Complete Guide to Coal Gangue Fired Brick Production Process and Key Equipment Selection

Coal gangue fired brick is a sustainable wall building material made from coal gangue as the main raw material. The design of its fired brick production line depends heavily on raw material properties and total project investment. If the project budget is sufficient, plant owners tend to adopt highly mechanized and automated production workflows. For projects with limited capital, manufacturers can select semi-automatic processes that still guarantee stable finished brick quality.

Overview of the Full Production Flow

Raw coal gangue first goes through primary crushing by a coarse hammer crusher. A belt conveyor transports crushed material to a plate feeder. After multiple crushing, screening and conveying steps, materials enter a double-shaft mixer for thorough homogenization. Then the mixture is delivered via a reversible belt conveyor to the aging silo for raw material aging treatment.

After aging, materials are extracted by a multi-bucket excavator and fed into a box feeder. The material then passes through the double-shaft mixing extruder and enters the two-stage vacuum brick extruder for forming. The produced green brick body will go through strip cutting, brick cutting and automatic brick stacking machine. The bricks are loaded onto kiln cars and sent into the brick dryer system (tunnel drying kiln) and tunnel kiln for bricks for drying and firing. Once firing is finished, finished bricks are unloaded automatically, inspected and packaged for delivery.

Raw Material Crushing Process

Crushing is the foundation of stable brick production. Different brick types require different particle sizes:

1.  1. Solid bricks and low-porosity perforated bricks (porosity <30%): particle size below 2.5 mm, two-stage crushing (jaw crusher + hammer crusher).
2.  2. High-porosity hollow bricks: particle size below 1.5 mm, two-stage or three-stage crushing. A fine roller mill with grinding function can be added to reach finer particle requirements. Poor-plasticity raw materials need aging after crushing to improve workability.

Coarse hammer crusher integrates primary and medium crushing, specially designed for coal gangue and shale. Large blocks hit the beam first and are impacted by high-speed hammers; smaller blocks directly enter the medium crushing chamber. The built-in bottom sieve ensures qualified particles discharge timely. It can handle blocks up to 500 mm, with a crushing ratio of 4–6, widely used in brick plant primary crushing.

Hammer crusher relies on rotating hinged hammers for impact crushing. It has vertical, horizontal, single-rotor and double-rotor types with adjustable outlet screens to control fineness. It works best for brittle raw materials like coal gangue and shale. The raw material moisture should stay under 8% to avoid screen blockage.

Raw Material Aging Technology

Aging treatment stores finely ground, properly moistened raw materials inside closed aging silos. This allows full wetting and dispersion of particles, improving plasticity, drying and firing performance of the mixture. Industrial data shows that 4-day aging reduces drying rejects by 12%, firing rejects by 6%, and raises the plasticity index by 1.2.

Common aging silo types:

•  1. Loader reclaim aging silo: cone stacking, suitable for materials with minor composition fluctuation.
•  2. Manual reclaim aging silo: smaller footprint, better sealing and aging effect, widely adopted by small & medium brick factories.
•  3. Multi-bucket excavator aging silo: semi-underground design, one worker can operate the multi-bucket excavator for uniform reclaiming, ideal for modern automatic automatic brick plant.

Forming Process of Coal Gangue Fired Bricks

Forming is a core procedure. Aged raw materials are extruded by two-stage vacuum brick extruder to form mud strips with stable strength and precise dimension. Mud strips are cut into standard green brick body by strip cutter and brick cutter.

Key control parameters: extrusion pressure ≥1.5 MPa, vacuum degree >80%. For high-grade load-bearing fired bricks, parameters need to reach ≥2.2 MPa and ≥88%. Low-plasticity raw materials demand higher extrusion pressure and vacuum level. Common forming defects include insufficient green body strength, low density and unstable cutting size, caused by excessive moisture, insufficient extrusion pressure, poor grading or misaligned cutting tools.

Drying Process

The brick dryer system directly controls cracking risk. Operators must manage temperature, humidity and airflow speed of drying medium. Recommended parameters at drying kiln inlet: 120℃–150℃; exhaust gas temperature:35℃–45℃; exhaust relative humidity:90%–95%; airflow velocity:1.5–4.5 m/s.

Temperature and humidity curves must change gradually without sharp jumps to prevent brick cracking. Stable zero-pressure point control is essential. Drying cycle is determined by raw material drying sensitivity coefficient K:

•  1. K＜1: 12–20 h
•  2. K=1~1.5:20–26 h
•  3. K=1.5~2:26–32 h
•  4. K＞2:32–48 h

Firing Technology in Tunnel Kiln

Three main kiln types for coal gangue hollow bricks: annular kiln, improved three-centered arch annular kiln, large-section flat-top tunnel kiln for bricks. Large-section flat-top tunnel kilns are the mainstream choice for modern coal gangue brick production due to high output, stable brick quality and low fuel consumption.

The complete firing curve includes preheating, high-temperature soaking and cooling stages. Preheating zone heats bricks slowly to remove residual water. The maximum firing temperature for coal gangue fired brick is generally 1050℃. The low-temperature long-soaking method delivers more uniform sintering. During cooling, special attention must be paid at 573℃ and 230℃ to avoid thermal cracking from quartz phase transformation.

FAQ

Q1: What is coal gangue fired brick?

A: It is a type of fired brick produced using coal gangue as raw material through crushing, aging, extrusion forming, drying and high-temperature firing. It is eco-friendly and widely used as wall material.

Q2: What core machines are needed for a coal gangue brick production line?

A: Main equipment includes crushers, double-shaft mixer, aging silo, two-stage vacuum brick extruder, brick stacking machine, brick dryer system and tunnel kiln for bricks.

Q3: What particle size is required for coal gangue raw materials for hollow bricks?

A: For high-porosity hollow bricks, raw material particles should be controlled below 1.5 mm.

Q4: Why is raw material aging important in brick manufacturing?

A: Aging improves raw material plasticity, reduces drying and firing waste rate, stabilizes green brick body quality.

Q5: What are the advantages of large-section flat-top tunnel kilns for brick firing?

A: High production capacity, uniform temperature field, low fuel consumption, better working environment and stable finished brick quality.