1 MEMORANDUM

TO: Flare Peer Review Panel Members

FROM: Research Triangle Institute for U.S. Environmental Protection Agency

DATE: May 1 st , 2012

SUBJECT: Review of the Parameters for Properly Designed and Operated Flares

This memorandum provides background informati on 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 Ai r Quality Planning and Standards (OAQPS). The report provides an examination of several factor s that are important fo r a properly designed and operated flare. Based on the analys is provided in the report, the data suggest that over steaming

on steam-assisted flares and excess aeration on air-a ssisted flares degrade flare performance. In addition, the data suggest that high winds and fl ame 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 [INSERT DATE].

Background

In May 2005, the Ohio Environmental Protec tion 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) a nd 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 determ ined that over steaming at the facility’s steamassisted flare was the likely cause of the ambient air issues.

In February 2010, the EPA, OhioEPA, and facili ty 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 Passive2 Fourier Transform Infrared Spectroscopy (PFTIR) remote testing be performed. PFTIR remote sensing involves using a spectro meter 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 drafte d, the EPA Office of Enforcement and Compliance Assurance (OECA) requested testing be c onducted pursuant to section 114 of the Clean Air Act on several other flaring facilities using PFTIR remote se nsing technology. OECA’s request included a requirement to test a range of operating conditi ons (including typical c onditions) at each flaring facility. All of the PFTIR testing carried out thro ugh these actions and used as part of this report were performed and analyzed by a single company.

In May 2009, the Texas Commission on Environm ental Quality (TCEQ) contracted with The University of Texas at Austin to conduct a comprehensive flare st udy project on full-scale

steam- and air-assist flares at the John Zink Co mpany flare demonstration facility in Tulsa, Oklahoma. The purpose of the project was to conduc t field tests to measure flare emissions and collect process and operational data in a se mi-controlled environment to determine the relationship between flare designs , operation, flare vent gas lowe r heating value and flow rate, destruction efficiency, and com bustion efficiency. The study also evaluated the performance of remote sensing technologies ag ainst 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 w ith varying amounts of steam (for steam-assisted flares) and air (for air-assisted flares); and high wind and flame lif t off situations (for both types of flares). EPA also reviewed available scient ific information from peer-reviewed studies and

other technical assessments about flammab ility, 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 c onfident that a flare is operated consistently and properly to ach ieve good combustion efficiency.

We have developed a report th at is organized into nine sections and nine technical appendices. Section 1.0 introduces the repor t and provides a summ ary of our primary3 observations. Section 2.0 identifies the experi mental flare efficiency studies and flare performance test reports used in this investigation. Secti ons 3.0 through 8.0 describe the development of our observations. Section 9.0 provid es a list of documents referenced in this

report.

The primary observations made in this report are as follows:

 To identify over steaming situations that ma y occur on steam-assisted flares, the data suggest that the lower flammability limit of combustion zone gas (LFL CZ ) is the most appropriate operating parameter. Specificall y, the data suggest that, in order to maintain good combustion efficiency, the LFL CZ must be 15.3 percent by volume or less for a steam-assisted flare. As an alternative to LFL CZ , the data suggest that the ratio of the net heating value of the combustion zone gas (NHV CZ ) to the net heating value of the flare vent gas if diluted to the lower flammability limit (NHV VG-LFL ) must be greater than 6.54.

 To identify excess aeration situations that may occur on air-assisted flares, the data suggest that the stoichiometric air ratio (SR) (the actual ma ss flow of assist air to the theoretical stoichiometric mass flow of air n eeded to combust the flare vent gas) is the most appropriate operating parameter. Specifi cally, 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 lim it of the flare vent gas (LFL VG ) should be 15.3 percent by volume or less to ensure the flare vent gas being sent to the air-assisted flare is ca pable of adequately burning when introduced to enough air.

 The data suggest that flare performance is not significantly affected by crosswind velocities up to 22 miles per hour (mph). Ther e are limited data for flares in winds greater than 22 mph. However, a wake-dom inated flame in winds greater than 22 mph may affect flare performance. The data available indicate that the wakedominated region begins at a momentum fl ux 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, observation s could be conducted to identify wakedominated flames during crosswind velocitie s greater than 22 mph at the flare tip.

 To avoid flame lift off, the data suggest that the actual flare tip velocity (i.e., actual flare vent gas velocity plus center steam velo city, if applicable) s hould be less than an established maximum allowable flare tip velo city calculated using an equation that is dependent on combustion zone gas compositi on, the flare tip diameter, density of the flare vent gas, and density of air.

 LFL CZ could apply to non-assist ed flares (i.e., the LFL CZ 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 associated4 with high crosswind velocity and flame lif t off could apply to non-assisted flares. Finally, because of lack of performance te st 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-a ssisted, and air-assi sted flares cannot be applied to pressure-assisted, or other flare designs without further information.

Document Availability

The report is being made available to the Pane l in the form of an electronic file, which has been posted on and FTP site and shar ed with 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 questio ns 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 fo r excluding available flare test run data from final analyses, and whether applica tion of these criteria may have lead 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 (LFL CZ ) as an operating parameter for indicating over steaming situations on steam-assisted flares. Comment on the agency’s use of th e ratio of the net heating value of the combustion zone gas (NHV CZ ) to the net heating value of the flare vent gas if diluted to the lower flammability limit (NHV LFL ) as an alternative to LFL CZ . Does the flare data adequately support the EPA’s observations?

3. Is there sufficient evidence that chemical interactions are occu rring that make the calculated LFL CZ inaccurate with respect to the 15.3% LFL CZ threshold discussed? Is there other data available (that is not discu ssed in this report) that may help clarify our discussion about specific chemical in teractions related to lower flammability limits of gas mixtures?

4. Did the agency adequately examine other operating parameters (different from LFL CZ ; or the ratio of NHV CZ to LFL VG-LFL ) that could indicate over steaming situations? Are there specific other parameters that should be given more or less emphasis?5 Section 4: Air and Flare Performance

5. Please comment on the stoichiometric air ra tio (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 (LFL VG ) is an appropriate operating parameter for determini ng whether the flare ve nt gas being sent to an air-assisted flare is cap able of burning? Does the flare data adequately support the EPA’s observations?

Section 5: Wind and Flare Performance

6. Please comment on the momentum flux ratio (MFR) as an operating parameter in crosswind velocities greater th an 22 mph at the flare tip to indicate wake-dominated flame situations. Additionally, also commen t on the agency’s observation that in the absence of crosswind greater than 22 m ph, a low MFR does not necessarily indicate poor flare performance. Comment on the effectiveness of observations identifying wake-dominated flames. Does the flar e data adequately support the EPA’s observations?

7. Did the agency adequately examine other ope rating 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 diam eter, density of the flare vent gas, and density of air. Does th e flare data adequately support the EPA’s observations? Are there specifi c other parameters or met hods/equations that should be given more or less emphasis?

Section 7: Other Flare Ty pe Designs to Consider

9. Please comment on the applicability of the LFL CZ parameter, maximum allowable flare tip velocity equation, and the observ ations regarding crosswind velocity to non-assisted flares, pressure-assiste d flares, and othe r flare designs.

Section 8: Monitoring Considerations

10. Please comment on the appropriate monito ring equipment needed to ensure good flare performance and on any other known m onitoring methods (not discussed in this report) for monitoring the following parameters: LFL CZ , LFL VG , LFL VG,C , the ratio of NHV CZ to NHV VG-LFL , C CZ , SR, MFR, and V max . Also, please comment on operating scenarios and conditions wher e less robust monitoring equipment could be used to determine the operating parameters of interest.