Summary/Motivation:

Currently, we spend alot of time building custom flowsheets that require full re-parametrization of each unit model. This makes the units non-portable, and results in duplicate code. We also use low-level API for building flowsheets, where all units have to be manually connected via arcs, and propagated. This can make sense in a few scenarios (Where a flowsheet has a very complex connection structure), but in most cases, the connections and their flow is mostly linear (even in complex processes like LSRRO).

The WaterTAPFlowsheetBlock brings a layer of abstraction for units with focus on providing a standard building platform for flowsheets where unit models become portable between flowsheets, and where time spent on configuring each unit model is minimized. It defines standard functions necessary to fully define a unit model from fixed operation variables to scaling factors, and additionally provides a method for standard connection management. A full example of benefits/implementation can be found in this branch and flowsheet

An example workflow with unit models build on watertapflowsheet block may look as follows:

# Define our flowsheet and properties
m.fs = FlowsheetBlock()
m.fs.costing = WaterTAPCosting()
m.fs.properties = MCASParameterBlock(**mcas_props)

# Watertap flowsheet units 
# Here feed specs would be a dict that contains information about feed composition.
m.fs.feed = MultiCompFeed(
        default_property_package=m.fs.properties,
        **feed_specs,
    )

#Here softening specs would be a dict that defines reactions and solids that would form
m.fs.softening_unit = PrecipitationUnit(
    default_property_package=m.fs.properties,
    default_costing_package=m.fs.costing,
    **softeining_specs)

# standard IDAES units
m.fs.product= Product(property_package=m.fs.seawater_props)
m.fs.solids_waste =  Product(property_package=m.fs.seawater_props)

# this builds all the arcs for us and adds tracking for thier propagation
m.fs.feed.outlet.connect_to(m.fs_softening_unit.inlet)
m.fs.fs_softening_unit.treated.connect_to(m.product.inlet) # connects to normal IDAES units!
m.fs.fs_softening_unit.waste.connect_to(m.solids_waste.inlet) # connects to normal IDAES units!
# standard arc expansion!
TransformationFactory("network.expand_arcs").apply_to(m)

m.fs.feed.fix_and_scale() # fixes operation and scales the unit model

m.fs.feed.initialize() # intialzies and propagates all outlet connections
m.fs.softening_unit.initialzie() #initlaizes and propages all outlet connections

# the outlets from softening were propagated by the WaterTAP flowsheet block, so we can just initialize these!
m.fs.product.initialize()
m.fs.solid_waste.initalize()

... do a box solve if wanted 

# use built-in optimization config function to do our optimization. 
m.fs.softening.set_optimization_operation()

.... go on to do optimization etc. 

Changes proposed in this PR:

• Add watertapflowsheet block
• Add connection utilities that manage arcs and equality constraints for unit connections
• Add reporting utility for building custom reports for flowsheet units.

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