exhaust treatment?

[gillyboc]

hi hope somebody can help,first I'll quickly explain present system, we have an incineration plant linked to a afterburner which then passes through a boiler,before going
to a bag filter,without being involved with any of the planning, work decided to install a scrubber system to
run the exhaust gases through, only now I'm being asked to get it up and running nobody seems to have a clue as to the correct dosing for the scrubber plant, the problem is the company which designed the plant followed somebody Else's
design, i have asked about caustic strength and size of dosing pump but nobody wants to hold there hands up,i have been trying 10 percent Naoh but the dosing pump can't keep up,so am now trying 25 percent but dosing pump is still not keeping up,i don't want to make the solution any stronger due to the weather.
any help much appreciated gilly.
PS I'm only trying to keep ph at 7 if this helps.

 

[ash9144]

Possibly lower the injection point on the scrubber (towards bottom). This would reduce the head pressure and should allow higher NaOH flow rate.

 

[siretb]

The amount of caustic will depend on the amount of acidic components you have. We do these systems all the time. Since you are refering to incineration (what are you burning ?), the major pollutant should be HCl. you may have also SO2 and HBr.
First thing to do is to calculate flows
you need max HCl, SO2 & HBr concentration
max gas flow rate
I assume that no reagent (like lime) is injected on the baghouse filter.
In order to scrub HCL (and only HCl) you do not need to go to pH 7 or more, but you need that for SO2. So if you have a single scrubber , you will spend NaOH both for SO2 and for HCl

As for the caustic strength you have two points to keep in mind
1* freezing point (if tank located outside)
2* too high a concentration may render pH control not very stable, with pH overshooting at values greater than 9, with scaling issues due to CaCO3
If you need more, please supply pollutant list & concentration, and describe the scrubber you have.