Horizontal CO2 reactor - Estimations for a big tank, or small tank

[22802]

For Info from Moderation Team: UKAPS is not against innovation in the hobby or new approaches and ideas on how to do things, CO2 is one that most struggle with and any new idea is viable if presented in the right manner, this thread will be closed and remain here, unless the original member contacts UKAPS and asks for it to be removed. The said member was banned because of constant flooding of the forum with misleading and contradicting information for new members, and also when people did not reply to this post went and flooded the entire forum instead, when approached to curtail on this behaviour, refused to see our point of view and carried on regardless, eventually we had no choice due to the wording of said members replies across the forum and mass PM's playing the victim!


Original post from here:

Conventional CO2 reactors are basically water columns with bubbles in a flow. The bubbles create a maximum surface area from CO2 to water, necessary for enough CO2 to be absorbed. CO2 reactors work fine, but need careful optimisation (dimensions, adjustable flow and bypass) to work well (no noise, not too much filter flow reduction, no bubbles escaping into tank, sufficient CO2 absorption capacity).
Especially for tanks larger than a few hundred litres, it becomes more challenging to create a good CO2 reactor setup.

CO2 Spray Bar is simpler than conventional CO2 reactors, and less complicated to set up and operate. It uses a laminar water flow under a pocket of CO2 gas to enable the CO2 absorption. It is an in-tank solution - for some this is great while others may not like it.
For really large tanks the dimensions of the Spray Bar could become an issue, and not look good in the tank.

My CO2 Spray Bar has a cross section of 1 Inch, 2.5 cm, and is 80 cm long. This is more than enough for my 250 litre tank, as it drops pH from outgassed water by approximately 1.5-1.6 with a reasonable tank surface agitation.
Now that I know how much absorption surface area I need for my tank, how would that scale up to larger tanks?

I took my experience from the CO2 Spray Bar, and came up with an horizontal CO2 reactor that applies the same principles. This horizontal reactor would have the full tank length, and be installed in the cabinet underneath the tank



This horizontal CO2 reactor obviously has no bubbles floating in a moving water column, does not care how much the water flow is, will be perfectly silent, will not release bubbles in the tank, and is of course not visible in the tank. As I will illustrate below it is straightforward to have it inject tanks with volumes of thousands of litres.

We can also design a multi stage horizontal reactor. When the lower reactor gets full with CO2, its maximum capacity reached, bubbles of CO2 will start to escape to the upper reactor, gradually fill it and boost the CO2 absorption with the second stage active.


The multi stage can be useful for really big tanks (thousands of litres), or when it is advantageous to work with smaller pipe diameters, while still having sufficient capacity.

I used @durb992000 tank, 2.300 litres as an example to do some estimations. I know what CO2 Spray Bar is good enough for a 1.5 pH drop in my 250 l tank, and estimate how the horizontal reactor needs to be scaled up for this 2.300 l tank.

First some basics, to understand how to scale up a reactor, so that it works for a larger tank.

When CO2 has stabilised during the photoperiod, most of the injected CO2 will be outgassed to the surface and ambient air, and a minor part will be taken by plants. We therefore take the assumption that steady state CO2 injection is proportional to the surface area (length*width) of the tank.
Therefore the surface area of a CO2 Spray Bar or Horizontal Reactor scales up with (tank length * width) for steady state during the photo period.

When we start injecting a fully outgassed tank, obviously the amount of CO2 needed in the process is proportional to the tank volume (length * width * height). However, this is not a fair assumption for a normal day ramp up, as the tank still has residual CO2 from the previous day. In fact, the amount of CO2 outgassed during the night is proportional to the surface area, NOT to the tank volume.
Therefore for a morning ramp up with CO2 Spray Bar or Horizontal Reactor, we need to scale the dimensions proportional to the surface area (length*width) of the tank.

Now let’s take one big 2.300 l tank as an example, and compare with 248 l 22802 tank. Keep in mind , a 1 inch full tank length CO2 Spray Bar on 22802 tank is good for 1.5-1.6 pH drop.



BigTank has a volume 9.6 times 22802 , and as surface area 5.8 times.
When we always use the full tank length for our reactor, the diameter should not be scaled up proportional to volume (length*width*depth), but rather with the width*height ratio (4.5).
Similar, when using full tank length and proportional to surface area, we can use width ratio (2.7) as the scaling factor.

