Burning bricks requires coal or other fuels. How to maximize the thermal efficiency is the technical key of brick kiln design. The sintering temperature of brick is between 850 ° C and 1050 ° C. In order to save coal, the heat insulation effect of the kiln must be improved. The rotary tunnel kiln is stacked with refractory fiber cotton, which not only reduces the weight of the kiln body, reduces the thermal expansion and contraction stress of the kiln body, but also improves the thermal insulation performance of the kiln body. The kiln temperature is maintained for a long time, and the bricks consumed at one time increase in large area. The internal combustion heat energy can more effectively improve the kiln temperature and save fuel.

In ordinary tunnel kilns, in order to prevent high-temperature flue gas from flowing into the kiln car and burning out the wheels and bearings, it is also necessary to set up a gas source under the kiln car. In the whole heating system, the air supply pressure at the bottom and surface of the vehicle must be kept balanced, and the high temperature flue gas and cold air at the bottom of the vehicle must not rise to reduce the kiln temperature.

 The bricks of the rotary tunnel kiln are directly stacked on the ground, without air supply under the vehicle, and the ground temperature is directly fully utilized. It is found that the aluminum silicate fiber blanket can still be calcined normally after 48 hours of coal and air shutdown in actual production, which is impossible for ordinary tunnel kilns. In the annular rotary tunnel kiln, when the firing temperature of bricks is reduced to room temperature, the heat released is enough to dry wet bricks of the same volume, so there is no need to build a hot air furnace, nor need to use the superheat roasting process to consume more coal to dry the heat.

In the heating system of the annular rotary tunnel kiln, dry air enters from the kiln tail and cools the sintered bricks through the cooling section to reduce the temperature of the sintered bricks at the outlet of the kiln tail to room temperature, that is, all the heat emitted by the sintered bricks is carried to the roasting section and drying section through the air entering the kiln for combustion support and drying. The energy saving of circular rotary tunnel kiln is its remarkable feature. Its reasonable process design, layout and simple logistics route also greatly reduce the energy consumption of the whole brick factory.

The circular rotary tunnel kiln fully adopts mechanized operation and automatic digital control system. The temperature in the kiln is directly displayed on the display screen of the control system. There is no need to hire high-paying fire-watching teachers, which fundamentally eliminates brick-making and greatly increases production.

Compared with the traditional tunnel kiln, the new energy-saving and environment-friendly mobile rotary tunnel kiln has great advantages. It can be predicted that the production mode of the new energy-saving and environment-friendly mobile rotary tunnel kiln will be widely used in the field of sintered bricks by comparing the Helu aluminum silicate fiber blanket.

1, Malformed adobe, appears large cracks. In more serious cases, the whole adobe will split.

Reasons: the plasticity index of pug is too low, almost no plasticity.

Solution: to increase the plasticity index of raw materials, such as clay, coal slime or clay agent, etc.

For raw materials of low plasticity index, it can also be improved after aging, watering, stirring, rolling, extruding and other methods.

2, The body of adobe is not smooth, the obvious particles, more sand pits, and horns or flutes are missing.

Reasons: The shatter of raw materials does not meet the requirements of making bricks because there is much large particles.

Solutions: Install fine grinding equipment, as required for crushing the raw materials to make particles 3 mm or less.

Some kiln owners are not willing to spend money in equipping the machinery of raw material pre-treatment, such as roller crusher,double shaftmixers. Some kilns are only equipped with a pair of rollers, some only with mixers, some even neither of them. How can we get good bricks if there are bricks, tile, stone and other debris in the mud raw materials? Even if it is hard to send someone to pick them out clean. The fundamental way to solve the problem is equipped with auxiliary equipment.

3, The quality of adobe is unstable, sometimes good and sometimes poor.

Reasons: uneven mixing of raw materials

Solutions: Increase the mixer and feeder

Some brick factories are not equipped with rollers and mixers, even without the feeders, all by artificially feeding into the brick machine with shovel, which inevitably occurs two major drawbacks.①, raw material soil cannot be stirred and mixed well. The plasticity of raw soil is not exactly the same, and sometimes the disparity is very great, the Yellow River sludge is like that.②, the inside fuels such as coal, coal gangue, slime and others cannot be stirred evenly. The two heterogeneous, will inevitably lead to the instability of adobes’ quality.

4, malformed adobe and mud column, will spread immediately after cutting.

