阅读说明：本技术 切除低压加热器的双机回热系统及其一次调频方法 (Double-machine regenerative system for cutting off low-pressure heater and primary frequency modulation method thereof ) 是由 常龙辉 于 2019-10-31 设计创作，主要内容包括：本发明提出了一种切除低压加热器的双机回热系统及其一次调频方法,该双机回热系统包括低压加热器和用于切除低压加热器的控制装置,低压加热器按照热力参数由高至低排列,依次编号为A组低压加热器、B组低压加热器和C组低压加热器,A组低压加热器一侧设置有第一水侧旁路,B组低压加热器一侧设置有第二水侧旁路,C组低压加热器一侧设置有第三水侧旁路,当电网频率下降时,控制装置切断低压加热器,从而释放出低压加热器抽汽的蓄能,借此,本发明具有实现了一次调频快速加负荷的功能的优点。(The invention provides a double-machine regenerative system for cutting off a low-pressure heater and a primary frequency modulation method thereof, the double-machine regenerative system comprises a low-pressure heater and a control device for cutting off the low-pressure heater, the low-pressure heater is arranged according to thermal parameters from high to low and sequentially numbered as an A group low-pressure heater, a B group low-pressure heater and a C group low-pressure heater, a first water side bypass is arranged on one side of the A group low-pressure heater, a second water side bypass is arranged on one side of the B group low-pressure heater, a third water side bypass is arranged on one side of the C group low-pressure heater, and when the frequency of a power grid is reduced, the control device cuts off the low-pressure heater, so that the energy storage of steam extracted by the low-pressure heater is released.)

1. A double-machine regenerative system for cutting off a low-pressure heater is characterized by comprising a low-pressure heater and a control device for cutting off the low-pressure heater, wherein the low-pressure heater is arranged from high to low according to thermodynamic parameters and sequentially numbered as a group A low-pressure heater, a group B low-pressure heater and a group C low-pressure heater;

a first water side bypass is arranged on one side of the group A low-pressure heater, a first regulating valve is arranged on the first water side bypass, and the first regulating valve is electrically connected with a control device;

a second water side bypass is arranged on one side of the group B low-pressure heater, a second regulating valve is arranged on the second water side bypass, and the second regulating valve is electrically connected with the control device;

and a third water side bypass is arranged on one side of the group C low-pressure heater, a third regulating valve is arranged on the third water side bypass, and the third regulating valve is electrically connected with the control device.

2. The dual regenerative system for cutting off the low-pressure heater according to claim 1, wherein the dual regenerative system comprises a boiler, a main turbine, a regenerative small turbine, a condenser, a group A low-pressure heater, a group B low-pressure heater, a group C low-pressure heater, a deaerator and a high-pressure heater;

the boiler comprises a first steam outlet and a second steam outlet;

the main steam turbine comprises a steam turbine ultrahigh-pressure cylinder, a steam turbine high-pressure cylinder, a steam turbine medium-pressure cylinder and a steam turbine low-pressure cylinder, and a second steam extraction port is formed in the steam turbine low-pressure cylinder;

the steam inlet of the small regenerative steam turbine is communicated with the steam outlet of the ultrahigh-pressure cylinder of the steam turbine, the small regenerative steam turbine is provided with a first steam extraction port, and the first steam extraction port is communicated with the steam inlet of the high-pressure heater;

the steam inlet of the condenser is respectively communicated with the steam outlet of the low-pressure cylinder of the steam turbine and the steam outlet of the backheating small steam turbine, and a steam exhaust regulating valve is arranged between the condenser and the steam outlet of the backheating small steam turbine;

the group A low-pressure heater, the group B low-pressure heater and the group C low-pressure heater are connected in series, wherein a water inlet of the group C low-pressure heater is communicated with a water outlet of the condenser, and a water outlet of the group C low-pressure heater is communicated with a water inlet of the deaerator;

the water inlet of the high-pressure heater is communicated with the water outlet of the deaerator, and the water outlet of the high-pressure heater is communicated with the water inlet of the boiler.

