By Neil Widmer, Business Development Manager, Emerson Process Management
Sulfur plant tail gas incinerators are used to oxidize sulfur compounds that cannot be released directly into the atmosphere. These sulfur compounds include H2S, COS and CS2. Incinerators are operated at temperatures that are sufficient for oxidation of the sulfur compounds to SO2, as well as providing the required mechanism for proper plume dispersion. Sulfur plant incinerator control is typically based on a closed loop control on the fuel gas flow to achieve the required incinerator temperature. Natural draft dampers that are manually opened or closed, traditionally supply combustion air. Modern incinerator design incorporates forced draft combustion air. This allows closed loop temperature control where combustion air is provided based on the required ratio to fuel gas. Closed loop control based on excess oxygen can be used to optimize fuel gas control.
Optimizing Sulfur Incinerator Operation with an In-Situ Oxygen Analyzer
Ideal operation of these incinerators is to provide an excess of oxygen in the flue gas stream that ensures complete oxidation of all sulfur compounds to SO2. Sulfur plant incinerators are typically operated with excess oxygen levels of 6 to 10 percent. The recommended operating range for excess oxygen is 2 to 5 percent. Operating below 2 percent may result in insufficient oxidation of the sulfur compounds to SO2. This may result in a violation of the allowable concentrations of H2S, COS and CS2 allowed in the incinerator effluent. Operating above 5 percent excess oxygen will result in an excessive use of incinerator fuel gas. Figure 1 to the right illustrates the relationship between relative fuel demand, stack temperature and excess oxygen concentration.
The most significant advantage of operating within the recommended range is two-fold: Operating above the minimum recommended 2 percent excess oxygen would ensure proper oxidation of sulfur compounds. Operating below the maximum recommended value of 5 percent excess oxygen will provide a reduction in fuel gas usage. An added bonus of operating with a decrease in excess oxygen is the reduction of CO2 (a greenhouse gas) emissions associated with a decrease in fuel gas consumption.
It’s possible to monitor excess oxygen concentrations within the sulfur plant incinerator by using the zirconium-oxide measurement principle. Zirconium oxide is an in situ measurement that provides a fast and reliable measurement of excess oxygen in the sulfur plant incinerator exhaust gas. To counteract the poisoning affect that SO2 has on standard zirconium-oxide sample cells, new sulfur resistant cells are available.
Summary of economic and environmental benefits:
To learn more about instrumentation that can optimize incinerator operation, click HERE.
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