Blowdown Steam Recovery System for Multi-pressure Boilers

Abstract

The present invention relates to a blowdown steam recovery system for a multi-pressure boiler. The present invention comprises a high-pressure steam drum, a medium-pressure steam drum, a low-pressure steam drum, a medium-pressure continuous expansion tank, a low-pressure continuous expansion tank, and a timed blowdown expansion tank. The high-pressure steam drum is connected to the medium-pressure continuous expansion tank through a high-pressure continuous blowdown pipeline. The medium-pressure continuous expansion tank is connected to the low-pressure continuous expansion tank through a first regulating valve and is connected to the medium-pressure steam drum through a first check valve. The medium-pressure steam drum is connected to the low-pressure continuous expansion tank through a medium-pressure continuous blowdown pipeline. The low-pressure continuous expansion tank is connected to the timed blowdown expansion tank through a second regulating valve and is connected to the low-pressure steam drum through a second check valve. The low-pressure steam drum is connected to the timed blowdown expansion tank through a low-pressure continuous blowdown pipeline. The present invention realizes step-by-step flash evaporation of the blowdown steam of the high-pressure steam drum in the medium-pressure continuous expansion tank and the low-pressure continuous expansion tank by adding a medium-pressure continuous expansion tank, thereby greatly improving the thermal efficiency of recovering and utilizing the blowdown steam.

Description

Technical Field

[0001] The invention relates to a waste heat boiler blowdown system, in particular to a blowdown steam recovery system for a multi-pressure boiler, and belongs to the technical field of power station boiler equipment. Background Art

[0002] As the proportion of clean energy usage increases, the construction of natural gas combined cycle power plants will continue to grow. One development trend of the combined cycle is that the capacity is getting larger and larger. In order to improve the efficiency of the combined cycle, the supporting waste heat boiler usually adopts a multi-pressure system to maximize the use of the energy of the gas turbine exhaust. Since the boiler's blowdown rate is generally fixed, the greater the evaporation volume of the boiler, the greater the blowdown volume, and the more energy is lost in the blowdown. Therefore, adding a blowdown steam recovery system to the blowdown system is a necessary measure to reduce energy waste and improve the thermal efficiency of the gas turbine. Existing blowdown steam recovery systems such as Figure 1 As shown, the system is provided with a low-pressure continuous expansion tank 5 and a timed blowdown expansion tank 6 for receiving the blowdown of the steam drum; the blowdown of the high-pressure steam drum 1 and the medium-pressure steam drum 2 is discharged into the low-pressure continuous expansion tank 5 through a connecting pipeline, the flash steam generated by the low-pressure continuous expansion tank 5 is sent to the low-pressure steam drum 3 for recycling, and the remaining wastewater is discharged into the timed blowdown expansion tank 6; the blowdown of the low-pressure steam drum 3 is directly discharged into the timed blowdown expansion tank 6, the flash steam generated in the timed blowdown expansion tank 6 is discharged into the atmosphere as waste gas, and the remaining wastewater is discharged into the sewage pool after cooling. This blowdown steam recovery system has the following defects during operation: the blowdown of the high-pressure steam drum and the medium-pressure steam drum is received by the low-pressure continuous expansion tank. Since the energy grade of the blowdown of the high-pressure steam drum 1 is relatively high, and the operating parameters of the low-pressure continuous expansion tank are relatively low, the flash steam generated can only be used in the low-pressure system. Therefore, the existing blowdown steam recovery system does not fully recover the heat energy of the blowdown of the high-pressure steam drum, resulting in large waste and low thermal efficiency of the system. Summary of the invention

[0003] The present invention mainly aims to solve the technical defect of the prior art that the heat energy recovery of the high-pressure steam drum wastewater is insufficient, resulting in low system thermal efficiency, and provides a waste steam recovery system for a multi-pressure boiler, which can fully recover the heat energy of the high-pressure steam drum wastewater and thus has higher thermal efficiency.

