|Title||Peer review of a report by U.S. EPA's Office of Air Quality Planning and Standards (OAQPS) "Parameters for Properly Designed and Operated Flares"|
|Creator||Seebold, James G.|
|Spatial Coverage||presented at Salt Lake City, Utah|
|Abstract||In the United States, alleged wind-induced combustion efficiency ("CE") degradation in the operation of real industrial flares in the field has become a big issue amongst environmental activists in consequence of which the United States Environmental Protection Agency is considering regulations related to wind effects. While it is true that wind effects have been reported in model-scale (typically ≤3"D and often «3"D, soda-straw like) tests in wind tunnels, there is no evidence whatsoever in recent and extensive in situ full-scale (typically »18"D) remote-sensing field testing of any significant wind-induced CE-degradation.|
|Rights||This material may be protected by copyright. Permission required for use in any form. For further information please contact the American Flame Research Committee.|
1 - Good Try - Peer review of a report by U.S. EPA's Office of Air Quality Planning and Standards (OAQPS) "Parameters for Properly Designed and Operated Flares" submitted by James G. Seebold, Chevron (Retired) Independent Consultant May 21, 2012 In the United States, alleged wind-induced combustion efficiency ("CE") degradation in the operation of real industrial flares in the field has become a big issue amongst environmental activists in consequence of which the United States Environmental Protection Agency is considering regulations related to wind effects. While it is true that wind effects have been reported in model-scale (typically ≤3"D and often «3"D, soda-straw like) tests in wind tunnels, there is no evidence whatsoever in recent and extensive in situ full-scale (typically »18"D) remote-sensing field testing of any significant wind-induced CE-degradation. Nothing has changed The regrettable absence of systematic variation in combustion efficiency found in past and present flare studies leads inevitably to the idea of "stochasticness" and great difficulties for regulatory interpretation. This fact is illustrated not only in recent USDOJ/USEPA consent-decree-imposed in situ PFTIR testing of real industrial flares in the field that is the subject of the USEPA OAQPS report now in peer review but over and over again in the decades since Siegel's monumental work1 in competently executed studies from the mid-1980s USEPAsponsored "Evaluation of the Efficiency of Industrial Flares" (illustrated above) on which the current failed federal law (40CFR60.18) was based to the most recent USDOJ/USEPA consent-decree-imposed field studies. A summing up of the valiant PFTIR-based in situ field investigations carried out by eminently qualified practitioners, the USEPA OAQPS report, "Parameters for Properly Designed and Operated Flares," 1 Siegel, K. D., "Degree of Conversion of Flare Gas in Refinery Elevated Flares," PhD Thesis in Engineering Science, Feb, 1980, Chemical Engineering Department, University of Karlsruhe, Germany 2 appears merely to be an elaborately perseverated defense of the blatantly conjectural nature (illustrated in "Figure 3-3" below) of the so-called "conclusions" in a report that does not come any closer than previous efforts to producing the long sought but to date elusive flare researchers' "Holy Grail;" viz., the omniscient, universal, all-encompassing, incontestable correlating parameter for flare combustion efficiency. "... suggests ..." or "... most appropriate ..." hardly implies data quality good enough for rule making or policy making "To identify over steaming situations that may occur on steam-assisted flares, the data suggest that the lower flammability limit of combustion zone gas (LFLCZ) is the most appropriate operating parameter. Specifically, the data suggest that, in order to maintain good combustion efficiency, the LFLCZ must be 15.3 percent by volume or less for a steam-assisted flare." 2 Are you kidding me? No better than the OAQPS long ago jumped-to "conclusions" on which today's failed federal law (40CFR60.18) is based. 2 Quote highlighted in the Research Triangle Institute for U.S. Environmental Protection Agency instructions to Peer Reviewers that are appended to this review. 