So if we use a standard 4 inch plumbing/sewer pipe as the main reactor for BigTank, we are exceeding the 2.7 ratio that would be required for a comparable steady state operation to 22802 (1.5 pH drop), and most likely a similar ramp up time in the morning (I use 3 hours to be on the safe side)

In summary, a 4 inch horizontal reactor installed in the cabinet over the full tank length is expected to effortlessly power a 2.300 l tank. Alternatively use a thinner 2 inch reactor, and a double multi stage reactor configuration.

Not much can go wrong with a horizontal reactor. No optimizations, adjustment, no noise and can it be made very powerful indeed. And it standard plumbing materials.

Finally, for a real big tank I would always use a CO2/pH controller, for stability and for CO2 savings (less need for a strong surface agitation and outgassing).

 

[Hufsa]

 

[palcente]

I think the flow will not remain laminar as it enters the wider pipe, but become turbulent. It would be interesting to see what the flow rate drop would be on long and wider reactor of this sort vs just the pipe of equivalent length. Looking forward to your findings!

 

[KirstyF]

I might be misunderstanding the concept but effectively this looks like a very wide very short almost traditional reactor with linear flow, so whilst I would agree that the likelihood is that it could ultimately give huge opportunity to increase Co2 absorption as there would be a significant amount of surface area contact, I would see the following issues:

Co2 absorption would only become stable at the point that the gas had filled to the level of the outflow, at which point, excess would escape. This could take a very long time due to the large capacity and is assuming that the design shape would allow this to occur in a pressurised system (as mentioned above)

The bubbles would then escape presumably into the aquarium itself which would also add a little perhaps to overall Co2 level but possibly again impact stability.

It would not be adjustable in the same way as your original concept was, as there would be no way to re-set the Co2 level that I can see, other than by the rate of injection, which was something you were looking to avoid.

The addition of a second unit to capture overflow would again increase available Co2 absorption but also increase stability time as above.

Comments are not a criticism because you could be on to something here and I totally support thinking outside the box 👍 but maybe just some ideas of things to think about. 😊

Also, as an aside; in order to run full length, on a large cabinet, you would need a design with no internal compartmentation, which is quite common for sump systems, or at least ensure that any materials used in existing compartments were not load bearing if removed. Certainly not a deal breaker for a lot of large tanks. 😊

 

[Zeus.]

Interesting read. I use to be able to drop my 500l tank 1.5pH in about 30mins, with the aid of duel solenoids, needle values, twin DIY reactors etc plus using a PLC for trimming control. I used a pH controller at first but found not using one I achieved a more stable pH. I also found the flow rate through the reactors had little to no effect on the CO2 uptake, so with aid of bypass had a low flow rate though reactors so they was silent.

 

[22802]

Interesting read. I use to be able to drop my 500l tank 1.5pH in about 30mins, with the aid of duel solenoids, needle values, twin DIY reactors etc plus using a PLC for trimming control. I used a pH controller at first but found not using one I achieved a more stable pH. I also found the flow rate through the reactors had little to no effect on the CO2 uptake, so with aid of bypass had a low flow rate though reactors so they was silent.

You had a really nice setup @Zeus. , but already for a biggish 500 l tank not trivial. With experience you can get bigger (dual) reactors to work, and you, @foxfish and several others on this forum enjoy the process and experiment. But try really big tank if your hobby is not reactor design, plumbing or control systems. The horizontal reactor is the simplest you imagine, and can be scaled up to a powerfull beast if needed.

I always liked your duel solenoids. With the example 2.300 l tank that I worked out it is easy to gas your fish when at max capacity and anything wrong with injection. Therefore having one solenoid on for a fast ramp up only, then on timer switched off during the day. Second solenoid injecting much lower CO2, only to maintain the level during the day. Much safer, especially with a big tank and real powerfull reactor.

with aid of bypass had a low flow rate though reactors so they was silent.

That's also what I did when I still used my reactor (I have now taken it out and prefer CO2 Spray Bar). The downside is that you only get water through your reactor if you partially close the bypass, and with that create a pressure drop that limits filter flow. Of course, for a big tank it makes sense to have a separate pump for the CO2 system. Yet for the horizontal reactor pressure drops are close to zero, there is no need to adjust the flow, and you can simply integrate it in the filter flow without any downsides.

