Date: February 18, 2013 

To: Andrew Bouchard and Brenda Shine, EPA/OAQPS/SPPD 

From: Jeff Coburn 

Subject: Meeting Minutes for February 13, 2013, Meeting Between the U.S. EPA and 

Representatives from John Zink Hamworthy Combustion 

On February 13, 2013, representatives of the U.S. Environmental Protection Agency 

(EPA) and their contractor (RTI International) participated in a teleconference meeting with 

flaring experts from John Zink Hamworthy Combustion (John Zink). The meeting was requested 

by the EPA to discuss minimum steam requirements for flares. Prior to the meeting, the EPA 

provided representatives of John Zink a list of questions to aid the discussion. These questions are 

provided below as the outline for the discussion topics. Prior to the meeting, John Zink 

representatives suggested that the diagrams from the Marathon consent decree be reviewed as 

these figures would be useful as references during the discussion. The Marathon consent decree 

figures are provided as Attachment 1 to this memorandum. 

Attendees

John Zink Hamworthy Combustion 

Jim Franklin 

Zach Kodesh 

U.S. EPA Representatives 

Andrew Bouchard 

Brenda Shine 

RTI International (EPA contractor) 

Jeff Coburn 

Discussion Topics

Q1. What determines the minimum steam usage rates for a flare? That is, for steam assisted 

flares that are generally on standby (no waste gas flow; purge gas flow only), why can’t the steam 

be turned way down or off? 

A1. Minimum amounts of steam are needed to prolong flare tip life. There are potentially three 

types of steam used, depending on the flare tip design: upper steam, center steam, and lower 
2

steam (see Attachment 1). The simplest flare design is Type I (see Attachment 1) and uses only 

upper steam. 

Upper steam helps to keep flame off of pilot tubing and to shape the flame. You want a curtain of 

steam around the nozzles (150 pounds of steam at about 350 degrees Fahrenheit) for tip 

protection. You need at least a minimum of “warming” steam to keep water from condensing in 

line (water in line would get blown out when steam rate increased and can knock out the pilot 

flame). “Cooling steam” is what usually is used for normal operation to keep from burning-up the 

flare tip or pilot nozzles. The amount of cooling steam needed is dependent on a number of 

factors including wind speed (which can push to flame towards pilot nozzles) and flare gas flow 

rate (to keep from smoking). Typically, the flare operator will just fix the upper steam flow rate at 

a certain level to ensure cooling, and may increase at times of high flaring rates when needed to 

maintain smokeless operation. 

 

For larger diameter flares, a Type II design that includes center and lower steam additions is often 

used (see Attachment 1). At low flow velocities (1-2 feet per second (ft/s)), center steam is used 

to make sure there is no oxygen ingress, so any flame does not start within the flare tip itself. 

Oxygen that comes in a few feet of the top of the flare can cause burning within the flare, which is 

very hard on flares and shortens tip life. Molecular seals, which utilize an “S-trap” in flare gas 

riser lines, act to use the buoyancy of methane to prevent air ingress. Flares equipped with 

molecular sieves and can get down to very low flow rates (approximately 0.01 ft/s purge gas) 

without needing center steam to prevent oxygen ingress. Molecular seals look like a large bulge 

around the top of the flare. The additional size/weight of a molecular seal flare tip often limits the 

number of flares that can be retrofitted to use molecular seals due to structural limitations of the 

existing flare stack. Velocity seals can be used reduce the minimum velocity at which center 

steam must be used down to 0.03-0.05 ft/s purge gas; velocity seals are smaller and are therefore 

easier (i.e., more widely applicable) for retrofits. 

“Lower steam” or “Steam/Air tubes (S/A tubes)” are used for certain applications when the flare is 

servicing gases that cracks so fast that it is hard to keep the flare from smoking. Lower steam is 

added so that the steam flow will educt air into tubes within the flare tip. This allows air to get 

into the middle of the flare to limit cracking/smoke formation. The internal tubes are also angled 

to spin and mix the flare gas with the air/steam to limit cracking. Larger flare tips are more likely 

to need lower steam (S/A tubes) to mix the flare gas and ensure some oxygen gets into the center 

portion of the flame. Larger flares are also more likely to have oxygen ingress. Having S/A tubes 

in the flare tip makes it more important keep the flame from burning within the flare tip (more 

internals that can burn-up/degrade), so it becomes more important to have and use more center 

steam for large flares with S/A tubes. 

