Calcium Reactor Design Concepts

[Luis Delgado]

Hello Guys!

Nice to be here with you

I'd like to discuss some aspects of calcium reactor design with you.

As we know, a reactor media is dissolved by the presence of carbonic acid (H2CO3) in saltwater that results form the chemical reaction of water (H2O) with Carbon dioxide (CO2).

But most calcium reactors tend to bet in mixing CO2 bubbles with the media with the help of a circulation pump. This turns to be rather inefficient because these bubbles get stucked in the media and tend to dissolve more slowly into carbonic acid than if they were quickly sucked by the circulation pump to be broken in hundreds of smaller bubbles.

My point is:

would'nt the reactor be more efficient on CO2 usage and effective in leveraging Calcium and KH levels if one would improve CO2 mixing with water, in a separate chamber, to get a lower PH as a result of increasing carbonic acid concentration and, then let this more acid water pass slowly through the all media, as opposed to the current philosophy used by all calcium reactors manufacturers?

Thanks
Luis Delgado

 

[NaH2O]

Welcome to Reef Frontiers!!!

I'm tagging along on this thread....

 

[Scooterman]

I went ahead & moved your thread to Reef Chemistry Discussion with Boomer, two reasons, one it is a good subject & two Boomer is the man that would most probably be most helpful, hope you don't mind.
BTW welcome Luis!

 

[Luis Delgado]

I went ahead & moved your thread to Reef Chemistry Discussion with Boomer, two reasons, one it is a good subject & two Boomer is the man that would most probably be most helpful, hope you don't mind.
BTW welcome Luis!

No problem ! Besides, I really apreciate that

Thanks,

Luís.

 

[DonW]

But most calcium reactors tend to bet in mixing CO2 bubbles with the media with the help of a circulation pump. This turns to be rather inefficient because these bubbles get stucked in the media and tend to dissolve more slowly into carbonic acid than if they were quickly sucked by the circulation pump to be broken in hundreds of smaller bubbles.

Most reactors now days do exactly that. The co2 is fed before the impeller and chopped. The smaller bubbles then are recirculated through the media. The key is "recirculated" the water is staying in the reactor plenty long enough to lower ph to a usable level.

Don

 

[Boomer]

As Don has said, many are that way already. The realy issue with most reactors is excessive CO2 or CO2 not used, lowering the pH of the effluent. This has been countered by using a second stage to raise the pH up by killng the CO2 so the effluent pH is not so low when it enters the tank. Here is an example

 

[Luis Delgado]

Hello Boomer:

Although many reactors can split the bubbles in smaller ones, the smaller bubbles will get into the media again and many may get stuck, dissolving very slowly, and reducing the area of contact between the media and the water. My point was if it would be better to reinforce bubbles complete dissolution in the water before it gets its way through the media.

What I'm saying is that the water would get a much lower PH obtain through a dissolution chamber (feed by the circulation pump). In this case de circulation pump would just circulate the water with the undissolved CO2 in the dissolution chamber and not through the media. Then the water with completely dissolved CO2, turned in carbonic acid, would circulate very slowly through the media, just like it happens in the second chamber.

Another doubt: Do I need a high flow of water through the media to get a good media dissolution?

 

[Boomer]

You do not need a lower pH. The pH you get from reactor is fine and you can run pH's even lower by increasing the CO2 input. You do not want the pH to low, as it is self defeating. Then CO2 in the bubbles will diffuse out of the bubbles into the water, as a function of partial pressure. Only if the water is saturated with CO2 will this stop, as the partial pressures are the same in which case the bubbles will remain.

Then the water with completely dissolved CO2,

There is really no such thing. pH is a pure function of CO2/carbonic acid and Alk. H2CO3 (carbonic acid) concentration is really CO2 (aq) in equilibrium with water. whether it is in a pure free CO2 state or in the H2CO3 makes no differance. Carbonic acid is just hydrated CO2. Meaning, if it is 80% CO2 and 20% carbonic acid or 20% CO2 and 80 % carbonic acid the pH will be the same.