 

[22802]

I might be misunderstanding the concept but effectively this looks like a very wide very short almost traditional reactor with linear flow, so whilst I would agree that the likelihood is that it could ultimately give huge opportunity to increase Co2 absorption as there would be a significant amount of surface area contact, I would see the following issues:

Co2 absorption would only become stable at the point that the gas had filled to the level of the outflow, at which point, excess would escape. This could take a very long time due to the large capacity and is assuming that the design shape would allow this to occur in a pressurised system (as mentioned above)

The bubbles would then escape presumably into the aquarium itself which would also add a little perhaps to overall Co2 level but possibly again impact stability.

It would not be adjustable in the same way as your original concept was, as there would be no way to re-set the Co2 level that I can see, other than by the rate of injection, which was something you were looking to avoid.

The addition of a second unit to capture overflow would again increase available Co2 absorption but also increase stability time as above.

Comments are not a criticism because you could be on to something here and I totally support thinking outside the box 👍 but maybe just some ideas of things to think about. 😊

Also, as an aside; in order to run full length, on a large cabinet, you would need a design with no internal compartmentation, which is quite common for sump systems, or at least ensure that any materials used in existing compartments were not load bearing if removed. Certainly not a deal breaker for a lot of large tanks. 😊

All good questions @KirstyF , and a good opportunity for me to clarify how it works 🙂

effectively this looks like a very wide very short almost traditional reactor with linear flow

This is correct, it is NOT a copy of a CO2 Spray Bar and does not use that overflow principle. Just like with traditional vertical reactors we use the CO2 regulator (needle valve) or pH/CO2 controller to adjust injection. The difference with a conventional CO2 reactor is that it can be scaled up to be super powerfull, yet still be very easy to operate.

Co2 absorption would only become stable at the point that the gas had filled to the level of the outflow, at which point, excess would escape. This could take a very long time due to the large capacity and is assuming that the design shape would allow this to occur in a pressurised system (as mentioned above)

Remember, it is not the overflow as in Spray Bar. Stability is set by constant injection with a precision needle valve (or pH controller if you like). Gas will only escape from the exit when injection exceeds absorption and the reactor get full. In a traditional vertical reactor that would be the point where a CO2 pocket builds (noise) in the top of the reactor. Now in a dual stage, when the lower stage gets at full capacity you see that the excess CO2 enters the second stage, where it is not lost or create any trouble (noise) but just starts to add to the absorption.

The bubbles would then escape presumably into the aquarium itself which would also add a little perhaps to overall Co2 level but possibly again impact stability.

Will not happen. With correct design all CO2 will be absorbed, nothing goes to tank. The problem of small bubbles in the tank, like some traditional reactors, will never happen in horizontal reactor.

The addition of a second unit to capture overflow would again increase available Co2 absorption but also increase stability time as above.

The second stage just makes sure that 100% of CO2 that came from regulator get's absorbed. Stability is therefore brought by the regulator, not by the reactor that just follows 100% what the regulator gives it.

Also, as an aside; in order to run full length, on a large cabinet, you would need a design with no internal compartmentation, which is quite common for sump systems, or at least ensure that any materials used in existing compartments were not load bearing if removed.

Fair point, then just do half of the tank length and dual stage design. Can go to 5 stages if needed, with little or no downsides. But always let the reactor work from lowest unit to highest, that is important.

Comments are not a criticism because you could be on to something here

Appreciate @KirstyF , and I am aware that you have a big tank 🙂

 

[22802]

I think the flow will not remain laminar as it enters the wider pipe, but become turbulent. It would be interesting to see what the flow rate drop would be on long and wider reactor of this sort vs just the pipe of equivalent length. Looking forward to your findings!

Water will be like a river in the 4 inch tube, no problem if this river is turbulent. If one would like to slow down the river a bit (unlikely) could throw in some bioballs.

You are right, turbulence will give some loss of kinetic energy. But at these low speeds, and no pressure drop, this will be a tiny impact in practice

Looking forward to your findings!

I am perfectly happy with my CO2 Spray Bar, and have no plans to build a horizontal reactor. There is no need for testing, there is really nothing that can go wrong.
In my dreams I would own a 2.300 l tank, buy 4 inch pipe for the fulll length, glue some 1 inch water inlet and outlet, drill small hole for CO2 (perhaps another for outgassing valve if required), and job done.

