The condenser rubber ball cleaning device can realize automatic online cleaning of the inner wall of the condenser cooling pipe, thereby improving the cleanliness of the cooling pipe, improving the condenser vacuum, reducing the coal consumption of power generation, avoiding corrosion under the scale, and extending the service life of the cooling pipe. Therefore, the rubber ball cleaning device is an important device to improve the thermal efficiency of thermal power generating units. However, most of the domestic rubber ball cleaning devices in power plants have not played their due role. This article comprehensively analyzes the factors that affect the cleaning effect of rubber balls, and proposes different pollution phenomena to improve the cleaning effect of rubber balls. The vacuum of condensers is reduced, and the cycle thermal efficiency of the unit is reduced. For reference.
Condensers in every power plant now have an impact on the safety and economics of the unit. In order to maintain the unit working under a good vacuum, most power plants use rubber ball automatic cleaning devices to reduce or eliminate the dirt on the condenser.
The condenser rubber ball continuous cleaning device was successfully developed in Germany in the early 1950s. Its basic working principle is to put a certain number of rubber balls into the condenser cooling tube in operation, so that they continuously circulate through the cooling tube. , Played a cleaning role on the inner wall of the cooling pipe. This cleaning method has many advantages that cannot be replaced by other methods. Such as manual shutdown brushing, load reduction or shutdown is required, and the labor intensity of the workers is large; although the pickling method is relatively clean, it will cause damage to the pipe wall, and the cost is high; rinse with high pressure water, dry clean or shot During cleaning, the machine needs to be shut down, which affects the normal production of the power plant, and the condenser is operated in a polluted state for a long time.
The use of rubber ball online automatic cleaning device can clean the dirt on the inner wall of the condenser cooling pipe without reducing the load of the turbine, thereby improving the cleanliness of the cooling pipe, improving the condenser vacuum, reducing the coal consumption of power generation, and avoiding corrosion under the scale. Extend the life of the cooling pipe. It can be seen that the condenser rubber ball cleaning device is an important device to improve the thermal efficiency of thermal power generating units. However, due to the influence of the selection of rubber balls, cleaning devices, cooling water, condenser structure, etc., at present, most domestic rubber ball cleaning devices of power plants have not played their due role. As each power plant has more warp, the water absorption of West German rubber ball is better than coke rubber ball. In addition, the diameter of West German rubber ball is about one millimeter larger than that of Jiaozuo rubber ball. These factors cause the cleaning effect of the two rubber balls to be very different.
The curve shown is the change curve of dirt thermal resistance with cleaning time when using Jiaozuo rubber ball to clean in a di experiment. Obviously, the thermal resistance of dirt does not decrease, indicating that the cleaning effect is not ideal; Figures 2 and 4 show It is the change curve of dirt thermal resistance when using West German rubber ball cleaning in the di secondary experiment. The dirt thermal resistance has a significant downward trend, indicating that the cleaning has played its due role. These all show that the diameter of the rubber ball and the density of the wet state really have an important effect on the cleaning process.
It should be said that only after understanding the type of dirt and its characteristics on the heat exchange surface and the density of the cooling water, the selection of the rubber ball can ensure the rationality and practicality of the selected rubber ball. Generally for softer dirt, the diameter of the rubber ball should be 1 to 2 mm larger than the inner diameter of the tube. At this time, the friction effect of the rubber ball on the inner wall of the tube is strong, and the problem of plugging of the rubber ball is not easy to occur. However, for harder dirt, the diameter of the rubber ball used should be slightly smaller than the inner diameter of the tube, otherwise the rubber ball will be easily blocked in the cooling tube. The movement of the rubber ball in the cooling pipe is driven by the flow head of the cooling water. Generally, the flow head is small, about 19.6 to 39.2 kPa. If the size of the rubber ball is larger than the inner diameter of the tube, and the surface of the hard dirt is very rough, the rubber ball is easily blocked in a large amount in the cooling tube, which affects the normal flow of cooling water and affects Recycling of rubber balls has adverse consequences.
