Yingfeng Machinery－More Than 30 Years Experience In Clay Brick Making Machine ,Tunnel Kiln, Rotary Tunnel Kiln.

Can Low-Grade Coal Gangue Produce High-Quality Fired Bricks?

2026-06-26

Coal gangue is a solid waste generated during coal mining and processing, which has long been regarded as a useless industrial residue. High-quality coal gangue with high carbon content, kaolin, alumina or pyrite can be reused for power generation, cement production, ceramic processing and chemical raw material manufacturing. However, most residual coal gangue belongs to low-grade raw materials with low effective component content, traditionally only used for road paving and pit filling, resulting in massive stockpiling and environmental pollution.

With mature and innovative firing technology, low-grade coal gangue can be fully utilized to produce high-quality fired bricks that meet national industrial standards. Different from high-value coal gangue used for chemical and building material raw materials, low-grade coal gangue relies on scientific testing, optimized batching and precise sintering processes to realize resource regeneration without secondary waste discharge.

The premise of low-grade coal gangue brick production is comprehensive physical and chemical performance testing and thermal sintering experiments. Manufacturers need to detect key indicators including chemical composition, calorific value, plasticity index, particle gradation, drying and firing shrinkage, water absorption, lime bursting and efflorescence. Notably, the plasticity index test requires crushing all samples to below 1mm to ensure accurate data, avoiding detection errors caused by excessive particle size.

Since there is no national standard for coal gangue calorific value detection, the industry uniformly adopts the national standard GB/T 213-2003 for coal calorific value testing instead of empirical industrial methods, which guarantees reliable parameter basis for subsequent production process design. Through systematic testing, enterprises can confirm the applicable brick types (solid bricks, hollow bricks, porous blocks) and match exclusive production equipment and kiln processes, eliminating blind investment and production risks.

Low-grade coal gangue fired bricks adopt internal combustion firing technology as the core process. The raw material calorific value of 450×4.17kj/kg is the most ideal standard for full coal gangue internal combustion brick production, requiring no additional fuel or auxiliary materials. For raw materials with excessive or insufficient calorific value, targeted adjustment measures such as blending inert materials, adding a small amount of clean coal or low-temperature decarbonization can balance the combustion heat value, realizing stable and high-yield production of high-strength fired bricks above WU20 grade.

Why Airflow Is Critical in Tunnel Kiln Brick Firing？

How to Choose a Reliable Brick Machine Manufacturer in China?

Related questions

Why Do Tunnel Kilns Have Large-Area Overburning and Severe Brick Sticking?

In modern automated brick and tile production lines, tunnel kiln firing quality is the core index that determines finished brick qualification rate and overall production profit. Large-area overburning defects and severe green brick sticking are typical frequent faults in tunnel kiln mass production. These quality issues not only ruin brick and tile finished quality but also cause unnecessary material waste and unexpected production shutdown losses. This article comprehensively analyzes all potential root causes of tunnel kiln overburning and brick adhesion, and compares defect mechanisms with ring kilns, helping brick manufacturers carry out fast and accuratekiln fault troubleshooting and production optimization.

Excessive internal combustion heat of green bricks is the most fundamental material-induced cause of firing overburning and adhesion. In standard brick and tile manufacturing processes, green blanks are formulated with a certain proportion of internal fuel to support self-firing. Once the internal combustible content is too high, the extra heat released during high-temperature sintering will far exceed the standard process temperature required for brick forming. In the relatively closed high-temperature operating environment of tunnel kilns, redundant heat cannot be dissipated timely, resulting in over-fired brick surfaces and tight mutual adhesion between adjacent green bricks.

Imperfect ventilation system configuration is the key environmental factor triggering large-scale overburning faults. A qualified tunnel kiln air supply and exhaust system relies on precise alignment between brick stack ventilation channels and kiln wall exhaust ducts to form balanced hot air circulation and stable temperature fields. Any duct misalignment or blocked ventilation passages will sharply reduce the kiln’s overall heat dissipation capacity. Accumulated internal combustion heat erupts violently in the high-temperature firing zone, creating localized ultra-high temperature zones that lead to widespread brick overburning and severe sticking problems.

