Servomex Process Oxygen Analyser is Used as Part of a SIL 2 Safety System, Enabling PTA Output to Be Increased
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ADVANSA UK is a major European manufacturer of PTA (pure terephthalic acid) and polyester resin products.Substantial investment has recently been made in the Wilton, UK, facility in the form of the T8 Revitalisation Project. As a result of this upgrade, annual production of PTA has increased by around 100,000 tonnes to over 500,000 tonnes. In order to maintain safety with this substantially increased throughput, ADVANSA UK has installed a Servomex 2200 series process oxygen analyser as part of a functional safety instrumented system.
A significant part of the upgrade project involved installing new equipment to enrich the process air fed to the reactor with oxygen; using oxygen-enriched air in the reactor increases the conversion rate in proportion to the additional oxygen. However, care must be taken to ensure that the oxygen level is not too high, otherwise a potentially explosive atmosphere could form. A safety instrumented system (SIS) was therefore preferred with a safety integrity level of 2 (SIL 2) in accordance with EN 61511 (Functional safety. Safety instrumented systems for the process industry sector).
To assist in the safety justification, Servomex provided a failure mode and effects analysis report to the system's engineers, which was generated by an independent specialist in functional safety. This report demonstrates that the Servomex 2200 transmitter safe failure fraction is suitable for operation at SIL2. Servomex is now actively considering functional safety requirements for all future product development.
ADVANSA UK have been using various Servomex paramagnetic oxygen analysers at the Wilton site for over 30 years. Based upon ADVANSA UK's first hand experience of the reliability, ease of use and simple maintenance of Servomex equipment, their engineers had no hesitation in approaching Servomex about the new application.
Servomex have extensive experience of supplying gas analysis equipment for PTA plants worldwide, for both Oxygen and Infrared measurements. Having discussed the system requirements and studied the specification, the Servomex engineers recommended using a 2200 series transmitter and control unit in a sampling system using a GRP cabinet. The transmitters utilise fast, rugged, non-depleting paramagnetic sensor cells, which means that zero drift is extremely low and frequent calibration is not required, which helps to minimise the operating cost. An auto-calibration facility also reduces the cost-of-ownership, and the unit's intuitive, multi-language text interface requires almost no training to use.
Colin Moore, the Responsible I/E Engineer at ADVANSA UK's Wilton PTA plant, comments: "We know Servomex and their capability, and the company has always performed very well in terms of pre-sales support, commissioning, and post-sales technical back-up. The paramagnetic sensing technology also works extremely well; our experience shows that instruments using this technology are reliable, feature very low drift, are easy to calibrate, simple to maintain and have a low cost of ownership. As a result, we were very happy to have the opportunity to use a Servomex 2200 analyser on the T8 Revitalisation project."
He concludes: "The 2200 analyser was installed on the plant around two years ago and has performed exactly as expected. Consequently we have recently purchased an additional two 2200 series analysers for another project, and these are just being commissioned now."
More information about the Servomex 2200 process oxygen analyser, as well as other Servomex gas analysers, all of which are available and fully supported worldwide, can be obtained from Servomex Group by calling +44 1892 652181, faxing +44 1892 662253, emailing info@servomex.com or visiting the website at www.servomex.com
