Frequently asked questions about steam generation

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?

   Answer: 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 = 40oC:
    Actual evaporation = 1731.60 kg/hr

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

    Answer: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.

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

    Answer: 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.

4. Can blowdown water heat be recovered ?

Answer: Yes, blowdown water heat can be recovered in different ways. Boiler Blowdown Control System  gives perfect solution to recover complete heat from the Blowdown water and use it to heat Feed Water.

5.How does excess air affect the boiler performance ?

Answer: Excess air is the extra air supplied to the burner beyond the air required for complete or stoichometric combustion. If the supplied air is less, not only will this result in a smoking stack, but it will significantly reduce the energy releases per unit of fuel. Too little excess air is inefficient because it permits unburned fuel, in the form of incombustible losses, to escape up the stack. But too much excess air is also inefficient because it enters the burner at ambient temperature and leaves back the stack hot, thus stealing useful heat from the process. This excess air is a very crucial parameter for the operator to monitor. The boiler efficiency analyzer EffiMax 2000 does this automatically by sensing the Oxygen in the stack, Steam Generated, Steam Temperature and blowdown loss using an integrated circuit.

6. Can boiler be monitored on-line continuously ?

Answer: Yes, the EffiMax 2000 package explained above provides a complete monitoring and data acquisition solution for your boiler performance. This sophisticated yet simple to use analyzer operates on-line continuously, monitoring your boiler efficiency every instant of its operation. EffiMax calculates the efficiency of the boiler based on indirect efficiency computation and computes individually the total amount of losses like stack loss, enthalpy loss, radiation loss and blowdown loss in your boiler. Using the data generated on the system losses, on-line suggestions can then be used to fine tune the system to generate more steam with a lower quantity of fuel.