What Is Ash Content?

Ash content refers to the inorganic residue left behind after coal has been fully combusted. This residue consists of minerals such as clay, oxides, and salts that do not burn and form two primary types of byproducts: fly ash (fine particles, <90μm, carried by flue gases) and bottom ash (coarser, molten or solid remnants expelled from the furnace bottom). Chemically, ash comprises metal and non-metal oxides like SiO₂, Al₂O₃, Fe₂O₃, and CaO, all of which originate from the coal's natural mineral matter.

From a coal quality perspective, ash content serves as a key indicator. High-quality coal or washed coal typically contains less ash (5–10% for washed anthracite), while raw or poorly processed coal can have ash levels exceeding 15%, which significantly impacts operational efficiency.

Why Ash Content Matters: Its Impacts on Industrial Processes

Reduced Combustion Efficiency:
Ash doesn’t contribute to heat generation; instead, it absorbs and dissipates heat. When ash content increases, the gross calorific value (GCV) in coal decreases, and the furnace temperature decreases, leading to higher fuel consumption and increased operational costs.

Equipment Damage and Downtime:
At high temperatures, ash can fuse and form slag, which clogs furnaces, boilers, and gasifiers. This slagging disrupts heat distribution, accelerates metal corrosion, and necessitates frequent maintenance or shutdowns for cleaning.

Quality Contamination:
In metallurgical processes, such as steelmaking, ash content too high can introduce impurities into molten steel, compromising product quality and raising waste rates.

Root Causes of High Ash Content

Low-Quality Raw Materials: Coal with inherently high ash content, such as lignite or sub-bituminous coal (especially if unprocessed), can severely impact briquette quality.

Inadequate Preprocessing:
Insufficient washing or screening processes fail to remove mineral impurities. For instance, improper crushing or washing may leave clay and silt particles mixed with coal powder.

Binder-Related Issues:
Some binders, particularly low-quality ones, can introduce additional inorganic elements or fail to adequately bind coal particles, resulting in poor impurity separation during the briquetting process.

Suboptimal Briquetting Parameters:
Inconsistent mixing of coal and binder, or insufficient compression pressure, can result in uneven distribution of ash-forming minerals, concentrating them in the final briquette.

Solutions to Reduce Ash Content

Source High-Quality Coal:
Prioritize low-ash coal varieties such as anthracite or washed bituminous coal. Rigorous quality checks on raw materials can ensure ash content aligns with process requirements.

Enhance Preprocessing Technology:
Invest in advanced washing and screening equipment to eliminate mineral impurities.

Optimize Binder Selection:
Choose binders that enhance particle cohesion without adding inorganic contaminants. Jianjie Binder for coal’s specialized formulations don’t contain inorganic substances and can improve coal-binder adhesion, facilitating better impurity exclusion during the briquetting process.

Fine-Tune Briquetting Processes:
Ensure uniform mixing of coal and binder (e.g., using mechanical stirrers) and apply consistent, high pressure (80–150 MPa) to tightly compact particles, minimizing voids where ash-forming minerals might accumulate.

Volatile Matter in Coal Briquettes: Definition and Significance

What Is Volatile Matter?

When coal is heated in air-free conditions at approximately 900°C, combustible gases (e.g., methane, CO, hydrogen, and tar-forming hydrocarbons) are released and they are called volatile matter. These gases are critical for ignition and flame propagation but pose challenges if not carefully controlled. Coals with lower metamorphism (such as lignite and sub-bituminous coal typically have higher volatile matter content (>35%), while anthracite coal has very low levels (<10%).

How Volatile Matter Affects Coal Briquette Performance

Combustion Behavior:

High Volatile Matter: Coal briquettes with high volatile matter ignite quickly and produce long flames, but they may burn unevenly, leading to incomplete combustion (evident as “black smoke” from unburned carbon) and reduced thermal efficiency.

Low Volatile Matter: Coal briquettes with low volatile matter burn more slowly but steadily (ideal for applications like blast furnace injection), reducing pollutant formation but requiring precise ignition control. The heat value can last longer.

Environmental Compliance:
Volatile matter contains volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs), which, if not efficiently burned, can exceed emission limits, leading to fines or operational restrictions.

Process Compatibility:
Different industries have specific volatile matter requirements. For instance, blast furnaces demand low-volatile briquettes (<15%) to avoid explosive gas buildup, while applications such as domestic heating may prefer higher volatility for quicker ignition

Strategies to Control Volatile Matter

Select Appropriate Coal Grades:
Use lower-volatile coal types, such as anthracite or semi-anthracite, for applications requiring stable combustion and minimal emissions.

Use Specialized Binders:
Jianjie Binder offers formulations designed for coal. These binders maintain structural integrity without contributing excess volatile compounds during thermal processing.

Summary

High ash content and volatile matter in coal briquettes are not merely technical challenges—they directly affect operational costs, product quality, and environmental compliance. Investing in effective solutions for controlling ash and volatile matter is an investment in the long-term reliability and profitability of your briquetting operations. Explore Jianjie Binder’s innovative products today to enhance your coal processing efficiency. Jianjie provides not only the binder for coal but also technical solutions for the clients.

If you need to increase your coal briquettes’ quality, lower the ash content and volatile matter, contact us now for professional solutions!

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