What is the general deaeration method used in hot water boilers?

Code for Boiler Room Design GB50041 2008

Atmospheric spray thermal deaerator should be used for deoxygenation of boiler feed water. The lower part of the deoxygenation water tank should be equipped with a steam pipe for reboiling.

When the water temperature after deaeration is not higher than 60, vacuum deaeration, analytical deaeration or other low-temperature deaeration systems can be used.

The deoxygenation of the make-up water of the hot water system can be deoxygenated by vacuum, analytical deoxygenation or chemical deoxygenation. When sodium sulfite is used to remove oxygen, the content of sodium sulfite in the pot water should be monitored.

The principle and approach of oxygen removal.

According to the law of gas dissolution: the solubility of any gas in water is related to the partial pressure and water temperature of this gas at the gas-water interface. According to the characteristics of oxygen, deoxygenation in water can be started from the following aspects:

1) Heat the water to reduce the solubility of oxygen, so that the oxygen in the water can escape;

2) Remove all oxygen molecules above the water surface or convert them into other gases. Since there are no oxygen molecules on the water surface, the partial pressure of oxygen is zero, the solubility of oxygen in the water is zero, and the oxygen in the water is constantly escaping;

3) The dissolved oxygen in the water is converted into compounds with metals or other agents before it enters the boiler and is consumed.

The commonly used deaeration methods for boiler feed water are: thermal deoxygenation, vacuum deoxygenation, desorption deoxygenation, steel scrap and dosing deoxygenation, sponge iron room temperature filter deoxygenation, etc.

Because it can corrode the boiler, the dissolved oxygen in the water drives the electrochemical corrosion reaction, which can cause severe oxygen corrosion in the boiler system. Therefore, the boiler feed water needs to be deaerated before it enters the boiler.

Deoxidation treatment can generally use physical methods, i.e., thermal deoxygenation. The feed water is heated and boiled with steam to remove the dissolved oxygen. When the water temperature is heated to 99, the dissolved oxygen in the water can be reduced to the following.

The principle of the boiler.

The main working principle of the boiler is a thermal equipment that uses the heat energy released after fuel combustion or the waste heat in industrial production to transfer to the water in the container, so that the water reaches the required temperature or a certain pressure of steam. The boiler is carried out in the "pot" and "furnace" parts at the same time, and after the water enters the boiler, the heat absorbed by the boiler is transferred to the water on the heating surface of the boiler in the steam-water system.

Hot water or steam is generated by heating water at a certain temperature and pressure, which is led out of the application. In the combustion equipment part, the fuel combustion continuously releases heat, and the high-temperature flue gas generated by combustion transmits the heat to the heating surface of the boiler through the propagation of heat, and the temperature itself gradually decreases, and finally discharges from the chimney.

The purpose of deoxygenation of boiler feed water is simple, that is, to prevent the oxidation reaction between the oxygen in the water and the metal on the heating surface. If the boiler feed water is not deoxygenated, the heating surface will be rapidly thinned after oxidation, resulting in safety accidents. It's as simple as that.

The main purpose of oxygen removal is to remove oxygen in the water, and the corrosive substances in the water, iron oxide, will enter the boiler to form iron scale, and the corroded iron scale will cause pits on the inner wall of the pipeline, and the resistance coefficient will increase. When the pipeline is seriously corroded, even a pipeline accident will occur. The state stipulates that steam boilers with an evaporation capacity of more than or equal to 2 tons per hour and hot water boilers with a water temperature greater than or equal to 95 must be deoxygenated.

At present, sponge iron is basically used for oxygen removal.

Summary. Pro, thermal deoxygenation: its principle is to heat the boiler feed water to the boiling point, so that the solubility of oxygen is reduced, the oxygen in the water continues to escape, and then the oxygen generated on the water surface is eliminated together with the water vapor, and various gases in the water (including free CO2, N2) can also be removed, such as the water treated by the ammonium sodium ion exchange method, 3 can also be removed after heating.

