2019 Volume 61 Issue 198 Pages 293-298
This paper describes research and future plan of ammonia cracking gas turbine system, which burns hydrogen decomposed from ammonia using exhaust heat of gas turbine. The system has two alternative configurations: a co-firing system which burns mixtures of natural gas and ammonia cracked gas, and a mono-firing system which burns ammonia cracked gas. The co-firing system has fewer development subjects, because heat necessary to crack ammonia is fed by steam branched from HRSG. The gross/net thermal efficiency of the mono-firing system was 102.4 % and 101.7 % of that of the natural gas fired GTCC, respectively, owing to the increase in the calorific value of the fuel during ammonia cracking and to the increase in the flow rate of the turbine working fluid. Among several known catalysts for cracking ammonia, a base metal catalyst and a noble metal catalyst which have high catalytic activity even under relatively low temperature conditions were selected and tested under at 5.2 MPa, which is the assumed operating condition of the system. Then, the rate equation as a function of temperature and pressure was derived from the measurement of ammonia cracking ratio. A laminar combustion burner which forms a flat plate flame was prepared and NOx concentration was measured. Also, NOx concentration was calculated by a one-dimensional laminar premixed flame calculation model combining the PREMIX code of CHEMKIN and the GRI 3.0 mechanism. These results indicate that the NOx concentration increases in proportion to the increase in the residual ammonia concentration. They also show that most of the residual ammonia in the fuel is converted into NOx.