Combustion efficiency of industrial flares revisited the current status of this multivariate, multiphysics, multichemistry morass and what to do about it

Last year, with its focus on "Industrial Flaring," TOTeM361 was the first in the IFRF TOTeM series to tap into an area which has been explored in AFRC Symposia for many years.2 Taking place 30 September - 1 October at the Sheraton Maui immediately following the AFRC 2010 Pacific Rim Combustion Symposium, TOTeM36 generated a great deal of interest.3 After a series of nine Distinguished Lectures and follow-up discussions, TOTeM36 delegates and distinguished lecturers engaged in a round table discussion during which it was unanimously suggested to have a flare session at AFRC meetings every year. Not only that, although industrial participation at TOTeM36 was significant, it was suggested that a meeting in the continental United States should help attract a stronger attendance from industrial members and, perhaps, regulators and non-governmental-organizations as well. My reaction? "We've been doing that for a decade or more so shut-up, wise-up, join-up, show-up and pay attention!" Or words to that effect. Somewhat unkind, I know. But that's just the way I am. In any event, that is exactly what we are up to beginning this morning at this edition of the AFRC Industrial Flares Colloquium held in conjunction with the AFRC Annual Meeting, Houston, Texas, September 18-21 2011. This paper together with its accompanying presentation is intended to be a sort of keynote "challenge" and erstwhile theme of a sequence of industrial flare sessions that will carry on through the length of the 2½-day meeting. Making reference to the archival mid-80s study and subsequent ones in which the flare emissions researcher's "Holy Grail," the magic universal all-encompassing correlating parameter for combustion efficiency was diligently sought but not found even unto this day, this keynote challenge will not, I hope, be so much an argumentative challenge as it is a factual failure theme that I hope others will want to take up, expand on, modify and take issue with.

Combustion Efficiency of Industrial Flares Revisited The current status of this multivariate, multiphysics, multichemistry morass and what to do about it James G. Seebold, Chevron (Retired) Independent Consultant AFRC International Combustion Symposium Houston, Texas, September 18-21, 2011 Abstract 1 Last year, with its focus on "Industrial Flaring," TOTeM36 was the first in the IFRF TOTeM series to tap into an 2 area which has been explored in AFRC Symposia for many years. Taking place 30 September - 1 October at the Sheraton Maui immediately following the AFRC 2010 Pacific Rim Combustion Symposium, TOTeM36 generated a 3 great deal of interest. After a series of nine Distinguished Lectures and follow-up discussions, TOTeM36 delegates and distinguished lecturers engaged in a round table discussion during which it was unanimously suggested to have a flare session at AFRC meetings every year. Not only that, although industrial participation at TOTeM36 was significant, it was suggested that a meeting in the continental United States should help attract a stronger attendance from industrial members and, perhaps, regulators and non-governmental-organizations as well. My reaction? "We've been doing that for a decade or more so shut-up, wise-up, join-up, show-up and pay attention!" Or words to that effect. Somewhat unkind, I know. But that's just the way I am. In any event, that is exactly what we are up to beginning this morning at this edition of the AFRC Industrial Flares Colloquium held in conjunction with the AFRC Annual Meeting, Houston, Texas, September 18-21 2011. This paper together with its accompanying presentation is intended to be a sort of keynote "challenge" and erstwhile theme of a sequence of industrial flare sessions that will carry on through the length of the 2½-day meeting. Making reference to the archival mid-80s study and subsequent ones in which the flare emissions researcher's "Holy Grail," the magic universal all-encompassing correlating parameter for combustion efficiency was diligently sought but not found even unto this day, this keynote challenge will not, I hope, be so much an argumentative challenge as it is a factual failure theme that I hope others will want to take up, expand on, modify and take issue with. Of course, with me at least, there is no escaping the long-known and much-lamented fact that compliance with the provisions of 40CFR60.18 hardly assures greater than 98% combustion efficiency even though today's EPA 4 scripture assures us that it does and I shall proceed to advocate the "It's the simulation, stupid!" approach that will be expanded upon much more competently by others during the course of this colloquium. In any event, it is my sincerest hope that those who see this challenge and actually care constructively about industrial flare emissions will want to take up the gauntlet, attend and contribute! One final introductory thought addressed to those who have an interest in industrial flares. The International Flare Consortium (IFC) completed its work last year with public release and publication of the IFC's complete results coming hopefully later in 2011. Meanwhile, the IFC's 100-page "Emissions from Elevated Flares - A Survey of the 5 Literature," by far the most comprehensive review ever published, can be accessed at the link footnoted below. It's pretty good if I do say so myself and is well worth the time of serious flare emissions aficionados to check out. N.B., "TOTeM" = Topic Oriented Technical Meeting To view the entire collection dating back to 2002 Houston, click on: http://www.afrc.net/index.jsp?page=1;&l2nid=6 3 AFRC/IFRF members can access the complete record of TOTeM36 at the following link: http://www.trends.ifrf.net/trends/project.html?pid=38 4 Unfortunately I was unable to get James Carville to come by and join us. 5 http://canmetenergy-canmetenergie.nrcan-rncan.gc.ca/fichier/81883/IFC%20Literature%20Review.pdf 1 2 "How do you know the destruction efficiency of your flare is >98%?" Today many plant managers are asking themselves and their operating staffs that question. It's a question that has actually been asked recently in some United States Environmental Protection Agency (EPA) Clean Air Act (CAA) Section 114 Information Requests. The problem is, in accordance with United States Federal Law, that's a misguided question. At 40CFR60.18(b) through (d) and at 40CFR63.11(b), United States Federal Law specifies operating conditions for flares and EPA itself assures us that compliance with those requirements guarantees operation at greater than 98% 6 destruction efficiency. EPA: "... flares operating in accordance with these specifications destroy volatile organic compounds (VOC) or volatile hazardous air pollutants (HAP) with a destruction efficiency of 98 percent or greater." Accordingly, an appropriately polite answer to the question posed above would appear to be, "We are pleased to respond that, taking EPA's advice, we rely upon compliance with United States Federal Law." Regretfully it is not quite that simple. Among other shortcomings of the current EPA regulations, it has long been known that flare gas heating value (Btu/Scf) hardly tells the whole flame stability story let alone the whole combustion efficiency story. Nevertheless, since the mid-1980s, EPA has perseverated in dancing around its own rules that EPA itself developed and that EPA itself codified into Federal Law. The perhaps inconvenient truth that "Btu/scf" is a poor predictor of combustion efficiency in industrial flares is amply illustrated by the chart at the right in which we see an undifferentiated collection of data taken from the landmark EPA studies of the mid-1980s and the as yet unpublished data of the International Flare Consortium (IFC) that was completed last year. We see that combustion efficiency results >98% and <98% are indiscriminately scattered amongst one another pretty much regardless of flare gas heating value (Btu/scf). 