3. The dual-machine regenerative system for cutting off the low-pressure heaters of claim 1, wherein the group A low-pressure heaters comprise a heater number 1, the group B low-pressure heaters comprise a heater number 2, and the group C low-pressure heaters comprise a heater number 3, a heater number 4 and a heater number 5;

the water outlet of the No. 1 heater is communicated with the water inlet of the deaerator, and the water inlet of the No. 1 heater is provided with a first water stop valve which is electrically connected with the control device;

a second water stop valve is arranged at the water inlet of the No. 2 heater, the first water side bypass is arranged between the water outlet of the No. 2 heater and the water inlet of the deaerator, and the second water stop valve is electrically connected with the control device;

the second water side bypass is arranged between the water outlet of the No. 3 heater and the water outlet of the No. 2 heater;

the water inlet of the No. 5 heater is communicated with the water outlet of the condenser, the water inlet of the No. 5 heater is provided with a third water stop valve, a third water side bypass is arranged between the water outlet of the condenser and the water outlet of the No. 3 heater, and the third water stop valve is electrically connected with the control device.

4. The double-machine regenerative system for cutting off the low-pressure heater according to claims 2-3, wherein the steam outlet of the small regenerative steam turbine is respectively communicated with the steam inlet of the heater No. 1 and the steam inlet of the heater No. 2, a first check valve is arranged between the steam outlet of the small regenerative steam turbine and the steam inlet of the heater No. 1, a second check valve is arranged between the steam outlet of the small regenerative steam turbine and the steam inlet of the heater No. 2, and the first check valve and the second check valve are electrically connected with the control device.

5. The dual regenerative system for removing a low pressure heater of claims 2-3, wherein the second steam extraction port comprises a number 1 steam extraction port, a number 2 steam extraction port, a number 3 steam extraction port, and a number 4 steam extraction port;

the steam extraction port No. 1 is communicated with the steam inlet of the heater No. 2, a third check valve is arranged between the steam extraction port No. 1 and the steam inlet of the heater No. 2, and the third check valve is electrically connected with the control device;

the steam extraction port No. 2 is communicated with the steam inlet of the heater No. 3, a fourth check valve is arranged between the steam extraction port No. 2 and the steam inlet of the heater No. 3, and the fourth check valve is electrically connected with the control device;

the steam extraction port No. 3 is communicated with the steam inlet of the heater No. 4, a fifth check valve is arranged between the steam extraction port No. 3 and the steam inlet of the heater No. 4, and the fifth check valve is electrically connected with the control device;

the steam extraction port No. 4 is communicated with the steam inlet of the heater No. 5, a sixth check valve is arranged between the steam extraction port No. 4 and the steam inlet of the heater No. 5, and the sixth check valve is electrically connected with the control device.

6. The dual-motor regenerative system for cutting off the low-pressure heater according to claim 5, wherein a condensate pump is arranged between the condenser and the heater No. 5, a circulating water path is arranged on one side of the condensate pump, the circulating water path is arranged between a water outlet of the condenser and a water inlet of the heater No. 5, a fourth regulating valve is arranged on the circulating water path, and the fourth regulating valve is electrically connected with the control device.

7. A primary frequency modulation method of a double-machine regenerative system for cutting off a low-pressure heater is characterized by comprising the following steps:

step 1, setting a primary load numerical value, a middle load numerical value and a high load numerical value at a control device;

step 2, when the frequency of the power grid is reduced and exceeds a primary load numerical value, the control device triggers an instruction for cutting off the low-pressure heaters in the group C, when the frequency of the power grid is reduced and exceeds a middle-level load numerical value, the control device triggers an instruction for cutting off the low-pressure heaters in the group B, and when the frequency of the power grid is reduced and exceeds a high-level load numerical value, the control device triggers an instruction for cutting off the low-pressure heaters in the group C;

step 3, the control device opens the fourth regulating valve to enable the condensed water in the condensed water pump to enter the low-pressure heater at the lowest flow rate;

step 4, adjusting the exhaust steam adjusting valve to enable the back pressure of the backheating type small steam turbine to accord with the set back pressure parameter;

and 5, after the grid frequency is recovered, the control device enables the low-pressure heater to recover to the initial running state.

