Lignite drying variable-load operation system of coal-fired power plant

Abstract

The invention discloses a lignite drying variable-load operation system for a coal-fired power plant, which comprises a boiler, an air feeder, an induced draft fan, a high-pressure cylinder, an intermediate-pressure cylinder, a low-pressure cylinder, a high-pressure heater, a low-pressure heater, a deaerator, a drying machine, a steam feed pump, a condensate pump, a condenser, a power generation system and a water circulation system, a water outlet end of the dryer is connected with an input end of the deaerator, a coal outlet of the dryer is connected with a coal inlet of a boiler combustion chamber, exhaust gas of the medium-pressure cylinder is used as a heat source required by lignite drying, and the steam extraction flow of the medium-pressure cylinder is determined according to a relation equation between the moisture content of lignite and the standard coal consumption rate. The technical problems that heat needed for drying lignite of an existing coal-fired unit under different working conditions is not matched with the coal flow, the economical efficiency of lignite drying is affected, and a reference basis is difficult to provide for lignite drying variable-load operation characteristics are solved.

Description

Technical Field

[0001] The invention relates to the technical field of coal-fired power generation, and in particular to a lignite drying variable load operation system for a coal-fired power plant. Background Art

[0002] Although the proportion of thermal power generation has declined due to the rapid development of photovoltaic, wind power, hydropower and biomass energy, coal-fired power generation still occupies a major position. Compared with civil or industrial coal, power plants often give priority to the use of lower-quality coal, such as lignite, long flame coal, non-caking coal, lean coal, etc., because they have many equipment to reduce pollutant emissions. This also poses greater challenges to the safe, efficient and clean operation of coal-fired units. However, the heat required for drying lignite under different operating conditions of existing coal-fired units does not match the coal flow rate, which affects the economic efficiency of lignite drying and is difficult to provide a reference for the variable load operation characteristics of lignite drying. Summary of the invention

[0003] The present invention provides a lignite drying variable load operation system for a coal-fired power plant, which is used to solve the technical problems that the heat required for drying lignite under different working conditions of existing coal-fired units does not match the coal flow rate, affecting the economy of lignite drying and it is difficult to provide a reference basis for the variable load operation characteristics of lignite drying.

[0004] In view of this, the first aspect of the present invention provides a lignite drying variable load operation system for a coal-fired power plant, comprising a boiler, a blower, an induced draft fan, a high-pressure cylinder, a medium-pressure cylinder, a low-pressure cylinder, a high-pressure heater, a low-pressure heater, a deaerator, a dryer, a steam-driven feed water pump, a condensate pump, a condenser, a power generation system and a water circulation system;

[0005] The blower is used to supply air to the combustion chamber of the boiler;

[0006] The induced draft fan is used to exhaust the gas in the combustion chamber;

[0007] The steam output end of the boiler is connected to the input end of the high-pressure cylinder and the input end of the medium-pressure cylinder respectively, the steam output end of the medium-pressure cylinder is connected to the input end of the low-pressure cylinder, the steam output end of the low-pressure cylinder is connected to the input end of the condenser, and the output end of the condenser is connected to the water circulation system;

[0008] The high-pressure cylinder, the medium-pressure cylinder and the low-pressure cylinder are respectively connected to the power generation system;

[0009] One exhaust end of the high-pressure heater and the low-pressure heater is connected to the input end of the deaerator respectively, the output end of the deaerator is connected to the input end of the steam-driven feed water pump, the output end of the steam-driven feed water pump is connected to the steam inlet end of the high-pressure heater, the other exhaust end of the high-pressure heater is communicated with the water-cooled wall inlet of the boiler, the other exhaust end of the low-pressure heater is connected to the input end of the condenser, the output end of the condenser is connected to the input end of the condensate pump, and the output end of the condensate pump is connected to the input end of the low-pressure heater;

[0010] The input end of the dryer is connected to the exhaust port of the medium pressure cylinder, the water outlet end of the dryer is connected to the input end of the deaerator, the coal outlet of the dryer is connected to the coal inlet of the boiler combustion chamber, and the heat required for the dryer to dry the lignite is determined by the moisture content of the lignite.

