## 4 Conclusions  
Based on the study results, the operation of the pilot OS steam pyrolysis unit was tested to obtain energy-valuable products (liquid hydrocarbons, semi-coke, non-condensable gas-phase compounds, and bitumen) with a subsequent approach of their physicochemical characteristics. The results of determining the material balance showed that the main energy products are liquid hydrocarbons (30.4 wt%), non-condensable gas-phase compounds (26.5 wt%), and semi-coke (39.6 wt%). In this case, semi-coke and non-condensable gas-phase compounds are considered as secondary energy carriers for generating thermal energy, which supports the technological process of pyrolysis. An analysis of non-condensable gas-phase products showed that the dominant compounds are CO (33.5 vol%), CH\({}_{4}\) (17.3 vol%), and H\({}_{2}\) (15.9 vol%). The CO\({}_{2}\) value was 12.6 vol%. The semi-coke had a high ash (63.7 wt%) and sulfur (1.7 wt%) content and a calorific value of 14.6 MJ/kg. In this case, the ash residue belonged to the medium-melting type (tc \(>\) 1250 \({}^{\circ}\)C) and mainly consisted of SiO\({}_{2}\) (63.4 wt%), Al\({}_{2}\)O\({}_{3}\) (12.1 wt%), and Fe\({}_{2}\)O\({}_{3}\) (10.4 wt%). The target product--liquid hydrocarbons--had low viscosity and a high content of the light fractions, which was expressed in a relatively low value of the flash point (T\({}_{\rm f}\) = 89 \({}^{\circ}\)C). The calorific value was 42.6 MJ/kg with a carbon and hydrogen content of 83.4 wt% and 11.4 wt%, respectively. Sulfur content was 0.8 wt%. Figure 14: Concentration profiles of the release of gas-phase compounds CO, CO\({}_{2}\), NO\({}_{x}\), and SO\({}_{2}\) formed in the combustion of liquid hydrocarbon droplets at T\({}_{\rm g}\) = 500–700 \({}^{\circ}\)C.  
During the spraying of liquid hydrocarbons using a pneumatic nozzle, the droplet velocity after spraying decreased by no more than 10%. The value of the jet spraying angle in the process did not exceed 25\({}^{\circ}\). The number of small droplets (no more than 400 \(\upmu\)m) increased by 16%, whereas the number of large droplets (more than 600 \(\upmu\)m) decreased by 24%. At the air temperature, T\({}_{\rm g}\) increased from 450 to 700 \({}^{\circ}\)C and the ignition delay time t\({}_{\rm i}\) decreased exponentially from 19.2 to 1.1 s. Starting from 500 \({}^{\circ}\)C, a flame was observed to form, and its duration increased at increased T\({}_{\rm g}\). At T\({}_{\rm g}\) = 450 \({}^{\circ}\)C, thermal conversion of the droplet of liquid hydrocarbons occurred in the smoldering mode. Droplet combustion in the temperature range of 600-700 \({}^{\circ}\)C was accompanied by the formation of intense microexplosions, which is explained by the high content of light fractions in this fuel composition. In addition, the release of CO, CO\({}_{2}\), NOx, and SO\({}_{2}\) was recorded during the combustion process. At the same time, the maximum concentrations of the emitted CO\({}_{2}\) and NOx compounds increased by an average of 30% with the T\({}_{\rm g}\) increase, which is associated with the combustion process intensification. The obtained results of the study, in view of their applied nature, may be useful in the future for the development of the pyrolysis industry, in particular, for the design of new types of reactors, and installations in general. The following are available online at [[https://www.mdpi.com/article/10.3390/app12031012/s1](https://www.mdpi.com/article/10.3390/app12031012/s1)]([https://www.mdpi.com/article/10.3390/app12031012/s1](https://www.mdpi.com/article/10.3390/app12031012/s1)), Video S1: droplet combustion of liquid hydrocarbons at T\({}_{\rm g}\) = 700 \({}^{\circ}\)C.  
Conceptualization, K.L. ; methodology, A.K., D.G., A.Z. and I.B. ; formal analysis, K.S. ; writing--original draft preparation, K.L., D.G. and M.K. ; writing--review and editing, K.L. ; visualization, A.K. ; project administration, V.G. ; funding acquisition, K.L. All authors have read and agreed to the published version of the manuscript.