38 Air Monitoring


Table 5. Chemical compositions of liquor in carbonation process (continuous trial 2).


Sl.No. Carbonation Time


1 2 3 4 5


Figure 3. Schematic drawing of flue gas generation via APH and Chimney. Table 1. Composition range of CO & CO2


gases at various sections of


Tummalapalle Mill. Sl.No.


1 2 3 4


Sections


Boiler House DG - I DG -II DG -III


CO (%V/V) CO2 BDL (DL 0.2)


BDL (DL 1) BDL (DL 1) BDL (DL 1)


5 Autoclave Scrubber BDL (DL 0.2) (%V/V)


7.6-8.3 8.5-9.6 9.1-9.4 9.1-9.4 7.3-7.9


Figure 5. Effective use of Boiler flue gas for carbonation of process liquor at Tummalapalle Mill.


6. Batch Experiment Trial 1 & Results: Trials were conducted at boiler house for carbonation of process liquor. Initial trials conducted by feeding flue gases inside 5 liter canes full of process liquor. Trials were done in 4 batch processes (figure 6) and satisfactory results observed after analysis in CR&D lab. (table 4), [graph 1(a),1(b)]


(minutes) nil


30 60 90


120 Na2 (gpl) CO3


35.65 41.00 48.13 53.47 49.91


NaHCO3 (gpl)


nil nil nil nil


8.48


NaOH (gpl)


14.80 11.43 5.38 1.35 nil


Graph 2 (a). Effect of flue gas in sodium carbonate (Na2 concentration during liquor carbonation (continuous trial 2).


CO3 )


Figure 6. Carbonation trial in batch process.


Table 4. Chemical compositions of liquor in carbonation process (batch trial 1). Sl.No. Carbonation Time


Na2


Figure 4. Cross sectional diagram of flue gas passing by Air Pre Heater (APH).


1 2 3 4


(minutes) nil 30 60 90


(gpl) CO3


39.21 46.34 57.04 51.69


NaHCO3 (gpl)


nil nil


1.41 9.89


NaOH (gpl)


17.49 9.42 nil nil


Graph 2 (b). Effect of flue gas in caustic lye (NaOH) concentration during liquor carbonation (continuous trial 2).


8. Environmental benefits of flue gas usage: Carbon dioxide (CO2


400,000 years, the concentration of CO2


), a trace gas, is the most important


greenhouse gas in the atmosphere. Similar to other gases, the concentration of CO2


is measured in parts per million. In the past varied between 200


ppm to 280 ppm. Since the mid-19th century, the concentration of CO2


Table 2. Boiler (15 MT) stack parameters at Tummalapalle Mill. [Test Method: IS11255(P 3)2008].


Sl.No. Sampling Date Stack Temp (⁰C)


1 2 3 4 5


06/03/2018 14/06/2018 12/09/2018 13/12/2018 15/02/2019


Table 3. Stack Volume details of CO2 at Tummalapalle Mill.


197 199 203 210 206


Stack Gas


Velocity (m/sec) 16.82 16.90 16.60 15.20 15.40


gas for Boiler (15 MT)


Sl.No. Sampling Date Stack Gas Flow Rate (Nm3


/hr)


1 2 3 4 5


06/03/2018 14/06/2018 12/09/2018 13/12/2018 15/02/2019


27362 27369 27371 28361 28389


8.1 8.3 8.1 7.6 7.8


5. Online Experiment Setup at Tummalapalle Mill: Three Pass Wet back smoke tube boiler each of capacity 15 Tons/Hr at 17.5 Kg/cm2g design pressure has been envisaged for the supply of steam to process plants under IBR Design Code 1950 (figure 3). Each unit is provided with control of fuel and water. Boilers are PLC system operated. Engineering modifications done by installing blower fan at the outlet side of APH (figure 4) for feeding of flue gas for Batch & Continuous trials (figure 5).


Graph 1 (b). Effect of flue gas in caustic lye (NaOH) concentration during liquor carbonation (batch trial 1).


CO2 (%V/V)


has been rising and reached 410 ppm in June 2018. In the late 1950s, the annual rate of increase of CO2


concentration was


about 0.73 ppm per year, and from 2005-2014 the increase was about 2.11 ppm per year. Main effects of CO2


as following;


Graph 1 (a). Effect of flue gas in sodium carbonate (Na2 during liquor carbonation (batch trial 1).


CO3 ) concentration


a) Climate change, b) Greenhouse effect, c) Global warming, d) Air, Soil and Water Pollution, e) Human Health Impacts, f) Ground-Level Ozone, g) Acid Rain,


h) Ocean Acidification, i) Carbon Fertilization.


in atmosphere are


7. Continuous Experiment Trial 2 & Results: Process liquor was collected inside 200 liter tank. Boiler flue gas (average 203°C) was fed continuously 120 minutes inside tank and samples were collected at time interval of 30 minutes (figure 6). Continuous increase in sodium carbonate and decrease in caustic lye values were achieved and sufficient carbonation achieved (table 5), [graph 2(a),2(b)]. Trials still continues before final implementation in Uranium mineral processing plant.


Figure 7. Atmospheric CO2


concentration in parts per million by volume (ppm) at Mauna Loa, Hawaii (Keeling & Whorf 1997).


AET October / November 2019 www.envirotech-online.com


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