Direct Air Capture

Direct Air vs Point Source Capture

There are four main types of carbon capture & sequestration (CCS) techniques recognized today. The most well-known is afforestation / reforestation. There are other nature based as well as bioenergy CCS methods, but all require a large area of agricultural land to sequester a significant amount of CO2. However, there are two technologies that are able to capture and store large amounts of carbon with a very small geographic area: Direct Air Capture (DAC) and Point Source Industrial CCS.

The difference between the two – as their names suggest – is where the carbon is being pulled from. It’s either sucked directly out of the atmosphere or obtained from an industrial facility. Each comes with its own technical applications, footprint, and costs.

In our previous piece, we discussed the origin of carbon capture and storage. Traditionally CCS has been installed to capture point source emissions from a variety of industrial facilities – natural gas processing plants, fertilizer manufacturing facilities, power plants and more. The capture, transport, and storage technologies used in these projects have been around for decades and are considered safe and reliable.

Point Source Capture

With Point Source, there are three main types of capture methods: pre-combustion, post-combustion, and oxyfuel combustion. The type of method used is based on the existing process and current infrastructure.

The post-combustion carbon capture method is a great choice for established plants with the goal to reduce their CO2 emissions. The capturing and separation process comes from the gases emitted from the flue stack. The advantages of this method are that capturing equipment can be added to an existing plant without having to change the plant’s design with limited or no interruptions to the plant’s operations. Pre-combustion and oxyfuel combustion capture methods have to be considered in the construction of a new plant or large changes will need to be made to the design of an existing plant.

Pre-combustion capture generally refers to separating CO2 from a fuel prior to burning the fuel for energy. These projects are typically deployed at industrial facilities that produce a large quantity of high purity CO2, such as some natural gas processing plants and ethanol production facilities. Pre-combustions projects are often the least expensive on a unit cost basis due to higher separation efficiency (higher CO2 partial pressure), smaller equipment, and lower energy costs.

Post-combustion capture is usually the main option for coal-fired or natural gas-fired power plants that need to capture their CO2 without decreasing the overall power generation capability of the facility. Flue stack emissions are collected, and CO2 is captured from the flue gas stream. These projects are often more expensive than pre-combustion given the lower CO2 content and pressure of the flue gas stream. Post-combustion projects were developed at the SaskPower’s Boundary Dam plant as well as NRG’s PetraNova plant, and future projects are expected to leverage learnings from these projects to continue to lower project costs.

Direct Air Capture

The newest type of capture is called Direct Air Capture (DAC); which is a process of pulling carbon dioxide directly out of ambient air. Surprisingly, the basic idea for this method was the result of an eighth-grade science project. Geophysicist Klaus Lackner discovered with his daughter that CO2 could be captured from the air in an acid/base reaction using a fish pump and sodium hydroxide. The device captured half of the CO2 in the test tube; which led Lackner to research large-scale capture of atmospheric CO2  as an approach to mitigate climate change.

“I believe that it is impossible to stop people from using fossil fuels,
so we have to develop technologies which allow us to use them
without creating environmental havoc to the planet.”

Geophysicist Klaus S. Lackner

To extract CO2 from air, a DAC facility employs large fans that pull atmospheric air through its system. The air goes through a series of non-toxic chemical reactions that binds the CO2 molecules and separates them from the air. The rest of the air is released back into the environment while the CO2 is processed into a pure, compressed form that is can be securely stored underground in deep geologic formations.

DAC has several benefits over traditional carbon sequestration methods. Carbon Engineering (CE), a global leader in DAC technology, has designed a DAC process that requires 100x less land and 200x less water than nature-based carbon removal solutions. One CE DAC facility can capture one million tonnes of CO2 per year – equivalent to the work of 40 million trees. These plants can also be located on almost any type of land while nature-based and bioenergy CCS methods require arable land.

Unlike Point Source, DAC does not need to be located near an emissions source since the concentration of CO2 in ambient air is almost equal all over the planet. Rather, DAC plants can be constructed as close to the injection site as possible, reducing or eliminating CO2 transportation / pipeline infrastructure needs.

The beauty of DAC is that anyone can offset his or her emissions by investing in and/or purchasing carbon removal credits from a DAC plant. Carbon removal credits from technological removal solutions like DAC are considered the highest-quality carbon credit. These credits can be pre-purchased through subscriptions with DAC technology companies as well as from some DAC plant developers, like Black Mountain. Though these types of credits are a small segment of carbon markets, they will soon play a much larger role in the overall decarbonization of the hardest-to-abate industries.

You can learn more about carbon credits here:

Carbon Credits 101