What is a thermal deaerator

What is a thermal deaerator?

Thermal deaerator (rotary membrane deaerator) is a new type of deaerator. It can remove dissolved oxygen and other gases in the feed water of thermal system and prevent the corrosion of thermal equipment. It is an important equipment to ensure the safe operation of power plant and industrial boiler.

20210920054058 13355 - What is a thermal deaerator

Thermal deaerator can be used for constant pressure, sliding pressure, negative pressure and other modes of operation. It has the characteristics of allowing high dissolved oxygen in inlet water, low inlet water temperature and large make-up water. It is suitable for deaeration of all kinds of power station boilers, industrial boiler feed water and make-up water of thermal power plant.

Advantages of thermal deaerator

  • 1. The deaeration efficiency is high, and the qualified rate of oxygen content in feed water is 100%. The oxygen content of feed water of atmospheric deaerator shall be less than 15% цɡ/50. The oxygen content of feed water of pressure deaerator shall be less than 7 цɡ/L.
  • 2. Stable operation without vibration. It can be applied to negative pressure start-up and sliding pressure operation, reducing the manual and complicated adjustment operation in start-up and operation.
  • 3. In addition to the advantages of good adaptability, no harsh requirements on water quality and water temperature, it can operate with a short-term output exceeding about 50%.
  • 4. Small steam exhaust and low energy consumption.

Structural principle of thermal deaerator

The structure of rotary membrane assisted deaerator is composed of deaerator head and water tank. The structure of deaerator head is composed of shell, rotating membrane unit, water grate, liquid steam network, steam distribution plate and steam water separator. The water tank is composed of main body and accessories.

  • 1. Shell: it is made of cylinder body and stamping oval head by welding.
  • 2. Membrane unit: it is composed of water chamber, membrane lifting pipe, condensate connecting pipe and make-up water connecting pipe. The materials of the film lifting pipe and the sewer pipe are made of stainless steel, which is also the main part of the rotary membrane deaerator without maintenance during perennial operation, and 98% of the oxygen is removed.
  • 3. Drenching grate: the feed water deaerated by the membrane section and the drain introduced by the drain pipe are reduced and distributed here for the second time, so that the water falls evenly in the form of rain, so as to protect the liquid vapor network at the lower part. The space area of the water grate shall not be less than 50% of the total section. It is of stainless steel structure and does not need maintenance for perennial operation.
  • 4. Packing liquid steam net: it is composed of mutually spaced flat steel strips and a cylinder, which is internally equipped with two layers of special O-type 0.3mm stainless steel flat wire net. The feed water is in full contact with the secondary steam, heated to the saturation temperature and deeply deaerated to ensure the content of deaerated water.
  • 5. Steam distribution plate: the main heating steam is connected from here. The regular evenly distributed structure can well ensure the heating quality and make the heating steam in an evenly distributed state. It rises to heat the demineralized water under no throttling condition to reach the working deaeration under saturation temperature.
  • 6. Steam water separator: the inner net is composed of stainless steel packing, and the shell is designed as a ventilation structure, which can effectively separate and return the steam with water during oxygen exhaust. It is an essential component for steam exhaust without water.
  • 7. Water tank: it is made by welding the cylinder body and the stamping oval head. A reinforcing ring is set inside. The base is fixed on the prefabricated workbench. One end is fixed and the other end is an expansion roller device. The water tank is equipped with maintenance manhole, safety valve nozzle, drain outlet, reboiler nozzle, water seal cylinder port, water level gauge interface, pressure gauge port, thermometer port, water inlet, etc.

Deaeration principle of thermal deaerator

In the container, the amount of gas dissolved in water is directly proportional to the partial pressure of gas on the water surface. The main method of thermal deaeration is adopted, that is, steam is used to heat the feed water and increase the water temperature, so that the partial pressure of steam on the water surface gradually increases, while the partial pressure of dissolved gas gradually decreases, and the gas dissolved in the water escapes continuously. When the water is heated to the boiling temperature under the corresponding pressure, the water surface is full of steam, and the partial pressure of dissolved gas is zero, Water no longer has the ability to dissolve gases, that is, gases dissolved in water, including oxygen, can be removed. On the one hand, the effect of deaeration depends on whether the feed water is added to the boiling temperature under the corresponding pressure, on the other hand, it depends on the removal rate of dissolved gas, which is closely related to the contact surface area of water and steam.

Working principle of rotary membrane deaerator (jet, entrainment, turbulence, heat and mass transfer, water film skirt, rain and saturation)

The condensate and make-up water first enter the water chamber of the internal rotating membrane unit of the deaerator head, and under a certain water level differential pressure, it is sprayed obliquely from the small hole of the membrane tube to the inner hole to form a jet. Because the inner hole is filled with rising heating steam, the water will suck in a large amount of heating steam during the jet movement (the test shows that the jet movement has the effect of entrainment); In a very short time and a very small stroke, it produces intense mixed heating, and the water temperature increases greatly, while the rotating water continues to rotate downward along the inner hole wall of the membrane tube to form a layer of rolling water film skirt (turbulent tumbling occurs when the critical Reynolds number of water decreases a lot during rotating flow). At this time, the heat and mass transfer effect of water in turbulent state is the most ideal, and the water temperature reaches the saturation temperature. Oxygen is separated. Because oxygen cannot diffuse freely in the inner hole, it can only be discharged to the atmosphere from the exhaust pipe with the rising steam. The feed water subjected to rough deaeration in the film lifting section and the drain introduced by the drain pipe are mixed here for secondary distribution, which falls into the liquid steam network installed under it in a uniform rain shape, and then flows into the water tank after deep deaeration. The oxygen content of water in the water tank is high pressure 0-7 цɡ/50. Low pressure less than 15 цɡ/L meet the operation standards issued by the Ministry.
Because the rotating membrane deaerator keeps the water in a turbulent state during operation and has a large enough heat exchange surface area, the better the heat and mass transfer effect, the smaller the steam exhaust volume (that is, the less the steam used and heated, the less the energy loss, and the considerable economic benefits) and the good deaeration effect. The surplus generated can make the deaerator overload operation (usually 50% of the rated output in a short time) Or fully replenish water at low water temperature to meet the operation standard.

Source: China Tube Sheet Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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