Natural gas, which we can assume is 100% methane, is combusted to generate electricity at a power plant. This is becoming increasingly popular as an NGCC process (Natural Gas Combined Cycle). In this process, the gas is burned in a turbine similar to a jet engine which produces electricity. The heat coming out of the gas turbine boils water which can be used to turn a steam turbine. This increases the overall electricity generation efficiency. The final step in making this process 21st century environmentally friendly is to compress the CO2 and store it underground.
a. In this process, 100 mol/hr of natural gas is 100 % combusted in a stream of pure 35 % excess oxygen. After exiting the combustion turbine at 1 atm and some temperature, the hot gases enter a heat exchanger where they are used to boil the water for a steam turbine. The gases exit the heat exchanger at 40o C and 1 atm. What is the temperature of the stream leaving the combustion turbine if there are 320.5 degrees of superheat? Note: You must use atomic species balances to solve for all of the reactive species. Failure to do so will result in no credit for this part of the problem.
b. Assuming the company uses extra drying techniques to remove the rest of the water and the remaining oxygen, we now have a pure stream of CO2 to compress and sequester underground. Assuming we hold the temperature at 40o C and increase the pressure to 400 atm, by how much have we changed the volume?
c. Why does this process use pure oxygen rather than air?