WO2008151484A1

WO2008151484A1 - A small bypass system of a generator set and a controlling method thereof

Info

Publication number: WO2008151484A1
Application number: PCT/CN2007/003431
Authority: WO
Inventors: Weizhong Feng
Original assignee: Shanghai Waigaoqiao No.3 Power Generation Co.Ltd
Priority date: 2007-06-11
Filing date: 2007-12-03
Publication date: 2008-12-18
Also published as: EP2175104A4; EP2175104A1; CN101096918A; EP2175104B1; CN100473805C

Abstract

A small bypass system of a generator set is provided, wherein the generator set at least comprises a boiler (1), a steam turbine (12), main steam pipes (13) connecting the boiler (1) with the turbine (12), and big bypass regulator valves (6, 7, 8, 9), the small bypass system comprises the steam pipes of the small bypass and at least a set of small bypass regulator valves (10, 11). A controlling method of the small bypass system is provided, which includes the steps that: firstly, before the big bypass system is opened, the small bypass regulator valves (10, 11) is opened gradually, until the small bypass system reaches the maximum rate of flow; secondly, after the small bypass system reaches the maximum rate of flow, the big bypass system is regulated to the degree corresponding to the maximum rate of flow of the small bypass system, at the same time the small bypass regulator valves (10, 11) is closed; then after the big bypass system reaches a bigger degree, the small bypass regulator valves (10, 11) is regulated to the maximum rate of flow gradually. The security of the generator set is enhanced and the starting time of the generator set is shorten by setting the small bypass system.

Description

Generator group small bypass system and control method thereof

The present invention relates to the field of electric heat engines and thermal automation, and in particular to a small bypass system and a control method thereof. Background technique

The coal-fired generating unit mainly consists of three main engines: boiler, steam turbine and generator. In the control strategy, the bulky boiler has a large inertia due to its state change and a slower change rate. The speed of change of the steam turbine's speed and output state is much faster than the state of the boiler. The bypass system is an indispensable part of the coordinated operation of the two. '

At present, the large-capacity bypass of domestic and foreign coal-fired generating units includes 100% capacity bypass, which is directly taken from the boiler superheater header outlet pipe near the boiler side and then connected to the reheater cold section, which leads to the side of the reheater. Only a small amount of new steam passes through all main steam lines from the valve to the turbine. On the one hand, it is easy to cause the temperature of this section of the pipeline to be low, and in the operating condition, this section is the pipeline with the highest temperature in the entire steam-water cycle. Therefore, the oxidation phenomenon in this section of the pipeline is generally quite serious. In the cold start condition, the thermal shock causes the scale falling off inside the pipe to directly enter the turbine high pressure cylinder, causing great damage to the turbine blade.

Second, when the unit is started, a large amount of foreign matter such as oxide scale and solid particles will flow through the large bypass valve with the high-speed steam flow, and during the normal starting process, when the large bypass valve is at a small opening, the spool and The gap between the seats is small, the flow rate is high, and the solid foreign matter carried by the high-speed steam will rush the bypass valve spool at high speed, which makes the bypass valve spool extremely prone to wounds. When the spool is returned to the seat, the sealing of the valve core and the valve body of the wound is significantly reduced, and the high-speed steam will continuously wash the wound, causing the wound to become larger and larger, which directly leads to the very expensive spool to be scrapped. At the same time, a large amount of steam will leak from this wound during operation, which will affect the economic operation of the unit.

Third, usually, when the unit starts, there is a section with a bypass start process. At this time, the main steam enters the reheater cold section through the large bypass valve and returns to the boiler reheater. In the process, when the steam passes Big When bypassing the valve, all pipes from the large bypass valve to the front of the turbine can only pass a small amount of steam through the trap, which will cause a considerable lag between the temperature of the main steam line and the actual main steam temperature. And the quality of the steam sampled from this pipeline is not true, which makes the turbine's cranking conditions difficult to meet, which will delay the start of the turbine, wasting a lot of fuel, plant power and time. Summary of the invention

In view of the above-mentioned deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a small bypass applied to the thermal power generating set in the starting stage, protecting the high side valve and solving the problem that the main steam line has a small steam flow. system.

Another object of the present invention is to provide a control method for the above small bypass system.

In order to achieve the above object, the present invention provides a small bypass system, including: the generator set includes at least a boiler, a steam turbine, and a main steam pipe connecting the boiler and the steam turbine, a large bypass system, the main steam A small bypass system is provided adjacent the turbine at the turbine, the small bypass system including a small bypass steam conduit and at least one small bypass regulator valve.

