A METHOD AND A DEVICE FOR SUPPLYING AIR TO A COMBUSTOR

Abstract: A method and a device for supplying air to a pressurized combustor (BK) in a gas turbine plant which for pressurization of the combustor (BK) comprises a compressor (C) driven by a gas turbine (GT), which in turn is driven by gases formed during combustion of a fuel in the combustor (BK). The invention is characterized in that the air is supplied to the low-pressure side of the compressor (C) via a pressurization device (F) in which the air is compressed such that air with a predetermined density is supplied to the compressor (C).

Description: A mPt- nrl and a device for supplying air to a combustor TECHNICAL FIELD The present invention relates to a gas turbine plant compri¬ sing a compressor, a gas turbine and a pressurized combustor, for example a Pressurized Fluidized Bed Combined Cycle (PFBCC) plant, or an Integrated Gasification Combined Cycle (IGCC) plant. BACKGROUND ART In a gas turbine plant, in which pressurized combustion is performed in a combustor, combustion gases are generated which drive a gas turbine. This gas turbine, in turn, drives a com¬ pressor which compresses air for pressurization of the combus¬ tor. The compressed air is simultaneously utilized as combus¬ tion air during the combustion. The gas turbine may be divided into a high-pressure and a low-pressure turbine. With such a division of the gas turbine, the low-pressure turbine may, on a separate first shaft, drive a low-pressure compressor for compression of the air in a first stage. The high-pressure turbine then drives, via a second separate shaft, a high- pressure compressor where air is compressed in a second stage before the air is supplied to the combustor. Between the low- pressure and high-pressure compressors, a cooler may be provided for cooling the air after the first stage in the compression. The fuel supplied to the combustor consists of gaseous, liquid or solid fuels, for example natural gas, oil or coal, depen¬ ding on the nature of the plant. A PFBC power plant is an example of a plant comprising a gas-turbine cycle according to the configuration described above, wherein a solid fuel, usually a finely-divided coal, is burnt in a fluidized bed in the combustor. In a gas-turbine plant, an electric generator for generating useful energy is usually connected to the high-pressure tur¬ bine via a gear. When starting the plant, it is possible to utilize the generator as an electric motor to speed up the compressor and thus pressurize the combustor. When dimensioning the plant, a compressor size is usually chosen which gives an optimum air flow rate at a known low exterior air temperature for the site of the plant. On the other hand, when higher temperatures prevail at the site, a lower density of the air is obtained, whereby the mass flow of air through the compressor decreases and hence the power of the plant. Another plant site may be located at a different height above sea level where the density of the air is diffe- rent, which necessitates a different dimensioning of the plant. A small incorrect dimensioning of the chosen capacity of the compressor cannot be compensated for by simple means after- wards. When the ordinary compressor ages, the capacity thereof decreases, which means that the originally calculated flows no longer correspond to reality. This cannot be compensated for. One conventional way of increasing the density of the air when the temperature of the exterior air increases is to cool the air either by water or by means of a refrigerating machine. Cooling by water is only possible when the humidity of the air is low. Cooling by means of a refrigerating machine is expensive. None of the two solutions functions in the event that the low air density is due to the plant being placed at a high height above sea level. SE 500 150 describes a method and a device wherein the problems described above have been solved by supplying additional air to a combustor in a gas-turbine plane with the aid of an additional compressor. The solution comprises compressing air in the additional compressor and supplying it to the combustor by conducting the compressed air completely or partially past the ordinary compressor which delivers air to the combustor for pressurization of the combustor and for maintenance of a combustion in the combustor. The problem with the solution of SE 500 150 is that it is complicated and expensive to install in the plant. It is difficult to mix an additional air flow into the main air flow of the plant without the aerodynamic properties being dis¬ turbed. Further, the gas turbine is dimensioned for a certain air flow rate. By increasing the air flow rate through the turbine without increasing the air flow rate through the compressor, the axial forces in the plant are disturbed. SUMMARY OF THE INVENTION The invention relates to a method and a device for supplying air to a combustor in a gas-turbine plant. The invention means that a compressor in the gas-turbine plant always receives an air flow