JPH04272993A - Method for operating heat-transfer tube dryer for moisture control of coal - Google Patents

Abstract

PURPOSE:To prevent excess drying of coal which is stored in a heat-transfer tube dryer for controlling the moisture of feed coal in case of urgent stop of the operation of the dryer and to reduce the generation of dust from the coal in restarting the process. CONSTITUTION:The rotation of a furnace is minimized so that no thermal strain is caused in a dryer 1 of the furnace and heating steam supply to a heat-transfer tube 2 is lowered while stopping the supply of feed coal to the dryer 1. Separately, water mist corresponding to the amount of water evaporated from the coal in the dryer 1 is supplied to a carrier gas which is delivered through a supplying tube for carrier gas 11 from a supplying tube for water mist 21 by controlling a control valve for water mist 22.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for controlling the humidity of raw material coal to be charged into a coke oven, and more specifically, it is a method for preventing overdrying of coal moisture in a tube dryer that uses heated gas such as steam as a heat source. The present invention relates to a method of operating a tube dryer for controlling humidity of coal.

0002

[Prior art] Moisture controlled coal (CMC) has been used as a pre-treatment method for coking coal in order to improve the productivity and economic efficiency of coke ovens.
), briquette and preheated charcoal methods are known. Among these methods, the moisture-controlled coal method reduces the amount of heat of carbonization by adjusting the moisture content of coking coal, which varies in the range of 7-12% depending on the weather, to usually 5-6% before charging it into a coke oven. The aim is to improve productivity by reducing the amount of carbon and increase bulk density, and to reduce raw material costs by incorporating a large amount of slightly cohesive coal. As humidity controllers, indirect heating tube dryers that use heated gas such as steam as a heat source, and direct heating multi-disc humidity controllers that use hot air are in operation in Japan.

FIG. 3 shows the flow of a humidity-controlled coal facility using a conventional steam tube dryer 1 (hereinafter referred to as dryer) that uses steam as a heat source of indirect heating type.
The dryer 1 has a heat transfer tube 2 for indirect heating through which water vapor (hereinafter referred to as steam) passes, and low-pressure steam is caused to flow into the heat transfer tube 2 through a steam tube 4 branched from a steam source tube 3. A technique is known in which raw coal charged in the dryer 1 is heated and dried using the heat of condensation when steam condenses (see, for example, Japanese Patent Laid-Open No. 17429/1983).

Raw coal cut from the raw coal hopper 24 and conveyed by the coal conveyor 5 is charged into a charging port 6 and then continuously charged into the dryer 1 by a screw feeder 7. The raw coal heated and dried in the dryer 1 is discharged from the discharge port 8 on the other end side to the discharge side screw feeder 9, and is further conveyed to the next process by the humidity-controlled coal conveyor 10.

[0005] A carrier gas is introduced into the dryer 1 from a carrier gas blow pipe 11 from one end, and moisture evaporated from raw coal by heating is entrained in the carrier gas, and is discharged from an exhaust port 12 connected to the other end. Since it contains dust, it is removed by a dust collector (not shown) and then discharged into the atmosphere. Such heat drying reduces the moisture content to 7 to 1.
The humidity of about 2% wet coal is adjusted to 6% dry coal. The amount of moisture reduction is 1 to 5%, and the humidity is adjusted to the target value of 6% by controlling the steam supply pressure to the dryer to 1 to 7 kg/cm2 as shown in FIG. Note that when the moisture content at the exit of dryer 1 is 6%, it is further dried by the sensible heat during drying while being transported from dryer 1 to the coke oven, and when it arrives at the coke oven, the final target of 5% is reached.
%become. In addition, the drain water resulting from steam condensation is discharged from the drain outlet 13 to the drain tank 14 via the drain pipe 25, and the drain water is recovered.