Preferably, the small bypass regulating valve is a small capacity desuperheating pressure regulating valve, and the small bypass steam pipe is further provided with a shutoff valve before and/or after the small bypass regulating valve.

Preferably, the flow rate of the small bypass system is 1% to 50% of the flow rate of the main steam pipe.

Preferably, the flow rate of the small bypass system is 5% to 30% of the flow rate of the main steam pipe.

The invention also provides a small bypass system control method, comprising the following steps:

Step 1: Before the large bypass system of the generator set is opened, first open a small bypass shut-off valve, and gradually open the small bypass regulating valve to pass the main steam from the boiler through the small bypass system. Discharging to the reheat system of the genset until the small bypass system reaches a maximum flow rate;

Step 2: after the small bypass system reaches the maximum flow rate, quickly adjust the large bypass system to an opening corresponding to the maximum flow of the small bypass, and simultaneously close the small bypass regulating valve, so that The flow of the small bypass system is quickly switched to the large bypass system;

Step 3: After the large bypass system gradually reaches a large opening degree, the small bypass regulating valve is gradually opened again to the maximum flow rate.

Preferably, after step 3, step 4 is further included, after the load of the generator set is gradually increased, Firstly closing the small bypass regulating valve, and then gradually closing the large bypass system until the steam flow in the large bypass system is slightly smaller than the maximum flow of the small bypass system, rapidly closing the a large bypass system; and simultaneously opening the small bypass system, switching the steam flow in the large bypass system to the small bypass system, and then closing the small bypass control valve until The steam flow rate of the entire bypass system is zero; the main steam pressure of the genset remains substantially stable throughout the fourth operation.

Preferably, when the unit is shut down, when the turbine generator gradually reduces the load until it is dismissed, the boiler gradually reduces the load until the furnace is stopped, and the operation steps of the small bypass may be opposite to the starting process of the unit, which is step 4 to step one.

Preferably, the opening and closing operations of the small bypass system and the coordination with the large bypass system are controlled by a program control mode.

Preferably, the small bypass regulating valve and the valve of the large bypass system together constitute a first bypass valve group and a second bypass valve group respectively located on the two inlet sides of the steam turbine; Before preparing to start the flushing, the bypass valve group may be first alternately opened and closed, the first bypass valve group is first opened, and the second valve group is closed, so that the boiler outlet is connected in the header The steam is discharged only on one side of the first bypass valve group in an open state; then, after the first bypass valve group is kept in an open state for a predetermined period of time, the first bypass valve group is closed, and simultaneously Opening the second bypass valve group such that the steam in the header is discharged only through the second bypass valve group in an open state; thereafter, maintaining the second bypass valve group is open After the state is a predetermined period of time, the alternate opening and closing operations are ended, and the normal control mode is switched; the main steam pressure of the genset remains substantially stable during the alternate opening and closing operations.

The invention only adds a small bypass system in the existing generator set, so that the large bypass valve can be prevented from operating at a small opening degree, and the foreign matter such as oxide scale falling off in the boiler is greatly alleviated to the large bypass valve spool. The erosion, while the steam of a certain flow enters the cold section through the small bypass system, improves the heating pipe efficiency of the main steam pipe in the section, and allows the scale falling off in the main steam pipe during the start-up phase to be eliminated by the small bypass system. , reducing the solid particle erosion of the turbine. Improve the safety of the unit. At the same time, the steam in the pipeline and the steam generated in the furnace can be basically synchronized, which shortens the startup time of the unit. The technical purpose of protecting the large bypass valve spool is obtained. The small bypass system is simple to install and debug, low in cost, and wide Universal applicability.

The small bypass system control method of the present invention, because a small bypass system is added in the existing unit, so that a certain flow of steam enters the cold re-segment through the small bypass system, and the main steam pipe can obtain a large amount of steam heating pipe. A warm pipe for the pipe is realized. During the start-up phase of the unit, there are more solid particles, and the flushing of the large bypass valve spool is more serious. Due to the addition of the small bypass system, the small bypass control valve is opened in the startup phase and the large bypass valve does not operate. It is reasonable to avoid damage to the large bypass valve spool by the scale inside the pipe and the foreign matter of solid particles. Although the solid particles in the pipe are also harmful to the valve body of the small bypass, the small bypass regulating valve body itself is small, and the price is much lower than that of the large bypass valve, because at the same time, the small bypass regulating valve The shut-off valve can also be installed before or after. After the start, the front or rear stop valve can seal well. Even if the small bypass control valve has cracks or wounds, it will not cause air leakage and will not affect. The economics of the unit operation.

