Turbine system

Abstract

Provided is a steam turbine system including: at least one high pressure turbine, and/or at least one intermediate pressure turbine, and at least one first low pressure turbine, mounted on a first rotary shaft that is coupled to drive at least one first electrical generator; and at least one further low pressure turbine, mounted on a further rotary shaft that is coupled to drive at least one further electrical generator; and the turbine system further including a steam supply system to supply low pressure steam to the low pressure turbines provided with a steam outlet to enable extraction of auxiliary process steam from a location in the steam supply system upstream of the further low pressure turbine but not upstream of the first low pressure turbine.

Claims

1. A steam turbine system comprising: at least one high pressure turbine, and/or at least one intermediate pressure turbine; at least one first low pressure turbine mounted on a first rotary shaft that is coupled to drive at least one first electrical generator; at least one further low pressure turbine located downstream from die first low pressure turbine, and mounted on a further rotary shaft that is coupled to drive at least one further electrical generator; steam supply conduits that supply low pressure steam to the first and further low pressure turbines; and a valve that diverts auxiliary process steam from a location in the conduits upstream of the further low pressure turbine but not upstream of the first low pressure turbine, wherein the valve configured to divert the auxiliary process steam to a post combustion carbon capture plant when the post combustion carbon capture plant is in operation and to not divert the auxiliary process steam to the post combustion carbon capture plant when the post combustion carbon capture plant is not in operation.

2. The steam turbine system in accordance with claim 1 further comprising fluidly in series: (i) a high pressure turbine set comprising at least one high pressure turbine, (ii) an intermediate pressure turbine set comprising at least one intermediate pressure turbine, and (iii) a low pressure turbine set comprising at least one first and at least one further low pressure turbine.

3. The steam turbine system in accordance with claim 1, wherein the conduits comprise a common receiving conduit to receive steam from the fluidly preceding higher pressure system and parallel delivery conduits to deliver steam separately to the further low pressure turbine.

4. The steam turbine system in accordance with claim 1, wherein variable/flexible couplings are provided between each of the first and further low pressure turbines and their respective generators to allow differential operation of the low pressure turbines.

5. The steam turbine system in accordance with claim 1, further comprising one or more fluid conduits fluidly continuous with the valves to convey auxiliary process steam to additional process module(s) as a source of motive power and/or latent heat.

6. The steam turbine system in accordance with claim 5 further comprising one or more fluid conduits fluidly continuous with the valves to convey auxiliary process steam to the post combustion carbon capture plant.

7. The steam turbine system in accordance with claim 1 further comprising a generator for generation of steam from combustion of carbonaceous fuel, and adapted for use with the post-combustion carbon capture plant.

8. A multiple unit steam turbine system having a plurality of steam turbine systems recited in claim 1.

9. The multiple unit steam turbine system in accordance with claim 8, wherein the or each further low pressure turbine of each steam turbine system is mounted on a common further rotary shaft that is coupled to drive at least one further electrical generator.

10. The multiple unit steam turbine system in accordance with claim 9 comprising at least a first steam turbine system having a first and a second low pressure turbine mounted on a first rotary shaft that is coupled to drive a first electrical generator and a further low pressure turbine, and a second steam turbine system having a first and a second low pressure turbine mounted on a second rotary shaft that is coupled to drive a second electrical generator and a further low pressure turbine, wherein the further low pressure turbine of each steam turbine unit is mounted on a common third rotary shaft that is coupled to drive a third electrical generator.

11. The multiple unit steam turbine system in accordance with claim 9, wherein the further low pressure turbines are mounted via flexible couplings configured to allow differential operation of the further low pressure turbines on a common shaft.

12. A steam generator system with post-combustion carbon capture capability comprising: a steam generator configured to produce steam using thermal energy from combustion of carbonaceous fuel; a steam turbine system in accordance with claim 1; wherein the post-combustion carbon capture apparatus is fluidly disposed to recover CO2 from combustion gases generated by the combustion of carbonaceous fuel when in use; a fluid conduit fluidly continuous with at least one of the valves of the steam turbine system to convey the auxiliary process steam to the post-combustion carbon capture apparatus.

