A wide range molten salt steam generation system and operation method

Abstract

The embodiment of the present application proposes a wide-range molten salt steam generation system and operation method, which is composed of a deaerator, a two-stage booster pump, a preheater, a steam distribution device, an electric heater, a steam generator, a superheater and related valves, and is suitable for a molten salt heat storage system that can provide industrial steam at various pressure levels. The present application can adjust the feed water temperature entering the steam generator according to the change of the molten salt type to prevent the risk of solidification of the molten salt, and can preheat the steam generator and superheater during the startup process. The hybrid preheater can realize steam heating and electric heating at the same time, reducing the cost of the heat exchanger.

Description

Technical Field

[0001] The present application relates to the field of molten salt energy storage technology, and in particular to a wide-range molten salt steam generation system and an operation method. Background Art

[0002] At present, renewable energy sources such as wind power and solar energy are developing rapidly year by year. In addition, the electricity consumption of the whole society is rising year by year, and the peak-to-valley difference of power grid electricity consumption is increasing day by day. The power grid has an increasing demand for low-cost and long-life energy storage technology. Molten salt energy storage technology can convert electrical energy into thermal energy for storage. It has the advantages of low average cost, long service life, clean and pollution-free. It is one of the main energy storage methods to cope with the development of new energy in the future.

[0003] Molten salt is an excellent medium- and high-temperature heat storage medium with low vapor pressure, good fluidity and high heat storage temperature. At present, the molten salt with the largest scale of engineering application is solar salt (potassium nitrate + sodium nitrate). The biggest advantage of solar salt is good thermal stability and low corrosiveness, and the disadvantage is that the freezing point is too high, about 220°C. Water / molten salt steam generator is a common equipment in molten salt heat storage system. Generally, water is deoxygenated water. When the water temperature entering the steam generator is lower than the freezing point of molten salt, there is a risk of solidification of molten salt, especially during the system startup and shutdown stages. Molten salt is extremely difficult to handle after solidification in the heat exchanger, which may cause the heat exchanger to be directly scrapped. Therefore, preventive measures must be fully considered when designing the system. In addition, the molten salt heat storage system needs to be designed to match the changes in water supply, steam pressure and flow on the user side. The design workload is large, and there is a strong uncertainty in the implementation process. When certain boundary conditions on site change, the original design scheme may no longer be suitable. Therefore, there is a strong market demand for molten salt heat storage systems that can achieve a wide range of work. Summary of the invention

[0004] The present application aims to solve one of the technical problems in the related art at least to some extent.

[0005] To this end, the purpose of this application is to propose a wide-range molten salt steam generation system and operation method, which consists of a deaerator, a two-stage booster pump, a preheater, a steam distribution device, an electric heater, a steam generator, a superheater and related valves, and is suitable for molten salt heat storage systems that can provide industrial steam at various pressure levels. This application can adjust the feed water temperature entering the steam generator according to the change of the molten salt type to prevent the risk of solidification of the molten salt. The steam generator and superheater can be preheated during the startup process. The hybrid preheater can realize steam heating and electric heating at the same time, reducing the cost of the heat exchanger.

[0006] To achieve the above objectives, the present application proposes a wide-range molten salt steam generation system, comprising:

[0007] A hybrid preheating component, comprising a deaerator component, a preheater, a steam distribution device and an electric heater; wherein the deaerator component comprises a deaerator and a primary pump arranged at the outlet of the deaerator; wherein the outlet of the primary pump 3 is connected to the water inlet of the preheater 4; the steam distribution device and the electric heater are arranged in the preheater, and the electric heater is immersed in the deaerated water in the preheater and is located below the steam distribution device;

[0008] A steam generating assembly, comprising a secondary pump, a steam generator and a superheater; wherein the water outlet of the preheater is connected to the water inlet of the steam generator through the secondary pump; the steam outlet of the steam generator is respectively connected to the steam outlet of the preheater, the steam distribution device and the cold side inlet of the superheater, and the steam outlet of the preheater is in communication with the cold side inlet of the superheater; the cold side outlet of the superheater is connected to a steam user;

[0009] The molten salt heat exchange component comprises a molten salt heat exchange passage formed by the hot side of the superheater and the hot side of the steam generator.

