CN103397918B - The back pressure type small turbine drive blower fan system of frequency conversion generator speed governing and method - Google Patents

Abstract

The invention discloses a system and method for driving a blower fan with a back-pressure type small steam turbine for speed regulation by a frequency conversion generator. The machine is connected coaxially; by controlling the output of the variable frequency generator, the speed of the back pressure small steam turbine is controlled, thereby controlling the speed of the fan. The system of the invention greatly reduces the loss of steam inlet throttling of the small steam turbine, improves operating efficiency, and fully exerts the working ability of the small steam turbine to increase operating income. The invention also discloses a back-pressure small steam turbine driven rotating equipment system with variable frequency generator speed regulation, a steam generator set and a method for adjusting the speed of the fan.

Description

Back-pressure small turbine-driven fan system and method for variable-frequency generator speed regulation

technical field

The invention relates to the technical field of energy saving of power generation systems, in particular to a back pressure small steam turbine driven fan system and method for speed regulation of frequency conversion generators.

Background technique

In large-capacity and high-parameter steam turbine power plants, fans such as steam-driven fans are usually equipped. These fans are driven by small back-pressure steam turbines, which can increase the pressure of working fluids such as air, flue gas or gas, and supply them to subsequent process systems. .

Due to the demand of the load change of the generator set, the output of the fan often changes accordingly. Therefore, the demand of the load change of the unit is usually met by changing the speed of the fan, and the speed of the fan is determined by the speed of the small steam turbine connected coaxially.

In order to meet the long-term full power of the generator set in summer, the rated output of the small steam turbine is usually larger than the rated output of the fan, and the rated output of the fan is usually larger than the output required by the rated load of the generator set, so the rated output of the small turbine is Large margin, generally above 50%. In the current small steam turbine driven fan system, the small steam turbine is equipped with a steam inlet regulating valve. By adjusting the opening of the valve, the speed of the small steam turbine can be controlled to meet the needs of the load change of the generator set. However, this configuration often causes relatively large throttling losses due to the relatively small opening of the inlet steam regulating valve of the small steam turbine during most of the running time.

In addition, since the load of the generating set is constantly changing with the demand of the grid every day, and the load varies from high to low, so at low load, the opening of the steam inlet regulating valve of the small steam turbine will be smaller, resulting in greater throttling loss . And because the ability of the small steam engine to do work cannot be brought into full play, there is also a relatively large economic loss.

Therefore, how to solve the problem of throttling and speed regulation of the existing back pressure small steam turbine driven fan system, how to develop a driving fan system that can effectively reduce the loss of small steam turbine throttling and make full use of the output of the small steam turbine is currently an issue. Problems to be solved urgently in the field of energy saving of steam turbine power plants.

Contents of the invention

The purpose of the present invention is to provide a back pressure type small steam turbine driven fan system with small throttling loss and high utilization rate of the output of the small steam turbine.

The first aspect of the present invention provides a back-pressure small steam turbine driven fan system with variable frequency generator speed regulation, the system includes a back pressure small steam turbine, a fan and a variable frequency generator, wherein,

The back pressure small steam turbine, fan and frequency conversion generator are coaxially connected;

By controlling the output of the frequency conversion generator, the rotation speed of the back pressure small steam turbine is controlled, thereby controlling the rotation speed of the fan.

In another preferred example, the small back pressure steam turbine further includes a steam extraction outlet.

In another preferred example, the steam extraction outlet is connected to a high-temperature heat source heater or a heat exchanger through a steam extraction pipeline.

In another preferred example, the steam extraction pipeline includes n-stage steam extraction pipelines, where n=1, 2, 3, 4, 5 or 6.

In another preferred example, the back-pressure small steam turbine is provided with a steam inlet pipe, and a regulating valve is arranged on the steam inlet pipe.

In another preferred example, the back-pressure small steam turbine is provided with an exhaust pipe, and the exhaust pipe is connected to a low-temperature heat source heater or a heat exchanger.

In another preferred example, the opening degree of the regulating valve is kept high for a long time, and the opening degree ranges from 70% to 100%.

In another preferred example, the fan and the variable frequency generator are respectively connected to the shaft ends on both sides of the back pressure small steam turbine; or the fan and the frequency conversion generator are connected to the same shaft of the back pressure small steam turbine end.

