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USE OF ADVANCED TECHNOLOGY TO REDUCE FLARING AND POLLUTION. . .1 INTRODUCTION:.................................................. 1 Flare.......................................................... 1 BURNERY........................................................ 2 NECESSITY OF LIQUID DISPOSAL SYSTEM............................2 PRECAUTIONS TO BE FOLLOWED IN THE BLOW DOWN SYSTEM.............2 Reasons for blow down.........................................3 PREVENTION :................................................... 4 ADVANTAGES AND DISADVANTAGES OF USING HIPS.....................5 MAKING THE DECISION TO USE HIPS................................5 Figure 1. Simplified Decision tree.............................6 Operational Actions to reduce the flare :....................7 RECOVERY....................................................... 8 PROPOSED SOLUTIONS:............................................8 Blow down recovery system for the burnery:....................8 Flare Gas Recovery Systems.....................................9 SOLUTIONS TO REDUCE THE SMOKE.................................10 USE OF ADVANCED TECHNOLOGY TO REDUCE FLARING AND POLLUTION INTRODUCTION : Flare Flare systems are used at Gas production / processing plants and petroleum refineries to collect and separate both liquid and vapour discharges from various units and equipment. The gaseous fraction, that may represent a planned or unplanned hydrocarbon discharge, may be either recycled or flared. Flaring provides a widely-used safety mechanism and emission control option for blowdown systems when the heating value of the emission stream cannot be recovered due to uncertain or intermittent releases during process upsets/emergencies.
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USE OF ADVANCED TECHNOLOGY TO REDUCE FLARING AND POLLUTION......1INTRODUCTION:..........................................................................................................................1Flare................................................................................................................................................1BURNERY......................................................................................................................................2NECESSITY OF LIQUID DISPOSAL SYSTEM......................................................................2PRECAUTIONS TO BE FOLLOWED IN THE BLOW DOWN SYSTEM............................2Reasons for blow down...........................................................................................................3PREVENTION :.............................................................................................................................4ADVANTAGES AND DISADVANTAGES OF USING HIPS.................................................5MAKING THE DECISION TO USE HIPS.................................................................................5Figure 1. Simplified Decision tree..........................................................................................6Operational Actions to reduce the flare :...........................................................................7RECOVERY...................................................................................................................................8PROPOSED SOLUTIONS:.........................................................................................................8Blow down recovery system for the burnery:....................................................................8Flare Gas Recovery Systems..................................................................................................9SOLUTIONS TO REDUCE THE SMOKE..............................................................................10

USE OF ADVANCED TECHNOLOGY TO REDUCE FLARING AND

POLLUTION

INTRODUCTION:

Flare

Flare systems are used at Gas production / processing plants and petroleum refineries to collect and separate both liquid and vapour discharges from various units and equipment. The gaseous fraction, that may represent a planned or unplanned hydrocarbon discharge, may be either recycled or flared. Flaring provides a widely-used safety mechanism and emission control option for blowdown systems when the heating value of the emission stream cannot be recovered due to uncertain or intermittent releases during process upsets/emergencies.

Non-condensed vapours from the blowdown system may be combusted in a flare which is designed to handle large fluctuations of both the flow rate and hydrocarbon content of the discharge.

Although different types of flares exist, the steam-assisted elevated flare systems are most commonly used at petroleum refineries whereby steam is injected in the combustion zone of the flare to provide turbulence and inspirated air to the flame.

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For waste gases of insufficient heating value, auxiliary fuels may also be used to sustain combustion.

BURNERY

NECESSITY OF LIQUID DISPOSAL SYSTEM.

