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Modeling and Control of Energy Conversion during Underground Coal Gasification Process

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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "H: Geo-Energy".

Deadline for manuscript submissions: closed (31 October 2021) | Viewed by 15988

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Special Issue Editors

Prof. Dr. Marek Laciak

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Institute of Control and Informatization of Production Processes, Faculty BERG, Technical University of Kosice, Letná 1/9, 040 01 Košice, Slovakia
Interests: modeling; monitoring; and control of technological processes; indirect measurement systems; underground coal gasification (UCG)
Special Issues, Collections and Topics in MDPI journals

Dr. Ján Kačur

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Guest Editor

Institute of Control and Informatization of Production Processes, Faculty BERG, Technical University of Kosice, Letná 1/9, 040 01 Košice, Slovakia
Interests: automation and control of technological processes; design and implementation of monitoring and control systems for underground coal gasification (UCG); optimal and adaptive control; indirect measurement systems; time series prediction; SCADA/HMI and Java applications; programming of supporting software applications for automation and control technological processes
Special Issues, Collections and Topics in MDPI journals

Dr. Milan Durdán

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Guest Editor

Institute of Control and Informatization of Production Processes, Faculty BERG, Technical University of Kosice, Letná 1/9, 040 01 Košice, Slovakia
Interests: modeling, monitoring, and control of technological processes; mathematical modeling of technological processes and their application in the design and creation of simulation model; underground coal gasification (UCG)
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue focuses on the energy conversion processes in the underground coal gasification (UCG) and also on the modeling and control of this process. 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). 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. Recently, various UCG models, e.g., models based on CFD, machine models for syngas composition, or temperature prediction, were 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 UCG is associated with many underground uncertainties and adverse environmental impacts. More detailed geological surveys can partially reduce these issues, but this does not guarantee their complete elimination. Anticipating the risk of, e.g., explosion or poisoning by synthesis gas is possible by measuring the composition of the gas or by models.

The results of various research and experiments in this field around the world are currently being analyzed and may be included in this Special Issue of Energies.

Dr. Marek Laciak
Dr. Ján Kačur
Dr. Milan Durdán
Guest Editors

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Keywords

UCG process
Energy conversion
Modeling
Controlling
Explosion
Environment

Published Papers (9 papers)

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Editorial

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6 pages, 880 KiB

Open AccessEditorial

Modeling and Control of Energy Conversion during Underground Coal Gasification Process

by Marek Laciak, Ján Kačur and Milan Durdán

Energies 2022, 15(7), 2494; https://doi.org/10.3390/en15072494 - 28 Mar 2022

Cited by 2 | Viewed by 1752

Abstract

The underground coal gasification (UCG) technology is an unconventional method of coal mining, and its approaches represent new scientific knowledge [...] Full article

(This article belongs to the Special Issue Modeling and Control of Energy Conversion during Underground Coal Gasification Process)

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Research

Jump to: Editorial

12 pages, 25286 KiB

Open AccessArticle

Characteristics of Water Contaminants from Underground Coal Gasification (UCG) Process—Effect of Coal Properties and Gasification Pressure

by Magdalena Pankiewicz-Sperka, Krzysztof Kapusta, Wioleta Basa and Katarzyna Stolecka

