Question: Air stored underground at 500 psia and 200 deg.F is first heated by natural gas...

Question: Air stored underground at 500 psia and 200 deg.F is first heated by natural gas combustion to 2,340 deg.F at constant pressure, then expanded in an 89% efficient turbine to atmospheric (14.7 psia) pressure. Part of the work of the turbine is used to compress ambient air at 70 deg.F and 14.7 psia to store it underground with an 85% efficient compressor. The air that is stored underground loses heat to the surroundings. The turbine powers an electric generator that is 93% efficient converting mechanical power to electrical power. Mass flow of air is 100 lb/s.

a. How much heat is added by the combustion of natural gas to the air stored underground that enters the turbine? [Answer: 513.6 Btu/lb]

b. What is the work produced by the turbine? [Answer: 379.7 Btu/lb]

c. What is the work of compression? [Answer: 260.2 Btu/lb]

d. At what temperature does the air exit the compressor? [Answer: 1154 deg.F]

e. Natural gas costs $3 per million Btu (MMBtu) and the electricity that is generated by this storage system is sold at $50/MWh. The system produces electricity from the stored compressed air for 5 hours per day. Calculate the net income from the system from electricity sales. [Answer: $2931 electricity sold, $2773 cost of natural gas, $158 net income from producing electricity 5 h/day.]

Expert Solution

samet mamat answered 3 days ago

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