Reasons: Failure of the vacuum chamber

Solutions: a, improve the maintenance, service, repair technology of brick machine to ensure the normal function of brick machines’ properties. b, make the necessary technical transformation

    b, Another reason for resulting in failure of the vacuum chamber, is the sand-based raw material, so the closed mud layer of the upper auger is too thin, easy to be drawn through, causing the vacuum failure, so the adobe could not be molded. The best way to solve this problem is to change the ratio of raw materials, to increase the plasticity index of raw materials. The other way is to cut the front end of the superiors auger to 2-10 centimeters according to the material properties of soil (must be conducted under the guidance of skilled technical personnel, don’t do it by yourself).

5, Many brick cracks on adobes or broke into two sections, more wastes after sintering.

Reasons: There are too many viscous ingredients in raw materials, so the plasticity index is too high.

Solutions: change the ratio of raw materials, reduce the plasticity index. The plasticity index of clay can be up to 25, can be properly incorporated into the coal ash, slag, fly ash or waste of brick powder to make it thin.

6, Soft adobe, easy to form, or crack after cutting.

Reason: the improper control of moisture in the mud.

Solution: soft adobe, easy to be deformed, showing that the water of sludge is too much, should reduce water. If the mud column quickly occurs crack or split of mud column after molding, which is caused by too little water in mud, it can be solved by increasing appropriate water.

7. Brick production capacity not stable

Reason: Not equip with box feeder

Solution : Some brick factory owners in order to save money, they refuse to use box feeder but some labors to feed soil manually .Therefore, soil feeding amount is not stable,sometimes more than what the extruder need, some times, less what extruder need, thus greatly influencing production capacity.

All in all, there are all kinds of raw materials to make bricks, in addition to the different climate, some abnormal situations inevitably occur in the production and it is really hard to avoid. If there are problems, knowing the following two points will be easy. One isto havea team with a strong sense of responsibility and a technical team ofprofessional mechanics. Two is to timely communicate high and difficult technical problems with industry colleagues.

In summer, with the change of climate, the moisture content in raw materials fluctuates, so pay close attention to the change of moisture content in production. When the moisture content is low, it is necessary to add water to the raw material in time to make it reach the moisture required for molding. When the moisture content in the raw material is too high, it is necessary to properly reduce the moisture content in the raw material. It can be reduced by adding some dry materials to the raw material, such as dry fly ash, coal gangue, slag, tailings of other mines and other industrial waste slag. When adding these components into the raw material, it is necessary to select the right time and specify the adding position. It must be added at the crushing position of the raw material. In this way, the added components can form a good mixture with the main components of the raw material to make the performance of the raw material uniform. If the adding time is too late, and then add after the raw material is broken, then the performance of the raw material is not uniform because several materials cannot be fully mixed, The molding work cannot be carried out smoothly. That is, the forming can be carried out, but the quality of the formed green body is also extremely unstable. When adding water to raw materials, it is also necessary to pay attention to the time of adding water. It is necessary to add 98%~100% of the water required for raw material molding when raw materials are broken and crushed, so that the water content of raw materials can meet the requirements of molding water. Don't wait until the raw material enters the extruder to add water, which is too late to ensure that the added water is evenly dispersed in the raw material, and the water content on the surface and inside of the particles will also be greatly different, which is not conducive to the consistency of the raw material performance, and will cause certain harm to the molding and green body performance.

In terms of lubricating water at the machine mouth, attention should also be paid to the amount of water added. Under the condition of ensuring normal molding, water should be added as little as possible. Although molding can also be carried out with more water, this will make the surface of the green body absorb too much water, which will have a certain impact on the drying process of the green body and the uniformity of the green body performance. It is inevitable to form delamination phenomenon in the forming body by using the screw extruder, which is generally called spiral striation. This texture (layering) is formed by the uneven extrusion of mud from the machine mouth section through the spiral blade. When raw materials are formed into mud strips, we hope to increase the density of the green body by the close combination of particles, rather than by the effect of lubricants. According to the principle of the densest packing of raw materials, when the proportion of each component in the coarse, medium and fine particles of raw materials is distributed according to "big at both ends and small in the middle", the density of the green body is the largest, that is, the particles can reach the densest packing. All particles with one particle size can not achieve good forming effect, and when the proportion of each component is out of balance, it can not achieve good forming effect, and it is easy to produce delamination during forming.

