A system for improving the load ramp rate of coal-fired power units

Abstract

The present invention relates to a system for improving the load-raising ramp rate of a coal-fired power unit, comprising at least one group of high-pressure heaters connected in series through water supply pipes, the high-pressure heater at the end having the highest working pressure; a boiler connected to the high-pressure heater with the highest working pressure through a pipe, and connected to a high-pressure cylinder through a pipe, and connected to a medium-pressure cylinder through a reheater through a pipe; a reheater heat storage and utilization system, comprising a control valve group connected to a drain pipe of the high-pressure heater with the highest working pressure, the control valve group connected to a water spray atomization device through a pipe, and the water spray atomization device is arranged in a cold section pipe from the high-pressure cylinder to the reheater. The reheater heat storage and utilization system sprays the drain of the heater with the highest working pressure in the unit into the cold section pipe of the reheater, mixes with the reheated steam, and quickly increases the steam volume of the medium and low pressure cylinders, thereby improving the unit's response capability to load raising.

Description

Technical Field

[0001] The invention relates to the technical field of thermal power units, and in particular to a system for improving the load-increasing ramp rate of a coal-fired power unit. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] In order to deal with the area error (AEC, Area Control Error) caused by the imbalance between power generation and power consumption and ensure the quality of power, the current load change ramp rate of coal-fired power units is not less than 1.5% of the rated load per minute. With the increase in the integration of renewable energy into the power grid and the increase in peak-to-valley differences, the load change ramp rate requirements for coal-fired power units are gradually increasing, for example, to not less than 4% of the rated load per minute.

[0004] Coal-fired power units have extremely large capacity and steam parameters. For example, supercritical units are currently in widespread use. Although they can bring about efficient energy saving, the reduction in boiler heat storage and the increase in inertia will reduce the load response capability of the unit. In order to meet the requirements of load change ramp rate, the existing technology can only operate the main steam regulating valve in a larger throttling state, which is not conducive to efficient energy saving. Summary of the invention

[0005] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a system for improving the load ramping rate of coal-fired power units. The unit is additionally provided with a reheater heat storage and utilization system. The drain water of the heater with the highest working pressure in the unit is sprayed into the reheater cold section pipeline, mixed with the reheated steam, and the steam volume of the medium and low pressure cylinders is quickly increased, thereby improving the unit's ability to respond to load.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A first aspect of the present invention provides a system for improving the load ramp rate of a coal-fired power unit, comprising:

[0008] The high-pressure heater has at least one group, which are connected in series through water supply pipes, and the high-pressure heater at the end has the highest working pressure;

[0009] The boiler is connected to the high-pressure heater with the highest working pressure through a pipeline, connected to the high-pressure cylinder through a pipeline, and connected to the medium-pressure cylinder through a reheater through a pipeline;

[0010] The reheater heat storage and utilization system includes a control valve group connected to a high-pressure heater drain pipe with the highest working pressure. The control valve group is connected to a water spray atomization device through a pipe. The water spray atomization device is arranged in a cold section pipe from the high-pressure cylinder to the reheater.

[0011] The control valve group comprises a first isolation valve and a second isolation valve connected by a pipeline, and a flow meter and a regulating valve are arranged between the first isolation valve and the second isolation valve.

[0012] A main regulating valve is provided on the pipeline between the boiler and the high-pressure cylinder.

[0013] The boiler is connected to the reheater and connected to the medium pressure cylinder through the reheater via a pipeline.

[0014] The high-pressure cylinder and the reheater are connected through the reheater cold section pipeline.

[0015] The high-pressure heater with the highest working pressure is the first high-pressure heater, and the first high-pressure heater is connected to the second high-pressure heater through a drain pipe and a control valve.

[0016] The opening of the main control valve 0-100% is a function of the integrated valve position command 0-100% of the digital electro-hydraulic control system. 1 (x), the opening of the regulating valve 0-100% is a function of the comprehensive valve position command D-100% of the digital electro-hydraulic control system f 2 (x) The main regulating valve and the control valve form split-range control, and the split-range point D is selected between 50% and 70% of the main regulating valve opening.

