Storage Tank Overspill Level Protection with Wireless Measurement

Sources of energy supply and shifts in demand increase the need for storage capacity to reduce imbalances. According to Industrial Info Resources:

Oil & gas storage terminals for both imports and exports are springing up throughout the world as North America experiences a dramatic increase in production and energy-hungry Asia continues to increase its oil & gas imports.

Tank Storage magazine

Tank Storage magazine

Gaining capacity from existing tank storage infrastructure requires operating closer to fill limits. Overspill level protection is critical to operating safely while maximizing capacity. A Tank Storage magazine article, Overspill level protection for remote tank storage installations, highlights technology advances that help operators with their process operation and safety efforts.

For remotely located tanks, wiring infrastructure has been a barrier for overfill protection systems:

The cost of installing new wiring can include ducting, cable trays and the digging of trenches, which can be significant and often cost prohibitive. There is also the inconvenience and issues of performing the work whilst the site is operating.

Two important technologies in overfill systems are guided wave radar (GWR) instruments for continuous level monitoring and vibrating fork sensors for high and low level alarms. WirelessHART technology introduced in 2007 and ratified as the global IEC 62591 standard in 2010 is now:

…widely implemented in refineries, oil fields, offshore platforms, chemical plants and other industrial facilities around the world to obtain real-time plant data to optimise operations, improve worker and plant safety, and reduce emissions and other environmental impacts.

Rosemount 3308 wireless GWR transmitter

For storage tanks without available wiring infrastructure, wireless GWR level transmitters are available. These devices provide continuous level readings back to operators and control systems to help optimize the tank usage and avoid spills. Where tanks were manually monitored, trips to the tanks, often classified as hazardous area locations, can be reduced with the levels automatically recorded by the control system.

For critical applications:

…more stringent legislation now requires a level of redundancy to be installed. In addition, many companies are adopting multiple technologies to further minimise risk. It is recommended that independent high level switch devices should be fitted to all tanks. These provide a safeguard from spills in the event of a fault or problem with the contents measuring instrumentation, or in case there has been an error in the translation of level measurement into volumetric contents. This provides a secondary method of overspill protection. Alarms are derived from fixed position switches or probes within the tank, which operate when the liquid makes contact with them. These should be used in addition to the measurement-derived high level alarms.

Rosemount 2160 wireless level switch

Rosemount 2160 wireless level switch

Vibrating fork level switches, used for safety high and low alarms, are also available as wireless devices. They are suitable:

…for almost all liquid applications, it is virtually unaffected by changes in flow and product variations. Easy to install and maintain, an integral LCD display shows switch output states and diagnostics provide real time, accurate verification of process conditions. Any build-up, fork blockage or excessive corrosion is shown immediately by a change in fork sensor frequency, indicating that maintenance may be required.

The article’s author concludes:

The introduction of wireless enabled GWR level transmitters to determine level, combined with wireless vibrating fork level sensors for low level and overspill protection, meet the need for accurate, reliable level and interface monitoring in remote or difficult to reach locations. They combine low cost installation with fast and simple commissioning and robust measurement data, providing remote visibility into operations, safely optimising tank usage and helping to avoid spills.

To connect and interact with other level measurement and process safety professionals, join the Level Measurement and Safety Instrumented Systems tracks in the Emerson Exchange 365 community.

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