7 In the early 1980s, landmark EPA-sponsored studies in which the author served as Technical Adviser led EPA to the codification of conditions that were intended to ensure the proper operation of industrial flares. "EPA determined the destruction efficiency of flares combusting volatile organic emissions in the early 1980s and developed the existing flare specifications as a 8 result of this work." 6 Basis and Purpose Document on Specifications For Hydrogen-Fueled Flares, Emission Standards Division, U.S. Environmental Protection Agency, Office of Air Radiation, Office of Air Quality Planning Standards, Research Triangle Park, North Carolina 27711, Mar 1998, p.1 Link: http://www.tceq.state.tx.us/assets/public/implementation/air/rules/Flare/Resource_5.pdf 7 Flare Efficiency Study, July 1983 (EPA-600/2-83-052 Link: http://www.tceq.state.tx.us/assets/public/implementation/air/rules/Flare/Resource_1.pdf; Evaluation of the Efficiency of Industrial Flares: Test Results, May 1984 (EPA-600/2-84-095) Link: http://www.tceq.state.tx.us/assets/public/implementation/air/rules/Flare/Resource_2.pdf; Evaluation of the Efficiency of Industrial Flares: Flare Head Design and Gas Composition, September 1985 (EPA-600/2-85-106) Link: http://www.tceq.state.tx.us/assets/public/implementation/air/rules/Flare/Resource_3.pdf; Evaluation of the Efficiency of Industrial Flares: H2S Gas Mixtures and Pilot Assisted Flares, September 1986 (EPA-600/2-86-080) Link: http://www.tceq.state.tx.us/assets/public/implementation/air/rules/Flare/Resource_4.pdf 8 Basis and Purpose Document on Specifications For Hydrogen-Fueled Flares, Emission Standards Division, U.S. Environmental Protection Agency, Office of Air Radiation, Office of Air Quality Planning Standards, Research Triangle Park, North Carolina 27711, March 1998, p.5 Link: http://www.tceq.state.tx.us/assets/public/implementation/air/rules/Flare/Resource_5.pdf The Control Device Requirements of 40CFR60.18 were first issued by EPA as a final rule on January 21, 1986. 9 10 Today, operating conditions for flares are specified at 40CFR60.18(b) through (d) and at 40CFR 63.11(b); and we are assured by EPA that "Flares operating in accordance with these specifications destroy volatile organic compounds (VOC) or volatile hazardous air pollutants (HAP) with a destruction efficiency of 98 percent or 11 greater." The flare specifications originally contained in 40CFR 60.18 and 40CFR 63.11 were based upon experience with waste streams containing organic substances. The rules mandate that flares be designed for, and operated with, no visible emissions, except for periods not to exceed a total of five minutes during any two consecutive hours. In addition, the flare specifications require that the flare must be operated with a flame present at all times. The presence of a flare pilot flame is to be monitored to ensure that a flame is present at all times. The minimum net heating value of the flared gas and the maximum exit velocity of steam-assisted, air-assisted, and non-assisted flares are specified in a table. The table lists the maximum allowable velocity for the heat content of the flared gas and an equation is provided to calculate the net heating value of the flared gas. Air-assisted flares must operate with an exit velocity less than a specified maximum allowable velocity which is calculated from an equation that is provided. Also, an equation is provided to calculate the maximum exit velocity for non-assisted and steam-assisted flares. Additionally, at 40CFR60.18(c)(3)(ii), EPA specified the minimum net heating value (Btu/scf) of the flared gas to assure flame stability and high destruction efficiency. However, E.I. DuPont de Nemours and Company (DuPont), among others, recognized that the net heating value (Btu/scf) of the flared gas hardly told the whole flame stability story. In particular, DuPont and others recognized that the requirement to enrich the flared gas by injecting a higherenergy gas such as natural gas should be unnecessary when flaring a gaseous mixture that, merely by virtue of the presence of hydrogen, has a heating value that is less than that required by 40CFR60.18(c)(3)(ii). Accordingly, DuPont carried out a comprehensive testing program that led EPA to conclude that "... hydrogen12 fueled flares achieve greater than 98 percent destruction efficiency." Subsequently, in the only substantive change in the operating condition requirements to this day, EPA amended the 40CFR60.18 and 40CFR63.11 specifications to allow compliance by adhering either to the heat content specifications that had already been set out for organic-mixture flares; or, in the case of hydrogen-mixture flares having a hydrogen content of 8.0 percent (by volume) or greater, by utilizing flares with a diameter of 3 inches or greater that are designed for and operated with an exit velocity less than 37.2 m/s. In the event that the United States Environmental Protection Agency (EPA) has now come to the realization that today's law as developed by EPA is inadequate to assure >98% combustion efficiency, it would seem that it is up to EPA, just as it was in the mid-1980s, to carry out or sponsor further research, propose revisions to the law and issue a basis and purpose document that supports EPA-proposed revised regulations that actually will carry out the intended purpose of 40CFR60.18 and 40CFR63.11. While it is a consummation devoutly to be wished, you may not want to hold your breath. Inhomogeneous distribution of combustion efficiencies in flare plumes - cautions for real world remote flare measurement test programs Flare flames are well known to produce plumes that are characterized by a distinctly inhomogeneous distribution of local combustion efficiencies. This inhomogeneity, illustrated by the two charts included in this section, imposes the requirement of careful combustion efficiency integration over the plume both radially and axially in order to obtain an accurate assessment of emission control performance. 9 40CFR60.18 Link: http://edocket.access.gpo.gov/cfr_2009/julqtr/pdf/40cfr60.18.pdf 40CFR63.11 Link: http://edocket.access.gpo.gov/cfr_2009/julqtr/pdf/40cfr63.11.pdf Basis and Purpose Document on Specifications For Hydrogen-Fueled Flares, Emission Standards Division, U.S. Environmental Protection Agency, Office of Air Radiation, Office of Air Quality Planning Standards, Research Triangle Park, North Carolina 27711, March 1998, p.1 Link: http://www.tceq.state.tx.us/assets/public/implementation/air/rules/Flare/Resource_5.pdf 12 Ibid. 10 11 For example, in the USEPA's 1983-86 landmark investigation 13 of the combustion efficiency of industrial flares, the archival data produced by the accurate agency-sanctioned extractive-sampling protocols demonstrated conclusively that to obtain the so-called "global" combustion efficiency, which is to say a combustion efficiency that is accurately reflective of a flare's overall emission control performance, requires detailed integration over the flare plume both radially and axially. Earlier studies had relied on estimating combustion efficiency from a sample drawn with a single probe at a fixed position on the vertical axis of the flare flame. These studies argued that rapid, random breeze-driven motion of the flame and long sampling times would yield the true overall combustion efficiency. We argued that this is true only under very restricted conditions but in general might result in inaccurate estimates of the global combustion efficiency of the flame. In the hope of establishing scaling principles, in that landmark 1983-86 USEPA investigation a homologous sequence of flare tips (1½″D, 3″D, 6″D, 12″D) was tested that included four 12"D flare tips of which 3 were proprietary commercial designs. On the larger flare tips, the necessary integration of local combustion efficiencies required the use of an extractive-sampling rake that could be systematically traversed over the flare plume. On the smaller flare tips, hood-sampling was carried out and compared with concurrent rake-sampling results to establish the rake-sampling traverse protocols. In more recent decades, pilot-scale flare tips have been tested in wind-tunnels where the well-mixed plume can be accurately sampled by extraction in the stack. This provides an alternative means of accounting safely, accurately and reliably for the decidedly inhomogeneous distribution of combustion efficiency in flare plumes. When it comes to real world flare plumes, the importance of the perhaps inconvenient fact of inhomogeneous distribution of combustion efficiencies is that it calls significantly into question the accuracy of today's safe "pointand-shoot" remote measurement techniques that are said to be able to measure real world flare combustion efficiencies. However, it is important to note that, today, NO successful blind-validation of ANY remote measurement technique has been carried out against reliable agency-sanctioned extractive-sampling results. In particular that is true of the PFTIR technique that has been used in recent field studies. Indeed, the PFTIR theory assumes, incorrectly, homogeneity of combustion efficiency in flare plumes. TCEQ 2010 Flare Study Update: Perhaps that is one of the sources of error in the recently reported TCEQ 2010 Flare Study in which the mean differences between the PFTIR and extractive-sampling measurements of combustion efficiency averaged plus-minus two percentage points with average standard deviations of plus-minus three percentage points. Quoting the report, "It is important to note that the difference in some of the values may due to less than ideal aiming due to interference of the plume sampling system. In a few instances, the remote sensing operators indicated that the position of the plume sampling system had restricted their ability to aim their instruments." Perhaps those results are promising for us "point-and-shoot" fans but if you seek to regulate or enforce flare performance at greater than 98% combustion efficiency [i.e., at less than 2% combustion inefficiency], that is hardly good enough. 