7 Cooling and heating - narradfffff.pptx
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Aug 04, 2024
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7 Cooling and heating - narratedfffff.pptx7 Cooling and heating - narratedfffff.pptx7 Cooling and heating - narratedfffff.pptx7 Cooling and heating - narratedfffff.pptx7 Cooling and heating - narratedfffff.pptx7 Cooling and heating - narratedfffff.pptx7 Cooling and heating - narratedfffff.pptx7 Cool...
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Chemical reaction engineering Revision Multiple reactions Reaction mechanisms and reactive intermediates Bioreactions and enzymes Bioreactors Energy balance Heat exchange and external work 8 The catalyst 9 Residence time distribution 10 Nonideal reactors
Batch reactor J W J Q 1 J Q2 J Q3 C p d T = - D H d x + J Q d t + J W d t heat delivered to the mixture heat produced by the reaction heat exchange work term (transferred to heat through viscous dissipation)
Plug flow reactor d L v v F mixture thermal fluid wall d V j h R c after residence time d t , temperature increases by d T double pipe heat exchange d d Q = j h d A d t j h = k h ( T F – T ) d A = 2 p R c d L d d x = r d V d t d V = p R c 2 d L d A = 2 p R c d L
Plug flow reactor d L v v F mixture thermal fluid wall d V j h R c double pipe heat exchange d d Q = j h d A d t j h = k h ( T F – T ) d A = 2 p R c d L d d x = r d V d t d V = p R c 2 d L after residence time d t , temperature increases by d T d A = 2 p R c d L
Plug flow reactor with heat exchange, reversible exothermic reaction
Plug flow reactor with heat exchange, reversible exothermic reaction mole balance: heat balance: heat balance for thermal fluid: v v F mixture thermal fluid wall j h
t [min] x V [M] t [min] T [ C] x V e x V thermal fluid mixture Co-flow double-pipe heat exchange (exothermic reaction) reaction rate r [ M/h ] heat up reaction
t [min] T [ C] mixture thermal fluid Co-flow double-pipe heat exchange (exothermic reaction) 500 kg/h 125 kg/h 2500 kg/h
t [min] x V [M] t [min] T [ C] x V e x V thermal fluid mixture Counter-flow double-pipe heat exchange (exothermic reaction) reaction rate r [ M/h ] heat up reaction cool down & alter X e heat up reaction cool down & alter X e won by cooling
Counter-flow double-pipe heat exchange (exothermic reaction) t [min] T [ C] mixture thermal fluid 500 kg/h 250 kg/h 2500 kg/h t [min] T [ C] mixture thermal fluid 500 kg/h 125 kg/h 2500 kg/h co-current: countercurrent : note the maximum of the exit temperature at 500 kg/h
Flow rate of the thermal fluid v F = +∞ +intensive +slow -slow -intensive -∞ regime (exothermic) constant T F regime use to keep the temperature down, esp. at the enterance (1) heat up the feed; (2) cool down the mixture near the peak of r adiabatic (1) deliver the reaction heat to the feed; (2) cool down the exiting mixture (good for reversible reactions) use to keep the temperature down, esp. at the exit constant T F regime countercurrent co-current
X V [L] T [ K ] thermal fluid mixture reaction rate r [ mol/m 3 h ] Co-flow double-pipe heat exchange ( endothermic reaction) V [L]
V [L] T [ K ] mixture thermal fluid 0.111 mol/s 0.02775 mol/s 0.444 mol/s V [L] X Co-flow double-pipe heat exchange ( endothermic reaction)
the fool zone heat up the mixture after the reaction Co-flow double-pipe heat exchange (exothermic reaction) X V [L] T [ K ] thermal fluid mixture reaction rate r [ mol/m 3 h ] V [L]
V [L] T [ K ] mixture thermal fluid 0.111 mol/s 0.444 mol/s V [L] X excess heating fluid adiabatic excess heating fluid adiabatic Co-flow double-pipe heat exchange (exothermic reaction)
CSTR J W J Q 1 J Q2 J Q3 c p ( T - T ) d V = - D H d x + J Q d t + J W d t heat delivered to the feed heat produced by the reaction heat exchange work term (transferred to heat through viscous dissipation)
Coil heat exchanger J W J Q T F T ∞ F
E7-3. CSRT, and multiple steady states D c p 0 v = v A + v B + v MeOH = 9.2 m 3 /h; t = V / v = 0.11 h
E7-3. CSRT, and multiple steady states 15 ○ C 15 ○ C T = 24 ○ C (to avoid phase separation) J Q J W T = ? X = ? - 83 kJ/mol
E7-3. CSRT, and multiple steady states A + B C, r = k [A] T lim = 330 K (vapour pressure of A) 15 ○ C 15 ○ C T = 24 ○ C (to avoid phase separation) J Q J W T = ? X = ? k ( T )[A]
E7-3. Adiabatic CSRT, and multiple steady states J Q ,excess [MJ/h] solution 3: 329 K, X = 66% solution 1: 309 K, X = 25% solution 2: 321 K, X = 50% Q: where will this heat go? T [K] (1) Adiabatic case Heat produced in the reactor Heat for warming up the feed at steady state, but otherwise,
J h ,excess [MJ/h] T = 36 C C 18 C F T [K] x x E7-3. CSRT with J Q & J W , and multiple steady states Heat produced in the reactor Heat that went to warm up the feed (2) CSRT with heat exchanger
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