Flares

PROCESS DRAINS AND FLARES FLARES

TRAINING MANUAL COURSE EXP-PR-PR125 Revision 0.1

Exploration & Production Process Drains and Flares – Flares

PROCESS DRAINS AND FLARES FLARES CONTENTS 1. OBJECTIVES ..................................................................................................................4 2. THE FUNCTIONS OF FLARES.......................................................................................5 3. HOW FLARES WORK .....................................................................................................7 4. THE DIFFERENT TYPES OF FLARE SYSTEMS ...........................................................8 4.1. Safety valves, rupture disks and thermal valves .......................................................9 4.1.1. Safety valves .....................................................................................................9 4.1.1.1. Conventional type ........................................................................................9 4.1.1.2. Balanced type ............................................................................................10 4.1.1.3. Piloted type ................................................................................................11 4.1.2. Rupture disks ..................................................................................................12 4.1.3. Thermal valves ................................................................................................12 4.2. Flare manifolds........................................................................................................13 4.3. Decompression valves (Blow Down Valves) ...........................................................14 4.4. Pressure Control Valves..........................................................................................14 4.5. Flare drum...............................................................................................................15 4.6. Sealing systems ......................................................................................................16 5. Different types of flare stacks.........................................................................................18 5.1. Conventional flare stacks ........................................................................................18 5.2. Sonic flares .............................................................................................................19 5.3. Low flare with combustion chamber ........................................................................23 5.4. Cold flares or vents .................................................................................................23 5.5. ADVANTAGES AND DISADVANTAGES OF THE DIFFERENT FLARES..............24 5.5.1. Sonic flares......................................................................................................24 5.5.2. Low flare with combustion chamber ................................................................24 5.6. Cold Vents...............................................................................................................25 5.6.1. Advantages & disadvantages ..........................................................................25 5.7. EXERCISES............................................................................................................26 6. FLARE REPRESENTATION AND DATA ......................................................................27 6.1. REPRESENTATION ON PROCESS FLOW DIAGRAM..........................................27 6.2. REPRESENTATION ON P&ID (PIPING & INSTRUMENTATION DIAGRAM)........29 6.3. EXERCISES............................................................................................................32 7. FLARES AND PROCESSES .........................................................................................33 7.1. LOCATION AND CRITICALITY ..............................................................................33 7.2. EXERCISES............................................................................................................33 8. OPERATING PARAMETERS ........................................................................................34 9. OPERATION..................................................................................................................36 9.1. START-UP ..............................................................................................................36 9.1.1. Inertance .........................................................................................................36 9.1.2. Start-up of the pilot light(s) ..............................................................................36 Training course: EXP-PR-PR125-EN Last revised: 27/04/2007

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9.1.3. Start-up of main burners..................................................................................37 9.2. SHUT-DOWN ..........................................................................................................38 9.3. EXERCISES............................................................................................................38 10. TROUBLESHOOTING.................................................................................................39 10.1. Valves ...................................................................................................................39 10.2. Flushing gas ..........................................................................................................40 10.3. Pilot lights ..............................................................................................................40 10.4. Flare drums ...........................................................................................................41 10.5. EXPERIENCE FEEDBACK...................................................................................42 11. GLOSSARY .................................................................................................................43 12. LIST OF FIGURES ......................................................................................................44

Training course: EXP-PR-PR125-EN Last revised: 27/04/2007

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1. OBJECTIVES


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2. THE FUNCTIONS OF FLARES The functions of a flare system are: safely collecting gas waste from the process to keep the equipment within their operating pressure limits in case of depressurisation or opening of the valves separating the gas and the condensates in the scrubbers sending the gas to the flare to be burned

Figure 1: Flare system The flare function is first and foremost a safety function. The flare system protects equipment against pressure build-up which could lead to explosions. Moreover, the flare system collects the “fatal gases” to vent them to the atmosphere. !!!!


