Process files

A process can be read from and written to a JSON file with read_process and write_process, and an adsorbent with load_adsorbent and save_adsorbent. Mocca has a library of both from published studies:

using Mocca
library_processes()     # "haghpanah_2013_four_stage_vsa", ...
library_adsorbents()    # "zeolite_13x_haghpanah_2013", ...
process = read_process("haghpanah_2013_four_stage_vsa")
write_process("my_vsa.json", process)

Conventions

• Numbers are plain SI: Pa, K, m, s, mol, kg, J. A number may also be a string with a unit, such as "0.1 bar", "25 °C", "14.45 cm", "-36.6 kJ/mol" or "100 cm/s".

• Compositions and per-component values are objects keyed by component name, such as {"CO2": 0.15, "N2": 0.85}. Components left out of a composition get a trace ().

• Unknown keys are errors, so that a misspelt setting is not silently ignored. Errors say where they are, such as MoccaInputError in step 3 (blowdown) of the cycle, to: ....

A process file

{
  "format": "mocca-process",
  "version": 1,
  "name": "four-step VSA",
  "gas": {
    "components": ["CO2", "N2"],
    "molar_masses": {"N2": 0.028},
    "heat_capacities": {"CO2": 697.5687, "N2": 1096.4},
    "viscosity": 1.72e-5,
    "density": 1.22638310956,
    "diffusivity": 1.6e-5
  },
  "feed": {"composition": {"CO2": 0.15, "N2": 0.85}, "temperature": "25 °C", "pressure": "1 bar"},
  "adsorbents": {"13X": "zeolite_13x_haghpanah_2013"},
  "columns": {
    "column": {"length": 1.0, "radius": 0.1445, "outer_radius": 0.162, "porosity": 0.37,
               "axial_conductivity": 0.0903,
               "wall": {"density": 7800, "heat_capacity": 502, "conductivity": 16},
               "inner_heat_transfer": 8.6, "outer_heat_transfer": 2.5, "ambient_temperature": 298.15}
  },
  "units": [
    {"name": "Bed", "type": "fixed_bed", "adsorbent": "13X", "column": "column", "ncells": 30,
     "thermal": "with_wall", "dispersion_velocity": "adsorption"}
  ],
  "devices": [
    {"name": "V_feed", "role": "feed", "at": ["Bed", "bottom"]},
    {"name": "V_product", "role": "product", "at": ["Bed", "top"]},
    {"name": "V_vacuum", "role": "extract", "at": ["Bed", "bottom"]}
  ],
  "cycle": {"steps": [
    {"type": "pressurise", "duration": 15},
    {"type": "adsorb", "duration": 15, "velocity": 1.0},
    {"type": "blowdown", "duration": 30, "to": "0.2 bar"},
    {"type": "evacuate", "duration": 40, "to": "0.1 bar"}
  ]},
  "time_stepping": {"max_dt": 1.0, "first_dt": 0.05, "keep_step_pattern": "auto"},
  "options": {"key_component": "CO2", "ambient_pressure": 1e5, "pump_efficiency": 0.72,
              "heat_capacity_ratio": 1.4, "ramp_rate": 0.5},
  "initial_state": {"Bed": {"pressure": "1 bar"}},
  "parameters": {"Bed": {"AdsorbentDensity": 1130}},
  "variables": [
    {"name": "P_L", "places": [{"step": "evacuation", "field": "to"}],
     "bounds": ["0.01 bar", "0.5 bar"], "description": "evacuation pressure"}
  ]
}

The sections:

Section	Contents
components	Optional: components not known to Mocca, each with name, molar_mass, heat_capacity and viscosity, and optionally formula and cas.
gas	The Gas: its components in order (the first is the one to capture), and optional overrides.
feed	The Feed: composition, temperature, pressure and optionally light_product.
adsorbents	By name: an adsorbent object (as in an adsorbent file), the name of a library adsorbent, or the path of an adsorbent file relative to the process file.
columns	By name: Column objects.
units	Beds, in order, as in add_bed!. thermal is "with_wall", "adiabatic" or {"type": "isothermal", "temperature": ...}.
devices	Devices, in order, as in add_device!: a role, and at (a [unit, port] pair) or, for a link, from and to. An optional boundary sets pressure, temperature and composition.
cycle	steps, a list of steps; or sequences, a list of {"label": ..., "steps": [...]} run side by side, and an optional cycle_time.
time_stepping	See TimeStepping.
options	See Process.
initial_state	Per bed: any of pressure, temperature, wall_temperature and composition.
parameters	Per unit: Jutul parameters to override.
variables	Design variables (see add_variable!), each with places: {"step": ..., "field": ..., "sequence": ...}, {"feed": "pressure"} or {"unit": ..., "parameter": ...}.

Steps

Each step has a type and its fields as keys:

type	Step	Fields
pressurise	Pressurise	duration, to, from, source ("feed" or "light_product"), bed, device, ramp_rate, conductance, name
adsorb	Adsorb	duration, one of velocity, superficial_velocity and flow_rate, pressure, bed, feed_device, outlet, conductance, name
blowdown	Blowdown	duration, to, from, through, device, bed, ramp_rate, conductance, name
evacuate	Evacuate	as blowdown
purge	Purge	duration, one of velocity, superficial_velocity and flow_rate, pressure, bed, conductance, name
equalise	Equalise	duration, beds, device, conductance, name
idle	Idle	duration, bed, name
concurrent	Concurrent	steps, name

Step types defined with register_step! are read and written the same way.

An adsorbent file

{
  "format": "mocca-adsorbent",
  "version": 1,
  "name": "zeolite 13X",
  "reference": "Haghpanah et al. (2013)",
  "density": 1130.0,
  "heat_capacity": 1070.0,
  "particle_diameter": 0.002,
  "particle_porosity": 0.35,
  "tortuosity": 3.0,
  "adsorbed_heat_capacity": {"CO2": 697.5687, "N2": 1096.4},
  "isotherm": {
    "type": "dual_site_langmuir",
    "reference_temperature": 298.15,
    "basis": "volume",
    "components": {
      "CO2": {"qsb": 3489.44, "b0": 8.65e-7, "dUb": -36641.21, "qsd": 2872.35, "d0": 2.63e-8, "dUd": -35690.66},
      "N2": {"qsb": 6613.551, "b0": 2.5e-6, "dUb": -15800.0}
    }
  }
}

basis is "volume" for capacities in mol per m³ of adsorbent or "mass" for mol/kg. Isotherm types defined with register_isotherm! are read the same way.

The earlier format

Mocca.parse_input reads the JSON files of Mocca 0.1.0 into constants structs, and convert_constants turns those into the objects above, to move such inputs over. Mocca no longer simulates them directly.