[0010] In some embodiments, the molten salt inlet is connected to the hot side inlet of the superheater and the hot side outlet of the superheater, respectively.

[0011] In some embodiments, a sixth valve is provided between the molten salt inlet and the hot side inlet of the superheater; and a fifth valve is provided between the molten salt inlet and the hot side outlet of the superheater.

[0012] In some embodiments, a pressure reducing valve is arranged between the steam outlet of the steam generator and the cold side inlet of the superheater; a fourth valve is arranged between the steam outlet of the steam generator and the steam distribution device; and a second valve is arranged between the steam outlet of the steam generator and the steam outlet of the preheater.

[0013] In some embodiments, a first valve is disposed between the outlet of the deaerator and the primary pump.

[0014] In some embodiments, a third valve is provided between the water outlet of the preheater and the secondary pump.

[0015] In some embodiments, a method for operating a wide-range molten salt steam generation system is proposed, and the system in any of the above embodiments is used to adjust the wide-range molten salt steam generation, including the following steps:

[0016] During the startup process: the steam generator and the superheater are preheated in sequence. After the preheating is completed, the first valve is opened, and the deoxygenated water temperature is heated to above the freezing point of the molten salt by using an electric heater, and then fed into the steam generator and the sixth valve is opened to allow the molten salt to pass through the superheater and the cold side of the steam generator;

[0017] During normal operation: the steam output from the steam outlet of the steam generator is mixed with deoxygenated water in the preheater, the temperature of the deoxygenated water is heated to above the solidification point of the molten salt, and then is passed into the secondary pump and transported to the steam generator; the deoxygenated water in the steam generator exchanges heat with the molten salt on the hot side of the steam generator to generate high-temperature and high-pressure saturated steam; the high-temperature and high-pressure saturated steam is respectively input into the steam distribution device and the cold side of the superheater; the high-temperature and high-pressure saturated steam on the cold side of the superheater is heated by heat exchange with the molten salt on the hot side of the superheater and then sent to the steam user.

[0018] In some embodiments, when the change in the type of molten salt causes the freezing point to rise, the steam flow rate from the steam outlet of the steam generator into the preheater and the outlet pressure of the first-stage pump are increased so that the saturation temperature of the water pressure at the outlet of the first-stage pump is higher than the freezing point temperature of the molten salt.

[0019] In some embodiments, when the steam pressure required by the user increases, the outlet pressure of the secondary pump is increased; when the steam pressure required by the user remains unchanged and the flow rate decreases, the outlet pressure of the secondary pump and the opening of the fifth valve are increased and the opening of the pressure reducing valve is reduced, so that the pressure before the pressure reducing valve is higher than the steam pressure required by the steam user; the pressure after the pressure reducing valve reaches the steam pressure required by the user.

[0020] In some embodiments, the method for preheating the steam generator and the superheater is: only open the first valve and the second valve to send deoxygenated water into the preheater through the first-stage pump and start the electric heater to generate steam and use the steam to preheat the steam generator; then open the pressure reducing valve to preheat the superheater.

[0021] Compared with the prior art, this application has the following advantages:

[0022] This application is applicable to the molten salt heat storage system, which can adjust the system operation mode to meet user needs when the parameters such as feed water temperature, feed water pressure, steam pressure, steam flow rate, etc. change. Therefore, this application can solve the problem of molten salt solidification in the steam generator caused by low feed water temperature and the narrow working range of the existing molten salt system, and is used to provide industrial steam at various pressure levels.

[0023] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0025] Figure 1 is a schematic structural diagram of a wide-range molten salt steam generation system proposed in one embodiment of the present application;

[0026] In the figure, 1, deaerator; 2, first valve; 3, primary pump; 4, preheater; 5, second valve; 6, steam distribution device; 7, electric heater; 8, third valve; 9, secondary pump; 10, steam generator; 11, fourth valve; 12, pressure reducing valve; 13, superheater; 14, fifth valve; 15, sixth valve. DETAILED DESCRIPTION

[0027] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be construed as limiting the present application. On the contrary, the embodiments of the present application include all changes, modifications and equivalents that fall within the spirit and connotation of the appended claims.

