News | June 8, 1999

Rosemount Monitor Measures Oxygen in Sulfurous Environments

Rosemount Analytical, Process Analytic Division, A Division of Emerson Electric Co.any%> (Orrville, OH) has introduced an in-situ zirconia-based oxygen sensor that lasts up to ten times than other oxygen analyzers in extreme environments while maintaining its accuracy within ±0.75%. It is the first fluegas oxygen analyzer certified to the Foundation fieldbus standard.

The company's Sulfur Resistant Oxymitter 5000 oxygen transmitter integrates a zirconia oxygen probe and field electronics into a single, compact package. It inserts directly into the exhaust flue to measure oxygen concentration in combustion gases.

The sulfur-resistant version of the Oxymitter 5000 contains a proprietary porous alloy that resists sulfidation and lasts 10 times longer than sensors based on platinum electrodes.

The data is used to measure the efficiency of industrial combustion systems. These range from process heaters, refinery waste boilers, and spent acid furnaces to pulp and paper mill recovery boilers, industrial boilers, and utilities burning high sulfur coal or heavy fuel oil.

Ordinarily, oxygen transmitters do well in high-oxygen environments but fall victim to corrosion within a few weeks in highly sulfurous environments. Unfortunately, the amount of sulfur in flue streams is on the rise.

"Industry's under pressure to be more efficient, and that means running at lower oxygen," says Rosemount Analytical product manager Doug Simmers. "People used to say that air is free, but you have to heat air in the furnace. That's tons of extra mass that you're moving every day. The difference between 2% and 5% excess oxygen can be a difference of 2-3% efficiency. That's a lot of money. Plus, when run lower oxygen, there's less oxygen available to make nitrogen oxides, so a pollution aspect to it."

Oxygen sensors are especially susceptible to sulfur attack because they rely on precise morphology in their electrodes. A typical oxygen sensor consists of zirconia sandwiched between two electrodes of porous platinum. The platinum ionizes oxygen molecules on the reference side. The oxygen then moves through the zirconia center and releases its electrons to a porous platinum electrode on the measurement side. The more oxygen in the flue, the greater the voltage generated by the sensor.

Sulfur attacks the electrodes, turning them into platinum sulfide which then sublimates. In-situ oxygen transmitters last only a few weeks in high-sulfur flues. Rosemount Analytical's solution: a proprietary alloy and processing method that yields a high conductive, porous, sulfur-resistant electrode. The company has filed for a patent on the material.

The new sensor cell has up to ten times the service life of conventional general-purpose Oxymitter products. Rosemount says Oxymitter 5000 is the only flue gas oxygen analyzer certified to the Foundation fieldbus standard. It is also compatible with Fisher- Rosemount's PlantWeb field-based architecture, as well as Fisher- Rosemount's DeltaV and AMS host systems.

Last summer, Rosemount Analytical its first sulfur-resistant oxygen sensor, the Oxymitter 4000. It transmits data using AMS/PlantWeb-compatible digital HART communications. Rosemount Analytic offers both models in general-purpose and CENELEC hazardous area designs.

For more information: Doug Simmers, Product Manager, <%=company%>., 1201 N. Main St., Orrville, OH 44667. Phone: 330- 684-4433. Fax: 330-684-4458.

By Alan S. Brown