CALCULATION OF AMMONIA SLIP

[ebwease]

Can anybody provide the necessary equation(s) to calculate ammonia slip? Also, what inputs and constants are required? The application is for a combined-cycle gas fired 2x1 power plant with an SCR. The system uses 28% aqueous ammonia and NOx is sampled before and after the SCR section.

 

[wde3477]

I don't know the equation, but I recall that our catalyst manufacturer (Cormetech) uses some form of equation involving some pretty nasty log functions, and it may be specific for each catalyst makeup and also proprietary. At any rate, given such an equation, you would most likely need to know the current reactivity of the catalyst, and the NOX reduction as a relation to design parameters for starters. We are a coal-based plant that tried to measure slip from fly ash without success and we now perform a wet chemistry analysis on a flue gas sample taken before the air heater. There is instrumentation becoming available to analyze slip, but we are cautious as it only measures in one point of the flue, and would be correct only if the flue gas was homogenous which we know that it is not. Any calculated value would only be as good as the input data, and based on the variances we're seeing in catalyst reactivities between operating seasons, may not provide the accuracy you're looking for.

 

[jayboz]

Has any new analyzers become available for testing ammonia slip? And do you do any testing for SO3 and what affects ammonia has on your results if any?

 

[bonzoboy]

It's probably easier if you have a gas or distillate oil only fuel system. You can estimate the ammonia slip by measuring the inlet and outlet NOx of the SCR. The molar flow-rate difference should be the molar consumption of NH3. The slip is the difference between this number and the actual measured ammonia injection rate.

 

[bonzoboy]

Not sure about new analyzerrs jayboz, but there is a program, funded by DOE or EPA at Battelle Labs in Columbus Ohio to evaluate new analyzers for ammonia. SO3 presents unique problems with the formation of sodium bi-sulfate (or sulfite?). It can deposit on heat exchanger fins, and it will be measured as particulates on the front half of a PM train.