A Review of Research on Advanced Control Methods for Underground Coal Gasification Processes

Abstract

Underground coal gasification (UCG) is a clean coal mining technology without significant environmental impacts. This technology can also be used in deep, hard-to-reach seams or deposits affected by tectonic disturbances, where conventional mining is impossible. Several techniques and methods have been investigated worldwide to support the process control of UCG. Global research focuses on the control of UCG operating parameters to stabilize or to optimize the performance of the underground reactor during energy conversion. This paper studies recent research in the field of UCG control and compares individual control techniques and possibilities for practical application. The paper focuses on advanced control methods that can be implemented in an in situ control system (e.g., adaptive control, extremum seeking control, and robust control). The study investigates control methods that ensure desired syngas calorific value or maximization. The review showed that robust control techniques such as sliding mode control and model predictive control have the most significant potential, and achieve the best results despite their complexity. In addition, some methods have been investigated through simulation or experimentally. The paper aims to give the reader an overview of the given issue and to alert the practice to recent research in the given area.

Critical review of methods for intensifying the gas generation process in the reaction channel during underground coal gasification (UCG)

“…By optimizing the design and structure of the gasifier, it is possible to provide better heat and mass exchange, which will improve gasification results. A series of experimental studies involving the gasification process modeling presented in research [171]- [175] has helped substantiate the effect of technological and technical innovations in gasifier designs on the parameters of the coal seam gasification process.…”

Investigation of Underground Coal Gasification in Laboratory Conditions: A Review of Recent Research

“…The above shows that an algorithm is needed to stabilize the temperature to the selected setpoint. The stabilization level of UCG control based on the adaptive discrete controller that continuously calculated the optimal airflow or exhaust ventilator power to stabilize the underground temperature or oxygen concentration in syngas at the desired value was proposed in [2,12]. The equation of the used proportional-integration controller has the following form:…”

“…The value of the iterative constant h is chosen to ensure that the values in ūi+1 will lead to the existence of the objective function and its continual maximization (i.e., J( ūi+1 ) > J( ūi )). Constraints represent limitations for manipulation variables (i.e., u 1 , u 2 , and u 3 ) and selected output variables (e.g., allowed concentration of oxygen in syngas) The principle of model-free ESC based on the gradient method applied on UCG is shown in Figure 9 [12,24]. The presented optimal control was tested during gasification on an ex situ reactor where the syngas's heating value was elevated from 4.4 MJ/m 3 to 8 MJ/m 3 (see Figure 10).…”

“…The new optimal values will ensure tracking of the desired calorific value of the syngas. Such a control method is also called adaptive MPC (APMC) [12,27]. Figure 15 presents the course of the syngas's heating value tracking and the behavior of optimized airflow by MPC and the discrete PI controller.…”

Thermo-Mechanical Numerical Analysis of Stress and Damage Distribution within the Surrounding Rock of Underground Coal Gasification Panels

“…Underground coal gasification (UCG) is an alternative way to convert underground coal reserves into a synthesis gas (syngas), such as methane, hydrogen, and carbon monoxide, in situ, where it is infeasible or uneconomical for traditional mining methods [1][2][3][4]. UCG has the potential to be a more environmentally friendly and cost-effective way to extract energy from coal, as it can reduce the amount of waste produced and the impact on the surface environment and increase energy efficiency and the availability of fuel resources [5][6][7][8]. The controlled retraction injection point (CRIP) configuration is a technique used in UCG to reduce cavitation instability in coal seams.…”