13 Evaluation of the Efficiency of Industrial Flares, United States Environmental Protection Agency, Office of Air Quality Planning and Standards, EPA-600/2-84-095, May 1984; EPA-600/2-85-106, September 1985; EPA-600/2-85-106, September 1986 To the extent that any "point-and-shoot" technique does not ... effectively integrate combustion efficiencies across the flare plume, or does not have an adequately oblique view of the flare plume, or is not effectively manipulated and pointed in such a way as to carry out a thorough integration of combustion efficiencies both radially and axially over the flare plume, ... it is impossible for any "point-and-shoot" technique, including PFTIR, to obtain a quantitatively accurate characterization of flare combustion efficiency. Understanding Over-Steaming - How Far We Have To Go! The role of steam injection in industrial flaring is to suppress smoke mainly by augmenting combustion zone aeration. Up to a point, steam injection not only suppresses smoke generation but also enhances the combustion efficiencies of industrial flares. But overdoing it by so-called "over-steaming" can reduce combustion efficiencies by reaction quenching and, eventually, reaction snuffing. One has to wonder if there is any hope at all of satisfactorily resolving experimentally (i.e., by brute-strength-and-awkwardness field testing) today's concerns about the effect of over-steaming on the combustion efficiency of steam-assisted industrial flares. The steam assist nozzles arrayed around the circumference of a simple flare tip must first entrain great volumes of air and then project the resulting steam/air jets into the flare combustion zone thus enhancing aeration and mixing. It seems reasonable to suppose that, everything else held constant, as the flare tip diameter increases it becomes harder and harder for the steam/air jets to penetrate the combustion zone. We believe that is why, as the tip diameter increases, more and more steam is required to provide the same enhancement of aeration. This idea is illustrated in this figure. The difficulty in flare combustion efficiency testing emerges from the "everything else held constant" caveat. For a given proprietary steam-assisted flare tip design tested in quiescent wind conditions, critical determinants of combustion efficiency are fuel composition [N.B., Importantly, NOT merely Btu/scf!], tip velocity and steam-to-fuel mass ratio. While other factors have an influence, too, those factors have long been recognized as important. For a given proprietary steam-assisted flare tip design tested in quiescent wind conditions, the prudent researcher who is interested in the effect of steam injection on the combustion efficiency of a particular fuel composition would systematically vary the steam-to-fuel mass ratio for each of several flare tips in a homologous diameter sequence (e.g., 3"D, 6"D; 12"D; 24"D and 48"D). 14 That was done in a very limited way in the EPA(84,85,86) testing on a fuel mixture of 56% propane in nitrogen. Designated "EPA," the data points for the 3"D tip (four), the 6"D tip (one) and the 12"D tip (none) are superimposed on the speculative curves in the figure above. Note that the colored speculative curves have 15 arbitrarily been given the same shape as the data produced by CMA(83) but for only one tip diameter (8"D) and a different fuel composition (100% propylene). Thus, while the speculation illustrated above may very well reflect how steam injection actually works, today's data is woefully insufficient either to support or refute that perhaps reasonable hypothesis or any other. Pohl, J.H., R. Payne and J. Lee, "Evaluation of the Efficiency of Industrial Flares: Test Results," EPA-600/2-84- 095, May 1984; Pohl, J.H. and N.R. Soelberg, "Evaluation of the Efficiency of Industrial Flares: Flare Head Design and Gas Composition," EPA-600/2-85-106, Sept 1985; Pohl, J.H. and N.R. Soelberg, "Evaluation of the Efficiency of Industrial Flares: H 2S Gas Mixtures and Pilot Assisted Flares," EPA-600 /2-86-080, Sept 1986 15 Davis, B.C., "Flare Efficiency Studies," Plant/Operations Progress (Vol.2, No.3), July 1983 14 To understand the effect of oversteaming on industrial flare combustion efficiency performance, experimental researchers will have to investigate at least a full range of proprietary designs, a full range of ambient wind conditions, a full range of fuel compositions, and a full range of tip velocities, all held constant whilst varying the steam-to-fuel ratio. Good luck! My suggestion? Spend your money on simulation science, the fully-chemical-kinetically-enabled large-eddy simulations that are today being carried out on massively-parallel multiple-processor arrays. And combine that with a lot of testing with advanced diagnostics. Forget the thus-far-failed decades-long quest for the "Holy Grail" of experimental flare combustion efficiency research, the magic universal combustion efficiency correlating parameter. Let it be the simulation coupled with experiments! You've got a long way to go. But that way you might get done in your lifetime. Does API 521 have anything at all to do with the combustion efficiency of industrial flares? The American Petroleum Institute's Recommended Practice 521, "Guide for Pressure-Relieving and Depressuring Systems, Fourth Edition, March 1997 contains "Table 11 - Suggested injection steam rates" that some misguided individuals are today suggesting might somehow relate to combustion efficiencies achieved in industrial flares. Regretfully, the unequivocal answer to the question posed above is "NO!" Indeed, the note at the bottom of the table says, plainly enough I should think, "The suggested amount of steam that should be injected into the gases being flared in order to promote smokeless burning (Ringlemann 0) can be determined from the table. The given values provide a general guideline for the quantity of steam required." The legitimate intent seems pretty plain to me. In any event, the information presented in API 521 is not related in any way whatsoever to combustion efficiency in industrial flares. Rather, API 521 Table 11 is a guide for the design of steam delivery systems for smoke suppression. API 521 Table 11 merely provides plant designers with rules of thumb for sizing the steam delivery system in the various moderate relief cases that the prospective plant owner has decided should operate smokelessly. The various proprietary commercial steam injection systems are of quite different design and inevitably, therefore, have differing degrees of effectiveness in smoke suppression. Thus, API 521 is in no sense a "specification." Nor is it intended in any way as an operational guide. API 521 Table 11 merely presents a range of steam requirements suggested by the various manufacturers of commercial flare tips that serves to give plant designers an idea of the smoke-suppressing steam capacity that they must provide. In short, API 521's Table 11 is intended merely to aid in the selection and design of the steam delivery system that is most appropriate for the risks and circumstances involved in various plant installations. Those who today attempt to ascribe some magical apocryphal connection to industrial flare combustion efficiency bark wistfully up the wrong tree. Remote "Measurement" and "Quantification" - A Brief Critique of Today's Technologies Today there is a desperate need for proven industrial flare emissions remote measurement and quantification. Nobody denies that and I count myself among the foremost of the wishful thinkers. The reason that measurement and quantification are enclosed in