Steam turbine system for low-pressure cylinder cutting coupling fused salt heat storage and operation method

Abstract

The invention discloses a low-pressure cylinder cutting coupling fused salt heat storage steam turbine system and an operation method, relates to the technical field of power plants, and is mainly used for solving the problem that the operation flexibility of the power plants is poor in the deep peak regulation process. The system mainly comprises a medium-pressure cylinder, a low-pressure cylinder, a hydraulic control butterfly valve, a cooler, a control valve, a molten salt heat exchanger and the like. An original communicating pipe between low-pressure cylinders is replaced with a hydraulic control butterfly valve which can be closed by 100% and has zero leakage, when a four-cylinder four-steam-exhaust unit operates under the low-load working condition, steam inlet of the low-pressure cylinder on one side is cut off, steam which should enter the low-pressure cylinder to do work is used for heating fused salt, heat is stored, and the effect that a steam turbine unit operates efficiently under the low load is achieved; the problem that when the coal-fired power generation unit is in a low load state, the operation efficiency is low due to the fact that the steam flow is reduced can be effectively solved, the fused salt heat storage system and the coal-fired power generation unit are effectively coupled, and the flexibility and peak regulation performance of the unit are improved.

Description

Technical Field

[0001] This invention relates to the field of power plant technology, and in particular to a steam turbine system and its operation method that features low-pressure cylinder cutting coupled with molten salt thermal storage. Background Technology

[0002] The power system is rapidly transitioning towards a higher proportion of renewable energy. As the current "ballast" of power supply, coal-fired power units urgently need improved operational flexibility to cope with the peak-shaving challenges brought about by the large-scale grid connection of intermittent renewable energy sources such as wind and solar power. However, during deep peak shaving, the turbine unit's operating conditions deviate significantly from its design conditions, leading to a rapid decrease in the relative internal efficiency of the low-pressure cylinder and reducing the system's thermal economy. Molten salt thermal energy storage technology, due to its advantages such as high thermal density, wide operating temperature range, and low cost, has been widely used in concentrated solar power (CSP) and large-scale thermal energy storage. Therefore, under the background of deep peak shaving, effectively coupling molten salt thermal energy storage systems with coal-fired power units is an important aspect of improving unit flexibility and deep peak-shaving capabilities. Summary of the Invention

[0003] To overcome the shortcomings of the existing technology, the present invention aims to provide a steam turbine system and operation method with low-pressure cylinder cutting coupling molten salt heat storage. By replacing the original connecting pipe between the low-pressure cylinders with a hydraulically controlled butterfly valve that can be 100% closed and has zero leakage, when the four-cylinder four-exhaust steam turbine unit is running under low load conditions, the steam inlet of one low-pressure cylinder is cut off, so that the steam that should have entered the low-pressure cylinder to do work is used to heat the molten salt and store the heat, thereby improving the operating flexibility and deep peak shaving capability of the steam turbine unit.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A steam turbine system with low-pressure cylinder cutting coupling molten salt heat storage includes an intermediate-pressure cylinder 1, a #1 low-pressure cylinder 2, a #2 low-pressure cylinder 3, a hydraulic butterfly valve 4, a cooler 5, a control valve 6, a shut-off valve 7, a molten salt cold tank 8, a molten salt pump 9, a molten salt heat exchanger 10, and a molten salt hot tank 11. The steam outlet of the intermediate-pressure cylinder 1 has four branches: the first branch leads to the deaerator; the second branch connects to the steam inlets of the #1 low-pressure cylinder 2 and the #2 low-pressure cylinder 3; the third branch connects to the #2 low-pressure cylinder 3 via the cooler 5 and the control valve 6; and the fourth branch connects to the steam inlet of the molten salt heat exchanger 10 via the shut-off valve 7. The steam outlet of the molten salt heat exchanger 10 leads to the feedwater system. The #1 low-pressure cylinder 2 and the #2 low-pressure cylinder 3 are connected via a hydraulically controlled butterfly valve 4. The steam outlets of the #1 low-pressure cylinder 2 and the #2 low-pressure cylinder 3 lead to the condenser. The molten salt outlet of the molten salt cold tank 8 is connected to the molten salt inlet of the molten salt pump 9. The molten salt outlet of the molten salt pump 9 is connected to the molten salt inlet of the molten salt heat exchanger 10. The molten salt outlet of the molten salt heat exchanger 10 is connected to the molten salt inlet of the molten salt hot tank 11.

