Environmental Management

Todays process industries expect more from flaresystems than ever before. Chemical and petroleumprocessing plants depend on flares to burn hydro-carbons, such as propane, propylene, ethylene, butadiene,butane and natural gas, found in waste gases. Landfills andwastewater treatment plants, oil-and-gas exploration andproduction facilities, and loading terminals also use flaresto destroy potentially harmful gases.

In each case, the flare system must separate the gasesfrom any liquids present, ignite the gases, and provide thestable combustion necessary for destruction, while mini-mizing smoke, thermal radiation and noise. And, it mustoperate reliably and safely under a wide range of operatingconditions, including weather extremes.

With a greater demand for increased smokeless capaci-ties, higher turndown and more-efficient plant production,a flare failure can carry a big price tag. Factor in theessential role flares play in the safe and environmentally

acceptable disposal of waste gases produced from industri-al operations (1, 2), and its easy to understand why pro-cessing industries can benefit from flare testing as a safe-guard against unexpected problems in the field. Testing aflare before installation is a proactive measure to minimizethe uncertainty of flare performance, emission levels, andthe expense of repairs in the event of a problem.

But testing flares in the field is generally difficult orimpossible for several reasons. Operating flares usually donot have the instrumentation required for assessing per-formance. Operating conditions are not easily modified orcontrolled, and taking the plant off-line to test the flare isimpractical. In addition, flares are nearly impossible to testunder critical design conditions once installed.

Characterizing flare performance for reliability and safe-ty requires comprehensive, accurate testing at full-scale andunder controlled conditions to collect and analyze criticaldata. Although flare performance might be estimated based

Industrial-ScaleFlare Testing

Jianhui HongCharles BaukalRobert SchwartzMahmoud FleifilJohn Zink Co.

Advanced flare testing at full-scale can helpensure that the system operates as designed.

This article explains whats involved and the parameters that should be

measured and evaluated to demonstrate performance, reliability and safety.

Figure 1. An industrial-scale flare test facility should be able to evaluate a wide range of flows.

CEP May 2006 www.cepmagazine.org 35

Reprinted with permission from CEP (Chemical Engineering Progress),May 2006. Copyright 2006 American Institute of Chemical Engineers.

on scaled-down experimentation and empirical data, industri-al-scale testing is the most reliable method due to the com-plexity of the process. While testing custom-designed burn-ers for process heaters has been common for decades, thathas not been true for large industrial flares, primarily due tothe lack of adequate testing facilities. With the advent ofstate-of-the-art flare test facilities, large-scale flare testing isrecommended to ensure proper performance.

Advanced flare testingJust as flares have evolved into modern-day, technology-

based systems, flare test facilities must also mature intostate-of-the-art, full-scale operations, offering extensivecapabilities with sophisticated tools and instrumentation.While flare manufacturers view these flare test facilities asthe vehicle for developing cleaner, more-efficient flareinnovations, global industries and environmental agenciesrecognize them as a valuable resource to measure flare per-formance, system reliability and environmental compliance.

In the past, industry lacked the ability to test flares in a com-prehensive manner. Todays test facilities (such as in Figures 1

and 2) should offer industrial-scale testing and measurement ofsmokeless capacity, required purge rate, blower horsepower orsteam requirements for assisted flares, radiation and noise. Toproperly characterize flare performance, a test facility musthave the capability and flexibility to evaluate a wide range ofground, enclosed and elevated flares, including a variety offlare sizes, operating conditions at full-scale, fuel compositions,flowrates, assist media and other factors. Advanced flow con-trol and data acquisition systems are required to control thetests and ensure accurate measurements.

Safety is one of two critical features of a world-classflare test facility. In addition to in-plant safety protocols,equipment safety features and trained specialists, a testfacility should include exhaustive, redundant safety meas-ures within its controls, automation software and operatingprocedures to protect against potential problems.

The second critical feature is flexibility. A test facilityshould support a wide range of fuel flowrates and test fuels,such as propane, propylene, ethylene, butane, natural gas, andblends of these, including inerts such as nitrogen. Higherflowrates can be achieved with a storage vessel filled with fuel

36 www.cepmagazine.org May 2006 CEP

Environmental Management

Figure 2. Acomprehensivetest facilityincludes ground,enclosed andelevated flares.

gases at an elevated pressure to increase the availablehydraulic capacity. A compressor can circulate the gases in thestorage vessel to ensure that blends are well-mixed. The fuelflows should be accurately controlled and measured beforegoing to the flare. Multiple metering runs of different sizescan significantly increase the available flow range. Betweentests, the lines should be purged with an inert gas for safetyand to prevent fuel contamination in subsequent tests.

A test facility should offer a variety of flare testing venuesto accommodate virtually every flare size and type used inindustry. In Figure 2, flare-testing venues are in place to testenclosed flares, multi-point ground flares, air-assisted flares,steam-assisted flares, high-pressure flares, and flare pilots.

