Boiler Blowdown Calculation – Formula, Significance and Online Calculator
What is Boiler Blowdown?
Boiler blowdown is the controlled removal of a portion of water from a steam boiler to control the concentration of dissolved and suspended impurities in boiler water.
How do the concentration of dissolved and suspended solids increase in Boiler?
As water is converted into steam, most dissolved solids such as salts, alkalinity-producing compounds and other non-volatile impurities remain inside the boiler. If these impurities are allowed to continuously accumulate, the boiler-water TDS increases.
What is the consequence of High TDS in Boiler water?
High TDS can lead to:
- Scaling on boiler heating surfaces
- Foaming and priming
- Steam carryover
- Poor steam quality
- Corrosion
- Increased chemical consumption
- Deposits in steam lines and downstream equipment
- Reduced boiler efficiency
Why is Boiler Blowdown Important?
The main objective of blowdown is to maintain boiler-water chemistry within the permissible operating limits recommended for the particular boiler and operating pressure.
What is the impact of excess blow down?
Boiler blow down should be optimum to maintain the desired water parameters, however excess blow down m leads to the losses.
Every kilogram of blowdown represents:
- Treated water lost from the boiler
- Heat energy lost with hot boiler water
- Water-treatment chemical loss
- Additional makeup-water requirement
- Increased fuel consumption
What are the inputs required to calculate the Blow down water quantity?
- Boiler operating load in TPH
- Feed water TDS in ppm
- Maximum allowable TDS in Boiler water
- % of makeup water
- Formula for Boiler Blow down calculation
Blowdown (%) = (Feedwater TDS × % Makeup Water) / (Maximum Allowable Boiler Water TDS-Feed water TDS)
Calculate the percentage of blow down and blow down water quantity if a Boiler is operating at 85 TPH with feed water TDS 7 ppm and maximum allowable TDS in boiler water is 150 ppm. Consider the % of make water 5
Blowdown (%) = (Feedwater TDS × % Makeup Water) / (Maximum Allowable Boiler Water TDS-Feed water TDS)
Blowdown (%) = (7 X 5/100) X 100 / (150-7) =0.24%
There fore quantity of blow down = Boiler operating load X Blow down %
There fore quantity of blow down = 85 X 0.24/100 =0.204 TPH = 204 Kg/hr
Boiler Blowdown Calculator
Blowdown (%) = (Feedwater TDS × % Makeup Water) ÷ (Maximum Allowable Boiler Water TDS − Feedwater TDS)
Blowdown Water Quantity (TPH) = Boiler Operating Load × Blowdown (%) ÷ 100