Q2. Are there some flare tip designs that can operate with lower or no steam flow as compared to 

other flare tip designs? If so, how long have these been available? What number (or percentage) 

of existing refinery flares have the lower steam design? 

A2. Molecular or velocity seals, discussed in A1 above, can limit the need for center steam. In 

general, the bigger the flare tip, the more steam needed for general and standby operation. To 
3

limit steam use and flare inefficiencies, it is generally preferable to use a staged flare system (two 

or three flares in series where flow only goes to the second flare when the first flare begins to 

reach capacity) rather than one large flare that can handle the full capacity at all times. In addition 

to improved efficiency and less steam use, smaller flare tips generally last longer than lager 

diameter flare tips. Type I small flares may last 10 to 12 years. Larger flares must be replaced 

every 4 to 6 years. 

Marathon is testing a new air-entrained-in-steam system to see if they can reduce the amount of 

supplemental natural gas that must be added in order to meet the combustion zone heat value 

requirements. The entrained air does less to quench combustion than steam so this should allow 

use of less natural gas to supplement flare gas when flare gas flow is low. This technique is just 

being tested and it is unclear how well this system will work to improve combustion efficiencies at 

low gas flow rates. 

Type III flare tip (see Attachment 1) has only “lower steam” (S/A tubes). This flare type design 

makes it easier to control steam usage rates because only one steam source/line is used. Based on 

the design and mixing afforded by this system, it typically uses 30 percent less steam (for 

smokeless rate) than Type I or II flares. Also, this flare design has better “premix” so it is 

expected to have higher combustion efficiencies (or a wider range of operating conditions for high 

efficiency) than other flare tip designs, but this has not necessarily been verified in field tests. 

Q3. Assuming there is a lower steam flare tip design, what would be the typical costs to retrofit 

an existing flare tip to a low minimum steam usage flare design? 

A3. Flare types are routinely replaced. Modifying the flare type design can reduce steam use. 

Molecular seals or velocity seals plus no leaks to flare (i.e., flare gas recovery system) could 

reduce minimum velocity and steam rates. Costs would be highly site-specific and the ability to 

retrofit would be dependent on the structural characteristics of the existing flare stack. 

One can generally retrofit the flare tips to Type III design. Type I flare tips are light, so the flare 

stack may not be able to structurally handle a Type III retrofit (since Type III would be a heavier). 

Most Type II flares (which are already heavy) would be able to retrofit to Type III. Type III flare 

tips have smaller restrictions at the outlet, which increases the back pressure of the flare slightly; 

this increased system back pressure must be considered on a refinery-specific basis and may limit 

the use of the Type III flare tip in a few applications. In general, a Type I tip replacement 

averages about $100,000; a Type II tip replacement is 2 to 3 times the cost of a Type I tip and a 

Type III tip is about 1.5 times the costs of a Type II tip. 

Q4. If retrofits cannot be made, how much would a typical flare replacement cost? 

A4. Replacing a large flare with a staged system would be an example of a flare replacement 

(versus a flare tip retrofit). Flare replacement costs are highly site-specific. 
4

Q5. When installing a new flare, is there any significant capital cost difference for a low 

minimum steam flare versus a traditional steam-assisted flare? 

A5. See cost differences in flare tip costs in A3. 

A cascade flare system would generally cost more than a single flare system but due to improved 

operation, less steam use, and longer tip life, cascade systems are often selected in preference to a 

single large flare. 

There are some flare designs (like ground flares with staged flare burners) that can operate with no 

gas flow to the burners that are shut-off. You would still have to use a minimum of “warming 

steam” to prevent condensation in the steam pipes, but you would not need purge gas flow to the 

burners that were shut-off, so you would have less steam and purge gas use. 

Q6. Are there any other issues associated with low minimum steam usage flares? E.g., do they 

need better flow monitoring and automated steam controls to adjust steam levels quickly if there is 

a sudden, large flaring event? 

