Reliability and Failure Analysis of Equipment Engineering in China Causes and Preventive Measures for the Decrease of Condenser Vacuum Degree Chen Zhongjian (Yunfu Sulfuric Acid Plant, Yunfu 527500, Guangdong, China) poses a great threat. This article summarizes various fault phenomena; analyzes the causes of failure from six aspects such as interruption of circulating water or lack of water, rise of condensing water level, and abnormal operation of the aspirator; proposed governance and prevention measures, and this experience also applies to other similar unit.
The degree of exhaust vacuum plays an important role in the normal operation of the steam turbine. The decrease of vacuum degree will increase the steam consumption of steam turbines and the degree of reaction of the last stages of blades and increase the axial thrust. As the exhaust temperature increases, it will cause the center of rotation of the turbine rotor to drift and cause vibration, and even cause the deformation of the cylinder. Increased dynamic and static clearances. If the fault is caused by insufficient cold water, it will also cause the copper tube to overheat and cause vibration and rupture, shortening the life of the condenser. Our factory uses two turbines of CN 1.5-35/5 pumping condensing type and one N3-35 pure condensing turbine produced by the reason of the turbine; The declining phenomenon poses a great threat to the normal operation of the steam turbine. We have summed up many experiences and lessons in our work. We now analyze the causes of the failures and propose solutions and preventive measures.
First, the failure phenomenon When the vacuum degree drops seriously, the air exhaust valve moves.
The inverse relationship, that is to say the conclusion, is that the length of the valve catheter is inversely proportional to the force acting on the valve guide tube by the valve stem. This can in principle explain why engine oil is associated with valve guides, which is why some engines frequently replace valves and valve guides.
Third, the short valve guide tube makes it easier for the valve stem and the valve guide tube to have larger clearances. As the length of the valve guide tube decreases, the lateral force of the valve relative to the valve guide tube increases. Therefore, the clearance between the valve rod and the valve guide tube will increase. Rapidly increasing, oil penetrates from the valve guide into the combustion chamber and the engine burns oil early.
At the same time, the expansion of the gap makes the valve guide tube lose its precise guide effect to the valve valve. When the valve is dropped, it is difficult to accurately and accurately contact the valve seat ring quickly, so the sealing effect is not good. Moreover, the excessively large fitting gap will cause the valve stem to generate a yaw oscillation during operation, resulting in a decrease in the oil blocking effect between the valve stem and the conduit oil seal, and leakage of the oil into the intake and exhaust passages. Therefore, excessive valve stems and valve guide clearances are one of the main causes of engine power loss and burning of oil.
This also shows that appropriate lengthening of the valve guide length can extend the service life of the guide tube and the engine.
Through the above analysis, we can know that the length of the valve guide tube in a certain sense determines the service life of the guide tube and the engine. This principle can be used to properly lengthen the length of the valve guide during maintenance of certain improved engines to prolong the life of the valve guide and the engine, and at the same time reduce the frequency of maintenance of the vehicle engine, thereby reducing maintenance costs.
Reliability and Failure Analysis When the vacuum degree gradually decreases, the temperature difference between the inlet and outlet of the circulating water increases.
Exhaust steam temperature and circulating water outlet temperature increase.
The fluid resistance in the condenser and the condenser increases.
The aspirator draws steam and the air mixture temperature increases.
Recycled water is interrupted or there is insufficient water. This failure was mainly due to the failure of the circulating water pump, the interruption of the pump power supply, and the blockage of the tube plates and copper pipes in the condenser.
Condensation level rises. The main reasons are: (1) Condensate pump failure, flow rate reduction; (2) Copper tube in the condenser breaks; (3) Damage to backup condensate pump check valve, backflow from the back-up pump to the condenser; (4) During normal operation Recirculation valve opens large.
The aspirator is not working properly. Mainly related to the following aspects: (1) lack of cooling water; (2) leakage of the tube plate or partition in the cooler, which causes some condensed water to be short-circuited out of the cooler without passing through the tube bundle; The vaporizer is filled with steam condensate; (3) The cooling water pipe bursts or the tube plate expands, relaxes, or the hydrophobic tube fails, causing the water in the aspirator to be ejected from the aspirator exhaust pipe; (4) before the aspirator is steamed Damage to the filter, causing nozzle clogging, wear, corrosion, or salt accumulation in the nozzle passages, which will worsen the work of the aspirator; (5) Exhaust pump overload will degrade the working efficiency, generally due to a large amount of air leaking into the system. This is caused, in addition, when the first-stage air extractor draws steam-side air into the condenser due to a failure of the water seal or the steam trap. (6) When the steam parameter changes, its steam pressure is not adjusted in time.
