Smart wireless transmitters monitor storage tanks

Paul Boughton

Self-organising wireless network reduces installation costs and enables online monitoring of vapour pressure and levels in tanks.

Emerson Process Management's Smart Wireless technology has been installed by Nynas AB to upgrade an underground storage tank monitoring system, creating an online integrated solution and reducing installation costs by EUR10,000 compared to a wired alternative.

Nynas is an international group that refines heavy crude oil to produce bitumen and naphthenic speciality oil products. The company owns four refineries, one of which is located at Nynäshamn in Sweden. The underground storage tanks at Nynäshamn are monitored for unequal vapour pressures which can indicate potential blockages in the pipes that connect the tanks. The existing pressure switches are ageing and due to be replaced. They were not continuous, only indicating when set levels had been exceeded.

The underground storage tanks are located a considerable distance from the control room and if Nynas had installed conventional instrumentation, new cabling would have been required to connect to the remote devices. With no line of sight between the location of the pressure transmitters and the ideal position for the gateway, Nynas selected Emerson's Smart Wireless products, which use self-organising technology, to connect the devices. With this technology, each wireless device can act as a router for other nearby devices, passing messages along until they reach their destination. If there is an obstruction, transmissions are simply re-routed along the network until a clear path to the Smart Wireless Gateway is found. The technology also offers redundant communication via two or three routes ensuring greater than 99 per cent communication reliability.

Two additional Rosemount wireless pressure transmitters provide measurements from the very large underground storage rooms (bunkers) containing crude oil. Measurements are taken to identify unequal vapour pressures in the different sections of the bunker. Data is transmitted every 60 seconds to a Smart Wireless Gateway located 650 metres from the pressure transmitters. The Gateway is connected to Emerson's DeltaV digital automation system using Modbus communications.

A further two Rosemount wireless transmitters installed on large vessels within the facility act as repeaters providing additional routes for the data and ensuring reliability of connection.

Having successfully trialled the Smart Wireless technology, Nynas has expanded the wireless network. Rosemount Rex radar level gauges, equipped with Smart Wireless THUM adapters replaced two existing mechanical servo gauges. A technology change of this type would require the replacement of the signal cables, but by using a THUM adapter wireless communication is added to the instrument, avoiding the need for expensive cable installation.

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