8. The primary frequency modulation method for the dual regenerative system for cutting off the low-pressure heater according to claim 7, wherein the primary load value in step 1 is 75%, the middle load value is 60%, and the high load value is 40%.

9. The primary frequency modulation method of the dual regenerative system for cutting off the low-pressure heaters according to claim 7, wherein the method for cutting off the group C low-pressure heaters in the step 2 is that the control device closes the third water stop valve, the fourth check valve, the fifth check valve and the sixth check valve, and opens the third regulating valve;

the method for cutting off the group B low-pressure heater comprises the following steps that the control device closes the second water stop valve, the second check valve and the third check valve and opens the second regulating valve;

the method for cutting off the group C low-pressure heater comprises the steps that the control device closes the first water stop valve and the first check valve and opens the first regulating valve.

10. The method for primary frequency modulation of a dual-machine regenerative system for cutting off a low-pressure heater according to claim 7, wherein the back pressure parameter set in the step 4 is 0.3-0.5 MPa.

Technical Field

The invention belongs to the technical field of thermal power generation, and particularly relates to a double-machine regenerative system for cutting off a low-pressure heater and a primary frequency modulation method thereof.

Background

At present, with the continuous improvement of the high-temperature performance of materials, the steam parameters of a coal-fired power generating unit are continuously improved so as to obtain higher cycle efficiency, further reduce the coal consumption of the unit and reduce the emission of greenhouse gases and other pollutants. Improving steam parameters is one of the most direct ways to improve the cycle efficiency of the power generation system.

With the continuous development of the power industry, the power generation proportion of new energy sources such as wind power and solar energy is increased year by year, but the adjustability of new energy power sources is poor, the power of a connecting line between power grids is high, and once the power is tripped, the load of a receiving-end power grid power source needs to be increased rapidly. For the reasons, the power grid has higher and higher requirements on the primary frequency modulation quality and the load regulation capacity of the unit. The large-capacity turbine set adopts double reheating, the reheating volume is large, the load regulation is slow, and the large-capacity turbine generally has no regulation stage and adopts throttling steam distribution. Compared with the regulation-level nozzle steam distribution, the throttling steam distribution can improve the operation efficiency of the unit under the rated working condition, and the unit proportion of the throttling steam distribution in a large-capacity thermal power unit is increased continuously in future. The most economical way of operating such units is for the high pressure governor to operate with full opening sliding pressure. However, the capacity that the adjusting door is opened fully, namely the adjusting door is lost to be opened continuously to increase the load of the unit rapidly, and how to meet the performance requirement of power grid dispatching on the primary frequency modulation of the unit is a great problem. Particularly, under the background of the current extra-high voltage power grid and large-scale direct current transmission, once the power supply load of a power receiving end is lost due to the fault of a power transmission line, the frequency of the power grid is rapidly reduced, and the load of a local unit is required to be rapidly increased to realize the primary frequency modulation function, so that a large contradiction exists between the economic operation mode and the primary frequency modulation capability of the throttling steam distribution units.

However, in order to reduce the throttling loss, the turbine regulating valve is close to full open, and in order to meet the performance requirement of primary frequency modulation, the high-pressure regulating valve has to be closed, and the mode of adopting the throttling operation of the regulating valve sacrifices the greater economy, and especially under the low load, the throttling loss of the regulating valve is greater.

Disclosure of Invention

The invention provides a double-machine regenerative system for cutting off a low-pressure heater and a primary frequency modulation method thereof, which realize the function of rapidly loading by primary frequency modulation.

