L4-5_Processes_and_Process_Variables

L4-5_Processes_and_Process_Variables - Material and Energy...

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Unformatted text preview: Material and Energy Balances 03/21/10 Processes and Process Variables Material and Energy Balances 03/21/10 Objectives At the end of this chapter, you should be able to: Understand the types of chemical processes Define important process variables in Chemical Engineering such as density, temperature, flow, composition, etc. Material and Energy Balances 03/21/10 Processes A process is any operation or series of operations by which a particular objective is accomplished Chemical processes involve operations that cause a physical or chemical change in a substance or a mixture of substances. The material that enters a process is referred to as the input or feed The material that leaves is the output or product Material and Energy Balances 03/21/10 Classification of processes Based on how the process was built to operate: Batch processes Continuous processes Semi-batch (semi-continuous) processes Material and Energy Balances 03/21/10 Classification of processes Batch Processes Feed is charged into a system. The system works on the feed until processing is complete. Products are then removed. System is closed, with no material transfer across system boundaries except during charging and product removal. Examples: Cooking. Brewing. Specialty chemicals. Material and Energy Balances 03/21/10 Classification of processes Continuous processes Feed and products flow continuously through process. System is open, and usually modeled as steady flow. Examples: Petroleum refining (except coking, blending). Material and Energy Balances 03/21/10 Classification of processes Semi-batch (semi-continuous) processes Hybrid of batch and continuous. In one form ("fedbatch") the feed is added continuously, but the product is removed all at once. In other cases ( i.e. batch distillation), the feed is charged into the vessel in one step, but the products are removed continuously during the run. Material and Energy Balances 03/21/10 Classification of processes Based on how the process varies with time Steady-state process Unsteady-state process Material and Energy Balances 03/21/10 Classification of processes Steady-state process Does not change with time - the variables have the same values at all times. Unsteady-state process changes with time - variables have different values at different time instances Material and Energy Balances 03/21/10 Process Variables Process variables characterize the operation of processes and individual process units Amounts - mass, volume, flow rates, etc Composition - mole %, wt %, ratio, etc Conditions - Pressure, Temperature, etc Proces s Stream Proces s Strea m Proces s Unit Proces s Unit Material and Energy Balances 03/21/10 Mass and Volume From the mass and volume of a substance, we can determine the density , ....
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L4-5_Processes_and_Process_Variables - Material and Energy...

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