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Flare stack structure revamp: A case history

03.01.2011  |  Singh, S. ,  Reliance Industries Ltd., Nagothane, Maharashtra, India

An innovative approach was used to repair an older flare structure online without an extensive shutdown

Keywords: [corrosion] [heat transfer] [refractory] [insulation]

A gas flare, alternatively known as a flare stack, is an elevated vertical conveyance that is part of installations such as oil and gas wells, oil rigs, refineries, chemical, petrochemical and natural gas plants, and other facilities (Fig. 1). On oil- production rigs and in refineries and petrochemical plants, the flare stacks primarily serve to protect vessels or pipes from over-pressuring during unexpected plant upsets.

 

  Fig. 1. Flare stack.




Safety system.

Whenever plant equipment is over-pressured, the pressure, relief valves on the equipment automatically release gases (and sometimes liquids as well) that are routed through large piping runs called flare headers after liquid hydrocarbons are completely vaporized and then send to the flare stack. The released gases are burned as they exit the flare stack. The size and brightness of the resulting flame depends on how much flammable material was released.

Steam can be injected near the end of the flare tip to reduce formation of black smoke. The injected steam does, however, increase the noise level of the burning gas. To keep the flare system functional and instantly useable, a small amount of purge gas is continuously burned. It thus resembles a pilot light, maintaining the system ready for its primary purpose as an over-pressure safety system. The continuous gas source also helps to prevent oxygen ingress into the system.

As mentioned earlier, flare systems enhance plant safety by dependably disposing of all hydrocarbons discharged during plant upsets. All safety valve releases go to the flare system. There are, however, two types of flare feeder systems in ISBL:

• A wet flare header is used to handle flare gases that contain moisture but are not “cold” gases.

• An intermediate flare header, which could contain some moisture and normally handles some cold vapors (up to –45°C).

• A dry flare header designed to handle dry flare gases. These will also be cold, with normal temperatures below –45°C.

• A low-pressure acetylene flare header, exclusively provided to handle acetylene-rich gases.

At Reliance’s Nagothane facility, a large flare stack with a design load of 1,000 metric tph is located on the north-east side of a gas-cracker plant. Flare headers from individual plants—polypropylene, low-density polyethylene, linear-low density polyethylene, gas cracker-OSBL and gas cracked-ISBL) join the main flare header, which routes to the flare stack (Fig. 2). The main flare header leads to a knockout drum in the flare area.

 

  Fig. 2.  Flare system schematic at the
  Nagothane plant in India


The purpose of the knockout drum is to separate entrained liquid droplets carried with the gases passing through relief valves. Liquid capture avoids the danger of burning droplets falling from the top of the flare stack. Flare gas free of liquid flows to a water-seal drum; its purpose is to provide protection against pulling a vacuum and to prevent a flash back in the flare header. Occasionally, the stack draft effect could decrease pressures below atmospheric at minimum flare gas loads. The water seal also eliminates the ingress of air into the flare system and any attendant risk of explosion. The flare stack at this facility is 100 m high and has a diameter of 1.52 m. The flare height of 100 m includes the flare tip and a molecular seal installed just above the flare stack and below the flare tip.

The molecular seal consists of a gas “lead pipe” and an inverted cylinder over the pipe. Gas flows in an upward direction, turns through 180° and flows downward for a short length before being redirected again through 180° and back to the original flow direction. In the static condition, gas lighter than air will tend to collect in the upper bend and heavier gases will tend to settle at the lower bend, sealing off the stack against backflow of air. The flare tip is mounted on top of the molecular seal and contains three pilot burners. Damage to the flare tip due to flame burn back near the tip is avoided through the use of refractory lining on all exposed anchor and mesh surfaces.

Exploring the failure history.

The flare stack at Nagothane was commissioned in 1989. Since then and at every plant shutdown, the flare tip was being replaced because it experienced damage during flaring operation. Until 2010, the flare stack structure had never been repaired and neither had it been repainted after plant commissioning because no time was available during annual or major shutdowns. However, inspections of the flare stack structure, ladders, grating, clamps and associated piping was conducted before a major turnaround scheduled for early 2010.

