drains & flares

P180drf.PPT - 1Shell Global Solutions

P180 Training CourseSGSI

HSE CONSULTANCY


OBJECTIVES:By the end of this session you will be able to:

– explain the function and purpose of drain systems,– explain some of their general design

considerations,– explain the function and purpose of flares and

vents,– discuss the key issues in the design of flares and

vents,– know where to seek guidance on drain and flare

design.

OBJECTIVES


WHAT STREAMS DO YOU

WANT TO HANDLE ?

WHAT STREAMS DO YOU WANT TO HANDLE?

At first site the facility drainage problem may seem like a simple one, but if you take some time to think about it you will find a large number of different system. A desire for convenience has led in the past to complex systems with many interconnections. In many cases there was a lack of thought to the way that systems should, could or would be operated and there have been some notable and quite serious incidents because of the mal-functioning or mal-operation of systems. Drain systems designed as an afterthought can be more hazardous than the main process. Therefore defining clearly what has to be drained and then providing appropriate well designed systems and operating procedures is essential.If given some thought it will be realised that the facilities drainage problem is a complex one. There are many different stream to be considered each needing a specific solution. Onshore and offshore need different solutions and offshore usually means a more complex disposal problem.It is essential that streams are kept segregated as far as possible and that interconnection between systems is minimised.


STREAMS TO BE HANDLEDRainwater Storm Water

Chemicals

Fire Water

Black Water (sewage)

Grey WaterAviation Fuel

Wash WaterDrilling Mud

Process Fluids

Lube Oil

Spills

STREAMS TO BE HANDLED.

At first site the facility drainage problem may seem like a simple one, but if you take some time to think about it you will find a large number of different system. A desire for convenience has led in the past to complex systems with many interconnections. In many cases there was a lack of thought to the way that systems should, could or would be operated and there have been some notable and quite serious incidents because of the mal-functioning or mal-operation of systems. Drain systems designed as an afterthought can be more hazardous than the main process. Therefore defining clearly what has to be drained and then providing appropriate well designed systems and operating procedures is essential.If given some thought it will be realised that the facilities drainage problem is a complex one. There are many different stream to be considered each needing a specific solution. Onshore and offshore need different solutions and offshore usually means a more complex disposal problem.It is essential that streams are kept segregated as far as possible and that interconnection between systems is minimised.


DRAINAGE SYSTEMSWhat are three most important things about Drains Systems

• Segregation,• Segregation, and

• Segregation

DRAINAGE SYSTEMS


WHY HAVE A DRAINAGE SYSTEMS ?

• cater for accidentally spilled flammable liquids

• handle surface water such as rain

• provide a route for the safe and environmentally• acceptable disposal of liquid inventory

• provide segregation

WHY HAVE A DRAINAGE SYSTEMS ?

The purpose of the drain systems is to collect and convey drainage streams to an appropriate disposal system in such a way as to protect personnel, plant and equipment, and to avoid environmental pollution. Note that the release of pollutants to the sea and hence the design features required of offshore drain systems are generally subject to the MARPOL convention, to which most countries are now signatories. Onshore disposal will be subject to local regulations.Drain systems provide the means of safely removing residual process and wash-down fluids from vessels, pipes, flooring and instruments, resulting either from operational activities or from preparation prior to carrying out maintenance work. The fluids are collected and transported to a recovery system or are disposed of in a safe and environmentally acceptable fashion. A fundamental safety consideration is that a drain system must not provide a route for migration of flammable liquids or vapours from one hazardous area to another, or to non-hazardous areas. Other factors affecting the safety and environmental acceptability of drain systems include: • interconnections between drain systems;• effect of blockages;• accidental or deliberate misuse;• preventing the spread of fires or flammable fluids;• pollution of the sea;• release of toxic materials to the atmosphere;• incorrect material specifications;• inability to be cleaned and maintained.


