Affordable CO 2 negative emission through hydrogen from biomass, ocean liming, and CO 2 storage

Abstract

A new process to remove carbon dioxide (CO₂) from the atmosphere, by combining commercial industrial technologies with ocean liming and CO₂ storage, is presented. The process aims to overcome the limiting factors of other negative emission technologies (cost and energy requirements, potential competition for land and freshwater) while simultaneously addressing the problem of ocean acidification. The overall proposed process is based on the following: (a) a gasifier where the biomass is converted to syngas; (b) a thermal steam reformer working at high temperature where the hydrocarbons and tar oils are converted to hydrogen (H₂) and carbon monoxide (CO); (c) a kiln to produce Ca(OH)₂ (slaked lime) from limestone by using the enthalpy of the hot syngas; (d) the spreading, by means of vessels, of the slaked lime into the seawater to achieve ocean liming; (e) the delivery of syngas to a water gas shift reactor producing CO₂ and H₂ that are then separated; (f) the final storage of all CO₂ produced in the process; (g) the use of H₂, being the valuable by-product of the whole process, for decarbonized energy production as well as for ammonia synthesis, offsetting part of the production cost, thus generating "low-cost" negative emissions. The mass and energy balances show that the total atmospheric CO₂ removed by the process is 2.6 ton per ton of biomass used. By adding an estimated 0.43 ton avoided—thanks to the use of produced H₂—the overall CO₂ benefit of the process increases to 3.0 ton per ton of biomass. A preliminary cost analysis resulted in an average levelized cost of 98 $ per ton of CO₂ removed; when considering the revenues from the produced energy, the cost falls to 64 $/tCO₂. The higher efficiency in carbon removal obtained allows to reduce the amount of biomass required by BECCS (bioenergy with carbon capture and storage) to achieve negative emissions, and thanks to the valuable H₂ produced it lowers the costs of CO₂ removal from the atmosphere.

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