3 Furthermore, "15.3" implies far more accuracy and reliability in LFLcz or any variant thereof than is actually there in the USEPA OAQPS adduced data. Similarly with the combustion efficiency demarcation arbitrarily set at "96.5." Those lines could be put pretty much any place else depending upon what one seeks to "prove." The fatal error lies in USEPA OAQPS's compulsion to extract a bullet-proof activist-indemnifying regulation-justifying argument from stochastically flawed data just as was done so many years ago in the formulation of today's failed federal law (40CFR60.18). MFR nonsense There is no evidence whatsoever in the test report data to support the pseudo-scientific speculations quoted below that are highlighted in the Research Triangle Institute for U.S. Environmental Protection Agency instructions to Peer Reviewers that are appended to this review. "The data suggest that flare performance is not significantly affected by crosswind velocities up to 22 miles per hour (mph)." No, the USEPA OAQPS adduced data demonstrates conclusively that in the extensive USDOJ/USEPA consent-decree-imposed testing of real industrial flares in the field there is no evidence whatsoever of wind-induced combustion efficiency (CE) degradation! "There are limited data for flares in winds greater than 22 mph." Actually, as far as I am aware, there are no data for real industrial flares in winds greater than 22 mph! Perhaps USEPA OAQPS might like to sponsor a study similar to Siegel's in which the blower is crankedup above 6 m/s? Or perhaps not ... "However, a wake-dominated flame in winds greater than 22 mph may affect flare performance." And pigs might fly. Show me the data for real industrial flares in the field! "The data available indicate that the wake-dominated region begins at a momentum flux ratio (MFR) of 3 or greater." No, not the USEPA OAQPS adduced data in the report currently under peer review to which "peers" should restrict their attention and to which USEPA OAQPS should restrict their attention in attempting to formulate regulations; and certainly not the USEPA OAQPS adduced data on real industrial flares in the field. This is pure pseudo-scientific speculation which, in my opinion, is ill-advisedly at best applied to reacting jets as explained below. "The MFR considers whether there is enough flare vent gas and center steam (if applicable) exit velocity (momentum) to offset crosswind velocity." No, it doesn't; the USEPA OAQPS MFR concept is severely flawed in that it completely neglects the physical and chemical realities of reacting jets! 4 To say that this is poorly understood today would be a gross understatement. But what is clear is that while it seemed appealing a few years ago, the manifest uselessness of the momentum flux ratio (MFR) in "correlating" combustion efficiency or anything else for that matter related to real industrial flare performance has by now become pretty well recognized. MFR may very well have some utility in describing the flow out industrial stacks or other unfired vents in windy conditions which is, in and of itself, a seriously complicated downwash, vortex street interactive fluid mechanics phenomenon.3 But MFR is not useful in the case of flares which are required by existing federal law to be lit. The reacting jet, even if it would not appropriately be described as a "jet" on its own compared with the crosswind velocity, gains a lot of upward and rapidly-building momentum the instant the reaction starts to heat it up. In short, the reactants get a sharp upward buoyancy-rise velocity jolt upon ignition. It may be that this marked upward momentum impulse partially accounts for the marked absence of downwash-induced wake-stabilized combustion efficiency degradation via partially reacted or unreacted eddy stripping in real full-scale industrial flares in the field. Additionally, the USEPA OAQPS report overlooks the fact that there are a number of different wake regimes that establish themselves at various stages in the development of the vortex street, each of which has different pull-down and wake-formation propensities. There exist Reynolds Number regimes in which the vortex street is more coherent than others and presumably, therefore, exerts a stronger pull-down to wake-stabilization and also, presumably, a greater propensity toward stripping partially-reacted eddies out of the trailing wake-stabilized combustion zone. We don't know. It hasn't been studied. Not on real industrial flares in the field. Too bad, so sad, but it remains poorly understood. Perhaps we are in that critical Reynolds Number regime for toy flares in a wind tunnel but not for the conditions in which real industrial flares have thus far been tested in the field. What we do know is that there is a great deal of data both recent and historical on real industrial flares reliably tested in situ in the field on which no CE-degrading wind effects whatsoever have been seen. 3 See for example: http://library.usask.ca/theses/available/etd-04212008-124717/unrestricted/MAdaramola.pdf Flow patterns for flow over a cylinder: (A) Reynolds number 0.2; (B) 12; (C) 120; (D) 30,000; (E) 500,000 5 And quite literally not "seen" - no trailing wake-stabilized plume and, therefore, no partially reacted eddy stripping combustion efficiency degradation. Toy flares vs. real industrial flares in the field Studies alleging a significant MFR influence on combustion efficiency are based on data from small diameter model-scale flares. How do these data scale up to real industrial flares? The key scaling concept can be found in any basic textbook on aerodynamics. In brief, assuming a smooth vertical cylindrical stack, the relative vacuum in the low pressure region in the wake behind the flare stack is proportional to the square of the wind velocity and inversely