# Sampling and measurements
The total amount of CO2 [captured or injected](#user-content-fn-1)[^1] is determined according to equation 6 or 7 in the [Project CO2 Removal](https://app.gitbook.com/o/zK7HMMBIcwhOSDhxzqPO/s/E1FUJsBoIj20nqp3CtMf/~/edit/~/changes/229/methodologies/biogenic-carbon-capture-and-storage-bioccs/ghg-quantification/~/comments#project-co2-removal) section, using input data from direct measurements of the stream characteristics, namely
* mass or volumetric flow measurements
* density measurements (for volumetric flow measurements)
* pressure and temperature measurements (for volumetric flow measurements)
* concentration of CO2 in the captured or injected stream
The following requirements apply for measuring the stream characteristics and for the calibration of the corresponding measurement equipment:
Mass or volumetric flow of the stream, m_{stream} or V_{stream}
The mass or volumetric flow of the captured/injected stream shall be measured
* **continuously**, at least every 15 minutes, and **aggregated over one day** (raw measurements data shall be made available upon request by Rainbow or the VVB), and
* before leaving the capture site or at the last monitoring point before entering permanent storage, for measurements of the captured or injected stream, respectively, and
* using a mass or volumetric flow meter. Project Developer shall prioritise metering technologies that are [widely used ](#user-content-fn-2)[^2] in CCS measurements, such as differential pressure meters (orifice plate meters), turbine meters and coriolis meter.
**Calibration:**
Flow meters shall be
* chosen according to the conditions and ranges under which it will operate,
* **calibrated prior to entering service** at an accredited calibration facility traceable to recognized national standards,
* **installed** in accordance with local/national standards or the manufacturer, and
* **recalibrated periodically**, meeting or exceeding local/national standards or the manufacturer, but at least annually.
Density of the stream, \rho_{stream}
The total amount of CO2 captured or injected is reported in tonnes of CO2, a mass unit. To convert volume to mass flow, the stream's density is required.
The density shall be measured either by using an in-line densitometer[^3] or similar devices, or modelled using an **equation of state (EoS)**. To model density from the EoS, the selection of an appropriate model, knowledge of the stream composition and reference pressure and temperature measurements are crucial. Various approaches for density determination using EoS can be found in the[ literature](#user-content-fn-4)[^4].
Measurements of the density, pressure and temperature (for the EoS approach) shall be conducted
* **continuously**, and at the same frequency as the flow metering, and
* as close to the metering point as possible.
**Calibration:**
* Densitometers shall be **calibrated with reference fluids**, ensuring traceability to accredited laboratories,
* **installed** in accordance with local/national standards or the manufacturer.
* **recalibrated periodically**, meeting or exceeding local/national standards or the manufacturer, but at least annually.
Pressure and temperature of the stream, p,T
Volumetric flow and density measurements are recorded at operational pressure and temperature but shall be converted to **standard temperature and pressure conditions, STP,** following equation 8.
Measurements of the operational pressure and temperature shall be conducted
* **continuously**, at the same frequency as the flow metering and **averaged over one day**. Raw measurements data shall be made available upon request by Rainbow or the VVB.
* as close to the metering point as possible
* using pressure and temperature meters (e.g., pressure transducers, thermocouples, thermistors)
**Calibration:**
* **calibrated and installed** in accordance with local/national standards or the manufacturer.
* **recalibrated periodically**, meeting or exceeding local/national standards or the manufacturer, but at least annually.
Concentration of CO2 in the stream, F_{mass,\ CO2}
The CO2 concentration of the captured/injected stream is measured either by direct measurement of the CO2 concentration in the stream, or by indirect measurement of the [chemical composition](#user-content-fn-5)[^5] (i.e. CO2 and impurities) of the stream.
The CO2 concentration using either of the two methods shall be measured
* **continuously**, at the same frequency as the flow metering and **averaged over one day** (raw measurements data shall be made available upon request by Rainbow or the VVB), and
* as close to the metering point as possible and prior to mixing with another stream, and
* using online analyzer.
Typical analyitical technologies are based on gas chromatography, non-dispersive infrared spectroscopy (NDIR), and ultraviolet-visible (UV-Vis) spectroscopy.
**Calibration:**
* chosen according to the expected and actual composition of the stream, covering the detection range required by local/national standards or operational requirements, and
* **on-site calibration at commissioning** shall be performed against traceable calibration gases, and
* **installed** in accordance with local/national standards or the manufacturer, and
* **recalibrated periodically**, meeting or exceeding local/national standards or the manufacturer, but at least annually.
[^1]: According to table 1 and 2 in the [data sources](https://app.gitbook.com/o/zK7HMMBIcwhOSDhxzqPO/s/E1FUJsBoIj20nqp3CtMf/~/edit/~/changes/229/methodologies/biogenic-carbon-capture-and-storage-bioccs/ghg-quantification#kpxsamb8logm) section, the characteristics of the **injected stream** are measured for **segregated streams**, while those of the **captured stream** are measured for **non-segregated streams**.
[^2]: [TÜV](https://www.researchgate.net/profile/Chris-Mills-6/publication/368881913_Flow_Measurement_in_support_of_Carbon_Capture_utilisation_and_Storage_CCUS/links/63ff432d0cf1030a5660c413/Flow-Measurement-in-support-of-Carbon-Capture-utilisation-and-Storage-CCUS.pdf),
[^3]: Common densitometer are nucleonic meter (using gamma-rays) meter or torsional resonators. Coriolis meter can also measure density of the stream.
[^4]: McKay, C; Nazeri, M.; Haghighi, H.; Erickson, D.; Recommendations for the selection of equation of state during design and operation of impure CO2 transport and storage, Proceedings of the 16th Greenhouse Gas Control Technologies Conference, **2022**. [DOI](https://doi.org/10.1016/j.ijggc.2023.103877)\
\
\
Vitali, M.; Leporini, M.; Masi, O.; Speranza, A.; Corvaro, F.; Marchetti, B.; Net zero Flow Assurance - Validation of various equations of state for the prediction of VLE and density of CO2-rich mixtures for CCUS applications, International Journal of Greenhouse Gas Control, *125,* 103877, **2023.** [DOI](https://doi.org/10.1016/j.ijggc.2023.103877)
[^5]: Components and their concentrations.
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