A method for combined auxiliary AGC regulation of high-pressure heater steam extraction and feedwater bypass of a heat supply unit

Abstract

The application provides a heating unit high-pressure heater steam extraction-feed water bypass combined auxiliary AGC regulation method, through control of valve opening, when the grid load instruction rises, the feed water flow entering the high-pressure heater is reduced, the pressure in the high-pressure heater is increased, the pressure difference between the third high-pressure heater and the steam turbine intermediate pressure cylinder is reduced, the steam extraction amount is reduced, and the steam turbine work is increased. When the grid load instruction decreases, the steam extraction amount of the heating bypass is increased, the pressure in the high-pressure heater is reduced, the pressure difference between the third high-pressure heater and the steam turbine intermediate pressure cylinder is increased, the steam extraction amount is increased, and the steam turbine work is reduced. The steam turbine work capacity changes with the load instruction, and the ability of the unit to quickly respond to AGC regulation is improved. The application has the advantages of simple structure, convenient operation, strong innovation, low cost of existing equipment modification, fast variable load rate of the unit, and the purpose of realizing high-quality primary frequency modulation demand of the power grid.

Description

Technical Field

[0001] This invention relates to the field of peak shaving technology in thermal power generation, specifically to a combined auxiliary AGC regulation method for high-pressure steam extraction and feedwater bypass in heating units. Background Technology

[0002] In addition to generating electricity, modern thermal power units also have a portion that provides heating. The return water to the heating network is heated to a designated temperature by steam extracted from the turbine at the first station of the heating network and then returned via the return water pipeline.

[0003] To enhance the ability of generating units to respond to grid load requirements under heating conditions, appropriate control strategies can be used to increase or decrease the turbine output in a timely manner, thereby increasing or decreasing the generator power and achieving the goal of quickly responding to grid load requirements.

[0004] The condensing pressure of the extracted steam in the high-pressure heater is approximately pc ≈ f(ts) = f(tw + Δt + δt), where tw is the feedwater inlet temperature, Δt is the feedwater temperature rise, and δt is the heat transfer terminal temperature difference. The extracted steam heats the feedwater entering the No. 3 high-pressure heater. With both the feedwater inlet temperature tw and the heat transfer terminal temperature difference δt remaining constant, a change in Δt can cause a corresponding change in the steam condensing pressure, which in turn changes the pressure difference between the turbine extraction point and the high-pressure heater. This pressure difference change increases or decreases the extraction steam power, thereby altering the turbine output and achieving the purpose of assisting AGC regulation. Summary of the Invention

[0005] To enable generating units to quickly respond to grid load requirements, this invention proposes a control strategy that coordinates the extraction of steam from the high-pressure heater and the feedwater bypass in heating units. This strategy can adjust the turbine output according to grid load requirements, assisting in intelligent AGC (Automatic Guided Control) regulation. The retrofit cost is low, and the operation is simple.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A combined auxiliary AGC regulation method for high-pressure heater extraction steam and feedwater bypass in a heating unit is characterized by: proposing a combined regulation system of high-pressure heater extraction steam bypass valve and feedwater bypass valve. By controlling the valve opening, when the grid load command increases, the feedwater flow into the high-pressure heater is reduced, increasing the pressure inside the high-pressure heater and decreasing the pressure difference between the third high-pressure heater and the intermediate-pressure cylinder of the turbine, resulting in a decrease in steam extraction and an increase in turbine work. When the grid load command decreases, the steam extraction flow of the heating bypass is increased, decreasing the pressure inside the high-pressure heater and increasing the pressure difference between the third high-pressure heater and the intermediate-pressure cylinder of the turbine, resulting in an increase in steam extraction and a decrease in turbine work. This allows the turbine's work capacity to change with the load command, improving the unit's ability to quickly respond to AGC regulation.

[0008] As a further improvement of the present invention, the combined regulating system of the high-pressure heater extraction steam bypass valve and the feedwater bypass valve includes a turbine high-pressure cylinder, a turbine intermediate-pressure cylinder, a first high-pressure heater, a second high-pressure heater and a third high-pressure heater. An extraction steam bypass is branched off from the extraction steam pipeline of the third high-pressure heater for extraction steam heating, and a control valve is installed on the bypass. A feedwater bypass is branched off from the feedwater pipeline entering the third high-pressure heater and a control valve is installed on it.

[0009] As a further improvement of the present invention, when the grid load command increases, the valve on the feedwater bypass is opened wider, the feedwater entering the third high-pressure heater decreases, and the steam extraction rate remains unchanged. The feedwater is heated to a higher temperature, that is, Δt increases, thereby increasing the pressure of the third high-pressure heater, reducing the pressure difference between it and the intermediate pressure cylinder of the turbine, reducing the steam extraction rate, and increasing the work done by the turbine.

