Flowsheet documentation for RO w/ ERD

docs/technical_reference/flowsheets/RO_with_energy_recovery.rst

@@ -0,0 +1,162 @@
+Reverse Osmosis with Energy Recovery
+====================================
+
+Introduction
+------------
+
+This flowsheet represents a reverse osmosis (RO) with energy recovery device (ERD). 
+The flowsheet is similar to the desalination block of the full-scale seawater RO treatment facility flowsheet,
+but includes an demonstration for optimization of the process. The user can select between pressure exchanger ERD, 
+pump-as-turbine ERD, or no ERD.
+
+Implementation
+--------------
+
+This flowsheet uses several different modeling features available in WaterTAP, including:
+
+Costing packages:
+    * :doc:`/technical_reference/costing/watertap_costing`
+    * :doc:`/technical_reference/costing/detailed_unit_model_costing`
+Property models:
+    * :doc:`/technical_reference/property_models/NaCl`
+Unit models:
+    * :doc:`/technical_reference/unit_models/reverse_osmosis_0D`
+    * :doc:`/technical_reference/unit_models/pressure_exchanger`
+    * :doc:`idaes:reference_guides/model_libraries/generic/unit_models/product`
+    * :doc:`idaes:reference_guides/model_libraries/generic/unit_models/separator`
+    * :doc:`idaes:reference_guides/model_libraries/generic/unit_models/mixer`
+
+The demonstration file itself contains several core functions that are used to build, specify, initialize, solve, and (optionally) optimize the model, 
+as well as helper functions that group these core functions together for convenience or to display results.
+
+* Creating and instantiating the model using ``build()``:
+
+    This function will create the core components and structure of the flowsheet including unit, property, and costing models.
+    Different components will be added depending on the type of ERD used (dictated by the ``erd_type`` argument).
+    An ``Arc`` is used to connect the different component flows to one another and default scaling factors are set.
+
+* Specify the operating conditions with ``set_operating_conditions()``:
+
+    Influent component flows and RO pump operating pressures are set with this function.
+    The user can set via keyword arguments the volumetric flow rate (``flow_vol``), mass fraction of NaCl (``salt_mass_conc``),
+    a target fractional mass-based water recovery ``water_recovery``, and a fractional over pressure (``over_pressure``). 
+    Over pressure is the fractional increase in pressure over of the brine osmotic pressure to use as the
+    an initial guess for the RO operating pressure as determined by the helper function ``calculate_operating_pressure``.
+    Initial values for relevant RO membrane parameters are provided in the Flowsheet Specifications section.
+    After the RO unit is initialized, the area is unfixed and the mass-based recovery is fixed to the 
+    user provided value.
+
+* Calculating the RO operating pressure with ``calculate_operating_pressure()``:
+
+    This helper functions takes in the RO feed state block and will calculate the needed operating pressure
+    to achieve the desired mass-based water recovery.
+
+* Initialize entire system with ``initialize_system()``:
+
+    After the model is built and specified, this function will initialize the feed, RO, and costing blocks.
+    Depending on the ``erd_type`` different helper functions are used to initialize the relevant 
+    ERD-related unit models.    
+
+* Optionally optimize the system with ``optimize_set_up()``:
+
+    The model is fully defined and can be solved with the provided ``solve()`` function after the user passes 
+    the model through ``initialize_system()``. This function is provided as a demonstration of how the system could be
+    optimized the minimize the levelized cost of water (LCOW). The optimization routine proceeds as follows:
+
+    #. An ``Objectve`` is placed on the flowsheet set to minimize the ``LCOW`` expression in the costing package.
+    #. Operating pressure for the RO booster pump is unfixed and realistic bounds are placed on the pressure.
