Circulating Fluidized Bed Waste Incinerator and Refractory Materials

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The circulating fluidized bed waste incinerator is designed based on circulating fluidized bed combustion technology. It has significant advantages for the incineration of waste such as garbage, sludge, and wastewater. The circulating fluidized bed waste incinerator is in line with the economic level of our country and is suitable for treating low-calorific-value waste. It is an environmentally friendly type of incinerator.

Circulating fluidized bed (CFB) incineration is an advanced and environmentally friendly technology for waste disposal. The process involves suspending waste materials in a flow of air or gas within a bed of solid particles, creating a fluidized state. The fluidized bed promotes thorough mixing and combustion of waste, ensuring efficient energy recovery and minimizing emissions.

fluidized bed waste combustion system

Characteristics of Circulating Fluidized Bed Incinerator

Best suited for incinerating low-calorific-value garbage fuel: Due to the presence of a certain amount of bed material in the incinerator, the gas and solid flows are strongly mixed. When garbage enters the furnace, it quickly and fully mixes with the hot quartz sand. The entire process from heating, drying to combustion is completed rapidly. The incinerator has a large heat storage capacity, good ignition conditions, and stable combustion.

Good environmental performance: The combustion temperature of the circulating fluidized bed boiler is controlled between 850-950°C, resulting in low nitrogen oxide emissions. Another important issue in the incineration of waste is the generation of toxic gases such as hydrogen chloride and dioxins. According to scientific experiments conducted by foreign scientists, the conditions for dioxin generation during waste incineration are: combustion temperature below 850°C, uneven combustion temperature in the furnace, incomplete combustion of garbage leading to the generation of many dioxin precursors (CP, CBs), short residence time of flue gas in the furnace, and metal catalysis. The circulating fluidized bed waste incinerator maintains a stable and uniform combustion temperature, extends the residence time of flue gas in the furnace through furnace design, thereby fundamentally reducing the production of harmful gases.

Highest degree of waste reduction, ash can be comprehensively utilized: The circulating fluidized bed incinerator has the highest incineration rate for garbage, and the ash does not contain organic matter and combustibles. The odorless ash can be directly landfilled or comprehensively utilized, and metals in the ash can be recycled.

Good economic benefits, high return on investment: The construction investment of the circulating fluidized bed incinerator is only about one-fifth of imported incinerators, and domestic technology ensures post-construction maintenance at a lower cost than imported equipment. When incinerating low-calorific-value garbage, the circulating fluidized bed incinerator requires less supplementary fuel (coal to garbage weight ratio less than 1:4), resulting in significantly lower operating costs than other incinerators.

Circulating Fluidized Bed Incineration Process

Refractory Materials for Circulating Fluidized Bed Garbage Incinerator

The application of refractory and wear-resistant materials in circulating fluidized bed garbage incinerators is mainly divided into several areas: air chamber, dense phase zone in the furnace bottom, combustion zone, feed port, high-temperature cyclone separator, and return pipe, among others. Different areas should use appropriate refractory and wear-resistant materials based on atmospheric conditions.

In general, regular areas are best suited for refractory bricks, while irregular areas that are difficult to construct can use castables or plastics. The water-cooled air chamber is usually designed as a single-layer wear-resistant structure, and materials can include medium-duty wear-resistant plastics, self-flowing corundum castables, or corundum wear-resistant plastics for the air distribution plate.

For circulating fluidized bed garbage incinerators, there is a significant difference in density between the bed material and garbage. The garbage is mainly concentrated in the dilute phase zone for combustion, where the temperature is relatively low, and wear is more severe. Generally, corundum castables or wear-resistant plastics are used. In this area, under-oxidation combustion occurs, and there is a strong reducing atmosphere, so the Fe₂O₃ content of materials should be strictly controlled to enhance their resistance to CO erosion.

The garbage discharge port and coal drop port are located at the junction of the dense and dilute phase zones, both of which are prone to wear. More wear-resistant materials, such as corundum combined with silicon carbide castables or a mixture of mullite and corundum castables, can be used.

A schematic diagram of a circulating fluidized bed waste incinerator

In the combustion zone, above the charging port, where the flue gas temperature is relatively high, generally above 850°C, wear-resistant and refractory castables with silicon carbide or corundum are suitable.

The furnace outlet and separator inlet are vulnerable components, especially the separator inlet, which can use high-strength wear-resistant castables or silicon carbide bricks. As this is an irregular area, construction methods and experience are particularly important.

The return pipe is also a critical component of the circulating fluidized bed, usually designed as a multi-layer wear-resistant structure. Materials such as high-strength wear-resistant castables, corundum wear-resistant bricks, etc., are used, and the specific construction method is determined based on the pipe diameter.

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