JPS596829B2 - Fly ash sintering control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an operation control method for stabilizing fly ash sintering operation and eliminating uneven sintering.

Exhaust gas generated from various boilers, heating furnaces, incinerators, etc. contains a large amount of fine dust (fly dust), but as the energy source changes and the switch to coal-fired combustion progresses, It is predicted that the amount of fly attack will increase dramatically.

Such fly ash is recovered using an electrostatic precipitator or the like, but in order to effectively utilize it, a method of granulating and sintering it into artificial lightweight aggregate has been put into practical use.

In other words, fly ash originally contains a small amount of unburned carbonaceous material, but if necessary, combustible carbonaceous material (fine powder of coal or coke) is added, kneaded and granulated with a binder (water) to form raw pellets, which are then transported. It is charged onto a grate and transported while being dried, preheated, ignited, sintered, heat-retained, and cooled to produce an artificial lightweight aggregate.

Figure 1 is an explanatory diagram showing such a sintering procedure.
Product (sintered) aggregate 2 is charged into hopper 13.
6 is loaded with green pellets 1 and stacked on a movable grate 3 on a pallet that rotates in the direction of the arrow.

The product aggregate 2 is supplied as a bedding, and the raw pellets 1 may be charged immediately after granulation, without using the hopper 16.

The raw material layer thus formed is sequentially transferred from left to right in the drawing as the grate moves, and is transferred to the drying/preheating furnace 4 and the ignition furnace 5.
and undergoes sintering through a sintering/retention furnace 6 and a cooling zone 7.
It is then sufficiently cooled to become product aggregate.

A plurality of wind boxes 8 are arranged along the conveyance direction at the bottom of the upper grate through which fresh pellets 1, etc. are conveyed, and the lower narrow diameter part of the wind boxes 8 is connected to the return side (
Lower side) In order to avoid the grate, it is deflected in the direction penetrating the page, and is opened and connected to the exhaust duct 9.

The interior of the duct 9 is evacuated by a blower 10, and due to the suction airflow, a suction airflow is formed that passes through the raw material layer from top to bottom.

Therefore, by connecting an air introduction pipe to the upper part of each furnace 4, 5, and 6, high-temperature air is introduced into each furnace, descends between the raw material layers, and is discharged into the wind box 8. .

That is, since the raw pellets have a spherical shape with a diameter of 5 to 25 mm, the ventilation resistance within the raw material layer is relatively low, and a downward airflow passing from the top to the bottom can be easily formed.

In addition, in the powder ore sintering method established for sintering powder ore to use as blast furnace raw material, the above-mentioned ventilation resistance is large because mini-pellets with a diameter of 5 mm or less are sintered.
The suction airflow was formed using a pressure of 0 00 mmAq, but for the raw pellets handled in the present invention, a pressure of 100 to 500 i
A pressure of mAq is sufficient, and by taking advantage of the long air permeability, cooling can be completed by the descending air flow while moving over the grate.

By the way, when sintering raw pellets for the purpose of producing artificial lightweight aggregate, the amount of unburned carbon in the sintered product should be reduced to 1
% or less (JIS standard).

Therefore, the flame ignited on the surface of the raw material layer needs to be gradually transmitted to the middle and lower layers by the downdraft, and if this speed is too fast, insufficient sintering will result. The suction pressure formed in the lower wind box of No. 6 is suitably about 100 mmAq.

On the other hand, since the burned berezot is finished as a high-strength product by rapid cooling, the suction pressure is approximately 5001iL71LAq.

Incidentally, the damper 14 is used to adjust the suction pressure generated inside the wind box.

In order to ensure the quality of the sintered product as described above, it is necessary to correctly manage the sintering completion point, in other words, the sintering speed as set.

However, when looking at the actual sintering situation, the properties of the fly ash, the moisture content in the raw pellets, the particle size distribution of the raw pellets, the feed rate of the raw pellets, the ignition conditions, etc. fluctuate, and the The sintering rate is changing irregularly.

Therefore, a control method must be established that can cope with such fluctuations and return the sintering speed to the set state.

The present invention has been made in view of these circumstances, and it is an object of the present invention to provide a control method that can cope with fluctuations in sintering speed.

That is, in the present invention, when the sintering completion point changes, what can be done about it? The gist is that the gas temperature or gas composition in the wind box is detected by measuring two or more points, and the amount of suction ventilation is adjusted by operating the damper 14 in the wind box.

To explain in more detail, when the sintering speed is fast, the amount of suction ventilation in the sintering region is reduced, and when the sintering speed is too slow, the amount of suction ventilation in the sintering region is increased.

The specific details of the means for detecting fluctuations in the sintering completion point will be explained in detail below.

That is, in the above-mentioned granulation and sintering method for fine ore, a system is built in which the sintering process is completed at the terminal end of a moving grate, and cooling is provided independently from the grate. This is done in a cooler.

Therefore, when looking at the granules falling from the terminal end of the moving grate, the lower layer in particular is often still in a red-hot state.
Sintering is in progress, so to speak.

