Low-backpressure vacuumizing optimization structure and method for high-countercurrent-ratio NDACC system

Abstract

The invention discloses a low-backpressure vacuumizing optimization structure and method for a high-countercurrent-ratio NDACC system, and relates to the energy-saving technology of air cooling systems, and the low-backpressure vacuumizing optimization structure and method for the high-countercurrent-ratio NDACC system are characterized in that the low-backpressure vacuumizing optimization structure comprises a cooling unit, a vacuumizing pipeline system and a vacuum pump set; each cooling unit comprises a plurality of cooling triangles, at least one cooling triangle in each cooling unit is set as a countercurrent area, the other cooling triangles are set as downstream areas, the number ratio of the cooling triangles in the downstream areas to the cooling triangles in the countercurrent areas is not smaller than 2: 1 and not larger than 4: 1, and the downstream areas and the countercurrent areas are provided with electric shutters respectively; the tops of the cooling triangles of the downstream area are communicated with one another through a first pipeline, the bottoms of the cooling triangles of the downstream area are communicated with the bottoms of the cooling triangles of the countercurrent area through a second pipeline, the countercurrent area of each cooling unit is provided with a vacuumizing connector, and the vacuumizing connectors are connected to a vacuum pump set through a vacuumizing pipeline system. The exhaust efficiency of non-condensable steam under the low-back-pressure working condition is effectively improved, and the operation back pressure and freezing risk are reduced.

Description

Technical Field

[0001] This invention relates to the field of energy-saving technology for air-cooled systems, and more specifically, to an optimized structure and method for low back pressure vacuuming in NDACC systems with a high backflow ratio. Background Technology

[0002] Natural draft direct air-cooled system (NDACC system) is a key cold-end equipment in large thermal power plants, and its operating performance directly affects the unit's economy and safety. During system operation, the exhaust steam from the turbine unit condenses in the air-cooled radiator, and the resulting non-condensable gases (such as air) need to be discharged in a timely manner through the vacuum system to maintain the required vacuum level of the system, which is crucial for the unit's back pressure and efficiency.

[0003] Traditional NDACC systems typically employ a design where the co-current and counter-current heat dissipation zones are combined in a fixed ratio (e.g., greater than 4:1). While this ratio and layout may meet operational requirements under normal conditions, in winter under low back pressure and low load conditions, the small steam flow rate and velocity, coupled with the relatively insufficient proportion of the counter-current zone, result in weak suction power. This makes it difficult to effectively carry and collect the non-condensable steam dispersed in the co-current zone and within the system to the vacuum port, leading to low non-condensable steam discharge efficiency. The accumulation of non-condensable steam not only increases the system back pressure and unit energy consumption but may also cause tube freezing due to localized low temperatures or accelerate equipment corrosion, seriously threatening system safety.

[0004] Therefore, a new solution is needed to address this problem. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide an optimized structure and method for vacuuming a high back pressure NDACC system with a high backflow ratio, which effectively improves the discharge efficiency of non-condensable steam under low back pressure conditions and reduces the risk of back pressure and freezing during operation.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a low back pressure vacuuming optimization structure for a high countercurrent ratio NDACC system, including a cooling unit, a vacuuming pipeline system, and a vacuum pump group;

[0007] The cooling unit includes multiple cooling triangles, and at least one cooling triangle in each cooling unit is set as a counter-flow zone, while the remaining cooling triangles are set as co-flow zones. The ratio of the number of cooling triangles in the co-flow zone to the number of cooling triangles in the counter-flow zone is not less than 2:1 and not more than 4:1. The co-flow zone and the counter-flow zone are respectively equipped with motorized louvers.

[0008] The tops of the cooling triangles in the forward flow zone are interconnected by a first pipe, and the bottoms of the cooling triangles in the forward flow zone and the bottoms of the cooling triangles in the counterflow zone are interconnected by a second pipe. Each cooling unit is provided with a vacuum port in the counterflow zone, and the vacuum port is connected to the vacuum pump group through the vacuum pipeline system.

