The Reasons and Improvement Measures Affecting the Qualified Rate of Fixed Carbon and Consumption of Blended Coal

Jiang Runke

[Abstract] This paper mainly analyzes the reasons that affect the fixed carbon index qualification rate and coal blending consumption exceeding the standard in alumina raw slurry furnish of our factory, and adopts the improvement measures and obtains good results.

[Keywords] raw slurry, fixed carbon, coal blending

The coal blending (fixed carbon) function in the raw slurry of our plant is desulfurization. For a long time, the passing rate of fixed carbon indicators has been low, while the consumption of blended coal has exceeded the standard. One of the reasons for the low pass rate of fixed carbon indicators is that fixed carbon runs low due to low coal blending, and second, fixed carbon runs high due to high coal blending capacity. The high amount of coal blended is the main reason for excessive consumption of blended coal.

1 Production status

1.1 The existing white coal transportation and distribution process (as shown below)

Minerals

Belt conveyor

Ore silo (white coal)

White coal

Grinding coal bunker (idle)

Raw material mill

Alkali red mud

White coal transportation and distribution process (solid part)

Slurry tank

Limestone (white ash)

The white coal is proportioned into aluminum ore and conveyed by a belt conveyor to the raw material grinding head ore bin. During the process of belt transport, the ore is fully homogenized, and the ore is ground into the raw material while grinding.

1.2 Calculation and Control of Coal Blending

Slurry ingredient list, generally only calculate the alkali ratio, calcium ratio, raw slurry water, aluminum-silicon ratio. The fixed carbon is calculated separately, and now the method of backward calculation and total amount control of the slurry consumption (K tank delivery) is adopted.

In Example 1, the K tank feed slurry is 3000m3/shift, the slurry water is 38.6% (specific gravity 1.66t/m3), the fixed coal content of white coal is 75%, the moisture content is 5%, and the set value of fixed carbon index It is 4%. The coal blending amount is G:

1.3 Adjustment of Coal Blending

The adjustment of coal blending is mainly the periodic calibration of the tachometer of the plate machine and the unloading amount of the weighing scale, and fine adjustment of the proportion of the charging of the ore and the white coal plate machine according to the fixed carbon index released every day.

In Example 1, assuming that the net time of the white coal-plate machine is 3 hours per shift, the amount of white coal transported per hour should be 171.65/3=57.21 t/h, and the speed of converting the reference table into a plate machine is 350 ~400 rpm.

2 Cause Analysis

2.1 The ratio of raw material grinding under different conditions is the main reason for the low qualification rate of fixed carbon and excessive consumption of blended coal under existing conditions.

Raw material grinding adjusts the proportion of ore and limestone (or white ash) according to the ratio of alkali ratio, calcium ratio, red mud water, and aluminum-silicon ratio of the slurry index, and cannot fully take into account the blending index.

2.1.1 Effect of red mud on fixed carbon

If the water content of the red mud is low, the amount of dry material added when the raw material mill is driven is small, that is, the amount of coal added is also small, resulting in a low fixed carbon content. On the contrary, if the red mud is high in water content, the amount of dry material added to the raw material mill will increase, which means that more coal will be added, resulting in higher fixed carbon content.

2.1.2 Effect of Calcium Ratio on Fixed Carbon

Due to the constant change of raw slurry-calcium ratio, the ratio of raw material-milled ore and limestone (or white ash) is adjusted at any time. When the calcium ratio of the raw slurry is low, the discharge amount of limestone (or white ash) is increased, and the amount of ore to be charged is reduced, that is, the amount of white coal blended is reduced, resulting in a low fixed carbon content. On the contrary, the fixed carbon is high.

2.1.3 Effect of Al-Si ratio on fixed carbon

Because the raw slurry prepared with high Al-Si ratio is used for hanging kilns in rotary kilns, the plate-type machine is often required to suspend the blending of white coal, which will inevitably lead to a low fixed carbon content.