quotation marks in the title of this brief critique is that today's promoters almost uniformly and seemingly very carefully refer to sensing and detection when 16 discussing today's available technologies. There is a very good reason for that. Take for example the Passive Fourier Transform Infrared (PFTIR) technology that is, today, wistfully being applied to "quantify" emissions and combustion efficiencies in the US Department of Justice / US Environmental Protection Agency Enforcement Division's Consent Decree regulatory activism. By "regulatory activism" I refer to the regulation by enforcement strategy that has been resorted to in the realization that today's industrial flare emissions law, the 40CFR60.18's General Requirements for Flares, is inadequate to ensure greater than 98% combustion efficiency. Perhaps it might be worth asking, "Whose fault is that?" but I digress ... Exceedingly well-founded theoretically, PFTIR has the potential to become an excellent remote measurement and quantification technology. Virtually everyone is rooting for it and I am one of the most enthusiastic of the rooters. But PFTIR remains unproven in blind-validation trials against well-established regulatory-agency-approved extractive sampling methods. In fact, despite the fact that the final report spins the results very positively, in TCEQ's well-executed "Phase I" trials PFTIR failed blind-validation. Any who are seriously and objectively interested could have read the report for themselves and extracted the 17 truth. The TCEQ Phase I tests utilized a hot gas generator whose plume was seeded with known concentrations of target compounds, concentrations that were verified by extractive sampling. PFTIR had a good oblique view of the plume. Nevertheless, PFTIR failed blind-validation. Considerable differences were observed between the known target compound concentrations and those obtained by remote PRTIR "measurement." To its credit, the report acknowledges that the differences "... are not well understood ..." but asserts that that an "... improved detector design should help improve the overall sensitivity for C 3+ and THC." Particularly to its credit notwithstanding the overall positive spin, the report acknowledges that "... more effort is needed to understand these differences in results before attempting further field tests." [emphasis mine] The TCEQ Phase I PFTIR trials also included a limited test of an elevated flare. The report confesses that the "... flare experiment provides valuable information for assessing logistical difficulties that might be encountered during field measurement campaigns." The prescient prediction of "... logistical difficulties ..." has certainly come true, in spades, in USDOJ/USEPA Enforcement Division Consent Decree field trials that have recently been completed or are currently under way. The TCEQ Phase I PFTIR report concludes that "... PFTIR appears to be a potentially viable method warranting further study based on the Phase I Study results ..." and that "... a second campaign should be conducted ... to validate the PFTIR method." [emphasis mine] The TCEQ Phase I PFTIR report concludes with three "Path Forward Recommendations;" viz., One series of tests would be conducted on the plume generator to validate the effectiveness of the proposed software and hardware modifications A second series of tests would then be performed on a well instrumented ground flare to demonstrate the robustness of the PFTIR method to accurately characterize emissions from flare plumes After method confirmation, a series of field tests on actual flare systems could then be scheduled That was then (2004), this is now (2011) and the second validation campaign was completed in September 2010 and has now been reported. [N.B., see "TCEQ 2010 Flare Study Update" in an earlier section of this paper and my more extensive comments on the TCEQ2010 Flare Study report appended to this paper.] The PFTIR method confirmation described in the TCEQ Phase I PFTIR report has never been carried out as far as I am aware. Nevertheless, PFTIR is being used in USDOJ/USEPA Enforcement Division Consent Decree field trials that are currently under way, producing scattered, uncertain, ambiguous and inexplicable results. It was to be hoped that TCEQ's much needed and long awaited PFTIR "Phase II" study would include the well thought out Phase I report See for example Proceedings of the Second International Workshop On Remote Sensing Of Emissions - New Technologies And Recent Work, April 1-3, 2008. Link: http://www.epa.gov/ttn/chief/efpac/workshops/remotesens08.html 17 TCEQ PFTIR Phase I Testing Final Report, URS(2004). Link http://www.tceq.state.tx.us/assets/public/implementation/air/am/contracts/reports/oth/Passive_FTIR_PhaseI_Flare_Testing_r.pdf 16 recommendations. That would have been great. It would have been even greater if Phase II were actually to have validated a point-and-shoot measurement and quantification technique. As the Prince of Denmark said, "'Tis a consummation devoutly to be wished!" While I, like others, am tired of waiting, that doesn't justify jumping the gun to use any method that we don't know works. If TCEQ's Phase II study would have produced one, great. I'd drink to that. Do the Danes have good beer? Regretfully, it didn't ... Industrial Flare Combustion Efficiency and the "Incipient Smoke Point" A couple of years ago I was asked by a plant operator how "... the incipient smoke point ..." might be related to the point of highest combustion efficiency in a steam-assisted elevated flare. "Hmmm ...." said I. Frankly, I was at first taken aback by the inquiry. I asked myself, "When have we lately or 30 years ago or at any time in between actually defined or, even, really talked about something called an "incipient smoke point?" But upon reflection it seemed to me to be a reasonable perhaps unquantified but certainly sensible concept that we perhaps should have been confronting more than we have. It seemed to me that we ought to be able to come up with data and charts from prior studies, particularly the landmark mid-80s EPA study with which I was so closely associated, that would at least go some way toward identifying and quantifying the concept of an "incipient smoke point." In that mid-80s study, an interesting and related overarching fact emerged; viz., out of a total of 74 tests in which 32 were observed to be "clear," 14 were "incipiently smoking" and 28 were "smoking," the average combustion efficiencies were 98.61%, 98.99% and 99.11% respectively. Yes, the smoking flare flames were slightly more efficient! [N.B., Not surprisingly, that result was replicated in the TCEQ 2010 Flare Study.] While that fact may distress some it is, nonetheless, incontestable and lends credence, it seems to me, to the concept of keeping the flare at the incipient smoke point to ensure at least near optimal combustion efficiency. In addition to the averaged results highlighted above, the results are also conveniently summarized in this figure. I emphasize "near" optimal because the landmark mid80s EPA study data actually suggests that for the best combustion efficiency you should run at least slightly smoking all the time! [N.B., so does the TCEQ 2010 Flare Study data.] That would not be wise, of course, because it is patently illegal in accordance with the USEPA's General Requirements for Flares at 40CRF60.18 and the rules of most local jurisdictions. Nevertheless, that a smoking flare is often the most efficient flare remains a perhaps inconvenient truth. Smoking flares are not inefficient, only illegal. It is not surprising and perhaps worth mentioning here that the results of the other landmark study of the mid-80s that was carried out by the Chemical Manufacturers Association and reported in Hydrocarbon Processing, October 1983, pp.78-80, produced similar results. Thus it seems to me that the efficacy of the concept of introducing a control system that would keep flare operation just above the incipient smoke point to ensure high near-optimal combustion efficiency is amply supported by the landmark studies of the past. How to get reliable combustion efficiency data - extractive-sampling of well-mixed plumes! Hooded experiments Hooded testing has been carried out quite successfully over the years. Extractivesampling of the well-mixed flare plume utilizing reliable agency-sanctioned protocols ensures accurate "global" combustion efficiencies and obviates the difficulty of sampling the heterogeneous unmixed flare plume. In the mid-80s EPA/EER testing discussed previously, flare tips up to 