[0004] The present invention is aimed at solving the above-mentioned technical problems mainly through the following technical scheme: the present invention comprises a high-pressure steam drum, a medium-pressure steam drum, a low-pressure steam drum, a low-pressure continuous expansion tank, and a timed blowdown expansion tank. The medium-pressure steam drum is connected to the low-pressure continuous expansion tank through a medium-pressure continuous blowdown pipeline, the low-pressure steam drum is connected to the timed blowdown expansion tank through a low-pressure continuous blowdown pipeline, the flash steam outlet of the low-pressure continuous expansion tank is connected to the low-pressure steam drum through a connecting pipeline provided with a second check valve, and the wastewater outlet of the low-pressure continuous expansion tank is connected to the timed blowdown expansion tank through a connecting pipeline provided with a second regulating valve, and is characterized in that it also comprises a medium-pressure continuous expansion tank, the high-pressure steam drum is connected to the medium-pressure continuous expansion tank through a high-pressure continuous blowdown pipeline, the wastewater outlet of the medium-pressure continuous expansion tank is connected to the low-pressure continuous expansion tank through a connecting pipeline provided with a first regulating valve, and the flash steam outlet of the medium-pressure continuous expansion tank is connected to the medium-pressure steam drum through a connecting pipeline provided with a first check valve.

[0005] Preferably, it also includes a high-pressure sewage bypass, the inlet of which is connected to the high-pressure continuous sewage pipeline and the outlet is connected to the timed sewage expansion tank, and a high-pressure bypass control valve is provided on the high-pressure sewage bypass.

[0006] Preferably, it also includes a medium-pressure sewage bypass, the inlet of which is connected to the medium-pressure continuous sewage pipeline and the outlet is connected to the timed sewage expansion tank, and a medium-pressure bypass control valve is arranged on the medium-pressure sewage bypass.

[0007] Preferably, a high-pressure sewage discharge control valve and a high-pressure manual control valve are provided on the high-pressure continuous sewage discharge pipeline. The high-pressure manual control valve is located at the rear side of the high-pressure sewage discharge control valve according to the direction of the sewage discharge, and the inlet of the high-pressure sewage discharge bypass is located between the high-pressure sewage discharge control valve and the high-pressure manual control valve.

[0008] Preferably, a medium-pressure sewage discharge control valve and a medium-pressure manual control valve are provided on the medium-pressure continuous sewage discharge pipeline. The medium-pressure manual control valve is located at the rear side of the medium-pressure sewage discharge control valve according to the direction of the sewage discharge, and the inlet of the medium-pressure sewage discharge bypass is located between the medium-pressure sewage discharge control valve and the medium-pressure manual control valve.

[0009] Therefore, the present invention has a reasonable structure and has the following advantages:

[0010] 1. In the present invention, a medium-pressure cascade expansion tank is added to the system. The medium-pressure cascade expansion tank is used to recover the blowdown water of the high-pressure drum. The flash steam generated by the blowdown water of the high-pressure drum in the medium-pressure cascade expansion tank is sent to the medium-pressure drum. Since the medium-pressure cascade expansion tank has relatively high operating parameters, the steam parameters and energy grade of the flash steam are improved, so the flash steam generated by the medium-pressure cascade expansion tank can be sent to the medium-pressure system for utilization. Therefore, compared with the prior art, the present invention recovers the heat energy of the blowdown water of the high-pressure drum more fully, greatly improving the thermal efficiency of the recovered blowdown steam.

[0011] 2. The pressure difference between the high-pressure steam drum and the medium-pressure continuous expansion tank is small, so the pressure difference when the sewage from the high-pressure steam drum is discharged into the medium-pressure continuous expansion tank is small, so the cavitation in the pipeline of the high-pressure continuous sewage pipeline is small, and the service life of the pipeline and valves is greatly extended.

[0012] 3. The main evaporation of the combined cycle comes from the high-pressure system, so most of the wastewater comes from the high-pressure drum. The wastewater from the high-pressure drum enters the medium-pressure cascade expansion tank to produce flash steam and wastewater. The flash steam is sent to the medium-pressure drum, and the remaining wastewater is discharged into the low-pressure cascade expansion tank; the wastewater from the medium-pressure cascade expansion tank enters the low-pressure cascade expansion tank for flash evaporation again, and the flash steam is sent to the low-pressure drum for recycling, and the remaining wastewater is discharged into the timed blowdown expansion tank. Since the wastewater from the high-pressure drum is recycled (flash evaporated) in stages through the medium-pressure cascade expansion tank and the low-pressure cascade expansion tank, the volume of the medium-pressure cascade expansion tank and the low-pressure cascade expansion tank is relatively small, which is conducive to optimizing the equipment layout in the boiler area.