The technical scheme of the invention is realized as follows: a double-machine regenerative system for cutting off a low-pressure heater comprises the low-pressure heater and a control device for cutting off the low-pressure heater, wherein the low-pressure heater is arranged from high to low according to thermodynamic parameters and sequentially numbered as a group A low-pressure heater, a group B low-pressure heater and a group C low-pressure heater;

a first water side bypass is arranged on one side of the group A low-pressure heater, a first regulating valve is arranged on the first water side bypass, and the first regulating valve is electrically connected with the control device;

a second water side bypass is arranged on one side of the group B low-pressure heater, a second regulating valve is arranged on the second water side bypass, and the second regulating valve is electrically connected with the control device;

and a third water side bypass is arranged on one side of the group C low-pressure heater, a third regulating valve is arranged on the third water side bypass, and the third regulating valve is electrically connected with the control device.

As a preferred embodiment, the double-machine regenerative system comprises a boiler, a main turbine, a regenerative small turbine, a condenser, a group a low-pressure heater, a group B low-pressure heater, a group C low-pressure heater, a deaerator and a high-pressure heater;

the boiler comprises a first steam outlet and a second steam outlet;

the main steam turbine comprises a steam turbine ultrahigh-pressure cylinder, a steam turbine high-pressure cylinder, a steam turbine medium-pressure cylinder and a steam turbine low-pressure cylinder, and a second steam extraction port is formed in the steam turbine low-pressure cylinder;

the steam inlet of the small regenerative steam turbine is communicated with the steam outlet of the ultrahigh-pressure cylinder of the steam turbine, the small regenerative steam turbine is provided with a first steam extraction port, and the first steam extraction port is communicated with the steam inlet of the high-pressure heater;

the steam inlet of the condenser is respectively communicated with the steam outlet of the low-pressure cylinder of the steam turbine and the steam outlet of the backheating small steam turbine, and a steam exhaust regulating valve is arranged between the condenser and the steam outlet of the backheating small steam turbine;

the group A low-pressure heater, the group B low-pressure heater and the group C low-pressure heater are connected in series, wherein a water inlet of the group C low-pressure heater is communicated with a water outlet of the condenser, and a water outlet of the group C low-pressure heater is communicated with a water inlet of the deaerator;

the water inlet of the high-pressure heater is communicated with the water outlet of the deaerator, and the water outlet of the high-pressure heater is communicated with the water inlet of the boiler.

As a preferred embodiment, the group a low pressure heaters include heater No. 1, the group B low pressure heaters include heater No. 2, and the group C low pressure heaters include heater No. 3, heater No. 4, and heater No. 5;

the water outlet of the No. 1 heater is communicated with the water inlet of the deaerator, and the water inlet of the No. 1 heater is provided with a first water stop valve which is electrically connected with the control device;

a second water stop valve is arranged at the water inlet of the No. 2 heater, the first water side bypass is arranged between the water outlet of the No. 2 heater and the water inlet of the deaerator, and the second water stop valve is electrically connected with the control device;

the second water side bypass is arranged between the water outlet of the No. 3 heater and the water outlet of the No. 2 heater;

the water inlet of the No. 5 heater is communicated with the water outlet of the condenser, the water inlet of the No. 5 heater is provided with a third water stop valve, a third water side bypass is arranged between the water outlet of the condenser and the water outlet of the No. 3 heater, and the third water stop valve is electrically connected with the control device.

As a preferred embodiment, the steam outlet of the small regenerative steam turbine is respectively communicated with the steam inlet of the heater No. 1 and the steam inlet of the heater No. 2, a first check valve is arranged between the steam outlet of the small regenerative steam turbine and the steam inlet of the heater No. 1, a second check valve is arranged between the steam outlet of the small regenerative steam turbine and the steam inlet of the heater No. 2, and both the first check valve and the second check valve are electrically connected with the control device.

