Carbon dioxide supply and scaling constraints on direct air capture using calcium oxide powder
Bibliographic record
Abstract
Calcium oxide (CaO; lime) looping is a carbon dioxide (CO 2 ) removal technology that can mitigate carbon emissions. However, scaling this technology requires a thorough understanding of the rate-limiting effects of CO 2 supply on CO 2 removal rates at and below atmospheric CO 2 concentration levels, as well as with various CaO thicknesses and plot areas. Here, we show that carbonation is readily limited by CO 2 supply even under high flow rates (e.g., 25 mmol CO 2 /h over 100 g CaO). Subsequently, the CO 2 capture efficiencies using CaO and Ca(OH) 2 powders were investigated under ambient CO 2 concentrations (397–490 ppm) to 100 ppm. Ca(OH) 2 carbonation rates increased exponentially with increasing CO 2 concentrations, e.g., 2.1 wt% CaCO 3 /h at 100 ppm compared to 5.2 wt% CaCO 3 /h at ambient CO 2 concentrations, thereby demonstrating the impact of CO 2 concentrations on carbonation efficiency. Column experiments determined CO 2 diffusion limitations for CaO deposits ≥0.5 cm, yielding 64 ± 2 wt% CaCO 3 and an average CO 2 removal rate of 32 kg CO 2 /m 2 /yr (24 days; 85–95% RH). Finally, the CO 2 removal efficiency of CaO plot areas was estimated, revealing the importance of scaling CO 2 supply in concert with increasing CO 2 removal that results from greater thicknesses and masses.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".