Unreasonable reserved gaps between brick stacks and the kiln main body is a easily neglected structural defect in daily kiln operation. The brick and tile industry has a clear standard: the gap between brick stacks, kiln walls and kiln roofs must not exceed 80mm. Excessively large gaps directly cause air short-circuiting in the kiln: more than 80% of circulating and cooling air flows rapidly through the peripheral gaps, while the inner area of brick stacks stays in a static air state. Insufficient preheating makes green bricks unable to adapt to the high-temperature sintering environment, and instant intense internal combustion after entering the high-temperature zone finally causes overburning and blank adhesion.

Non-standard brick stacking technology directly hinders internal heat exchange and air convection inside brick stacks. Excessively dense stacking layouts and insufficient reserved ventilation gaps between adjacent stacks completely block vertical and horizontal air flow. Heat generated by blank internal combustion is fully trapped inside the dense brick stack, forming local ultra-high temperature areas. Under such conditions, brick surfaces precipitate liquid phases in advance, which is the direct cause of persistent sticking and large-area overburning phenomena.

Irregular manual operation and unreasonable process adjustment are critical human factors leading to recurrent firing defects. To pursue higher daily output or simply stabilize flame position, many operators adopt improper gate control strategies, including overusing near gates, refusing to lift far gates properly, and allowing excessive fan suction to press down gate height. These wrong operations disrupt the standard firing temperature curve, shorten the reasonable heat preservation period of green bricks, and trigger premature liquid phase sintering, forming irreversible overburning and brick adhesion faults.

Mismatched kiln body structural parameters are the essential equipment-level cause of poor firing quality. If the tunnel kiln is manufactured with an overly short body, the effective length of the preheating zone and high-temperature roasting zone will be insufficient. Green bricks cannot complete gradual, gradient temperature rise preheating, and directly rush into the high-temperature firing zone. The sharp temperature difference leads to instantaneous intense combustion of internal fuel, causing overall temperature field imbalance and large-area firing overburning and sticking defects.

Compared with tunnel kilns, traditional ring kilns have more concentrated and single causes of overburning and sticking. The four core fault factors include excessive internal combustion heat of green blanks, insufficient preheating zone design length, unreasonable high near-gate operation habits, and inadequate overall kiln exhaust suction, which cover almost all common ring kiln firing adhesion problems.

How Drying Sensitivity Coefficient Governs Hot Air Temperature Setting of Fired Brick Green Bodies?

The fundamental reason for adopting differentiated hot air temperature in fired brick drying lies in the varying drying sensitivity of raw materials. The drying sensitivity coefficient is positively correlated with the plasticity index of brick raw materials. Raw materials with high plasticity index have strong drying sensitivity, slow internal water migration, and high risk of drying cracks, which require lower hot air temperature and longer drying time; low-sensitivity raw materials can adapt to high-temperature rapid drying.

This raw material characteristic directly guides the hierarchical setting of drying chamber hot air temperature. Low-sensitivity raw materials with a coefficient less than 1 have uniform water evaporation and extremely low cracking risk, so the hot air temperature can be raised to 120℃-125℃. This high-temperature drying mode only requires a drying cycle of 12-20 hours, achieving the highest production efficiency while ensuring drying quality.

For medium-sensitivity raw materials with a drying sensitivity coefficient of 1 to 2, temperature setting must be strictly classified by brick type. Solid bricks with dense internal structure have high water resistance, suitable for 100℃-120℃ hot air drying; hollow bricks with porous structure are prone to stress concentration, so the temperature needs to be reduced to 80℃-100℃ to ensure gradual and balanced dehydration. Correspondingly, the drying time of such raw materials is extended to 20-32 hours with the change of temperature parameters.

In industrial production, blind high-temperature drying for high-sensitivity raw materials (coefficient > 2) is prohibited. Such raw materials have severe unbalanced internal and external water loss, and can only adopt low-temperature slow drying with extended drying time up to 32-48 hours. Unreasonable temperature matching will directly lead to a surge in defective bricks and waste production energy consumption.

Scientific temperature differentiation also matches fixed energy consumption standards for brick drying. Evaporating 1kg of green brick water consumes 1300kcal of heat (equivalent to 0.186kg standard coal), and requires 33m³ of 30℃ hot air to take away water vapor. Reasonable temperature adjustment based on raw material sensitivity can avoid excessive heat waste caused by blind high temperature and incomplete dehydration caused by low temperature, realizing energy-saving and efficient drying.

