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Condenser
Article source: unknown Publisher: admin
product name
Condenser
Specifications
custom made
Product Usage
Acts as a cold source in the thermal cycle of a steam turbine plant
Detailed description

Condenser

Condenser Overview:
A type of heat exchanger where the condenser exhaust steam condenses into water is also called a re-waterer. It is mainly used in steam turbine power units and is divided into two types: water-cooled and air-cooled. In addition to condensing the steam from the steam turbine into water for reuse by the boiler, the condenser can also establish and maintain a vacuum at the steam turbine exhaust.
Condenser classification:
Different condensers according to the steam condensation method can be divided into two types: surface type (also called partition type) and hybrid type (also called contact type). In a surface condenser, the vapor separated from the cooling medium is condensed into a liquid on the cooling wall surface (usually a metal pipe). The cooling medium can be water or air. Water-cooled surface condensers (condensers) are divided into single-flow and dual-flow according to the cooling water flow mode. In a hybrid condenser, steam is condensed into a liquid when mixed with a cooling medium. The condensed steam can be either water vapor or vapor of other substances.
Condenser structure composition:
The dual-process condenser water-cooled surface condenser is mainly composed of a shell, a tube bundle, a hot well, and a water chamber. The exhaust steam of the steam turbine enters the shell through the throat, condenses into water on the cooling tube bundle and collects in the hot well, and is drawn out by the condensate pump. Cooling water (also known as circulating water) enters the cooling tube bundle from the inlet water chamber and is discharged from the outlet water chamber.
Condenser Features:
In order to ensure the high vacuum and good heat transfer effect in the condenser when the steam condenses, it is also equipped with extraction equipment, which continuously extracts the air and other non-condensable gases leaking into the condenser. The air extraction equipment mainly includes water jet air extractor, steam air extractor, mechanical vacuum pump and combined vacuum pump. The air-cooled surface condenser air is laterally or naturally ventilated outside the tube bundle by means of a fan, and the steam flows in the tube bundle and is condensed into water. In order to improve the heat transfer outside the tube, this condenser uses outer finned tubes. Its back pressure is much higher than that of a water condenser. There are two types of hybrid condensers: spray type and plane jet type. In the spray condenser, the cooling water is atomized into drops; in the plane jet type, the cooling water contacts the exhaust steam of the turbine in a film shape. Generally, the plane jet structure is used because it has a higher vacuum and can discharge all non-condensable gases.
Outstanding advantages
Outstanding advantages and applications of condensers:
He has been engaged in the design, manufacture, technical transformation, installation and replacement of cooling pipes, anti-corrosion sealing of thermal power plant condensers and heat exchangers for 15 years. It has an engineering department and three professional condenser retrofit construction teams. There are 7 middle and senior professional technicians and more than 50 special operation technicians, equipped with a full set of special testing equipment. The company's technicians design the best construction plan according to the specific site conditions such as the capacity of the customer's unit, and are carried out by experienced professionals in accordance with the project content, process quality requirements, safety measures and national power engineering construction standard DL5011-92 stipulated in the contract Construction ensures high-quality, timely and complete completion of the project. We have accumulated rich experience in the long-term condenser, heat exchanger design, technical transformation and cooling pipe (stainless steel pipe) replacement. The construction period is short, the construction cost is low, and the construction quality stable.
Condenser design:
When designing, the back pressure and cooling water ratio (referring to the mass ratio of cooling water to condensed steam) should be based on the steam discharge capacity, steam discharge area, annual or monthly average water temperature, and water supply method. Technical and economic comparison of cooling water pipe flow velocity, etc., to determine the best solution. The condenser should have a reasonable arrangement of tube bundles in the structure to improve the overall heat transfer coefficient and reduce the steam side resistance; arrange the air cooling zone and air outlet reasonably to prevent the formation of dead air zone; equipped with effective air extraction equipment to ensure Good heat exchange; the throat must have good aerodynamic characteristics to ensure that the exhaust steam enters the cooling tube bundle more evenly, so that no steam flow vortex is formed and part of the cooling area is wasted; the entire shell must have good air tightness and sufficient rigidity In order to improve the tightness of the vacuum and prevent the deformation of the shell; make the steam flow heat the condensate well and achieve a certain deoxidation effect; choose a reasonable intermediate support plate span according to the calculation of the tube vibration to avoid the tube bundle resonance caused by the operation Damage to the tube.
