The Bacharach Method: A Low-Cost Tool for Small-Scale Combustion Units’ Flue Gas Quality Control

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Author Response

Dear Reviewer, Kindly see the our responses in the attached document.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper combined Bacharach method with an innovative evaluation approach, and then evaluted the method as a rapid and cost-effective tool for assessing particulate matter mass concentration in flue gas. But, the writing and grammar are terrible. For exmples, but not limited

1. Line 207, “16 brightness values were always assinged to soot number value (see Table 1)”. But, where were “16 brightness values” from?

2. In Function (1), B should be the average value?

3. Check the titles of Figure 3 and Figure 4.

4. In Figuer 4, please add the relevances R² of the two functions.

5. In Table 2, the unit of mass concentration of particulate matter?

Comments on the Quality of English Language

The writing and grammar are terrible. So, the quality of English in this paper must be improved.

Author Response

Dear Reviewer, Kindly see the our responses in the attached document.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

I thank the Editor for the opportunity to review this article.

I thank the Authors for the work done and provided for review.

 

The topic of the article is relevant, there is obvious novelty and modern. Particulate matter in particular is particularly important and control is needed, including new ways of determining/controlling emissions to find solutions to this type of pollution. This type of research is really very interesting. Judging from the results, this paper is quite an initial stage, so it is important that both the merits and negatives of the study were found. The manuscript is quite well organized, but there were many questions for its completeness and quality as a future publication.

 

I present my recommendations for future additions.

 

Introduction. The article presents in enough detail the situation in the world, which concerns the problems of determination of particulate matter emissions. However, it is known that at the moment there is research on replacing fossil fuels within the framework of green economy as well as sustainable development. I advise you to submit for citation the following papers, which present solutions for the replacement of non-renewable fuels, also combustion of secondary raw materials, taking into account the necessary additional requirements for operation systems:

 https://doi.org/10.3390/su13094881

https://doi.org/10.3390/en14248471

https://doi.org/10.3390/en12163072

 

Methods

How was it possible to perform sampling for the Bacharach method under isokinetic conditions?

 

To what standard were the sample collection sites selected? It would be useful to provide a schematic diagram of the test bench with measurement points and instruments.

How far apart were the sampling locations using Wöhler SM 500, Afriso STM 225, and ABB AO2020 in the same channel? What magnitude of discrepancies between parameter values were obtained and how were the errors minimized?

 

What is the point of such a procedure?

On each filter, two samples were taken 160 immediately after each other, while only the second sample was taken into consideration

 

How were the filters prepared before sampling (paying attention to residual moisture)? Were any operations performed on the filters after sampling?

How were the filters transported and preserved to avoid possible loss of ash on the filter surface?

Usually, the surface of the filters may contain obvious particles that are not firmly attached to the filter surface; hence they may change their position on the filter. Was this taken into account when analyzing the 30x30 pixels area?

 

How was it possible to establish two sample collections in the same channel under the same conditions? Was the mismatch of results due to their location calculated?

 

What considerations led to the use of the Wohler SM96 rather than the Wohler SM500 for simultaneous comparative measurement together with the Bacharach filters?

 

The selection of the zone to be analyzed is quite subjective. What is the method used to determine the zone to be analyzed (30x30 pixels)? How uniform is the ash distribution on the filter? How is the zone selected if the distribution is not uniform?

 

As the Authors indicated in the methodology, the multiplication factor was changed to be more consistent with the correlation. This interpretation will probably increase the error of the method, especially since this procedure has to be performed each time for a new source of contamination. How can the authors justify the appropriateness of such statistical fitting and what measures should be taken to minimize the human factor?

 

The error and selection of the ash factor is rather inaccurate. For what concentration intervals do the authors assume it is possible to use this method? Are there other factors that can change the dependence of solids concentration on ash factor and how can they affect the parameter values (decrease or increase)?

 

Results and Discussion

For the scientific study, I question whether it was best to choose that: “21 small-scale combustion units...These sources were almost exclusively operated by their operators (owners), not by trained technicians during the certification process”. In this way the actual results of the operation of these units were obtained, but it is not clear to what extent the rules of operation were followed, i.e. to what extent they were standardized, and with such an approach there is a high probability of errors and consequently impossibility to compare the results between different cases.

 

How much can fuel type, even fuel subtype, affect filter brightness? Was any trend noticed, e.g. biomass pellets and biomass chips?

 

Figure 2: Indicate what the filter numbering means and what exactly these samples are

 

If I understand correctly, the results obtained using the SM 96 are accepted as appropriate. Has the metrological calibration of this measuring instrument been carried out? What deviations in the results were obtained?

 

In the paper a lot of emphasis is given to the fact that the measuring instruments are highly sensitive to highly contaminated gases. However, no special analysis of the measurement difference depending on the concentration of particulate matter was presented in the paper. Besides, what do the authors mean by “high concentration”, what is the limit concentration, according to them, that is already considered high?