In another preferred example, the fan and the variable frequency generator are respectively connected to the shaft ends on both sides of the back pressure small steam turbine, and the system also includes a constant speed ratio gearbox, and the constant speed ratio gearbox is connected to the The back pressure small steam turbine, fan and frequency conversion generator are coaxially connected, wherein,

The fixed speed ratio gearbox is located between the back pressure small steam turbine and the frequency conversion generator; and/or

The fixed speed ratio gearbox is located between the blower fan and the back pressure small steam turbine.

In another preferred example, the fixed speed ratio gearbox has a clutch function.

In another preferred example, the fixed speed ratio gearbox is a clutch.

In another preferred example, the fixed speed ratio gearbox is located between the back pressure small steam turbine and the variable frequency generator, and the input end of the constant speed ratio gearbox is connected to one of the back pressure small steam turbines. The shaft end on one side is connected, and the input end of the fan is connected to the shaft end on the other side of the back pressure small steam turbine.

In another preferred example, the fixed speed ratio gearbox is located between the fan and the back pressure small steam turbine, and the input end of the constant speed ratio gearbox is connected to one side of the back pressure small steam turbine. The shaft end is connected, and the input end of the frequency conversion generator is connected with the shaft end on the other side of the back pressure small steam turbine.

In another preferred example, the input end of the frequency conversion generator is connected to the shaft end on one side of the back pressure small steam turbine, and the output end of the frequency conversion generator is connected to the input end of the fan.

In another preferred example, the fan and the variable frequency generator are connected to the same shaft end of the back pressure small steam turbine, and the system further includes a constant speed ratio gearbox, and the constant speed ratio gearbox is connected to the The back pressure small steam turbine, fan and frequency conversion generator are coaxially connected, among which,

The fixed speed ratio gearbox is located between the back pressure small steam turbine and the frequency conversion generator; or

The fixed speed ratio gearbox is located between the fan and the variable frequency generator.

In another preferred example, the fixed speed ratio gearbox is located between the back pressure small steam turbine and the variable frequency generator, and the input end of the constant speed ratio gearbox is connected to one of the back pressure small steam turbines. The shaft ends on the side are connected, and the output end of the variable frequency generator is connected with the input end of the fan.

In another preferred example, the constant speed ratio gearbox is located between the fan and the variable frequency generator, and the input end of the constant speed ratio gearbox is connected to the output end of the variable frequency generator, and the constant speed ratio gearbox is connected to the output end of the variable frequency generator. The output end of the speed ratio gearbox is connected with the input end of the fan.

In another preferred example, the fan includes: a fan whose medium is air or flue gas, a compressor whose medium is air or gas, and a gas turbine.

The second aspect of the present invention provides a back-pressure small turbine-driven rotating equipment system with variable-frequency generator speed regulation, the system includes a back-pressure small steam turbine, rotating equipment and a frequency-variable generator, wherein,

The back pressure small steam turbine, rotating equipment and frequency conversion generator are coaxially connected;

By controlling the output of the frequency conversion generator, thereby controlling the rotational speed of the back pressure small steam turbine, thereby controlling the rotational speed of the rotating equipment;

Wherein, the rotating equipment includes: a fan and a water feed pump.

The third aspect of the present invention provides a steam generator set configured with the system described in the first aspect or the second aspect.

The fourth aspect of the present invention provides a method for adjusting the fan speed in a back-pressure small steam turbine driven fan system. The system includes a back-pressure small steam turbine and a fan. A frequency conversion generator is added to the system. By adjusting the The output of the frequency conversion generator is used to control the speed of the back pressure small steam turbine, thereby controlling the speed of the fan.

It should be understood that within the scope of the present invention, the above-mentioned technical features of the present invention and the technical features specifically described in the following (such as embodiments) can be combined with each other to form new or preferred technical solutions. Due to space limitations, we will not repeat them here.

Description of drawings

Figure 1 is a schematic diagram of an existing pure condensing small steam turbine driven fan system.

Fig. 2 is a schematic diagram of the system of Embodiment 1 of the present invention.

FIG. 3 is another schematic diagram of the system of Embodiment 1 of the present invention.

Fig. 4 is a schematic diagram of the system of Embodiment 2 of the present invention.

