Affordable CO2 negative emission through hydrogen from biomass, ocean liming and CO2 storage

A new patented process that allows the removal of CO2 from the atmosphere, combining industrial technologies already available 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) and at the same time addresses the problem of ocean acidification. The overall proposed process is based on: 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 H2 and CO; c) a lime kiln that exploits the enthalpy of the hot syngas to produce CaO from limestone, then converted in Ca(OH)2 (slaked lime); d) the spreading, by means of vessels, of the slaked lime into the sea water to achieve ocean liming in proper locations where local impacts are minimized; e) the delivery of syngas to a water gas shift reactor producing CO2 and H2, that are then are separated; f) the final storage of all CO2 produced in the process either in geological (i.e. in saline aquifers) or submarine glass containers [1]; 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 CO2 removal generated by the process is 2.6 ton per ton of biomass used; by assuming that the avoided emission related to the energy content of H2 exported to external users is 0.43 ton, 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 119 $ per ton of CO2 removed; considering the revenue from the produced energy, the cost falls to 63 $/tCO2. The higher efficiency in carbon removal obtained by combining biomass gasification, calcination, and ocean liming allows to reduce the amount of biomass required by BECCS to achieve negative emissions, and thanks to the valuable H2 produced it lowers the costs of CO2 removal from the atmosphere.