Vacuum pump for steam turbine

At present, 600MW Steam Turbines at home and abroad mostly adopt the combination of water ring vacuum pump and air ejector. The vacuum pumping system mainly includes sealing device of steam turbine, vacuum pump and corresponding valves, pipelines and other equipment and components. 

The vacuum pumping system of a 600 MW steam turbine unit in a power plant is as follows: the main exhaust pipe of the steam turbine condenser is connected to the air extraction system, and enters the vacuum pump through the valve, the ejector type air extractor and the check valve. In the water ring vacuum pump, the pressure of the gas is increased through the first and second stages of pressing, and then enters the gas water separator together with some sealing water. In the separator, water and gas are separated. Most of the gas is discharged to the atmosphere through the upper exhaust pipe. A small part of the gas enters the nozzle of the air ejector. At the outlet of the nozzle, this part of gas has certain kinetic energy; The water separated by the separator is led out from the lower pipe and sent to the cooler. After cooling, it is returned to the vacuum pump for recycling. 

The vacuum pumping system of the unit is equipped with two 100% water ring vacuum pumps. During start-up, two pumps are put into operation at the same time. In normal operation, one is in operation and the other is in standby.

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Lubrication and maintenance of vacuum pump

The vacuum pump in use will produce more or less friction, we need to constantly lubricate it to keep it in good working condition, and after use, we need to maintain it for a longer time. 

Under normal working conditions, the waste grease and its dirt in the bearing and accessory space should be removed and new grease should be added after the rotating speed is 20000 h or the longest 3 years. The additional grease should account for 50% of the bearing free space and 65% of the bearing cover space. If the working conditions are very bad, the grease change cycle should be shortened accordingly.

1. If hard water is used as working fluid, it can only be used after softening treatment, or the pump can be cleaned with solution within a certain period (in order to avoid abrasion of impeller, pump body or impeller jamming, dust particles entering pump cavity along with gas and working fluid shall be washed through the flushing port at the bottom of pump cover; if hard water is used as working fluid, hard water shall be softened or periodic solvent shall be used to flush vacuum pump ）。

2. The temperature of the bearing in normal operation of the motor is 15 ℃ - 20 ℃ higher than the surrounding temperature, and the maximum temperature is not allowed to exceed 55 ℃ - 60 ℃.

3. Always pay attention to check the running state of the vacuum pump and observe whether the rotation of the shaft and bearing is stable. In case of instability or jamming, the relevant parts shall be replaced and repaired immediately.

4. In case of leakage of the mechanical seal used, check whether the dynamic and static rings of the mechanical seal have been damaged, or the seal ring is aging. In case of the above situation, new parts need to be replaced.


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Roots vacuum unit operation

The operating safety and stability of Roots vacuum unit is high because the unit has the function of operation protection. Its operation protection function has many, the following vacuum pump to briefly introduce. 

Roots vacuum unit has more than 30 protection functions, including compressor overload, overheating, locked rotor protection; system high pressure, low pressure and differential pressure protection; evaporator water temperature too low protection, evaporator antifreeze protection, condenser water temperature too low protection, abnormal water flow protection.

There are also over-voltage, under voltage, three-phase imbalance, under reverse phase protection for the power supply to the unit from the client; and password protection function to prevent the unit failure caused by the wrong operation of the unauthorized person; at the same time, it has the power on self-test function to avoid the abnormal start-up of the unit; in addition, it has the condenser cleaning reminder function.

These operation protection functions make the use of Roots vacuum unit more convenient and safe. If you want to better use roots vacuum unit, you must do regular inspection and maintenance work to ensure the normal operation of Roots vacuum unit.

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Characteristics of high pumping speed of single stage rotary vane vacuum pump

Single stage rotary vane vacuum pump oil-free (corrosion-resistant) vertical reciprocating vacuum pump is an updated product of horizontal vacuum pump, and is the main equipment to obtain rough vacuum. Due to the full sealing device, the complete isolation between the crankcase and the cylinder is realized, and the self-lubricating material is used for the piston ring, so the advanced oil-free lubrication is realized. Since there is no sewage discharge, this type of vacuum pump is especially suitable for vacuum distillation, vacuum evaporation, vacuum drying, vacuum concentration and vacuum impregnation in chemical, pharmaceutical and food industries. 

