ClientServer Application, Using ActiveX Automation Servers Aspen

1
Client-Server Application, Using ActiveX
Automation Servers Aspen Plus, Aspen
Properties and SuperTarget, to Extend Pinch
AnalysisThrough Virtual Temperature and Virtual
Heat Exchanger Concept Dr. V. Lavric1, Prof. V.
Plesu1, Prof. J. De Ruyck2
1University POLITEHNICA of Bucharest,
Chemical Engineering Department-CTTPI, Bucharest,
Romania 2Vrije
Universiteit Brussel,Mechanical Engineering
Department,B-1050, Pleinlaan 2, Brussels,
Belgium
INCLUDING CHEMICAL REACTORS IN PINCH ANALYSIS
ABSTRACT
PINCH ANALYSIS - BASICS
The energy crisis spectrum, which was a constant
of the last decades, urged the need to develop
tools appropriate for the design or retrofit of
complex industrial processes. Second law analysis
emerged as an important instrument, permitting
the development of adequate techniques ensuring a
better thermal integration aiming the
minimization of entropy production or exergy
destruction. Techniques like Pinch Analysis
implemented the second law analysis in an
algorithmic manner using heat or mass flows as
carriers and temperature or concentration of some
species to express the driving force for the heat
or mass transfer. The extended use of the exergy
optimization concepts revealed the reactor as the
space in which the chemical processes are
responsible for large amounts of entropy
generation and, thus, exergy losses. In response
to the need to understand the reactors behavior
using the 2nd law of thermodynamics concepts, in
order to minimize the entropy generation, while
keeping the state and working parameters of the
reactor in the range of industrial interest, the
concept of Chemical Reactors Energy Integration
materialized. The basic idea of this concept is
that the chemical process releasing/consuming
heat could be viewed as a heat transfer process
between a hot current at a theoretical
equilibrium temperature (at which the entropy
production is zero) and a cold current, at the
actual temperature of reaction. A client
application, working with a process simulator
(Aspen Plus), a physical properties
computational tool (Aspen Properties) and a
pinch analyzer (SuperTarget Process) in a
pendulum fashion, was developed, implementing
this new technique. The automation controller
analyses the flowsheet, through the interface
provided by the simulator server, makes any
necessary adjustments to have maximum of
information available, runs the simulator, and
collect all needed data regarding the streams and
unit operations. After that, starts the physical
properties computational tool, retrieving from
simulator all the data linked to these properties
and implementing them in it, then computing all
the needed properties at specified temperatures,
compositions and pressures. Then, it computes the
objective function, the global generated entropy,
and the new point in the chemical process space,
and prepares the input file for the pinch
analyzer, introducing some fake heat exchangers,
according to the Chemical Reactors Energy
Integration concepts. Subsequently, runs the
pinch server, retrieving, then, the new HEN
topology, which is implemented into the
simulators flowsheet, closing, thus, the
iterative optimization loop. This whole process
is stopped when no improvement can be detected
after some reasonable number of iterations.

• Identifies
• sources (hot streams)
• sinks (cold streams)
• Builds
• composite hot cold curves
• grand composite curves
• problem table
• Designs
• HEN topology avoiding heat transfer across the
  pinch
• economically optimum configuration - transfers
  some heat across the pinch, breaking loops
  accordingly

• Local approach
• (minimize the entropy production for each
  reactor, freezing the input and output
  parameters)
• At plant level
• Utility approach (every reactor is viewed as an
  energy source or sink, and used accordingly)
• Chemical Reactors Energy Integration (CREI)
  approach (allows some modifications in input
  parameters temperature, mainly)

CREI Analysis - Basics
ImplementationA) Reversible Temperature
Computation

• Identifies
• heat generated by the chemical process
• reversible reaction temperature
• Builds
• virtual heat exchangers
• Designs
• optimal plant topology, through extended pinch
  analysis
• Trev reversible temperature (no entropy)
• T actual working temperature
• ?qchem heat of chemical process
• ?q heat exchanged with the surroundings

• zero order approach
• Trev is computed for the entire chemical reactor
• first order approach
• (Trev) in is computed considering an infinitely
  small advancement of the chemical process at
  entrance
• (Trev) out is computed following the same
  procedure, but for the exit conditions.

THE CLIENT-SERVER APPLICATION
DESCRIPTION OF THE MAIN TASKS (CONT.)
B) Reactor Replacement Adiabatic (exo case)

• Retrieve information for streams and units
• Streams
• name, source, destination, flow, temperature,
  enthalpy, entropy, etc
• Unit Operations
• type, name, completion status, operating
  conditions, parameters
• concentration or other parameters profiles
• enthalpy-temperature curves
• Retrieve Interconnectivity Between Unit
  Operations and Streams
• Extract the topology of the flowsheet in a
  convenient manner for the pinch analyzer (Super
  Target Process 5.0.9)
• Generate Input File for Super Target Process
  5.0.9
• Interface file - Super Target Data Extraction
  Interface File Format
• Base Case - the reactors are preserved
• Extended Mode - the reactors replaced by fake
  counter-current heat exchangers.
• Convert Reactors into Virtual Heat Exchangers
• For every reactor
• thermal effect
• Degree(s) of advancement
• heat of chemical process
• reversible temperature

Reactor Replacement Nonadiabatic (endo case)
Reactor Replacement Nonadiabatic (exo case)
Strategic Tasks
CASE STUDY-2BED METHANOL SYNTHESIS REACTOR
Cascade with PA last (Two-bed direct cooling)
Cascade with CREI last (Two-bed direct cooling)
The main window of the client application
CONCLUSIONS

• Advantages
• CREI is a global optimizing tool, operating upon
  the whole flowsheet and not only on the chemical
  reactors
• CREI seems to give useful guidelines for finding
  an optimum topology and working conditions, but
  the engineering judgment plays a key roll in
  closing the analysis
• Drawbacks
• CREI and PA should be used in cascade, several
  times, to have a convergent towards the lowest
  entropy production process
• With networks larger than two reactors, the
  virtual hot/cold streams could be completely
  decoupled form their counterpart chemical process
  stream, rendering the analysis impossible
• Guideline
• The general guideline, emerged from chemical
  pinch analysis, is to use a low grade utility to
  preheat as much as possible the reactants and to
  generate, with the supplemental chemical heat,
  some high grade utility, lowering the total
  entropy production
• Recommendation
• Chemical Pinch should be integrated with an
  economic analyzer, to avoid uneconomic optima.

General flowsheet data window
Plug flow reactor Trev at output
Detailed stream information window
Select item to display window