Zinc oxide volatilizing kiln,medical hazardous waste,chemical hazardous waste and urban sludge drying
Solid waste and hazardous waste rotary kiln
With the rapid increase in the amount of hazardous waste, harmless treatment is imperative. Hazardous waste has the characteristics of complex composition, large differences in acidity and alkalinity, and large fluctuations in calorific value, which also causes increasingly severe erosion and damage to refractory castables. The process temperature of rotary kiln hazardous waste treatment is 850-1200℃. The lining of the rotary kiln is in direct contact with the slag, so the erosion resistance, spalling resistance, and wear resistance of the refractory castable are required to be high.
The acidic flue gas and a large amount of active fly ash generated in the rotary kiln enter the secondary combustion chamber. The flue gas is incinerated at a high temperature for the second time under the condition that the auxiliary burner provides a heat source, and the combustion temperature reaches more than 1100℃. In the secondary combustion chamber, combustible components, fly ash particles, and dioxins are incinerated and decomposed, and the reaction is violent. Moreover, when the burner in the secondary combustion chamber is running, the temperature in the surrounding area of the furnace fluctuates frequently. The refractory lining is eroded, slags, and peels off, and cracks are severely damaged.
Products Description
In view of the working conditions of the secondary combustion chamber, the main cause of damage to the refractory castable is the erosion and penetration of ash, which leads to the gradual melting and peeling of the refractory lining. The ash is mainly composed of dicalcium silicate, calcium feldspar, cancryogenite, etc. These ash are mainly fly ash produced by the combustion of hazardous waste, which adheres to the surface of the refractory castable and aggregates, and seriously erodes and penetrates the aluminum-silicon lining material. The reaction forms a large amount of feldspar and nepheline low-melting products, which not only reduces the material's load softening temperature and melting point, but also produces a large amount of volume expansion, resulting in loose structure of the lining material, cracks, and severe thermal peeling under temperature fluctuations.
In order to improve the matrix composition and enhance the slag resistance and spalling resistance of the material, 80 homogenized material, special grade alumina, 97 silicon carbide and other materials were used as the main raw materials, calcium aluminate cement was used as the binder, and appropriate amount of additives were added to prepare silicon carbide corundum castables. After testing, it was found that the inner pores of the refractory castables improved by adding silicon carbide were sharp and there was no obvious erosion and penetration layer, indicating that the material has a strong ability to resist the erosion and penetration of active ash slag.
Compared with oxide materials, non-oxide materials such as silicon carbide not only have good refractoriness, high hardness and good thermal shock resistance, but also silicon carbide materials are not easy to wet and have good corrosion resistance. They also have good inertness in acid and alkali environments and are not easy to react with Si02 and Ca0 in ash slag. Therefore, after adding silicon carbide to improve, the material's thermal shock resistance and resistance to ash slag reaction erosion can be significantly improved, which can effectively inhibit the reaction erosion and penetration of the lining material and the active fly ash, as well as the spalling damage caused by it.
Solid waste and hazardous waste rotary kilns have many advantages in dealing with complex industrial waste and medical waste, such as wide adaptability, stable and reliable operation, convenient management and operation, and simple equipment maintenance. Therefore, they are widely used in the incineration and disposal of hazardous waste internationally. Incineration is a relatively reliable and effective means to achieve harmlessness, reduction and resource utilization of solid and hazardous waste.
Application range: used for various solid and hazardous waste disposal in medical, industrial comprehensive solid and hazardous waste, petroleum, chemical and other industries.
Working Principle
The rotary kiln is equipped with a pusher at the feed port to ensure continuous feeding. The outlet temperature of the rotary kiln is 800~850℃. After the flue gas enters the secondary combustion chamber, secondary air is sprayed tangentially around the secondary combustion chamber, so that a strong vortex field is formed in the secondary combustion chamber, and the combustible components in the flue gas can be fully burned. At the same time, the secondary combustion chamber adopts a unique structural design to make the secondary combustion chamber also have a cyclone dust removal function. The flue gas outlet temperature of the secondary combustion chamber is greater than 1100℃, and the flue gas stays in the high temperature zone for more than 2 seconds, ensuring that the harmful components in the flue gas, including dioxins, are completely decomposed and meet the requirements for the incineration of hazardous waste. Solid (hazardous) waste is fed into the rotary kiln body through the feeding mechanism for high-temperature incineration. After high-temperature incineration, the material is incinerated into high-temperature flue gas and ash. The speed of the rotary kiln can be adjusted. Maintaining a stable slag layer of about 50mm thick can protect the refractory layer. Its operating temperature should be controlled at about 850℃. High-temperature flue gas and ash enter the secondary combustion chamber from the kiln tail, and the incineration ash enters the slag discharger from the kiln tail and is regularly sent to the stabilization/solidification workshop for treatment.
