GB2508199A

GB2508199A - Slag granulation device with a tundish and a slag flow control means

Info

Publication number: GB2508199A
Application number: GB1221121.5A
Authority: GB
Inventors: William Barry Featherstone
Original assignee: Siemens VAI Metals Technologies GmbH Austria
Current assignee: Primetals Technologies Austria GmbH
Priority date: 2012-11-23
Filing date: 2012-11-23
Publication date: 2014-05-28
Also published as: GB201221121D0; CN203741354U

Abstract

A slag granulation device comprises a tundish 2 and a granulation chamber 13 where a slag outlet 3 from the tundish 2 is coupled to a slag inlet of the granulation chamber 13. A flow control device such as a stopper rod 14 with a plug 17 is mounted in the tundish slag outlet 3. The level of the slag in the tundish 2 or the weight of the tundish 2 is measured and compared with a desired minimum. If the tundish 2 contains too little slag, slag flow is reduced by moving the flow control device towards the tundish slag outlet 3, preferably the slag level can be maintained at a desired value by movement of the flow control device. Granulation can either be performed dry in which case the device can further comprise a rotary slag granulator 5 and means 12 for recovering heat from air which is passed through the chamber, or wet.

Description

SLAG GRANULATION DEVICE AND METHOD OF OPERATION

This invention relates to a slag granulation device and a method of operation, in particular for dry slag granulation with heat recovery.

Granulation of slag is carried out by either dry or wet granulation methods.

With dry slag granulation, it is also possible to recover heat during the process. It is desirable to be able to control the rate of slag flow in both types of granulation, but a particular benefit is achieved if slag flow rate can be controlled during dry slag granulation with heat recovery, as this enables improved efficiency of the heat recovery.

In conventional dry slag granulation, slag is delivered to a granulation chamber via a pipe connected to a slag runner from the blast furnace. The pipe is designed to be oversized in order to cope with peak flow rates of slag, so the slag flow often does not fill the pipe, allowing air to pass in either dircction. This can have a ncgativc impact on the effectiveness of the heat recovery process.

In accordance with a first aspect of the present invention, a slag granulation device comprises a tundish and a granulation chamber, the granulation chamber comprising a slag inlet, and the tundish comprising a slag inlet and a slag outlet, the tundish slag outlet being coupled to the chamber slag inlet; the device further comprising a flow control device mounted in the tundish slag outlet.

The flow control device forms a seal with a layer of slag between the flow control device and the tundish slag outlet to prevent air flow through the chamber slag inlet, or to control rate of flow of slag through the tundish slag outlet.

Preferably, the device further comprising a process air supply inlet and a process air extraction outlet.

Preferably, the device further comprises a hcat recovery mechanism connected to the process air outlet.

Although the device is useful for controlling flow in both wet and dry slag granulation, its main benefits come for dry slag granulation when combined with a process air heat recovery mechanism, so preferably a rotary atomising granulator is mounted in the granulation chamber to receive slag from the chamber slag inlet.

Preferably, the chamber slag inlet comprises a pipe having a diameter sufficient for a predetermined maximum flow rate.

Preferably, the tundish further comprises at least one of a slag level sensor, a tundish weight sensor and a flow control device position sensor.

Preferably,the flow control device comprises a stopper and an actuator.

In accordance with a second aspect of the present invention, a method of operating a slag granulation process in a slag granulation device comprising a tundish and a granulation chamber comprises supplying molten slag to the granulation chamber, granulating the molten slag, the method further comprising moving a flow control device in the tundish through a range of positions to control slag flow rate through a slag delivery outlet of the tundish to the granulation chamber and forming a slag seal between the flow control device and the slag delivery outlet to prevent passage of air through the slag delivery outlet.

Preferably, the method further comprises passing process air through the granulation chamber to cool the granulated molten slag, thereby heating the process air.

Preferably, the method further comprises recovering heat from the process air using a heat recovery mechanism.

Preferably, the method further comprises measuring a level of slag in the tundish, comparing the measured level with a required minimum and causing the flow control device to move towards the tundish slag delivery outlet if the measured level falls below the required minimum.

Preferably, the method comprises carrying out a rotary atomising dry slag granulation process in the granulation chamber.

An example of a slag granulation device and method according to the present invention will now be described with reference to the accompanying drawings in rh i ch: Figure 1 illustrates an example of the invention applied to a dry slag granulation device with heat recovery; Figures 2a and 2b illustrate an example of the invention applied to a wet slag granulation device; Figure 3 illustrates a method of controlling slag during granulation in the devices of Figs.l and 2.