 

[Hanuman]

Not to disregard the effort but how are you going to achieve laminar flow in a systems filled with sharp corners and bends? If I am not wrong, in order to achieve laminar flow you need a pre-chamber that aligns the flows. You would then have a secondary chamber where you'd have the water passing linearly and exposed to CO2. Preferably that chamber would need to be slightly under pressure for efficiency. I don't know enough about fluid dynamics so take what I say with a grain of salt. It's just what I assume and I could be completely wrong.

 

[22802]

Not to disregard the effort but how are you going to achieve laminar flow in a systems filled with sharp corners and bends? If I am not wrong, in order to achieve laminar flow you need a pre-chamber that aligns the flows. You would then have a secondary chamber where you'd have the water passing linearly and exposed to CO2. Preferably that chamber would need to be slightly under pressure for efficiency. I don't know enough about fluid dynamics so take what I say with a grain of salt. It's just what I assume and I could be completely wrong.

Perhaps I should have avoided the word laminar, it was only intended to say that it is a flow of water, with a pocket of water above it, as opposed to a bubble column. The flow of the water is really not critical, laminar or some turbulence, the key thing is the interface surface from water to CO2 where absorption takes place.
I could have expressed myself more clearly I guess.

 

[Hanuman]

So in basic terms, increase the surface interface between water and CO2 just like your CO2 spray bar?

 

[22802]

So in basic terms, increase the surface interface between water and CO2 just like your CO2 spray bar?

Yes that’s it. With the Spray Bar I found how much surface interface is needed, and used that knowledge to scale up with the Horizontal Reactor. As we don’t need to juggle bubbles, just use a simple flow, everything becomes much easier 😊

 

[palcente]

There is no need for testing, there is really nothing that can go wrong.

Famous last words 😀 good luck 🙂

 

[KirstyF]

Appreciate @KirstyF , and I am aware that you have a big tank 🙂

Thanks for the clarification. 👍

I’m quite curious about how well this would work tbf!

I think you might need some kind of purge valve as the top half of the pipe would fill with air when first filled and tipping to release it could be a bit of a faff.

Also, it would need to be cleanable so fully sealing both ends would make that a bit of a ‘mare even with the inlet/outlet pipes for access, but there are a couple of plumbing gadgets that could be adjusted for that purpose I think.

I might just have a play with this, out of curiosity as much as anything. In fairness, I’m getting solid results from my two current reactors on 700ltrs so no desperate need for me, but I think I’m close to the max these reactors could offer and Co2 is a bit of a challenge in big tanks. This could be nicely scaleable and fairly easy to DIY, if it works well.

Might just be a little winter project for me. 🤔😊

 

[22802]

Famous last words 😀 good luck 🙂

Well, if you have any doubts, please share so that I can clarify.

I took pictures and estimated the surface area of CO2 bubbles and came to some new insights.

It appears that injecting CO2 in water is very easy to do, that was also for me an eye opener. Even for a big tank.
As a hobby we have developed several sophisticated approaches to doing something that could be simple, and it may take some time to unlearn and see again that simplicity sometimes works better than complexity 🙂

Note: of course the principle can be applied for small tanks as well. Take a Tupperware box, glue water inlet and exit and a CO2 line, a de-gas valve, and just place it under the canister. No need for a diffuser, no adjustments, no bypass, no mist, virtually no water flow reduction, no maintenance and always 100% efficiency.
For my 250 l tank, my CO2 Spray Bar has 200 cm2 surface area for a 1.6 pH drop if I want. So a 15*15 cm2 box, 225 cm2, would do, less than the cross section of my FX4 canister. (The good news for the vendors is that they can still sell high end regulators in that case, which would not be needed for CO2 Spray Bar)

Note: Changed title of the thread, as it occurs to me that small tanks may benefit equally.

 

[22802]

Also, it would need to be cleanable so fully sealing both ends would make that a bit of a ‘mare even with the inlet/outlet pipes for access, but there are a couple of plumbing gadgets that could be adjusted for that purpose I think.