Author Response

Dear Reviewer, Kindly see the our responses in the attached document.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The article deals with the possibility of using the Bacharach method to evaluate and inspect small heating devices as an alternative to laboratory methods including the gravimetric method. The research presented in the article does not fully evaluate the method as truly useful.  The largest cognitive aspect is the subsection on the economics of using this method as a cheaper alternative, but the precision of this measurement relative to the gravimetric method gives strong doubts and concerns about its validity. I believe that the article should be carefully rewritten, written in the concept of showing preliminary research with a strong emphasis on the need for further work that in the future will allow its alternative use relative to gravimetry, especially in the context of the development or approximation of equations describing the actual emission: dust - its chemical composition versus the color obtained on the filter with the Bacharach method. For the moment, the article may mislead the viewer, moreover, affect the legislation so that this method can be considered as an alternative to gravimetry, however, the quality of measurement by this method may deviate from reality, which will affect the release in the EU market of devices that do not actually meet the environmental parameters. Hence, I believe that the article should be withdrawn, carefully rewritten by the author(s) as indicated by the reviewer(s) and sent for re-evaluation by the same review panel.

Below are the notes/comments for each section of the article.

 

Abstract:

- In the case of the first sentence, the provision about omitting domestic heating appliances from pollution studies is not true. According to current regulations within the EU regarding: EU Directive 2015/1189 on eco-design for solid fuel boilers, as well as Directive 2015/1188 in accordance with the Machinery Directive 2006/42/EC which is harmonized with EN 303-5 regardless of the version (starting from 2002, 2012 and 2021), a manufacturer of an appliance wishing to place it on the market by means of CE marking must meet the emission requirements of a given spline component listed in the standard for a given class of appliance (as cited in the article) of course, testing of these parameters is not mandatory, but marking an appliance with the CE mark without backing it up with reliable testing risks, in the event that irregularities are discovered (random testing by market surveillance services), withdrawal of the product from sale and financial penalties. I suggest in this vein to convert the first sentence of the summary and point out that in order to deepen the legitimacy of the development and use of the described method for rapid testing of devices, legislation should be introduced for this group of devices that will oblige the manufacturer to carry out tests on the quality of exhaust gases, of course, to deepen the improvement of air quality and ecological parameters of these devices.

- The sentence about the effectiveness of the Bacharach method of measuring the mass concentration of particulate matter in exhaust gases should be removed or converted to a provision about fast and effective testing of blackness exhaust gases (similar to that for liquid fuel devices including internal combustion engines) and add that further research and development of this method may allow in the future to measure the mass concentration (mg/m^3) of particulate matter in exhaust gases relatively correctly.

- The last sentence should be converted so that the recipient understands that the flue gas test for a biomass burning boiler gives the best representation for testing according to the limit for class 3 and 4 and in the case of a fossil fuel boiler (please specify which - hard coal, lignite ?) the best representation of the Bacharach method is for boilers according to the limit for class 5. I also suggest to add both for biomass and fossil fuels caloricity range (in MJ/kg) for which these observations have validity - caloricity and mainly the content of elemental carbon in the fuel and ballast will strongly affect the combustion process, and thus directly affect the dustiness of flue gases .

 

Introduction:

- In the paragraph about solid fuel combustion sources of up to 300 kW, it should be changed to 500 kW in accordance with the range of the EN 303-5 standard because solid fuel heating boilers are classified up to this power in the EU (the 300 kW range was a provision in the 2002 standard, but it is no longer valid).

- In the sentence about actual operation, it should also be taken into account before alternative fuel that the discrepancy between actual and laboratory emissions is mainly affected by different parameters of boiler operation in real conditions (range from about 0% to 50 -60% max) as in the laboratory (only two operating points 30% of rated power and 100%), which strongly distorts the level of emissions between actual and laboratory operation of the device (please also increase the bibliography with items treating these studies).

- In the sentence about the measurement of the gravimetric method during certification tests, it should be supplemented with the sentence that this is due to the provisions of the 303-5 standard, which indicates this method as correct for the implementation of the measurement of dust of combustion, you can also supplement the sentence with the provision that in the EN 303-5:2012 standard there is presented a scheme and a method (measuring apparatus) for the correct implementation of the measurement of dust of flue gases for solid fuel heating boilers up to 500 kW.

- I have a serious objection to the description in the text (lines 75-78) of the Wohler brand device model SM 500 with a gravimetric dust meter. Well, this device should not be called a gravimetric dustmeter, I allow it to be referred to as a semi-gravimetric one for the following reason: the total mass concentration of particulate matter in the flue gas is calculated with reference to an adjustable oxygen reference value in mg/m3 and the weighing (gravimetric) procedure itself is carried out online using a digital mass balance unit (data provided by the manufacturer of the device). From my observations and use of this device, the mass measurement is done by measuring the buckling of the incremental mass of dust on the filter, while the given result is calculated (it is not a direct mass reading), and in the gravimetric method it is a direct measurement of the mass before and after (that is, the mass increment), moreover, the adjustment of the exhaust gas flow is done automatically without the supervision of an observer - and this control is extremely important for the determination of the air stream correctly (e.g. with a Prandtl or Pitot probe), and the removal of total flue gas moisture by the Wohler analyzer is questionable, which is of great importance in the case of biomass combustion (especially fresh). Comparing the results obtained by the Wohler device against actual gravimetric dust meters (MRU - FSM Particulate matter measurement or EMIOTEST 3114) the deviation between gravimetric and semi-gravimetric results could be as high as 15% (about 6 mg/m^3) which often disqualified the devices from receiving emission bonuses (PM emissions < 20 mg/m^3).