The support structure of the flare stack was found damaged, and loss of thickness was observed and measured at various locations, mainly under the support plates (Figs. 3 and 4). Fuel gas and steam piping were found damaged as well and some grating had been totally eaten away by corrosion. Replacement or repair of the entire structure during a projected 17- day maintenance shutdown was contemplated but judged very difficult. It was also realized that working on a flare stack structure during normal plant operation involves high risks; needless to say, flaring can occur at any time due to plant upsets.

 

  Fig. 3.  Damaged structure. 



 

  Fig. 4.  Extreme corrosion on a flare stack in
  India



Repair approach.

The conventional mode of replacing or repairing a flare structure, piping and subsequent painting would take more than 100 days. It was, therefore, judged impossible to do the entire job during a planned shutdown of only a 17-day duration. With that in mind, initial discussions were aimed at completing the job in discrete phases; specifically up to 44 m elevation, in steps dubbed non-shutdown or pre-shutdown tasks. The remaining work from 44 m to 100 m elevation was to be done during the scheduled major shutdown.

Scaffolding and crane arrangements were implemented as pre-shutdown work (Fig. 5). That left about 24 days as the time required for work conducted while the facility was shut down. Therefore, and after further deliberations, it was agreed to plan additional pre-shutdown work to a height of 65 m during non-shutdown and carry out the remaining jobs from 65 m to 100 m elevation with the facility shut down.

 

  Fig. 5.   Pre-shutdown scaffolding work. 



Risk assessment and safety.

 Listed among the special risks and risk mitigation steps were:
• Heat radiation due to flaring
• Exposure to work at heights above grade
• Descending “fire balls” during heavy flaring
• Stinging insect attack or bites.

Among the major work items were protective metal shields of 1 mm thickness. These were installed at elevations 26 m, 44 m and 65 m (Fig. 6). The sheet-metal guards were affixed to the grating of all scaffolding grating. In addition, ceramic blankets were fastened to the sheet metal to substantially reduce the intensity of the radiant heat and avoid burning risks.

 

  Fig. 6.   Lift arrangement and protective
  metallic shields. 



Flood lights were provided for job execution at night, and water shields were installed at the 66-m elevation to effect cooling during flare events. As part of the water-shield system, two water-curtain nozzles were affixed horizontally to the structure. Their effectiveness was demonstrated before they were mounted at the jobsite.

Two lifts and a crane (hoist) were deemed appropriate for worker rescue and to facilitate the lifting of both personnel and materials. One crane was designated for emergency rescue of workers; and a suitable cage was fabricated and load tested before usage. Of course, the crane was also used for lifting and lowering of materials. The rack and pinion lifts were rated at 1 ton and 0.4 ton capacities, respectively. They too could be used for rescue purposes and up to 22 persons could be evacuated in case of an emergency.

Nomex coveralls were mandatory for all workforce members and their supervisors. Whenever heavy flaring was to take place, warnings would be issued to the workforce in the flare area through redundant means, including mobile handsets and a plant-wide loudspeaker (audio) system activated from the control room. The water-spray curtain would commence immediately so as to proactively cool the working area. All persons could immediately retreat safely to the protective area below the metallic shield (Fig. 7).

 

  Fig. 7.   Water shield at 66 m. 



In essence, the non-shutdown and shutdown work encompassed:
• Erection and dismantling of crane and lifts
• Scaffolding erection and removal up to 100-m elevation
• Affixing of metallic shields on the scaffolding gratings at elevations of 26 m, 44 m and 65 m
• Water-shield system installation at the 66 m elevation
• Replacement or repair of 20 metric tons of structure and replacement of 2.3 metric tons of grating (Figs. 8 and 9)
• High-pressure water blasting of structure and flare stack; power tool cleaning instead of manual wire brush; all followed by painting
• Insulation and cladding replacement of 3-in. and 8-in. steam lines up to 100 m elevation
• Damaged fuel gas and steam line replacement.

