Boiler horsepower is a boiler’s capacity to deliver steam to a steam engine and is not the same unit of power as the 550 ft-lb/s definition. One boiler horsepower is equal to the thermal energy rate required to evaporate 34.5 lb of fresh water at 212 °F in one hour. In the early days of steam use, the boiler horsepower was roughly comparable to the horsepower of engines fed by the boiler.

steam-boiler

A unit for measuring the power of a steam boiler, being the equivalent of 34.5 pounds of steam evaporated from and at 212° F per hour. One BHP denotes ability to produce 34.5 pounds of dry steam per hour at 100°C (212°F), and corresponds to 10 square feet of heated surface, 33479 British thermal units (BTU), or 9.809 kilowatt per hour (equal to more than 13 mechanical horsepower).

Boiler horsepower is used to rate boiler capacities to deliver steam to steam engines.

The term “boiler horsepower” was originally developed at the Philadelphia Centennial Exhibition in 1876, where the best steam engines of that period were tested. The average steam consumption of those engines (per output horsepower) was determined to be the evaporation of 30 pounds of water per hour, based on feed water at 100 °F, and saturated steam generated at 70 psig. This original definition is equivalent to a boiler heat output of 33,485 Btu/hr. Years later in 1884, the ASME re-defined the boiler horsepower as the thermal output equal to the evaporation of 34.5 pounds per hour of water “from and at” 212 °F. This considerably simplified boiler testing, and provided more accurate comparisons of the boilers at that time. This revised definition is equivalent to a boiler heat output of 33,469 Btu/hr. Present industrial practice is to define “boiler horsepower” as a boiler thermal output equal to 33,475 Btu/hr, which is very close to the original and revised definitions.

One boiler horsepower is the amount of energy required to produce 34.5 pounds (15.65 kg) of steam per hour at pressure and temperature 0 psig (0 bar) and 212oF (100oC) – with feed water at pressure 0 psig and temperature 212oF.

One boiler horsepower is about 33475 btu per hour (about 9811 watts, 8436 kcal/hr).

Boiler horsepower can be calculated from the boiler heat transfer area

PBoHP = A / 17        

where

PBoHP = boiler horsepower

A = heat transfer area (ft2)

PBoHP tends to be used only in the USA, Australia, and New Zealand. Be aware that the a boiler horsepower is not the commonly accepted 550 ft lbf/s and the generally accepted conversion factor of 746 Watts = 1 horsepower does not apply.

Boiler Conversion Ratios

from

multiply

to

sq.ft. EDR steam

240

Btu per hr.

sq. ft. EDR water

160

Btu per hr.

Boiler hp

33.5

MBtu per hr.

Boiler hp

140

sq.ft. EDR steam

Boiler hp

223

sq.ft. EDR steam

Boiler hp.

34.5

lb. per hr. steam

lb. per hr. steam

970

Btu per hr.

to

divide by above

from

Boiler horsepower is still used to measure boiler output in industrial boiler engineering in Australia, the US, and New Zealand. Boiler horsepower is abbreviated BHP, not to be confused with brake horsepower, below, which is also called BHP.

Save

Save

Advertisements