[0013] Furthermore, a high-pressure blowdown bypass is provided on the high-pressure continuous blowdown pipeline, and a medium-pressure blowdown bypass is provided on the medium-pressure continuous blowdown pipeline. When a medium-pressure continuous blowdown expansion vessel or a low-pressure continuous blowdown expansion vessel fails, the high-pressure drum blowdown wastewater can be directly discharged into the timed blowdown expansion vessel through the high-pressure blowdown bypass, and the medium-pressure drum blowdown wastewater can be directly discharged into the timed blowdown expansion vessel through the medium-pressure blowdown bypass, thereby ensuring continuous and normal blowdown of the high-pressure drum and the medium-pressure drum.

[0014] The present invention can also be solved by the following technical solutions for the above-mentioned technical problems: the present invention includes a high-pressure steam drum, a medium-pressure steam drum, a low-pressure steam drum, a low-pressure continuous expansion tank, and a timed blowdown expansion tank. The medium-pressure steam drum is connected to the low-pressure continuous expansion tank through a medium-pressure continuous blowdown pipeline, the low-pressure steam drum is connected to the timed blowdown expansion tank through a low-pressure continuous blowdown pipeline, and the wastewater outlet of the low-pressure continuous expansion tank is connected to the timed blowdown expansion tank through a connecting pipeline provided with a second regulating valve, characterized in that the flash steam outlet of the low-pressure continuous expansion tank is connected to the low-pressure saturated steam outlet pipeline of the low-pressure steam drum through a connecting pipeline provided with a second check valve, and also includes a medium-pressure continuous expansion tank, the high-pressure steam drum is connected to the medium-pressure continuous expansion tank through a high-pressure continuous blowdown pipeline, the wastewater outlet of the medium-pressure continuous expansion tank is connected to the low-pressure continuous expansion tank through a connecting pipeline provided with a first regulating valve, and the flash steam outlet of the medium-pressure continuous expansion tank is connected to the saturated steam outlet pipeline of the medium-pressure steam drum through a connecting pipeline provided with a first check valve.

[0015] In the present invention, the flash steam outlet of the medium-pressure cascade expander is connected to the medium-pressure saturated steam outlet pipeline of the medium-pressure drum through a connecting pipeline provided with a first check valve, and the flash steam outlet of the low-pressure cascade expander is connected to the low-pressure saturated steam outlet pipeline of the low-pressure drum through a connecting pipeline provided with a second check valve. This technical solution is particularly suitable for the case where a medium-pressure cascade expander is required to be added when the blowdown steam recovery system of a multi-pressure boiler that has been put into operation is modified. The flash steam generated by the cascade expander can be directly sent to the saturated steam outlet pipeline without entering the drum, avoiding the need to add an opening on the drum for recovering flash steam, which not only ensures the safety of the drum, but also simplifies the process of system modification and reduces the difficulty of modification.

[0016] The present invention can also be solved by the following technical scheme for the above-mentioned technical problems: the present invention includes a high-pressure steam drum, a medium-pressure steam drum, a low-pressure steam drum, a low-pressure continuous expansion tank, and a timed blowdown expansion tank. The medium-pressure steam drum is connected to the low-pressure continuous expansion tank through a medium-pressure continuous blowdown pipeline, the flash steam outlet of the low-pressure continuous expansion tank is connected to the low-pressure steam drum through a connecting pipeline provided with a second check valve, and the wastewater outlet of the low-pressure continuous expansion tank is connected to the timed blowdown expansion tank through a connecting pipeline provided with a second regulating valve, and is characterized in that it also includes a medium-pressure continuous expansion tank, the high-pressure steam drum is connected to the medium-pressure continuous expansion tank through a high-pressure continuous blowdown pipeline, the wastewater outlet of the medium-pressure continuous expansion tank is connected to the low-pressure continuous expansion tank through a connecting pipeline provided with a first regulating valve, and the flash steam outlet of the medium-pressure continuous expansion tank is connected to the medium-pressure steam drum through a connecting pipeline provided with a first check valve.

