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Tunnel Kiln Brick Production: Energy Control Technologies Explained
Fuel cost, electricity cost, and labor cost constitute the three major expenses in sintered brick production. However, due to improper construction and operation, fuel waste is extremely common. Therefore, reducing energy consumption is a long‑term objective for any brick production machine line.
Kiln Body Insulation and Energy Consumption
The insulation performance of the kiln body is critical to energy saving. In a continuously operated brick firing system, approximately 30–40% of the heat is absorbed and dissipated by the kiln structure. As fuel prices rise, improving kiln insulation becomes increasingly important. The kiln body consists of two main parts: the walls and the roof.
The external wall is in direct contact with the ambient air. To reduce heat loss, an additional 150–250 mm layer of insulating wool should be added inside the wall. Roof heat dissipation is the main path of energy loss, making roof insulation particularly important. In addition to using insulating wool in the arch brick layers, lightweight insulating materials such as perlite should be filled in the upper part to enhance thermal performance. Common high‑performance insulation materials include aluminum silicate fiber wool, rock wool, perlite, and lightweight insulating bricks. In comparable regions, adding insulation to kiln walls can reduce energy consumption by more than 50 kcal per kg of fired product compared to non‑insulated walls.
National standards specify that the temperature rise on the outer wall of the kiln shall not exceed 15°C, and on the roof not exceed 25°C. If a brick kiln meets these criteria, its energy consumption will be greatly reduced. Achieving this requires high‑quality insulation materials — for a 4.6 m wide tunnel kiln, the additional investment is approximately RMB 100,000–120,000.
Kiln Car Insulation and Energy Consumption
Heat loss through kiln cars is another major pathway. In many tunnel kilns, the temperature under the car reaches as high as 300°C, resulting not only in severe heat loss but also in frequent bearing failures. The main causes are poor thermal insulation of the car’s masonry and inadequate sealing at the joints between adjacent cars. A well‑designed kiln car must have insulating wool, perlite, and lightweight insulating bricks laid on the underframe, followed by refractory bricks. The joints require a two‑stage sealing system with embedded insulating wool to effectively reduce heat transfer to the undercar area.
Kiln Car Sand Seal and Energy Consumption
Poor sealing performance of the sand seal in a tunnel kiln not only causes heat loss but, more importantly, leads to erratic airflow inside the kiln — a primary cause of underfired bricks. Cold air infiltrating through the sand seal directly affects the bricks on both sides of the kiln car. The side areas already experience lower temperatures due to heat absorption by the kiln walls; the additional cold air further reduces the temperature, inevitably producing underfired bricks along both sides of the kiln. Integrating a reliable sand seal is a key design feature of any efficient brick machine line.
Tunnel Kiln Ventilation and Energy Consumption
Fuel combustion requires sufficient oxygen. Approximately 30–40 m³ of air is needed to burn 1 kg of pure carbon. Although the airflow inside the kiln is driven by the induced draft of the exhaust fan, the cross‑sectional area of the ventilation duct is the key to ensuring adequate air volume. Without sufficient airflow, fuel cannot burn completely. Under sufficient oxygen, 1 kg of pure carbon generates about 8500 kcal of heat and produces CO₂. Under oxygen‑deficient conditions, only about 1700 kcal is released, and the unburned carbon converts into carbon monoxide (producer gas), which is exhausted from the kiln.
Based on the requirement of 30–40 m³ of air per kg of pure carbon, and approximately 1.1 tons of pure carbon per 10,000 standard bricks, a tunnel kiln with a daily output of 200,000 standard bricks (about 8,000 bricks per hour) needs about 880 kg of pure carbon per hour. The ventilation duct must supply 880 × 40 = 35,200 m³ of air per hour. At an air velocity of 8 m/s, the required cross‑sectional area is 35,200 / 3600 / 8 = 1.22 m². In practice, the duct area should be 1.5 times larger than the calculated value, because the internal fuel and externally added coal used in brickmaking contain ash and have lower calorific values, requiring significantly more air than pure carbon combustion.
Kiln Insulation and Green Brick Drying Performance
The heat used for drying green bricks comes from the flue gas and waste heat of the firing kiln. Waste heat is released during the cooling stage of fired bricks. A well‑insulated brick firing system not only reduces heat loss and energy consumption during firing but also extracts sufficient heat from the cooling zone to send to the drying chamber. Only with ample heat can the drying chamber ensure proper drying of green bricks, which directly affects the efficiency of the brick production machine line.
Kiln Length and Thermal Efficiency
Increasing the length of the kiln not only improves output and quality but, more importantly, enhances thermal efficiency. A longer kiln allows a longer firing zone and extended residence time, enabling a “low‑temperature, long‑firing” strategy. Extending the soaking time at a relatively lower temperature equalizes the cross‑sectional temperature profile, increases product strength, and reduces underfired bricks. Moreover, with a longer firing zone, the car advancing speed can be appropriately increased to raise output. In addition, a longer kiln makes it possible to fully extract waste heat from the cooling zone and send it to the drying chamber. If the tunnel kiln is too short, bricks exiting the kiln are still hot, and a large amount of waste heat is dissipated into the atmosphere. Only the heat retained inside the kiln can be extracted by fans and utilized for drying. Therefore, an appropriate increase in kiln length not only boosts production and ensures product quality but also maximizes the use of waste heat for drying green bricks.
Production Output and Energy Consumption
The heat absorbed by the kiln structure is time‑dependent, not output‑dependent. From ignition at the beginning of the year to shutdown at the end, the kiln consumes a fixed amount of heat every day regardless of how many bricks are produced. Thus, increasing daily output is an effective way to reduce energy consumption per brick. Increasing the ventilation rate to promote rapid fuel combustion is a prerequisite for higher output. Higher output inherently reduces the energy consumed per brick — a key performance indicator for any modern brick making machine line.
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