4. (40 points) Hydrogen gas to power fuel cells is sometimes produced from metha

Question

4. (40 points) Hydrogen gas to power fuel cells is sometimes produced from methane in a synthesis gas reactor. In the reformer reactor considered here, a methanelcarbon dioxide stream is combined with superheated steam over catalyst, and four reactions may occur: CHa CO2 2CO+ 2H2 (i) (2) CH H20 CO+ 3H2 CHa 2H20 CO2 4H2 (4) The composition of the feed is (0.2 kmol CO2 per 1 kmol CHa). When the reformer is heated at a rate of 42.8 kcal/gmol dry feed gas, 80% of the methane reacts, and halfofthe CO2 fed is consumed. All streams are gases and you may assume that the reactor operates atlatm. The material balance solution is provided below. You are to complete an energy balance using a reference state of elements at 25°C and latm. Material Balance Table as component flows (kmol/hr) methane feed steam feed syngas product CH4 (F) 1000 2000 CO2 (D) 200 H2O (W) fw2-700 H2 (H) 2300 COC) 9000 COC) 500°C 600°C 200°C Specific Enthalpy Table (kJ/gmol) methane feed steam feed syngas product CH (F) CO2 (D) H20 (W) H2 (H) CO (M) T (°C) 200°C 500°C 600°C Stream Enthalpy Hi (kJ/hr)

Explanation / Answer

a)
If we add up all the 4 equations:

3CH4 + 2CO2 + H2 + 3H2O => 4CO + CO2 + 9H2 + H2O

So, it becomes:
3CH4 + CO2 + 2H2O => 4CO + 8H2
It takes 3 moles of CH4 and 1 mole of CO2 to form 8 moles of H2.


b)
Specific enthalpy = Cp * (T2 - T1)
Cp of steam at 600C = 23.58 kJ/gmol K
Cp varies with temperature.
Cp = Q / m*(T2-T1)
where Q = heat supplied, m=mass.

c)
In steam 1,
Q = 42.8 kcal,
For equation 3:
for 1 mole of CH4, 1 mole of H2O is consumed.
If 80% of CH4 is consumed = 0.8 kmol is consumed,
In equation 3,
CH4 used = 0.8/3 kmole
H2O used = 0.8/3 kmole = 4800 g

Temperatre change = 200 C from 25C.

So we can calculate Cp using Q, m and T2-T1

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