 

  Fig. 8.   Platform and clamps after
  replacement. 

 

 

  Fig. 9.   Piping, insulation and cladding
  replacement. 



Goals.

Initially, the non-shutdown tasks were planned to be done during daylight hours. With unscheduled flaring on some days, the daytime work had to be suspended. Lost time was recovered and work execution scheduled on a round-the-clock basis using floodlights at night to make up for lost time and to complete the non-shutdown part of the repair job in time.

All repair work on the flare stack structure was successfully done without incident within the scheduled period—-85 days for non-shutdown work and 16 days for shutdown work. This was the first time in the history of Reliance that repair work on a rather massive flare stack structure (Fig. 10) has been done online without any safety incident. HP

 

  Fig. 10A.   Massive flare stack at full usage. 



 

  Fig. 10B.   Flare stack structure after repair
  and painting. 



Abbreviations

NMD- Nagothane Manufacturing Division

PP- Poly propylene

LDPE- Linear density polyethylene

LLDPE- Linear-low density polyethylene

GC- Gas cracker

OSBL- Outside battery limit

ISBL- Inside battery limit

The author 

 
 

Surinder Singh is vice president (mechanical) with Reliance Industries Ltd. at the Nagothane Manufacturing Division in Maharashtra, India. He has over 30 years of petrochemical industry experience. At present, he is assigned as head of plant mechanical maintenance for the entire complex. He has had wide experience in plant downtime reduction and major turnaround planning. He is credited with filling lead roles and involvement in the development of various safety procedures. Mr. Singh graduated with a BSc degree in mechanical engineering from Regional Engineering College, Kurukshetra, India.  





Have your say
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Mohammad
03.21.2014

Is there any way to estimate the temperature of highest point of structure during emergency time (for example 10 or 15 min with max gas flow rate to flare)?

Euro-Rigging
02.20.2014

Dear Rahul, we would be interested to advise you on this matter, please contact Euro-Rigging. info@euro-rigging.nl

Rahul
01.13.2014

Dear Sir,We are doing maintenance work in Flare stack at Saudi Arabia.We have to replace the existing flare tip with a new one and later the guide ropes also.Please can you tell me the best way to check the verticality of flare stack after changing the flare tip and guide rope.Your immediate response will be highly appreciated.

Pratik Sharma
11.11.2013

proud to be part of supervision of this project :')

montazer
09.30.2013

Dear Author
I am searching for some information and flare design guidelines for export gas pipeline. something like minimum required flare stack for 128 km buried pipeline and .... can you help me?

thanks

Shell Global Solutions
02.13.2013

Interesting indeed! Appreciate, if it be clarified if the scaffold was erected up to 100 Metres high during the pre-shutdown period.

Thanks & regards,
V. Kurup.
Please reply to:
V,Kurup@shell.com

Nael
10.31.2012

Dear All

Thanks for Surinder Singh for the explenation which I found it really interesting, I saw the solution of the scaffolding which in europe is less used for such projects in oil & Gas, We used some machinery from a supplier name SAFI - www.safi.it where we used mast climber work platform which it was more safe and much more quick in the use where for such job wi reduce the time of hand over of 60% with less workers invovled in the site, 8 people instead of 40 which mean a lot in terms of cost and time in job termination.

Safi is an Italian supplier invovled in Oil & GAS where they made also Explosion proof Elevators & climber platforms for Chimeny construction & maintenance.

C N Chandraraj, Director, Ceyen Technoprojects pvt. Ltd
09.17.2012

Our second flare stack online revamping works has been successfully completed at HPCL Visag Refinery during T&I 2012.

