← benzene and hydrogen sulfide in LNG

At peak shaving facilities, natural gas is liquefied and stored on-site, ready to be gasified and delivered to the grid when peak demand occurs. Two major concerns are incident benzene, which readily freezes in liquefaction and destroys storage equipment, and H2S, notorious for its corrosivity. Both contaminants pose additional environmental dangers: benzene is carcinogenic and H2S is an EPA-regulated toxic pollutant. Since multiple gas sources bring variation in incoming gas quality (specifically, contaminant levels), online monitoring of benzene and H2S is required.

total suflur and Wobbe Index →

To verify natural gas quality, the EPA regulates both the energy content and total sulfur content inside the pipeline. To effectively measure the Wobbe Index (similar to heating value) of a gas stream, a continuous sample is combusted while a tunable diode laser analyzes residual oxygen. At the same time, the total sulfur load in the stream is determined by combusting all sulfur compounds in the sample to sulfur dioxide; while a pyrolyzer handles controlled oxidation, the SO2 concentration is determined by UV absorbance.

← hydrogen sulfide and ammonia in sour water

"Sour" water essentially refers to wastewater containing significant hydrogen sulfide. Ammonium bisulfide is a salt that often forms in sour water from the reaction of H2S and NH3. Notorious for causing accelerated corrosion and maintenance problems, ammonium bisulfide is a problem best handled by preventative measures--namely, stripping H2S and NH3 from the stream. Since sour water can be very opaque or contain light-blocking particulates, analyzing its composition requires making a representative gaseous sample. A double headspace system is used to simultaneously measure both H2S and NH3 in vapor states and thus relialbly determine if the levels threaten ammonium bisulfide formation.

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