GAS TURBINE POWER GENERATION PLANT AND METHOD FOR OPERATING SUCH A PLANT

Abstract

A gas turbine power generation plant including: a solid fuel gasifier for the production of a fuel gas stream, an arrangement for fuel gas treatment, a combustor for receiving the fuel gas stream and for the production of a flue gas stream, a gas turbine unit having an inlet for said flue gas stream and being mechanically coupled to an electric generator for the extraction of useful work; a compressor unit for the supply of compressed oxygen to the combustor. A steam generator is arranged for heat recovery in the flue gas stream downstream of the turbine unit, a condenser is positioned for water recovery in the flue gas stream, said condenser having a connection for water supply to the steam generator, and the steam generator is connected for supply of steam to the combustor for contributing as process gas. The invention also concerns a method for operating a power plant and an arrangement and a method for fuel gas treatment.

Claims

1. Gas turbine power generation plant including: a solid fuel gasifier for the production of a fuel gas stream, a fuel gas treatment arrangement including at least one fuel gas treatment device, a combustor for receiving the fuel gas stream and for the production of a flue gas stream, a gas turbine unit having an inlet for said flue gas stream and being mechanically coupled to an electric generator for the extraction of useful work, and a compressor unit for the supply of oxygen to the combustor, wherein a steam generator is arranged for heat recovery in the flue gas stream downstream of the gas turbine unit, wherein a condenser is positioned for water recovery in the flue gas stream, said condenser having a connection for water supply to the steam generator, wherein a mixing device is arranged downstream of the solid fuel gasifier and upstream of the fuel gas treatment device, said mixing device being connected to a water conduit for supply of condensed water recovered in the condenser, and wherein the mixing device is arranged for mixing said recovered water into the hot fuel gases for cooling purposes, and wherein the steam generator is connected to the fuel gas treatment device for the supply of steam for the treatment of the fuel gas stream, wherein steam supplied to the fuel gas treatment device and used for treatment of the fuel gas stream is subsequently transmitted, and thereby indirectly supplied, to the combustor for contributing as process gas.

2. Plant according to claim 1, wherein the compressor unit is coupled for the supply of oxygen also to the gasifier.

3. Plant according to claim 1, wherein the steam generator is also connected for direct supply of steam to the combustor for contributing as process gas.

4. Plant according to claim 1, wherein a fuel gas-steam mixer is arranged upstream of or in the combustor for adding additional steam as process gas.

5. Plant according to claim 1, wherein the fuel gas treatment device includes one or more from the group: a fuel gas heat exchanger using steam as cooling medium, a steam injector coupled so as to inject steam generated by the steam generator into the fuel gas stream, a fuel gas cleaning device, a fuel gas conversion device, a separation device, a fuel gas reheater device.

6. Plant according to claim 5, wherein the fuel gas treatment device includes a fuel gas conversion device, wherein the fuel gas conversion device is a hydrogen production device coupled to supply hydrogen as main fuel to the combustor.

7. Plant according to claim 5, wherein the fuel gas treatment device includes a steam injector and a fuel gas cleaning device, wherein the steam injector is positioned in or upstream of the fuel gas cleaning device.

8. Plant according to claim 5, wherein the fuel gas treatment device includes a fuel gas reheater device, wherein the arrangement includes a heat exchange device being comprised of a fuel gas reheater device, wherein the heat exchanger device has a primary side for an incoming flow of hot fuel gases from the gasifier, wherein a fuel gas exit from the primary side connects to a device for further fuel gas treatment, wherein the heat exchange device has a secondary side for a flow of further treated fuel gases from the device for further fuel gas treatment, and wherein the secondary side fuel gases are arranged to heat exchange for reheating purposes with the primary side fuel gases.

9. Plant according to claim 8, wherein a water circuit is arranged between said primary side and said secondary side and such that the water is arranged to support heat exchange between said primary side and said secondary side and that means are arranged for water coating surfaces inside said primary side and said secondary side that are passed by the fuel gases, and wherein the fuel gases are arranged to be humidified in said secondary side, and that water contents in fuel gases is arranged to be condensed at said primary side.

10. Plant according to claim 8, wherein the primary and secondary sides are interconnected for heat exchange between these sides such that the flow of treated fuel gases from the treatment device is reheated by the incoming flow of hot fuel gases from the gasifier.

