water jet air ejector

1、 Application of the new water jet air extractor:
This product is the latest type of water jet air pump in China, belonging to the sixth generation of environmentally friendly and anti vibration type (noise less than 85 decibels). Used for vacuum suction of steam turbine units in thermal power plants and other equipment that requires vacuum suction. The water jet air pump designed and improved by Huaneng Company in 2015 is currently the most advanced type of water jet air pump in China. The new type of air extractor produced by our company has been widely promoted due to its advantages such as low power consumption, stable operation, and large air extraction margin. The sixth generation water jet air pump developed on this basis has an optimized water chamber diversion chamber structure, throat area ratio, irregular throat group, and optimal water jet kinetic energy, which makes the performance of the air pump at the leading technological level at home and abroad, with a unit power consumption as low as 1.5 kW/kg Qi.

2、 Design features of the new water jet air extractor:
1. Patent technology: In response to the erosion, cavitation, and perforation phenomena that are prone to occur in high flow velocity components such as the nozzle and contraction section of the water jet pump, our company adopts patented technology: surface melted microcrystalline material, with a surface smoothness of nanometer level and corrosion resistance.

2. Reasonable structural layout: In order to enhance the mixing process of gas water two-phase flow in the throat, the throat structure is divided into three parts: gas injection section, vortex enhancement section, and pressurization section. And optimized the geometric structure of the suction chamber, throat shape, throat diameter nozzle area, throat length to throat diameter ratio, etc. The suction chamber structure adopts a splitter chamber structure as the main channel and a combination of small holes as auxiliary channels, which effectively reduces air resistance and increases energy exchange between two-phase particles.
3. Utilization of residual energy: The new type of water jet air extractor is equipped with a residual air extractor at the end of the equipment. Based on the principle of high flow velocity at the end of the equal section throat and non-interference between the entire throat, this type of air extractor provides post suction for segmented extraction of the lower section and outlet of the throat, which is used to extract non condensable gas from the shaft seal heater of the steam turbine in different fields.
4. Material selection for air check valve:
According to the operational experience of multiple power plants, the copper alloy air check valve used with the water jet air extractor has poor corrosion resistance. Short term operation under poor water quality conditions may result in malfunctions such as loose closure, air leakage, and valve cover sticking and not returning to its original position. Our company will change the material of the air check valve used to high-quality stainless steel, which has the characteristics of sensitive reset and long service life.

5. Main performance characteristics:

a. There is no wear and tear of moving or stationary bodies, the lifespan loss is extremely low, the suction efficiency is not affected by operating time, and the maintenance interval is long.

b. The requirements for the quality concentration and volume concentration of impurities in working water are low.

c. Has good start-up capability.

d. Can achieve residual utilization: This type of air extractor is equipped with a rear mounted air extractor at the outlet of the throat pipe, which is used for extracting condensed gas from the shaft seal heater of the steam turbine field.

3、 Selection of pumping volume:
The number of air extractors for the condenser of a steam turbine unit is generally stipulated both domestically and internationally: for medium and small steam turbine units with a capacity of 25MW or less, one air extractor shall be installed per unit; For units with a capacity of 50MW and above, two extractors with 100% capacity each should be installed, one of which is a backup.

The capacity of the air extractor refers to the amount of air suction per hour. Its meaning is: when the working water temperature is 20 ℃ and the suction chamber pressure is 0.004MPa, the dry air weight flow rate G/H unit that can be suctioned per hour is kilograms per hour  
Choosing the appropriate capacity of a single exhaust fan is crucial for the safe and economical operation of the unit. If the capacity is too large, it will consume more power, while if the capacity is too small, it will affect the vacuum due to the suction volume being less than the amount of air present in the condenser. .

4、 Specification and model of water jet air extractor:

5、 Selection of matching water injection pump for new type of air extractor:

The design of a "low consumption and high-efficiency water jet air extractor" is the optimal configuration process for the structure, geometric dimensions, and working water parameters of the air extractor. In fact, every type of vacuum pump has its most economical water pressure value, and the definition of "economical water pressure" is:; The maximum vacuum that can be drawn by the vacuum pump when the water temperature is 0 ℃, the atmospheric pressure is 0.1MPa, and there is no air intake. ”In this case, the air extractor will achieve the designed suction capacity at the lowest power consumption.

