DEVICE IN A POWER PLANT

Abstract: The invention relates to a device in a power plant comprising a combustion chamber for combustion of fuel at overpressure, a turbine (11) driven by combustion gases generated in the combustion chamber, a compressor (12) driven by the turbine for compression of combustion air, and a gas conduit (15) for transferring combustion gases from the combustion chamber to the turbine. The gas turbine drives the generator (13). The device according to the invention includes at least one start-up combustor (19). The generator (13) can be switched to motor operation for rotation of the compressor (12) upon start-up, whereby the compressor supplies combustion air to the start-up combustor(s). Fuel, for example oil, is transferred to the start-up combustor (19) which in turn delivers gases to the turbine (11), the turbine power thus being supplied to the compressor (12).

Description: Device in a power plant TECHNICAL FIELD The present invention relates to a device in a power plant comprising a combustion chamber for combustion of a fuel at overpressure, a turbine driven by generated combustion gases, a compressor driven by the turbine for compression of combustion air, a generator driven by the gas turbine, as well as a gas conduit for transferring combustion gases from the combustion chamber to the turbine. BACKGROUND ART A plant of the above-mentioned type is described in Swedish patent specification 8700960-1 (456 757; corresponding to EP 881012041 (0 285 825) and US 4 860 535) . In such a plant the plant is started by the generator therein being switched to a motor, which accelerates the gas turbine of the plant to full, synchronous speed. This requires energy from the network, and this limits the applicability to relatively small plants, for example with a gas turbine power of 15-17 MW. Starting equipment for a larger plant of the above-mentioned type would become very extensive, both from the points of view of design and economy, and it is desired not to take out such great power for starting as would be required from the network in case of generator-motor start. SUMMARY OF THE INVENTION The present invention aims to provide a solution to the above-mentioned and similar problems and it is characterized in that the device in a power plant includes at least one start-up combustor and in that the generator can be switched to motor operation with a relatively low power, of the order of magnitude of 5-10 % of the generator power, for rotation of the compressor upon start-up, the compressor supplying combustion air to the start-up combustor, and that fuel, for example oil, is transferred to the start-up combustor and burnt, the start-up combustor in turn delivering gases to the turbine, the turbine power thus being supplied to the compressor. By such a device, also large plants of the kind referred to here can be started up without any major power output from the network. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in greater detail with reference to the accompanying drawings, wherein Figure 1 shows parts of the power plant with a start-up combustor, and Figure 2 is a view of the gas turbine with a generator. DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 2 shows a gas turbine unit according to the inven- tion, comprising a turbine' 11, a compressor 12 and a gene¬ rator 13 which may also serve as a starting motor. The gas outlet 14 from the turbine 11 is connected through a conduit to a waste heat boiler (not shown) , in which the residual heat in the gases leaving the turbine 11 is utilized. The combustion gases from a boiler are passed in a conduit 15 to the turbine 11 (see arrow F in Figure 1) , which drives the compressor 12 and the generator 13 (Figure 2) . Air compressed in the compressor 12 is passed in the conduit 16 to the boiler. The valve unit includes cut-off valves 17 and 20 which are operated by operating devices (see below) . The conduit 16 includes at least one by-pass (short-circuit) valve 18 and at least one air valve 21 (see below) . By valve unit is meant the unit between the flange A and the flange B in Figure 1. Figure 1 shows, besides the combustion gas conduit 15 and the air conduit 16, cut-off valves 17 for the compressor air, in this case of butterfly type, for switching on and off the air from the compressor 12 to the boiler, the cut- off valves being suitably operated by operating (servo) devices (not shown) . The by-pass valve 18 is intended to conduct the compressor air directly to the turbine. The valve 21 controls the air supply to the start-up combustor 19 upon start-up. The start-up combustor 19, which may be one or more in number (see also Fig. 2 where a plurality, for example six, are arranged radially with respect to the gas conduit 15) , is arranged at the combustion gas conduit 15 or at a separate location (not shown) . It is supplied with air from the compressor when the valve 21 is in the shown position, and fuel, for example oil, is also supplied to the start-up combustor 19. With the valves 17, 18 and 20 shut and the valve 21 open, the generator 13 is now switched in as motor for operation of the compressor 12. The starting cycle is initiated by passing combustion air via the open valve 21 to the start-up combustor 19, to which also oil, for example, is supplied and ignited. Upon start¬ up, the start-up combustor 19 delivers combustion gases to the turbine 11, whereby power from the turbine is supplied to the compressor 12, and the compressor in turn delivers an increasing quantity of air to the start-up combustor, which supplies an increasing quantity of hot gas to the turbine. In this way, the gas turbine can accelerate until it reaches idling speed and later on synchronous speed. After this, pressurization and heating of the pressure vessel of the total plant can be performed by successively opening the valves 17 and 20. The invention can be varied in many ways within the scope of the following claims.

Claims: CLAIMS 1. A device in a power plant comprising a combustion chamber for combustion of a fuel at overpressure, a turbine (11) driven by generated combustion gases, a compressor (12) driven by the turbine for compression of combustion air and a generator (13) driven by the gas turbine, as well as a gas conduit (15) for transfer of combustion gases from the combustion chamber to the turbine, characterized in that the device includes at least one start-up combustor (19) and that the generator (13) can be switched to motor operation for rotation of the compressor (12) upon start-up, whereby the compressor (12) supplies combustion air to the start-up combustor (19), and that fuel, for example oil, is transferred to the start-up combustor (19) and is burnt, the start-up combustor in turn delivering gases to the turbine (11) , whereby the turbine power is supplied to the compressor (12) . 2. A device according to claim 1, characterized in that when the number of start-up combustors (19) is more than one, the combustors are suitably located radially around the gas conduit (15) . 3. A device according to claim 1 or 2, characterized in that the start-up combustor/s (19) is/are connected to the gas conduit (15) . 4. A device according to claim 1 or 2, characterized in that the device includes at least one valve (21) for switching on and off combustion air to the start-up combustor/s (19) .

Inventors: MAANSSON MARTIN, MAANSSON, MARTIN
Applicants: ABB CARBON AB
Application year: 1991
Main classification: F01D19
IPC codes: F02C7