11. Plant according to claim 1, wherein the plant includes an air inlet to the compressor, and that supply of oxygen to the combustor and/or to the gasifier is through supply of compressed combustion air from the compressor.

12. Plant according to claim 1, wherein the gas turbine unit is mechanically coupled to the compressor unit.

13. Plant according to claim 1, wherein a flue gas recirculation conduit is connected upstream of or to the combustor.

14. Method for operating a gas turbine power generation plant including: a gas turbine unit being mechanically coupled to an electric generator, and a compressor unit supplying compressed oxygen to the combustor, the method including: gasifying a solid fuel for the production of a fuel gas stream, treatment of the fuel gases, production of a flue gas stream in a combustor which receives the fuel gas stream, and supplying said flue gas stream to an inlet of the gas turbine unit and extracting useful work by means of the electric generator, wherein heat is recovered in the flue gas stream downstream of the gas turbine unit by a steam generator, wherein water contents in the flue gas stream is recovered by a condenser having a connection for water supply to the steam generator, wherein condensed water recovered in the condenser and supplied over a water conduit is mixed into the hot fuel gases, for cooling purposes, in a mixing device being arranged downstream of a solid fuel gasifier for gasifying the solid fuel and upstream of a fuel gas treatment device, and - wherein steam is supplied from the steam generator for the treatment of the fuel gas stream, wherein steam supplied to and used for treatment of the fuel gas stream is subsequently transmitted, and thereby indirectly supplied, to the combustor for contributing as process gas.

15. Method according to claim 14, wherein steam is supplied directly from the steam generator to the combustor.

16. Method according to claim 14, wherein oxygen is also supplied by the compressor unit to the gasifier.

17. Method according to claim 14, wherein fuel gas and additional steam are mixed upstream of or in the combustor.

18. Method according to claim 14, wherein the fuel gas treatment includes one or more from the group: fuel gas heat exchange using steam as cooling medium, steam injection by injecting steam generated by the steam generator into the fuel gas stream, fuel gas cleaning, fuel gas conversion, fuel gas separation, fuel gas reheating.

19. Method according to claim 18, wherein the fuel gas treatment includes fuel gas conversion, wherein the fuel gas conversion is hydrogen production, wherein hydrogen is supplied as main fuel to the combustor.

20. Arrangement for fuel gas treatment for use in a gas turbine power generation plant, said plant including a solid fuel gasifier for the production of a fuel gas stream, at least one fuel gas treatment device, a combustor for receiving the fuel gas stream and for the production of a flue gas stream and a gas turbine unit for receiving the flue gas stream, wherein the arrangement includes a heat exchange device being comprised of a fuel gas reheater device, and wherein the heat exchanger device has a primary side for an incoming flow of hot fuel gases from the gasifier, and wherein a fuel gas exit from the primary side connects to a device for further fuel gas treatment, and wherein the heat exchange device has a secondary side for a flow of further treated fuel gases from the device for further fuel gas treatment, and wherein the secondary side fuel gases are arranged to heat exchange for reheating purposes with the primary side fuel gases.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0039] The invention will now be described in greater detail at the background of embodiments and with reference to the drawings, wherein:

[0040] FIGS. 1-5 show different embodiments of the gas turbine power generation plant according to the invention,

[0041] FIGS. 6-7 show different arrangements for fuel gas treatment according to the invention.

DESCRIPTION OF EMBODIMENTS

[0042] FIG. 1 shows diagrammatically a first embodiment of an inventive gas turbine power generation plant, wherein a turbine unit 1 is mechanically coupled to an electric generator 2 for generation of electric energy. The gas turbine unit 1 is also mechanically coupled to a compressor unit 3, which has an air inlet 21 and an outlet, where a combustion air stream is supplied through a conduit 22, on the one hand directly over a conduit 23 to a combustor 4 and, on the other hand, over a conduit 24 to a gasifier 5.

[0043] The gasifier 5 receives solid raw fuel over a raw fuel inlet conduit 25, said fuel for example being biological mass such as peat, wood or energy crop, but also different qualities of fossil fuel such as lignite and coal. Typically, the gasifier is pressurised to about 60-70 bar.

[0044] Inside the gasifier 5, a fraction of the solid raw fuel is combusted with oxygen provided in the combustion air stream in conduit 24 in order to create a sufficiently high temperature for producing a hot fuel gas stream in the gasifier 5. The hot gas stream is, through a conduit 26, passed on to a fuel gas treatment arrangement 11 including a fuel gas treatment device 7, which in the embodiment in FIG. 1 is a fuel gas clean-up device, wherein i.a. unwanted impurities are removed from the gas stream.