As a preferred embodiment, the second steam extraction ports include a No. 1 steam extraction port, a No. 2 steam extraction port, a No. 3 steam extraction port, and a No. 4 steam extraction port;

the steam extraction port No. 1 is communicated with the steam inlet of the heater No. 2, a third check valve is arranged between the steam extraction port No. 1 and the steam inlet of the heater No. 2, and the third check valve is electrically connected with the control device;

the steam extraction port No. 2 is communicated with the steam inlet of the heater No. 3, a fourth check valve is arranged between the steam extraction port No. 2 and the steam inlet of the heater No. 3, and the fourth check valve is electrically connected with the control device;

the steam extraction port No. 3 is communicated with the steam inlet of the heater No. 4, a fifth check valve is arranged between the steam extraction port No. 3 and the steam inlet of the heater No. 4, and the fifth check valve is electrically connected with the control device;

the steam extraction port No. 4 is communicated with the steam inlet of the heater No. 5, a sixth check valve is arranged between the steam extraction port No. 4 and the steam inlet of the heater No. 5, and the sixth check valve is electrically connected with the control device.

In a preferred embodiment, a condensate pump is arranged between the condenser and the heater No. 5, a circulating water path is arranged on one side of the condensate pump, the circulating water path is arranged between a water outlet of the condenser and a water inlet of the heater No. 5, a fourth regulating valve is arranged on the circulating water path, and the fourth regulating valve is electrically connected with the control device.

A primary frequency modulation method of a double-machine regenerative system for cutting off a low-pressure heater comprises the following steps:

step 1, setting a primary load numerical value, a middle load numerical value and a high load numerical value at a control device;

step 2, when the frequency of the power grid is reduced and exceeds a primary load numerical value, the control device triggers an instruction for cutting off the low-pressure heaters in the group C, when the frequency of the power grid is reduced and exceeds a middle-level load numerical value, the control device triggers an instruction for cutting off the low-pressure heaters in the group B, and when the frequency of the power grid is reduced and exceeds a high-level load numerical value, the control device triggers an instruction for cutting off the low-pressure heaters in the group C;

step 3, the control device opens the fourth regulating valve to enable the condensed water in the condensed water pump to enter the low-pressure heater at the lowest flow rate;

step 4, adjusting the exhaust steam adjusting valve to enable the back pressure of the backheating type small steam turbine to accord with the set back pressure parameter;

and 5, after the grid frequency is recovered, the control device enables the low-pressure heater to recover to the initial running state.

In a preferred embodiment, the primary load value in step 1 is 75%, the medium load value is 60% and the high load value is 40%.

In a preferred embodiment, the method for cutting off the group C low-pressure heaters in step 2 is that the control device closes the third water stop valve and the fourth check valve, the fifth check valve and the sixth check valve, and opens the third regulating valve;

the method for cutting off the group B low-pressure heater comprises the following steps that the control device closes the second water stop valve, the second check valve and the third check valve and opens the second regulating valve;

the method for cutting off the group C low-pressure heater comprises the steps that the control device closes the first water stop valve and the first check valve and opens the first regulating valve.

As a preferred embodiment, the back pressure parameter set in step 4 is 0.3 to 0.5 MPa.

After the technical scheme is adopted, the invention has the beneficial effects that:

1. the invention adopts the method of extracting steam from the small regenerative steam turbine and supplying heat to the high-pressure heater, and extracting steam from the low-pressure cylinder of the steam turbine and supplying heat to the low-pressure heater, thereby solving the problem of overheat of extracted steam caused by extracting steam from the medium-pressure cylinder of the steam turbine in the prior art.

2. The invention can lead the water supply not to pass through the low-pressure heater by cutting off the low-pressure heater according to the load value, thereby releasing the energy storage of the steam extraction of the low-pressure heater, realizing the function of rapid loading by primary frequency modulation, and ensuring the back pressure of the regenerative small steam turbine while cutting off the low-pressure heater.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic cross-sectional view of the present invention;

fig. 2 is a schematic structural view of the low pressure heater.