[0009] Preferably, the vacuum piping system includes a regional main pipe and multiple sector branch pipes. Each cooling triangle in the counterflow zone of each cooling unit is provided with a vacuum port at its top. Each vacuum port is connected to a sector branch pipe. The multiple sector branch pipes are connected to the regional main pipe. The regional main pipe is connected to the vacuum pump group. A flow regulating valve is provided between each vacuum port and the sector branch pipe.

[0010] Preferably, it also includes a steam inlet header and a condensate header, wherein the steam inlet header is connected to the first pipeline and is used to transport turbine exhaust steam, and the condensate header is connected to the second pipeline and is used to collect and discharge condensate.

[0011] Preferably, it also includes a first temperature sensor, a second temperature sensor, a first pressure transmitter, and a second pressure transmitter;

[0012] The first temperature sensor is located at the vacuum port and is used to detect the pumping temperature at the top of the counterflow zone.

[0013] The second temperature sensor is installed on the second pipeline near the counterflow zone and is used to detect the temperature of non-condensable steam.

[0014] The first pressure transmitter is installed on the first pipeline and is used to detect the steam inlet pressure;

[0015] The second pressure transmitter is installed on the area main pipe and is used to monitor the pressure of the area main pipe.

[0016] Preferably, the sector branch pipe and the area main pipe are made of seamless steel pipe, and the inner walls of the sector branch pipe and the area main pipe are respectively provided with a corrosion-resistant layer.

[0017] Preferably, the vacuum pump set is a liquid ring vacuum pump set with a backing gas-cooled Roots pump or a liquid ring vacuum pump with 10℃-15℃ low-temperature cooling water cooling.

[0018] A method for optimizing low back pressure vacuum pumping in a high countercurrent ratio NDACC system, applicable to any of the aforementioned high countercurrent ratio NDACC system low back pressure vacuum pumping optimization structures, the method comprising the following steps:

[0019] S1. Under low back pressure operating conditions, the opening degree of the electric louvers in the counter-current zone is increased to the first control range, and the opening degree of the electric louvers in the downstream zone is decreased to the second control range.

[0020] S2. Real-time acquisition of the vacuum temperature at the top of the counter-current zone, the condensation temperature between the bottom of the co-current zone and the bottom of the counter-current zone, and the steam inlet pressure at the top of the co-current zone;

[0021] S3. Determine the corresponding steam inlet saturation temperature based on the steam inlet pressure, calculate the condensation subcooling by the difference between the steam inlet saturation temperature and the condensation temperature, and calculate the extraction subcooling by the difference between the steam inlet saturation temperature and the extraction temperature.

[0022] S4. Monitor the pressure of the main regional pipe and adjust the operating parameters of the vacuum pump group based on the monitored pressure value of the main regional pipe to maintain the stability of the pressure of the main regional pipe.

[0023] Preferably, in step S1, the first control range is determined by the extraction subcooling, and the second control range is determined by the condensation subcooling.

[0024] Preferably, in step S2, the condenser subcooling is controlled at 1℃-3℃, and the extraction subcooling is controlled at 4℃-8℃.

[0025] Preferably, adjusting the operating parameters of the vacuum pump group in step S3 specifically involves adjusting the speed of the vacuum pump group by means of frequency conversion or start-stop.