13. The system in accordance with claim 12, wherein the post-combustion carbon capture apparatus comprises an absorber where CO2 is separated from a flue gas by means of absorption/adsorption onto or into a capture medium by passing the gas through a volume containing the capture medium.

14. The system in accordance with claim 13, wherein the post-combustion carbon capture apparatus comprises an absorber column where CO2 is separated from the flue gas by means of absorption by passing the gas through a column where the gas flows in an opposite direction to an absorbent in liquid phase.

15. The system in accordance with claim 13, wherein the post-combustion carbon capture system further comprises a regeneration column where CO.sub.2 is removed from capture medium by regenerative heating.

16. The system in accordance with claim 15 comprising a condenser reboiler disposed to receive absorbent solution and reboil the solution to regenerate lean absorbent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Reference is made by way of example only to FIGS. 1 to 6 of the accompanying drawings, in which:

(2) FIG. 1 is a general schematic of a prior art tandem compound arrangement of turbine train;

(3) FIG. 2 is a general schematic of a prior art cross compound arrangement of turbine train;

(4) FIG. 3 is a general schematic of a prior art coupled gas turbine/steam turbine arrangement;

(5) FIG. 4 shows a typical exhaust loss curve for a typical LP turbine operating regime;

(6) FIG. 5 is a schematic of an embodiment of the invention involving a single unit;

(7) FIG. 6 is a schematic of an embodiment of the invention involving two coupled units;

(8) FIG. 7 is a schematic of a typical post combustion carbon capture plant.

DETAILED DESCRIPTION

(9) FIG. 1 illustrates a general schematic of a typical prior art tandem compound arrangement of turbine train in which a high pressure turbine (HP), an intermediate pressure turbine (IP) and a pair of low pressure turbines (LP1, LP2) are coupled and mounted on a single shaft connected to a single generator (GEN). In conventional manner the high pressure turbine (HP) typically draws steam from the super-heating (SH) section of a steam generating boiler, while the intermediate pressure turbine (IP) draws steam from the reheating (RH) section of a steam generating boiler. The LP turbines are fluidly connected to a condenser arrangement (CON) comprising either separate or common condensers.

(10) FIG. 2 illustrates a general schematic of a typical prior art cross compound arrangement of turbine train. Where applicable like references are used. A high pressure turbine (HP), an intermediate pressure turbine (IP) and a first low pressure turbine (LP1) are coupled and mounted on a first shaft (ROTOR1) connected to a generator. A second low pressure turbine (LP2) is coupled and mounted on a second shaft (ROTOR2) connected to a second generator. In conventional manner the high pressure turbine (HP) typically draws steam from the super-heating (SH) section of a steam generating boiler, while the intermediate pressure turbine (IP) draws steam from the reheating (RH) section of a steam generating boiler. The LP turbines are connected to a condenser arrangement (CON) typically comprising separate condensers.

(11) FIG. 3 shows a single shaft gas turbine (21) coupled with steam turbine modules (23) and generator (25) via flexible couplings (27) such as clutch couplings.

(12) FIG. 4 shows the operating regimes of a low pressure steam turbine. The figure shows a plot of exhaust loss against flow through the turbine.

(13) Steam extraction for PCC reduces flow to LP, shifting the point of operation to the left along this ordinate. For LP turbines with longer blade sizes (which is limited by speed), the above curve would shift further to the right, maintaining approximately the same ordinates, but with increasing latus rectum of the parabola.

(14) In principle the highest efficiency point of operation is at the vertex of the curve, but this is practically unsustainable. The area to the left of this point should be considered a forbidden zone of operation because exhaust losses increase rapidly with reducing flow. The graph plots highest and lowest specified cooling water temperatures. The zone of stable operation will lie between. A threshold of operation is plotted at lowest possible cooling water temperature. The output would have to be reduced to retain plant controllability below this temperature.

