On November 8, 2018, US EPA issued final amendments to the Refinery Sector Rule. These final amendments are based on EPA’s April 10, 2018 proposal. As of November 19, this final rule has not been published in the Federal Register, so this analysis is based on the pre-publication copy of the rule. The amendments covered many topics but this summary will only address impacts to the portions of the rule dealing with flares. For the red-line/strikeout rule language in this blog post, I relied on a document detailing the full rule recently provided by AFPM. That document was prepared by my other good friends at Barr Engineering. My appreciation to both parties for their excellent work. The notes that accompany many of the sections below are mine. The green underlined text indicates text added to the current regulatory language. The red strikethrough text indicates deletions from the current regulatory language. I'm feeling the holiday spirit early this year… The flare-related amendment changes are helpful for flare operators. They provide more clarity and, in some places, needed flexibility to meet the RSR flare requirements. Definition Changes [63.641] Flare purge gasmeans gas introduced between a flare header's water seal and the flare tip to prevent oxygen infiltration (backflow) into the flare tip . or for other safety reasons. For a flare with no water seal, the function of flare purge gas is performed by flare sweep gas and, therefore, by definition, such a flare has no flare purge gas. Flare supplemental gas means all gas introduced to the flare in order to improve the combustible characteristics heat content of combustion zone gas. Flare supplemental gas does not include assist air or assist steam. My Note: Hydrogen can be added to flare vent gas to reduce the propensity of the flare to smoke. Does this mean that hydrogen used in this way is not supplemental gas if NHVcz is above 294 Btu/scf? If it’s not, what is it? Perimeter Assist Air Added to Upper/Lower Steam [63.670(f)] (f) Dilution operating limits for flares with perimeter assist air. Except as provided in paragraph (f)(1) of this section, for each flare actively receiving perimeter assist air, the owner or operator shall operate the flare to maintain the net heating value dilution parameter (NHVdil) at or above 22 British thermal units per square foot (Btu/ft2) determined on a 15-minute block period basis when regulated material is being routed to the flare for at least 15-minutes. The owner or operator shall monitor and calculate NHVdil as specified in paragraph (n) of this section. (1) If the only assist air provided to a specific flare is perimeter assist air intentionally entrained in lower and/or upper steam at the flare tip and the effective diameter is 9 inches or greater, the owner or operator shall comply only with the NHVcz operating limit in paragraph (e) of this section for that flare. My Note: See also my blog post, Btu per SQUARE FOOT? What the heck is EPA’s Flare Dilution Factor?, on the derivation of the EPA Dilution Factor. Visible Emissions Monitoring [63.670(h)] (h) Visible emissions monitoring. The owner or operator shall monitor visible emissions while regulated materials are vented to the flare. conduct an initial visible emissions demonstration must be conducted using an observation period of 2 hours using Method 22 at 40 CFR part 60, appendix A-7. The initial visible emissions demonstration should be conducted the first time regulated materials are routed to the flare. Subsequent visible emissions observations must be conducted using either the methods in paragraph (h)(1) of this section or, alternatively, the methods in paragraph (h)(2) of this section. The owner or operator must record and report any instances where visible emissions are observed for more than 5 minutes during any 2 consecutive hours as specified in §63.655(g)(11)(ii). (1) At least once per day for each day regulated material is routed to the flare, conduct visible emissions observations using an observation period of 5 minutes using Method 22 at 40 CFR part 60, appendix A-7. If at any time the owner or operator sees visible emissions while regulated material is routed to the flare, even if the minimum required daily visible emission monitoring has already been performed, the owner or operator shall immediately begin an observation period of 5 minutes using Method 22 at 40 CFR part 60, appendix A-7. If visible emissions are observed for more than one continuous minute during any 5-minute observation period, the observation period using Method 22 at 40 CFR part 60, appendix A-7 must be extended to 2 hours or until 5-minutes of visible emissions are observed. Daily 5-minute Method 22 observations are not required to be conducted for days the flare does not receive any regulated material. My Note: On November 14, 2018, EPA amended Method 22 allowing digital photography to be used for some of the recordkeeping requirements of the method (sky background, sun position, etc). Measuring Perimeter Assist Air [63.670(i)] (5) Continuously monitoring fan speed or power and using fan curves is an acceptable method for continuously monitoring assist air flow rates. (6) For perimeter assist air intentionally entrained in lower and/or upper steam, the monitored steam flow rate and the maximum design air-to-steam volumetric flow ratio of the entrainment system may be used to determine the assist air flow rate. My Note: Paragraph 6 is a welcome change since there is no straightforward way to measure air entrained in steam. I’ll be very curious to see how this affects the NHVcz of these types of flares since, previously, this entrained air was not accounted for in the NHVcz calculation used prior to RSR. Standard Flow for Exit Velocity [63.670(k)(3)] In the RSR, the flare exit velocity calculation (Vtip) used actual cubic feet for volumetric flow. This was a change from previous calculations using standard cubic feet and would have resulted in many flares reporting higher flows based solely on this calculation artifact. This has been corrected back to standard cubic feet. Supplemental Gas Description In several locations in the amendments, the description of supplemental gas has changed in equation term descriptions. Below is one instance. All other instances where the change is made are consistent with this. NHVNG = Net heating value of flare supplemental natural gas to the flare for the 15-minute block period determined according to the requirements in paragraph (j)(5) of this section, Btu/scf.
