Monitoring various parameters for the Inert Gas (IG) system used on board ships

Introduction

In the previous article we learnt about the pressure vacuum breakers and how their simplified design could be used to solve the big problem of breaking excess of pressure or vacuum. It is very good to have such safety devices but apart from that, there is a need for monitoring various parameters at different points of the IG system. Since human observation alone is not sufficient for such purposes, various instruments and alarms are used to point out any possible defect in the system so that rectification could be done at the earliest possible opportunity.

Alarms, Monitors and Controls

All the important components in the IG system require some sort of monitoring or alarm arrangements which have been described as follows.

• Pressure gauges to measure adequate water supply to scrubber
• Alarm to be set when scrubber inlet water pressure drops below a pre-specified level.
• Another alarm for high level of water in the scrubber if it increased beyond a certain level.
• High temperature alarm of the outlet gas from the scrubber or IG blowers is beyond a specified range (could be between say 65 – 750C)
• In case a precooler is present in the system, there should be gauges for monitoring inlet and outlet water temperature and an associated high temperature alarm
• Low water level alarm in case of deck water seal
• Pressure alarm when the pressure of the IG gas has reached a certain preset limit. In case the pressure falls below a critical level there should be auto shutdown of cargo pumps so that there is not risk of atmosphere inside the tank going into the flammable triangle range.

Since inert gas is used on the deck for cargo operations and hence comes under the responsibility of navigating officers, whilst the flue gases are processed in the engine room or machinery spaces which is handled by the engineering staff, any critical alarms associated with the IG system should be visible/audible in the machinery spaces as well as the bridge.

As per regulation 82 of SOLAS, all the above mentioned instrumentation and alarms should be sturdy enough to withstand various conditions during their working. These condition could include moisture, corrosion, excessive vibrations, large variations in temperature and so forth.

Since inerting is all about reducing and maintaining oxygen at lower levels, an oxygen analyzer is very important part of the instrumentation paraphernalia as we shall see in our next article .