A heat recovery system for shaft seal overflow steam of direct air-cooled units

Abstract

The present invention discloses a heat recovery system for shaft seal overflow steam of a direct air-cooling unit, which belongs to the technical field of thermal power generation, and includes: a steam-water heat exchanger is newly set up, the steam source is taken from the shaft seal overflow steam, the heat energy in the shaft seal overflow steam is used to heat the condensate, and the condensate recovers the heat energy in the shaft seal overflow steam; the shaft seal overflow steam heats the condensate by heat conduction in the heater, the condensate temperature is increased to ensure that the low-temperature economizer can be put into operation normally, and the drain generated by condensation is connected to the exhaust device. The system recycles the shaft seal overflow steam, effectively reduces coal consumption, improves the operating safety of the low-temperature economizer, improves energy utilization, and improves production efficiency. The present invention has a significant effect and is suitable for wide promotion.

Description

Technical Field

[0001] The invention relates to the technical field of thermal power generation, and in particular to a direct air-cooling unit shaft seal overflow steam heat recovery system. Background Art

[0002] The main function of the turbine shaft seal system is to provide a suitable steam source for the cylinder end shaft seal under various operating conditions such as startup, operation and shutdown, and to recover the leakage of the turbine shaft end steam seal and the high and medium pressure main steam regulating valve stem and the steam-gas mixture, so as to prevent steam from entering the plant, entering the bearing box to cause water to enter the lubricating oil, or atmospheric air from leaking into the cylinder to affect the unit vacuum. When some units are operating normally, the leakage steam from the high and medium pressure cylinder shaft end steam seal is used as the steam turbine system for low pressure shaft end steam supply after being cooled by water spraying, and the excess leakage steam overflows to the condenser through the overflow station. The spare steam source of the shaft seal steam is connected to the main steam, the reheat cold section steam, and the auxiliary steam, which can be used for startup and low load.

[0003] A large amount of shaft seal overflow steam from the self-sealing steam seal system is directly discharged into the main engine exhaust device, causing a large amount of heat loss and also having a negative impact on the vacuum of the exhaust device. In addition, the shaft seal of the unit has been worn after years of operation, and the actual shaft seal overflow steam volume is greater than the design value of each operating condition. At the same time, when the unit is under low load, the condensate temperature is lower than the input condition of the low-temperature economizer on the boiler side, resulting in the low-temperature economizer being unable to be put into operation for a long time, greatly reducing the economic efficiency of the unit operation.

[0004] At present, existing equipment all introduces shaft seal overflow steam into the low-pressure heater system. The disadvantage of this setting is that the design parameters of the low-pressure heater are relatively low. As the unit runs, the shaft seal steam leakage parameters cannot be controlled, which will directly affect the safety of the low-pressure heater system. Summary of the invention

[0005] In view of the above-mentioned defects, the technical problem solved by the present invention is to provide a heat recovery system for the shaft seal overflow steam of a direct air-cooled unit, so as to solve the problem that a large amount of shaft seal overflow steam is directly discharged into the main engine exhaust device in the existing technology, causing a large amount of heat loss, and also bringing negative impact on the vacuum of the exhaust device; when the unit is at low load, the condensate temperature is lower than the start-up condition of the low-temperature economizer on the boiler side, resulting in the low-temperature economizer cannot be put into operation for a long time, which greatly reduces the economy of the unit operation.

[0006] The present invention provides a method for recovering heat from shaft seal overflow steam of a direct air-cooled unit, comprising: adding a steam-water heat exchanger, the steam source being taken from the shaft seal overflow steam, and utilizing the heat energy in the shaft seal overflow steam to heat condensate; the shaft seal overflow steam heats the condensate in a heater by heat conduction, thereby increasing the condensate temperature to ensure that a low-temperature economizer can be put into normal operation, and the drain generated by condensation is connected to a steam exhaust device.

[0007] Preferably, the temperature of the shaft seal overflow steam with reduced temperature is 325°C-375°C.

