Experimental investigation of ammonia combustion in a bench scale 1.2 MW-thermal pulverised coal firing furnace

Abstract

The use of carbon-free fuel in fossil fuel firing power stations is one solution for CO2 reduction, and renewable hydrogen, when produced by renewable sources and energy can be a potential alternative fuel. Ammonia is one of promising hydrogen carriers, because it offers a high energy density, is easily liquefied, and is already widely used in the industry as fertiliser, raw chemical material, or selective catalytic reactant. Furthermore, it is well known that ammonia can be co-fired with pulverised coal. However, for utilising as fuel there are often concerns like expected flame instabilities due to slow reaction, higher NOx emission because of higher nitrogen content and lower thermal radiation because of lower flame temperature. This paper focuses on the first two items. A coal-fired furnace with capacity of 1.2MWth is used to evaluate the characteristics of ammonia co-firing with different ammonia guns. The study shows that CO2 emission can be reduced in proportion to the co-firing ratio as expected. A properly designed gas gun enables successful operation of pure ammonia firing with zero CO2 emission. The same NOx (nitrogen oxides such as NO, NO2 etc.) emission levels as achieved in pure coal-firing can be realised when co-firing ammonia with coal. Even in the case of pure ammonia firing low NOx emission can be realized without ammonia slip. Concerning unburnt carbon residues in the fly-ash under co-firing condition, large reductions have been recognised compared to pure coal-firing.