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Mobile tunnel kilns or modern rotating tunnel kilns are a type of kiln that is very popular in our country today. Compared to previous traditional tunnel brick kilns, this type of mobile kiln saves a lot of time, effort, and energy consumption while the output and quality of bricks created are better. To better understand Tunnel furnace structureits operating principle and its advantages and disadvantages, please follow the article below.

Image of mobile tunnel furnace

Structure of tunnel furnace

1. Structural principle of mobile tunnel furnace

Structure diagram of tunnel furnace

Mobile tunnel furnace is a modern rotating tunnel furnace researched and developed in China. It includes the following main parts:

(1) The round kiln floor is designed to be fixed: The top surface of the kiln floor is paved with samot refractory bricks. This type of brick has high heat resistance and fire resistance, allowing the furnace to operate for a long time without cracking or sinking.

(2) Round rails are installed on the inside and outside of the kiln bottom.

(3) The kiln shell consists of 2 side walls and a ceiling designed into a scarf-shaped block covering about 1/3 of the circumference of the kiln floor: The kiln shell structure is assembled from panels, including a load-bearing steel frame and steel shell covering the outside, inside is a 126 degree Celsius insulating layer of ceramic wool pressed into a block about 250mm thick, then tightly assembled into the kiln frame. Above the roof of the furnace, at the firing zone, charcoal doors are arranged to ensure a stable burning process in the furnace. Along both sides of the furnace, a pipeline system will be arranged to transport and convect hot air to the necessary areas inside the furnace.

(4) The wheel system can move on rails on both sides of the furnace floor by electric motor and the entire furnace shell is placed on this system. So that the kiln shell can move along circular rails.

(5) The space inside the kiln: This is the place used to install shaping equipment as well as other auxiliary equipment.

Structure of tunnel furnace

2. Details of the components of the mobile tunnel furnace

2.1. Basic parameters of the furnace

Long	168m
Wide hearth of the furnace	8.6m
High inside the furnace	1,420 mm
Number of brick floors	10 floors
Center line diameter	117.7m
Outside rail diameter	130m

2.2. Specifications of brick stacking blocks

– Arrange according to the cross section of the furnace: Divide into 6 blocks, each block has 24 pieces. When stacking blocks and pellets, make sure there is space between the pellets and blocks and between the outer block and the furnace wall to ensure good ventilation and convection for heat and air during the firing process.

– Arrange according to furnace height: Arrange 10 rows of vertical bricks (side 110mm) so that the space from the top of the block to the furnace ceiling is 300mm.

– Arranged according to kiln length: Each firing chamber will have 6 rows of bricks arranged in length of 220mm. When stacking, ensure space between blocks and space to open and close the kiln door.

The time interval between two movements of the furnace shell is 3 hours.

2.3. Brick transfer system

Bricks are transported on a circular conveyor controlled by an inverter system, ensuring a speed synchronous with the extrusion speed of the brick extruder. Each time, two lines of rustic bricks with a total length of about 300m will be transported to the brick picking point.

2.4. Moving system

The moving system includes 150 wheels made from cast steel and has been treated to prevent corrosion. 28 drive wheels made of pure steel controlled by an inverter system along with specialized equipment will reduce impact force when stopping and moving continuously.

2.5. Steel frame of furnace body

The 95-foot steel door frame, roof beams, horizontal beams, side beams, bottom beams… are all treated to prevent corrosion and ensure the hardness of the furnace body. Support frames for auxiliary equipment include drive system racks, inspection and repair path racks, brake door racks, flue pipe racks, probe hole racks, electrical line installation racks, etc.

2.6. Furnace body insulation system

The entire kiln shell is insulated with heat-resistant ceramic wool to ensure the insulation of the kiln shell from the outside so that the outside of the kiln in the drying zone does not exceed 45°C and in the firing zone does not exceed 55°C. Outside the insulation layer is a heat-resistant stainless steel plate shell 1.5mm thick.

2.7. Channel and chimney system

The desiccant chimney is made from anti-corrosion insulation material with a total length of 112m. The dehumidifying branch chimney includes 26 auxiliary chimneys made of anti-corrosion stainless steel, covered with an insulation layer on the outside. The total chimney is made of highly anti-corrosion insulation material and is 85m long. The heat-extracting branch chimney is made of anti-corrosion stainless steel, the outside is covered with a 10m thick insulation layer, including 12 sets of heat-extracting branch pipes. The 45m long chimney to utilize residual heat is made of stainless steel and insulation materials.

The heating stage brake door is connected to the interlock of the high heat-resistant stainless steel door to ensure a closed structure. The drying door is made of anti-corrosion composite panels and has an integrated smart function that ensures the oven body only moves after all doors have been opened.

2.8. Electric line system

The furnace uses 3-phase 380 V – 250A electricity to operate. The main electrical control cabinet will control the inverter of the entire power line and eliminate shock voltage using soft start to protect the main circuit. Decentralized lines will provide electricity, and the line load must ensure the excess load design.

2.9. Furnace chamber air monitoring system

The monitoring system includes a central control floor, a 19-inch LCD display screen with 6 cameras, and a hard drive camera that will display the temperature at 32 air monitoring points in the kiln through temperature sensors and heat charts.