+    #. Similarly, the RO membrane area is unfixed and bounds are placed on the membrane area.
+    #. To ensure the product water is still of acceptable quality, a ``Constraint`` is placed on the effluent 
+       concentration of the RO to be less than 500 mg/L.
+    #. Additionally, there is a minimum water flux placed on the RO model to be over 2.8e-4 kg/m :math:`\text{}^2`/s.
+
+There are other helper functions, like ``display_system()``, ``display_design()``, and ``display_state()``, that 
+are used to print out the results of the model solve. The ``main()`` function is an example of building, specifying, 
+initializing, and optimizing an RO-ERD system with WaterTAP.
+
+
+Figure 1 presents the process flow diagram if ``erd_type == pressure_exchanger``.
+
+.. figure:: ../../_static/flowsheets/RO_w_ERD-PXR.png
+    :width: 600
+    :align: center
+
+    Figure 1: Process flow for RO with pressure exchanger ERD.
+
+Figure 2 presents the process flow diagram if ``erd_type == pump_as_turbine``.
+
+.. figure:: ../../_static/flowsheets/RO_w_ERD-turbine.png
+    :width: 600
+    :align: center
+
+    Figure 2: Process flow for RO with pump-as-turbine ERD.
+
+
+Figure 3 presents the process flow diagram with no ERD (i.e., ``erd_type == no_ERD``).
+
+.. figure:: ../../_static/flowsheets/RO_w_ERD-no_ERD.png
+    :width: 600
+    :align: center
+
+    Figure 3: Process flow for RO without ERD.
+
+
+Degrees of Freedom 
+------------------
+
+The degrees of freedom (DOF) for the flowsheet can change depending on model configuration options.
+For either ``pump_as_turbine`` or ``pressure_exchanger`` as ``erd_type``, there are 15 DOF. Running
+the model with ``no_ERD`` results in 13 DOF.
+
+* Influent conditions (component flows, temperature, pressure)
+* RO membrane properties
+* RO operating pressure
+* Pump and ERD efficiencies
+
+Passing any model build to the provided function ``set_operating_conditions()`` will result in a model with zero DOF.
+
+
+Flowsheet Specifications
+------------------------
+
+The influent and operating conditions for the different flowsheet configurations are presented in the following table,
+including the different build options for ``erd_type``:
+
+.. csv-table::
+   :header: "Description", "Default Value", "Units"
+
+    **Influent Conditions**
+   "Volumetric flow rate", "1e-3", ":math:`\text{m}^3/\text{s}`"
+   "TDS mass fraction", "0.035", ":math:`\text{dimensionless}`"
+   "Temperature", "298", ":math:`\text{K}`"
+   "Pressure", "101325", ":math:`\text{Pa}`"
+
+   **Desalination**
+   "RO water permeability coefficient", "4.2e-12", ":math:`\text{m/Pa/s}`"
+   "RO salt permeability coefficient", "3.5e-8", ":math:`\text{m/s}`"
+   "RO spacer porosity", "0.85", ":math:`\text{dimensionless}`"
+   "RO channel height", "1e-3", ":math:`\text{m}`"
+   "RO membrane width per stage", "5", ":math:`\text{m}`"
+   "RO total membrane area per stage", "50", ":math:`\text{m}^2`"
+   "RO permeate side pressure", "101325", ":math:`\text{Pa}`"
+   "Pump 1 efficiency", "0.8", ":math:`\text{dimensionless}`"
+   "Pump 1 operating pressure", "70e5", ":math:`\text{Pa}`"
+
+   *if* ``erd_type == "pressure_exchanger"``
+   "Pressure exchanger efficiency", "0.95", ":math:`\text{dimensionless}`"
+   "Pump 2 efficiency", "0.8", ":math:`\text{dimensionless}`"
+
+   *if* ``erd_type == "pump_as_turbine"``
+   "Energy recovery device pump efficiency", "0.95", ":math:`\text{dimensionless}`"
+   "Energy recovery device permeate side pressure", "101325", ":math:`\text{Pa}`"
+
+
+Code Documentation
+------------------
+
+* :mod:`watertap.examples.flowsheets.RO_with_energy_recovery`
+
+References
+----------
+
+References for each component and model used in this flowsheet can be found using the links provided in the Implementation section of this documentation.

docs/technical_reference/flowsheets/index.rst

@@ -15,4 +15,5 @@ Flowsheets
    crystallization
    ion_exchange
    gac
+   RO_with_energy_recovery
    seawater_RO_desalination