MOI UNIVERSITY
SCHOOL OF ENGINEERING
DEPARTMENT OF CHEMICAL & PROCESS ENGINEERING
EXAMPLES ON FLAME TEMPERATURE AND BOILER PERFORMANCE
1. Hydrogen is burned with a stoichiometric amount of air during an adiaba c steady-flow
combus on process. Both the fuel and the air enter the combus on chamber at 25° C and
1 atm. Using JANAF Tables calculate the exit temperature of the product gases, assuming
complete combus on.
2. Determine the theore cal (adiaba c) flame temperature obtained from the combus on
of coke with 20% excess air. Assume that the inlet air is at a temperature of 20°C. The heat
of combus on of coke is -97, 000 cal/g-mol.
3. A sugar processing plant requires 150,000 kg/h of steam at 200 bars and 240°C superheat
from water entering the economizer at 60°C below satura on and leaves at 10ºC below
satura on. Air is fed at a rate of 1.5×105 kg/h to be preheated from 25 to 250°C. There is
no steam reheat cycle available. The coal used has ul mate analysis of a bituminous coal:
Moisture - 2.7, Carbon - 73.6, Hydrogen - 4.6, Sulphur - 2.5, Nitrogen - 1.3, Ash - 8.4 and
Oxygen - 6.9
a) Calculate the total heat requirement for this process, determining the heat
consump on in each part of the boiler.
b) If boiler is to use the bituminous coal in the furnace as fuel, how much coal must
be used if the boiler efficiency is taken to be 75%?
4. The following observa ons were made on a boiler plant during one hour test:
Steam pressure = 20 bar; Steam temperature = 260 ℃; Steam generated = 37,500 kg;
Temperature of temperature entering the economizer = 15 ℃; Temperature of water
leaving the economizer = 90 ℃; Fuel used = 4,400 kg; Energy of combustion of fuel =
30,000 kJ/kg.
Calculate (a) The equivalent of evaporation per kg of fuel; (b) The thermal efficiency of
the plant; (c) The percentage heat energy of the fuel utilized by the economizer.
5. The following par culars refer to a steam plant consis ng of a boiler, economizer and
superheater:
Steam pressure = 14 bar; Mass of steam generated = 5,000 kg/h; Mass of coal used = 675
kg/h; Calorific value of coal = 29,800 kJ/kg of coal; Temperature of feed water entering
the economizer = 30 ℃; Feed water leaving the economizer = 130 ℃; Dryness fraction of
steam leaving the boiler = 0.97; Temperature of steam leaving the superheater = 320 ℃.
Determine: (a) Overall efficiency of the plant; (b) The percentage of the available heat
utilized in the boiler, economizer and superheater.
6. In a boiler, the following observa ons were made:
Pressure of steam = 10 bar; Steam condensed 540 kg/h; Fuel used = 65 kg/h; Moisture in
fuel = 2%; Mass of dry flue gases = 9 kg/kg of fuel; Lower calorific of fuel = 32,000 kJ/kg;
Temperature of flue gases = 325 ℃; Temperature of boiler house = 28 ℃; Feed water
temperature = 50 ℃; Mean specific heat of flue gases = 1 kJ/kg K; Dryness fraction of
steam = 0.95.
Draw up a heat balance sheet for the boiler.