OK… This is a long one. In the Refinery Sector Rule, EPA established an interesting parameter they named the “Net Heating Value Dilution Parameter” or NHVdil. It is measured in Btu/ft2. What? We are all familiar with the net heating value of gases which, volumetrically, are measured in Btu/ft3. That makes sense. But what exactly is Btu/ft2? There seems to be a lot of confusion about this parameter. So I thought I would try to clear things up by answering two questions… Where did it come from? and Does it really matter? First of all, let’s clarify that only flares using what EPA calls “perimeter assist air” need to be concerned about NHVdil. What is perimeter assist air? Well… EPA’s assist air naming conventions are somewhat non-intuitive and confusing (and will be the subject of an upcoming blog post) but it’s a safe assumption that any air-assisted flare is affected and must maintain an NHVdil greater than 22 Btu/ft2 [40 CFR 63.670(f)]. This is in addition to the 270 Btu/ft3combustion zone net heating value (NHVcz) limit [40 CFR 63.670(e)] that applies to all flares. In the case of air flares though, NHVcz = NHVvg (Vent Gas Net Heating Value). I know, it’s confusing. The other flavor of assist air defined by EPA is called pre-mix air. For the purpose of this discussion I am completely ignoring pre-mix air. It is rarely found on flares and just needlessly complicates the discussion. Why did EPA establish an additional limit for air-assisted flares? Isn’t the NHVcz limit adequate for air flares? As It turns out, NHVcz works perfectly well for air flares – except for nine data points collected in 1985. More on this in a moment. Prior to the promulgation of the Refinery Sector Rule, the informal parameter for air flares was the stoichiometric ratio (SR). The results of the 2010 TCEQ air flare tests (70 data points) indicated that at an SR less than about 10, the flare had good combustion efficiency. And that makes sense. If the SR gets too high (too much excess air) eventually the flame is cooled and diluted to the point where combustion begins to decline. However, when you look at the nine data points EPA collected on air flares in 1985, the SR doesn’t seem to work. There are some charts further down that will show this. IMPORTANT FACT TO KNOW ABOUT THE AIR FLARE IN THE 1985 EPA TEST… It had a 1.5-inch effective diameter. Barely more than a soda straw with a flame on top. Size Does Matter... When It Comes to Flares We know that other effects seen on tiny flarelets don’t scale up to industrial sized flares. Wind effects for example. Several Canadian studies on tiny flarelets in a wind tunnel, some no bigger than a few millimeters in diameter, indicated that wind can cause a condition on flares known as “wake dominated flow” resulting in a combustion efficiency decline. In response to these test results, EPA considered a wind-based parameter in the Refinery Sector Rule proposal. Some early flare consent decrees incorporate a parameter called the “Momentum Flux Ratio” to address this. However, no evidence of a wind effect impacting combustion efficiency has ever been measured on a full-size flare. Fortunately, this concept was abandoned by EPA in the final rule. So is there a similar “scale up” issue impacting the 1985 air flare data? Hold that thought. EPA concluded, and not without some logic, that flare diameter is a factor in assisted flare performance. They reasoned that on flares with small effective diameters, the assist-air will mix with the vent gas more rapidly than on larger diameter flares and potentially cause premature cooling and dilution which will affect combustion efficiency. Therefore, they concluded, flare diameter needs to be considered. Why not for steam-assisted flares? I don’t know. Stop asking hard questions. EPAs NHVdil Approach To address this perceived issue, EPA came up with the NHVdil approach. You can look up the actual equation in the Refinery Sector Rule but I’m going to give you the simplified version. Here’s how you get a parameter in units of Btu/square foot. Step 1: Determine the vent gas fraction. That is, what volume fraction of the total material exiting the flare, vent gas and assist-gas, is vent gas. So… In the unusual case where you are adding both steam and air, you would add the steam volume to the denominator as well. This is a unitless value. By EPA’s definition, vent gas includes supplemental gas, purge gas, and sweep gas. Step 2: Multiply the vent gas fraction by the flare effective diameter. This product is what EPA calls the dilution factor (DF). It is in units of feet. Since the vent gas fraction