Recently, studies have been made on a gas turbine facility in which CO2 in exhaust discharged from a turbine is partly circulated to a combustor. In this gas turbine facility, studies have been made on achieving a thermal power generation system that performs power generation simultaneously with the separation and recovery of CO2.
In this highly environmental-conscious gas turbine facility, studies have been made on a thermal power generation system in which, for example, oxygen is used as an oxidant and supercritical-pressure CO2 is circulated to a combustor. This thermal power generation system achieves no-emission of NOx by effectively using CO2.
In this thermal power generation system, for example, a fuel (natural gas or methane) and the oxidant (mixture of oxygen and CO2) are introduced into the combustor to be combusted, and CO2 as a cooling medium is also introduced to the combustor. Then, a turbine is rotated by high-temperature combustion gas generated by the combustion to generate electricity. The combustion gas (CO2 and vapor) discharged from the turbine is cooled by a heat exchanger and is then deprived of the moisture to become CO2. This CO2 is compressed into high-pressure CO2 by a high-pressure pump. Most of the high-pressure CO2 is heated by the heat exchanger and is circulated to the combustor. The rest of the high-pressure CO2 is recovered to be used for other purposes.
In the combustor in this thermal power generation system, mixed gas of the fuel and the oxidant mixed in the combustor is ignited using an ignition device. At the time of the ignition, a flow rate of the oxidant and a flow rate of the fuel are set low in order to reduce a sudden heat load to devices. Then, after the ignition, the flow rate of the oxidant is increased, thereby increasing the pressure in the combustor, and the flow rate of the fuel is increased, thereby increasing the temperature of the combustion gas in the combustor. The pressure in the combustor is thus increased up to, for example, a rated load condition of the turbine, for instance.
A typical ignition method in a conventional gas turbine combustor is to use spark discharge caused by the application of voltage to an ignition device disposed on a wall surface of the combustor. A leading end of the ignition device where the spark discharge occurs is exposed to flame after the ignition.
As a solution to this, studies have been made on a structure to make the ignition device advance/retreat into/from the combustor, from a viewpoint of durability and the like of the ignition device. This ignition device is made to advance/retreat into/from the combustor by, for example, an air cylinder using air jetted from a compressor. Then, after the ignition, the leading end of the ignition device, which is a spark discharge portion, is pulled out from the inside of the combustor. At this time, the leading end of the ignition device is pulled out up to, for example, an insertion hole which is formed in a combustor liner to allow the ignition device to advance/retreat therethrough, or pulled out up to a position between the combustor liner and a casing.
In the above-described thermal power generation system using the supercritical-pressure CO2, the pressure at the turbine rated load in the combustor is ten times or more as high as that in the conventional gas turbine combustor. If the conventional structure of the ignition device is used, the leading end of the ignition device is exposed to this high-pressure condition even after pulled out from the inside of the combustor.
This high-pressure condition greatly exceeds a withstand pressure specification of the ignition device in the conventional gas turbine combustor. This does not permit the specification of the conventional ignition device to be applied as it is to the thermal power generation system using the supercritical pressure CO2.