2.1.4 Effect of Alkali Ratio and Red Mud Water on Fixed Carbon

In the production, due to the adjustment of the slurry alkali ratio and the red mud water, only the circulation of alkaline red mud is often used, and no dry material (ore, white coal, limestone) is allocated, which will result in low fixed carbon.

2.2 Analysis results of fixed carbon mislead coal blending

2.2.1 The analysis result of coal blending and fixed carbon lags behind

The coal blending amount calculated by backcasting the slurry consumption (K tank delivery) is an expired analysis. Therefore, unscientific guidance is given.

The raw slurry fixed carbon indicators are only three samples per day and are released at the same time. It is usually at about 10 o'clock in the morning to publish white classes, 4 o'clock classes and 0 o'clock classes on the day before. It is generally found that the fixed carbon deviation has become an unchangeable result. Due to the large stock of slurry, the fixed carbon index released on the same day does not coincide with the amount of coal produced in the same day, and generally lags behind 3 to 4 classes. If due to the sequential changes in the slot adjustment, it may lag 3 to 4 days, and even continuous extreme deviations may occur.

2.2.2 Effect of Sampling Point on Fixed Carbon

The current fixed carbon sampling point is sampled in the K-tank, which is the finished raw slurry, which has no guideline for the fixed carbon index of the raw slurry being prepared.

2.3 The Effect of White Coal Composition on Fixed Carbon

White coal quality standards require that the fixed carbon content be not less than 75%. If the fixed carbon content of white coal is much higher than 75%, the fixed carbon index can easily cause a high run. Adjusting the blending amount in time can reduce the consumption of blending coal. If it is far below 75%, it is easy to cause the fixed carbon index to run low. Increasing the amount of coal blended will cause excessive consumption of blended coal.

The moisture content of white coal also has a very important effect on the amount of coal blended.

3 Improvement measures

3.1 Calculating Coal Blending Amount in the Same Period

Because the fixed carbon index of the slurry is calculated separately, the amount of coal blended can be calculated based on the capacity of the raw material mill at the same time.

Example 2, if the productivity of a raw material mill is 125m3/h, the slurry moisture is 38.6% (specific gravity 1.66t/m3), the fixed carbon content of white coal is 75%, the moisture content is 5%, and the fixed carbon index is set. The fixed value is 4%. The coal blending amount is G:

3.2 White Coal Transportation and Distribution

The white coal is conveyed by the belt conveyor to the white coal bin of the raw material grinding head, and the raw material grinding system is stabilized by the bottom belt weigher. No matter how to adjust the proportion of raw materials, adjust the aluminum-silicon ratio, alkali ratio, calcium ratio, or slurry moisture, can be stably allocated to white coal, to ensure the qualified rate of fixed carbon indicators. And can effectively control the allocation of white coal, the implementation of the low limit (3 ~ 4%) operation, reducing coal consumption.

The white coal is transported and mixed separately, and it is necessary to recover the idle raw material white coal bunker and increase the bottom belt scale.

Minerals

Belt conveyor

Mineral warehouse

White coal

Grinding coal warehouse

Raw material mill

Limestone (white ash)

White coal transportation and distribution improvement process (solid line)

Slurry tank

Alkali red mud

3.3 Periodic Determination of White Coal Composition

The fixed carbon content in the white coal has an effect on the passing rate of the fixed carbon index and the consumption of coal blending, and the other components of the white coal also have certain influence on the other indexes of the slurry, especially the moisture content of the white coal to the slurry. The influence of moisture is large, and this should be given enough attention. Therefore, it is very important to determine the composition of white coal on a regular basis.

4 improvement effect

Now, by measuring the amount of raw material milled, using the computer to achieve the same period of coal calculations. For a period of time, the qualified rate of fixed carbon indicators reached 96%, and the average value of coal blending was close to the lower limit. Achieve low limit control, reduce coal consumption and achieve the desired goal.