Sir, thanks for your great instructions and advice for our First revamping works at RIL NMD

Shabinsha
06.15.2012

Hello Sir,
I am working as project engineer for a rope access company in uae. We used to do similar during the shutdown within 14 days in uae for many of the oil and gas companies without any LTI. If required the project report please email me at Shabinsha@megarme.com

Ramdas A. Wani , Chief ( Energy audits at KEC Makarpura Baroda )
05.01.2012

Good work done . Congratulations .
Is there any legal provision for flaring the gas in India?
or the flaring is done for safety of the process?

Ganeshan.R
03.01.2012

Dear Mr Surinder, I was the planning engineer from EIL for the complex during 1985- 89 ( from ock blasting/ grading up to commissioning). It was nostalgic to see the picture- Regds / Ganeshan.R

Yogesh dayal
02.21.2012

I am working in HPCL maint, we would like to know who was the contractor who didi thid flare job.

algeriño
10.11.2011

I have one question!!
what about of ligthining system? is necesary? which normative apply? thanks


08.23.2011

Surinder,
Good project. It show us that We can do a repair thinking way head. I liked very much about the use of the ceramic blankets, it´s agood idea.

I form Brasil at Braskem.


07.23.2011

Dear Sir,
Pls. let me know if you know any robotic equipment used in painting of very tall flare stack (~150 m) without interrupting any flare operation. If you know such info, please let me know.

Thanks and regards
Umesh Shah


07.20.2011

very good
my thesis in Flare gas recovery design for olefin plants.
1 chapter of that is about Flare gas desc. and design.
it was interesting for me.(ghadyanlou@yahoo.com)


06.10.2011

This case has been very interesting!!!


05.19.2011

Great planning and team work typical of Mr. Singh. All the best for success in similar efforts for better functioning of the RIL-NMD plant.


05.17.2011

Excellent planning and innovation and good to see no one was hurt during repairs.
"Necessity is the mother of invention" so when a job cannot be done in a t/a, innovative ideas are created to achieve the desired results withing the time frame.


04.16.2011

Good planning to get the revamp in this equipment that is the last barriers to of the protection plant....


04.01.2011

Excellent article.Good ideas.Better planification


03.26.2011

Excellant approach to get such a massive revamp work on-line without safety incindents. Appreciate the risk assessment done to address heat radiation exposure and mitigation actions. I understand that the , the installation of mechanical shed, scaffolding, water shed etc. are also done while Operation continues. It would be quite intersting and eduacting, if the risk assessment and duration of the work and safety measures considered for the workers during this phase of the work are addressed.


03.26.2011

The vision , guidance and effective planning was the key contributers for this projects.Team work between RIL and the contractor team made the valuable impact.




Great work Team.......


03.26.2011

The vision , guidance and effective planning was the key to sucess .The safety measures taken were remarkable and would be baselines for many future projects in Nagothane.

Great work Team.....


03.26.2011

A great display of team work of RIL team and contractors.The guidance and effective planning were major contributors for the completion of this huge quantum of work.People involved with it was a life time oppurtunity for the team.

Great work Team.....


03.21.2011

Amazing efforts ... I worked more than 10 years in RIL-NMD. During my tenure, flare structure was never repaired but i can understand the quantum of work.
The case study brings the nice example of correct risk assessment, effective protective measures, innovation and precise planning . Putting all these efforts together, team was able to achieve the goal in record time.


03.15.2011

The entire job was awarderd to us by RIL NMD(ceyen enterprises, ceyenentp@gmail.com).
"it was be a mission"
As the fine instruction from Sri. S Sing Sir for safe working method and extream planning, we have had completed the whole works without single injury.
Also, It was a best work ever we did.


03.14.2011

Execellent planning and execution while maintaining the working of the refinery.


03.12.2011

Impressive planning and maintaining the same. Idea of providing Heat protective shield is innovative.


03.12.2011

Excellent planning and execution. Good to receive mail from HydrocarbonProcessing [hpfeedback@gulfpub.com] as I was one of the team member for design the scaffolding. Very good article.

Regards


03.11.2011

Excellent planning and execution has done for Flare revamping at RIL - Nagothane,

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