will always be less than or equal 1, this product will always be less than or equal to the effective diameter. As the vent gas fraction and effective diameter increase, so does DF. But a larger dilution factor actually means LESS dilution… confusing. The DF is more like a "un-dilution factor." Step 3: Multiply the DF by NHVvg to get NHVdil. Since DF is in units of feet and NHVvg is in units of Btu/cubic foot, the feet cancels one of the foots (I think that makes sense) and you are left with the somewhat improbable unit for NHVdil of Btu/square foot. Another way to look at it is... So does this NHVdil parameter actually work? Do we need a separate parameter for air flares? The chart below compares three air flare parameters – NHVdil, NHVcz, and stoichiometric ratio – and how each relates to flare combustion efficiency. The data are taken from the 2010 TCEQ flare test (70 points), EPA’s 1985 flare study (9 points), and more recent tests on air flare combustion efficiency (77 points). The EPA data points are shown as circles. The NHVcz data are calculated using assist air flow rate in place of the steam flow rate required in the EPA NHVcz equation. Figure 1 Figure 1 shows all the data but it is not particularly informative since everything on the first two graphs is squished to the left. It does show the EPA 1985 data as outliers in both the NHVcz and stoich ratio graphs. Let’s zoom in for a closer look. Figure 2 Figure 2 shows a zoomed in view including EPA’s “good combustion” line of 96.5% combustion efficiency (in red) and some parameter limits (in blue). Look very closely at the NHVdil and NHVcz graphs.The two graphs are identical (ignoring scale). The two parameters are completely interchangeable for all air flare data. This makes sense since NHVdil and NHVcz are both just scaled versions of NHVvg. NHVdil is just NHVvg scaled by vent gas to total gas ratio and diameter while NHVcz is just NHVvg scaled by assist gas to vent gas ratio. The effect of the diameter in the NHVdil equation is just to squash the data more as flare diameter decreases. What about the stoich ratio? This works very well for all the air flare data except... the 1985 EPA data. The EPA data shows good combustion only at sub-stoichiometric levels -- 0.10, 0.23, and 0.45. Anything higher and combustion efficiency rapidly drops off. Does this make sense? I don't know. Maybe some combustion savvy readers can weigh in on that one. So the bottom line on NHVdil? It certainly makes sure that all those people operating 1- and 2-inch flares are effectively brought into the regulatory fold. My belief… from a practical standpoint, we could have gone with either NHVcz or the stoich ratio and it wouldn’t have made any real difference. Here is a final question… Why are air flares required to meet BOTH NHVdil and NHVcz limits? The data shows that as long as NHVdil > 22 Btu/ft2, the flare is good. Requiring the flare also meet the 270 Btu/scf limit in many cases can be a significant penalty for air flare owners. But that is a question for another blog… If you, Loyal Reader, have any flare-related questions, or any other air-quality questions for that matter, let us know. We love answering reader questions.
US EPA’s flare velocity limits were originally issued in 1986. Since then, they have found their way into flare regulations around the world. They were developed following a series of EPA sponsored tests conducted in the 1980’s that examined how various flare operating parameters, including velocity, affect flare performance. The limits were established using only one or two data points from a limited data set. Surprisingly, there is no evidence in the 1980’s data that high velocity in any way degrades flare performance. So how did we end up limiting flare velocity to, in most cases, 60 feet per second? What impact has this had on flare design and emissions? CleanAir has prepared a short white paper that describes the history of these limits. It also reviews the new flare data that has been collected over the past 10 years. The new data reinforces the 1980’s data showing no flare performance degradation at higher velocities. In fact, flare combustion is improved at higher velocities. It’s time for EPA to consider either scrapping flare velocity limits entirely, or at least significantly modifying them. Given the recent issues permitting multi-point ground flares which require high velocity to properly function, a change in regulation is needed and would be welcomed by flare vendors and users alike. Hit the button below to receive your copy of the CleanAir white paper on flare velocity.