Drains System Classification

a) hydrocarbon drainsb) non hydrocarbon drains

subdivided into:i) open drainage systemsii) closed systems

Drains System Classification 1.


Drains System Classification

Classify your drains into each group

Drains System Classification 2.


GUIDELINES

• interconnection between different drain systems

• Capacity – worst case• effect of blockages• accidental or deliberate misuse• possibility to spread fire or flammable liquids• provisions to clean and maintain the system

GUIDELINES.

Drain systems have been involved in a large proportion of accidents within oil and gas processing facilities. There design demands careful consideration. The factors listed above affect the safety and environmental acceptability of drain systems. Careful design can avoid problems in operation and prevent the occurrence of accidents.In addition to considering the above factors the drains system design should be optimised based on an analysis of the following:• the nature of the product (flammable, toxic)• the pressure of the disposal stream• the degree of contamination (continuous or accidental)

• the hazardous area of the disposal point.Where necessary segregated disposal streams should be provided.Kerbs or drip pans should be provided around vessels, pumps and other sources of leakage to limit the spread of small spills.Codes and StandardsFor onshore facilities DEP 34.14.20.31: Drainage and Primary Treatment Systems; gives guidance on the design of onshore treatment systems. For offshore drains systems reference can be made to DEP 37.14.10.10-Gen.: Drain Systems for Offshore Installations.For storage tanks the worst case credible spill is associated with tank rupture. In this case suitablebunding provisions should be made in accordance with the IP Code Part 3 - Refinery Safety Code. Also provision for bund evacuation needs to be addressed.The release of pollutants, and hence the design features required for offshore drainage systems, is subject to the MARPOL convention, to which most countries are now signatory. As yet no specific codes or standards exist within the Shell Group for offshore drainage systems apart from those developed by individual operating companies.


GENERAL DESIGN CONSIDERATIONS

Avoid thisit won’t work

Slope 1:100 to 1:75

FPSOs & floating facilities?• liquid seals and dip pipes• floor drains• drip pans• tundishes and funnels• vents• disposal to sea Tank inerted and

under pressure

Dip leg arrangementfor floating storagedrains/slops tanks

GENERAL DESIGN CONSIDERATIONS.

Drain lines from open drains shall enter drains collection vessels via a liquid seal, typically a U-bend, to prevent possible backflow of vapour. The liquid seal requires regular checking to ensure its integrity and accessibility aspects shall therefore be considered during detailed piping design.Dip pipes shall be provided if a caisson is used for the CD or OHD systems even though it might appear that they are not strictly required where non-hazardous and hazardous area drainage systems, including collection caissons, are totally segregated from one another. However, they are useful in minimising vapour release into the modules in the event of backflow or other system upset conditions by creating an extra water seal between the process and the drainage systems.FLOOR DRAINS: Where the risk of hydrocarbon spillage can reasonably be expected to be negligible, grating should be used instead of solid plate wherever possible. Rain and deluge water will then be discharged directly overboard, thereby reducing the volumes of uncontaminated water which would otherwise be collected through the drains system.Drip pans shall be installed under equipment, such as wellheads and pig traps, where spillage of hydrocarbons direct to the sea is possible. However, since drip pans are likely to form a hazardous zone, they should preferably be avoided as far as possible by designing out potential sources of leaks.The atmospheric vents associated with the drainage systems, e.g. from the collection vessels or the drains caissons, shall not be interconnected with each other and should preferably be dedicated vents. They shall be designed and positioned so that ignition by static electricity (or other ignition source) is precluded. The top of the vent pipe shall be sharp-edged to prevent brush discharges. Consideration should be given to placing the vent within the protective "umbrella" of the facility’s lightning conductor system or inside the Faraday cage formed by part of a structure, such as the flare boom. When sizing the vents, abnormal vapour flow rates shall be taken into account, such as those resulting from an incompletely depressurised vessel. The vents shall be sited away from HVAC inlets and shall not be fitted with flame arrestors.