Components and structure

A typical clay brick kiln consists of several main parts:

Chamber: This is where the bricks are stacked and fired. It is designed to withstand high temperatures and has proper ventilation to ensure even heating.

Fuel supply system: Depending on the type of kiln, it may use coal, gas, or other fuels. The fuel supply system controls the amount of fuel entering the kiln to maintain the desired temperature.

Ventilation system: Necessary for removing excess heat, gases, and ensuring proper air circulation during the firing process. This helps in achieving consistent quality bricks.

Types of clay brick kilns

There are different types of clay brick kilns, including:

Bull's trench kiln: This is a long, trench-like structure where bricks are placed on the sides and fired from one end. It is a relatively simple and low-cost kiln but may have less efficient heat utilization.

Fixed chimney kiln: It has a fixed chimney for exhaust gases. Bricks are stacked inside and fired. This type of kiln offers better control over the firing process compared to some other traditional kilns.

Tunnel kiln: A more advanced and industrialized kiln. Bricks are moved through a long tunnel on a conveyor belt while being fired at different temperatures in different zones. This provides a continuous production process and better quality control.

The firing process

The firing process in a clay brick kiln involves several stages:

Drying: Before firing, the bricks need to be dried to remove moisture. This is usually done in a separate drying chamber or by natural air drying.

Preheating: The bricks are gradually heated to a certain temperature to drive off remaining moisture and prepare them for the high-temperature firing stage.

Firing: The bricks are subjected to high temperatures, typically ranging from 800 to 1200 degrees Celsius, depending on the type of brick being produced. This causes chemical and physical changes in the clay, making the bricks hard and durable.

Cooling: After firing, the bricks need to be cooled slowly to avoid cracking. This can be done by natural cooling or by controlled ventilation.

Environmental impact

Clay brick kilns can have an environmental impact:

Air pollution: The burning of fuels in the kiln releases pollutants such as sulfur dioxide, nitrogen oxides, and particulate matter, which can contribute to air pollution.

Land use: The extraction of clay for brick production can lead to land degradation and loss of agricultural land.

Energy consumption: Kilns require a significant amount of energy for firing, which can contribute to greenhouse gas emissions if fossil fuels are used.

To address these issues, efforts are being made to develop more sustainable brick production methods, such as using alternative fuels, improving kiln efficiency, and recycling waste materials.

Coal-Fired Tunnel Kiln:

•  The tunnel kiln is equipped with a comprehensive combustion system, exhaust system, cooling system, heat dissipation system, pressure balance system, operating system, and monitoring system. By adjusting these systems, the roasting curve inside the kiln becomes more rational, and production operations are better coordinated. The tunnel kiln features a preparation room at the loading end, a stop door at the connection between the preparation room and the preheating zone, and end doors at both ends, effectively preventing cold air from entering the kiln and ensuring uninterrupted operation and roasting unaffected by external conditions.
• It will generate pollution, so it is necessary to install a desulfurization tower for air purification.
• The precision of temperature control is not high.Suitable for low end construction material ,like construction bricks.
• Investment is lower compared with natural gas tunnel kiln.
• Thermal efficiency: 60%~70%

Natural Gas Tunnel Kiln:

• Natural gas tunnel kilns are divided into two types: side-fired and top-fired.  1. Side-fired kilns are designed based on the characteristics of clay product firing. Several pairs of combustion channels are arranged along the lower sections of the kiln walls on both sides of the firing zone. Suitable side-fired burners are installed outside these channels, allowing flames to enter the kiln's combustion space through the channels to heat and fire the products.  2. Top-fired kilns feature burners positioned at the roof of the firing zone. Natural gas and air are directly injected into the kiln's combustion space via burner ports from the top, eliminating the need for side-fired combustion channels. This significantly simplifies the kiln structure, allows for a wider kiln cross-section, and thereby increases kiln volume and production capacity.
• It will not create pollution.
• The precision of temperature control is high.Suitable for high end ceramic brick and tiles, clay panels, architectural ceramics,face bricks etc.
• Due to the need to lay pipelines and various valve control systems for gas storage tanks in natural gas tunnel kilns, and compared to coal burning tunnel kilns, the width of the kiln car and tunnel kiln in natural gas tunnel kilns is much wider, therefore the investment is much higher compared with coal fired tunnel kiln.
• Thermal efficiency: More than 80%