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Specialty Gases and Equipment
Successful chemical, industrial and refinery operation relies on accurate process control. Yield optimisation, efficient use of energy, reliable quality control of finished products and monitoring of environmental emissions are mission critical goals that are only possible through robust process control.
A range of on-line analysers are used for process control applications. They continuously measure the composition of the process stream and their output signals are hard-wired into continuous process control loops which adjust other parameters, such as control valve settings or blower power inputs, to fine tune the process. Pulsed UV fluorescence (PUVF) analysers for total sulphur content in fuels, Fourier transform infrared (FTIR) analysers for continuous emissions monitoring, non-dispersive infrared (NDIR) analysers used for flue gas CO or CO2 analysis, near infrared (NIR) analysers used for fuel octane level assay and zirconia oxygen analysers are examples of such direct read instruments.
Off-line analytical techniques that take a sample batch and deliver results soon after are used in production laboratories and quality control labs for longer term process optimisation and troubleshooting. For example, x-ray fluorescence is used for quality control in steel production to investigate the crystalline structure and composition of the steel. Unfortunately a direct response on-line analytical technique is not possible due to the changes in crystalline structure that take place during the cooling of the steel.
In some cases these batch-type analysers are achieving response times of less than two minutes and are therefore finding applications in some on-line process control loop strategies, especially for use as a slow response feed forward strategy combined with a direct read fast response feedback control loop. An example of this is the use of a rapid response gas chromatograph fitted with TCD detectors for heating value analysis of natural gas in glass burners to ensure thermal management and precise temperature control in the melting process.
All of the instrumentation referred to above requires calibration with high precision certified specialty gases mixtures and a zero gas such as Nitrogen 5.0 grade. Some of the analysers, such as the gas chromatograph, will also require instrumentation gases such as Helium 5.0 as carrier gases and Hydrogen 5.0 as detector gases.