Carbon Activity

This example shows the calculation of the carbon activity for methane mixtures in thermodynamic equilibrium.

import gaspype as gp
import numpy as np
import matplotlib.pyplot as plt

Setting temperatures and pressure:

t_range = np.array([600, 700, 800, 900, 1100, 1500])  # °C

p = 1e5  # Pa

fs = gp.fluid_system(['H2', 'H2O', 'CO2', 'CO', 'CH4'])

Equilibrium calculation for methane steam mixtures:

ratio = np.linspace(0.01, 1.5, num=128)

fl = gp.fluid({'CH4': 1}, fs) + ratio * gp.fluid({'H2O': 1}, fs)

The shapes of the fluid and the temperature are broadcast against each other. So we can calculate the carbon activity for all compositions times all temperatures in t_range with a single call:

carbon_activity = gp.carbon_activity(fl, t_range[:, None] + 273.15, p)

Plot carbon activities, a activity of > 1 means there is thermodynamically the formation of sold carbon favored.

fig, ax = plt.subplots(figsize=(6, 4), dpi=120)
ax.set_xlabel("H2O/CH4")
ax.set_ylabel("carbon activity")
ax.set_ylim(1e-1, 1e3)
ax.set_yscale('log')
ax.plot(ratio, carbon_activity.T)
ax.hlines(1, np.min(ratio), np.max(ratio), colors='k', linestyles='dashed')
ax.legend([f'{tc} °C' for tc in t_range])

<matplotlib.legend.Legend at 0x7fd1ac9d3ac0>

Let’s do the equilibrium calculation for methane CO2 mixtures as well:

fl_co2 = gp.fluid({'CH4': 1}, fs) + ratio * gp.fluid({'CO2': 1}, fs)
carbon_activity_co2 = gp.carbon_activity(fl_co2, t_range[:, None] + 273.15, p)

And plot carbon activities over the CO2 to CH4 ratio:

fig, ax = plt.subplots(figsize=(6, 4), dpi=120)
ax.set_xlabel("CO2/CH4")
ax.set_ylabel("carbon activity")
ax.set_ylim(1e-1, 1e3)
ax.set_yscale('log')
ax.plot(ratio, carbon_activity_co2.T)
ax.hlines(1, np.min(ratio), np.max(ratio), colors='k', linestyles='dashed')
ax.legend([f'{tc} °C' for tc in t_range])

<matplotlib.legend.Legend at 0x7fd1aa47ece0>

gaspype.carbon_activity is a shortcut for the more general function gaspype.activity, which calculates the activity of any substance in the equilibrated gas. Condensed species (solids and liquids) can be listed with gaspype.species(condensed=True). For example the activity of liquid water shows if steam condenses, here for a fuel gas at 50 °C:

fl_wet = gp.fluid({'H2': 0.8, 'H2O': 0.2}, fs)

gp.activity(fl_wet, 50 + 273.15, p, 'H2O(L)')

array(1.62473423)