BOILER
PERFORMANCE TESTS
Boiler Efficiency
Care shall be taken to maintain the losses to practical minimum and as far as possible, the original design values for input, input, such as C.V. of fuel, % excess Feed water temperature etc., shall be maintained. The following sources of loss from the boiler shall be taken into account: a. Heat leaving through flue gas going to stack, b. unburnt fuel (specially liquid fuels), c, heat contained in moisture formed by burning hydrogen and d. radiation and convection losses etc. The following two acceptable methods, as described in ASME Codes shall be use to calculate the Boiler Efficiency: a.
Input – Output Method :
η b =
b.
η b
III.6.2.2
Heat Absorbed by Working Fluid (i.e., output) ---------------------------------------------------------- -------------------------------------------------- × 100 (Heat in Fuel + Heat Credits) (i.e. Input)
Heat Loss Method :
=
100 - { [
Heat Losses ----------------------------------------------------- -------------- ] × 100 } (Heat in Fuel + Heat Credits )
Data Collection and Efficiency Calculations
The unit operating parameters shall be fixed for performance test, based on guaranteed values (Steam Pressure & temperature, rate of blow blow down, Air to fuel ratio, fuel heating value, % excess air, feed water temperature etc.). If there is an unavoidable deviation, it shall be considered in the calculation.
With the assistance of Operations staff, E&S staff will measure the following data needed for the Boiler efficiency (η b) calculations: a. b. c. d. e. f. g. h. i. j.
Steam pressure at S/H outlet Steam Temperature at S/H outlet Steam Drum Pressure Water Temp. entering Economizer Saturated steam flow to Auxiliaries Superheater (S/H) steam flow Feed Water (F.W.) flow to Economizer F. W. flow to Desuperheater Fuel flow rate F. D. fan power
Laboratory shall provide the fuel heating (calorific) value & relative density of fuel and the flue gas analysis (%by volume of CO 2, CO, O2 and N2). The steam-water specific enthalpies for the following shall be obtained from standard ‘Steam Tables / Chart’: a. b. c. d.
Drum saturated liquid Drum saturated steam S/H Steam Economizer feed water
Mass / Heat balance calculations for the Unit shall be made to ensure all the values are OK and also their reproducibility shall be checked. The input and output energies and efficiency shall be computed using equation (1) above for Input –Output method, as indicated below (per Hour basis ): a. Input Energy (Million BTU) = [Mf ×35.3147 × C. V. ×10 -6] + FD Fan power × 3.412 b.
Output Energy (Million BTU) = [(MS/Hst × hS/Hst + Msat × hsat - MFW × hFW) / 1.055] × 10 -3
c.
Efficiency = Output Energy / Input Energy
Where : 1. 2. 3. 4. 5. 6. 7. 8. 9.
FD Fan Power = Forced Draft Fan Power , MW C.V. = Calorific value, BTU/SCft hFW = Feed Water Enthalpy, KJ/Kg hsat = Saturated Steam Enthalpy, KJ/Kg hS/Hst = Super Heated Steam Enthalpy, KJ/Kg Mf = Fuel Flow Rate, Nm3/hr MFW = Feed Water Flow Rate, m3/hr MS/Hst = Super Heated Steam Flow rate, Ton/hr MSat = Saturated Steam Flow Rate, Ton/hr
Using the ASME test form for abbreviated efficiency test, heat loss through the following sources shall be computed: a. b. c. d. e. f.
dry gas moisture in fuel moisture from combustion of H2 combustion refuse radiation / convection H2O in Air
Utilising the data computed, the Boiler efficiency shall again be calculated using equation (2) above. This mode of calculation is preferable, as any error in the computation of losses will not affect the efficiency calculated significantly. The calculated Boiler efficiency shall be compared with the acceptable / guaranteed values, given in Page 11. In case of deviations, the same shall be discussed with recommendations. These values shall be plotted over time to monitor the ‘Boiler Performance’ with time.