Condenser protection:
Carbon steel tubes, stainless steel tubes, and copper tubes are the main materials of condenser heat exchangers. Among them, when carbon tube steel tube sheets are used as condensers, corrosion leaks often occur between the tube sheet and the tube. Leakage entering the cooling water system will cause environmental pollution and waste of materials. At the time of production, manual arc welding is generally used for tube sheet and column tube welding. There are different degrees of defects in the shape of the weld, such as depressions, pores, slag inclusion, etc., and the stress distribution of the weld is uneven. When in use, the tube sheet part is in contact with industrial cooling water, and impurities, salts, gases, and microorganisms in the industrial cooling water will cause corrosion to the tube sheet and the weld. Studies have shown that whether industrial water is freshwater or seawater, there will be various ions and dissolved oxygen. The changes in the concentration of chloride ions and oxygen play an important role in the shape of metal corrosion. In addition, the complexity of the metal structure also affects the corrosion morphology. Therefore, the corrosion of the weld between the tube sheet and the tube is mainly pitting and crevice corrosion. Viewed from the outside, there will be many corrosion products and deposits on the surface of the tube sheet, with bubbles of varying sizes distributed. When seawater is used as a medium, galvanic corrosion will also occur. Bimetal corrosion is also a common phenomenon of tube sheet corrosion.
working principle
Condenser working principle:
Condensers are typical steam turbines widely used in modern thermal and nuclear power plants. Condensing equipment is an important part of steam turbine equipment. The quality of its design, manufacturing and operation quality directly affects the economics and safety of steam turbine equipment. Condensing equipment acts as a cold source in the thermal cycle of the steam turbine plant. Reducing the exhaust temperature and pressure of the steam turbine can improve the efficiency of thermal cycle cleaning. The main role of the condenser is to establish and maintain a high vacuum at the steam turbine outlet, and the second is to condense the water in the steam turbine exhaust as the boiler feed water, forming a complete cycle. And through heat exchange with circulating water, the condenser maintains a high degree of vacuum. Too low vacuum will seriously affect the safe and economic operation of power plant units, and one of the important reasons for too low vacuum is the scaling of cooling water pipes. The fouling of the steam turbine has a great impact on the performance of the condenser. It not only increases the turbine end difference, but also reduces the vacuum degree of the steam turbine and the exhaust gas temperature, which affects the economy and safety of the steam turbine. For a long time, traditional cleaning methods such as mechanical methods (scraping, brushing), high-pressure water, and chemical cleaning (pickling) have caused many problems when cleaning the equipment: the deposits such as scale cannot be completely removed, and acid liquid causes corrosion to the equipment to form holes. The residual acid causes secondary corrosion or sub-scale corrosion of the material, which eventually leads to the replacement of the equipment. In addition, the cleaning waste liquid is toxic and requires a large amount of funds for wastewater treatment.
Condenser cleaning rules:
Using a cleaning agent to clean the condenser, Fustek is highly efficient, environmentally friendly, safe, and non-corrosive. It not only has a good cleaning effect, but also does not corrode the equipment, which can ensure the long-term use of the condenser. Fustek cleaning agent (specific addition of wetting agent and penetrant) can effectively remove the most stubborn scale (calcium carbonate), rust, oil scale, slime and other deposits generated in water equipment, and will not cause human body Injury, will not cause corrosion, pitting, oxidation and other harmful reactions to steel, copper, nickel, titanium, rubber, plastic, fiber, glass, ceramics and other materials, which can greatly extend the service life of the equipment.
Condenser cleaning process:
1. Isolate the equipment system and drain the water from the condenser.
2. Use high pressure water to clean the sludge, algae and other impurities in the pipeline, and then close the system.
3. Install a ball valve (not less than 1 inch = 2.54 cm) between the isolation valve and the exchanger. Both the water inlet and the water outlet should be installed.
4. Connect the delivery pump and the connecting pipe so that the cleaning agent is pumped in from the bottom of the condenser and out of the top.
5. Start pumping the required Fuchstek cleaning agent into the condenser (the ratio can be adjusted according to specific conditions).
6. Repeat the cycle to the recommended cleaning time. With the progress of the cycle and the dissolution of the sediment, the gas generated during the reaction will also increase, and the excess air should be exhausted through the vent valve at any time. As the air is expelled, the space in the condenser will increase. Appropriate water can be added. Do not inject a large amount of water at the beginning, which may cause water overflow.