3"D were hood-sampled and the results compared and aligned with rake-sampling probes to set the sampling protocols be used later in 6"D and 12"D flare tip testing for which hood-sampling was impractical. In later decades hood-sampling was employed to good effect in both the DuPont and Praxair testing of hydrogen-fueled flares as previously discussed. Those rigs are shown in the pictures at the right. Wind-tunnel experiments In the last couple of decades, wind tunnel tests have become all the rage amongst flare emissions researchers and more power to them because we have learned that wind can be, indeed, a big deal in compromising industrial flare combustion efficiency. For example, the recently completed International Flare Consortium (IFC) work, probably the most comprehensive flare emissions trials ever conducted, were carried out in the Natural Resources Canada Flare Test Facility wind tunnel shown in the picture at the right. Again, extractive sampling of the the well-mixed plume in the stack produces accurate "global" combustion efficiencies and obviates the severe difficulties related to integrating the distinctly inhomogeneously distributed combustion efficiencies over the length and breadth of the flare plume. Through the window you can see a 3"D flare tip from which the flame trails, having been blown-over into the wake-stabilized fluid mechanical mixing regime by the imposed cross wind. At higher tip velocities (more flared gas) the flame begins to straighten-up into a more bouyancy-dominated mixing regime. Regretfully, in this rig it was not possible to run a continuous transition from bouyancy-dominated mixing through wake-stabilized mixing because the bouyancy-dominated flame standing-tall would burn up the wind tunnel's roof. Even more so would a jet-mixing sonic flare flame have wrecked havoc with the rig so testing was mostly restricted to lower exit velocities and stronger cross winds. Nonetheless, that left plenty of research territory for investigation! Scaling As shown in the figure at the right, the range of conditions tested in the landmark EPA/EER studies of the mid-80s covered the majority of the operating conditions which are 18 common practice commercially. The figure shows the range of flare diameters, exit velocities, Reynolds and Richardson numbers that were tested. The relief gas Reynolds number (Re) and Richardson number (Ri) at the nozzle exit determine the aerodynamic structure of the flare flames. We explained that, with respect to influence on flame performance, Re can be thought of as the ratio of inertial to viscous forces while Ri is proportional to the ratio of buoyant to inertial forces. A flame with Ri greater than one is dominated by buoyant mixing and one with Ri less than one is dominated by inertial (jet) mixing. The figure compares Re and Ri for the 1/16-in through 12-in flare heads tested. The shaded area indicates the most common region of flare head size and exit velocities for typical industrial flares. Were the results of the EPA/EER studies of the mid-80s truly reflective of the performance of real world industrial flares? Based on Ri and Re scaling principles it seemed reasonable to suppose so. We believed so then. We believe so now. But the truth is that we couldn't test flare heads larger than 12-in diameter so we don't really know. It was the best we could do. Concluding rant and thought for moving forward - Why does "combustion efficiency" so fascinate the regulatory agencies today? In today's regulatory circles and, therefore, in industrial circles, too, the hot topic is "over steaming" and its effect on "combustion efficiency" in industrial flaring. My reaction? Who cares?! "Combustion efficiency" per se tells us nothing at all about the former regulatory hot topic at least in ozone exceedence regions, the mass emissions of the so-called "HRVOCs," the ozone precursor highly reactive volatile organic compounds like ethylene, propylene and butadiene that might lead to regional episodic ozone exceedences. Or they might not, depending entirely upon the magnitude of the episodic speciated mass emission that nobody has any way at all to measure or estimate today. Nor does "combustion efficiency" per se tell us anything at all about what ought to be a hot topic today, localized emissions of, for example, the class-archetypal carcinogens formaldehyde, benzene and benzo(a)pyrene that might pose a threat to the public health and welfare. Or they might not, depending entirely upon the magnitude of the episodic speciated mass emission mass emission that nobody has any way at all to measure nor estimate today. Isn't anybody concerned about that?! Well, I am ... 18 Evaluation of the Efficiency of Industrial Flares: Flare Head Design & Gas Composition, September 1985 (EPA-600/2-85-106), Fig.3-1, p.3-2 Link: http://www.tceq.state.tx.us/assets/public/implementation/air/rules/Flare/Resource_3.pdf Burn laboratory-grade methane pure as the drifted snow, get HRVOCs and carcinogens; burn any mixture containing hydrocarbons, get HRVOCs and carcinogens, whether they were there to begin with or not. Got a problem with that? Take it up with God ... It is true that the inevitable production of HRVOCs and carcinogens owing to hydrocarbon combustion is usually in unimportant trace concentrations but not always. Isn't anybody concerned about that? "Combustion efficiency" per se tells us nothing at all about the quantitative mass emissions of individual species. So what good is today's perseveration of regulatory interest in "combustion efficiency?" Beats me ... I'd give worlds to know! What is needed? Speciated mass emissions factors! For example, lbs-ethylene/mmBtu-flared or lbsbenzene/mmBtu-flared and so forth. Why are we not focusing on what is really needed?! Beats me ... I'd give worlds to know! About The Author: James G. Seebold served as Technical Advisor for the mid-1980s USEPA Evaluation of the Efficiency of Industrial Flares; conceived and led the Petroleum Environmental Research Forum's 4year $7-million 20-participant industry-government-university collaboration that actually quantified the speciated trace emissions from gaseous hydrocarbon external combustion,* widely acknowledged as one of the most successful collaborations ever; and was the Founding Principal Investigator of the International Flare Consortium that completed its work last year. Web site link: http://home.earthlink.net/~jim.seebold/. ________________ * ... which required detection limits as low as 100 parts per quadrillion! APPENDIX Comments on TCEQ 2010 Flare Study Final Report Submitted by James G. Seebold, Chevron (Retired) Independent Consultant, Atherton, CA June 20, 2011 Severely limited scope This study project, although exceedingly well executed by TCEQ's University of Texas contractor and numerous subcontractors; and despite the project's $2-million plus cost and year-plus planning span; and like all the other experimental studies that have been competently conducted over the past decades, this study project was necessarily severely limited in its scope of parametric variation. Commenting on the TCEQ Flare Study, one member of the Technical Review Panel hit the nail on the head when he advised, "Remove ‘comprehensive' from title of study." 19 I could hardly agree more. We have learned over the past decades that "comprehensive" is a tall order. "Comprehensive" is hard to achieve ever experimentally and particularly so when mucking about with full-scale combustion systems in the field. The reader of these comments should understand that this is not so much a criticism as it is merely a simple recognition of the plain facts proven over and over again during the past decades; viz., that a "comprehensive" experimental full-scale flare emissions study project is a practical impossibility; and, thus, that regulatory generalization is doomed at best to be an unrequited and abandoned dream or, worse, to be a misguided broad generalization carried out anyway. 19 TCEQ Flare Study Technical Review Panel Comment Summary, p.7; Link: http://www.tceq.texas.gov/assets/public/implementation/air/rules/Flare/2011.05.24_Summary%20of%20Comments_FNL.pdf Misguided broad generalization The consequence of the foregoing perhaps inconvenient truth is that in the sequel there inevitably will arise misguided and ill-conceived attempts to generalize the results of this study project for regulatory purposes. To the credit of the principal investigator and his staff, care has assiduously been taken not to make this mistake in the draft report, although there is an ominous reference to future analyses; viz., "The Study team recognizes that follow-on work with the data collected in this project would be valuable and looks forward to the opportunity to participate in those analyses." 