Gas quality specifications and testing procedures for RNG derived from dairy or other waste
Outlined below are the current renewable natural gas (RNG) quality standards and required testing procedures applicable to RNG derived from dairy or other animal waste, which must be met for the initial and ongoing acceptance of RNG into Minnesota Energy Resources’ natural gas distribution system. RNG producers interconnecting to Minnesota Energy Resources natural gas distribution system must comply with these standards and procedures as well as all terms and conditions under applicable tariffs and agreements. RNG interconnection and ongoing acceptance of RNG must be consistent with Minnesota Energy Resources obligation to provide safe and reliable service and any applicable federal and state standards. Minnesota Energy Resources will continuously evaluate its gas quality standards and these RNG Gas Quality Standards and Testing Procedures may be revised from time-to-time at Minnesota Energy Resources sole discretion.
RNG Gas quality specifications
All RNG received into Minnesota Energy Resources distribution system shall conform to the gas quality specifications listed, which may be updated from time to time. All gas shall be free from objectionable odors, solid matter, dust, or any other substance which might interfere with the operation of the gas distribution lines and equipment through which it flows. The RNG producer shall demonstrate that the receipt gas meets the gas quality specifications. Prior to the initial delivery of gas into the distribution system, the RNG producer must provide test results from a sample of the receipt gas from an approved laboratory. The sample analysis must demonstrate an acceptable level for each constituent before the gas will be allowed into the distribution system.
Gas quality specifications for dairies/feedlots RNG
| Constituent |
Tolerance limits |
| Heating Value |
≥ 970 BTU/scf |
| H2O Content |
≤ 5 lbs/MMscf |
| O2 |
≤ 0.2 % |
| CO2 |
≤2 % |
| H2S |
≤4 ppm |
| Total Sulfur |
≤48 ppm |
| Ammonia |
≤10 ppm |
| Biologicals |
Technically free of |
| VOC |
Technically free of |
| Temperature |
≤120 |
Minnesota Energy Resources Interconnection equipment will have automatic and remote shut off capabilities for quality standards measured at the receipt station. Minnesota Energy Resources reserves the right to continuously monitor the constituents identified in the table above, and shut off the supply of gas into Minnesota Energy Resources distribution system if the gas exceeds the action limits. Minnesota Energy Resources may allow deviations from these standards on a case-by-case basis at its sole discretion.
Chromatograph and real-time testing
| Constituent |
Interconnection agreement tolerance limits |
Retesting required and allowed to flow |
Retesting required and instantaneous shut in |
Monitoring frequency |
| Heating Value |
≥ 970 BTU/scf |
N/A |
≤ 970 BTU/scf |
On-line, 5 min readings |
| H2O Content |
< 5 lbs/Mmcf |
> 6 lbs/Mmcf |
> 7 lbs/Mmcf |
On-line, real-time |
| O2 |
< 0.20 % |
> 0.30 % |
> 0.50% |
On-line, real-time |
| CO2 |
< 2.0 % |
> 2.5 % |
> 3.00 % |
On-line, real-time |
| H2S |
< 4.00 ppm |
> 4.25 ppm |
> 5.00 ppm |
On-line, real-time |
| Total Sulfur |
< 48 ppm |
> 65 ppm |
> 80 ppm |
On-line, real-time |
Constituent laboratory testing
Minnesota Energy Resources will require an RNG producer interconnecting to Minnesota Energy Resources distribution system to complete laboratory testing for the constituents listed in the following table. Required testing will be performed using independent certified third-party laboratories (Environmental Laboratory Accreditation Program (ELAP) certified, where applicable). Minnesota Energy Resources shall be notified of the RNG sampling and tests and have the option to observe the samples being taken. Test results will be shared with Minnesota Energy Resources within five calendar days of the test results being received by the RNG producer.
| Constituent |
Interconnection agreement tolerance limits |
Retesting required and allowed to flow |
Retesting required and instantaneous shut in |
Monitoring frequency |
| Ammonia |
< 10 ppm |
> 10 ppm |
> 15 ppm |
Off-site lab testing |
| Biologicals |
Technically free of |
> 4 x 10^4/scf |
> 8 x 10^4/scf |
Off-site lab testing |
| VOC |
Technically free of |
|
|
As needed |
1 Further details described in the “RNG Pre-Interconnection Verification Testing” and “RNG Periodic Testing” sections.
RNG Pre-interconnection verification testing
- Prior to the injection of RNG into Minnesota Energy Resources distribution system, samples shall be retrieved weekly for 2 weeks and sent for laboratory testing. Each gas sample should be taken no later than 8 days from the previous test.