In the figure, 1-boiler; 2-a turbine ultrahigh pressure cylinder; 3-a high-pressure cylinder of the steam turbine; 4-a turbine medium pressure cylinder; 5-low pressure cylinder of steam turbine; 6-a backheating type small steam turbine; 7-a deaerator; 8-a high pressure heater; heater number 9-1; heater No. 10-2; heater No. 11-3; heater No. 12-4; heater number 13-5; no. 14-1 steam extraction port; no. 15-2 steam extraction port; a No. 16-3 steam extraction port; no. 17-4 steam extraction port; 18-a first non-return valve; 19-a second non-return valve; 20-a third check valve; 21-a fourth check valve; 22-a fifth check valve; 23-a sixth check valve; 24-a first waterside bypass; 25-a first regulating valve; 26-a first water stop valve; 27-a second waterside bypass; 28-a second regulating valve; 29-a second water stop valve; 30-a third waterside bypass; 31-a third regulating valve; 32-a third water stop valve; 33-a condenser; 34-a steam exhaust regulating valve; 35-a condensate pump; 36-fourth regulating valve.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1 and 2, the dual-machine heat recovery system for cutting off the low-pressure heater comprises the low-pressure heater and a control device for cutting off the low-pressure heater, wherein the low-pressure heater is arranged according to thermal parameters from high to low, and is sequentially numbered as a group a low-pressure heater, a group B low-pressure heater and a group C low-pressure heater, a first water side bypass 24 is arranged on one side of the group a low-pressure heater, a second water side bypass 27 is arranged on one side of the group B low-pressure heater, and a third water side bypass 30 is arranged on one side of the group C low-pressure heater.

When the frequency of the power grid is reduced, the control device cuts off the low-pressure heater, and condensed water flowing out of the condenser 33 flows out through a water side bypass on one side of the low-pressure heater, so that energy storage of steam extraction of the low-pressure heater is released, and the function of quick load application of primary frequency modulation is realized.

The double-machine regenerative system comprises a boiler 1, a main turbine, a regenerative small turbine 6, a condenser 33, a group A low-pressure heater, a group B low-pressure heater, a group C low-pressure heater, a deaerator 7 and a high-pressure heater 8;

the boiler 1 comprises a first steam outlet and a second steam outlet;

the main steam turbine comprises a steam turbine ultrahigh pressure cylinder 2, a steam turbine high pressure cylinder 3, a steam turbine medium pressure cylinder 4 and a steam turbine low pressure cylinder 5, and a second steam extraction port is arranged on the steam turbine low pressure cylinder 5;

the steam inlet of the small regenerative steam turbine 6 is communicated with the steam outlet of the ultrahigh-pressure cylinder 2 of the steam turbine, the small regenerative steam turbine 6 is provided with a first steam extraction port, and the first steam extraction port is communicated with the steam inlet of the high-pressure heater 8;

the steam inlet of the condenser 33 is respectively communicated with the steam outlet of the turbine low-pressure cylinder 5 and the steam outlet of the backheating type small turbine 6, and a steam exhaust regulating valve 34 is arranged between the condenser 33 and the steam outlet of the backheating type small turbine 6;

the group A low-pressure heater, the group B low-pressure heater and the group C low-pressure heater are connected in series, wherein a water inlet of the group C low-pressure heater is communicated with a water outlet of the condenser 33, and a water outlet of the group C low-pressure heater is communicated with a water inlet of the deaerator 7;

the water inlet of the high-pressure heater 8 is communicated with the water outlet of the deaerator 7, and the water outlet of the high-pressure heater 8 is communicated with the water inlet of the boiler 1.

The steam inlet of the steam turbine ultrahigh-pressure cylinder 2 is communicated with the first steam outlet of the boiler 1, and the steam outlet of the steam turbine ultrahigh-pressure cylinder 2 is respectively communicated with the steam inlet of the boiler 1, the steam inlet of the high-pressure heater 8 and the steam inlet of the small regenerative steam turbine 6;

the steam inlet of the steam turbine high-pressure cylinder 3 is communicated with the second steam outlet of the boiler 1, the steam outlet of the steam turbine high-pressure cylinder 3 is communicated with the steam inlet of the steam turbine medium-pressure cylinder 4,

the steam inlet of the turbine low-pressure cylinder 5 is communicated with the steam outlet of the turbine medium-pressure cylinder 4, and the steam outlet of the turbine low-pressure cylinder 5 is communicated with the steam inlet of the condenser 33.