[0017] In the present invention, a medium-pressure continuous expansion tank is provided to recover the wastewater from the high-pressure drum, and the wastewater from the high-pressure drum generates flash steam in the medium-pressure continuous expansion tank and is sent to the medium-pressure drum. Compared with the prior art, the present invention recovers the heat energy of the wastewater from the high-pressure drum more fully, greatly improving the thermal efficiency of recycling the wastewater steam; at the same time, in view of the fact that the evaporation amount of the low-pressure drum is often low in the multi-pressure boiler, and most of the water in the low-pressure drum is used as the water source for the high- and medium-pressure drums, the water quality in the low-pressure drum is better, and there is no need for continuous sewage discharge. Therefore, in the present invention, the low-pressure continuous sewage discharge pipeline used for continuous sewage discharge of the low-pressure drum is cancelled, which not only saves the production and management costs of the equipment, but also avoids the heat energy loss caused by the continuous sewage discharge of the low-pressure drum. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Attached Figure 1 It is a schematic diagram of the prior art;

[0019] Attached Figure 2 It is a schematic diagram of a preferred embodiment of the present invention;

[0020] Attached Figure 3is a schematic diagram of another preferred embodiment of the present invention;

[0021] Attached Figure 4 is a schematic diagram of a second preferred embodiment of the present invention;

[0022] Attached Figure 5 It is a schematic diagram of a third preferred embodiment of the present invention.

[0023] Explanation of the reference numerals in the accompanying drawings: 1. High-pressure steam drum; 2. Medium-pressure steam drum; 21. Medium-pressure saturated steam outlet pipeline; 3. Low-pressure steam drum; 31. Low-pressure saturated steam outlet pipeline; 4. Medium-pressure continuous expansion tank 5. Low-pressure continuous expansion tank; 6. Timed sewage expansion tank; 7. High-pressure continuous sewage pipeline; 71. High-pressure sewage control valve; 72. High-pressure manual control valve; 8. Medium-pressure continuous sewage pipeline; 81. Medium-pressure sewage control valve; 82. Medium-pressure manual control valve; 9. Low-pressure continuous sewage pipeline; 91. Low-pressure sewage control valve; 10. First regulating valve; 11. Second regulating valve; 12. First check valve; 13. Second check valve; 16. Medium-pressure sewage bypass; 161. Medium-pressure bypass control valve; 17. High-pressure sewage bypass; 171. High-pressure bypass control valve. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0025] Embodiment 1: As attached Figure 2 As shown, the present invention comprises a high-pressure steam drum 1, a medium-pressure steam drum 2, a low-pressure steam drum 3, a medium-pressure cascade expansion vessel 4, a low-pressure cascade expansion vessel 5, and a timed blowdown expansion vessel 6;

[0026] The blowdown outlet of the high-pressure steam drum 1 is connected to the medium-pressure continuous blowdown expansion tank 4 through a high-pressure continuous blowdown pipeline 7, and a high-pressure blowdown control valve 71 is provided on the high-pressure continuous blowdown pipeline 7;

[0027] The flash steam outlet on the medium-pressure cascade expander 4 is connected to the medium-pressure steam drum 2 through a connecting pipeline provided with a first check valve 12, and the wastewater outlet of the medium-pressure cascade expander 4 is connected to the wastewater inlet of the low-pressure cascade expander 5 through a connecting pipeline provided with a first regulating valve 10;

[0028] The blowdown outlet of the medium-pressure drum 2 is connected to the low-pressure continuous blowdown expansion tank 5 through a medium-pressure continuous blowdown pipeline 8, and a medium-pressure blowdown control valve 81 is provided on the medium-pressure continuous blowdown pipeline 8;

[0029] The flash steam outlet in the low-pressure cascade expansion tank 5 is connected to the low-pressure drum 3 through a connecting pipeline provided with a second check valve 13, and the wastewater outlet of the low-pressure cascade expansion tank 5 is connected to the wastewater inlet of the timed blowdown expansion tank 6 through a connecting pipeline provided with a second regulating valve 11;

[0030] The sewage outlet of the low-pressure steam drum 3 is connected to the timed sewage expansion tank 6 through a low-pressure continuous sewage pipeline 9, and a low-pressure sewage control valve 91 is provided on the low-pressure continuous sewage pipeline 9.