A facility should have the capability of testing flareswith capacities up to 300,000 lb/h or more of fuel. Flare-pilot test stands should be capable of simulating windspeeds in excess of 150 mph (blowing against both the pilotand the pilot mixer) and rain at more than 30 in./h (3).

Because many flares use some type of assisting media,typically steam or air, to meet the specified smokelesscapacity, a test facility must be able to provide adequatequantities of both media. For flares that do not require anyassisting media, such as high-pressure flares, the facilityshould be able to produce the higher gas pressuresencountered in those applications.

Test parametersDepending on the information required, the variables

typically measured during a flare test include flame length,smokeless capacity, blower horsepower for air-assistedflares, steam consumption for steam-assisted flares, andcross-lighting distance for multi-point flares. Two types ofmeasurements are taken inputs and outputs.

Inputs are the controlled parameters set by the test

objectives. These include, for example, the gas flowrates,fuel pressures and compositions specified by the test pro-tocol. For assisted flares, the steam or air flowrate to theflare is generally controlled for a given test point.Atmospheric conditions (wind speed and direction, ambi-ent temperature and pressure, and relative humidity),while not controllable, need to be measured because theymay have a significant effect on flare performance.

Outputs, on the other hand, include noise, thermal radi-ation, flame stability, smokeless capacity and flame quali-ty. Some of these measurements (e.g., flame stability) aresubjective and require the expertise of qualified engineer-ing staff, while others (e.g., noise) can be measured withappropriate instrumentation.

To ensure data accuracy and to minimize testing costs,the facilitys flow control system must be capable ofreaching the target flowrate very quickly and maintainingthat rate. This is best accomplished with automatic con-trols (Figure 3). Because a wide range of flows may betested from purge rates up to the maximum hydrauliccapacity of a large flare tip multiple sets of flow meter-ing and control runs are recommended to ensure accuracyand controllability for both extremes.

Thermal radiationThermal radiation is one of the most important consid-

erations in flare design. Stack height is often chosen so theflare is tall enough to meet certain radiation heat-flux cri-teria at specified locations. Effective tip design, however,can have a tremendousimpact on the radiationcharacteristics of a flare,as it can reduce the radi-ation fluxes from theflame and make it possi-ble to use a shorter flarestack, which reduces thecost of the flare system.

To test a flares radia-tion flux, multipleradiometers (Figure 4)are recommended tomeasure the radiationfield, which is typicallynon-uniform due towind effects and varieswith distance from theflare. Through sophisti-cated mathematicalanalysis, the measuredradiant fluxes can be

Figure 4. This radiometer isused, as part of an array, to determine the radiation fieldfrom a flare.

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Figure 3. Target flowrates can be reached quickly and maintained more tightly with automatic controls.

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Environmental Management

used to determine the coordinates of the effective epicen-ter of the flame and the radiant fraction (i.e., the fractionof heat released from combustion that is emitted as ther-mal radiation).

Numerous calculation methods have been proposed forestimating the radiation from a flare. Predictions can varyover a wide range, depending on which model is used andwhat assumptions are made (4). Overestimating radiationresults in a flare stack that is taller and more costly thannecessary. Underestimating radiation means the radiant

flux at the ground will be higher than desired, which maybe dangerous to personnel and equipment in the area dur-ing a flaring event.

Figure 5 is a plot of constant radiation lines (isofluxlines) at ground level for a high-pressure flare test. Thisplot was generated using measurements from an array ofradiometers positioned at various distances and anglesfrom the flare.

NoiseNoise from a flare must be adequately controlled to

protect personnel in the vicinity of a flare event. To studythe effects of noise from flares, a test facility requires asound measurement system that includes multiple micro-phones, such as the one shown in Figure 6. The durationof measurements, microphones, type of data recorded, and

Figure 6. This microphone is part of the sound measurementsystem used for flare testing.

Figure 5. Isoflux radiation profiles for a high-pressure flare.

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JJIIAANNHHUUII HHOONNGG,, PPhhDD,, is an advanced development engineer at John Zink Co. LLC(11920 E. Apache, Tulsa, OK 74116; Phone: (918) 234-5845; Fax: (918) 234-1827; E-mail: jianhui.hong@johnzink.com). He has several U.S. patents onthe ultra-stable WindProof flare pilot, low-NOx incinerator control apparatusand methods, steam-assisted and air-assisted flares, and flare controlmethods. He has also worked in the areas of kinetic simulation involvingNOx, SOx, and soot; global optimization of steel stack structures; andphased array of thermal radiometers for measuring the flame epicenter andradiant fraction of industrial flares. He holds a BS from Tsinghua Univ.(Beijing) and a PhD from Brigham Young Univ., both in chemical engineering.

