Heat Balance Exercise

HEAT BALANCE EXERCISES

1. Dry solid fuel (no moisture) with the composition C 85%, 85%, H 12% dan S 3% is burned burned in the furnace. The fuel does not contain ash at all. Orsat analysis of the stack gas is shown as follows: CO2 13.03% and CO 0.38%. Air and solid fuel enter the furnace at 25°C, and the stack gas temperature is 340°C. Calculate excess air and thermal efficiency of the furnace. CO + 0,5 O2  CO2 H2O (liquid)  H2O (gas)

 HR,298 = - 67636 cal  H298 = 10520 cal

HHV 6800 cal/gram. Mean specific heat:  N2 7

O2 7.3

H2O 8

CO2 10

CO 7.1

SO2 8.2

2. This catalytic catalytic reaction is run adiabatically in a fixed bed reactor: CH4 + 2 O2  CO2 + 2 H2O (exothermic) CH4 + 2 H2O  CO2 + 4 H2 (endothermic) Oxygen from air totally reacts, and methane-steam feed has a ratio of CH 4 : H2O = 1:1 (mol/mol). Methane-steam enters the reactor at 220ºC, while air enters at 25ºC. The reactor’s effluent has a temperature of 500ºC. If the total conversion of methane is 60%, calculate the air needed per mol of methane feed and the composition of effluent.

CH4 CO2 H2O (gas) O2  N2 H2

Hf ,298K (cal/mol) - 17,889 - 94,051 - 57,798 -------

Cp average (cal/mol/K) 11.5 10.8 8.5 7.5 7.2 7.0

3. Adiabatic reaction of NH 3 oxidation is conducted at gas phase:  NH3 + O2 → NO + H2O (complete the stoichiometric coefficient!)  NH3 is completely oxidized. Air and NH3 gas are charged into the reactor at 40°C. The reactor effluent is 950°C. How much air is charged into the reactor?

 NH3 H2O  NO  N2 O2

hf,298 (cal/mol) - 11000 - 57798 21600 -----

Cp mean 6.7 8.2 8.1 6.7 6.8

4. Hydrocarbon fuel is burned with excess air in the combustion chamber. Orsat analysis of  flue gas shows that flue gas consists of: CO 2 10.2% ; CO 1% ; O 2 8.4% and the rest is N 2.

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Air and fuel enter the chamber at 25°C, and the combustion takes place adiabatically. Calculate % excess air and exit flue gas temperature! HHV of fuel is 10500 cal/gram. Average Cp can be taken at Exercise no. 1! 5. Gas with the composition CH 4 40%, CO 30% and H 2 30% is burned adiabatically, with 300% excess air. Gas and air enter the burner at 25°C. Calculate adiabatic flame temperature.

CH4 CO CO2 H2O (gas) O2  N2 H2

Hf ,298K (cal/mol) - 17,889 -26,415 - 94,051 - 57,798 -------

Cp average (cal/mol/K) 11.5 7.2 10.8 8.5 7.5 7.2 7.0

6. In the manufacture of nitric aicd, NH 3 is adiabatically oxidized with air.  NH3 + O2 → NO + H2O (complete the stoichiometric coefficient!)  NH3 gas enters the reactor at NA0 mol/hr, and the ratio of NH 3 : air = 1 : 9 (mol/mol). The reaction rate of ammonia is r A = k(C NH3)(CO2) mol/(L.hr). Develop differential equation for  conversion XA and temperature T under steady-state process in tubular reactor! dX A/dz and dT/dz. 7. Liquid as much as 5 m 3 in stirred tank vessel is heated in batch operation. The vessel is equipped with heating coil: heat transfer area 3 m2 and overall heat transfer coefficient UD = 4200 cal/(m2.hr.°C). Liquid density is 0.95 g/cc and its specific heat is 0.3 cal/(g.°C). The initial temperature of liquid in the stirred tank is 30°C, and the target temperature is 110°C. Steam is used as heating médium, which condenses in the coil at 150°C (constant). Due to poor pipe fitting and connection in the outlet stream, there is leak flow from the effluent stream, around 0.3 m3/hr. The volume of liquid in the tank is maintained by feeding the fresh liquid into the tank, at the flowrate of 0.3 m 3/hr and 30°C. How long is the target temperature reached?

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