[0026] Compared with existing technologies, the advantages of the high counter-current ratio NDACC system low back pressure vacuum optimization structure and method disclosed in this invention are as follows: By limiting the ratio of the number of cooling triangles in the co-current and counter-current zones within each cooling unit to a range of not less than 2:1 and not more than 4:1, the design ratio of the counter-current zone is increased. This high counter-current ratio structure can actively generate stronger suction power under low back pressure and low load conditions, enhancing the discharge efficiency of non-condensable gases under low back pressure operation conditions. By calculating the subcooling degree of the pumping gas and the subcooling degree of the condensing gas in real time, the opening of the electric louvers in the counter-current and co-current zones is dynamically and collaboratively adjusted, thereby improving the overall discharge efficiency of non-condensable gases to a higher level. This not only effectively reduces the back pressure during winter operation and saves turbine energy consumption, but also reduces the risk of radiator tube bundle freezing caused by local accumulation of non-condensable gases. At the same time, by shortening the residence time of non-condensable gases in the system, the corrosive damage of corrosive components such as oxygen to system components is reduced, comprehensively improving the economy, safety and reliability of the system. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the optimized low back pressure vacuuming structure of the NDACC system with high backflow ratio according to an embodiment of this application.

[0029] The numbers or letters in the attached diagram represent the names of the corresponding components:

[0030] 1. Counter-current zone; 2. Co-current zone; 3. First pipeline; 4. Second pipeline; 5. Steam inlet main pipe; 6. Condensate main pipe; 7. Sector branch pipe; 8. Regional main pipe; 9. Vacuum pump set. Detailed Implementation

[0031] The technical solution of the present invention will now be clearly and completely described through specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] Please see Figure 1 The embodiments of this application provide a low back pressure vacuum optimization structure for a high backflow ratio NDACC system, including a cooling unit, a vacuum pipeline system and a vacuum pump group 9, wherein the cooling unit is configured with upper and lower layers.

[0033] The cooling unit comprises multiple cooling triangles, with at least one cooling triangle designated as a counter-flow zone 1 within each unit, and the remaining cooling triangles as co-flow zones 2. The ratio of the number of cooling triangles in co-flow zones 2 to counter-flow zones 1 is not less than 2:1 and not greater than 4:1. In a preferred embodiment, this ratio is set to 3:1. Each cooling unit includes four cooling triangles, with the third cooling triangle being the counter-flow zone 1 and the remaining cooling triangles being the co-flow zones 2. Both co-flow zones 2 and counter-flow zones 1 are equipped with motorized louvers. The motorized louvers are installed on the air inlet side of each cooling triangle, specifically on the outside of the steel structure frame of the cooling triangle, completely covering the entire rectangular air inlet surface of its respective cooling triangle. By changing the opening of the motorized louvers, the cooling airflow into the radiator tube bundle of the corresponding cooling triangle can be adjusted, thereby controlling the local and overall heat transfer intensity and ultimately regulating the system's back pressure. The top inlets of each cooling triangle in the forward flow zone 2 are interconnected via a first pipe 3. The first pipe 3 includes multiple first branch pipes connecting to the top inlets of each cooling triangle and a first main pipe for connecting the multiple first branch pipes in parallel. The bottom outlets of each cooling triangle in the forward flow zone 2 and the bottom inlets of each cooling triangle in the counter-flow zone 1 are interconnected via a second pipe 4. The second pipe 4 includes second branch pipes connecting to the bottom outlets of each cooling triangle in the forward flow zone 2 and the bottom inlets of each cooling triangle in the counter-flow zone 1, and a second main pipe for connecting the multiple second branch pipes in parallel. A vacuum port is provided at the top outlet of the counter-flow zone 1 of each cooling unit, and the vacuum port is connected to the vacuum pump group 9 via a vacuum piping system.

[0034] It also includes a PLC controller, an electric louver, and a vacuum pump unit 9, which are electrically connected to the PLC controller.

[0035] In the aforementioned optimized vacuum structure, during operation in the co-current zone 2, steam enters from the top of the cooling triangle and flows downwards through the heat dissipation tube bundle, gradually condensing. The condensate produced by condensation collects downwards and is discharged. Simultaneously, non-condensable gases, carried by the steam flow, also mainly move downwards and eventually accumulate in the lower part of the co-current zone 2. In the counter-current zone 1, steam enters from the bottom of the cooling triangle, flows upwards through the heat dissipation tube bundle, and condenses. The condensate produced also collects downwards. Under the suction effect of the system's vacuum pump group 9, the non-condensable gases inside the counter-current zone 1 and those flowing in from the lower part of the co-current zone 2 are jointly drawn and converge towards the vacuum port at the top of the counter-current zone 1, where they are efficiently discharged.

