Characterizing moisture occurrence state in coal gasification fine slag filter cake using low field nuclear magnetic resonance technology

ABSTRACT

Gasification fine slag, a carbon-rich solid waste produced during coal gasification, is currently disposed of through conventional landfilling methods. Its high-water content hampers resource utilization by reducing its calorific value. This study employs low field nuclear magnetic resonance (LF-NMR) analysis to investigate the water occurrence states in a filter cake with 70.7% moisture content derived from fine gasification slag of the Ningxia coal water slurry furnace. The analysis reveals that free water constitutes a major proportion (68.28%), while combined and capillary water accounts for 2.62% and 2.33%, respectively. The removal of moisture from the coal gasification fine slag filter cake is significantly affected by the drying temperature. The drying rate initially increases and then decreases with different temperatures. For drying temperatures of 60, 70, 80, 90, and 100°C, the maximum drying rates are achieved at 1.09, 1.23, 2.18, 3.86, and 4.01%/min, respectively, with corresponding durations of 40, 40, 25, 30, and 35 min. The T₂₂ relaxation peak area continually decreases and shifts leftward on the coordinate axis. The behavior of the T₂₃ and T₂₂ peaks follows a similar pattern, indicating that water with higher mobility is easily eliminated during drying, while the T₂₁ peak exhibits a robust signal strength throughout the drying process. At a drying temperature of 100°C, the proportion of free water (A₂₂) decreases from 87.3% to 0, the A₂₃ fluctuates between 0 and 5.3%, and the bound water peak area (A₂₁) increases from 10.4% to 94.7% as drying time prolongs. A relationship model is developed between the moisture content of the coal gasification fine slag filter cake and the total integral area of the LF-NMR test, enabling rapid detection and analysis of the total moisture content and distinct occurrence states in the filter cake.

KEYWORDS:

• coal gasification fine slag
• drying
• low field nuclear magnetic resonance
• water occurrence states
• relaxation time

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The work was supported by the Natural Science Basic Research Program of Shaanxi Province [2021JLM-15].

Notes on contributors

Wei Yu

Wei Yu is a lecturer at Xi'an University of Science and Technology,and is studying for a doctor's degree in Xi'an Jiaotong University. His main research interests is the reduction, harmless and resource utilization of solid waste. He has been the first and co-author of more than 5 papers published in prestigious publications.

Xuebin Wang

Professor Xuebin Wang is an expert in efficient combustion and pollutant control, solid waste resource utilization technology, carbon reduction and sequestration technology, and other related fields. He graduated from the Department of Thermal Engineering of Xi’an Jiaotong University in 2012 with a doctorate degree in engineering, and has conducted research at the University of California, Berkeley and Washington University in St. Louis. He has led more than 10 national and provincial-level projects on topics such as high alkali coal fouling prevention, biomass combustion emissions, biomass and coal co-utilization, and low NOx control. He has also published 41 SCI papers as the first author or correspondent author.

Lijun Liu

Lijun Liu is an associate professor of Xi'an University of Science and Technology. Her main research interests are coal slime separation, flocculation, sedimentation and dehydration. She has been the first and co-author of more than 5 papers published in prestigious publications.

Houzhang Tan

Professor Houzhang Tan is an expert in basic research and engineering application of clean coal utilization, efficient utilization of biomass, new technologies for energy saving and water saving, design and energy-saving retrofit of burners/mills/fans in thermal power plants, combustion reaction Kinetics and solid waste treatment and resource utilization.

Zia Ur Rahman

Zia ur Rahman is a postdoctoral researcher at Hainan University. His research interests are in the thermochemical conversion of solid fuels (coal, biomass, and solid wastes) into energy resources. He has a comprehensive understanding of experimental and CFD simulation-based research in his field. He has been the first and co-author of more than 15 papers published in prestigious publications.