- Additionally, Minnesota Energy Resources will analyze a minimum of 12 hours of continuous RNG to ensure gas quality before opening the valve into the Minnesota Energy Resources distribution system.
- If at any time, the gas does not meet the gas quality specifications, testing shall continue on a weekly basis until two consecutive weeks of results meet all RNG gas quality specifications.
RNG Periodic testing
Minnesota Energy Resources will require periodic testing as follows:
Monitoring Period 1 – Month 1- 6 (after RNG Verification). During Monitoring Period 1 (Month 1-6), samples are retrieved monthly for six months and sent for laboratory testing. Gas samples should be taken no later than 35 days from the previous test. If, at any time, the gas does not meet the gas quality specifications, the RNG producer will be required to repeat the RNG Verification Testing.
Monitoring Period 2 – Month 7-18. Upon successful completion of Monitoring Period 1, samples are retrieved quarterly (every 3 months) for an additional 12 months and sent for laboratory testing. Gas samples should be taken no later than 15 weeks from the previous test. If, at any time, the gas does not meet the gas quality specifications, the RNG producer will be required to repeat Monitoring Period 1.
Monitoring Period 3 – Month 19-36. Upon successful completion of Monitoring Period 2, samples are retrieved bi-annually (ever 6 months) for an additional 18 months and sent for laboratory testing. Gas samples should be taken no greater than 28 weeks from the previous test. If, at any time, the gas does not meet the gas quality specifications, the RNG producer will be required to repeat Monitoring Period 2.
Monitoring Period 4 – Months 37 and after. Upon successful completion of Monitoring Period 3, samples are retrieved annually for the length of time the RNG facility is in operation and sent for laboratory testing. Gas samples should be taken no greater than 13 months from the previous test. If, at any time, the gas does not meet the gas quality specifications, the RNG producer will be required to repeat Monitoring Period 3.
Minnesota Energy Resources shall have the right to share test results taken by Minnesota Energy Resources or provided by the RNG supplier with appropriate parties.
RNG Shut-off and restart procedures
An RNG producer interconnecting to Minnesota Energy Resources distribution system may be shut-off at Minnesota Energy Resources sole discretion if any of the following occurs:
- RNG is found to be not in compliance with any of the gas quality specifications.
- Minnesota Energy Resources determines that a change in the biogas source at the facility or the upgrading equipment will potentially increase the level of any constituent over the previously measured baseline levels.
- The RNG contains constituents at concentrations which are at levels that are injurious to pipeline facilities or are at levels that present a health and/or safety hazard to Minnesota Energy Resources employees, contractors, and/or the general public.
- Any other issue Minnesota Energy Resources determines may jeopardize the safety or reliability of its employees, customers, service, or systems.
In the event Minnesota Energy Resources rejects RNG for being outside of any specified gas quality range, it is the RNG producer’s responsibility to accept the rejected RNG from the point of interconnection. In order to restart injection after an RNG interconnect has been shut-in, the RNG producer must have at least one continuous hour of gas quality within specifications per real-time monitoring and confirm the gas quality issue has been resolved to Minnesota Energy Resources satisfaction, as noted below.
For each occurrence when RNG is shut-in from Minnesota Energy Resources distribution system due to quality reasons (real time or laboratory testing), the RNG producer shall promptly deliver to Minnesota Energy Resources a detailed report describing:
- Cause of the out-of-specification parameter
- Steps taken to rectify the situation
- Upgraded process/operation/maintenance plan to ensure the situation does not occur again
For on-line real-time testing, flow can continue before the report is received. For off-site laboratory testing, RNG producer report must be received before Minnesota Energy Resources valve is opened.
Notice of change in feedstock or conditioning process
RNG producer shall provide thirty (30) days advance notice to Minnesota Energy Resources before changing its RNG feedstock, feedstock source, or RNG conditioning process.