7. The effectiveness of the cleaning agent should be periodically checked during the cycle, which can be measured using a PH test paper. If the solution is maintained at pH 2-3, the cleaning agent is still effective. If the pH value of the cleaning agent reaches 5-6, it is necessary to add an appropriate amount of Forstek cleaning agent. The pH value of the final solution remained unchanged for 30 minutes at 2-3, which proved that the cleaning effect was achieved. Note: Fustec cleaning agents can be recycled and reused. Discharge will cause waste.
8. After the cleaning time is reached, the cleaning solution is recovered. Rinse the exchanger repeatedly with clean water until it is flushed to neutrality, and use a pH test paper to measure the pH value 6 ~ 7.
9. After cleaning, it can be started up. You can also suppress the test to see if there is a leak.
10. After the equipment is stable, record the current media overflow, working pressure, heat exchange efficiency and other data.
11. Comparing the changes in the values before and after cleaning, we can calculate the production costs such as electricity and coal costs saved by the company per hour and improve the work efficiency. This is exactly the value compensation that the company uses Fustech technology.
12. The same operation method can also be used for cleaning of plate and frame heat exchangers.
13. If the enterprise needs equipment for passivation pre-film treatment, it can be operated according to the following process: pump the passivation pre-filming agent into the equipment at the recommended dilution ratio (while hanging the test piece in the circulation tank); cycle and soak according to the recommended time; Detect the pre-film effect (red dot method or blue dot method); discharge; rinse with water to neutrality (use a PH test paper to measure the pH value 6 ~ 7).
14. After the passivation pre-film is over, it is better to blow the system with ventilation equipment such as a fan to ensure and improve the effect of the passivation pre-film.
A heat exchange device that turns the steam discharged after driving a steam turbine into condensate. After the steam has completed an expansion process in the steam turbine, during the condensation process, the volume of the exhaust steam shrinks sharply, and the space filled with steam originally forms a high vacuum. Condensate is transferred to the boiler through the feed water heater, feed water pump, etc. through the condensate pump, so as to ensure the continuous operation of the entire thermal cycle. In order to prevent pipeline corrosion caused by the increase of oxygen content in condensate, modern large-capacity steam turbines are also equipped with vacuum deaerators.
The main role of the condenser:
1) Create a high vacuum at the steam turbine exhaust port, make the steam expand to the lowest pressure in the steam turbine, increase the available enthalpy drop of steam in the steam turbine, and improve the cycle thermal efficiency;
2) The steam discharged from the low pressure cylinder of the steam turbine is condensed into water and sent back to the boiler for circulation;
3) Collect all kinds of hydrophobicity to reduce the loss of soda.
4) Also used to increase demineralization (normal hydration)
Condenser surface type working principle:
The condenser is equipped with a large number of copper pipes and is circulated with cooling water. When the exhaust gas of the turbine comes into contact with the outer surface of the copper tube of the condenser (condenser), it is cooled by the water flow in the copper tube, and the latent heat of vaporization becomes condensed water. The released latent heat is continuously transmitted to the copper tube wall. Circulate the cooling water and take it away. In this way, the exhaust steam is continuously condensed through the condenser. When the exhaust steam is cooled, its specific volume decreases sharply, so a high vacuum is created inside the condenser under the steam turbine exhaust port. Condensers are large heat exchange equipment for thermal power plants.
Condenser Figure 1 shows the structure of the surface condenser
The condenser is equipped with a large number of copper pipes and is circulated with cooling water. When the exhaust gas of the turbine comes into contact with the outer surface of the copper tube of the condenser (condenser), it is cooled by the water flow in the copper tube, and the latent heat of vaporization becomes condensate. Circulate the cooling water and take it away. In this way, the exhaust steam is continuously condensed through the condenser. When the exhaust steam is cooled, its specific volume decreases sharply, so a high vacuum is created inside the condenser under the steam turbine exhaust port. Condensers are large heat exchange equipment for thermal power plants.
Condenser Figure 1 is a schematic diagram of the surface structure.
Condenser
When the condenser is running, the cooling water comes in from the lower half of the front water chamber, enters the rear water chamber through the cooling water pipe (heat exchange pipe), folds upward, and then flows through the upper half of the cooling water pipe to the forward water chamber and is finally discharged. The low-temperature steam comes in from the steam inlet, flows down through the gap between the cooling water pipes, and condenses into water after releasing heat to the pipe wall.