Under the condition of fully understanding the cooling water properties, the wet density of the rubber ball should be similar to the density of the cooling water. From a running point of view, if the wet density distribution of the rubber balls is a normal distribution with mathematical expectation of cooling water density and a small mean square error, then the rubber balls can be basically uniformly distributed in the water chamber, so that each The chances of the tube being washed are almost the same. This is consistent with the wet-ball density range of 0.95 to 1.16 g / cm3 specified in the literature. Of course, strictly speaking, the mean square error of the wet density distribution should also be less than a certain value, but this value should be determined through technical and economic analysis.
Case: Comparison of physical properties of two rubber balls used in a power plant
Case: The power plant uses seawater as cooling water. The dirt on the inner wall of the pipe is mostly a mixture of microorganisms, algae, small shells, small fish, shrimp, sediment, and salt, but the proportion of salt scale is small, and its texture is soft, and Has a creamy feel. In this case, it is better to use a rubber ball with a diameter larger than the inner diameter of the tube to clean the cooling tube by 1 to 2 mm. The West German rubber ball exactly meets this condition. Its average diameter is more than one millimeter larger than the inner diameter of the tube, which ensures the necessary cleaning of the inner wall of the tube, and the possibility of ball blocking is small. However, the average diameter of Jiaozuo rubber ball is slightly smaller than the inner diameter of the tube, and the friction effect of the rubber ball on the inner wall of the tube is weak, and it can not perform the cleaning effect.
In addition, the average wet density of the West German rubber ball after being fully immersed in tap water is similar to the density of water, so when fully soaked in seawater, the density should be similar to the density of seawater, so that the rubber ball enters the condenser The cooling water is evenly distributed behind the water chamber, ensuring that each pipe has the same probability of being cleaned, that is, the probability that the rubber ball enters each pipe is the same. The wet density of Jiaozuo rubber ball is small, which makes the rubber ball mainly distributed in the upper part of the water chamber. The upper cooling tube of the condenser is more likely to be cleaned than the middle and lower tube. Under the combination of these factors, the cleaning effect of West German rubber ball is better than Jiaozuo rubber ball.
The characteristics of the rubber ball not only affect the cleaning effect, but also affect the recovery of the rubber ball. Of course, the two are unified. The wet density, diameter, viscosity of the rubber ball, and the hardness of the rubber ball will affect the ball collection rate. For example, if the wet density of the rubber ball is small, the rubber ball is easy to accumulate in the upper part of the condenser water chamber, and only a small amount of the rubber ball circulates in the cooling pipe, which affects the recovery of the rubber ball; Most rubber balls are deposited in the lower part of the water chamber, and only a few balls participate in the cycle, which affects the ball collection rate. If the diameter of the selected rubber ball is large, the driving force of the rubber ball in the tube is the pressure difference of the cooling water. Small, so the rubber ball is easily blocked in the tube, resulting in a decrease in the recovery rate of the ball; If the ball is more viscous, the ball is likely to stick to the surface of the net, the inner wall of the tube, the tube plate, etc., and affect the ball collection rate When the ball is soft, it is easy for the ball to be caught by the traces left by some burrs on the equipment it passes, which affects the ball collection rate.
Impact of rubber ball cleaning device on cleaning effect
Whether the rubber ball cleaning device is reasonable or not has a great influence on the cleaning effect, which mainly affects the recovery rate of the rubber ball. The rubber ball recovery rate reflects the running status and cleaning effect of the rubber ball cleaning device from one side. A high ball-receiving rate indicates that the system is operating normally, and the number of passes in a unit time is large, so the cleaning effect is good. It is generally believed that the ball reception rate should be higher than 90%. The low or rapid reduction of the ball receiving rate will not only cause an increase in the number of balls replenished, but also may block the cooling pipe and the ball receiving net, which of course means that the cleaning effect is poor. Experience has shown that the rate of ball collection is also a key factor that determines the quality of rubber ball cleaning. In fact, a considerable part of the power plants have stopped the rubber ball cleaning system because the ball collection rate is too low.