Fig. 5 is a schematic diagram of the system of Embodiment 3 of the present invention.

detailed description

After in-depth and extensive research, the inventor found that by coaxially connecting the variable-frequency generator with the back-pressure small steam turbine, not only the output mode of the variable-frequency generator can be controlled, but also the mode of regulating valve can be partially or completely replaced to control the speed of the small steam turbine, thereby The speed of the fan is controlled, and the variable frequency generator can be used to generate electricity, so that the output of the small steam turbine can be fully utilized. The opening of the regulating valve of the small steam turbine in the present invention can maintain a high opening (70%-100%) for a long time, greatly reducing the loss caused by throttling, and making full use of the output of the small steam turbine, so that the operating efficiency of the small steam turbine is improved. 8%-20%. The present invention has been accomplished on this basis.

As used herein, "variable frequency generator" refers to a generator whose frequency of power generation varies over a larger range at any time compared to a generator with a fixed frequency for conventional power generation.

As used herein, "back pressure small steam turbine", "back pressure small steam turbine", "small steam turbine" and "small steam turbine" are used interchangeably and refer to a heat exchanger or heat network that exhausts steam to a pressure above atmospheric pressure The steam turbine is called a back pressure small steam turbine.

As used herein, "coaxially connected" means that each device is connected on the same rotating shaft system.

Back pressure small steam turbine driven fan system with variable frequency generator speed regulation

The back-pressure small turbine-driven fan system with variable frequency generator speed regulation of the present invention is used in a large-capacity high-parameter steam turbine power plant. It is one of the indispensable systems for supplying subsequent process systems.

The system of the present invention includes: a back-pressure small steam turbine, a blower fan, and a variable frequency generator, wherein the back-pressure small steam turbine is provided with a steam inlet pipeline, an exhaust steam pipeline and a regulating valve, and the steam in the steam inlet pipeline comes from the high pressure of the thermal system of the generating set Steam, the exhaust pipe is connected to the low-temperature heat source (low-pressure steam source) heater or heat exchanger, and the regulating valve is set on the steam inlet pipe to adjust the steam flow of high-pressure steam;

The fan of the present invention includes a fan whose medium is air, a compressor whose medium is air, other fans whose working medium is flue gas, a compressor or a gas turbine whose medium is gas, and the like.

The variable frequency generator and the fan are connected together on the same rotating shaft system of the back pressure small steam turbine. The variable frequency generator and fan can be respectively connected to the shaft ends on both sides of the back pressure small steam turbine, and can also be connected to the same shaft end of the back pressure small steam turbine.

When the frequency conversion generator and the fan are located at the shaft ends on both sides of the back pressure small steam turbine, and when the speed ratio between the fan and the back pressure small steam turbine, or between the back pressure small steam turbine and the frequency conversion generator is large, it can be Between the back-pressure small steam engine and the variable frequency generator, and/or on the rotating shaft between the fan and the back-pressure small steam engine, a gear box or a clutch with a clutch function and a constant speed ratio is arranged. To adjust the speed ratio of the two to meet the needs of generator load changes.

When the constant speed ratio gearbox or clutch is located between the back pressure small steam turbine and the variable frequency generator, the input end of the constant speed ratio gearbox or clutch is connected to the shaft end on one side of the back pressure small steam turbine, and the input end of the fan is connected to the The shaft ends on the other side of the back pressure small steam turbine are connected.

When the fixed-speed ratio gearbox or clutch is located between the fan and the back-pressure small steam turbine, the input end of the constant-speed ratio gearbox or clutch is connected to the shaft end on one side of the back-pressure small steam turbine, and the input end of the variable frequency generator is connected to the The shaft ends on the other side of the back pressure small steam turbine are connected.

When the variable frequency generator and the fan are located at the same shaft end of the back pressure small steam turbine, the input end of the variable frequency generator is connected to the shaft end on one side of the back pressure small steam turbine, and the output end of the variable frequency generator is connected to the input end of the fan. According to specific needs, a fixed speed ratio gearbox or a clutch with a clutch function can be set between the back-pressure small steam turbine and the variable frequency generator, or on the rotating shaft between the fan and the variable frequency generator.

When the constant speed ratio gearbox or clutch is located between the fan and the variable frequency generator, the input end of the constant speed ratio gearbox or clutch is connected to the output end of the variable frequency generator, and the output end of the constant speed ratio gearbox or clutch is connected to the input end of the fan. end connected.