[0008] The present invention also provides a direct air-cooling unit shaft seal overflow steam heat recovery system, comprising:

[0009] a first low-pressure heater, connected to the steam turbine, for reducing the amount of steam discharged from the steam turbine to the exhaust device, wherein the first low-pressure heater comprises a first heating pipe, and the first heating pipe is connected to the condensate supply device;

[0010] A heat exchanger, one side of which is connected to the first low-pressure heater and the other side of which is connected to the shaft seal overflow steam pipeline, for recovering the heat of the shaft seal overflow steam to increase the temperature of the condensed water;

[0011] A low-temperature economizer, connected to the heat exchanger, for utilizing the heat of the low-temperature flue gas to increase the temperature of condensed water;

[0012] The second low-pressure heater is connected to the low-temperature economizer on one side and to the steam turbine on the other side, and is used to utilize the steam that has done part of the work in the steam turbine to be pumped into the heater to heat the feed water and increase the water temperature.

[0013] Preferably, the heat exchanger comprises:

[0014] Steam operation pipeline;

[0015] A water running pipeline, comprising a water supply inlet and a water supply outlet, wherein the water supply inlet is connected to the first heating pipe, and the water supply outlet is connected to the low-temperature economizer;

[0016] A drain assembly, connected to the steam running pipeline, for adjusting the water level in the heater (shaft seal overflow cooler);

[0017] A pressure regulating assembly, connected to the steam running pipeline and to the exhaust device, for extracting gas from the heater;

[0018] The condensate chamber is communicated with the steam running pipeline and is used for storing condensed shaft seal overflow steam.

[0019] Preferably, a liquid level gauge is provided in the condensate water cavity, and the liquid level gauge is electrically connected to an alarm. The alarm includes a low-level alarm, a high-level alarm and a high-level cutter. The high-level cutter is electrically connected to the heat exchanger for controlling the start and stop of the heat exchanger.

[0020] Preferably, the hydrophobic component comprises:

[0021] A normal drain pipe, which is connected to the condensate cavity and the exhaust device at the same time;

[0022] The emergency drain pipe is connected to the condensate cavity and the exhaust device at the same time. The normal drain pipe and the emergency drain pipe are both provided with regulating valves. The regulating valves are electrically connected to the alarm, and the alarm controls the opening of the regulating valves.

[0023] It can be seen from the above scheme that the present invention provides a heat recovery method for shaft seal overflow steam of a direct air-cooled unit. By utilizing the heat energy in the shaft seal overflow steam to heat the circulating water, the condensate temperature at the inlet of the low-temperature economizer is increased, so that the low-temperature economizer is always in the condition of being put into operation, and the working efficiency of the low-temperature economizer is improved; the shaft seal overflow steam is used as the heating gas source of the No. 7 low-pressure heater and the heating gas provided by the external equipment is mixed to heat the circulating water. On the one hand, the utilization rate of the heat generated by the exhaust device is improved to ensure the operation needs while reducing coal consumption. On the other hand, the supply of heating gas in the external equipment is reduced, the cost is reduced, and energy loss is reduced. The present invention also provides a heat recovery system for shaft seal overflow steam of a direct air-cooled unit. The system uses the above method to recycle the shaft seal overflow steam, controls the temperature of the shaft seal overflow steam by cooling water, ensures that the heater can operate within the design parameter range, ensures the safety of the low-pressure system, and effectively reduces coal consumption, improves energy utilization, and improves production efficiency. The present invention has a significant effect. According to research, the overflow temperature of the steam turbine shaft seal of most thermal power plants that have been in operation for less than 5 years is about 350°C. As the operating life of the unit increases, the overflow temperature of the shaft seal will continue to rise. The A-level maintenance cycle of the power plant is as long as 5-6 years. After the treatment, there is still overflow steam from the shaft seal input into the steam turbine exhaust device, resulting in a large amount of heat waste. Therefore, it is very necessary to recover the overflow steam from the steam turbine shaft seal. If the heat exchanger (2) is installed before the first heater (1), after the condensate temperature at the outlet of the heat exchanger (2) increases, according to the principle of hydrophobic displacement, the steam extraction amount of the first heater (1) will decrease. Therefore, the outlet water temperature of the first heater (1) increases to a limited extent, and the inlet condensate temperature of the low-temperature economizer (3) still does not meet the requirements for de-operation. Therefore, the heat exchanger (2) needs to be arranged before the condensate pipeline of the low-temperature economizer (3), and the interlocking protection of the steam-water side of the heat exchanger (2) is designed simultaneously. After being connected to the LP heater, the extraction steam volume of the LP heater will be affected and the operating efficiency of the unit will decrease. This type of direct air-cooled unit shaft seal overflow steam heat recovery system occupies a small area, has a small investment amount, and has a high recovery efficiency, and is suitable for wide promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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 drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 A schematic structural diagram of a heat exchanger of a shaft seal overflow steam heat recovery system for a direct air-cooling unit provided by the present invention;