Condenser structure description:
The condenser structure is single shell, bisect, single flow, surface type. The condenser is a single-shell split-single-flow surface type, which is arranged laterally under the low-pressure cylinder. The housing is placed on a spring support, and the upper part of the housing is rigidly connected with the steam engine exhaust cylinder. The circulating water flows through the tube bundle to condense the steam turbine exhaust in the shell, and the condensed water is collected in the hot well and discharged by the condensate pump. A tube bundle is arranged in the casing, and the hot well is placed below the casing. At normal water level, the water volume is not less than 4 minutes. The single process consists of a shell and a tube bundle. The tube is a copper alloy tube and is cooled with fresh water. The tube bundle is arranged as a strip tube bundle, also known as a "general cap" arrangement. The throat of the condenser is connected to the exhaust pipe of the low-pressure cylinder of the steam turbine. The upper caliber size: 7532 × 6352 is manufactured in two halves, which is 7890 × 3355 × 1980. 16mm thick 20g steel plate is used for the neck wall plate. The internal welded ribs (δ16) are reinforced, and the side plates are reinforced with 18 # angle steel and 20a channel steel φ102--φ159 20 # steel pipes to make them have sufficient rigidity. The lower part of the neck is in the shape of a truncated cone. It is manufactured in three sections. The size of the left and right sections is 12100 × 2600 × 3841, and the size of the middle section is 12100 × 2300 × 3841. Plates, tubes and diagonal supports are strengthened. There are two desuperheaters on the right side of the lower neck (the side of the cooling water inlet pipe). It belongs to the scope of supply of the low-pressure bypass device. The steam extraction duct of the six-seven-eighth section of the steam turbine leads out through the right side of the neck (the side of the cooling water outlet pipe). Expansion joints are used for pipeline thermal compensation. The space between the tube plates is 12330mm, and 14 partition plates with different elevations are set in the middle. The cooling tube plates are inclined at an angle of 5 between the tube plates. At the same time, the installation angle of the tube sheet is also 5 to ensure that the two are perpendicular, so that the center elevation difference between the inlet and outlet chambers is 62mm. The tube sheet and the shell are connected by a transition section, and the length of the transition section is 300 mm. The bottom of each partition is supported by three round steels 1026, and between the partition and the pipe is 2201107.5 I-beam and a pair of inclined irons to adjust the installation size of the partition. The bottom of the partition is on the same plane. The shell is directly connected to the hot well through the backing plate. The height of the hot well is 2041, which is manufactured in two parts: left and right. There are I-beams in the hot well, which support the round pipe and have good rigidity. Three 500 1000 square holes are connected to the bottom of the hot well and connected to the condensate water outlet device. The partitions are connected by three 895 steel pipes, and the edges of the partitions are welded to the side plates of the casing. Each row of partitions is welded by three 70 round steel bars, and the two ends of the round steel bars are also welded to the tube sheet transition section. The upper part of the condensed water outlet device is provided with a grid plate to prevent debris from entering the condensed water pipeline and at the same time to prevent people from falling off after entering the hot well. A baffle is provided above the air cooling zone to prevent the vapor-gas mixture from directly entering the air cooling zone. Both sides of the air baffle are sealed and welded to the partition. Each row of tube bundles has 199,100 square holes in the three baffles, and the three square tubes are combined to form an exhaust pipe of 2736.5. The arc-shaped semi-spherical water chamber has the characteristics of uniform water flow, difficult to generate eddy current, reasonable cooling water pipe filling, and good heat exchange effect. The water chamber side plate is made of 25mm thick 16Mn steel plate, and the water chamber flange is made of 60mm thick 16MnR, and is connected with the tube plate and the shell by bolts. The rubber ring is used as a gasket to ensure the tightness of the water chamber. The inlet and outlet pipe diameter is 2000. There is a manhole in the water chamber with a diameter of 450. During maintenance, in order to prevent workers from falling into the circulating water pipe after entering the manhole, a mesh plate is added at the water inlet and outlet pipes. The stainless steel sheet does not increase water resistance and can ensure water resistance. Safety. There are air vents, drainage holes, hand holes, and temperature and pressure measuring points on the water chamber. The water chamber wall is coated with an epoxy protective layer and protected by sacrificial anode. There are 8 vacuum measurement points at 300mm above the top row of tubes. The measurement points are two 5mm thick plates that form a 30mm spaced measurement plate. 143 tubes are led from the middle joint of the plate to eight vacuum measurement points at the neck. Vacuum measurement. Condenser (condenser) hot well: A water collecting well under the condenser to collect condensate is placed under the steam engine room. The function is to collect condensate water and provide a certain static pressure head for the condensate pump. It is mounted on a spring and a base plate. The spring is designed by the stress of the turbine. Taking into account the horizontal force generated by the friction angle of the spring, the 78 springs use half left and half right to balance the forces. In order to prevent the condenser from moving back and forth, left and right during operation, the condenser and the low-pressure cylinder are not concentric, which is not good for the low-pressure cylinder. Welded fixing plates on the bottom of the hot well make the floor adhere to the steel plate embedded in the spring foundation column. The steamer can only move up and down.