[0028] To achieve the above purpose, see Figure 1 The present application proposes a wide-range molten salt steam generation system, comprising: a hybrid preheating component, a steam generation component and a molten salt heat exchange component; wherein

[0029] The hybrid preheating component includes a deaerator component, a preheater 4, a steam distribution device 6 and an electric heater 7; wherein the deaerator component includes a deaerator 1 and a primary pump 3 arranged at the outlet of the deaerator 1; wherein the outlet of the primary pump 3 is connected to the water inlet of the preheater 4; the steam distribution device 6 and the electric heater 7 are arranged in the preheater 4, and the electric heater 7 is immersed in the deaerated water in the preheater 4 and is located below the steam distribution device 6;

[0030] Specifically, the hybrid preheating component includes a deoxygenation component, a preheater 4, a steam distribution device 6 and an electric heater 7, wherein the deoxygenation component includes a deoxygenator 1 and a primary pump 3 arranged at the outlet of the deoxygenator 1; and the water outlet of the deoxygenator 1 is connected to the inlet of the primary pump 3, and the outlet of the primary pump 3 is connected to the water inlet of the preheater 4, so that deoxygenated water is generated in the deoxygenator 1, and the deoxygenated water in the deoxygenator 1 is input into the preheater 4 through the primary pump 3, so that the preheater 4 contains a certain liquid level of deoxygenated water.

[0031] Preferably, a first valve 2 is provided between the outlet of the deaerator 1 and the primary pump 3, and the flow rate of the deoxygenated water is adjusted by controlling the opening of the first valve 2. In this embodiment, the primary pump 3 can control the pressure on the water side of the preheater 4. When the saturation temperature corresponding to the outlet water pressure of the deaerator 1 is lower than the freezing point temperature of the molten salt, the primary pump 3 can increase the pressure of the deoxygenated water until its saturation temperature is higher than the freezing point temperature of the molten salt.

[0032] In this embodiment, the steam distribution device 6 and the electric heater 7 are both arranged in the preheater 4, wherein the electric heater 7 is immersed in the deoxygenated water. In other words, the electric heater 7 is always below the liquid level of the deoxygenated water when working to prevent the deoxygenated water from being damaged when the deoxygenated water is converted into steam; and the electric heater 7 can achieve peak and frequency regulation by controlling the change of electric power, and in this embodiment, the steam distribution device 6 is arranged above the electric heater 7. When steam is introduced into the steam distribution device 6, the high-temperature steam can be mixed with the deoxygenated water and the temperature of the deoxygenated water can be rapidly increased.

[0033] A steam generating assembly, comprising a secondary pump 9, a steam generator 10 and a superheater 13; wherein the water outlet of the preheater 4 is connected to the water inlet of the steam generator 10 via the secondary pump 9; the steam outlet of the steam generator 10 is respectively connected to the steam outlet of the preheater 4, the steam distribution device 6 and the cold side inlet of the superheater 13, and the steam outlet of the preheater 4 is communicated with the cold side inlet of the superheater 13; the cold side outlet of the superheater 13 is connected to a steam user;

[0034] Specifically, the steam generating assembly includes a secondary pump 9, a steam generator 10 and a superheater 13; wherein the steam generator 10 and the superheater 13 are both heat exchange devices, each including a hot side and a cold side; wherein the cold side inlet and the cold side outlet of the steam generator 10 correspond to the water inlet and the steam outlet of the steam generator 10, respectively. In this embodiment, the water outlet of the preheater 4 is connected through the secondary pump 9 and the water inlet of the steam generator 10, that is, deoxygenated water is introduced into the cold side inlet of the steam generator 10, and a heat medium, i.e., molten salt, is introduced into the hot side of the steam generator 10, and the deoxygenated water entering the steam generator 10 is heated to generate high-temperature and high-pressure saturated steam.