The deoxygenated water will not increase the salt content, nor will it increase the dissolved amount of other gases, the operation control is relatively easy, and the operation is stable and reliable, which is the most widely used deoxygenation method at present.

Why should boiler feed water be deoxygenated? What is the main way to remove oxygen in power plants? How does it work?

Dear, I'm very happy to defeat your question, why should the boiler feed water be deoxygenated? Help you find out: because when the lead of the water mass is in contact with the air, a part of the gas will be dissolved into the water, which will cause the boiler feed water to collapse and dissolve a certain volume of gas.

I hope mine can help you and I wish you good health and a happy mood!

Pro, thermal oxygen removal: its principle is to heat the water of the pot furnace to the boiling matter point, so that the solubility of oxygen is reduced, the oxygen in the water continues to escape, and then the oxygen generated on the water surface is eliminated together with the water vapor, and various gases in the water (including free CO2, N2) can also be removed, such as the water treated with ammonium sodium ion exchange method, 3 can also be removed after heating. The deoxygenated water will not increase the salt content, nor will it increase the dissolved amount of other gases, the operation control is relatively easy, and the transportation of the ant car is stable and reliable, which is the most widely used deoxygenation method at present.

Reason: If the boiler feed water contains oxygen, it will cause corrosion of the feed water pipes, boiler equipment and steam turbine flow parts, and the rotten skin corrosive iron oxide will enter the boiler, deposit or attach to the boiler tube wall and heating surface, forming iron scale with poor heat transfer that is difficult to melt. In addition, corrosion will cause pitting on the inner wall of the pipe, which will eventually lead to the shortening of the life of the stove equipment.

The most effective way to prevent the corrosion of boiler feed water is to remove dissolved oxygen and other gases in the water, which is called the deoxygenation of feed water, and the specific deaeration methods are: thermal deoxygenation, vacuum deoxygenation, steel scrap deoxygenation, sodium sulfite deoxygenation, hydrazine deoxygenation, analytical deoxygenation, resin deoxygenation, etc.

Oxygen corrosion is the most common and serious corrosion in boiler systems. Since the feed water is generally in contact with the atmosphere, the dissolved oxygen in the water is basically saturated, so the pipelines and equipment through which the feed water flows have the possibility of oxygen corrosion.

The form of oxygen corrosion is generally ulcer type corrosion and small hole type local corrosion, so the damage to the strength of metal components is very serious. According to the analysis of the causes of industrial boiler damage and scrapping accidents across the country, due to the poor deoxygenation of boiler feed water, which causes corrosion and damage, scrapping or pipe bursting accounts for a considerable proportion. Therefore, in order to eliminate the corrosion and harm of dissolved oxygen to the boiler water vapor system, the national standard stipulates:

For boilers with an evaporation capacity greater than 2t h, deoxygenation measures should be taken for the feed water, and the dissolved oxygen in the feed water should be controlled within a qualified range according to the different working pressures of the boiler.

At present, there are two main deaeration methods for boiler feed water: thermal deaeration and chemical deoxygenation.

What are the characteristics of thermal deoxygenation?

Thermal deoxygenation has the following characteristics:

The thermal deoxidation method can not only remove oxygen, but also remove gases such as C02, NH3, H2S, etc., and reduce the corrosive effect of these gases on the boiler water vapor system.

The oxygen removal effect is stable, which can reduce the oxygen content in the feed water to less than O 01mg l after oxygen removal, and promote the decomposition of bicarbonate in the water and reduce the total amount of carbonate compounds in the water.

Do not pollute the quality of the feed water.

It needs to be heated with steam and consumes a lot of money.

How does thermal deoxygenation work?

The atmosphere is mainly composed of nitrogen, oxygen, carbon dioxide, water vapor and a small amount of other gases, and atmospheric pressure is the sum of the partial pressures of the various gases that make up the atmosphere.

According to the law of gas dissolution (Henry's Law): the solubility of any gas in water is directly proportional to the partial pressure of that gas at the gas-water interface, regardless of atmospheric pressure. In other words, the dissolved oxygen content in the water is only related to the partial pressure of oxygen in the atmosphere, and the smaller the partial pressure of oxygen, the dissolved oxygen content in the water also tends to be close to zero.

