How Do You Identify Actual Boiler Capacity

What is Boiler Capacity ? 

Boiler capacity can express as Steam Evaporation Rate or Energy Transfer Rate of Boiler.

Factors Depends on the Evaporation Rate

1. Operating Pressure.

2. Operating Temperature.

3. Feed water temperature.

4. Dryness fraction. (dryness fraction = mass of steam / mass of Steam & water)

5. Energy Input ratio. (This would be constant because furnace design for specific combustion ratio)

6. Surface area of the water plane of boiler. (this would be constant because it is design factor but level can change due to )

Boiler Capacity Measurements

1. Pounds per hour (PPH)

 pound is a unit of mass.

1 lb = 0.453 592 37 kg

2. British Thermal Unit (BTU)

Boiler capacity express as Energy Transfer rate. Energy measured by BTU. Capacity express as BTU/hr.

W = (hg - hf) x m 

 W - Boiler Capacity(Btu/hr)
hg - Enthalpy Steam (Btu/lb)
hf - Enthalpy Condensate (Btu/lb)
m - Steam Evaporation (lb/hr)  

3. Boiler House Power (BHP)

Amount of Energy required to produce 34.5 lb of steam / hr. Operating Pressure and Temperature respectively 1 bar absolute pressure  and 100^oC and feed water temperature 100^oC at 1 bar (absolute).

1 BHP = 33479 Btu/hr

4. Ton per hr (TPH)

Amount of Steam generate by the boiler per hour at 1 bar(absolute) pressure and 100^oC temperature. Feed water temperature should be 100^oC at 1 bar (absolute).

Evaporation Capacity of Boiler  = 1000 kg /hr (F&A 100^oC)

This means the boiler Evaporation capacity 1000 kg of steam at feed water temperature 100^oC and boiler operating pressure  1 bar(Absolute) or 0 bar(gauge)

 

What Factors to be Consider When Selecting Boiler Capacity

First step is calculate the Average Energy requirement for the Plant. Peak Energy consumption rate also very important when selecting new Boiler for the Plant. Energy consumption rate can shown by kJ/hr or k cal/hr. After define the energy consumption rate; need to know the maximum temperature requirement of the plant. Because operating pressure will change according to the temperature requirement. at 1 bar (absolute) operating pressure and 100^oC feed water temperature boiler out put is optimum. But in higher operating pressure and low feed water temperature cause to reduce the boiler capacity. 

Extra Energy use to

1. Increase the feed water temperature up to 100^oC.

2. Increase water temperature up to boiling temperature which is higher than 100^oC due to high operating pressure. 

Actual Capacity Calculation of Boiler

Defined capacity                 =    A  [1000 kg /hr (F&A 100^oC) ] 

Operating Pressure             =    q  [10 bar(g)]

Feed water temperature      =    T  [80^oC]

 

Actual Boiler Capacity =  A x  hfg @ 1 bar / ( hg @ q bar - hf @ T )

This Equation can use easily to calculate the actual boiler capacity. Specific Enthalpy Should be taken from Steam Table. (Google Down load search - Thermodynamic and Transport Properties of Fluid - SI Units -  G.F.C Rogers and Y.R Mayhew )