[0006] When coal is charged into a coke oven with a constant moisture content of 5%, the carbonization conditions are constant compared to when the coal humidity is not controlled, so uniform coke can be obtained, and there is no clogging when pushing coke from the coke oven. Such troubles are also reduced. It also has the advantage of increasing the density when charging coal into a coke oven, improving coke quality and increasing production volume. Therefore, in recent years, this coal moisture control method has been generally adopted in coke ovens.

In this way, in order to control the moisture content of the coking coal at the outlet of the dryer 1 at a constant level, the amount and moisture content of the coking coal supplied to the dryer 1 are measured using the coal flow meter 16 and the moisture meter 17, and the coal supply amount data is measured. and input moisture data to the controller 18. The control device 18 normally controls the dryer drive device 2 in response to fluctuations in the amount of coal supplied.
The steam pressure control valve 19 controls the steam pressure supplied to the heat transfer tubes 2 of the dryer 1 in response to fluctuations in evaporated water content (difference between inlet water content and outlet water content). It is operated so that the moisture content of the humidity-controlled raw coal reaches the target value.

[0008]

[Problems to be Solved by the Invention] In addition to the normal startup and shutdown operations, the steam tube dryer operation method described above includes emergency shutdowns in case of trouble with downstream transportation equipment, or when the coal tank of a coke oven is full. , there is a restart operation. FIG. 2 shows an example of a dryer operation pattern during an emergency stop and restart. As shown in Figure 2, during steady operation, automatic control is carried out by feed-forward to respond to fluctuations in the moisture content at the coal inlet. However, in the event of an emergency stop, the coal supply to the dryer must first be stopped and the coal retained in the dryer 1. If necessary, the steam pressure and dryer rotational speed are simultaneously set to the minimum controllable values.

The main reason for venting the steam at the minimum pressure is to keep the dryer body warm so that it can be restarted immediately when the emergency stop is canceled. The reason why the dryer continues to rotate at a low speed is to prevent deformation due to the temperature difference between the coal contact area (20 to 30% of the dryer shell cross-sectional area) and the space. The above operating method has the following problems. If the supply of coal is stopped for some reason, with conventional technology, the extrusion force by the upstream coal in the dryer gradually decreases, so the discharge capacity from the dryer is lost and the residence time of coal in the dryer is reduced to normal. There was a problem that the coal was in an overdry state with less than the target moisture content because the drying time was longer than during operation. Further, even when the discharge from the dryer was stopped, the residence time of coal in the dryer was longer than during normal operation, resulting in an over-dry state.

[0010] That is, at the time of emergency shutdown, raw coal remains in the dryer, and heat from the low-pressure steam is supplied to the raw coal even though the temperature is low, so that drying of the residual coal progresses. If the emergency stop is canceled within a few minutes, the degree of dryness is low, but if it lasts for a long time, the moisture limit for dust generation may be 5.
Dry to ~6% or less. When the dryer is restarted from such a state, overdried coal with a large amount of dust is discharged from the dryer outlet, which poses an extremely serious problem in terms of handling and the environment. Furthermore, even if the dryer rotates at a low speed, coal is discharged little by little from the dryer outlet due to the dryer's rotation, and if the dryer is stopped for a long time, the chute may become clogged.

However, in the prior art, the supply of coal to the dryer 1 or the discharge of coal from the dryer 1 is stopped,
There was no way to properly prevent coal from over-drying when the coal had to stay in the dryer 1, and moisture control in the coal depended solely on steam volume control by the steam pressure control valve 19. , it was not possible to avoid overdrying of the coal remaining in the dryer 1.

[0012] The present invention aims to solve the above-mentioned problems.
It is an object of the present invention to provide a method of operating a steam dryer for controlling humidity of coal, which can prevent overdrying of coal moisture in the dryer and perform highly accurate coal adjustment.

