JPS606476B2 - Grinding and drying control method for combustible materials - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for controlling the crushing and drying of combustible materials.

Generally, when pulverizing easily combustible materials such as coal, high-temperature dry gas is supplied into the pulverizer to remove moisture from the material, and the pulverized pulverized coal is preheated and dried, and at the same time, the same gas is used to pump it to the target location. method is adopted.

When implementing such a method, for example, powdered coal has an oxygen concentration of 10
There is a risk of explosion in an atmosphere of ~13% or more, and to prevent this, it is necessary to maintain the oxygen concentration of the dry gas below the explosive limit concentration of coal dust. Therefore, inert gas or combustion exhaust gas is usually used as the same gas, and air or exhaust gas for temperature adjustment is often mixed with this at a concentration below the above range.

By the way, the operating method for such a crushing and drying system is as follows.
There is a positive pressure system that maintains positive pressure in the system and a negative pressure system that maintains negative pressure.The former is operated and controlled by a forced blower installed at the inlet of the system, and the latter is operated and controlled by a suction blower installed at the outlet of the system. .

However, each of these methods had the following problems, and all of them were unsatisfactory. In other words, the former positive pressure method has disadvantages such as the leakage of dry gas and fine coal to the outside of the system, and the risk of a secondary explosion occurring at the same time as the dry gas causes an oxygen deficiency and loss of fine coal. ``On the other hand, the latter negative pressure method has drawbacks such as air easily leaking from outside the system in the rotating parts of the crusher and the coal feeding part, increasing the oxygen concentration in the system and potentially causing a coal dust explosion. The present invention was made with the aim of eliminating the above-mentioned conventional disadvantages and disadvantages.Specifically, the main drying gas and the temperature adjustment gas are mixed in advance, and the mixed gas is used as the drying gas. After the combustible material in the pulverizer is fed under pressure to the combustible material pulverizer using a forced air blower and the flammable material in the pulverizer is dried under low heat, the dry gas is discharged from the pulverizer along with the pulverized combustible material by a suction blower. , the pressure of the dry gas at the inlet or outlet of the pulverizer is measured, and when the combustible material is separated from the dry gas by pressure-feeding and leading to a dust collector, the pressure is maintained at approximately atmospheric pressure. The pressure control of the drying gas is adjusted to adjust the suction pressure of the suction blower, and the flow rate of the drying gas at the inlet of the crusher is measured, and the forced flow rate of the main drying gas of the forced blower is adjusted to maintain a constant flow rate. and controlling the flow rate of the drying gas to adjust the drying gas, and measuring the temperature of the drying gas at the outlet of the pulverizer, and adjusting the mixing ratio of the temperature adjusting gas to the main drying gas so that the temperature is constant. It is characterized in that temperature control is performed independently of each other.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a flow sheet illustrating an example of coal pulverization, drying and pressure feeding operation and control according to the present invention. Here, 1 is a coal pulverizer such as a ball mill, and coal is passed through a belt conveyor 2. It is charged into the machine and pulverized to a target particle size (for example, 80% under 200 mesh).

In addition, the crusher has a gas inlet on one side and a gas outlet on the other side, and high-temperature child heat, drying and pressurizing gas 3 (hereinafter simply referred to as drying gas) are supplied into the machine from the gas inlet. ,
The fine coal after pulverization is heated and dried to reduce and remove the moisture contained in it to below the target value (approximately 1%), and the fine coal to be used as a product is classified and separated, and the fine coal is extracted from the gas outlet. It is continuously discharged accompanied by dust and is pumped to a dust collector.

The dust collector is composed of a cyclone 6 and a bag filter 7, and most of the pulverized coal entrained in the drying gas 3 is collected and separated by the cyclone, and is supplied to a coal bin 8 and stored. The dry gas 3 is further filtered to remove fine particles by a bag filter 7, and is then released into the atmosphere as a clean gas. The powder collected in the bag filler 7 is collected in a cole bin 8. Now, in this method, the drying gas and the pulverized coal after pulverization are pumped by two blowers, a push blower 9 and a suction blower 10, which are installed at the inlet and outlet ends of a sealed system.

