NEW FLARE REQUIREMENTS FOR MACT CC
DEFINITIONS
Assist air – all air that intentionally is introduced prior to or at a flare tip through nozzles or other hardware conveyance for the purposes including, but not limited to, protecting the design of the flare tip, promoting turbulence for mixing, or inducing air into the flame. Assist air includes premix assist air and perimeter assist air. Assist air does not include the surrounding ambient air.
Center steam – the portion of assist steam introduced into the stack of a flare to reduce burn back.
Combustion zone gas – all gases and vapors found just after a flare tip. This gas includes all flare vent gas, total steam, and premix air.
Flare purge gas means gas introduced between a flare header's water seal and the flare tip to prevent oxygen infiltration (backflow) into the flare tip. For a flare with no water seal, the function of flare purge gas is performed by flare sweep gas and, therefore, by definition, such a flare has no flare purge gas.
Flare Smokeless Design Capacity – the maximum flow of waste gases that can be sent to the flare without producing significant levels of smoke.
Flare supplemental gas – all gas introduced to the flare in order to improve the combustible characteristics of combustion zone gas.
Flare sweep gas means, for a flare with a flare gas recovery system, the gas intentionally introduced into the flare header system to maintain a constant flow of gas through the flare header in order to prevent oxygen buildup in the flare header; flare sweep gas in these flares is introduced prior to and recovered by the flare gas recovery system. For a flare without a flare gas recovery system, flare sweep gas means the gas intentionally introduced into the flare header system to maintain a constant flow of gas through the flare header and out the flare tip in order to prevent oxygen buildup in the flare header and to prevent oxygen infiltration (backflow) into the flare tip.
Flare vent gas means all gas found just prior to the flare tip. This gas includes all flare waste gas (i.e., gas from facility operations that is directed to a flare for the purpose of disposing of the gas), that portion of flare sweep gas that is not recovered, flare purge gas and flare supplemental gas, but does not include pilot gas, total steam, or assist air.
Lower steam – the portion of assist steam piped to an exterior annular ring near the lower part of a flare tip, which then flows through tubes to the flare tip and ultimately exits the tubes at the flare tip.
Perimeter assist air – the portion of assist air introduced at the perimeter of the flare tip or above the flare tip. Perimeter assist air includes air intentionally entrained in lower and upper steam. Perimeter assist air includes all assist air except premix assist air.
Premix assist air – the portion of assist air that is introduced to the flare vent gas, whether injected or induced, prior to the flare tip. Premix assist air also includes any air intentionally entrained in center steam.
Total steam – the total of all steam that is supplied to a flare and includes, but is not limited to, lower steam, center steam and upper steam.
Upper steam – the portion of assist steam introduced via nozzles located on the exterior perimeter of the upper end of the flare tip.
SLIDE INFORMATION
Slide 1: New Flare Requirements for MACT CC
The final rule was published December 1, 2015 and is currently directed at petroleum refineries. This new rule is on a ubiquitous control utilized throughout the chemical and petroleum processing world. This is coming for all flares.
Slide 2: Presentation Objectives
Overview of requirements, point out the significant changes, and provide the TCEQ perspective and how this will impact permitting.
Slide 4: Historical Perspective
Federal Rules associated with flares have been virtually unchanged for nearly 30 years and were based on flare studies in the ‘80s. Flares do no lend themselves to direct testing for emissions, and they were more commonly utilized as safety devices as opposed to control devices. In Texas, Mr. Sam Crowther, with the Texas Air Control Board, was a champion of flares as a readily available means of control already available at chemical and petroleum processing plants. The TCEQ guidance was last updated in October of 2000 and is in need of some adjustment. However, it has long been recognized that steam and air assist, when properly operated, can help the flare combustion mixing process to reduce or eliminate smoking. In 2003, Texas published rules for Highly Reactive Volatile Organic Compounds that added continuous monitoring of flares to ensure the federal §60.18 standards for heating value and velocity were being met on a continuous basis. With advancement of infrared cameras, more recent studies by the TCEQ identified problems with flares being over-steamed at low flow conditions resulting in poor combustion, and additional testing was conducted on test flares. This is the first rule to focus on addressing the issue and data found in the new studies.
Slide 6: Current Focus – Permit Boilerplate Language
Permit boilerplate language has keyed off of concepts in §60.18, which is referenced specifically in the conditions:
· Pilots and pilot monitoring 24/7 to ensure ignition of the waste gas when routed to the flare.
· No Visible Emissions (the TCEQ and the neighbors do not want to see smoke, and we don’t think the neighbors like the flame or the noise).
· Generally, we have not moved to address any particulate matter from flares generally, even though some incidental visible soot during transition is allowed, the five minutes in any two hours.
· The waste gas has to burn, so it must contain sufficient heating value [200/300 British thermal units per standard cubic foot (Btu/scf)] to ignite and cannot be moving too fast such that the flame lifts off or blows itself out [60/400 feet per second (fps)]. Except for special circumstances, generally very simple operations, the agency will require flares to be monitored for flow and composition or heat content.
Slide 8: Compliance Date
Monitoring and compliance with MACT CC must be in place for refiners by January 30, 2019.
Slide 10: Changes
Requirements Comparison /§63.11(b) / §63.670
Always have a flame / Operate with a pilot flame
Performance test - No visible emissions except periods not to exceed 5 minutes during any two consecutive hours / In addition to the initial demonstration previously required, ongoing monitoring is required. Additional details and corrective actions must be provided for each event.
