Sequestering Biomass for Natural, Efficient, and Low-Cost Direct Air Capture of Carbon Dioxide (Version 2)

Abstract

Many corporations and governments aspire to become Net Zero Carbon Dioxide by 2030-2050. Achieving Net Zero CO2 requires understanding where energy is produced and consumed, the magnitude of CO2 generation, and the Carbon Cycle. It is unreasonable to assume that fossil fuel can be completely replaced, and thus, atmospheric CO2 will continue to accumulate. Many prior proposed solutions focus on reducing future CO2 emissions from continued use of fossil fuels. Examination of these technologies exposes their limitations and shows that none offer a complete solution. Direct Capture technologies are needed to reduce CO2 already in the air. However, some of those already proposed would lead to a very high cost of Carbon Capture, Use, and Storage (CCUS). Biofuels can help achieve reduction goals. However, two of the six carbons in sugar fermented to bioethanol produce CO2 per the stoichiometry of the reaction. Four carbons go to ethanol, which go back to the atmosphere upon burning in an engine. Thus, without CCUS, which most current bioethanol plants do not practice, bioethanol would at best be sustainable. The only way to permanently remove CO2 already in the atmosphere is to break the Carbon Cycle by growing biomass from atmospheric CO2 and permanently sequestering that biomass carbon. Permanent sequestration can be achieved in landfills modified to discourage biomass decomposition to CO2 and methane. Sequestration of biomass carbon is proposed as a simple and natural means of Direct Capture. Tree leaves are proposed as a good source of biomass for this purpose. Left unsequestered, leaves decompose with a short Carbon Cycle time constant releasing CO2 back to the atmosphere. Leaves represent a substantial fraction of the total biomass generated by a tree when integrated over a tree’s lifetime. High yield crops, such as switchgrass would also be a good source of biomass. The cost for growing switchgrass and sequestering it in a landfill is estimated to be on the order of $120/mt CO2 for a conservative yield of 3.5 tons/acre and may be reduced to as low as $88/mt CO2 if the development of high yield switchgrass is successful. This compares to an estimated cost of CCUS from the Steam Reforming of Methane to produce hydrogen of about $190/mt. Thus, sequestration of biomass is shown to be a natural, carbon efficient, and low-cost method of Direct Capture.