What is the correct way to add boiler deaerator?

Dissolved oxygen in water is the main cause of oxygen corrosion in boiler feedwater pipelines, economizers, and steam drums.Boiler deoxygenation agentWhether the dosing method is standardized and commonly used as a supporting means of thermal deoxygenation or an independent chemical deoxygenation scheme directly affects the deoxygenation effect, chemical utilization rate, and long-term operational stability of the boiler. Many on-site operation and maintenance personnel have problems such as improper selection of dosing points, arbitrary dispensing processes, and imbalanced control of dosage, which can easily lead to inadequate deoxygenation, waste of chemicals, and secondary water quality issues. This article systematically outlines the standardized dosing process, point selection, dosage control, and operational control points of boiler deoxygenation agents.

1、 Preparation Specification for Pre dosing Medication

Deoxidizers on the market are divided into two categories: liquid finished products and solid powders. The preparation process is the foundation, and improper preparation can cause the drug to fail prematurely.

Selection of dilution water source

Priority should be given to using boiler desalinated water and softened water for dilution, and the direct use of untreated raw water is prohibited. Raw water contains dissolved oxygen inside, which will consume deoxygenated components in advance and reduce the concentration of effective chemicals.

Reasonably control the dilution concentration

Liquid deoxidizer: can be moderately diluted under low dosage conditions, facilitating stable delivery by the metering pump; The concentration of the drug should not be excessively diluted to avoid excessive solution volume.

Solid deoxidizer (sodium sulfite, carbazide, etc.): Slowly add it to the mixing tank in stages, stir thoroughly until completely dissolved, filter and remove insoluble impurities to prevent blockage of the metering pump pipeline. The concentration of the conventional preparation is controlled within the range of 2% to 10%, and adjusted according to the measuring range of the metering pump.

Solution storage protection

The dispensing box should be kept sealed as much as possible to reduce extensive contact between the medication solution and air. Reductive deoxygenation agents are prone to react with oxygen in the air, and long-term open storage will gradually become ineffective. It is recommended to prepare them as needed to avoid long-term storage of large amounts of solutions.

2、 Point selection for investment (core process)

The dosing location determines the mixing time and reaction temperature between the drug and the water body. The industry's preferred sequence is as follows:

Location: outlet of thermal deaerator, inlet pipeline of feedwater pump

Suitable for supporting medium and high pressure boilers with thermal deoxygenation. After thermal deoxygenation, a small amount of dissolved oxygen remains in the feedwater, which is added at this location. The high temperature of the water body is conducive to accelerating the oxidation-reduction reaction; The medicine follows the feedwater into the economizer and has sufficient reaction time. Choose turbulent flow areas as much as possible for the pipeline, and install static mixers if conditions permit to promote uniform dispersion of the medication.

Alternative location: Inside the deoxygenated water tank

A small low-pressure boiler without a thermal deoxygenation device can be directly added to the deoxygenation water tank. Suitable for sodium sulfite deoxygenation system, relying on the residence time in the water tank to complete the reaction. Continuous stirring is required to prevent local enrichment of the medication.

Not recommended addition location: inside the boiler drum

The reaction time of the reagent entering the steam drum is insufficient, making it difficult to fully remove dissolved oxygen from the water supply pipeline and economizer. The risk of corrosion in the front pipeline cannot be controlled, and it can only be used as an emergency supplementary measure, not as a regular dosing plan.

Important reminder: It is strictly prohibited to directly add deoxidizer to the front end of return water and condensate water recovery to avoid uneven distribution of reagents caused by fluctuations in working conditions.

3、 Conveyor equipment and dosing control method

Measuring and conveying equipment

Priority should be given to using diaphragm metering pumps for continuous dosing, relying on frequency conversion to adjust the flow rate and achieve continuous dosing according to the proportion of feedwater flow. It is not recommended to use manual intermittent dumping and dosing, as intermittent dosing can cause fluctuations in drug concentration and deoxygenation effect.

The pipeline is equipped with filters and back pressure valves to prevent water from flowing back and diluting the chemicals in the medicine tank after the pump is stopped. The pipeline material should be selected with anti-corrosion pipes according to the type of chemicals to reduce corrosion and leakage.

Linkage control scheme (optimization scheme)

Establish a linkage between the metering pump and the boiler feedwater flow rate, and increase the dosage synchronously with the increase of feedwater load; A system with complete conditions can be combined with online monitoring data of dissolved oxygen in water supply to form a closed-loop regulation and achieve on-demand dosing.

