A leading supplier of calcium chloride dihydrate and other mineral salts used in intravenous and dialysis solutions operates several production facilities in Europe, including one in the Czech Republic.

To prevent the ingress of moisture and oxidation during production, and to ensure product quality and pharmaceutical process reliability, the manufacturer uses nitrogen. The pharmaceutical company obtains this nitrogen via a central industrial gas distribution network serving its industrial estate. The nitrogen is delivered as a high-purity liquefied gas, vaporised in evaporators, and ultimately supplied to the mineral salt manufacturer in gaseous form.

The technical gas is billed by the gas supplier. A flowmeter approved for custody transfer applications was required for the billing of the supplied gas volumes. As the European Measuring Instruments Directive (MID) 2014/32/EU for custody transfer does not apply to this application, the instrumentation was required to hold a national type approval for fiscal metering instead.

The application required a flowmeter with a wide measuring range of 15…250 Nm³/h and a normal operating range of 30…150 Nm³/h. The gaseous nitrogen has a process pressure of 13 barg / 188.5 psig and a temperature range of +5…+35°C / +41…+95°F. As the pressure and temperature of the technical gas can vary depending on the total gas demand and the consumption of the individual plant units, accurate measurement under changing operating conditions was essential.

For the custody transfer measurement of gaseous nitrogen, the OPTIMASS 6400 was selected. This high-end Coriolis mass flowmeter has a long track record in custody transfer applications for both liquids and gases. It is available with numerous national type approvals for gas flow measurement, including approval for use in the Czech Republic.

As the flowmeter measures mass flow and density directly, it can calculate and output the actual volumetric flow rate without the need for additional pressure and temperature compensation or an external flow computer. The flowmeter also features integrated temperature measurement, providing valuable additional process information. The Coriolis mass flowmeter was installed as a compact version (C) with size 15 twin-bent stainless steel measuring tubes (S15).

Installation was carried out in accordance with the requirements applicable to custody transfer meters. The flowmeter is installed with a bypass arrangement so that, in the event of recalibration and metrological verification, the nitrogen supply to the continuously operating production plant is not interrupted. At the same time, tampering with the bypass fittings is prevented. The bypass is therefore fitted with a sealed blanking plug. A shut-off valve is installed downstream of the flowmeter, allowing the meter to be zeroed during commissioning. The electrical power supply to the flowmeter is backed up to ensure uninterrupted operation.

The OPTIMASS 6400 mass flowmeter is equipped with a local display for on-site monitoring of readings and also communicates via Modbus. The gas supplier uses this communication protocol to retrieve the measurement data required for billing the nitrogen volumes supplied.

The OPTIMASS 6400 provides the basis for the accurate and reliable commercial billing of gaseous nitrogen, ensuring the highest possible level of transparency for both the plant operator and the gas supplier.

The consumption data recorded by the flowmeter provides valuable insights into the overall efficiency of the plant. It enables the operator to assess how efficiently the costly gas is being utilised throughout the facility. Over time, changes in consumption patterns become visible, helping to identify potential opportunities for further optimisation.