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What analytical techniques are recommended for predicting FCC regenerator NOx emissions and monitoring NOx additive performance?
 
Answers
28/07/2007 A: Tim Dougan, Grace Davison, tim.dougan@grace.com
FCC NOx emissions can be highly variable. Variation of +/-30% is not uncommon. Ascertaining additive performance by simply looking at raw emissions data can be very misleading. A rigorous statistical analysis is usually necessary to account for changing unit operations. This is best done by establishing a baseline NOx emissions model. Because it is not possible to predict which variables are important in any given unit, we recommend that the refiner collect data on as many unit variables as possible including but not limited to emission data, regenerator, riser and stripper operating data, feed rate, feed composition and feed properties, catalyst and additive addition rates, e-catalyst properties, and ambient conditions. Statistical tools, such as Six Sigma can be used to develop a base line emissions model that can then be used to quantify additive performance.
28/07/2007 A: Adrian Humphries, Albemarle , adrian.humphries@albemarle.com
Unlike SOx or CO2, it's very difficult to predict FCC regenerator NOx emissions. FCCU hardware plays a critical role in NOx emissions. Units with very good spent catalyst distribution and very good air distribution within the regenerator are able to get by with very low levels of excess oxygen. Units with these features are quite rare, but refiners who are fortunate enough to have such hardware are able to use NOx additives with a high degree of efficiency. Indeed, we have achieved more than 90% NOx reduction in a North American unit (under EPA Consent Decree). Albemarle always utilizes statisticians to evaluate stack emissions data in order to develop a model.