EPA today published their response to Alternative Means of Emission Limitation (AMEL) requests from four refineries and a chemical plant. These are: ExxonMobil (Baytown), Marathon (GBR and Garyville), Chalmette (Chalmette), and the chemical plant is LACC (Lake Charles). Each of these facilities operates flares designed to work at exit velocities greater than those allowed under current EPA rules at 40 CFR 60.18 and 63.11. These facilities conducted extensive testing to determine that under the operating conditions specified in the AMEL request, the flares achieved VOC and HAP reductions as good as or better than what is required under the various standards that apply to them. Under a framework established by EPA and published in the Federal Register on April 21, 2016, sources operating pressure assisted multi-point ground flares (MPGFs), may request an AMEL for exemption from the exit velocity requirements. The CleanAir Flare Team has developed several of these AMELs for our refinery and chemical clients and also collected the data used to support them.
On Monday, March 19, 2018, US EPA issued proposed amendments to the Refinery Sector Rule (RSR). These amendments are based on three petitions of reconsideration filed with the agency -- two of these were joint submissions by the American Petroleum Institute (API) and the American Fuel and Petrochemical Manufacturers (AFPM) and the third from Earthjustice filed on behalf of several environmental groups. The proposed changes to Subpart CC (Refinery MACT 1) are listed below. Changes to Subpart UUU (Refinery MACT 2) and Subpart Ja will be posted in a follow-up blog. Definitions 1. Changing the definition of Flare Purge Gas to clarify that purge could be interpreted to include gases introduced to the flare for safety reasons other than to prevent oxygen infiltration. 2. Changing the definition of Flare Supplemental Gas to exclude added steam or air and include only gas that increases the heating value of the flare gas. Also, the definition clarifies that natural gas is not the only option for flare supplemental gas. 3. Adding a definition of Pressure Relief Device and revising the definition of Relief Valve and consistently using the term "pressure relief device" throughout the rule. 4. Revising the definition of Reference Control Technology for Storage Vessels to be consistent with the storage vessel rule requirements at 40 CFR 63.660. Miscellaneous Process Vent Provisions 1. Add language to 40 CFR 63.643(c) to explicitly state that maintenance vents need not be identified in the NOCS report. 2. Amend 40 CFR 63.643(c)(1)(iv) to read (new text highlighted in bold): “If the maintenance vent is associated with equipment containing pyrophoric catalyst (e.g., hydrotreaters and hydrocrackers) and a pure hydrogen supply is not available at the equipment at the time of the startup, shutdown, maintenance, or inspection activity, the LEL of the vapor in the equipment must be less than 20 percent, except for one event per year not to exceed 35 percent.” 3. Amend 40 CFR 63.643(c)(1) to read: “Prior to venting to the atmosphere, process liquids are removed from the equipment as much as practical and the equipment is depressured to a control device meeting requirements in paragraphs (a)(1) or (2) of this section, a fuel gas system, or back to the process until one of the following conditions, as applicable, is met.” 4. Blind installation for maintenance... Require depressuring the equipment to 2 pounds (lb) per square inch gauge (psig) or less prior to equipment opening and maintaining the pressure of the equipment where purge gas enters the equipment at or below 2 psig during the blind flange installation. The low allowable pressure limit will reduce the amount of process gas that will be released during the initial equipment opening and ongoing 2-psig pressure requirement will limit the rate of purge gas use. Together, these requirements will limit the emissions during blind flange installation and will result in comparable emissions allowed under the existing maintenance vent provisions. 5. Documentation of each release from maintenance vents which serve equipment containing less than 72 lbs of VOC is not necessary, as long as there is a demonstration that the event is compliant with the requirement that the equipment contains less than 72 lbs of VOC. Revise 40 CFR 63.643(c)(1) to require a record demonstrating that the total quantity of VOC in the equipment based on the type, size, and contents is less than 72 lbs of VOC at the time of the maintenance vent opening. 