[0017] The main regulating valve is used as the object to control the main steam flow rate to increase the load. The regulating valve only controls the water injection amount in the D-100% range to increase the reheat steam flow rate and assist in increasing the load.

[0018] As the steam production of the boiler gradually increases, the openings of the main regulating valve and the control valve gradually decrease. The control valve is closed first, and the main regulating valve controls the unit load alone.

[0019] Compared with the prior art, one or more of the above technical solutions have the following beneficial effects:

[0020] 1. The unit is equipped with a reheater heat storage and utilization system to spray the drain water from the heater with the highest working pressure in the unit into the reheater cold section pipeline, mix it with the reheated steam, and quickly increase the steam volume of the medium and low pressure cylinders, thereby improving the unit's response ability to load increase.

[0021] 2. The system utilizes the heat storage in the reheater when the unit increases its load, thereby increasing the overall heat storage utilization rate of the boiler. The heat storage in the reheater, which accounts for about 40% of the total heat storage capacity of the boiler, increases the flow rate of reheat steam.

[0022] 3. The heat storage of the high-pressure heater with the highest working pressure in the unit is utilized. Under rated conditions, the high-pressure heater is equivalent to a heat storage container, and its drain specific enthalpy is greater than 1000kJ / kg, and the drain flow rate is about 10% of the reheat steam flow rate. It is a device with a large heat storage capacity on the steam turbine side. The system utilizes both boiler heat storage and steam turbine heat storage, giving full play to the overall heat storage capacity of the unit.

[0023] 4. It can reduce the fluctuation of boiler parameters during load increase and ensure the safe operation of the unit. When the load is increased by the main regulating valve in the conventional way, the main regulating valve opens quickly, which can easily cause the main steam pressure and main steam temperature to drop, exceeding the operating regulations. However, the timely intervention of the reheater heat storage utilization system can quickly increase the load of the unit and quickly reduce the deviation from the target value, which can prevent the main regulating valve from opening and the main steam pressure and main steam temperature from falling. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0025] Figure 1 It is a schematic diagram of the system structure capable of improving the load ramp rate of a coal-fired power unit provided by one or more embodiments of the present invention;

[0026] Figure 2 It is a schematic diagram of the corresponding relationship between the valve opening and valve position instruction of the main regulating valve and the control valve in the system provided by one or more embodiments of the present invention.

[0027] In the figure: 1. boiler, 2. reheater, 3. first high-pressure heater, 31. first high-pressure heater drain pipe, 4. second high-pressure heater, 5. third high-pressure heater, 6. feed water pipe, 7. main regulating valve, 8. reheater cold section pipe, 9. water spray atomization device, 101. high-pressure cylinder, 102. medium-pressure cylinder, 11. first isolating valve, 12. second isolating valve, 13. flow meter, 14. regulating valve. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0029] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0030] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0031] As described in the background technology, coal-fired power units have extremely large capacity and steam parameters. For example, supercritical units are currently used more frequently. Although they can bring efficient energy saving, the load response capability of the unit will be reduced due to the reduction of boiler heat storage and the increase of inertia. In order to meet the requirements of load change ramp rate, the existing technology can only operate the main steam regulating valve in a larger throttling state, which is not conducive to efficient energy saving.

[0032] Due to the inherent characteristics of coal-fired power boilers, their load response has an inertial lag of more than 2 minutes. In the initial stage of load increase, the unit only uses the heat storage of the boiler water-cooled wall and superheater. For small load changes below 2% of the rated load, the unit's ramp rate can meet the requirements, but for larger load changes, the ramp rate will not meet the standard due to the limited main steam pressure.

[0033] Boiler heat storage includes working fluid heat storage and metal heat storage. Studies have shown that metal heat storage is more than 1.5 times that of working fluid heat storage; the amount of metal in the reheater exceeds the sum of the water-cooled wall and superheater, and its heat storage accounts for about 40% of the total heat storage of the boiler. It is possible to consider adding a system that utilizes reheater heat storage to compensate for the inertial lag of the boiler and increase the load ramp rate of the coal-fired power unit.