- I don't understand why Ringelmann's method is considered inaccurate relative to Bacharach's in the text since both compare exhaust blackness. Technical aspects in the form of filter and pump are secondary, however, both methods are based on visual assessment of exhaust blackness hence this allegation is not valid and two it calls into question the validity of using this method (Bacharach) as a subsidiary method for exhaust blackness measurements (e.g. by gravimetry) which in my opinion negates the point of the whole work and the need for a thorough rewrite.

 

Materials and methods

- I strongly doubt the precision of the Bacharach method because: in the case of liquid fuels such as heating oils, we are talking about combustion under controlled conditions (most devices have regulation and control systems) of a known volume of liquid fuel at a known excess air ratio, moreover, the chemical composition of heating oils is strongly controlled and usually deviates little from the assumptions of standards. In such a case, we know the parameters responsible for the combustion process and the result of the stoichiometric combustion process, which allows us to use a 10-degree scale of blackening of exhaust gases in a very simplified manner. This blackening is only the result of a non-stoichiometric combustion process, which will result in soot (elemental unreacted carbon). In the case of solid fuel combustion, we are talking not only about soot, but also about particulate matter (mineral particles and other solid components of solid fuel that will no longer oxidize). Moreover, the color of soot, for example, from the combustion of biomass can give the illusory feeling that it is not heavy / harmful often say so about light-colored ash, but the composition of this ash often includes particles of mineral salts, precious metals other impurities taken by the plant in the vegetation cycle. It turns out, however, that the mass of this ash, despite its neutral color (not indicative of a large amount of soot, i.e. non-stoichiometric combustion), has a significant mass that is detectable, for example, in the gravimetric method. Therefore, I doubt the quality of the representation of the mass of exhaust dust using the Bacharach method. The evaluation method using the Bacharach scale has a large distribution of standard deviation between the values obtained. In the Bacharach method, soot growth is considered consistent with the change (deterioration of stoichiometry) on a scale from 0-10 represented by an appropriate comparative scale at which the standard deviation between each successive point is constant in your method, these deviations fluctuate, which makes it possible to judge the density or dilution of dust (exhaust gas) for a given measurement point and low precision of measurement.

- Figure 4 shows a significant distribution of particle sizes for a given scale point (e.g., between the 6th and 7th points the range of particles is from about 55 to about 480) that is eight times more. Equation 2 is not described exactly how it was developed.

- In Table 2 there are errors swapped are the values for automatic vs. manual fuel feeding.

 

Results and discussions

- A large number of incorrectly classified devices respectively: 15.2%, 19.2% and 19.4%, makes it possible to strongly doubt the quality and validity of using this method to assess the dustiness of flue gases from solid fuel appliances. The deviations can be even greater when the measurement uncertainty of the gravimetric method is taken into account, which will further deepen the quality and precision of the Bacharach method. How the overall success rate in determining the class of the device was determined for the 80% value. - Due to the errors in Table 2 (incorrectly assigned limits), I have doubts about the quality of the performance of classification and non-classification for the Bacharach and gravimetric methods as a comparison made throughout the chapter.

- The economic evaluation has the only cognitive aspect and I do not see any shortcomings in it.

 

Conclusions

They are formulated very generally and shallowly should be more broadly discussed the observed phenomena and necessarily highlight the need for further precise methods to refine measurements using the Bacharach method including and the need to create a correlation of dust mass - dust color - dust chemical composition - 10 degree scale.

Comments on the Quality of English Language

 Minor editing of English language required

 

Author Response

Dear Reviewer, Kindly see the our responses in the attached document.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thanks for response to my comments. I do not have further comments.

 

Reviewer 3 Report

Comments and Suggestions for Authors

The main recommendations of the Authors have been implemented correctly, diligently and in an appropriate manner, although some issues may be subject to further discussion. I am sure that these issues will be realized in future works of the Authors. I wish you much luck and it has been a pleasure to review your work.

This article has been prepared for publication

Reviewer 4 Report

Comments and Suggestions for Authors

Dear authors, thank you very much for sending a revised manuscript and a comprehensive cover letter (as many as 12 pages!). My decision to postpone the work was based on the short time available to make the corrections (and there were quite a few of them) in order to give you time to make them, which turned out to be unnecessary as you handled them very well. All my concerns and points of disagreement have been rectified or clearly explained. The version currently on the table is satisfactory and of a high academic standard. I believe that the current version gives a complete overview of the situation and the research you have carried out, while at the same time giving room for polemics on the use of the methods presented. The additions about the possibility of using the Bacharach method as an alternative, low-cost method for rapid versification fully reflect the point of the article and allow other researchers and decision-makers to decide on the validity and applicability of alternative methods, such as the one described by you. The article, from the introduction to the conclusions, meets the requirements for an academic paper and, in the revised version with minor editorial corrections, I consider it ready for publication in Fire.