This article appears in the Spring 2024 issue of Tanks and Terminals magazine, a copyrighted publication of Palladian Publications.
On October 4, 2023, the Environmental Protection Agency (EPA) proposed New Source Performance Standard (NSPS) Subpart Kc for Volatile Organic Liquid Storage Vessels (Including Petroleum Liquid Storage Vessels), EPA’s first NSPS for this equipment type in 40 years. EPA is expected to finalize NSPS subpart Kc by a court-ordered date of September 30, 2024. The new regulation will apply to storage tanks in volatile organic liquid (VOL) service that commence construction, reconstruction, or modification after October 4, 2023. In the subpart, EPA proposes a broad, unprecedented approach to determining when a tank becomes subject to the rule by “modification.” Among other changes, EPA also proposes to require more stringent emission control requirements for certain tanks, annual Lower Explosive Limit (LEL) monitoring within internal floating roof (IFR) tanks, and control of degassing events.
Background
EPA promulgated NSPS subpart K, specific to storage vessels for petroleum liquids, in 1974.[1] These standards were amended several times before 1980, when EPA proposed to establish revised NSPS for storage vessels for petroleum liquids as NSPS subpart Ka.[2] In 1982, EPA published a list of priority sources for which additional NSPS should be established, and VOL storage vessels at synthetic organic chemical manufacturers were included in the priority list.[3]
In 1987, EPA promulgated an emission standard for VOL storage vessels (including petroleum liquid storage vessels) for which construction, reconstruction, or modification commenced after July 23, 1984, as NSPS subpart Kb. This subpart regulates storage vessels with a capacity of 75 cubic meters (m3) (∼20,000 gallons) or more that store VOLs with a true vapor pressure over 15.0 kilopascals (kPa) (2.18 pounds per square inch [psia]), and from storage vessels with a capacity of 151 m3 (∼40,000 gallons) or more that store organic liquids with a true vapor pressure over 3.5 kPa (0.51 psia). NSPS subpart Kb required storage vessels with the following parameters to install emission controls that include the use of either an IFR, an external floating roof (EFR), or a closed vent system and a control device:
- A capacity of 75 m3 (∼20,000 gallons) or more that store VOLs with a true vapor pressure of 27.6 kPa (4.0 psia) or greater; and
- A capacity of 151 m3 (∼40,000 gallons) or more that store organic liquids with a true vapor pressure of 5.2 kPa (0.75 psia) or greater.
Subpart Kb also required use of a fixed roof tank with a closed vent system and emission control device for storage of organic liquids with a true vapor pressure of 11.1 psia or greater.
The standards set in NSPS subpart Kb for storage vessels with an EFR or IFR are a combination of design, equipment, work practice, and operational standards. These standards require, for tanks complying using a floating roof, that a rim seal be installed continuously between the inner wall of the vessel and the floating roof to prevent VOC emissions from reaching the atmosphere. Subpart Kb also contains several requirements for fittings on the floating roof.
Applicability and Exemption
The following tanks will be subject to emission requirements set forth in NSPS subpart Kc:
Storage tanks with capacities between 20,000 and 40,000 gallons which store liquids with a maximum true vapor pressure greater than or equal to 1.5 psia and storage tanks with capacity greater than or equal to 40,000 gallons which store liquids with a maximum true vapor pressure greater than or equal to 0.5 psia that is used to store VOL for which commence construction, reconstruction, or modification after October 4, 2023.[4]
The thresholds requiring emission control are lower in the proposed rule than in subpart Kb. EPA’s proposed threshold for tanks of capacity 40,000 gallons or greater is 1.5 psia (contrast 4.0 psia in subpart Kb); for tanks of capacity 20,000 to 40,000 gallons, the proposed threshold is 0.51 psia (contrast 0.75 psia in subpart Kb). Also, unlike subpart Kb, the proposed NSPS subpart Kc affected facility definition does not exempt certain tanks above 20,000 gallons’ capacity based on maximum true vapor pressure. Any VOL tank above 20,000 gallons’ capacity, and constructed, modified, or reconstructed after October 4, 2023, must compare its maximum true vapor pressure to the emission control thresholds.
