I-DEV0461: Measurement of methane content of biogas and flare efficiency

Reference I-DEV0461
Submitted by DNV (27 Dec 2011)
Project activity 1270: AWMS Methane Recovery Project MX06-S-20, Yucatan, México
Selected monitoring period 29 Sep 2007 - 31 Aug 2010
Title/subject of deviation Measurement of methane content of biogas and flare efficiency
Description
This request is to allow deviation of measurement of methane content of biogas as specified by the parameter MC in Table B.6 of the registered PDD by measuring the CO2 content of biogas and calculating the methane content instead of directly measuring the methane content. This request is also to allow for deviation of testing flare efficiency as specified by the parameter EFP in Table B.6 of the registered PDD by applying the default value allowed in “Tool to determine project emissions from flaring gases containing methane” for periods where the flare efficiency was measured less frequenty than annually.

MC
The project developer has undergone an extensive evaluation and selection process to find the most reliable and durable equipment for measuring methane at its project activities. This process took considerably longer than anticipated by the project developer. At this time, the project developer has identified and begun using this monitoring equipment and, as of October 2008 (for sites 25752 and 25792) and April 2009 (for site 26102), the direct measurement of methane has been implemented in accordance with the monitoring methodology and the monitoring plan and this practice will be used for all subsequent monitoring periods.

Prior to measuring the methane content the project developer has monitored the methane content of biogas using practices considered to be correct during validation and identical to the monitoring practices at other registered and verified projects by the same project developer applying AM0016 version 02.

Biogas consists of mainly CO2 and methane. Recent measurements of both the methane and CO2 content of biogas taken from sites within this project activity showed that the sum of CO2 and methane averaged 97.38% with a 95% confidence level of 94.2%. An earlier analysis of other similar advanced Animal Waste Management Systems (AWMS) projects in Brazil and Mexico, developed by the same project developer and applying the same project technology showed that the sum of CO2 and methane averaged 99.0% with a 95% confidence level of 96.7%. For the similar AWMS project in Brazil and Mexico the project developer thus generally applied a value of 94% for the sum of CO2 and methane with 6% trace or other gas unless measurements for specific sites showed that the sum of CO2 and methane is less than 94%.

For the project activity in question, the sum of CO2 and methane was observed to be less than 94% at the sites described below. Hence, the project developer has opted to use the minimum value of the sum of CO2 and methane found in its testing as the value to be applied for these sites. This value is 93.8%, rounding down to 93%, for the sum of CO2 and methane with 7% trace or other gas for sites 25752 and 26102 and 94.2%, rounding down to 94% for the sum of CO2 and methane with 6% trace or other gas for site 25792. Hence, if this request for deviation is accepted, the percentage of methane in biogas will be calculated as 93% minus the percentage of CO2 for sites 25752 and 26102 and 94% minus the percentage of CO2 for site 25792.

Measurements of the percentage of CO2 in biogas have the same accuracy as measurements of the percentage of methane. Hence, the monthly measurement of the percentage of CO2 and the calculation of the percentage of methane as described above ensures in our opinion the same level of accuracy.

EFP
According to the monitoring plan, the flare efficiency shall be measured at least annually. This frequency meets the general guidance for SSC CDM Methodologies which states in paragraph 12b, “Data elements that are generally constant and indirectly related to the emission reductions (e.g. Emission factors, Calorific Value, System Efficiencies) should be measured or calculated at least once in a year, unless detailed specifications are provided as part of the indicated methodology”. AMS-III.D, version 11, applied by the project does not specify the frequency of measuring the flare efficiency.

The frequency of flare efficiency measurements was less than annually for the sites with the following IDs: 25752, 25792, and 26102. The period of time elapsed per site without coverage of annual flare efficiency measurements is as follows:

Site ID Period Applicable Applied FE
25752 8 January 2008 -28 January 2009 50.00%
25792 9 January 2008 - 28 January 2009 50.00%
26102 27 December 2008-30 December 2008 50.00%

This thus represents a deviation from the monitoring plan. Hence, in the periods covered in column “Applicable period” it is suggested to apply a conservative flare efficiency of 50% as stipulated by the “Tool to determine project emissions from flaring gases containing methane”. The flare was confirmed to be operational on the basis of the weekly observations performed. Flare efficiency measurements show that the actual flare efficiencies are considerably higher than the 50% default. Therefore, applying the default value to the periods in column “Applicable period” is in our opinion a conservative approach.

Continuous monitoring of compliance of the flare with manufacturer’s specification is ensured by inspecting the flare regularly (typically weekly) and recording malfunctioning of the flare. If malfunctioning of the flare is recorded, the reported emission reductions are adjusted by not including the biogas produced from the day the flare was last observed to function properly to the day the flare is again functioning properly after malfunctioning of the flare has been observed. Moreover, the flares at all farms have a temperature and pressure measure device that assures the effective combustion of methane during the time the biogas is directed to the flare. If the temperature decreases, the electronic system closes the main valve and restarts after a few minutes with an electric spark. The flare design ensures that no gas is sent through the flare without the flare being ignited.
Assessment
As of October 2008 (for sites 25752 and 25792) and April 2009 (for site 26102), the direct measurement of methane has been implemented in accordance with the monitoring methodology and the monitoring plan and this practice will be used for all subsequent monitoring periods. To use measurements of the CO2 content of biogas to calculate the methane content instead of directly measuring the methane content is required due to the project participants initially not finding reliable and durable equipment for measuring methane at its project activities. Also the flare efficiency measurements have, and will continue to, occur on a regular basis at least annually. Hence, a request for deviation is suitable in accordance with paragraph 212 of the Validation and Verification Manual (Version 01.2).
Impact
The deviation is expected to result in an underestimation of the emission reductions as it is conservatively assumed that biogas contains 7% trace gases for sites 25752 and 26102 and 6% trace gases for site 25792. In addition the flare efficiency is 50%, for the respective periods.
Annexes Spreadsheet with recent methane and CO2 content measurements at sites within this project activity (n/a)
Link to the documentation made available at validation stage or monitoring report Link to relevant documentation
Signed form Signed form (n/a)
Decision This request for deviation has been accepted.

The Chairs have accepted the proposed request for deviation to the monitoring and reporting process for the first monitoring period.

Current status 29 Feb 2012 - Deviation accepted
Historic statuses 27 Dec 2011 - Submission received
23 Jan 2012 - Successfully passed the Completeness Check
14 Feb 2012 - Awaiting EB decision