EP1183395A1

EP1183395A1 - Method for reducing and granulating slag and a device for carrying out this method

Info

Publication number: EP1183395A1
Application number: EP00924965A
Authority: EP
Inventors: Alfred Edlinger
Original assignee: Holcim Ltd
Current assignee: Holcim Ltd
Priority date: 1999-05-05
Filing date: 2000-05-04
Publication date: 2002-03-06
Also published as: ATA80299A; AT407153B; WO2000068439A1; AU4384800A

Abstract

The invention relates to a method for reducing and granulating slag, according to which the molten slag is expelled into a granulating chamber by a propulsion jet. Gases, in particular, air or oxygen are fed into the molten slag to form foamed slag and the temperature of said foamed slag is raised to a temperature ranging between 1420 DEG and 1680 DEG C by the introduction of fuels, such as coal. The foamed slag is then expelled into a granulating chamber. The device has a tundish (1), into which a gas lance (20) opens and/or in whose base nozzles are located (2), in addition to a foamed slag overflow (5) and a slag outlet (6). The tundish (1) is provided with a pressure-tight lid (8), to which a sluice (9) is connected above the slag bath for introducing solid matter and coal. A lance (7) for introducing a carrier gas which expels the foamed slag (4) opens into the slag outlet (6).

Description

Process for crushing and granulating slag and device for carrying out this process

The invention relates to a method for comminuting and granulating slag, in which the molten slag is ejected into a pelletizing chamber with a propellant jet, and to an apparatus for carrying out this method.

For crushing and granulating slag, it has become known to introduce liquid slag into a slag tundish and to discharge it into a granulation room by means of a propulsion jet. The liquid slag was mostly discharged into the pelletizing room with steam or high-pressure water and atomized as it emerged into the pelletizing room, with rapid cooling in the pelletizing room being carried out, for example, by exposure to high-pressure water or by introducing hydrocarbons. Due to the rheological properties of liquid slags, such slags had to be heated to a relatively high temperature and, in order to achieve a correspondingly fine atomizing jet, boundary conditions with regard to the basicity of the slag must also be taken into account if there is a sufficiently fine distribution and thus a sufficiently fine comminution without subsequent Grinding was desired. Optimizing the slag composition with a view to the finest possible size reduction and granulation is therefore necessarily a compromise with regard to the possible slag compositions if extremely high slag temperatures are not to be selected. High slag temperatures, in turn, cause high wear on the refractory lining of the slag tundish.

In order to achieve a faster division of such liquid slags into a subsequent granulating room, it has already been proposed to introduce gases into the slag in order to saturate the slag bath with gases. As a rule, inert gases were entered for this purpose, with oxygen mostly only to the extent necessary to ensure that a fully oxidized slag is present, which eliminates the risk of undesirable explosions when the liquid slag is subsequently subjected to high pressure water.

The invention now aims to provide a process of the type mentioned at the outset with which the composition of the slag and in particular the slag basicity can be varied within wide limits without losing the advantages of rapid comminution and rapid granulation of the slags and at the same time the possibility is created to ensure the relatively high temperature required for the rheology of the escaping slag in a particularly economical and simple manner without this leading to increased wear of refractory materials in the slag tundish. Furthermore, the invention aims to carry out the comminution and granulation with small-scale devices in such a way that subsequent grinding becomes unnecessary, so that a sufficiently fine particle size distribution of the solidified particles can be achieved immediately.