The so-called three wastes refer to waste, waste liquid and waste gas, as well as their mixtures. If these substances are properly handled, they can protect the environment and benefit people's lives. At the same time, some wastes can be reused after treatment, turning waste into treasure. However, secondary pollution should be strictly prevented during incineration, that is, no harmful gases should be released into the air.
Waste incinerators are generally divided into two categories: intermittent and continuous. For example, according to the waste state, it can be divided into solid waste incinerators, liquid waste incinerators, solid and liquid mixed waste incinerators and waste gas incinerators, etc. The operating temperature is generally 1000-1500℃.
Solid waste incinerators are mainly used to treat urban garbage and industrial flammable waste. There are many types of incinerators. For example, Japan has more than a dozen types of incinerators. Japan's large-scale mechanized garbage incinerators are divided into drying area, main combustion area, auxiliary combustion area, air preheater and dust collector. They use heavy oil as fuel and can be automatically controlled and operated. The daily incineration capacity can reach 1,200 tons. After the solid waste is loaded into the furnace, it enters the drying area, main combustion area and auxiliary combustion area in turn with the help of the reciprocating motion of the movable grate until it is burned out; the ash after combustion falls into the slag trough, and the exhaust gas is discharged from the chimney after dust removal. The whole operation is carried out continuously. The refractory materials used in solid waste incinerators should be selected according to the different use locations, properties of waste treatment and operation methods, and they must not react chemically with the gas after waste incineration. At the same time, the refractory materials must have good high temperature strength and thermal shock stability to resist the abrasion of solid waste and thermal stress caused by sudden temperature changes. Generally speaking, the use of refractory bricks or amorphous refractory materials as furnace linings can meet the needs of garbage incinerators.
Urban garbage generally contains 10-60% water and has a low calorific value. Auxiliary fuels must be used to assist combustion during incineration, otherwise it will be difficult to burn out. Recently, the composition of garbage in industrially developed countries has changed, and its calorific value has a tendency to increase, so the working surface of aluminum silicate bricks is severely eroded or slag is produced, which hinders the normal operation of the furnace. In this case, the important parts of the solid waste incinerator lining are generally built with silicon carbide bricks or poured with silicon carbide refractory castables, and good use results have been achieved. However, the use of silicon carbide bricks is not completely without problems, mainly because they are damaged by oxidation, so the performance must be improved to meet the needs of the incinerator.
Liquid waste incinerators are mainly used to treat waste liquids from petrochemical and other departments, so as to reduce the degree of emission pollution and recover by-products for utilization.
Liquid waste is divided into two types: acidic and alkaline. Since waste liquid contains a large amount of water, spray combustion is generally used for incineration, and most of its furnaces are round. In general, the waste liquid nozzle and burner are installed on the top of the furnace, and the waste liquid and fuel are sprayed from top to bottom, mixing and burning; there are also burners placed on the furnace wall, and in a tangential direction with it, when the waste liquid is sprayed from the top of the furnace into the furnace, it is rolled into the flame, rotating and mixing, with a long contact time and high incineration efficiency; in addition, there are also horizontal countercurrent jet incinerators, but the waste liquid is easy to stay on the bottom of the furnace, causing great damage to the lining, so it is rarely used.
The operating temperature of the waste liquid incinerator is generally around 1000℃, and the temperature near the burner and the high-temperature part of the combustion chamber can sometimes reach around 1500℃. At the same time, the waste liquid has a chemical erosion effect on the furnace lining. Therefore, when treating acidic waste liquid, acid-resistant castables or plastics should be selected as furnace linings; when burning alkaline waste liquid, magnesium and magnesium-chromium refractory castables should be used to pour the furnace lining. High-strength refractory castables should be used as furnace linings for easily worn parts of the furnace. Waste gas incinerators are mainly used to treat hydrogen chloride (HC1), carbon monoxide (CO), chlorine (C1) and sulfur dioxide (SO2). Most of the furnaces are horizontal and circular, and combustion-supporting burners are installed at the same time to ensure that the waste gas is fully burned. The refractory materials used in this furnace are mainly high-alumina refractory castables or refractory plastics, and sometimes aluminum silicate bricks are used for masonry.