6. Amend 40 CFR 63.644(c) to make clear that open-ended valves or lines that are capped and plugged sufficiently to meet the standards in NSPS subpart VV at 40 CFR 60.482-6(a)(2), (b) and (c), are exempt from the bypass monitoring in 40 CFR 63.644 (c). Pressure Relief Device Provisions 1. Add the phrase -- “affected pressure relief device”-- to 40 CFR 63.648(j)(3)(v) to clarify that the requirements in (j)(3)(v) also apply only to releases from PRDs that are in organic HAP service. 2. Revise 40 CFR 63.648(j)(3)(ii)(A) to make clear that independent, non-duplicative systems count as separate redundant prevention measures. 3. Amend the reporting requirements at 40 CFR 63.655(g)(10) and the recordkeeping requirements at 40 CFR 63.655(i)(11) to retain the requirements to report and keep records of each release to the atmosphere through the pilot vent that exceeds 72 lbs/day of VOC, including the duration of the pressure release through the pilot vent and the estimate of the mass quantity of each organic HAP release. Delayed Coking Unit Decoking Operation Provisions 1. Clarify provisions in 40 CFR 63.657(e) that the water overflow requirements in 40 CFR 63.657(e) are only applicable if the primary pressure or temperature limits in 40 CFR 63.657(a) were not met prior to overflowing any water. However, if water overflow is used before the primary pressure or temperature limits in 40 CFR 63.657(a) are met, then the owner or operator must use “controlled” water overflow until the applicable temperature limit is achieved. 2. Add provisions to 40 CFR 63.657(e) requiring the use of a separator or disengaging device operated in a manner to prevent entrainment of gases from the coke drum vessel to the overflow water storage tank. Gases from the separator must be routed to a closed vent blowdown system or otherwise controlled following the requirements for a Group 1 miscellaneous process vent. Fenceline Monitoring Provisions 1. Proposing an alternative to the additional monitor siting requirement for pumps, valves, connectors, sampling connections, and open-ended lines sources that are actively monitored monthly using audio, visual, or olfactory means and quarterly using Method 21 or the AWP. 2. Clarify that if a root cause analysis was performed and corrective action measures were implemented prior to the exceedance of the annual average Δc action level, then these documented actions can be used to fulfill the root cause analysis and corrective action requirements in 40 CFR 63.658(g) and recordkeeping in 40 CFR 63.655(i)(8)(viii). 3. Revise reporting requirements so that quarterly reports are to cover calendar year quarters (i.e., Quarter 1 is from January 1 through March 31; Quarter 2 is from April 1 through June 30; Quarter 3 is from July 1 through September 30; and Quarter 4 is from October 1 through December 31) rather than being directly tied to the date compliance monitoring began. 4. Modify reporting requirements associated with collecting and analyzing QA/QC samples. First, require only one field blank per sampling period rather than two. Second, decrease the number of duplicate samples that must be collected each sample period. Instead of requiring a duplicate sample for every 10 monitoring locations, facilities with 19 or fewer monitoring locations are only required to collect one duplicate sample per sampling period and facilities with 20 or more sampling locations only be required to collect two duplicate samples per sampling period. 5. Require that duplicate samples be averaged together to determine the sampling location’s benzene concentration for the purposes of calculating Δc. 6. Revise the Table 6 entry for 40 CFR 63.7(f) to indicate that 40 CFR 63.7(f) applies except that alternatives directly specified in 40 CFR part 63, subpart CC do not require additional notification to the Administrator or the approval of the Administrator. Also, editorial revisions to the fenceline monitoring section; these proposed revisions are included in Table 2 in section III.A.7 of the preamble. Flare Control Device Provisions 1. Allow owners or operators of flares whose only assist air is from perimeter assist air entrained in lower and upper steam at the flare tip and with a flare tip diameter of 9 inches or greater to comply only with the NHVcz operating limit. Steam-assisted flares with perimeter assist air and an effective tip diameter of less than 9 inches would remain subject to the requirement to account for the amount of assist air intentionally entrained within the calculation of NHVdil. 2. Add provisions to specify that owners or operators of these smaller diameter steam-assisted flares use the steam flow rate and the maximum design air-to-steam ratio of the steam tube’s air entrainment system for determining the flow rate of this assist air. Using the maximum design ratio will tend to over-estimate the assist air flow rate, which is conservative with respect to ensuring compliance with the NHVdil operating limit. 