How to choose limestone and fuel for light calcium?

The quality of light calcium (precipitated calcium carbonate) depends largely on the quality of the raw limestone . The chemical composition of limestone not only affects the technical quality index of the product, but also has a great influence on the calcination process of limestone.

The quality of light calcium (precipitated calcium carbonate) depends largely on the quality of the raw limestone. The chemical composition of limestone not only affects the technical quality index of the product, but also has a great influence on the calcination process of limestone.

Light calcium carbonate production process flow chart

The calcium carbonate chain produces calcium hydroxide, heavy calcium carbonate, light calcium carbonate, activated calcium carbonate, nano calcium carbonate, and calcium serialized extension products. Mechanically processing natural calcium carbonate minerals to appropriate particle sizes, commonly referred to internationally as heavy calcium carbonate - GCC for short; natural calcium carbonate minerals as raw materials, by calcination, digestion, carbonation and other chemical methods, The crystalline product formed by the precipitation reaction is commonly referred to internationally as light calcium carbonate - PCC for short.

In inorganic industrial products, calcium carbonate production is part of a great, highly versatile chemical products, produced in the industrial production of high quality calcium carbonate of lime (CaO), widely used in metallurgy, building materials, desiccants, environmental treatment Calcium hydroxide Ca(OH)2, also known as slaked lime, is used as an acid neutralizer in the non-ferrous metallurgy and atomic energy industries and is a good binder in building materials.

Requirements for the production of limestone by light calcium

Requirements for the physical properties of limestone produced by the production of precipitated calcium carbonate:

Requirements: The limestone is dense and blocky, the crystal particles are fine and do not recrystallize.

Density: 2.65~2.80g/cm3

Porosity: ≤1%

Mo type hardness: ≥3

Compressive strength: 147.11Mpa

Since limestone is produced in different ages, the crystals formed are different, so the limestone is subjected to a calcination test. Ordovician limestone is generally used, it is best not to use the Permian Period limestone, particularly those containing iron, large-containing magnesium, silicon mine changes, generally can not be selected. In the chemical index, the index of alkali magnesium salt is often an indicator that many people ignore, and almost no one detects it. Actually, this is related to the yield of production, and it is very related to the ability to produce high quality PCC of different crystal forms.

First, stone (limestone) technical requirements:

1. Chemical composition:

The ingredients should be understood and the particle size should be uniform. The composition of the stone varies greatly from place to place. Even at different mining sites in the same mine, the composition of the ore is quite different. The general users need to understand the components of calcium oxide, magnesium oxide, silicon dioxide, and aluminum oxide. The content of iron oxide.

The higher the content of calcium oxide, the better the quality of the stone. Below 50 is a poor quality, 50-52 is a general stone, and above 52 is a good quality. Above 55 is especially good. Generally, the direct grinding of stone is heavy calcium powder. The stone material that has not been tested is judged. Generally, after burning lime, the smaller the crystal, the higher the content of calcium oxide. The content of the stone of 53 is hydrated and the powder is as fine as flour.

In the specific operation, the difference in the content of calcium oxide is different in the firing temperature. The general firing temperature is between 900 and 1100. Because the decomposition temperature of calcium carbonate is high, the higher the content, the higher the temperature required for firing. High, such as 53 stone firing temperature is set at 1080 degrees, 52 stone set at 1050 degrees, and 50 stone set at 950 degrees, each family according to the situation to determine their own operating temperature.

The content of magnesium oxide has the greatest influence on the calcination. The main components in the same stone are calcium oxide and magnesium oxide. The temperature difference between them is relatively large. Generally, the decomposition of calcium oxide begins after the decomposition of magnesium oxide is completed. If the calcium oxide is completely decomposed, the magnesium oxide is burned, and the activity is greatly reduced. Therefore, it is said that the light burning dolomite is actually to ensure the reactivity of the magnesium oxide. The temperature is low, some calcium carbonate is not decomposed, and raw burning is inevitable.

The requirements for magnesium oxide in raw materials are too different due to different uses. The general smelting requirements are not high. Even the indicators of magnesium oxide are not specified. Only the total content of calcium oxide and magnesium oxide is required, and high magnesium for steelmaking is also required. Gray, the required content is greater than 15%, which requires the stone content to exceed 8 percent in order to burn. The higher the magnesium content of the raw materials required for the ash of metal magnesium, the better, generally more than 18%. If it is made of calcium carbide for calcium carbide, the lower the magnesium content in the lime is as good as possible. The general requirement is less than one percent, and the highest can not exceed one or two.

It is the difference between the decomposition temperature of calcium oxide and magnesium oxide, and there are several statements about light burning, re-burning, and dead burning. It should be pointed out that this is for magnesium oxide. In actual operation, their temperature is Stepped requirements are high. Of course, in this process, the decomposition of calcium oxide to the degree of sputum can only be followed by the owner.

