Briquette and coal powder briquetting are important technologies in coal processing and utilization. By molding raw materials such as coal powder, their combustion performance, transportation convenience, and environmental benefits are improved. The following provides a detailed introduction from the perspectives of concept, process, and application:
I. Briquette
Briquette refers to a coal product with a certain shape and strength, made by mixing coal powder (or other carbonaceous raw materials, such as coke powder, coal gangue, etc.) with a binder and then pressing it into shape.
1. Main Features
Improved combustion performance: The dense structure after molding allows for more complete combustion, reducing black smoke and unburned emissions.
Increased utilization efficiency: Converts originally difficult-to-use "low-quality" raw materials such as coal powder and slime into usable fuel.
Ease of transportation and storage: Fixed shape reduces dust and loss, making it suitable for long-distance transportation.
Environmental advantages: Desulfurizing agents (such as limestone) can be added to reduce sulfur dioxide emissions during combustion.
2. Common Types
By use: Civil briquettes (e.g., honeycomb briquettes), industrial briquettes (used in boilers, kilns, gasification, etc.).
By shape: Cylindrical, elliptical, square, honeycomb-shaped, etc. (Honeycomb briquettes are common for civil use due to their good ventilation).
3. Production Process
Raw material preparation: Crushing and screening coal powder (controlling particle size, usually less than 3mm) to remove impurities.
Mixing ingredients: Coal powder is mixed with binders (such as clay, asphalt, cement, biomass slurry, etc.) in proportion. Some processes require adding water to adjust humidity.
Molding: Pressurizing the raw materials (usually at 10-50 MPa) using briquetting machines or molding equipment to form dense shapes.
Drying/curing: Drying wet briquettes (naturally or using drying furnaces) or allowing the binder to undergo chemical reactions for curing (e.g., cement-based briquettes).
II. Coal Powder Briquetting
Coal powder briquetting is the core step in briquette production, referring to the process of extruding coal powder (which may contain binders or additives) into spherical or block shapes using briquetting equipment. It is a key step in briquette molding.
1. Briquetting Principle
Mechanical force (pressure) is used to bring coal powder particles into close contact, generating van der Waals forces, friction, etc., while leveraging the adhesive effect of binders to form pellets with a certain strength. Higher pressure generally results in greater pellet density and strength, but excessive crushing of raw materials must be avoided.
2. Key Equipment: Briquetting Machine
Structure: Mainly consists of roller skins (with mold cavities), transmission systems, and pressure devices.
Types:
Double-roller briquetting machine (most common): Two rollers rotate oppositely, squeezing coal powder into mold cavities to form shapes.
High-pressure briquetting machine: Suitable for low-adhesion raw materials, requiring higher pressure (up to 100 MPa or more).
Mold cavity design: Affects the shape and size of pellets. Common diameters range from 20-60 mm, and the depth and curvature of the cavities must match the characteristics of the raw materials.
3. Factors Affecting Briquetting Results
Type and amount of binder: Different binders (organic/inorganic) affect strength and combustibility. For example, asphalt-bound briquettes have high strength but high cost, while clay-bound briquettes have low cost but increased ash content.
Molding pressure: Must be adjusted according to the raw materials. Insufficient pressure may cause pellets to break easily, while excessive pressure may lead to equipment wear or pellet cracking.