Tokyo Gas is developing new technologies to recover and reduce carbon dioxide when generating hydrogen.
While hydrogen is generally considered to be the ultimate in clean energy, there is a contradiction in that in the process for generating hydrogen, production of the global warming substance carbon dioxide is unavoidable.
Tokyo Gas is promoting the development of technology which would lead to a solution to this problem.
In one corner of the Japan Hydrogen and Fuel Cell Demonstration Project (JHFC) in the Senju Hydrogen Station, operated by the company, there is a verification test facility whereby a CO2 separation and recovery facility has been installed in a hydrogen generator and a hydrogen production efficiency of about 80% has been achieved, the world’s highest level.
Furthermore, they are developing technology which will reduce the amount of CO2 emitted during the production of hydrogen to about half of what it has been up to now.
The new technology comprises a hydrogen separation-type reformer, or membrane reforming system (MRF) which generates hydrogen and CO2 through a chemical reaction between city gas and water vapour.
Unusually however, through the use of a hydrogen permeable membrane in the reforming unit where this reaction occurs, the equipment selectively extracts only hydrogen, and allows it to pass through.
Recovery of CO2 by liquefaction is comparatively easy because the density of the CO2 in the reform of gas emitted from the MRF is at the high level of 70-90%.
Because of this, by connecting a CO2 separation and recovery unit to MRF the CO2 can be recovered and the amount of CO2 emitted during the production of hydrogen reduced by half.
The unit, which has a compressor built in, can raise the pressure of the reform off gas to 7 MPa, and by cooling this to minus 20˚C, the CO2 in the reformed off gas is liquefied, separated from other gases such as methane and hydrogen, as well as carbon monoxide, and recovered as liquid carbon dioxide.
The other residue gases separated from CO2 are used as recycled gas in MRF heating.