Crude oil temperature monitoring in storage tank protection systems
08 January 2010
Emerson Process Management’s wireless temperature transmitters have been installed at BP Exploration’s Dalmeny onshore terminal. Once in place the wireless network confirmed that the existing tank protection system is capable of providing the necessary protection.
Emerson’s Smart Wireless temperature transmitters have been installed at BP Exploration’s Dalmeny onshore terminal
Dalmeny, located near Edinburgh, UK, has the capacity to store about four million barrels of stabilised crude oil from the Forties oil field. Eight interconnected storage tanks, 40-50m in diameter, are used to regulate the flow of oil between production wells and the tankers or pipeline that will transport it to the refinery.
BP was already measuring oil temperature at the side of the tanks. But, because of the size of the tanks there was a concern that there could be a significant difference between temperatures at the edge of the tank and at the centre. A number of measurements were therefore required to confirm any differences in temperature. This presented a challenge because the tanks needed to remain in use, making installation of temperature probes impossible.
An out of service tank with no existing temperature measurement in place presented the perfect opportunity to install the necessary instrumentation. However, there was no cabling infrastructure in place for this specific tank so if BP had installed wired transmitters they would have also had to install a cable recoil system to cope with the floating roof. This would have cost over £15,000.
Wireless presented a cost effective alternative, and having successfully applied Emerson’s Smart Wireless technology to monitor wellhead annular pressure at its Wytch Farm site, BP was confident that it would be suitable for this application.
"We were keen to install a wireless infrastructure that would enable us to expand and add additional devices beyond this application without the need for additional cabling infrastructure and the cost associated with it," said Robin Hamill, electrical instrumentation engineer, BP Exploration Operating Company. "Having reviewed the wireless technologies on the market, we felt Emerson’s Smart Wireless was the best solution."
Two Rosemount wireless temperature transmitters were installed, one in the centre and one two thirds across to determine if there was a difference in temperatures throughout the tank. A further transmitter was installed on the main inlet feed. The transmitters are located roughly 300m from a Smart Wireless Gateway positioned on the outside wall of the control room. Using a serial connection, data is fed from the gateway into the existing SCADA system.
Using the data from the Smart Wireless transmitters, BP discovered that there was not a significant difference in temperature at different points in the tank.
"Using Smart Wireless we were able to quickly and cost effectively install the temperature measurement equipment required," said Hamill. "The results we have obtained mean that we have not needed to add additional devices to the other tanks."
BP continues to measure crude oil temperatures in the tank using the Smart Wireless devices. The wireless transmitters are part of a network that uses self-organising technology. As part of the network, two additional wireless transmitters were placed at strategic positions within the facility to act as repeaters. Despite the long distance, all of the devices communicate directly with the gateway rather than via the repeaters. The extra transmitters increase the reliability of the network by offering additional paths for the data to travel to the gateway should a path become obstructed. The self-organising wireless network adjusts automatically to re-route signals around any obstructions, resulting in greater than 99% communications reliability. The resulting wireless infrastructure enables additional wireless instruments to be added quickly and easily.
"We have been very impressed with the Smart Wireless technology and regard the installation to be a great success," said Hamill. "This site experiences extreme weather conditions, but this has not affected reliability at all."
Installing the Smart Wireless devices was very easy. It took only a day to complete the entire project including configuring the serial link to the SCADA system. Emerson’s AMS Suite predictive maintenance software is used to manage the wireless network. Since the wireless network was installed it has been extremely reliable with no data lost.
Smart Wireless is an extension of PlantWeb digital architecture that offers solutions for field instrumentation and plant operations. In addition to the products installed at the Dalmeny terminal other wireless products include Fisher position monitors, Rosemount Analytical devices and Machinery Health Management transmitters, and native wireless interfaces to Ovation digital automation systems, and SmartStart services.
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