3. Include specific provisions for continuously monitoring fan speed or power and using fan curves for determining assist air flow rates. 4. Clarify that the initial 2-hour visible emissions demonstration should be conducted the first time regulated materials are routed to the flare. 5. Clarify at 40 CFR 63.670(h)(1) to provide that the daily 5-minute observations must only be conducted on days the flare receives regulated material and that the additional visible emissions monitoring is specific to cases when visible emissions are observed while regulated material is routed to the flare. 6. Clarify, at 40 CFR 63.670(o)(1)(iii)(B), that the owner or operator must establish the smokeless capacity of the flare in a 15-minute block average and at 40 CFR 63.670(o)(3)(i) that the exceedance of the smokeless capacity of the flare is based on a 15-minute block average. 7. Correct an error in the units for the cumulative volumetric flow used in the flare tip velocity equation in 40 CFR 63.670(k)(3). 8. Clarify that certification of compliance for these flare vent gas flow meter accuracy requirements can be made based on the typical range of flare gas compositions expected for a given flare. Electronic Reporting and Other Corrections 1. Revise the introductory text in 40 CFR 63.660 to clarify that owners or operators of affected Group 1 storage vessels storing liquids with a maximum true vapor pressure less than 76.6 kilopascals (11.0 psi) can comply with either the requirements in 40 CFR part 63, subpart WW or SS and that owners or operators storing liquids with a maximum true vapor pressure greater than or equal to 76.6 kilopascals (11.0 psi) must comply with the requirements in 40 CFR part 63, subpart SS. 2. Clarify that the additional compliance time at 40 CFR 63.1063(a)(2)(ix) (Subpart WW) applies to the implementation of controls in 40 CFR 63.660(b) (Subpart CC). 3. Amend paragraphs 40 CFR 63.655(f) and 40 CFR 63.655(f)(6) to expressly provide that sources having a compliance date on or after February 1, 2016, may submit the NOCS in the periodic report rather than as a separate submission. 4. Clarify at 40 CFR 63.660(e) that the initial inspection requirements that applied with initial filling of the storage vessels are not required again simply because the source transitions from the requirements in 40 CFR 63.646 to 40 CFR 63.660. 5. Revise 40 CFR 63.655(f)(1)(i)(B)(3) and (C)(2), (f)(1)(iii), (f)(2), and (f)(4) to clarify that when the results of performance tests [or performance evaluations] are to be reported in the NOCS, the results are due by the date the NOCS report is due (report is due 150 days from the compliance date) whether the results are reported using the Compliance and Emissions Data Reporting Interface (CEDRI) or in hard copy as part of the NOCS report. If the source submits the test results using CEDRI, we are also proposing to specify that the source need not resubmit those results in the NOCS, but may instead submit specified information identifying that a performance test [or performance evaluation] was conducted and the unit(s) and pollutant(s) that were tested. 6. Add the phrase “Unless otherwise specified by this subpart” to 40 CFR 63.655(h)(9)(i) and (ii) to make clear that test results associated with a NOCS report are not due within 60 days of completing the performance test or performance evaluation. 7. Amend several references in Table 6–General Provisions Applicability to Subpart CC that discuss reporting requirements for performance tests or performance evaluations to recognize that performance test results may be written or electronic. 8. Revise the ERT Web site to clarify that electronic reporting is not required where the ERT does not support the test method for the pollutant of interest. This has implications where a particulate test and HCN test are conducted coincidentally. In this case, the PM test (supported by ERT) would be submitted through ERT while the HCN test (not supported by ERT) would be submitted in hard copy. 9. Revise 40 CFR 63.655(h)(10) to address the situation where an extension may be warranted due to a force majeure event, which is defined as an event that will be or has been caused by circumstances beyond the control of the affected facility, its contractors, or any entity controlled by the affected facility that prevents them from complying with the requirement to submit a report electronically as required by the rule. 10. Revise 40 CFR 63.655(i)(5) to include the subparagraphs (as previously codified in subparagraph (i)(4)) that were inadvertently not included in the published CFR. 11. Move the paragraphs at 40 CFR 63.655(h)(5)(iii) to 40 CFR 63.655(i)(3)(ii)(C).