In a conventional dry method for granulating molten slag, slag is discharged from a slag runner on to a rotating atomiser device which may be in the form of a flat disk or a shallow cup or dish. The slag is atomised at the edge of the disk and the resulting slag droplets partially cool to the point where they have a sufficiently robust shell that they do not stick on impact with the surrounding inclined water cooled wall.

After impact the slag falls into an air cooled bed where further cooling takes place before discharge. The design is such that the air temperature leaving the granulating enclosure is sufficiently high to allow valuable heat recovery in the form of hot process air for drying etc or for steam generation. In turn, the steam may be used for electricity generation. In the case of blast furnace slag, the granulate has a very high proportion of glassy slag, making it suitable for cement production.

To allow for variations in slag flow rate, particularly when the granulator is connected directly to the end of the furnace slag runner, the refractory lined slag delivery pipe directing the slag onto the rotating disk is typically oversized. Hence, the delivery pipe does not run full. The granulator chamber is typically run under positive pressure, resulting in a loss of hot air and reduced heat recovery. Similarly, if the granulator chamber were to be run under suction, cold air would be drawn in, resulting in a similar loss of recovered heat. The magnitude of the heat loss in either case depends upon the operating chamber pressure and the free space in the slag delivery pipe.

In the example of Fig. 1, a rotary atomising granulator comprising a rotating elementS, typically a disk or dish, rotating on a drive shaft 6 in the direction of arrow 7 is mounted in a granulation chamber 13. In this example, which also allows for heat recovery, an air inlet 10 and air outlet 11 provide a path for air flow through the granulation chamber 13 to a heat exchanger 12. There may be multiple air inlets along the base of the granulation chamber. The chamber may also be provided with water cooled walls 15 and a cooled bed 16. In a preferred embodiment, a vertical, refractory lined slag delivery pipe 4 is coupled via an outlet 3 of a tundish 2, which receives slag 9 from a slag runner 8. The slag delivery pipe helps direct the molten slag to the required position in the granulation chamber. A flow control device 1, in this example a stopper rod in the form of a conical plug, is movably mounted in the tundish outlet.

The moveable conical plug adjusts the flow rate, so that when the slag starts to solidi1 in the pipe, more flow is permitted to prevent solidified slag from blocking the pipe. High flow rates are typically in the range of 2 to 6 tonnes per minute.

The flow rate control also improves the efficiency of the heat recovery process by applying slag flow control during dry granulation of slag. By controlling the slag flow using the flow control device, a slag seal between the flow control device I and the tundish outlet 3 is formed, preventing air passage through the slag delivery pipe 4, so avoiding loss of hot air from the granulation chamber, or ingress of cold air into the chamber. The flow control device is positioned above the outlet 3 of the tundish 2, which is typically refractory lined, containing molten slag 3. The flow control device I shown in Fig. I takes the form of an actuator rod 14 connected to a stopper 17 which, in this example, is a frustum of a cone, although other shapes of flow control device may be used to reduce the cross section of slag so as to form the slag seal. The outlet 3 from the tundish 2 and the tube 4 are also typically refractory lined. Molten slag 9 is delivered from the tube 4 onto the rotating element 5. At the rim of the rotating element 5, the slag is atomised. The refractory lined tube 4 is designed to convey the maximum design slag flow rate on to the rotating element 5. The slag properties, such as head calculations, depth of slag to size of opening and cross section may be used to determine this, but as slag solidifies in the tube, the cross section changes, hence the need for an oversize tube. Moving the stopper 17 away from the tundish outlet 3 by raising the rod 14 allows an increased slag flow to pass through the tube 4. The flow control device I is constrained to move under the influence of a control system 18 to maintain a slag level in the tundish 2, thus providing a seal to prevent air passing through the tube 4.

When the surface of the slag is heated using e.g. a hood burner (not shown) and blast furnace gas, the temperature of the surface of the slag is maintained to prevent formation of a crust of solidified slag, but allow a slag seal between the stopper and the molten slag in the tundish to form. Then a level sensor (not shown) in the tundish may be used to provide data to the controller. As the level drops to its lowest allowable level, the stopper is moved closer to the outlet 3 to prevent air passage past the stopper.

As the level increases, the stopper 17 can be moved further away from the outlet without the slag seal being compromised and can then be used to control the slag flow rate. Where there is no heating of the surface of the slag in the tundish, the formation of the slag crust prevents a level sensor from being effective. In this case, weight of the tundish, may be used to provide control data. This in combination with the position of the stopper itself enables the controller to move the stopper as required.

