Presenting Author AVINASH CHANDRA, Ph.D. (Assistant Professor) Department of Chemical Engineering, Thapar University Patiala (INDIA)

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1 Meenakshi Sheoran a, Avinash Chandra a, Haripada Bhunia a, Pramod K. Bajpai a, Harish J. Pant b, Jayashree Biswal b, S. Madhukar Rao c a Department of Chemical Engineering, Thapar University, Patiala (INDIA) b Radiotracer Application Section, IPAD (BARC), Mumbai (INDIA) c Satia Industries Limited, Sri Muktsar Sahib (INDIA) Paper ID: 57 Presentation ID: B05-03 Presenting Author AVINASH CHANDRA, Ph.D. (Assistant Professor) Department of Chemical Engineering, Thapar University Patiala (INDIA) 1

2 Global Pulp & Paper Industry World India Global Demand 482 million tonnes 13 million tonnes Consumption rate 58 kg/capita 9 kg/capita Annual production 407 million tonnes 14.7 million tonnes Number of mills ~6000 ~850 Annual Turnover million dollar 7500 million dollar Paper mills Wood based Agro residue & recycle based Wheat straw Bagasse Rice straw Corn stalk Cotton stalk Reeds Kenaf bast Banana stem 2

3 Typical Pulping Process Raw material Digester Washing Bleaching Drying White liquor Re-caustization Black liquor Concentration Recovery boiler Pulp Chemical recovery section Batch vs Continuous Reduces waste Saves money by reducing inventory & transportation costs Increases productivity more units completed in less time Improves quality by making it easier to spot and correct errors Cuts down on overhead costs via increased stability and reduced lead times. Adapts to customer needs more effectively than batch processing. 3

4 Industrial Pulp Digester (Continuous) Introduction of radio-tracer 198 Au (Impulse input) 1. White liquor storage tank 2. White liquor feeding pump 3. Radiotracer injection port 4. Wheat straw feeder 5. Detectors (D1, D2, D3, D4) 6. Digester tube 7. Steam 8. Blow tank 9. Pulp washer 10. Black liquor storage tank 11. Pulp 4 Feeds: Biomass White liquor (Alkaline solution of NaOH, Na 2 SO 3 with trace amount of Na 2 CO 3 & NaCl) Delignification: Removal of lignin from biomass to separate Cellulose fibers in the form of pulp at high temperature and pressure

5 Why? RTD of digester using radiotracer Frequent occurring problems in pulping digester: Non-uniform pulp quality Overcooked pulp Undercooked pulp Probable Reasons: Non-uniform times spent by different portions of the material inside the digester Diversified and non-uniform feed material Improper operating conditions RTD study using radiotracer may diagnose the system even in running condition, which may lead to take corrective action 5

6 Experimental RTD measurement Industrial scale experiments using radiotracer 198 Au (as Chloroauric acid) to trace liquid phase Impulse injection of 198 Au at inlet of 1 st digester tube RTD data were recorded as tracer concentrations vs time at 4 locations of digester (inlet of 1 st digester tube and outlet of each tube) using NaI scintillation detectors attached with data acquisition system (DAS) Industrial trials: Operating and output conditions Operating Pressure: kg/cm 2 Operating Temperature: o C Exp. No. Feed Screw RPM White liquor flow rate (l/min) Kappa number (K) Residual alkali (g/l)

7 RTD Analysis of digester Impulse (ideal) input for first Tube Case Section Input conditions Case 1 Whole digester Impulse input Case 2 1 st tube Impulse input Case 3 2 nd tube Non-ideal input Case 4 3 rd tube Non-ideal input Solution procedure RTD modeling RTD modeling Convolution Convolution Non-ideal input for 2 nd and 3 rd tube Impulse (ideal) input for whole digester 7