In addition, the green brick forming moisture will affect the temperature adaptation effect. Properly reducing forming moisture (2 percentage points for lean raw materials, 4-6 percentage points for fat raw materials) can double green brick strength, reduce drying shrinkage, and make the raw materials more adaptable to differentiated hot air temperature drying, further reducing the risk of quality defects.

Is An Automatic Brick Stacking Machine Worth It? 3-Year ROI and Cost Analysis

For overseas brick plant owners, high labor costs, unstable manual brick stacking, and excessive brick damage rates are the top operational pain points that severely reduce factory profit margins. Most brick factory operators struggle to decide whether to purchase an automatic brick stacking machine, worried about high upfront equipment investment. In practical brick production operations, a fully automatic brick palletizing machine can perfectly replace 6 to 8 on-site manual stacking workers. For medium-sized and large-scale automated brick plants, the one-time investment of an automatic brick stacking machine can be fully recovered within 2 to 3 years. After crossing the ROI payback period, the equipment delivers stable 24-hour production, zero manual operation errors, and long-term operational cost savings, making it one of the most cost-effective profit-upgrading equipment for modern brick factories.

Manual Brick Stacking vs Automatic Brick Stacking Machine: Full Cost and Benefit Comparison

Frequently Asked Questions About Automatic Brick Stacking Machines

Q1: Are automatic brick setting machines suitable for small brick factories?

Yes. Small brick factories with a daily output of over 8,000 standard bricks are very suitable for installing automatic brick stacking machines. Although small-scale brick plants have lower production capacity than large factories, the long-term savings in labor costs and the reduction of brick damage losses can bring stable and reliable investment returns. It is a forward-looking upgrade choice for small brick factories that plan to expand production scale and improve automation level.

Q2: Is the daily maintenance of automatic brick setting machines complicated?

Automatic brick stacking machines adopt simplified and wear-resistant industrial structure design, with ultra-low failure rate and stable long-term operation performance. The daily maintenance work is simple, labor-saving and time-efficient, requiring no professional senior technical personnel. Factory staff can master all daily inspection, cleaning and maintenance skills through basic free training, with extremely low later operation and maintenance costs.

For all formal overseas brick plants with stable production demands and long-term operation plans, investing in an automatic brick stacking machine is absolutely worthwhile. This automated brick stacking equipment perfectly solves the core pain points of high manual labor costs, unstable brick quality and high product scrap rates, helping traditional brick factories realize standardized, intelligent and low-cost production. It is an essential upgrade equipment for modern brick plants to reduce operational costs and increase long-term profits.

How Optimized Kiln Ventilation and Heat Exchange Reduce Energy Consumption in Fired Brick Production？

High energy consumption is one of the biggest operational challenges for modern tunnel kiln brick plants and automatic clay brick production lines worldwide. For brick manufacturers aiming to cut operational costs and boost profit margins, optimizing tunnel kiln ventilation and internal heat exchange is the most practical, cost-efficient solution to lower fuel consumption while stabilizing brick firing quality. Mastering core kiln airflow and heat exchange principles is essential for low-carbon, energy-saving brick manufacturing operations.

The entire firing process in a tunnel kiln is a continuous circulating heat exchange process between unfired green brick blanks and high-temperature flue gas generated by fuel combustion. During mass production, fuel combustion releases massive thermal energy, which transfers to brick blanks to raise their internal temperature gradually. Once the temperature reaches the critical standard for chemical reactions of raw materials including clay, shale, coal gangue and fly ash, all internal components of brick blanks react completely, forming high-quality qualified solid bricks and hollow fired bricks.

Airflow circulation penetrates every key stage of brick firing, making it an indispensable element for normal kiln operation. Fuel combustion requires sufficient oxygen, which is delivered to the high-temperature firing zone by preheated airflow from the kiln cooling zone; the preheated hot air further accelerates full fuel combustion and improves combustion efficiency. High-temperature flue gas serves as the primary heat transfer medium, responsible for preheating wet brick blanks and sustaining constant firing temperature in the firing zone. After sintering, high-temperature finished bricks are cooled to room temperature by incoming cold airflow for smooth kiln discharge. In addition, the removal of residual moisture from wet green bricks and continuous preheating of dry blanks entirely rely on hot flue gas flowing from the firing zone to the preheating zone.