Influence of the receiving net on the receiving rate
The ball collecting net is the main equipment of the rubber ball cleaning device. Its function is to collect the rubber balls passing through the condenser and recycle them. Therefore, its performance and quality directly affect the level of the ball collecting rate.
The clearance between the movable screen of the receiving net
and the inner wall of the cylinder and the fixed screen has a large effect on the rate of receiving the ball. Some ball nets have large gaps due to the manufacturing quality of the manufacturer. Impurities in the cooling water are likely to get stuck here, or because the screen cannot be restored to its original position after backwashing, and the bolts of the card shaft are loose. The gap is too large, causing the ball to run.
The tilting angle of the receiving net screen is also one of the factors that should be considered, and its angle should be designed according to the cooling water flow rate. If the angle is too large, the rubber ball will easily get stuck in the gap between the grids of the screen, which will cause the accumulation of balls and it is difficult to circulate. When the net is backwashed, it will go with the water. The rust of the receiving net screen will also affect the recovery of the rubber ball. Because after rusting, the surface of the screen becomes rough, and it is easy to hang the ball, so that the number of recycled rubber balls is reduced. The accumulation of balls in the small net at the bottom of the receiving net will also affect the recovery rate of the rubber ball. This phenomenon mainly occurs in the ball receiving net installed in the outlet pipe with negative pressure, which is closely related to the suction height of the pump. In addition, when the design of the receiving net is irrational and the vortex is generated in the water flow in the net, the rubber ball will swirl in the net following the water flow, which will affect the recovery of the rubber ball.
Effect of rubber ball pump on ball collection rate
The rubber ball pump is a power equipment for rubber ball recirculation. The performance of the rubber ball pump directly affects the level of ball collection. During the summer operation of the unit, due to the increase of the condenser cooling water volume and the increase of the inlet pressure, the output of the rubber ball pump is insufficient, which affects the recovery of the rubber ball.
The suction vacuum height of the rubber ball pump has a great impact on the pump operation, which has an indirect impact on the cleaning of the rubber ball. If the pump's flow rate increases, the suction vacuum height will decrease, and the cooling water at the pump inlet temperature will easily vaporize, making the rubber ball pump unable to work normally. In the open system, if the pump is installed geometrically If the height is too high, the vacuum suction height will also be reduced. If the pump inlet pipe is long, the pipe diameter is small, and the valve elbow and other factors cause the pipe resistance to increase, it will also reduce the vacuum suction height. These factors can affect the normal operation of the pump and further affect the work of the cleaning system.
Effect of cooling water system on cleaning effect
The effect of impurities in the first cooling water. Many data show that due to the inadequate filtering or poor performance of the primary and secondary filters, the cooling water cannot be filtered clean, causing various sundries to enter the condenser water chamber, some sealing the inlet of the cooling pipe, and some blocking In the cooling pipe, some are stacked on the receiving net, which affects the passing of the rubber ball, resulting in a decrease in the receiving rate and affecting the cleaning effect.
For power plants in the north, because the cold climate in the north often freezes the cooling towers in winter, when the ice is hit, the filling layer of the cooling towers is often destroyed, and the small and fast fillers enter the condenser with the cooling water, clogging the pipes or The accumulation in the receiving net affects the passing of the rubber ball, resulting in a decrease in the cleaning effect. For seawater-cooled units, as a large number of mussel embryos contained in the seawater pass through the primary and secondary filters, attached to the pipes and tube sheets, they are separated from the tube wall when they are mature, and blocked in the cooling water pipe, which directly affects the passing of the rubber balls. , Resulting in a decline in the rate of catch. Taking the cooling water situation of coastal power plants in Tianjin as an example, April to November is the breeding and active period of marine life, especially June to August, it is the high-speed breeding and growing period of marine life. If no measures are taken, more than half Most of the condenser's cooling pipes can be blocked in a month, resulting in a drop in the ball collection rate.
