Tokyo Gas has been implementing trial project to supply liquid carbon dioxide, which is recovered from exhaust gas emitted at hydrogen station of Haneda Airport and is purified, to plant factory in Chiba University since December 2011.

CO2 is produced as a byproduct when hydrogen is produced through cracking of city gas. It is recovered, purified, and then reused. This is the first attempt in Japan to recover and purify CO2 at a hydrogen station.

The liquid CO2 transported to the plant factory is used for promoting the photosynthesis of agricultural plants. A joint project between Tokyo Gas and Chiba University, Tokyo Gas is looking into the economic viability of the system, while Chiba University is examining the means of effective use of recovered CO2 at plant factories.

This test looks into the possibility that as time goes by hydrogen stations in municipal areas could become production centers for liquid CO2 and dry ice.

The recovered liquid CO2 is filled into an LCG with a capacity of 160kg, and is transported by truck to the Chiba University plant in Kashiwa City. At the food factory at Chiba University plans call for raising the density of the gas from the conventional 400ppm to 1,000ppm. It is hoped that the gas will be able to promote photosynthesis of tomatoes during cultivation, increase their sweetness, and increase the production of high quality tomatoes. Plans now call for the supplying of 320 kg (2 LGCs) of liquid CO2 in January.

Tokyo gas already has a CO2 recovery and purifying test facility at its Senju hydrogen station in Tokyo. The new facility has added improvements. During the production of hydrogen through natural gas (methane) cracking, after the natural gas is cracked along with steam (steam reforming), the purity of the hydrogen is raised to 99%. At this time, the waste gas, which contains 40% CO2, has conventionally been returned to the reformer, been reused as combustion gas. Now this waste gas is recovered, and using CO2 PSA it is purified to CO2 to a level of 98%-99%. After purification, the CO2 is raised to a pressure of 2 MPa with a compressor, cooled to -20℃, and turned into liquid gas. The CO2 recovery capacity is 10 kg an hour.

A verification test is to be conducted to verify whether supplying the CO2 recovered is economically viable. In terms of cost and productivity, the CO2 from a hydrogen station is far from the level of competitiveness which the CO2 employed for industrial use now has under present conditions. As Hirotaka Furuta, head of the Technology Team at Tokyo Gas explained regarding the significance of the verification, “If the station were to go to the practical level of an output of 300 m3 an hour, and if the number of stations installed were to increase, the amount recovered would increase. There is also the idea of installing hydrogen stations adjacent to food plant factories. Previously the idea was that from the point of view of the environment, the recovery of CO2 should increase, and in terms of technology this has now become a challenge for the future.”

Regarding the supply of liquid CO2 and dry ice, oil refineries and ammonia plants, which are the sources, are on the decline due to the appreciation of the yen and the changes in the supply and demand structure. There is a danger now that supply could dry up. Still, the demand for CO2 for cooling and dry ice is large in municipal areas. In accordance with the FCV permeation into society, if hydrogen stations were installed in densely populated areas, it is quite possible that they could be used as a new manufacturing basis for municipal type CO2 and dry ice. Hydrogen stations would not only be a supply source of energy, but quite possibly also be used as supply centers for CO2. Because of this focus is now being placed on the verification test.