Views: 34 Author: Site Editor Publish Time: 2021-08-02 Origin: Site
As we all know, boiler water quality is not qualified to cause boiler system scaling. The poor thermal conductivity of scale causes uneven heating surfaces in the furnace, which can affect boiler energy efficiency, steam quality and cause serious tube bursts or boiler explosions. Therefore, for boiler systems, water treatment is the most important aspect, especially for high-pressure boilers and systems with high process quality requirements. So today we will take a look at what methods of water treatment and their scope of application.
Boiler water treatment mainly includes make-up water treatment, condensate treatment, feed water deaeration treatment, feed water dosing treatment four parts.
01 Charge water treatment methods
When the raw water is surface water, usually add coagulants for pretreatment. When the recharge water is groundwater or municipal water, the pre-treatment steps can be omitted, or only the filtration process.
An ion exchange resin is used to convert the calcium and magnesium hard salts in the water into non-scaling salts. For water containing calcium and magnesium bicarbonates with high alkalinity, hydrogen-sodium ion exchange can also be used or addressed in the pre-treatment.
With the increasing requirements of boiler water quality, all salts in the boiler feed water need to be removed. Chemical salt removal is most commonly used with cation exchange resins and anion exchange resins. In an ion exchanger, the saline water flows through the resin and the cations and anions in the salts are removed after being transformed with the cations (H+) and anions (OH-) in the resin respectively.
For high pressure above the pot boiler or DC boiler, must also remove the trace silicon in the feed water; for atmospheric pressure small hot water boiler, can be used in the boiler dosing treatment for softening treatment or partial desalination treatment, mainly to remove the hardness of the water, usually H-type or Na-type ion exchange resin softening or lime softening method of treatment.
For water with high salt content,reverse osmosis or electrodialysis process can also be used to desalinate the water first, before entering the ion exchanger for deep desalination.
02 Condensate treatment
Effective recovery of condensate can result in significant savings in boiler operating costs, but for some open systems, condensate is often substandard and requires attention.
For supercritical pressure boilers condensate should be treated in its entirety; for ultra-high pressure and subcritical pressure boilers the treatment is 25% to 100%; for boilers below high pressure with a boiler barrel generally no treatment is carried out.
03 Feedwater de-oxygenation treatment
Oxygen in the feed water system will corrode the boiler feed water system and components, corrosive substances iron oxide will enter the boiler, deposited or attached to the boiler tube wall and heat surface, forming insoluble and poor heat transfer iron scale, corrosive iron scale will cause the inner wall of the pipe to appear point pits.
Commonly used oxygen removal methods include thermal oxygen removal, vacuum oxygen removal, chemical oxygen removal and analysis of oxygen removal. The principle is to heat the boiler feed water to the boiling point, so that the solubility of oxygen decreases, oxygen in the water constantly escapes, and then the oxygen generated on the water surface together with water vapour is removed, so that the water can be removed from the various gases (including free state of CO2, N2). The water after oxygen removal does not increase the salt content, nor does it increase the dissolved amount of other gases, and it is relatively easy to operate and control, and the operation is stable and reliable.
04 Feed water dosing treatment
After the above water treatment methods, it is also generally required to add ammonia or organic amines to the feed water to improve the pH value of the feed water and prevent the acidic water from causing corrosion to the boiler barrel. Usually add the right amount of sodium phosphate or other chemicals in the boiler barrel to turn the salt impurities that are prone to form scale in the water into slag that can be discharged by sewage to prevent or slow down the formation of scale.