Related Experiment Video
Updated: Sep 7, 2025
10:27
A Uniaxial Compression Experiment with CO2-Bearing Coal Using a Visualized and Constant-Volume Gas-Solid Coupling Test System
Published on: June 12, 2019
8.8K
Crystalline-SiO2-Component-Induced Cracking in Coal Ash Deposits Exposed to Temperature Changes
Yohei Matsui1, Nobuyuki Wakabayashi2
1Energy Chemistry Division, Energy Transformation Research Laboratory, Central Research Institute of Electric Power Industry, Yokosuka 240-0196, Japan.
ACS Omega
|June 20, 2022
Summary
Thermal power plant operations cause temperature fluctuations, leading to cracks in coal ash deposits. Crystalline silicon dioxide (SiO2) components, like quartz, significantly promote crack generation and ash shedding.
Area of Science:
- Materials Science
- Chemical Engineering
- Thermodynamics
Background:
- Thermal power plants face operational challenges due to integrating renewable energy sources, necessitating frequent load changes and shutdowns.
- These operational adjustments induce thermal cycling in boiler furnaces, potentially causing cracks in coal ash deposits.
- Cracked ash deposits can spontaneously shed from heat-transfer surfaces, impacting plant efficiency and maintenance.
Purpose of the Study:
- To microscopically investigate the origin of cracks induced by temperature changes in coal ash deposits.
- To elucidate the role of crystalline silicon dioxide (SiO2) components in crack formation.
- To explore methods for promoting the shedding of ash deposits through controlled cracking.
Main Methods:
- Microscopic analysis of coal ash clinker from a utility boiler.
- Temperature cycle tests performed on coal ash clinkers in an electric furnace.
- Controlled addition of quartz additives to ash clinkers during testing.
Main Results:
- Cracks in coal ash clinkers were predominantly observed near crystalline SiO2 phases, such as quartz and cristobalite.
- Temperature cycling across the transition temperatures of crystalline SiO2 components significantly promoted crack generation.
- The addition of quartz additives demonstrably enhanced crack formation in coal ash clinkers.
Conclusions:
- Crystalline SiO2 components are critical nucleation sites for temperature-change-induced cracks in coal ash deposits.
- Understanding the role of SiO2 in cracking can inform strategies for managing ash deposit shedding.
- Further research into crack propagation and shedding mechanisms is needed for practical applications in thermal power plants.
More Related Videos
Related Concept Videos
01:20Microcracking in Concrete
204
Microcracking in concrete refers to the tiny cracks that can form within the material even before any external load is applied. These microcracks typically occur at the interface between the coarse aggregate and the hydrated cement paste, often as a result of differential volume changes prompted by variations in stress-strain behavior, as well as thermal and moisture movement. Initially, these microcracks remain stable and do not grow substantially until the concrete is stressed to about 30...
204
01:26Alkali Aggregate Reaction in Concrete
183
The alkali-aggregate reaction in concrete involves natural siliceous minerals in aggregates reacting with alkaline hydroxides derived from cement alkalis. This reaction forms an alkali-silica gel that absorbs water, swells, and increases in volume, which is confined by the surrounding cement paste, creating internal pressures that crack and disrupt the concrete. The extent of expansion and damage can be partly attributed to the alkali-silica reaction's osmotic hydraulic pressure and the...
183
01:26Unsoundness of Aggregate due to Volume Change
174
Unsoundness in aggregates due to volume changes is primarily caused by the physical alterations aggregates undergo, such as freezing and thawing, thermal changes, and wetting and drying. Unsound aggregates, when subjected to these changes, result in volume change upon disintegration. This, in turn, contributes to the deterioration of concrete, including scaling, pop-outs, and cracking. Particular types of aggregates, such as porous flints, cherts, and those containing clay minerals, are...
174
01:28Types of Non-structural Cracks in Concrete
243
Non-structural cracks are primarily of three types: plastic, early-age thermal, and drying shrinkage cracks. Plastic cracks are further classified into plastic shrinkage cracks and plastic settlement cracks.
Plastic shrinkage cracks typically form within hours after the concrete is poured. The concrete's surface dries faster than the bottom, creating tensile stress that the still-plastic concrete cannot withstand, leading to diagonal or randomly patterned cracks on the concrete surface.
Plastic shrinkage cracks typically form within hours after the concrete is poured. The concrete's surface dries faster than the bottom, creating tensile stress that the still-plastic concrete cannot withstand, leading to diagonal or randomly patterned cracks on the concrete surface.
243
01:27Frost Action on Concrete
148
Concrete structures in cold climates, such as those along roadsides, can retain moisture. This moisture makes them susceptible to frost-related damage when temperatures fall below freezing. Adding moisture worsens the damage during temperature fluctuations, leading to repeated freezing and thawing. De-icing salts, spread over these structures to melt ice, add to the freeze-thaw cycle, and draw even more moisture into the concrete.
This freeze-thaw cycle primarily causes surface scaling, where...
This freeze-thaw cycle primarily causes surface scaling, where...
148
01:25Deleterious Substances in Aggregate
245
Deleterious substances in aggregates can be detrimental to the quality and durability of concrete. These substances include organic impurities like loam, which interfere with cement hydration and are usually present in the sand. These prevent a good bond between aggregate and cement paste. Organic impurities can be detected using the colorimetric test, where the darkness of a solution after agitation indicates the level of organic content.
Another type of impurity is clay and fine material that...
Another type of impurity is clay and fine material that...
245