Most exemptions from subpart Kb based on equipment type are continued under the proposed subpart Kc. Exemptions include mobile vehicle vessels, pressure vessels of 204.9 kPa (29.7 psia) or greater, petroleum or condensate vessels prior to custody transfer, beverage alcohol storage vessels, and vessels at bulk gasoline plants and service stations. EPA proposes not to carry forward the exemption for vegetable oil storage vessels regulated by 40 CFR 63 subpart GGGG.[5]
Existing storage vessels become subject to new NSPS only when they are “modified,” or “reconstructed,” as those terms are used in 40 CFR part 60.[6] Under NSPS subpart Kb, EPA has held that storage vessel “modifications” are rare, because construction specifications of the vessel rarely need to be changed to accommodate various liquids.[7] EPA’s rule proposal anticipates a similarly low rate of modifications, but the proposed text is open to interpretations that would heavily accelerate the number of tanks “modifying” into subpart Kc.[8] The proposed rule text holds that “if the storage vessel is used to store a VOL that has a higher maximum true vapor pressure than the VOL previously stored,”[9] the vessel is modified.[10] This approach departs starkly from EPA’s policy of over 40 years.
Best System of Emission Reduction
EPA is proposing performance standards to the Best System of Emission Reduction (BSER) as well as alternative compliance standards for affected storage vessels. Many of the NSPS subpart Kc standards follow standards established in NSPS subpart Kb, or render them more stringent.
For storage vessels storing VOL with maximum true vapor pressures less than 11.1 psia, EPA proposes the following standards of performance for newly constructed and reconstructed IFRs:
- For a New or Reconstructed Tank, an Internal Floating Roof with a liquid-mounted or a mechanical shoe seal primary seal and a rim-mounted secondary seal.[11]
- For a New or Reconstructed Tank, an External Floating Roof with a liquid-mounted or a mechanical shoe seal primary seal and a rim-mounted secondary seal, welded deck seams, an unslotted guidepole with gasketed sliding cover and pole wiper may be used, or if a slotted guidepole is used, a liquid mounted primary seal is required and the slotted guidepole must have a gasketed sliding cover, pole sleeve and pole wiper (with or without float).[12]
For storage vessels with maximum true vapor pressures greater than or equal to 11.1 psia, EPA is proposing to determine that the BSER is closed vent system and control, and the standard of performance reflecting the BSER is a 98 weight-percent or greater reduction in VOC emissions. The weight percent in NSPS subpart Kc is greater than the 95 percent in NSPS subpart Kb.
Changes to Rim Seal and Deck Fitting Requirements
EPA is proposing new rim seal requirements for IFR tanks, aligning EFR and IFR standards: a primary seal of either liquid-mounted or mechanical shoe seal type, with a rim-mounted secondary seal.
As stated above, EPA proposes that new or reconstructed EFR tanks either use no slotted guidepole, or a liquid-mounted rim seal. However, slotted guidepoles are often used for essential purposes such as fuel sampling or level gauging. Whereas, replacing a liquid-mounted rim seal with shorter service life would require a roof landing, causing emissions.
NSPS subpart Kc also includes numerous design requirements for deck fittings on floating roofs. Unlike subpart kb, the proposed subpart would require bolts on access hatches and gauge float wells, and would prohibit the use of slit fabric seals on gauge hatch sample wells.[13]
Controlled Degassing
EPA proposes controlled degassing for all fixed-roof tanks that use a control device for routine emissions. Based on cost effectiveness, EPA selected a one-million-gallon capacity threshold for floating roof storage vessels:
Control degassing for storage vessels with a capacity of 1-million gallon or more storing organic liquids with a maximum true vapor pressure of 1.5 psia or more.[14]
The requirements set forth in NSPS subpart Kc need to be met until the vapor space in the storage vessel is measured to be less than 10 percent of its LEL.[15]
Annual Monitoring of IFR LEL
EPA proposes that affected IFR storage vessels use an LEL monitor as a supplement to visual inspection, with an action threshold of 25 percent.[16] If a concentration reading exceeds 25 percent for the highest 5-minute period within a 20-minute monitoring period, the result would be considered an inspection failure similar to a visual inspection failure.