This is done by using wa in combination. Among these, the forced blower 9 has a function of sending the dry gas 3 to the crusher 7,
The suction blower 10 also has the function of pumping the dry gas sent into the crusher and the accompanying crushed powdered coal to the dust collector, and dissipating the collected clean gas into the atmosphere.

In this method, the pressure inside the crusher 1, which is at risk of gas leakage within the system and gas leakage outside the system, is controlled to approximately atmospheric pressure by utilizing the pressure feeding functions of both blowers in combination. is an important feature. Specifically, this control pressure is set so that it ranges from -10 to 11 at the center of the crusher, and this is set to 0 to 11 at the gas inlet.
-400 to 0 line corresponds to 0 at the 140 broadside & ○ gas outlet.

By the way, the drying gas 3 consists of the main drying gas 4 and the temperature adjustment gas 5.
It is obtained by mixing in an appropriate ratio. The main drying gas 4 is composed of inert gas for preheating A or combustion exhaust gas discharged from various combustion furnaces and firing furnaces, and the oxygen concentration of the gas is at least 10% or less in order to prevent the aforementioned coal dust explosion. Retained. The temperature adjustment gas 5 is used to adjust the temperature of the dry gas according to changes in the properties and moisture content of the coal, and in this case, it is a combustion exhaust gas generated by mixed combustion of the fuel gas 5' and the combustion air 5''. Next, the pressure inside the crusher 7 according to this method is controlled as follows.

A pressure gauge 11 is provided on the inlet side or outlet side (inlet side is shown in the flow diagram) of the gas supply duct of the crusher 7, and the pressure of the drying gas in this part is constantly measured by the pressure gauge. , this measurement signal is sent to the drying gas pressure control section 12. The control unit j2 compares and calculates the actual measured value with a preset target set value (for example, 110 to 110 days 20), and if the actual measured value deviates from the set value, the controller j2 is installed in front of the suction blower 10. The opening degree of the damper 13 is changed, the suction pressure of the suction blower is automatically adjusted, and the pressure of the crusher is controlled to be within the target setting range. That is, when the actual value of the pressure gauge 11 is higher than the set value, the opening degree of the damper 13 is increased and the suction amount of the suction blower 10 is controlled to increase, and when the actual value is lower than the set value, the opposite is done. The damper]3 is reduced and the suction amount of the blower 10 is controlled to be reduced. Therefore,
By implementing this pressure control, the pressure inside the crusher 1 is always maintained at the target almost atmospheric pressure, which prevents air from leaking out of the system and gas and pulverized coal from flowing out of the system. Leakage can be reliably prevented. Further, in this method, in order to stabilize the classification performance of the crusher 1, in addition to the pressure control described above, gas flow rate control on the inlet side of the crusher is performed.

That is, in addition to the pressure gauge 11, a flow meter 14 is provided in the gas supply duct on the inlet side of the crusher 1, and the flow rate of the dry gas continuously fed into the crusher 1 is measured here. This measurement signal is transmitted to the flow rate control section 15. The flow rate control unit 15 sets a target gas flow rate (for example, 280 to 350 Nm3/m
in) and the actual value measured by the same flowmeter 14 are compared and calculated,
If the actual measured value is outside the set value range, the damper 16 installed on the front side of the forced blower 9 is changed to adjust the flow rate of the main drying gas 4, which is supplied to the crusher 1. The flow rate of the drying gas 3 is controlled to be constant within the target set value range. In this case, when the actual measured value is higher than the set value, the opening degree of the damper 16 is decreased, while when the actual measured value is lower than the set value, the opening degree of the damper 16 is increased.

In this way, the flow rate of the drying gas 3 supplied to and discharged from the crusher 1 is maintained constant, and as a result, the classification performance of the crusher is stabilized, and powdered coal having the target particle size can be obtained with high accuracy. Furthermore, in this method, in addition to the pressure control and flow rate control described above, temperature control of the drying gas is performed in parallel.

That is, a thermometer 1 is installed in the discharge duct on the outlet side of the crusher 1.
7 is installed, and this thermometer measures the temperature of the dry gas that has finished heating and drying in the crusher, and a temperature control signal is sent to the temperature control section 18. The control unit compares and calculates the target value of the gas temperature (for example, 70 to 90°C) set in advance with the actual value measured by the thermometer to ensure that the desired moisture content of the product-class pulverized coal stored in the coal bin 8 is met. If the actual measured value is outside the set value, the mixing ratio of the temperature adjustment gas 5 to the main drying gas 4 is changed and the drying gas 3 is changed.
Based on this, the gas temperature on the outlet side of the crusher 1 is controlled to be maintained within a certain range.

