computer by means of a digital contact. Should an irregularity of the system occur, it is possible to intervene on time to carry out correctional verification and action. Inaccurate measurements may imply high amounts of gas which is unaccounted for. The measurement system provided by Sick, besides considerably increasing the measurement capacity of the fiscal plant, also brought measurement accuracy to very high levels, guaranteeing its stability over time and a constant control of the performance level.
Author: Luca Basaglia, Product Manager Flow Solutions & System Manager Flow Metering Systems, Sick