Modeling of a Two-Bed Reactor for Low-Temperature Removal of Nitrogen Oxides in Nitric Acid Production

Round 1

Reviewer 1 Report

In the present work, effective low-temperature purification of tail gases after weak nitric acid plant in a single two-bed reactor was analyzed using mathematical modeling. The catalyst bed was determined by the modeling to ensure the residual nitrogen oxides less than 50 ppm under the temperature and spacial limitations inside the reactor, also the influence of physical and chemical factors during the process were carefully studied. The results can be applied for further in-depth researches of the nitrogen oxides abatement at the plants for industrial weak nitric acid production. It is interesting and the explanations are often reasonable. And the presented manuscript could be recommended for publication after a minor revision and amendments following these comments: 1. The language needs further polishing. 2. The main objectives and novelty aspects in this study should be highlighted clearly within the introduction section. 3. Line 132 “2.1. Kinetic Experiments” should be “2.2. Kinetic Experiments” 4. The part of Conclusions needs to be simplified, for example, the sentence “The kinetic parameters of SCR reaction were taken from our previous studies.” should not appear in the part of conclusions.

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Reviewer 2 Report

The presented article deals with the reduction of NOx and N2O in the tail gases in HNO3 production palnt. The authors combined their own kinetic data on the low-temperature decomposition of N2O on a spinel catalyst and literature data on SCR and incorporated them into a mathematical model of a two-bed reactor. The paper follows the "classical"  catalysis+kinetics+modelling scheme, and the final results are coherent and can provide insight into the behavior of a two-bed reactor. However, the manuscript in its current form suffers from the following problems (listed below) and I consider its release after a "major revision".

 

    1. The catalyst characterization section would deserve a better description (on which instrument was the BET measurement performed?). Was the chemical composition of the catalyst checked by XRF?

    2. In the description of the kinetic experiment, there is no information about the total pressure, or about its changes with the flow rate variation.

    3. The conversion curves in Figure 3 do not correspond to the experimental points at all. Experimental values suggest that the curves should be more S-shaped. There is an insufficient number of experimental points in the region of rapid increase in conversion (residence time 0.1 - 0.3 s). 

    4. The evaluation of the kinetic parameters (k and Ea) is based only on a few points on the Arrhenius plot (Figure 4), but in Figure 3 (kinetic experiments) the authors measured at several temperatures and loadings (residence time), were all these points considered in the parameter estimation procedure? I strongly suggest a different procedure involving non-linear parameter estimation (no linearization!) over all measured data. This procedure will also provide an estimate of the uncertainty of the parameters (inverse of the Hessian matrix). Since the parameters (k, Ea) are the basis of the next modeling section, maximum care must be taken in their estimation.  

    5. I don't agree with the statement that we can neglect the radial mass and heat transfer at a low ratio of the height of the catalyst bed to its length (lines 157-9), the opposite is true.

    6. The boundary conditions for the inlet section (equation (5) should be of the Danckwerts type, i.e. include composition and temperature gradients. The boundary condition for the catalyst temperature in the inlet section is missing.

    7. In equation 11, to calculate the Knudsen diffusion coefficient, the mean pore radius must be known, how was this value obtained?

    8. Internal transport is not considered in the kinetic equation for SCR (Table 3), even though the reaction takes place on large catalyst particles. How do you justify it?

Formal issues:

    1. A list of symbols should be given at the end of the paper, with the symbols in alphabetical order and with the Greek symbols in a separate paragraph. 

    2.  Definitions of some symbols are missing, e.g. symbol  (Eq. 17), Peclet number (Eq. 9).

    3. The text contains an acceptable number of typos, nevertheless they has to be corrected Non-exhaustive list below: 

        ◦ line 69 NH3 subscript

        ◦ line 94 octahedral_one 19] 

        ◦ line 198 “?? bulk density” symbol

        ◦ Lines 204-210 whole section is incorrectly formatted (line spacing and font)

        ◦ line 223 the “exponent” 1.35E11 instead of 10 power to ...

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

1) Write the novelty of the work in 6 sentences.

2) Before the conclusions, write the practical applications of the reactor, the removal of N compounds, and their benefits to society and industry, in 250 words.

3) What are the various methods and reactions for nitric acid production? Summarize them.

4) What are the regulations concerning N2O emissions - compare the regulations from your country with EU guidelines/USEPA, etc.

5) For tail gas purification, what are the commercially available technologies - summarize their key features, design, reactions, etc in one new TABLE.

6) Write the purity of all chemicals used.

7) State the model number, and name of all instruments, equipment, analytics, electrodes, and columns used.

8) Figure 3 = Move it to the results and discussions.

9) What are the different factors that affect the reaction rate of nitrous oxide decomposition? Discuss with REF support.

10) Equation 18 is not your result. MOVE.

11) Don't write any text or equation related to methodology in the results and discussions. More than 14 mistakes can be seen.

12) What are the benefits of catalyst loading by layers? Discuss with REF support.

13) Too many small paragraphs in this document. Each paragraph should have 7-8 sentences. MERGE and modify.

14) Compare the results of he hydraulic resistance of the beds and weight of catalysts and their effects on N2O removal with literature.

15) Write conclusions in one paragraph, < 150 words.

16) Check REF formatting manually.

17) Add 10-15 more recent literature from 2022 and 2023. use your keywords and search.

18) A detailed author's response is required + answer all the questions and implement them in the revised text. 

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

I would like to thank the authors for considering my comments and for (in my opinion) improving the manuscript.