Maximizing Recovery Boiler Availability with an Online Ash Analyzer and Ash Balance Advisor

ABSTRACT
An online analyzer for recovery boiler electrostatic precipitator (ESP) ash chemical composition
has been developed and piloted in a recovery boiler. The analyzer measures CO3, SO4, Cl, K
and Na concentrations from a dry ESP ash. Sample is automatically taken from the ash stream.
In addition to the full chemical composition the melting temperatures of the ash are calculated.
By combining recovery boiler flue gas and steam temperature information with ESP ash
chemical composition, an advanced ash balance advisor has also been developed. The solution
calculates the location in the superheaters where ash is sticky, i.e., 15 – 70 % of ash is molten,
and recommends the ash treatment amount to minimize boiler plugging as well as enabling
sootblowing focus to critical areas. The first ash melting temperature is compared to
superheater steam temperatures which determines if there is corrosion risk in the superheaters.
Overall, the advisor suggests an ash treatment target that maximizes recovery boiler availability
and minimizes makeup chemical needs. Additionally, optimal ash chemistry allows certain
boilers to operate at a higher steam temperature leading to more electricity being generated.
ESP ash chemical information is also valuable for the ash treatment plants such as ash leaching
or ash crystallization processes. Currently the balance is not closed due to the ash composition
being infrequently measured. The online measurement of inlet and outlet streams makes it
possible to optimize ash treatment plant operation and improve availability.
This paper presents the results from the ash composition analyzer with comparisons to
laboratory measurements. Further application possibilities utilizing the analyzer are also
discussed.
Keywords: recovery boiler availability, ash composition, online measurement, ash treatment,
ash balance advisor

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