(15) A brief description of this invention, as it might be implemented in a first example embodiment for a single unit implementing carbon capture (as shown in FIG. 5) and the extension of the concept for two units within a single power plant implementing carbon capture (as shown in FIG. 6) is provided below. An extension of the outlined concept to include more than two units within a single power plant would be readily within the compass of the skilled person and is considered included within the scope of this invention.

(16) The embodiment of FIG. 5 applies the invention to a generator system of a power plant implementing carbon capture made up of a single power unit. It comprises two rotor trainsROTOR 1 and ROTOR 2.

(17) The first rotor train, ROTOR 1 typically comprises a high pressure turbine (HP), an intermediate pressure turbine (IP), and one or more low pressure turbines (LP1one shown in the example) and an electric generator (GEN) mounted on bearings and attached with couplings for transmission of power.

(18) The high pressure turbine (HP) typically draws steam from the super-heating (SH) section of a steam generating boiler, while the intermediate pressure turbine (IP) draws steam from the reheating (RH) section of a steam generating boiler. While the present description depicts by way of example a typical arrangement with separate HP, IP and low pressure (LP) turbines with re-heating, the scope of the invention will be understood to include all combinations of turbine modules such as integrated high-pressure/intermediate-pressure (HIP) modules or integrated intermediate-pressure/low-pressure modules with or without reheating.

(19) It will be understood that the invention may include all potential installations of a turbine train as in nuclear power stations (boiling water or pressurised water reactors) with or without reheat and in gas turbine driven power stations with or without reheat. Applications are deemed to include both half-speed and full-speed machines (compared to grid frequency).

(20) In all such cases the steam generating boiler (or heat recovery steam generator) which may be designed with or without reheating sections, or the nuclear reactor is designed to generate the required quantity of steam at the maximum temperature and pressure permitted by equipment design for generating the desired quantity of power.

(21) The principal turbine train is designed in such a way that the necessary steam extraction for the post combustion carbon capture is effected from the IP/LP cross-over line. However, the consequences of steam extraction from any other location upstream of the one depicted above (e.g. steam extractions from the IP turbine, the cold reheat line, etc.) would also be manifest in reducing the quantity of flow in a steam supply conduit 30 through the low pressure turbine(s) in ROTOR 1 compared to a conventional tandem compound steam turbine driven power plant operating without carbon capture, and the consequent problems in such alternative approaches would also be considered to be resolved by adoption of the present invention.

(22) In the embodiment there is provided a further steam supply conduit 40 and a further LP turbine (LP2) not mounted on the same rotor train as the principal turbine train for each unit. This is depicted as ROTOR 2 in FIG. 5.

(23) Steam extracted from the IP/LP crossover is taken from the supply to this LP turbine. The steam flow supplying this LP turbine is routed by means of opening and closing appropriate flow restricting devices (e.g. valves 31, 41) to the carbon capture plant (PCC 50) or alternately routed to the further LP turbine (LP2).

(24) The first and further LP turbines (LP1, LP2) are connected to a condenser arrangement (CON) generally comprising separate condensers.

(25) Using the valves 31, 41 for the extraction of steam to supply the carbon capture plant (PCC 50) reduces the mass flow to the low pressure system compared to the scenario of design without carbon capture.

(26) The implementation shown in FIG. 5 enables the volumetric sizing of the low pressure turbine in ROTOR 1 to be designed for optimum efficiency based on a mass flow with steam being diverted to the post combustion carbon capture process in the PCC 50. This addresses the oversizing problem associated with low pressure turbines in a tandem compound steam turbine train within a power plant implementing the post combustion carbon capture process.

(27) The implementation shown in FIG. 5 enables the volumetric sizing of the low pressure turbine in ROTOR 2 (in the cross-compound arrangement) to be designed for optimum efficiency with respect to the steam flow required for the post combustion carbon capture process. The inlet valve 41 upstream of this turbine would be closed when the post combustion carbon capture (PCC 50) plant is in operation and the steam diverted to the PCC plant is to be used for power generation. This valve 41 would be open when the post combustion carbon capture (PCC 50) plant is not in operation to allow steam to flow through the conduit 40 to the further turbine (LP2).

