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PollutionEngineering November 2012 : Page 35

Advertorial AMETEK HOWTO: measure sulfur content in crude and fuel oils on-line – Process & Analytical Instruments Division S ulfur content plays a signifi-cant role in the economy, performance, and environ-mental impact of process-ing crude oil, hydrocarbon fuels, and other hydrocarbons. The combustion of sulfur-containing fuel oils produces sulfur oxides that are further oxidized in the presence of oxy-gen and moisture to create sulfurous and sulfuric acids that are detrimental to equipment and the environment. For this reason, the sulfur content of fuels is regulated, and recent Marpol Annex VI regulations lower the per-missible sulfur content in marine fuels as well. On-line analysis of sulfur content has become the norm, primarily using X-ray spectrographic analyzers that offer cost-effective, nondestructive direct measurement of sulfur content. Two main X-ray technologies are use-ful for sulfur content determinations: X-ray Transmission (XRT) and X-ray Fluorescence (XRF). Each offers par-ticular advantages and limitations. Analyzing these pros and cons, and comparing them to the requirements of various applications can help in deciding which is the right technology for each. In many cases, the analyzer must be able to operate at the pressures and temperatures typical of process pipe-lines, and that means the analyzer should require little or no sample condition-ing. At the same time, tested samples should be returnable to the process to eliminate the need for effluent sumps or storage systems. And operating condi-tions typically involve high pressure and temperature. These conditions generally favor XRT systems. AMETEK ASOMA Model 682T-HP XRT online sulfur analyzer. How X-Ray Transmission/ Absorption (XRT) Sulfur Analyzers Work X-ray Transmission/Absorption (XRT) systems consist of an X-ray source, a sample flow cell and an X-ray detector or counter. In on-line XRT analyzers, like the AMETEK 682T-HP, X-rays emitted from the X-ray source have high enough energy to pass through the flow cell’s beryllium entrance window, through the volume of oil inside the flow cell, through the beryllium exit window, and into the detector on the opposite side. As they pass through the sample, some of the emitted X-rays will be absorbed by molecules in their path. Sulfur absorbs X-rays at approximately ten times the rate of the primary components of crude and fuel oils (hydrogen, carbon and oxy-gen). Therefore, the number of X-rays emitted from the source that are count-ed at the detector is inversely propor-tional to sulfur content; i.e., the higher the sulfur content, the more X-rays are absorbed travelling through the sample and the fewer are counted at the detector. The analyzer can be calibrated in such a way that it can translate counts and dis-play results directly in % sulfur. XRT analyzers, like the 682T-HP, offer several distinct advantages for on-line sulfur measurement. They require lit-tle, if any, sample conditioning, and no recovery system. They use a noncontact, nondestructive measuring technique that generates no waste products and requires no consumables. The technology is well suited for high-temperature and high-pressure processes, and the relatively long X-ray path eliminates the effect of window fouling on results (fouling thick-ness is very small compared to the overall path length). No routine maintenance is required other than calibration. Among the limitations of XRT on-line analyzers is that only one element is detectable and the minimum detectable concentration is 200 ppm. For at-line and laboratory detection of very low sulfur content oils like low-sulfur diesel, energy-dispersive X-ray Fluorescence (EDXRF) systems offer a suitable alternative. Caption_2: XRT Analyzer Schematic NOVEMBER 2012 35

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