The problem of boiler corrosion has always been bothering customers. How to solve the problem of boiler corrosion has become an important issue. Currently, there are many ways to solve this problem, including adding scale inhibitors to the boiler, deoxygenating the boiler feed water, etc. Among them, deoxygenating the boiler feed water requires special equipment. Let’s introduce the boiler supporting auxiliary equipment: thermal deaerator .

Thermal Deaerator Working Principle

Oxygen removal mechanism:

The thermal deaerator mainly uses boiler steam to heat the feed water to remove oxygen from the water, thereby solving the problem of corrosion of the water supply system and boiler tubes caused by dissolved oxygen in the water.

Principle of oxygen removal:

The basic principle of the thermal deaerator is based on the dissolved gas law (Henry's law); the solubility of a gas in water is proportional to the partial pressure of the gas at the steam-water interface and has nothing to do with the atmospheric pressure. When water is heated to boiling in the atmosphere , the saturation pressure of water is equal to the atmospheric pressure at the steam-water interface, and the partial pressure of oxygen is zero. 

At this time, the dissolved amount of oxygen in water is zero. Thermal deaeration is based on this principle. The steam is passed through the deaerator to heat the water to be deoxygenated to the saturation temperature under the corresponding pressure (that is, the boiling temperature of the water), so that the gas dissolved in the water is precipitated and mixed with the remaining gas. Discharge the deaerator to achieve the purpose of removing oxygen from the water (oxygen content <15 ug/L). Generally, medium and high-pressure boilers use thermal deaeration as the main method, supplemented by chemical deaeration. Low-pressure boilers can use thermal deaeration or chemical deaeration.

Thermal Deaerator Structure and composition

Thermal deaerator is divided into two parts: deaerator head and water tank

(1) Deaerator head

The function of oxygen removal head：

1. Divide the deoxygenated water into small water flows or water droplets to form a larger steam-water interface, which is conducive to the normal progress of the heating of water and the precipitation of dissolved oxygen from water.

2. Heat the water to the saturation temperature under atmospheric pressure and maintain sufficient boiling time.

3. Timely and effectively eliminate the gas separated from the water and reduce the partial pressure of the gas in the steam-water mixture.

4. The thermal deaerator has a spray-packing structure. The deaerator head is composed of a nozzle and a filler. The deaerator water is sprayed upward through the nozzle in the form of extremely fine water droplets, and conducts preliminary heat exchange with the heating steam in the upper part of the tower, and then falls into the Filling layer. The water is divided into a very thin water film in the filler layer. During the downward flow, the water film again exchanges heat with the steam entering from the bottom, so that the water reaches the saturation temperature under the working pressure, thereby achieving deoxygenation of the water.

(2) Water tank

The function of the water tank is to store a certain amount of deaerated water to protect the water demand of the boiler. In order to enhance the deaeration effect, a steam pipe is installed in the deaerator water tank to send higher-pressure steam to make the water in the water tank It has always maintained a boiling state. This device is a reboiling device. The functions of this device are:

1. Keep the water temperature in the water tank always boiling and keep the dissolved oxygen content in the water low.

2. It can promote the decomposition of bicarbonate in water to reduce the total content of carbon compounds in water. The steam consumption for reboiling is generally 10%-20% of the steam consumption for deaerator heating, while the overall heating consumption of the deaerator is generally about 20% of the steam production of the boiler.

Main Technical Parameters Table

 Installation Method:

1. When the thermal deaerator is installed at a high position, it should be placed above the feed water pump. The height difference between the lowest water level of the deaeration water tank and the center line of the feed water pump should be no less than 6 to 7 meters.

2. The mixing temperature of the feed water before entering the deaerator is generally not lower than 40°C.

3. The reliable operation of the thermal deaerator is only possible when the pressure and temperature of the deaerator and the water level in the deaerator tank are automatically adjusted.

4. When replenishing a large amount of relatively cold chemically treated water, it should be fed in as evenly as possible. Before the steam condensed water is sent to the deaerator, it is best to accumulate it in the intermediate water storage tank, and then send the condensed water evenly into the deaerator. Deaerator to ensure the stability of the deaerator load.

5. The deaerator device should have the following control measuring instruments: a pressure gauge for monitoring the steam pressure in the deaeration head, a pressure gauge and a temperature gauge before and after decompression of the steam pipe, a glass water level gauge on the deaeration water tank, a Thermometers on water pipes and outlet pipes.

6. It is best to use an oxygen meter to automatically monitor water quality. In the absence of an oxygen meter, in order to supervise the work of the deaerator, install a water temperature or pressure recording meter.