CCHHAARRLLEESS EE.. BBAAUUKKAALL,, JJrr..,, PPhhDD,, PP..EE..,, is the director of the John Zink Institute(11920 E. Apache, Tulsa, OK 74116; Phone: (918) 234-2854; Fax: (918) 234-5895; E-mail: charles.baukal@johnzink.com). He has over 25 years ofexperience in the field of industrial combustion in the metals, minerals,petrochemical, textile and paper industries. He has nine U.S. patents andhas authored two books, edited four books, and written numeroustechnical publications. He holds a BS and an MS from Drexel Univ. and aPhD from the Univ. of Pennsylvania, all in mechanical engineering, and anMBA from the Univ. of Tulsa. He is a Board Certified EnvironmentalEngineer (BCEE) and a Qualified Environmental Professional (QEP), and is amember of ASME, AWMA and the Combustion Institute.

RROOBBEERRTT EE.. SSCCHHWWAARRTTZZ,, PP..EE..,, is a senior technical specialist at John Zink Co.LLC (11920 E. Apache, Tulsa, OK 74116; Phone: (918) 234-5753; Fax: (918)234-1986; E-mail: bob.schwartz@johnzink.com). He has over 40 years ofexperience in the fields of combustion, heat transfer and fluid flow, andhas been granted 51 patents for inventions on a wide range of combustion-and process-related products and methods. He has authored numerousarticles and papers on flares, and is a contributing author and associateeditor of The John Zink Combustion Handbook. He holds BSME andMSME degrees from the Univ. of Missouri.

MMAAHHMMOOUUDD FFLLEEIIFFIILL,, PPhhDD,, is an acoustics engineer with John Zink Co. LLC(11920 E. Apache, Tulsa, OK 74116; Phone: (918) 234-2748; Fax: (918) 234-1827; E-mail: mahmoud.fleifil@johnzink.com). His areas of expertise arefluid dynamics, combustion instability and noise control. He has over 23publications on active control of combustion instability in IEEE,Combustion Science and Technology, and Combustion and Flame Journals.He has a PhD in mechanical engineering from a co-supervisory programbetween Ain Shams Univ. and MIT. He is listed in Whos Who in America,Whos Who in Science and Engineering, and Lexington Whos Who, and onThe National Aviation and Space Exploration Wall of Honor. He is a memberof ASME and AIAA.

type of spectrum analyzers used are amongthe numerous conditions that can be variedfor noise testing.

Figure 7 illustrates the sound pressuredata recorded by two microphones at differ-ent locations during a typical flare test. Thespikes at 0 s and 10 s are not related to flarenoise, but represent noise from the safetyhorn alerting personnel in the area of animpending flare test. In this example, thereis a rapid rise in the sound level at the startof the test, followed by a steady decline asthe fuel flowrate is reduced according tothe test plan.

Collecting accurate data for measure-ment and analysis requires a sophisticateddata-acquisition system. In the control roompictured in Figure 8, three time-synchro-nized computers capture critical test infor-mation, which is recorded on a single testrecord. The first computer collects generaldata, such as ambient conditions, fuel tem-perature and flowrates, tip pressure, radia-tion fluxes, and locations of radiometersand microphones. Another computer recordsdigital video from multiple cameras strate-gically positioned at various locations,while the third computer records noise data.

A new era in problem-solvingIn the past, flares have been designed

using semi-empirical and simplified analyti-cal models that can sometimes produce less-than-optimum results. This has primarilybeen due to the inability to gather compre-hensive experimental data from industrial-scale flares and the lack of industrial-scaleflare testing capabilities. Today, industrial-scale test facilities should provide importantdata for greatly improving flare design andin-field performance of existing flares.

The quest for flare knowledge hastaken many leaps forward with theadvancement of these test facilities, andhydrocarbon and chemical processingindustries will benefit from this progress.Through a better understanding of com-bustion science, full-scale testing and real-world simulation, cleaner, more-reliableflare performance can stay a stepahead of industry requirements.

Figure 8. Data acquisition during tests is monitored from the control room.

CEP May 2006 www.cepmagazine.org 39

Literature Cited

1. Schwartz, R., et al., Flares, Chapter 20 in The John Zink CombustionHandbook, Baukal, C. E., ed., CRC Press, Boca Raton, FL (2001).

2. American Petroleum Institute, Recommended Practice 537: Flare Details forGeneral Refinery and Petrochemical Service, API, Washington, DC (2004).

3. Schwartz, R. E., et al., The Flare Pilot, Hydrocarbon Engineering, 7 (2), pp.6568 (2002).

4. Schwartz, R. E., and J. W. White, Flare Radiation Prediction: A CriticalReview (Paper 12a), presented at the 30th Annual Loss Prevention Symposium,American Institute of Chemical Engineers, Spring National Meeting, NewOrleans, LA (Feb. 29, 1996).

Figure 7. Sound levels decrease as flowrate is reduced during a flare test.

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