During operation, driven by the motor, the piston in the cylinder moves reciprocally through the action of crank connecting rod mechanism (rotation movement changes into linear motion). When the piston moves from the left end to the right end of the cylinder, the volume of the left chamber of the cylinder is increasing, and the pressure of the left chamber space is continuously reduced. When the pressure in the left chamber space is lower than the pressure in the extracted container, according to the principle of gas pressure balance, the gas in the extracted container is continuously pumped into the left cavity through the suction valve 5, which is in the process of suction. When the piston reaches its rightmost position, the left chamber of the cylinder is filled with gas. Then the piston moves from the right end to the left end, and the suction valve 5 automatically closes. The gas is compressed as the piston moves from right to left. When the gas in the cylinder reaches the exhaust pressure, the exhaust valve 4 is opened and the gas is discharged to complete a working cycle. When the piston moves from the left end to the right end, repeat the above cycle until the extracted container reaches a certain equilibrium pressure.

Roots pump with relief valve is widely used in all aspects of vacuum acquisition. It extends the working range of mechanical vacuum pump with oil seal under low inlet pressure. It has the characteristics of small volume and large pumping speed. It has large pumping speed in the range of 1 ~ 100 Pa inlet pressure. It is especially suitable for the vacuum system which needs high pumping speed under low inlet pressure, such as power transformer, power capacitor, power capacitor, etc Vacuum drying, vacuum impregnation treatment, vacuum heat treatment, vacuum smelting exhaust, vacuum coating equipment pre pumping, large test wind tunnel exhaust and lighting lamp production line exhaust.

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Usage of centrifugal pump

The basic structure of centrifugal pump is composed of six parts: impeller, pump body, pump shaft, bearing, sealing ring and stuffing box. 

1. Impeller is the core part of centrifugal pump. It has high speed and high output. The blades on the impeller play an important role. The impeller should pass the static balance test before assembly. The inner and outer surface of impeller is required to be smooth to reduce the friction loss of water flow.

2. Pump body also known as pump shell, it is the main body of the pump. It plays a supporting and fixing role and is connected with the bracket for installing the bearing.

3. The function of the pump shaft is to connect the motor with the coupling, and transmit the torque of the motor to the impeller, so it is the main part of transferring mechanical energy.

4. The sliding bearing uses transparent oil as lubricant. Add oil to the oil level line. Too much oil will seep along the pump shaft, too little bearing will overheat and burn out, causing accidents! In the process of pump operation, the temperature of bearing is the highest at 85 degrees, and generally it is about 60 degrees.

5. Sealing ring is also called leakage reducing ring.

6. Stuffing box is mainly composed of packing, water sealing ring, packing barrel, packing gland and water sealing pipe. The function of the stuffing box is mainly to close the gap between the pump shell and the pump shaft, so as not to let the water flow in the pump to the outside, and also to prevent the outside air from entering the pump. Always keep the vacuum in the water pump! When the pump shaft and packing friction heat, rely on the water seal tube to hold water to the water seal ring to cool the packing! Keep the pump running normally. Therefore, in the process of circulating inspection of pump operation, the inspection of stuffing box should be paid special attention to! The packing should be replaced after 600 hours of operation.

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Vacuum system of pumping steam

In the process of vacuum impregnation, vacuum drying and vacuum freeze-drying, the gas extracted from the vacuum system is mainly steam and other condensable steam, and the working vacuum degree is mostly 10 ~ 10-1pa. In foreign countries, roots pump and oil seal mechanical pump are usually used for air extraction. For this reason, in recent years, the maximum inlet pressure of water vapor is the index of foreign oil sealed mechanical pumps (usually 103 ~ 3 × 103pa), while the domestic oil sealed mechanical pumps generally do not have this index. Moreover, the check function of some mechanical pumps equipped with air ballast valve is not strong, and the gas ballast effect is not obvious, which can not achieve the purpose of large amount of steam pumping, resulting in a large amount of steam condensation in the pump oil, Oil and water mixed to form white emulsion, reducing the sealing and lubricating performance of mechanical pump. The corrosion liquid will cause rust inside the pump body, and the rusty iron powder will fall into the oil and become reddish brown, and circulate in the pump together with the pump oil, which will have adverse effects on the service life and limit vacuum degree of the pump. 