In lay terms pH = CO2 + Alk, Alk = CO2 + pH, CO2 = pH + ALk. As the pH falls the CO2 increases. As the pH rises the CO2 decreases. You can not stop it. At any particular pH there is an exact amount of CO2 and Alk. That amount of CO2 and Alk dictates the pH.


This graph may help you understand the relationship better.

 

[DonW]

Boomer I think he's just trying to increase overall efficiency not the ph level, less co2 same ph.
One easy way to increse a reactor efficiency is to start at a lower ph and unbuffered water. Easily done by feeding the reactor with just rodi top off. The ph is already fairly low and no buffering.

Don

 

[Boomer]

Don

In order to have the same pH with less CO2 there will have to be less Alk, or lets say a balanced Alk with CO2. Meaning the Alk and CO2 must be balanced. If they are not balanced there will be a shift in the 3. If you stated with a lower pH then there would be less of a need or less CO2 injection required, maybe, if that is what you mean. RO/DI water also has no CO2, unless it is exposed to ambient air where it will then pull in CO2. This may be a gain as you suggested, if this is what you are driving at. Don't forget as soon as that RO/DI water mixes with the incoming seawater there is going to be a big shift. All this may be difficult to control and may do little if anything, as it would depend on the evaporation rate which would be a function of the RO/DI input water to the reactor. Many sup reactor systems, do to low pH, with RO/DI water with kalk drips. Another new issue for most. It would be an interesting experiment. And would only have merit on reactor only systems, where RO/DI top-off is only added. The we are stuck with this example ; 5 gal of RO/DI / day from evap, where that evap water is only added to the reactor, is not going to do much of anything. That equates to about <1 quart of water / hr. Now think of how many gallons / hr go through a calcium reactor / hr. and then re-equate the same for a system with only 1 or 2 gal evap / day. I doubt there would be any noticeable increase in efficiency.

 

[DonW]

Its not really a big savings in co2 but will cut back the amount of co2 used over 24hr period. My tank for example would have a average co2 on time duration of 23 hours. Now its 19 hours after a simple plumbing modification to allow the reactor to pull in rodi water when the top-off is active. Thats around 1460 hours per year that the co2 is not running, so no real savings.

Don

 

[Boomer]

I don't see that at all Don As soon as the RO/DI water hits that incoming seawater, unless you shut it off, the pH will rise to the point where there will be little if any dissoltuion of CaCO3. Reactors are usually dialed in around mid 6's pH. The new pH in the reactor without CO2 injection and just RO/DI will be in the mid 7's, not good at all. It would be more of a RO/DI with CO2 injection to do anything. It would be a tab more efficient maybe and a tad more of savings maybe but I dont' think it is worth .

 

[DonW]

I just monitor on time of a given automated operation. For example yesterday the co2 solenoid was on for 1141 seconds and cycled off 4 times btween the hours of 0700 and 0659 when is when the counter was reset to 0. Days of operation was 30 which is when it was manually reset after the plumbing change. The prior year the on time averaged 1380 per day without the ro feed. Granted its only been 30 days but so far its pretty conclusive.

Don

 

[Boomer]

Hah, so you are doing this right Don, RO/DI into reactor ? I thought it was just an example. Well, then you are the test bed

 

[DonW]

Yes not an example. I run my reactor with negative pressure so that the water is pulled through. Makes it easy to pull in rodi if its on or sea water if its not. This way rodi has no effect on effluent outflow.

Don

 

[Boomer]

Don have you measured the difference in the pH/Alk effluent between the on-off RO/DI ?

 

[DonW]

No, I know its wrong to assume but.... I just review the variables, since the tanks water chemistry stays solid and the co2 consumptions is down from day 1. My guess is its works, but honestly I was hoping for a big number but as cheap as co2 is there isnt much of a benefit. My little schuran is pretty efficient anyway.

Don

 

[Boomer]

Thanks Don