proportional to the stack diameter; i.e., Vwind 2/Dstack. This means that for a given vent gas flow rate, larger diameter stacks are inherently more resistant to wind effects than smaller diameter stacks. In short, everything else being equal, the larger the stack diameter, the less "suck" there is in the wake of the stack. Therefore, at a given wind speed, larger diameter flares are more resistant to the formation of the stationary "suck-down" vortex and hence more resistant to crosswind-induced combustion efficiency degradation. Thus, on large flare stacks, one would not expect to see wake dominated flow except perhaps under hurricane conditions nor any so-called "MFR"-related combustion efficiency degradation as, indeed, we do not. Both historical and recent in situ tests of real industrial flares in the field show no evidence whatsoever of wind related combustion efficiency degradation nor any evidence of wake stabilized behavior. What about real stacks terminated at the top? Then there is the question of the fluid mechanics at the top of a finite circular cylinder and that local influence on pull-down. It turns out that the strongest pressure deficit is not downwind 180-degrees from the upwind face of the cylinder but on the sides at 90-degrees and 270-degrees from the front, a perhaps inconvenient truth. What does that mean with respect to alleged but increasingly discredited crosswind-induced combustion efficiency degradation on real industrial flares in the field? We don't know. Nobody has studied it. But it probably matters ... "Because wake-dominated flames can be identified visually ..." Maybe. Maybe not. What is certain is that in the USDOJ/USEPA consent-decree-imposed testing of real industrial flares in the field, NO (no) so-called "wake-dominated behavior" whatsoever was observed as far as I am aware! 6 Regulating the wind There exists a veritable plethora of authoritative articles on the aerodynamics of flow across infinite cylinders and finite cylinders terminated at the top.4 While I do not recommend it, in the event that USEPA OAQPS are determined to regulate or engineer the wind, perhaps the many and varied erudite dissertations that have appeared over the years in the Journal of Wind Engineering and Industrial Aerodynamics5 might be found useful. But I doubt it ... Flame liftoff hardly implies degraded combustion efficiency "To avoid flame lift off, the data suggest that the actual flare tip velocity (i.e., actual flare vent gas velocity plus center steam velocity, if applicable) should be less than an established maximum allowable flare tip velocity calculated using an equation that is dependent on combustion zone gas composition, the flare tip diameter, density of the flare vent gas, and density of air." 6 Hardly! Sonic flares are characterized by flames that are lifted to a perfectly stable calculable position some distance above the tip. Just because today's failed federal law (40CFR6018) doesn't recognize sonic flares doesn't mean we can't go there perfectly safely and with combustion efficiencies »98%! MFR disconnect Momentum Flux Ratio (MFR) is appropriately defined for unfired stacks as the momentum of the stack gas divided by the momentum of the wind. It is true that for MFR defined that way for relatively cold vents, an MFR < 1 generally indicates that the wind momentum predominates and the plume begins to deflect from the vertical as the plume trajectory develops. However, for hot plume dispersion, depending upon just how hot, of course, buoyancy rise invariably greatly exceeds velocity rise. The USEPA OAQPS MFR calculation considers only the ambient process temperature of the vented flare gases. Accordingly, by overlooking buoyancy rise for fired "stacks" such as flares, USEPA OAQPS are not even looking at the dominant plume rise mechanism! 4 See for example: Free end effects on the near wake flow structure behind a finite circular cylinder (http://www.postech.ac.kr/lab/me/efml/html/publication/pdf/64.pdf); Flow Around a Circular Cylinder with a Free End (http://library.usask.ca/theses/available/etd-07252011-090143/unrestricted/Heseltine_Johnathan_Lucas_sec_2003.pdf): Tubes: cross-flow over (http://www.thermopedia.com/content/1216/?tid=104&sn=1410) 5 http://www.sciencedirect.com/science/journal/01676105 6 Quote highlighted in the Research Triangle Institute for U.S. Environmental Protection Agency instructions to Peer Reviewers that are appended to this review. 