Chemical deaeration of feed water

Sponge iron is a new type of deoxidizer that has been successfully developed in the past decade based on the deoxidation of iron filings. The principles and equipment of sponge iron deoxidation and iron chip deoxidation are basically the same, but sponge iron is more convenient and has a much better deoxidation effect than iron chips. Currently, hot water boilers and small boilers are more commonly used for deoxidation.

Sponge iron is made of low-carbon steel and undergoes special processing because it has a porous, mesh like, thick and loose structure like a sponge. It is called sponge iron, and its surface is much larger than iron filings, reaching over 80 square meters per gram, with a particle size diameter of 1.0-5.0 millimeters, a bulk density of 1.79g/cm, and a total iron content of over 95%. It also contains a certain amount of loosening agent, boosters, and other components.

(1) Deoxygenation principle of sponge gland

When water containing dissolved oxygen passes through a sponge like iron filter, the dissolved oxygen in the water undergoes an oxidation-reduction reaction with the sponge like iron, thereby removing dissolved oxygen from the water. The chemical reaction is as follows:

2fe+2H2O+O2=2fe（OH）2

2fe（OH）2+H2O+1/2O2=2fe（OH）3

Reaction generator Fe (OH); For soft cotton, when it accumulates to a certain extent, it is washed by backwashing, which also restores the sponge iron to its original deoxidation ability.

(2) Sponge iron deficiency deoxidizer structure

The design of sponge iron deficiency deaerator is similar to the structure of ordinary mechanical filters, except that in order to increase the backwash strength, some cylinders are divided into two chambers and backwash processes are carried out separately.

In order to facilitate the loading and unloading of sponge iron, loading and unloading holes or holes should be installed on the upper and lower parts of the cylinder to prevent corrosion of the cylinder body. When using a steel structure, the internal treatment should be anti-corrosion or made of stainless steel.

(3) Factors affecting sponge iron deoxidation

(1) The higher the water temperature, the faster the oxidation-reduction reaction and the better the deoxidation effect. However, due to the large surface area ratio of sponge iron, even low-temperature water entering the deoxidant can achieve good deoxidation effect.

The longer the contact time between water and sponge iron, the better the deoxidation effect. The contact time between water and sponge iron is ultimately reflected in the flow rate, and the flow rate at room temperature should be controlled between 15 and 20 meters per hour.

(3) Oxygen containing water can better purify oxygen in water. Unsoftened water quality can slow down oxidation and reduction processes, and affect deoxygenation efficiency.

(4) Preventive measures

The height of sponge iron filling is generally 1.1-1.2 meters. If it is less than 0.8 meters, filters should be added in a timely manner to ensure that the sponge iron filling heights of the two chambers in the cylinder are equal.

When the pressure difference between the inlet and outlet water is ≥ 0.05 MPa, the backwash process must be carried out, and the backwash flow rate is usually about twice the inlet water flow rate (40m/h).

(3) Before the new equipment or device is put into operation on sponge iron, the filter must be thoroughly cleaned before production.

When the deaerator stops working when the equipment is shut down, the sponge iron should be cleaned to ensure insulation inside the cylinder and keep it under air.

(5) The applicable sponge iron deoxidation method is fully suitable for hot water boilers and steam boilers, as the deoxidation water contains some iron ions with an iron content exceeding 0.3mg/l. Conventional sodium ion exchangers and other iron removal devices should be added after the sponge iron deoxidation machine. Na2SO3 and NaCl (2%) can be regenerated after resin failure.

When dealing with deoxygenated water in a deoxygenated water tank, such as when entering an open deoxygenated water tank, the water level in the tank must be sealed with a plastic float ball.