ANSSER This is a tail end plant and so must handle everything that is thrown at it including all the fluctuations / variations that can occur with the two front end plants. To handle the steam emissions from ANS 1 (6 t/h) or ANS 2 (11 t/h) or from both ANS Plants (17 t/h). To operate is such a way that the ANS plants production will not be affected if the ANSSER plant is off line for any reason. To operate is such a way that if either of the ANS plants is taken off line or trips or is restarted then the ANSSER plant operates seamlessly under the new conditions. To handle all ammonia emissions generated by the ANS plants and to neutralize them by using 60 % nitric acid. Acid design requirements 0.8 m3/h for both plants at full rates. Pumps ordered to be able to feed in 1.2 m3/h
ANSSER Cooling Tower Fire On 14 June 2012, at approximately 09h49, a fire started in the ANSSER Plant cooling tower Number D. Two contractors and one AEL employee were in the cooling tower carrying out grinding and welding work when the fire started. They managed to escape without injury. The fire spread rapidly and all four cooling towers burnt down completely within 10 to 15 minutes, despite efforts to fight the fire with water hoses. The fire produced a cloud of black noxious smoke which was blown upwards and towards the South of the ANSSER Plant. As a result the ANSSER, ANS and ANPP plants were evacuated.
ANSSER FIRE – Relevant History The ANSSER Plant has been off for a period of 2 weeks due to a corroded condensing unit end plate. During routine scheduled maintenance inspection, the engineering maintenance team identified cracks on the cooling tower fan motor mountings. These cracked mountings were planned to be repaired on the 14 th of June 2012. The repair involved preparation and welding of the cracked areas, and the installation of the jacking bolts for motor and fan adjustment.
ANSSER FIRE – What Transpired? Work to be done was identified. The erection of the scaffold to enable easy access to the working area inside cooling tower D was done the day before. The preparation of the relevant scaffold access permits were also completed the day before. Plant Clearance Certificate was prepared. Take 5 completed. The place was otherwise made safe and the plant was handed over from production to engineering and the contractor engaged to perform the work. The contractor employees laid out sisalation, a fire retardant material cover, to stop welding rods from falling into the cooling tower. They were not aware that the packing material inside the cooling tower was flammable.
ANSSER FIRE – What Transpired? They started to grind and then welded the cracks on the fan mounting brackets. The work was completed without an incident. They could not start the work on the jacking bolts as they had to wait for one of the Nitrates Department fitters to confirm the position of the jacking bolts. When the fitter came back, they tacked the jacking bolts in position but the Standby stopped them form continuing as it was his tea break. After the Standby returned from tea they resumed work. Whilst welding the jacking bolts, he was stopped by the Standby as he had noticed smoke emerging form the PVC fill material.
ANSSER FIRE – What Transpired? The Standby tried to extinguish the fire with the ABC extinguisher with no effect. He then told the two contractors to evacuate the tower. They rushed out without removing their tools. Standby continued to try to fight the fire with the extinguisher and started calling for help on his radio, but by this time the size of the fire had increased significantly and started to go out of control. The Standby had to jump between scaffolds and platforms and eventually slip down a scaffold pole to reach a safe area.
Recommendations Avoid doing hot work on cooling towers when the fill material is dry. Draw up and issue an Engineering Standard for cooling towers to define fire prevention measures and post fire hazard warning signs at all cooling towers (Address the relevant Basis of Safety). Review the level of qualification and experience required for Authorisers in the Permit to Work system. Review the fire fighting training and fire drill programme at the plant to improve levels of competence and fire fighting effectiveness.
Learning Points – Cooling Towers About cooling towers –Cooling towers’ material of construction is now predominantly fibre glass but concrete towers also burn due to the PVC fill material being covered with dry biomass. –Ensure strict cooling tower cleaning regimes are in place including an effective water treatment programme. –Most cooling tower fires are caused by hot work and electrical faults. –Ensure electrical maintenance regimes are in place to cover motors, cabling and thermo graphic imaging to determine hot connections. –Lubrication of bearings for the fan mountings etc. need to be done. –Upgrade the PVC packing with flame retardant packing. –Consider the option of putting fire protection system on the towers. –Ensure a legal appointee with the necessary knowledge is assigned to cooling towers
Learning Points – Hot Work Never do hot work on a dry cooling tower. The dry biomass on the tower acts as a fire lighter on top of charcoal. When doing hot work on a dry tower ensure that the tower water sprays are run to wet the internal elements of the pack. Hot work sign-off needs to be done at the highest plant and engineering management level. Equip Permit to Work Authorisers with the necessary knowledge of cooling towers’ Basis of Safety (i.e. prevent unplanned ignitions; and, if such an ignition occurs, minimize the consequences).
Thank You ANNSER COOLING TOWER FIRE CIE Conference 2013 – Oviedo - Spain