Cooling of copper tubes in the condenser. Due to poor circulating water quality, a layer of soft organic scale or inorganic hard scale was deposited on the inner wall of the copper tube, which seriously reduced the heat transfer capacity of the copper tube and reduced the flow area of ​​the copper tube.
The vacuum system is not tight and the leakage increases.
Reduced load or air pressure, failure to timely adjust shaft seal failure.
When the vacuum level drops, the circulating water temperature increases, the condenser discharge pressure decreases, and the circulating water volume decreases, the following treatment should be performed.
(1) Open the large cooling water inlet valve and, if necessary, increase the circulating pump; (2) If the circulating water pipe or copper pipe leaks or plugs, it should be eliminated. If it is serious, it should be shut down.
During the operation of the steam turbine, the vacuum degree drops sharply, the inlet pressure of the condenser drops sharply, indicating that the circulating water is interrupted, and the following treatment should be performed.
(1) Start the backup circulating water pump and reduce the load of the unit at the same time; (2) Start the auxiliary air extractor; (3) The vacuum degree drops to 60kP-, the circulating water does not recover, and it should be shut down; (4) The steam turbine is in the process of picking up If the circulating water has recovered, even if the temperature of the exhaust gas does not exceed 120°C, the water cannot be sent to the condenser immediately, and the water can not be sent to the condenser until the temperature of the exhaust gas drops below 50°C.
If other equipment is abnormal or damaged, and the pressure of the condenser and the load change cause the vacuum of the condenser to drop, the following treatment should be performed.
(1) When the load and air pressure change, the steam pressure of the air extractor should be adjusted accordingly; (2) Try to restore the normal operation of the condensate pump; if necessary, start the auxiliary air extractor; (3) Restore the normal work of the condensate pump and check the condensate water Conductivity; (4) Try to eliminate the leak point of the vacuum system.
IV. Preventive measures against the decrease of the vacuum degree In order to ensure the heat transfer capacity of the copper tube in the condenser, the quality of the circulating water should be strictly controlled. Generally, the Ca2+ and hardness of the circulating water are not more than three times that of the tap water. No special circumstances, usually a major overhaul in one year, put the water inside the condenser to vent, uncover the two end caps, brush all the inner wall of the copper pipe, and wash all the dirt with water.
Strengthen the monitoring of circulating water inlet and outlet temperature, pressure and exhaust temperature.
Air extractor and condenser leak test. When empty load is running, close the air valve between the condenser and the air extractor to make the vapor pressure of the two-stage air extractor reach the rated value, record whether the vacuum level of the first stage is close to 100% vacuum normally, the vacuum degree per minute. Whether the drop number is in the normal range of 400~933Pa, the vacuum degree during the test can't be lower than 66.66kPa. If the vacuum degree drops sharply, it should be checked for shutdown.
When the cylinder overhauls the paint on the scraping joint surface, it is first poured with kerosene to make it saturate, and then the shovel is cleaned with a blade made of carbon steel. When the shovel should be along the direction of the cylinder joint surface, not allowed to scrape against the inside of the cylinder; must not scrape the metal surface of the joint surface, so as not to damage the tightness of the cylinder joint surface and cause leakage.
By analyzing, processing and adopting effective preventive measures for the reasons for the above-mentioned lowering of the degree of vacuum of the condenser exhaust gas, the turbine unit of our plant has not been involved in accidents for many years, and the fouling of the condenser has been effectively controlled due to the effective control of the circulating water quality. The degree is greatly reduced, and the cooling effect is improved. The vacuum degree of the exhaust gas is between 93.32 and 96.65 kP-, so that the enthalpy in the steam is utilized as much as possible to generate electricity. The enterprise has received good economic benefits.
Ningbo Senmiao Trading Co., Ltd. , https://www.senmiaowasher.com