Hot-Wet Measurement in a Sulfur Recovery Unit

Posted by TechStar on Jun 10, 2022 2:10:00 PM

Hot-wet continuous emission monitoring (CEM) measurement means analyzing the stack gas sample on an as-is basis, which ensures that the integrity of the sample, from extraction through analysis, is maintained. Keeping a good heat integrity in hot-wet measurement is very important to prevent the condensation of acid mist or water vapor.

Cold-dry analysis refers to cooling a hot-wet stack gas sample to condense out the water. Here we will mainly focus on hot-wet applications.

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Hot-wet analysis is especially well suited to the measurement of sulfur dioxide (SO) and oxides of nitrogen (NOx) emissions from a Claus sulfur recovery unit (SRU) incinerator for the following reasons:

  1. A Claus SRU incinerator can generate significant quantities of sulfur trioxide (SO) at high temperatures during upset conditions (sulfur entrainment, off-ratio, etc.). SO is very corrosive and can damage sample handling systems and more in process. Keeping the sample above the acid dew point simplifies maintenance. Hot-wet measurement does not require specific sample handling, drying, and diluting, and therefore higher reliability and accuracy can be achieved.

  2. Unlike cold-dry measurement which requires removing water, which results in removing some soluble components, hot-wet measurement doesn’t require any sample alteration. For example, if a sample containing a finite amount of SO is cooled to below the water dew point, SO dissolves in the water phase, reducing the SO concentration in the vapor phase, where it is being measured. If the sample is cooled to the point where SO condenses, corrosion can result.

  3. Measuring the sample on an as-is basis is compatible with mass emission measurement (kg/h of SO), in which both the stack gas velocity and the component of interest are measured on a wet basis. In the cold-dry analysis however, the analyte and the stack flow rate if required, are measured dry and wet, respectively.

  4. In the hot-wet system, there are no moving parts in the analyzer, the sample is extracted and drawn through the analyzer with an air-driven eductor. No mechanical pump is used, and the analyzer is designed to be extremely robust.

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Topics: AMETEK Process Instruments, Analyzer

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