Product category:
Level and tank contents instrumentation
News Release from: Siemens Automation and Drives | Subject: Sitrans Probe LU
Edited by the Processingtalk Editorial
Team on 13 February 2006
LNG cooling water monitored with Sitrans
Probe LU
The level controller in the LNG cooling water sump at National Grid was unreliable and inaccurate: now the Sitrans LU probe gives an ATEX approved reliable 4-20 transmitter output
The level controller in the LNG coolant sump at National Grid was unreliable and inaccurate Siemens provided the solution: the high performance Sitrans Probe LU, with Sonic Intelligence signal-processing technology
This article was originally published on Processingtalk on 10 Apr 2006 at 8.00am (UK)
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National Grid owns and operates the major gas transmission network across the UK.
Gas is extracted from the national gas grid, purified, liquefied and stored.
The liquefied gas is vaporised prior to return to the grid in times of need by 40 power stations, large industrial customers, and 12 local distribution zones that supply consumers.
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The company must maintain a constant and secure gas supply for users.
If the network ever ran out, not only would customers face power outages, but air entering the pipeline would seriously upset operations.
For security of supply, National Grid operates a number of Liquefied Natural Gas (LNG) facilities, including Dynevor Arms, which stores 21,000 tonnes of LNG for commercial operations and emergency transmission support.
LNG takes less storage space: If the gas was not refrigerated, it would require 660 tanks the size of the current storage holder! For this reason, LNG storage is like a giant refrigerator, and it is vital to maintain a constant low temperature.
This is achieved with compressors that use refrigerants that are, in turn, cooled with water.
The process is prone to wide temperature changes and water evaporation.
Cooling water is delivered from a cooling tower sump.
Sump level control is important for pump suction and as a heat sink.
The sump is located in a hazardous area so the level equipment must be compliant with ATEX standards.
For maintenance purposes, level measurement instruments must be external, non-contacting instruments.
Previously, the site used a pneumatic controller to measure level in the cooling water sump.
This device required a lot of maintenance and did not provide the accuracy desired for this critical application.
Looking for a better solution, Mike Morris, site Instrument Manager, agreed to a trial with the Siemens Sitrans Probe LU.
The Probe LU is a 2-wire, loop-powered ultrasonic transmitter specially designed for continuous monitoring of liquids in storage vessels.
It offers high accuracy of +/- 0.15% of range and a high signal-to-noise ratio for high performance.
It features patented Sonic Intelligence signal-processing technology with advanced algorithms based on field data from more than 500,000 level applications.
Its Auto False-Echo Suppression software ignores false signals from vessel obstructions.
The result is accurate, repeatable, and reliable level measurement.
The Probe LU is easy to install and set up with as few as two parameters.
It has a built-in alpha-numeric display and a rotating head that aligns with conduit and adjusts for best visibility.
It can be programmed without opening the lid, even in hazardous areas, by using the patented infrared handheld programmer.
It includes a volume conversion table for the eight most common tank shapes, including a custom linearisation table.
The Probe LU was installed on the cooling water sump in July 2005, and was integrated with the site control system.
"Following the initial setup and training from Siemens, our site has successfully run the process with excellent level control," said Morris.
"I think the unit is first class.
Because of the ease of setup, we have since purchased and installed a new Probe LU.
It continues to operate, irrespective of the liquid surface condition.".
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