Flowsheet documentation for seawater RO desalination

docs/technical_reference/flowsheets/index.rst

@@ -15,3 +15,4 @@ Flowsheets
    crystallization
    ion_exchange
    gac
+   seawater_RO_desalination

docs/technical_reference/flowsheets/seawater_RO_desalination.rst

@@ -0,0 +1,235 @@
+Seawater RO Desalination
+========================
+
+Introduction
+------------
+
+This flowsheet represents a full-scale seawater reverse osmosis treatment facility.
+The flowsheet includes pretreatment, desalination, post-treatment, and waste handling unit processes available in WaterTAP.
+Unit models used on this flowsheet span the spectrum from simple to detailed.
+
+
+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`
+    * :doc:`/technical_reference/costing/zero_order_costing`
+Property models:
+    * :doc:`/technical_reference/core/water_props`
+    * :doc:`/technical_reference/property_models/seawater`
+Unit models:
+    * :doc:`/technical_reference/unit_models/zero_order_unit_models/index`
+    * :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, and solve the model, as well as
+some helper functions that group these core functions together for convenience. Building and solving the flowsheet proceeds in six steps:
+
+1. Creating and instantiating the model using ``build()``:
+
+    This function will create the core components and structure of the flowsheet. The keyword argument ``erd_type`` dictates the type
+    of energy recovery device to be used, with options ``pressure_exchanger`` or ``pump_as_turbine``.
+    First, the ``FlowsheetBlock``, ``Database``, and property models are created. The zero order property models require the user
+    to provide a ``solute_list`` (e.g., TDS and TSS), while the seawater property model is pre-populated with TDS as the only solute.
+    Separate ``Block`` are created to contain all the unit models required to model the pretreatment, desalination, and post-treatment
+    parts of the treatment train:
+
+        * Pre-treatment (``m.fs.pretreatment``): comprised entirely of zero order models, this block contains the intake, chemical addition, media, and cartridge filtration unit models.
+        * Desalination (``m.fs.desalination``): contains all the unit models needed to represent the pumping, reverse osmosis (RO), and energy recovery device (ERD) processes.
+        * Post-treatment (``m.fs.posttreatment``): includes post desalination disinfection, remineralization, and storage unit models.
+
+    Outside of these, there is a feed, distribution, landfill, and disposal block that are placed directly on the flowsheet.
+    ``Translator`` blocks are added with appropriate constraints and ``Arc`` are used to connect the unit processes in the proper order.
+    Finally, default scaling factors are set and scaling factors are calculated for all variables.
+
+2. Specify the operating conditions with ``set_operating_conditions()``:
+
+    This function begins by specifying the inlet conditions. Then, starting with the ``pretreatment`` block, the operating 
+    conditions for each unit model are set. The inlet conditions and specific unit model operating conditions are in the Flowsheet Specifications section of this page.
+
+3. Initialize the unit and costing models with ``initialize_system()``:
+
+    Starting with the ``Feed`` block and continuing sequentially through each part of the treatment train, this function sets the initial condition
+    for all the unit models on the flowsheet and propagates ``Arcs`` that connect each block either to ``Translator`` blocks or treatment blocks. 
+    Each block is initialized and solved by using the local ``solve()`` function to ensure each block solves optimally before trying to solve the next.
+    Note that the order in which blocks/unit models are solved/initialized in WaterTAP is important because the initial conditions are *only* set 
+    for the ``Feed`` block. For these conditions to cascade to downstream unit models, and for the downstream unit models to include the impacts of upstream 
+    process (e.g., component removal), sequential initialization is necessary. Thus, initialization of this flowsheet proceeds as follows:
+
+        #. ``Feed`` block where initial flow rates and solute concentrations are set.
+        #. ``pretreatment`` block 
+        #. translator block from ``pretreatment`` to ``desalination`` (i.e., ``m.fs.tb_prtrt_desal``)
+        #. ``desalination`` block
+        #. translator block from ``desalination`` to ``posttreatment`` (i.e., ``m.fs.tb_desal_psttrt``)
+        #. ``posttreatment`` block
+
+4. Add the system- and unit-level costing packages with ``add_costing()`` and initialize with ``initialize_costing()``:
+
+    Because of the nature of the unit models used in this flowsheet (i.e., both zero order and detailed models), two separate system-level costing packages are required. 
+    ``m.fs.zo_costing = ZeroOrderCosting()`` is used to aggregate costs for zero-order models, and ``m.fs.ro_costing = WaterTAPCosting`` is for the more detailed desalination models. 