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A flare system is made up of: A set of depressurisation components (safety valves, rupture disks, blow down valves (BDV), automatic pressure control valves) A main collection network and one or two secondary collectors (also called manifolds) A separator drum for the various phases (water, liquid and gaseous hydrocarbons), located at the foot of the flare A sealing device to prevent any air entry into the system (purge gas, hydraulic guard) A flare stack on top of which a flare tip is placed In a lit flare, a pilot light gas network is installed to permanently supply the pilot lights placed close to the flare tip An ignition system for these flares


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3. HOW FLARES WORK Each drum, column or capacity that operates under hydrocarbon pressure is linked to the flare network by means of one or many valves and / or various pressure control valves (PCV) and blow down valves (BDV). During the installation’s normal operation the quantity of gas sent to the flare is minimal and only represents the incondensable fraction of the processed hydrocarbons with a fraction of the Fuel-Gas to ensure a regular flowrate (see § below). Some flush or purge gas is permanently injected to maintain the safety flowrate at the flare by keeping the burner flames ignited and thereby preventing air from going back. In case of malfunctioning of part of the installation, mainly due to an increase in pressure in a vessel, the pressure relief valve opens to send more gas to the flare. If the pressure increases too sharply and / or becomes uncontrollable, the equipment’s safety valves open to protect the vessel. In case of a more serious incident or the emergency shut-down of the installation, the safety system activates the opening of the blow down valves (BDV). The flare system is therefore a priority system on a hydrocarbon processing installation, since it protects the equipment against pressure increases that could make them explode. To permanently ensure the proper operation of the flare system, a certain number of safety and control components are installed: A flush gas network for the flare manifolds to avoid the entry of air inside the flare stack A pilot light gas network that maintains a flame at the flare tip, for flares that are permanently lit Two or several pilot lights according to the installation’s diameter A remote flare ignition system A nitrogen network that can be connected to the flare manifolds for inerting the system before maintenance operations Or in the case of Cold Vents, in stormy weather conditions, to quench a fire started by lightening More and more installations have surveillance cameras to monitor the presence and the condition of the flame


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4. THE DIFFERENT TYPES OF FLARE SYSTEMS The number of flares depends on: The process diagram The characteristics of the products used It also depends on Safety criteria such as Radiation & Dispersion.

The main criteria are: The various pressure levels that could lead to an excessive back-pressure in the manifolds. Avoid the simultaneous collection of high pressure products in a system that can receive low pressure products. The nature of the products used. Avoid mixing wet products as well as dry products outside of specifications with cold products to avoid the formation of ice and / or hydrates that could block the flare system. The corrosiveness of the various gasses. An independent flare system should be envisaged when the H2S concentration is higher than 10%mol. The maintenance operations and the operating philosophy may require always having one flare in operation and thereby doubling the flare system.


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4.1. Safety valves, rupture disks and thermal valves These mechanical organs perform a decompression without the need for human intervention and without the system’s requiring a USS (Ultimate Safety System).

4.1.1. Safety valves 4.1.1.1. Conventional type With the conventional safety valve, the pressure calibration depends on the backpressure. The maximum admissible backpressure is 10% of the calculation pressure.

Figure 2: Conventional valve


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4.1.1.2. Balanced type The balanced type, for which the pressure calibration is independent of the back pressure. The back-pressure should be limited to 50% of the calculation pressure.

Figure 3: Balanced valve


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4.1.1.3. Piloted type The piloted type, for which the pressure calibration is independent of the back (or counter) pressure. The opening pressure should be limited to 50% of the calculation pressure.

Figure 4: Piloted valve


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4.1.2. Rupture disks These devices are used to either replace the valve or to protect the valve from corrosion due to the nature of the fluids.

4.1.3. Thermal valves These are conventional calibrated spring valves that open proportionally to the increase of the static pressure in the equipment following a rise in temperature (moreover their true, [and commonsense] name is TSV (for Temperature Safety Valve) in comparison with PSV (Pressure Safety Valve). These valves are used mainly with incompressible fluids. All these protection components must be installed at high points.