If you keep it empty, I frankly do not see why you would need to open it for cleaning as there is no light there and also no pressure drops in the big tube even when some algae develop over time. Anyway, it doesn't hurt if you do 🙂

Now if you throw in some bioballs or similar biofiltration material, (@dw1305 approved 🙂), as bonus you'll get a significant bio filter volume as well. Doing so will not reduce the water to CO2 surface area, nor flow (we have a big tube diameter), so the reactor capacity remains intact.
In that case of course, you may want to open your horizontal reactor once in a while to refresh the biomaterial.


Amazon product ASIN B00HZSKZ0A

 

[LMuhlen]

Why do you want laminar flow in there? You could make it much more effective with some turbulence at the surface, allowing you to make it much smaller.

I don't think your spraybar operates at strictly laminar flow, the edge of the spraybar probably induces some turbulence, which may be significant since it is a very short path across its path.

 

[dw1305]

Hi all,

Now if you throw in some bioballs or similar biofiltration material, (@dw1305 approved 🙂), as bonus you'll get a significant bio filter volume as well

I think I would go for neutrally buoyant and plastic, so Bioballs, plastic washing-up scrunchies or "K1" type media. I'm not sure what effect the elevated CO2 levels would have on the scrunchies, so Bioballs or floating cell media might be safer.

You could make it much more effective with some turbulence at the surface, allowing you to make it much smaller.

That might be an advantage of adding Bioballs etc.

cheers Darrel

 

[22802]

Why do you want laminar flow in there? You could make it much more effective with some turbulence at the surface, allowing you to make it much smaller.

I don't think your spraybar operates at strictly laminar flow, the edge of the spraybar probably induces some turbulence, which may be significant since it is a very short path across its path.

That might be an advantage of adding Bioballs etc.

You are absolutely right 🙂

Perhaps I should have avoided the word laminar, it was only intended to say that it is a flow of water, with a pocket of water above it, as opposed to a bubble column

I would argue that any flow in the horizontal reactor creates already enough turbulence on the interface to maximize absorption (avoid a diffusion limited stagnant boundary layer). We are all in agreement here.

As absorption of CO2 in water is already efficient, we also see that it is hardly necessary to optimise the flow dynamics in order to get to sufficient CO2 absorption. Just imagine that a 15*15 cm2 Tupperware box could give you a 1.6 pH drop in a 250 l tank. Even if my estimation were 20% off, this is really a no brainer. Just oversize the reactor a bit so that it is guaranteed to have enough power for your tank, and have the whole system work and finetuned with the setting of the needle valve.

That might be an advantage of adding Bioballs

What I like about bioballs is that they will never clogg the flow, even if the flow messes with them. I would not put too many in, as the primary objective is to have a maintenance free CO2 reactor, and we're not looking for complications trying to make it a sump at the same time.

 

[Unexpected]

Hello all!

I recently purchased a new aquarium with the sole intension of selling my other tanks to simplify life and reduce maintenance load on my wife and myself. To go even further, I chose an all in one tank as I'm quite tired of lifting and cleaning multiple canister filters or forgetting to attach hoses after the canisters were turned on. General drips and splashes were getting old too. Long story short, the tank is running.

Now the problem I had, how to inject a larger tank efficiently. I crafted a 10 inch and 20 inch Cerges reactor for my older tanks and of course they worked well enough. I figured I would toss one of these in (20 incher) and all would be well. Wow, did 4 inches of DIY Cerges reactor look ugly sticking out of the back chamber. I was absolutely dead set on no equipment (containing water) be outside of the tank. Luckily, I found this topic!

I went to the hardware store and grabbed 25 dollars in supplies and here's preassembly. My tank is 70 inches long and could only make the pipe 39 inches because of space constraints within the overflow chamber. I chose 2 inch diameter pipe to compensate. I just used food grade silicon lubricant to seal the pieces together.

Here's assembled and in the tank.

I've only had 24 hours of operation, but my pH was 7.3 at CO2 on, and reached a peak of 6.24 with the injection rate I set. Not too bad for the first cycle and I can easily push harder.
22802 really helped me get this together and I can't thank him enough! Oh, and I had no CO2 purging at any time, so there's room to inject faster if I need to.

A few issues, but minor at best is a bit of trickle noise while injecting. I believe my pump is over powered and the construction reduces laminar flow. I'm positive this could be improved upon but my goals are met and couldn't be happier. This method works plain and simple, Cheap too. I just need to work out my ramp up and ramp down times.

Here's the operation of the tank and the trickle noise.



I'll update with any changes or developments.