with a predetermined density which is independent of the height above sea level at which it is placed and indepen¬ dent of the ambient air temperature. Distribution of air with a predetermined density to the compressor is achieved by arranging a pressurization device, for example a conventional fan upstream of the compressor. In the fan the air is compressed to the extent necessary to be able to deliver air with a predetermined density to the low- pressure side of the compressor. By arranging a pressurization device before the compressor of the gas-turbine plant to maintain the air density at a predetermined value, the original aerodynamic properties of the gas turbine are not disturbed. By distribution of air with a predetermined density to the compressor, improved possibilities of adaptation of the compressor to other components in the plant are achieved as well as the necessary air flow to the combustion process in the combustor, the air flow being dependent on these components. The invention provides a possibility of compensating for the power reduction in the plant as a result of reduced air flow to the combustor at a higher ambient temperature. An addi¬ tional advantage is that a possibility is created of read¬ justment of the air-flow capacity for the compressors, which occurs, for example, in case of incorrect dimensioning of the ordinary compressor or when a reduction of the air flow occurs because of changes in the ordinary compressor caused by, for example, ageing and fouling of the compressor. Still another advantage of the invention is that the other properties of the plant are not disturbed by the installation of a pressurization device upstream of the compressor. Further, the solution is simple and cost-effective. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in greater detail with reference to the accompanying drawings. Figure 1 schematically shows one embodiment of a gas-turbine plant wherein air is supplied to the low-pressure side of a compressor via a pressurization device to be further trans¬ ported to a combustor. The dashed lines indicate a gasifier which may be disposed between the compressor and the com- bustor. Figure 2 shows an embodiment of a gas-turbine plant wherein air is supplied to the low-pressure side of a compressor via a pressurization device to be further transported to a combus- tor. The gas-turbine plant is combined with a steam cycle and a valve means. Figure 3 shows an embodiment of a gas-turbine plant wherein the gas turbine and the compressor are divided into high- pressure and low-pressure units. Air is supplied to the low- pressure side of the low-pressure compressor via a pressuri¬ zation device to be further transported to a combustor. The dashed lines indicate that the gas-turbine plant can be com¬ bined with a steam cycle and a valve means. DESCRIPTION OF THE PREFERRED EMBODIMENTS In Figure 1, which schematically illustrates a gas-turbine plant, BK designates a combustor in which a fuel is burnt under a high pressure. The high pressure is achieved by means of a compressor C which compresses air which is passed to the combustor BK via the air pipe 8' '. The combustion gases which are generated in the combustor BK are conducted to a gas turbine GT, via the pipe 9, for utilization of the energy in the combustion gases, whereupon the consumed waste gases are discharged via a waste gas pipe 10. The gas turbine GT is mounted on the same shaft Al as the compressor C and thus drives the compressor. On the same shaft Al on which the compressor C and the gas turbine GT are mounted, a generator G is also provided for conversion of energy used in the gas- turbine plant into electrical energy. Air to the compressor is sucked in via the pipe 8' and a pressurization device F, for example a fan and a pipe 8. The pressurization device F has the ability to raise the density of the air flowing therethrough to a predetermined value. The pressurization device F is driven by a drive means M, which, for example, is in the form of a controllable motor which may be of electric, hydraulic, diesel or explosion type, or it may be in the form of a steam turbine. The drive means M is adapted to drive the pressurization device F via a shaf A3. The drive means M is driven in dependence on the value of the density in the pipe 8' . A measuring element 13 is adapted to measure the density in the pipe 8' and a control element 14 is adapted, in dependence on this measured result, to control the drive means M. The drive means M is activated in those cases where the exterior air temperature is higher than that for which the plant is designed or if the density of the air needs to be adjusted for some other reason, for example due to ageing of the plant. The pressurizing device F may, for example, be controlled by arranging guide vanes, comprised therein, to be rotatable for control of the quantity of the air flow therethrough. Alter¬ natively, the pressurizing device F may be controlled by changing its speed in dependence on the measurement result from the