【Weekly Topic】What are the methods to ensure the quality of boiler feedwater? (8.22-8.29)

Sample and analyze daily to monitor the levels of sodium hydroxide and sodium phosphate, and ensure proper deoxygenation.

1. Reduce water and steam losses in thermal systems, thereby decreasing the amount of water that needs to be replenished. 2. Adopt reasonable and advanced water treatment processes to produce high-quality boiler make-up water. 3. Prevent condenser leaks to avoid contamination of condensed water. 4. Implement effective anti-corrosion measures for the feedwater and condensate systems to reduce corrosion in the thermal system. 5. Implement proper protection measures for standby systems to reduce corrosion in the thermal system.

This post was last edited by dongjiang1001 on 2011-8-25 08:14: Continuous drainage from the boiler drum； Regular sewage discharge ； Add chemical reagents.

The last edit to this post was made by zgj2405 on 2011-8-25 at 19:43. 1. Thermal deaerator: Thermal deaeration may be required for deoxidizing feedwater in order to ensure the quality of boiler feedwater, thereby reducing the dissolved oxygen level in it to below the standard value of 7 μg/L. 2. Chemical deoxygenation of feedwater: The majority of the dissolved oxygen in the feedwater can be removed using a thermal deoxygenator; chemical deoxygenation is then applied as a supplementary measure, involving the addition of reducing agents that can react with oxygen to further reduce the level of dissolved oxygen in the feedwater. 3. Ammonia addition in water supply: The following conditions must be maintained during ammonia addition to achieve the best treatment results. (1) The amount of ammonia added should not be excessive; generally, the allowable ammonia content in the feed water is 1–2 mg/L, in order to reduce local accumulation of ammonia in the condenser and prevent ammonia-induced corrosion of the copper tubes. (2) Ammonia treatment and hydrazine treatment are often carried out together, which significantly reduces the copper and iron contents in the treated water. (3) The dosage of chemicals added should be adjusted according to the requirements of the water chemistry conditions during operation; the appropriate location for adding ammonia should be selected based on different situations. Ammonia can be added to the feedwater, make-up water, condensate, or even directly into the steam drum.

Reply 1# zgj2405: Strictly controlling the quality of the boiler feedwater is of great importance; it is a necessary measure to prevent scaling, corrosion, and salt deposition in the equipment of thermal systems, and it provides a favorable guarantee for the safe and economical operation of the boiler. There are three specific purposes to strict monitoring of the quality of boiler feedwater: ① To prevent scaling. If the water quality entering the boiler does not meet the standards and is not addressed properly in a timely manner, after some time of operation, a layer of solid deposits—scale—will form on the heating surfaces that come into contact with the water. Due to its poor thermal conductivity, scale is hundreds of times worse than metals. As a result, the temperature at the scaled areas becomes too high, leading to a decrease in the metal’s strength, localized deformation, and bubbling; in severe cases, this can even cause explosions, threatening safe operation ； Scaling also **reduces the economic efficiency of boiler operation; for example, if there is 1 mm thick scale in the economizer, 1.5%~2.0% more fuel is required** ； Since scaling reduces the vacuum level in the turbine condenser, it lowers the thermal efficiency and output of the turbine. In severe cases, production must even be halted for repairs. Therefore, it is very important to control water quality to prevent scaling. 　　②Prevent corrosion. Poor quality of boiler feedwater can cause corrosion of the water wall of the economizer, feedwater pipes, various heaters, superheaters, and the turbine condenser. Corrosion not only shortens the service life of equipment and causes economic losses, but the corrosion products also end up in water, contaminating its quality. This in turn exacerbates scaling on the heated surfaces, and scaling promotes under-scaling corrosion, creating a vicious cycle of corrosion and scaling. 　　③Prevent salt buildup. Excessive impurities and salts in the boiler feed water are carried away by the steam and deposited in the superheater and turbine; this phenomenon is known as salt deposition. Salt accumulation in the superheater can cause overheating of the metal tube walls, and even lead to their rupture ； Salt accumulation inside the turbine reduces output and efficiency, and in severe cases, it can cause accidents.

Adjust the continuous blowdown based on the furnace water analysis results. When the total solid content of the boiler water is high, the valve should be opened wider; when the content is low, the valve should be closed more tightly. To reduce heat loss, the opening degree of the continuous blowdown should be kept low. Waste discharge is carried out regularly at each shift; the discharge time for each valve is 10–15 seconds. Two valves are installed at each discharge point, with the first valve being opened fully first, followed by the opening of the second valve for discharge. After the waste discharge is complete, close the second valve first, then open the first valve. The valves should be closed slowly and tightly, with no leakage allowed at all. The amount of waste discharged should be adjusted based on the analysis results of the boiler water quality. A 10% phosphate solution is prepared, and this solution is continuously added to the boiler drum via a dosing pump. The dosage is adjusted according to the phosphate content in the boiler water, and trisodium phosphate on the pump is regularly washed away with clean water. Conduct a periodic inspection once.

This post was last edited by dongjiang1001 on 2011-9-22 at 17:36. 1. Steady operation of the deaerator ； The laboratory is unable to determine the accurate oxygen content ； 2. Test PH, conductivity, silicate, chloride, hardness, phosphate, and sodium ions once a day ； 3. Fixed shifts are arranged for each shift; generally, there are no major changes to the consecutive shifts ； 4. Monitor the oil and iron content in the condensate water on a daily basis.