Boiler Feed Pump Calculator

To accurately calculate the boiler feed pump capacity (flow rate), you must base it on the boiler's Maximum Continuous Rating (MCR). The standard formula is:

Pump Flow (m³/h) = Boiler Steam Output (kg/h) × Evaporation Factor × Safety Margin.

Typically, engineers add a 10% to 20% safety margin to account for blowdown losses, steam leaks, and future plant expansion. For example, if your boiler produces 10,000 kg/h of steam, a standard BFP would be sized for roughly 11,000 to 12,000 kg/h.

The BFP pump head calculation (Total Dynamic Head) determines the pressure the pump must generate to push water into the boiler drum. The formula is:

Total Head (m) = (Boiler Drum Pressure - Deaerator Pressure) + Static Elevation Head + Suction/Discharge Friction Losses.

Because boiler drums operate at high pressures, the boiler feed water pump head is usually very high (often between 150m to over 1000m for large power plants). You must convert the boiler's operating pressure (in bar or MPa) into meters of water column to complete this calculation.

NPSHa (Net Positive Suction Head available) is critical to prevent cavitation, which can destroy the pump impeller. The NPSHa calculation formula is:

NPSHa = H_abs - H_vap + H_static - H_friction

• H_abs: Absolute pressure head from the deaerator.
• H_vap: Vapor pressure head of the hot feedwater.
• H_static: Static height of the water level above the pump centerline.
• H_friction: Friction losses in the suction piping.

The calculated NPSHa must always be greater than the pump manufacturer's required NPSHr by a safe margin.

The boiler feed water pump power calculation is done in three steps to find the required electrical motor size:

1. Hydraulic Power: The actual power transferred to the water. Formula: (Flow × Head × Density × Gravity) / 3,600,000.
2. Shaft Power: The power required at the pump shaft. Formula: Hydraulic Power ÷ Pump Efficiency.
3. Motor Power: The electrical input needed. Formula: Shaft Power ÷ Motor Efficiency.

Always select a standard motor size that is at least 10% larger than your calculated required motor power to prevent overloading during peak demand.

Unlike standard water pumps that handle cold water (density ~1000 kg/m³), a boiler feed pump handles hot condensate coming directly from the deaerator, often at temperatures around 100°C to 105°C. At these temperatures, the boiler feed water density drops to roughly 958 kg/m³ or lower.

If you use 1000 kg/m³ in your pump efficiency formula and power calculations, you will miscalculate the NPSHa, which could lead to severe cavitation issues. Always use the exact density for your operating temperature!