Secondly, when the amount of cooling water and the pressure difference between the inlet and outlet are small, it will cause the rubber ball to pass through the condenser cooling pipe and be blocked in the pipe. This kind of situation mostly occurs in the units operating in winter. Because the ambient temperature in winter is relatively low, the inlet temperature of the cooling water is relatively low. In this case, the amount of cooling water required is small, and the pressure difference between the inlet and outlet is also small.
Influence of condenser structure and cooling pipe on cleaning effect
There is a "dead zone" or vortex zone in the condenser inlet water chamber, causing the rubber balls to accumulate or swirl here. Sometimes there are still gaps at the joints in the water chamber. Due to the impact of the water flow, ball jams are caused here, resulting in a reduction in the amount of balls passing through the cooling pipe and affecting the ball collection rate.
The upper part of the condenser water chamber is not full of water, and an air cavity is left, which causes the rubber ball to float on the upper part, which makes it difficult to recover the rubber ball. This often happens when the new unit is put into operation. Sometimes, because the water in the auxiliary water pipe of the condenser water chamber stands still and forms a "dead zone", the rubber ball may also accumulate there.
In addition, in the double-flow condenser, the gap between the cooling water inlet and outlet chambers and the end cap, or the connection with the tube sheet, often leaves a slit (string) due to inadvertent manufacturing or maintenance. The cooling water in the water inlet chamber will flow through the slit to the water outlet chamber, and this part of the water will be "short-circuited". When the rubber ball is circulated, a part of the rubber ball may flow into the slit with the cooling water, and may be caught in the slit. A steam turbine had stuck nearly a hundred balls here, but was found after several inspections.
The integrity of the cooling tube in the condenser and the length of the tube extending out of the tube sheet have an impact on the recovery of the rubber ball. If the cooling tube has a flat tube or a stern tube, the rubber ball will easily become blocked in these incomplete tubes, which will affect the recovery of the rubber ball. If the cooling tube extends too far from the tube sheet, it will easily form a dead zone and the rubber ball When running to this area, because the nozzle is too high, it cannot participate in the cycle smoothly, resulting in a reduction in the ball collection rate.
Impact of cleaning system management on cleaning results
The cleaning system of a general rubber ball cleaning device is qualified after the ball collection rate is adjusted to meet the specified requirements. However, some power plants do not have a person responsible for it, and there are no rules and regulations to follow. The cleaning system is not put into operation for a long period of time or the shutdown of the cleaning system is very arbitrary. There is no reliable basis, which causes scaling in the condenser cooling pipe. More serious, when the rubber ball cleaning system is put into operation again, it is easy to form rubber ball accumulation, which affects the ball collection rate, and the cleaning effect is also poor. For example, in a seawater cooling power plant, due to poor management of the rubber ball cleaning device, the device has not been put into operation for more than half a year, causing a large number of sea creatures to breed. The receiving net is covered with sea creatures, and the rubber ball circulation pipeline is almost blocked, resulting in rubber balls. Device does not work.
The rubber ball cleaning device of some power plants lacks routine maintenance, and it is found that the problems are not dealt with in a timely manner, and there is no random group inspection and simultaneous inspection. For example, the new rubber ball cleaning device of Taprogge Company installed on a 600 MWe unit of a power plant has also reduced the ball collection rate due to poor management. Then there are some operators who have not fully realized the rubber ball
The importance of cleaning, taking the cleaning system as a decoration, has not been carefully maintained and put into operation. For example, when pitching the ball, do not fully soak the rubber ball according to the requirements, so that the rubber ball floats on the upper part of the water chamber due to the low density during the cycle. Only the upper tube bundle of the condenser can be cleaned, which will have a cleaning effect. influences.