At the same time, after adopting the small bypass control method of the present invention, since the quality of the steam passing through the entire main steam pipe and entering through the large bypass valve is substantially the same, the steam quality from the large bypass valve to the front pipe of the steam turbine is closer. The true value of the main steam, thus greatly shortening the time required to wait for the large bypass to reach the steam quality in the pipeline before the turbine, and also shorten the starting time.

Moreover, for the scale from the large bypass valve to the front pipe of the steam turbine, the steam impulse in this section of the pipe is small during the conventional start-up process, and it is difficult to completely clean the scale, and the small side is installed. After the road system, the small bypass can be opened at the start of the startup, and the small bypass can be integrated into the startup process control of the original large bypass, so that the steam flows through the small bypass first, which greatly increases the impulse of steam in the pipeline. It can remove solid particles accumulated in this pipeline, reduce the erosion of solid particles of steam turbine, and improve the safety of the unit.

If combined with the original large bypass, the small bypass regulating valve can be operated together with the large bypass valve, and the one-side opening and closing action is first performed, and the large bypass valve is protected during the continuous opening and closing process. At the same time, in the initial stage of startup, if it is cold, the small bypass regulating valve can be opened first to avoid the steam after the throttling to flush the large bypass valve. If it is hot and extremely hot, the large bypass valve should be opened first to avoid overcooling. The soda water enters the high-temperature pipeline to cause a large amount of scale in the pipeline to fall off. The above steps are used to reduce the generation of scale in the header, which has a good punching effect.

The concept, the specific structure and the technical effects produced by the present invention will be further described in conjunction with the accompanying drawings in order to fully understand the objects, features and effects of the invention. DRAWINGS

1 is a schematic view showing the arrangement of a unit of a small bypass system to which the present invention is applied;

Figure 2 is a schematic block diagram of the starting process of the unit shown in Figure 1. (Small bypass valve in the figure refers to small bypass regulation)

detailed description

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view showing the arrangement of a unit employing the small bypass system of the present invention. In the thermal power unit, at least two main engines are included: the steam turbine 12 and the boiler 1 and the piping system, and the bypass system is the main component of the two main engines. During the operation of the unit, the water vapor from the boiler 1 enters the superheater outlet header 5 through the superheater 2, and then enters the high pressure cylinder (not shown) of the steam turbine 12 through the main steam pipeline 13 through the steam turbine 12 to perform work, exhausting steam After the cold section 4 enters the reheater 3 in the boiler. The large bypass is located between the boiler outlet header 5 and the reheater cold section 4. In this embodiment, the large bypass includes large bypass valves 6, 7, 8 respectively located on both sides of the boiler superheater outlet header. 9 and a communication pipe connected to the reheater cold section; the invention is characterized in that a small bypass system is installed on the main steam pipe near the steam turbine 12 side and the reheater cold section 4, this embodiment The small bypass system includes two small bypass regulating valves 10, 11 and a communication pipe respectively located on both sides of the high pressure cylinder of the steam turbine 12. The small bypass system's regulating valve is not required to have a quick opening and closing function. The regulating valve is only used during the start and stop phases of the unit and is not required to withstand the full pressure of the unit.

The present invention also provides a control method of the above small bypass system.

In normal operating conditions, steam enters the high pressure cylinder of the turbine 12 through the main steam line 13 to perform work. In the start-up phase of the unit, the large bypass valve begins to open. Unlike the prior art, the small bypass system of the present invention first opens the small bypass control valve before the large bypass valves 6, 7, 8, 9 are opened. The system, that is, slowly opening the small bypass regulating valve 10, 1 1, so that the steam from the boiler 1 passes through the superheater outlet header 5 through the small bypass regulating valve 10, 1 1 into the reheater cold section pipe until the small bypass The system is open; in this embodiment, the flow of the small bypass system is 20% of the steam flow in the unit, so it is also referred to as the 20% small bypass system.