[0035] Preferably, a third valve 8 is provided between the water outlet of the preheater 4 and the secondary pump 9, and the third valve 8 is used to adjust the flow rate of the deoxygenated water entering the steam generator 10. In this embodiment, the secondary pump 9 can control the pressure on the water side of the steam generator 10. In addition, the high-temperature and high-pressure saturated steam generated in the steam generator 10 is introduced into the cold side inlet of the superheater 13. After the high-temperature and high-pressure saturated steam generated in the steam generator 10 exchanges heat with the heat medium on the hot side of the superheater 13, i.e., molten salt, the generated steam is connected to the user steam.

[0036] In this embodiment, the steam outlet of the steam generator 10 is connected to the steam outlet of the preheater 4, the steam distribution device 6 and the cold side inlet of the superheater 13, respectively, and in some embodiments, a pressure reducing valve 12 is provided between the steam outlet of the steam generator 10 and the cold side inlet of the superheater 13; a fourth valve 11 is provided between the steam outlet of the steam generator 10 and the steam distribution device 6; and a second valve 5 is provided between the steam outlet of the steam generator 10 and the steam outlet of the preheater 4. That is, a part of the high-temperature and high-pressure saturated steam generated in the steam generator 10 passes through the pressure reducing valve 12, is reduced to the steam pressure required by the user, and then passes into the cold side of the superheater 13, and the other part passes into the steam distribution device 6 through the fourth valve 11 to be mixed with the deoxygenated water in the preheater 4.

[0037] It should be noted that a second valve 5 is provided between the steam outlet of the steam generator 10 and the steam outlet of the preheater 4, and the steam outlet of the preheater 4 is connected to the cold side inlet of the superheater 13. In the initial startup stage of the system, the steam of the preheater 4 can be passed into the steam generator 10 and the superheater 13 through the second valve 5 to preheat the steam generator 10 and the superheater 13.

[0038] In this embodiment, the preheater 4 uses the electric heater 7 to heat the deoxygenated water until its temperature exceeds the freezing point of the molten salt when the wide-range molten salt steam generation system is started. After the equipment is operating normally, the steam generated by the steam generator 10 is used to heat the deoxygenated water until its temperature exceeds the freezing point of the molten salt, so that the temperature of the deoxygenated water entering the steam generator 10 is always greater than the freezing point temperature of the molten salt.

[0039] A molten salt heat exchange assembly, which includes a molten salt heat exchange path formed by a hot side of a superheater 13 and a hot side of a steam generator 10;

[0040] Specifically, the molten salt inlet is connected to the hot side inlet and the hot side outlet of the superheater 13 respectively. Preferably, a sixth valve 15 is arranged between the molten salt inlet and the hot side inlet of the superheater 13; a fifth valve 14 is arranged between the molten salt inlet and the hot side outlet of the superheater 13.

[0041] For example, in this embodiment, the high-temperature molten salt enters the hot side inlet of the superheater 13 through the molten salt inlet through the sixth valve 15, and after heat exchange with the high-temperature and high-pressure saturated steam on the cold side of the superheater 13, enters the hot side inlet of the steam generator 10, and after heat exchange with the deoxygenated water entering the steam generator 10, flows out through the hot side outlet of the steam generator 10 to become low-temperature molten salt. The sixth valve 15 is used to control the molten salt flow rate to achieve the steam superheat required by the user. In this embodiment, the high-temperature molten salt can also be directly introduced into the hot side inlet of the steam generator 10 through the molten salt inlet or through the fifth valve 14, and heat exchange with the deoxygenated water of the steam generator 10. In this embodiment, the load adaptive function can be realized by linking the secondary pump 9, the pressure reducing valve 12 and the sixth valve 15, and the working pressure and steam output of the steam generator 10 can be flexibly adjusted; the working pressure is increased under partial load of the steam generator 10.

