At which stage of the water treatment process is the boiler deaerator located? Complete process analysis

Boiler water treatment is the core process that ensures the safe and stable operation of thermal equipment. The complete process includes multiple modules such as pretreatment, softening and desalination, deoxygenation treatment, furnace conditioning, and condensate return water maintenance. Many operation and maintenance personnel are prone to confusionDeoxidizerThe addition nodes and process positioning are unclear about their role and logic in the entire water treatment system. In fact, boiler deoxygenation agent belongs to the anti-corrosion process of water supply precision treatment. It connects physical deoxygenation with boiler furnace conditioning, and is a key process for controlling dissolved oxygen in water supply and suppressing pipeline and equipment corrosion. This article combines the standard process flow of industrial boilers to provide a detailed breakdown of the process location, dosing scenarios, supporting functions, and process value of deoxidizers.

1、 Complete boiler water treatment process flow (clarify hierarchical relationships)

To accurately locate the deoxygenation agent process, it is necessary to first clarify the sequence of the entire boiler water treatment. The industry standard process is as follows:

Raw water pretreatment → softening/reverse osmosis desalination treatment → thermal deoxygenation (physical deoxygenation) → chemical deoxygenation agent addition (fine deoxygenation) → water supply pipeline transportation → economizer → boiler drum → furnace chemical conditioning → condensate return water recovery

From the process, it can be clearly seen that the boiler deoxygenation agent does not belong to the front-end pretreatment, softening and filtration process, nor does it belong to the back-end furnace anti scaling and conditioning process. Instead, it is a deep precision treatment process for the feedwater after physical deoxygenation, specifically used to eliminate trace amounts of dissolved oxygen remaining in physical deoxygenation and fill the gaps in anti-corrosion.

2、 Accurate process positioning of deoxidizer: supplementary precision treatment of physical deoxygenation

1. Process connection logic

The commonly used rotary film and vacuum thermal deoxygenation equipment in industrial boilers can remove most of the dissolved oxygen in water. However, due to equipment operating conditions, water temperature, and pressure fluctuations, trace amounts of dissolved oxygen may still remain in the effluent, which cannot fully meet the water quality standards of medium and high pressure boilers and continuous operation boilers. If residual oxygen enters the subsequent pipelines and furnace body, it will continue to cause metal oxidation, pitting corrosion, thinning of the pipe wall, and long-term operation is prone to equipment failure.

The core function of boiler deoxygenation agent is to undertake the final work after thermal deoxygenation, deeply remove residual dissolved oxygen through chemical reactions, and form a passivation protective film on the metal inner wall of the pipeline. It belongs to the anti-corrosion finishing process of the water supply end and is a supplementary process that cannot be replaced by physical deoxygenation.

2. Standard investment point position (industry standard)

There are clear process specifications for the addition of deoxygenation agents, and physical deoxygenation equipment outlets and front-end pipelines at the inlet of feed pumps are preferred. Some small boilers can be added to the deoxygenation water tank and condensate water tank

-Mainstream injection points: at the outlet end of the thermal deaerator and the inlet pipeline of the feed water pump, where the water flow is stable and the water temperature is suitable for the reaction conditions of the reagent, the reagent can be fully mixed with the water body, and the deoxygenation effect is uniform and stable;

-Small boiler adaptation point: Low pressure small boilers without thermal deoxygenation equipment are directly added to the supply water tank and condensate return water tank as the core process of chemical deoxygenation throughout the process;

-Prohibited addition location: Do not add it inside the furnace, at the steam outlet, or at the end of the return water, as it cannot achieve pre corrosion protection and may cause waste of chemicals and water quality fluctuations.

3、 The difference between the deoxidizer process and other water treatment processes

1. Different from softening and pre-processing steps

The core goal of pre-treatment and softening processes is to remove sediment, impurities, calcium and magnesium ions from water, reduce water hardness, and prevent boiler scaling; The deoxidizer stage focuses on removing dissolved oxygen and inhibiting metal corrosion, and their treatment goals and principles of action are completely different and cannot be replaced by each other.

2. Different from the scale inhibition and conditioning process inside the furnace

The main functions of the reagents such as trisodium phosphate and scale inhibitors added to the furnace are to adjust the water quality, disperse scale, and regulate the pH value of the furnace water; Deoxidizer acts on the water supply stage to prevent oxygen from entering the furnace body from the source, and to prevent oxidation and corrosion of pipelines, economizers, and furnace walls in advance. It belongs to the pre corrosion prevention process and complements the furnace quenching and tempering process.

3. Different from physical thermal deoxygenation

Thermal deoxygenation relies on physical methods such as temperature rise and pressure drop to remove oxygen, with a large processing capacity but residual dead corners; Deoxidizers rely on chemical reactions to deeply remove oxygen, adapt to trace oxygen removal, and have metal passivation function. The combination of the two forms a standard combination process of "physical crude deoxygenation+chemical precision deoxygenation", which is suitable for the operation needs of various industrial boilers.

4DeoxidizerThe core process value of each link

As a key process in water treatment, the addition of deaerator is an important link to ensure the long-term stable operation of the boiler system, and its core value is reflected in three points:

Deep oxygen control to prevent hidden corrosion: remove trace amounts of dissolved oxygen from thermal deoxygenation residues, avoid oxidation pitting and rust peeling on the inner walls of economizers, water supply pipelines, and boilers, and reduce equipment wear and tear;

Metal passivation, long-term protection: compliant deoxidizers can form a dense protective film on the metal pipe wall, isolating water from metal contact, reducing the probability of subsequent corrosion, and extending the service life of pipelines and boiler equipment;

Stabilize water quality and adapt to working conditions: adapt to special working conditions such as boiler start stop, load fluctuations, and unstable water temperature and pressure, compensate for the performance shortcomings of physical deoxygenation, and ensure that the dissolved oxygen index of the feedwater continues to meet the standard.

5、 Logical combination of deoxygenation processes under different boiler operating conditions

1. Medium and high pressure industrial boilers

Adopting a dual process combination of "thermal deoxygenation+deoxygenation agent precision deoxygenation", strictly controlling the dissolved oxygen content in the feedwater, adapting to continuous high load operating conditions, and avoiding the risk of accelerated corrosion under high pressure conditions.

2. Low pressure small boilers and gas boilers

Most of them do not have supporting thermal deoxygenation equipment, and the addition of deoxygenating agent becomes the core deoxygenation process. Through the entire process of chemical deoxygenation, the water quality is guaranteed to be qualified, meeting the daily anti-corrosion needs of operation.

3. Condensation recovery system boiler

Condensed return water is prone to air mixing and the growth of dissolved oxygen. It is necessary to add a deoxygenation agent at the return water end to block the accumulation of oxygen circulation and avoid secondary corrosion of the equipment.

summary

In the entire boiler water treatment process,DeoxidizerThe water treatment stage, which is located after softening and desalination and before furnace conditioning, is a deep supplement to the physical deoxygenation process. Its core function is not to purify water and prevent scaling, but to remove residual dissolved oxygen and passivate metal pipelines in advance, preventing and controlling boiler and pipeline corrosion from the source. During the operation and maintenance process, controlling the feeding nodes and dosage of deoxygenation agents, combined with a complete water treatment process, can effectively stabilize boiler water quality, reduce equipment failure rates and operation and maintenance costs.