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EP-4737692-A1 - METHOD OF OPERATING A SUPER-CRITICAL CO2 POWER PLANT AND SUPER-CRITICAL CO2 POWER PLANT

EP4737692A1EP 4737692 A1EP4737692 A1EP 4737692A1EP-4737692-A1

Abstract

The invention relates to a method of operating a supercritical CO2 power plant (1) comprising a combustor (3) and a gas turbine (4) having a turbine shaft (9) sealed against a turbine housing (11) in at least two sealing sections (10) by several shaft seals (12, 13, 14, 15), in particular non-contacting shaft seals, the method including the steps of burning a gaseous fuel with oxygen and a CO 2 working fluid in the combustor (3) and expanding the exhaust gas in the gas turbine (4), characterized in that a seal steam is fed to the gas turbine (4) to avoid that CO2 can leave the turbine housing (11) into the atmospheric environment (17) and to avoid that ambient air can enter the turbine housing (11), wherein the seal steam is water steam.

Inventors

  • TERWEY, BERND
  • PIEPER, NORBERT
  • JONSHAGEN, KLAS

Assignees

  • Siemens Energy, Inc.

Dates

Publication Date
20260506
Application Date
20241029

Claims (14)

  1. Method of operating a super-critical CO2 power plant (1) comprising a gas turbine (4) having a turbine shaft (9) sealed against a turbine housing (11) in at least two sealing sections (10) by several shaft seals (12, 13, 14, 15), in particular non-contacting shaft seals, the method including the step of expanding a hot and pressurized CO2 working fluid in the gas turbine (4), characterized in that a seal steam is fed to the gas turbine (4) to avoid that CO2 can leave the turbine housing (11) into the atmospheric environment (17) and to avoid that ambient air can enter the turbine housing (11), wherein the seal steam is water steam.
  2. Method according to claim 1, characterized in that the CO2 working fluid has a share of CO2 larger than 85% by mass.
  3. Method according to claim 1 or 2, characterized in that the seal steam is introduced into an annular chamber (18) provided between two shaft seals (12, 13), in particular provided between two inner shaft seals (12, 13) .
  4. Method according to claim 1 or 2, characterized in that the seal steam is introduced into an annular chamber directly upstream of at least one sealing section (10).
  5. Method according to claim 3 or 4, characterized in that the introduced seal steam has a pressure, which is higher than the pressure within a chamber of the gas turbine (4) arranged in an inward direction directly next to the annual chamber (18) into which the seal steam is introduced.
  6. Method according to one of the foregoing claims, characterized in that a pressure within an annular chamber (19) between two outermost shaft seals (14, 15) of a sealing section (10) is kept below the pressure of atmospheric environment (17).
  7. Method according to one of the foregoing claims, characterized in that the CO2 working fluid is heated before expansion using a combustor (3) or a heat exchanger (20).
  8. Method according to claim 7, characterized by the further steps of cooling the exhaust gas in a heat exchanger (6), separating the water contained in the exhaust gas in a condenser (7), compressing the remaining exhaust gas in a compressor (8), returning at least a part of the exhaust gas to the combustor (3) or to the heat exchanger (20) via the heat exchanger (6).
  9. Method according to claim 8, characterized by the further step of discharging at least a part of the exhaust gas leaving the compressor (8) for further use.
  10. Method according to claim 7 or 8, characterized in that water separated in the condenser (7) is superheated, in particular in the heat exchanger (6), and is reintroduced in the gas turbine (4) as seal steam.
  11. Super-critical CO2 power plant (1) comprising a gas turbine (4) designed to be operated with CO2 as a working fluid, wherein the gas turbine (4) comprises a turbine housing (11), a turbine shaft (9) extending through the turbine housing (11) and at least two sealing sections (10) sealing the turbine shaft (9) against the turbine housing (11), each of said sealing sections (10) comprising several shaft seals (12, 13, 14, 15), characterized in that the super-critical CO2 power plant (1) comprises a water steam source fluidly connected to at least one chamber arranged within at least one of the sealing sections (10), wherein the at least one chamber (18) is preferably positioned between two inner shaft seals (12, 13) of the at least one sealing section (10), or to at least one chamber of the gas turbine arranged directly next to at least one of the sealing sections (10) in an inward direction.
  12. Super-critical CO2 power plant (1) according to claim 11, characterized in that the water steam source comprises a condenser (7) designed and arranged for separating water from exhaust gas of the gas turbine (4), and a heat exchanger (6) fluidly connected to the condenser (7) to heat water coming from the condenser (7) .
  13. Super-critical CO2 power plant (1) according to one of claims 11 or 12, characterized in that at least one sealing section (10) is provided with an annular chamber (19) fluidly connected to a vacuum source of the super-critical CO2 power plant (1).
  14. Super-critical CO2 power plant (1) according to one of claims 11 to 13, characterized in that it comprises a heat exchanger (6) fluidly connected to the downstream end of the gas turbine (4) to receive and cool the exhaust gas of the gas turbine (4), a condenser (7) fluidly connected to the heat exchanger (6) and designed for separating water from the exhaust gas, a compressor (8) fluidly connected to the condenser (7) to receive CO2 from the condenser (7), wherein the compressor (8) is fluidly connected to the combustor (3), preferably via the heat exchanger (6).

