EPA PROPOSED AMENDMENTS TO THE HAZARDOUS ORGANIC NESHAP (HON)
Background:
The U.S. EPA published proposed amendments to the National Emission Standards for Hazardous Air Pollutants (NESHAP) that apply to the Synthetic Organic Chemical Manufacturing Industry (SOCMI) on April 25, 2023. The rules commonly referred to as the Hazardous Organic NESHAP or the HON are contained in 40 CFR Part 63 Subparts F, G, H, and I. The HON was last amended in December 2006, but the Clean Air Act requires EPA to complete residual risk assessments every 8 years. By not meeting this 8-year requirement, EPA is now under court order to finalize the amendments to these regulations and issue a final rule by March 29, 2024. Comments on the proposed amendments were due July 7, 2023. While the amendments to the HON are not yet final, it is important that companies with a chemical manufacturing process unit (CMPU) subject to the HON start to make note of the new compliance requirements, and that these companies make every effort to ensure that resources are available to make any changes that would be necessary to be in compliance. Most requirements must be implemented within 3 years of the HON amendments being finalized, but certain requirements must be implemented within 2 years of the final rule.
Key changes to the HON can be categorized into the following topics:
Flexible Operation Units | Storage Vessels |
Process Vents | Transfer Operations |
Performance Tests | Surge Control Vessels |
Flares | Pressure Relief Devices |
Maintenance Vents | Ethylene Oxide |
Heat Exchange Systems | Fenceline Monitoring |
These topics are discussed briefly in this article with reference to the proposed rule for further reading.
Flexible Operation Units §63.100(d)(3)(iii)
As defined, flexible operation units are chemical manufacturing process units that manufacture different chemical products periodically by alternating their raw materials or their operating conditions. The primary product of these units determines its applicability under the HON. The product manufactured for the greatest annual operating time shall be the primary product unless operating time is equal for multiple products, then the product with the greatest annual production on a mass basis shall be the primary product. The HON updates include language that requires a facility to determine the primary product using data from the past 5 years. If that product is subject to the HON, and if the owner or operator intends to produce that primary product in the future, then the unit must comply with the HON requirements.
Process Vents
For process vents, EPA is proposing to remove the total resource effectiveness (TRE) concept in its entirety (see proposed 40 CFR §63.113(a)(4)). This effectively makes any process vent that emits greater than or equal to 1 lb/hour of total organic hazardous air pollutants (HAP) a Group 1 process vent. All Group 1 process vents have to be controlled, and therefore, performance testing is required to demonstrate compliance with the emissions standards. EPA is also proposing to add an emission standard of 0.054 nanograms per dry standard cubic meter at 3 percent oxygen (toxic equivalency basis) for dioxins and furans from chlorinated process vents.
Performance Tests
For Storage Vessels, EPA is proposing initial performance tests and subsequent annual performance tests for leaks using EPA Method 21 and 40 CFR 60, appendix A-7 to demonstrate no detectable emissions (see proposed 40 CFR §63.119(a)(7)).
For Group 1 process vents, which are now more broadly defined as indicated in the above changes, initial and subsequent performance tests are now required to be conducted no later than 60 calendar months (5 years) after the previous performance test(§63.103(b)(1)). Group 1 process vents must vent to a flare or reduce emissions of HAPs by at least 98% or reduce emissions of HAPs to 20 ppmv, whichever is less stringent. If using a recovery device, at least 98% HAP emissions reduction is required.
Flares
By effectively removing the 50 ppmv and 0.005 standard cubic meter per minute Group 1 process vent thresholds from the Group 1 process vent definition, owners and operators are required to reduce emissions of total organic HAP emissions from process vents using a flare meeting the proposed operating and monitoring requirements for flares in NESHAP Subpart F; or reduce total organic HAP emissions by 98 percent by weight or an exit concentration of 20 ppmv, whichever is less stringent. (see proposed 40 CFR §63.101 and 40 CFR §63.113(a)(1) and (2)). Additionally, owners and operators that are subject to the new requirements for equipment in ethylene oxide (EtO) service are allowed to control EtO emissions with a flare. However, EPA is proposing a requirement that owners and operators can send no more than 20 tons of EtO to all of their flares combined in any consecutive 12-month period (see proposed 40 CFR §63.108(p)) to get to an acceptable level of risk from all HON emission sources at a facility.