Off spec product and hydrocarbon drain from Gas production plant are having

very high vapour pressure. It is not possible to store the same due to high

vapour pressure and low temperature. Therefore the same has to be burnt

immediately. Liquid which is being drained are at low temperature and will not

vaporize, so it cannot be sent to elevated Flare. The only option available is to

burn the same in the burnpit ( burnery). The main use of a burn pit is to dispose

off liquid or mixed liquid/vapour relieves generally as emergency flows or on

intermittent basis when blowing down pipelines or vessels. The nature of the pit is

simply a shallow depression or hole in the ground which acts as a reservoir for

the burning liquid. The pit is normally lined with refractory material (castable or

bricks).. The design of the pit should take into consideration the maximum input

rate of liquid and the rate at which this can burn. The most conservative and

consequently the usual method of sizing is to assume that it is required to burn

the flammable liquid at the same rate at which it is relieved to the pit. The liquid in

the pit burns , supports its own combustion by radiating heat back from the flame

into the liquid at the top of the pool which then vaporizes and heats up further

before burning in the flare. The rate of vaporization occurs is dependant on the

thermal heat output of the flame . As the air for combustion of the liquid

supported flame is drawn only from around the outside and mixing is poor and

the resulting flame which un-combusted hydrocarbon together with the smoke

plume.

PRECAUTIONS TO BE FOLLOWED IN THE BLOW DOWN SYSTEM

The hydrocarbon liquid flows through the blow down system to the burn pit

located in the offsite area. Due to low temperatures produced by auto-

refrigeration of the hydrocarbon on loss of pressure, it is essential that water is

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not allowed to enter the blow down system to avoid ice formation, line plugging,

line fracture etc. After usage of the blow down system, the liquid from the system

should be purged . Methanol injection points have also been provided for the

removal of water.

Reasons for blow down

LPG will be disposed off into the blow down system under the following

conditions:

Due to failure of the control system or mal operations.

Due to maintenance of some equipment.

Emergency situation due to fire / power failure etc.

THREE PROLONGED STRATEGY IS USED TO REDUCE THE SMOKE .

THEY ARE PREVENTION OF FLARING , IF THE FLARING IS

UNAVOIDABLE INSTALL RECOVERY SYSTEM AND PROCESS BACK TO

PLANT . FLARE DISPOSAL SYSTEMS HAS TO BE UPGRADED SO THAT

IT DONOT SMOKE.

PREVENTION :

RECOVERY / RECYCLE :

CHANGE THE SYSTEM FOR TO REDUCE POLLUTION :

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PREVENTION :

In many countries in the world, regulatory agencies place greater restrictions on flaring..

A properly designed and applied HIPS may be used to reduce loads to existing flare systems or provide additional safeguards where conventional pressure relief devices have proven to be unreliable. When units are expanded, modified, or when a new unit is being integrated into a plant, existing flare capacity may be inadequate. As plant experience increases, new, larger contingencies for flare sizing may be identified. This application brief describes a typical High Integrity Protective Systems (HIPS) to minimize overpressure events in reactors and distillation columns, and thereby reduce the frequency of relieving to the flare. Industry design practices describe the basic principles that underlie the application of safety considerations for all new and existing plant design. Flare capacity, an essential safety design feature, is typically set by the largest single contingency for a unit. Conventional design of overpressure protection systems require additional flare capacity either by installing another flare system or reducing contingencies of existing flare systems. An alternative is to apply High Integrity Protective System (HIPS) to reduce some single contingencies to double contingencies, thereby allowing continued operation without compromising safety, or requiring additional expansion or investment in the flare system.

Industry is moving towards the use of high integrity protection systems (HIPS) to reduce flare loading and alleviate the need to upgrade existing flare systems when expanding facilities. Latest revision of API521 Included separate appendix –E for the same. The use of HIPS can minimize capital project costs, while meeting an evolving array of standards and regulations. API and ASME standards and ANSI/ISA S84.01-1996 and IEC 61508 are allowing the same .

“Reduction of flare size for common failures

In oil and gas processing facilities a cause of overpressure could be a common failure affecting a number of pressure systems simultaneously. An example of this is the simultaneous loss of overhead condensing capacity on a number of columns due to loss of cooling medium (either loss of cooling water supply or loss of all air cooler fans due to power failure). To reduce the total load on the common relief system, it may be considered to use Instrumented Protective Functions (IPFs) consisting of high pressure initiators on each pressure system to close the heat input and thus prevent the individual relief case”.