Energies 2021, 14(20), 6533; https://doi.org/10.3390/en14206533 - 12 Oct 2021

Cited by 10 | Viewed by 1560

Abstract

One of the most important issues during UCG process is wastewater production and treatment. Condensed gasification wastewater is contaminated by many hazardous compounds. The composition of the generated UCG-derived wastewater may vary depending on the type of gasified coal and conditions of the gasification process. The main purpose of this study was a qualitative and quantitative characterization of the UCG wastewater produced during four different UCG experiments. Experiments were conducted using semi-anthracite and bituminous coal samples at two distinct pressures, i.e., 20 and 40 bar. The conducted studies revealed significant relationships between the physicochemical composition of the wastewater and the coal properties as well as the gasification pressure. The strongest impact is noticeable in the case of organic pollutants, especially phenols, BTEX and PAH’s. The most abundant group of pollutants were phenols. Conducted studies showed significantly higher concentration levels for bituminous coal: 29.25–49.5 mg/L whereas for semi-anthracite effluents these concentrations were in much lower range 2.1–29.7 mg/L. The opposite situation occurs for BTEX, higher concentrations were in wastewater from semi-anthracite gasification: 5483.1–1496.7 µg/L, while in samples from bituminous coal gasification average BTEX concentrations were: 2514.3–1354.4 µg/L. A similar relationship occurs for the PAH’s concentrations. The higher values were in case of wastewater from semi-anthracite coal experiments and were in range 362–1658 µg/L while from bituminous coal gasification PAH’s values are in lower ranges 407–1090 µg/L. The studies conducted have shown that concentrations of phenols, BTEX and PAH’s decrease with increasing pressure. Pearson’s correlation analysis was performed to enhance the interpretation of the obtained experimental data and showed a very strong relationship between three parameters: phenols, volatile phenols and COD_cr. Full article

(This article belongs to the Special Issue Modeling and Control of Energy Conversion during Underground Coal Gasification Process)

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27 pages, 17342 KiB

Open AccessArticle

Determination of the Extent of the Rock Destruction Zones around a Gasification Channel on the Basis of Strength Tests of Sandstone and Claystone Samples Heated at High Temperatures up to 1200 °C and Exposed to Water

by Krzysztof Skrzypkowski, Krzysztof Zagórski and Anna Zagórska

Energies 2021, 14(20), 6464; https://doi.org/10.3390/en14206464 - 09 Oct 2021

Cited by 8 | Viewed by 1428

Abstract

This article presents the results of laboratory tests regarding the influence of high temperatures on changes in the strength and structural parameters of rocks that are present in the immediate vicinity of a gasification channel. Sandstone and claystone samples were heated at 300 °C, 600 °C, 900 °C and 1200 °C. Additionally, the heated samples were placed in water for 24 h. The results of the laboratory tests were used in the numerical simulation using RS2 software. The main goal of modeling was to determine the extent of the rock destruction zone around the gasification channel for dry and wet rock masses. In the numerical simulations, three widths of the gasification channel and three ranges of high-temperature impact were modeled. On the basis of the obtained results, it was found that the extent of rock destruction, both in the roof and in the floor, is greater by several percent for a wet rock mass. For the first time, this research presents the effect of water on heated rock samples in terms of the underground coal gasification process. The results of laboratory tests and numerical simulations clearly indicate a reduction in strength, deformation and structural parameters for the temperature of 1200 °C. Full article

(This article belongs to the Special Issue Modeling and Control of Energy Conversion during Underground Coal Gasification Process)

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11 pages, 5146 KiB

Open AccessArticle

Effect of Lignite Properties on Its Suitability for the Implementation of Underground Coal Gasification (UCG) in Selected Deposits

by Krzysztof Kapusta

Energies 2021, 14(18), 5816; https://doi.org/10.3390/en14185816 - 14 Sep 2021

Cited by 8 | Viewed by 1354

Abstract

Two experimental simulations of underground coal gasification (UCG) processes, using large bulk samples of lignites, were conducted in a surface laboratory setup. Two different lignite samples were used for the oxygen-blown experiments, i.e., “Velenje” meta-lignite (Slovenia) and “Oltenia” ortho-lignite (Romania). The average moisture content of the samples was 31.6wt.% and 45.6wt.% for the Velenje and Oltenia samples, respectively. The main aim of the study was to assess the suitability of the tested lignites for the underground coal gasification process. The gas composition and its production rates, as well as the temperatures in the artificial seams, were continuously monitored during the experiments. The average calorific value of gas produced during the Velenje lignite experiment (6.4 MJ/Nm³) was much higher compared to the result obtained for the experiment with Oltenia lignite (4.8 MJ/Nm³). The Velenje lignite test was also characterized by significantly higher energy efficiency, i.e., 44.6%, compared to the gasification of Oltenia lignite (33.4%). The gasification experiments carried out showed that the physicochemical properties of the lignite used considerably affect the in situ gasification process. Research also indicates that UCG can be considered as a viable option for the extraction of lignite deposits; however, lignites with a lower moisture content and higher energy density are preferred, due to their much higher process efficiency. Full article