7 Upcoming papers/presentations The foregoing issues and others will be amply illustrated and explained and in two upcoming papers, one to be presented at the International Flame Research Foundation's triennial Members Conference, Chateau Maffliers, France, June 11-13, 2012 (Link:http://www.ngcom.it/17thMC/); and the other to be presented at the American Flame Research Committee's Annual Meeting, University of Utah, Salt Lake City, Utah, September 5-7, 2012 (Link:http://www.afrc.net/assets/fordownload/pdfs/afrc_2012_call_for_papers.pdf). I should like to take this opportunity once again to suggest that the latter meeting would be an excellent opportunity to promote agency/industry cooperation around flare innovation. I have extended to USEPA several cordial invitations to participate in any manner USEPA chooses, thus far without any affirmative commitment at the USEPA end, and I am more than pleased to extend the invitation again here. AFRC would be happy to host the USEPA representatives. Supposing that USEPA are interested, at the AFRC end I can get it done in whatever form and format the agency would actually be interested in doing it. At last year's AFRC-sponsored Industrial Flare Colloquium in Houston in which USEPA and TCEQ participated, the industrial participation was great. I expect this year, especially after the recent USEPA announcements, the interest and attendance will be even stronger at the AFRC 2012 gathering. I am sure that, just as last year, there will be a lot of AFRC industrial delegates who are interested in "EPA's Vision," whatever that means, vis-à-vis industrial cooperation on flare issues going forward and how their companies might cooperate and fit in. In the event that USEPA would be interested in taking advantage of what seems to me to be a marvelous opportunity to promote such agency/industry cooperation on flare innovation, I would be more than pleased to make all the arrangements. Is there a better way? Perhaps. One of the worst that mistakes "we" - regulators, activists and industrialists alike - ever made was to allow emergency flares to become "emission control devices," thus compromising the emergency flare's legitimate and overarching safety functionality. Far better to have a fire in plain sight safely up there in the nighttime sky than a devastating explosion back there in the plant. Nobody would disagree with that. Perhaps that historic mistake has been viewed, in some quarters as least, as a good thing, particularly today. Over the decades since the commission of that mistake it has, after all, provided gainful employment to generations of regulators, process engineers and activist lawyers seeking injunctive relief. But rather than perseverating in trying to specify what have proven over the last three decades to be an increasing number of to date stochastically uncorrelatable independent governing parameters, a few of which doubtless have even yet to be discovered, why not consider returning to the use of flares strictly as emergency devices, not emissions control devices? If a plant has "too many" emergencies, fine them. When the CEO takes notice, the plant operators and process engineers will figure out how better to run and design. They always have. And there are lots of other ways to deal with the frequent but typically piddly releases that require environmental control. It just might be a better way to a better end. I commend it to your consideration. 8 Appendix MEMORANDUM TO: James G. Seebold, Independent Consultant FROM: Research Triangle Institute for U.S. Environmental Protection Agency DATE: April 5, 2012 SUBJECT: Review of the Parameters for Properly Designed and Operated Flares This memorandum provides background information and specific charge questions to the Flare Review Panel in its review of a report on parameters for properly designed and operated flares prepared by U.S. EPA's Office of Air Quality Planning and Standards (OAQPS). The report provides an examination of several factors that are important for a properly designed and operated flare. Based on the analysis provided in the report, the data suggest that over steaming on steam-assisted flares and excess aeration on air-assisted flares degrade flare performance. In addition, the data suggest that high winds and flame lift off can influence flare performance on all types of flares. This document will be the focus of review by the Flare Review Panel that must be completed by the end of the day on May 21st, 2012. Background In May 2005, the Ohio Environmental Protection Agency (OhioEPA) installed monitors at a school to investigate odor complaints. The monitoring showed high human health risk (i.e., hazard quotient 6.21 and cancer risk of 5 in 10,000) and the district closed the school. The school was located across the street from a chemical plant. In September 2005, the U.S. EPA Region 5 began investigating the chemical plant and determined that over steaming at the facility's steam-assisted flare was the likely cause of the ambient air issues. In February 2010, the EPA, OhioEPA, and facility agreed to a consent decree requiring a new paradigm in flare monitoring that focuses on steam usage at the flare tip (i.e., combustion zone heating value and steam-to-vent-gas ratio). The consent decree also required that Passive Fourier Transform Infrared Spectroscopy (PFTIR) remote testing be performed. PFTIR remote sensing involves using a spectrometer positioned on the ground to view hot gases from the flare plume, which radiate spectra that are unique to each compound. Around the same time this consent decree was being drafted, the EPA 9 Office of Enforcement and Compliance Assurance (OECA) requested testing be conducted pursuant to section 114 of the Clean Air Act on several other flaring facilities using PFTIR remote sensing technology. OECA's request included a requirement to test a range of operating conditions (including typical conditions) at each flaring facility. All of the PFTIR testing carried out through these actions and used as part of this report were performed and analyzed by a single company. In May 2009, the Texas Commission on Environmental Quality (TCEQ) contracted with The University of Texas at Austin to conduct a comprehensive flare study project on full-scale steam- and air-assist flares at the John Zink Company flare demonstration facility in Tulsa, Oklahoma. The purpose of the project was to conduct field tests to measure flare emissions and collect process and operational data in a semi-controlled environment to determine the relationship between flare designs, operation, flare vent gas lower heating value and flow rate, destruction efficiency, and combustion efficiency. The study also evaluated the performance of remote sensing technologies against extractive techniques. EPA Review of Flares EPA used the test data from the recent PFTIR testing and TCEQ flare studies (as well as other older experimental flare efficiency studies conducted by the EPA in the early 1980s) to investigate the effects of flare performance with varying amounts of steam (for steam-assisted flares) and air (for airassisted flares); and high wind and flame lift off situations (for both types of flares). EPA also reviewed available scientific information from peer-reviewed studies and other technical assessments about flammability, wind, and flame lift off to support our observations. Based on an analysis of the data, we have determined that there are numerous operating parameters that should be considered in order to be confident that a flare is operated consistently and properly to achieve good combustion efficiency. We have developed a report that is organized into nine sections and nine technical appendices. Section 1.0 introduces the report and provides a summary of our primary observations. Section 2.0 identifies the experimental flare efficiency studies and flare performance test reports used in this investigation. Sections 3.0 through 8.0 describe the development of our observations. Section 9.0 provides a list of documents referenced in this report. The primary observations made in this report are as follows: To identify over steaming situations that may occur on steam-assisted flares, the data suggest that the lower flammability limit of combustion zone gas (LFLCZ) is the most appropriate operating parameter. Specifically, the data suggest that, in order to maintain good 10 combustion efficiency, the LFLCZ must be 15.3 percent by volume or less for a steamassisted flare; i.e., ≤0.153. As an alternative to LFLCZ, the data suggest that the ratio of the net heating value of the combustion zone gas (NHVCZ) to the net heating value of the flare vent gas if diluted to the lower flammability limit (NHVVG-LFL) must be greater than 6.54. (Quoted from FINAL USEPA Flare Technical Report, p.1-2) To identify excess aeration situations that may occur on air-assisted flares, the data suggest that the stoichiometric air ratio (SR) (the actual mass flow of assist air to the theoretical stoichiometric mass flow of air needed to combust the flare vent gas) is the most appropriate operating parameter. Specifically, the data suggest that, in order to maintain good combustion efficiency, the SR must be 7 or less for an air-assisted flare. Furthermore, the data suggest that the lower flammability limit of the flare vent gas (LFLVG) should be 15.3 percent by volume or less to ensure the flare vent gas being sent to the air-assisted flare is capable of adequately burning when introduced to enough air. (Quoted from FINAL USEPA Flare Technical Report, p.1-2) The data suggest that flare performance is not significantly affected by crosswind velocities up to 22 miles per hour (mph). There are limited data for flares in winds greater than 22 mph. However, a wake-dominated flame in winds greater than 22 mph may affect flare performance. The data available indicate that the wake-dominated region begins at a momentum flux ratio (MFR) of 3 or greater. The MFR considers whether there is enough flare vent gas and center steam (if applicable) exit velocity (momentum) to offset crosswind velocity. Because wake-dominated flames can be identified visually, observations could be conducted to identify wake-dominated flames during crosswind velocities greater than 22 mph at the flare tip. (Quoted from FINAL USEPA Flare Technical Report, p.1-3) To avoid flame lift off, the data suggest that the actual flare tip velocity (i.e., actual flare vent gas velocity plus center steam velocity, if applicable) should be less than an established maximum allowable flare tip velocity calculated using an equation that is dependent on combustion zone gas composition, the flare tip diameter, density of the flare vent gas, and density