Drawn on P&ID Piping elevation and as built

DrainsCaisson(atmospheric)

HP SeparatorMAOP 3500 psi

DrainValve

ANSI 1500# ANSI 150#

Maintenance Procedure: Drain vesselliquids through process, blow down, ventopen drain valve for atmospheric draining.

Practice: Open drain valve to drain vessel whilst underpressure or drain vessel liquids through process, blow down and vent then breakdrain piping and collect final liquids in abucket.

Gas out

Liquid out

Drawn vs. as built

On the left a simplified P&ID of the closed drain system for a high pressure knock out vessel on an offshore gas platform. The well stream enters the vessel operating at 3500 psi, gas and liquids are separated and flow out to the gas and liquids processes respectively. The drain detail shown is described as a maintenance drain for the disposal of residual liquids and washout water when the process is shutdown and the vessel is under maintenance. Operating procedures stipulate that vessel process liquids are drained through the process. The process is then shutdown, blown down and vented before the drain valve can be opened and the residual liquids (and any subsequently added wash water) drained.An inspection at site revealed the as built plant to be as shown on the right. With a drain valve positioned above the bottom of the vessel it was impossible to comply with the draining procedure. This is a real case and it was reported that the only variation to the written procedure was that after blow down and venting the drain piping at the base of the vessel was disconnected and any residual liquids drained to the drip pan.It is easy to imagine though that even with properly laid out piping the temptation exists to open the valve whilst the vessel is under pressure and use the available force to clear the liquids. This is a dangerous and unacceptable practice which risks overpressuring the drains caisson which (although not shown) has connections to open hazardous and non hazardous drains.The best solution is to avoid the closed drain altogether (unless dealing with particularly hazardous or toxic materials e.g. H2S) and drain to the inlet of a open hazardous drain.


Open Drains

Schematic for a drain system with closed drains.

The above drawing shows the arrangement of an offshore drain system with closed drains. Again the open hazardous and open non-hazardous drain systems are completely segregated.In this case discharge to the closed drains is by hard-piped connections that shall be positively isolated from the process during normal operation. The drain points should be fitted with double block valves with an intervening spade or spectacle blind rated for the upstream connection pressure. This ensures isolation from both the vessel and drain system when removing the spade or swinging the spectacle blind. An alternative isolation system for sight-glass drainage is a double-block-and-bleed arrangement. The main drainage header should be fabricated from 150# rated piping class and terminate at a closed drains drum. The branch connections from the vessels to the main header or up to the first pipe diameter increase shall be rated for the same pressure as the vessel itself. This is because it is in the smaller branch pipes that hydrates are likely to form, should the vessel be inadvertently drained under pressure. Branches shall be connected to the top of the main header(s). There shall be no block valves in the drain system except for those at the individual drainage points. The need for hydrotesting the CD system means that a flange must be installed at the specification break in the piping so that the two pipe classes can be isolated from one another.It is intended that the CD system shall be used only to empty residual liquids from equipment prior to maintenance. No process shall be drained via the CD system unless that process has been fully depressurised. The closed drains drum shall be designed with sufficient volume to receive the drained fluids and to permit vapour disengagement.. The contents of the vessel should be pumped out under level control to a suitable low pressure location in the process to minimise the potential for back flow.


Typical Seal Trap Arrangement

Typical Seal Trap Arrangement


Design a simple drains System

Design a simple drains System


What are the 3 most important things about drains.

What are the Drain system classifications

DRAINS


FLARES AND VENTS

WHY have themWHAT makes a flare system

HOW to design themWhat is NEW in flares

FLARES AND VENTS 1.

There are


FLARES AND VENTS

WHY BLOW DOWN

• Emergencies• Maintenance

FLARES AND VENTS 2.