When water is heated to boiling in the atmosphere, the saturated vapor pressure of the water is equal to the atmospheric pressure at the air-water interface, and the partial pressure of oxygen is equal to zero. At this time, the solubility of oxygen in the water drops sharply and is removed from the water, which is the principle of thermal deoxygenation.

This is because if the boiler feed water contains oxygen, it will corrode the feed pipes, boiler equipment and steam turbine flow parts, and shorten the life of the equipment. The most effective way to prevent corrosion is to remove dissolved oxygen from the water.

and other gases, this process is called deoxygenation of feed water.

A boiler is an energy conversion device, and the energy input to the boiler has the chemical energy in the fuel.

Electrical energy, the boiler outputs steam, high-temperature water, or organic heat carriers with a certain amount of thermal energy. The original meaning of pot refers to a container of water heated on a fire, and a furnace refers to a place where fuel is burned, and a boiler includes two parts: a pot and a furnace. The hot water or steam generated in the boiler can directly provide the heat energy required for industrial production and people's lives, and can also be converted into mechanical energy through steam power units.

Or the mechanical energy can be converted into electrical energy by means of a generator. The boiler that provides hot water is called a hot water boiler, which is mainly used in life, and there are also a small number of applications in industrial production. The boiler that produces steam is called a steam boiler, often referred to as a boiler for short, and is mostly used in thermal power stations.

Ships, locomotives and industrial and mining enterprises.

Because when the water is mixed with air or a certain gas, a part of the gas will be dissolved into the water, and the boiler water also dissolves a certain amount of gas, among which the most harmful gas in the dissolved gas in the feed water is oxygen, which causes oxidation and corrosion to the thermal equipment, and seriously affects the safe and economic operation of the power plant. In addition, the presence of gases in heat exchange equipment can also hinder heat transfer and reduce the heat transfer effect, so the boiler feed water must be deaerated.

Reason: If the boiler feed water contains oxygen, it will corrode the feed water pipes, boiler equipment and steam turbine flow parts, and the corrosive iron oxide will enter the boiler, deposit or adhere to the boiler tube wall and heating surface, forming iron scale with poor heat transfer. In addition, corrosion can cause pitting on the inner wall of the pipeline, which will eventually shorten the life of the equipment.

The most effective way to prevent the corrosion of boiler feed water is to remove dissolved oxygen and other gases in the water, this process is called the deaeration of feed water, and the specific deaeration methods are: thermal deoxygenation, vacuum deoxygenation, steel chip deoxygenation, sodium sulfite deoxygenation, hydrazine deoxygenation, analytical deoxygenation, resin deoxygenation, etc.

Because under high temperature and high pressure conditions, oxygen will react with the boiler liner, making the liner rust and brittle, which is more harmful.

The temperature of the deaerator does not have much effect on the boiler, only on the deoxygenation effect. When the deaerator is running under sliding pressure, the temperature is controlled at the saturation temperature, and the temperature changes with the pressure. When the deaerator is running at constant pressure, it shall be executed according to the parameters specified in the operation regulations.

Under normal circumstances, the water level of the deaerator is generally controlled between 1900-2300mm, and the regulations of each plant are slightly different. The low water level of the deaerator may cause the feed pump to not work properly. When the water level is high, it may cause water shock from the steam turbine.

Personally, I don't think it has much impact on the boiler, and if it is, it may affect the safety of the water on the boiler.

Effect of water temperature of deaerator on boiler.

Increasing the temperature of the deaerator to remove oxygen from the water can reduce the corrosion of dissolved oxygen to the equipment, and increasing the temperature of the boiler feed water by pumping the air from the steam turbine can improve the economic thermal efficiency of the system. In addition, if the drum wall temperature of the boiler is high, if the feed water temperature is low, it is equivalent to cooling the steam drum, as for the water level of the deaerator, I personally feel that it has no impact on the boiler, and the water level is controlled within the design range.