[0013]

[Means for Solving the Problems] The present invention to achieve the above object is to continuously charge raw coal from one end side into a dryer having heat exchanger tubes, and to flow heated gas through the heat exchanger tubes. The raw coal is indirectly heated, and the heat-dried humidity-controlled coal is sequentially discharged from the other end. At the same time, by supplying and circulating carrier gas inside the dryer during heating and drying, evaporated water is removed from the machine. In a method of operating a heat exchanger tube dryer for humidity control of discharging coal, when the operation of the dryer is to be stopped urgently, the supply of coal to the dryer is stopped, and at the same time, the minimum furnace size that can prevent thermal distortion of the dryer furnace body is installed. While reducing the number of body rotations and reducing the supply of heated gas to the heat exchanger tubes, the amount of water evaporation in the raw coal during normal operation is added to the carrier gas supplied to the dryer.
(t/hr), a method for operating a heat exchanger tube dryer for coal humidity control, characterized in that a water mist consisting of 100 μm or less is mixed so that the amount of sprayed water x is x > 0.5y. It is.

Further, according to the present invention, the moisture content of the humidity-controlled coal can be set to a target value by controlling the amount of spray water sprayed into the carrier gas and the steam pressure supplied to the heat transfer tubes.

[0015]

[Function] When stopping the dryer operation in an emergency, the supply of coal is stopped and the rotation speed of the dryer furnace body is reduced, so that even if coal remains in the dryer, the amount of steam supplied to the heat transfer tubes is At the same time, water mist of 100 μm or less is mixed into the carrier gas supplied to the dryer with spray water under the condition that x > 0.5y as described above, so moisture is replenished to the coal remaining in the dryer. , overdrying is prevented.

[0016] Here, the particle size of the water mist is 100 μm.
The reason for setting it below is that if a mist exceeding 100 μm is mixed into the carrier gas, there is a risk that the coal will become too wet. Also, when the amount of water evaporation in raw coal is y (t/hr), the spray water amount x is set to x > 0.5y because
This is because if the amount of spray water is less than 0.5 y, overdrying cannot be sufficiently prevented due to insufficient amount of mist.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the flow of a humidity control coal facility using an indirect heating type steam tube dryer 1 of the present invention. In FIG. 1, the same parts as the conventional example shown in FIG. This is intended to be simplified.

In the present invention shown in FIG. 1, carrier gas is supplied by connecting a water mist supply pipe 21 to a carrier gas blowing pipe 11 and controlling a water mist control valve 22 disposed in the water mist supply pipe 21. The structure is such that the water mist supplied from the water mist supply pipe 21 can be mixed with the carrier gas supplied to the dryer 1 from the pipe 11. During steady operation of the dryer 1, automatic feed-forward control is mainly carried out in response to fluctuations in inlet water content, and the rotational speed of the dryer 1 is controlled in response to fluctuations in the amount of coal supplied, as in the conventional example described above. On the other hand, for an emergency stop of the dryer 1, as shown in FIG. The minimum rotation speed that does not cause thermal distortion of the furnace body,
For example, the rotational speed is reduced to about 1 rotation/min.

At the same time, the steam pressure control valve 19 disposed in the steam pipe 4 is controlled to reduce the amount of steam supplied to the minimum level to the extent that the inside of the heat transfer tube 2 does not become under negative pressure. In this case, although the heat input from the heat transfer tubes 2 to the coal in the dryer 1 decreases,
Since heat input continues, it is inevitable that the coal will become over-dried after a certain period of time. Therefore, in the present invention,
Based on a command from the control device 18, the opening degree of the water mist control valve 22 is controlled, and a water mist of 100 μm or less is supplied from the water mist supply pipe 21 to the carrier gas blow pipe 11, and the carrier gas is blown into the dryer 1. It increases the moisture content of By supplying this water mist and rotating the dryer 1 at that time, the rise in moisture becomes uniform. In this way, the evaporation of water in the coal remaining in the dryer 1 is controlled, and the temperature rise of the coal is suppressed by the latent heat of evaporation of the water mist in the carrier gas, thereby preventing overdrying of the coal.