[0031] When the boiler of the present invention is in operation, the continuous blowdown of the high-pressure drum 1 is discharged into the medium-pressure cascade expansion tank 4 through the high-pressure continuous blowdown pipeline 7, and the high-pressure blowdown control valve 71 is used to control the blowdown amount of the high-pressure drum 1; the blowdown water from the high-pressure drum 1 is expanded and flashed in the medium-pressure cascade expansion tank 4, and the flash steam is sent to the medium-pressure drum 2 through a connecting pipeline provided with a first check valve 12, and the first check valve 12 is used to prevent the steam in the medium-pressure drum 2 from flowing back to the medium-pressure cascade expansion tank 4; the waste water remaining after the flash evaporation is discharged into the low-pressure cascade expansion tank 5 through a connecting pipeline provided with a first regulating valve 10, and the first regulating valve 10 is used to control the water level of the medium-pressure cascade expansion tank 4 to prevent the flash steam from entering the low-pressure cascade expansion tank 5 through the first regulating valve 10;

[0032] The continuous blowdown of the medium-pressure drum 2 is discharged into the low-pressure continuous expansion tank 5 through the medium-pressure continuous blowdown pipeline 8, and the medium-pressure blowdown control valve 81 is used to control the blowdown amount of the medium-pressure drum 2; the blowdown water from the medium-pressure drum 2 and the wastewater from the medium-pressure continuous expansion tank 4 are expanded and flashed in the low-pressure continuous expansion tank 5, and the flash steam is sent to the low-pressure drum 3 through a connecting pipeline provided with a second check valve 13, and the second check valve 13 is used to prevent the steam in the low-pressure drum 3 from flowing back to the low-pressure continuous expansion tank 5; the wastewater remaining after flashing is discharged into the timed blowdown expansion tank 6 through a connecting pipeline provided with a second regulating valve 11, and the second regulating valve 11 is used to control the water level of the medium-pressure continuous expansion tank 5 to prevent the flash steam from entering the timed blowdown expansion tank 6 through the second regulating valve 11;

[0033] The continuous sewage of the low-pressure drum 3 is discharged into the timed sewage expansion tank 6 through the low-pressure continuous sewage pipeline 9, and the low-pressure sewage control valve 91 is used to control the sewage discharge amount of the low-pressure drum 3; the sewage from the low-pressure drum 3 and the wastewater from the low-pressure continuous sewage expansion tank 5 are expanded and flashed in the timed sewage expansion tank 6, and the flash steam is discharged into the atmosphere through the exhaust pipe. The remaining wastewater after flash evaporation is cooled by cooling water and discharged into the wastewater pool.

[0034] Embodiment 2: As attached Figure 3 As shown, the present invention comprises a high-pressure steam drum 1, a medium-pressure steam drum 2, a low-pressure steam drum 3, a medium-pressure cascade expansion vessel 4, a low-pressure cascade expansion vessel 5, and a timed blowdown expansion vessel 6;

[0035] The sewage outlet of the high-pressure steam drum 1 is connected to the medium-pressure continuous discharge expansion tank 4 through a high-pressure continuous sewage discharge pipeline 7. A high-pressure sewage discharge control valve 71 and a high-pressure manual control valve 72 are provided on the high-pressure continuous sewage discharge pipeline 7. The high-pressure manual control valve 72 is located at the rear side of the high-pressure sewage discharge control valve 71 according to the direction of sewage discharge;

[0036] The flash steam outlet of the medium-pressure cascade expander 4 is connected to the medium-pressure steam drum 2 through a connecting pipeline provided with a first check valve 12, and the wastewater outlet of the medium-pressure cascade expander 4 is connected to the wastewater inlet of the low-pressure cascade expander 5 through a connecting pipeline provided with a first regulating valve 10;

[0037] The blowdown outlet of the medium-pressure drum 2 is connected to the low-pressure continuous blowdown expansion tank 5 through a medium-pressure continuous blowdown pipeline 8. A medium-pressure blowdown control valve 81 and a medium-pressure manual control valve 82 are provided on the medium-pressure continuous blowdown pipeline 8. The medium-pressure manual control valve 82 is located at the rear side of the medium-pressure blowdown control valve 81 according to the direction of the blowdown water.