[0011] Optionally, the relationship between the moisture content of lignite and the standard coal consumption rate is:

[0012]

[0013] Among them, a is the moisture content and y is the standard coal consumption rate.

[0014] Optionally, the high-pressure heater includes a first high-pressure heater, a second high-pressure heater and a third high-pressure heater, the first high-pressure heater and the second high-pressure heater are respectively connected to the high-pressure cylinder through a steam supply pipeline, and the third high-pressure heater is connected to the medium-pressure cylinder through a steam supply pipeline.

[0015] Optionally, the low-pressure heater includes a first low-pressure heater, a second low-pressure heater, a third low-pressure heater and a fourth low-pressure heater, and the first low-pressure heater, the second low-pressure heater, the third low-pressure heater and the fourth low-pressure heater are respectively connected to the low-pressure cylinder through a steam supply pipe.

[0016] Optionally, a first high-pressure shut-off valve is arranged on the steam supply pipeline between the high-pressure heater and the high-pressure cylinder, a second high-pressure shut-off valve is arranged on the steam supply pipeline between the high-pressure heater and the medium-pressure cylinder, and a low-pressure shut-off valve is arranged on the steam supply pipeline between the low-pressure heater and the low-pressure cylinder.

[0017] Optionally, the blower and the induced draft fan are electrically connected to the power generation system respectively, and the condensate pump and the water circulation system are powered by the power generation system.

[0018] Optionally, the shaft work required by the steam-driven feedwater pump is provided by extracting steam from the intermediate pressure cylinder to drive a small steam turbine.

[0019] Optionally, the first high-pressure heater, the second high-pressure heater and the third high-pressure heater use a step-by-step gravity flow method to collect steam to the deaerator.

[0020] Optionally, the fourth low-pressure heater, the third low-pressure heater, the second low-pressure heater and the first low-pressure heater use a step-by-step gravity flow method to collect steam to the condensate pump.

[0021] Optionally, the output end of the condensate pump uses a step-by-step gravity flow method to collect the condensate through the fourth low-pressure heater, the third low-pressure heater, the second low-pressure heater and the first low-pressure heater in sequence to the deaerator.

[0022] Optionally, a condensate regulating valve is arranged between the condensate pump and the fourth low-pressure heater.

[0023] Optionally, a high-pressure cylinder main regulating valve is arranged between the steam output end of the boiler and the input end of the high-pressure cylinder, and a medium-pressure cylinder main regulating valve is arranged between the steam output end of the boiler and the input end of the medium-pressure cylinder.

[0024] Optionally, a high-pressure cylinder main steam valve is further configured between the steam output end of the boiler and the input end of the high-pressure cylinder, and a medium-pressure cylinder main steam valve is further configured between the steam output end of the boiler and the input end of the medium-pressure cylinder.

[0025] It can be seen from the above technical solutions that the lignite drying variable load operation system for a coal-fired power plant provided by the present invention has the following advantages:

[0026] The invention provides a lignite drying variable load operation system for a coal-fired power plant, comprising a boiler, a blower, an induced draft fan, a high-pressure cylinder, a medium-pressure cylinder, a low-pressure cylinder, a high-pressure heater, a low-pressure heater, a deaerator, a dryer, a steam-driven water supply pump, a condensate pump, a condenser, a power generation system and a water circulation system, wherein the input end of the dryer is connected to the exhaust port of the medium-pressure cylinder, the water outlet end of the dryer is connected to the input end of the deaerator, the coal outlet of the dryer is connected to the coal inlet of the boiler combustion chamber, the exhaust gas of the medium-pressure cylinder is used as the heat source required for lignite drying, the steam extraction flow rate of the medium-pressure cylinder is determined according to the relationship between the moisture content of the lignite and the standard coal consumption rate, thereby solving the technical problems that the heat required for drying lignite under different working conditions of the existing coal-fired units is not matched with the coal flow rate, affecting the economy of lignite drying, and it is difficult to provide a reference basis for the variable load operation characteristics of lignite drying. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 It is a structural schematic diagram of a lignite drying variable load operation system of a coal-fired power plant provided in an embodiment of the present invention;

