**Preface to "Modeling and Control of Energy Conversion during Underground Coal Gasification Process"**

The underground coal gasification (UCG) technology is an unconventional method of coal mining, and its approaches represent new scientific knowledge. This continually evolving technology is a large energy source that can be obtained at a lower cost than convection mining and is also safer. The UCG process transforms the coal's energy into the gas produced (i.e., syngas) during the underground coal gasification process in the coal seam.

For successful energy conversion, i.e., obtaining the syngas with a higher calorific value, it is essential to develop new modeling methods and control this process. Modeling methods will make it possible to identify the individual stages of the UCG process more precisely and, thus, improve the knowledge of this process. Various UCG models, e.g., models based on CFD, machine models for syngas composition, or temperature prediction, were recently investigated. By synthesizing suitable algorithms and mathematical models, it is possible to obtain simulation models of the process. These simulation models can be used to design the control systems and the optimal setting of process parameters. In the control of UCG, the significant issue is to ensure sufficient underground temperature and the calorific value of syngas. This issue can be solved by advanced control methods and optimization of operating variables.

The present book contains nine articles that were accepted and published in the Special Issue "*Modeling and Control of Energy Conversion during Underground Coal Gasification Process*" of the MDPI Energies journal. This book focuses on the energy conversion processes in underground coal gasification (UCG), as well as on the modeling and control of this process.

> **Marek Laciak, J´an Kaˇcur, and Milan Durd´an** *Editors*