[0038] The flash steam outlet of the low-pressure cascade expansion tank 5 is connected to the low-pressure drum 3 through the second check valve 13, and the wastewater outlet of the low-pressure cascade expansion tank 5 is connected to the wastewater inlet of the timed blowdown expansion tank 6 through a connecting pipeline provided with a second regulating valve 11;

[0039] The blowdown outlet of the low-pressure drum 3 is connected to the timed blowdown expansion tank 6 through a low-pressure continuous blowdown pipeline 9, and a low-pressure blowdown control valve 91 is provided on the low-pressure continuous blowdown pipeline 9;

[0040] The high-pressure continuous sewage discharge pipeline 7 is also connected to a high-pressure sewage discharge bypass 17. The inlet of the high-pressure sewage discharge bypass 17 is connected to the high-pressure continuous sewage discharge pipeline 7 at a position between the high-pressure sewage discharge control valve 71 and the high-pressure manual control valve 72, and the outlet is connected to the timing sewage discharge expansion tank 6. The high-pressure sewage discharge bypass 17 is provided with a normally closed high-pressure bypass control valve 171;

[0041] The medium-pressure continuous sewage discharge pipeline 8 is also connected to a medium-pressure sewage discharge bypass 16. The inlet of the medium-pressure sewage discharge bypass 16 is connected to the medium-pressure continuous sewage discharge pipeline 8 at a position between the medium-pressure sewage discharge control valve 81 and the medium-pressure manual control valve 82, and the outlet is connected to the timed sewage discharge expansion tank 6. A normally closed medium-pressure bypass control valve 161 is provided on the medium-pressure sewage discharge bypass 16.

[0042] In the process of boiler operation, the present invention can not only realize the cascade recovery (flash evaporation) of the sewage discharged from the high-pressure drum 1, but also, when a fault occurs in the medium-pressure continuous discharge expansion tank 4, by closing the high-pressure manual control valve 72 and opening the normally closed high-pressure bypass control valve 171, the continuous sewage discharged from the high-pressure drum 1 is directly discharged into the timing sewage discharge expansion tank 6 through the high-pressure sewage discharge bypass 17, so as to ensure the continuous and normal sewage discharge of the high-pressure drum 1;

[0043] Similarly, when a fault occurs in the low-pressure continuous expansion tank 5, by closing the medium-pressure manual control valve 82 and opening the normally closed medium-pressure bypass control valve 161, the continuous sewage discharge of the medium-pressure steam drum 2 is directly discharged into the timed sewage expansion tank 6 through the medium-pressure sewage bypass 16, thereby ensuring continuous and normal sewage discharge of the medium-pressure steam drum 2.

[0044] Embodiment 3: As attached Figure 4 As shown, the present invention comprises a high-pressure steam drum 1, a medium-pressure steam drum 2, a low-pressure steam drum 3, a medium-pressure cascade expansion vessel 4, a low-pressure cascade expansion vessel 5, and a timed blowdown expansion vessel 6;

[0045] The blowdown outlet of the high-pressure steam drum 1 is connected to the medium-pressure continuous blowdown expansion tank 4 through a high-pressure continuous blowdown pipeline 7, and a high-pressure blowdown control valve 71 is provided on the high-pressure continuous blowdown pipeline 7;

[0046] The flash steam outlet of the medium-pressure cascade expander 4 is connected to the medium-pressure steam drum 2 through a connecting pipeline provided with a first check valve 12, and the wastewater outlet of the medium-pressure cascade expander 4 is connected to the wastewater inlet of the low-pressure cascade expander 5 through a connecting pipeline provided with a first regulating valve 10;

[0047] The blowdown outlet of the medium-pressure drum 2 is connected to the low-pressure continuous blowdown expansion tank 5 through a medium-pressure continuous blowdown pipeline 8, and a medium-pressure blowdown control valve 81 is provided on the medium-pressure continuous blowdown pipeline 8;

[0048] The flash steam outlet of the low-pressure cascade expansion tank 5 is connected to the low-pressure steam drum 3 through a connecting pipeline provided with a second check valve 13, and the wastewater outlet of the low-pressure cascade expansion tank 5 is connected to the wastewater inlet of the timed sewage expansion tank 6 through a connecting pipeline provided with a second regulating valve 11.

[0049] In this embodiment, the low-pressure continuous blowdown pipeline is cancelled in the low-pressure drum 3, that is, the low-pressure drum 3 does not discharge blowdown continuously, thereby reducing the heat energy loss caused by the low-pressure continuous blowdown.