On February 5, 2018, the EPA finalized its review of the existing VOC emissions factor for flares at natural gas production sites. EPA evaluated test data available for flares at natural gas production sites, data from testing conducted by manufacturers under 40 CFR part 60, subparts OOOO and OOOOa and 40 CFR part 63, subpart HH and HHH, and information submitted during the public comment period. The available flare data pertained to THC emissions and did not provide sufficient information for estimating VOC emissions from the tested flares. Therefore, EPA's review did not result in a revision to this VOC emissions factor. While EPA did not revise the existing VOC emissions factor, They did use the available THC emissions data for enclosed ground flares to develop six new THC emissions factors for enclosed ground flares. The six emissions factors are finalized as an update to Section 13.5 of AP-42, Compilation of Air Pollutant Emission Factors. AP-42 is the primary compilation of EPA's emissions factor information. They also clarified the heating value basis for the emissions factors in AP-42 Tables 13.5-1 through 13.5-3 and clarified that the emissions factors in the tables represent the emissions at the exit of a flare, not the uncontrolled VOC or THC emissions routed to the flare. Federal Register notice here: https://www.gpo.gov/fdsys/pkg/FR-2018-03-05/html/2018-04373.htm AP-42 here: https://www3.epa.gov/ttn/chief/ap42/ch13/final/C13S05_02-05-18.pdf EPA's webpage on the change: https://www.gpo.gov/fdsys/pkg/FR-2018-03-05/html/2018-04373.htm
EPA has published a broadly applicable approved alternative test method (ALT-124) allowing refineries subject to 40 CFR 63, Subpart CC to use mass spectrometers to measure the net heating value of flare vent gas. The original language of the refinery sector rule (RSR) only referenced gas chromatographs (GCs) and direct measurement of net heating value (calorimeters). Essentially, EPA will treat mass spectrometers just like gas chromatographs. In ALT-124, EPA approves the following measurement approach: Perform a pre-survey to determine the list and concentrations of components that are present in a flare vent gas feed and an appropriate analysis method. Calibrate the mass spectrometer using calibration gas standards consisting of the mix of compounds identified in the pre-survey. Compounds that are not detected during the pre-survey, but have mass fragments identical to compounds detected during the pre-survey will be included in the NHVvg calculation if they are present during flare gas analysis. This is basically stating that compounds found in very low concentrations in vent gas may “show up as” compounds included in the analysis method. The average instrument calibration error for each calibration compound must not differ by more than 10% from the cylinder gas value or tag value. For triplicate injections at each calibration concentration, no calibration measurement shall deviate more than 5% from the average concentration measured at that level. EPA approved this measurement approach while also issuing requirements that mirror those established for continuous GC monitoring systems in Performance Specification 9. Also, the alternative method states that all other requirements of §63.670 and §63.671 (which includes daily calibration requirements) must be followed. If you have any questions about flare gas measurements, give the CleanAir Flare Team a call or send an email. We love to talk about flares.
1) Flares tend to smoke (produce soot) in fuel-rich areas of the combustion zone when there is insufficient oxygen/temperature to complete the combustion process. In high efficiency flames, visible soot is produced within the combustion zone and subsequently oxidized. A bright orange flame with black “marbling” (soot) in the luminous zone is a reliable sign of high combustion efficiency. 2) Fuels have different smoking tendencies. Heavier hydrocarbons with more complex structures tend to more readily smoke than lighter hydrocarbons with simpler structures. Smoking tendency for hydrocarbon fuels: alkanes < alkenes
I know, I know.... You are asking yourself "Where has this video on flare velocity limits been all my life?" Well, the wait is over. In this first (of potentially several) videos on miscellaneous flare topics, I discuss those pesky flare velocity limits found at 40 CFR 60.18 and 63.11. Where did they come from? Are they necessary? What happens if the limits are exceeded? All this and more await you in the video below. Enjoy.
On a recent project, CleanAir used an open-path Active FTIR (AFTIR) system coupled with a drone (or unmanned aerial vehicle, UAV) to analyze pollutants in on a high, inaccessible stack. This is not the Passive FTIR system employed in many of the recent flare tests. The AFTIR analyzer utilized an optical telescope to transmit an infrared (IR) beam through the measurement region. The IR beam was reflected back to the analyzer by a suspended retroreflector array. The analyzer measured the absorption of the IR radiation to determine the composition of the gas in the measurement region. The retroreflector array was suspended from a UAV hovering behind the emission plume relative to the AFTIR about 100 feet in the air. This is the first time (we believe) that anyone has used a UAV-suspended mirror array as one end of an open path monitoring system. Learn more about CleanAir's drone technology for analyzing plumes in dangerous or hard to reach locations here.