Heterogeneous Bunsen Reaction Analysis & Experimental study of
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Heterogeneous Bunsen Reaction
Analysis & Experimental study of
Chemical absorption of Sulfur dioxide and
dissolution of Iodine into aqueous
reacting system
C. S. R. Prasad, H. Z. Fani, S. B. Menon
Chemical Technology Division, ChTG
Bhabha Atomic Research Centre, Trombay
Mumbai – 400 085, IndiaThermo Chemical Process for H2 Production
HIGH TEMPERATURE
NUCLEAR REACTOR
Heat
OXYGEN
THERMO CHEMICAL
PROCESS HYDROGEN
WATERIodine-Sulfur (I-S) Process – Reaction Scheme
3 SECTIONS HEAT
Sulfuric acid 850oC
Decomposition H2SO4 H2O + SO2 + ½ O2
HEAT H2O + SO2 + ½ O2
H2SO4
Acid Production
(Bunsen Reaction) 120oC
OXYGEN 2HI + H2SO4 I2 + SO2 + 2H2O WATER
HEAT
2HI I2
HI Decomposition 450oC
2HI H2 + I 2
HYDROGENHeterogeneous Bunsen Reaction is the focus of this study Objective is to derive crucial engineering information A. Overall reaction rate B. Reaction regimes C. Controlling kinetic/mass transfer resistances D. Coefficients E. Enhancement factor This information helps in chemical reactor selection, flow/contacting scheme choice and design
Region of experimental study
Data points of
reference
Experimental
SO2 cc(273.15 K, 101 kPa)
points of this
study
A- Region
Transparent one phase
Product solution
I2 conc. g/5g of H2O
Absorption limit of SO2 by the Bunsen reaction vs. the initial iodine fraction in the
absorbent
Ref: KAORU ONUKI, et at., IS Process For thermo chemical Hydrogen Production JAERI - Review 94 –
006Sketch of experimental setup
Bunsen reaction stoichiometric : SO2+ I2 + 2H2O 2HI + H2SO4 with excess of I2 & H2O : SO2 + xI2 + y H2O 2HI + H2SO4 + (x-1) I2 + (y-2) H2O is represented as follows for analysis SO2 , A + I2 , B + H2O ,Aq (H2SO4 +HI),Products A(g) A(aq) B(s) B(aq) A(aq) + zB (aq) Products
This multiphase process involving mass transfer and chemical
reaction has following steps
1) Diffusion of SO2 (species A) through gas film
2) Dissolution of Iodine (species B)
3) Diffusion and simultaneous chemical reaction in the
liquid filmConcentration profiles based on film theory for gas (sulphur
dioxide) – liquid (water) – solid (Iodine) system
Solid (I2)
Liquid (H2O) CB,s
CB,l
CB,i
Gas (SO2)
pA,g
pA,i Reaction zone
Fast (pseudo first order)
CA,i reaction in film
with high cB
0 δ
Gas film Liquid film Bulk Liquid Liquid film
surrounding
solidGas phase mass transfer rate is given by,
− rA = k g a ( p Ag − p Ai )
Rate of iodine dissolution is given by,
− rB = k s a p (cBs − cBl )
Liquid phase reaction rate is given by,
− rB
− rA = k1c A =
z
The overall rate of reaction is given by,
p Ag
− rA =
1 H H
( + + )
k g a kl aE k1 (1 − ε )
Gas film Liquid film kinetic
resistance resistance resistance
Mass balances for the diffusing gas A and dissolving solid species B in the
liquid film are as follows:
d 2c A d cB
2
DA 2
= k1c A DB = zk1c A
dx dx 2Reactor model schematic for analysis
Gc pAout
At any instant cB is same
everywhere in the tank.
However cB decreases
with time because of
Vr volume of G/L reaction with A (Yet much
emulsion more than stoichiometric
V l (Batch of Reacting liquid) requirement during most
= of the batch time).
(1 − ε )
At the start cB=cBo
At the end cB=cBf
GC pAin
Mixed gas and completely mixed liquid.E=Liquid film enhancement factor
= Rate of uptake of A with chemical reaction
Rate of uptake of A for straight mass transfer
Enhancement factor for infinitely fast reaction is,
DB cB H
Ei = 1 +
zDA p Ai
Hatta no is, Henry’s Law const is,
k1 DA pA
Ha = H=
kl cA
By overall mass balance across the reactor,
⎡ p Ain p Aout ⎤
GC ⎢ − ⎥ = (−rA )Vr
⎣ P − p Ain P − p Aout ⎦
Vl
Where, Vr = and
(1 − ε )
Batch time for the conversion of Iodine is calculated by,
(1 − ε )dcB
c Bo
t= ∫
c Bf
− rA zSO2 absorption rate vs. SO2 partial pressure for different Iodine
loading
Absorption rate mol/m3.sec
SO2 Inlet partial pressure kPaBatch time calculated vs. Batch time experimental
Typical parameters and values for Bunsen Reaction analysis
Batch time (calculated) (min) tcalc 34
Batch time (experimental) (min) texp 30
Gas film resistance (Pa m3 s/kmol) 1/(kga) 1.1x106
Liquid film resistance (Pa m3 s/kmol) H/(klaE) 1.0x107
Liquid bulk resistance (Pa m3 s/kmol) H/(k1(1-ε)) 7.5x102
Hatta no Ha 3.4
Enhancement factor (calculated) E 2.1
Enhancement factor (experimental) E 2.2
Solid dissolution parameter (ksapDA2)/(4klDB) 1.6x10-6Conclusions 1) SO2 absorption rate in chemically reacting system of Bunsen Reaction is experimentally studied and found to be a linear function of partial pressure (0-100 kpa) of SO2 in inlet gas stream at atmospheric pressure. This functional relation is expected to hold good even under prototypical conditions of Bunsen Reaction 2) Multiphase Bunsen Reaction can be viewed as ‘Fast pseudo first order’ due to high concentration/rate of dissolution of Iodine and reaction zone is located in Liquid film near Gas-Liquid interface 3) Liquid film resistance constitutes ~90% of overall resistance 4) Experimental and theoretical results of this study indicated that this complex reacting system can be analyzed by invoking judicious simplifying assumptions for deriving practical engineering information 5) Rigorous model requires accurate thermodynamic, transport and physical properties 6) This study helps in selection/design of multiphase chemical reactor under prototypical conditions
Acknowledgements • Authors are grateful to DAE, Government of India, Director BARC, Director ChTG for support and encouragement • Help rendered by Head, Chemical Technology Division, Head, Chemistry Division, Head Chemical Engineering Division and colleagues in respective divisions is gratefully acknowledged • All members of ChTG who worked very hard for this R&D are specially thanked • Authors also express their thanks to IAEA and JAEA for the opportunity of participation in this conference
THANK YOU
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