FIG. 2 shows an example of the results of measuring the temperature and gas composition of the gas discharged from the lower part of such a moving grate over the entire movement locus.

That is, looking at the gas temperature, it shows a peak value just before reaching the terminal end of the moving grate, and the gas temperature at the time it falls from the terminal end is quite high, indicating that it is in a state immediately after sintering is completed. I understand.

Also, when looking at CO and CO in the exhaust gas composition, it shows a curve that slightly precedes the fluctuation of gas temperature.
At the time of falling from the terminal end, it shows almost zero value.

Furthermore, looking at the fluctuations in 02, it is decreasing to match the rise in CO and CO2, and at the peak of CO and CO, the content of 0 indicates the bottom, and at the time of falling from the terminal end, it is almost the standard in the atmosphere. content has returned.

In this way, it can be seen that the gas temperature and/or gas composition are valuable indicators of the progress of sintering.

Therefore, by detecting the gas temperature and/or gas composition at at least one location in or near the part where sintering is scheduled to be completed, it is possible to determine whether the sintering progress is progressing as planned or not. It was thought that it would be possible to find out whether it is slow or slow.

However, the fluctuation curve in the case of sintering fine ore is
As shown in the figure, the slope is extremely gentle, so the accuracy of judgments made based on detected values is not very high.
There is some hesitation in applying it to actual operations.

On the other hand, when similar measurements were performed on sintered fly ash, a fluctuation curve as shown in FIG. 3, for example, was obtained.

That is, in the case of fly ash granules, the particle size is large as mentioned above, so sintering is completed in the middle of the moving grate by taking advantage of its good ventilation, and the latter half is used as a cooling zone. From, after completing the sintering, waste
It is necessary to enter a cooling process, and the fluctuations are generally extremely sharp.

Therefore, it is expected that the sintering progress status can be grasped with a relatively high degree of accuracy based on these detected values.

Based on these considerations, in actual sintering equipment, the first
When the exhaust gas passing through two or more positions of the wind box 8' shown in the figure is extracted and the gas temperature or gas composition is detected, not only qualitative signals indicating whether the sintering progress is faster or slower than planned are obtained. I learned that it is possible to obtain quantitative signals on how fast or slow things are.

For example, Fig. 4 shows the exhaust gas temperature in the wind box 8a installed just before sintering is completed, and the wind boxes 8b and 8c before and after the wind box 8a, when the individual wind boxes are formed small and a large number of them are installed together. Ta
, Tb and Tc are measured.

Curves A, B, and C shown below each window box are
These are temperature distribution curves when sintering is progressing as planned, earlier than planned, and later than planned.

Therefore, if the temperature distribution curve now looks like B, then T
The temperature gradient shown by b-+T a is quantitatively detected as a negative value, and if the temperature distribution curve becomes like C, the temperature gradient shown by Ta-+Tc is quantitatively detected as a positive value. be done.

In the former case, it means that the sintering progresses too quickly from the top to the bottom, and the sintering progresses faster than necessary, reducing the strength of the product. The opening degree of the damper is reduced to reduce the amount of air passing through, thereby suppressing the progress of sintering.

In addition, in the latter case, it means that the sintering progresses too slowly, and in this case, unburned carbon content is likely to remain inside each pellet.
Further, since this may cause inconveniences such as insufficient cooling time after sintering, the opposite command is issued to the above command, that is, the opening degree of the damper is increased to increase the amount of air passing through, thereby promoting the progress of sintering.

In the latter case, the pellets with unburned carbon content have already moved to the cooling zone and are starting to be rapidly cooled by the pressure of 500 m7 ILAq, so the damper opening of the wind box at that position is reduced to allow cooling to proceed. The operations of suppressing the sintering and waiting for the completion of sintering by embers may be performed in parallel.

In the present invention, the above-mentioned control is performed, so when there is a fluctuation in the sintering speed, the amount of suction ventilation is adjusted accordingly, and the sintering speed can be returned to a steady state.

Therefore, the occurrence of sintering unevenness is prevented, and rapid cooling after sintering is ensured, thereby preventing a decrease in product strength.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the sintering process of fly ash.
2 and 3 are graphs showing fluctuations in exhaust gas temperature and exhaust gas composition, and FIG. 4 is an explanatory diagram of an example. 1... Raw pellets, 3... Moving grate, 4... Drying/preheating furnace, 5... Ignition furnace, 6... Sintering/heat retention furnace, 7... Cooling zone, 8... Wind box, 14...
...damper.

Claims (1)

[Claims] 1 Add appropriate amounts of combustible carbon material and binder to fly ash generated from coal-fired boilers, etc., and knead.
In a fly ash sintering method in which raw pellets obtained by granulating the raw pellets are charged onto a moving grate of a sintering device and sintering is performed continuously while moving the grate, the moving grate is A number of wind boxes are disposed below along the moving direction of the grate, and the raw pellets are ignited, sintered, and cooled while sucking the gas on the movable grate through the wind boxes. A fly ash sintering control method characterized in that the amount of suction ventilation from the wind box is adjusted based on the fluctuation of the sintering completion point by measuring the gas temperature or gas composition in the wind box at two or more points. .