[0034] Therefore, the following embodiment provides a system for improving the load ramping rate of a coal-fired power unit. The unit is additionally provided with a reheater heat storage and utilization system, and the drain water from the heater with the highest working pressure in the unit is sprayed into the reheater cold section pipeline to mix with the reheated steam, thereby rapidly increasing the steam volume of the medium and low pressure cylinders, thereby improving the unit's responsiveness to load increases.

[0035] The high pressure heater (HPH) in the following embodiments is a device that utilizes part of the exhaust gas from the steam turbine to heat the feed water. A coal-fired power unit may have multiple groups / sets of these devices used in combination according to their capacity.

[0036] Embodiment 1:

[0037] like Figure 1-2 As shown, a system for improving the load ramp rate of a coal-fired power unit comprises:

[0038] The high-pressure heater has at least one group, which are connected in series through water supply pipes, and the high-pressure heater at the end has the highest working pressure;

[0039] The boiler is connected to the high-pressure heater with the highest working pressure through a pipeline, connected to the high-pressure cylinder through a pipeline, and connected to the medium-pressure cylinder through a reheater through a pipeline;

[0040] The reheater heat storage and utilization system includes a control valve group connected to a high-pressure heater drain pipe with the highest working pressure. The control valve group is connected to a water spray atomization device through a pipe. The water spray atomization device is arranged in a cold section pipe from the high-pressure cylinder to the reheater.

[0041] The above system sprays the drain from the heater with the highest working pressure in the unit into the cold section pipe of the reheater through the control valve group, where it is mixed with the reheat steam and heated into superheated steam, which is then sent into the medium-pressure cylinder to increase the load of the medium and low-pressure cylinders, thereby filling the gap in steam production caused by the large inertia of the boiler in the initial stage of load increase of the unit, ensuring that the unit's climbing rate meets the requirements.

[0042] Specific:

[0043] There are three groups of high-pressure heaters in this embodiment, which are connected in series via a water supply pipe 6 to form a third high-pressure heater 5, a second high-pressure heater 4 and a first high-pressure heater 3. The first high-pressure heater 3 at the end is the heater with the highest working pressure, i.e., No. 1 high-pressure heater.

[0044] Boiler 1 is connected to No. 1 high pressure heater with the highest working pressure through a pipeline, and is connected to the high pressure cylinder 101 through a pipeline. Boiler 1 is connected to reheater 2 and is connected to the medium pressure cylinder 102 through reheater 2 through a pipeline.

[0045] A main regulating valve 7 is provided on the pipeline between the boiler 1 and the high-pressure cylinder 101 for regulating the steam from the boiler 1 entering the high-pressure cylinder 101 .

[0046] The high-pressure cylinder 101 is connected to the reheater 2 through the reheater cold section pipeline 8, and the steam after work in the high-pressure cylinder 101 is mixed with the steam in the reheater 2, heated and sent to the medium-pressure cylinder 102.

[0047] The No. 1 high pressure heater has a drain pipe, namely, the first high pressure heater drain pipe 31. The first high pressure heater 3 is connected to the second high pressure heater 4 via the first high pressure heater drain pipe 31 and a control valve.

[0048] The reheater heat storage utilization system takes out a pipeline from the first high-pressure heater drain pipeline 31, passes through the control valve group and is connected to the reheater cold section pipeline 8 using the water spray atomization device 9, such as Figure 1 The dotted part in the figure sprays the drain from the heater with the highest working pressure in the unit into the cold section pipe of the reheater through the control valve group, mixes with the reheat steam and is heated into superheated steam, which drives the medium and low pressure cylinders to increase the load, thereby filling the gap in the initial stage of the unit's load increase caused by the large inertia of the boiler and ensuring that the unit's climbing rate meets the requirements.

[0049] The control valve group comprises a first isolation valve 11 and a second isolation valve 12 connected by a pipeline, and a flow meter 13 and a regulating valve 14 are arranged between the first isolation valve 11 and the second isolation valve 12.

[0050] The flow rate of the reheater heat storage system is designed according to the rated drainage volume of No. 1 high pressure heater. The flow meter 13 and the regulating valve 14 are monitored and operated in the centralized control room through the DCS (distributed control system, a common control system in coal-fired power units). The regulating valve 14 operator has monitoring functions such as valve position instructions and feedback signals, input and exit switching buttons, manual and automatic switching buttons, etc. The two isolation valves play the role of isolation and auxiliary throttling, and manual doors or electric doors can be selected.