Maintenance Vents
EPA is proposing a work practice standard for maintenance vents requiring that, prior to opening process equipment to the atmosphere, the equipment must be either:
- Be drained and purged to a closed system so that the hydrocarbon content is less than or equal to 10 percent of the lower explosive limit (LEL);
- Be opened and vented to the atmosphere only if the 10-percent LEL cannot be demonstrated and the pressure is less than or equal to 5 psig, provided there is no active purging of the equipment to the atmosphere until the LEL criterion is met;
- Be opened when there is less than 50 lbs of VOC that may be emitted to the atmosphere; or
- For installing or removing an equipment blind, depressurize the equipment to 2 psig or less and maintain pressure of the equipment where purge gas enters the equipment at or below 2 psig during the blind flange installation, provided none of the other proposed work practice standards can be met (see proposed 40 CFR §63.113(k)).
Heat Exchange Systems
EPA is proposing that current leak monitoring for heat exchange systems will be replaced with the Modified El Paso Test Method. The method includes setting up an air stripper field instrument to strip off hydrocarbons and an FID analyzer, collecting the exhaust into stainless steel canisters or tedlar bags. Monitoring using the Modified El Paso Method will need to be conducted monthly for 6 months and then quarterly. Owners and operators must repair leaks within 45 days if the method detects a leak of 6.2 ppmv or greater of total strippable hydrocarbons. (see proposed 40 CFR §63.104(g) through (j)).
Storage Vessels
EPA is proposing a work practice standard to allow storage vessels to be vented to the atmosphere once a storage vessel degassing concentration threshold is met (i.e., less than 10 percent of the LEL) and all standing liquid has been removed from the vessel (see proposed 40 CFR §63.119(a)(6)). EPA is adding a definition for pressure vessel and removing the exemption from the HON for “pressure vessels designed to operate in excess of 204.9 kilopascals and without emissions to the atmosphere” (see proposed 40 CFR §63.101). New requirements for Internal floating roof tanks (IFR) are being proposed in 40 CFR §63.119(b)(5). Lastly, EPA is also revising the Group 1 storage capacity criterion for storage vessels at existing sources from between 75 m3 and 151 m3 to between 38 m3 and 151 m3 (now tanks above 10,038 gallon capacity will be Group 1 vessels); and the criterion for maximum true vapor pressure of total organic HAP for Group 1 vessels will be lowered from 13.1 kPa to 6.9 kPa (or 1 psi) – see proposed Table 5 to subpart G.
Transfer Operations
For transfer racks, EPA is proposing to remove the applicability exemption for transfer operations that load “at an operating pressure greater than 204.9 kilopascals” from the definition of transfer operation (see proposed 40 CFR §63.101).
Surge Control Vessels
The HON defines a surge control vessel to mean feed drums, recycle drums, and intermediate vessels. Surge control vessels are used within a CMPU when in-process storage, mixing, or management of flow rates or volumes is needed to assist in production of a product. The HON defines a bottoms receiver as a tank that collects distillation bottoms before the stream is sent for storage or for further downstream processing. Surge control vessels and bottoms receivers are not considered storage vessels under the HON because they are covered by the equipment leak provisions. In the proposed amendments to the HON, at 40 CFR 63.170(b), owners and operators of all surge control vessels and bottoms receivers that emit greater than or equal to 1.0 lb/hr of total organic HAP would be required to reduce emissions of organic HAP using a flare meeting the proposed operating and monitoring requirements for flares; or reduce emissions of total organic HAP or TOC by 98 percent by weight or to an exit concentration of 20 ppmv, whichever is less stringent. These requirements are in line with the proposed requirements for process vents.