[0029] Figure 2 It is a schematic diagram of standard coal consumption rate under five working conditions provided in an embodiment of the present invention;

[0030] Wherein, the accompanying drawings are marked as follows:

[0031] 100, boiler; 110, combustion chamber; 200, blower; 300, induced draft fan; 400, high-pressure cylinder; 500, medium-pressure cylinder; 600, low-pressure cylinder; 700, deaerator; 800, steam-driven feed water pump; 900, dryer; 1100, condensate pump; 1200, condenser; 1300, power generation system; 1400, water circulation system; #1, first high-pressure heater; #2, second high-pressure heater; #3, third high-pressure heater; #4, first low-pressure heater; #5, second low-pressure heater; #6, third low-pressure heater; #7, fourth low-pressure heater. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] For easier understanding, see Figure 1 The present invention provides an embodiment of a lignite drying variable load operation system for a coal-fired power plant, comprising a boiler 100, a blower 200, an induced draft fan 300, a high-pressure cylinder 400, a medium-pressure cylinder 500, a low-pressure cylinder 600, a high-pressure heater, a low-pressure heater, a deaerator 700, a dryer 900, a steam-driven feedwater pump 800, a condensate pump 1100, a condenser 1200, a power generation system 1300 and a water circulation system 1400;

[0034] The blower 200 is used to supply air to the combustion chamber 110 of the boiler 100;

[0035] The induced draft fan 300 is used to exhaust the gas in the combustion chamber 110;

[0036] The steam output end of the boiler 100 is connected to the input end of the high-pressure cylinder 400 and the input end of the medium-pressure cylinder 500 respectively, the steam output end of the medium-pressure cylinder 500 is connected to the input end of the low-pressure cylinder 600, the steam output end of the low-pressure cylinder 600 is connected to the input end of the condenser 1200, and the output end of the condenser 1200 is connected to the water circulation system 1400;

[0037] The high pressure cylinder 400, the medium pressure cylinder 500 and the low pressure cylinder 600 are respectively connected to the power generation system 1300;

[0038] One exhaust end of the high-pressure heater and the low-pressure heater are respectively connected to the input end of the deaerator 700, the output end of the deaerator 700 is connected to the input end of the steam-driven feedwater pump 800, the output end of the steam-driven feedwater pump 800 is connected to the steam inlet end of the high-pressure heater, the other exhaust end of the high-pressure heater is communicated with the water-cooled wall inlet of the boiler 100, the other exhaust end of the low-pressure heater is connected to the input end of the condenser 1200, the output end of the condenser 1200 is connected to the input end of the condensate pump 1100, and the output end of the condensate pump 1100 is connected to the input end of the low-pressure heater;

[0039] The input end of the dryer 900 is connected to the exhaust port of the medium pressure cylinder 500, the water outlet end of the dryer 900 is connected to the input end of the deaerator 700, the coal outlet of the dryer 900 is connected to the coal inlet of the combustion chamber 110 of the boiler 100, and the heat required for the dryer 900 to dry the lignite is determined by the moisture content of the lignite.

[0040] It should be noted that the high-pressure heater includes a first high-pressure heater #1, a second high-pressure heater #2 and a third high-pressure heater #3. The first high-pressure heater #1 and the second high-pressure heater #2 are respectively connected to the high-pressure cylinder 400 through a steam supply pipeline, and the third high-pressure heater #3 is connected to the medium-pressure cylinder 500 through a steam supply pipeline. The low-pressure heater includes a first low-pressure heater #4, a second low-pressure heater #5, a third low-pressure heater #6 and a fourth low-pressure heater #7. The first low-pressure heater #4, the second low-pressure heater #5, the third low-pressure heater #6 and the fourth low-pressure heater #7 are respectively connected to the low-pressure cylinder 600 through a steam supply pipeline. In the present invention, taking a 600MW supercritical unit with a single intermediate reheat and a three-cylinder and four-exhaust arrangement as an example, the main steam parameters are 1782t / h, 24.2MPa, 566℃. The reheat steam parameters are 1531t / h, 4.954MPa, 566℃. The unit has eight stages of steam extraction, which are used for heating three high-pressure heaters, one deaerator 700 and four low-pressure heaters. The shaft work required for the blower 200, the induced draft fan 300, the condensate pump 1100 and the water circulation system 1400 is provided by the electric motor driven by the power generation system 1300. The shaft work required for the steam-driven feedwater pump 800 is provided by the small steam turbine driven by the steam extraction of the medium-pressure cylinder 500. The extracted steam after work is combined with the exhaust steam of the low-pressure steam turbine and sent to the condenser 1200 for cooling.

