WO2000030989A1 - Method for crushing and granulating slag - Google Patents

Abstract

The invention relates to a method for crushing and granulating slag, according to which liquid slag (8) is expelled with steam into a granulating chamber (11) and cooled. According to said method superheated steam at temperatures of more than 1000 DEG C is injected into the liquid slag (8) near the slag discharge opening. Cooling is carried out in the adjoining granulating chamber (11) by an endothermic reaction of the superheated steam and hydrocarbons introduced into said granulating chamber, which results in the formation of CO and H2.

Description

Process for crushing and granulating slag

The invention relates to a method for comminuting and granulating slag, in which liquid slag is ejected with steam into a granulation chamber and cooled.

According to an older proposal by the applicant (AT-GM 94/98), a method for granulating and comminuting liquid slag was proposed, in which pressurized water was injected into the slag melt in particular for the comminution of liquid blast furnace slag and the slag as a jacket of the pressurized water jet a grinding room was spent. In this older method, the direct conversion of the internal energy and especially the sensible heat of slag melts into grinding work was used directly. As an alternative to the use of pressurized water, the use of steam under relatively high pressure and temperatures of approximately 300 ° C. has already been proposed. The vapor was quickly heated by the liquid slag, which has temperatures of about 1500 ° C, whereby rapid expansion was achieved. The resulting kinetic energy was used to break up the jet and shred the slag, with the result that the cooling could be improved and accelerated by additional injection of pressurized water. In such processes using pressurized water and steam, large amounts of steam are required to generate the required kinetic energy. These amounts of steam can be circulated, although relatively high losses must be expected. As a rule, the steam was condensed after granulating the slag and evaporated again.

In order to improve the energy balance of such a method, coal, hydrocarbons or coal water mixtures were now directly injected into the slag in accordance with a further, as yet unpublished proposal, the hydrocarbons introduced in this way into the pelletizing chamber or the coal with injected water being converted into cracked gas. With With such a process, the energy balance could be significantly improved.

The invention now aims to further simplify such a method and to further improve the energy balance while minimizing the amount of water or steam to be introduced. To achieve this object, the process according to the invention essentially consists in that superheated steam at temperatures of over 1000 ° C. is blown into the liquid slag near the slag outlet opening and that the cooling in the subsequent pelletizing chamber by endothermic conversion of the superheated steam with hydrocarbons introduced into the pelletizing chamber is carried out with the formation of CO and H2. Because superheated steam with extremely high temperatures is used in deviation from all previously known proposals, the slag and the steam can be introduced into the pelletizing space in a quasi-isothermal manner. The fact that hydrocarbons are now introduced into the pelletizing chamber enables the introduction of hydrocarbons to be metered precisely and optimized for the amount of steam introduced, and because of the high degree of superheating of the steam, an extremely rapid reaction with the hydrocarbons introduced into the pelletizing chamber can be carried out. In this extremely rapid endothermic reaction of hydrocarbons with superheated steam, there is rapid cooling, the superheated steam introduced being largely or completely used up and the energy being stored in the reaction product of the strongly endothermic reaction. In the case of the strongly endothermic reaction with rapid cooling, carbon monoxide and hydrogen are formed, which can be drawn off largely without steam, so that the problems with condensing water can be largely eliminated. Overall, due to the rapid reaction of the superheated steam due to the high temperature with the hydrocarbon, a significant increase in volume is initially observed under local pressure rise with simultaneous subsequent strong cooling with a corresponding volume reduction. intensive shredding work takes effect in the smallest space. The fission gas or synthesis gas generated, consisting of carbon monoxide and hydrogen, can be drawn off at a relatively high temperature at which the slag particles have already largely solidified, and immediately not only with the sensible heat, but above all with the stored chemical heat be used. Due to the rapid conversion, caused by the high temperatures of the superheated steam, the steam requirement compared to known processes can be reduced to a fraction of the amount previously required and, at the same time, the energy released during the desired rapid cooling can be quickly set off by chemical conversion and onto it Way to deduct.

The process according to the invention is advantageously carried out in such a way that steam with temperatures between 1300 ° and 1500 ° C. is used. Since liquid slags are usually introduced into granulation rooms at temperatures of around 1500 ° C., it is largely possible to work isothermally in the area of the slag outlet of a slag storage container, for example a tundish, with such high steam temperatures, so that the desired implementation work is actually performed locally in the granulation room becomes.

Compared to known processes, steam can be used not only in a significantly smaller amount, but also at a significantly lower pressure level, with the procedure advantageously being that the superheated steam is used at a pressure of 1.5 to 3 bar.

The strongly superheated steam is generated in a particularly simple manner by superheating the steam, in particular saturated steam, in a regenerative heater. Such regenerative heaters can be found, for example, as so-called "COWPER" regenerative heaters in steelworks and are used, for example, for hot-blast heating of blast furnaces. Since the saturated steam at relatively low pressure due to such rain rative heater, conventional devices can achieve a high degree of overheating.

The desired targeted cooling in the pelletizing chamber can advantageously be achieved by injecting the hydrocarbons into the pelletizing chamber. Such injection of hydrocarbon or injection of gaseous hydrocarbons via appropriate gas outlet nozzles allows the desired cooling effect to be regulated in a targeted manner and adjusted to the minimally required amount of superheated steam.