The lining thickness of the above-mentioned various incinerators is 300-350 mm. When using refractory bricks for masonry, generally add a layer of insulation board and a layer of lightweight bricks; when using amorphous refractory materials as lining, anchor bricks or metal anchor nails should be placed, first pour lightweight refractory castables with a thickness of 100-150 mm, and then use refractory castables or refractory plastics as working linings with a thickness of 150-200 mm. During construction, various anchors should be installed firmly according to the design size, and pouring should be carried out continuously. If expansion joints are left, fire-blocking bricks should be placed on the back.
There are types of solid-liquid mixed waste incinerators, such as rotary, fluidized bed and multi-layer vertical. Its characteristics are that mixed waste can be incinerated during rotation, boiling or movement, and the treatment effect is better, but the corrosion of the lining is more serious. Better refractory materials should be selected to extend the service life of the lining.
The rotary incinerator is composed of a rotary drum main combustion chamber and a fixed vertical auxiliary combustion chamber. When the mixed waste is loaded into the furnace, the waste rolls along the wall of the drum due to the rotation of the rotary drum, so that it is fully burned. After the incomplete combustion products in the exhaust gas enter the auxiliary combustion chamber, they continue to burn, and the ash falls into the ash hopper.
The inner lining of the main combustion chamber of the rotary incinerator is generally built with dense clay bricks or high-alumina bricks. At present, most of them are lined with high-strength refractory castables. The lining of the auxiliary combustion chamber and the furnace cover is generally poured with high-strength lightweight refractory castables, and the ash hopper is lined with clay refractory castables. When refractory castables and plastics are used as furnace linings, anchor bricks or metal anchor nails must be used to tightly connect the lining with the furnace shell to form a whole to prevent falling off or collapse.
When the fluidized bed incinerator is operated, first load the medium such as river sand or limestone from the medium loading port, then blow hot air to make it in a boiling state, and then load the mixed waste and ignite the burner for incineration. At this time, the waste and the medium are fully mixed and the combustion is relatively complete. It can be seen from this that the working conditions of the porous refractory plate at the bottom of the combustion chamber and the lower furnace wall are relatively poor. They not only have to withstand high temperatures, but also are subject to impact and wear from boiling medium particles and solid waste. Therefore, high-quality refractory materials should be selected.
In general, the bottom of the combustion chamber of the fluidized bed incinerator is a porous plate made of high-strength refractory castables; the lower part of the furnace wall is lined with high-strength refractory castables, and can also be built with high-alumina bricks; the lining of the middle and upper parts of the furnace wall is lining with refractory castables or clay bricks; the lining of the hot air channel is generally poured with lightweight refractory castables.
When the waste contains components such as phenol, aniline and benzene, the lining is severely corroded, so silicon carbide bricks and fused bricks should be used to build the lining, and high-strength refractory castables or phosphate refractory plastics can also be used for on-site pouring. No matter what material is used, attention should be paid to the construction quality, otherwise the service life of the incinerator will be reduced.
In addition, when the waste incinerator is installed and used together with the industrial production kiln, the service life of the lining of the two should be basically the same, otherwise it will affect the normal production.
The selection of refractory materials for hazardous waste incinerators is based on the chemical properties of the refractory materials and the materials with the same or similar properties as the corrosive medium, which is conducive to ensuring sufficient corrosion resistance of the refractory materials. Silicon-aluminum refractory bricks are based on the Al 2 O 3 -SiO 2 binary phase as the basic structure. The main products include silica bricks, quartz glass, clay bricks, high-aluminum refractory bricks, corundum refractory bricks, etc. The mineral composition of high-aluminum refractory bricks is corundum, mullite and glass phase. The refractory bricks are classified according to the Al 2 O 3 content. When the Al 2 O 3 mass fraction is ≥90%, it is a corundum refractory brick. This type of refractory brick is widely used in the lining of hazardous waste incineration rotary kilns.
1) Appropriate apparent porosity. The apparent porosity refers to the ratio of the volume of all open pores on the refractory to the total volume. The higher the apparent porosity, the more open pores it contains, the easier it is for permeable substances to penetrate into the interior of the refractory, and the more serious the erosion. Generally, the porosity needs to be controlled within a low range, but it should be noted that too low porosity will affect the thermal insulation effect. At present, the apparent porosity of domestic refractory bricks is generally controlled at about 20%.
2) Good thermal stability and sufficient load softening temperature. Refractory materials should have sufficient thermal stability and load softening temperature, that is, refractory materials do not soften or melt at high temperatures, and can not lose structural strength or deform and collapse under large loads and other thermal mechanical stresses.
3) Good slag erosion resistance and chemical stability. The clinker liquid phase and molten fuel ash at high temperature in the kiln have strong chemical erosion ability. Therefore, refractory materials must have good slag erosion resistance and chemical stability to reduce the erosion and thinning of the kiln environment and extend the service life of refractory materials
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