Through-flow design method for small-flow high-temperature high-pressure steam turbine

Abstract

The invention discloses a through-flow design method for a small-flow high-temperature high-pressure steam turbine. The method comprises the following steps that S1, a high-rotating-speed single-cylinder engine is selected according to the volume flow; s2, primarily selecting a creep-resistant variable blade according to parameters after the regulation stage, and iteratively designing an impeller and a blade root; s3, under the strength constraint, optimizing the dynamic and static area, the blade profile, the blade number and the root diameter to obtain the highest efficiency by taking the optimal temperature after stage regulation as a target, and if the strength is insufficient, gradually reducing the temperature and then performing optimization; and S4, designing the regulating stage structure of the steam turbine on the basis of the optimal design temperature after the regulating stage. By increasing the rotating speed of the steam turbine, the regulating stage intensively bears a large part of enthalpy drop, the optimal design temperature after the regulating stage is found under the condition that the strength and the steam-driven efficiency are both met by taking a steam parameter after the regulating stage as an iteration variable, and the materials and structures of a blade root, an impeller and a rotor are reversely selected according to the optimal design temperature after the regulating stage, so that the enthalpy drop is reduced. Adjusting-stage customized design is achieved, then the material grade of the cylinder is reduced, and a traditional high-pressure cylinder is replaced with a single-cylinder structure.

Description

Technical Field

[0001] This invention relates to the field of steam turbine flow path technology, specifically a flow path design method for high-temperature, high-pressure, low-power steam turbines. Background Technology

[0002] A steam turbine is a device that uses steam to drive a generator and produce electrical energy. The flow path of a steam turbine refers to the entire flow channel through which steam travels from the inlet to the outlet, and the entire process by which the steam converts thermal energy into mechanical work step by step within this channel. A conventional steam turbine has a regulating stage in its high-pressure cylinder. A nozzle grid and the following moving blade grid constitute the basic unit of the steam turbine—a "stage." Multiple stages connected in series form a multi-stage steam turbine. The first stage, because it also has a flow regulation function, is called the "regulating stage" (also known as the velocity stage), and its diameter is usually larger than that of the subsequent pressure stages; it achieves load regulation by partially changing the flow area through the steam inlet. After the main steam expands through the nozzle of the regulating stage, its pressure and temperature drop sharply, and its velocity increases sharply. The high-speed steam flow impacts the moving blades, completing the main work.

[0003] Current flow path designs for high-temperature, high-pressure steam turbines are based on rated operating conditions, distributing enthalpy drops at each stage according to the "constant speed ratio" principle. This method is suitable for turbines with a double-cylinder structure, where the high-pressure section is located in the inner cylinder. However, when applied to high-temperature, high-pressure steam turbines with small volumetric flow rates, this traditional design method is limited by the double-cylinder structure. This structure forces the high-pressure section to use partial steam intake to maintain the speed ratio, leading to a surge in partial steam intake losses and a sharp drop in overall efficiency. Furthermore, the double-cylinder design results in larger dimensions, higher material consumption, and the rotor must be made of high-grade creep-resistant alloys with good high-temperature, high-pressure creep resistance, further increasing material costs. Therefore, the traditional flow path design method is no longer suitable for the high-efficiency and economical requirements of small-volume-flow high-temperature, high-pressure steam turbines. Summary of the Invention

[0004] This invention aims to solve at least one of the technical problems existing in the prior art. Therefore, the purpose of this invention is to provide a flow path design method for a low-flow-rate, high-temperature, and high-pressure steam turbine, mainly to address the problems of low steam inlet efficiency in the high-pressure section and high material costs for the cylinder structure and high-temperature rotor.

[0005] The flow path design method for a low-flow-rate, high-temperature, and high-pressure steam turbine according to the present invention includes the following steps: S1. Determine the operating speed of the steam turbine and select a high-speed single-cylinder unit based on the volumetric capacity; S2. Preliminary design of the regulating stage structure: Based on the steam parameters after the regulating stage, select moving blades that meet the high-temperature creep strength. Simultaneously, based on the creep limit of the medium-temperature rotor material, iteratively design the impeller and blade root structure of the regulating stage so that the blade root, impeller, and rotor simultaneously meet the strength requirements at the highest allowable temperature. S3. Optimize the steam turbine efficiency of the regulating stage. Under strength constraints, with the optimal design temperature after the regulating stage as the target, optimize the dynamic and static area, dynamic blade profile, number of blades, and root diameter of the regulating stage to obtain the highest efficiency. Then, perform strength verification of the regulating stage. If the strength verification fails, gradually reduce the temperature after the regulating stage and repeat this step until the optimal design temperature after the regulating stage is found. S4. After performing variable operating condition calculations for the entire machine, adjust the flow path structure and design the turbine regulating stage structure based on the optimal design temperature after the regulating stage.

[0006] The aforementioned flow path design method for a low-flow-rate, high-temperature, and high-pressure steam turbine increases the turbine's rotational speed, causing the regulating stage to bear a larger portion of the enthalpy drop. Using the steam parameters after the regulating stage as iterative variables, the optimal design temperature after the regulating stage is found while satisfying both strength and steam kinetic efficiency. Based on this optimal design temperature, the materials and structures of the blade root, impeller, and rotor are selected in reverse order to achieve customized design of the regulating stage. This allows for a reduction in the grade of cylinder materials, thereby replacing the traditional high-pressure cylinder with a single-cylinder structure.

[0007] As a preferred embodiment of the present invention, in step S1, if the volumetric flow rate is ≤0.4606m / s, a high-speed single-cylinder unit with a speed of 8000rpm is selected; if the volumetric flow rate is >0.4606m / s, a high-speed single-cylinder unit with a speed of 7200rpm is selected.