2, the requirements of the granularity

Light calcium production process The requirements for shaft kiln calcined stone are 50-150 mm. Most of the vertical kiln is designed according to this particle size. In actual production, some raw materials will have a slightly larger particle size. They mainly use raw materials as much as possible. Especially in my own mine, I want to burn all kinds of particle sizes as much as possible. If the method does not produce a burn-through rate, the product will increase. The correct method is that the maximum can not exceed the minimum of 3 times, that is to say, if the minimum is 30 mm, the maximum can not exceed 90 mm, otherwise the difficulty of operation will increase, and the raw materials are sorted according to different batches. The second time, the effect is much better.

Because of various conditions, the size ratio exceeds three to one. In some kiln, it is commonplace. What should be paid attention to in the operation? Let me talk about the problem of the amount of each ratio. Generally, this problem is easy to ignore. Some kiln did not ignite when the furnace was opened, and the material was hung. Some kiln did not operate at the same temperature in production, and there was no over-burning in the ash, which was suspended or not hung for a while. I can't get it to work normally. This problem has puzzled me for a while. Later I finally figured it out and changed the amount of the scale. If it is a little bigger or smaller, it will not hover. This situation is very easy to solve, but under what circumstances there will be suspending materials, there is no accurate statement, I handle a few suspensions are mostly 30 mm, accounting for one-third, 30-80, accounting for three-thirds one, more than one third 80, jaw crusher further out than the sheet-like material Hammer Crusher out easily hanging garden-type material. In other words, this problem can only be solved after the emergence, there is no way to prevent it. Unless the particle size is acceptable.

The smaller the particle size, the shorter the time required for decomposition, the larger the stone size, and the longer the decomposition takes. If it is a round stone with a diameter of 60 mm, it takes about three hours to decompose completely at 1050 degrees. If the diameter is increased to 100 mm, it takes five hours to fully decompose. In furnaces where the particle size difference is too large, it is well understood that the large particle size of the product tends to have a sandwich.

In production, the particle size of the first stone is related to the utilization factor. In layman's terms, it is related to the speed of the incoming and outgoing materials. The larger the particle size, the other the conditions are unchanged, the slower the speed of the incoming and outgoing materials, that is, the lower the utilization coefficient. The particle size of the second stone is designed to be related to the effective height of the furnace. Theoretically, the larger the particle size, the higher the effective height of the furnace. Third, from the energy consumption, the larger the particle size of the stone, the more coal , the smaller the particle size, the less weight, the less coal is burnt.

Compared with other kiln types, the vertical kiln is not advanced, especially the vertical kiln that burns coal is not as good as the gas-fired kiln. There are not many ways to adjust it during operation. In addition to changing the blast parameters and the speed of the feed and discharge, the stone and The particle size of the fuel is also an important means.

Second, the fuel requirements:

The general shaft kiln uses coke or anthracite as fuel. Due to the cost of coke, most of the anthracite coal is used. It is also useful for bituminous coal close to anthracite, commonly known as semi-anthracite, and coal briquettes made of coke powder or anthracite powder. There are so many indicators that need to be understood in relation to operations.

1, the level of calorific value

The heat consumption of a typical shaft kiln is about 1100 calories per kilogram of finished ash. Each kilogram of ash requires 1.7 kilograms of stone, which means that 450 kilograms of calories per kilogram of stone, such as 6000 kilocalories of coal, Each time the material is loaded with 1.5 tons of stone, the required heat is 1500 × 450 = 675000 kcal, converted to coal is 675000 ¥ 6000 = 112.5 kg of coal, need to pay attention to two conditions, one is that refers to Ten percent of the ash, if the quality requirements of the ash is not very high, you can allocate less points, the other is to direct the coal of no more than 9 percent of the hair, if the volatile content is too high, then the appropriate amount of more points.

2, volatiles

The volatile matter of the general kiln anthracite is about 8 percent. If the volatile content is too low, the combustion is too slow, and the utilization coefficient of the furnace is low, that is, the yield is low. If the discharge is slightly faster, the ash temperature is again It is very high and energy-saving. It is only reasonable to raise the kiln body when designing the stove, but it can't be done normally. The volatile content is too high. It is not good at first. It does not save energy. The flammable gas such as methane, hydrogen, carbon monoxide and other volatile gases actually burns in the furnace. Most of them burn away from the chimney with the exhaust gas. In part, the position at which heat is released is not suitable, so the volatiles play little role in the heat required for preheating and decomposition. It is economically the least costly to use coal with too high volatility. The only advantage is that other If the conditions are the same, the level of the volatiles is basically proportional to the speed of combustion, and the level of the volatiles and the size of the particles absolutely control the length of the calcined zone.