When the constant speed ratio gearbox or clutch is located between the back pressure small steam turbine and the variable frequency generator, the input end of the constant speed ratio gearbox or clutch is connected to the shaft end on one side of the back pressure small steam turbine, and the output of the variable frequency generator The terminal is connected to the input terminal of the fan.

In the system of the present invention, the back-pressure small steam turbine may also include a steam extraction outlet, which is connected to a heater or a heat exchanger of a high-temperature heat source (high-pressure steam source) through a steam extraction pipeline. The back-pressure small steam turbine can be equipped with a first-level steam extraction pipeline, a second-level steam extraction pipeline or a second-level or higher extraction steam pipeline (such as a third-level steam extraction pipeline, a fourth-level steam extraction pipeline, etc.) according to the needs.

Since the back-pressure small turbine-driven fan system of the present invention adjusts the speed of the fan by controlling the output of the variable frequency generator to meet the needs of the load change of the generator set, therefore, in most of the operating hours of the year, the back-pressure small steam turbine The opening of the control valve can be kept high for a long time (the opening range is 70%-100%), even when the load of the unit becomes low, the output of the back pressure small steam turbine can be fully utilized through the change of the fan speed. Frequency conversion generator power generation not only significantly reduces the throttling loss, but also improves the operating efficiency of the back-pressure small steam turbine and increases the power sales income of the power plant.

The invention also includes a steam generator set equipped with a back pressure small steam turbine driven fan system with variable frequency generator speed regulation.

The system of the present invention can not only meet the needs of the load change of the generating set through the adjustment of the fan speed, but also can increase the power sales income of the power plant through the power generation of the frequency conversion generator. The frequency conversion power generated by the frequency conversion generator can be directly supplied to the frequency conversion Electricity users can also convert all or part of them into variable frequency electricity that matches the power grid through converters, and supply them to the power grid inside or outside the plant. If the voltage of the electricity generated by the variable frequency generator is different from that of the grid, a transformer can be installed to transform the generated electricity to a voltage that matches the grid.

In the back-pressure small steam turbine-driven fan system configured in the existing steam generator set, the output of the small steam turbine is not fully utilized during most of the running time throughout the year, especially when the unit is under low load. For example, in order to meet the needs of the unit for full power generation throughout the year and summer, a 1000MW steam generator set is usually equipped with two 50% capacity small steam turbine-driven fan systems. The power required for the rated working condition of the fan is about 6000kW, and the maximum output of the supporting small steam turbine is about 10000kW, and the output margin of the small steam turbine of each unit is (10000-6000) x2 = 8000kW. Therefore, the average unutilized power of the small steam turbines of each unit is more than 8000kW, and there is a big problem in this margin configuration.

In addition, since small steam turbines need to throttle, reduce output, and match the power required by fans (such as blowers), the opening of the control valve of small steam turbines is relatively small, and the opening is usually below 50%. There are significant throttling losses. Affect the operating efficiency of small steam turbines by more than 8%.

Compared with the prior art, the present invention has the following main advantages:

(1) Increase the common opening of the back pressure small steam turbine control valve in the current system from below 50% to 70%-100%, and can maintain a high opening level for a long time, which significantly reduces the small steam turbine and the driving equipment. The loss caused by throttling when the power is matched.

(2) The operating efficiency of the back-pressure small steam turbine of the present invention can be increased by 8%-20%, and each 1000MW unit can save more than 4000 tons of standard coal per year, greatly reducing operating costs and achieving comprehensive benefits of reducing pollutant emissions.

(3) The system of the present invention makes full use of the working ability of the small steam turbine, generates power through the frequency conversion generator, and each 1000MW unit can supply 60 million kilowatts of extra power to the outside world every year, and the direct economic income is more than 12 million yuan.

The above-mentioned features mentioned in the present invention, or the features mentioned in the embodiments can be combined arbitrarily. All the features disclosed in the specification of this case can be used in combination with any combination, and each feature disclosed in the specification can be replaced by any alternative feature that provides the same, equivalent or similar purpose. Therefore, unless otherwise specified, the disclosed features are only general examples of equivalent or similar features.

Below in conjunction with specific embodiment, further illustrate the present invention. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. For the experimental methods without specific conditions indicated in the following examples, usually follow the conventional conditions or the conditions suggested by the manufacturer.