Definition of condenser vacuum:
The value read from the vacuum gauge is called the degree of vacuum. The vacuum value is a value indicating that the actual pressure of the system is lower than the atmospheric pressure, that is: vacuum = absolute pressure of the atmospheric pressure
The main reasons for the formation of condenser vacuum:
During the startup process, the vacuum is formed by the main and auxiliary pumping out a large amount of air in the steam turbine. In normal operation, the formation of a vacuum is caused by the sharp reduction of the specific volume of the steam turbine when it suddenly condenses into water. For example, when the steam pressure is 4kpa, the volume of steam is 30,000 times larger than that of water. When the steam is condensed into water, the volume is greatly reduced, so that a high vacuum is formed in the condenser.
Three conditions must be met to form and maintain the condenser vacuum:
1) Copper pipes must pass a certain amount of cooling water;
2) The condensate pump must continuously remove the condensate to avoid the water level rising and affecting the condensation of steam;
3) The air extractor must extract the leaked air and other gases in the exhaust steam.
Causes of reduced condenser vacuum:
(1) Reduced or interrupted circulating water:
Circulating water pump trips, the progressive valve is closed by mistake, the circulating valve outlet butterfly valve spool is dropped, the progressive filter is blocked: the water volume is interrupted, the inlet water pressure is reduced, the outlet water vacuum is zero, the circulating pump current is zero or increased, and the vacuum must not be damaged Shut down; if not shut down, immediately reduce the load and recover;
The valve is closed by mistake, the water side plate and tube of the condenser are blocked, and the large screen plate is not in the operating position: the circulating water pressure increases and the temperature rise increases;
Poor water inlet: The pump current shakes, the inlet water pressure decreases, the outlet water vacuum decreases, the circulating water temperature increases, and the water volume is insufficient; Air leakage from the water side): When the siphon effect is reduced, the amount of water is reduced, but the pressure of the circulating jellyfish tube is increased, and the high pressure is beneficial to maintain the water volume, so the siphon destruction must be a process. The effluent vacuum shakes and slowly decreases, and the temperature rise increases.
Condenser operation:
(1) Increase the pressure of the circulating water (close the small water outlet valve), and re-establish the vacuum of the outlet water for the circulating air.
(2) Low shaft seal steam pressure: Increase the pressure and close the small shaft and add the exhaust fan intake valve; cold air will shrink the rotor and increase the negative differential expansion.
(3) High water level: At the same time as the temperature of exhaust steam rises, the temperature of condensate drops and the degree of subcooling increases. Increased terminal difference; water level, height of steam extraction port, trip of condensate pump, blockage of pipeline, bad back-up valve of backup pump, failure of main gas control valve of system, large leak of titanium pipe: backup condensate pump starts automatically, outlet pressure reaches zero Or rise, the current of the condenser pump shakes or rises or falls to a no-load value;
(4) Air leakage in vacuum system: pipes, flanges, welds, manhole doors, air doors, drain valves, water level gauges, small machine exhaust butterfly valves, air exhaust membranes, U-shaped pipe water seals;
(5) Air extraction equipment failure: vacuum pump, pump inlet air, check valve core drop, valve is broken.
Causes and treatment of sharp drop in condenser vacuum
1. Circulating water interruption: The failure of circulating water interruption can be judged from the working condition of the circulating pump. If the circulating pump motor current and water pump outlet pressure reach zero, it can be confirmed that the circulating pump has tripped. At this time, the standby circulating pump should be started immediately. If the pump is forced to trip, check whether the pump is reversed; if it is reversed, it is strictly forbidden to close the motor to avoid overloading the motor and breaking the shaft. If there is no backup pump, the load should be quickly reduced to zero, and the brake should be stopped. The outlet pressure of the circulating water pump and the current swing of the motor are usually caused by the low water level in the suction inlet of the circulating water pump and the clogging of the filter. At this time, measures should be taken as soon as possible to raise the water level or clear debris. If the circulating water pump outlet pressure and motor current are greatly reduced, it may be caused by the failure of the circulating water pump itself. If the outlet of the circulating pump is closed by mistake during operation, or the outlet door of the standby pump is incorrectly opened, causing the circulating water to flow backward, the vacuum will also drop sharply.
