Synergistic removal of dust using the wet flue gas desulfurization systems

Coal is still a major energy source, mostly used in power plants. However, the coal combustion emits harmful SO2 and fly ash. Wet flue gas desulfurization (WFGD) technology is extensively used to control SO2 emissions in power plants. However, only limited studies have investigated the synergistic dust removal by the WFGD system. Spray scrubbers and sieve-tray spray scrubbers are often used in WFGD systems to improve the SO2 removal efficiency. In this study, the synergistic dust removal of WFGD systems for a spray scrubber and a sieve-tray spray scrubber was investigated using the experimental and modelling approaches, respectively. For the spray scrubber, the influence of parameters, including dust particle diameters and inlet concentrations of dust particles, and the flow rates of flue gas and slurry of limestone/gypsum on the dust removal efficiency, was investigated. For the sieve-tray spray scrubber, the influence of parameters such as the pore diameter and porosity of sieve trays on the dust removal efficiency was examined. The study found that the dust removal efficiency in the sieve-tray spray scrubber was approximately 1.1–10.6% higher than that of the spray scrubber for the same experimental conditions. Based on the parameters investigated and geometric parameters of a scrubber, a novel droplets swarm model for dust removal efficiency was developed from the single droplet model. The enhanced dust removal efficiency of sieve tray was expressed by introducing a strength coefficient to an inertial collision model. The dust removal efficiency model for the sieve-tray spray scrubber was developed by combining the droplets swarm model for the spray scrubber with the modified inertial collision model for the sieve tray. The results simulated using both models are consistent with the experimental data obtained.

in the experiments? 2.-The form of eq 27 is not the same as that in the theoretical part, eqs. (12)-(13). Why didn't you use the same form to obtain the fitting? 3.-The models you compare to should be described in the text. A fitting model may be better in a particular case but with less fundamental meaning. 4.-A general comparison on the fitting of the model to experimental data with error bars is needed and a discussion of the usefulness of the correlation. The editors assigned to your paper ("Synergistic removal of dust using the wet flue gas desulfurization systems") have now received comments from reviewers. We would like you to revise your paper in accordance with the referee and Associate Editor suggestions which can be found below (not including confidential reports to the Editor). Please note this decision does not guarantee eventual acceptance.
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Comments to Author:
Reviewers' Comments to Author: Reviewer: 1 Comments to the Author(s) This paper reports the synergistic dust removal by the WFGD system, which has a certain practical significance. Besides, the following contents need to be explained further: 1. It is not mentioned in this paper that the effect of temperature as well as pH to removal efficiency. In addition, please explain how to keep pH of the solution in a constant range? 2. It is recommended to add the effect of the liquid gas flow rate ratio (liquid-gas ratio) on the removal efficiency in the sections 4.1.1.2 and 4.2.1.2, which will be more convinced. 3. Please explain effect of gas residence time on the removal effect and the liquid level in the reactor? 4. What does "efficiency" specifically means in all charts? The dust removal rate or the desulfurization rate?
Reviewer: 2 Comments to the Author(s) The work deals with evaluating the dust removal efficiency in a wet SO2 removal system as a complementary removal system to the traditional electrostatic precipitator. The work is not easy to follow since the theory is later not connected to the experimental part. Furthermore, the model use must be clearly presented due to the fact that it is based on lab scale experiments, in spite of the use of dimensionless numbers. 1.-There are two removal mechanisms, nsp and ns. But later over the development of the empirical model only nsp is considered. Can you elaborate on the reasons? Can you obtain data only for one particular efficiency. How do you decouple the removal efficiency of the foam layer in the experiments? 2.-The form of eq 27 is not the same as that in the theoretical part, eqs. (12)-(13). Why didn't you use the same form to obtain the fitting? 3.-The models you compare to should be described in the text. A fitting model may be better in a particular case but with less fundamental meaning. 4.-A general comparison on the fitting of the model to experimental data with error bars is needed and a discussion of the usefulness of the correlation.