(28) LP1 and GEN1 may be optimised for steam flow excluding PCC. LP2 and GEN2 may be optimised for steam flow required for PCC when it is not operational.

(29) The adoption of this scheme potentially addresses and mitigates the problem of departure from best efficiency points for low pressure turbines in a tandem compound arrangement towards to the minimum point in the Exhaust Loss vs. Flow characteristic. It simultaneously provides the following benefits: Reduced probability of operation to the left of the minimum point. Increased range of part load operation enabling carbon capture. Enhanced flexibility to increased cooling water temperature in condenser (which results in reduced vacuum, lowering exhaust loss and nudging the operating point to the minimum Exhaust Loss).

(30) The thermodynamic efficiency may be increased for the turbine modules due to reduced clearance necessary between the sealing fins corresponding to reduced length of rotor train compared to traditional tandem compound designs.

(31) The rotor-dynamic stability of each turbine train may be improved corresponding to the reduced length and slenderness ratio compared to traditional tandem compound designs.

(32) Shorter start-up times are possible due to the reduced length of the rotor trains compared to the traditional tandem compound designs. Additional flexibility for start-up is achieved for the cross-compound solution implementing carbon capture compared to tandem compound designs.

(33) The placement of a separate turbine capable of accepting steam from PCC on a separate train may increase the availability of the power plant in case of any malfunctions or trips occurring in the PCC plant. This scenario can be conceptualised in the following ways: In case of carbon capture implemented in tandem compound designs, a trip in the PCC would necessitate the provision an adequately designed bypass arrangement to divert steam intended for PCC to the steam dump device (SDD) of the main condenser, considerably increasing the size/cost of the equipment together with the strength of tubes to withstand increased impact and vibrations. The controlled re-entry of steam into the low pressure turbines (already operating at synchronous speed) of a tandem compound arrangement in case of a PCC trip would have to be monitored against increased vibration and eccentricity of turbine bearings, which act as trip signals for the entire train. This scenario is to be analysed with respect to the loading of blades, sealing fins, etc. A separate turbine mounted on a cross-compound train (with PCC) can accept steam in a sequential manner by the manipulation of the inlet valves. The start-up of the secondary turbine would not influence the operation of the principle turbine train and would be able to provide the maximum flexibility of optimising power generation in case of a PCC trip scenario. Any malfunction of the secondary turbine can be provided for a bypass arrangement into the steam dump device of the secondary condenser, without affecting the sizing, costing and operational complexity of the main condenser, catering to the low pressure turbine(s) in ROTOR 1.

(34) The low pressure turbine in ROTOR 2 is coupled to a different Generator, GEN2. The size of each generator, GEN 1 and GEN 2 and the associated auxiliary systems are optimised for power generation with and without carbon capture respectively. Compared to traditional tandem compound designs, this can reduce oversizing.

(35) The embodiment of the cross-compound arrangement for carbon capture reduces the oversizing, costs and departure from best efficiency points of major capital intensive equipment like low pressure heaters, condenser, cooling tower, turbine foundations, etc.

(36) The selection of smaller low pressure turbines in a cross compound design optimised for carbon capture compared to tandem compound designs reduces the height of turbine generator building by reducing the clearance necessary for the main turbine hall crane to move the outer casing of the low pressure turbines above the isolated phase bus connections to the generator.

(37) The splitting of generation capacity into smaller generators located in different trains of the cross compound solution reduces the rotor tube withdrawal length compared to the bigger generator of tandem compound designs. This reduces the overall length of the turbine generator building.

(38) The width of the turbine generator building for the cross compound arrangement can be optimised for the additional lay-down area by proper location of the control room.

(39) Independent start-up/shut-down, overspeed testing, is possible.

(40) The response of the power plant with PCC with regard to load fluctuations and transient/peaking power capability is considerably improved compared to a tandem compound arrangement.

