Dr. F. IskanderaniChE 201 Spring 2003/20042 Types of reaction studied in this course: 1.Combustion reactions 2.General reactions

Dr. F. IskanderaniChE 201 Spring 2003/ Combustion reactions Example 3: A coal containing 81 mass % C, 6% H 2, and 13% solid inert (or ash), is burned completely in air. The amount of air used is 30% more than is theoretically required to completely oxidize all the carbon to CO 2 and all the hydrogen to H 2 O. Calculate the number of Kg of air per Kg of coal and the composition of the stack gas leaving the furnace.

Dr. F. IskanderaniChE 201 Spring 2003/20044 Definitions: Fuel: Coal (or carbon) or any hydrocarbon Theoretical or Required Air or Oxygen = amount of air required for complete combustion of the fuel to CO 2 (and water) combustion: The process of burning a fuel with air or oxygen completely to CO 2 (and water).

Dr. F. IskanderaniChE 201 Spring 2003/20045 Partial or incomplete combustion: The process of burning a fuel with air or oxygen to produce CO and CO 2 (and water) O 2 required or theoretical % Excess air = %excess O 2 = O 2 in – O 2 required or theoretical X 100

Dr. F. IskanderaniChE 201 Spring 2003/20046 Stack gas or Flue gas or Wet basis: all the gases resulting from a combustion process including the water vapor Orsat analysis or dry basis: all the gases resulting from a combustion process not including the water vapor

Dr. F. IskanderaniChE 201 Spring 2003/20047 Example 3: A coal containing 81 mass % C, 6% H 2, and 13% solid inert (or ash), is burned completely in air. The amount of air used is 30% more than is theoretically required to completely oxidize all the carbon to CO 2 and all the hydrogen to H 2 O. Calculate the number of Kg of air per Kg of coal and the composition of the stack gas leaving the furnace.

Dr. F. IskanderaniChE 201 Spring 2003/20048 Theoretical (or required) O 2 = theoretical O 2 for rxn 1 + theoretical O 2 for rxn 2 = 6.75 x 1/1 + (3.00) x ½ = 8.25 Kg mole O 2 The reactions : C + O 2  CO 2 and H 2 +1/2 O 2  H 2 O Basis : 100 Kg coal, Let us change to moles ComponentKgM Wtkgmoles C H2H Ash13-

Dr. F. IskanderaniChE 201 Spring 2003/20049 O 2 in = x 30% = 8.25 ( )= N 2 =10.73 x 79/21 Theoretical air = theoretical O 2 x = Kg mole Air in = 1.3 x = kgmol O2 in = x 0.21 = kgmol N2 in = x 0.79 = kgmol remember 30% more

Dr. F. IskanderaniChE 201 Spring 2003/ Then we can calculate easily the composition of the stack gas.

Dr. F. IskanderaniChE 201 Spring 2003/ Let us now re-calculate using atomic balances 1. N 2 is an inert  N 2 in = N 2 out = moles 2. Atomic balances IN = OUT In coal streamIn air stream C6.750n CO2 H3 x 202 X n H2O O0n H2O n H2O +2 n CO2 +2n O2 Then n CO2 = n H2O = n O2 = 3. total mass in = total mass out ( this is used for checking answers)

Dr. F. IskanderaniChE 201 Spring 2003/ Sludge wt% S 32 C 40 H 2 4 O Stack gas wt% SO CO O N CO2.02 Example 4 : A dry sludge with the following analysis is mixed with fuel oil and burned in a furnace with air and the stack gas resulting has the analysis shown. Calculate: The wt % of Carbon and Hydrogen in the fuel oil, and The ratio of Kg sludge/Kg fuel oil in the mixture fed to the furnace.

Dr. F. IskanderaniChE 201 Spring 2003/ z

Dr. F. IskanderaniChE 201 Spring 2003/ Unknown Variables: S, A, F, P, m 1, W (total = 6) Balances : C, S, H, O, N 2, total mass balance (total = 5 independent) Basis : P = 100 Kgmoles Let us carry the atomic balances ( in Kg moles)

Dr. F. IskanderaniChE 201 Spring 2003/200415

Dr. F. IskanderaniChE 201 Spring 2003/ NOTE : we are changing from mass to moles Solve the equations and find answers to a) and b) Check answers using the total mass equation

Dr. F. IskanderaniChE 201 Spring 2003/ A = 500 moles of air EXAMPLE ( How to carry elemental or atomic balance on a stream) Fuel F is burned with air. Let F=25 Kg, and carry atomic balance on F in moles

Dr. F. IskanderaniChE 201 Spring 2003/200418

Dr. F. IskanderaniChE 201 Spring 2003/200419