Carbon capture and storage, or sequestration, is a frequent topic in the mainstream media and in the academic/professional/technical literature. Regardless of the technology employed, the goal is to remove, transport, and store CO2 before it enters the atmosphere – for the longest time possible (hundreds or thousands of years) – in order to reduce atmospheric greenhouse gas (GHG) levels.
Many carbon sequestration concepts include underground or ocean injection, although some experts have advised against using environmentally active carbon pools such as the oceans, since that may create new environmental problems. In my August 2020 column and again earlier this year, I discussed negative-emissions technologies that remove and sequester CO2 from the air. Unlike carbon capture that removes CO2 only from point sources, these technologies remove the CO2 directly from the atmosphere.
Carbon capture and utilization (CCU) differs from sequestration in that the CO2 is not stored, but instead is converted into useful products, such as plastics, chemical feedstocks, biofuels, or even concrete.
Last month, several researchers from the University of Michigan (UM), Dwarakanath Ravikumar, Gregory A. Keoleian, Shelie A. Miller, and Volker Sick, published a paper titled “Assessing the Relative Climate Impact of Carbon Utilization for Concrete, Chemical and Mineral Production” in Environmental Science and Technology. According to their estimates, by 2050 some 6.2 gigatons (13.6 trillion pounds, equivalent to the weight of approximately 62,000 fully-loaded aircraft carriers!) of CO2 can be captured across the three pathways the title suggests: concrete, chemicals, and minerals.
Since our firm is a partner in a general contractor company that does a lot of concrete restoration projects, the concrete potential really jumped out at me.
Concrete is the single most widely used material in the world, and it’s been around for thousands of years. The Ancient Egyptians had it and it was widely used by the Greeks and the Romans. The Greek Royal Palace in Tiryns, built in 1400-1200 BC, had concrete floors and the Romans built with it extensively from 300 BC to 476 AD. The Pantheon, 1900 years after it was built, still boasts the world's largest unreinforced concrete dome. Most of us in the HVAC industry probably pay little or no attention to the concrete pads, decks, and floors on which we set our AC equipment.
In their paper, the UM researchers present a “stochastically determined climate return on investment (ROI) metric to rank and prioritize CO2 utilization across 20 concrete, chemical and mineral pathways based on the realized climate benefit.” Their conclusion is that concrete production that uses CO2 during mixing generates a positive climate ROI, producing a greater climate benefit than burden.
Now I’m hoping that after my wife reads this, she’ll let me use concrete for our new kitchen countertops!
A regular contributor to HPAC Engineering and a member of its editorial advisory board, the author is a principal at Sustainable Performance Solutions LLC, a south Florida-based engineering firm focusing on energy and sustainability. Email him at [email protected].