It is evident that stable, orderly gas flow is the basic guarantee for complete brick sintering. To fundamentally cut down the energy consumption of brick production with gas-fired tunnel kiln equipment, manufacturers must prioritize optimizing two core indicators: kiln ventilation efficiency and internal heat exchange performance. Scientific airflow management eliminates incomplete fuel combustion and invalid heat loss, enabling low-energy, high-yield, high-stability operation for all types of brick factories.

Professional kiln energy saving does not rely on blind fuel reduction, which easily causes unqualified brick products. Instead, it focuses on improving the overall heat transfer efficiency inside the kiln through optimized ventilation and heat exchange systems. This technology maximizes the thermal utilization rate of fuel combustion, avoids repeated heating and redundant fuel waste, effectively reduces comprehensive production costs, and helps brick manufacturing enterprises comply with global green and low-carbon building material production standards.

What Is the Correct Low-Temperature Preheating Wind Brake Adjustment for Tunnel Kiln Brick Firing?

Many brick factory owners, production technicians and procurement customers frequently ask this question: what is the standard adjustment method for low-temperature preheating wind brakes on tunnel kilns, and how does it affect brick firing quality and production output? In tunnel kiln automatic firing systems, the low-temperature preheating zone (from kiln entry to 560℃) is the most critical stage to prevent green brick cracking and stabilize subsequent high-temperature firing. The opening size, quantity combination and brake shape of low-temperature preheating wind brakes directly control the total circulating air volume, flue gas flow speed and temperature distribution in the front kiln section. Correct wind brake adjustment is the simplest and most effective way to stabilize firing speed, eliminate preheating defects and improve finished brick yield in daily tunnel kiln operation.

Low-temperature preheating wind brakes refer to the group of wind brakes installed at parking spaces 1 to 10 of the tunnel kiln, covering the temperature range from ambient inlet temperature to 560℃. The total opening degree of all wind brakes determines the overall preheating air volume of the tunnel kiln, while the different opening combinations of individual wind brakes can precisely adjust the temperature of each front-section parking space. Reasonable adjustment ensures uniform preheating of green bricks, avoiding common quality problems such as uneven heating, local overheating, or insufficient preheating that easily cause brick cracking and deformation after firing.

Low-temperature preheating wind brake opening has strict industrial standardized calculation rules to avoid unnecessary air pressure loss and ensure maximum heat exchange efficiency.

The maximum lifting height of a single wind brake is limited to the radius of the wind brake body. The number of fully opened wind brakes is calculated by squaring the multiple of the total flue duct diameter and the single wind brake diameter. For example, when the total flue duct diameter is 1.2m and the single wind brake diameter is 0.4m, the diameter multiple is 3, and the standard number of full-open wind brakes is 9. If adopting an average half-open state, 18 wind brakes (9 pairs) are required for matching, which completely eliminates air pressure loss on the wind brake structure.

When using variable frequency fans for automatic tunnel kiln control, operators must fully open the ventilation area of all low-temperature preheating wind brakes.

Partially closed wind brakes will cause severe air pressure loss and wind energy waste, making the fan frequency conversion adjustment ineffective and unable to accurately control the drying air volume and kiln temperature. Only fully opened wind brakes can ensure that the fan operating power is completely applied to internal flue gas circulation and heat exchange, realizing precise and sensitive automatic temperature control.

It is crucial to match exclusive wind brake shapes and opening standards according to different brick types and green brick states in automatic firing production. Hollow bricks, porous bricks, and standard solid bricks have different thermal expansion rates and heat resistance, so they cannot adopt the same wind brake scheme. In addition, wet green bricks and dry green bricks require completely different preheating parameters, which means their wind brake opening degrees and shapes must be adjusted separately. In actual production, if the fan speed has been reduced to the lower limit that meets drying room air demand but the firing speed is still too fast, adjusting the wind brake shape and opening is the most effective solution to balance drying air pressure, air volume and kiln firing speed.

