Alkaline Injection for SO3 Removal

[wtflippin]

I am looking for information/experience utilizing alkaline injection (MgO, NaHSO3, etc) in an oil-fired utility boiler to reduce SO3 emissions.

Due to stricter emission standards, we are planning to reduce opacity and particulate emissions utilizing dry ESP's in combination with alkaline injection. Any information (reagent cost, effectiveness, reliability, etc) regarding the use of alkaline injection with dry ESPs would be appreciated.

 

[Davidhewson]

Alkaline injections to reduce SO3 (and SO2) emissions is a common process now. However, according to the chemical compound used (NaOH, MgO, Mg(OH)2, Na2CO3...), results will vary to a large range.
I actually experiment a new range of chemicals which demonstrate the same SOx sorption behaviour and also react on chlorine derivatives and reduce the particulate emissions in one chemical injection. Only electrostatic precipitators or baghouses will be required to recover the salts and large particles.

If you need more information, contact me: cleanfire2000@yahoo.co.uk

 

[JEB66]

Mg, Ca will hurt ash resistivity

Na, K will will help

 

[orenda1168]

Wtflippin:

MgO, mostly as a stabilized oil dispersion, has been very successfully used for at least the past thirty years in oil-fired boilers ranging from small saturated steam units to 850 MW utility units for inhibition of SO3 formation and cold end corrosion protection. Properly applied by proportional injection into the fuel stream just prior to the burners, it is entirely reasonable to expect control of catalytically formed SO3 to not more than 1-3 ppm.

With a MgO dispersion formulation properly structured to incorporate some low micron/submicron particulate MgO material, these fines will transport to the cold end heat recovery zones and lay down as a micro-fine, non-fouling neutralizing protective screen against residual SO3, and therefore H2SO4, deposition and corrosion.

A somewhat more recent development incorporates the application of Mg(OH)2 as a stabilized water dispersion for the same purpose, with about the same results.

Do not go with the use of alkaline sodium compounds, as these will complicate the boiler's hot end slag by complexing with vanadium compounds and forming sulfated materials, both of which a relatively low melting, slag producers and potentially corrosive.