[0050] Embodiment 4: As attached Figure 5 As shown, the present invention comprises a high-pressure steam drum 1, a medium-pressure steam drum 2, a low-pressure steam drum 3, a medium-pressure cascade expansion vessel 4, a low-pressure cascade expansion vessel 5, and a timed blowdown expansion vessel 6;

[0051] The blowdown outlet of the high-pressure steam drum 1 is connected to the medium-pressure continuous blowdown expansion tank 4 through a high-pressure continuous blowdown pipeline 7, and a high-pressure blowdown control valve 71 is provided on the high-pressure continuous blowdown pipeline 7;

[0052] The flash steam outlet of the medium-pressure cascade expander 4 is connected to the medium-pressure saturated steam outlet pipeline 21 of the medium-pressure drum 2 through a connecting pipeline, and the wastewater outlet of the medium-pressure cascade expander 4 is connected to the wastewater inlet of the low-pressure cascade expander 5 through a first regulating valve 10;

[0053] The blowdown outlet of the medium-pressure drum 2 is connected to the low-pressure continuous blowdown expansion tank 5 through a medium-pressure continuous blowdown pipeline 8, and a medium-pressure blowdown control valve 81 is provided on the medium-pressure continuous blowdown pipeline 8;

[0054] The flash steam outlet of the low-pressure cascade expansion tank 5 is connected to the low-pressure saturated steam outlet pipeline 31 of the low-pressure drum 3 through a connecting pipeline, and the wastewater outlet of the low-pressure cascade expansion tank 5 is connected to the wastewater inlet of the timed blowdown expansion tank 6 through a connecting pipeline provided with a second regulating valve 11;

[0055] The sewage outlet of the low-pressure steam drum 3 is connected to the timed sewage expansion tank 6 through a low-pressure continuous sewage discharge pipeline 9, and a low-pressure sewage discharge control valve 91 is provided on the low-pressure continuous sewage discharge pipeline 9.

[0056] In the present invention, the flash steam outlet of the medium-pressure cascade expander 4 is connected to the medium-pressure saturated steam outlet pipeline 21 of the medium-pressure steam drum 2, and the flash steam outlet of the low-pressure cascade expander 5 is connected to the low-pressure saturated steam outlet pipeline 31 of the low-pressure steam drum 3. The flash steam can be directly sent into the saturated steam outlet pipeline as saturated steam for use by the unit.

[0057] Of course, the above drawings and embodiments are only used to explain and illustrate the present invention, and cannot be used as improper limitations of the present invention. Any technical solutions obtained by those skilled in the art making equivalent adjustments and changes based on the present invention fall within the protection scope of the present invention.

Claims

1. A blowdown steam recovery system for a multi-pressure boiler, comprising a high-pressure steam drum (1), a medium-pressure steam drum (2), a low-pressure steam drum (3), a low-pressure continuous expansion tank (5), and a timed blowdown expansion tank (6), wherein the medium-pressure steam drum (2) is connected to the low-pressure continuous expansion tank (5) via a medium-pressure continuous blowdown pipeline (8), the low-pressure steam drum (3) is connected to the timed blowdown expansion tank (6) via a low-pressure continuous blowdown pipeline (9), the flash steam outlet of the low-pressure continuous expansion tank (5) is connected to the low-pressure steam drum (3) via a connecting pipeline provided with a second check valve (13), the wastewater outlet of the low-pressure continuous expansion tank (5) is connected to the timed blowdown expansion tank (6) via a connecting pipeline provided with a second regulating valve (11), and characterized in that: The invention also comprises a medium-pressure cascade expander (4), wherein the high-pressure steam drum (1) is connected to the medium-pressure cascade expander (4) via a high-pressure continuous sewage discharge pipeline (7), the wastewater outlet of the medium-pressure cascade expander (4) is connected to the low-pressure cascade expander (5) via a connecting pipeline provided with a first regulating valve (10), and the flash steam outlet of the medium-pressure cascade expander (4) is connected to the medium-pressure steam drum (2) via a connecting pipeline provided with a first check valve (12).

2. A blowdown steam recovery system for a multi-pressure boiler according to claim 1, characterized in that: It also includes a high-pressure sewage discharge bypass (17), the inlet of the high-pressure sewage discharge bypass (17) is connected to the high-pressure continuous sewage discharge pipeline (7) and the outlet is connected to the timed sewage discharge expansion tank (6), and the high-pressure sewage discharge bypass (17) is provided with a high-pressure bypass control valve (171).