[0041] The lignite with moisture contents of 30%, 23%, 15% and 8% after drying to different degrees were defined as drying conditions 1 to 4, and the undried lignite (moisture content of 38.7%) was defined as the original condition. The contents of each component and the low calorific value of the five conditions are shown in Table 1.

[0042] Table 1 Lignite composition and low calorific value

[0043]

[0044] The heat required for drying lignite consists of four parts: the increase in raw coal temperature, the vaporization heat absorption and sensible heat of the raw coal to remove moisture, the increase in air temperature required for drying, and the heat dissipation of the drying system. The heat required to obtain 1t / h of lignite with a certain moisture content is shown in Table 2.

[0045] Table 2 Heat required for lignite with different moisture contents

[0046]

[0047] Commonly used heat sources in lignite power generation units are hot flue gas and steam extraction from steam turbines. When hot flue gas is used as the drying heat source, excessively high temperatures will cause overheating and spontaneous combustion of the lignite and even cause an explosion. When the temperature is too low, the drying efficiency is low, especially under high loads, and it is difficult to meet the coal supply requirements of the power plant. In the present invention, the heat source required for lignite drying is the exhaust steam of the medium-pressure cylinder 500. The exhaust steam of the medium-pressure cylinder 500 flows through the dryer 900 to release heat and condenses into water before flowing into the deaerator 700. A controller is used to adjust the steam extraction flow rate of the medium-pressure cylinder 500 to meet the heat demand of the dryer 900. When setting the controller, the controller target value is the heat required for drying the lignite, and the control value is the steam extraction flow rate flowing through the heat user.

[0048] In the process of reducing the moisture content from 38.7% to 30%, the raw coal quantity and standard coal consumption rate decreased rapidly, among which the standard coal consumption rate decreased by 2.912g / ( ). However, as the dryness increases, although the unit's raw coal volume and standard coal consumption rate are decreasing, the decreasing trend is getting smaller and smaller. When the moisture content decreases from 15% to 8%, the standard coal consumption rate only decreases by 1.106g / ( ). The relationship between the moisture content of lignite and the standard coal consumption rate is obtained by using Newton interpolation method:

[0049]

[0050] Among them, a is the moisture content and y is the standard coal consumption rate.

[0051] Since the total low calorific value of lignite increases after drying, and the increase of lignite with different drying degrees is not the same, when calculating the standard coal consumption rate of the unit, using the mass flow rate of dry lignite and the low calorific value will lead to a high result, which is not conducive to the unified comparison of multiple working conditions. In order to uniformly describe the impact of burning lignite with different drying degrees on the unit, the mass flow rate and low calorific value of the raw coal before entering the dryer 900 are used when calculating the energy input to the system. The standard coal consumption rate under five working conditions is as follows Figure 2 As shown. Figure 2It can be seen that with the increase of dryness, the standard coal consumption rate is gradually decreasing. But the increase is gradually decreasing. At 600MW, when burning dry lignite with a moisture content of 30%, 23%, 15%, and 8%, the standard coal consumption rate of the unit decreased by 4.93, 7.42, 9.71, and 11.36 g / ( At 300MW, they are 9.20, 11.79, 14.17, and 15.88 g / ( ). According to the results, when the unit is running at low load, burning dry lignite is more beneficial to reducing the unit's standard coal consumption rate. This is because the unit has a higher standard coal consumption rate when running at low load, and the low-quality heat is more, and the impact of extraction steam drying lignite on the unit is smaller, making the advantage of burning dry lignite more obvious when running at low load.

[0052] The raw coal consumption (unit / ) of the lignite drying variable load operation system for coal-fired power plants provided by the present invention under different working conditions and loads ) as shown in Table 3.

