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Dynamic Steady State PowerPoint PPT Presentation


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Continuous Discrete. Deterministic Stochastic. Dynamic Steady State. Needs. Synthesi s. Heat and Material Balances. Size and Costing. Economic Evaluation. Parameter Optimization. Structual Optimization. Final Flowsheet. Flowsheet. Analysis. Problem:.

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Dynamic Steady State

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Dynamic steady state

Continuous Discrete

Deterministic Stochastic

Dynamic Steady State


Dynamic steady state

Needs

Synthesis

Heat and Material Balances

Size and Costing

Economic Evaluation

Parameter Optimization

Structual Optimization

Final Flowsheet

Flowsheet

Analysis


Dynamic steady state

Problem:

Compute Material Balance

Compute Energy Balance

How to compute?


Dynamic steady state

Sequential Modular Approach

Equation Solving Approach

Simultaneous Modular Approach


Dynamic steady state

Aspen & ChemCad use the sequential modular approach

Specify flowsheet (topology) as series of process blocks connected by process streams

You specify inputs, process conditions and how to compute physical properties

System determines a computational sequence -- you can override

Simulator computes output flows from these data.

Simulator also computes energy usage, etc.


Dynamic steady state

Simple Example

Flash a water stream

Flow: 1000 lb/hr

Pressure: 200 psia

Temperature: 300 F

Composition: 100% water

Given Inputs

Operating Conditions

Flash vessel is well insulated

Flashed to 20 psia

All flows

Temperature

Pressure

Desired


Dynamic steady state

Flow: ?

Temperature: ?

Pressure: 20 psia

Vapor

Q = 0

20 psia

Flow: 1000 lb/hr

Pressure: 200 psia

Temperature: 325 F

Flow: ?

Temperature ?

Pressure: 20 psia

Liquid


Dynamic steady state

F = V + L

Mass Balance:

F*HF = V*HV + L*HL

Energy Balance:

Note: Since vapor and liquid, system is at saturation, so temperature is known (from steam tables)


Dynamic steady state

Mass Balance:

1000 lb/hr = V + L

Energy Balance:

1000lb/hr*296 Btu/lb = V*1156.2 Btu/lb+ L* 196.25 Btu/lb

Note: Since vapor and liquid, system is at saturation, so temperature is known (from steam tables = 228 F and get enthalpy data from steam tables)

L = 896.1 lb/hr

V = 103.9 lb/hr

T = 228 F


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