19:28 23 May 19
I-DEV0320: Measurement of methane content of biogas and flare efficiency
|Submitted by||DNV (17 Jun 2010)|
|Project activity||658: AWMS Methane Recovery Project MX06-S-36, Coahuila, Durango and Nuevo León, México|
|Selected monitoring period||19 Dec 2006 - 31 Jan 2010|
|Title/subject of deviation||Measurement of methane content of biogas and flare efficiency|
This request is to allow deviation of measurement of CH4 content of biogas as specified by ID2 in Table D1 of the registered PDD by measuring the CO2 content of biogas and calculating the CH4 content instead of directly measuring the CH4 content. This request is also to allow for deviation of testing flare efficiency as specified by ID4 in Table D1 of the registered PDD by applying the default value allowed in “Tool to determine project emissions from flaring gases containing methane”.
The project developer has undergone an extensive evaluation and selection process to find the most reliable and durable equipment for measuring CH4 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 September/November 2008, the direct measurement of CH4 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 CH4 content the project developer has monitored the CH4 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 CH4. Recent measurements of both the CH4 and CO2 content of biogas taken from sites within this project activity showed that the sum of CO2 and CH4 averaged 98.76% with a 95% confidence level of 96.20%. An earlier analysis of other similar advanced Animal Waste Management Systems (AWMS) in Brazil and Mexico, developed by the same project developer and applying the same project technology showed that the sum of CO2 and CH4 averaged 99.0% with a 95% confidence level of 96.7%. However, in order to be most conservative, the project developer has opted to use the minimum value of the sum of CO2 and CH4 found in its testing as the value to be applied across the all projects of this methodology version. This value is 94% for the sum of CO2 and CH4 with 6% trace or other gas. Hence, if this request for deviation is accepted, the percentage of CH4 in biogas will be calculated as 94% minus the percentage of CO2.
Measurements of the percentage of CO2 in biogas have the same accuracy as measurements of the percentage of CH4. Hence, the monthly measurement of the percentage of CO2 and the calculation of the percentage of CH4 as described above ensures in our opinion the same level of accuracy.
In order to test flare efficiency, the project developer had to develop sampling methods and tools specific for the flare type installed. One of the necessary tools for this procedure was identifying the proper equipment for measuring CH4 in the flare exhaust gas. This equipment is the same as used to measure ID2 and, therefore, due to the same reasons as listed above, the initial testing of flare efficiency did not occur within the first months of installation. Since the project developer has now fully deployed the required tools and methods, flare efficiency testing has, and will continue to, occur on a regular basis 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 9, applied by the project does not specify the frequency of measuring the flare efficiency.
In absence of mesurements of the flare efficiency shortly after installation of the flare, a default flare efficiency is suggested to be applied until the date of the first flare efficiency measurements. A flare efficiency of 50% as stipulated by the “Tool to determine project emissions from flaring gases containing methane” is suggested to be applied when the flare was confirmed to be operational on the basis of the weekly observations performed. Recent test results of flare efficiency on sites within this project activity demonstrate that the actual flare efficiencies are considerably higher than the 50% default. Therefore, applying the default value to the period prior to the initial flare efficiency test 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 have a continuous ignition device that assures the effective combustion of CH4 during the time the biogas is directed to the flare. Approximately 60 times a minute the spark is ignited in order to ensure complete combustion. The flare design ensures that no gas is sent through the flare without the flare being ignited and thus ensures appropriate destruction of CH4.
As of September/November 2008, the direct measurement of CH4 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 CH4 content instead of directly measuring the CH4 content is required due to the project participants initially not finding reliable and durable equipment for measuring CH4 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 209 of the validation and verification manual (Version 01.1).
The deviation is expected to result in an underestimation of the emission reductions as it is conservatively assumed that biogas contains 6% trace gases and that the flare efficiency is 50%, respectively.
|Annexes||Spreadsheet with recent CH4 and CO2 content measurements at sites within this project activity (31 KB)|
|Link to the documentation made available at validation stage or monitoring report||Link to relevant documentation|
|Signed form||Signed form (445 KB)|
|Decision||This request for deviation has been accepted.|
|Current status||24 Aug 2010 - Deviation accepted|
17 Jun 2010 -
15 Jul 2010 - Successfully passed the Completeness Check
09 Aug 2010 - Awaiting EB decision