Tokyo Gas is engaged now in research and development for a new combustion process to generate N2+CO2+heat, which takes out heat with nitrogen and carbon dioxide gas by means of the redox reaction of metal through the use of natural gas and other fuels.

This combustion process, known as “Chemical-looping Combustion”, is flame-free to generate heat and industrial gases, leading to easier separation and collection of CO2 from waste gases. It can be applied to power generation, petrochemical and steelmaking processes such as IGCC into which we want to incorporate CCS (Carbon Dioxide Capture and Storage). The technology also has a potential to bring out a new method to supply industrial gases to nitrogen gas users who apply heat to their metal treatment or food processing. Tokyo Gas who has built an experimental unit is carrying out a characteristic evaluation of the process and seeking applicable fields of the new combustion process at the same time.

The chemical-looping combustion system is based on the cyclic movement of metal as a carrier of oxygen between two reaction systems of fuel and air. In the aerial reaction system metal causes an oxidizing reaction with oxygen in the air. As oxidization is an exothermic reaction (at reacting temperature between 800 and 1200℃), we can take out heat and nitrogen-enriched gas (with purity of 99% or more) as waste gas.

The oxidized metal which moves from the aerial reaction system into the fuel reaction system reacts with such a fuel as natural gas and is reduced. Reduction is an endothermic reaction with reacting temperature somewhere between 600 and 1,000℃. As oxygen in the oxidized metal reacts with a fuel in the fuel reaction system, only carbon dioxide and water become waste gas.

The reaction itself is identical with the combustion of pure oxygen, but it does not require any energy necessary for the supply of oxygen because it employs oxygen in the air. Furthermore, as there is no combustion flame during the process, nearly no thermal NOx may be emitted. Particularly in case of using a nitrogen-free fuel like natural gas, it is said that NOx emission can be reduced to nearly zero. As you can take out waste gas separately from two reaction systems of fuel and air in this chemical-looping combustion, it is a combustion system to attain less loss of the exergy which shows energy availability.