Do you have any ethical concerns with this paper? No
Have you any concerns about statistical analyses in this paper? No

Recommendation? Accept as is
Comments to the Author(s) this revised manuscript can be accepted by journal.

Review form: Reviewer 2
Is the manuscript scientifically sound in its present form? Yes

Are the interpretations and conclusions justified by the results? No
Is the language acceptable? Yes

Do you have any ethical concerns with this paper? No
Have you any concerns about statistical analyses in this paper? No

Recommendation?
Accept with minor revision (please list in comments)

Comments to the Author(s)
The work deals with evaluating the dust removal efficiency in a wet SO2 removal system as a complementary removal system to the traditional electrostatic precipitator. The work is not easy to follow since the theory is not connected to the experimental part. I will summarise the question On behalf of the Editors, I am pleased to inform you that your Manuscript RSOS-181696.R1 entitled "Synergistic removal of dust using the wet flue gas desulfurization systems" has been accepted for publication in Royal Society Open Science subject to minor revision in accordance with the referee suggestions. Please find the referees' comments at the end of this email.
The reviewers and Subject Editor have recommended publication, but also suggest some minor revisions to your manuscript. Therefore, I invite you to respond to the comments and revise your manuscript.
• Ethics statement If your study uses humans or animals please include details of the ethical approval received, including the name of the committee that granted approval. For human studies please also detail whether informed consent was obtained. For field studies on animals please include details of all permissions, licences and/or approvals granted to carry out the fieldwork.
• Data accessibility It is a condition of publication that all supporting data are made available either as supplementary information or preferably in a suitable permanent repository. The data accessibility section should state where the article's supporting data can be accessed. This section should also include details, where possible of where to access other relevant research materials such as statistical tools, protocols, software etc can be accessed. If the data has been deposited in an external repository this section should list the database, accession number and link to the DOI for all data from the article that has been made publicly available. Data sets that have been deposited in an external repository and have a DOI should also be appropriately cited in the manuscript and included in the reference list.
If you wish to submit your supporting data or code to Dryad (http://datadryad.org/), or modify your current submission to dryad, please use the following link: http://datadryad.org/submit?journalID=RSOS&manu=RSOS-181696.R1 • Competing interests Please declare any financial or non-financial competing interests, or state that you have no competing interests.
• Authors' contributions All submissions, other than those with a single author, must include an Authors' Contributions section which individually lists the specific contribution of each author. The list of Authors should meet all of the following criteria; 1) substantial contributions to conception and design, or acquisition of data, or analysis and interpretation of data; 2) drafting the article or revising it critically for important intellectual content; and 3) final approval of the version to be published.
All contributors who do not meet all of these criteria should be included in the acknowledgements.
We suggest the following format: AB carried out the molecular lab work, participated in data analysis, carried out sequence alignments, participated in the design of the study and drafted the manuscript; CD carried out the statistical analyses; EF collected field data; GH conceived of the study, designed the study, coordinated the study and helped draft the manuscript. All authors gave final approval for publication.
• Acknowledgements Please acknowledge anyone who contributed to the study but did not meet the authorship criteria.
• Funding statement Please list the source of funding for each author.
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Once again, thank you for submitting your manuscript to Royal Society Open Science and I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch. Comments to the Author(s) The work deals with evaluating the dust removal efficiency in a wet SO2 removal system as a complementary removal system to the traditional electrostatic precipitator. The work is not easy to follow since the theory is not connected to the experimental part. I will summarise the question What is the point in presenting all the model if in the end you develop an empirical correlation and just fit it o the data. Comments to the Author(s) this revised manuscript can be accepted by journal.