The working principle of low-temperature preheating wind brakes is to control the flow rate and residence time of high-temperature flue gas inside the preheating zone. A larger wind brake opening allows more high-temperature flue gas to pass through and extends the heat exchange time between hot flue gas and green bricks, effectively raising the local kiln temperature. Conversely, a smaller opening reduces flue gas flow and lowers preheating temperature. Scientific and graded wind brake opening configuration forms a stable gradient temperature curve in the preheating zone, eliminates green brick cracking caused by uneven temperature difference, and significantly improves tunnel kiln production stability and finished brick qualification rate.

What Are the Correct Drying Room Parameters for Clay, Fly Ash, Shale and Coal Gangue Bricks?

Improper drying room parameters are the leading cause of brick rewetting, surface cracking, low green brick strength and high kiln loss in professional brick and tile manufacturing. For B2B brick factories and global building material suppliers, matching accurate drying room parameters to different raw materials and brick styles is the core key to stable brick product quality and high production yield. Unlike ordinary industrial drying processes, professional brick drying requires strictly customized temperature, humidity, airflow and exhaust standards based on raw material drying characteristics to meet standardized brick production requirements.

The hot air temperature inside the brick drying room must be scientifically adjusted according to the unique drying tolerance of different brick raw materials. For conventional clay hollow bricks and sintered fly ash bricks, the optimal drying room hot air temperature is controlled between 60℃ and 80℃, which prevents rapid dehydration and avoids common surface cracks on green bricks. For shale and coal gangue raw materials with a drying sensitivity coefficient of 1 to 2, differentiated drying parameter settings are essential: solid bricks made of these materials adopt a drying temperature of 100℃ to 120℃, while hollow bricks of the same raw materials apply a milder temperature range of 80℃ to 100℃. For low-sensitivity shale bricks and coal gangue bricks with a drying sensitivity coefficient below 1, the drying room temperature can be increased to 120℃ to 125℃, realizing efficient and thorough brick dehydration without causing any quality risks.

Stable exhaust and airflow parameters ensure uniform drying effects for all green bricks in the drying room. The standard exhaust gas temperature of a qualified brick drying room is maintained at 35℃ to 45℃, with a relative humidity stably kept at 90% to 95%. The internal air flow speed of the drying room is steadily controlled at 1.5m/s to 4.5m/s, ensuring even heat and moisture exchange for every batch of bricks. In addition, mud material preheating during hot water or steam mixing needs to be kept at 45℃ to 60℃. This step optimizes raw material plasticity and lays a solid foundation for subsequent stable brick drying operations.

A critical operational rule that all professional brick production lines must strictly follow: the temperature of green bricks entering the artificial drying room must be higher than the humidity temperature of the gas discharged from the kiln inlet. This core technical standard completely prevents green brick reabsorbing moisture, effectively solving common brick quality problems such as peeling, blistering and uneven hardness. Our integrated brick and tile production equipment supports full intelligent drying parameter adjustment, realizing one-click switching of drying room schemes for different raw materials and brick specifications, and providing consistent high-quality brick products for global B2B bulk procurement orders.

GET IN TOUCH WITH Us

input must not exceed 280 in length!

name

Please enter a valid email address!

input must not exceed 280 in length!

phone/whatsApp

textarea must not exceed 65530 in length!

content

Ready to work with us ?

kai@zzyfmc.com

We are dedicated to the overall solution of large-scale production line of new energy-saving and environmentally friendly wall materials and the integration of high-end building resources.

Company

Products

Name: Mr. Kai

Skype: fanchen588

WhatsApp: +86 18638712391

WeChat: +86 18638712391

Address: Block 5, South Longhai Road and East Tongbai Road, Zhongyuan District, Zhengzhou City, Henan Province, China

Can Low-Grade Coal Gangue Produce High-Quality Fired Bricks?

Manual Brick Stacking vs Automatic Brick Stacking Machine: Full Cost and Benefit Comparison

1. Labor Cost Gap

2. Product Quality & Defect Rate Optimization

3. Exact 3-Year ROI Calculation for Brick Plants

Frequently Asked Questions About Automatic Brick Stacking Machines

Q1: Are automatic brick setting machines suitable for small brick factories?

Q2: Is the daily maintenance of automatic brick setting machines complicated?