3. A blowdown steam recovery system for a multi-pressure boiler according to claim 1 or 2, characterized in that: It also includes a medium-pressure sewage bypass (16), the inlet of the medium-pressure sewage bypass (16) is connected to the medium-pressure continuous sewage pipeline (8) and the outlet is connected to the timed sewage expansion tank (6), and the medium-pressure sewage bypass (16) is provided with a medium-pressure bypass control valve (161).

4. The blowdown steam recovery system of a multi-pressure boiler according to claim 2, characterized in that: The high-pressure continuous sewage discharge pipeline (7) is provided with a high-pressure sewage discharge control valve (71) and a high-pressure manual control valve (72); the high-pressure manual control valve (72) is located at the rear side of the high-pressure sewage discharge control valve (71) according to the sewage discharge flow direction; and the inlet of the high-pressure sewage discharge bypass (17) is located between the high-pressure sewage discharge control valve (71) and the high-pressure manual control valve (72).

5. The blowdown steam recovery system of a multi-pressure boiler according to claim 3, characterized in that: The medium-pressure continuous sewage discharge pipeline (8) is provided with a medium-pressure sewage discharge control valve (81) and a medium-pressure manual control valve (82); the medium-pressure manual control valve (82) is located at the rear side of the medium-pressure sewage discharge control valve (81) according to the flow direction of sewage discharge; and the inlet of the medium-pressure sewage discharge bypass (16) is located between the medium-pressure sewage discharge control valve (81) and the medium-pressure manual control valve (82).

6. A blowdown steam recovery system for a multi-pressure boiler, comprising a high-pressure steam drum (1), a medium-pressure steam drum (2), a low-pressure steam drum (3), a low-pressure continuous expansion tank (5), and a timed blowdown expansion tank (6), wherein the medium-pressure steam drum (2) is connected to the low-pressure continuous expansion tank (5) via a medium-pressure continuous blowdown pipeline (8), the low-pressure steam drum (3) is connected to the timed blowdown expansion tank (6) via a low-pressure continuous blowdown pipeline (9), and the wastewater outlet of the low-pressure continuous expansion tank (5) is connected to the timed blowdown expansion tank (6) via a connecting pipeline provided with a second regulating valve (11), characterized in that: The flash steam outlet of the low-pressure cascade expander (5) is connected to the low-pressure saturated steam outlet pipeline (31) of the low-pressure drum (3), and the invention also includes a medium-pressure cascade expander (4). The high-pressure drum (1) is connected to the medium-pressure cascade expander (4) through a high-pressure continuous sewage discharge pipeline (7), the wastewater outlet of the medium-pressure cascade expander (4) is connected to the low-pressure cascade expander (5) through a connecting pipeline provided with a first regulating valve (10), and the flash steam outlet of the medium-pressure cascade expander (4) is connected to the medium-pressure saturated steam outlet pipeline (21) of the medium-pressure drum (2).

7. A blowdown steam recovery system for a multi-pressure boiler, comprising a high-pressure steam drum (1), a medium-pressure steam drum (2), a low-pressure steam drum (3), a low-pressure continuous expansion tank (5), and a timed blowdown expansion tank (6), wherein the medium-pressure steam drum (2) is connected to the low-pressure continuous expansion tank (5) via a medium-pressure continuous blowdown pipeline (8), the flash steam outlet of the low-pressure continuous expansion tank (5) is connected to the low-pressure steam drum (3) via a connecting pipeline provided with a second check valve (13), the wastewater outlet of the low-pressure continuous expansion tank (5) is connected to the timed blowdown expansion tank (6) via a connecting pipeline provided with a second regulating valve (11), and is characterized in that: The invention also comprises a medium-pressure cascade expander (4), wherein the high-pressure steam drum (1) is connected to the medium-pressure cascade expander (4) via a high-pressure continuous sewage discharge pipeline (7), the wastewater outlet of the medium-pressure cascade expander (4) is connected to the low-pressure cascade expander (5) via a connecting pipeline provided with a first regulating valve (10), and the flash steam outlet of the medium-pressure cascade expander (4) is connected to the medium-pressure steam drum (2) via a connecting pipeline provided with a first check valve (12).

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