In-line neutralisation of Effluent pH with sulphuric acid

[Quentin]

I have been assigned to a project involving the neutralising of high pH spikes in our plant effluent.
The effluent currently flows at up to 80 litres/sec (avg 30 litres/sec) in a 8" galvanised pipe from a contrashear pit (solids removal) via a buffer tank to a DAF (dissolved air flotation) unit.
I am considering installing a 8" static mixer in the pipeline just prior to the DAF, with a 50% (or 98%)sulphuric acid dosing point immediately prior to the mixer, and a pH probe just after.
I am concerned about localised high concentrations of corrosive acid in and around the injection point (even though we are neutralising to pH 6 - 8) as well as through the static mixer, and so am wondering if I need to replace the pipework around this area and consider use of exotic stainless steels or plastic as the mixer's material of construction?

Quentin

 

[MJCronin]

Quentin,

You need to use something called an "injection quill"..

This device is specifically for injection of a chemical into the center of a flowing stream

Quills are made from corrosion resistant materials and will resist heat.

http://www.process-controls.com/PFS/Injection_Quills_literature.html

Use a Hastalloy-C quill for injection of acid into water as heat will also develop at the injection point.

You still may have a problem with your design of your system....may engineers have tried to neutralize waste effluent streams "on the fly" as they exit the plant......The problem is that the control of the pH is nearly impossible without a little time and mixing.....a batching operation may work much better....

My opinion only

MJC