of air. (Quoted from FINAL USEPA Flare Technical Report, p.1-3) LFLCZ could apply to non-assisted flares (i.e., the LFLCZ must be 15.3 percent by volume or less in order to maintain good combustion efficiency). Also, the same operating conditions that were observed to reduce poor flare performance associated with high crosswind velocity and flame lift off could apply to non-assisted flares. Finally, because of lack of performance test data on pressure-assisted flare designs and other flare design technologies, it seems likely that the parameters important for good flare performance for non-assisted, steam-assisted, and air-assisted flares cannot be applied to pressure-assisted or other flare designs without further information. (Quoted from FINAL USEPA Flare Technical Report, p.1-3) 11 Document Availability The report is being made available to the Panel in the form of the attached electronic file, which we request be forwarded to all members of the Panel. Specific Charge in Reviewing the Parameters for Properly Designed and Operated Flares We ask the Panel to focus on the charge questions below in their review of the report, but we would appreciate comments on any aspects of the information in the report or other flare topics. In addition, all references used in this report are available upon request. Section 2: Available Flare Test Data 1. Please comment on the agency's criteria for excluding available flare test run data from final analyses, and whether application of these criteria may have led to inappropriate exclusions of relevant data points. Section 3: Steam and Flare Performance 2. Please comment on the lower flammability limit of combustion zone gas (LFLCZ) as an operating parameter for indicating over steaming situations on steam-assisted flares. Comment on the agency's use of the ratio of the net heating value of the combustion zone gas (NHVCZ) to the net heating value of the flare vent gas if diluted to the lower flammability limit (NHVLFL) as an alternative to LFLCZ. Does the flare data adequately support the EPA's observations? 3. Is there sufficient evidence that chemical interactions are occurring that make the calculated LFLCZ inaccurate with respect to the 15.3% LFLCZ threshold discussed? Is there other data available (that is not discussed in this report) that may help clarify our discussion about specific chemical interactions related to lower flammability limits of gas mixtures? 4. Did the agency adequately examine other operating parameters (different from LFLCZ; or the ratio of NHVCZ to LFLVG-LFL) that could indicate over steaming situations? Are there specific other parameters that should be given more or less emphasis? Section 4: Air and Flare Performance 5. Please comment on the stoichiometric air ratio (SR) as an operating parameter for indicating excess aeration situations on air-assisted flares. Additionally, also comment on whether the lower flammability limit of the flare vent gas (LFLVG) is an appropriate operating parameter for determining whether the flare vent gas being sent to an air-assisted flare is capable of burning? Does the flare data adequately support the EPA's observations? Section 5: Wind and Flare Performance 12 6. Please comment on the momentum flux ratio (MFR) as an operating parameter in crosswind velocities greater than 22 mph at the flare tip to indicate wake-dominated flame situations. Additionally, also comment on the agency's observation that in the absence of crosswind greater than 22 mph, a low MFR does not necessarily indicate poor flare performance. Comment on the effectiveness of observations identifying wake-dominated flames. Does the flare data adequately support the EPA's observations? 7. Did the agency adequately examine other operating parameters (different from MFR) for identifying wake-dominated flames? Are there specific other parameters that should be given more or less emphasis? Section 6: Flare Flame Lift Off 8. Please comment on the maximum allowable flare tip velocity equation which considers combustion zone gas composition, the flare tip diameter, density of the flare vent gas, and density of air. Does the flare data adequately support the EPA's observations? Are there specific other parameters or methods/equations that should be given more or less emphasis? Section 7: Other Flare Type Designs to Consider 9. Please comment on the applicability of the LFLCZ parameter, maximum allowable flare tip velocity equation, and the observations regarding crosswind velocity to non-assisted flares, pressure-assisted flares, and other flare designs. Section 8: Monitoring Considerations 10. Please comment on the appropriate monitoring equipment needed to ensure good flare performance and on any other known monitoring methods (not discussed in this report) for monitoring the following parameters: LFLCZ, LFLVG, LFLVG, C, the ratio of NHVCZ to NHVVG-LFL, CCZ, SR, MFR, and Vmax. Also, please comment on operating scenarios and conditions where less robust monitoring equipment could be used to determine the operating parameters of interest.