When coal with low humidity is supplied into the dryer 1 after coal with high humidity, in order to dry the high humidity coal to the target value, it is necessary to dry the high humidity coal to the heat transfer tube 2 until the discharge of the high humidity coal is completed. Although the steam supply pressure must remain high,
If left as is, low-moisture coal will become over-dried. Therefore, around the time when high-humidity coal has been discharged from the dryer 1, water mist having a particle size of 100 μm or less is mixed with the carrier gas to bring the coal moisture closer to the target value. The amount of mist spray x is when the amount of water evaporation is y>
As described above, it is controlled to be 0.5y.

Specifically, the amount of evaporated coal moisture in the dryer 1 is detected based on the moisture measured by the moisture meter 17 at the inlet of the dryer 1 and the moisture meter 23 at the outlet, and this is transmitted to the control device 18. Then, the water mist control valve 22 is controlled by a command from the control device 18 to mix a required amount of water mist into the carrier gas. The water mist supplied to the water mist supply pipe 21 can be obtained by taking out a steam pipe (not shown) from the steam pipe 4 and connecting it to the water mist supply pipe 21, or by using a separate system to supply water with a diameter of 100 μm or less. A mist may also be supplied.

[0022]

As explained above, according to the present invention, water mist is mixed with the carrier gas supplied to the dryer during an emergency stop of the dryer, so that the coal staying in the dryer does not become over-dry and reaches the target moisture content. Can be maintained for minutes. Therefore, dust generation when the dryer is restarted is reduced, and environmental problems can be completely eliminated. Additionally, the dryer can be restarted smoothly.

[Brief explanation of the drawing]

FIG. 1 is a flow diagram of an apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a dryer operation pattern according to a conventional example.

FIG. 3 is a flow diagram of a conventional device.

FIG. 4 is a diagram showing the relationship between steam pressure (kg/cm2G) and moisture reduction %.

[Explanation of symbols]

1 Dryer 2 Heat exchanger tube 3 Steam main pipe 4 Steam pipe 5 Coal conveyor 6 Loading port 7 Supply side screw feeder 8 Coal discharge port 9 Discharge side screw feeder 10 Humidity control coal conveyor 11 Carrier gas blow pipe 12 Exhaust port 13 Drain outlet 14 Drain tank 16 Coal flow meter 17 Moisture meter 18 Control device 19 Steam pressure control valve 20 Dryer drive device 21 Water mist supply pipe 22 Water mist control valve 23 Moisture meter 24 Coking coal hopper 25 Drain pipe

Claims (2)

[Claims] Claim 1: Raw coal is continuously charged from one end into a dryer having heat transfer tubes, and heated gas is passed through the heat exchanger tubes to indirectly heat the raw coal, resulting in heat-dried humidity control. In the method of operating a heat exchanger tube dryer for controlling humidity in which coal is sequentially discharged from the other end side while evaporated moisture is discharged outside the machine by supplying and circulating carrier gas inside the dryer during heating drying, When stopping the operation of the dryer, the coal supply to the dryer is stopped, and at the same time, the rotation speed of the dryer furnace is reduced to the minimum that can prevent thermal distortion of the dryer furnace, and the heating gas is supplied to the heat transfer tubes. While reducing the supply, a water mist of 100 μm or less is sprayed into the carrier gas supplied to the dryer, where the amount of water evaporation in the raw coal during normal operation is y (t/hr). x is x > 0.5
A method of operating a heat exchanger tube dryer for controlling coal humidity, characterized by mixing the coal so that the temperature is y. 2. The coal humidity control method according to claim 1, wherein the moisture content of the humidity-controlled coal is set to a target value by controlling the amount of spray water sprayed into the carrier gas and the steam pressure supplied to the heat transfer tubes. How to operate a heat transfer tube dryer.