# reaction-with-purge.in
#
# Conceptual level design for a reaction/separation problem with a
# purge unit. The problem includes the simple reaction A+B -> 2C and
# distillation units to perform the separation steps. The initial feed
# consists of three components, A, B and an inert D. The desired
# product is C.  The reaction is not complete and hence recycling is
# necessary. Additionally, there is a purge unit which may or may not
# be used (the synthesis procedure decides this).
#
# Copyright (c) 2000, Eric S Fraga, All rights reserved.
#
# ---------------------------------------------------------------------
#
# Give the synthesis problem a name and a description. These are used
# for report generation. All output will appear in a subdirectory
# named after the project name.
#
project ReactionWithPurge
title "Reaction with purge example"
#
# tell the system where to find the classes referenced below
use jacaranda.design.ps		# for base stream and component classes
use jacaranda.design.units	# for the unit models and unit variables

#
# The first step is to define the feed. We use the PseudoComponent
# class to define the 4 components in the system. This class
# implements very simple physical property estimation methods:
# essentially, all physical properties are constant. The only physical
# property actually required for this problem is the vapour pressure
# from which all VLE calculations required by the distillation unit
# can be derived.  The components are ranked from C1 to C4 in terms of
# relative volatility, C1 being the lightest and C4 the heaviest.
#
# Note, although it may be tempting to use the letters A through D to
# name the components, this is not a good idea because some of the
# units use these as variables for some of the computed results. For
# instance, the distillation column defines B and D to be the bottoms
# and distillate flow rates respectively.
#
PseudoComponent C1
	base 1
	vapourpressure 8
end
PseudoComponent C2
	base 1
	vapourpressure 4
end
PseudoComponent C3
	base 1
	vapourpressure 2
end
PseudoComponent C4
	base 1
	vapourpressure 1
end
Phase phase
	add C1 10
	add C2 10
	add C4 10
	phase liquid
end
PStream feedstream
	add phase
	T 300
	P 1
end
#
# The feed is associated with a feed tank
#
FeedTank feed
  Stream feed feedstream
end
#
# The reaction is embodied in a Reaction class. We describe the rate
# (which is used to calculate the design information for the reactor)
# and the stoichiometry for the reaction.
#
Reaction reaction
	comps C1 C2 C3
	stoich -1 -1 2
	rate	10
end
#
# The reactor uses the reaction defined above and we specify the
# desired reaction conversion. We could of course define a range of
# conversions.  The length to diameter ratio is also specified; the
# volume of the reaction is determined from the conversion rate.
#
# We also specify that the use of the reactor unit is limited. This
# means that the synthesis procedure can only use this unit a pre-set
# number of times in any given flowsheet. The number of times it can
# be used is specified in the synthesis problem class itself.
#
# Note the difference in input for conversion and ldratio: the former
# is a design specification which can, in synthesis mode, be varied to
# determine the optimum choice whereas the latter is an input
# specification which remains constant for the run. Therefore, the
# former must be specified with min and max values and number of
# discrete alternatives even when only one value is to be considered.
#
Reactor reactor
	limit
	reaction reaction
	Real conversion 0.7 0.7 1
	Real ldratio 2
end
#
# Distillation unit which operates is purely conceptual design
# mode. This means that most physical property calculations are not
# required. Only the ability to estimate relative volatilities is
# required. No estimates of heating or cooling requirements are made.
#
Distillation dist
	Boolean conceptual true
	Real P "1 *atm" "1 *atm" 1
	Real rrf 1.2 1.2 1
end
#
# We need a mixer unit to handle recycle streams.  This unit has no
# real design information.
#
Mixer mixer
	Boolean conceptual true
end
#
# A product tank which accepts the desired product C3 and gives it a
# value based on the flow (F), the number of hours in a year (hpy) and
# the number of seconds in an hour (hr).  Essentially, therefore,
# the value is 1 unit per kmol produced in a year.
#
ProductTank pureC3
	Expression spec "(x[C3]>0.90)"
	Expression valuefn "F*hpy*hr"
	interesting
end
#
# Another valid output of the process will be the C4 component. This
# component must come out relatively pure (>90%) but has no value.
#
ProductTank pureC4
	Expression spec "x[C4]>0.90"
	interesting
end
#
# We also need a purge unit. Like the mixer, this unit has no
# specifications given.
#
Purge purge
end
# 
# The ranking criteria for processes in this problem is the "value"
# variable which the product tanks generate.  As the optimizer
# minimizes the criteria given, we need to use the negative of this
# value as we want to maximize the value overall.
#
Criteria criterion
  criterion Value sum "-value"
end
#
# define all the global data for the system prior to attempting the
# synthesis run. these data include the ranking criteria (only one in
# this case) and the list of units which are available for the
# synthesis procedure to use.
#
Data
	criteria	criterion
	unit feed
	unit dist
	unit reactor
	unit mixer
	unit pureC3
	unit pureC4
	unit purge
end
#
# The iterative dynamic programming problem class is based on the use
# of hierarchies to rank partial solutions. These partial solutions
# (described by Fraga, Chem Eng Res Des, 1998 [see
# http://www.ucl.ac.uk/~ucecesf/ for a list of publications]) are
# necessary when tackling problems with recycle streams. We change the
# default hierarchy to encourage the production of valid products. The
# default value of this is 0; the smaller the value, the greater the
# attractiveness of the particular feature.
#
Hierarchy hier
	product	-10
end
#
# Finally, define the synthesis problem which, because we will require
# recycle streams, must be based on the IDP class (iterative dynamic
# programming). This is similar to the Qualified problem class except
# that it will iterative to converge tear streams (recycle streams)
# identified by the procedure itself.
#
IDP problem
	hierarchy hier
	maxdepth 2		# when to consider iterating
	maxiter 1		# how many iterations to allow
	limit reactor		# only one instance of the reactor
	# 
	# An interesting facet of the type of problem we are tackling
	# here is that we can not use the branch and bounding strategy
	# that is available by default. The reason for this is that we
	# have product values (negative costs) and negative valued
	# hierarchy entries. Negative values in either aspect mean
	# that the bounding procedure will produce the wrong results.
	#
	bounding false
	sud true		# save unit designs
	show
	solve			# solve the problem
	print			# output results
	print short
	# *** NOTE: exporting solutions with recycle streams is currently
	# *** not working (2001.08.15). This will hopefully be fixed
	# *** soon
	# although we can create a flowsheet object for this problem,
	# it should be noted that the flowsheet evaluation method
	# currently does not support flowsheets with recycle
	# streams...
	# export			# generate flowsheets
end