2. Abnormal working of the water jet aerator: If the outlet pressure of the water jet pump is found and the motor current reaches zero at the same time, it indicates that the water jet pump has tripped; for example, the water pump pressure. The current drops, indicating that the pump itself is faulty or the water level in the pool is too low. When the above situation occurs, the standby water jet magnetic and water jet aspirator should be activated. When the water level is too low, water should be replenished to the normal water level.
3. Full water: In a short time, full water is usually caused by a serious leak of the condenser copper tube, a large amount of circulating water entering the steam side or the failure of the condensate pump. The treatment method is to immediately open the large water level regulating valve and start the standby condensate pump. If necessary, drain the condensate into the trench until the water level returns to normal. Copper pipe leakage also manifests as increased hardness of condensate. At this time, the leaking condenser should be stopped, and in severe cases, it should be stopped. If the condensate pump fails, it can be judged from the outlet pressure and current.
4. Shaft seal steam supply interruption: If the shaft seal steam supply pressure reaches zero or there is a slight negative pressure, the shaft seal steam supply is interrupted. The reason may be the failure of the shaft seal pressure regulator, the valve core of the regulating valve falling off, or water in the steam seal system. . At this time, the bypass valve of the shaft seal regulator should be opened to check whether the deaerator is full of water (when the shaft seal is supplied with steam from the deaerator). If it is full of water, quickly lower its water level and replace the spare steam source of the shaft seal.
Causes and treatment of slow condenser vacuum drop
Because the vacuum system is huge and there are many factors that affect the vacuum, it is difficult to find the cause when the vacuum is slowly falling. The following items can be checked and treated.
1. Insufficient circulating water: Insufficient circulating water is manifested under the same load, the temperature difference between the inlet and outlet of the circulating water of the condenser increases, and the reason may be that it is blocked by entering debris. For a unit equipped with a rubber ball cleaning device, backwashing should be performed. For the unit with siphon in the outlet pipe, check whether the siphon is damaged. The phenomenon is that the vacuum on the outlet side reaches zero and the inlet pressure increases. When the above situation occurs, the auxiliary air extractor of the circulating water system should be used to restore the vacuum at the outlet. If necessary, the amount of circulating water entering the condenser can be increased. The increase in the temperature difference between the outlets of the condenser (condenser) may also be due to the accumulation of air in the circulating water outlet pipe or the serious scaling of the copper pipe. At this time, the air outlet valve of the outlet pipe should be opened to remove air or put into a rubber ball cleaning device for cleaning, and if necessary, rinse with high pressure water after shutdown.
2. Condenser water level rise: The water level rise may be caused by vaporization of the inlet of the condensate pump or rupture of copper pipes and leakage of circulating water. The vaporization of the condensate pump inlet can be judged by the reduction of the current of the condensate pump. When it is confirmed that the water level is increased due to this reason, it should be checked whether the blue packing on the inlet side of the pump is not strict and leaking air. Rupture of copper pipes can be judged by examining the hardness of the condensate.
3. Raising the working water temperature of the water-jet aspirator: Increasing the working water temperature raises the pressure of the extraction chamber and reduces the efficiency of the aspirator. When the water temperature is found to increase, the industrial water should be turned on to reduce the working water temperature.
4. Air leakage from vacuum system: Whether the vacuum system leaks air can be checked by rigorous test. In addition, air leaking into the vacuum system also shows an increase in the degree of subcooling of the condensate and an increase in the end difference.
Hazard of Condenser Vacuum Drop:
(1) The exhaust pressure is increased, the available enthalpy drop is reduced, it is uneconomical, and the unit output is reduced;
(2) The increased exhaust temperature may loosen the copper pipe and damage the tightness;
(3) The exhaust temperature rises, which causes the exhaust cylinder and the bearing seat to expand thermally, causing the center to change and generating vibration;
(4) The axial displacement of the steam turbine increases, causing the thrust bearings to overload and wear;
(5) The vacuum drop reduces the volume flow of the exhaust steam, which generates a large excitation force to a certain part of the final stage blade, which may damage the blade and cause an accident.
Main causes of poor tightness of condenser and steam side
1. Air leakage at the throat flange or weld of the exhaust cylinder of the steam turbine and the condenser. If the sleeve water seal connection method is adopted, the deformation of the throat causes the packing to move, the packing is not pressed tightly, or the amount of water sealed is insufficient.
