During the operation of the steam boiler, the water quality will be regularly tested to ensure the quality of steam. At the same time, blowdown will also be frequently discharged. So, why should the steam boiler discharge blowdown? How to calculate the boiler blowdown rate?
1. Reasons for steam boiler blowdown
The feed water entering the drum always contains a certain amount of salt. After the boiler is treated with chemicals, the scaling substances in the boiler water are converted into water slag. In addition, the boiler water corrodes the metal and also produces some corrosion products. Therefore, there are various soluble and insoluble impurities in the boiler water. During the operation of the boiler, only a small part of these impurities are taken away by the steam, and most of them remain in the boiler water. As the boiler water continues to evaporate, the concentration of these impurities gradually increases. Excessive concentration of impurities in the boiler water not only affects the quality of steam, but also causes scaling and corrosion of the heating surface, affecting the safe operation of the boiler. In order to control the quality of boiler water, boiler blowdown must be carried out to discharge part of the boiler water contaminated by salt and water slag, and replenish it with clean feed water.
2. How to calculate the boiler blowdown rate
The blowdown rate refers to the ratio of the continuous blowdown flow rate of the boiler to the actual evaporation amount.
Blowdown rate = continuous blowdown flow rate during the calculation period (t) / actual evaporation of the boiler during the calculation period (t)
During boiler operation, boiler water with more salt and slag is discharged to the outside of the boiler to become boiler blowdown. Boiler blowdown is divided into periodic blowdown and continuous blowdown. The inlet of the continuous blowdown pipe is installed below the water surface of the drum and arranged along the entire length of the drum to continuously and uninterruptedly discharge a part of the boiler water. The periodic blowdown inlet is at the lowest part of the boiler where there is more precipitated slag. Most of them are discharged from the lower header of the water-cooled wall. They are discharged once every certain period of time, mainly to discharge the slag precipitated from the boiler water.
If there is a boiler blowdown metering device, it can be measured directly. If it cannot be measured directly, it can be calculated by chemical salt balance or water replenishment rate method; chemical salt balance means that the salt brought in by the feed water should be equal to the sum of the salt taken away by the steam and the salt discharged with the sewage. Therefore, the blowdown rate can be calculated by analyzing the salt content in the feed water, boiler water, and saturated steam. The water make-up rate method refers to calculating the boiler blowdown rate by adjusting the change in the unit water make-up rate when the boiler is turned on or off to discharge blowdown when the steam turbine maintains a constant operating condition.
During the operation of the steam boiler, the water quality will be regularly tested to ensure the quality of steam. At the same time, blowdown will also be frequently discharged. So, why should the steam boiler discharge blowdown? How to calculate the boiler blowdown rate?
1. Reasons for steam boiler blowdown
The feed water entering the drum always contains a certain amount of salt. After the boiler is treated with chemicals, the scaling substances in the boiler water are converted into water slag. In addition, the boiler water corrodes the metal and also produces some corrosion products. Therefore, there are various soluble and insoluble impurities in the boiler water. During the operation of the boiler, only a small part of these impurities are taken away by the steam, and most of them remain in the boiler water. As the boiler water continues to evaporate, the concentration of these impurities gradually increases. Excessive concentration of impurities in the boiler water not only affects the quality of steam, but also causes scaling and corrosion of the heating surface, affecting the safe operation of the boiler. In order to control the quality of boiler water, boiler blowdown must be carried out to discharge part of the boiler water contaminated by salt and water slag, and replenish it with clean feed water.
2. How to calculate the boiler blowdown rate
The blowdown rate refers to the ratio of the continuous blowdown flow rate of the boiler to the actual evaporation amount.
Blowdown rate = continuous blowdown flow rate during the calculation period (t) / actual evaporation of the boiler during the calculation period (t)
During boiler operation, boiler water with more salt and slag is discharged to the outside of the boiler to become boiler blowdown. Boiler blowdown is divided into periodic blowdown and continuous blowdown. The inlet of the continuous blowdown pipe is installed below the water surface of the drum and arranged along the entire length of the drum to continuously and uninterruptedly discharge a part of the boiler water. The periodic blowdown inlet is at the lowest part of the boiler where there is more precipitated slag. Most of them are discharged from the lower header of the water-cooled wall. They are discharged once every certain period of time, mainly to discharge the slag precipitated from the boiler water.
If there is a boiler blowdown metering device, it can be measured directly. If it cannot be measured directly, it can be calculated by chemical salt balance or water replenishment rate method; chemical salt balance means that the salt brought in by the feed water should be equal to the sum of the salt taken away by the steam and the salt discharged with the sewage. Therefore, the blowdown rate can be calculated by analyzing the salt content in the feed water, boiler water, and saturated steam. The water make-up rate method refers to calculating the boiler blowdown rate by adjusting the change in the unit water make-up rate when the boiler is turned on or off to discharge blowdown when the steam turbine maintains a constant operating condition.