ADVANCED NH3 AND CO_2 TDL GAS ANALYZERS FOR PETROCHEMICAL PROCESS CONTROL AND PRODUCT QUALIFICATION

摘要

Petrochemical process industries have a keen interest in advanced gas sensing techniques whichrnprovide sensitive, accurate, reliable, fast and cost effective online measurement for processrncontrol purposes. Tunable diode laser absorption spectroscopy (TDLAS) has become a powerfulrntool for trace gas detection by offering significant advantages over conventional measurementrntechniques due to high sensitivity, high spectral resolution, fast response time, operationalrnrobustness and low maintenance requirements.rnThis paper describes the latest progress achieved in the development of advanced TDL trace gasrnanalyzers for petrochemical process control and product qualification. Three examples are beingrndiscussed, which include detection of trace ammonia (NH_3) in ethylene, detection of carbonrndioxide (CO_2) in synthol reactor tail gas for synfuel production and carbon dioxide (CO_2) in arncaustic wash inlet stream for ethylene production. All three applications are based on wavelengthrnmodulation spectroscopy with second harmonic detection, using multipass Herriott cells tornenhance sensitivity. The spectroscopy scheme and system configurations are designed accordingrnto the specific applications. Employing the advanced designs, the CO_2 analyzers have bothrndemonstrated repeatability of within ±1% of the full measurement range for expected pressurernand background variations. The NH_3 analyzer has demonstrated repeatability of better thanrn±50ppb_v over the full span of 0 to 20ppmv in pure ethylene. A lower detection limit of < 20ppb_v