There are numerous classification methods depending on the perspective. Based on the design of the combustion chamber, incinerators can be categorized as single-chamber or multi-chamber types. Furthermore, according to the relative flow directions of the flue gases and the waste, furnace configurations can be classified into co-current, counter-current, cross-flow, and secondary‑flow types.

　　Incinerators are commonly used as harmless treatment equipment for medical and municipal waste, as well as for the safe disposal of animal carcasses. Their operating principle involves combusting fuels such as coal, fuel oil, or natural gas to subject the materials to high‑temperature incineration and carbonization, thereby achieving disinfection.

　　There are numerous classification methods, depending on the perspective. By furnace type, they can be categorized into fixed‑grate furnaces, mechanical‑grate furnaces, fluidized‑bed incinerators (primarily used for industrial waste), rotary kiln furnaces, and others. To enhance the efficiency of municipal solid waste incineration, pyrolysis and gasification (or melting) technologies are often employed. The operating principle of a grate‑type incinerator is to feed waste onto a heat‑resistant cast‑iron or steel grate and supply air from beneath the grate to facilitate combustion. In a fluidized‑bed incinerator, air is blown through porous nozzles at the base of a tower‑shaped chamber, causing a bed of sand to fluidize and form a moving bed. After finely shredded waste is introduced, it comes into contact with the hot, circulating sand (at 650–800°C), resulting in rapid combustion; the resulting ash is carried by the flue gases to the flue‑gas treatment system. The gasification‑melting furnace operates by first thermally decomposing waste in a reducing atmosphere at 450–600°C, producing combustible gases and a carbon‑rich solid residue, which are then combusted and melted. When designing an incinerator, one must comprehensively consider factors such as the plant’s processing capacity, the characteristics of the waste to be treated, the mechanical and thermal loads on the grate, the thermal load of the combustion chamber, the outlet temperature of the combustion chamber, the flue‑gas residence time, and the loss on ignition, among others.

　　 Working principle

　　Waste incineration technology has been applied and developed abroad for several decades. Relatively mature furnace types include pulsating grate furnaces, mechanical grate furnaces, fluidized‑bed furnaces, rotary kiln furnaces, and CAO (controlled‑atmosphere oxidation) furnaces. The following provides a brief overview of these furnace configurations.

　　Mechanical grate incinerator

　　Operating principle: Waste enters the inclined grate via the feed hopper (the grate is divided into a drying zone, a combustion zone, and an after‑burning zone). The alternating motion of the grate bars pushes the waste downward, causing it to pass sequentially through each zone. As the waste moves from one zone to the next, it undergoes a thorough turning over, eventually reaching the after‑burning zone and exiting the furnace. Combustion air is introduced beneath the grate and mixes with the waste; the high‑temperature flue gases then flow through the boiler’s heating surfaces to generate steam while being cooled. Finally, the flue gases are treated by an exhaust‑gas cleaning system before being discharged.

　　Characteristics: The grate material and machining accuracy requirements are stringent, demanding exceptionally smooth contact surfaces between grates and very narrow gaps between adjacent grates. Additionally, the mechanical structure is complex, with a high failure rate and substantial maintenance needs. The high capital and maintenance costs of grate-fired boilers pose significant challenges to their widespread adoption in China.

　　Fluidized bed incinerator

　　Operating principle: The furnace consists of a porous distribution plate, and a large quantity of quartz sand is loaded into the combustion chamber. The sand is heated to above 600°C, while hot air at temperatures exceeding 200°C is blown into the furnace bottom, causing the hot sand to fluidize. Waste is then fed into the bed. As the waste and hot sand fluidize together, it rapidly dries, ignites, and burns. Unburned residues, being lighter in density, continue to fluidize and burn, whereas fully combusted ash, which is denser, settles at the furnace bottom. After water cooling, sorting equipment removes coarse and fine slag for off‑site disposal, while a small portion of medium‑sized slag and the quartz sand are lifted back into the furnace for continued use.

　　Characteristics: Fluidized-bed combustion is highly efficient, and in‑furnace combustion is well controlled; however, the flue gas contains a high dust load, operation is complex, and operating costs are relatively high. The process demands strict uniformity in fuel particle size, necessitating a high‑capacity crushing unit. Moreover, quartz sand causes severe equipment wear, resulting in substantial maintenance requirements.

