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## Introduction

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**Process Simulation**Introduction**Classification of the models**• Black box – white box • Black box – know nothing about process in apparatus, only dependences between inputs and outputs are established. Practical realisation of Black box is the neural network • White box – process mechanism is well <??> known and described by system of equations**Classification of the models**• Deterministic – Stochastic • Deterministic – for one given set of inputs only one set of outputs iscalculated with probability equal 1. • Stochastic – random phenomenon affects on process course (e.g. weather), output set is given as distribution of random variables**Classification of the models**• Microscopic- macroscopic • Microscopic – includes part of process or apparatus • Macroscopic – includes whole process or apparatus**Elements of the model**• Balance dependences • Based upon basic nature laws • of conservation of mass • of conservation of energy • of conservation of atoms number • of conservation of electric charge, etc. • Balance equation (for mass): (overall and for specific component without reaction)Input – Output = Accumulation or (for specific componentif chemical reactions presents)Input – Output +Source = Accumulation**Elements of the model**• Constitutive equations • Newton eq. – for viscous friction • Fourier eq. – for heat conduction • Fick eq. – for mass diffusion**Elements of the model**• Phase equilibrium equations – important for mass transfer • Physical properties equations – for calculation parameters as functions of temperature, pressure and concentrations. • Geometrical dependences – involve influence of apparatus geometry on transfer coefficients – convectional streams.**Structure of the simulation model**• Structure corresponds to type of model equations • Structure depends on: • Type of object work: • Continuous, steady running • Periodic, unsteady running • Distribution of parameters in space • Equal in every point of apparatus – aggregated parameters (butch reactor with ideal mixing) • Parameters are space dependent– displaced parameters**Process simulation**• the act of representing some aspects of the industry process (in the real world) by numbers or symbols (in the virtual world) which may be manipulated to facilitate their study.**Process simulation (steady state)**• Flowsheeting problem • Specification (design) problem • Optimization problem • Synthesis problem by Rafiqul Gani**FLOWSHEET**SCHEME INPUT PRODUCTS OPERATING CONDITIONS EQUIPMENT PARAMETERS Flowsheeting problem • Given: • All of the input information • All of the operating condition • All of the equipment parameters • To calculate: • All of the outputs**FLOWSHEET**SCHEME INPUT PRODUCTS OPERATING CONDITIONS EQUIPMENT PARAMETERS Specyfication problem • Given: • Some input& some output information • Some operating condition • Some equipment parameters • To calculate: • Undefinedinputs&outputs • Undefinedoperating condition • Undefinedequipment parameters**Specyfication problem**• NOTE: degree of freedom is the same as in flowsheeting problem.**Given: feed composition and flowrates,**target product composition Assume value to be guessed: D, Qr Find: product flowrates, heating duties Solve the flowsheeting problem Adjust D, Qr Is target product composition satisfied ? STOP**Process optimisation**• the act of finding the best solution (minimize capital costs, energy... maximize yield) to manage the process (by changing some parameters, not apparatus)**Given: feed composition and flowrates,**target product composition Assume value to be guessed: D, Qr Find: product flowrate, heating duty Solve the flowsheeting problem Adjust D, Qr Is target product composition satisfied AND =min. STOP**Process synthesis/design problem**• the act of creation of a new process. • Given: • inputs (some feeding streams can be added/changed latter) • Outputs (some byproducts may be unknown) • To find: • Flowsheet (topology) • equipment parameters • operations conditions**Process synthesis/design problem**flowsheet undefined INPUT OUTPUT**Given: feed composition and flowrates,**target product composition Assume value to be guessed: D, Qr, N, NF, R/D etc. Find: product flowrate, heating duty, column param. etc. Solve the flowsheeting problem Adjust D, Qr As well as N, NF, R/D etc. Is target product composition satisfied AND =min. STOP**Process simulation - why?