Copyright INVESTIGATION THE FLOW BEHAVIOR OF CONTINUOUS PULPING DIGESTER USING RADIOTRACER TECHNIQUE TO OPTIMIZE THE OPERATING CONDITIONS (Paper Code- Zonal-16/ 602) By Meenakshi Sheoran, Avinash Chandra, Haripada Bhunia, Pramod K. Bajpai, Harish J. Pant, S. Madhukar Rao Department of Chemical Engineering Thapar University, Patiala THAPAR UNIVERSITY, PATIALA

Copyright contents Operation of pulp digester Residence time distribution (RTD) Introduction to radiotracer Conventional versus radiotracer Principal of RTD measurement Analysis of pulp digester Digester parameters and experimental set up Results Conclusions Other applications of radiotracer Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 2

Copyright Operation of pulp digester  Problems in digester: Non-uniformity of product Overcooking Undercooking  Reasons: Different times spent by the different portions of the materials inside the digester Improper operating conditions  Diagnosis by RTD study in running condition to take corrective action Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 3

Copyright Residence time distribution (RTD) Time spent by the process material inside the reactor Product quality depends upon RTD Every reactor designed as ideal (plug flow or completely mixed). During operation it deviates from ideal flow behavior and cause: Non-uniformity of the product High energy requirement High operating cost High waste generation Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 4 Techniques of RTD study Using conventional tracer Using radiotracer

Copyright Introduction to Radiotracer  Radioactive isotopes of different elements  Unstable, decay and give out radiation emission  Naturally occurring or produced artificially  Used to follow the process fluid for online diagnosis  applications of radioisotope in industry ensures about the quality of product and minimize the production cost by sensitive non-destructive testing and efficient in process control Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 5 Commonly Used Radiotracers in Industry and Environment Tritium -3 Sodium-24 Bromine-82 Lanthanum-140 Gold-198 Iodine-131 Molybdenum-99 Technetium-99m Scandium-46 Krypton-79

Copyright Radiotracer versus conventional tracer ADVANTAGES High detection sensitivity Online sampling Limited memory effect Availability of wide range of radiotracer Physico-chemical compatibility Uninterrupted and easy detection In situ detection Very small dose required Conventional tracer Poor detection Offline sampling Poor selectivity Possible interference with process Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 6

Copyright Procedure for RTD measurement (2-5 ml) of radiotracer diluted in 100 ml of water Injected at feed point of digester to trace the liquid phase Concentration of radiotracer monitored at four position by locating the scintillation detector at feed point (D1) and the outlet of digester tubes (D2, D3 and D4) Detectors are connected to data acquisition system (DAS) for continuous monitoring & recording of radiotracer concentration DAS connected to laptop RTD analysis Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 7

Copyright Principal of Injection and detection AND MEASUREMENT OF RADOTRACER Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 8 Detector Injection system Data acquisition system SYSTEM DAS Injection point Detectors Laptop Inlet Outlet

Copyright ANALYSIS of pulp digester Radiotracer 82 Br is used to trace the liquid phase of the digester Tracer injected as an impulse at the inlet of the reactor and measured at inlet and outlet of each tube of digester Residence time distribution gives the time spent by process material inside the reactor and characterize the flow behavior inside it Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 9 1-white liquor storage tank, 2-liquor feeding pump, 3- radiotracer injection port, 4-wheat straw feeder, 5- scintillation detectors (D1, D2, D3, D4), 6-digester tube, 7- steam, 8-blow tank, 9-pulp washer, 10-black liquor storage tank, 11-pulp.

Copyright OPERATING conditions AND OUTPUT PARAMETERS OF DIGESTER Wheat straw feed rate White liquor flow rate Kappa number Residual alkali Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 10 Run No. Screw speed (RPM) Liquor flow rate (l/min) Steam Flow (Ton/hr) Steam Pressure (kg/cm 2 ) Temp ( o C) Kappa number (k) Residual alkali RA (g/l) Tube 1Tube 2, 3 Run Run Run Run

Copyright MEAN RESIDENCE TIME (MRT) FOR PULP DIGESTER Run No.Theoretical MRT (min.)Experimental MRT (min.) Run Run Run Run Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 11

Copyright Result for first run Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 12 Back mixing Plug flow behavior

Copyright Result for second run Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 13 Uniform cooking Distributed cooking

Copyright Result for third run Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 14 Little back mixing

Copyright Result for fourth run Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 15 Plugging

Copyright Conclusions Radiotracer technique has been successfully tried on an industrial scale continuous pulping digester (for the first time) to trace the liquid phase flow inside the digester (without disturbing its operation) for the RTD analysis. The optimum operating conditions for the digester were found as: Screw speed for wheat straw feed: 65 rpm White liquor flow rate: 355 l/min At certain conditions, some dead pockets are observed inside the digester and at high liquor flow rates, channeling and bypassing is observed. At lower liquor flow rates, undercooking (high kappa number) is observed. Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 16

Copyright Some other application of radiotracer Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 17  Flow rate measurement  Leak detection in industrial system  RTD for troubleshooting Bypassing, Parallel flow, Channeling, Internal & External Recirculation  Evaluation of design Gamma scanning, Flow Visualization, RTD

Copyright Acknowledgements  Thapar University, Patiala  DAE-BRNS for project funding  Satia Industries Ltd., Mukatsar (Punjab) for industrial level experimental facility Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 18

Copyright Monday, November 21, 2016 THAPAR UNIVERSITY, PATIALA 19 Thank you for your kind attention