Comprehensive study on heat transfer and pyrolysis of materials in rotary kiln


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Comprehensive study on heat transfer and pyrolysis of materials in rotary kiln

The research on pyrolysis process of materials in different stages is more and more abundant. At the same time, because of the complexity of materials and the chemical reactions in the pyrolysis process, the mechanism of different types of products can not be determined. Because the research on the pyrolysis mechanism of material flow is still in the aspect of pyrolysis reaction, therefore, it is necessary to strengthen the research on the pyrolysis mechanism of materials Rotary kiln It is of great significance to study the heat transfer and pyrolysis of the composite.

 Rotary kiln

1、 Heat transfer in rotary kiln

Rotary kiln has a high position in the application, such as in the calcination or drying of cement, limestone and other materials. At the same time, due to the differences between uses, drying or heating methods are usually used in the process of rotary kiln rotation and movement, so as to make the materials can be absorbed in the rotary kiln Sufficient heat and heat exchange reaction are important aspects of rotary kiln design and motion engineering.

Generally, there are many ways of heat transfer in rotary kiln, that is, the heat transfer between the wall covered by materials and the material bed, the convection heat transfer with unstable heat conduction state, and the comprehensive heat transfer process of contact heat transfer and radiation heat transfer at the interface.

Compared with other types of fixed windows or moving beds, the heat transfer formed in the rotary kiln is different. As mentioned above, there is a very close relationship between the movement state of materials in the rotary kiln and the conversion. Collapse and rolling bed state are common in practical application. In this process, the material will have different types of division in the movement process of the transverse interface.

 Rotary kiln

2、 Analysis of flow and pyrolysis mechanism in rotary kiln

The composition of rotary kiln cement, limestone and other materials is complex, and the formula is diverse, including dozens of chemical elements. Taking a common material as the research object, through the analysis, it can be seen that the components in the material are rubber compounding oil, and the main materials are raw rubber and carbon black. Because of its complex composition, the mechanism of flow, heat transfer and pyrolysis in the cellar is relatively complex. Generally, the chemical reaction of carbon black in the material composition does not appear at a reasonable temperature, and its pyrolysis reaction is mainly the secondary reaction with compound oil, rubber and other substances or hydrocarbons. When the temperature range of the material is gradually expanded and the temperature is obviously increased, the polymer organic matter in the material will appear obvious cracking reaction, mainly pyrolysis gas and pyrolysis oil, which are small molecular substances. When the temperature is higher, the cracked liquid material will be endothermic and phase change, and then produce material bubbles to completely separate it from the material particles. In this process, there will be a secondary reaction, namely pyrolysis oil reaction, which aims at the intervention effect of volatile substances.

The factors affecting the flow and heat transfer of materials in rotary kiln mainly include the following points:

(1) Heat transfer effect of materials and surrounding materials. According to the above analysis of the influence on the transmission of the material particles inside the rotary kiln and the heat transfer analysis of the particles around the materials, it can be seen that the heat exchange between the materials and the kiln wall, and between the materials and the particles in the bed.

(2) The heat exchange inside the particle itself.

(3) The thermal effect of tire pyrolysis reaction, kinetic energy parameters of tire pyrolysis reaction.

(4) The evaporation phase transition occurs when the pyrolysis volatile products escape from the bed.

(5) Second reaction of pyrolysis volatile products.

(6) The properties of materials produced by pyrolysis are different.

Combined with the pyrolysis mechanism analysis and the flow and heat transfer model of cement, limestone and other materials in the rotary kiln, the specific process of thermal decomposition in the rotary kiln can be tested and analyzed. The rotary kiln is heated by electric furnace outside the kiln, and the heat can be effectively transferred to the kiln for material and gas heat treatment.

It should be noted that the rapid pyrolysis reaction at the kiln body makes the material temperature rise rate decrease effectively, which is directly related to the overall heating speed and material rotation of the system.

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