CO2 Sparging pH Neutralization

[chopperz]

We want to do a study to determine the effect of CO2 sparging in our coarse mixing tank for our pH Neutralization
system. Currently we used sodium hydroxide to bring the pH down. Our goal is to reduce the volume of sodium hydroxide used(less cost and handling of material) and better control the system.
Our plan is to use an empty port on the bottom of the tank, buy a sparging tip w/valve and connect it to the tank from a CO2 dewar throttle the valve back and let it go. Plan is to let it run for a week while trending the pH and sodium hydroxide usage.
My problem is that I am not sure of the amount of CO2 that will be needed to accomplish the task. Will the dewar run out every hour or day ?? We have a house CO2 system, but its a critical utlity for our manufacturing area and we cant use it.
pH enters the tank all over the place from 2-12 we need to get it to 7.5 . The 10,000 gallon tank has a running volume of @4500 gallons.

 

[m777182]

Your task is not described entirely correctly: you very probably do not use sodium hydroxid to bring pH down. The inflow pH range 2 to 12 is an extremly wide range, does it correspond to reallity?
Of course you can use CO2 to neutralize your alkaline waste water but still you will need a caustic addition in case of acidic waste water.Please check the inflow pH range and your present neutralization sheme!
M777182

 

[chopperz]

m777182 ... you are right. I sometimes type faster than I think. We use Hydrochloric Acid to bring the pH down and sodium Hydroxid to bring it up. We currently use alot of Hydrochloric acid, and would like to try introducing CO2 to the tank to see if it lowers the hydrochloric acid intake.
The pH range is correct depending on what tanks we are dumping, but 80% of the time its a basic solution between 9-12.

 

[bimr]

First off, you are in the wrong forum. You should be here:

Civil / Environmental Engineers > Activities > Waste disposal & treatment Forum

Secondly, adding CO2 is not simple. CO2 forms carbonic acid (H2CO3) when dissolved in water; and it is carbonic acid that leads to the neutralization of alkalinity in solution. Carbon dioxide is not easy to use and its use is limited.

Carbon dioxide can be difficult to use because the gas must be dissolved into solution to be used. This requires the use of a carbonator, or some method to dissolve the gas into solution. Generally a tall tank must be used to ensure that there is sufficient fluid pressure to promote the dissolution of CO2 in water. Significant out-gassing will occur, which is not a problem unless the process also requires the settling of solids. Of course, out-gassing is wasting of the chemical and effects the economics.

Asphyxiation may be a hazard since CO2 is heavier than air. The gas is also stored at hazardous pressures.

You have not provided a water analysis so it is not possible to determine the volume of CO2 required. But you should be aware that if you have high alkalinity, you will generate suspended solids when the CO2 reacts with the alkalinity.

Contact this firm if you have any questions:

http://www.phcontrol.com/home.htm

 

[siretb]

When you sparge CO2, almost certainly only a fraction will dissolve and react, the rest will go and vent out, unless you pressurize the system. Also the mass transfer kinetics of CO2 into alcaline solutions is not good.
The kind of waste you'll neutalize is important, because you may have precipitation of carbonates. Be careful here.
Fouling at the distributor is also an issue.

 

[Pulpboy]

Our reactor clarifier operates at a ph of 10 to 11 in winter to counteract the hardness. We use a CO2 (recarb) chamber to bring the PH back in line to 6.5 to 7.5. Our flow rate is approximately 1100 l/s and the design of our system is 7200 kg/day of CO2. Now that's a little high for actual use of CO2. With out going to track down the numbers on our C02 tank I know we fill up using a typical CO2 tanker every 5 to 7 days.

Good luck.

P.S Bmir is right about the difficulty of dissolving CO2 into the water. The dissolving will be helped by having the co2 be spread out and increase contact by introducing very small bubbles. We have many bubbler to acheive results.