Fixed Roof Tank Requirements
For storage tanks using a closed vent system (CVS) to route routine emissions to a control device, fuel gas system, process, or flare, EPA proposes several requirements, including initial and annual leak inspections for the CVS; bypass prevention practices such as a car seal; and pressure relief device monitoring.[17]
Reporting Requirements
EPA proposes reporting requirements including initial notifications and semiannual reports. In contrast with Part 63 NESHAP, EPA proposes that subpart Kc tank owners or operators would be subject to different semiannual reporting timeframe windows for individual storage vessels.[18] Tracking the reporting timeframes for each tank could create additional compliance burden for owners and operators.
Preparing for the Changes
EPA has proposed substantial changes to air emission standards for VOL storage vessels. The proposed changes include revisions to the definition of modification, a new set of emission standards, seal and fitting requirements, and reporting requirements. Understanding that requirements are not final, tank owners and operators should begin assessing whether tank projects will be subject, and should begin developing compliance strategies.
Harold Laurence ([email protected]), Managing Consultant at Trinity Consultants, is based out of Trinity’s Seattle office. For the past 10 years, Mr. Laurence has provided Clean Air Act consulting support to the U.S. liquid terminal and petroleum refining industries. He leads Trinity’s nationwide group of storage tank subject matter experts. Mr. Laurence earned his bachelor’s in chemical engineering from the University of Kansas and is a licensed Professional Engineer in Washington and Hawaii.
Ben Safavinia ([email protected]), Senior Consant at Trinity Consultants, is based out of Trinity’s Phoenix office. For the past 5 years, Mr. Safavinia has provided environmental permitting, reporting, and compliance support for facilities across the U.S. Mr. Safavinia graduated from Louisiana State Engineering with an M.S. degree in chemical engineering.
[1] 39 Fed. Reg. at 9317 (March 8, 1974).
[2] 45 Fed. Reg. at 23379 (April 4, 1980).
[3] 47 Fed. Reg. at 951 (January 8, 1982).
[4] 88 Fed. Reg. at 68535 (October 4, 2023).
[5] 40 CFR 60.110b(d). Cf. proposed § 60.110c(b).
[6] Cf. the definition of modification in § 60.2, “change in the method of operation of, an existing facility which increases the amount of any air pollutant” or in § 60.14(a) “operational change to an existing facility which results in an increase in the emission rate to the atmosphere of any pollutant to which a standard applies.”
[7] 49 Fed. Reg. at 29707 (July 23, 1984). EPA has historically applied the “alternative fuel or raw material” exemption of § 60.14(e)(4).
[8] When EPA proposed NSPS subpart Kc, EPA expected 27 to 30 tanks to become “modified” into the rule within 5 years. 88 Fed. Reg. at 68545; 68551. According to EPA’s cost basis for the proposed rule thousands of tanks are subject to NSPS subpart Kb at present, and many more tanks have not yet been modified into a K series subpart. At stake is the rate at which tanks become “modified” and enter subpart Kc.
[9] Proposed § 60.110c(e).
[10] In the proposal preamble for NSPS subpart Kc, EPA proposes that changing the stored liquid does not constitute a ‘‘use of an alternative fuel or raw material,’’ and § 60.14(e)(4) does not exempt service changes from the §§ 60.2 and 60.14 modification definition. 88 Fed. Reg. at 68544 (October 4, 2023).
[11] Proposed § 60.112c(b).
[12] Proposed § 60.112c(c).
[13] Proposed § 60.112c(b)(6), (7); (c)(2)(iv), (v).
[14] Proposed Federal Register/Vol. 88, No. 191. Table 7
[15] Proposed § 60.112c(e).
[16] Proposed § 60.112c(b)(16).
[17] Proposed § 60.112c(d)(2) contains a detailed list of requirements.
[18] Proposed § 60.116c(d).
