David's Cyan: First run and progress

Having finally received all the parts and materials, I built and tested my first “Cyan Lite”, which is the small box of Dahl’s original design without the larger box, fans, etc.

I followed Dahl’s instructions (Home · openair-collective/openair-cyan Wiki · GitHub) as closely as possible, with two exceptions:

  1. I used a different, smaller hummus container because we have not finished the Sabra hummus. This one has a lid diameter of about 4.75 in. vs. 6 in. for the Sabra.
  2. I used a different brand of Hydrated Lime, because I don’t have room to store a 10-pound bag. The composition should be similar.

The completed, operating Cyan box:

I started with 12.98g of hydrated lime, instead of the usual 10g (after I accidentally put too much in, I decided not to risk making a bigger mess by scooping some out).

I ran the “wet” part of the process for 15 hours. Then I shut off the pump, and moved the material and coffee filter to the top of the box to air dry. I ran a floor fan on low from a few feet away to create a gentle breeze, and periodically weighed the material. Here’s how it looked when it had fully dried:

I periodically weighed the paper and material until the weight reached a minimum, indicating that the powder was completely dry. This took about 13 hours. After that, the weight started increasing by very slight amounts as I watched for a total of 24 hours. Evidently, the chemical reaction was still proceeding, albeit slowly, even in a dry environment.

The final weight of the material (less filter) was 14.441g, which works out to an increase of 11.3% over the starting weight. Total CO2 captured was
(14.44g - 12.98g) * (1.693 g/g) = 2.47g.

The CO2 capture proportionally to the material supplied was slightly less than Dahl’s result, which I attribute to the fact that I used too much material, so it was piled deeper and provided less surface area.

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Excellent graph and results! I’ve also seen the reaction proceed even after several days past reaching a minimum in weight. This is likely due to CO2 making its way through the passivating layer of CaCO3 around the grains of Ca(OH)2, forming new CaCO3 beneath the passivating layer. This is a much slower process due to the greater distance the CO2 has to diffuse and the lower availability of water now that the powder is dry. In concrete, the carbonation of Ca(OH)2 can take years as a result.