[0026] Figure 2 A schematic block diagram of the structure of one side (water side) of a shaft seal overflow steam heat recovery system for a direct air-cooling unit provided by the present invention;

[0027] Figure 3 A structural schematic block diagram of another direct air-cooling unit shaft seal overflow steam heat recovery system provided by the present invention;

[0028] Figure 4 A structural schematic block diagram of another direct air-cooling unit side (steam side) shaft seal overflow steam heat recovery system provided by the present invention.

[0029] Figure 1-4 middle:

[0030] 1. The first low-pressure heater; 2. Heat exchanger; 3. Low-temperature economizer; 4. The second low-pressure heater; 5. Exhaust device; 6. No. 5 low-pressure heater; 7. Deaerator; 8. Shaft seal heater; 21. Steam operation pipeline; 22. Water operation pipeline; 23. Drain assembly; 24. Pressure regulating assembly; 25. Liquid level gauge; 26. Cooling section vent; 27. Shell side drain; 28. Inlet; 29. ​​Shell side safety valve interface; 211. Steam inlet; 221. Water inlet; 222. Water outlet; 231. Normal drain pipe; 232. Emergency drain pipe; 241. Air extraction inlet; 242. Shell side vent. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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.

[0032] Please also read Figures 1 to 4, a specific implementation method of the heat recovery method of the shaft seal overflow steam of a direct air-cooling unit provided by the present invention is now described. The heat recovery method of the shaft seal overflow steam of the direct air-cooling unit includes: a steam-water heat exchanger is newly installed, the steam source is taken from the shaft seal overflow steam, and the heat energy in the shaft seal overflow steam is used to heat the condensate; the shaft seal overflow steam heats the condensate by heat conduction in the heater, and the condensate temperature is increased to ensure that the low-temperature economizer can be put into normal operation, and the hydrophobic water generated by condensation is connected to the exhaust device. The heat energy in the shaft seal overflow steam is used to heat the condensate, and the condensate recovers the heat energy in the shaft seal overflow steam; the shaft seal overflow steam with reduced temperature is condensed into water and merged into the circulating water, and the energy released during the condensation process continues to heat the circulating water; the uncondensed gas after cooling is discharged to ensure the vacuum environment of the circulation process.

[0033] In this embodiment, the temperature of the shaft seal overflow steam with reduced temperature is 325℃-375℃. For example, the temperature of the shaft seal overflow steam is reduced from 510℃ to 350℃. The purpose of reducing the original overflow temperature of 510℃ to 325-375℃ is to save the heater cost. The shaft seal overflow steam is recovered by the No. 7 low-pressure heater, releasing heat energy to heat the circulating water; the shaft seal overflow steam with reduced temperature enters the shaft seal overflow cooler, and the shaft seal overflow cooler adjusts the temperature of the circulating water passing through it and the temperature and pressure of the condensed water generated therein according to the temperature and pressure. The circulating water heated by the shaft seal overflow cooler enters the low-temperature economizer 3 and is heated again by the low-temperature economizer 3; the circulating water is heated again by the exhaust gas temperature; the heated circulating water is circulated to the high-temperature area to be heated to form high-temperature steam for use; after the high-temperature steam completes the work, it enters the No. 7 low-pressure heater, and the shaft seal overflow steam generated in the turbine pressure regulation process is recycled again, and the cycle continues.