3, the size of the size

The size of the particle size is proportional to the length of the calcined zone. The larger the particle size, the longer the burning time in the furnace, the longer the calcining zone, the smaller the particle size, the shorter the burning time in the furnace, and the shorter the calcining zone. The general ratio of coal and stone is matched before entering the furnace, which means that the amount of heat released by coal combustion is certain. The difference is how long it takes to release it. The time is short and it is easy to form high temperature locally. Burning and agglomerating, the time is long, and it is easy to be low temperature, the decomposition temperature is not enough, and the raw burning is too large. The more advanced furnaces are the length of the designed calcining belt, which matches the amount of ash. The time it takes for the stone to pass through the calcining zone is basically consistent with the time it takes for the particle size to decompose at this temperature. The length and height of the calcined ribbon are substantially relatively stable. The earthen stoves used in the past are mostly burnt coals, which are layer by layer of fabric. The particle size requirements of coal are not strict, but its furnace utilization factor is too low and the energy consumption is too high. The more advanced the furnace, the higher the utilization coefficient, the lower the energy consumption, and the stricter the requirements for raw materials. Sometimes the proportion of powder in coal is large. First, the stone can not be evenly mixed, sometimes it is after the furnace. The stone gaps are drilled together to form a local high temperature. The scattered powder is burned to the lower part of the pre-tropical zone or the upper part of the calcining zone. The heat mainly enters the exhaust gas. If the heat of our coal blending just breaks down the stone, it is there. If the burned place consumes more heat, there will be a place where there is a lack of heat to form a raw burn. In order to ensure that there is no raw roasting, only more coal is blended, which also poses a threat to the lining. Therefore, it is said that the powder in the coal is harmless. Sometimes there are blocks with a large particle size in the coal. They burn in the calcined zone. When the cooling zone is reached, the outer layer of the outer layer has become very small. In the process of falling off the ash, some fall into the complete decomposition. In the finished lime, the exotherm continues, and most of the over-burning in the product is formed in the upper part of the cooling zone, and the proportion formed in the calcined zone is small. There is a powder or a large particle size in the coal, which is not economical or operational. Some lime kiln is equipped with an auxiliary production line for the production of briquette. From the perspective of the use effect, it is worth promoting. Using coal as fuel, the operation is stable, energy consumption can be reduced, and the quality of the product can be improved. The price difference between powdered coal and lump coal is very large across the country, and it is also very economical.

4, the level of ash melting point

Generally, the melting point of anthracite ash is not problematic. A small part of the remaining ash has a too low melting point and is in a paste-like shape in the calcined zone. It is easy to form a wall or agglomerate as the lime moves down gradually. This kind of fuel can't be used. In operation, only lowering the operating temperature can alleviate this situation. Low temperature operation will bring out many unfavorable situations such as slow ash, burning and burning, and coal burning. Without too much consideration, it is to change the coal to solve the problem fundamentally.

5, the height of the fire point

That is, the temperature at which the fuel begins to burn. The lower the ignition temperature, the shorter the pre-tropical zone and the higher the temperature of the exhaust gas. The heat taken away by the exhaust gas is the largest in the heat loss of the furnace. The approximate data is that the heat required per kilogram of lime is about 1050 calories, and 250 calories are required to heat from the normal temperature to the decomposition temperature. It takes 400 calories from the beginning to the complete decomposition. When cooling, it can release 100 calories. In theory, it is enough to burn one kilogram of gray 450 calories. Why is it necessary to match 1050 or even 1100 calories in practice? There is heat loss, including exhaust gas. The volatiles that did not participate in the combustion ran away, the wall of the furnace was scattered, and the ash cooling was not carried away at room temperature. The biggest one is the heat taken away by the exhaust gas, which accounts for about 70% of the total loss. Lowering the temperature of the exhaust gas, it is reasonable from an economic point of view to select coal with a high fire point. Using exhaust gas to generate electricity or boiling water is based on this theory.

5, the size of sulfur

The level of this indicator is not much different in operation, mainly affecting two aspects. First, the exhaust gas equipment is easy to be bad, because the sulfur-containing gas corrodes the pipeline and the fan and other equipment very quickly. Second, the quality of the product has a great impact, because some of the sulfur enters the lime, and some users require that the sulfur should not exceed the standard. For example, the requirement for steelmaking is that the sulfur content is less than 0.1. The amount of sulfur in the general stone material is relatively small, mainly brought into the fuel, and some products do not have high requirements for sulfur content, such as electric lime. In general, coal with the same calorific value has a large price difference in the market. Understanding this point is economically significant.

Centrifugal Sifters

Centrifugal Sifter,Turbo Sieve,Flour Airflow Sieve,Flour Sifter Machine

Xinxiang Zhenying Mechanical Equipment Co., Ltd , https://www.beltconveyor.nl