The group A of low-pressure heaters comprises a No. 1 heater 9, the group B of low-pressure heaters comprises a No. 2 heater 10, and the group C of low-pressure heaters comprises a No. 3 heater 11, a No. 4 heater 12 and a No. 5 heater 13;

the water outlet of the No. 1 heater 9 is communicated with the water inlet of the deaerator 7, the water inlet of the No. 1 heater 9 is provided with a first water stop valve 26, and the first water stop valve 26 is electrically connected with the control device;

a second water stop valve 29 is arranged at the water inlet of the heater No. 2 10, the first water side bypass 24 is arranged between the water outlet of the heater No. 2 10 and the water inlet of the deaerator 7, a first regulating valve 25 is arranged on the first water side bypass 24, and the second water stop valve 29 and the first regulating valve 25 are electrically connected with the control device;

the second water side bypass 27 is arranged between the water outlet of the No. 3 heater 11 and the water outlet of the No. 2 heater 10, a second regulating valve 28 is arranged on the second water side bypass 27, and the second regulating valve 28 is electrically connected with the control device;

the water inlet of heater No. 5 13 and the delivery port of condenser 33 are linked together, and the water inlet department of heater No. 5 13 is provided with third check valve 32, third waterside bypass 30 sets up between the delivery port of condenser 33 and the delivery port of heater No. 3 11, is provided with third governing valve 31 on the third waterside bypass 30, and third check valve 32, third governing valve 31 all are connected with controlling means electricity.

The steam outlet of the small regenerative steam turbine 6 is respectively communicated with the steam inlet of the heater No. 1 and the steam inlet of the heater No. 2, a first check valve 18 is arranged between the steam outlet of the small regenerative steam turbine 6 and the steam inlet of the heater No. 1 and the steam inlet of the heater No. 2 and a second check valve 19 is arranged between the steam outlet of the small regenerative steam turbine 6 and the steam inlet of the heater No. 2 and the first check valve 18 and the second check valve 19 are electrically connected with the control device.

The second steam extraction port comprises a No. 1 steam extraction port 14, a No. 2 steam extraction port 15, a No. 3 steam extraction port 16 and a No. 4 steam extraction port 17;

the steam extraction port 1 14 is communicated with the steam inlet of the heater 2, a third check valve 20 is arranged between the steam extraction port 1 14 and the steam inlet of the heater 2, and the third check valve 20 is electrically connected with the control device;

the steam extraction port 2 is communicated with the steam inlet of the heater 11 No. 3, a fourth check valve 21 is arranged between the steam extraction port 2 and the steam inlet of the heater 11 No. 3, and the fourth check valve 21 is electrically connected with the control device;

the steam extraction port 3 16 is communicated with the steam inlet of the heater 4 12, a fifth check valve 22 is arranged between the steam extraction port 3 16 and the steam inlet of the heater 4, and the fifth check valve 22 is electrically connected with the control device;

the steam extraction port 4 17 is communicated with the steam inlet of the heater 5 13, a sixth check valve 23 is arranged between the steam extraction port 4 17 and the steam inlet of the heater 5 13, and the sixth check valve 23 is electrically connected with the control device.

A condensate pump 35 is arranged between the condenser 33 and the No. 5 heater 13, a circulating water path is arranged on one side of the condensate pump 35 and is arranged between a water outlet of the condenser 33 and a water inlet of the No. 5 heater 13, a fourth regulating valve 36 is arranged on the circulating water path, and the fourth regulating valve 36 is electrically connected with the control device.