To achieve this object, the process according to the invention essentially consists in that gases, in particular air or oxygen, are introduced into the molten slag to form a foam slag, and that the foam slag temperature is brought about by fuels introduced into the foam slag, such as coal, to temperatures of above 1350 ° C. , in particular 1420 ° to 1680 ° C and that the foam slag is ejected into a pelletizing room. Because a foam slag is now deliberately formed, the specific weight of the slag is first reduced significantly and in particular reduced to approximately 1/10 of the original specific weight of the compact slag melt. When such a foam slag is formed, closed-pore structures with a bubble size with diameters in the range of millimeters are created, such foam slags being introduced accordingly of shear forces, such as can be generated with little effort depending on the slag basicity, for example by blowing in gases over porous flushing blocks and by maintaining critical temperature ranges. It is essential that temperatures above 1350 ° C. and in particular between 1420 ° and 1680 ° C. are reached, this temperature being easy to achieve inside the foam slag due to the structural properties of foam slag and at the same time building up a temperature gradient to the edge regions of the foam slag volume can be. The required temperature can be maintained in such foam slags by introducing solid fuels into the foam slag, which burn together with the injected oxygen inside the foam slag to form the foam slag and at the same time ensure the high melting temperatures in the manner. In a foam slag of this type, the desired slag composition can now be set in a particularly simple manner, and solid additives such as CaO, Al2O3 and SiO2 can be added in the foam slag to set the slag basicity to a value of preferably 0.8 to 1.3 become. It is thus possible to build up the desired slag chemistry at the same time as the temperature of the molten bath in the foam slag, and to make matters worse, inexpensive fuels, such as cheap coal, can be used. A possibly increased sulfur value of such cheap coal is immediately and immediately bound in the slag, the foam slag being a kind of flameless burner with which the exhaust gas temperatures can also be set in the desired manner. Since the resulting exhaust gas in the foam slag is already completely dedusted and any dust is slagged in situ and fuel sulfur is also incorporated into the slag due to the basicity of the slag, a high-purity exhaust gas is produced immediately, which can be directed, for example, to gas turbine showers . The fact that such a foam slag with the desired composition and the desired temperature is now ejected into a pelletizing chamber means that much easier and finer microgranulation can be achieved compared to compact slag melts. The slag is already pre-comminuted in the foam slag melt, so that much finer particles are formed during a subsequent rapid cooling. In principle, cooling can take place in any conventional manner, the foam slag being able to be passed directly into a conventional water bath, onto a plate cooling belt or via a centrifugal wheel. However, the procedure according to the invention is preferably such that the foam slag is expelled with steam and high pressure water is applied in countercurrent. For this purpose, steam with temperatures between 200 ° and 1200 ° C and a pressure between 5 and 15 bar is advantageously used to eject the foam slag, whereby high pressure water with a pressure between 50 and 300 bar is advantageously directed against the foam slag steam jet. In this case, the high-pressure water jet enters the grinding or evaporation chamber with high kinetic energy as a counter jet to the steam jet. The water jet evaporates due to the enthalpy flow of the slag droplets and the high-temperature steam. The high kinetic energy of the high-pressure water is transferred to the evaporated high-pressure water, so that a rapidly directed steam volume is created which is directed at a high axially oriented speed towards the particle-laden high-temperature steam jet. These two energetic potential fields mutually penetrate each other, so that the dissipated energy leads directly to particle size reduction, whereby the desired speed vector of the high pressure water, the high pressure water pressure, the free jet length and the distance to the high temperature steam inlet are available for further setting the desired size reduction. In addition to the adjustability of the desired comminution effect, ie the particle size that can be achieved, the comminution efficiency can also be optimized by appropriate selection of the distances. so that a high grinding efficiency can also be set, for example, by appropriate adjustment of the high pressure water pressure.

Overall, the formation of the foam slag in the slag tundish allows not only the setting of the desired slag composition but also the formation of a correspondingly high and high-purity hot gas volume, which can be used energetically, for example, in a gas turbine, without the need for separate exhaust gas purification systems. As already mentioned, the slag basicity can be adjusted to a value of 0.8 to 1.3 in the foam slag in a simple manner by adding CaO, Al2O3 and / or SiO2.

The best results with regard to the size reduction effect and the desired fineness of grinding could be observed if the density of the foam slag was set below 0.35 kg / dm- ^, in particular about 0.28 kg / dm.3.

Surprisingly, it has been shown that foam slags have increased stability under superatmospheric pressure. It is therefore advantageous in the process according to the invention that the foam slag is kept under a pressure between 3 and 7 bar. With such a design, a pressure gradient is simultaneously formed at the outlet of the foam slag tundish, so that the hot foam slag emerges with high kinetic and thermal energy. The hot exhaust gas has essentially the same temperature as the foam slag and is practically dust and sulfur-free and is therefore preferably suitable, for example, as a propellant gas for a gas turbine, with part of the mechanical energy obtained being used for air compressors for the bottom gas to be introduced to form the foam slag can.

Overall, the foam slag generator in the slag tundish presents itself as a flameless combustion chamber of a gas turbine, with which relatively coarse alternative fuels can be used directly and can be used economically.

