Why do we need to blow down the boiler? How much wastewater is discharged?

Boiler bottom blowdown

1. Why do we need to perform boiler bottom blowdown

To control the salt content and silica content in the boiler water within the specified range, avoid poor steam quality, or cause blockage of boiler tubes, endangering the safe operation of the boiler, it is necessary to regularly discharge a portion of the boiler water (i.e., blowdown) and replenish with an equal amount of demineralized water, requiring regular and quantified blowdown, or continuous blowdown.

2. Calculation method

The bottom blowdown of the boiler is calculated based on the boiler with different parameters, calculated by the measured salt content, sodium content, silica content, and chloride ion content, for example, boilers with high pressure or ultra-high pressure, the blowdown rate can be calculated as follows:

In practical operation control, (processing wastewater into energy) is to select the largest wastewater discharge ratio in the calculation result to determine the amount of wastewater.

For boilers with demineralized water as makeup water, the blowdown rate can be calculated using the salt content or chloride ion content. Since the salt content (or Cl- content) in boiler water is much lower than that in feedwater when demineralized water is used as makeup water, it can be ignored. It can be calculated by the following formula:

The symbols in the formula are the same as above.

It should be noted that to prevent the accumulation of water scale in the boiler, the boiler blowdown ratio should not be less than 0.3%. At the same time, bottom blowdown also takes away heat and wastes fuel, so careful measurement and calculation are needed to ensure economic considerations. If you need direct consulting support, please contact us immediately, our experienced engineers at Naan will answer your questions and provide detailed guidance. Thank you for reading the article.