Combustion of Hydrogen in Hydrogen Combustion Gas Stream and Its Characteristics of Emissions
Kazuyoshi HARUMI*, Katsuhide HIRAOKA*, Masaru IKAME*, and Hideyuki SHIROTA*
Authors had developed an experimental single stage turbine for demonstration of an internal hydrogen reheat gas turbine, in which hydrogen was discharged from the trailing edges of the nozzle vanes into the turbine passage to reheat the working gas. A series of experiments indicated increments in output power due to the reheat process and showed the possibility of the concept of the internal reheat.
In the present study, combustion characteristics of the reheat process were experimentally investigated in a high temperature wind tunnel with hydrogen combustion gas stream. Almost complete combustion efficiencies of the hydrogen discharged for the reheat were achieved. The emission index of NOx in the reheat process by discharging hydrogen increased along with the inlet temperature but it was much lower than that of the main combustor and that of reheat with methane mixture with 20% hydrogen. The ratio of NO to NOx was lessened by the reheat process and it was lower at a lower inlet temperature of the reheat section.
Key Words: Reheat Gas Turbine, Hydrogen Combustion, NOx emission
The thermal efficiency of a simple cycle gas turbine has been improved by means of increase in turbine inlet temperatures. Higher temperatures, however, result in higher cost of parts in hot sections and higher NOx emissions.
In the case of a reheat cycle gas turbine, its output power, achieved at moderate turbine inlet temperatures (TIT), results in the same level as that of a simple cycle one with higher TIT. This means that the higher output power can be obtained keeping NOx emissions at lower level. In addition to this profitable aspect of the reheat cycle turbine, its exhaust gas temperature is relatively high. This results in a higher thermal efficiency in a combined cycle mode with a steam turbine.
For a reheat cycle gas turbine compact reheat combustion space with lower NOx emissions is preferred. From this point of view hydrogen gas seems to be a possible fuel for a reheat cycle gas turbine because of its high flame velocity. It is also characterized by its high specific heat and heat conductivity regarding a coolant. In view of these features, a new concept of reheat cycle gas turbine, an internal hydrogen reheat gas turbine, was proposed by Kan S. et al .
The concept is shown in Fig.1. The fuel gas, hydrogen, is firstly introduced into the blades and internally cools them, then it is discharged from the trailing edges into the wakes for the blades, and it finally bums and reheats the downstream gas. In other words, the working gas in the internal reheat gas turbine expands receiving heat in the turbine passage. The concept of the internal reheat gas turbine provides a compact reheat combustion space inside the turbine and a multi-stage reheat process.
After the experiments with a nozzle vane cascade from which hydrogen was discharged in a high temperature wind tunnel , a single stage experimental turbine (Fig.2) was manufactured in order to demonstrate the internal reheat concept. Preliminary design conditions are listed in Table 1.