There are


Flare Header

Flare knock-out drum

To process

Flare boom

Reliefvalve

Automaticblowdownvalve

Manualblowdownvalve

Liquids recovery pump

Liquids capacity forworst blowdown

Typical Flare/Relief System

Typical Flare/Relief System


Considerations on whether to vent or flare:

• DO NOT VENT

• the impact on the environment

• the safety and integrity of the disposal system

• local regulations

• economic evaluations

Flaring versus venting

Wherever possible disposal streams shall be collected in a closed system and directed to a flare or vent, except when they can be sent back to the process or stored. In this context, the use of a gas recover system can be considered.In principle flaring is the preferred solution but this my not be possible where disposal streams contain products that are not combustible.Local regulations have largely been responsible for the control of flaring


HP Relief System•••

LP Relief System•••

Venting•••

WHAT GOES WHERE

WHAT GOES WHERE


HP Relief System• high pressure vessels• heat exchangers• pumps• compression systems

LP Relief System• low pressure vessels• low pressure equipment• atmosphere tanks• blanketing systems

Venting• drains tanks• purge posts• inerting systems• ???

WHAT GOES WHERE


•Liquid carry over

•Back pressure

•Radiation

•Purging

MOST IMPORTANT DESIGN IMPACTS

MOST IMPORTANT DESIGN IMPACTS

LIQUID CARRY OVERHORIZONTAL KNOCK-OUT DRUM

LIQUID CARRY OVER HORIZONTAL KNOCK-OUT DRUM

HYDROCARBON FLARE SYSTEM AND H2S FLARE SYSTEM

HYDROCARBON FLARE SYSTEM AND H2S FLARE SYSTEM.

The above flare system is typical of a refinery or chemical plant and is a more complex system than we would normally encounter in E&P, but there are examples that come close. Below are the notes applicable to the drawing.

1. The need for steam tracing depends on climatic conditions.

2. The pump capacity shall be such that the liquid hold-up of the knock-out drum can be disposed of within two hours.

3. For LNG plants no water seal vessel and no steam injection in the flare tip is applied.

4. Water seal column height, "H" shall be greater than P/J, where P = maximum pressure in the water seal vessel (in metres water column) and J = specific density of liquid. H shall be at least 2 metres.

5. Steam flow depicted for electronic transmission of signals.

6. Operator set maximum steam flow.

7. Range of required steam flow may necessitate more than one transmitter (auto range selection).

8. TIC is optional but shall be applied when liquid which is too hot or too cold (e.g. LPG) is pumped to slops.

9. Ultrasonic flow meter.

10. A level alarm shall be provided if large quantities of liquid are expected.

Flare Radiation Calculation

Flare Radiation Calculation

44

Shell FRED

Shell Global Solutions

Shell FRED


To request a free evaluation CD-Rom containing full software products, please fill in an enquiry form or e-mail us at

[email protected] .

www.shellshepherd.com

Alternatively you may contact HSE Consultancy at:

Shell Global Solutions (UK)Cheshire Innovation Park

PO Box 1Chester

CH1 3SH. UK

Tel. +44 151 373 5010Fax. +44 151 373 5058

Information


Shell FRED

The following are currently used by Shell to reduce emissions from purging:

• Purging with nitrogen instead of hydrocarbon gases• Provision of low purge flare tips• Installation of fluidic/molecular seals

Proven techniques not currently used by Shell:

• Purging with combustion gases• Eliminate purge gas requirement by designing vent

system/degasser for flashback

Shell FRED

A number of low impact purge operations are available. These are identified above and should be reviewed on a case by case basis as applicable. In addition, purge rates can be minimised by accurate rather than conservative methods for calculating purge gas rates.


STRUCTURES FOR FLARES AND VENT STACKS AND LIQUID BURNERS

• free standing stack• guyed stack• derrick structure• angled boom structure (especially on

offshore platforms• Also Ground flares and Burner pits

STRUCTURES FOR FLARES AND VENT STACKS AND LIQUID BURNERS

Guidance on the design of structures can be found in DEP 34.00.00.30-Gen., DEP 34.24.26.31-Gen. And DEP 34.28.00.31-Gen.The type selected is based on economic and operational grounds. If only one stack is required, any of the four types noted above may be selected.