[0034] Compared with the prior art, this method of heat recovery of shaft seal overflow steam of a direct air-cooled unit increases the condensate temperature at the inlet of the low-temperature economizer 3 by utilizing the heat energy in the shaft seal overflow steam to heat the circulating water, so that the low-temperature economizer 3 is always in the condition of being put into operation, thereby improving the working efficiency of the low-temperature economizer 3; the shaft seal overflow steam is used as the heating gas source of the No. 7 low-pressure heater and the heating gas provided by external equipment to be mixed into the circulating water for heating. On the one hand, it improves the utilization rate of the heat generated by the exhaust device 5, ensuring the operation needs while reducing coal consumption; on the other hand, it reduces the supply of heating gas in the external equipment, reduces costs, and reduces energy loss.

[0035] Please also read Figures 1 to 4Now, a specific implementation of a direct air-cooling unit shaft seal overflow steam heat recovery system provided by the present invention is described. The direct air-cooling unit shaft seal overflow steam heat recovery system comprises a first low-pressure heater 1, a heat exchanger 2, a low-temperature economizer 3 and a second low-pressure heater 4, wherein the steam side of the first low-pressure heater 1 is connected to the steam turbine, and the exhaust steam is used to heat the condensate. The first low-pressure heater 1 comprises a first heating pipe, and the first heating pipe is used to connect to the condensate supply equipment; the water side of the heat exchanger 2 is connected to the first low-pressure heater 1, and the steam side is connected to the shaft seal overflow steam pipeline, which is used to recover the shaft seal overflow steam, and recover the heat of the turbine shaft seal overflow steam to increase the condensate temperature; the water side of the low-temperature economizer 3 is connected to the heat exchanger 2, which uses the heat of the low-temperature flue gas to increase the condensate temperature; the water side of the second low-pressure heater 4 is connected to the low-temperature economizer 3 and the steam turbine at the same time, the water side is connected to the low-temperature economizer 3, and the steam side is connected to the steam turbine, and the steam that has done part of the work in the steam turbine is pumped into the heater to heat the feed water, thereby increasing the water temperature and reducing the steam turbine from being discharged to the exhaust device. The first low-pressure heater 1 uses the steam that has done some work in the steam turbine to heat the feed water in the heater, increase the water temperature, reduce the amount of steam discharged from the steam turbine to the exhaust device, reduce energy loss, and improve the cycle efficiency of the thermal system.

[0036] The first low-pressure heater 1 can be a No. 7 low-pressure heater, and the second low-pressure heater 4 can be a No. 6 low-pressure heater. The circulating water enters the first heating tube, and the shaft seal overflow steam enters the No. 7 low-pressure heater to heat the circulating water. The shaft seal overflow steam is input from the No. 7 low-pressure heater to the heat exchanger 2; the heat exchanger 2 includes a desuperheater, which cools the shaft seal overflow steam, and the exemplary temperature is reduced from 500°C to 350°C. The heat exchanger 2 also includes a shaft seal overflow cooler, which condenses the shaft seal overflow steam into water and heats the circulating water passing through it at the same time. The condensed water and the circulating water merge into the low-temperature economizer 3, and the low-temperature economizer 3 heats the circulating water again and then transports it to the No. 6 low-pressure heater or the exhaust device 5; the circulating water treated by the No. 6 low-pressure heater enters the No. 5 low-pressure heater 6 again for heating, and the deaerator 7 extracts the air in the circulating water to ensure a vacuum environment during the operation of the circulating water. Here, as long as the above-mentioned heat exchanger 2 and the first heating pipe can achieve the relevant performance functions, they are within the scope of protection of this application document. The condensate system process is: No. 7 low-pressure heater-shaft seal overflow cooler-low-temperature economizer 3-No. 6 low-pressure heater.