+    The costing block for each unit model is ``UnitModelCostingBlock`` that points to a system-level aggregation costing package via the configuration keyword ``flowsheet_costing_block``.
+    Each system-level costing package has a ``.cost_process()`` method that is called to aggregate unit level costs and calculate overall process costs.
+    To aggregate results from both costing packages, a separate ``Expression`` is created for ``total_capital_cost`` and ``total_operating_cost``, and each of these are used
+    to calculate the ``LCOW``. Finally, like the unit models, the costing packages are initialized.
+
+5. Solve the entire flowsheet and display final results with ``display_results()``:
+
+    After building, specifying, initializing, and costing the models, the flowsheet is solved a final time with the local ``solve()`` function
+    and the ``.report()`` method is called for each unit model using ``display_results()``.
+
+The local function ``build_flowsheet()`` combines steps 1 and 2. The local function ``solve_flowsheet()`` combines 3, 4, and 5.
+
+.. note::
+
+    ``Translator`` blocks are used in flowsheets when more than one property package is used in different parts of the flowsheet.
+    In this example, the zero order property package contains state variables that are only indexed by component (e.g., ``conc_mass_comp['TDS']``)
+    while the seawater property package contains state variables indexed by both phase and component (e.g., ``conc_mass_phase_comp['Liq', 'TDS']``).
+    The translator blocks in this flowsheet are used to communicate properties between unit models that use these two property packages and simply
+    say, e.g., ``conc_mass_comp['TDS'] = conc_mass_phase_comp['Liq', 'TDS']``.
+
+Pre-Treatment
+^^^^^^^^^^^^^
+
+Figure 1 presents the process flow diagram for ``m.fs.pretreatment``. The first unit model on this block, ``intake``, is connected to the
+flowsheet level ``Feed`` block.
+
+.. figure:: ../../_static/flowsheets/SW_RO_fs_pretreat.png
+    :width: 800
+    :align: center
+
+    Figure 1: Process flow diagram for pre-treatment block.
+
+Desalination
+^^^^^^^^^^^^
+
+Figure 2 presents the process flow diagram for ``m.fs.desalination`` if ``erd_type == "pressure_exchanger"``.
+Figure 3 presents the process flow diagram for ``m.fs.desalination`` if ``erd_type == "pump_as_turbine"``.
+In either case, the first unit model on this block is connected to the flowsheet level translator block ``tb_prtrt_desal``.
+
+.. figure:: ../../_static/flowsheets/SW_RO_fs_desal_PXR.png
+    :width: 800
+    :align: center
+
+    Figure 2: Process flow diagram for desalination block for pressure exchanger ERD.
+
+.. figure:: ../../_static/flowsheets/SW_RO_fs_desal_turbine.png
+    :width: 600
+    :align: center
+
+    Figure 3: Process flow diagram for desalination block for pump-as-turbine ERD.
+
+Post-Treatment
+^^^^^^^^^^^^^^
+
+Figure 4 presents the process flow diagram for ``m.fs.posttreatment``. The first unit model on this block is connected to the
+flowsheet level translator block ``tb_desal_psttrt``.
+
+.. figure:: ../../_static/flowsheets/SW_RO_fs_posttreat.png
+    :width: 800
+    :align: center
+
+    Figure 4: Process flow diagram for post-treatment block.
+
+Full Flowsheet
+^^^^^^^^^^^^^^
+
+Figure 5 presents the process flow diagram for the entire flowsheet for both ERD options.
+
+.. figure:: ../../_static/flowsheets/SW_RO_fs_full.png
+    :width: 1500
+    :align: center
+
+    Figure 5: Process flow diagram for entire flowsheet.
+
+
+Degrees of Freedom
+------------------
+
+The degrees of freedom (DOF) for the flowsheet can change depending on model configuration options.
+For either ``erd_type``, after building the flowsheet with the provided ``build()`` function, there are 58 DOF.
+Many of these DOF are related to the not-yet-propagated Arcs between each of the unit process blocks.
+Others are related to influent conditions and specific operating conditions for each unit model that must be specified by the user.
+The operating conditions for this demonstration are provided in the following section, and include:
+
+* Influent conditions (component flows, temperature, pressure)
+* Chemical doses
+* RO membrane properties
+* RO operating pressure
+* Pump and ERD efficiencies
+* Storage duration
+
+Passing the default build to the provided function ``set_operating_conditions()`` will result in a model with zero DOF.