Specifically, when the actual value measured by the thermometer 17 is higher than the set value, the opening degrees of the flow rate control valves 19 and 20 for the fuel 5 and combustion air 5'' are vertically reduced, and the mixing ratio of the temperature control gas 6 is reduced. is reduced and the temperature of the drying gas is lowered, and when the actual measured value is lower than the set value, the flow rate control valve 19
The degree of opening of and 20 is increased, and accordingly, the mixing ratio of the temperature adjusting gas 5 is increased, and the temperature of the drying gas is adjusted to increase. By controlling the temperature of the drying gas, even if the moisture content of the coal supplied to the pulverizer fluctuates, the moisture content of the product powdered coal can be efficiently and stably reduced to a desired value. In addition, when controlling the pressure of the crusher, considering the pressure loss of the back filter 7, the pressure drop is periodically controlled from the minimum pressure drop immediately after brushing off the powdered coal that has accumulated on the back filter to the maximum pressure drop immediately after the dust is brushed off. This causes a disturbance in the pressure control system. In order to eliminate this disturbance and perform more efficient pressure control, it is preferable to perform differential pressure compensation control of the bag filter as described below. That is, pressure gauges 21 and 22 installed on both the inlet and outlet sides of the back filter 7 measure the pressure before and after the back filter.

This measurement signal is sent to the differential pressure compensation control section 23, where the differential pressure based on both actual measurement values is calculated, and this differential pressure value and a preset target setting value (for example, 100 Yanagiday 2
0 to 150 side day 20) are compared and calculated, and when the differential pressure value is outside the set value range, the function of the damper 24 provided in front of the detection end of the pressure gauge 22 on the outlet side is adjusted, The measured differential pressure value is controlled to be within the set value range. When the measured differential pressure value is higher than the set value, the damper 24 is increased, and when it is lower, the damper opening is vertically decreased. Such reed pressure compensation control eliminates disturbances to the pressure control system caused by fluctuations in the pressure of the back filter. In addition, in the example described above, the suction blower is installed behind the backfill station 7, but the present invention is not limited to this, and the suction blower is installed between the cyclone 6 and the backfill station 7. format may be adopted.

As explained above, according to the present invention, by controlling the pressure of dry gas when pulverizing, drying, and pumping combustible materials such as coal, air leakage into the system, dry gas, and powdery particles are prevented. Materials are reliably prevented from flowing out of the system.
This eliminates the dangers of coal dust explosions caused by increased oxygen within the system, oxygen deficiency outside the system, and secondary explosions, ensuring safe operation, and controlling the flow rate of drying gas. This provides excellent effects such as stabilizing the classification performance of the pulverizer and also efficiently removing moisture from the pulverized material by controlling the temperature of the gas.

[Brief explanation of drawings]

FIG. 1 is a flow sheet illustrating an example of coal pulverization, drying, pumping operation, and control according to the present invention. Figure 1

Claims (1)

[Claims] 1. Mix the main drying gas and temperature adjustment gas in advance,
The mixed gas is forced as a dry gas and supplied to the crusher using a forced blower to preheat and dry the easily combustible material in the crusher, and then the dry gas is transferred together with the crushed combustible material to the crusher using a suction blower. When the pulverized coal is discharged and fed under pressure to a dust collector, and the pulverized coal is separated from the dry gas by the dust collector,
drying gas pressure control that measures the pressure of the drying gas at the inlet or outlet of the pulverizer and adjusts the suction pressure of the suction blower so that the pressure is maintained at approximately atmospheric pressure; Measure the flow rate of the drying gas, adjust the forced flow rate of the main drying gas of the forced air blower so that the flow rate remains constant, and measure the temperature of the drying gas at the outlet of the pulverizer. pulverization of easily combustible materials, characterized in that drying gas temperature control is carried out independently of each other, adjusting the mixing ratio of the temperature adjusting gas to the main drying gas so that the temperature is constant;
Drying control method.