23-May-2019
Dear Dr qirong, I am pleased to inform you that your manuscript entitled "Synergistic removal of dust using the wet flue gas desulfurization systems" is now accepted for publication in Royal Society Open Science.
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Kind regards, Andrew Dunn Royal Society Open Science Editorial Office Royal Society Open Science openscience@royalsociety.org on behalf of Prof R. Kerry Rowe (Subject Editor) openscience@royalsociety.org systems are mostly between 50-60°C and 5.5~6.0 in a stable level ， we also controlled them at a stable level in order to study other factors of particles removal, which is usually the changeable running parameters in different power plants.
The PH is controlled by a combined system with a PH meter and peristaltic pump. The PH meter measured the PH value of the slurry in the tank in real time, meanwhile, the peristaltic pump transport the CaO slurry from the MT(Mixing tank) to ST(Slurry tank), if the PH exceed 6.05 in the experiment, the pump was stopped, and was started while the PH dropped to 5.95. In the experience, we controlled the CaO slurry in a stable value, the PH value can also be kept in a stable level, because the consumption of the CaO slurry is stable. It is specially to notice is that the MT and ST should be mixing with a stirrer, otherwise the PH is hardly to be controlled because of the uneven distribution.
2. It is recommended to add the effect of the liquid gas flow rate ratio (liquid-gas ratio) on the removal efficiency in the sections 4.1.1.2 and 4.2.1.2, which will be more convinced.
L/G (liquid-gas ratio) is the ratio of gas flow rate to liquid flow rate. There are usually two ways to change the L/G, the first one is to fix the liquid flow rate and adjust the gas flow rate, another one is to fix the gas flow rate and adjust the liquid flow rate. In this study, we found the change of gas flow rate or slurry flow rate have a different effect in removing particles form WFGD system. In order to avoid confusing the L/G changed with the changes of gas flow rate or slurry flow rate, we use them directly to analysis the effect of the particles removal, not the L/G directly.
3. Please explain effect of gas residence time on the removal effect and the liquid level in the reactor?
The gas residence time is equals to the high of the scrubber divided to the gas velocity and the liquid level also can be expressed with the slurry flow rate.
We analyzed the gas flow rate and slurry flow rate in the article directly.
or the desulfurization rate?
The dust removal rate, we have pointed out it again in the article and mark out of them in every figures title.

Reviewer #2
The work deals with evaluating the dust removal efficiency in a wet SO2 removal system as a complementary removal system to the traditional electrostatic precipitator. The work is not easy to follow since the theory is later not connected to the experimental part. Furthermore, the model use must be clearly presented due to the fact that it is based on lab scale experiments, in spite of the use of dimensionless numbers. 2.-The form of eq 27 is not the same as that in the theoretical part, eqs.
(12)-(13). Why didn't you use the same form to obtain the fitting?

Eqs. (12)-(13) is an theoretical model with the method of discrete material
balance equation in a cell volume, many parameters that effect the dust removal, such as are missing, and the results cannot effectively reflect the , , , , , effect of the parameters in the experiments (we compared the equations results as shown in Fig. 2 and Fig.3). The form of eq 27 is the better way we found to construct the model for simulating the dust removal efficiency for different parameters of the WFGD system.
3.-The models you compare to should be described in the text. A fitting model may be better in a particular case but with less fundamental meaning.
We added the descriptions of the models in the text, and mark out of them with color (lines 221-226). with the referee suggestions. We appreciate your and the two reviewers' very helpful comments and suggestions, and we have incorporated them in our amendments.
We have made a revision to the manuscript according to the reviewer 2.
Some points have been highlighted (in green) and some have been re-written.
Meanwhile, we upload the manuscript and comments file in the system.

Corresponding answers to the reviewers comments：
Reviewer: 2 Comments to the Author(s) The work deals with evaluating the dust removal efficiency in a wet SO2 removal system as a complementary removal system to the traditional electrostatic precipitator. The work is not easy to follow since the theory is not connected to the experimental part. We add a table in the article to reveal the connection of the theory models to the predicted efficiency, and compares results of the predicted efficiency and experimental data are shown in Figures 4 and 5. In the model analysis, we introduced a corrected parameter into the models to describe the enhanced efficiency ( ′ ) of forth layer in the sieve-tray scrubber, which is the dominant for ηe. The dedusting efficiency of sieve-tray spray scrubber is a combination efficiencies contributed by spray layer and enhanced efficiency of foam layer (ηe). Based on of this, the dedusting efficiency of sieve-tray scrubber can be predicted.
We add the descriptions of above in the article with green.