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4.2. Flare manifolds The collection network is made up of a set of lines linking the protection components (valves) to the flare drum. It is divided into sub-manifolds and a main manifold (also called a collector or header). All these manifolds must have a sufficient diameter to reduce back-pressure when several protection components are opened simultaneously. In addition they must be installed at a slope of 2mm per meter towards the flare drum so as to ensure the natural drainage of liquids carried over during burning off.

Figure 5: Network of flare manifolds


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4.3. Decompression valves (Blow Down Valves) These are ON/OFF valves that link the process equipment to the flare manifolds. They are activated remotely by the operator or automatically by the Emergency Shutdown System (ESD).

Globe gate valve & FB

Orifice calibrated to flowrate

Figure 6: Blow Down System

4.4. Pressure Control Valves These are process control valves activated by an electronic, pneumatic or hydraulic system that permanently or intermittently allow a flow of excess fluid to the flare, mainly in transitory situations such as start-up or programmed shut-down. NB: PCV usually discharge to the B.D. circuit, but are not part of this system. Training course: EXP-PR-PR125-EN Last revised: 27/04/2007

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4.5. Flare drum A drum is installed between the flare manifold and the flare stack to separate the effluent liquids carried along with the gas. The reasons for such a separation are: Preventing an accumulation of liquid at the bottom of the flare stack that could obstruct the path of the gas Minimising the risk of liquid combustion at the flare tip Recovering the usable fractions carried along to the flare

Figure 7: Equipment around the Flare Drum


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4.6. Sealing systems The aim of these systems is to prevent air from entering the flare network We distinguish between 2 types of systems Hydraulic seals Gas seals

Figure 8: Hydraulic seal (1)

Figure 9: Hydraulic seal (2) Training course: EXP-PR-PR125-EN Last revised: 27/04/2007

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Figure 10: Gas seal


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5. Different types of flare stacks The flare stack is the last element of the flare system. It is used to burn the gas without liquid. Different types are used: conventional stacks sonic flare low flare with combustion chamber cold vents

5.1. Conventional flare stacks The stack is always installed vertically and the gas velocity is limited to Mach 0.5 / 0.6 for discontinuous flows (emergency shut-down) and Mach 0.3 for a continuous flow. A flare stack must be able to function under all atmospheric conditions and must have a reliable ignition system. The stabilisation of the flame is ensured by a flame maintenance ring that is specially designed for and installed into the flare stack. This equipment stabilises the flame front by creating vortexes that prevent the flame from being blown out. We distinguish between several types of conventional stacks: forced draught for strong flows equipped with a fan water or steam injection to reduce the radiations and the smoke emission Figure 11: Flare drum These types of flares are not recommended except when there is a smoke problem that has to be addressed. Training course: EXP-PR-PR125-EN Last revised: 27/04/2007

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5.2. Sonic flares The gas speed is at least Mach 1 The jets of fluid ejected into the atmosphere induce air that improves the air / gas mixture. The improved combustion gives a whiter flame (actually more oxygen makes the flame whiter, thereby increasing the temperature and in these conditions radiation cannot decrease!!) The back-pressure for the nominal flow can reach 4 to 10 bar (normally: 4 to 5 bar) when properly calculated; owing to the back pressure, the upstream equipment can be smaller due to the reduced gas volume. The main manufacturers are: AIR OIL BIRWELCO EET JOHN ZINK KALDAIR

Figure 12: EET sonic flare stack Training course: EXP-PR-PR125-EN Last revised: 27/04/2007

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Figure 13: FCG sonic flare stack


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Figure 14: John Zink sonic flare stack


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Figure 15: BIRWELCO sonic flare stack


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5.3. Low flare with combustion chamber This type of flare consists of a chimney in which a forced draught burner is installed. These flares are installed: On land when the environmental regulations do not allow for a visible flame or when there is no space to install a different type of flare. Off-shore on a FPSO when it is not possible to install a different type of flare.