The device according to the invention for carrying out this method is essentially characterized by a tundish in which a gas lance and / or in the bottom of which nozzles are arranged, that a foam slag overflow and an outlet opening for slag are provided so that the tundish carries a pressure-resistant lid, to which a lock for the entry of solids and coal is connected above the slag bath and that a lance for the entry of a carrier gas for ejecting the foam slag opens into the slag outlet opening. The comminution takes place in a downstream grinding or evaporation chamber, for which the training is advantageously carried out in such a way that a grinding and evaporation chamber is connected to the slag outlet opening, that a pressure water line opens at the side of the chamber opposite the slag outlet and that a classifier for discharging the comminuted and granulated material is connected to the grinding and evaporation chamber. In principle, in the grinding and evaporation chamber it is also possible to work with reducing liquids or gases in addition to or as a replacement for the high-pressure water, with which residual iron oxide in the slag is reduced and, at the same time, rapid cooling is achieved due to the decomposition energy or cracking energy of hydrocarbons. The fine iron formed in this way can be separated separately, for example by magnetic separators. A major advantage of the formation of a foam slag is in addition to the fact that relatively high temperatures can be produced in a simple and controlled manner inside the foam slag, and also that any metallic slag iron is safely burned, so that slag granulation explosion risks are basically eliminated. Due to the high specific foam slag volumes, much larger slag outlet openings can be provided in the slag tundish, which increases the risk of clogging or overgrowth can be decisively minimized by possibly entrained solid particles, such as a refractory eruption. Compared to known devices, in which compact slags are ejected into a grinding or evaporation room, it is possible to build with comparatively large clear diameters, which are increased by a factor of 10 to 100 compared to known devices.

Advantageously, an exhaust pipe is connected to the tundish, which is led via a gas turbine and / or heat exchanger, which further improves the energy use and results in an economical procedure.

The invention is explained in more detail below on the basis of an exemplary embodiment schematically shown in the drawing of a device suitable for carrying out the method according to the invention. 1 shows a schematic cross section through a slag tundish for carrying out the method according to the invention, and FIG. 2 shows a schematic arrangement of a grinding or evaporation chamber following such a foam slag generator.

In Fig. 1, 1 denotes a slag tundish, to the bottom of which porous floor stones 2 are connected. Air and / or oxygen is introduced via a line 3 into a melt 4 via the porous floor stones 2, a foam slag subsequently being formed in the interior of the melt. The foam slag reaches a slag outlet opening 6 via a foam slag weir 5. Coaxial with the slag outlet opening 6 there is the mouth of a lance 7, through which, for example, high pressure steam can be injected and the foam slag can be quickly dispersed and comminuted after the outlet.

In order to increase the stability of the foam slag, the slag tundish is closed and a cover 8 is provided. Solids and especially CaO, Al2O3 and SiO2 to adjust the slag basicity, a cellular wheel sluice 9 can be introduced directly into the foam slag bath, and due to the high turbulence, thorough mixing and homogeneous distribution are ensured at the same time. Solid fuels, such as cheap coal, can also be introduced via the same cellular wheel lock 9 in order to ensure the desired foam slag temperature. The combustion of such lumpy coal takes place rapidly in the interior of the foam slag by reaction with the oxygen contained in the pores at correspondingly high temperatures, it being possible to draw off highly pure exhaust gas via a line 10 at a temperature which essentially corresponds to the temperature of the slag. Slag temperatures of up to 2000 ° C and thus exhaust gas temperatures of the same order of magnitude are readily possible, such high temperatures primarily occurring inside the foam slag and a temperature gradient being able to form at the edge of the foam slag bath, whereby the refractory lining of the slag tundish 1 is protected accordingly . The slag tundish can be kept under a pressure of 3 to 7 bar, which also significantly improves the ejection of the foam slag.

The foam slag burner output can be varied to a large extent. In particular, for the formation of correspondingly high pure exhaust gas flows at high temperature, a corresponding mode of operation can be selected as a flameless burner, from which the slag is discharged in each case after the desired composition has been reached and / or further slag can be introduced continuously to form the desired foam slag.