+
+Flowsheet Specifications
+------------------------
+
+The influent conditions are defined from the case study used to develop this flowsheet. 
+Additionally, some unit models have case-specific operating conditions.
+The influent conditions and case-specific operating conditions for certain unit models are presented in the following table,
+including the different build options for ``erd_type``:
+
+.. csv-table::
+   :header: "Description", "Value", "Units", "Flowsheet Model Name"
+
+    **Influent Conditions**
+   "Volumetric flow rate", "7.05", ":math:`\text{MGD}`"
+   "TDS :sup:`1` concentration", "35", ":math:`\text{g/L}`"
+   "TSS :sup:`2` concentration", "0.03", ":math:`\text{g/L}`"
+   "Temperature", "298", ":math:`\text{K}`"
+   "Pressure", "100000", ":math:`\text{Pa}`"
+
+   **Pre-Treatment**
+   "Ferric chloride dose", "20", ":math:`\text{mg/L}`", "``m.fs.pretreatment.ferric_chloride_addition``"
+   "Storage tank 1 storage time", "2", ":math:`\text{hr}`", "``m.fs.pretreatment.storage_tank_1``"
+
+   **Desalination**
+   "RO water permeability coefficient", "4.2e-12", ":math:`\text{m/Pa/s}`", "``m.fs.desalination.RO``"
+   "RO salt permeability coefficient", "3.5e-8", ":math:`\text{m/s}`", "``m.fs.desalination.RO``"
+   "RO spacer porosity", "0.97", ":math:`\text{dimensionless}`", "``m.fs.desalination.RO``"
+   "RO channel height", "1e-3", ":math:`\text{m}`", "``m.fs.desalination.RO``"
+   "RO membrane width per stage", "1000", ":math:`\text{m}`", "``m.fs.desalination.RO``"
+   "RO total membrane area per stage", "13914", ":math:`\text{m}^2`", "``m.fs.desalination.RO``"
+   "RO permeate side pressure", "101325", ":math:`\text{Pa}`", "``m.fs.desalination.RO``"
+   "Pump 1 efficiency", "0.8", ":math:`\text{dimensionless}`", "``m.fs.desalination.P1``"
+   "Pump 1 operating pressure", "70e5", ":math:`\text{Pa}`", "``m.fs.desalination.P1``"
+
+   *if* ``erd_type == "pressure_exchanger"``
+   "Pressure exchanger efficiency", "0.95", ":math:`\text{dimensionless}`", "``m.fs.desalination.PXR``"
+   "Pump 2 efficiency", "0.8", ":math:`\text{dimensionless}`", "``m.fs.desalination.P2``"
+
+   *if* ``erd_type == "pump_as_turbine"``
+   "Energy recovery device pump efficiency", "0.95", ":math:`\text{dimensionless}`", "``m.fs.desalination.ERD``"
+   "Energy recovery device permeate side pressure", "101325", ":math:`\text{Pa}`", "``m.fs.desalination.ERD``"
+
+   **Post-Treatment**
+   "Anti-scalant dose", "5", ":math:`\text{mg/L}`", "``m.fs.posttreatment.anti_scalant_addition``"
+   "Lime dose", "2.3", ":math:`\text{mg/L}`", "``m.fs.posttreatment.lime_addition``"
+   "Storage tank 2 storage time", "1", ":math:`\text{hr}`", "``m.fs.posttreatment.storage_tank_2``"
+   "Storage tank 3 storage time", "1", ":math:`\text{hr}`", "``m.fs.posttreatment.storage_tank_3``"
+   "UV/AOP :sup:`3` reduction equivalent dose", "350", ":math:`\text{mJ/}\text{cm}^2`", "``m.fs.posttreatment.uv_aop``"
+   "UV/AOP :sup:`3` UV transmittance", "0.95", ":math:`\text{dimensionless}`", "``m.fs.posttreatment.uv_aop``"
+
+.. note::
+
+   :sup:`1`  TDS = total dissolved solids
+   |
+   :sup:`2`  TSS = total suspended solids
+   |
+   :sup:`3`  UV = Ultraviolet; AOP = Advanced oxidation process
+
+Code Documentation
+------------------
+
+* :mod:`watertap.examples.flowsheets.case_studies.seawater_RO_desalination`
+
+References
+----------
+
+References for each unit model can be found using the links provided in the Implementation section of this documentation.