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ADVANTAGES AND DISADVANTAGES OF USING HIPS

In some areas of the world, this is becoming important as regulatory agencies place greater restrictions on flaring.. They are becoming the option of choice to help alleviate the need to replace major portions of the flare system in existing facilities when adding new equipment or units. If the header and flare system must be enlarged, significant downtime is incurred for all of the units that discharge to that header. The relatively low capital cost of HIPS compared to flare system piping upgrades and the ability to install HIPS without incurring significant additional downtime during a turnaround, makes these systems an extremely attractive option. Another benefit is that the process unit will not flare as much as a process unit designed for full flare loading. The main disadvantage of HIPS is these systems are more complex and require that many different components work as designed. The effectiveness of the system is highly dependent on the field design, device testing, and maintenance program. The ability of the HIPS to adequately address overpressure is limited by the knowledge and skill applied in the identification and definition of overpressure scenarios. When a PRV is not installed, the HIPS becomes the "last line of defense," whose failure potentially results in rupture of the vessel or pipeline.

MAKING THE DECISION TO USE HIPS

A decision tree can be utilized to facilitate the use of HIPS in the process industry. Figure 1 is a highly simplified decision tree showing only the key steps in assessing and designing a HIPS.

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Figure 1. Simplified Decision tree

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Operational Actions to reduce the flare :

In order to control any thing the flow to be measured .

Measurement

Many flare system do not have meters . As first steps meters are installed

in main header and sub headers . This has helped in identifying the

source .

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CONTROL VALVE

All the control valves which are connected to flare are being monitored

through RTDB –IP21 . Based on which amount flow is measured and

suitable action are taken to avoid the same in future . Dead band has

been introduced to avoid simultaneously opening of splitting range valve

SAFETY VALVE

All the safety valves are periodically monitored through thermovison

camera and or ultrasonic v pack detector . This has helped in identify

passing safety valve and reduced flaring .

GAS TRAPS

Old gas traps which are not functional were repaired . This has helped in

reduced flaring.

RECOVERY

PROPOSED SOLUTIONS:

It is proposed to install a blow down recovery system for recovery system for the

North storage, agrp and Cold burnery

Blow down recovery system for the burnery:

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Burnery is operating at very low temperature. Recovered material is very cold

and light and the same cannot be routed to Gas plant. Therefore it is proposed to

heat this material to acceptable limit and route the same to Fuel gas system.

Accordingly, a new blow down recovery drum has been proposed to collect the

liquid received through this system and route the same to a new fuel gas

vaporizer through a newly installed pump. Steam will vaporize the liquid and

gases will be routed to the fuel gas system or flare as long as temperature is

more than -20 °C. If temperature falls below –20 °C the same it will be routed

to the burnery.

This approach only needs small pump (10 m3/hr & discharge pressure of 5

kg/cm2) a vessel and a vaporizer. The required details are given Attachment-2.

Depending on the temp , it can be collected in to a drum and sent to the feed

accumulator for further processing.

Flare Gas Recovery Systems

Environmental and economic considerations have resulted in the use of flare gas recovery systems to capture and compress flare gases for other uses. Many times the recovered flare gas is treated and routed to the refinery fuel gas system. Depending upon flare gas composition, recovered gas may have other uses. Flare systems are used for both normal process releases and emergency releases. Emergency streams, such as those from pressure relief valves, depressuring systems, and so on, must always have flow paths to the flare available at all times. Several methods of accomplishing this are described below

Flare gas recovery systems often are installed to comply with local regulatory limits on flare operation and, therefore, must be sized to conform to any such limits Flare loads vary widely over time, and the normal rate may represent some average flare load, or a frequently encountered maximum load. Actual loads on these systems will vary widely, and they must be designed to operate over a wide range of dynamically changing loads..

