A roller kiln is a tunnel kiln with a narrow and elongated cross-section. Unlike car tunnel kilns, it operates not with vehicles loaded with products but with a series of parallel rollers that cross the working cross-section of the kiln, forming a "roller track." Products are placed on the roller track and conveyed into the kiln as the rollers turn, completing the firing process within the kiln, hence the name "roller kiln." Roller kilns can be categorized by the combustion structure used, the heating method, or the number of channels. Typically, roller kilns in the building tile industry are classified by the combination of fuel and heating methods.
Mingyan Roller hearth furnace – the flame enters the space above and below the roller, contacts and directly heats the products.
(1) Gas-fired flame辊窑. Common gas fuels include natural gas, blast furnace gas, liquefied petroleum gas, etc., with a requirement for clean gas.
(2) Diesel-fueled flameless roller kilns. Due to the simpler fuel supply system and lower investment compared to the gas supply system, most of the flameless roller kilns built domestically in recent years have been fueled by light diesel oil.
2. Flame Retardant Roller Kiln - The flame typically enters only the muffle channel isolated from the kiln chamber, where it radiates heat to the products and heats them through a flame-retardant plate.
(1) Coal-burning flame-separation roller hearth kilns burn coal in a firebox, with the flame entering the flame-separation channel (muffle channel) beneath the roller, indirectly heating the products. Some domestic coal-burning roller hearth kilns, to stabilize kiln temperature and reduce the temperature difference between the upper and lower sections, install several electric heating elements (silicon carbide rods) on the roller to compensate for the heating of the products, which has a certain effect on improving product quality. Such roller hearth kilns can be called coal-electric mixed-firing roller hearth kilns, but they still fall under the category of coal-burning flame-separation roller hearth kilns.
(2) Oil-burning flame-separation roller kilns use heavy oil or residuum oil as fuel, with the flame typically entering the kiln's muffle zone below, indirectly heating the products. The oil-burning flame-separation roller kilns constructed in China in the early 1980s, in addition to having muffles below the rollers, also had muffles on the rollers, but these upper muffles were generally removed later. In the mid-late 1980s, most heavy-oil roller kilns were improved to oil-burning semi-flame-separation roller kilns, where fire outlets were left at appropriate locations to allow some combustion products into the working channel. Since the semi-flame-separation roller kilns, apart from the fire outlets, have the same structure as the full flame-separation roller kilns, they can be categorized together.
3. Electric heated roller kiln - Utilizes electric heating elements (silicon carbide rods or electric heating wires) installed above and below the rollers as a heat source for radiant heating of the products. Suitable for manufacturers with abundant electric power resources or small-scale roller kilns. Among the aforementioned types of roller kilns, the flameless roller kiln, with its combustion products directly contacting the products, is beneficial for improving heat transfer efficiency, uniforming the temperature field across the kiln cross-section, and energy conservation, representing the mainstream of roller kilns. Of course, each region has its own resource characteristics, and other types of roller kilns are also widely used in our country.
The roller kiln can also be categorized by the number of working channels: single-layer roller kiln, double-layer roller kiln, triple-layer roller kiln, and so on. Multi-layer roller kilns can save fuel, shorten the kiln length, reduce land use, and lower investment costs. However, as the number of layers increases, it complicates the transportation lines, interlock control systems, and the structure of the kiln itself, making it more difficult to remove brick fragment debris.
Mostly, we use single-layer roller kilns in China, with some employing double-layer channels. One layer is used for baking the products, and the other for drying the green bodies. The drying heat source utilizes the excess heat from the baking layer. Generally speaking, it's advisable to use multi-layer kilns when the kiln width is narrow, the operating temperature is not too high, and the space is limited. However, it's usually not recommended to exceed three layers.
