Ind. Eng. Chem. Res. 2009, 48, 5565
5565
Reply to “Comments on ‘Removal of SO2 from Industrial Effluents by a Novel Twin Fluid Air-Assist Atomized Spray Scrubber’” B. Rajmohan, S. Biswas, and B. C. Meikap* Department of Chemical Engineering, Indian Institute of Technology, Kharagpur, India Sir, we would like to offer our point-by-point response to the comments made by Dr. A. Bandyopadhyay. We also appreciate in receiving these comments on our paper that are prepared stemming from deeper understanding of the subject of SO2 scrubbing in spraying systems. The presented study was carried out on SO2 removal on the laboratory scale that was basically simulating the industrial scenario. In view of this consideration, the title was selected by us. However, the comment raised is correct. The Introduction section was developed with the aim at projecting research works on SO2 and/or particulate scrubbing, since devices for removing both SO2 and particulate scrubbing are also fitting for SO2 scrubbing alone. Inclusion of a “modified multi-stage bubble column” in this section was due to our previous working experience on it. However, we give great value to the comments raised about this aspect, and the references cited therein are of immense significance in relation to our work as well. The comments relating to the Experimental Setup and Technique section are clarified by the fact that experiments were carried out by generating hot gas by using an air heater connected to a blower. The hot air from the air heater was passed through galvanized iron (GI) pipeline and entered into the bottom of the scrubber at its sidewall. Temperatures were measured and controlled through a control panel placed at the exit of the air heater. Admittedly, Figure 1 should have included this fact symbolically as pointed out in the comments. As regards the deformation of the scrubber material, it is reported here that we did not notice any deformation of Perspex-made column visually at the working temperature. The water droplets cooled the hot gas to nearly ambient temperature before it reached half of the column height vertically. Moreover, the wall of the Perspex-made column was wetted continuously by thin films of water generated by the down flowing water droplets. However, the technical points indicated in the comments relating to the scrubber material deformation and droplet evaporation are of considerable significance which we would like to incorporate into our future research work. It is true that gaseous sampling does not require isokineticity to be followed. But in the presented study, though the experimental setup described was for the removal SO2, the same setup could also be operated for particulate scrubbing. With this objective in mind, sampling was carried out and reported to be * To whom the correspondence should be addressed. Tel.: +913222-283958. E-mail:
[email protected].
maintained following isokinetic conditions. “Isokinetics” should be read as “isokinetic” as pointed out. The comments made in relation to the applicability of the Nukiyama and Tanasawa correlation is absolutely correct. In fact, the droplet sizes were estimated by the correlation developed by Rizkalla and Lefebvre1 as given below:
[ ](
droplet SMD)10-3
√σFL FGvG
1+
1 AWR
6 × 10-5
0.5
)
+
[ ](
µL2 1 1+ σFG AWR
)
0.5
µm
This correlation was derived from the Nukiyama and Tanasawa correlation for measuring droplet sizes which is applicable for the twin fluid air-assisted atomizer. This should be used as an adjunct to our presented paper. We appreciate the identification of the mistakes associated with Figures 4 and 7. The captions of these figures are to be interchanged so as to clear up this mistake. Similar mistakes are also associated with other figures mentioned in the comments, and the confusion would be resolved if the captions are interchanged. Furthermore, the exponents in the Liquid Flow Rate and Gas Flow Rate should not have negative signs in the legends of Figures 4-9. The comment made in relation to Figure 10 is absolutely correct, and we admit that the paper should be read without this figure and its associated description in the text. Details of the “Number of Transfer Units (NTU) Calculation” were not furnished as per the suggestions of the reviewers as these are available in a standard text on mass transfer.2 It is true that Weber number (We) includes “a characteristic length of the flowing stream” that we did not incorporate in the presented work; however, this may be considered in our future work. On the other hand, the comment on Euler number (Eu) made is absolutely correct and “modified Dispersion number (DNm)” may be read instead of “Eu”. In the conclusions, the efficiency of “98.98%” should read as “97.25%” [see Figure 6]. Literature Cited (1) Rizkalla, A. A.; Lefebvre, A. H. The Influence of Air and Liquid Properties on Air blast Atomization. ASME J. Fluids Eng. 1995, 97, 316. (2) Treybal R. E. Mass Transfer Operations, 3rd ed.; McGraw Hill Book Co.: New York, 1986; p 303.
IE900188R
10.1021/ie900188r CCC: $40.75 2009 American Chemical Society Published on Web 05/07/2009