[0037] Compared with the prior art, the heat recovery system of the shaft seal overflow steam of this direct air-cooled unit is equipped with a heat exchanger 2 after the No. 7 low-pressure heater, and the shaft seal overflow steam is connected to the shaft seal overflow cooler after being cooled. The shaft seal overflow steam is recovered by the shaft seal overflow cooler, and the condensate temperature at the inlet of the low-temperature economizer 3 is increased, so that the low-temperature economizer 3 is always in the condition for being put into operation, thereby improving the overall work efficiency, energy utilization rate, and significantly improving the economic efficiency of the unit operation.

[0038] As another embodiment of the present invention, the heat exchanger 2 of the direct air-cooling unit shaft seal overflow steam heat recovery system includes a steam running pipeline 21, a water running pipeline 22, a drain component 23, a pressure regulating component 24 and a condensate cavity, wherein the steam running pipeline 21 includes a steam inlet 211, the steam inlet 211 is connected to the first low-pressure heater 1, and the steam running pipeline 21 is used for recycling the shaft seal overflow steam; the water running pipeline 22 includes a feed water inlet 221 and a feed water outlet 222, the feed water inlet 221 is connected to the first heating pipe, the feed water outlet 222 is connected to the low-temperature economizer 3, and the water running pipeline 22 is used for the circulation of circulating water to facilitate the heating of the circulating water; the drain component 23 is connected to the steam running pipeline 21, and is used to adjust the water level in the heat exchanger 2; the pressure regulating component 24 is connected to the steam running pipeline 21 and to the exhaust device 5, and is used to extract the gas in the heater; the condensate cavity is connected to the steam running pipeline 21, and is used to store condensed shaft seal overflow steam.

[0039] As another embodiment of the present invention, the first low-pressure heater 1 of the direct air-cooling unit shaft seal overflow steam heat recovery system also includes a steam container and an aeration device, wherein the steam container includes a steam inlet and a steam outlet, the steam inlet is connected to the steam turbine, the steam outlet is connected to the steam inlet 211, and the first heating pipe is arranged in the steam container. The steam inlet is connected to an aeration device for providing hot gas for heating circulating water. The aeration device provides gas for heating circulating water. Since the shaft seal overflow steam simultaneously enters the first low-pressure heater 1 to heat the circulating water, the demand and loss of heating gas provided by the aeration device are greatly reduced, and the same heating effect is achieved while reducing costs and energy consumption, which is more economical.

[0040] As another embodiment of the present invention, a liquid level gauge 25 is provided in the condensate water cavity of the shaft seal overflow steam heat recovery system of the direct air-cooling unit. The liquid level gauge 25 is electrically connected to the alarm. The alarm includes a low-level alarm, a high-level alarm and a high-level cut-off device. The high-level cut-off device is electrically connected to the heat exchanger 2 and is used to control the start and stop of the heat exchanger 2. There are multiple liquid level gauges 25, which are respectively used to sense low alarm water level, low water level, normal water level, high water level, high alarm water level and high-level cut-off water level information, and transmit the acquired water level information to the alarm. According to the water level information acquired by the liquid level gauge 25, the alarm sends out alarm information and controls the working state of the heat exchanger 2.

[0041] As another embodiment of the present invention, the drain assembly 23 of the direct air-cooling unit shaft seal overflow steam heat recovery system includes a normal drain pipe 231 and an emergency drain pipe 232, wherein the normal drain pipe 231 is connected to the condensate cavity and the exhaust device 5 at the same time; the emergency drain pipe 232 is connected to the condensate cavity and the exhaust device 5 at the same time, and the normal drain pipe 231 and the emergency drain pipe 232 are both provided with a regulating valve, and the regulating valve is electrically connected to the alarm, and the alarm controls the opening of the regulating valve. According to the water level information, the alarm controls the speed of the drain assembly 23 to transport the condensate in the condensate cavity, ensures that the water level in the heat exchanger 2 is in a normal state, and makes the heat exchanger 2 run stably.