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Location

Typically, flare gas recovery systems are located on the main-flare header downstream of all unit header tie-ins and at a point where header pressure does not vary substantially with load. Locations upstream of process unit tie-ins should be carefully considered because of the potential for back-flow and high-oxygen concentrations. Limited downstream tie-ins for material not suitable for recovery may be required.Provisions must be made to prevent back flow of air from the flare into the flare-gas recovery system. All compressors should be equipped with highly reliable low-suction-pressure shutdown controls. Consideration should also be given to installation of additional instrumentation in the section of header between the flare and the compressor suction take-off to detect reverse flow and automatically shut down the flare gas recovery system.

Flare-Gas Recovery Controls

The most positive and preferred method for recovery systems operate over venting air ingress is the installation of a water seal vessel wide ranges, usually within very suction pressure between the flare knockout drum and the flare The bands. A typical system might operate over a suction pressure provides a 'Onstant low backpressure On the flare range of 2 to 5 inches of water to 10 to 12 inches of water. header and provides a narrow, but usually adequate The flare-gas recovery compressors should be equipped with range for the flare-gas recovery control system. The water several stages of unloaders and a compressor recycle valve. which the flare gas recovery system is designed to operate. At cle valve, with additional loading unloading of the com the flare. Design provisions must be made to maintain the seal level, prevent high flare rates from carrying the seal water up load unload the compressors. pressure are reached. Usually, the controls are set up to the flare, and prevent seal freeze-up. See Figure D.l for typibe designed to function Over the Pressure for Suction pressure is maintained by control of a recy higher flare gas flows though the seal and Out pressors when limits of valve opening or ,-losing or suction cal seal drum design.

SOLUTIONS TO REDUCE THE SMOKE

Although different types of flares exist, the steam-assisted elevated flare systems are most commonly used at petroleum refineries whereby steam is injected in the combustion zone of the flare to provide turbulence and inspirated air to the flame. For waste gases of insufficient heating value, auxiliary fuels may also be used to sustain combustion.

TechniquesSteam-assisted elevated flares are installed at a sufficient height above the plant and

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located at appropriate distances from other refinery facilities. The flare generally comprises a refractory flame platform with a windshield, steam nozzles, auxiliary gas/air injectors and a pilot burner mounted upon a stack containing a gas barrier. As reported (U.S. EPA 1980,1992, MacDonald 1990), the flare combustion efficiency typically exceeds 98% with dependence on the following factors (i.e., for efficient performance):

excess steam assist (i.e., steam/fuel gas ratio less than 2), sufficient gas heating value (i.e., greater than 10 MJ/m3), low wind speed conditions (i.e., above 10 m/sec.), sufficient gas exit velocity (i.e., above 10 m/sec.)

Similarly, different types of flare burners, designed primarily for safety requirements, may result in different efficiencies.

Emissions/ControlsDepending on the waste gas composition and other factors, the emissions of pollutants from flaring may consist of unburned fuel components (e.g., methane, NMVOC), by-products of the combustion process (e.g., soot, partially combusted products, CO, CO2, NOx) and Sulphur oxides (e.g., SO2) where sulphur components are present in the waste gas. Steam injection is used to enhance combustion for smokeless burning and to reduce NOx by lowering the flame temperature. Increased combustion efficiency may reduce CH4 and NMVOC.

DETAILED METHODOLOGYThe detailed methodology requires each refinery to estimate its flaring emissions usingavailable information on the composition of flare gas, the types of smoke control used and the flare combustion efficiency in combination with flare gas volumes, using either measurement data, available emission factors or mass balance approaches. It is recognised that flareemissions are challenging to estimate and/or quantify with certainty, since: conventional ordirect extractive source testing is not feasible for elevated flares; both flare gas volumedeterminations and/or gas composition may be very uncertain especially during processupsets or emergency releases; and very limited data are available with respect to flarecombustion efficiencies which depend on both process and external wind condition factors.

