*3.3. Determination of the Share of Combustible Parts in the Slag*

The contents of the combustible parts in the slag, measured for the three considered air distributions, are presented in Figure 10. The dashed line shows the trend line, which is the extrapolated trend line beyond the scope of the tests (by 0.1 of the R parameter).

**Figure 10.** Curve describing changes in the content of combustible parts in the slag as a function of R parameter. The dashed line—extrapolated trend line beyond the test range (by the value of 0.1 of the R parameter).

#### **4. Discussion**

The following discussion is based on the results of the research carried out in a furnace chamber with a fixed grate, working at the operating parameters given in Section 2 of this paper.

The changes in air streams introduced during the tests caused disturbances in the combustion process, which contributed to the irregular course of the streams of gaseous emissions of exhaust gas components.

In the case of the curves showing the changes in CO2 (Figure 5), the relationship between gas emissions and the changes in the primary air stream is clearly visible. And with the increase in parameter R, the occurrence of the largest CO2 stream is increasingly ahead of the moment of maximum air stream supply.

Almost the entire emission of CO (Figure 6), regardless of the distribution of the supplied air, takes place up to the moment of the largest stream of supplied air (approx. to 8, 16 and 20 min, respectively). The combustion process with air separation, for which R = 1/6, is characterized by the shortest duration of high CO emissions and the lowest total emissions of CO2 and CO. This may be the reason to conclude that the large air stream at the beginning of the combustion process did not allow the fuel to be properly ignited. For this reason, the amount of air quickly turned out to be sufficient to completely burn down the occurring CO to CO2.

The largest streams of NOx emission (Figure 7) are accompanied by a rapid decrease in the stream of CO emission. The above observation is consistent with the results of the research presented in [20,47,48].

The shapes of the curves showing changes in SO2 emissions (Figure 8), in the case of combustion processes with air distribution for R = 1/6 and R = 2/3, approximately correspond to the shapes of the curves showing changes in CO2 emissions (it is most evident in the case of air separation for R = 2/3). For the third combustion process, the discussed relationship can be observed only after 13 min.

The information provided in Figures 9 and 10 shows that within the range of the analyzed air distribution R from 1/6 to 2/3, as it increases, a rise in the emissions of CO2, CO and SO2 was reported, respectively by 53%, 125%, and 27%, as well as a drop of NOx emission and the share of combustible parts in the slag by 12% and 79%, respectively. This allows us to assess the impact of air distribution on incomplete and fragmentary fuel combustion and to evaluate the ecological harmfulness of the conducted combustion processes.

The following general comments and observations result from the conducted analyses:

• The generalized air distribution curve corresponds well with the practical methods of air supply (distribution) in industrial grate furnaces.


When analyzing the obtained measurement results, one should notice the presence of too-high contents of combustible parts in the slag and the related too-low values of CO2 emission. It is caused by too short fuel combustion assumed in the tests. The resulting fact made it possible to more clearly demonstrate the influence of the method of air supply in the grate furnace on the emission of solid and gaseous fuel combustion products.

**Author Contributions:** Conceptualization, M.K. and J.K.; methodology, M.K. and J.K.; validation, M.K.; formal analysis, J.K.; investigation, M.K.; resources, M.K.; data curation, M.K. and J.K.; writing original draft preparation, M.K. and J.K.; writing—review and editing, M.K. and J.K.; visualization, M.K.; supervision, J.K.; project administration, M.K.; funding acquisition, M.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** The APC was funded by the Silesian University of Technology from the research subsidy (SUBB) for 2023, number 08/030/BK\_23/0116.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