measuring element 13. An alternative embodiment is shown within dashed lines in Figure 1, in which the gas-turbine plant is combined with a gasifier GF. The gasifier GF is arranged between the com¬ pressor and the combustor, which symbolizes a so-called IGCC plant. The IGCC plant operates in such a way that part of the compressed air from the compressor C is passed to the gasifier GF for gasification of a fuel, for example coal, which is supplied to the gasifier GF via a pipe 6. The gasified fuel is then passed from the gasifier GF to the combustor BK via a pipe 7. The main part of the air compressed in the compressor C, however, is forwarded via the pipe 8' ' to the combustor BK. Figure 2 shows an alternative embodiment of the invention wherein the gas-turbine plant is combined with a steam cycle and a valve means forming a so-called PFBC plant. The steam circuit is symbolized by feed water which, with the aid of a pump 15, is circulated from a condenser tank 16 via a pipe 17 to tube bundles 18 in the combustor BK for generation/- superheating of steam. The steam is forwarded to a steam turbine 19 via a pipe 20. Condensate and expanded steam are returned to the condenser 16 via a pipe 21. Figure 2 also shows an intercept and bypass valve V. Air to the compressor C is admitted via the air pipe 8' . The combustion gases genera¬ ted in the combustor BK are led via the intercept and bypass valve V to a gas turbine GT via the pipe 9 to utilize the energy in the combustion gases, whereupon the consumed waste gases are discharged through a waste gas pipe 10. The gas turbine GT are mounted on the same shaft Al as the compressor C and thus drives the compressor. By means of the shaft Al, the gas turbine GT also drives a generator G for conversion of energy utilized in the gas-turbine plant into electrical energy. In addition to a shut-off valve for compressor air to the combustor BK and a shut-off valve for supply of combustion gases to the gas turbine GT, the intercept and bypass valve V also comprises a bypass line with a shut-off valve to make possible short-circuiting of the compressor C and the gas turbine GT. In the same way as described with reference to Figure 1, air is sucked into the compressor C via the pipe 8' and the pressurization device F. Further, the pressurization device F is controlled, in the same way as described above, by a con¬ trollable drive means M. Figure 3 shows an additional alternative embodiment of the invention, wherein both the gas turbine GT and the compressor C are divided into several stages. In other respects, the design conforms to the more general connection according to Figure 1. In the embodiment according to Figure 3, the com¬ bustion gases from the combustor BK drive a high-pressure turbine HPT, which is mounted together with a high-pressure compressor HPC on a first shaft Al. The gases expanded in the high-pressure turbine HPT are forwarded to a low-pressure turbine LPT, from which the waste gases from the plant are discharged via a waste gas pipe 10. On the same shaft, a second shaft A2, as that on which the low-pressure turbine LPT is mounted, also a low-pressure compressor LPC is arranged. To this low-pressure compressor, air is supplied via the air pipe 8''', whereupon the air after compression in the low-pressure compressor LPC is brought to the high-pressure compressor HPC, where the air is compressed further before it is supplied to the combustor BK, possibly via an intercept and bypass valve V indicated in dashed lines and having the same function as indicated in Figure 2. After compression of the air in the low-pressure compressor LPC, the air may be cooled in an intercooler IC before being supplied to the high-pressure compressor HPC. The first shaft Al drives the generator G, possibly via a gear 12, for generation of electrical energy. In this embodiment, air to the low-pressure compressor LPC is sucked in via the pipe 8 to the pressurization device F and further via the pipe 8' ' ' . The pressurization device F is driven via the shaft A3 in dependence on the density of the air in the pipe 8' . An element 13 is arranged to measure the density in the pipe 8' and a control element 14 is adapted, in dependence on this measurement result, to control the drive means M for driving the pressurization device F. Alternatively, the pressurization device F is driven via the shaft A3 in dependence on the density of the air in the pipe 8' ' ' . An element 13 ' is then adapted to measure the density in the pipe 8' ' ' and a control element 14' is adapted, in depen¬ dence on this measurement result, to control the drive means M for driving the pressurization device F. Further, Figure 3 shows in dashed lines a steam circuit combined with the gas-turbine plant. The steam circuit is symbolized in the same way as in Figure 2. It is principally in combination with this steam circuit that an intercept and bypass valve V can be used. Thus, the invention is applicable both to single-shaft and multi-shaft gas-turbine plants and to combined cycles.