[0051] Through manual or automatic control of the regulating valve 14, the injected No. 1 high pressure heater drain is heated into superheated steam through the reheater heat storage, driving the medium and low pressure cylinders to increase the load. In this way, the insufficient steam production caused by the large inertia of the boiler in the early stage of the unit load increase is compensated, ensuring that the unit climbing rate meets the requirements. The specific method is as follows:

[0052] Add the automatic control logic configuration of the regulating valve 14 in the control system. The "automatic" input conditions of the regulating valve 14 are that all the following conditions are met:

[0053] 1) The operator is in the "on" state;

[0054] 2) The water level of No. 1 high pressure heater (first high pressure heater 3) is normal;

[0055] 3) The No. 1 high pressure water level control is set to "automatic";

[0056] 4) The deaerator water level control is set to "automatic";

[0057] 5) Unit coordination control input;

[0058] 6) The unit load is greater than 50% of the rated load (the set value can be changed);

[0059] The regulating valve 14 is regarded as an expansion valve of the main regulating valve 7, which is directly controlled by the comprehensive valve position command of the DEH (digital electro-hydraulic control system) and forms a split-range control system with overlapping degree with the main regulating valve 7. Specifically:

[0060] The opening of the main control valve 7 0-100% is a function f of the integrated valve position command 0-100% of the DEH (digital electro-hydraulic control system) 1 (x), the opening degree of the regulating valve 14 0-100% is a function of the comprehensive valve position instruction D-100% f 2 (x), the split point D is selected between 50% and 70% of the opening of GV (main control valve 7); f 1 (x), f 2(x) and D are first determined based on the actual flow characteristics of GV and V (regulating valve 14), and then optimized based on the application of the reheater heat storage utilization system. Ultimately, the comprehensive valve position command should be as linear as possible with the unit load, such as Figure 2 shown.

[0061] Figure 2 The corresponding relationship between the valve opening of GV (main regulating valve 7) and V (control valve 14) 0-100% and the comprehensive valve position instruction in this embodiment is shown, and there is a split point D in the middle. D in this embodiment is between 50%-70% of the opening of the main regulating valve 7 (GV).

[0062] This overlapping step-range control method mainly uses GV to control the main steam flow rate to increase the load throughout the entire process, and V is only in the step-range interval of D-100%. It controls the water injection volume to increase the reheat steam flow rate and assist in increasing the load. As the boiler steam production gradually increases, the openings of GV and V are gradually closed, V is closed first, and GV controls the unit load alone.

[0063] When one of the following conditions is met, the regulating valve 14 is automatically closed:

[0064] 1) The operator is in the "Exit" state;

[0065] 2) The water level of No. 1 high pressure heater reaches the lower limit.

[0066] The load increase response process of the unit under the automatic control of the regulating valve 14 is as follows:

[0067] When the unit load increase is small and the comprehensive valve position command is less than D, the regulating valve 14 is in the closed state, and the steam turbine adjusts the main regulating valve to increase the load by 7, using the heat storage of the boiler water-cooled wall and superheater; at the same time, the boiler gradually increases the steam production by increasing combustion. Finally, the load and main steam pressure reach the new target value.

[0068] When the unit load increase is large and the comprehensive valve position instruction is greater than D, the load is increased by adjusting the main regulating valve 7 and the regulating valve 14 at the same time, utilizing the heat storage of the boiler water-cooled wall, superheater and reheater, and at the same time increasing the combustion of the boiler to increase the main steam pressure.

[0069] As the load and main steam pressure approach the new target values, the comprehensive valve position command gradually decreases, and the main regulating valve 7 and the regulating valve 14 change from open to closed, so that the load and the main steam pressure finally reach the new target values, the main regulating valve 7 is in a new throttling state, and the regulating valve 14 is in a closed state.

[0070] When the operator of the regulating valve 14 is in the "manual" state, the operator can manually adjust the opening according to the load increase needs, change the water spray flow rate, and use the heat storage of the boiler reheater to intervene in the load increase climbing rate.

