Under the FutureGen 2.0 project (http://www.futuregenalliance.org/) sponsored by
ID: 950646 • Letter: U
Question
Under the FutureGen 2.0 project (http://www.futuregenalliance.org/) sponsored by the U.S. Department of Energy, a novel process is used to convert coal into electricity with minimal greenhouse gas (CO2) emissions to the atmosphere. In the process, coal is combusted in a boiler with pure O2; the heat released produces steam, which is then used for heating and to drive turbines that generate electricity. An excess of O2 is supplied to the boiler to convert all the coal into a flue gas consisting of carbon dioxide, steam, and any unreacted oxygen. The mass flow rate of coal to the boiler is 50 kg/s, and O2 is fed in 8.33% excess. For the purposes of this analysis, the chemical formula of coal can be approximated as C5H8O2. (a)Draw and label the flowchart and carry out the degree-of-freedom analysis using balances on atomic species. (b)Determine the molar flow of oxygen supplied to the boiler. (c)Solve for the remaining unknown flow rates and mole fractions. Determine the molar composition of the flue gas on a dry basis. (d)A feature that makes the FutureGen power plant unique is the intent to capture the CO2 generated, compress it, and pump it into deep geological formations in which it will be permanently stored. List at least two safety or environmental issues that should be considered in the construction and operation of this plant. (e)List at least two pros and two cons of using pure O2 versus air.
Explanation / Answer
C5H8O2+6O2----> 5CO2+4H2O
Given flow rate of Fuel = 50 kg/s and amount of excess oxygen supplied
Known : Flow rate unknown : CO2 , H2O and amount of oxygen
Oxygen flow rate can be calculated from the stoichiometry of the reaction and flow rate of Fuel supplied.
Based on the Carbon atom , amount of CO2 can be calculated.
Based on the number of hydrogen atoms, flow rate of water can be calculated.
C5H8O2+6O2----> 5CO2+4H2O
From the stoichiometry, 1 mole of C5H8O2 requires 6 moles of oxygen
Flow rate of C5H8O2= 50 kg/s Molecular weight= 5*12+8+32= 100
Moles of C5H8O2= Mass/ Molecular weight =50/100 = 0.5 moles/s
Moles of Oxygen required=0.5*6= 3 moles/s
Oxygen supplied is 8.33% excess, oxygen supplied = 1.0833*3=3.25 moles/s
CO2 produces = 5 times molar flow rate of Fuel =5*0.5= 2.5 moles/s , moles of water produced= 4*0.5=2 moles/s
Excess oxygen =3*0.0833=0.25 moles
Products : CO2= 2.5 moles/s Water =2 moles/s and Oxygen =0.25 moles/s
Product total flow rate= 2.5+2+0.25= 4.75 moles/s
Composition of product : CO2= 2.5/4.75= 0.53 , water =2/4.75 =0.42 and oxygen =0.05
d)
Since CO2 during sequestration accumulates in soils can suppress respiration in the root zone or result in soil acidification, which would be harmful to plants.
Catastrophic releases even unlikey, can kill vegetation and animals.
b) Pros :
The adibatic flame temperature will be more. Less fuel is required since NoX formation is prevented,
Cons :
The combustion reaction can become uncontrollable.
Additional cost in producing enriched oxygen from air.
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