Enter the steam generation rate (steam mass flow) and blowdown (if applicable) to estimate the required feedwater flow. The enthalpy and efficiency fields are optional and can be used to estimate boiler heat input, but they do not determine the feedwater mass flow for a given steam rate.
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Feed Water Flow Formula
The following formula is used to estimate the feedwater flow needed to produce a given steam generation rate. For a simple steady-state mass balance (ignoring attemperation sprays and other side streams), the feedwater equals the steam produced plus any continuous blowdown.
F_w = \frac{S_f}{1 - BD}Variables:
- F_w is the feedwater mass flow rate (e.g., kg/h, lb/h)
- S_f is the steam generation rate (steam mass flow rate)
- BD is the blowdown fraction of the feedwater (e.g., 0.05 for 5% blowdown)
To calculate the feedwater flow, divide the steam generation rate by (1 − BD). If blowdown is negligible (BD ≈ 0), then F_w ≈ S_f.
What is Feed Water Flow?
Feed water flow refers to the rate at which water is supplied to a boiler to be converted into steam. This is a critical parameter in the operation of boilers and steam generation systems. The feed water must be carefully controlled to ensure stable boiler operation, maintain the desired steam output, and prevent issues such as overheating or scaling. For a given steam production rate, feedwater flow is primarily determined by the steam demand and losses such as blowdown (and any other side streams), not by boiler efficiency.
How to Calculate Feed Water Flow?
The following steps outline how to calculate the Feed Water Flow.
- First, determine the steam generation rate (S_f).
- Next, determine the continuous blowdown rate as a percent of feedwater (BD), if applicable (otherwise assume 0%).
- Finally, calculate the Feed Water Flow using the formula F_w = S_f / (1 − BD).
- After inserting the values and calculating the result, check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
Steam generation rate (S_f) = 500 kg/h
Assume blowdown = 5% of feedwater (BD = 0.05)
Feedwater flow (F_w) = 500 / (1 − 0.05) = 526.3 kg/h
(Optional for heat input estimates) Steam enthalpy (H_s) = 2800 kJ/kg
(Optional for heat input estimates) Feedwater enthalpy (H_w) = 500 kJ/kg
(Optional for heat input estimates) Boiler efficiency (η) = 85%