1 / 73

Process Simulation

Introduction. Process Simulation. The model. It is a representation of real object (apparatus or part of the apparatus) It let us foresee behavior of physical objects without experiments in the real world. However , usually the basis of the models are experiments

satya
Télécharger la présentation

Process Simulation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Introduction Process Simulation

  2. The model • It is a representation of real object (apparatus or part of the apparatus) • It let us foresee behavior of physical objects without experiments in the real world. • However, usually the basis of the models are experiments • Approximation of constants/coefficients in model equations • Physical parameters of chemicals, etc.

  3. Classification of the models • Physical – mathematical • Physical – one physical quantity replaced with another (easier to measure) or use of scaled down objects (cars, planesin wind tunnels) • Mathematical - representation by the use of equations.

  4. 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

  5. Classification of the models • Deterministic – Stochastic • Deterministic – for one given set of inputs only one set of outputs are found with probability equal 1. • Stochastic – random phenomenon affects on process course (e.g. weather), output set is given as distribution of random variables

  6. Classification of the models • Microscopic- macroscopic • Microscopic – includes part of process or apparatus • Macroscopic – includes whole process or apparatus

  7. Elements of the model • Balance dependences • Based upon basic nature laws • of conservation of mass • of conservation of energy • of conservation of electric charge, etc. • Balance equation: Input – Output = Accumulation

  8. Elements of the model • Constitutive equations – apply to unconvectional streams • Newton eq. – for viscous friction • Fourier eq. – for heat conduction • Fick eq. – for mass diffusion

  9. 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.

  10. Structure of the simulation model • 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 vary with space – displaced parameters

  11. Structure of the model

  12. 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.

  13. Process simulation (steady state) • Flowsheeting problem • Design (specification) problem • Optimization problem • Synthesis problem by Rafiqul Gani

  14. FLOWSHEET SCHEME INPUT PRODUCTS OPERATING CONDITIONS EQUIPMENT PARAMETERS Flowsheeting problem • Given: • All input information • All operating condition • All equipment parameters • To calculate: • All outputs

  15. R.Gani

  16. FLOWSHEET SCHEME INPUT PRODUCTS OPERATING CONDITIONS EQUIPMENT PARAMETERS Specyfication problem • Given: • Some input&output information • Some operating condition • Some equipment parameters • To calculate: • Rest of inputs&outputs • Rest of operating condition • Rest of equipment parameters

  17. Specyfication problem • NOTE: degree of freedom is the same as in flowsheeting problem.

  18. Given: feed composition and flowrates, target product composition To gues: D, Qr Find: product flowrates, heating duties Solve the flowsheeting problem Adjust D, Qr Is target product composition satisfied ? STOP

  19. 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)

  20. Given: feed composition and flowrates, target product composition To gues: D, Qr Find: product flowrate, heating dutie Solve the flowsheeting problem Adjust D, Qr Is target product composition satisfied AND =min. STOP

  21. Process synthesis/design problem • the act of creation of a new process. • Given: • inputs (some feeding streams can be added/changed) • Outputs (some byproducts may be unknown) • To find: • flowsheet • equipment parameters • operations conditions

  22. Process synthesis/design problem flowsheet undefined INPUT OUTPUT

  23. Given: feed composition and flowrates, target product composition To gues: D, Qr Find: product flowrate, heating dutie Solve the flowsheeting problem Adjust D, Qr As well as N, NF, R/D etc. Is target product composition satisfied AND =min. STOP

  24. Process synthesis/design problem methanol Separation method & equipment methanol water water Methods: distillation, membrane separation, flash, extraction Equipment: how many apparatus are needed what is apparatus design and conditions

  25. Process simulation - why? • COSTS • Material – easy to measure • Time – could be estimated • Risc – hard to measure and estimate

  26. Software for process simulation • Universal software: • Worksheets – Excel, Calc (Open Office) • Mathematical software – MathCAD, Matlab • Specialized software – flowsheeting programs. Equipped with: • Data base of apparatus models • Data base of components properties • Solver engine • User friendly interface

  27. Software process simulators (flawsheeting programs) Started in early 70’ At the beginning dedicated to special processes Progress toward universality Some actual process simulators: ASPEN One HYSIM ChemCAD PRO/II ProMax

  28. 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)

  29. Chemical plant system • characteristic parameters can be specified for every system according to separately: • Material streams • Apparatus

  30. Apparatus-streams separation Why separate? It’s make calculations easier Assumption: All processes (chemical reaction, heat exchange etc.) taking places in the apparatus and streams are in the chemical and thermodynamical equilibrium state.

  31. Streams parameters Flow rate (mass, volume, mol per time unit) Composition (mass, volume, molar fraction) Temperature Pressure Vapor fraction Enthalpy

  32. Streams degrees of freedom DFs=NC+2 • e.g.: NC=2 -> DFs=4 • Assumed: F1, F2, T, P • Calculated: • enthalpy • vapor fraction

  33. Apparatus parameters 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

  34. Calculation subject Number of equations of mass and energy balance for entire system Can be solved in two ways:

  35. Types of balance calculation Overall balance (without apparatus mathematical model use) Detailed balance on the base of apparatus model

  36. Overall balance Apparatus is treated as a black box Needs more stream data User could not be informed about if the process is physically possible to realize.

  37. 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).

  38. 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=f(t)

  39. Apparatus model involved Process is being described with use of modeling equations (differential, dimensionless etc.) Only physically possible 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

  40. 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 • initial parameters of cut stream has to be defined • Calculations has to be repeated until cut streams parameters are converted.

  41. Loops and cut streams

  42. Simulation of system with heat exchanger using Excel

  43. 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.

  44. II.Flawsheet 5 s6 s7 2 4 1 3 s1 s2 s3 s4 s5 s8 7 6 s10 s9

  45. Numerical data: Stream s1 Ps1 =200kPa, ts1 = 85°C, f1s1 = 1000kg/h Stream s6 Ps6 =200kPa, ts6 = 20°C, f2s6 = 1000kg/h

  46. Equipment parameters: • L1=7m d1=0,025m • L2=5m d2=0,16m, s=0,0016m, n=31... • L3=6m, d3=0,025m • z4=50 • L5=7m d5=0,025m • L6=10m, d6=0,025m • z7=40

More Related