Chapter 7 Recycle Streams
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<span class='text_page_counter'>(1)</span>Undergraduate Lectures on . . Material Balances for Chemical Engineers April 8-‐ 23, 2013. Chapter 7: Lecture 2: Recycle Systems!. Brian G. Higgins Department of Chemical Engineering and Materials Science University of California, Davis .
<span class='text_page_counter'>(2)</span> CatalyJc Reactor with Recycle . Molar flow rate of recycle stream depends on the degree of completeness of the reac5on. . Recycle streams create “loops” in the flow informaJon .
<span class='text_page_counter'>(3)</span> Recycle stream in an Ammonia Converter . To avoid build-‐up of argon . Feed stream has inert compound-‐ argon . Recycle streams contain mixers and spliQers .
<span class='text_page_counter'>(4)</span> Method for Analyzing Recycle Systems Generally more than one control volume is needed to analyze recycle systems .
<span class='text_page_counter'>(5)</span> Mixers and SpliQers . Chemical reac5ons can be ignored in mixers and spli>ers. These devices consist of tubes joined in convenient ways. Analysis involves: .
<span class='text_page_counter'>(6)</span> Mixers . Degree of Freedom Analysis for Mixer: Number of generic variables: . N (S + 1) mole fractions + S + 1 molar flow rates Number of generic constraints: . N species balances + (S + 1) mole fraction constraints Number of specific constraints/specifica5ons: Feed Streams: . S molar flow rates + S(N Degrees of Freedom =0 . 1) mole fractions.
<span class='text_page_counter'>(7)</span> SpliQer The spli>er physics requires that the composi5ons of all the outgoing streams be equal to composi5on of the incoming stream . Mole frac5on constraints: . N-‐1 mole frac5ons can be specified: .
<span class='text_page_counter'>(8)</span> SpliQer cont. . Can also specify species molar flow rates .
<span class='text_page_counter'>(9)</span> SpliQer CalculaJon .
<span class='text_page_counter'>(10)</span> SpliQer CalculaJon Cont. .
<span class='text_page_counter'>(11)</span> SpliQer CalculaJon Cont. .
<span class='text_page_counter'>(12)</span> SpliQer CalculaJon Cont. .
<span class='text_page_counter'>(13)</span> SpliQer CalculaJon Cont. .
<span class='text_page_counter'>(14)</span> Pyrolysis of Dichloroethane with Recycle .
<span class='text_page_counter'>(15)</span> Pyrolysis of Dichloroethane with Recycle .
<span class='text_page_counter'>(16)</span> Analysis . ConservaJon of Atoms: .
<span class='text_page_counter'>(17)</span> Determining the Constraints on Rates of ProducJon Axiom II gives .
<span class='text_page_counter'>(18)</span> Rules for SelecJng Relevant Control Volumes .
<span class='text_page_counter'>(19)</span> Specifying Control Volumes .
<span class='text_page_counter'>(20)</span> Degree of Freedom Analysis . Assumed known-‐ value not given .
<span class='text_page_counter'>(21)</span> Analysis Species Balances: . Convenient Variables: . Species Balances for CV 1: .
<span class='text_page_counter'>(22)</span> Species Balances for Control Volumes . Ethane does not react = 0 .
<span class='text_page_counter'>(23)</span> Species Balances in Terms of Conversion . Species Balance over Mixer: . conversion .
<span class='text_page_counter'>(24)</span> Solving for the Molar Flow Rates Convenient to specify all molar flow rates in terms of dichloroethane entering CV1 . Total molar flow rate of stream #1 .
<span class='text_page_counter'>(25)</span> Solving for the Molar Flow Rates cont. .
<span class='text_page_counter'>(26)</span>