What is NEW in flares

What is NEW in flares

There are


For intermittent flaring resulting from process upsets, the following are currently considered by to reduce the impact of flare emissionsand effects:

� use of leaner flare gas� steam/water injection or air assisted flares� high velocity tips� enclosed ground flares, box flares or low intensive flare tips

for reduced light effect� flaring window� Low noise burners

FLARE EMISSIONS

Proven technology, but new to Shell are in-ground enclosed flares and low profile enclosed ground flares for smoke reduction, marketed by NAO IncFor continuous flaring, the following should be considered:� Use of energy from continuous flares for WHR� Use of vent gas for power generation rather than flaring

Optimised combustion technology - including efficient burner design, low purge flare tips etc - is provided by:� Elmac� Birwelco� Kaldair� NAO Inc To reduce emissions, low consumption pilot ignition packages (Birwelco) or pilots on demand should be considered. Alternatives for non continuous pilots are:• Electrical ignition• Projectile ignitionBoth methods are well established, although there is some concern regarding the efficiency of projectile ignition with vertical stacks. Existing flare systems can be readily modified to accommodate non continuous pilots.


Flare GasKnock-out Drum

Flare Header

To Process To Flare Tip

RecoveryEquipment

Rupture Disc

Flare Valve

Flare Recovery System

FLARE GAS RECOVERY

Flare gas recovery is a proven process and is currently used by Shell. The flare gas recovery system is designed for normal leakage rates, vent gases normally flared and minor process upsets. During recovery, the flare line is closed by the valve installed downstream of the KO drum. For safety, a bursting disc is installed in parallel. The flare gas is compressed and recycled to the process or used as fuel gas. For larger releases, the valve will open and the recovering equipment will be isolated. During this operation, the gas will be ignited.

Each flare system requires evaluation on a case by case basis as there is the potential for high compression duty, depending on the recycle pressure required. Installation needs to be weighed against the “cost” of CO2 (tax in Norway or environmental targets)

Vendors supplying flare gas recovery systems are:� Kaldair� Umoe� Elmac

THE UMOE SAFE FLARE

The new and patented UMOE SAFE FLARE gas recovery system eliminates the need for continuous flaring of gas on Offshore Platforms and Petrochemical Plants. The gas is safely and effectively recovered to be utilised for other purposes. The system claims a cost effective recovery of flare gas and a substantial reduction of CO2 emissions. The concept comprises flare closing components, a gas recovery system and a separate system for igniting the flare.Reference is made to the illustration of the basic flaring technology. Basic components are a flare valve in the flare line fitted with a rupture disc in parallel. When pressure in the flare system reaches a predetermined level, the flare valve opens. In normal operation, the flare gas recovery system should capture the underlying flare gas that continuously leaks into the flare collection header and direct it back into the gas processing for compression, dehydration and export. If a problem occurs the flare valve will open promptly and the gas will be diverted to the flare. The flare is an essential safety system, used for safe disposal of flows from pressure safety valves and depressurisation of processing equipment. The flare gas recovery system must not compromise this capability: 1. The system must be able to open quickly, before the pressure rises and reaches a predetermined level. 2. The reliability must comply with all security standards of the project. 3. The gas recovery system must be simple and reliable. You can find details about the UMOE flare at the following web site:

http://www.umoetech.no./

UMOE SAFE IGNITION

UMOE SAFE IGNITION consists of a compressed nitrogen driven launcher contained in astainless steel cabinet at the deck level.In addition, a striker plate is located below the flare tips to ignite the specially designed ignition pellet being automatically launched from the launching unit. When hitting the striker plate, the pellet will explode and generate a shower of sparks, each igniting along its entire path. Guaranteed ignition in all weather conditions.

Umoe Safe Ignition has been designed by Umoe Process Technology AS, Techno Consult AS andRaufoss Technology AS and is protected by several Norwegian and international patents


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