Current Status of Waste Incineration and Technical Comparison of Incinerator Types

In the application of waste incineration technology, the thermal technology form is primarily adopted to decompose waste, achieve harmless treatment and volume reduction, and analyze energy, minerals, and inherent chemical components within the recovered waste. Waste incineration can reduce the volume and hazardous state of waste, diminishing the presence of harmful substances within the garbage. Moreover, in the analysis of waste incineration technology, its equipment and pollution prevention facilities exhibit a continuously improving status. Therefore, in China's waste treatment process, incineration technology is the most fundamental waste disposal method.

1 Current Status of Waste Incineration Treatment

Under the current background of urban development, municipal solid waste (MSW) incineration is primarily conducted through mechanical grate furnaces and fluidized bed incinerators. In European countries, 90% of incineration plants adopt the mechanical grate furnace method for waste. Large cities in Japan also utilize mechanical grate furnaces in their waste incineration plants. In China's development, by 2014, 178 MSW incineration power plants had been built, employing mechanical grate furnace technology, while 67 plants utilized fluidized bed technology.

Pyrolysis gasification incineration technology has been applied in environmental protection in recent years. This technology mainly includes two processes: pyrolysis and gasification. The pyrolysis technology primarily involves the process of decomposing organic matter in waste at high temperatures under anaerobic or oxygen-deficient conditions, resulting in solid coke after the removal of volatile substances. Gasification mainly involves the reaction of reactants in their original state with a gasifying agent, generating a thermal conversion process primarily producing combustible gas.

2 Technical Comparative Analysis of Incinerator Types

2.1 Grate Furnace Type Incinerator

The grate furnace type incinerator is a kind of mechanical grate furnace. It forms the furnace bed through a mechanical grate. During the waste treatment process, the movement of the grate continuously agitates the waste throughout the mechanical system, propelling it forward or backward. Typically, the basic process of waste combustion can be divided into three stages: the drying stage, the combustion stage, and the burnout stage.

During the operation of the entire incineration process, the primary air fan extracts odorous gases produced by the fermentation and accumulation of waste from the upper part of the waste storage pit. These gases are then heated via a steam (or air) preheater and fed into the incinerator as combustion-supporting air, ensuring the waste is dried within a relatively short time. In the combustion stage, to ensure the waste is fully burned, secondary air is introduced above the combustion chamber. This is primarily to enhance the disturbance of the oxygen flow, increase the volume of combustion-supporting air, and achieve complete combustion of the waste in one pass.

During the use of grate furnace type incinerator technology, there is no need to add coal or other auxiliary fuels; consequently, the resulting clinker (slag) is relatively less. Moreover, the capacity of a single incinerator unit for waste treatment is relatively large, and there is no need to classify the waste during processing. Through the mechanical application of the grate, stable combustion of the waste inside the furnace can be ensured. Furthermore, the combustion process is relatively complete, and the thermal reduction phenomenon of the bottom ash gradually decreases.

Analysis of the grate furnace type incinerator technology reveals that mechanical grate incinerators have relatively high initial investment, operation, and maintenance costs. Additionally, the wear and corrosion of the grate bars are relatively severe. Therefore, during the selection of waste treatment technology, a systematic analysis of the advantages and disadvantages of this technology is necessary to ensure the safety and efficiency of waste disposal.

2.2 Fluidized Bed Incinerator Technology Analysis

In the application of fluidized bed incineration technology, its combustion principle primarily relies on fluidization technology to burn waste, utilizing sand for safe disposal. This achieves the ultimate goals of uniform heat transfer and complete combustion for the MSW incineration medium. During the waste incineration process, air is injected from the bottom of the fluidized bed, causing reasonable agitation of the sand medium, thereby fluidizing the waste.

Through the application of fluidized bed incinerator technology, the high-temperature resistance characteristics of the lower furnace arrangement can be fully guaranteed. Furthermore, the system plate is equipped with heat-carrying inert particles. While air is distributed under the bed, these inert particles become fluidized (boiling state), forming the fluidized bed section. During the fluidized bed waste incineration process, the waste needs to be crushed to achieve a certain particle size. Moreover, through short-duration fluidized incineration, it can be processed within a short time aided by combustion air, thus forming the rationality of the fluidized bed incinerator.

The efficiency of the fluidized bed combustion furnace is relatively high, and the unburned material rejection rate is only 1%. During combustion inside the furnace, there are no mechanical moving parts within the furnace, and the durability is relatively good, which can extend the service life of the machinery.

The fluidized bed incinerator primarily relies on air for waste treatment and combustion. It imposes particle size requirements on the waste fed into the furnace. Typically, the particle size of the incoming waste should not exceed 50mm. Large, dense particles will fall directly to the furnace bottom, achieving the ultimate goal of complete combustion. The boiling state of the waste inside the furnace entirely depends on large-volume, high-pressure air, leading to problems of high electricity consumption and large amounts of ash production. This imposes a certain load on the downstream flue gas purification system.

2.3 Rotary Kiln Incinerator Technology Analysis

In the application of rotary kiln incineration technology, its combustion technology primarily adopts a two-stage combustion process. The primary stage (first combustion chamber) employs a horizontal cylindrical combustion chamber similar to a cement kiln, rotating at a constant speed to achieve the ultimate goal of agitating the waste. After the waste is burned in the first combustion chamber, it directly enters the second combustion chamber. Exhaust gases generated in the first combustion chamber, if containing organic compounds, need to be directed into the second combustion chamber. There, complete combustion is achieved using auxiliary fuel oil or excess combustion-supporting air.

During the treatment in the first combustion chamber, variations in rotational speed lead to separate processing of bottom ash and fly ash, affecting the waste's residence time in the kiln. Simultaneously, it applies strong mechanical collisions to the waste in the high-temperature air, achieving effective treatment of combustible materials in the waste. During the application of rotary kiln incineration technology, both advantages and disadvantageous factors exist.

The adaptability of rotary kiln incineration technology is relatively broad. During waste treatment, the rotational speed of the rotary kiln can be adjusted, thereby regulating the waste's residence time. Simultaneously, due to the operational state involving mechanical motion of the system, thorough mixing of the waste can be achieved, enhancing the overall efficiency of waste treatment.

During the operation of the rotary kiln incinerator, its combustion requires excess air, leading to lower operating efficiency of the entire system. The waste processing capacity is not large, and combustion issues cannot be effectively controlled, necessitating auxiliary fuel to achieve combustion objectives. Spherical solid waste is prone to rolling within the rotary kiln and is not easy to burn completely. Furthermore, during waste treatment, there is a relatively high amount of entrained particles in the flue gas. Also, when treating sludge waste, slagging phenomena are prone to occur.

In summary, during the current stage of waste treatment, it is necessary to conduct a systematic analysis of the waste incineration situation to optimize the selection of incinerator type technology, achieve the ultimate goal of effective waste disposal, and provide stable support for environmental optimization.

3 Concluding Remarks

In summary, during the current application of waste incinerator technology, it is necessary to recognize the current status of waste treatment, achieve stable waste combustion without adding auxiliary fuel, and then optimize waste processing through the analysis of the characteristics of mechanical grate furnaces. Moreover, in waste treatment using different incinerator types, the optimized application of technology can ensure the completeness and reliability of waste treatment technology. Through the optimized processing of large-capacity waste, waste treatment efficiency can be improved, and the stable operation of the system can be guaranteed.