How NC DAQ Will Evaluate Natural Gas Curtailment

DAQ received the following question:
With respect to gas curtailments, the way that we know if we're under a curtailment is if Transco puts the system under an "Operational Flow Order". The other way we could know is if our provider issues an "Operational Alert". The reason I ask is that it appears that Transco has issued an OFO starting Monday and wanted to make sure that my notes were correct before I told operations we could burn fuel oil in our natural gas package boiler during that time if we needed to.

Text from 40 CFR 63 5D/6J Boiler rules regarding curtailment:

§63.7575 (5D) / §63.11237 (6J)
What definitions apply to this subpart?
Period of gas curtailment or supply interruption means a period of time during which the supply of gaseous fuel to an affected boiler or process heater is restricted or halted for reasons beyond the control of the facility. The act of entering into a contractual agreement with a supplier of natural gas established for curtailment purposes does not constitute a reason that is under the control of a facility for the purposes of this definition. An increase in the cost or unit price of natural gas due to normal market fluctuations not during periods of supplier delivery restriction does not constitute a period of natural gas curtailment or supply interruption. On-site gaseous fuel system emergencies or equipment failures qualify as periods of supply interruption when the emergency or failure is beyond the control of the facility.

DAQ interprets the MACT/GACT language to mean that whenever there is an operational flow order issued by Transco (which provides all NG to suppliers in North Carolina) or an operational alert from the supplier based upon notices from Transco that a curtailment event will or has occurred. DAQ applies the MACT 5D/6J definitions and logic to compliance determinations made for Boiler 112(j) permits in terms of curtailment (see below). Burning oil during periods of curtailment does not change the boiler classification.

Transco website listing operational flow orders:
You can find the operational flow orders under "Notices" and then "Critical"

Potential reporting issues (5D)

§63.7545 What notifications must I submit and when? (f) If you operate a unit designed to burn natural gas, refinery gas, or other gas 1 fuels that is subject to this subpart, and you intend to use a fuel other than natural gas, refinery gas, gaseous fuel subject to another subpart of this part, part 60, 61, or 65, or other gas 1 fuel to fire the affected unit during a period of natural gas curtailment or supply interruption, as defined in §63.7575, you must submit a notification of alternative fuel use within 48 hours of the declaration of each period of natural gas curtailment or supply interruption, as defined in §63.7575. The notification must include the information specified in paragraphs (f)(1) through (5) of this section. (1) Company name and address. (2) Identification of the affected unit. (3) Reason you are unable to use natural gas or equivalent fuel, including the date when the natural gas curtailment was declared or the natural gas supply interruption began. (4) Type of alternative fuel that you intend to use. (5) Dates when the alternative fuel use is expected to begin and end.

§63.7555 What records must I keep? (h) If you operate a unit in the unit designed to burn gas 1 subcategory that is subject to this subpart, and you use an alternative fuel other than natural gas, refinery gas, gaseous fuel subject to another subpart under this part, other gas 1 fuel, or gaseous fuel subject to another subpart of this part or part 60, 61, or 65, you must keep records of the total hours per calendar year that alternative fuel is burned and the total hours per calendar year that the unit operated during periods of gas curtailment or gas supply emergencies.

112(j) permit holders - read your permit. Some early Boiler 112(j) permits included a limitation on the amount of oil that could be combusted over a period of time that might require testing without a specific exemption to exclude periods of curtailment. If you have this type of limitation, you will need to request a permit modification in order to avoid deviating from your permit.

Here is one example of that language being applied to boilers and Dowtherm heaters:

1. Emissions from boilers 1 and 2 and Dowtherm heaters 3, 4, and 5 shall not exceed the emissions limitations listed below as a result of firing No. 6 fuel oil:

Compliance Testing [15A NCAC 2Q .0508(f)] 

2. To demonstrate compliance with the standards provided in Section 2.1 E.5.b, above, the Permittee shall conduct compliance tests on boilers 1 and 2 and Dowtherm heaters 3, 4, and 5 for each listed pollutant.​

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