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Dynamic Steady State

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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  1. Continuous Discrete Deterministic Stochastic Dynamic Steady State

  2. Needs Synthesis Heat and Material Balances Size and Costing Economic Evaluation Parameter Optimization Structual Optimization Final Flowsheet Flowsheet Analysis

  3. Problem: Compute Material Balance Compute Energy Balance How to compute?

  4. Sequential Modular Approach Equation Solving Approach Simultaneous Modular Approach

  5. 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.

  6. 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

  7. 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

  8. 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)

  9. 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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