[0036] In the above configuration, by limiting the ratio of the number of cooling triangles in the co-current zone 2 to the counter-current zone 1 in each cooling unit to a range of not less than 2:1 and not more than 4:1, the design proportion of the counter-current zone 1 is increased. This high counter-current proportion structure can actively generate stronger suction power under low back pressure and low load conditions, thereby enhancing the discharge efficiency of non-condensable gas under low back pressure operating conditions.

[0037] In this embodiment, the vacuum piping system includes a regional main pipe 8 and multiple sector branch pipes 7. Each cooling triangle in the counter-current zone 1 of each cooling unit has a vacuum port at its top, and each vacuum port is connected to a sector branch pipe 7. The multiple sector branch pipes 7 are then connected to the regional main pipe 8, which is connected to the vacuum pump group 9. A flow regulating valve is installed between each vacuum port and a sector branch pipe 7. Specifically, the flow regulating valve is an electric proportional valve, electrically connected to the PLC controller. By setting the flow regulating valve, if there are multiple cooling triangles in the counter-current zone 1, the PLC controller can drive each flow regulating valve to perform automatic balancing adjustments, quickly making the air extraction volume of each cooling triangle in the counter-current zone 1 tend to be uniform.

[0038] In this embodiment, the steam inlet header 5 and the condensate header 6 are also included. The steam inlet header 5 is connected to the first pipeline 3 and is used to transport the exhaust steam from the steam turbine. The condensate header 6 is connected to the second pipeline 4 and is used to collect and discharge condensate.

[0039] This embodiment also includes a first temperature sensor, a second temperature sensor, a first pressure transmitter, and a second pressure transmitter, all electrically connected to the PLC controller. The first temperature sensor is located at the vacuum port and is used to detect the pumping temperature at the top of the countercurrent zone 1. The second temperature sensor is located on the second pipeline 4 near the countercurrent zone 1 and is used to detect the non-condensable steam temperature. The first pressure transmitter is located on the first pipeline 3 and is used to detect the inlet steam pressure. The second pressure transmitter is located on the zone main pipe 8 and is used to monitor the pressure in the zone main pipe 8. Both the first and second pressure transmitters use PTX5072 type pressure transmitter sensors, and the first and second temperature sensors can be Pt100 platinum resistance temperature sensors.

[0040] In this embodiment, the sector branch pipe 7 and the regional main pipe 8 are made of seamless steel pipes, and the inner walls of the sector branch pipe 7 and the regional main pipe 8 are respectively provided with corrosion-resistant layers. It can be understood that the inner walls of other pipelines involved in this invention can be provided with this corrosion-resistant layer. The corrosion-resistant layer is an epoxy resin corrosion-resistant layer. The epoxy resin coating can effectively isolate and resist the erosion of the metal pipe wall by corrosive components such as oxygen in non-condensable steam.

[0041] In this embodiment, the vacuum pump group 9 is a liquid ring vacuum pump group 9 with a backing gas-cooled Roots pump or a liquid ring vacuum pump with 10℃-15℃ low-temperature cooling water cooling. The specific model of the liquid ring vacuum pump group 9 with the backing gas-cooled Roots pump is 2BEC-70+ZJ-40. The backing gas-cooled Roots pump can maintain a large pumping rate in the high vacuum range, and perform preliminary compression and transportation of non-condensable vapors. The liquid ring vacuum pump, on the other hand, efficiently and stably discharges the gas to the atmosphere in the higher pressure range. By connecting the two in series, their respective advantages are fully utilized, and the overall pumping efficiency and operational stability of the vacuum pump group 9 in the low back pressure range are improved.

