The boiler water balance
boiler cyclesboiler blowdowncondensate returnflash steamboiler horsepowermakeup water
Boiler cycles, blowdown percent and rate, condensate return, makeup, flash steam and boiler horsepower — the steam side's water balance.
Boiler Cycles of Concentration
Cycles of concentration in a steam boiler: boiler water TDS divided by feedwater TDS, since steam leaves the dissolved solids behind.
Boiler Blowdown Percent
Boiler blowdown as a percentage of feedwater, set by the ratio of feedwater TDS to the maximum TDS allowed in the drum.
Boiler Blowdown Rate from Steam Rate
Continuous blowdown a steam boiler must carry, in pounds per hour, from its steam production rate and target cycles of concentration.
Condensate Return Percentage
Percentage of generated steam that comes back to the boiler house as condensate — the headline efficiency number for any steam plant.
Boiler Makeup from Condensate Return
Fresh makeup water a steam plant must treat, from the steam production rate and the fraction of condensate that comes back.
Flash Steam Percentage
Percentage of hot condensate that flashes to steam when let down to a lower pressure, from the saturated liquid and latent enthalpies.
Boiler Horsepower to Heat Output
Converts boiler horsepower to heat output using the ASME definition of 33,475 BTU per hour per boiler horsepower.
Boiler Horsepower to Steam Rate
Steam output of a boiler from its horsepower rating, at the ASME definition of 34.5 lb/h of steam from and at 212 °F per BHP.
How they fit together
A boiler concentrates dissolved solids exactly the way a cooling tower does — steam leaves pure and the solids stay behind — but the driving flow is condensate return rather than evaporation. Cycles is feedwater solids divided into boiler water solids, blowdown percent is 100 divided by cycles, and the blowdown rate follows from steam rate. Condensate return sets makeup, makeup sets the solids load, and the solids load sets how hard you have to blow down. One boiler horsepower is 34.5 lb of steam per hour from and at 212 °F, or 33,475 BTU/hr — a nineteenth-century equivalence to an actual horse's work, not a modern unit.
Work backwards from the conductivity limit your boiler pressure allows — roughly 3,500 µS/cm at low pressure, far less above 600 psi — because that fixes cycles, which fixes blowdown, which fixes fuel wasted. Two things get missed. Blowdown leaves at saturation temperature, so it carries real energy out: at 100 psi about 10% of it flashes back to steam in the receiver, which is what the flash steam formula quantifies and what a flash tank recovers. And condensate return is worth more than its volume — it is hot, soft, deaerated and already treated, so a plant that drops from 80% to 60% return does not just buy 20% more water, it buys more fuel, more chemical, more blowdown and a bigger softener, all at once.