[0045] Before the inlet to the treatment device 7, the fuel gas stream is mixed with steam in a mixing device 8 to bring temperature down to levels which are manageable by the treatment device 7. The mixing device 8 also being part of the fuel gas treatment arrangement 11.

[0046] The steam is produced in a steam generator 6 which produces steam through heat exchange with a flue gas stream, flowing in a conduit 30, downstream of the turbine unit 1 and led through a conduit 28, to the mixing device 8.

[0047] After fuel gas clean-up in the treatment device 7, which for example can be achieved through various filtering steps, or other per se known steps for removal of unwanted gaseous components in the fuel gas stream, the cleaned gas is, along with the steam entering from a conduit, led through a conduit 27 to the combustor 4. Here it is combusted together with oxygen supplied in the combustion air stream so as to produce a flue gas stream, which is passed on through a conduit 29 to the turbine unit 1 for expansion and for conversion into rotational energy.

[0048] Inside the combustor 4 the amounts of combustion air delivered into the combustor 4 are held at a level resulting in near stoichiometric conditions. In order to achieve this, steam is entered into the combustor 4 also directly from the steam generator 6. This gives the result that the compressor unit essentially will perform only so much compressor work that is necessary in order to have complete combustion of the fuel in the combustor, together with, of course, provision of compressed air to the gasifier 5.

[0049] Further, downstream of the steam generator 6, there is a condenser 9 for flue gas stream water recovery, before the cooled exhaust gases are passed-on to an exhaust conduit 32. The condenser 9 also recovers part of remaining heat in the flue gas stream downstream of the steam generators 6 and passes on feed water to the steam generator 6. There is also shown an optional air cooling device 10 coupled to the condenser 9 in FIG. 1.

[0050] FIG. 1 illustrates a typical bio fuel plant where typically the temperature in conduit 26 is normally at least 1000 C. Directly downstream of the mixing device 8 the temperature is reduced to, as an example, 500 C., which in this case is a tolerable temperature for a filter inside the treatment device being a ceramic filter.

[0051] A second embodiment of the invention is shown in FIG. 2 which instead of having air supply to the gasifier 5 from the compressor unit 3 is provided with a separate oxygen supply 31, which delivers oxygen over the conduit 41 to the gasifier.

[0052] Delivered oxygen is such that the oxygen portion is higher than in ambient air, even 100% oxygen in the delivered gas is of course possible. The gasifier can be reduced in size by supplying concentrated oxygen (O.sub.2). This is because having air as medium requires larger gasifier volumes since the oxygen contents in the air is only about 20%. One further advantage with this is that smaller amounts of nitrogen have to be introduced into the process which can further reduce harmful formation of NOx gases and make it possible to introduce even higher portions of steam in the process. It is also possible, and in certain cases advantageous, to recycle flue gases to the combustor in addition to steam.

[0053] The risks of the formation of unwanted NOx gases are drastically reduced in a process according to the invention also because of the introduction of high amounts of steam in or upstream of the combustor.

[0054] Required compressor work is also reduced.

[0055] In this embodiment, the flue gas treatment arrangement 11 includes:A heat exchanger 12 is arranged for cooling fuel gases with steam produced in the steam generator 6, said steam being passed on to said heat exchanger 12 over the conduit 28. Steam heated by the fuel gas is passed on to the combustor through conduit 33.A mixing device 43 for mixing hot water supplied over conduit 42 into the hot fuel gases is arranged directly downstream of the gasifier 5 and upstream of the heat exchanger 12.A treatment device 7.

[0056] In other aspects, the embodiment in FIG. 2 corresponds to that of FIG. 1.

[0057] The embodiment of FIG. 3 differs from that of FIG. 1 in that the arrangement 11 for fuel gas treatment is laid out differently. Fuel gas first passes a (dry) fuel gas heat exchanger 35, whereupon it is passed-on through a conduit 36 to a second heat exchange device 40 being a fuel gas reheater device having a primary side (to the right in the Fig.) for an incoming flow of fuel gases from the gasifier at the bottom of the device 40.