[0005] The operation method of the steam turbine system with low-pressure cylinder cutting coupling molten salt thermal storage is as follows: when the load of the coal-fired generator set is higher than 30%, the hydraulic control butterfly valve 4 is opened and the cooler 5, control valve 6 and shut-off valve 7 are closed to realize the normal operation of the four-cylinder four-exhaust steam turbine unit. When the load of the coal-fired generator set is below 30%, close the hydraulic butterfly valve 4 to completely shut off the steam inlet of the #2 low-pressure cylinder 3, open the cooler 5 and control valve 6 to ensure that a small amount of cooling steam enters the #2 low-pressure cylinder 3 to remove the heat generated by the rotor rotation; at the same time, open the shut-off valve 7 to allow the steam that should have entered the #2 low-pressure cylinder 3 to do work to enter the molten salt heat exchanger 10 to heat the molten salt. At this time, the molten salt flows out from the molten salt cold tank 8, is pressurized by the molten salt pump 9, enters the molten salt heat exchanger 10 for heat exchange, and finally flows into the molten salt hot tank 11 for storage.

[0006] The operation method of the steam turbine system with low-pressure cylinder cutting coupling molten salt thermal storage is as follows: after opening the cooler 5 and control valve 6, the flow rate of cooling steam introduced into the #2 low-pressure cylinder 3 is 10% to 20% of the outlet steam flow rate of the intermediate-pressure cylinder 1.

[0007] Compared with the prior art, the present invention has the following advantages: (1) During deep peak shaving, the steam inlet of one side of the low-pressure cylinder is cut off, so that the steam that should have entered the low-pressure cylinder to do work enters the molten salt thermal storage system to heat the molten salt, thereby improving the operational flexibility and deep peak shaving capability of the coal-fired power generation unit.

[0008] (2) When the low-pressure cylinder is cut off, a small amount of cooling steam is introduced into the cut-off low-pressure cylinder to remove the heat generated by the rotor rotation and reduce the damage to the low-pressure cylinder blades. Attached Figure Description

[0009] Figure 1 This is a system diagram of the present invention; Among them, 1. Medium-pressure cylinder, 2. #1 low-pressure cylinder, 3. #2 low-pressure cylinder, 4. Hydraulic butterfly valve, 5. Cooler, 6. Control valve, 7. Shut-off valve, 8. Molten salt cold tank, 9. Molten salt pump, 10. Molten salt heat exchanger, 11. Molten salt hot tank. Detailed Implementation The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0010] like Figure 1 As shown, the present invention discloses a steam turbine system with low-pressure cylinder cutting coupling molten salt heat storage, including intermediate-pressure cylinder 1, #1 low-pressure cylinder 2, #2 low-pressure cylinder 3, hydraulic butterfly valve 4, cooler 5, control valve 6, shut-off valve 7, molten salt cold tank 8, molten salt pump 9, molten salt heat exchanger 10, and molten salt hot tank 11. The steam outlet of the intermediate-pressure cylinder 1 has four branches: the first branch leads to the deaerator; the second branch connects to the steam inlets of the #1 low-pressure cylinder 2 and the #2 low-pressure cylinder 3; the third branch connects to the #2 low-pressure cylinder 3 via the cooler 5 and the control valve 6; and the fourth branch connects to the steam inlet of the molten salt heat exchanger 10 via the shut-off valve 7. The steam outlet of the molten salt heat exchanger 10 leads to the feedwater system. The #1 low-pressure cylinder 2 and the #2 low-pressure cylinder 3 are connected via a hydraulic butterfly valve 4. The steam outlets of the #1 low-pressure cylinder 2 and the #2 low-pressure cylinder 3 lead to the condenser. The molten salt outlet of the molten salt cold tank 8 is connected to the molten salt inlet of the molten salt pump 9. The molten salt outlet of the molten salt pump 9 is connected to the molten salt inlet of the molten salt heat exchanger 10. The molten salt outlet of the molten salt heat exchanger 10 is connected to the molten salt inlet of the molten salt hot tank 11.

[0011] The operation method of a low-pressure cylinder cut-off coupled molten salt thermal storage steam turbine system is described above. When the load of the coal-fired generator set is higher than 30%, the unit efficiency is relatively high. Therefore, the hydraulic control butterfly valve 4 is opened, and the cooler 5, control valve 6 and shut-off valve 7 are closed to realize the normal operation of the four-cylinder four-exhaust steam turbine unit.