Description

The invention relates to a method of operating a super-critical CO2 power plant comprising a gas turbine having a turbine shaft sealed against a turbine housing in at least two sealing sections by several shaft seals, in particular non-contacting shaft seals, the method including the step of expanding a hot and pressurized CO2 working fluid in the gas turbine. As an alternative to water-steam-cycles there are concepts using CO2 as a working fluid for thermal cycles in power plants. The main advantages of using CO2 are the more compact design of the turbomachinery due to the higher density of the fluid and the reduced complexity of the cycle. In these cycles CO2 may be used for waste heat recovery or with internal combustion with pure oxygen. In the case of internal combustion, the CO2 is a product and thus the surplus can be captured for subsequent sequestration or usage of CO2. The leakage of CO2 from a turbine through the shaft seals in this context is disadvantageous for the capture rate. In both cases it is important to avoid or reduce the CO2 leakage at the outermost rotor-stator seals near the radial bearings of the turbine. The leakage of hot CO2 gas can pose a safety risk due to its high temperature, which can potentially cause burns. Moreover, CO2 is a hazardous substance. In high concentrations, it can displace oxygen in the air, leading to an increased risk of asphyxiation for people in the vicinity. It is also a greenhouse gas that contributes to global warming. Furthermore, CO2, when captured, can be utilized for various industrial purposes, such as in the food and beverage industry for carbonation, in enhanced oil recovery operations, or even as a raw material for producing fuels and chemicals. Therefore, preventing CO2 leakage ensures that this valuable resource is not wasted. In a typical steam turbine with non-contacting outer seals, seal steam is managed across multiple interstage chambers, with the final chamber, known as gland steam, operating under vacuum conditions maintained by the condenser. This vacuum draws in ambient air, mixing it with the steam. However, for a CO2 turbine, such ingress of ambient air is problematic as it contains gases like oxygen and nitrogen that cannot be recompressed and reintroduced into the cycle without contaminating the CO2 working fluid. Starting from this prior art it is an object of the present invention to provide an optimized method of the above-mentioned kind. In order to solve this object the present invention provides a Method of operating a super-critical CO2 power plant comprising a gas turbine having a turbine shaft sealed against a turbine housing in at least two sealing sections by several shaft seals, in particular non-contacting shaft seals, the method including the step of expanding a hot and pressurized CO2 working fluid in the gas turbine, characterized in that a seal steam is fed to the gas turbine to avoid that CO2 can leave the turbine housing into the atmospheric environment and to avoid that ambient air can enter the turbine housing, wherein the seal steam is water steam. The introduced seal steam prevents ambient air from entering the turbine housing through the at least one sealing section and contaminating the exhaust gas. Moreover, the seal steam prevents exhaust gas from leaving the turbine housing. The behaviour of shaft seals with water steam is well understood, allowing for reliable operation based on established steam turbine practices. Preferably, the CO2 working fluid has a share of CO2 larger than 85% by mass. The seal steam can be introduced into an annular chamber provided between two shaft seals, preferably between two inner shaft seals. Alternatively or additionally, the seal steam can be introduced into an annular chamber directly upstream of at least one sealing section. In this case, a separation barrier is preferably used to maintain the integrity of the system. Preferably, the introduced seal steam has a pressure, which is higher than the pressure within a chamber of the gas turbine arranged in an inward direction directly next to the annual chamber into which the seal steam is introduced. This higher pressure ensures that no CO2 can leave the turbine hosing potentially enabling a 100% CO2 capture rate and enhancing CO2 storage efficiency. Rather, a small proportion of the seal steam will enter the turbine housing and mix with the exhaust gas. However, this is not a problem as the water steam can be easily separated from the exhaust gas at the cold end of the cycle. A pressure within an annular chamber between two outer shaft seals of a sealing section is preferably kept below the pressure of atmospheric environment in order to prevent a leakage of seal steam through the outermost shaft seal. Preferably, the CO2 working fluid is heated before expansion using a combustor or a heat exchanger. The heat exchanger can, for example, be operated with the waste heat from another gas turbine process or a chemical proces