K2O · 23CaO · 12SiO2 (KC23S12), Na2O · 8CaO · 3A12O3 (NC8A3), K2SO4, Na2SO4, K2O · 8CaO · 3A12O3, etc.

They enter the kiln together with the raw meal sedimentation, forming a circulation and enrichment process between the preheater and the kiln.

However, the SM value is too low, the clinker strength is low, and it is easy to form circles and large blocks in the kiln, making operation difficult.

2、 In the precalciner kiln system, the circulation and enrichment of alkali, sulfur, and chlorine are accompanied by two processes, one called “internal circulation” and the other called “external circulation”.

On the other hand, it is related to the reciprocating circulation of alkali, chlorine, and sulfur in the calcination system.

When the silicon and aluminum ratios are low, and the temperature control of the calciner is high, resulting in high decomposition rate, excessive liquid content, and premature occurrence of raw meal entering the kiln.

Although it is beneficial to the formation of mineral A, the sintering range in the kiln is narrow, which is prone to block formation in the kiln, which is unfavorable for calcination and difficult to master; It is also known that when the silicon content (SM) decreases and the liquid content increases, it is beneficial to the combustibility and operation of the clinker.

Once the balance is broken, abnormal kiln skin will form.

It is precisely this type of batching that meets the inherent conditions of caking, egg formation, and long and thick kiln skin formation in the kiln, coupled with issues such as inaccurate accuracy of metering equipment, design defects in the batching silo, and poor fluidity of material blanking that interfere with the accuracy of the metering equipment, The kiln entry rate fluctuates greatly, fluctuating from high to low, resulting in continuous low and high kiln entry rate values KH and SM.

Alkali chloride is more volatile than alkali sulfate.

1、 Cause analysis: The inducement for the change of kiln skin in the kiln is the change of liquid phase quantity, that is, the rationality of the three ratio values and the content of harmful components.

When the sulfuric acid and chlorinated alkali in the normal kiln gas condense, they will settle down in a molten state and form cohesive substances together with the incoming materials and dust in the kiln.

will be retained in the clinker.
.

The abnormally long and thick distribution of the auxiliary kiln skin has led to poor ventilation in the kiln, reduced production, and frequent return of materials at the kiln end, which seriously affects the quality of clinker production and the smooth, safe, and stable operation of the kiln.

According to the definition of the three ratio value of cement clinker, we know that the aluminum ratio (IM) is too low and the liquid viscosity is low.

The presence of chloride ions will promote the volatilization of alkali.

The stability of the auxiliary kiln skin is very poor, and will fluctuate with changes in raw material composition, liquid content, harmful components, and other factors.

The amount of circulation is related to the volatilization coefficient.

“We know that alkali, Cl -, and SO3 in the system exist in the form of salts.

Due to the special nature of the carbide slag production line, and in order to improve various factors such as clinker granulation and cement adaptability, after years of production experience, it has been concluded that the three rate values are KH: 0.910, SM: 2.10, IM: 1.30.

At 1450 ℃, the volatilization rate of alkali chloride is almost 99.9%, so the content of chloride ions in cement clinker is very low.

The volatilization rate of sulfur and alkali is related to the residence time in the high-temperature zone and the physical form of the material.

The content of alkali, chlorine, and sulfur in the crust is higher than that in the raw meal and clinker crusts, On the one hand, due to the influence of upstream acetylene process conditions and the selection of surrounding raw materials, the alkali, CI -, and SO3 content of raw materials entering the kiln is much higher than that of normal enterprises.

Due to the formation of liquid phase on the material surface, low surface tension, and high viscosity, under the action of centrifugal force, It is easy to bond with the refractory brick surface or the formed “kiln skin” surface to form a kiln skin, further promoting the thickening of the kiln skin.

Normally, the auxiliary kiln skin is only a thin layer, with a thickness of ≤ 70mm and a maximum thickness of no more than 100mm.

It protects the lining of the firing belt from direct contact with flame and high-temperature materials, reducing the chemical erosion, wear, and high-temperature damage of flame and materials to the lining, thereby extending the service life of the lining; The kiln skin also acts as an insulating layer, thickening the kiln lining at high temperatures, thereby reducing heat loss on the surface of the kiln barrel and improving the thermal efficiency of the kiln.

The 36m~48m auxiliary kiln shell was relatively thin (80mm~200mm), the 48m~64m kiln shell was relatively thick (200mm~300mm), and the 48m~64m cylinder temperature displayed a minimum of 87 ℃.

After maintenance, it was learned from the kiln shell scanner display that there were frequent abnormalities in the kiln tail auxiliary kiln shell.

However, why did the harmful components such as alkali, sulfur, and chlorine originally condense in the preheater system in the precalciner kiln system, and then run to the kiln end for recycling and enrichment, resulting in abnormalities in the kiln end auxiliary kiln skin and kiln end material return.

The higher the sulfur alkali ratio, the higher the volatilization coefficient.

We have conducted a preliminary analysis of the abnormal kiln skin and taken a series of measures to achieve certain results.

This liquid phase material film formed on the raw meal particles,”, It can hinder the flow of raw meal particles, and in severe cases, it can cause backflow.

The compounds of alkali, chlorine, and sulfur that are brought into the system from raw meal gradually evaporate into a gaseous state in the high-temperature zone of the kiln.

Generally speaking, the firing zone kiln skin is the main kiln skin, and we call the exothermic reaction zone kiln skin after the transition zone the auxiliary kiln skin.

Kiln skin refers to the layer of clinker attached to the surface of the fired belt kiln lining for sintering.

2500t/d single series three-level carbide slag production line, with a rotary kiln specification of Φ 4.3m × 60m, decomposition furnace specification: Φ 5800mm+ Φ 4300mm, with an annual average daily output of 2640t/d.

The secondary causes are still attributed to operational mismatches and incomplete combustion of pulverized coal.

The so-called internal circulation refers to the circulation and enrichment process between the preheater and the kiln in which alkali, sulfur, and chlorine volatilize from the raw meal and fuel at a high temperature zone in the kiln, and when they reach the lower temperature area of the lowest primary preheater in the kiln system, they are immediately condensed on the raw meal at a lower temperature.

The volatilization coefficient of sulfur is affected by the sulfur alkali ratio.

Lifting Anchor

What we understand is that the order of volatilization of alkali, Cl -, and SO3 is first the hydroxide of the alkali, then the chloride of the alkali, and finally the sulfate of the alkali.