A hydrogen fuel cell consumes hydrogen (geltaG^0 = 236, 100 kJ/kmol, deltaH^0 =

Question

A hydrogen fuel cell consumes hydrogen (geltaG^0 = 236, 100 kJ/kmol, deltaH^0 = 285, 600 kJ/kmol) at a rate of 17,000 kg per day. If the fuel cell has an efficiency of 68% and inverter efficiency of 90%, estimate The output power of the fuel cell in MW (2 marks) (Solution: 14.2 MW) The exergetic efficiency of the fuel cell (2 marks) (Solution: 50.6%) If the hydrogen is obtained from a methane steam reformation (MSR) process that is 65% efficient and the energy input for the MSR process is obtained by combusting methane, estimate The mass of methane required per day (1 marks) (Solution: 72, 890 kg) The overall efficiency of the fuel cell (2 marks) (Solution: 30.3%) The mass of C02 released per year in tons (1 marks) (Solution: 73, 132 tons) If the same amount of methane was consumed in a Brayton cycle with an overall efficiency of 40%, estimate The power output of the Brayton cycle (1 mark) (Solution: 18.7 MW) The mass of CO2 released per year in tons (1 mark) (Solution: 73, 060 tons)

Explanation / Answer

(a) hygrogen consumed in 1 sec=0.196 kg=n=97.37 mole

enegy produced=E=0.90*0.68*n*236100=14.2 MW

(b)exergenic efficiency=E/(m*delta G)=50.6 %

(c)CH4 + H2O CO + 3 H2

from 16 g methane ,hydrogen prepared=6 g

to make 17000 kg per day ,ideally methane required=M(16/6)*17000=45333.33 kg

if efficiency is 65 percent,methane required=(100/65)*M=69743.58 kg per day

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