I-DEV0351: Application of correction factor to correct measurements of flow meter designed for measuring air flows but not biogas flows

According to the PDD, the biogas will be measured through the use of a thermal gas flow meter. However, the
project developer initially installed a thermal flow meter designed for measuring air flows and not designed for
the measurement of biogas flows. On 20 October 2008 the project developer replaced the flow meter initially
installed with a flow meter suitable for measuring biogas flows.
Consequently, the measurements of the biogas flow from 28 Jan 2007 – 19 Oct 2007 are not precise. For this
reason, the project participants propose to apply a correction factor to the measurements of the biogas flow
during the period where the measurements were taken with the meter device designed for measuring air. The
correction factor of 79.98% is proposed to be applied to the biogas flows determined with the thermal mass air
flow meter in order to correct that the meter was measuring biogas and not air.
The determination of the correction factor was as follows:
New thermal biogas flow meters (BFM) Proline 651 manufactured by Endress + Hauser were installed in the
same pipe as the thermal mass air flow meters (AFM) at CDM project activities 0644 (Methane Recovery and
Electricity Generation Project GCM 8), 0633 (Methane Recovery and Electricity Generation Project GCM 19)
and 0637 (Methane Recovery and Electricity Generation Project GCM 24) as shown in file GCM_Flow
Meter_correction factor.xls. The new biogas flow meters were Proline 651 measurement devices applying
Heat-Loss Thermal Dispersion Technology and are designed specifically for measuring flows of biogas.
In order to establish a correction factor for the thermal air flow meters, parallel measurements were carried out
during two weeks (from 17 October 2008 to 05 November 2008) with both the air flow meters and the new
biogas flow meters and the readings from each flow meter were daily recorded (on operational days) as shown
in the spreadsheet GCM_Flow Meter_correction factor.xls.

The correction factor (CF) for the air flow meters was determined as:
Correction Factor (CF - %) = AFM / BFM
where,
AFM – volumetric flow measured by the air flow meters.
BFM – volumetric flow measured by the biogas flow meters
The lowest correction factor identified during the tests after applying a standard deviation with 95%
confidence in each of the meter lectures at these three sites was selected as the correction factor to be applied
to correct the measurements made with the air flow meter during the monitoring period in question. The
Corrected Biogas Flow (CBF) is thus determined as
CBF = CF * volumetric biogas flow measured by air flow meter

As of 20 October 2008, the biogas flow is measured with a suitable flow meter. The deviation does not
require any amendment to the registered Monitoring Plan and to the methodology AMS-III.D.

The correction factor selected is the most conservative value identified during the tests implemented at three
sites where similar manure management projects were implemented. Hence, the deviation is expected to rather
result in an underestimation of the emission reductions.