45 lines
1.5 KiB
Markdown
45 lines
1.5 KiB
Markdown
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# Thermodynamics of Hydrogen Production
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The minimal energy required to produce hydrogen from liquid water is given by the
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Higher Heating Value (HHV). The HHV is the sum of the difference
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between the enthalpies of products and educts (LHV: Lower Heating Value) and
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the Heat of Evaporation for water.
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```python
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import gaspype as gp
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lhv = gp.fluid({'H2': 1, 'O2': 1/2, 'H2O': -1}).get_H(25 + 273.15)
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dh_v = 43990 # J/mol (heat of evaporation for water @ 25 °C)
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hhv = lhv + dh_v
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print(f'LHV: {lhv/1e3:.1f} kJ/mol')
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print(f'HHV: {hhv/1e3:.1f} kJ/mol')
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```
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Thermodynamics also defines which part of the energy must be
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provided as work (e.g., electric power) and which part can be supplied
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as heat. This depends on temperature and pressure. For generating 1 bar
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of hydrogen the temperature dependency can be calculated as follows:
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```python
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import numpy as np
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import matplotlib.pyplot as plt
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t = np.linspace(0, 2000, 128) # 0 to 2000 °C
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p = 1e5 # Pa (=1 bar)
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g_products = gp.fluid({'H2': 1, 'O2': 1/2, 'H2O': 0}).get_G(t + 273.15, p)
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g_educts = gp.fluid({'H2': 0, 'O2': 0, 'H2O': 1}).get_G(t + 273.15, p)
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work = g_products - g_educts # J/mol
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heat = lhv - work # J/mol
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fig, ax = plt.subplots(figsize=(6, 4), dpi=120)
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ax.set_xlabel("Temperature / °C")
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ax.set_ylabel("Energy / kWh/kg")
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k = 1e-3 / 3600 / 0.002 # Conversion factor from J/mol to kWh/kg for hydrogen
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ax.stackplot(t, k * work, k * heat, k * dh_v * np.ones_like(t))
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```
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Green is the heat of evaporation, orange the additional heat provided at
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the given temperature and blue the work.
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