(1) The steam jet pump is suitable for the vacuum system with large displacement, and the system needs to be equipped with working steam source.

(2) Oil booster pump + oil seal mechanical pump, the system is not suitable for the gas phase drying of transformer, especially in the oil booster pump, the naked electric furnace is strictly used, otherwise the open fire is easy to cause explosion accident.

(3) ZJ Roots pump + ZJ Roots pump + double stage water ring vacuum pump, the pumping system can obtain higher limit vacuum degree and larger displacement. However, the investment cost of the system is high, and it is easy for the working fluid of the water ring pump to flow back into the vacuum container, and the pumping efficiency of the water ring pump is low, and the unit power consumption is 50% higher than that of the slide valve pump. For example, various types of roots water ring vacuum unit.

(4) Slide valve pump + water ring pump or ZJ Roots pump + slide valve pump + water ring pump, because the slide valve pump is equipped with a front stage pump (water ring pump) in the system, so its compression ratio is reduced, so the water vapor is rarely condensed in the slide valve pump, but there is still a defect in Item 3.

(5) ZJ Roots pump + rotary vane vacuum pump is equipped with high-efficiency gas ballast valve, reliable oil-water separator and reasonable design of lubrication system, so that the system can operate continuously at the inlet steam pressure of 3000pa. This is an economical and reliable vacuum system for pumping steam abroad in recent years. For example, various types of rotary disc vacuum unit.

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Working principle of oil sealed vacuum pump

The mechanical vacuum pump, which uses vacuum pump oil to keep the seal of moving parts and realizes pumping by changing the volume of pump chamber, is called oil sealed mechanical vacuum pump. 

The working principle of oil sealed mechanical vacuum pump is to make the volume of pump chamber chamber increase and decrease mechanically and pump air. When the volume of the working chamber in the pump chamber becomes the minimum, it is connected with the inlet pipe of the pump, so the gas enters into the suction chamber of the pump until the volume of the suction chamber is maximum and is separated from the air inlet again. When the volume is reduced, the gas is compressed until the pressure of the gas is greater than one atmospheric pressure, and the exhaust valve is opened to discharge the gas. This completes the whole pumping process of oil sealed mechanical vacuum pump.

At present, a large number of mechanical vacuum pumps are widely used, even if the design is the best, the matching accuracy between parts moving in opposite direction is very high. When the pump reaches the limit vacuum, it is difficult to prevent the gas from the low vacuum end to the inlet end. In addition, due to the harmful space in the design, manufacture and assembly of the pump, it also reduces the limit vacuum degree of the pump.

Oil sealed mechanical vacuum pump is to seal the opposite moving parts and exhaust valve parts with oil to fill the harmful space, so that the chances of high-pressure gas reverse "breakthrough" are much less, and the sealing performance is much better, so that the pump can achieve a higher vacuum degree.

Oil sealed rotary mechanical vacuum pump can be divided into fixed plate vacuum pump, rotary vane vacuum pump, slide valve vacuum pump and cycloidal vacuum pump. At present, the mechanical vacuum pump with oil seal is the most widely used pump in domestic vacuum acquisition technology. It can be used as the exhaust pump of low vacuum equipment alone, or as the front stage vacuum pump for high vacuum exhaust. At present, rotary vane vacuum pump is the most popular mainstream product.

Therefore, it has been playing an increasingly important role in many sectors of the national economy, such as electric vacuum, electronics, light chemical industry, iron and steel, nonferrous smelting and other industrial sectors. As these pumps are equipped with gas ballast device, it can also pump out the wet gas. However, it is not suitable for pumping out gases with high oxygen content, explosive, corrosive to ferrous metal, chemical action on pump sealing oil, and gas containing particle dust.


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