1. 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 Plus®, Aspen Properties® and SuperTarget®, to Extend Pinch Analysis Through Virtual Temperature and Virtual Heat Exchanger Concept Dr. V. Lavric 1, Prof. V. Pleşu 1, Prof. J. De Ruyck 2 1 University POLITEHNICA of Bucharest, Chemical Engineering Department-CTTPI, Bucharest, Romania 2 Vrije Universiteit Brussel,Mechanical Engineering Department,B-1050, Pleinlaan 2, Brussels, Belgium 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 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 2 nd 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 ANALYSIS Local approach (minimize the entropy production for each reactor, freezing the input and output parameters) At plant level sourcesink –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) PINCH ANALYSIS - BASICS 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 CREI Analysis - Basics Identifies: heat generated by the chemical process reversible reaction temperature Builds: virtual heat exchangers Designs: optimal plant topology, through extended pinch analysis T rev = reversible temperature (no entropy) T= actual working temperature  q chem = heat of chemical process  q= heat exchanged with the surroundings Implementation Implementation A) Reversible Temperature Computation zero order approach T rev is computed for the entire chemical reactor; first order approach (T rev ) in is computed considering an “infinitely” small advancement of the chemical process at entrance; (T rev ) out is computed following the same procedure, but for the exit conditions. Adiabatic (exo case) B) Reactor Replacement – Adiabatic (exo case) Reactor Replacement – Nonadiabatic (endo case) Reactor Replacement – Nonadiabatic (exo case) THE CLIENT-SERVER APPLICATION Strategic Tasks DESCRIPTION OF THE MAIN TASKS (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 application General flowsheet data window Detailed stream information window Select item to display window Plug flow reactor – T rev at output CASE STUDY-2BED METHANOL SYNTHESIS REACTOR Cascade with PA last (Two-bed direct cooling) Cascade with CREI last (Two- bed 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.