A6. At low flow rates, the flame is closer to the tip so you are more likely to burn-up a tip at low 

flow rates than high flow rates. Therefore, controlling steam addition at these low flow conditions 

is important. However, most operators do not really monitor flow rates and do not have 

valves/controls needed to accurately adjust steam usage at low flow conditions. As such, most 

refineries will likely need to add a small parallel steam line to better control steam at low rates. 

Q7. Are there similar minimum air flow issues associated with air assisted flares? If so, why and 

are there different tip designs for minimizing air assist rates during “idle” conditions? 

A7. Instances have been observed where too much assist gas can blow out the flare flame. Air 

assist systems designed with multiple blowers operate over a larger range of flows than a one 

blower system. Typically, a one blower system can operate with a minimum turndown of 

approximately 5 to 1. Assist air is typically added around the outside of a flare only (no “center 

air). Steam is generally more “energy” efficient than air so facilities generally only use air-assist 

when steam is not available. 

Unassisted flares generally do not have the combustion efficiency issues as air or steam assisted 

flares and would not need combustion zone analysis. Most refinery flares are assisted to prevent 

smoking. Enclosed flares can often operate with no assist steam or air and not smoke, so these 

flares can be unassisted. Enclosed flares can be ground flares or large diameter stack flares. The 

enclosed stack flares, even though they may have a large diameter stack (as much as 40 feet in 

diameter), take less space than other flares since they do not have the radiant heat, although it is 

important to make sure the heat plume from the flare stack does not cross another stack or elevated 

structure that someone might climb. 
ATTACHMENT 1 

Diagrams of Flares Showing Steam Assist Locations 

(from Marathon Consent Decree) 
VNJTED sTA rs;s 

'. ~R TlIO....·PETROLEl'M CO.UPA_\ T 

APPENDIC ES TO CONSENT n t:CREE 

APPENDIX 1.6 

CALCULATING H IE UNOBSTRUCTED CROSS 

SECTIONAL AREA OF VARIO US TY I'ES OF 

FLARE T Il'S 
APPENDIX 1.6 

Type I LD T Type l[ 

Em l ower 

SteamlAl. 

Tubes 

.D

I D'T 

p Stabiity Tab,"" Stab'kty Ring 

""'- Stean\lAir 

Tubes 

A,,,.,,,,,,,," 1T(I.D r ~f4-( "As,. )I 

Where: ~"Unobstructed Cross 

Sectional Area of Flare TIp 

I D T = Inside Diameter Flare TIp 

X, '" Number of Stability Tabs 

Am" scea of a Stability Tab 

W here: A"p.""", " Unobstructed Cross 

Sedonal Areaof Flare TIp 

ID T" Insde Diameter Flare Tip 

As, '" Area 01 Stability RIng 

AD., "Outside Diameter of 

Steam/Air Tubes 

NT" Number 01 Sleam/Au Tubes 

Example , LD T= 41.S fr'lches 

Xt " 3 

As, " 3 Sq inches 

Example. I D., " 41.5 mches 

As, " 100 sc inches 

O.D, = 6 5 inches 

N,- " 8 

1T 41 5}'14 - (3 ·3) 

34 Sq tnceee 

" 1T (47,5)'14- 100·8'11' ' (6 .5)114 

A,,_" 1322 Sq Inches 
APPENDIX 1.6 

Type III Type llZ: 

1,0 ,y 

... • (TT ·{I.D....)1{4 - x, . As-rll 

,10 .. 

r--

Where: "\''-'" Unobstrucled Cross Sedional Area 

of Flare Tip 

10 .. : Insode Dlameter of One Tip Module 

N.. " Number of Mod ule5 

X. '" Number of Sfability Tabs per Module 

As r '" Area 01 a Stability Tab 

Example . 10.... " 17IIlches 

N.. = 6 XT= 3 

AST " 3 Sq inches 

A,,,,..-" 6 ' ('Tl"{ 17f214 - 3 ' 3) 

1\",,,,,,,,, " 1308 Sq inches 

W here , A...o....ot, ,, Unobslrlicled Cross 

Sectional Areaof FlareTip 

I D., " Inside Diameter 01Flare Tip 

Exa mple: 10'1" 41.5inches 

A,h _ =" (41 5)1/4 

..... =13S3$q inches