8 RTD modelling of Exp. 1 Experimental data 1 st tube 2 nd tube 3 rd tube 8

9 Model parameters for Exp. 1 Flow Models Model Parameters 1 st tube 2 nd tube 3 rd tube Plug flow Model τpf N Tank in series with α back-mixing model τts Axial dispersion model τ PF Mean Residence Time (MRT) for plug flow Pe Peclet number α Back-mixing ratio τ AD MRT of axial dispersion τ TS MRT of tank in series with back-mixing N Number of tanks Inlet Pe τad Inlet RTD Model -1 Tank in series with back-mixing PFR 9 PFR RTD Model -2 ADM Outlet Outlet

10 RTD modeling of Exp. 2 Experimental data 1 st tube 2 nd tube 3 rd tube 10

11 Model parameters for Exp. 2 Flow Models Model Parameters 1 st tube 2 nd tube 3 rd tube Plug flow Model τpf N Tank in series with α back-mixing model τts Axial dispersion model τ PF Mean Residence Time (MRT) for plug flow Pe Peclet number α Back-mixing ratio τ AD MRT of axial dispersion τ TS MRT of tank in series with back-mixing N Number of tanks Inlet Pe τad Inlet PFR 11 PFR RTD Model -1 Tank in series with back-mixing RTD Model -2 ADM Outlet Outlet

12 RTD modeling of whole digester Flow Models Model Parameters Exp. 1 Exp. 2 Plug flow Model τpf Tank in series N with backmixing α model τts Axial Pe dispersion model τad Exp. 1 RTD Model -1 Tank in series with back-mixing Exp. 2 Inlet PFR Outlet RTD Model -2 Inlet PFR ADM Outlet 12

13 Discussion Axial dispersion inside the digester decreases from 1 st tube to 3 rd tube Increase in Peclet number shows decrease in axial dispersion Highest value of Peclet number is observed in the 3 rd tube Inside 1 st tube liquid have low viscosity and specific gravity Due to the delignification process of the viscosity of the slurry increases continuously from 1 st tube to 3 rd tube Viscosity increases in 2 nd and 3 rd tube due to dissolved lignin contents Low value of N shows high mixing in 1 st tube High value of N also indicate the plug flow behaviour in 3 rd tube 13

14 Conclusions The radiotracer technique was successfully used to measure the RTD of the liquid phase in an industrial-scale continuous pulp digester Radiotracer 198 Au is found suitable for RTD of the liquid phase Axial dispersion / tank-in-series with back-mixing models with a plug flow component connected in series were found equally suitable to describe flow of the liquid phase inside the pulp digester 14

15 Acknowledgments I am very grateful to Board of Research in Nuclear Science (BRNS), Department of Atomic Energy, India, for providing the financial support for this research (sanction No. 35/14/33/2014-BRNS/0886) SATIA Industries Ltd. for permitting us to conduct industrial scale experiments and providing their continuous support / cooperation Thapar University, Patiala (INDIA) to facilitate us for this work IAEA for providing me this platform to present our work including financial support 15

16 Selected References CPPRI, (2015). Compendium of Census Survey of Indian Paper Industry. Central Pulp and Paper Research Institute, Saharanpur, India Sheoran, M., Goswami, S., Pant., H.J., Biswal, J., Sharma, V.K., Chandra, A., Bhunia, H., Bajpai, P.K., Rao, S.M., Dash, A. (2016). Measurement of residence time distribution of liquid phase in an industrial-scale continuous pulp digester using radiotracer technique. Applied Radiation and Isotopes, 111, DOI: /j.apradiso Levenspiel, O. (2004). Chemical Reaction Engineering. 4th edition. Wiley India. Roemer, M.H. and Durbin, L.D. (1967). Transient response and moments analysis of backflow cell model for flow systems with longitudinal mixing. Industrial & Engineering Chemistry Fundamentals, 6(1), DOI: /i160021a021. Pant, H.J., Kundu, A., and Nigam, K.D.P. (2001). Radiotracer Applications in Chemical Process Industry. Reviews in Chemical Engineering, 17(3): DOI: /revce Seker, M., (2005). Residence time distributions of starch with high moisture content in a singlescrew extruder. Journal of Food Engineering. 67(3), DOI: /j.jfoodeng

17 Thank you for your kind Attention! 17