[0042] In some embodiments, a method for operating a wide-range molten salt steam generation system is proposed, and the system in any of the above embodiments is used to adjust the wide-range molten salt steam generation, including the following steps:

[0043] During the startup process: the steam generator 10 and the superheater 13 are preheated in sequence. After the preheating is completed, the first valve 2 is opened, and the deoxygenated water is heated to a temperature above the freezing point of the molten salt by the electric heater 7, and then fed into the steam generator 10 and the sixth valve 15 is opened to allow the molten salt to pass through the superheater 13 and the cold side of the steam generator 10;

[0044] During normal operation: the steam output from the steam outlet of the steam generator 10 is mixed with deoxygenated water in the preheater 4, the temperature of the deoxygenated water is heated to above the solidification point of the molten salt, and then is passed into the secondary pump 9 to be transported to the steam generator 10; the deoxygenated water in the steam generator 10 exchanges heat with the molten salt on the hot side of the steam generator 10 to generate high-temperature and high-pressure saturated steam; the high-temperature and high-pressure saturated steam is respectively input to the steam distribution device 6 and the cold side of the superheater 13; the high-temperature and high-pressure saturated steam on the cold side of the superheater 13 is heated by heat exchange with the molten salt on the hot side of the superheater 13 and then sent to the steam user.

[0045] Specifically, during the startup process: open the first valve 2 and the second valve 5, and close the other valves; first send a portion of the deoxygenated water into the preheater 4 through the primary pump 3, start the electric heater 7 to heat the deoxygenated water to generate steam, and use the steam to preheat the steam generator 10; after the preheating of the steam generator 10 is completed, open the pressure reducing valve 12 to start preheating the superheater 13; after the overall preheating is completed, close the second valve 5 and the pressure reducing valve 12, first use the electric heater 7 to heat the temperature of the deoxygenated water to above the freezing point of the molten salt, and then send the high-temperature deoxygenated water into the steam generator 10 through the secondary pump 9, and then open the sixth valve 15 to allow the molten salt to enter the superheater 13 and the steam generator 10.

[0046] During normal operation: close the second valve 5 and the fifth valve 14, and open other valves; the deoxygenated water at the outlet of the deaerator 1 is sent to the preheater 4 through the primary pump 3, the outlet pressure of the primary pump 3 is determined according to the solidification temperature of the molten salt, the steam from the outlet of the steam generator 10 is mixed with the deoxygenated water, and the deoxygenated water absorbs heat and the temperature rises above the solidification point of the molten salt; the high-temperature deoxygenated water enters the steam generator 10 after passing through the third valve 8 and the secondary pump 9, and the outlet pressure of the secondary pump 9 is determined according to the steam pressure required by the user; the deoxygenated water absorbs the heat of the molten salt and is converted into high-temperature and high-pressure saturated steam, a part of the saturated steam enters the steam distribution device 6 through the fourth valve 11, and then mixes with the low-temperature deoxygenated water in the preheater 4, and the remaining saturated steam enters the superheater 13 through the pressure reducing valve 12 for further superheating and then is transported to the steam user; the high-temperature molten salt enters the superheater 13 and the steam generator 10 in turn through the sixth valve 15 to release heat.

[0047] In some embodiments, when the change in the type of molten salt causes the freezing point to rise, the steam flow rate from the steam outlet of the steam generator 10 into the preheater 4 and the outlet pressure of the first-stage pump 3 are increased so that the saturation temperature of the water pressure at the outlet of the first-stage pump 3 is higher than the freezing point temperature of the molten salt.

[0048] In some embodiments, when the steam pressure required by the user increases, the outlet pressure of the secondary pump 9 is increased; when the steam pressure required by the user remains unchanged and the flow rate decreases, the outlet pressure of the secondary pump 9 and the opening of the fifth valve 14 are increased and the opening of the pressure reducing valve 12 is reduced, so that the pressure before the pressure reducing valve 12 is higher than the steam pressure required by the steam user; the pressure after the pressure reducing valve 12 reaches the steam pressure required by the user.

[0049] It should be noted that, in the description of this application, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. In addition, in the description of this application, unless otherwise specified, the meaning of "plurality" is two or more.