[0042] This invention also discloses an optimization method for low back pressure vacuuming in a high countercurrent ratio NDACC system, applicable to any low back pressure vacuuming optimization structure of a high countercurrent ratio NDACC system. The method includes the following steps:

[0043] S1. Under low back pressure operating conditions, the opening degree of the electric louvers in the counter-current zone 1 is increased to the first control range, and the opening degree of the electric louvers in the downstream zone 2 is decreased to the second control range.

[0044] S2. Real-time acquisition of the vacuum temperature at the top of the counter-current zone 1, the condensate temperature between the bottom of the co-current zone 2 and the bottom of the counter-current zone 1, and the steam inlet pressure at the top of the co-current zone 2.

[0045] S3. Determine the corresponding steam inlet saturation temperature based on the steam inlet pressure. Calculate the condensation subcooling by the difference between the steam inlet saturation temperature and the condensation temperature, and calculate the extraction subcooling by the difference between the steam inlet saturation temperature and the extraction temperature. The steam inlet saturation temperature is obtained by consulting the steam saturation pressure-temperature comparison table and calculating the difference. Alternatively, a third temperature sensor can be installed on the first pipeline 3.

[0046] S4. Monitor the pressure of the regional main pipe 8, and adjust the operating parameters of the vacuum pump group 9 based on the monitored pressure value of the regional main pipe 8 to maintain the stability of the pressure of the regional main pipe 8.

[0047] In this embodiment, in step S1, the first control range is determined by the subcooling of the extraction gas, and the second control range is determined by the subcooling of the condensing gas.

[0048] In this embodiment, in step S2, the condenser subcooling is controlled at 1℃-3℃, and the extraction subcooling is controlled at 4℃-8℃. These values ​​can be used as feedback parameters, and algorithms such as PID or fuzzy control can be employed to dynamically adjust the opening of the louvers in the counter-current and co-current flow zones.

[0049] In this embodiment, adjusting the operating parameters of the vacuum pump group 9 in step S3 specifically involves adjusting the speed of the vacuum pump group 9 by means of frequency conversion or start-stop.

[0050] In the above method, by calculating the subcooling of the extraction steam and the subcooling of the condensing steam in real time, the opening of the electric louvers in the counter-current zone 1 and the co-current zone 2 is dynamically and collaboratively adjusted, thereby improving the overall discharge efficiency of non-condensable steam to a higher level. This not only effectively reduces the back pressure during winter operation and saves the energy consumption of the turbine unit, but also reduces the risk of radiator tube bundle freezing caused by the local accumulation of non-condensable steam. At the same time, by shortening the residence time of non-condensable steam in the system, the corrosive damage of corrosive components such as oxygen in the system to system components is reduced, thus comprehensively improving the economy, safety and reliability of the system.

[0051] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those 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 invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An optimized structure for low back pressure vacuuming in a high countercurrent ratio NDACC system, characterized in that: Includes cooling units, vacuum piping systems, and vacuum pump sets; The cooling unit includes multiple cooling triangles, and at least one cooling triangle in each cooling unit is set as a counter-flow zone, while the remaining cooling triangles are set as co-flow zones. The ratio of the number of cooling triangles in the co-flow zone to the number of cooling triangles in the counter-flow zone is not less than 2:1 and not more than 4:

1. The co-flow zone and the counter-flow zone are respectively equipped with motorized louvers. The tops of the cooling triangles in the forward flow zone are interconnected by a first pipe, and the bottoms of the cooling triangles in the forward flow zone and the bottoms of the cooling triangles in the counterflow zone are interconnected by a second pipe. Each cooling unit is provided with a vacuum port in the counterflow zone, and the vacuum port is connected to the vacuum pump group through the vacuum pipeline system.

