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Factors affecting decomposition rate of preheater system

As the key equipment of cement clinker firing system, the quality of pre-decomposition system directly affects the output and quality of kiln.There are many factors that affect the decomposition rate of the preheater system.this paper discusses some methods to improve the decomposition rate of the preheater from several parts of the preheater system.

As cement clinker burning process and the level of production technology constantly improve and perfect, preheater precalcining system of the preheater system of the bearing with preheating, gas-solid separation materials, evaporation materials, part of the carbonate decomposition and a series of physical and chemical process of key equipment is also in constant development and progress, the maximum heat transfer as far as possible, the lowest flow resistance, high separation efficiency are ideal goals of preheater precalcining system.


1. Basic composition of pre-decomposition system of kiln tail

The kiln tail predecomposition system is mainly composed of cyclone preheater and decomposing furnace.Specifically, it includes cyclone tube, decomposing furnace, connecting air pipe, discharging pipe and its accessories, feeding box, flap valve, blowing plug device, etc. They play a very important role in improving the decomposing rate of the preheater system.

2. Factors affecting the decomposition rate of the preheater system


2.1 influence of cyclone preheater on decomposition rate

The task of cyclone preheater in the pre-decomposition system of kiln tail is to make full use of a large amount of heat energy discharged from the exhaust gas of kiln tail to heat and raise temperature of raw material powder, and feed it into the decomposition furnace for the next suspended carbonate decomposition after the completion of raw material drying, clay mineral dehydration and partial mineral decomposition.Therefore, the following measures can be taken to improve the decomposition efficiency of raw materials by accelerating the heat transfer rate of materials and hot air flow:

(1) appropriately increase the exhaust air of the system.

For the cyclone preheater, the exhaust air rate not only affects the complete combustion degree of the fuel, but also affects the suspension dispersion degree of the material in the preheater.Appropriately increasing the exhaust air at the end of the kiln during operation can improve the calcining condition in the kiln, increase the wind speed of the preheater system, strengthen the suspension and dispersion of materials, speed up the heat exchange rate, and thus improve the decomposition rate of raw materials into the kiln.

(2) try to avoid system air leakage.

Preheater system because most of the five level cyclone preheater is made on the spot, the processing quality is poor, especially the pipe connection flange, preheater manhole door, observation hole, material hole and other places are not tightly sealed, resulting in obvious air leakage.Plus preheater cyclone tube, smoke chamber on the blow plug compressed air often open, reduce the temperature of hot air flow.Therefore, in the production process, in addition to strengthening the sealing measures of all parts of the system, under the normal and stable pressure and temperature of the system, the compressed air should be blown and blocked as little as possible to minimize the chance of outside cold air infiltration.

(3) properly adjust the flap valve.

The flap valve (air lock valve) on the preheater's blanking pipe plays an important role in air lock and blanking.If the flap valve weight of torque and load torque is not balance will appear two situations: the former significantly greater than the latter, the flap valve is not easy to start, until the board broken material accumulation to a certain extent on the moment balance when suddenly greatly open, and open for a long time, cause material on and off, to form a smooth dough into shares into the next level of preheater, cause less material dispersion, uneven heating, both affect the heat transfer effect, easy cause local overheating, produce product of leather.When the former is equal to or less than the latter, the flap valve is prone to open and open, causing serious internal air leakage in the preheater, which causes the material to fly twice, and causes the hot air flow in the heat exchange pipeline to enter the cyclone tube through the bottom of the superior cyclone tube without heat exchange of the same material, causing unnecessary heat loss and reducing heat exchange efficiency.In order to avoid the above situation, the weight hammer of the flap valve should be adjusted correctly according to the installation position of the flap valve and the direction of the blanking tube, so that the weight hammer closing moment is slightly larger than the bearing closing moment. In this way, the barycenter line displacement of the flap valve during operation is small, and the blanking can be guaranteed to be even when working, the wind lock performance is good, giving full play to the heat transfer effect of the preheater.

(4) reasonably set up the spreading device,

so that when raw material powder enters the heat exchange pipeline, it can be rapidly dispersed, mixed and evenly distributed in the hot air flow, and strengthen the function of dispersion and evenly distributed, so as to increase the solid heat exchange area of the atmosphere.

2.2 influence of decomposing furnace on decomposing rate

The main function of the decomposing furnace is to make the exothermal process of fuel combustion and the heat-absorbing process of the decomposition of raw material carbonate be carried out very quickly in the suspended or fluidized state, so as to ensure a high decomposition rate. The raw material after pre-decomposition has been decomposed by 90% ~ 95% after entering the decomposing furnace and being decomposed into the kiln.

Temperature plays a decisive role in the decomposition rate of calcium carbonate in raw materials.The temperature of decomposing furnace depends on the exothermic rate of fuel combustion and the endothermic rate of raw material decomposition.According to the study, at 720°C, the decomposition rate of calcium carbonate in raw cement requires about 136s to reach 80%, at 900°C, it requires about 4s to reach 80%, and at 1000°C, it takes only 1.1s to reach 80%.As can be seen from figure 2, when the average temperature in the furnace is above 950°C, the decomposition rate of calcium carbonate can reach more than 90%.Therefore,

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