[0008] As a preferred embodiment of the present invention, the blade root structure in step S2 adopts a four-forked blade root, and the impeller structure adopts a trapezoidal shape. Attached Figure Description

[0009] Figure 1 A step-by-step diagram of a flow path design method for a low-flow, high-temperature, and high-pressure steam turbine. Detailed Implementation

[0010] like Figure 1 As shown, a flow path design method for a low-flow-rate, high-temperature, and high-pressure steam turbine includes the following steps: S1. Determine the operating speed of the steam turbine and select a high-speed single-cylinder unit based on the volumetric capacity; S2. Preliminary design of the regulating stage structure: Based on the steam parameters after the regulating stage, select moving blades that meet the high-temperature creep strength. Simultaneously, based on the creep limit of the medium-temperature rotor material, iteratively design the impeller and blade root structure of the regulating stage so that the blade root, impeller, and rotor simultaneously meet the strength requirements at the highest allowable temperature. S3. Optimize the steam turbine efficiency of the regulating stage. Under strength constraints, with the optimal design temperature after the regulating stage as the target, optimize the dynamic and static area, dynamic blade profile, number of blades, and root diameter of the regulating stage to obtain the highest efficiency. Then, perform strength verification of the regulating stage. If the strength verification fails, gradually reduce the temperature after the regulating stage and repeat this step until the optimal design temperature after the regulating stage is found. S4. After performing variable operating condition calculations for the entire machine, adjust the flow path structure and design the turbine regulating stage structure based on the optimal design temperature after the regulating stage.

[0011] The aforementioned flow path design method for a low-flow-rate, high-temperature, and high-pressure steam turbine increases the turbine's rotational speed, causing the regulating stage to bear a larger portion of the enthalpy drop. Using the steam parameters after the regulating stage as iterative variables, the optimal design temperature after the regulating stage is found while satisfying both strength and steam kinetic efficiency. Based on this optimal design temperature, the materials and structures of the blade root, impeller, and rotor are selected in reverse order to achieve customized design of the regulating stage. This allows for a reduction in the grade of cylinder materials, thereby replacing the traditional high-pressure cylinder with a single-cylinder structure.

[0012] In the aforementioned flow path design method for low-flow-rate high-temperature and high-pressure steam turbines, in step S1, if the volumetric flow rate is ≤0.4606 m³ / s, a high-speed single-cylinder unit of 8000 rpm is selected; if the volumetric flow rate is >0.4606 m³ / s, a high-speed single-cylinder unit of 7200 rpm is selected. The high-speed single-cylinder module is optimally matched according to the volumetric flow rate threshold of 0.4606 m³ / s. Increasing the speed can reduce the root diameter of the high-pressure section, achieving full-circumference steam intake and maximizing the high efficiency advantage under low-flow conditions. After increasing the flow rate, the speed is appropriately reduced to balance flow capacity and efficiency.

[0013] The blade root structure in step S2 adopts a four-forked blade root, and the impeller structure adopts a trapezoidal shape, which can improve the structural strength of the blade root and the impeller.

[0014] Specifically, in step S3, based on the creep strength characteristics of the rotor material (i.e., the higher the temperature, the faster the yield strength decreases), 450℃ is initially determined as the temperature after the regulating stage. The specific steps for determining the temperature after the regulating stage are as follows: 1. Select the condenser rotor material 30Cr2Ni4MoV, and fit the creep strength of the rotor material to the material's characteristic curve. 2. Perform preliminary thermodynamic calculations of the turbine to determine the impact of temperature changes after the regulating stage on the overall efficiency. 3. Based on the thermodynamic calculation results, design the regulating stage structure at the optimal efficiency point. Since the structural design is affected by the material, especially its creep properties, if the structural design cannot meet the requirements, the temperature after the regulating stage should be appropriately reduced. Furthermore, the structural design requires a lower temperature after the regulating stage, while the thermodynamic performance requires a higher temperature. Both factors need to be considered and continuously adjusted to ultimately determine the optimal design temperature after the regulating stage as 465℃.

Claims

1. A flow passage design method for a small flow high temperature and high pressure steam turbine, characterized by, The method comprises the following steps: S1, determining the working rotating speed of the steam turbine, and selecting a high rotating speed single cylinder unit according to the volume capacity; S2, preliminarily designing the structure of the governing stage, selecting the blade of the governing stage preliminarily according to the steam parameter after the governing stage to meet the high temperature creep strength, and simultaneously designing the structure of the impeller and the blade root of the governing stage according to the creep limit of the medium temperature rotor material to make the blade root, the impeller and the rotor meet the strength at the highest allowable temperature; S3, optimizing the steam driving efficiency of the governing stage, and optimizing the dynamic and static area, the dynamic blade profile, the blade number and the root diameter of the governing stage to obtain the highest stage efficiency under the strength constraint and taking the optimal design temperature after the governing stage as the target, then checking the strength of the governing stage, if the strength checking fails, gradually reducing the temperature after the governing stage and repeating the step until the optimal design temperature after the governing stage is found; S4, adjusting the flow structure after the variable working condition calculation of the whole machine, and designing the structure of the governing stage of the steam turbine according to the optimal design temperature after the governing stage.

2. The method of flow path design of a small flow high-temperature high-pressure steam turbine according to claim 1, characterized by, In the step S1, the high rotating speed single cylinder unit of 8000 rpm is selected when the volume flow is less than or equal to 0.4606 m / s, and the high rotating speed single cylinder unit of 7200 rpm is selected when the volume flow is greater than 0.4606 m / s.

3. The method of flow path design of a small flow high-temperature high-pressure steam turbine according to claim 1, characterized by, The blade root structure in the step S2 adopts the four-way fork type blade root, and the impeller structure adopts the ladder shape.

Images