Sufficient Heating value of vent steam to maintain flame / Count the added steam and air effect on heating value in the combustion zone
Limited flow velocity / Limited Flow Velocity
Monitor / Monitor and Report
Slide 12: Pilot Flame
There are several subtle changes in the wording of the new rule that adjust the requirements. Refinery flares can no longer simply have a flame but must have a pilot. The more important distinction is when there needs to be a flame. When regulated material is routed to the flare is of course when the flare needs to work. However, the TCEQ Air Permits Division is not in lock-step with this change, and a recent permit action to implement the MACT CC in lieu of §60.18 still requires the pilot when the vent gas may be directed to the flare. If the site has pressure relief valves that can send a burp down the line, we want you to keep the light on for us. It is also important to note this requirement has a one-minute limit of no pilot when regulated material is flowing and is not tied to the fifteen minutes of regulated material flow triggering other limitations.
Slide 14: No Visible Emissions
Both rules specify that flares shall be designed and operated without visible emissions. Current requirements specify a performance test (NSPS Method 22) to demonstrate that no visible emissions are occurring. The new rule requires permit holders to specify the flare’s smokeless design capacity and monitor for visible emissions.
Slide 15: Smokeless Design Capacity
The smokeless design capacity is the maximum flow of waste gases that can be sent to the flare without producing significant levels of smoke. The Environmental Protection Agency (EPA) has acknowledged that even when flares produce smoke, the combustion and destruction efficiency of the flare can be very good. Our understanding is that the efficiency is generally the best at or near the insipient smoke point or when the flare is on the verge of smoking. However, smoking from flares is still not permitted.
Slide 16: Visible Emissions and TCEQ Permits
The new rule specifies monitoring for visible emissions in which the monitoring and associated recordkeeping will be incorporated into the permit.
Slide 17: Visible Emissions Monitoring
In addition to the initial visible emissions demonstration, the new rule specifies monitoring for visible emissions. At least once per day, permit holders will conduct visible emissions observations for a period not less than five minutes. In addition to the daily test, if at any time visible emissions are identified, an immediate five-minute visible observation using Method 22 shall occur. If visible emissions are observed for more than one continuous minute during the five-minute observation period, the observation period must be extended to two hours or until five minutes of visible emissions are observed. The rule also allows the use of a video surveillance camera to continuously monitor for visible emissions. All instances of more than five minutes in two hours must be recorded and reported.
Slide 18: Velocity and Heat Content – NEW
Compliance with the new rule will be determined on a block fifteen-minute basis with monitoring, recordkeeping, and reporting for all. The EPA has not previously focused on a compliance time frame in association with flares. NSR permits have been specifying that the vent gas heating value and velocity requirements applied at all times rather than with a compliance averaging time. Depending on how the heat content is now determined, monitoring may not always allow a continuous determination. Monitoring for the new EPA rule does not start until regulated material has flowed to the flare for at least fifteen minutes. The block fifteen-minute evaluations are always from the top of the hour and each subsequent fifteen minutes (e.g., 12:00, 12:15, 12:30, and 12:45). The fifteen-minute averaging time is a double edged sword in that it will prevent issues with short incidences but does not allow a longer averaging time to show compliance. The reasoning is associated with the rapid potential loss of destruction efficiency during periods when the gas stream loses heating value in the combustion zone. Flare control with the heating value in the combustion zone and within the velocity limits is expected to consistently achieve a 96.5% combustion efficiency and a 98% destruction efficiency. A drop or loss of destruction efficiency for even six minutes may drop the hourly average destruction efficiency to less than 90%.
Slide 19: Flare Tip Velocity
In general, the EPA let these requirements technically remain the same as in previous rulemaking. The base rate of the vent gas needs to be less than 60 fps with the allowance to go up to 400 fps based on the heating value of the fuel. They did not address the growing use of pressure assist flares, which would not be compliant with this requirement by design and will need an alternate method determination to be utilized.
Slide 20: Flare Tip Velocity
The new face in the equation for the maximum velocity (Vmax) is that it is presented in English units of Btu/scf and addresses the effect of hydrogen on the flare combustion by creating a surrogate heating value.
Slide 21: Flare Tip Area
Nothing new here; just dust off the old geometry book and calculate the unobstructed path of the vent gas. EPA presented some nice diagrams at the end of their technical report for the Flare Review Panel in 2012.
Slide 22: Flare Tip Area Calculation
Atip-unobstructed = NM * π *(I.D.M)2 / 4 – XT * AST
Atip-unobstructed = Unobstructed Cross Sectional Area of the Flare Tip
NM = Number of Modules
I.D.M = Inside Diameter of One Tip Module
XT = Number of Stability Tabs per Module
AST = Area of a Stability Tab
Slide 24: Vent Gas Net Heating Value (NHVvg)
The net heating value of the vent gas is the integral term and base factor of the revised limitations. It is essentially the same term as is currently referred to in §60.18 and §63.11 as “the gas being combusted.” How compliance was achieved generally required steam and air assist flares to meet 300 Btu/scf and unassisted flares to meet 200 Btu/scf. The NHVvg is substantially more specific in the new rule due to how it is determined with an averaging time and detailed measurement approaches.
Slide 25: The New Standards
The new limitations in the rule associated with heating value now address the combined flow of the flare vent gas and the assist gases. The combustion zone operating limit (NHVcz), a minimum of 270 Btu/scf determined on a block fifteen-minute period, is the net heating value of the vent gas as diluted by the ratio of the vent gas flow to the vent gas flow plus the total steam assist and premix air flows.
The dilution operating limit (NHVdil), a minimum of 22 Btu per square foot (BTU/ft2) determined on a block fifteen-minute period, is the net heating value of the vent gas multiplied by the effective diameter of the unobstructed tip diluted by the ratio of the vent gas flow to the vent gas flow plus the total steam assist, premix air flows, and perimeter air flow.