20 My suggestion? Beware ill-advised broad generalizations and unwarranted extrapolations patently beyond the reach of the experimental data variation relating to, for example, other flare designs not tested (of which there are many), other combinations of flare head exit velocity and diameter not tested (of which there are many), other combinations of pilot design, heat release, number and location not tested (of which there are many), other operating conditions not tested (of which there are many), other flare gas compositions not tested (of which there are many), o not least hydrogen-bearing mixtures which are well-known and recognized even in 40CFR60.18 to behave entirely differently, 21 22 23 o and including the markedly differing effects of dilution by nitrogen vs. carbon dioxide, and certainly the variable effect of wind, well-known to be significant but necessarily excluded from this study. Just to make that rather important point, one has only to make reference to the 25 year old warnings of the principal investigator and others regarding unwise generalization of the data produced by the archival and archetypal but similarly severely limited USEPA mid-1980's studies on which 40CFR60.18 was based; for example, "All conclusions are based on the data of this study and are limited to the head geometries, gases and variables examined." 24 [emphasis mine]; and reflect on how well the subsequent ill-advised broad generalization worked out 25 years ago in the case of the formulation of the now broadly discredited 40CFR60.18. My suggestion? Beware making that mistake again. 20 TCEQ draft study report, Sec. 1.0 Introduction, p.40; Link: http://www.tceq.texas.gov/assets/public/implementation/air/rules/Flare/TCEQ2010FlareStudyDraftFinalReport.pdf 21 § 60.18(c)(3)(1)(A) General control device and work practice requirements. p.91; Link: http://edocket.access.gpo.gov/cfr_2010/julqtr/pdf/40cfr60.18.pdf 22 Demonstration of Hydrogen Use in Steam- and Air-Assisted Flares, Alexis McKittrick, Combustion R&D, Praxair, Inc., June 9, 2009; Link: http://www.afrc.net/assets/fordownload/flareforum/2009_boston/demonstration_of_hydrogen_use_in_steamand_air-assisted_fla.pdf 23 Flame Stability Limits and Hydrocarbon Destruction Efficiencies of Flares Burning Waste Streams Containing Hydrogen and Inert Gases; Peter M. Walsh, GE - Energy and Environmental Research Corporation, et al, November 6, 2002; Link: http://www.afrc.net/assets/fordownload/flareforum/2002_houston/flame_stability_limits_and_hydrocarbon_destruction_efficienc.pdf 24 Evaluation of the Efficiency of Industrial Flares: Test Results, May 1984, J.H. Pohl, et al, p.2-13, Link: http://www.tceq.state.tx.us/assets/public/implementation/air/rules/Flare/Resource_2.pdf Design differences critical Just to make the point, consider these two flare heads that employ entirely different modes of steam-assisted combustion zone aeration. One would hardly expect these two flare heads to behave "similarly" with respect, for example, to CE, DE or DRE, would one? One has only to consider the observed sensitivity of CEs and DREs that is attributed in the TCEQ study project draft report merely to minor variations in the modes of center and upper steam usage in the only steam-assisted flare head tested! Then, of course, there are staged elevated flares, annular elevated flare heads, multipoint elevated flare heads, high-pressure sonic elevated flare heads, low-pressure steam nozzles, high-pressure sonic steam nozzles, etc. and so forth, all of which would be expected to behave differently one from another. Wind differences critical And just to make the point about the importance of accounting for wind variation and to appreciate the variable and potentially severely disruptive effect of crosswinds, particularly at the extreme turn down conditions of the TCEQ Flare Study that were necessitated by the practical limitations of carrying out full-scale experiments at grade, one has only to look at the visualization of two different flare plumes shown at the right. 25 These are volume rendered images of a large eddy simulation (LES) of a flare operating under two different crosswind conditions, lower in the top view resulting in a largely buoyant flame, higher in the bottom view resulting in a wake-stabilized flame. The hot colors (red) represent low combustion efficiency or, equivalently, "... high combustion inefficiency." The marked inhomogeneous distribution of local CEs in flare plumes raises a question that troubles some of us "point-and-shoot" fans. Where do you aim to get an accurate measure of the overall combustion efficiency as a measure of overall emission control performance? I'd give worlds to know. 25 Source: http://www.flaresimulations.org/index.jsp "Multiple DREs" -- and CEs, too! The draft report makes a big point about finding multiple destruction and removal efficiencies ("DREs") for propylene in the propylene-firing tests while in point of fact multiple destruction efficiencies ("DEs") 26 and combustion efficiencies ("CEs") have been the bane of flare emissions researchers for decades. Been there, done that; lots and for a long time! Multiple CEs and DEs and, more fashionably today, "DREs," occur when the assumed governing parameter 27 against which data is plotted fails to collapse the data. Classic examples, not surprisingly looking much like the plots in the draft report, can be found for example in Pohl(84) 28 and Seebold(04) 29 as shown in the two charts in this section. Quoting the draft report text. "It can be seen from Figures ES-4a and ES-4b that in this range of S/VG ratios there can be multiple DREs. This is due in part to the fact that, in this range of S/VG ratios, steam added at the center has a different effect on DRE than steam 30 added at the upper nozzles." Again, "Figures ES-6a and ES-6b show DRE (propylene) versus S/VG ratio and CE versus S/VG ratio, respectively, for all of tests series S5 and S6 on one graph. Figures ES-7a and ES-7b are the same graphs focusing on the range DRE (propylene) ≥ 84%. It can be seen from Figures ES-7a and ES-7b that in 31 this range of S/VG ratios there can be multiple DREs." And again, "Figures ES-9b and ES-10b focus on the range of DRE ≥ 84 % to better examine the relationship between these two parameters. There can be multiple DREs for CZG NHVs up to at least 250 Btu/scf and perhaps as high as 300 Btu/scf. Once again, this is due in part to the fact that, in this range of S/VG ratios, steam 32 added at the center has a different effect on DRE than steam added at the upper nozzles." 26 Referring to the concentration of a particular inlet species remaining in the plume following completion of combustion. 27 Often the long lusted after but to date elusive universal correlating parameter. 28 Evaluation of the Efficiency of Industrial Flares: Test Results, May 1984, J.H. Pohl, et al, p.2-14, Link: http://www.tceq.state.tx.us/assets/public/implementation/air/rules/Flare/Resource_2.pdf 29 Practical Implications of Prior Research on Today's Outstanding Flare Emissions Questions and a Research Program to Answer Them, AFRC Int'l Symposium, Maui, Hawaii, Oct 2004, J.G. Seebold, et al, p.4, Link: 30 2010 TCEQ Flare Study Project Final Report [ D R A F T ], p.7; Link: 31 2010 TCEQ Flare Study Project Final Report [ D R A F T ], p.12; Link: http://www.afrc.net/assets/fordownload/flareforum/2004_maui/practical_implications_of_prior_research_on_todays_outstand.pdf http://www.tceq.texas.gov/assets/public/implementation/air/rules/Flare/TCEQ2010FlareStudyDraftFinalReport.pdf http://www.tceq.texas.gov/assets/public/implementation/air/rules/Flare/TCEQ2010FlareStudyDraftFinalReport.pdf 32 2010 TCEQ Flare Study Project Final Report [ D R A F T ], p.12; Link: "... in part ..." indeed! More comprehensively, the multiple DREs simply reflect the fact that the long lusted after "best operating practice envelope" is an exceedingly complex multivariate multiparameter hypersurface in which "CE" and "DE" and "DRE" are simply three amongst a legion of governing and dependent parameters. Reacting jet hydrocarbon gaseous external combustion is well-known to be exceedingly robust, exhibiting high CEs, DEs and DREs. 33 In the industrial flare world these flares are called "jetting" or "jet-assisted" or "highpressure" and, standing tall and proud even in a high wind, they look like this. Flares like the one pictured here