2. There is a problem or abnormal operation of the shaft end seal of the turbine.
3. The joint surface of the low-pressure cylinder of the steam turbine and the meter connector are not tight.
4. The valve is not tight or the water volume of the water-sealed valve is insufficient.
5. The axial seal of the condensate pump is not tight.
6. The steam space of the low-pressure feedwater heater is not tight.
7, equipment, pipelines are damaged or there is a problem with the weld.
Condenser water side
1. Leakage at the tube end of the expansion tube. When the pipe and the tube sheet are connected by the padding method, the sealing of the packing part is not good.
2. Erosion occurs at the inlet end of the pipe.
3. The cooling pipe is damaged.
Condenser terminal difference:
The difference between the saturation temperature under pressure and the cooling water outlet temperature. For a certain condenser, the magnitude of the end difference is related to the cooling water inlet temperature, the steam load per unit area, the cleanliness of the surface of the copper pipe, the amount of air leaked into the pipe, and the cooling water flow rate in the pipe. A clean condenser has a certain end difference index under a certain circulating water temperature and circulating water volume and unit steam load. Generally, the end difference index is that when the circulating water volume increases, the lower the cooling water outlet temperature, the end difference The larger it is, and vice versa; the larger the unit steam load, the larger the end difference, and vice versa. In actual operation, if the end difference value is much higher than the end difference index value, it indicates that the cooling surface copper pipe is dirty, which causes the heat conduction conditions to deteriorate.
Causes of increased condenser terminal difference
1. Fouling on the water or steam side of the copper pipe;
2. Air leaked into the steam side;
3. The cooling water pipe is blocked;
4. Reduced cooling water volume, etc.
Condenser subcooling
When the temperature of the liquid reaches the theoretical crystallization temperature, crystallization cannot be performed, but the crystallization must start at a temperature below its temperature (called the actual crystallization temperature). In the actual crystallization process, the actual crystallization temperature is always lower than the theoretical crystallization temperature. This phenomenon becomes a supercooling phenomenon. The temperature difference between the two is called the supercooling degree.
Causes of condenser subcooling:
Because the partial pressure of steam on the outer surface of the cooling water pipe is lower than the average partial pressure of steam between the tube bundles, the condensation temperature of the steam is lower than the temperature of the mixed steam flow between the tube bundles, thereby generating supercooling.
Due to the existence of vapor resistance in the condenser, the steam encounters resistance when it flows downward from the exhaust port, causing the lower steam pressure to be lower than the upper pressure, and the lower condensate temperature to be lower than the upper pressure, resulting in supercooling.
When the steam is cooled into droplets, it flows between the cooling water pipes and is cooled by the circulating water in the pipe. Because the temperature of the droplets is higher than the temperature of the cooling water pipe wall, the condensate temperature is lowered below its saturation temperature, resulting in supercooling.
Due to the accumulation of air on the steam side, the partial pressure of the air increases, and the partial pressure of the steam relatively decreases. The steam is still condensed under its own partial pressure, so that the temperature of the condensed water is lower than the exhaust temperature and supercooling occurs.
There are structural defects, and the arrangement of cooling water tube bundles is not reasonable, so that the condensed water forms a layer of water film outside the cooling water pipe. When the water film thickens and sags into water droplets, the temperature of the water droplets, that is, the average temperature of the inner and outer layers of the water film is lower than water Saturation temperature of the outer surface of the film, resulting in supercooling.
There is too much air leakage or the air extractor does not work properly, the air cannot be drawn out in time, and the partial pressure of the air increases, which increases the degree of subcooling.
The water level of the hot water well is higher than the normal range, and some copper pipes of the condenser are submerged, so that the circulating water in the submerged copper pipe takes away the heat of the condensate and generates supercooling.
The temperature of the circulating water is too low and the amount of circulating water is too large, so that the condensed water is excessively cooled, and the degree of subcooling is increased.
The copper tube of the condenser is broken, and the circulating water leaks into the condensed water, which reduces the temperature of the condensed water and increases the degree of subcooling. The subcooling degree of condensate is an important index to measure the economical operation of the condenser. A small subcooling degree means that the heat taken away by the circulating water is small and the unit is economical. On the contrary, the degree of supercooling is large and the heat taken away by the circulating water is large. Unit economy is poor.
According to the data, for each increase in the degree of subcooling, the unit heat consumption rate increases by 0.02%.
Hazard of rising condenser water level
(1) Rising water level will cause condensate to overcool;
(2) Affect the economic operation of the condenser;
(3) If the water level is too high, submerging the copper pipe (bottom) will reduce the entire cooling area. In severe cases, the air pipe will be submerged, causing the aspirator to pump water, and the vacuum will drop severely.