The solidified and comminuted particles can be discharged in one or more stages. For this purpose, the procedure is advantageously such that the granules are withdrawn from the granulating chamber at temperatures <650 ° C., preferably <600 ° C., via a lock, in particular cellular wheel lock, and that the cracked gas or synthesis gas formed is removed via a dust separator, for example Hot cyclone, is withdrawn. Further particularly finely ground material can be drawn off from the dust separator, so that granules with the desired particle size distribution can be obtained directly.

For the subsequent use of the cracked gas or synthesis gas formed and in particular for the preferred use in the context of a direct reduction of ores, it is particularly advantageous if the cracked gas or synthesis gas formed is drawn off at temperatures between 600 ° and 700 ° C.

A portion of the cracked gas or synthesis gas formed can be used directly for heating the regenerative heat exchanger for the superheating of steam. Such regenerative heat exchangers can of course also be heated by burning fossil fuels if the high-quality synthesis gas can be used directly, for example, for direct reduction. The substantial saving in steam required, as is the case with a preferred procedure, allows the procedure to be used in such a way that 0.15 to 0.25 t of steam are used per ton of slag.

The invention is explained in more detail below on the basis of an exemplary embodiment shown schematically in the drawing. In the drawing, 1 schematically denotes a saturated steam source, from which saturated steam can be extracted at a pressure of approximately 2 bar. The saturated steam is fed via line 2 and a changeover valve 3 to a first regenerative heat exchanger 4, two superheaters or heat exchangers 4 and 5 being provided, which are operated alternatively. The heat exchangers 4 and 5 are charged with hot combustion gases via lines 6, saturated steam being passed in countercurrent through the heated heat exchangers 4 and 5, respectively. Whenever one of the two heat exchangers 4 or 5 is operated in countercurrent with saturated steam to overheat the saturated steam, the other heat exchanger 5 or 4 is in turn charged by hot combustion exhaust gases to the correspondingly high temperature for the subsequent overheating of the steam.

The superheated saturated steam reaches temperatures of approximately 1500 ° C. in a gas lance 7, which is immersed in a liquid slag bath. The slag bath 8 is contained in a tundish indicated by 9 and leaves this tundish via a slag outlet opening 10, the liquid slag 8 surrounding the overheated steam jet of the lance 7 essentially concentrically. The liquid slag is subsequently discharged into a pelletizing chamber 11, in which hydrocarbons are blown in via lines 12, which lead, for example, to ring nozzles. The reaction of the hydrocarbons with the superheated steam leads to the formation of cracked gas or synthesis gas, with rapid cooling to temperatures below 700 ° C. being achieved since this reaction is highly endothermic. Due to the high steam temperatures, this runs endothermic implementation extremely quickly. If additional water or water vapor is required for the reaction for the purpose of cooling, additional lines 13 can be pressurized with pressurized water or water vapor and a pressurized water jet or water vapor directed against the slag jet.

The rapidly solidifying material accumulates in the grain size range of approximately 10 to 50 μm at the lower end of the granulation chamber 11, this accumulation of material being designated 14 schematically. This material can be discharged via a lock, for example a cellular wheel lock 15.

The resulting cracked gas or synthesis gas consisting of carbon monoxide and hydrogen passes in the direction of arrow 16 to a subsequent dust separator 17, which is designed as a hot cyclone. The dust particles, whose particle size in the

Usually less than 20 μm, accumulate at the lower end of the hot cyclone and can be discharged via a lock, in particular another cellular wheel lock 18. The gap or

Synthesis gas, which has been cleaned of solid particles and is largely free of water vapor, can be withdrawn via line 19 and subsequently used for other purposes in a steel mill. In addition to the sensible heat, this cracked gas or synthetic gas contains a significant proportion of chemical heat which is stored in the cracked gas or synthesis gas.

Claims

Claims: 1. A process for comminuting and granulating slag, in which liquid slag (8) is expelled and cooled with steam into a granulating chamber (11), characterized in that superheated steam at temperatures of over 1000 ° C in the liquid slag (8) is blown in near the slag outlet opening and that the cooling in the subsequent pelletizing chamber (11) is carried out by endothermic reaction of the superheated steam with hydrocarbons introduced into the pelletizing chamber (11) to form CO and H2. 2. The method according to claim 1, characterized in that steam is used at temperatures between 1300 ° and 1500 ° C. 3. The method according to claim 1 or 2, characterized in that the superheated steam is used under a pressure of 1.5 to 3 bar. 4. The method according to claim 1, 2 or 3, characterized in that the steam, in particular saturated steam, is overheated in a regenerative heater (4,5). 5. The method according to any one of claims 1 to 4, characterized in that the hydrocarbons are injected into the granulating chamber (11). 6. The method according to any one of claims 1 to 5, characterized in that the granules (14) at temperatures <650 ° C, preferably <600 ° C, via a lock, in particular cellular wheel lock (15), from the pelletizing chamber (11th ) is withdrawn and that the cracked gas or synthesis gas formed is withdrawn via a dust separator (17), for example a hot cyclone. 7. The method according to any one of claims 1 to 6, characterized in that the cracked gas or synthesis gas formed is withdrawn at temperatures between 600 ° and 700 ° C. 8. The method according to any one of claims 1 to 7, characterized in that the cracked gas or synthesis gas is fed to a direct reduction of ores. 9. The method according to any one of claims 1 to 8, characterized in that the cracked gas or synthesis gas for heating the regenerative heat exchanger (4,5) is used for the superheating of steam. 10. The method according to any one of claims 1 to 9, characterized in that 0.15 to 0.25 t steam is used per ton of slag.