Unless otherwise defined, all professional and scientific terms used herein have the same meanings as commonly understood by those skilled in the art. In addition, any methods and materials similar or equivalent to those described can be applied to the method of the present invention. The preferred implementation methods and materials described herein are for demonstration purposes only.

Example 1

As shown in Figure 2-3, the back pressure small steam turbine driven fan system of the frequency conversion generator speed regulation in this embodiment includes a back pressure small steam turbine 1, a fan 2 and a frequency conversion generator 3, wherein the back pressure small steam turbine 1 There are steam inlet pipeline 11, exhaust steam pipeline 12, regulating valve 13 and steam extraction pipeline 14. The steam in the steam inlet pipeline 11 comes from the high-pressure steam of the thermal system of the generator set, and the exhaust steam pipeline 12 is connected with the low-temperature heat source (low-pressure steam source) heater. Or a heat exchanger (not shown in the figure) is connected, and the regulating valve 13 is arranged on the steam inlet pipe 11 to adjust the steam flow of the high-pressure steam. In this embodiment, the opening of the regulating valve is kept high for a long time (The opening range is 70%-100%). The steam extraction pipeline 14 is connected with a high-temperature heat source (high-pressure steam source) heater or a heat exchanger (not shown in the figure).

The fan 2 is located at the shaft end on one side of the back-pressure small steam turbine 1, and the constant speed ratio is selectively set between the fan 2 and the back-pressure small steam turbine 1 according to the speed ratio between the fan 2 and the back-pressure small steam turbine 1 Gear box 4, the constant speed ratio gearbox 4 is coaxially connected with the back pressure small steam turbine 1, the input end of the constant speed ratio gearbox 4 is connected with the shaft end on one side of the back pressure small steam turbine 1, the constant speed ratio gearbox 4 The output terminal of is connected with the input terminal of fan 2.

The frequency conversion generator 3 is located at the shaft end on the other side of the back pressure small steam turbine 1, and is located between the frequency conversion generator 3 and the back pressure small steam turbine 1 according to the speed ratio between the frequency conversion generator 3 and the back pressure small steam turbine 1. Selectively set the constant speed ratio gearbox 4 or the clutch 5, the constant speed ratio gearbox 4 or the clutch 5 is coaxially connected with the back pressure type small steam engine 1, the input end of the constant speed ratio gearbox 4 or the clutch 5 is connected with the back pressure type The shaft end on the other side of the small steam turbine 1 is connected, and the output end of the constant speed ratio gearbox 4 or the clutch 5 is connected with the input end of the variable frequency generator 3 .

The back-pressure small steam turbine 1 also includes a steam extraction outlet (not shown in the figure), which is connected to a high-temperature heat source (high-pressure steam source) heater or heat exchanger (not shown in the figure) through the steam extraction pipeline 14 . The back-pressure small steam turbine can be equipped with a first-level steam extraction pipeline, a second-level steam extraction pipeline or a second-level or higher extraction steam pipeline (such as a third-level steam extraction pipeline, a fourth-level steam extraction pipeline, etc.) according to the needs.

The working principle of the system of this embodiment is as follows:

When the small turbine is running normally, the regulating valve of the small turbine maintains a high opening (the opening range is 70%-100%). The high-pressure steam enters the small turbine through the steam inlet pipe, and the low-pressure steam after doing work is discharged to the low-temperature heat source (low-pressure steam source) heater or heat exchanger and other heat users through the exhaust pipe. The steam drives the small steam turbine to rotate, thereby dragging the coaxial fan to rotate.

The other shaft end of the back-pressure small steam turbine drives the variable frequency generator to rotate. By adjusting the output of the variable frequency generator to increase or decrease, the load of the back-pressure small steam turbine is controlled to increase or decrease accordingly, so that the back pressure The speed of the small steam turbine decreases or increases accordingly, and then the speed of the fan is controlled to decrease or increase to meet the requirements of different working conditions.

In other words, by controlling the output (output) of the variable frequency generator, the throttling mode of the regulating valve can be partially or completely replaced to control the speed of the small steam turbine, thereby efficiently meeting the speed control requirements of the fan and improving the operation of the back pressure small steam turbine. efficiency.