**• COSTS • Material – easy to measure • Time – could be estimated • Risc – hard to measure and estimate**Software for process simulation**• Universal software: • Worksheets – Excel, Calc (Open Office) • Mathematical software – MathCAD, Matlab • Specialized software – process simulators. Equipped with: • Data base of apparatus models • Data base of components and mixtures properties • Solver engine • User friendly interface**Software process simulators (flawsheeting programs)**Started in early 70’ At the beginning dedicated to special processes Progress toward universality Some actual process simulators: ASPEN Tech /HYSYS ChemCAD PRO/II ProSim Design II for Windows**Chemical plant system**• The apparatus set connected with material and energy streams. • Most contemporarysystems are complex, i.e. consists of many apparatus and streams. • Simulations can be use during: • Investigation works – new technology • Project step – new plants (technology exists), • Runtime problem identification/solving – existing systems (technology and plant exists)**Chemical plant system**• characteristic parameters can be specified for every system separately according to: • Material streams • Apparatus**Apparatus-streams separation**Assumption: All processes (chemical reaction, heat exchange etc.) taking places in the apparatus and streams are in the chemical and thermodynamical equilibrium state. Why separate? It’s make calculations easier**Streams parameters**Flow rate (mass, volume, mol per time unit) Composition (mass, volume, molar fraction) Temperature Pressure Vapor fraction Enthalpy**Streams degrees of freedom**DFs=NC+2 • e.g.: NC=2 -> DFs=4 • Assumed: F1, F2, T, P • Calculated: • enthalpy • vapor fraction**Apparatus parameters & DF**Characteristics for each apparatus type. E.g. heat exchanger : Heat exchange area, A [m2] Overall heat-transfer coefficient, U (k) [Wm-2K-1] Log Mean Temperature Difference, LMTD [K] degrees of freedom are unique to equipment type**Calculation subject**Number of equations of mass and energy balance for entire system Can be solved in two ways:**Types of balance calculation**Overall balance (without use of apparatus mathematical model) Detailed balance on the base of apparatus model**Overall balance**Apparatus is considered as a black box Needs more stream data User could not be informed about if the process is physically possible to realize.**3**2 1 4 Overall balance – Example Countercurrent, tube-shell heat exchanger Given three streams data: 1, 2, 3 hence parameters of stream 4 can be easily calculated from thebalance equation. DF=5 There is possibility thatcalculated temp. of stream 4 can be higher then inlet temp. of heating medium (stream 1).**3, mA**2 1, mB 4 Overall balance – Example Given: mA=10kg/s mB=20kg/s t1= 70°C t2=40°C t3=20°C cpA=cpB=idem**Apparatus model involved**• Process is being described with use of modeling equations (differential, dimensionless etc.) • Only physically acceptable processes taking place • Less stream data required (smaller DF number) • Heat exchange example: given data for two streams, the others can be calculated from a balance and heat exchange model equations**Loops and cut streams**• Loops occur when: • some products are returned and mixed with input streams • when output stream heating (cooling) inputs • some input (also internal) data are undefined • To solve: • one stream inside the loop has to be cut (tear stream) • initial parameters of cut stream have to be defined • Calculations have to be repeated until cut streams parameters are converted.**I.Problem definition**Simulate system consists of: Shell-tube heat exchanger, four pipes and two valves on output pipes. Parameters of input streams are given as well as pipes, heat exchanger geometry and valves resistance coefficients. Component 1 and 2 are water. Pipe flow is adiabatic. Find such a valves resistance to satisfy condition: both streams output pressures equal 1bar.**II.Flawsheet**5 s6 s7 2 4 1 3 s1 s2 s3 s4 s5 s8 7 6 s10 s9**Numerical data:**Stream s1 Ps1 =200kPa, ts1 = 85°C, f1s1 = 10000kg/h Stream s6 Ps6 =200kPa, ts6 = 20°C, f2s6 = 10000kg/h**Equipment parameters:**• L1=7m d1=0,025m • L2=5m d2=0,16m, s=0,0016m, n=31... • L3=6m, d3=0,05m • z4=50 • L5=7m d5=0,05m • L6=10m, d6=0,05m • z7=40**III. Stream summary table**• Uknown:Ts2, Ts3, Ts4, Ts5, Ts7, Ts8, Ts9, Ts10, Ps2, Ps3, Ps4, Ps5, Ps7, Ps8, Ps9, Ps10, f1s2, f1s3, f1s4, f1s5, f2s7, f2s8, f2s9, f2s10 number of unknown variables: 26 WE NEED 26 INDEPENDENT EQUATIONS.**Equations from equipment information**• f1s2= f1s1 f1s7= f1s6 f1s3= f1s2 f1s8= f1s7 f1s4= f1s3 f1s9= f1s8 f1s5= f1s4 f1s10= f1s9 14 equations. Still do define 26-14=12 equations**Heat balance equations**New variable: Q Still to define: 12+1-2=11 equations