Efficient carbon dioxide recovery using microbubbles

Background

Many industrial processes produce carbon dioxide (CO₂) as a by-product. This CO₂ needs to be captured and managed. Ideally, the captured CO₂ should be repurposed for high-value uses to make the overall process as cost-effective as possible.

The two biggest challenges related to carbon dioxide capture and re-use are cost and scalability.

• $100 total cost per tonne of CO₂ captured and stored has been cited as a realistic target to mitigate climate change.
• Any carbon capture process needs to scale efficiently, both technically and economically, so that it can be deployed in a wide range of industrial processes.

Microbubble magic 

At the University of Sheffield, a team has developed a process that utilises microbubbles for capturing and releasing high-purity CO₂ from off-gas streams. These microbubbles, which typically have diameters in the range 0.01 - 0.1 mm, are uniquely beneficial in this regard. Using our fluidic oscillation process, we are able to generate specific sizes of bubbles uniformly, without turbulence and with very low power consumption. In this way, we can tailor the bubble size for the optimum capture and purification of CO₂ through interfacial transport at the surfaces of the bubbles.

Application: anaerobic digestors

The team's initial focus is on the recovery of CO₂ from the off-gas streams of anaerobic digestors. This is because biogenic CO₂ does not typically have the trace levels of carcinogens found in fossil fuel combustion exhausts, readily allowing for high-purity capture and human food chain entry.

• Modular process that readily scales to any scale, including large industrial use, but also anaerobic digestor volumes.
• Low power consumption.
• Increased product rate - by injecting pure CO₂ microbubbles for only 5 minutes per day, anaerobic digestor production rates in laboratory testing and pilot scale trials with wet food waste feedstocks have been more than doubled.
• The high-purity biogenic CO₂ that is captured can be used for fine chemicals or beverage production. Other potential uses of the captured CO₂ include food preservation and fertilisers.
• The operating cost is estimated to be only $3-$18 per tonne of CO₂ purified, depending on scale and purity requirements.

Application: cement, brick and tile manufacturing

Processing plants for cement and related products are notoriously high CO₂ producers. The CO₂ released from the calcination of limestone is sufficiently pure (no carcinogens) that it can enter the human food chain in food ingredients. The sector is pursuing sinking CO₂ with polycarbonate cements, but, as far as we know,  uses in fine chemicals, food, feed, and fertiliser have not been explored.  

We are interested in exploring potential synergies for our CO₂ capture and utilisation with cement production.

Application: post-combustion capture

Post-combustion capture, more recently and widely termed direct air capture, is a crowded market with many promising technologies, most of which only have potential for large industrial-scale production.  With trace carcinogens an issue from the combustion of fossil fuels, the purity requirement for higher value-added food, feed, and fertiliser production is problematic. 

Our advantages of material efficiency (losses of carbon capture fluids are minimal), low power consumption, low OPEX and potentially low CAPEX (by inference from parallel applications of our technology at pilot scale) should translate to highly competitive, low-cost carbon capture. Given the scale of post-combustion CO₂ production, whether our co-products can make the overall capture and utilisation process profitable requires more investigation. Hence, our initial focus on anaerobic digestion and cement markets.