Example 2

As shown in Figure 4, the difference between the back pressure type small steam turbine driven fan system of the variable frequency generator speed regulation of this embodiment and the system of embodiment 1 is that:

The fan 2 and the frequency conversion generator 3 are located at the same shaft end of the back pressure small steam turbine 1, between the back pressure small steam turbine 1 and the frequency conversion generator 3, a fixed speed ratio gearbox 4 is selectively installed, and the constant speed ratio gearbox 4 is connected on the same shaft system of the back pressure type small steam turbine 1. The input end of the constant speed ratio gearbox 4 is connected with the shaft end on one side of the back pressure small steam turbine 1 . The input end of the frequency conversion generator 3 is connected with the output end of the constant speed ratio gearbox 4 , and the output end of the frequency conversion generator 3 is connected with the input end of the fan 2 .

The working principle of the system of this embodiment is as follows:

When the steam pushes the small steam turbine to rotate, it simultaneously drags the coaxially connected fan to rotate, because the variable frequency generator and the fan are located at the same shaft end of the small steam turbine, and the fan is located outside the variable frequency generator. Therefore, through the adjustment of the fixed speed ratio gearbox, the small steam turbine drives the variable frequency generator to rotate and generate electricity. By adjusting the output of the variable frequency generator to increase or decrease, the speed of the fan can be controlled to meet the requirements of different working conditions.

Example 3

As shown in Figure 5, the difference between the back pressure type small steam turbine driven fan system of the variable frequency generator speed regulation of this embodiment and the system of embodiment 2 is that:

Between the fan 2 and the variable frequency generator 3, a constant speed ratio gearbox 4 is selectively arranged, and the constant speed ratio gearbox 4 is connected to the same shaft system of the back pressure small steam turbine 1. The input end of the constant speed ratio gearbox 4 is connected with the output end of the variable frequency generator 3 , and the output end of the constant speed ratio gearbox 4 is connected with the input end of the fan 2 .

All documents mentioned in this application are incorporated by reference in this application as if each were individually incorporated by reference. In addition, it should be understood that after reading the above teaching content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Claims (5)

1. a back pressure type small steam turbine driven blower fan system of frequency conversion generator speed regulation, it is characterized in that, described system comprises back pressure type small steam turbine, blower fan, fixed speed ratio gear box and variable frequency generator, wherein, The back pressure small steam turbine, fan and frequency conversion generator are coaxially connected; By controlling the output of the frequency conversion generator, thereby controlling the rotation speed of the back pressure small steam turbine, thereby controlling the rotation speed of the fan; wherein The fan and the variable frequency generator are connected to the same shaft end of the back pressure small steam turbine, the constant speed ratio gearbox is coaxially connected with the back pressure small steam turbine, the fan and the variable frequency generator, and the constant speed ratio The speed ratio gearbox is located between the back pressure small steam engine and the frequency conversion generator; and The back-pressure small steam turbine is provided with a steam inlet pipe, and the steam inlet pipe is provided with a regulating valve, and the opening degree of the regulating valve is kept high for a long time, and the opening degree ranges from 70% to 100%. 2. The system according to claim 1, characterized in that the back-pressure small steam turbine is provided with an exhaust pipe, and the exhaust pipe is connected with a heat exchanger. 3. The system according to claim 1, wherein the fan comprises: a fan whose medium is air or flue gas. 4. A steam generator set, characterized in that the steam generator set is equipped with the system according to claim 1. 5. A method for adjusting the fan speed in a backpressure-type small turbine-driven blower fan system, said system comprising a backpressure-type small steam turbine and a fan, characterized in that a speed ratio gearbox and a variable frequency generator are added to the system ,in The back pressure small steam turbine, fan and frequency conversion generator are coaxially connected, The fan and the variable frequency generator are connected to the same shaft end of the back pressure small steam turbine, the fixed speed ratio gearbox is coaxially connected with the back pressure small steam turbine, the fan and the variable frequency generator, and the constant speed ratio The speed ratio gearbox is located between the back pressure small steam engine and the frequency conversion generator; and The back-pressure small steam turbine is provided with a steam inlet pipeline, and the steam inlet pipeline is provided with a regulating valve, and the opening of the regulating valve is kept high for a long time, and the opening range is 70%-100%; By adjusting the output of the frequency conversion generator, the rotation speed of the back pressure small steam turbine is controlled, thereby controlling the rotation speed of the fan.