Long-term practices make people realize that the quality of water and steam in thermal system of coal-fired power plant  is one of the important factors affecting the safe and economic operation of the thermal equipment of coal-fired  power plant ( such as boiler and steam turbine, etc.). The natural water without purification treatment contains many impurities, this kind of water is not allowed to enter the water and steam cycle system. In order to ensure that the thermal system has good water quality, the natural water must be properly purified and the quality of water and steam in circulation system of water and steam must be strictly supervised, otherwise the it will cause scaling, corrosion and salification of thermal equipment. The water treatment of coal-fired power plant is to ensure that each part of the thermal system has a good water and steam quality, in order to prevent the scaling, salification and corrosion of thermal equipment. Water treatment to ensure safe and economic operation of power plants is of great significance.

1. To prevent the fouling of heating equipment: If the boiler feed water quality does not meet the standard and it has not been correctly handled in time, then after a period of operation, on the heating surface contacting with water, there will be a layer of attachments, which is water scale. Due to poor thermal conductive performance of water scale, which is worse than that of metal by dozens of times and even to hundreds of times,  therefore, the temperature at the scaling parts is too high, which will cause the metal strength dropping, local deformation and bubbling, in server case, it will cause bursting accident and endanger the safe operation. The scaling will seriously affect the heat transfer effect of boiler and greatly reduce the economy of the boiler operation. Due to the scale, the vacuum in condenser of steam turbine decreases, thus reducing the thermal efficiency and output of steam turbine, in severe case, the steam turbine shall be shut down for maintenance, therefore, it is very important to control water quality to prevent scaling. 

2. To prevent the scaling of heating equipment: The poor boiler feed water quality will cause corrosion to the economizer, water-cooled wall, water supply pipeline, superheater and the steam turbine condenser. Corrosion will not only shorten the service life of equipment and result in economic losses, and in the mean time the corrosion products will be transferred to the water to pollute water quality, thus aggravating the scaling on the heating surface, and the scaling will accelerate the corrosion under the scaling, causing vicious cycle of corrosion and scaling. 

3. To prevent salt deposition inside the superheater and steam turbine: The excessive impurities and salt in feed water of boiler is carried by the steam and deposit on the superheater and steam turbine, this phenomenon is called salt deposition; The salt deposition of superheater of will cause metal wall overheating, even bursting; the salt deposition inside steam turbine will reduce the output and efficiency of the steam turbine. When salt deposition is serious in steam turbine, it will make the thrust bearing load increase, partition bend and cause emergency shutdown.