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DISTRIBUTION OF RESIDENCE TIMES FOR REACTORS PART I

DISTRIBUTION OF RESIDENCE TIMES FOR REACTORS PART I. BY PUAN AZDUWIN BINTI KHASRI 10 DECEMBER 2012. NON-IDEAL REACTOR. Deviations from ideal reactor behavior. EXAMPLE: Tank Reactors: inadequate mixing, stagnant regions, bypassing or short-circuiting

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DISTRIBUTION OF RESIDENCE TIMES FOR REACTORS PART I

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  1. DISTRIBUTION OF RESIDENCE TIMES FOR REACTORSPART I BY PUAN AZDUWIN BINTI KHASRI 10 DECEMBER 2012

  2. NON-IDEAL REACTOR • Deviations from ideal reactor behavior. EXAMPLE: • Tank Reactors: inadequate mixing, stagnant regions, bypassing or short-circuiting • Tubular Reactors: mixing in longitudinal direction, incomplete mixing in radial direction, by-passing (especially in Fixed bed reactors)

  3. NON-IDEAL REACTOR-3 CONCEPT RTD -The distribution of residence times in the system MIXING - The quality of mixing MODEL - The model used to describe the system

  4. RESIDENCE-TIME DISTRIBUTION (RTD) • The residence time is how long a particle stays in the reactor once entering. • RTD-to characterize the mixing and flow within reactors and to compare the behavior of real reactors to their ideal models. • RTD can be determined by two experimental method: 1. Pulse input experiment 2. Step input experiment

  5. 1. PULSE INPUT EXPERIMENT • In a pulse input, an amount of tracer N0is suddenly injected in one shot into the feedstream entering the reactor in as short a time as possible. The outlet concentration is then measured as a function of time. We find the RTD function, E(t), from the tracer concentration C(t)

  6. 1. PULSE INPUT EXPERIMENT

  7. 2.STEP TRACER EXPERIMENT • TheRTD function E(t) can be determined directly from a pulse input, the cumulative distribution F(t) can be determined directly from a step input.

  8. INTEGRAL RELATIONSHIP Cumulative distribution curve, F(t). RTD Function, E(t). The cumulative RTD function F(t)

  9. MEAN RESIDENCE TIME AND VARIANCE

  10. NORMALIZED RTD FUNCTION A normalized RTD (Θ) is used instead of the function E(t).; A dimensionless function E(Θ) can be defined as; • The purpose : the flow performance inside reactors of different sizes can be compared directly. • If the E (Θ)is used, All perfectly mixed CSTRs have numerically the same RTD. If the simple function E(t) is used,numerical values of E(t) can differ substantially for different CSTRs

  11. For a perfectly mixed CSTR, The value of E(t) at identical times can be quite different for two different volumetric flow rates v1 and v2. The same value of E(Θ) is the same irrespective of the size of a perfectly mixed CSTR.

  12. RTD IN IDEAL REACTORS 1.RTDs in Batch and Plug-Flow Reactors 2.Single-CSTR RTD 3.Laminar Flow Reactor (LFR)

  13. 1. RTDs IN BATCH AND PLUG-FLOW REACTORS E(t) for a plug flow reactor The Dirac delta function has the following properties:

  14. 2. SINGLE-CSTR RTD E(t) and E(Θ) for a CSTR

  15. 3.LAMINAR FLOW REACTOR (LFR) E(t) for a laminar flow reactor Normalized RTD function for a laminar flow reactor

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