5.4. Cold flares or vents The cold flares are similar to the other types of flares, but the gas is released into the atmosphere instead of being burnt. The height of the cold flare is determined only by the calculation of the gas dispersion in the atmosphere. The cold flare is equipped either with a sonic tip or with a conventional tip. The speed of the gas at the outlet is about Mach 0.8 to ensure adequate dispersion into the atmosphere.


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5.5. ADVANTAGES AND DISADVANTAGES OF THE DIFFERENT FLARES 5.5.1. Sonic flares The advantages and disadvantages of a sonic flare as opposed to a classic flare are: Advantages Lower emissivity coefficient due to better combustion Recommended installation for off-shore installations (less space required) Disadvantages More maintenance (replacement of the flare tip every 2 to 3 years depending on the manufacturer) Heavier flare tip Higher cost Required separation of the HP and LP flare networks due to the back-pressure

5.5.2. Low flare with combustion chamber Advantages Little radiation No visible flame (environment) Little noise Disadvantages Higher cost due to the presence of a burner and the necessity of having a chimney lined with a resistant material on the inside Heavy Flow rate limited by the size of the chimney No flame visible to the operator Training course: EXP-PR-PR125-EN Last revised: 27/04/2007

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Fan runs continuously for safety reasons Maintenance of the fan and the chimney’s internal components.

5.6. Cold Vents Built of stainless steel. Usually heat insulated to avoid the accumulation of ice during depressurisation. Wind nozzle designed to support high temperatures in case of accidental ignition by lightening.

5.6.1. Advantages & disadvantages Major economic advantage: does not require permanent flushing with Fuel Gas Less costly in terms of return on investment when constructed because no pilot burners and satellite burners needed. Disadvantages: Sends large quantities of gas into the atmosphere at rather low temperatures. Presents an evident potential danger: the explosive mixing zone cannot be seen in the sky. Slow gas dispersion when there is no wind ; possibility of stagnation for condensate gases with carbon chains longer than C2. Absolutely requires informing aeronautical navigation and helicopter crews prior to operation. In the event of an ESD1, which gives no forewarning before it occurs, information can only be retroactive. Such an accident, in which a helicopter ignited an oil slick just by flying by, has occurred in the past. The Cold Vent must be fitted with a nitrogen flushing system to extinguish any fire ignited by lightening (N2 frame at base of flare). Presence of H2S in circulating gas must be prohibited.


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5.7. EXERCISES


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6. FLARE REPRESENTATION AND DATA 6.1. REPRESENTATION ON PROCESS FLOW DIAGRAM Process Flow Diagram (PFD): This document, compiled in the project phase, presents the principal process lines and vessels in a simple format, as well as their principal operating parameters.


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Figure 16:Example PFD of flares Training course: EXP-PR-PR125-EN Last revised: 27/04/2007

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6.2. REPRESENTATION ON P&ID (PIPING & INSTRUMENTATION DIAGRAM) This document, compiled in the project phase, presents the principal process lines and vessels in a simple format, as well as their main operating parameters.


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Figure 17:Example P&ID flares (1) Training course: EXP-PR-PR125-EN Last revised: 27/04/2007

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Figure 18: Example P&ID flares (2) Training course: EXP-PR-PR125-EN Last revised: 27/04/2007

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6.3. EXERCISES

Training course: EXP-PR-EQ125-EN Last revised: 27/04/2007

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7. FLARES AND PROCESSES 7.1. LOCATION AND CRITICALITY The flare system is the first process system that must be started up before the commissioning of the installations. The shut-down of the flare imposes a total production shut-down.

