During start-up and shut-down, any time a sulfur recovery unit (SRU) transitions from ambient temperature through fuel gas warm up to the introduction of acid gas, measurement of O2 stoichiometry is critical. Historically, operators have manually taken samples using a portable electrochemical type O2 analyzer. While giving more or less satisfactory results, the requirement for more stringent operating limits, hazard exposure and the non-continuous nature are reasons to consider a permanent solution. A fixed system that draws a continuous sample during the operational transition period, without intervention from operations or analyzer maintenance, can be rationalized. AMETEK Process Instruments has extensive experience making a continuous process oxygen measurement in Claus SRUs and has developed the Model 5100 HD Tunable Diode Laser Absorption Spectroscopy (TDLAS) system specifically for start-up and shut-down applications.
Paramagnetic analyzers have also been used to make this measurement but the technology is relatively fragile and the analyzers fail frequently. In contrast, TDLAS diode laser lifetimes are typically in excess of ten years and there are no sensitive elements of the analyzer in contact with sample, a particular advantage in this application. There is consequently no regular replacement spares requirement for the TDLAS technology.