- LNG cargo handling comes with a high risk and complex procedure.
- The use of boil-off gas as the propulsion fuel further elevates the problem.
- An integrated automation systems (IASs) with a proper alarm management system is the way out.
LNG cargo handling operations is a complex and risky procedure as it requires handling of homogeneous cargo close to its boiling point, says a report written by Mike Corkhill. The use of boil-off gas as propulsion fuel and the inclusion of new ship types like floating storage and regasification units, bunker tankers, further adds to the problem.
In order to ensure safe and secure transport of LNG cargo, an integrative system should be operational which can be easily controlled and monitored. Marine technology firms such as Kongsberg, Honeywell, Emerson and Yokogowa have helped LNGC owners to deal with increasingly complex ship operations by developing integrated automation systems (IASs). The basic functions of an IAS are sensing, monitoring, alarm and control and its basic components are engineering workstations, the control network, distributed and scalable controllers and the human/machine interface in the form of supervisory computers with mimic diagram screens in the cargo control room (CCR).
An independent emergency shutdown (ESD) system is integrated with the cargo-control system (CCS) through the hardware and software of both. The IAS enables simultaneous oversight of boiler and power management, cargo loading/unloading operations, custody-transfer measurement, cargo containment-system control, cargo ESD, BOG control, ballasting operations and alarm management. It also incorporates open interfaces to allow the supervisory computers to access trend data, messages and process data.
LNG carriers use among the most sophisticated IASs in commercial shipping. A typical vessel hosts upwards of 500 data collection points that gather readings from gas detectors and pressure, temperature and tank level sensors. An IAS with 3,000 digital input and output modules is usual for a modern ship.
Using complex algorithms and computation techniques the IAS suppliers aims to make the system more understandable for the crew members so that recommendations generate straightforward unambiguous responses which will make the system more integrative and useful.
The focus has shifted to the ergonomic region. Hence, the Society of International Gas Tanker and Terminal Operators (SIGTTO) has established a new human element committee last year, to consider competency and training, design and ergonomics and the human element in incident investigation. SIGTTO wants to study the details of incidents and near misses on the ship so that they can rectify the loopholes and create a rigorous safety regime.
In recent years, investigations into LNG carrier ship/shore interface mishaps have revealed difficulties in interpreting CCR screens and alarms. Misinterpretations can prompt incorrect responses and, sometimes, a reluctance to act for fear of the consequences of being over-zealous. The new committee therefore aims at understanding the ship CCR design and ergonomics. The initial focus of the committee is the alarm management, as highlighted in it’s 3rd meeting in August.
The group is prioritising cargo alarms as per the IMO Code on Alerts and Indicators 2009, reviewing the ship-shore checklist and highlighting the importance of safety-critical systems and the timely activation of ESDs. Once it has completed the alarm-management task, the CCR working group will consider the layout of workstations and positioning of mimic screens in the CCR, along with the content and layout of the screens.
The IMO Code on Alerts and Indicators 2009 identifies four categories of alert: emergency alarm, alarm, warning and caution. Emergency alarms and alarms require immediate action to be taken, whereas warnings and cautions alert seafarers to changes in conditions to which they may need to respond, to prevent a hazardous situation. This a standard maritime code used in all types of ship instruments which emphasizes on alarms related to propulsion machinery and navigational devices. Thus, taking the load off from instruments that deal only with cargo-handling equipments.
However, the lack of alarm prioritisation can be confusing on gas carriers is the “cargo pump low amp” alert. This can be activated when the pump is inactive or active. In the former case, this alert makes perfect sense and has the status of a caution. But if the pump is operational and cargo handling is underway, this alert constitutes an alarm that requires immediate action to find and respond to the cause of activation.The group is formulating a draft to prioritize this gas-ship alarm system. The draft will be ready by the first half of 2018 as soon the committee approves the guidelines.
Other ergonomic challenges
The lack of coordination between shipyards, naval architects and IAS suppliers can also hinder a gas carrier’s cargo monitoring and control equipment from achieving its optimal performance. This is especially true when a series of ships is ordered and stems from the characteristics of today’s new building contracts.
Yards contract IAS suppliers to provide the same equipment, set up in the same way, for each ship in a series of gas carriers. However, it is inevitable that the IAS arrangement in the lead vessel will be tweaked as the ship is commissioned and after feedback from early cargo-handling duties. There is no formal route to feed the experience of the lead ship back into the IAS setups of later ships during their fitting-out phases at the yard.
Artificial intelligence has a role to play in the drive for more consistency in the CCR and still greater levels of ship safety. The gathering, transmission and storage of real-time ship operational data will no doubt facilitate machine learning in future.
But prior to that, the immediate necessity is to integrate the software that manufactures critical LNGC components like compressors, reliquefaction plants, cargo pumps, gas combustion units and fuel gas supply system into the IAS suppliers system. Although this adds to the challenge of providing the shipowner with a user-friendly, integrated monitoring and control system yet this is the only way out in eradicating human errors from the IAS packages making it more safer for LNG cargo handling.
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Source: Lng World Shipping