Boilers rated capacity are specified by their capacity to hold water and the steam generation rate. The capacity to generate steam is specified in terms of equivalent evaporation.
(kg of steam / hour at 100 Degree C).
Equivalent evaporation- “from and at” 100 Degree C. The equivalent of the evaporation of 1 kg of water at 100 Degree C to steam at 100 Degree C.
F& A means From & At rating of a boiler and it is defined as follows:
F&A rating:-
The boiler is rated to work at a certain pressure and at that pressure it can generate a defined quantity of steam. This can also be written as the F & A rating of the boiler.
This is used as a measure of the boiler ability to produce steam. It gives us the amount of steam (in kgs) that a boiler will produce if supplied with water at 100 Degree C. e.g., a 2 ton boiler gives us 2,000 kgs of steam per hour. It is written as 2 TPH F&A 100 Degree C.
This means that when the water inside the boiler is at 100 Degree C and the steam take-off is also at 100 Degree C, the boiler will gives us 2 tons/hour of steam.
F&A Rating X 540 = Actual Rating X ( hg – hf FW) where, hg = enthalpy of steam at generation pressure hf FW = Feed water enthalpy
Example:-
Take a 10 TPH boiler, @ 10.54 bar (g), 75 Degree C = 9152 kg/hr net
So, a 10TPH boiler will never give you 10,000 kg/hr of steam.
This disparity is because the feed is not at 100 deg C. Water at 100ºC has 100 k cal /kg latent heat. The F&A rating assumes an ideal condition: + 540 k cal/kg
100 k cal/kg ----------------------------> 640 k cal/kg (water at 100°C) (+heat) (steam's latent heat)
But actually, the feed water is at ambient temperature. So we need more heat to first raise the temperature to saturation (100°C). This is what gives rise to the difference in boiler output.
+ 610 k cal/kg
30 k cal/kg ----------------------------> 640 k cal/kg (water at 30°C) (+heat) (steam's latent heat)
(kg of steam / hour at 100 Degree C).
Equivalent evaporation- “from and at” 100 Degree C. The equivalent of the evaporation of 1 kg of water at 100 Degree C to steam at 100 Degree C.
F& A means From & At rating of a boiler and it is defined as follows:
F&A rating x 540 = actual rating x (hg - Tf) hg = the total enthalpy in each kg of steam, it is the sum of the liquid enthalpy and the enthalpy of evaporation,
Tf = the temperature of the feed water in Degree C The energy from the steam is the actual evaporation, which is defined as:
Actual evaporation = (boiler capacity x 540) / (hg - Tf)
F&A rating:-
The boiler is rated to work at a certain pressure and at that pressure it can generate a defined quantity of steam. This can also be written as the F & A rating of the boiler.
This is used as a measure of the boiler ability to produce steam. It gives us the amount of steam (in kgs) that a boiler will produce if supplied with water at 100 Degree C. e.g., a 2 ton boiler gives us 2,000 kgs of steam per hour. It is written as 2 TPH F&A 100 Degree C.
This means that when the water inside the boiler is at 100 Degree C and the steam take-off is also at 100 Degree C, the boiler will gives us 2 tons/hour of steam.
F&A Rating X 540 = Actual Rating X ( hg – hf FW) where, hg = enthalpy of steam at generation pressure hf FW = Feed water enthalpy
Example:-
Take a 10 TPH boiler, @ 10.54 bar (g), 75 Degree C = 9152 kg/hr net
So, a 10TPH boiler will never give you 10,000 kg/hr of steam.
This disparity is because the feed is not at 100 deg C. Water at 100ºC has 100 k cal /kg latent heat. The F&A rating assumes an ideal condition: + 540 k cal/kg
100 k cal/kg ----------------------------> 640 k cal/kg (water at 100°C) (+heat) (steam's latent heat)
But actually, the feed water is at ambient temperature. So we need more heat to first raise the temperature to saturation (100°C). This is what gives rise to the difference in boiler output.
+ 610 k cal/kg
30 k cal/kg ----------------------------> 640 k cal/kg (water at 30°C) (+heat) (steam's latent heat)