What are some causes of preheater clogging?

Date: 2019-07-18 Views:

There are many and complicated factors causing the blockage, so it is necessary to carefully analyze and study the process, raw combustion materials, equipment, thermal engineering system, operation and management.According to the production experience of some factories, the main causes of skin clogging are as follows.
 

1. Skin clogging


The skin is the high temperature material in the smoke chamber, the rise pipeline, all levels (mainly for five, four levels) on the inner wall of the cyclone tube cone bonding layer by layer hard skin, serious place is a circle - shaped shrinkage mouth.It hinders the normal operation of the materials, and makes the bonding and melting alternate, gradually increasing the quantity and thickness of the cortex, affecting the ventilation in the kiln, changing the running speed and direction of the materials and air flow in the preheater, and finally leading to blockage.There are three main reasons for this phenomenon:
 

(1) influence of returning ash


Preheater bag dust collecting materials (including the humidifying tower) closed down, high-temperature physical and chemical reaction, have this kind of material to enter the preheater, it is easy to cause the material decomposition, as early as possible in advance in the liquid phase, too late to innovation, form a molten state within the preheater, adhesion on the cyclone cylinder wall, form a crust, serious when cause congestion.
 

(2) the influence of harmful elements


Harmful elements in the original fuel a high content of K, Na, Cl, S, a lot of alkali will be from burning high volatile and other components in the gas phase reaction, first react with chlorine and sulfur dioxide, along with the air preheater system of to, after temperature lowering, sulfate and chloride in the shape of the condensation on the raw material.The precipitate appears at lower temperatures in a molten phase, forming a fine melt, followed by consolidation of solid particles.
 

(3) local high temperature causes skin blockage


Local high temperature of kiln end is the key factor to form skin.If local high temperature is generated in the kiln tail system, on the one hand, the volatilization and condensation cycle of harmful components in raw materials and fuels will be promoted, and the area of internal cycle will be further expanded.In addition, the liquid phase may occur in advance, the raw material adhesion in the lining of the inner wall and form a skin.
 

2. Blockage caused by air leakage


Air leakage is one of the main obstacles to the decomposition kiln outside the kiln. The air leakage of the pre-decomposition system not only reduces the separation efficiency of the cyclone cylinder and increases the heat consumption, but also causes the clogging of the preheater system.When the preheater leaks into the cold air, the material temperature and decomposition rate will decrease. In order to maintain the production system, the exhaust gas quantity will increase and the cycle load will increase.And cold air and hot materials contact, it is easy to condense hot materials and adhere to the inner wall of the system and produce skin;In addition, the coal powder taken to the end of kiln or preheater meets fresh cold air, and the combustion speed is accelerated, resulting in local high temperature and skin formation.At the same time, due to the imbalance of the proportion of wind used in kiln and furnace, the poor ventilation in the kiln leads to the frequent formation of circles and balls in the kiln.

3. Blockage caused by improper operation

 

(1) untimely feeding


When the decomposition furnace is ignited and the feeding temperature (900℃) is reached, the feeding must be timely, otherwise the system temperature will be high, and therefore the amount of material is small, more likely to cause skin.
 

(2) improper air discharge when the kiln is started and stopped.


When the material and kiln need to be stopped for some reason, the exhaust air volume should not be greatly reduced, otherwise it is easy for the material to deposit in the pipe (mainly in the horizontal pipe) due to too small wind speed, resulting in accumulation.When the kiln starts feeding again, the air exhaust volume is too small, and the accumulated materials cannot be taken away smoothly. With the continuous increase of the feeding volume, the material inside the pipe accumulates more and more, which will lead to the accumulation and blockage in serious cases.
 

(3) improper control of exhaust air volume.


When the exhaust air volume is too large, the airflow speed of the pre-decomposition system is high, and the centrifugal force of the material thrown to the wall in the preheater is large, the material rotates and falls down along the wall, and the material contacts with the high-temperature airflow for a relatively long time, which is easy to paste on the inner wall of the preheater, forming a layer covering from loose to solid, causing blockage.

When the exhaust air volume is too small, the air flow speed decreases, making it difficult for the material group to disperse, forming the collapse material blockage, and the material is easy to stay in the horizontal connection pipe, resulting in the horizontal pipe blockage.

 

(4) uneven distribution of air volume in kilns and furnaces and uncoordinated operation.


Improper operation and regulation, improper opening of shrinkage gate at the end of the kiln and air gate in the decomposition furnace for three times, easily lead to uneven distribution of air volume in the kiln.If the end shrinkage mouth wind speed is too low, or decomposing furnace inlet wind speed is too low or too

High, will cause the material in the pre-decomposition system skin, shed material, collapse material, pile up until blocking.Kiln and furnace operation can not be both before and after;Poor coordination;One-sided emphasis on ventilation and negative pressure in the kiln;Improper pursuit into the kiln decomposition rate, two fire coordination is not good, also easy to cause high temperature crust, accumulation, collapse, blockage.

 

(5) uncoordinated kiln operation.


The operation of rotary kiln and decomposing furnace cannot be taken into account before and after. The one-sided emphasis on ventilation in the kiln or negative pressure in the system can easily cause high temperature skinning, accumulation, shed material and collapse material blocking the preheater.

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