Industrial automation puts to sea

An automated chemical dosing system for marine boilers is the first to use closed loop industrial automation technology, and looks set to bring massive operational savings to ship owners and operators

A new automated chemical dosing system for marine boilers is the first to use closed loop industrial automation technology, and looks set to bring massive operational savings to ship owners and operators.

Mitsubishi programmable logic controllers (PLCs) and human machine interfaces (HMIs) have been integrated into a system that has been developed by a specialist maritime supply and service company which aims to keep ships productively at sea by minimising the time that needs to be spent in harbour and maintenance yards.

Overhauling a ship's boiler can easily cost $250,000 and take the ship out of service for two or three weeks, with consequent loss of revenue.

Poor water treatment can cause this operation to be scheduled every 4 to 5 years throughout the ship's life.

The new system ensures the constant optimisation of chemical dosing, so that problems with water contamination are nipped in the bud before they can begin to develop.

Previously there were some semi-automated systems available to ships' engineers, but nothing truly outstanding.

A completely automated system offers the possibility of perfect boiler maintenance and optimised performance, achieved at reduced manpower costs.

The system probes for levels of pH, dissolved oxygen, electrical conductivity and turbidity through sample lines fed from the boiler and feedwater systems.

Data from these probes is collected by a Mitsubishi FX2N programmable logic controller (PLC) and run through a control algorithm.

If the values change from the set points the dosing level for the appropriate chemical additive is adjusted.

The change in dosage rate is related to the error between the probe value and the set point.

The FX2N is the Mitsubishi most powerful micro PLC.

It has a comprehensive range of maths functions and self-tuning PID loops, so is ideal for process control applications.

The 8K on-board memory is expandable to 16K using optional cassettes, a feature the maintenance system uses for the creation of extended period record keeping.

Traditionally a ship's operational procedures will typically require the crew to 'blow down' the boiler at least once a day, draw samples of the boiler water for manual analysis with simple test kits and record the results.

The boiler controls would then be adjusted in light of the findings.

The PLC can run a fully automatic blow down and use its memory to automatically generate records of the systems' operation performance.

Automating the procedure completely, monitoring can be done constantly and blow downs initiated as soon as they are needed, which may be several times a day.

'Blowing down' involves opening a special valve at the bottom of the boiler.

When blowing down, sludge deposits that have built up within the boiler can be removed.

Boilers used in land-based installations are subject to similar procedures, the new system may have applications here too.

Working in conjunction with the Mitsubishi PLC is a Mitsubishi E910, a full colour touch screen, human machine interface (HMI).

The E910 is the Mitsubishi flagship HMI and was chosen for this job because its IP65 rating which means it is well able to withstand the hostile working environment expected in a ship's boiler room.

Furthermore, its 10.4 inch screen is large enough to depict the whole process in an easily appreciated graphical format.

It can handle formulations, schedules and alarms; generate, store and print reports; log trend histories and is protected by multiple passwords.

The large memory capacity allows several months of results to be stored, invaluable when the ship may only be in its home port a couple of times a year - and then only briefly.

The graphical screen is a cornerstone element in the system design.

The internal software developed for the project is necessarily complex and critical, but the HMI makes it so simple for the crew to understand that it is intuitive.

Mitsubishi operating software is designed to be robust and tolerant of less than ideal operating conditions.

Similarly, there is no worry about how the hardware will cope in a ship engine room that is hot, noisy and vibrating (often through resonant frequencies), as well as having air that is potentially laden with salt, grease, oil, dirt and other potential contaminants.

An Internet interface is to be developed, so that there can be two-way communication between the dosing system and a shore-based control centre, which could be quite literally half a world away.

This would normally be for simple data logging and record keeping, but would also mean that an expert can dial into any ship, anywhere at any time should a problem arise.

Remote condition monitoring of ships' systems is the becoming the norm; so that boilers, engines, gearboxes, navigation systems, and even the crew healthcare all have constant access to expert attention.

Marine boiler dosing chemicals are critical to ensure the optimal efficiency of the boiler system but are only effective if applied properly.

Manual dosing regimes are difficult to regulate precisely, which has lead many boiler failures.

A fully automated system will make this problem a thing of the past and significantly increase the operational efficiency of every ship on which it is installed.

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