International Process Safety Workshop Essar Steel, Surat 29 th 30 th November Explosion in 1 st Ammonia Scrubber

Transcription

1 International Process Safety Workshop Essar Steel, Surat 29 th 30 th November 2017 Explosion in 1 st Ammonia Scrubber. Presentation by - Vilas Gaikwad Chief Safety India & SEA 1

2 Explosion in First Ammonia Scrubber Date of Incident : Time: 10:28 am Department : Coke Plant, Jamshedpur Section : By-Product Plant Injury : 5 LTI s & 14 First Aid Cases Incident Description: An explosion took place in 1st Ammonia Scrubber of Old By-Product Plant, Coke Plant at Jamshedpur Steel Works causing extensive damage to the 1st Ammonia Scrubber, the connecting gas & liquor lines, associated structures and Pre Scrubber. The explosion led to the rupture and complete blow-off of the Ammonia Scrubber 1 roof. ThisScrubber was under MSD since 2nd Nov'15, which was isolated by metallic blanks. Total 19 people injured.. First Ammonia Scrubber Scrubber (Explosion in this unit) Demister Element Box of Pre Scrubber Pre Scrubber Investigation Process Audio recorded interview of about 25 people, including TSL & Contractor employees - cross verification of statements with data & physical evidences CFD & Gas Mixing simulation underway to determine location of combustion inside the scrubber system Use of technology in investigation process Drone, Endoscopy, CFD Simulation, Metallurgical & Chemical analysis 2

3 Details of the Incident Pre Scrubber and First Ammonia Scrubber was under shut down for maintenance work since 2 nd Nov 15 Gas lines and circulating liquor lines were disconnected from operating system by providing blanks. The shutdown was taken to replace the damaged demister element box, structural, platforms, pipelines and for strengthening of top portion of shell up to 2.5 mts by patching from outside. Height of First Ammonia Scrubber is : 35.2 mts and Dia: 5.6 mts Last major shutdown of these scrubbers was carried out in Jan-Mar 2011 and before that in Nov- Dec 2008 On 16th Nov 15 job started after taking work permit. At around am an explosion occurred in ammonia scrubber 3

4 Key Findings 1. Purging was done in reverse direction to what s prescribed in SOP Purging Process as per SOP (CP/SOP/BPP/OPN/68) Purging Process Followed 4

5 Key Findings 2. Purging done for a total of 29 mins only (14 mins on 2nd Nov, 5 mins on 16th Nov, 10 mins on 16th Nov until the incident), since shutdown N2 purging started (2 nd Nov, 3:17PM) N2 purging stopped (2 nd Nov, 3:31PM) 2 nd 3 rd Nov N2 purging started (2 nd Nov, 3:17PM) 16 th Nov Purging started at 9:50AM Purging started at 10:18AM N2 purging stopped (2 nd Nov, 3:31PM) Purging stopped at 9:55AM 3. Ammonia liquor delivery pipe of pump 2P109 for Ammonia Scrubber1 was being gas cut during the incident Min temp of Oxy acetylene flame is 3200 deg C AS1 Ammonia liquor delivery Pump flange: Except the bottom bolt, all others were gas cut Gas cut delivery pipe 5

6 Cause of the Incident a. The primary cause of the incident was entrapment of combustible gases (Coke Oven gas) inside AS1. This resulted due to the fact that the SOP for purging of 1st pair of scrubbers was violated intentionally since a safe access to AS1 roof was not available to open the bleeder valve of AS1. b. The gas cutting flame used to cut open the pump delivery pipe provided the heat and air source for auto-ignition of constituent combustible gases (Hydrogen and Methane) of Coke Oven Gas. The SOP for dismantling of ammonia liquor pipe lines of scrubbers was found to be inadequate and incorrect as it allowed for gas cutting & welding at a hazardous area, which is a violation of the Safety Standard on Gas Cutting & Welding. 6

7 Root Cause & Recommendations Category Immediate Cause Underlying Cause Gaps 1. Purging SOP not followed: Incorrect purging method led to entrapment of combustible gases in AS1 2. Purging SOP inadequate: No system to determine extent of presence of combustible gases inside scrubber 1. No specific SOP for dismantling of ammonia liquor pipe line of scrubbers was available. 2. Gas cutting of liquor delivery pipe line of 2nd stage spray header of AS1 provided the heat required for combustion of entrapped gases. 1. Safe access to AS1 vent valve was not available due to corroded structure 2. No hazard identification was done to assess the risks that arose due to deviation from SOP. 3. Plan to open AS1 bleeder valve on completion of scaffolding erection upto the AS1 roof level was not communicated to the shift in-charge or recorded in log-book 7

8 Recommendations & Action Taken Recommendation Check the condition of all existing structures, staircases and platforms at all By-product Plants Periodic corrosion assessment audit of structures & subsequent corrosion management strategies to be developed Develop and deploy Code of Practice for effective purging of vessels, scrubbers (Explore the possibility of complete instrumentation & automation of purging process) Develop and deploy Code of Practice for Hot Work (refer TSE Doc# HSC34.2 Code of Practice: Control of hot work operations) Existing Standard for MOC to be revised and should be followed in case of any deviation from SOP Study and eliminate provision for incorrect purging of all Scrubber Pairs at BPP Online or Offline process to be developed for determining the extent and completion of purging process Action taken FRP gratings was provided at some places as a substitute of steel gratings Corrosion assessment study was done through M/s Bureau Veritas and system developed for transporting pipe materials selection as per the chemical compatible material mapping New Guidelines on purging developed & being deployed across the organization New Guideline on Hot work was developed & planned for implementation Being done Physical Changes done to make scrubber Fool proof system SOP revision as per the New purging Guidelines 8

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