The present invention has a number of advantages. It enables a more controllable slag flow and prevents air passage into the slag delivery pipe, either from the outside, or from the slag chamber, resulting in a reduction cooling air entering or hot air being lost and therefore an improvement in heat recovery efficiency.

Fig. 2a illustrates use of the flow control device of the present invention in a wet slag granulation system. Although this does not assist with heat recovery, as this is not available with wet slag granulation, it does help to make the granulation process more efficient by evening out peaks in the flow rate and discourage solidified slag from blocking the delivery pipe 4. In one example of a wet granulation system, the slag is supplied by a slag runner 8 to the tundish 2, which may be heated as mentioned above to prevent a solid layer of slag from forming, so that the slag seal 30 formed between the molten slag 31 and the flow control device is maintained as the stopper 17 is moved towards or away from the entry 3 to the slag delivery pipe 4. As the slag 9 passes out of the slag delivery pipe into a first granulation tank 32, high pressure water sprays 33 supplied by a water supply 34 rapidly cool the slag to cause granulation. The water and granulated slag flow 35 out of the first granulation tank, over a lip 36, to another tank 37 and then a screw conveyer (not shown) extracts the granulated slag from the water.

The water sprays may be supplied from plates 38 set at an angle around the flow of slag 9 emerging from the slag delivery pipe as shown from above in Fig.2b. The temperature of the cooling water supplied and the cooling water after granulation may be measured by temperature sensors (not shown) and compared by the controller. If the temperature difference increases, then the slag flow is assumed to have increased. If the increase falls outside a predetermined range, then the stopper may be moved to modi the slag flow rate.

Fig. 3 is a flow diagram illustrating the method of the present invention.

Molten slag is supplied 20 to a tundish. The level of molten slag, or weight of the tundish and position of the flow control stopper are monitored 21 by sensors in the tundish, or a tundish weighing system and the level, or weight and position reported back to the eontrollerl8. A comparison 22 is made with a required minimum level for a given stopper position and if the level is at or below the minimum required for that stopper position, then the stopper is moved 23 closer to the outlet 3. If the stopper is not at or below the minimum, then it may be moved away from the outlet in order to increase the flow rate to the granulator and to control the slag flow to the granulator.

The slag flowing onto the granulator is granulated 24 and cooled 25. For diy slag granulation, the additional steps of flowing 26 process air over the slag as it is cooled and passing 27 the heated air to a heat recovery facility are then carried out. For dry slag granulation, the mechanism of measuring power or current of the rotary atomising granu'ator drive motor described in our co-pending patent reference 201 2P1 7453 GB may be used to provide feedback to the controller for flow control.

Claims

CLAIMS1. A slag granulation device, the device comprising a tundish and a granulation chamber, the granulation chamber comprising a slag inlet, and the tundish comprising a slag inlct and a slag outlet, the tundish slag outlet being coupled to the chamber slag inlet; the device further comprising a flow control device mounted in the tundish slag outlet.
2. A device according to claim I, further comprising a process air supply inlet and a process air extraction outlet.
3. A device according to claim 2, further comprising a heat recovery mechanism conncctcd to thc proccss air outlet.
4. A device according to any of claims I to 3, wherein a rotary atomising granulator is mounted in the granulation chamber to receive slag from the chamber slag inlet.
5. A device according to any preceding claim, wherein the chamber slag inlet comprises a pipe having a diameter sufficient for a predetermined maximum flow rate.
6. A device according to any proceeding claim wherein the tundish further comprises at least one of a slag level sensor, a tundish weight sensor and a flow control device position sensor.
7. A device according to any preceding claim, wherein the flow control device comprises a stopper and an actuator.
K A method of operating a slag granulation process in a slag granulation device comprising a tundish and a granulation chamber, the method comprising supplying molten slag to the granulation chamber, granulating the molten slag, the method further comprising moving a flow control device in the tundish through a range of positions to control slag flow rate through a slag delivery outlet of the tundish to the granulation chamber and forming a slag seal between the flow control device and the slag delivery outlet to prevent passage of air through the slag delivery outlet.
9. A method according to claim 8, further comprising passing process air through the granulation chamber to cool the granulated molten slag, thereby heating the process air.
10. A method according to claim 9, further comprising recovering heat from the process air using a heat recovery mechanism.
11 A method according to any of claims 8 to 10, further comprising measuring a level of slag in the tundish, comparing the measured level with a required minimum and causing the flow control device to move towards the tundish slag delivery outlet if the measured level falls below the required minimum.
12. A method according to any of claims 8 to 11, comprising carrying out a rotary atomising dry slag granulation process in the granulation chamber.