We have chosen 0.35 MPa (gauge pressure) in front of the nozzle as the "economic water pressure" for the "TD type vacuum pump". The relationship between the pumping volume and water pressure of this type of air extractor is shown in the following equation:

        Gh=

       In the formula: Gh - suction volume, suction volume, kg/hour

---The water flow rate through the vacuum pump, in kilograms per hour;

K - Influence coefficient of water pressure on suction capacity

The TD type water jet air pump determines the inlet chamber pressure to be 0.35 MPa, and the known water consumption is 13 m3/kg gas. The water pumps of various types of air pumps can be selected based on this. The matching situation for domestically produced condensing units is shown in the table below.

TD type water jet air pump and water pump matching table:

                                                                                    Note: ① Outer diameter of impeller after turning is 340mm ② Outer diameter of impeller after turning is 350mm

      This new type of water jet air pump is suitable for single-stage double suction, horizontal split centrifugal pumps. The pump type is mainly selected as the "S" type. If a suitable model is missing, it should be selected from the "SH" pump type. Lianyungang Huaneng Electric Power can also turn the outer diameter of the impeller of certain units' pumps as shown in the table, and equip them with smaller capacity motors to further achieve energy-saving effects.

6、 Installation and precautions of water jet air extractor:

1. There are two water supply methods to choose from for the water jet air extractor

① Closed loop

This is the traditional arrangement method, where the water jet air pump is placed on top of the water jet tank, and the water is supplied in a cycle of water jet pump air pump water tank. A certain amount of water should be added to control the water temperature of the water jet tank used in summer.

② Open cycle

Open cycle "means that the water inlet of the water jet pump comes from the circulating water inlet pipe, and the drainage pipe is connected to the trench. Its advantages are: a. In summer, the water temperature can be reduced by 4 to 8 ℃, which can increase the vacuum by 7 to 15 mmHg; b、 The use of the residual air extractor will not affect the water temperature; c、 Avoiding power loss caused by over compression of exhaust gas, the disadvantage is that it increases the consumption of circulating water.

Before placing an order with our factory, it is best to determine in advance which cycle method to use, or we can entrust our factory to determine and install the design on behalf of the user.

2. Selection of inlet parameters

Selecting this series of low consumption and high-efficiency water jet air pumps according to regulations, including water pumps and motors, will achieve low consumption and high efficiency. The inlet parameters (flow rate, pressure) of the water jet air pump are crucial for improving the internal efficiency of the water jet and reducing power consumption. This is because the diameter and water pressure of the working water nozzle in the design determine the flow rate at the nozzle outlet. The flow rate is also related to factors such as jet angle, nozzle throat distance, area ratio, and throat length. Improper combination of water pump and air extractor will affect the effectiveness of use.

3. Precautions during installation:

The installation quality of the water jet air extractor is closely related to its suction capacity, and the following aspects should be noted:

① The installation of the air extractor should be vertical, and each section should be strictly aligned when combined. The support bracket should be stable.

② The installation height of the air extractor is appropriate, and for air extractors that use closed circulation, the other speed interfaces should be higher than the water surface by more than 1.5 meters. This low consumption and high-efficiency vacuum pump should not be buried too deep in water at the outlet due to the relatively small residual velocity at the outlet. Otherwise, it may affect the suction capacity when the water pressure is low or the water temperature rises in summer. The recommended depth for outlet management is 250-300mm. The supplementary cooling water for the air pump should be added to the inlet of the water pump to maximize its cooling effect.

③ The outlet pipe of the split type circulating water jet air pump should be as short as possible, with no more than one elbow, and a large radius elbow should be used. The horizontal section of the pipe should be inclined outward, with an inclination of more than 3/1000mm. When inserting the pipe into the circulating water outlet pipe, one elbow should be connected in the direction of the water outlet to facilitate the discharge of the gas water mixture.

④ For closed cycle air pumps, in summer, the lower mounted air pump should not be used. The structure of the water injection tank should be conducive to the discharge of air, and the above measures can help reduce the water temperature in the tank.

⑤ Before installing the vacuum pump body, a water pressure test with a pressure of 0.5MPa should be conducted, and there should be no leakage for five minutes.

⑥ When only one air extractor is installed on each machine, the air duct does not need to be too high; When installing two air extractors, in order to prevent water from flowing back into the condenser through the backup air extractor check valve, the height of the air connecting pipe should be ≥ 11 meters.

⑦ The diameter of the air inlet pipe of the air extractor is generally the same as that of the air outlet pipe of the condenser, and the length should be shortened as much as possible to reduce resistance; On the pipeline, flange connections are not used except for valves and equipment interfaces to reduce air leakage.

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