[0053] Table 3 Raw coal quantity under different load conditions

[0054]

[0055] From the data in Table 3, it can be seen that at the same load, as the degree of dryness increases, the amount of raw coal consumed is gradually decreasing, but the reduction is getting smaller and smaller. At 600MW, dry condition 4 reduces raw coal by 4.70kg / s compared with the original condition, and at 300MW it reduces by 3.29 kg / s. Considering the power supply load, burning dry lignite has greater advantages when the unit is running at low load.

[0056] A first high-pressure shut-off valve is arranged on the steam supply pipeline between the high-pressure heater and the high-pressure cylinder 400, a second high-pressure shut-off valve is arranged on the steam supply pipeline between the high-pressure heater and the medium-pressure cylinder 500, and a low-pressure shut-off valve is arranged on the steam supply pipeline between the low-pressure heater and the low-pressure cylinder 600.

[0057] The first high-pressure heater #1, the second high-pressure heater #2 and the third high-pressure heater #3 use a step-by-step gravity flow method to collect steam through the exhaust end to the deaerator 700. The fourth low-pressure heater #7, the third low-pressure heater #6, the second low-pressure heater #5 and the first low-pressure heater #4 use a step-by-step gravity flow method to collect steam through the exhaust end to the condensate pump 1100. The output end of the condensate pump 1100 uses a step-by-step gravity flow method to collect condensate through the fourth low-pressure heater #7, the third low-pressure heater #6, the second low-pressure heater #5 and the first low-pressure heater #4 to the deaerator 700. A condensate regulating valve is arranged between the condensate pump 1100 and the fourth low-pressure heater #7 to adjust the flow rate of condensate flowing to the fourth low-pressure heater #7. A main regulating valve of the high-pressure cylinder 400 is arranged between the steam output end of the boiler 100 and the input end of the high-pressure cylinder 400, and a main regulating valve of the intermediate-pressure cylinder 500 is arranged between the steam output end of the boiler 100 and the input end of the intermediate-pressure cylinder 500. A main steam valve of the high-pressure cylinder 400 is also arranged between the steam output end of the boiler 100 and the input end of the high-pressure cylinder 400, and a main steam valve of the intermediate-pressure cylinder 500 is also arranged between the steam output end of the boiler 100 and the input end of the intermediate-pressure cylinder 500.

[0058] The present invention provides a lignite drying variable load operation system for a coal-fired power plant, comprising a boiler 100, a blower 200, an induced draft fan 300, a high-pressure cylinder 400, a medium-pressure cylinder 500, a low-pressure cylinder 600, a high-pressure heater, a low-pressure heater, a deaerator 700, a dryer 900, a steam-driven feed water pump 800, a condensate pump 1100, a condenser 1200, a power generation system 1300 and a water circulation system 1400, wherein the input end of the dryer 900 is connected to the exhaust port of the medium-pressure cylinder 500, and the input end of the dryer 900 is connected to the exhaust port of the medium-pressure cylinder 500. The water outlet is connected to the input end of the deaerator 700, the coal outlet of the dryer 900 is connected to the coal inlet of the combustion chamber 110 of the boiler 100, and the exhaust gas of the medium-pressure cylinder 500 is used as the heat source required for lignite drying. The extraction steam flow rate of the medium-pressure cylinder 500 is determined according to the relationship equation between the moisture content of lignite and the standard coal consumption rate. This solves the technical problem that the heat required for drying lignite under different working conditions of the existing coal-fired units is not matched with the coal flow rate, which affects the economy of lignite drying and is difficult to provide a reference basis for the variable load operation characteristics of lignite drying.

