A roller kiln is a tunnel kiln with a narrow and elongated cross-section. Unlike car tunnel kilns, it operates not with a carriage loaded with products but with a "roller track" consisting of parallel rollers that span the cross-section of the kiln's working channel. 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. Generally, roller kilns for the building ceramics industry are classified by the combination of fuel and heating methods.

Bright Flame Roller Furnace - Flames enter the space above and below the roller track, coming into contact with the products and heating them directly.

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

(2) Open-flame roller kilns fueled by light diesel oil. Due to the simpler and less expensive fuel supply system compared to the gas supply system, most of the open-flame 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 heats the products by radiation through the flame-retardant plate.

(1) Coal-fired flame-separation roller kilns burn coal in a firebox, with the flame entering the flame-separation channel (muffle channel) beneath the roller to indirectly heat the products. Some domestic coal-fired roller kilns, to stabilize kiln temperature and reduce temperature differences between the top and bottom, install several electric heating elements (silicon-carbide rods) on the rollers to compensate for the heating of the products, which has a certain effect on improving product quality. Such roller kilns can be called coal-electric mixed combustion roller kilns, but they also fall under the category of coal-fired flame-separation roller kilns.

(2) Oil-burning flameless roller hearth kilns use heavy oil or residuum oil as fuel, with the flame typically entering the muffle channel below the kiln. They indirectly heat the products. The oil-burning flameless roller hearth kilns built in China in the early 1980s, in addition to the muffle channel below the roller, also had one above the roller, but the upper muffle channel was generally removed later. In the mid-late 1980s, roller hearth kilns burning heavy oil were mostly improved to oil-burning semi-flameless roller hearth kilns, where a fire outlet is left at an appropriate location to allow some combustion products to enter the working channel. Since the oil-burning semi-flameless roller hearth kilns, except for the fire outlet, have the same structure as the oil-burning full-flameless roller hearth kilns, they can be categorized together.

3. Electrically heated roller hearth kiln - Utilizes electrically heated elements (silicon carbide rods or electric heating wires) installed above and below the rollers as the heat source for radiant heating of the products. Suitable for manufacturers with abundant electricity resources or small-scale roller hearth kilns. Among the aforementioned types of roller hearth kilns, the flameless roller hearth kiln is advantageous for increasing heat transfer efficiency, evenly distributing the temperature field within the kiln, and energy conservation, as its combustion products directly contact the products, representing the mainstream of roller hearth kilns. Of course, each region has its own resource characteristics, and other types of roller hearth kilns are also widely used in our country.

The roller kiln can also be categorized by the number of working channels: single-layer, double-layer, triple-layer, and so on. Multi-layer roller kilns can save fuel, shorten the kiln length, reduce land use, and lower investment costs. However, the increased number of layers complicates the transportation lines for loading and unloading, the interlock control system, and the kiln structure itself, which also brings many 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 excess heat from the firing layer. Generally speaking, multi-layer kilns are preferable when the kiln width is narrow, the working temperature is not too high, and the land area is limited; however, it is usually not advisable to exceed three layers.