Claims: CLAIMS 1. A method for supplying air to a pressurized combustor (BK) in a gas-turbine plant which for pressurization of the com- bustor (BK) comprises a compressor (C) driven by a gas turbine (GT) , which in turn is driven by gases formed during com¬ bustion of a fuel in the combustor (BK) , wherein the air is supplied to the low-pressure side of the compressor (C) via a pressurization device (F) , characterized in that the pressurization device (F) is arranged separate from the gas- turbine plant and is driven by a drive means (M) which is controlled in dependence on the density of the air in a supply pipe (8') provided between the pressurization device (F) and the compressor (C) , the air in the pressurization device (F) being compressed such that air with a predetermined density is supplied to the compressor (C) . 2. A method for supplying air to a pressurized combustor (BK) in a gas-turbine plant which for pressurization of the com- bustor (BK) comprises a compressor (C) driven by a gas turbine (GT) , which in turn is driven by gases formed during com¬ bustion of a fuel in the combustor (BK) , wherein the com¬ pressor (C) is divided into a high-pressure compressor (HPC) and a low-pressure compressor (LPC) and the gas turbine (GT) is divided into a high-pressure turbine (HPT) and a low- pressure turbine (LPT) , characterized in that the air is supplied to the low-pressure side of the low-pressure com¬ pressor (LPC) via a pressurization device (F) in which the air is compressed such that air with a predetermined density is supplied to the low-pressure compressor (LPC) . 3. A method according to claim 2, characterized in that the pressurization device (F) is driven by a drive means (M) which is controlled in dependence on the density of the air in a supply pipe (8') provided between the pressurization device (F) and the high-pressure compressor (HPC) . 4. A method according to claim 2, characterized in that the pressurization device (F) is driven by a drive means (M) which is controlled in dependence on the density of the air in a supply pipe (8' ') provided between the pressurization device (F) and the low-pressure compressor (LPC) . 5. A device for supplying air to a pressurized combustor (BK) in a gas-turbine plant which for pressurization of the com¬ bustor (BK) comprises a compressor (C) driven by a gas turbine (GT) , which in turn is driven by gases formed during com¬ bustion of a fuel in the combustor (BK) comprising a pressu¬ rization device (F) , characterized in that the pressuri¬ zation device (F) is arranged as a unit separate from the gas- turbine plant upstream of the compressor (C) and that a drive means (M) is connected to the pressurization device (F) via a shaft (A3) and that the drive means (M) is adapted to drive the pressurization device (F) in dependence on the density of the air in a supply pipe (8') provided between the pressuri¬ zation device (F) and the compressor (C) for supply of air with a predetermined density to the low-pressure side of the compressor (C) . 6. A device according to claim 5, characterized in that a drive means (M) is connected to the pressurization device (F) via a shaft (A3) and that the drive means (M) is adapted to drive the pressurization device (F) in dependence on the density of the air in a supply pipe (8') provided between the pressurization device (F) and the compressor (C) . 7. A device for supplying air to a pressurized combustor (BK) in a gas-turbine plant which for pressurization of the com¬ bustor (BK) comprises a compressor (C) driven by a gas turbine (GT) , which in turn is driven by gases formed during com¬ bustion of a fuel in the combustor (BK) wherein the compressor (C) is divided into a high-pressure compressor (HPC) and a low-pressure compressor (LPC) and the gas turbine (GT) is divided into a high-pressure turbine (HPT) and a low-pressure turbine (LPT) , characterized in that it comprises a pressu- rization device (F) arranged upstream of the low-pressure compressor (LPC) for supply of air with a predetermined densi¬ ty to the low-pressure side of the low-pressure compressor (LPC) . 8. A device according to claim 7, characterized in that it comprises a drive means (M) which is connected to the pressu¬ rization device (F) via a shaft (A3) and that the drive means (M) is adapted to drive the pressurization device (F) in dependence on the density of the air in a supply pipe (8") provided between the pressurization device (F) and the high- pressure compressor (HPC) . 9. A device according to claim 7, characterized in that it comprises a drive means (M) which is connected to the pressu¬ rization device (F) via a shaft (A3) and that the drive means (M) is adapted to drive the pressurization device (F) in dependence on the density of the air in a supply pipe (8' ' ' ) provided between the pressurization device (F) and the low- pressure compressor (LPC) . 10. A device according to claim 5, 8 or 9 , characterized in that it comprises a measuring element (13 and 13', respecti¬ vely) adapted to measure the density in the supply pipe (8' and 8' ' ' , respectively) and a control element (14 and 14' , respectively) adapted, in dependence on this measurement result, to drive the drive means (M) . 11. A device according to claim 5, 8, 9 or 10, characterized in that the drive means (M) is an electric motor.

Inventors: ANDERSON JIM, ANDERSON, JIM
Applicants: ABB CARBON AB, ANDERSON JIM, ANDERSON, JIM
Application year: 1996
Main classification: F02C9
IPC codes: F02C3, F02C9, F23C10, F23L5