4、 Calculation of dosage and control of operational indicators

The dosage cannot rely solely on fixed values and needs to be dynamically adjusted in conjunction with water quality conditions.

Theoretical basic dosage

Calculate the basic dosage based on the measured dissolved oxygen content in the water supply, while reserving a reasonable excess amount to ensure sufficient deoxygenation reaction. There are differences in the reaction ratios of different types of reagents: the theoretical consumption ratios corresponding to sodium sulfite, oxime, and carbazide reagents are different. Please refer to the technical data of the reagent manufacturer as a reference.

Relying on residual indicators to calibrate drug dosage

Sodium sulfite system is commonly used in low-pressure boilers to maintain a reasonable range of residual sulfite ions in the boiler water; Medium and high pressure boilers use salt free oxygen scavengers such as carbazide and dimethyl ketoxime, and monitor the residual chemical content in the feedwater.

Low residual indicators indicate insufficient dosage and poor removal of dissolved oxygen; The residual indicators remain high, indicating that excessive dosage increases the cost of chemicals, and some excessive chemicals may also affect the quality of steam.

The influence of environmental conditions on drug dosage

The higher the water temperature, the faster the deoxygenation reaction rate; Maintaining the pH of the water in the alkaline range is more conducive to the effectiveness of most oxygen scavengers. When the water supply temperature is low, the dosage can be slightly increased to compensate for the impact of the decrease in reaction rate.

5、 Feeding strategies corresponding to different boiler operating conditions

Medium and high pressure steam boilers equipped with thermal deaerators

Thermal deoxygenation is the main process, and deoxygenation agent is used as a supplement for deep deoxygenation. The injection point is located at the outlet of the deaerator, using small doses of continuous injection to remove residual dissolved oxygen and form a passivation protective film on the metal inner wall.

Small low-pressure boiler without thermal deoxygenation device

Mainly relying on chemical deoxygenation, chemicals are added to the deoxygenation water tank to ensure sufficient water retention reaction time, and dissolved oxygen and residual chemicals at the water outlet are regularly monitored.

Special operating conditions for starting and stopping the furnace

During the start-up phase of the boiler, the temperature of the feedwater system is low and there is a high risk of oxygen corrosion. Therefore, the dosage can be temporarily and moderately increased; After stable and normal operation, callback to the standard range. Before shutting down for maintenance, maintain the dosing of chemicals according to specifications and passivate the pipelines for protection.

6、 Common Misconceptions and Avoidance of Investment Operation

Misconception: One time large dosage instead of continuous micro dosage

Analysis: A one-time addition can only temporarily increase the concentration, which is quickly consumed, resulting in a prolonged blank period of the drug and continuous oxygen corrosion of the pipeline.

Misconception: Changing the dilution ratio arbitrarily without filtering

Analysis: Undolved solid impurities can easily clog metering pumps and nozzles, causing interruptions in drug delivery.

Misconception: Only focusing on boiler water indicators, neglecting dissolved oxygen monitoring in feedwater

Analysis: Corrosion mostly occurs in water supply pipelines and economizers, and monitoring only the water quality of the steam drum cannot determine the effectiveness of front-end deoxygenation.

Misconception: Mixing and preparing multiple water treatment agents at will

Analysis: Some scale inhibitors, acid-base regulators, and oxygen scavengers react when mixed, damaging the effective components. It is recommended to prepare and add different agents independently.

7、 Requirements for daily operation and maintenance support

Establish a regular sampling and testing system to monitor dissolved oxygen, residual concentration of chemicals, and pH values in the water supply; Regularly check the flow rate of the metering pump and whether there are any blockages or leaks in the pipeline; Regularly clean the medicine box and remove sediment from the bottom. At the same time, keep operation records and adjust the dosing parameters in a timely manner when the load changes or water quality fluctuates.

epilogue

Boiler deoxygenation agentThe standardized dosing process can be summarized as follows: standardizing closed dosing → optimizing the turbulent flow point at the outlet of the deaerator → continuous proportional dosing by the metering pump → dynamically adjusting the dosing amount based on residual water quality indicators.

A reasonable dosing method can not only stably reduce dissolved oxygen in the feedwater, inhibit oxygen corrosion, but also reduce the consumption of chemicals; On the contrary, incorrect dosing points, improper dispensing, and uncontrolled dosage can lead to insufficient deoxygenation effect, waste of chemicals, and secondary water quality problems. Boiler operation and maintenance personnel should develop a suitable normalized dosing plan based on whether their own equipment is equipped with thermal deoxygenation, operating pressure, and feedwater quality, to continuously ensure the safe and stable operation of the thermal system.