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Steam & boiler duty

Enter the steam you need and the condition you need it at. The calculator returns the boiler duty in kilowatts and horsepower, the equivalent evaporation boilers are compared by, and what it costs in fuel.

How this works โ†’

Your figures

Gauge pressure at the boiler, not at the point of use.

Higher feedwater means less fuel. Economisers and condensate return raise it.

Around 80โ€“85% on gas or oil, 65โ€“72% on bagasse or husk.

Furnace oil ~42, natural gas ~48, coal ~25, bagasse ~9.5, rice husk ~13.

Result

Boiler duty

Heat duty

2,000 kg/h ร— (2,781 โˆ’ 335) kJ/kg

1,359 kW
Boiler horsepower

1 BHP = 9.81 kW = 34.5 lb/h from and at 100 ยฐC

138.5 BHP
Equivalent evaporation

From and at 100 ยฐC โ€” how boilers are compared to each other

2,168 kg/h

Steam condition

Absolute pressure

Gauge + 1.013

11.01 bar a
Saturation temperature
184 ยฐC
Enthalpy of steam

hf + hfg, saturated

2,781 kJ/kg
Latent heat

The part that does the work

2,000 kJ/kg

Saturated steam. Superheat adds enthalpy the condensing load cannot use, so it is not assumed here.

Fuel

Fuel consumption

Duty รท (82% ร— 42 MJ/kg)

142.1 kg/h
Per day

Continuous running

3,409 kg
Steam to fuel ratio

kg of steam per kg of fuel โ€” the number a boiler house is judged on

14.08 : 1

Questions

What is equivalent evaporation?
The steam a boiler would raise if it were fed water at 100 degrees and produced steam at 100 degrees, where the latent heat is 2,257 kJ/kg. It is a comparison basis, not a real operating figure, and it is how boilers of different pressures are compared with each other.
Why does feedwater temperature matter so much?
Because the boiler only has to add the difference. Raising feedwater from 30 to 90 degrees cuts roughly a tenth off the fuel bill, which is why economisers and condensate return systems pay back quickly. It is usually the cheapest efficiency improvement available to an existing boiler house.
Is superheat included?
No. The calculation assumes saturated steam, which is what most process plants use. Superheat adds enthalpy that a condensing load cannot use, so assuming it would overstate the duty for the majority of cases.
Where do the steam properties come from?
A short saturated steam table, interpolated between points, covering 1 to 30 bar absolute. A table is used rather than a fitted curve because it is exact at the points that matter and a curve that is two percent out at eight bar is two percent out on somebody's boiler.