7.2. EXERCISES


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8. OPERATING PARAMETERS The operating parameters that must be monitored in normal operation are: Sufficient flow rate of the flushing gas Gas and air flow rates sent to the pilot lights Pressure of the flare drum Level of the flare drum related to start-up and shut-down of collection pumps Temperature of the liquid in the flare drum if the latter is equipped with a heating pin The proper operation of the collection pumps at the bottom of the flare drum, if these are present. A weekly test is carried out in the emergency pump. These pumps operate in ON/OFF mode between LSH and LSL: ¾ The LSH starts the selected pump ¾ The LSL stops the pump The temperature of the pilot lights (this parameter is not always available on the DCS).

The flare drum is equipped with a certain number of safety devices that are linked to the installation’s general activation system. Very high liquid level LSHH (careful, this triggers an ESD 1) Very low liquid level LSLL (this inhibits the start-up of the Very high temperature of the heater TSHH (shuts down heating, to be rearmed on site) Very low heater temperature TSLL


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Figure 19: The layout around a flare drum


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9. OPERATION The flare system is the first process system that must be started up before the commissioning of the installations.

9.1. START-UP 9.1.1. Inertance In an installation that has been shut down, the flare network contains air. Therefore, the system must be inerted before any start-up procedure can be undertaken. This is done by flushing an inert gas (usually nitrogen, if available, otherwise LP steam can be used if the utilities include a boiler) from the furthest points of the sub-manifolds to the flare drum and the flare itself. The flushing continues until the atmosphere in the system is free of oxygen when measured with an oxygen meter (< 0.2%) (2% suffice for Hydrogen).

9.1.2. Start-up of the pilot light(s) Check the availability of the flushing gas network Check the availability of the remote pilot light ignition system Provide an emergency ignition device (Very gun) Supply the circuit with pilot light gas (propane cylinders are usually available) Supply the air circuit with a pilot light Activate the piezoelectric lighter until the mixture in the pilot light line is ignited Activate the emergency lighter if no flame is visible at the flare tip


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NB: Do not do what is seen regularly all over the world! When the mixture lighting test is completed (and you see the flame through the viewer): Do not close down the isolation valves upstream of the FG & Air control valves (which would cut off the supply to the burning mixture. Open them and then wait a certain time until the mixture reaches the top of the flare!!! Turn on the pilot light again What may then happen might make you jump (not unlike what happens in an engine when the spark plug lights but this time it is not the piston that would come down!!)

9.1.3. Start-up of main burners Only open the flushing gas after having observed the presence of a flame at the top of the flare, request confirmation from the control room crew, who will have observed the “take off” of the flare tip TIs. Then, adjust the flushing gas flow rate as soon as the installation is put on production.


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9.2. SHUT-DOWN The shut-down of the flare imposes a total shut-down of production. Immediately after the shut-down of the flushing gas injection, nitrogen injection must be available to inert the flare network in the same manner as before the start-up procedure. You must absolutely prevent air from reaching the hydraulic guard while the drum is at more than 200°C as, in the case, the three elements needed to start a fire are united: the air that entered is now present presence of gas which is still not entirely vented pas encore to the atmosphere The temperature which may be high enough to cause an explosion No intervention must be carried out on the flare network before it has been inerted.

9.3. EXERCISES 1. Analyse and explain what might happen if you incorrectly execute the pilot lighting procedure.

2. Wait until the mixture reaches the top of the flare? How shall we know when the mixture is at the top of the flare?


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10. TROUBLESHOOTING 10.1. Valves In certain circumstances of downgraded operation, the equipment pressure may rapidly trigger the opening of a P.S.V. Generally, during the pressure drop that follows, the valve closes again and stays sealed. Usually, at this stage, the installation should have been shut down by triggering of a PSHH. However, sometimes a valve remains open, which can seriously disrupt the installation’s operation. The valve arrangement devices make it possible to isolate the faulty valve and to operate on the emergency valve. An interlock system ensures that there is always an operational valve and an emergency valve. This interlock system is not installed on all equipment and when there is only one PSV, it is the shutdown system of the entire installation that is connected to the flare system to which the faulty PSV is vented.

