Brick and tile production line

　　The production process of clay-fired bricks has existed for more than 2000 years. Fired bricks, also known as red bricks, are a common building wall material. The main raw materials used include clay, coal slag, lake silt, shale, etc. The production involves four stages: raw material preparation,坯体成型 (this term needs clarification for accurate translation), wet坯 drying, and finished product firing, ultimately producing the finished product. Currently, the most advanced furnace types are rotary kilns and tunnel kilns, which can achieve fully automated operation throughout the plant, allowing for the highest levels of product output and quality. Our company can provide a complete EPC solution for tunnel kiln clay brick production lines.

　　 I. Working Principle of Tunnel Kilns
　　A tunnel kiln is generally a long, straight channel. The sides and top have fixed kiln walls and a kiln roof (the top can be flat or arched). Kiln cars run on tracks laid on the bottom, carrying the products to be fired. The cars enter at the kiln head and exit at the kiln tail. The kiln body forms fixed preheating, firing, and cooling zones, often referred to as the "three zones" of the tunnel kiln. The high-temperature flue gas produced by combustion flows towards the kiln head under the action of a chimney at the front of the tunnel kiln or an induced draft fan, gradually preheating the products entering the kiln. This section constitutes the preheating zone of the tunnel kiln. The middle section of the tunnel kiln is the firing zone. Cold air is blown into the kiln tail to cool the products in the latter section of the tunnel kiln. After being heated by the products, the blown cold air is then extracted and sent to the drying kiln as a heat source for drying the green ware. This section constitutes the cooling zone of the tunnel kiln. Tunnel kilns for firing bricks use three different types of fuel: solid, liquid, and gas. Currently, most tunnel kilns in China use solid fuel, namely coal. This is called internal combustion firing. Where conditions permit, external firing is also used, with oil and gas as the combustion materials.
　　Tunnel kilns enable continuous production without interruption, with short firing cycles, high output, and independence from natural weather conditions, resulting in fuel savings. They primarily operate using the counter-current principle, thus achieving high thermal efficiency; compared to conventional ring kilns, the thermal efficiency is as high as approximately 50%. Tunnel kiln production saves labor, improves the working environment, reduces environmental pollution, is easy to operate, and facilitates mechanized loading and unloading of products, reducing the labor intensity of workers. In terms of improving product quality, compared to ring kilns, it reduces secondary handling by workers, and the firing temperature is controllable and adjustable. The firing process is easy to control, resulting in a lower breakage rate. The tunnel kiln and its internal equipment are relatively durable because, unlike ring kilns, the kiln interior is not subject to rapid heating and cooling, so the kiln body has a longer service life, generally requiring no major repairs within 5 years. The land area occupied by a tunnel kiln is 2/3 less than that of a ring kiln with the same output and specifications. Tunnel kilns and ring kilns use different masonry materials and equipment. Therefore, the initial investment cost is higher than that of ring kilns, but the later production cost is lower.

　　 II. Types and Structure of Tunnel Kilns
　　Tunnel kilns can be classified according to various indicators such as internal width, output, structure, and degree of automated operation.
　　(I) Classification by Tunnel Kiln Cross-Sectional Width
　　Tunnel kilns are available in various widths, such as 3.0m, 3.3m, 3.6m, 4.6m, 4.8m, 6.9m, 7.3m, 9.3m, and 10.3m.
　　(II) Classification by Kiln Structure
　　(1) According to the kiln roof structure, they can be divided into arched-roof tunnel kilns and suspended flat-roof tunnel kilns.
　　(2) According to the kiln body structure, there are kilns with all-brick masonry structures, brick-concrete structures with steel columns and tie rods, and reinforced concrete frame structures.
　　(3) Assembled, all-fiber, and modular kiln body structures.
　　(III) Classification by Single-Line Output
　　They are available in various specifications and models, with annual outputs of standard bricks ranging from 120 million, 80 million, 60 million, 50 million, 30 million, and 20 million pieces.
　　(IV) Classification by Production Process
　　They can be classified into single-layer firing, one-and-a-half-layer firing, and double-layer firing.
　　(V) Classification by Degree of Automation
　　They can be classified into fully automatic control tunnel kilns, semi-automatic tunnel kilns, and manually controlled tunnel kilns.
　 　III. Tunnel Kiln Construction Investment
　　In terms of construction investment, flat-roof tunnel kilns have higher construction costs than arched-roof tunnel kilns. Tunnel kilns with arched or suspended arched roofs and brick-concrete side walls have lower costs, while those with suspended roofs or suspended arched roofs, brick-concrete side walls with steel column support structures, and small cross-section flat suspended roofs have higher costs. Tunnel kilns with reinforced concrete frame structures, steel frame structures, and profiled steel plate structures have the highest costs.

　　 IV. Application Scope of Tunnel Kilns
　　As a production process with advanced technology, tunnel kilns have wide applicability. They are suitable for producing brick and tile products using coal gangue, fly ash, shale, low-quality flash rock, and other industrial waste and scrap as raw materials, and are also suitable for the production of other building ceramic products. Using this type of kiln not only greatly reduces the labor intensity of workers but also improves production efficiency and ensures product quality and output.
　 　V. Selection of Tunnel Kilns
　　The performance of various tunnel kilns has been analyzed above. During construction, various factors should be considered comprehensively, and appropriate tunnel kilns should be selected based on the properties of the raw materials and the scale of investment. If the investment is relatively low, a tunnel kiln with an arched roof and brick-concrete side walls can be selected. If the investment is not very low, a tunnel kiln with a flat roof or flat suspended roof and reinforced concrete frame side walls can be selected. For construction projects with large output and sufficient investment, the firing equipment can use a large cross-section single-layer firing tunnel kiln with a suspended flat roof, reinforced concrete frame structure, steel frame structure, or profiled steel plate structure. In summary, the selection of tunnel kiln type should focus on factors such as raw materials, total investment, product structure, market sales, comprehensive management level, and technological development.
　　 VI. Tunnel Kiln Production Process Flow