Client-Server Application, Using ActiveX Automation Servers Aspen Client-Server Application, Using ActiveX Automation Servers Aspen Plus®, Aspen Properties® and SuperTarget®, to Extend Pinch AnalysisPlus®, Aspen Properties® and SuperTarget®, to Extend Pinch Analysis

Through Virtual Temperature and Virtual Heat Exchanger ConceptThrough Virtual Temperature and Virtual Heat Exchanger Concept

Dr. V. Lavric1, Prof. V. Pleşu1, 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

ABSTRACTABSTRACT

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 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 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 simulator’s flowsheet, closing, thus, the iterative optimization loop. This whole process is stopped when no improvement can be detected after some reasonable number of iterations.

INCLUDING CHEMICAL REACTORS IN PINCH INCLUDING CHEMICAL REACTORS IN PINCH ANALYSISANALYSIS

• 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 sourcesource or sinksink, and used accordingly)

– Chemical Reactors Energy Integration (CREI) approach (allows some modifications in input parameters – temperature, mainly)

PINCH ANALYSIS - BASICSPINCH ANALYSIS - BASICS

Identifies:• sources (hot streams)• sinks (cold streams)Builds:• composite hot & cold curves• grand composite curves• problem tableDesigns:• HEN topology avoiding heat transfer across the

pinch• economically optimum configuration - transfers

some heat across the pinch, breaking loops accordingly

CREI Analysis - BasicsCREI Analysis - Basics

Identifies:• heat generated by the chemical process• reversible reaction temperatureBuilds:• virtual heat exchangersDesigns:• optimal plant topology, through

extended pinch analysisTrev = reversible temperature (no entropy)T = actual working temperatureqchem = heat of chemical processq = heat exchanged with the surroundings

ImplementationImplementationA) Reversible Temperature Computation

1 11

i ii

rev chem chem

d n sq

T T q q

zero order approachTrev 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.

B) Reactor Replacement – Adiabatic (exo case)Adiabatic (exo case)

Reactor Replacement – Nonadiabatic (endo case)Reactor Replacement – Nonadiabatic (endo case) Reactor Replacement – Nonadiabatic (exo case)Reactor Replacement – Nonadiabatic (exo case)

THE CLIENT-SERVER APPLICATIONTHE CLIENT-SERVER APPLICATION

Strategic Strategic TasksTasks

DESCRIPTION OF THE MAIN TASKSDESCRIPTION OF THE MAIN TASKS (CONT.) (CONT.)

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

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.

The main window of the client applicationThe main window of the client application

General flowsheet data windowGeneral flowsheet data window

Detailed stream information windowDetailed stream information window

Select item to display windowSelect item to display window

Plug flow reactor – TPlug flow reactor – Trevrev at output at output

CASE STUDY-2BED CASE STUDY-2BED METHANOL METHANOL

SYNTHESIS REACTORSYNTHESIS REACTOR

Cascade with PA last (Two-bed direct cooling)

Cascade with CREI last (Two-

bed direct cooling)

CONCLUSIONSCONCLUSIONSAdvantages: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: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: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:Recommendation:• Chemical Pinch should be integrated with an economic analyzer, to avoid

uneconomic optima.