[0042] Normal working condition of shaft seal overflow: bypass butterfly valve B of overflow regulating valve is closed, overflow regulating valve A is opened, electric gate valve C of shaft seal overflow heater inlet is opened, and electric shut-off door D of shaft seal overflow steam to exhaust device is closed. 2` accident working condition of shaft seal overflow regulating valve: bypass butterfly valve of overflow regulating valve is opened, overflow regulating valve A is closed, electric gate valve C of shaft seal overflow heater inlet is opened, and electric shut-off door D of shaft seal overflow steam to exhaust device is closed. 3` high water level of shaft seal overflow heater: electric gate valve C of shaft seal overflow heater inlet is interlocked and closed, and electric shut-off door D of shaft seal overflow steam to exhaust device is interlocked and opened.

[0043] As another embodiment of the present invention, the heat exchanger 2 of the direct air-cooling unit shaft seal overflow steam heat recovery system further includes a cooling section vent 26 , a shell side drain 27 , an inlet 28 , and a shell side safety valve interface 29 .

[0044] The pressure regulating assembly 24 includes an air extraction port 241 and a shell-side air release port 242 .

[0045] For example, according to the actual operation of the unit, two operating conditions of 200MW and 310MW are selected to analyze the operation effect of the shaft seal overflow cooler and the low-temperature economizer 3. The inlet and outlet temperatures of each heater at a unit load of 200MW are obtained, and the specific temperatures are shown in the following table:

[0046] Not put into operation Commissioning Shaft seal overflow cooler inlet (℃) 65.9 Shaft seal overflow cooler inlet temperature (℃) 73 Shaft seal overflow cooler temperature rise (℃) 7.1 Low temperature economizer inlet temperature (℃) 63.7 73 Low temperature economizer outlet temperature (℃) 74.3 82.5 Low temperature economizer temperature rise (℃) 10.6 9.5 No. 6 low pressure heater inlet temperature (℃) 74.3 82.5 No. 6 low pressure heater outlet temperature (℃) 84.4 86.4 No. 6 low-pressure heater temperature rise (℃) 10.1 3.9 No. 5 low pressure heater inlet temperature (℃) 84.7 86.7 No. 5 low pressure heater outlet temperature (℃) 128.4 129.2 No. 5 low-pressure heater temperature rise (℃) 43.7 42.5

[0047] According to the inlet and outlet temperatures of each heater at a unit load of 200MW in the above table, when the shaft seal overflow cooler was not put into operation, the inlet and outlet temperatures of low-temperature economizer 3 rose by 10.6℃, and when the shaft seal overflow cooler was put into operation, the inlet and outlet temperatures of low-temperature economizer 3 dropped from 10.6℃ to 9.5℃. The inlet temperature rise of low-temperature economizer 3 dropped by 1.1℃, which was mainly affected by the 9.3℃ increase in the inlet condensate temperature of low-temperature economizer 3 after the shaft seal overflow cooler was put into operation. When the shaft seal overflow cooler was not put into operation, the inlet and outlet temperatures of low-pressure heater No. 6 rose by 10.1℃, and after the shaft seal overflow cooler was put into operation, the inlet and outlet temperatures of low-pressure heater No. 6 dropped from 10.1℃ to 3.9℃, which was mainly due to the reduction in the steam extraction volume of low-pressure heater No. 6 due to the hydrophobic crowding effect. After the shaft seal overflow cooler was put into operation, the inlet condensate temperature of low-pressure heater No. 5 increased by 2℃, and the inlet and outlet temperatures of low-pressure heater No. 5 dropped by 1.2℃.

[0048] When low-temperature economizer 3 is put into operation under load (180MW), the inlet flue gas temperature of the electrostatic precipitator drops from 103-110℃ to 89-98℃; the daily power consumption of the induced draft fan drops by about 1440kWh, and the daily power consumption of the electrostatic precipitator drops by about 230kWh; through calculation, it is found that the coal consumption drops by about 0.9g / kWh. The annual power generation is calculated as 2.38 billion kWh, which means that the annual coal saving is about 2,142 tons and the coal cost is about 660,000 yuan; the annual power saving of fans and electrostatic precipitators is about 809,950kWh, and the power cost of auxiliary equipment is about 150,000 yuan. The total annual saving is about 810,000 yuan.

