How is a CO2 reactor suppose to work?

**vinz** · 2nd Apr 2003, 13:06

Something that crossed my mind sometime ago.

This is with regards to the CO2 reactors that have bioballs in them.

According to the diagrams on the boxes, the balls are suppose to spin and stir up the CO2 and thus dissolve them more effectively. But what if, the original design of a CO2 reactor was for the bioballs to provide more surface area to encourage gaseous exchange between the water and gas in the reactor... much like a wet-dry or trickle filter?

The design of the ones we get in the LFS does not really allow for the wet-dry effect, as the inlets are designed to make the water flow round the wall and not fall directly onto the bioballs.

This is for pondering and general discussion.

**juggler** · 2nd Apr 2003, 15:25

Got a point.
Initially I thought the bioballs must spin to help the CO2 dissolve. When too much of my DIY CO2 went into the chamber, the bioballs stopped spinning. So I removed 2 and left 1 of the bioball in there to spin.

Here's a pic of the reactor:

**bclee** · 2nd Apr 2003, 15:58

Actually I feel Dennerle's design may give better results due to the counter-current flow.

The CO2 is injected from below and the water flow from the top. The CO2 bubbles contact the water as they slowly spiral upwards. At the top of the reactor, the bubbles will get drawn in the water jet and breaks into small bubbles.

BC

**vinz** · 2nd Apr 2003, 16:04

The thing is, I'm wondering if the spinning is really effective... how much CO2 bubbles actually get drawn under water? In the one ball version... the atomiser is so long that if you keep the water high enough for the ball to spin, its not near enough to the water surface. In the 3 ball version, what is the bottom 2 for?

Wonder how much thot or testing the manufacturer put into this product?

**hoppinghippo** · 2nd Apr 2003, 16:04

vinz: i dont think that was the orginal intent for having the balls, cuz else the surface area is limited to surface area of the balls and that is assmuming co2 and water meet exactly at the surface are of the ball....hhmmm hahah lost? I also.... what I mean is where water meets co2 there will be diffusion, even in the form of surface area on co2 bubbles in the water. without the bioball, the only surface area would be the co2 layer-water interface. but with bioball and without spinning, the only extra surface area increase is in turbulence where co2 bubbles form. but this is very limited and can't be attributed to the design of bioball cuz any interference can produce it. BUT if the ball spins, it not only creates turbulence, but the spiraling effect actually draws co2 bubbles further down the water hence increasing surface area again.

**vinz** · 2nd Apr 2003, 16:18

Hippo,

If the water level is low (i.e, the balls are exposed to the gas in the reactor) and the water falls on the bio-balls, there is more surface area than the small bubbles and water surface combined in the manufacturer-intended operation. Assuming, that the gas inside is almost entirely CO2, the greater surface area should allow for greater gaseous exchange.

However, this reactor is not designed to work like that, as the water will be flowing down and across the walls.

Hmmm... if only I had a spare CO2 tank to test this.

**ZeRoC00l** · 2nd Apr 2003, 22:15

I run mine the opposite direction.

I swop the top and bottom pieces.

&gt;&gt;&gt; The CO2 now comes in from the bottom of the reactor, and slowly rises to the top of the reactor.

&gt;&gt;&gt; Reason: to increase the contact time betwn CO2 and water.

&gt;&gt;&gt;&gt; I find tt the balls run freely for 1-2bps for mine.

**bclee** · 3rd Apr 2003, 09:49

Zerocool's method is good. Gives more contact time as the CO2 bubble rises through the bio balls.

This reminds me of the packed column used in chemical/petroleum industries.

The whole column is filled with packings(similar to bioballs). The difference is that the whole column is filled with gas and the liquid will trickle down through the packings contacting and absorbing the gas. This maximises the contact surface area btw the gas and liquid. Thus, you'll get a very high rate of absorption.

BC

**hoppinghippo** · 3rd Apr 2003, 14:01

zerocool: that's a really smart idea!

vinz: yes but if that is the case, assuming the ball is half floating and half exposed to co2, the water hitting the ball does have more surface area but only at part of the ball and not the whole ball, ie only the exposed part of the ball which has water splashing on it. unless you can ensure water splashes on the whole ball, else it won't optimise the whole ball.

**vinz** · 3rd Apr 2003, 16:11

Ok, let's clarify... I'm not saying that this reactor is supposed to work like a wet-dry. In fact, I specifically said that this reactor is not designed to work as a wet dry style.

What I'm trying to say is that maybe the earlier ideas for a CO2 reactor was to work like a wet-dry. The manufacturers have either purposely or unknowingly modified the actual way it was meant to work.

**bclee** · 3rd Apr 2003, 16:15

I am toying with the idea of replacing the bio balls will smaller ones or even ceramic rings. Fill the column with CO2 and let the water splash over the packings.

I wonder whether that will work.

BC

**vinz** · 3rd Apr 2003, 17:01

BC, you'll need to divert the water or convert the nozzle to spray/trickle over the media.

**juggler** · 3rd Apr 2003, 17:14

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On 4/3/2003 4:15:40 PM

I am toying with the idea of replacing the bio balls will smaller ones or even ceramic rings. Fill the column with CO2 and let the water splash over the packings.

I wonder whether that will work.

BC
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It may affect the efficiency of the filter with this added resistance.

**geoffrey** · 3rd Apr 2003, 17:58

Remove all the bio-balls. Fill it up with ceramic rings will help. Make sure the chamber is half filled with CO2 too, so that gaseous exchange can occurs between water and gas trapped in cavities of the rings. The more the chamber is filled with CO2, the more the gaseous exchange takes place.

**ZeRoC00l** · 3rd Apr 2003, 22:34

&quot;Remove all the bio-balls. Fill it up with ceramic rings will help. Make sure the chamber is half filled with CO2 too, so that gaseous exchange can occurs between water and gas trapped in cavities of the rings. The more the chamber is filled with CO2, the more the gaseous exchange takes place.&quot;

&gt;&gt;&gt; I've tried this method, however the problem arises at night when there is still a colume of CO2 left undissolved into the water. Well, turning off the CO2 earlier could solve this. Also, sometimes if there is too much pressure, at least in my case, my top cap burst out..

&gt;&gt;&gt; IMO, I still prefer the reverse bio ball spinning method I've seen around. Dissolve the CO2 faster. At least tt is what i &quot;see&quot; in my tank.
[

]

&gt;&gt;&gt; Just try out a few method around, and see which seems the most effective to you. No harm trying.. well, maybe just waste a few cents of CO2, and getting your hand wet.

&gt;&gt;&gt;&gt; I would like to hear other methods, cos I have only seen a few:
co-current bioballs
counter current bio balls &lt;currently my method&gt;
co-current bio rings
flipper ?? falpper?
inverted colume

Care to share?

**bclee** · 3rd Apr 2003, 23:07

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On 4/3/2003 10:34:11 PM

I've tried this method, however the problem arises at night when there is still a colume of CO2 left undissolved into the water. Well, turning off the CO2 earlier could solve this. Also, sometimes if there is too much pressure, at least in my case, my top cap burst out..

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Zerocool, I always tot that excess CO2 will just be expelled by the water outlet. I dun quite understand how the pressure build up.

Only reason I can think of is the bouyancy that force the top cap open rather than pressure build up. That can be solve easily.

BC

**geoffrey** · 4th Apr 2003, 09:22

In addition to BC, after filling to the level you want, you should also lower your bps so that the CO2 level ( be it 1/4, 1/2 or 3/4) in the chamber is maintained instead of letting it build-up with the initial higher than normal bps needed to quickly fill up the chamber.