Condenser operating condition sign
(1) Whether the most favorable vacuum can be reached;
(2) Whether the quality of the condensate can be guaranteed;
(3) Whether the degree of subcooling of condensate can be kept to a minimum.
Formation of condenser vacuum:
During startup, the vacuum is formed by the main and auxiliary steam extractors extracting a large amount of air from the turbine and condenser. In normal operation, the formation of a vacuum is caused by the sharp reduction in the specific volume of the steam turbine when it suddenly condenses into water in the condenser.
Reasons for the rise of the circulating water temperature of the condenser:
The temperature of the inlet water increases, and the temperature of the outlet water increases accordingly. Turbine load increases. Tube sheet and copper tube are dirty and blocked. Reduced circulating water. The secondary water filter of the circulating water is dirty and blocked. Exhaust steam increases. The vacuum drops.
The reasons for the pressure change of the circulating water of the condenser are:
Circulating water volume changes or is interrupted. Air leaks from the outlet pipe. Water level change in siphon well. The opening of the water inlet and outlet of the circulating water changes. The air valve of the circulating water outlet pipe has been opened by mistake. A large amount of air in the circulating water pipe poured into the condenser, and the siphon was destroyed. The heat load is large, the effluent temperature is too high, and the siphon effect is reduced. The copper pipe is severely blocked.
The low inlet and high outlet of the condenser may explain the working process of double back pressure:
When the condenser works normally, the cooling water enters from the two water inlet chambers on the low pressure side, passes through the cooling water pipes in the housing on the low pressure side, and flows into the other two water chambers on the low pressure side. Each water chamber flows through the cooling water pipe in the high-pressure side casing to the two water outlet chambers on the high-pressure side and is discharged. The steam enters through the steam outlet of the turbine and is evenly distributed over the entire length of the cooling water pipe, passing through the central channel of the tube bundle and the channels on both sides The steam can enter the main beam area in an all-round way and be condensed after heat exchange with cooling water; part of the steam enters the hot well from the middle channel and the channels on both sides to reheat the condensed water. The condensed water on the LP side shell is introduced into the condensate reheating piping system after the steam on the LP side shell is reheated. It is merged with the condensate in the HP side shell through the drip tray, and is also reheated by the steam in the HP side shell. To reduce the subcooling of condensate. The condensed water that has been reheated is collected in the hot well, pumped out by the condensate pump, and input into the main condensate system after the pressure is increased. After the remaining vapor mixture of the HP-side casing and the LP-side casing is heat-exchanged again through the air cooling zone, a small amount of non-condensed vapor and air mixture is extracted by the vacuum equipment through the exhaust port. The 600,000 double back pressure has slight differences in the internal structure of different manufacturers.
Advantages of double back pressure of condenser:
According to the principle of heat transfer, the average back pressure of the double back pressure is lower than the back pressure of the single back pressure under the same conditions, so the enthalpy drop of the low pressure cylinder of the steam turbine is increased, thereby improving the economic efficiency of the steam turbine. (The double back pressure of a 600MW unit is generally 4.4 / 5.4KPA, and the average back pressure is 4.9 KPA).
Another advantage of double back pressure is that the low temperature condensate in low back pressure can enter the high back pressure for heating, which not only raises the temperature of the condensate, but also reduces the loss of cold source taken away by the high back pressure by the cooling water. The low-temperature condensate in the low back pressure enters the drip tray at the lower part of the high-back pressure tube bundle through the pipe using the height difference. In the drip tray, the low-temperature condensate is mixed with the high-temperature condensate, and then flows through the small holes in the tray. During the process of the condensate falling from the hole of the drip tray, the condensate is heated to the corresponding saturation temperature by the exhaust steam of the high back pressure low pressure cylinder.
Basic structure of double back pressure of condenser: {reference}
The 660MW three-cylinder four-exhaust steam turbine is equipped with four condensers, one set of two each, two low back pressure condensers as a group, and two high back pressure condensers as a group, which are respectively arranged in the low pressure cylinder. Below. Different back pressures are formed by different circulating water inlet temperatures of the condenser. The circulating water pipelines are arranged in series and enter from two low back pressures, and the effluent enters the siphon well after being discharged from two high back pressures. In other words, the water side of each group is double-in and double-out. Each group is just a whole shell, which can be disassembled and cleaned in half during normal operation.
Technical Parameters
Condenser specifications and technical parameters:
Condenser model

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