[0059] The terms "first", "second", "third", etc. in the specification of the present invention are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0060] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lignite drying variable load operation system for a coal-fired power plant, characterized in that: Including boiler, blower, induced draft fan, high pressure cylinder, medium pressure cylinder, low pressure cylinder, high pressure heater, low pressure heater, deaerator, dryer, steam-driven feed water pump, condensate pump, condenser, power generation system and water circulation system; The blower is used to supply air to the combustion chamber of the boiler; The induced draft fan is used to exhaust the gas in the combustion chamber; The steam output end of the boiler is connected to the input end of the high-pressure cylinder and the input end of the medium-pressure cylinder respectively, the steam output end of the medium-pressure cylinder is connected to the input end of the low-pressure cylinder, the steam output end of the low-pressure cylinder is connected to the input end of the condenser, and the output end of the condenser is connected to the water circulation system; The high-pressure cylinder, the medium-pressure cylinder and the low-pressure cylinder are respectively connected to the power generation system; One exhaust end of the high-pressure heater and the low-pressure heater is connected to the input end of the deaerator respectively, the output end of the deaerator is connected to the input end of the steam-driven feed water pump, the output end of the steam-driven feed water pump is connected to the steam inlet end of the high-pressure heater, the other exhaust end of the high-pressure heater is communicated with the water-cooled wall inlet of the boiler, the other exhaust end of the low-pressure heater is connected to the input end of the condenser, the output end of the condenser is connected to the input end of the condensate pump, and the output end of the condensate pump is connected to the input end of the low-pressure heater; The input end of the dryer is connected to the exhaust port of the medium pressure cylinder, the water outlet end of the dryer is connected to the input end of the deaerator, the coal outlet of the dryer is connected to the coal inlet of the boiler combustion chamber, and the heat required for the dryer to dry the lignite is determined by the moisture content of the lignite.

2. The lignite drying variable load operation system of a coal-fired power plant according to claim 1 is characterized in that: The high-pressure heater includes a first high-pressure heater, a second high-pressure heater and a third high-pressure heater. The first high-pressure heater and the second high-pressure heater are respectively connected to the high-pressure cylinder through a steam supply pipeline, and the third high-pressure heater is connected to the medium-pressure cylinder through a steam supply pipeline.

3. The lignite drying variable load operation system of a coal-fired power plant according to claim 1, characterized in that: The low-pressure heater includes a first low-pressure heater, a second low-pressure heater, a third low-pressure heater and a fourth low-pressure heater, and the first low-pressure heater, the second low-pressure heater, the third low-pressure heater and the fourth low-pressure heater are respectively connected to the low-pressure cylinder through a steam supply pipeline.

4. The lignite drying variable load operation system of a coal-fired power plant according to claim 1, characterized in that: A first high-pressure shut-off valve is arranged on the steam supply pipeline between the high-pressure heater and the high-pressure cylinder, a second high-pressure shut-off valve is arranged on the steam supply pipeline between the high-pressure heater and the medium-pressure cylinder, and a low-pressure shut-off valve is arranged on the steam supply pipeline between the low-pressure heater and the low-pressure cylinder.

5. The lignite drying variable load operation system of a coal-fired power plant according to claim 1, characterized in that: The shaft work required for the steam-driven feedwater pump is provided by the small steam turbine driven by steam extracted from the intermediate pressure cylinder.

6. The lignite drying variable load operation system of a coal-fired power plant according to claim 1, characterized in that: The first high-pressure heater, the second high-pressure heater and the third high-pressure heater use a step-by-step gravity flow method to collect steam to the deaerator through the exhaust end.

7. The lignite drying variable load operation system of a coal-fired power plant according to claim 1, characterized in that: The fourth low-pressure heater, the third low-pressure heater, the second low-pressure heater and the first low-pressure heater use a step-by-step gravity flow method to collect steam to the condensate pump through the exhaust end.

8. The lignite drying variable load operation system of a coal-fired power plant according to claim 1, characterized in that: The output end of the condensate pump uses a step-by-step gravity method to collect the condensate through the fourth low-pressure heater, the third low-pressure heater, the second low-pressure heater and the first low-pressure heater to the deaerator.

9. The lignite drying variable load operation system of a coal-fired power plant according to claim 8, characterized in that: A condensate regulating valve is arranged between the condensate pump and the fourth low-pressure heater.

10. The lignite drying variable load operation system for a coal-fired power plant according to any one of claims 1 to 9, characterized in that: The relationship between the moisture content of lignite and the standard coal consumption rate is: Among them, a is the moisture content and y is the standard coal consumption rate.

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