A primary frequency modulation method of a double-machine regenerative system for cutting off a low-pressure heater comprises the following steps:

step 1, setting a primary load numerical value, a middle load numerical value and a high load numerical value at a control device;

step 2, when the frequency of the power grid is reduced and exceeds a primary load numerical value, the control device triggers an instruction for cutting off the low-pressure heaters in the group C, when the frequency of the power grid is reduced and exceeds a middle-level load numerical value, the control device triggers an instruction for cutting off the low-pressure heaters in the group B, and when the frequency of the power grid is reduced and exceeds a high-level load numerical value, the control device triggers an instruction for cutting off the low-pressure heaters in the group C;

step 3, the control device opens the fourth regulating valve 36 to enable the condensed water in the condensed water pump 35 to enter the low-pressure heater at the lowest flow rate;

step 4, adjusting the exhaust steam adjusting valve 34 to enable the back pressure of the regenerative small steam turbine 6 to accord with the set back pressure parameter;

and 5, after the grid frequency is recovered, the control device enables the low-pressure heater to recover to the initial running state.

In step 1, the primary load value is 75%, the intermediate load value is 60%, and the high load value is 40%.

The method for cutting off the group C low-pressure heater in the step 2 is that the control device closes the third water stop valve 32, the fourth check valve 21, the fifth check valve 22 and the sixth check valve 23 and opens the third regulating valve 31;

the method for cutting off the group B low-pressure heater comprises the steps that the control device closes the second water stop valve 29, the second check valve 19 and the third check valve 20 and opens the second regulating valve 28;

the method for cutting off the group C low-pressure heater is that the control device closes the first water stop valve 26 and the first check valve 18 and opens the first regulating valve 25.

The backpressure parameter set in the step 4 is 0.3-0.5 MPa.

In this embodiment, the control device selects DEH, when the grid frequency is reduced to a high-level load value, the control device controls to cut off the group a low-pressure heater, the control device controls the first water stop valve 26 and the first check valve 18 to be closed, and opens the first regulating valve 25 and the fourth regulating valve 36, the condensed water flowing out of the heater No. 2 10 does not enter the group 1 low-pressure heater, but directly enters the deaerator 7 through the first water side bypass 24, according to the backpressure parameter, the backpressure parameter in this embodiment selects 0.45MPa, the large exhaust regulating valve 34 is opened, most of the exhaust steam of the regenerative small turbine 6 enters the condenser 33, and at this time, the condensed water in the condenser 33 circularly flows on the side of the condensed water pump 35 and enters the group C low-pressure heater at the minimum flow rate.

When the frequency of the power grid is reduced to a middle-level load value, the control device cuts off the low-pressure heater in the group B, controls the second water stop valve 29, the second check valve 19 and the third check valve 20 to be closed, opens the second regulating valve 28 and the fourth regulating valve 36, enables the condensed water flowing out of the heater 11 No. 3 not to enter the low-pressure heater No. 2 but directly enter the heater 9 No. 1 through the second water side bypass 27, opens the large exhaust regulating valve 34 according to back pressure parameters, enables most of the exhaust steam of the small regenerative turbine 6 to enter the condenser 33, and enables the condensed water in the condenser 33 to circularly flow on the side of the condensed water pump 35 at the moment and enter the low-pressure heater in the group C at the minimum flow rate.

When the power grid frequency is reduced to a primary load value, the control device cuts off the C group of low-pressure heaters, controls the third water stop valve 32 and the fourth check valve 21, the fifth check valve 22 and the sixth check valve 23 to be closed, opens the third regulating valve 31 and the fourth regulating valve 36, enables the condensed water flowing out of the condenser 33 not to enter the No. 5 low-pressure heater but directly enters the No. 2 heater 10 through the third water side bypass 30, opens the large exhaust regulating valve 34 according to the backpressure parameter, enables most of the exhaust steam of the small regenerative steam turbine 6 to enter the condenser 33, and enables the condensed water in the condenser 33 to circularly flow on the side of the condensed water pump 35 at the moment and enter the B group of low-pressure heaters at the minimum flow rate.

And after the frequency of the power grid is recovered, the group A low-pressure heaters, the group B low-pressure heaters and the group C low-pressure heaters are all put into normal use.

The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present invention.