arise during major plant upsets such as total loss of electrical power. They are intended to be emergency flares. By comparison, used as low-flow emissions control devices, the necessarily monster flare burners that rarely if ever operate at anything like their design emergency capacities look like this next picture that is taken from the TCEQ flare study project draft report. Regrettably, both the difference in and the plainly expectable compromises of CEs, DEs and DREs are painfully obvious just from the appearance of the reaction zone. One has to wonder if the wimpy flow rates of the normally idling emergency flares in the Greater Houston region, like those tested in the TCEQ flare study project, contribute total yearly HRVOC emissions that have any impact whatsoever on ozone exceedences in the region. Nobody has ever looked at that probably not least because some don't want to look; and, for sure, the collection of wimpy flow rate, normally idling emergency flares contributes nothing like the total HRVOC emissions that emerge 24/7/365 from the billions of Btu/hr that are consumed in process heating in the region's oil refineries, petrochemical and chemical plants. Relatedly, it may be significant to observe that more recently the environmental lobby have been much more concerned, perhaps rightly so, about major emergency flare releases that have occurred in consonance with episodic ozone exceedences. 34 35 It is important to note, however, that whether or not any observed consonance of a major local flare release is causal of or merely coincidental with a general regional episodic ozone exceedence has never been established by photochemical modeling or by any other scientifically reliable means. Follow-up on Phase I Conclusions & Recommendations? It seems to be missing from the TCEQ flare study project draft report. A brief recount of both the Phase I report and follow-up on its conclusions and recommendations would be useful, at least to those who have followed this effort over the years since 2004 and before. http://www.tceq.texas.gov/assets/public/implementation/air/rules/Flare/TCEQ2010FlareStudyDraftFinalReport.pdf 33 Products of incomplete combustion from petroleum, petrochemical & chemical sector process heaters and industrial boilers, J.G. Seebold & R.T. Waibel, 10th PIC Congress, Ischia, Italy, June 2007; Available by request: [e-mail] 34 Links: http://www.environmentalintegrity.org/law_library/documents/FactSheet-CPChemSettlement.doc; 35 http://www.environmentalintegrity.org/law_library/documents/PressRelease-CPChemSettlement.doc Links: http://www.environmentalintegrity.org/law_library/documents/FactSheet-ShellSettlement.doc http://www.environmentalintegrity.org/law_library/documents/PressRelease-ShellSettlement.doc Exceedingly well-founded theoretically, PFTIR certainly has the potential to become an excellent and much-needed remote measurement and quantification "point-and-shoot" technology. But until now, at least and despite its perhaps premature wide-spread use, PFTIR remained unproven in blind-validation trials against well-established regulatory-agency-approved extractive sampling protocols. In fact, despite the fact that the final report spins the results quite positively, in TCEQ's well-executed 2004 "Phase I" trials PFTIR failed blind-validation. 36 The TCEQ Phase I tests utilized a hot gas generator to generate a plume that was seeded with known target compounds, the concentrations of which were verified by extractive sampling. PFTIR had a good oblique view of the plume. Nevertheless, PFTIR failed blind-validation. Considerable differences were observed between the known target compound concentrations and those obtained by PRTIR. To its credit, the report acknowledged that the differences "... are not well understood." The Phase I report asserted that that an "... improved detector design should help improve the overall sensitivity for C3+ and THC." It is unclear from reading the present TCEQ flare study project draft report whether or not that improvement was actually accomplished. If it was, the report should say so. If it was not, the report should say why not. To what extent did 2004's Phase I recommended improvements enhance 2010's Phase II PFTIR performance? Perhaps it would be useful to explain that in the TCEQ flare study project final report. Particularly to its credit notwithstanding the overall positive spin, the Phase I report acknowledged that "... more effort is needed to understand these differences in results before attempting further field tests." [emphasis mine] Was that done? If it was, the TCEQ flare study project final report should elucidate and state the conclusions. If it was not done, the report should say why not. The TCEQ Phase I PFTIR trials also included a limited test of an elevated flare. The report confessed that the "... flare experiment provides valuable information for assessing logistical difficulties that might be encountered during field measurement campaigns." The prescient prediction of "... logistical difficulties ..." has certainly come true, in spades, in USDOJ/USEPA Enforcement Division Consent Decree field trials that have recently been completed or are currently under way. The TCEQ Phase I PFTIR report concluded that "... PFTIR appears to be a potentially viable method warranting further study based on the Phase I Study results ..." and that "... a second campaign should be conducted ... to validate the PFTIR method." [emphasis mine] The TCEQ Phase I PFTIR report concluded with three "Path Forward Recommendations;" viz., "One series of tests would be conducted on the plume generator to validate the effectiveness of the proposed software and hardware modifications." [emphasis mine} "A second series of tests would then be performed on a well instrumented ground flare to demonstrate the robustness of the PFTIR method to accurately characterize emissions from flare plumes." [emphasis mine} "After method confirmation, a series of field tests on actual flare systems could then be scheduled." [emphasis mine} That was then (2004) and this is now (2011). The second validation campaign was completed in September 2010 and appears to have taken a welcome big step forward toward proving PFTIR. 36 TCEQ PFTIR Phase I Testing Final Report, URS(2004). Link http://www.tceq.state.tx.us/assets/public/implementation/air/am/contracts/reports/oth/Passive_FTIR_PhaseI_Flare_Testing_r.pdf But is PFTIR really ready for reliable, robust field use? One has to wonder. PFTIR has been used recently in USDOJ/USEPA Enforcement Division Consent Decree field trials, sometimes producing scattered, uncertain, ambiguous and inexplicable results. An objective, unbiased assessment of PFTIR's suitability for regulatory and enforcement uses would be a great addition to the TCEQ flare study project final report. Plume composition "mystery" resolved? Perhaps. But the "Table ES-1 List of Hydrocarbons Typically Found in Plume during Propylene Flare Tests [1-6]" found on page 27 of the TCEQ flare study project draft final report is hardly a revelation. Burn even a fuel as simple as laboratory-grade methane pure as the drifted snow, get in the plume traces of virtually all of the approximately 100 hydrocarbon intermediates. Got a problem with that? Take it up with God. For example, in the 14-year-old now-famous "PERF" study of gaseous hydrocarbon external combustion,37 43 hydrocarbon species were detected and quantified; viz., ALDEHYDES: Acetaldehyde, Formaldehyde*, Acrolein, Acetone, Propanal, Methylethylketone, Benzaldehyde, Isopentanal, Pentanal, o-Tolualdehyde, m-Tolualdehyde, p-Tolualdehyde, Hexanal LIGHT VOLATILE ORGANIC COMPOUNDS: Acetylene, Ethylene**, Ethane, Propyne, Propane, Propylene**, 1,3-Butadiene**, 1-Butene, cis-2-Butene, Butane HEAVY VOLATILE ORGANIC COMPOUNDS: 1-Butene, Benzene*, Toluene, Hexane, mp-Xylene, Heptane, Octane POLYCYCLIC AROMATIC HYDROCARBONS: Naphthalene, Acenapthylene, Acenaphthene, Phenanthrene, Anthracene, Fluoranthene, Pyrene, Benzo(b)fluoranthene, Benzo(e)pyrene, Indeno(1,2,3- cd)pyrene, Benzo(g,h,i)perylene, Benzo(a)pyrene*, Coronene The PERF study required detection limits as low as 100 ppq would have produced even more detections in all classes. 