2. The optimized low back pressure vacuum pumping structure for the high countercurrent ratio NDACC system according to claim 1, characterized in that: The vacuum piping system includes a regional main pipe and multiple sector branch pipes. Each cooling triangle in the counterflow zone of each cooling unit is provided with a vacuum port at its top. Each vacuum port is connected to a sector branch pipe. The multiple sector branch pipes are connected to the regional main pipe, which is connected to the vacuum pump group. A flow regulating valve is provided between each vacuum port and the sector branch pipe.

3. The optimized low back pressure vacuum pumping structure for the high countercurrent ratio NDACC system according to claim 2, characterized in that: It also includes a steam inlet header and a condensate header. The steam inlet header is connected to the first pipeline and is used to transport turbine exhaust steam. The condensate header is connected to the second pipeline and is used to collect and discharge condensate.

4. The optimized low back pressure vacuum pumping structure for the high countercurrent ratio NDACC system according to claim 3, characterized in that: It also includes a first temperature sensor, a second temperature sensor, a first pressure transmitter, and a second pressure transmitter; The first temperature sensor is located at the vacuum port and is used to detect the pumping temperature at the top of the counterflow zone. The second temperature sensor is installed on the second pipeline near the counterflow zone and is used to detect the temperature of non-condensable steam. The first pressure transmitter is installed on the first pipeline and is used to detect the steam inlet pressure; The second pressure transmitter is installed on the area main pipe and is used to monitor the pressure of the area main pipe.

5. The optimized low back pressure vacuum pumping structure for the high countercurrent ratio NDACC system according to claim 2, characterized in that: The sector branch pipe and the regional main pipe are made of seamless steel pipe, and the inner walls of the sector branch pipe and the regional main pipe are respectively provided with a corrosion-resistant layer.

6. The optimized low back pressure vacuum pumping structure for the high countercurrent ratio NDACC system according to claim 1, characterized in that: The vacuum pump set is a liquid ring vacuum pump set with a backing gas-cooled Roots pump or a liquid ring vacuum pump with 10℃-15℃ low-temperature cooling water cooling.

7. A method for optimizing low back pressure vacuum pumping in a high countercurrent ratio NDACC system, applied to the low back pressure vacuum pumping optimization structure of the high countercurrent ratio NDACC system as described in any one of claims 1 to 6, characterized in that: The method includes the following steps: S1. Under low back pressure operating conditions, the opening degree of the electric louvers in the counter-current zone is increased to the first control range, and the opening degree of the electric louvers in the downstream zone is decreased to the second control range. S2. Real-time acquisition of the vacuum temperature at the top of the counter-current zone, the condensation temperature between the bottom of the co-current zone and the bottom of the counter-current zone, and the steam inlet pressure at the top of the co-current zone; S3. Determine the corresponding steam inlet saturation temperature based on the steam inlet pressure, calculate the condensation subcooling by the difference between the steam inlet saturation temperature and the condensation temperature, and calculate the extraction subcooling by the difference between the steam inlet saturation temperature and the extraction temperature. S4. Monitor the pressure of the main regional pipe and adjust the operating parameters of the vacuum pump group based on the monitored pressure value of the main regional pipe to maintain the stability of the pressure of the main regional pipe.

8. The low back pressure vacuuming optimization method for a high countercurrent ratio NDACC system according to claim 7, characterized in that: In step S1, the first control range is determined by the extraction subcooling, and the second control range is determined by the condensation subcooling.

9. The low back pressure vacuuming optimization method for a high countercurrent ratio NDACC system according to claim 7, characterized in that: In step S2, the condenser subcooling is controlled at 1℃-3℃, and the extraction subcooling is controlled at 4℃-8℃.

10. The low back pressure vacuuming optimization method for a high countercurrent ratio NDACC system according to claim 7, characterized in that: In step S3, adjusting the operating parameters of the vacuum pump group specifically involves adjusting the speed of the vacuum pump group via frequency conversion or start-stop mode.

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