[0010] As a further improvement of the present invention, when the grid load command decreases, the extraction steam bypass valve is opened to increase the extraction steam volume, which leads to a decrease in the amount of steam entering the third high-pressure heater and the feedwater being heated to a lower temperature, i.e., Δt decreases; thus, the pressure of the third high-pressure heater decreases, the pressure difference between it and the intermediate pressure cylinder of the turbine increases, and the extraction steam volume increases; after reaching equilibrium, the extraction steam volume is greater than the initial state, which leads to a decrease in the work done by the turbine.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0012] Based on the condensation characteristics of extracted steam in the high-pressure heater, and in accordance with heating requirements, AGC (Automatic Generation Control) is assisted by a high-pressure heater extraction steam bypass combined with a feedwater throttling valve. The valve opening is controlled according to grid load commands, altering the pressure difference between the turbine extraction point and the heater by changing the pressure of the No. 3 high-pressure heater. This affects the extraction steam volume, leading to changes in the turbine's work capacity and responding to grid load requirements. The system is simple in structure, easy to operate, highly innovative, requires low-cost retrofitting of existing equipment, and offers a fast load change rate, achieving the goal of meeting the grid's high-quality primary frequency regulation needs. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of the present invention.

[0014] In the diagram, HP represents the high-pressure cylinder of the steam turbine, and IP represents the intermediate-pressure cylinder of the steam turbine. 1 is the first high-pressure heater, 2 is the second high-pressure heater, and 3 is the third high-pressure heater. 4 is the control valve on the extraction steam bypass, and 5 is the control valve on the feedwater bypass. Detailed Implementation

[0015] The invention will be further described below with reference to the accompanying drawings.

[0016] During normal operation, valves 4 and 5 maintain the set opening degree.

[0017] When the grid load demand increases, valve 5 of the feedwater bypass is opened wider. The feedwater bypass flow increases, reducing the amount of feedwater entering the third high-pressure heater. With the steam extraction rate remaining constant, the feedwater is heated to a higher temperature, i.e., Δt increases. This increases the pressure in the high-pressure heater, reduces the pressure difference between it and the intermediate-pressure cylinder of the turbine, decreases the steam extraction rate, and increases the turbine's work output.

[0018] When the grid load demand decreases, valve 4 of the extraction steam bypass is opened wider. The increased extraction steam flow from the heating bypass leads to a decrease in the amount of steam entering the third high-pressure heater, causing the feedwater to be heated to a lower temperature, i.e., Δt decreases. This results in a decrease in the pressure of the high-pressure heater and an increase in the pressure difference between it and the intermediate-pressure cylinder of the turbine, further increasing the extraction steam flow. After reaching equilibrium, the extraction steam flow is greater than the initial state, leading to a decrease in the work done by the turbine.

[0019] By controlling valves 4 and 5 together, the turbine's work capacity changes with the load command, realizing intelligent AGC control of combined high-pressure heater extraction and feedwater bypass.

[0020] The above description is merely a preferred embodiment of the present invention; other effective embodiments are also possible. Any effective improvements proposed by those skilled in the art based on the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A combined auxiliary AGC regulation method for high-pressure heater extraction steam and feedwater bypass in a heating unit, characterized in that: The system includes a combined regulation system of a high-pressure heater extraction steam bypass valve and a feedwater bypass valve. The combined regulation system of the high-pressure heater extraction steam bypass valve and the feedwater bypass valve includes a high-pressure cylinder of a steam turbine, a medium-pressure cylinder of a steam turbine, a first high-pressure heater, a second high-pressure heater, and a third high-pressure heater. An extraction steam bypass is branched off from the extraction steam pipeline of the third high-pressure heater for extraction steam heating, and a control valve (4) is installed on the extraction steam bypass. A feedwater bypass is branched off from the feedwater pipeline entering the third high-pressure heater and a control valve (5) is installed on it. By controlling the opening of the valves, the steam turbine's work capacity can be changed according to the load command, thereby improving the unit's ability to quickly respond to AGC regulation. When the grid load command increases, the control valve (5) on the feedwater bypass is opened, the feedwater flow rate into the third high-pressure heater decreases, and the steam extraction rate remains unchanged. The feedwater is heated to a higher temperature, that is, the feedwater temperature rise increases, which increases the pressure of the third high-pressure heater, thereby reducing the pressure difference between the third high-pressure heater and the intermediate pressure cylinder of the turbine, resulting in a decrease in the steam extraction rate and an increase in the work done by the turbine. When the grid load command decreases, the control valve (4) on the extraction steam bypass is opened to increase the extraction steam volume of the heating bypass, resulting in a decrease in the amount of steam entering the third high-pressure heater, and the feedwater is heated to a lower temperature, i.e., the feedwater temperature rise decreases; the pressure of the third high-pressure heater decreases, thereby increasing the pressure difference between the third high-pressure heater and the intermediate pressure cylinder of the turbine, resulting in an increase in the extraction steam volume; after reaching equilibrium, the extraction steam volume is greater than the initial state, resulting in a decrease in the work done by the turbine.

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