For normal operations, the general types of refinery and other information required toestimate flare emissions, as currently done at Canadian refineries (CPPI 1991), are:

the actual quantities of gases flared at each flare (e.g. m3/year) based upon measured flare gas flowmeter or other records,the average composition of flare gas including: H/C molar ratio on the basis of flare design or test data, the molecular weight and sulphur content,the types of smoke controls used, such as: steam/air, manual/automatic and/or TV monitor,an emission HC factor based upon typical steam/fuel gas ratios, gas heating values and/or flare combustion efficiencies,

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a sulphur mass balance of fuels consumed by flaring and other refinery process heaters/boilers.

In some instances, flare emissions may only be estimated currently by difference or roughapproximations.

Remote sensing (DIAL) measurements of full-sized flare emissions at a Norwegian petroleum refinery under normal operating conditions also has indicated that the flare combustion efficiency exceeded 98%, comprising various amounts of methane and C2 to C6+ alkane components (Boden, Moncrieff and Wootton, 1992).

Flare combustion efficiencies, under atypical operating or other conditions and presumably during upset conditions, may have lower destruction efficiencies.

Definition: Smokeless Flare  "Smokeless flare" means a combustion unit and the stack to which it is affixed in which organic material achieves combustion by burning in the atmosphere such that the smoke or other particulate matter emitted to the atmosphere from such combustion does not have an appearance density or shade darker that No. 1 of the Ringlemann Chart.  (Source:  17 Ill. Reg. 16504, Sep. 27, 1993 of Joint Committee on Adminstrative Rules in TITLE 35: ENVIRONMENTAL PROTECTION, CHAPTER I: POLLUTION CONTROL BOARD, SECTION 211.6050 SMOKELESS FLARE)

PIPE FLARESThe Pipe Flares offer an economical way to safely dispose of waste gas streams. These flares also incorporate features that enhance both performance and longevity, providing reliable electronic or flame front pilots.     The conventional Pipe flare includes wind deflectors

that break up the low-pressure region on the down wind side of the flare. This reduces flame lick and leads to greatly extended life. Other features that can be provided include flame stabilizers (for high velocity streams or low heating value gases) and “air lock” purge reduction seals.

SONIC FLARESHigh pressure Sonic Flares combine the best features with the longevity of multi-arm flares.

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This flare is capable of providing low heat radiation flaring while maintaining the design principles required to ensure longevity.

  The Sonic flare uses the energy associated with pressurized gas to entrain and mix large quantities of air. The difference in this multi-arm sonic flare is in the nozzle. The annulus design of the nozzle enhances the mixing rate of the entrained air into the primary mixing zone of flame. This highly aerated gas and air stream burns with a clean short flame and with F-Factors ranging from 0.06 to 0.10.

As an added feature, a low-pressure duct can easily be incorporated within the wind deflectors of the Sonic flare. The top of the LP duct is at the same elevation as the Sonic nozzles. This HP / LP design further reduces the possibility of continuous flame lick.

  Most flares spend very little time at the peak design rate. Yet, many flares are unable to handle the conditions which happen most of the time – low flow turndown.

An carefully designed Sonic flare ensures that combustion occurs above the flare tip. This eliminates nearly all of the continuous flame lick on the flare. And, by using properly designed wind deflectors, low flow rate flames are allowed to lift away from the flare, further reducing the chance of flame lick. These two features greatly improve longevity and guard against flare tip failure. 

AIR ASSISTED FLARE

When pressure is not available, an assist medium is required to achieve clean combustion of the waste gas. The air assisted flare uses forced air via a low-pressure blower to provide smokeless flaring. The air assisted flare tip includes mixing vanes which ensure that the air and gas are kept separate until both exit the tip of the flare. These vanes improve efficiency by maximizing the air to gas surface area contact.

Maintaining the philosophy of annulus flaring, the Air assisted mixing head allows the gas to be channeled to the outer annulus and the air to be fed through the center of the flame. This decreases the thickness of the waste gas stream, allows the surface of the waste gas stream to come in contact with

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surrounding air, and further increases overall efficiency. Additionally, the forced air ensures continuous internal cooling which extends the life of the flare tip.