While with conventional compact slags the viscosity decreases primarily with increasing temperatures and increasing iron oxide content, with foamed slag which shows a structurally viscous flow behavior, regardless of the composition, there is a significantly lower viscosity, so that slag compositions can also be sprayed effortlessly, the temperature of which should be much higher in the case of a compact slag melt. At the same time, inside the foam slag it is possible to set almost arbitrarily high temperatures in an economical manner using cheap fuels, without this leading to increased wear of the refractory lining.

FIG. 2 now shows an advantageous comminution device which is connected downstream of a slag generator or slag tundish, as shown in FIG. 1. The foam slag supply is indicated schematically by the chamber 11, into which a high-temperature steam lance 12 opens. The foam slag 13 enters a grinding or evaporation chamber via the opening 14, a high-pressure water jet 15 being directed toward the emerging jet via a high-pressure water lance 16. The high pressure water lance 16 can be slidably mounted in the direction of the double arrow 17 so that the desired parameters and in particular the spreading angle α can be set, which has a significant influence on the degree of grinding and the degree of efficiency. High pressure water is used with a pre-pressure of around 50 to 300 bar. High temperature steam can be used in the temperature range between 200 ° and 1200 ° C and in a pressure range of 5 to 15 bar. The spreading angle α shown in FIG. 2 can also be interpreted as an evaporation gradient, the angle α increasing correspondingly at a lower pressure of the high-pressure water. The larger this angle α, the smaller the grinding efficiency and the coarser the ground material. Overall, simple adjustments make it possible to set both the grinding efficiency and the degree of comminution in accordance with the desired parameters, the fine ground material subsequently being able to be drawn off via a classifier 18 and the line 19.

As indicated by dashed lines in FIG. 1, air / oxygen can optionally be added together in the foam slag via a blowing lance 20 be blown with carbon to achieve the formation of the foam slag and the desired foam slag temperature. In these cases it is even possible to dispense with porous sink stones 2 in the floor.

Claims

Claims:

1. A process for crushing and granulating slag, in which the molten slag is ejected with a propellant jet into a granulating room, characterized in that gases, in particular air or oxygen, are introduced into the molten slag to form a foam slag, that the foam slag temperature by the foam slag introduced fuels, such as Coal is brought to temperatures of over 1350 ° C, in particular 1420 ° to 1680 ° C and that the foam slag is discharged into a pelletizing room.

2. The method according to claim 1, characterized in that the foam slag ejected with steam and with high pressure water in

Countercurrent is applied.

3. The method according to claim 1 or 2, characterized in that steam with temperatures between 200 ° and 1200 ° C and a pressure between 5 and 15 bar is used to eject the foam slag.

4. The method according to claim 1, 2 or 3, characterized in that high pressure water is directed at a pressure between 50 and 300 bar against the foam slag steam jet.

5. The method according to any one of claims 1 to 4, characterized in that the slag basicity is adjusted to a value of 0.8 to 1.3 in the foam slag by adding CaO, Al2O3 and / or SiO2.

6. The method according to any one of claims 1 to 5, characterized in that the density of the foam slag is set to below 0.35 kg / dm ^, in particular about 0.28 kg / dπ.

7. The method according to any one of claims 1 to 6, characterized in that the foam slag is kept under a pressure between 3 and 7 bar.

8. The method according to any one of claims 1 to 7, characterized in that the combustion exhaust gases of the foam slag are fed to a gas turbine.

. Device for carrying out the method according to one of claims 1 to 8, characterized by a tundish (1) in which a gas lance (20) opens and / or in the bottom of which nozzles (2) are arranged, that a foam slag overflow (5) and an outlet opening (6) for slag is provided that the tundish (1) carries a pressure-resistant cover (8) to which a lock (9) for the entry of solids and coal is connected above the slag bath, and that in the slag outlet opening (6) a lance (7) for the entry of a carrier gas for ejecting the foam slag (4) opens.

10. The device according to claim 9, characterized in that a grinding and evaporation chamber is connected to the slag outlet opening (6), that on the side of the chamber opposite the slag outlet (6) a pressurized water line (16) opens and that to the grinding and Evaporation chamber is connected to a classifier (18) for discharging the crushed and granulated material.

11. The device according to claim 9 or 10, characterized in that an exhaust pipe (10) is connected to the tundish (1), which is guided via a gas turbine and / or heat exchanger.