After the small bypass system is opened, quickly open the large bypass valves 6, 7, 8, 9 and close the small bypass regulating valves 10, 1 1 to transfer the steam from the small bypass regulating valves 10, 1 1 to the side. The road valves 6, 7, 8, and 9 enter the reheater cold section 4. When implementing the bypass shutdown operation, firstly close the large bypass valves 6, 7, 8, and 9, until the steam flow in the pipeline is less than or equal to 20% of the total steam, quickly close the large bypass valves 6, 7, 8 9 is completely closed, and the small bypass regulating valve 10, 1 1 is opened at the same time to keep the main steam pressure from decreasing stably; thereafter, the small bypass regulating valve 10, 1 1 is gradually closed until the steam flow in the pipeline is zero.

At this point, the unit continues the rest of the startup process in the normal startup mode.

By adopting the small bypass system control method of the invention, the main steam line of the unit from the large bypass valve to the small bypass regulating valve section is preheated in the starting stage, and the solid particles and the scale are also removed. At the same time, a large amount of solid particles are first discharged through the small bypass regulating valve at the beginning of the startup, which reduces the impact of solid foreign matter on the large bypass valve spool and protects the large bypass valve spool from damage.

As a further improvement, the control method of the present invention can also realize the opening and closing control of the small bypass system by means of program control. More preferably, the small bypass control system can be integrated into the control system of the entire unit for fully automated management.

In this embodiment, it is also possible to add a front or rear stop valve (not shown) before and after the small bypass regulating valves 10, 11 to improve the safety of the small bypass regulating valve, and prevent the small bypass regulating valve from being flushed. A steam leak that causes a normal operating condition.

It will be apparent that in other embodiments of the invention, the flow of the small bypass system is not limited to 20% of the steam flow in the unit. In theory, a bypass that is less than 50% of the steam flow in the unit can be called a small bypass. In actual use, considering the effects of various aspects, the preferred solution is to use the flow of the small bypass system between the steam flow in the unit. 5% to 30% is preferred.

As shown in Fig. 2, a schematic block diagram of the startup process using the small bypass system of the present invention in combination with the one-sided alternating opening and closing control method is shown.

The starting process with bypass unit can be basically divided into the following process minimum opening stage, minimum pressure stage, boosting stage, fixed pressure stage and following mode stage.

As shown in Fig. 2 in conjunction with Fig. 1, in the initial stage of starting, it is first determined whether it is a cold start. If it is a cold start, first open the small bypass control valve 10, 11. Maintain the pressure according to the above several procedures according to the predetermined procedure, until The small bypass regulator valve is fully open, and then quickly open the large bypass valve 6, 7, 8 , 9, while closing the small bypass regulator valve 10, 11, then, from the large bypass valve 6, 7, 8, 9 The main steam line 13 to the small bypass regulating valve 10, 11 is also pre-warmed and flushed, and at the same time, a large amount of solid particles have passed through the small side. The passage regulating valves 10, 11 are exhausted, and the rapid opening of the large bypass valves 6, 7, 8, 9 also reduces the time it takes to operate under throttling conditions, protecting the large bypass valve spool.

When the start-up progresses to a certain stage (set to the solid-pressure stage in this embodiment), the bypass one-side alternate opening and closing operation is started, and the superheater outlet header 5 is flushed due to the transition from the boosting phase. At this time, the large bypass valves 6, 7, 8, and 9 are in the open state, so first close the first group of large bypass valves on the same side of the superheater header, and slowly close the large bypass valves 6, 7. At this time, in order to maintain the pressure stability, the second group of two large bypass valves 8, 9 located on the other side of the high pressure cylinder 12 remain open, when the first group of large bypass valves 6, 7 are all closed to the small bypass capacity. Quickly open the small bypass regulating valve, and speed up the second group of large bypass valves 6, 7 to close. The large bypass valve cooperates with the small bypass regulating valve to maintain the pressure according to the predetermined curve, and wait for the last small bypass regulating valve. After all are closed, the steam generated from the superheater 3 of the boiler 1 passes through the superheater outlet header 5 through the first group of large bypass valves 8, 9 on one side into the cold section 4, while part of the steam passes through the first group. The main steam line 13 on the same side of the large bypass valves 8, 9 also enters the cold section 4 via the small bypass regulating valve 11 and returns to the reheater 2. The main steam line 13 and the outlet header 5 on this side are flushed, and the solid particulate foreign matter is flushed out of the outlet header 5.

