How Incinerators Work

The application and development of garbage incineration technology in foreign countries has a history of several decades. The more mature furnace types include pulse grate incinerator, mechanical grate incinerator, fluidized bed incinerator, rotary incinerator and CAO incinerator. The following is a brief introduction to these furnace types.
Mechanical grate incinerator
Working principle: The garbage enters the downward-inclined grate through the feed hopper (the grate is divided into drying area, combustion area and burnout area). Due to the staggered movement between the grates, the garbage is pushed downward, so that the garbage passes through each area on the grate in turn (when the garbage enters from one area to another, it plays a big role of turning over) until it is burned out and discharged from the furnace. The combustion air enters from the bottom of the grate and mixes with the garbage; the high-temperature flue gas generates hot steam through the heating surface of the boiler, and the flue gas is also cooled. Finally, the flue gas is treated by the flue gas treatment device and discharged.
Features: The material requirements and processing accuracy requirements of the grate are high, and the contact surface between the grates is required to be quite smooth and the gap between the rows is quite small. In addition, the mechanical structure is complex, the damage rate is high, and the maintenance volume is large. The high cost of grate furnace construction and maintenance makes it difficult to promote and apply in China.
Fluidized bed incinerator
Working principle: The furnace body is composed of a porous distribution plate. A large amount of quartz sand is added to the furnace, and the quartz sand is heated to above 600℃. Hot air above 200℃ is blown into the bottom of the furnace to make the hot sand boil, and then the garbage is put in. The garbage boils with the hot sand, and the garbage is quickly dried, ignited, and burned. The unburned garbage has a lighter specific gravity and continues to boil and burn. The burnt garbage has a larger specific gravity and falls to the bottom of the furnace. After water cooling, the coarse slag and fine slag are sent out of the factory by sorting equipment, and a small amount of medium slag and quartz sand are sent back to the furnace through the lifting equipment for continued use.
Features: The fluidized bed burns fully and the combustion control in the furnace is better, but the amount of dust in the flue gas is large, the operation is complicated, the operating cost is high, the fuel particle size uniformity requirements are high, and a high-power crushing device is required. Quartz sand causes serious wear on the equipment and the equipment maintenance is large.
Rotary incinerator
Working principle: The rotary incinerator is arranged along the furnace body with cooling water pipes or refractory materials, and the furnace body is placed horizontally and slightly tilted. Through the continuous operation of the furnace body, the garbage in the furnace body is fully burned, and at the same time moves in the direction of the furnace body until it is burned out and discharged from the furnace body.
Features: High equipment utilization rate, low carbon content in ash, low excess air volume, and low harmful gas emissions. However, combustion is not easy to control, and it is difficult to burn when the calorific value of garbage is low.
CAO incinerator
Working principle: The garbage is transported to the storage pit and enters the biochemical treatment tank. It is dehydrated under the action of microorganisms, so that natural organic matter (kitchen waste, leaves, grass, etc.) is decomposed into powder. Other solids, including synthetic organic matter such as plastic rubber and inorganic matter in garbage, cannot be decomposed and powdered. After screening, the waste that cannot be powdered enters the first combustion chamber (temperature is 600℃) first, and the combustible gas generated enters the second combustion chamber, and the non-combustible and non-pyrolyzable components are discharged in the first combustion chamber in the form of ash. The temperature of the second chamber is controlled at 860℃ for combustion, and the high-temperature flue gas heats the boiler to produce steam. After being treated, the flue gas is discharged to the atmosphere through the chimney. The metallic glass will not oxidize or melt in the first combustion chamber and can be sorted and recovered in the ash.
Features: Useful substances in the garbage can be recycled; but the processing capacity of a single incinerator is small and the processing time is long. The maximum daily processing capacity of a single furnace is 150 tons. Since the residence time of the flue gas at above 850℃ is difficult to exceed 1 second, the content of dioxins in the flue gas is high, and it is difficult to meet environmental protection standards. [5]
Pulse-throwing grate incinerator
Working principle: The garbage is fed into the drying bed of the incinerator through the automatic feeding unit for drying, and then fed into the first-level grate. It is volatilized and cracked at high temperature on the grate. The grate is thrown under the impetus of the pulse air power device, and the garbage is thrown into the next level of grate step by step. At this time, the high molecular weight substances are cracked and other substances are burned. This continues until it is finally burned out and enters the ash pit, and is discharged by the automatic slag removal device. The combustion air is injected from the air holes on the grate and mixed with the garbage for combustion, while the garbage is suspended in the air. The volatilized and cracked substances enter the second-stage combustion chamber for further cracking and combustion, and the unburned flue gas enters the third-stage combustion chamber for complete combustion; the high-temperature flue gas heats the steam through the boiler heating surface, and the flue gas is discharged after cooling.
Its advantages are:
(1) A wide range of garbage can be processed. It can process industrial garbage, domestic garbage, hospital garbage, waste rubber tires, etc.
(2) High combustion thermal efficiency. The normal combustion thermal efficiency is more than 80%, and even for domestic garbage with a large amount of water, the combustion thermal efficiency is more than 70%.
(3) Low operation and maintenance costs. Due to the adoption of many special designs and a high level of automation control, there are fewer operators (including ash removal personnel, only two people are required for one furnace), and the maintenance workload is also less.
(4) High reliability. After nearly 20 years of operation, it has been shown that the failure rate of this incinerator is very low, with an annual operation of more than 8,000 hours and a general utilization rate of more than 95%.
(5) High emission control level Due to the use of secondary flue gas re-combustion and advanced flue gas treatment equipment, the flue gas is fully treated. After long-term testing, the CO content in the flue gas emissions is 1-10 PPM, the HC content is 2-3 PPM, and the NOx content is 35 PPM, which fully meets the European and American emission standards. When the flue gas burns in the second and third stage combustion chambers, the temperature reaches 1000℃, and the residence time is more than 2 seconds, which can basically decompose dioxins. The dioxin content in the flue gas is 0.04 ng/m3, which is much lower than the European and American standard of 0.1 ng/m3.
(6) The grate has a self-cleaning function under the purge of compressed air.