[0049] According to the inlet and outlet condensate temperature and pressure of the No. 1 unit shaft seal overflow cooler after the commissioning, it is calculated that the heat energy utilized by the 200MW shaft seal overflow cooler is 4.786MW. And according to the inlet and outlet condensate pressure and temperature of the No. 6 low-pressure heater, the equivalent enthalpy drop method is used to calculate that the steam extraction volume of the No. 6 low-pressure heater is reduced by 4.19kg / s after the shaft seal overflow cooler and low-temperature economizer 3 are put into operation.

[0050] Saving steam working capacity KW = (4.1 × 2757.54) - (4.1 × 2468) = 1187.114KW,

[0051] In the formula, 2468 kj / kg is the exhaust steam enthalpy under 75% THA condition, and the resulting cold source loss.

[0052] 58% THA condition power generation coal saving Wj

[0053] Wj = 1187.114 / 200000 × (8314 / 29270 × 1000) = 1.6 g / kwh (standard coal),

[0054] In the formula, 200000kw is the power generation under 58% THA condition; 8314kj / (kw.h) is the heat consumption of steam turbine under 75% THA condition; 29270kJ / kg is the calorific value of standard coal.

[0055] Through the analysis of various parameters when the unit is running at a load of 310MW, the inlet and outlet temperatures of each heater at a unit load of 310MW are obtained. The specific temperatures are shown in the following table:

[0056]

[0057]

[0058] According to Table 2, when the shaft seal overflow cooler was not put into operation, the inlet and outlet temperature of low-temperature economizer 3 at 310MW rose by 12.1℃, and when the shaft seal overflow cooler was put into operation, the inlet and outlet temperature of low-temperature economizer 3 dropped from 12.1℃ to 6.8℃. The inlet and outlet temperature of low-temperature economizer 3 dropped by 5.3℃, which was mainly affected by the 6℃ increase in the inlet condensate temperature of low-temperature economizer 3 after the shaft seal overflow cooler was put into operation. When the shaft seal overflow cooler was not put into operation, the inlet and outlet temperature of low-pressure heater No. 6 rose by 8.3℃, and after the shaft seal overflow cooler was put into operation, the inlet and outlet temperature of low-pressure heater No. 6 dropped from 8.3℃ to 7.4℃, which was mainly due to the reduction in the steam extraction volume of low-pressure heater No. 6 due to the hydrophobic crowding effect. The operation of the shaft seal overflow cooler had no impact on low-pressure heater No. 5 6.

[0059] According to the inlet and outlet condensate temperature and pressure of the No. 1 unit shaft seal overflow cooler after commissioning, it is calculated that the heat energy utilized by the 310MW shaft seal overflow cooler is 7.192MW. And according to the inlet and outlet condensate pressure and temperature of the No. 6 low-pressure heater, it is calculated by using the equivalent enthalpy drop method that the steam extraction volume of the No. 6 low-pressure heater is reduced by 5.7kg / s.

[0060] Saving steam working capacity KW = (5.9 × 2712) - (5.9 × 2468) = 1439.6KW,

[0061] In the formula, 2468 kj / kg is the exhaust steam enthalpy under 75% THA condition, and the resulting cold source loss.

[0062] 100% THA condition power generation coal saving Wj

[0063] Wj = 1439.6 / 310000 × (8117 / 29270 × 1000) = 1.28 g / kwh (standard coal),

[0064] In the formula, 310000kw is the power generation under 100% THA condition; 8117kj / (kw.h) is the heat consumption of steam turbine under BMCR condition; 29270kJ / kg is the calorific value of standard coal.