After that, the single-side valve is alternately closed and closed, and the small bypass regulating valve 10 is first slowly opened. At this time, the first group of large bypass valves 8, 9 are slowly closed, and after the small bypass regulating valve 10 is opened, The second set of large bypass valves 6, 7 on the same side are opened again and the small bypass regulating valve 10 is quickly closed, causing the second group of large bypass valves 6, 7 to open rapidly, the specific process being similar to the above process.

After the one-side valve opening process is completed, enter the reversing phase. At this time, close the small bypass regulating valve 10, 11, and then close the large bypass valve 6, 7, 8, 9, to reach the small bypass regulating valve. The flow is quickly closed, and the small bypass is opened to maintain the pressure stability, and then the pressure is stabilized by the small bypass regulator until the small bypass regulator is closed to prevent the throttle steam from flushing the large bypass valve spool.

If it is hot start, the whole start process is carried out according to the original mode. Finally, the solid pressure stage is as described above, and the single bypass valve is opened in combination with the small bypass control valve.

In summary, the description in this specification is only a few preferred embodiments of the present invention. Any technical solution that can be obtained by a person skilled in the art according to the prior art by logic analysis, reasoning or limited experimentation based on the prior art is within the scope of the claims of the present invention.

Claims

A small bypass system for a generator set, the generator set comprising at least a boiler, a steam turbine, and a main steam pipe and a large bypass system connecting the boiler and the steam turbine, wherein: the main steam pipe is close to the The steam turbine is provided with a small bypass system comprising a small bypass steam line and at least one set of small bypass regulating valves.

2. The small bypass system according to claim 1, wherein: said small bypass regulating valve is a small capacity desuperheating and depressurizing regulating valve, and said small bypass steam conduit is said small bypass regulating valve A shut-off valve is also provided before and/or after.

3. A small bypass system according to claim 1 or 2, wherein: said small bypass system has a flow rate of from 1% to 50% of said main steam conduit flow.

4. The small bypass system of claim 3 wherein: said small bypass system has a flow rate of between 5% and 30% of said main steam conduit flow.

5. The control method of any small bypass system according to any one of claims 1 to 4, comprising the following steps: Step 1: Before the large bypass system of the genset is opened, first open a small bypass shut-off valve, Stepping up the small bypass regulating valve to discharge main steam from the boiler through the small bypass system to the reheating system of the generator set until the small bypass system reaches a maximum flow rate;

6. The control method according to claim 5, wherein: after the step three, the method further comprises the step four: after the load of the generator set is gradually increased, the small bypass regulating valve is gradually closed first, and then gradually Turning off the large bypass system until the steam flow rate in the large bypass system is slightly smaller than the maximum flow rate of the small bypass system, rapidly closing the large bypass system; and simultaneously opening the small bypass at the same time a regulating valve that switches all of the steam flow in the large bypass system to the small bypass system, and then closes the small bypass regulating valve until the steam flow of the entire bypass system is zero, and finally closes Next to Road stop valve; The main steam pressure of the genset remains substantially stable throughout the fourth operation.

7. The control method according to claim 5, wherein: when the unit performs the shutdown operation, when the steam turbine generator gradually reduces the load until the disengagement, the boiler gradually reduces the load until the furnace is stopped, the small bypass The operation steps are exactly the opposite of the unit startup process, which is step 4 to step 1.

8. The control method according to claim 6, wherein: when the unit performs the shutdown operation, when the steam turbine generator gradually reduces the load until the disengagement, the boiler gradually reduces the load until the furnace is stopped, and the small bypass The operation steps are exactly the opposite of the unit startup process, which is step 4 to step 1.

9. The control method according to claim 5, wherein: the opening and closing operations of the small bypass system and the coordination with the large bypass system are controlled by a program control mode.

10. The method of controlling a small bypass system according to claim 5, wherein: said small bypass regulating valve and said wide bypass system are respectively formed in a first portion of said steam inlet side of said steam turbine. a bypass valve group and a second bypass valve group; before the steam turbine is ready to start the cranking, the bypass valve group may be alternately opened and closed, first opening the first bypass valve group, and closing the first a second valve group, wherein the steam in the boiler outlet header is discharged only on one side of the first bypass valve group in an open state; and then, the first bypass valve group is kept in an open state After the time period, the first bypass valve group is closed, and the second bypass valve group is opened, so that the steam in the header is discharged only through the second bypass valve group in an open state. After that, after the second bypass valve group is kept in the open state for a predetermined period of time, the alternate opening and closing operations are ended, and the normal control mode is switched; the generator set is in the alternating 幵 and closing operations. Main steam pressure remains substantially stable.