Steam Generation FAQ 1

           •    What is F & A rating of a boiler?  If my feedwater temperature is 40^°C and
                         the boiler capacity is 2000 kg/hr, how much steam can I expect to
                         generate?

F& A means from & at rating of a boiler and it is defined as follows:

F&A rating * 540 = actual rating * (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 feedwater in ^oC

The energy from the steam is the actual evaporation, which is defined as:

Actual evaporation = (boiler capacity * 540) / (hg - Tf)

With the boiler capacity = 2000 kg/hr, hg = 663.7 kcal/kg and Tf = 40^oC:
Actual evaporation = 1731.60 kg/hr

•   What is dryness fraction of saturated steam boilers ? In Indian context, which is better :      IBR or Non IBR boiler? (IBR : Indian Boiler Regulation Act)

The dryness fraction is the proportion of completely dry steam present in the steam being considered. The steam becomes "wet" if water droplets in suspension are present in the steam space, carrying no specific enthalpy of evaporation.

Non IBR boilers have a higher steam release velocities leading to generation of wet steam when steam demand increases (normal dryness fraction between 0.7 and 0.8). The IBR boilers respond well to fluctuating loads without affecting steam quality due to lower steam release velocities (dryness fraction - 0.98). According to this the IBR boiler is the better choice if dry steam is important.

•    What is the recommended TDS in boiler water and what is the best way to maintain it ?

Boiler Type

Maximum TDS (ppm)

Lancashire

10000

2 pass Economic

4500

Package Boiler and 3 pass Economic

3500

Low pressure water tube

2000-3000

Coil boilers and steam generators

2000 (in the feedwater)

The total number of dissolved parts should be held on a low level with feedwater treatment. The original method of "blowing down" a boiler was to manually operate a blowdown valve fitted to a discharge pipe at the lowest point of the boiler shell, at the same time hoping that the frequency of evaporation of the blowdown valve and the length of time for which it is open is sufficient for the needs of the boiler. A better way is the use of an Automatic TDS / Blowdown control system, which can help save a lot of heat energy.

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