| Pollution from Inert Gas Scrubber overboard discharge |
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 There has been a recent increase in number of incidents involving pollution from the Inert Gas Scrubber overboard discharge. The purpose of this Safety Alert Bulletin is to highlight this trend to all tanker operators especially those who are, may be, or aspire to be engaged in ExxonMobil affiliate business. It is hoped that this bulletin will cause such operators to review their internal procedures / guidelines for operations relating to Boilers and the Inert Gas Generator / System, including inspection and maintenance of machinery and equipment.
This safety alert bulletin is not intended to instruct operators on how to operate, maintain or inspect their vessels; Operators shall continue to be fully and solely responsible for the maintenance, operation, and management of their vessels. This bulletin is a mechanism to raise awareness and for exchanging information relating to commonly identified contributing factors and causes which have led to such pollution.For the production of Inert Gas, it is required to burn fuel oil with low excess air (LEA) in the boiler / Inert Gas Generator. However, on lowering the amount of excess air, good atomization and distribution of fuel is required for efficient combustion. Where fuel atomization is not optimum and excess air is minimized there is the potential for incomplete combustion. An early indicator of incomplete combustion is an increase in Carbon Monoxide (CO) concentrations. Later, unburned carbon and hydrocarbon particles may be detected as black smoke emanating from the funnel and in worse combustion conditions, fine oil droplets may be carried away by flue gas from which they precipitate. As the flue gas is washed and cooled in scrubber for Inert Gas, unburned Hydrocarbons and oil droplets may enter this water and could be taken overboard with the Scrubber Wash Water causing oil pollution. Poor initial startup or poor restart after flame failure in the Boiler may also cause this type of carryover and may lead to pollution from the Scrubber Discharge. Following are some of the commonly identified contributing factors (Equipment failures) which led to such spills: • Malfunction of the feed water level controller caused the boiler to trip due to high water level in the boiler. Improper restart caused carryover of oil to the scrubber discharge. • Crack inside combustion chamber at pilot burner penetration. Cooling water spraying from this crack effectively stopped main burner being ignited by (burning) pilot burner. Burner control system allows a short time between opening fuel supply to main burner and actual ignition of main burner. During this period, some quantity of fuel was atomized into the combustion chamber. This unburned air fuel mixture passed the scrubber where the atomized fuel was washed overboard. • Cracks were found in the pilot burner penetration tube. Cooling water spraying from cracks effectively stopped main burner. During restart attempts, burner control system will allow few seconds for actual ignition of main burner. In this time some quantity of fuel was atomized into the combustion chamber. This unburned fuel passed the scrubber and mixed with the scrubber cooling/washing water. • In some Inert Gas Generators (IGG), the auto drain valve would open during a flame failure in order to drain the scrubber goose-neck into the Bilge Holding Tank. In this case, the valve turned out to be seized. • During the initial start up the secondary air damper for the combustion air inlet to the IGG jammed and failed to open when the servo motor actuated, it resulted in deformation of the operating linkage between the servo motor and the damper. Key Learning’s: To avoid similar equipment failures and poor restarting operations that lead to pollution from the Scrubber discharge, the following corrective actions / measures have been identified: • Complete the planned maintenance properly and timely to ensure that transmitters, diaphragms and switches are clear from any build up of dissolved solids. • Review maintenance regimes in consultation with equipment manufacturers. • Investigate possibility of fitting of additional lubrication points as appropriate for critical combustion control mechanisms. • Conduct operational tests of the IGG and IGS at least 24 Hours prior to arrival in port. • Familiarity and knowledge of the limitations of the equipment by all personnel using / operating the system will contribute towards trouble free operations. Key Messages: • It is essential to assign well trained, competent and adequate personnel to tasks. • Inspection / maintenance by competent individuals will enhance equipment reliability. • Never make assumptions, all alarms or alerts should be treated as real and appropriate actions taken. • Ensure the scrubber system is cleaned after use and that it is confirmed as being clean prior to arrival. • The scrubber pump should be started well before arrival at the discharge berth. • Ensure the scrubber system is functioning correctly and efficiently. • Clear, precise and repeat back communication amongst involved personnel is a key to safer marine operations and ensures a fuller understanding of intentions and plans of action. • Rigorous procedures should be formulated, implemented and executed on board. • Verification of knowledge, and compliance with, the company’s procedures should be undertaken at regular intervals. • Minimise carbon build up in the boiler by maintaining good and efficient combustion. THE INFORMATION ABOVE IS COMPILED BY IMT MARINE SERVICES AND IS BASED ON INDUSTRY INCIDENT INFORMATION Disclaimer Nothing in this Safety Alert Bulletin shall constitute a standard, an endorsement, or recommendation of IMT Marine Services. The Bulletin is not, and is not intended to represent, advice on which the reader should rely, and nothing in the Bulletin should be relied on without independent and/or professional advice being sought. Whilst every effort has been made to ensure the information has been compiled from sources believed to be accurate, current and reliable at the time of posting, IMT Marine Services and the authors take no responsibility for any information contained in the Bulletin, including errors or omissions, and denies any liability whatsoever for any costs, loss or damage which any person, group, organisation or agency may claim, incur or suffer as result of using any information in the Bulletin.
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