Figure 20: System with 1 isolating valve The isolating valves of the operational valve will necessarily be locked in the ‘open’ position and those of the downstream emergency valve locked in the open position and the upstream valves closed. Poor arrangement of the valves described here have, in the past, led to a large number of incidents, not just in the Oil & Gas industry. Training course: EXP-PR-EQ125-EN Last revised: 27/04/2007

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The repairs on a faulty valve will require a disassembly according to a strict specific procedure with the laying of flush joints upstream and downstream of the valve.

Figure 21: System with 2 isolating valves

10.2. Flushing gas In case of flushing fuel gas supply problems on the flare network, the flushing will be done with nitrogen in order to avoid air getting into the circuits or with LP steam if this facility is present in the installation.

10.3. Pilot lights The pilot lights are equipped with thermocouples that permanently measure the temperature at the pilot light outlet. When a pilot light is extinguished, the temperature drops and the thermocouple activates an alarm in the control room. Any extinguished pilot light must be re-ignited as soon as possible.


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10.4. Flare drums The safety devices installed on the flare drum are linked to a general installation shutdown system: A very low level (LSLL) results in the shut-down of the condensate collection pumps and the closing of the suction valve A very high level (LSHH) results in a general production shut-down, ESD1, to avoid overflow of liquid hydrocarbons at the flare tip, which would flare up immediately A very high temperature at the heater results in the shut-down of the heater

Figure 22: Flare drum safety system


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10.5. EXPERIENCE FEEDBACK How do you melt a flare line by following a normal start-up procedure? An LNG unit at the end of the start-up procedure early one Christmas morning: Recirculation is proscribed in a closed circuit due to the temperature, which being too low would inevitably cause slugs in the cryogenic exchangers. The process gas, in the liquefaction process, terminates its itinerary at the flare, and must be routed to the storage tank as it nears its dewpoint temperature. Obviously there is another parameter to be monitored, i.e. the gas temperature at the exchanger outlet. So, around 6 :00 am suddenly packets of LNG appear at the tip of the flare, igniting almost instantaneously. One aggravating circumstance was that the flare line was made of special aluminium that melts around 220°C, which is what happened with the flare stack melting over several tens of metres, when the ROVs were opened on the flow line to the tank, which was already set up for reception.

In view of the time of day, the incident did not result in any casualties; however, a good part of the flare line had to be rebuilt, but with a LNG umbrella, this time, installed above the line.


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11. GLOSSARY


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12. LIST OF FIGURES Figure 1: Flare system .........................................................................................................5 Figure 2: Conventional valve ...............................................................................................9 Figure 3: Balanced valve ...................................................................................................10 Figure 4: Piloted valve .......................................................................................................11 Figure 5: Network of flare manifolds ..................................................................................13 Figure 6: Blow Down System.............................................................................................14 Figure 7: Equipment around the Flare Drum......................................................................15 Figure 8: Hydraulic seal (1)................................................................................................16 Figure 9: Hydraulic seal (2)................................................................................................16 Figure 10: Gas seal ...........................................................................................................17 Figure 11: Flare drum ........................................................................................................18 Figure 12: EET sonic flare stack ........................................................................................19 Figure 13: FCG sonic flare stack .......................................................................................20 Figure 14: John Zink sonic flare stack ...............................................................................21 Figure 15: BIRWELCO sonic flare stack ............................................................................22 Figure 16:Example PFD of flares.......................................................................................28 Figure 17:Example P&ID flares (1) ....................................................................................30 Figure 18: Example P&ID flares (2) ...................................................................................31 Figure 19: The layout around a flare drum.........................................................................35 Figure 20: System with 1 isolating valve ............................................................................39 Figure 21: System with 2 isolating valves ..........................................................................40 Figure 22: Flare drum safety system .................................................................................41


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Flares

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