Dynamic Steady State Continuous Discrete Deterministic Stochastic

Synthesi s Needs Flowsheet Analysis Heat and Material Balances Size and Costing Economic Evaluatio n Parameter Optimization Structual Optimization Final Flowsheet

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

Sequential Modular Approach Equation Solving Approach Simultaneous Modular Approach

Aspen & ChemCad use the sequential modular approach Specify flowsheet (topology) as series of process blocks connected by process streams System determines a computational sequence -- you can override You specify inputs, process conditions and how to compute physical properties Simulator computes output flows from these data. Simulator also computes energy usage, etc.

Simple Example Flow: 1000 lb/hr Pressure: 200 psia Temperature: 300 F Composition: 100% water Flash a water stream Flash vessel is well insulated Flashed to 20 psia Given Inputs Operating Conditions Desired All flows Temperature Pressure

Flow: 1000 lb/hr Pressure: 200 psia Temperature: 325 F 20 psia Flow: ? Temperature: ? Pressure: 20 psia Flow: ? Temperature ? Pressure: 20 psia Vapor Liquid Q = 0

Mass Balance: F = V + L Energy Balance: F*H F = V*H V + L*H L Note: Since vapor and liquid, system is at saturation, so temperature is known (from steam tables)

Mass Balance:1000 lb/hr = V + L Energy Balance: 1000lb/hr*296 Btu/lb = V* Btu/lb+ L* 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 = lb/hrV = lb/hrT = 228 F