Summary of UT Austin Carbon Farm

Hello all !

I think this may become a bit of a running document, so bear with its basic bones for now.

TLDR: This post is meant to recap and contain the DAC work done for the Carbon Farm, a sculptural DAC device built initially as a senior design project by mechanical engineers at UT Austin. Everything is included in this google drive folder. The first document UTME-Sculpture-23SP-FinalReport is a 142 page document overviewing the design decisions that myself and my engineering team made creating our direct air capture device. The report is broken down into sections: sorbent, contactor, heat exchange, algal photobioreactor, controls and sensing, fabrication, recommendations, and an extensive appendix. Beyond that, there are three other documents specific to our sorbent analysis. The first is Calf20 James Calcs, which is our analysis of a preeminent physisorbent CALF20; the document demonstrates how hard it is to get a positive working capacity from a DAC physisorbent (if looking for a pure CO2 outlet). The next is Comparing Sorbents Matrix which goes over some of our potential sorbent candidates and qualitatively evaluates them. Last is our Cost Comparing the Bigguns which models the amount of CO2 capture each of our top sorbents can provide for a given constrained volume, and the cost of that amount of sorbent. Aside the report, the excel sheets are poorly documented, so I am happy to have any larger more relevant conversations about them.

For a longer description of the Carbon Farm, it’s intention, function, and shortcomings, I offer the below:

The Carbon Farm is a part of the work of the Negative Emissions Technology Project’s Direct Air Capture (DAC) subteam, constructed alongside the help of 3 of UT Mechanical Engineering’s finest undergraduates. This project has been the culmination of so many different contributions across my four years in college, and it’s been a complete dream come true to see this come to fruition. I am beyond thankful for all of the help that I’ve received and the paths taken to get here. First, I’ll provide a summary of what the Carbon Farm is, what it does, and why it exists.

Under normal operation, the unit uses a fan to pull ambient air in, contacting the air with a chemical sorbent that reacts with the CO2 present at 400 parts per million in the air. This sorbent is suspended at the widest part of the hourglass shape which houses an electric resistive heater coil within it. During this first stage, air flows vertically through the metal hourglass system, coming out of the bottom with a lowered concentration of CO2. The second stage, desorption, involves activating the heater within the sorbent bed to release collected CO2 from the sorbent. This creates an air stream with a high concentration of CO2, which is then pumped into the 6 algae photobioreactors surrounding the metal hourglass, or contactor. In response to this heightened partial pressure of CO2, the algae increase their uptake rates, ultimately leading to a higher, more efficient rate of carbon sequestration per land area by the algae. Paramount in importance to this system, though, is what is done with the algae after it is grown; since left to rot, any CO2 fixed by the algae will be metabolized by microbes back into CO2. In such a case, the device will have achieved nothing in terms of carbon removal and instead have used an excessive amount of electrons to open valves, turn on fans, and make metal hot. As such, this system will utilize our harvested algae to create durable bioplastics, 3-D printable algae-based PLA, or algae-based garments, all showcased around the sculpture. Two collaborators, Siyu Fang and Ceren Ozgen, respectively created the bioplastic sheath around the microphone, the beautiful hanging hanfu garment (a fully wearable piece of clothing made from algae !!), and all of the other samples around the sculpture.

Speaking of the microphone, let’s get into the interactive component of this sculpture. While the Carbon Farm is collecting CO2 from the ambient atmosphere, individuals can also contribute their own higher concentration input stream of CO2. Participants are asked to take a bioplastic straw, insert it into the microphone, and then exhale their breath into the Carbon Farm. Using flow and CO2 concentration sensors, the device calculates the grams of CO2 provided by an individual, an estimate of that CO2’s conversion into algae biomass, and, last, a comparison of one’s contribution to the emissions associated with the production of a hamburger. As an example of some average values, after blowing into the device, the LCD screen could read “CO2 contributed: 0.4 grams”, then “algae biomass produced: 0.2 grams”, and finally, “blowing 20,127 more times would offset one hamburger”. To note, the emissions associated with a hamburger are purely for a ¼ pound of beef, not including any other parts of the burger, the emissions associated with the restaurant, transportation, or anything else. The adsorption stage in normal DAC operation would transition to desorption once the sorbent had reached CO2 saturation; however, in this system, desorption is triggered by having two participants contribute their CO2. The number of participants who have gone (0, 1, or 2) is tracked visually by different colors of the LED lights ringing the algae photobioreactors.