　　Rotary incinerator

　　Operating principle: The rotary incinerator features cooling water pipes or refractory materials arranged along the furnace body, which is mounted horizontally with a slight inclination. As the furnace continuously rotates, the waste inside is thoroughly combusted while being conveyed in the direction of the tilt until it is completely burned and discharged from the furnace.

　　Features: High equipment utilization, low carbon content in ash and slag, low excess air ratio, and reduced emissions of harmful gases. However, combustion is difficult to control, and low‑calorific‑value waste can be challenging to burn.

　　CAO incinerator

　　Operating principle: Waste is transported to a storage pit and fed into a biochemical treatment tank, where microbial action dehydrates it, breaking down natural organic materials—such as food scraps, leaves, and grass—into a powdery form. Other solid components, including synthetic organics like plastics and rubbers, as well as inorganic constituents in the waste, remain undegraded and unconverted into powder. Following screening, non‑powderable residues are directed to an incinerator, first entering the primary combustion chamber at a temperature of 600°C. The resulting combustible gases then proceed to the secondary combustion chamber, while non‑combustible and non‑pyrolyzable fractions are discharged from the primary chamber as ash and slag. The secondary chamber maintains a controlled temperature of 860°C for complete combustion, with high‑temperature flue gases heating a boiler to produce steam. After treatment, the flue gases are released into the atmosphere via a chimney. Metals and glass, which neither oxidize nor melt in the primary combustion chamber, can be separated from the ash and recovered.

　　Characteristics: It can recover valuable materials from recyclable waste; however, each incinerator has a small processing capacity and long treatment times. The maximum daily processing capacity of a single unit is 150 tons. Moreover, because the flue gas cannot maintain a residence time above 850°C for more than one second, the dioxin content in the exhaust gas remains high, making it difficult to meet environmental standards.

　　Pulse‑firing grate incinerator

　　Operating principle: Waste is fed into the incinerator’s drying bed via an automatic feeding unit, where it is dried. It is then conveyed to the first‑stage grate, where high‑temperature volatilization and pyrolysis occur. The grate is agitated by a pulsed air‑dynamic system, which throws the waste progressively onto the next lower‑level grate. At this stage, polymeric materials undergo pyrolysis, while other constituents are combusted. This process continues until complete combustion, after which the residual ash and slag fall into the ash pit and are discharged by an automated slag‑removal device. Combustion air is injected through nozzles in the grate, mixing with the waste to facilitate combustion and keeping the material suspended in the furnace. Volatiles and pyrolytic gases generated during the initial stages enter the second‑stage combustion chamber for further decomposition and oxidation; any unburned flue gases are routed to the third‑stage combustion chamber for complete combustion. The high‑temperature flue gases pass through the boiler’s heating surfaces to generate steam, and are subsequently cooled before being exhausted.

　 　Its advantages are:

　　(1) The scope of waste treatment is broad, capable of handling industrial waste, municipal solid waste, hospital waste, and discarded rubber tires, among others.

　　(2) High combustion thermal efficiency: Under normal operating conditions, the thermal efficiency exceeds 80%; even for household waste with high moisture content, the thermal efficiency remains above 70%.

　　(3) Low operation and maintenance costs: Thanks to numerous specialized design features and a high degree of automated control, the plant requires a small operating staff—only two personnel per furnace, including ash and slag removal—and entails minimal maintenance workload.

　　(4) High Reliability: Nearly 20 years of operation have demonstrated that this incinerator exhibits an extremely low failure rate, with annual operating hours exceeding 8,000 and a typical availability of over 95%.

　　(5) High levels of pollutant control: Thanks to the use of secondary flue-gas re‑combustion and advanced flue-gas treatment equipment, the flue gas is thoroughly treated. Long-term testing has shown that the flue gas emissions contain CO at 1–10 ppm, HC at 2–3 ppm, and NOx at 35 ppm, fully complying with European and American emission standards. During combustion in the second- and third-stage combustion chambers, the flue gas reaches temperatures as high as 1,000°C and remains at these temperatures for more than 2 seconds, enabling near-complete decomposition of dioxins. The dioxin concentration in the flue gas is 0.04 ng/m³, significantly below the European and American standard of 0.1 ng/m³.

　　(6) The grate features a self-cleaning function under the purging action of compressed air.