Unocal Science & Technology Division is the first to use the selective catalytic reduction (SCR) process to reduce NOx emissions in high-temperature, gas turbine-exhaust operation.
The system is installed as part of a full-scale, gas turbine cogeneration plant that supplies steam and electricity to Unocal's research facility in Brea, Calif. It has been in continuous operation there since December 1990.
The system has consistently Maintained outlet NOx emissions at less than 9 ppmv, with less than 10 ppmv ammonia slip, as required by the South Coast Air Quality Management District.
Norton Chemical Process Products Corp.'s NC-300(R) catalyst system controls NO, emissions from the 3.9 Mw facility.
The catalyst is installed upstream of the heat recovery boiler, resulting in reduced costs and simplified operation of the boiler (see flow diagram).
Conventional SCR catalysts require operating temperatures in the range of 600-700 F. This necessitates splitting the heat recovery boiler into two sections to provide a space for the SCR catalyst wherein the exhaust gas is at the required temperature.
Norton's NC-300 catalyst allows operation of the SCR at temperatures above 900 F.
This means that the SCR system can be installed in front of the heat recovery boiler.
Boiler operation is simplified by one-piece construction instead of two separate sections. This saved Unocal about $100,000 in boiler costs.
NC-300 catalysts are composed of a unique zeolite-based material that offers several advantages:
- Operation at temperatures above 900 F. without degradation
- Resistance to poisoning by sulfur and other flue gas components
- Homogeneous catalyst construction, which means no potential for loss of active catalyst material from the underlying support.
The NC-300 catalyst system is designed for all types of NOx emission sources such as refinery heaters and boilers, reciprocating engines, and electric utility boilers.
The high-temperature capability of the catalyst is especially attractive for retrofitting existing cogeneration facilities.
Norton also designed and supplied the ammonia injection and dilution air systems, as well as the computer-based control system at the Unocal facility. The system components were of a modular design, which minimized on site installation requirements.
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