[0050] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing the steps of a specific logical function or process, and the scope of the preferred embodiments of the present application includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present application belong.

[0051] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0052] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A wide-range molten salt steam generation system, characterized in that: include: A hybrid preheating assembly, including a deaerator assembly, a preheater, a steam distribution device and an electric heater; The deaerator assembly includes a deaerator and a primary pump disposed at the outlet of the deaerator, and a first valve is disposed between the outlet of the deaerator and the primary pump; the outlet of the primary pump is connected to the water inlet of the preheater; the steam distribution device and the electric heater are disposed in the preheater, and the electric heater is immersed in the deoxygenated water in the preheater and is located below the steam distribution device; A steam generating assembly, comprising a secondary pump, a steam generator and a superheater; wherein the water outlet of the preheater is connected to the water inlet of the steam generator through the secondary pump; the steam outlet of the steam generator is respectively connected to the steam outlet of the preheater, the steam distribution device and the cold side inlet of the superheater, and a pressure reducing valve is arranged between the steam outlet of the steam generator and the cold side inlet of the superheater; a fourth valve is arranged between the steam outlet of the steam generator and the steam distribution device; a second valve is arranged between the steam outlet of the steam generator and the steam outlet of the preheater; the steam outlet of the preheater is communicated with the cold side inlet of the superheater, and the cold side outlet of the superheater is connected to a steam user; The molten salt heat exchange component comprises a molten salt heat exchange passage formed by the hot side of the superheater and the hot side of the steam generator; a sixth valve is arranged between the molten salt inlet and the hot side inlet of the superheater; and a fifth valve is arranged between the molten salt inlet and the hot side outlet of the superheater.

2. The system according to claim 1, characterized in that A third valve is arranged between the water outlet of the preheater and the secondary pump.

3. A method for operating a wide-range molten salt steam generation system, characterized in that: Using the system described in any one of claims 1 or 2 to regulate wide-range molten salt steam generation, comprising the following steps: During the startup process: the steam generator and the superheater are preheated in sequence. After the preheating is completed, the first valve is opened, and the deoxygenated water temperature is heated to above the freezing point of the molten salt by using an electric heater, and then fed into the steam generator and the sixth valve is opened to allow the molten salt to pass through the superheater and the cold side of the steam generator; During normal operation: the steam output from the steam outlet of the steam generator is mixed with deoxygenated water in the preheater, the temperature of the deoxygenated water is heated to above the solidification point of the molten salt, and then is passed into the secondary pump and transported to the steam generator; the deoxygenated water in the steam generator exchanges heat with the molten salt on the hot side of the steam generator to generate high-temperature and high-pressure saturated steam; the high-temperature and high-pressure saturated steam is respectively input into the steam distribution device and the cold side of the superheater; the high-temperature and high-pressure saturated steam on the cold side of the superheater is heated by heat exchange with the molten salt on the hot side of the superheater and then sent to the steam user.

4. The method according to claim 3, characterized in that When the change in the type of molten salt causes the freezing point to rise, the steam flow rate entering the preheater from the steam outlet of the steam generator and the outlet pressure of the primary pump are increased so that the saturation temperature of the water pressure at the outlet of the primary pump is higher than the freezing point temperature of the molten salt.

5. The method according to claim 3, characterized in that: When the steam pressure required by the user increases, the outlet pressure of the secondary pump is increased; when the steam pressure required by the user remains unchanged and the flow rate decreases, the outlet pressure of the secondary pump and the opening of the fifth valve are increased and the opening of the pressure reducing valve is reduced, so that the pressure before the pressure reducing valve is higher than the steam pressure required by the steam user; the pressure after the pressure reducing valve reaches the steam pressure required by the user.

6. The method according to claim 3, characterized in that The method for preheating the steam generator and the superheater is: only open the first valve and the second valve to send deoxygenated water into the preheater through the first-stage pump and start the electric heater to generate steam and use the steam to preheat the steam generator; then open the pressure reducing valve to preheat the superheater.

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