[0058] A flow of water is let in through a conduit 53 at the top of the primary side of the device 40 and is arranged to support heat exchange between said incoming fuel gas flow at the primary side for cooling the primary side fuel gases. It should be noted that conduit 53 for supplying feed water being connected from a condenser water flow from the flue gas condenser to the heat exchange device 40 fill-up of water in the water flow. Because of the cooling of the primary side fuel gases, water vapor in the fuel gases in the primary side are condensed out along a surface of a wall between the primary side and a secondary side of the second heat exchange device 40 and is transferred into liquid water. The main part of the heat exchange is in this embodiment between the primary side and the secondary side of the second heat exchange device 40 as will be explained below.

[0059] A fuel gas exit from the primary side, at the top thereof, connects for further treatment, which in this case is (as seen in the flow direction) a fuel gas shift or conversion device 50, a fuel gas clean-up device including at least a sulphur remover 51 and a CO.sub.2 removal device 52. These devices are examples of devices for further fuel gas treatment. In the conversion device, fuel gas is shifted into hydrogen (H.sub.2), whereupon the shifted fuel gas being H.sub.2 rich or essentially purely being H.sub.2 is led through a fuel gas clean-up device. This arrangement is an embodiment only. Other arrangements are also possible. A preheater is optionally arranged in the fuel gas flow before the conversion device 50.

[0060] The second heat exchange device 40 has a secondary side (to the left in the Fig.) for receiving a flow, at its top, of fuel gases coming from the conversion device 50, the clean-up device 51 and the CO.sub.2 removal device 52. The secondary side fuel gases are herein arranged to heat exchange for reheating purposes with the primary side fuel gases through heat passage through the wall separating these sides. Said flow of water coming from the bottom of the primary side is injected at the top of the secondary side for humidifying the fuel gases and contribute to heating the fuel gases by wetting the separating wall. The wall separating the primary side and the secondary side of the second heat exchange device 40 thus becomes wet on both sides from being sprayed or otherwise coated with water. At the primary side it becomes wet because of condensation. This is important in order for the heat exchange between the primary and the secondary sides to be as efficient as required.

[0061] The fuel gases that now are relatively warm are passed on from the bottom of said secondary side to the combustor via the heat exchanger 35, where they contribute to cooling the hot fuel gases coming directly from the gasifier at the same time as they are heated before entry to the combustor.

[0062] A feed water supply to said water flow is ensured through a conduit 53 from the conduit 38 from the flue gas condenser.

[0063] In the fuel gas heat exchanger 35, hot fuel gases coming from the gasifier which, as an example, could reach between 1000 and 1500 C. are heat exchanged with steam coming from the steam generator 6 through a conduit 28, said steam typically being of a temperature of about 300 C. Heat exchange is in this case through convection between the two media passing the heat exchanger.

[0064] After having passed the shown arrangement 11 for fuel gas treatment, it is also possible to pass on the treated and cleaned-up fuel gases through a conduit to a mixing device (not shown), where it is mixed with steam that has been heated inside the fuel gas heat exchanger 35. Inside a conduit leading to the combustor 4 it is, thus, possible to pass on a mix of overheated steam and cleaned and reheated fuel gas delivered to the combustor 4 for burning together with air emanating from the compressor unit 3. The gas mix is thereby advantageously hot, resulting in advantageous combustion conditions in the combustor.

[0065] The gasifier also here has a separate supply of air/oxygen 31. 39 indicates an outlet for possible excess water at the secondary side.

[0066] The embodiment of FIG. 4 has a slightly different configuration also in respect of the fuel gas stream production. Fuel gas is passed from the gasifier 5 to an arrangement 11 for fuel gas treatment:

[0067] Through a heat exchange device 40 corresponding to the one in FIG. 3. Before entering the heat exchange device 40, the fuel gases coming from the gasifier are passed through a quenching device 45, wherein the fuel gases are cooled, as an example, to about 250 C. and are saturated to 100% relative humidity. Downstream of the heat exchange device 40, the fuel gases have reached a temperature of, as an example, about 80 C. and are passed on to a fuel gas clean-up device 7 via a cooler 46. The cooler 46 being arranged for creating a driving force in the heat exchange device 40.

[0068] Cleaned-up fuel gas is led over the heat exchange device 40 into the combustor 4. In other aspects, this embodiment corresponds to the embodiment in FIG. 1.

