Client-Server Application, Using ActiveX Automation Servers Aspen
Plus®, Aspen Properties® and SuperTarget®, to Extend Pinch Analysis
Through Virtual Temperature and Virtual Heat Exchanger Concept
1
Pleşu ,
Dr. V.
Prof. V.
Prof. J. De
1University POLITEHNICA of Bucharest, Chemical Engineering Department-CTTPI, Bucharest, Romania
2Vrije Universiteit Brussel,Mechanical Engineering Department,B-1050, Pleinlaan 2, Brussels, Belgium
1
Lavric ,
2
Ruyck
INCLUDING CHEMICAL REACTORS IN PINCH
ANALYSIS
ABSTRACT
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 •
Local approach
algorithmic manner; using heat or mass flows as carriers and temperature or concentration of some species to express (minimize the entropy production for each reactor, freezing the
the driving force for the heat or mass transfer. The extended use of the exergy optimization concepts revealed the
input and output parameters)
reactor as the space in which the chemical processes are responsible for large amounts of entropy generation and,
At plant level
thus, exergy losses. In response to the need to understand the reactor’s 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
–
Utility approach (every reactor is viewed
the range of industrial interest, the concept of Chemical Reactors Energy Integration materialized. The basic idea of this
as an energy source or sink, and used
concept is that the chemical process releasing/consuming heat could be viewed as a heat transfer process between a
accordingly)
hot current at a theoretical equilibrium temperature (at which the entropy production is zero) and a cold current, at the
–
Chemical Reactors Energy Integration
actual temperature of reaction. A client application, working with a process simulator (Aspen Plus®), a physical
(CREI) approach (allows some
properties computational tool (Aspen Properties®) and a pinch analyzer (SuperTarget’ Process®) in a pendulum
modifications in input parameters –
fashion, was developed, implementing this new technique. The automation controller analyses the flowsheet, through
temperature, mainly)
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
CREI Analysis - Basics
physical properties computational tool, retrieving from simulator all the data linked to these properties and implementing
Identifies:
them in it, then computing all the needed properties at specified temperatures, compositions and pressures. Then, it
•
heat generated by the chemical process
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
•
reversible reaction temperature
Reactors Energy Integration concepts. Subsequently, runs the pinch server, retrieving, then, the new HEN topology,
Builds:
which is implemented into the simulator’s flowsheet, closing, thus, the iterative optimization loop. This whole process is
•
virtual heat exchangers
stopped when no improvement can be detected after some reasonable number of iterations.
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
THE CLIENT-SERVER APPLICATION
DESCRIPTION OF THE MAIN TASKS (CONT.)
Strategic Tasks
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)

“Extended Mode” - the reactors replaced by
fake counter-current heat exchangers.
The main window of the client application
composite hot & cold curves
grand composite curves
problem table
HEN topology avoiding heat transfer across the
pinch
economically optimum configuration - transfers
some heat across the pinch, breaking loops
accordingly
Implementation
A) Reversible Temperature Computation
zero order approach


 Trev is computed for the entire
d  ni si 
chemical reactor;
1
1
q 
 i


1




first order approach
T rev T   q chem 
 q chem
 (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.
B) Reactor Replacement – Adiabatic (exo case)

Cascade with PA
last (Two-bed
direct cooling)
Convert Reactors into Virtual Heat Exchangers

•
sources (hot streams)
sinks (cold streams)
CASE STUDY-2BED
METHANOL
SYNTHESIS REACTOR
Interface file - Super Target Data Extraction Interface File Format
“Base Case” - the reactors are preserved;
Identifies:
•
•
Builds:
•
•
•
Designs:
•
Reactor Replacement – Nonadiabatic (endo case) Reactor Replacement – Nonadiabatic (exo case)
Generate Input File for Super Target Process® 5.0.9

PINCH ANALYSIS - BASICS
For every reactor

thermal effect

Degree(s) of advancement

heat of chemical process

reversible temperature

The reactor’s input stream - exits to environment;

Replace the reactor with a virtual heat exchanger

define three new virtual streams;

keep the reference for the virtual heat
exchanger;

observe exo/endo-thermic process.
General flowsheet data window
Plug flow reactor – Trev at output
Detailed stream information window
Select item to display window
Cascade with
CREI last (Twobed direct
cooling)
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.