The point of this device is multifaceted. Its first and primary goal is to bring awareness about carbon removal, the need for it, and its shortcomings. Research indicates that there is a discrepancy between the perceived carbon intensity of actions and their actual carbon ramifications, especially prevalent in dieting choices. This is part of the reason why we chose to provide participants with a physical awareness of how carbon-intensive an item like a burger can be. Another goal was to make tangible an invisible gas. It’s difficult to connect the massive terraforming ramifications that CO2 has to the odorless, colorless, invisible gas, and as such, the Carbon Farm visually—through algae—represents captured CO2 while also providing participants with a physical perspective. To contribute one’s own breath, participants must overcome flow resistance and push air into the system, providing weight to the exercise. Carbon removal is predicted in 2050 to utilize 1% of the world’s total final energy, 6% of the world’s total arable land, and make up 3% of the world’s total global water demand. Given that carbon removal provides an intangible public good that is notoriously difficult to capitalize on and can be potentially misused to justify less stringent commitments to decarbonization, there is a serious case for public understanding and support of the subject. The sculpture’s description serves to further this goal: “It’s important to note that carbon removal, in its current form, is not a comprehensive solution to climate change. Carbon removal is only useful in creating a net-neutral world if there are massive amounts of emissions mitigation from world leaders, companies, and consumers. Though a necessary tool, carbon removal cannot be used as an excuse by nations as a false panacea providing the moral ease of mind for our fossil fuel addiction. For perspective, one would need to capture every breath into the Carbon Farm for an entire year to offset the personal carbon footprint of a one-way flight from Austin to Denver.” The sculpture’s full description is linked below.

The thesis for this device’s creation is rooted in literature, and with that, I’d like to briefly mention some of the most important arguments guiding the Carbon Farm’s creation. The motivating question that created the Carbon Farm was: what role does the general public play in carbon removal coming to scale? To my surprise, Buck 2016: offers an explanation and review of the current literature’s neglect of public acceptance as a major barrier for implementation of CDR, marking this as an understudied potential issue. Given this looming issue and the general lack of public knowledge about carbon removal, studies after this begin to investigate how public awareness can be raised, and a social license to operate secured. Bellamy and Raimi 2023: synthesize the success and failures of different studies attempting to measure public acceptance of CDR after different methods of education. This article details the mitigation salience reduction hazard, which describes how poor communication of CDR can actually dampen people’s support for mitigation efforts, due to an overestimation of the potential of CDR. Scott-Buechler et al. 2023: offer a wonderful focus group study that demonstrates the effect of dedicated education on a DAC system. It shows that upon education, people became more supportive of DAC within their nation, near their community, and in their community. Shrum et al. 2020: take a more low-level investigation of social psychology behavioral frameworks to understand how publics might coalesce opinion about CDR, guiding my thinking in the ultimate communication, design, and embodiment of the Carbon Farm. Last, Sommer et al. 2019: demonstrate the efficacy of a project called “pollution pods” which tries to evaluate the effectiveness of climate art in motivating climate action. All this research—and certainly more—helped to guide, motivate, and shape the direction of the Carbon Farm and my thesis at large.

There is so much more to be done with this system still. One of the first things to note is that we have not yet utilized any of the algae grown in our photobioreactors (in part because it’s in China and that’s kind of far away). This means currently that this system is massively carbon-positive in its operations, as it is utilizing nonrenewable energy to do work that doesn’t durably sequester CO2. Second, many of the components in the Carbon Farm were manufactured in China, shipped to Austin, built here, and then flown back to China in a 70-pound duffle bag. Boy, are there a lot of emissions there, too. I say this to be brutally honest: the Carbon Farm has racked up a massive carbon debt over its short life, despite its existence as a “carbon removal” device. Now, you might think this means that this is a useless endeavor. Well, the point of the Carbon Farm wasn’t to remove the most amount of CO2 possible; if that were the case, then we failed miserably. Again, this system is intended to serve as an educational tool. As such, one of the next steps that I envision for it is a genuine and honest tracking of its emissions contributions, which in perpetuity can be made negative. If this device can inspire more sustainable behavior, future careers in carbon removal, or civic support for green initiatives, then it serves its purpose. As an engineer, the less quantitative nebulous benefits are difficult to hold up against cold hard emissions, and it’s a tradeoff to be cognizant of. It’s a tradeoff that I hope (and think) was worth it. I hope to also not think about this device in solitary. I will be reaching out to different experts in the CDR space, some of the authors already mentioned here, as well as other climate artists to source feedback, opinions, and advice on the project. We’ve built a springboard for collaboration, and I can’t wait to see what sticks.

The sculpture’s description: Carbon Farm — Jiabao Li 李佳宝
(as a note, some of the ideas discussed in the description here are more on the speculative side for future integration)

The exhibition’s description: Progenitorial Hysteresis — Jiabao Li 李佳宝