(This article belongs to the Special Issue Modeling and Control of Energy Conversion during Underground Coal Gasification Process)

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28 pages, 12542 KiB

Open AccessFeature PaperArticle

Regression Models Utilization to the Underground Temperature Determination at Coal Energy Conversion

by Milan Durdán, Marta Benková, Marek Laciak, Ján Kačur and Patrik Flegner

Energies 2021, 14(17), 5444; https://doi.org/10.3390/en14175444 - 01 Sep 2021

Cited by 2 | Viewed by 1499

Abstract

The underground coal gasification represents a technology capable of obtaining synthetic coal gas from hard-reached coal deposits and coal beds with tectonic faults. This technology is also less expensive than conventional coal mining. The cavity is formed in the coal seam by converting coal to synthetic gas during the underground coal gasification process. The cavity growth rate and the gasification queue’s moving velocity are affected by controllable variables, i.e., the operation pressure, the gasification agent, and the laboratory coal seam geometry. These variables can be continuously measured by standard measuring devices and techniques as opposed to the underground temperature. This paper researches the possibility of the regression models utilization for temperature data prediction for this reason. Several regression models were proposed that were differed in their structures, i.e., the number and type of selected controllable variables as independent variables. The goal was to find such a regression model structure, where the underground temperature is predicted with the greatest possible accuracy. The regression model structures’ proposal was realized on data obtained from two laboratory measurements realized in the ex situ reactor. The obtained temperature data can be used for visualization of the cavity growth in the gasified coal seam. Full article

(This article belongs to the Special Issue Modeling and Control of Energy Conversion during Underground Coal Gasification Process)

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23 pages, 7823 KiB

Open AccessArticle

Gas Permeability Model for Porous Materials from Underground Coal Gasification Technology

by Grzegorz Wałowski

Energies 2021, 14(15), 4462; https://doi.org/10.3390/en14154462 - 23 Jul 2021

Cited by 4 | Viewed by 1497

Abstract

Underground coal gasification (UCG) technology converts deep coal resources into synthesis gas for use in the production of electricity, fuels and chemicals. This study provides an overview of the systematic methods of the in situ coal gasification process. Furthermore, the model of the porous structure of coal has been presented and the gas movement taking place in the carbon matrix—which is part of the bed—has been described. The experimental tests were carried out with the use of air forced through the nozzle in the form of a gas stream spreading in many directions in a porous bed under bubbling conditions. The gas flow resistance coefficient was determined as a function of the Reynolds number in relation to the diameter of the gas flow nozzle. The proprietary calculation model was compared to the models of many researchers, indicating a characteristic trend of a decrease in the gas flow resistance coefficient with an increase in Reynolds number. The novelty of the study is the determination of the permeability characteristics of char (carbonizate) in situ in relation to melted waste rock in situ, taking into account the tortuosity and gas permeability factors for an irregularly shaped solid. Full article

(This article belongs to the Special Issue Modeling and Control of Energy Conversion during Underground Coal Gasification Process)

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18 pages, 2035 KiB

Open AccessArticle

Experimental Studies of the Effect of Design and Technological Solutions on the Intensification of an Underground Coal Gasification Process

by Oleg Bazaluk, Vasyl Lozynskyi, Volodymyr Falshtynskyi, Pavlo Saik, Roman Dychkovskyi and Edgar Cabana