[0069] The arrangement for fuel gas treatment 11 in the embodiment in FIG. 5 differs from the one in FIG. 4 essentially in that the heat exchange device 47 and 47 is comprised of two separate parts: 47 being the primary side and 47 being the secondary side. The heat exchange device 47 and 47 resembles the heat exchange device 40 in FIG. 3, but in this embodiment, all heat exchange is in this heat exchange device 47 and 47 through the flow of water in a circuit. The water flow is in this case much greater than in respect of the heat exchange device 40 in FIG. 3. One solution for efficient heat exchange is to distribute, spray, coat or pour water over contact surface increasing fill bodies being positioned in the respective parts, whereby the gas flow passes the water coated fill bodies for heat transfer between gas and liquid. An optional flue gas recirculation conduit 55 is arranged to connect the exhaust conduit 32 downstream of the condenser 9 to the compressor unit 3 for optional supply of flue gases as process gas (upstream of the combustor 4). See the discussion of this aspect above.

[0070] In other aspects, this embodiment corresponds to the embodiment in FIG. 4.

[0071] FIG. 6 shows separately an arrangement for fuel gas treatment according to the invention. This arrangement is basically according to what is shown in FIG. 3.

[0072] It should be noted that the heat exchange device 40 can be inverted in respected of top and bottom such that supply and discharge of gas and water can be inverted. Supply of fuel gases from the gasifier can be arranged at the top of the primary side and discharge to combustion at the top of the secondary side.

[0073] This aspect of the invention concerns an arrangement for fuel gas treatment for use in a gas turbine power generation plant, said plant includes a solid fuel gasifier for the production of a fuel gas stream, a fuel gas treatment device, a combustor for receiving the fuel gas stream and for the production of a flue gas stream and a gas turbine unit for receiving the flue gas stream. The arrangement includes a heat exchange device being comprised of a fuel gas reheater device. The heat exchange device has a primary side for an incoming flow of hot fuel gases from the gasifier. A fuel gas exit from the primary side connects to a device for further fuel gas treatment. The heat exchange device has a secondary side for a flow of further treated fuel gases from the device for further fuel gas treatment. The secondary side treated fuel gases are arranged to heat exchange for reheating purposes with the primary side fuel gases.

[0074] In accordance with one aspect, a water circuit is arranged between said primary side and said secondary side and such that the water is arranged to support heat exchange between said primary side and said secondary side and that means are arranged for water coating surfaces inside said primary side (by condensating water vapour) and said secondary side (by distributing, spraying, pouring etc) that are passed by the fuel gases. The fuel gases are humidified in said secondary side and the water vapor in the fuel gases are condensed out in said secondary side, and

[0075] The primary and secondary sides are preferably interconnected for heat exchange between these sides such that the flow of treated fuel gases from the treatment device is reheated by the incoming flow of hot fuel gases from the gasifier.

[0076] Alternatively, heat exchange is through the water circuit flow. This is illustrated in FIG. 7 which basically is a part of the plant in FIG. 5.

[0077] The invention can be modified within the scope of the claims. It is thus possible, for example, to add other functions in the fuel gas treatment device such as sulphur reduction, different kinds of filtering, CO.sub.2 separation, particle separation etc. The invention provides an advantageous integration of previous processes for power generation in one single gas turbine plant.

[0078] The inventive process can be said to be an open process being a combined gas turbine and steam turbine process. This is in particular true when, according to one aspect of the invention, hydrogen rich fuel is combusted in air oxygen for forming flue gases almost exclusively including steam and gas components not contributing to the combustions such as nitrogen (N.sub.2) etc. The steam comes partly from the combustion of H.sub.2 in the hydrogen rich fuel, partly from amounts from steam being fed into the combustor directly or indirectly as process gas.

[0079] Introduction of steam into the combustor is very advantageous, in particular for combusting fuel with a great amount of H.sub.2 since the flame will be less reactive or calmer and thereby more controllable. Thereby the whole process will be more controllable. Steam can also be premixed with H.sub.2 or air before introduction into the combustor. Previous plants for burning hydrogen rich fuels notoriously instable since these fuels act almost explosively in the presents of oxygen in the combustor.

[0080] Generally spoken, steam is advantageous in this respect because of its high specific heat capacity.

[0081] A further advantageous modification is to provide the compressor gas flow to a primary oven before entering them into the combustor chamber. Obtained increased temperatures in the gas stream from the compressor to the combustor will result in more stable combustion, in particularly when using hydrogen, H.sub.2, as fuel.