[0065] Through comparison, it is concluded that after the shaft seal overflow cooler is put into operation, it is verified that the condensate temperature can be increased by about 7°C in all working conditions. In the 200MW working condition, the heat utilization of the shaft seal overflow cooler reaches 4.786MW, and in the 310MW working condition, the heat utilization of the shaft seal overflow cooler reaches 7.192MW. After the shaft seal overflow cooler is put into operation, the inlet temperature of the low-temperature economizer 3 in all working conditions can reach 65°C, which can ensure that the low-temperature economizer 3 can be put into operation in all working conditions. Using the equivalent enthalpy drop method, it is calculated that after the shaft seal overflow cooler and the low-temperature economizer 3 are put into operation, the 200MW working condition can reduce the power generation coal consumption by 1.6g / kwh, and the 310MW working condition can reduce the power generation coal consumption by 1.28g / kwh.

[0066] It can be seen from the above data that when the direct air-cooling unit shaft seal overflow steam heat recovery method is applied for thermal power generation, the low-temperature economizer 3 maintains stable operation under the input conditions, the working efficiency is greatly improved, and the safety and economy of the unit operation are greatly improved; at the same time, the heat is more fully applied, the coal consumption is lower, the energy application efficiency is higher, and the low-cost and high-efficiency effect is very significant.

[0067] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced. The contents not described in detail in the embodiments of the present invention belong to the prior art known to professional and technical personnel in this field.

[0068] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A direct air-cooling unit shaft seal overflow steam heat recovery system, characterized in that: include: A first low-pressure heater (1) is connected to the steam turbine and is used to reduce the amount of steam discharged from the steam turbine to the exhaust device. The first low-pressure heater (1) comprises a first heating pipe, and the first heating pipe is used to communicate with the condensate supply device; A heat exchanger (2), one side of which is in communication with the first low-pressure heater (1) and the other side of which is in communication with the shaft seal overflow steam pipeline, and is used to recover the heat of the shaft seal overflow steam to increase the temperature of the condensed water; A low-temperature economizer (3) is connected to the heat exchanger (2) and is used to increase the temperature of condensed water by utilizing the heat of the low-temperature flue gas; The second low-pressure heater (4) is connected to the low-temperature economizer (3) on one side and to the steam turbine on the other side, and is used to utilize the steam that has done part of the work in the steam turbine to be pumped into the heater to heat the feed water and increase the water temperature.

2. A direct air-cooling unit shaft seal overflow steam heat recovery system according to claim 1, characterized in that: The heat exchanger (2) comprises: Steam operation pipeline (21); A water running pipeline (22), comprising a water supply inlet (221) and a water supply outlet (222), wherein the water supply inlet (221) is in communication with the first heating pipe, and the water supply outlet (222) is in communication with the low-temperature economizer (3); A drain assembly (23), which is in communication with the steam running pipeline (21) and is used to adjust the water level in the heat exchanger (2); A pressure regulating assembly (24) is connected to the steam running pipeline (21) and to the exhaust device (5), and is used to extract gas from the first low-pressure heater (1); The condensate water cavity is in communication with the steam running pipeline (21) and is used for storing condensed shaft seal overflow steam.

3. A direct air-cooling unit shaft seal overflow steam heat recovery system according to claim 2, characterized in that: A liquid level meter (25) is provided in the condensate water cavity, and the liquid level meter (25) is electrically connected to an alarm. The alarm includes a low-level alarm, a high-level alarm and a high-level cut-off device. The high-level cut-off device is electrically connected to the heat exchanger (2) and is used to control the start and stop of the heat exchanger (2).

4. A direct air-cooling unit shaft seal overflow steam heat recovery system according to claim 3, characterized in that: The hydrophobic component (23) comprises: A normal drain pipe (231) is connected to the condensate cavity and the exhaust device (5); The emergency drain pipe (232) is connected to the condensate cavity and the exhaust device (5) at the same time. The normal drain pipe (231) and the emergency drain pipe (232) are both provided with regulating valves. The regulating valves are electrically connected to the alarm, and the alarm controls the opening of the regulating valves.

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