Development of Ammonia Combustion Technology for NOx Reduction

This study comprehensively reviewed the engineering theories and technologies required for using ammonia as a fuel. The slow reaction rate and high NOx emissions of ammonia remain challenging issues with existing combustion technologies. Accordingly, the causes of these problems with ammonia were analyzed and the results of research aimed at solving these issues and commercializing ammonia combustion were examined to explore future directions for the development of ammonia combustion technology. The equivalence ratio (ER) emerged as the most important factor, closely related to operational stability and NOx emissions. Various combustion technologies, such as staged combustion and flameless combustion, have been attempted, but NOx emissions remain high at overall ER < 1, necessitating post-treatment processes. The internal recirculation of combustion gases is a key technology that enhances the stability of ammonia combustion, and its extreme case, flameless combustion technology, is predicted to form stable ammonia combustion. This is related to supplying the radicals that are lacking in the pure ammonia combustion process through the recirculation of combustion gases. By utilizing this, if the stability of ammonia combustion is secured and staged ER control technology is established, it is believed that the commercialization of pure ammonia combustion technology will be possible in the future.