Pressure Relief Devices
Another measure to reduce equipment leaks is the monitoring and repair of pressure relief devices. In the proposed HON amendments, EPA has included a work practice standard for pressure relief devices (PRDs) that vent to the atmosphere that would require owners and operators to implement at least three prevention measures, perform root cause analysis and corrective action in the event that a PRD does release emissions directly to the atmosphere, and monitor PRDs using a system that is capable of identifying and recording the time and duration of each pressure release and of notifying operators that a pressure release has occurred (see proposed 40 CFR 63.165(e)).
Ethylene Oxide
As a result of EPA’s risk review, there are now specific, tightened requirements for processes involving Ethylene Oxide (EtO). The proposed rules have a new definition for “in ethylene oxide service” for different equipment and processes subject to the HON. The definition and the associated requirements are summarized in the below table.
SOURCE TYPE | DEFINITION OF “IN ETHYLENE OXIDE SERVICE” | REQUIREMENTS |
Heat Exchange Systems | Each heat exchange system in a process that cools process fluids that are at least 0.1% by weight of EtO. | Required to conduct weekly leak monitoring and repair leaks within 15 days from the sampling date, and delay of repair would not be allowed (§63.104 (g)(6) and (h)(6)). |
Process Vents | Each process vent with an uncontrolled concentration of greater than or equal to 1 ppmv of EtO and when combined, the sum of all process vents is greater than or equal to 5 lbs/year. | Reduce emissions of EtO from process vents in EtO service by either: (1) venting emissions through a closed-vent system to a control device that reduces EtO by greater than or equal to 99.9 percent by weight, to a concentration less than 1 ppmv for each process vent, or to less than 5 lb/yr for all combined process vents; or (2) venting emissions through a closed-vent system to a flare meeting the proposed operating and monitoring requirements for flares in NESHAP subpart F (§63.113(j), §63.108, and §63.124). |
Maintenance Vents | See process vents in EtO service definition. | Owners and operators of process vents in EtO service would not be allowed to use the proposed maintenance vent work practice standards; instead, owners and operators would be prohibited from releasing more than 1.0 ton of EtO from all maintenance vents combined in any consecutive 12-month period (§63.113(k)(4)). |
Storage Vessels | Each storage vessel where the concentration of ethylene oxide in the stored liquid is at least 0.1% by weight. | Reduce emissions of EtO from storage vessels in EtO service by either: (1) venting emissions through a closed-vent system to a control device that reduces EtO by greater than or equal to 99.9 percent by weight or to a concentration less than 1 ppmv for each storage vessel vent; or (2) venting emissions through a closed-vent system to a flare meeting the proposed operating and monitoring requirements for flares in NESHAP subpart F (§63.119(a)(5), §63.108, and §63.124). |
Wastewater | Each wastewater stream that has an annual average concentration of EtO greater than or equal to 1 ppmw at any flow rate. | Revised definition of Group 1 wastewater streams to include all wastewater streams in EtO service. Thus, these streams must be treated as Group 1 wastewater streams and controlled as required (§63.132(c)(1)(iii) and (d)(1)(ii)). |
Equipment Leaks | Any equipment that contains or contacts a fluid that is at least 0.1% by weight EtO. | Connector components in gas/vapor and light liquid service require leak monitoring on a monthly basis with a leak definition of 100 ppm (§63.174). Pumps in light liquid service require leak monitoring on a monthly basis with a leak definition of 500 ppm (§63.163). Valves in gas/vapor and light liquid service require leak monitoring on a monthly basis with a leak definition of 100 ppm (§63.168). |
Fenceline Monitoring
EPA is proposing to add a fenceline monitoring standard that requires owners and operators to monitor for any of 6 specific HAP they emit (i.e., benzene, 1,3-butadiene, ethylene dichloride, vinyl chloride, EtO, and chloroprene) and conduct root cause analysis and corrective action upon exceeding the annual average concentration action level set forth for each HAP (see proposed 40 CFR §63.184). Since the proposed HON amendments do not include a minimum emission rate threshold for the fenceline monitoring requirements for these 6 HAPs, even facilities with low level emissions of benzene from the combustion of natural gas would have to comply with these new requirements.
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