(41) The embodiment of FIG. 6 applies the invention to a generator system of a power plant implementing carbon capture made up of two power units and having two steam turbine trains.

(42) It comprises two main rotor trains identified as ROTOR 1 and ROTOR 2.

(43) Each rotor train (typically) comprises of a high pressure turbine (HP), an intermediate pressure turbine (IP), one or more low pressure turbines (LP11, LP12, LP21, LP22) and an electric generator (GEN1, GEN2) mounted on bearings and attached with couplings for transmission of power.

(44) Further the LP turbines from the two units (LP 13 and LP 23) are mounted on a different rotor train (ROTOR 3) connected to either side of a common electric generator (GEN 3) with flexible couplings (23) for example clutch couplings. Thus GEN3 serves as the generator for the cross compound mounted turbine for each of the two units. This does away with the requirement of having two electric generators for each unit implementing the cross-compound arrangement.

(45) The LP turbines are connected to a condenser arrangement (CON) generally comprising separate condensers.

(46) This provides a unique solution optimised for carbon capture and storage. A third LP (LP13, LP23) of each of the first and second steam turbine trains is coupled to a common generator on a third rotor shaft via a flexible coupling. These third LPs and GEN3 may be optimised for steam flow required for PCC when it is not operational.

(47) The advantages of the cross-compound arrangement for a power plant implementing PCC set out in respect of FIG. 5 apply. Steam supplying the PCC plant can be drawn without influencing the main turbine trains (ROTOR 1 and ROTOR 2).

(48) However the coupling of the cross-compound turbines from multiple units into a single train offers further complementary advantages.

(49) The size of the generator in the turbine train dedicated for carbon capture (ROTOR 3) can be optimally selected for combined generation capacity to only cater for the loss in generation capability as a result of anticipated modes of carbon capture across multiple units within a single power station.

(50) This embodiment permits enhanced flexibility of operation of each unit within a power plant with or without carbon capture and with partial levels of carbon capture.

(51) Independent start-up/shut-down scenarios and sequences are possible for multiple units with and without carbon capture in the most optimum way.

(52) This invention provides for independent fail safe modes of disengaging low pressure turbines for carbon capture corresponding to individual trip scenarios for each unit.

(53) Independent provisions for part load operation and peaking transients for various units of a power plant with or without carbon capture can be optimally incorporated through this invention.

(54) Independent synchronisation is possible for multiple units with or without carbon capture in the most optimal manner.

(55) Independent testing of over-speed, valve-looping, no-load (barring gear) operation is possible for each turbine train with or without carbon capture.

(56) Provision of flexible couplings allows synchronous compensation for the generator in the turbine train dedicated for carbon capture, which maximises revenue earning potential.

(57) For more than two units within a single power plant with integrated carbon capture, additional units can be located on either side of the generator on ROTOR 3 (dedicated to carbon capture). The mounting of additional turbine modules in this rotor train would be dictated by engineering decisions pertaining to layout, coupling strength and rotor-dynamics.

(58) As noted above, FIG. 7 shows a simple schematic of a typical post combustion carbon capture plant such as is illustrated for example in EP2333255, for use in accordance with the invention for example with the turbine system of the previous figures.

(59) Shown schematically, a steam generator 101 is adapted in use to produce steam in use using thermal energy from combustion of carbonaceous fuel and supply steam 102 to a steam turbine system 104. It also produces combustion gases 103 generated by the combustion of carbonaceous fuel including CO2. The combustion gases including CO2 are passed to a PCC apparatus 105. The PCC apparatus has an absorber column 106 where CO2 is separated from the flue gas by means of by passing the gas through a column where the gas flows in an opposite direction to an absorbent solution in liquid phase. The PCC apparatus has a regeneration column 107 where CO2 is removed from absorbent solution by regenerative heating. The PCC apparatus has a condenser reboiler 108 disposed to receive absorbent solution and reboil the solution to regenerate lean absorbent 109. Auxiliary process steam 110 from the steam outlet(s) of the steam turbine system is used to supply latent thermal energy for the above processes.