Number:
Name:
25.11.2016
CHE 205 Mass and Energy Balances
Homework III (due date 01.12.2016 15:00)
Problem 1:
a) Most of the fuel used in power plant combustion furnaces is either coal (C, H, S and
various noncombustible materials), fuel oil (hydrocarbons, S), gaseous fuel (such as
natural gas, which is primarily methane), or liquefied petroleum gas (propane and/or
butane). Write down the stack gases that forms after the combustion of these fuel
types. Prepare an informative short paragraph on the negative effects of the stack
gases to the environment.
b) The dry basis molar composition of a stack gas is given as: 70% CO2, 3% CO, 0.06%
SO2 and balanced O2. To burn the fuel completely, 30% of excess O2 is fed to the
system. Calculate the elemental composition of the fuel. Note: The fuel does not
contain any oxygen and the products are all in gas/vapor form.
Problem 2:
Butane is burned with air and no carbon monoxide is present in the combustion
products. Calculate the molar composition of the product gas for each three cases:
a) air is fed at theoretical amount and 100% conversion of butane is achieved
b) 15% of excess air is fed and 100% conversion of butane is achieved
c) 30% of excess air is fed and 85% conversion of butane is achieved
Problem 3:
Natural gas, produced over eons by decay of ancient plants, is recovered from wells
and used widely as a source of heat and energy. The composition of natural gas varies
from well to well. Here are analyses of natural gas from three different sources:
Composition of Natural Gas (mol%)
Component
Rio Arriba,
New Mexico
CH4 (methane)
96.91
C2H6 (ethane)
1.33
C3H8 (propane)
0.19
C4H10 (butane)
0.05
C5H12 (pentane)
0.02
CO2 (carbon dioxide)
0.82
N2 (nitrogen)
0.68
San Juan,
New Mexico
77.28
11.18
5.83
2.34
1.18
0.80
1.39
Cliffside,
Texas
67.0
3.8
1.7
0.8
0.5
0.0
26.2
A furnace operating at steady state burns 1.00 MMSCFD (1 million standard cubic
feet per day) of natural gas from different sources, with 23.0 MMSCFD air (assumed
to be 79 mol% N2, 21 mol% O2). The only detectable compounds in the flue gas are
CO2, H2O, O2, and N2.
Complete combustion of hydrocarbons is described by the general chemical equation
y
y
Cx Hy + (x+ ) O2 → xCO2 + H2 O
4
2
Write the equations for each combustion reaction. What is the flow rate (kgmol/h) and
composition (mol%) of the fuel gas ? Prepare a table showing the components and
molar flow rates of each component inlet and outlet streams. (Assume that the natural
gas and air behave as ideal gases. The volumetric flow rate is reported at standard
temperature and pressure: 0°C and 1 atm)
Note:
Students with surnames,
A-D will use natural gas from Rio Arriba, New Mexico
E-Ö will use natural gas from San Juan, New Mexico
P-Z will use natural gas from Cliffside, Texas
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Problem 4:
Write the definitions of the following terms, both in English and Turkish:
Latent heat
Sensible heat
Heat of fusion
Heat of vaporization