2.10. Fan system and air volume control

The system includes 2 axial fans for ventilation in the oven, 2 sets of air volume control systems with 6 drying air control doors made of stainless steel, 12 heat intake doors, 2 cold air control doors made of stainless steel and 8 residual heat doors.

2.11. Dehumidification system

The dehumidifying system includes 4 dehumidifying ventilators and 4 variable air volume control systems along with 4 sets of anti-corrosion exhaust pipes.

2.12. Road system for staff and maintenance services

The system includes a walkway with a total length of 300m, 700mm wide with a walking staircase and a central control operating floor of 7.5 m2.

2.13. Coal feeding equipment

Including a 15m2 coal loading floor and 260 furnace tubes made of high temperature resistant stainless steel

2.14. External system

The outside of the tunnel kiln body has a protective layer made of 1.8mm steel plate sprayed with color as specified by the investor.

2.15. Surveillance camera system

Includes 9 infrared cameras, camcorder with memory drive and displayed on a 21 inch LCD screen.

Operating principle of mobile tunnel furnace

After leaving the extruder, the bricks will be transferred to an automatic brick cutting system, then stacked by the robot into blocks on the kiln floor, ensuring there is space between the brick blocks as well as between the brick blocks and the kiln wall to maintain stable air convection during kiln operation. The entire length of the mobile tunnel furnace is divided into zones including: drying zone, heating zone and cooling zone.

The bricks are automatically arranged into blocks by the robot

– At the drying zone: Rustic bricks are dried using hot air drawn from the firing zone. At this time, the entire amount of physical water in the bricks is separated before entering the firing zone. This helps minimize the phenomenon of cracking or exploding the tile surface due to steam loss during firing. Through the smoke extraction channel under the furnace floor, the exhaust gas from the drying process is sucked to the desulfurization tower to remove impurities, dirt and toxic gases before being discharged into the environment through the chimney.

– At the calcination zone: Charcoal from the kiln combined with coal mixed in rustic bricks when burned will generate heat to sinter the block into bricks. Depending on the nature and chemical composition of the mixed materials, the amount of charcoal and the highest heating heat are adjusted accordingly. Normally, the heating temperature will range from 900 – 1050 oC.

– At the cooling zone: Air is pushed into the kiln by a fan to cool the bricks, lowering the temperature to below 50 oC before being taken out of the kiln. When hot air is blown into the brick block, it will move from the drying zone to the firing zone and from the firing zone to the cooling zone.

Operating principle of tunnel furnace

During the kiln’s operation, the kiln floor containing bricks remains stationary, only the kiln shell moves cyclically to carry out drying according to the preset mode. However, the positions of the drying zone, firing zone and cooling zone do not change much compared to the tunnel kiln.

Advantages and disadvantages of tunnel kilns compared to traditional kilns

1. Advantages

– Mobile tunnel kilns can produce large brick output, about 100 – 300 million bricks per year.

– All processes from brick extrusion, shaping, brick stacking, transfer to drying, exhaust gas treatment, etc. are completely performed by robots. Thanks to that, the brick stacking block size as well as the kiln stacking density are uniform, ensuring the quality of fired bricks is also very uniform, over 80% of finished bricks are of good quality.

Finished bricks are uniform in size

– The furnace structure is made of stainless steel that can withstand high temperatures, firmly placed on a closed rail system with a large diameter, up to 100m.

– The kiln operates continuously around brick blocks that are fixed on the floor of the kiln.

– Because the cart system is not used to transport bricks into the kiln, the kiln floor is always in a static state. Thanks to that, the life of the furnace floor is very long and there is no need to use a steel frame structure with a steel frame, helping to reduce investment costs.

– It takes less construction time than traditional tunnel kilns, it only takes about 3 months to complete both the kiln and the kiln shaping.

– Low operating and maintenance costs, only losing about 1% of the total initial investment value within 10 years. The furnace shell is made of ceramic wool, which has great heat-insulating ability, so insulating the furnace is more effective, while also contributing to saving a lot of energy. Furthermore, compared to the brick material used to build the furnace, ceramic wool is more heat-resistant and has much higher elasticity.

– The furnace is designed to be very environmentally friendly, exhaust gases are treated before being released into the environment.

– The brick blocks are in a static state during the firing process, so cracking and chipping at the edges are minimized with a cracking rate of less than 2%, ensuring the finished bricks are square, sharp, and of high quality.

– Reduce labor by about 50% thanks to automation and synchronization of kilns and auxiliary equipment systems, contributing to increased income for workers.

2. Disadvantages

– It takes up a lot of space to build the furnace, so it is necessary to arrange the production steps in the area inside the furnace to make the most of the available space.

Building a tunnel kiln takes up a lot of construction area

– The amount of electricity needed to operate and maintain the kiln is quite large, so the investor needs to calculate accordingly, ensuring it does not exceed the allowable rated value.

Above is some information that labvietchem.com.vn wants to share with readers Tunnel furnace structure as well as the operating principles and advantages and disadvantages when choosing this type of furnace. Hopefully this will be useful knowledge to help you make the most appropriate decision before building a tunnel kiln.