  Proper control of the airflow is essential for successful operation of an air flare through its smokeless range. This is especially true for large air flare systems. This system includes a pressure transmitter (monitoring the waste gas stream), a PLC, and a blower damper. For more control, a two-speed motor can be easily incorporated.  Air Blower

If assist air is required, an optional air blower will be included. The combustion airflow shall be automatically controlled based on waste gas flow rate to the flare. A flanged inlet and outlet as well as access door and housing drain is standard. Air duct is usually supplied from the fan outlet to the inlet of the flare stack.

STEAM ASSISTED FLARE

The steam assisted flare relies on the energy associated with pressurized steam to entrain air and provide the mixing required for smokeless flaring. Additionally, the water / gas reaction improves the hydrocarbon combustion breakdown while reducing the flame temperatures. Both enhance the steam flare’s ability to reduce smoke formation.

The steam assist flare is part of the utility line of flares. This flare uses a ring of

nozzles to inject steam into the base of the waste gas flame. The nozzles are angled to improve the air entrainment and maximize the air / gas mixing. (view Animation to left) For larger flares, a center stream nozzle can easily be incorporated.   For more stringent applications, the Steam assisted flare provides low noise and high efficiency.

VENT FlareFor low-pressure systems, a simple pipe vent can be used . To increase safety, an “air lock” purge reduction seal is normally included.

Natarajan, 03/18/04,
Proper animation will be attached – Now this is linked to mark there’s attachment
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When pressure is available, the vents provide reduced radiation in the event of accidental ignition. And, because of the high rate of air entrapment, the dispersion characteristics are superior to a low velocity vent.

Within the flare industry, there is a desire to provide smokeless flaring from purge to peak flow rates. While some flares are better suited to provide smokeless flaring at high (sonic) flows, others are specifically geared towards smokeless flaring at low flows. The most sensible arrangement for providing smokeless flaring at high and low flows requires a variable orifice and, for heavy molecular weight streams, a small assist medium.

Existing technology provided this ability, however, the available flares suffered from short life. Excessive metal temperatures, large diameter uncooled surfaces, and inherent flame impingement needed to be eliminated to extend life. Variable orifice flare is designed to provide the desired flaring characteristics while extending the flare tip life. Multiple arm technology (known to increase life), annulus gas exit areas, smaller inserts and properly directed air assists were all incorporated into such Variable orifice flares.

NON-ASSISTED STAGED MATRIX Flares

Smokeless turn-down is enhanced by staging the flow to the unit. This ensures that the minimum of burners are in operation at any time, keeping the pressure in the operational stage high enough to provide sufficient turbulence so that the flare will be smokeless throughout its entire operating range.

GROUND LEVEL MATRIX FLARE SYSTEMStaged matrix flares are designed to burn very large quantities of gas smokelessly through-out the entire operating range.

Smokeless performance is achieved using high pressure, high turbulence burners, arranged in a matrix so that combustion air is available to each burner. These flares can be used to burn a very wide range of gases smokelessly.

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This grade level unit has a design capacity of more than 3,000,000 lb/h, all flows completely smokeless. It has about 600 burners, arranged in 7 stages.

 

Matrix flare design requires that particular attention be made to the layout of the flare to ensure that sufficient air gets to each burner. The layout can be tailored to the topography of the location, and the flames can be hidden from sight by berms, sight fences, or a combination of the two.

A typical large matrix flare will have from 6 to 8 stages, using fast-acting, tight shut-off butterfly valves with rupture disk bypass to divert gas to each successive stage. These images are of the burners and manifolds during construction they will later be covered with a layer of gravel for radiation protection.

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Although most matrix flares use non-assisted burner systems which use the pressure of the waste gas in specially designed high pressure burners to promote smokeless combustion, they can also be designed with assisted (steam or air) burners in cases where the waste gas is only available at low pressure.

ELEVATED STAGED MATRIX FLARE SYSTEM

This image shows an elevated staged matrix flare system, installed in refinery service. A significant benefit of putting the burner matrix in an elevated structure is that it becomes more compact since combustion air more easily brought to each of the burners. The plot area taken up by the system is also much reduced.

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