It consists of a vertical vessel lined with refractory materials and inert particles (usually silica sand). The air enters the furnace through the ventilation device at the bottom of the incinerator. The vertically rising air flow blows the particles in the furnace and keeps them in the flow The state of fluidization has the characteristics of fluid, so it is called fluidized bed. The combustion principle of the fluidized bed incinerator is to achieve the purpose of complete combustion through the uniform heat transfer and heat storage effect of the sand medium, because the pores provided between the medium are narrow
It is too small to accept larger particles, so if you are dealing with solid waste, you must first break it into small particles to facilitate the reaction. The combustion-supporting air is mostly sent from the bottom, and the furnace can be divided into grid area, bubble area, bed surface area and freeboard area. The upward airflow velocity controls the degree of particle fluidization. When the airflow velocity is too large, the medium will be taken into the air pollution control system by the upward airflow. A cyclone dust collector can be installed to capture the large particle medium and return it to the furnace. The air pollution control system usually only needs to install an electrostatic dust collector or a filter bag dust collector to remove suspended particles. Add some lime powder or other alkaline substances in the feed port, the acid gas can be directly removed in the fluidized bed, which is another advantage of the fluidized bed. There are five types of fluidized bed that can be used to treat waste: bubble bed, circulating bed, multiple bed, spouted bed and pressure bed. The first two have been commercialized, and the latter three are still in the research and development stage. gas
Foam beds are mostly used to treat municipal waste and sludge, and circulating beds are mostly used to treat hazardous industrial waste. The bubble bed is to put inert medium (such as quartz sand) that does not react into the bottom of the reaction tank. Through the air supply of the air box (combustion air) and the ignition of the burner, the medium can be gradually expanded and heated. The combustion temperature can be maintained at a lower temperature, so the nitrogen oxide production is also lower. At the same time, if lime powder is added during the feeding, the acid gas can be directly removed during the incineration process, so the incineration process also completes the acid gas washing work. Generally, the temperature range of incineration is kept at 400-980 ℃, and the apparent gas flow rate of the bubble bed is about
At 1 ～ 3m / s, some medium particles will be blown out of the freeboard area. In order to reduce the amount of medium replenishment, a cyclone dust collector can be installed outside to capture the medium with large particles. The media may gradually wear out during operation and be discharged from the bottom ash, or be taken into the fly ash and enter the air pollution control system. Since the medium in the fluidized bed is in a suspended state, the gas and solid are fully mixed and contacted, and the temperature of the entire furnace combustion section is fairly uniform; some heat exchange tubes can be installed in the bubble area, and some are in the freeboard area; With the vortex fluidized bed, there is a sand screen conveyor and sand circulation conveyor belt in the bottom discharge area, which can discharge larger particles of sand and return it to the furnace through an inclined riser. Heat exchange tubes can also be installed in the bubble zone to preheat the combustion air. Like the rotary kiln, the fluidized bed has no moving parts inside the furnace, so the friction is low. The grille area, bubble area, and bed surface area provide a dry and burning environment. After organic volatile substances enter the exhaust gas; they can be burned after the freeboard area is completed, so the freeboard area functions like a secondary combustion chamber.
In many places in Japan, vortex bubble bed fluidized bed incinerators are used to incinerate municipal waste. The principle of this type of fluidized bed incineration is to take advantage of the good heat storage and heat transfer characteristics of the sand medium. Combustion-supporting air is generally sent from the air box under the sand bed to the sand bed from the bottom up, which expands the sand bed upwards. It requires a longer residence time and agitation degree, but the design of the furnace wall around the zigzag shape makes the rising air collide with the zigzag part and form a vortex downward, which greatly enhances the effect of disturbance. If lime can be added during feeding, the fluidized bed itself becomes a good acid gas scrubber, so the exhaust gas only needs to remove suspended particles. Exhaust gas can be led to the waste heat recovery boiler or cooling tower downstream, and then enter the electrostatic precipitator to remove particulate pollutants. Steam can also be sent to turbine generators to generate electricity. After the bottom ash is discharged, it can be recovered by vibrating screen and magnetic separator, and then mixed with fly ash for solidification treatment.
The advantages of the fluidized bed are: high incineration efficiency, simple design, flexibility in starting and stopping the furnace during operation, and low investment cost. However, most of the fluidized bed devices usually only accept certain specific wastes with relatively simple properties. Different solid wastes will interfere with the operation or damage the equipment; due to the fast burning speed, when the amount of input materials is uneven, it is easy to generate CO , Temperature control in the furnace is more difficult. In addition to the above-mentioned commonly used basic furnace types, incinerators for processing industrial waste include: multi-chamber furnaces, liquid injection furnaces, smoke furnaces, multi-combustion furnaces, cyclone furnaces, spiral combustion furnaces, marine incinerators and other small-scale incineration furnace.