7. When two deaerators are running in parallel, in order to balance the pressure and water level in the deaerator, each deaerator water tank must have a steam and water balance pipe that can be connected.

Installation Precautions:

1. When the hot water temperature of the deaerator outlet is higher than the allowable water temperature at the entrance of the boiler feed water pump and boiler water replenishment constant pressure pump, and the height of the boiler room civil structure cannot meet the height difference requirements, the steam boiler feed water pump and hot water boiler replenishment pressure may be affected. Vaporization (cavitation) may occur at the pump inlet and the water pump may not work properly. A water-water heat exchange device can be installed between the softened water pump (condensate water pump) and the deaerator. The first is to increase the temperature of the inlet water of the deaerator and make the working condition of the deaerator stable. The second is to reduce the temperature of the hot water coming out of the deaerator so that vaporization does not occur at the entrances of the steam boiler feed water pump and the hot water boiler water replenishment constant pressure pump ( cavitation) phenomenon.

2. When the installation conditions cannot meet the high-level arrangement, you can make concessions for low-level installation, but the steam boiler feed water pump and the hot water boiler water replenishment constant pressure pump must be installed as anti-cavitation pumps.

Operation Instructions:

1. First, calibrate the pressure gauge, temperature gauge, safety valve (trip pressure 0.022Mpa) and other control instruments until they are qualified.

2. Start the soft water pump, feed water from the supply water inlet, stop the pump after the liquid level in the deaerator water tank is normal, and open the reboiling steam valve to make the water temperature in the water tank reach 100°C.

3. Open the deaeration overhead exhaust valve (one-quarter to one-half opening) and open the soft water and steam valves respectively. When the safety water seal overflows and the water temperature reaches 104°C, open the water outlet valve and start the boiler feed water pump at the same time ( If the boiler is not yet in operation, all feed water will return to the deaeration water tank through the water pump and valve) cycle test.

4. After the above manual operations are checked and everything is normal, open the steam and condensate inlet valves and the boiler feed water valve and put them into normal operation.

5. The normal operation of the boiler deaerator requires condensate water. When the condensate water is insufficient, soft water can be used to replenish it.

6. If the user needs to use automatic control, install relevant control instruments according to the requirements of the system diagram. After completing the above procedures 1 to 3, it will switch to automatic operation.

7. When the deaerator is out of service, the internal water should be drained.

How to Choose the Right Thermal Deaerator?

At present, the application range of thermal deaerators is getting wider and wider, and there are many varieties of deaerators on the market. When choosing a deaerator, you should pay attention to:

Determine the type and specifications of the deaerator

Determine the type and specifications of the deaerator based on actual needs and equipment limitations, including equipment materials, working pressure, working temperature, deaeration efficiency and other parameters.

Pay attention to the safety of the deaerator

 As a special equipment, the deaerator must pay attention to its safety. During the customization process, qualified manufacturers should be selected to ensure that the quality and safety of the equipment meet standard requirements.

Consider the repairability of the deaerator

The repairability of the equipment is also one of the factors that needs to be considered. During the customization process, consideration should be given to whether the equipment is easy to disassemble, maintain, and replace wearing parts so that it can be repaired in time when problems occur with the equipment.

Determine the energy efficiency of the deaerator

Energy efficiency is one of the important indicators of deaerator performance. During the customization process, equipment with high energy efficiency and low energy consumption should be selected to reduce operating costs.

Consider the environmental performance of the deaerator

During the customization process, the environmental performance of the equipment should also be considered. Equipment with low noise and low emissions should be selected to reduce environmental pollution.

Determine the appearance and installation dimensions of the deaerator

During the customization process, the appearance and installation dimensions of the device should also be considered. Equipment should be selected that has a beautiful appearance and is compact so that it can be easily used with the boiler and other auxiliary equipment during on-site installation.

In short, customizing boiler deaerators requires determining the type and specifications of the equipment based on actual needs and equipment limitations, and paying attention to issues such as its safety, maintainability, energy efficiency, environmental performance, appearance, and installation size. Only in this way can we customize an efficient, safe and reliable boiler deaerator that meets actual needs.

Conclusion

Setting up suitable deoxidation facilities in the boiler room to remove dissolved oxygen from the boiler feed water is an indispensable means to protect the economic operation of the thermal system equipment. Oxygen dissolved in water is an important factor causing boiler corrosion. Tests have confirmed that the corrosion rate is closely related to the oxygen content in the solution. Therefore, in order to prevent the boiler from affecting the service life of the boiler due to corrosion, the deaerator has become an essential boiler auxiliary equipment.