ON LINE CONTINUOUS pH CONTROL
ON LINE CONTINUOUS pH CONTROL
(OP)
Dear all,
What is the reliable, accurate and quick response way for on line pH control for waste water flowing in a 16" pipe, 500 m3/hr, do we need one electrode for the injection of acid or base solution and a second electrode, after the mixing time pipe length required to achieve the desired pH, for checking if the pH is in the required range ?
Do we need a special injection nozzle ? what is the time required for the pH correction ?
The 16" pipe is about 60 m long feeding a DGF (coagulant and flocculent are also added).
Best regards,
roker
What is the reliable, accurate and quick response way for on line pH control for waste water flowing in a 16" pipe, 500 m3/hr, do we need one electrode for the injection of acid or base solution and a second electrode, after the mixing time pipe length required to achieve the desired pH, for checking if the pH is in the required range ?
Do we need a special injection nozzle ? what is the time required for the pH correction ?
The 16" pipe is about 60 m long feeding a DGF (coagulant and flocculent are also added).
Best regards,
roker
RE: ON LINE CONTINUOUS pH CONTROL
The problem is that the control tubing has to be very gentle, the response time will be long.
Injection is done with quills that place the chemical near the center of the pipe. If you have both acid and caustic injection those will be separate quills because different metallurgy is required. Don't go cheap on the quills, if they fail the acid will be injected along the wall of the pipe and eat right through it.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: ON LINE CONTINUOUS pH CONTROL
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
RE: ON LINE CONTINUOUS pH CONTROL
RE: ON LINE CONTINUOUS pH CONTROL
Some Alkylation units in refineries employ special neutralization basins with mixing, with basin walls made of special concrete and high-metallurgy mixer devices. This helps in avoiding localized pH excursions, and in avoiding differences between pH in the measurement point and pH of the bulk fluid which essentially ruins all control efforts. Perhaps you should consider something similar and also make sure there is a proper sample off-take system for reliable pH measurement.
Dejan IVANOVIC
Process Engineer, MSChE
RE: ON LINE CONTINUOUS pH CONTROL
The process design and process control is decided based on the range of ph change in the wastewater and the required acceptable range of ph after adjustment.
But generally speaking the in-line ph adjustment is not a good idea unless the ph swinging of the wasterwater is low and at the same time the acceptable range of target ph is wide (e.g. target ph = 6- 9).
If for whatever reason you don't want to put a static mixer, the pipe length before DGF(Dissolved gas Flotation vessel) should be minimum 150D, I mean 150*16" or 60 otherwise the coagulant (and flocculant?) may not work properly. Ask the coagulant vendor for the range of coagulator application.
Hope this help
RE: ON LINE CONTINUOUS pH CONTROL
ROKER
RE: ON LINE CONTINUOUS pH CONTROL
Because of the logarithmic nature of the pH scale, pH control is usually done in two stages. The first stage adjustment will bring the pH within the desired range. The second stage adjustment fine tunes the pH to a precise setpoint.
RE: ON LINE CONTINUOUS pH CONTROL
Just experienced this first-hand a month ago. Turns out the quill was too short and only protruded into the water steam about 1/2". Mixing water and sulfuric acid that close to a steel pipe wall doesn't bode well for the steel.
Photo is just water spraying out but not really an easy fix since this header can't come offline without taking down a whole lot of other equipment...
RE: ON LINE CONTINUOUS pH CONTROL
REGARDS,
ROKER