[0071] The system utilizes the heat storage of the reheater when the unit increases the load, thereby increasing the overall heat storage utilization rate of the boiler. The conventional method of increasing the load through the main regulating valve utilizes the heat storage of the boiler water-cooled wall and the superheater to increase the flow rate of the main steam. On the basis of the conventional method, this embodiment utilizes the heat storage of the reheater, which accounts for about 40% of the total heat storage of the boiler, to increase the flow rate of the reheated steam.

[0072] The system also utilizes the heat storage of No. 1 high-pressure heater, which is equivalent to a heat storage container. Under rated conditions, its drain specific enthalpy is greater than 1000kJ / kg, and the drain flow is about 10% of the reheat steam flow, which is a device with a large heat storage capacity on the turbine side. This system utilizes both boiler heat storage and turbine heat storage, giving full play to the overall heat storage capacity of the unit.

[0073] The system can reduce the fluctuation of boiler parameters during load increase and ensure the safe operation of the unit. When the load is increased by a large amount through the main regulating valve in the conventional way, the main regulating valve opens quickly, which is very likely to cause the main steam pressure and main steam temperature to drop, exceeding the operating regulations. However, the timely intervention of the reheater heat storage utilization system can quickly increase the unit load and quickly reduce the deviation from the target value, which can prevent the main regulating valve from opening and the main steam pressure and main steam temperature from falling.

[0074] The system makes the main steam regulating valve operate at a more economical opening, reducing the throttling loss of the unit. In order to meet the grid's requirements for the unit's ramp rate, the conventional method has to control the main regulating valve in a state of large throttling, sacrificing economy to ensure regulation. The system adds an additional power source to increase the load, which can replace part of the main regulating valve pre-throttling volume and reduce the throttling loss of the unit in steady state.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A system for improving the load ramp rate of coal-fired power units, characterized in that: include: The high-pressure heater has at least one group, which are connected in series through water supply pipes, and the high-pressure heater at the end has the highest working pressure; The boiler is connected to the high-pressure heater with the highest working pressure through a pipeline, connected to the high-pressure cylinder through a pipeline, and connected to the medium-pressure cylinder through a reheater through a pipeline; The reheater heat storage utilization system comprises a control valve group connected to a high-pressure heater drain pipe with the highest working pressure, the control valve group is connected to a water spray atomization device through a pipe, and the water spray atomization device is arranged in a cold section pipe from a high-pressure cylinder to a reheater; the control valve group comprises a first isolation valve and a second isolation valve connected through a pipe, and a flow meter and a regulating valve are arranged between the two; A main regulating valve is provided on the pipeline between the boiler and the high-pressure cylinder; The opening degree of the main regulating valve 0-100% is a function f1(x) of the integrated valve position instruction 0-100% of the digital electro-hydraulic control system, and the opening degree of the regulating valve 0-100% is a function f2(x) of the integrated valve position instruction D-100% of the digital electro-hydraulic control system; The main regulating valve and the regulating valve form a split range control, and the split range point D is selected between 50% and 70% of the main regulating valve opening; The main regulating valve is used as the object to control the main steam flow rate to increase the load. In the D-100% range, the regulating valve controls the water spraying amount to increase the reheat steam flow rate and assist in increasing the load. As the steam production of the boiler increases, the openings of the main regulating valve and the control valve become smaller, the control valve closes first, and the main regulating valve controls the unit load alone.

2. A system for improving the load ramp rate of a coal-fired power unit as claimed in claim 1, characterized in that: The boiler is connected to the reheater and is connected to the medium-pressure cylinder via a pipeline through the reheater.

3. A system for improving the load ramp rate of a coal-fired power unit as claimed in claim 1, characterized in that: The high-pressure cylinder and the reheater are connected via a reheater cold section pipeline.

4. A system for improving the load ramp rate of a coal-fired power unit as claimed in claim 1, characterized in that: The high-pressure heater with the highest working pressure is the first high-pressure heater, and the first high-pressure heater is connected to the second high-pressure heater through a drain pipe and a control valve.

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