Energies 2021, 14(14), 4369; https://doi.org/10.3390/en14144369 - 20 Jul 2021

Cited by 17 | Viewed by 2292

Abstract

This paper represents the results of experimental studies of physical modeling of the underground coal gasification process in terms of implementation of design and technological solutions aimed at intensification of a gasification process of thin coal seams. A series of experimental studies were performed in terms of a stand unit with the provided criteria of similarity to field conditions as well as kinetics of thermochemical processes occurring within a gas generator. Hard coal (high volatile bituminous coal) was selected as the raw material to be gasified, as that coal grade prevails in Ukrainian energy balance since it is represented by rather great reserves. Five blow types were tested during the research (air, air–steam, oxygen–steam, oxygen–enriched, and carbon dioxide and oxygen). As a result, the effect of tightness of a gas generator on the quantitative and qualitative parameters of coal gasification while varying the blow by reagents and changing the pressure in a reaction channel has been identified. Special attention was paid to the design solutions involving blow supply immediately into the combustion face of a gas generator. The experimental results demonstrate maximum efficiency of the applied gas generator design involving flexible pipelines and activator in the reaction channel and a blow direction onto the reaction channel face combined with blow stream reversing which will make it possible to improve caloricity of the generator gas up to 18% (i.e., from 8.4 to 12.8 MJ/m³ depending upon a blow type). Consideration of the obtained results of physical modelling can be used with sufficient accuracy to establish modern enterprises based on the underground coal seam gasification; this will help develop more efficiently the substandard coal reserves to generate heat energy as well as power-producing and chemical raw material. The research conclusions can provide technical reference for developing a new generation of underground coal gasification technology. Full article

(This article belongs to the Special Issue Modeling and Control of Energy Conversion during Underground Coal Gasification Process)

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26 pages, 2910 KiB

Open AccessArticle

Model-Free Control of UCG Based on Continual Optimization of Operating Variables: An Experimental Study

by Ján Kačur, Marek Laciak, Milan Durdán and Patrik Flegner

Energies 2021, 14(14), 4323; https://doi.org/10.3390/en14144323 - 18 Jul 2021

Cited by 8 | Viewed by 1610

Abstract

The underground coal gasification (UCG) represents an effective coal mining technology, where coal is transformed into syngas underground. Extracted syngas is cleaned and processed for energy production. Various gasification agents can be injected into an underground georeactor, e.g., air, technical oxygen, or water steam, to ensure necessary temperature and produce syngas with the highest possible calorific value. This paper presents an experimental study where dynamic optimization of operating variables maximizes syngas calorific value during gasification. Several experiments performed on an ex situ reactor show that the optimization algorithm increased syngas calorific value. Three operation variables, i.e., airflow, oxygen flow, and syngas exhaust, were continually optimized by an algorithm of gradient method. By optimizing the manipulation variables, the calorific value of the syngas was increased by 5 MJ/m³, both in gasification with air and additional oxygen. Furthermore, a higher average calorific value of 4.8–5.1 MJ/m³ was achieved using supplementary oxygen. The paper describes the proposed ex situ reactor, the mathematical background of the optimization task, and results obtained during optimal control of coal gasification. Full article

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15 pages, 1293 KiB

Open AccessArticle

The Usage of UCG Technology as Alternative to Reach Low-Carbon Energy

by Stefan Zelenak, Erika Skvarekova, Andrea Senova and Gabriel Wittenberger

Energies 2021, 14(13), 3718; https://doi.org/10.3390/en14133718 - 22 Jun 2021

Cited by 11 | Viewed by 1735

Abstract

Countries of the European Union have stated transition to carbon-neutral economy until the year of 2050. Countries with a higher share of coal-fired power generation currently have no solution to end their combustion and use clean, emission-free energy immediately. The solution to this problem in the energy industry appears to be the increased use of natural gas, which significantly reduces CO₂ emissions. In this article, we investigated the possibility of using coal in situ, using UCG (underground coal gasification) technology. We focused on verified geological, hydrogeological, and tectonic information about the selected brown coal deposit in Slovakia. This information has been assessed in research projects in recent years at the Technical University. From the abovementioned information, possible adverse factors were evaluated. These factors affect the rock environment around the underground generator by UCG activity. As part of the process management, measures were proposed to eliminate the occurrence of pollution and adverse effects on the environment. In the final phase of the UCG technology, we proposed to carry out, in the boreholes and in the generator cavity, water flushing and subsequent grouting. The proposed are suitable materials for solidification and stabilization. Results of this article´s solutions are crucial in the case of usage of this so-called clean technology, not only in Slovakia but also worldwide. Full article

(This article belongs to the Special Issue Modeling and Control of Energy Conversion during Underground Coal Gasification Process)

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