38 for the PAHs. Lower detection limits That many more compounds were not detected in the TCEQ flare study presumably simply reflects the fact that the measurement contractors employed sample trains with analytical detection limits that were inadequately low to detect more of the hydrocarbon species that were surely there for the detecting, if you are good enough at detecting. A flame is an amazing reactor - a hot, rich, effectively dissociated well-mixed reaction zone in which the role of inlet gas is simply to provide its elemental constituents to the flame reactor. The external combustion of gaseous hydrocarbon mixtures by any means, including flaring, literally manufactures and subsequently emits to the atmosphere traces of all possible molecular combinations of the elemental constituents present either in the fuel or in the air including ozone precursor highly reactive volatile organic compounds (HRVOCs) and carcinogenic hazardous air pollutants (HAPs). So it is hardly a revelation that burning even methane pure as the drifted snow and in the best possible well-mixed way produces trace emissions of ethylene, propylene, butadiene, and all the other highly 37 The Origin and Fate of Toxic Combustion Byproducts in Refinery Heaters: Research to Enable Efficient Compliance with the Clean Air Act, Petroleum Environmental Research Forum Project 92-19, Final Report, August 1997; Links:http://www.epa.gov/ttn/atw/iccr/dirss/perfrept.pdf ; http://www.epa.gov/ttnatw01/iccr/dirss/perfrept.pdf; * Class archetypal carcinogen ** HRVOC 38 Yes, parts per quadrillion! reactive volatile organics; formaldehyde, benzene and benzo(a)pyrene, the class-archetypal hazardous air pollutant carcinogens; and all the other hydrocarbon compounds in the gas phase up through 300 mw coronene. In short, the gaseous hydrocarbon external combustion reaction zone behaves like an effectively dissociated highly reactive elemental soup in which all possible combinations of the inlet elemental reactants are formed in accordance with their chemical kinetic propensity to do so; and, there being no zero in nature, traces of all possible molecules remain in the flue gas for the detection if you are good enough at the detecting. Smoking flares most efficient?! A couple of years ago I was asked by a plant operator how "... the incipient smoke point ..." might be related to the point of highest combustion efficiency in a steam-assisted elevated flare. "Hmmm ...." said I. Frankly, I was at first taken aback by the inquiry. I asked myself, "When have we lately or 30 years ago or at any time in between actually defined or even really taken an interest in something called an "incipient smoke point?" But upon reflection it seemed to me to be a reasonable perhaps unquantified but certainly sensible concept that we perhaps should have been confronting more than we have. It seemed to me that we ought to be able to come up with data and charts from prior studies, particularly the landmark mid-80s EPA study with which I was so closely associated, that would at least go some way toward identifying and quantifying the concept of an "incipient smoke point." In that mid-80s study, an interesting and related overarching fact emerged; viz., out of a total of 74 tests in which 32 were observed to be "clear," 14 were observed to be "incipiently smoking" and 28 were observed to be "smoking," the average combustion efficiencies were 98.61%, 98.99% and 99.11% respectively. Yes, the smoking flares were slightly more efficient! While that fact distresses some it is, nonetheless, incontestable and lends credence, it seems to me, to the concept of trying to keep flare operation near the incipient smoke point to ensure at least near optimal combustion efficiency. In addition to the averaged results highlighted above, the results are also conveniently summarized in this figure. I emphasize "near" optimal because the landmark mid-80s EPA study data actually suggests that for the best combustion efficiency you should run at least slightly smoking all the time! That would not be wise, of course, because it is patently illegal in accordance with the USEPA's General Requirements for Flares at 40CRF60.18 and the rules of most local jurisdictions. Nevertheless, that a smoking flare is often the most efficient flare remains a perhaps inconvenient truth. Smoking flares are not inefficient, only illegal. It is not surprising and perhaps worth mentioning here that the results of the other landmark study of the mid-80s that was carried out by the Chemical Manufacturers Association and reported in Hydrocarbon Processing, October 1983, pp.78-80, produced similar results. And now so does the 2010 TCEQ flare study. Thus it seems to me that the efficacy of the concept of introducing a control system that would keep flare operation just above the incipient smoke point to ensure high near-optimal combustion efficiency is amply supported by the landmark studies of both past and present. That's easier said than done, however. Regrettably I am aware of quite a number of failed attempts at inventing and implementing just such a control system. Been there, done that. My advice? Keep on trying ... somebody is going to make it work! Understanding steam injection The role of steam injection in industrial flaring is to suppress smoke mainly by augmenting combustion zone aeration. There is a little water gas shift and a little cooling to suppress cracking. But it's mainly steam-motivated aeration and mixing. Up to a point, steam injection not only suppresses smoke generation but also enhances the combustion efficiencies of industrial flares. But overdoing it by so-called "over-steaming" can reduce combustion efficiencies by reaction quenching and, eventually, reaction snuffing. One has to wonder if there is any hope at all of satisfactorily resolving experimentally (i.e., by field testing) today's concerns about the effect of over-steaming on the combustion efficiency of steam-assisted industrial flares. The steam assist nozzles arrayed around the circumference of a simple flare tip must first entrain great volumes of air and then project the resulting steam/air jets into the flare combustion zone thus enhancing aeration and mixing. It seems reasonable to suppose that, everything else held constant, as the flare tip diameter increases it becomes harder and harder for the steam/air jets to penetrate the combustion zone. That is why, as the tip diameter increases, more and more steam is required to provide the same enhancement of aeration. The difficulty in flare combustion efficiency testing emerges from the "everything else held constant" caveat. For a given proprietary steam-assisted flare tip design tested in quiescent wind conditions, critical determinants of combustion efficiency are fuel composition, 39 tip velocity and steam-to-fuel mass ratio. While other factors like steam pressure (low-pressure vs. sonic nozzles) have an influence, too, those factors have long been recognized as important. For a given proprietary steam-assisted flare tip design tested in quiescent wind conditions, the prudent researcher who is interested in the effect of steam injection on the combustion efficiency of a particular fuel composition would systematically vary the steam-to-fuel mass ratio for each of several flare tips in a homologous diameter sequence (e.g., 3"D, 6"D; 12"D; 24"D and 48"D). That was done in a very limited way in the EPA(84,85,86) 40 testing on a fuel mixture of 56% propane in nitrogen. To understand the effect of oversteaming on industrial flare combustion efficiency performance, experimental researchers will have to investigate at least a full range of proprietary designs, a full range of ambient wind conditions, a full range of fuel compositions, and a full range of tip velocities, all held constant whilst varying the steam-to-fuel ratio. Good luck and God speed! My suggestion? Spend your money on simulation science, the fully chemical kinetically enabled large eddy simulations that are today being carried out on massively parallel multiple processor arrays. And combine that with a lot of testing with advanced diagnostics. Forget the thus far failed, decade's long quest for the "Holy Grail" of experimental flare combustion efficiency research, the magic universal combustion efficiency correlating parameter. Let it be the simulation coupled with advanced diagnostics experiments! You've got a long way to go. But that way you might get done in your lifetime. 39 40 N.B., Importantly, NOT merely Btu/scf! Pohl, J.H., R. Payne and J. Lee, "Evaluation of the Efficiency of Industrial Flares: Test Results," EPA-600/2-84095, May 1984; Pohl, J.H. and N.R. Soelberg, "Evaluation of the Efficiency of Industrial Flares: Flare Head Design and Gas Composition," EPA-600/2-85-106, Sept 1985; Pohl, J.H. and N.R. Soelberg, "Evaluation of the Efficiency of Industrial Flares: H 2S Gas Mixtures and Pilot Assisted Flares," EPA-600 /2-86-080, Sept 1986