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Show 3.4.2 Detection The next step that will is necessary is the -detection- of the eluted compound, and these methods were discussed above. The most promising methods for online analysis appear to be the Wet Sulfide, Ultraviolet and Flame Photometric detection. One vendor utilizing the wet sulfide method claims a ± 2 % accuraC-)' in the overall measurement, and this detector is in present refinery use for total sulfur. With the FP detector, a possible interference problem in measuring RFG can stem from the potentially wide variations in hydrocarbon composition. The hydrocarbons also bum in the combustion step prior to the Photo detector, and the resulting emissions can vary as the gas hydrocarbons vary. Chromatographs using this conversion and detection method have not yet been converted to an online format, and doing this would require some development effort and time. Measuring at the required low levels that are now of interest has been shown to be very painstaking work in the laboratory. The problems of maintaining the same accuraC-)' in an online, field instrument are traditionally a large task. One other detection method that has some proven plant experience is one that converts all of the sulfur species to S02 and then proceeds to a UV detector. WSP A and SCAQMD have an ongoing project in one LA refinery to study online RFG sulfur analyzers in an attempt to develop a certified total sulfur meter for monitoring purposes. B. Gas Desulfurization Technology Relative to refinery fuel gas (RFG), other hydrocarbon gas streams are reduced to lower levels of sulfur in a number of other plant environments. Among these are a number of different refinery areas, and the gas processing and natural gas pipeline industries. Technology from these areas are potentially applicable to the enhanced treatment of RFG to achieve lower sulfur levels. Other refinery areas include sulfur recovery plants, hydrogen plant and cat reforming feed pretreating, and light ends caustic washing. A literature search was conducted to identify and evaluate the applicability of these alternate technologies to fuel gas. The technological scope of the Gas Desulfurization field is very broad. It encompasses hundreds of potential processes and schemes in a number of different industries. The study attempted to survey a massive amount of information and condense it down to basic principles and how they might be applied to the enhanced removal of sulfur compounds in refinery fuel gas. Most of the sulfur reduction processes (including the Amine-based ones) do not actually convert the sulfur compounds removed to another form, but simply transfer them to another stream in a more concentrated form. mtimately, the gaseous sulfur compounds have to be converted to a salable or disposable form (usually as a liquid or a solid). The Sulfur Plant is the main element in accomplishing this in refineries and it efficiently converts highly concentrated (50 %+) HzS streams to salable, elemental sulfur by the classic Claus vapor phase reaction. 1.0 Types of Sulfur Removal Processes The technological areas of hydrocarbon desulfurization that were investigated may be categorized according to their basic principles of operation. The following categories have been identified : • Absorption - Chemical (Amine) • Absorption - Physical • Absorption - Chemical/Physical • Hot Carbonate Scrubbing • Caustic Washing • Regenerative Caustic Washing -7- |