A roller kiln is a tunnel kiln with a narrow and elongated cross-section. Unlike the car tunnel kiln, it operates not with a car loaded with products but with a series of parallel rollers that span the kiln's working channel cross-section, forming the "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 ceramics industry are classified by combining fuel and heating methods.

Bright Flame Roller Kiln - The flame enters the space above and below the roller, contacting and directly heating the products.

(1) Gas-fired flame roller kiln. Common gas fuels include natural gas, producer gas, liquefied petroleum gas, etc., with a requirement for clean gas.

(2) Direct flame roller hearth kilns burning light diesel oil. Due to the simpler fuel supply system and lower investment compared to the gas supply system, most of the direct flame roller hearth kilns built domestically in recent years have been designed for burning light diesel oil.

2. Flame Retardant Roller Kiln - The flame typically enters only the muffle channel separated from the kiln chamber, where it is radiated to the products through flame-retardant plates for heating.

(1) The coal-fired flame-retardant roller kiln burns coal in a firebox, with the flame entering the flame-retardant channel (muffle channel) under the roller to indirectly heat the products. Some domestic coal-fired roller kilns, in order to stabilize the 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 heat of the products, which has a certain effect on improving product quality. Such roller kilns can be called coal-electric mixed-firing roller kilns, but they also fall under the category of coal-fired flame-retardant roller 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 channel below to indirectly heat the products. The oil-burning flame-separation roller kilns constructed in China in the early 1980s, in addition to having a muffle channel below the roller, also had one above. However, the upper muffle channel was generally removed later. By the mid-late 1980s, most heavy-oil roller kilns were upgraded to oil-burning semi-flame-separation roller kilns, which involve leaving a fire outlet at appropriate locations to allow some combustion products to enter the working channel. Since the semi-flame-separation roller kilns, aside from the fire outlets, share the same structure as the full flame-separation roller kilns, they can be categorized together.

3. Electric Heat Roller Kiln - Utilizes electric heating elements (silicon carbide rods or electric heating wires) installed above and below the roller track as a heat source to radiate heat onto the products. Suitable for manufacturers with abundant electrical resources or small-scale roller kilns. Among the aforementioned types of roller kilns, the flameless roller kiln is beneficial for improving heat transfer efficiency, achieving uniform temperature distribution within the kiln cross-section, and energy conservation, as its combustion products directly contact the products, representing the mainstream of roller kilns. Of course, different regions have their 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: there are single-layer roller kilns, double-layer roller kilns, triple-layer roller kilns, 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 for entering and exiting the kiln, the interlock control system, and the kiln structure itself, which also poses considerable difficulties in removing brick fragments.

Mostly in China, single-layer roller kilns are used, with some employing two layers of channels—one for firing products and the other for drying green bodies. The drying heat source utilizes the waste heat from the firing layer. Generally speaking, multi-layer kilns are suitable when the kiln width is narrow, the working temperature is not too high, and the space is limited, but it is generally not advisable to exceed three layers.