Scaling DAC: Learning from age-old industrial design principles
Image: Chemical plant
What will it take to scale Direct Air Capture? Look to what has worked.
Direct Air Capture may be new, but process engineering - and the principles that govern its application - is grounded in centuries of theory and practice.
In this post, we discuss key concepts from process engineering (continuous & batch processes, modularity, and economies of scale), and how using these principles early in the Direct Air Capture technology design process can unlock fundamental cost advantages compared to other approaches.
Continuous vs. Batch Processes: a Critical Decision Point
A key starting point for any process design is choosing between a continuous or batch approach.
Batch processes move discrete “batches” of material through a production line. While this approach gives operators the flexibility to stop equipment or modify conditions as needed, it comes at the cost of batch-to-batch variation, increased need for inspection and human intervention, and time wasted resetting equipment in between runs. These trade-offs are best suited for low-volume, high-cost industries, like pharmaceuticals and specialty chemicals, where complexity and the need for customization is high.
Continuous processes, in contrast, run nonstop, with a constant, “steady state” flow of materials moving through a fully automated system. This approach maximizes capital utilization while also minimizing variation, allowing fixed costs to be spread across the largest possible volume of outputs. Continuous processes are typically found in high-volume, low-cost industries, such as fuels and commodity chemicals, where aggressive unit economics are essential in gaining a competitive edge.
Applying this Concept to DAC
For DAC to move the needle from a climate perspective, it needs to reach million ton per year or even billion ton per year scale. That can only happen if prices fall far enough (and fast enough) to entice buyers. This type of high-volume, low-cost scenario is precisely where the economic advantages of continuous processes stand out.
Economies of Scale and Modularity: Finding Balance
Another key to designing the lowest-cost DAC approach is finding the best way to leverage economies of scale and modularity.
Economies of scale refer to cost advantages that occur as production output increases. Sometimes these advantages arise from efficiency and scaling laws rooted in physics; for example, pipes, fans, and storage vessels become more economical the larger they get. Other benefits derive from larger firms exerting negotiating power to secure attractive financing terms and bulk pricing, or having the resources to hire specialized workforces.
Modularity, by comparison, is a design principle that considers how large systems can be assembled from smaller “modules” (self-contained, standardized units) that can be independently created, modified, and exchanged. This allows module-level improvements to be developed and implemented in the system in parallel, for faster learning rates and lower-cost system innovation.
The concepts of economies of scale and modularity become especially powerful when combined. As large firms use mass production to drive down the cost of standardized modules, systems using those modules can benefit from a virtuous feedback loop of improved performance, decreased costs, and faster learning rates. These feedback loops are at the root of the success of mass-scale production of automobiles, semiconductors, and most recently, solar panels.
Applying this Concept to DAC
Some DAC companies are proposing fully modular deployments consisting of vast arrays of interlinked units built around centralized sequestration infrastructure. While there is no doubt that mass-producing these modules would lower manufacturing costs at the unit level, we must consider the practical implication of interlinking these modules in a final plant concept. Each module would require dedicated piping, power, and monitoring. Smaller diameter fans and pipes in these systems would fail to leverage the physical scaling laws that improve the economics of larger systems. And the increased number of parts in these systems increase the need for maintenance and human intervention, increasing labor costs and the potential for human error.
Instead, DAC technology developers should seek to leverage economies of scale and modularity in a practical, targeted way, to lower costs across the entire system. For example, DAC processes using mass-produced air-liquid contactors are effectively modularizing one part their process by allowing drop-in solutions to improve cost and performance. Finally, project developers can adopt plant-level modularity concepts like "copy exactly," as used in the semiconductor industry, as DAC technologies mature and large plants are built.
A Strategic Path Forward for Cost-Effective DAC Deployment
Design for Continuous Processes: DAC approaches using a continuous process will have improved capital utilization as compared to batch approaches. Capture agents that can flow through the system, especially liquids, also offer a more promising path than immobilized sorbents for continuous DAC processes. While batch processes may be sufficient for pilot-scale projects, maintaining a clear roadmap to continuous processing at commercial scale will prove essential.
Find Synergies between Economies of Scale and Modularity: DAC approaches should use economies of scale and modularity in a balanced way that maximizes the benefits of each. For example, using larger fans, pipes, and storage vessels in a plant concept leverages physical scaling laws that smaller, “containerized” systems cannot. At the same time, mass-producing standardized components like air-liquid contactors can help drive down the costs of DAC while improving learning rates and system performance. Modular concepts like “copy exactly” can also be applied at the plant level as the field matures.
Use Systems Thinking to Unlock Compounding Benefits: DAC technologies will see the most cost improvements when the principles described above are applied in a balanced way - in proportion to their benefit, and in alignment with each other. To do this, we can learn from the ways production has evolved in high-volume, low-cost industries, where continuous processes are run in large, centralized plants using modular design where possible.
DAC technology developers should consider these design elements long before honing in on individual unit operations or materials. By incorporating these process design fundamentals, developers will have the best shot at achieving a cost effective process, and in turn to make the largest commercial and environmental impact possible.
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