[0012] When the load of the coal-fired power generation unit is below 30%, the steam flow into the #1 low-pressure cylinder 2 and #2 low-pressure cylinder 3 is significantly reduced, causing the relative internal efficiency of the #1 low-pressure cylinder 2 and #2 low-pressure cylinder 3 to decrease rapidly. At this time, the hydraulic butterfly valve 4 is closed, completely shutting off the steam inlet to the #2 low-pressure cylinder 3. The cooler 5 and control valve 6 are opened to ensure that a small amount of steam enters the #2 low-pressure cylinder 3 after being de-cooled and depressurized, in order to remove the heat generated by the rotor rotation. At this time, the #2 low-pressure cylinder 3 does no work and has zero output. The low-pressure rotor only plays the role of transmitting torque. At the same time, the shut-off valve 7 is opened, allowing the steam that should have entered the #2 low-pressure cylinder 3 to do work to enter the molten salt heat exchanger 10 to exchange heat with the molten salt. The steam after heat exchange goes to the feedwater system. The low-temperature molten salt flows out from the molten salt cold tank 8, is pressurized by the molten salt pump 9, and then enters the molten salt heat exchanger 10 to exchange heat with the high-temperature steam. The high-temperature molten salt after heat exchange flows into the molten salt hot tank 11 for storage.

[0013] By using the system and method of this invention, the original connecting pipe between the low-pressure cylinders is replaced with a hydraulically controlled butterfly valve that can be 100% closed and has zero leakage. When the coal-fired power generation unit is operating under low-load conditions, the steam intake to one side of the low-pressure cylinder is cut off, allowing the steam that should have entered the low-pressure cylinder to perform work to be used to heat the molten salt and store the heat. This invention can effectively reduce the problem of low operating efficiency of coal-fired power generation units under low load due to reduced steam flow, and also effectively couples the molten salt thermal storage system with the coal-fired power generation unit, improving the unit's flexibility and peak-shaving performance.

Claims

1. A low-pressure cylinder cut-off coupled molten salt heat storage steam turbine system, characterized in that, The application relates to a four-cylinder four-steam-exhaust unit, which comprises a medium-pressure cylinder (1), a #1 low-pressure cylinder (2), a #2 low-pressure cylinder (3), a liquid-controlled butterfly valve (4), a cooler (5), a control valve (6), a stop valve (7), a molten salt cold tank (8), a molten salt pump (9), a molten salt heat exchanger (10) and a molten salt hot tank (11); the steam outlet of the medium-pressure cylinder (1) has four branches, the first branch is connected with an oxygen remover, the second branch is connected with the steam inlets of the #1 low-pressure cylinder (2) and the #2 low-pressure cylinder (3), the third branch is connected with the #2 low-pressure cylinder (3) through the cooler (5) and the control valve (6), the fourth branch is connected with the steam inlet of the molten salt heat exchanger (10) through the stop valve (7), and the steam outlet of the molten salt heat exchanger (10) is connected with a feedwater system; the #1 low-pressure cylinder (2) and the #2 low-pressure cylinder (3) are connected through the liquid-controlled butterfly valve (4), and the steam outlets of the #1 low-pressure cylinder (2) and the #2 low-pressure cylinder (3) are connected with a condenser; the molten salt outlet of the molten salt cold tank (8) is connected with the molten salt inlet of the molten salt pump (9), the molten salt outlet of the molten salt pump (9) is connected with the molten salt inlet of the molten salt heat exchanger (10), and the molten salt outlet of the molten salt heat exchanger (10) is connected with the molten salt inlet of the molten salt hot tank (11).

2. The method of claim 1, wherein the turbine system is a low-pressure cylinder cut-cylinder coupled molten salt thermal storage turbine system. When the load of the coal-fired generator unit is higher than 30%, the liquid-controlled butterfly valve (4) is opened, the cooler (5), the control valve (6) and the stop valve (7) are closed, and the four-cylinder four-steam-exhaust unit is normally operated; When the load of the coal-fired generator unit is lower than 30%, the liquid-controlled butterfly valve (4) is closed, the steam inlet of the #2 low-pressure cylinder (3) is completely closed, the cooler (5) and the control valve (6) are opened, a small amount of cooling steam is ensured to enter the #2 low-pressure cylinder (3) and is used for taking away the heat generated by the rotation of the rotor, and the stop valve (7) is opened, so that the steam which should enter the #2 low-pressure cylinder (3) to do work enters the molten salt heat exchanger (10) and is used for heating the molten salt; at this time, the molten salt flows out from the molten salt cold tank (8), is pressurized by the molten salt pump (9) and then enters the molten salt heat exchanger (10) to exchange heat, and finally flows into the molten salt hot tank (11) to be stored.

3. The method of claim 2, wherein the turbine system is a low-pressure cylinder cut-cylinder coupled molten salt heat storage turbine system. After the cooler (5) and the control valve (6) are opened, the flow of the cooling steam entering the #2 low-pressure cylinder (3) is 10%-15% of the steam flow at the outlet of the medium-pressure cylinder (1).

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