WO2001031070A1

WO2001031070A1 - Multiple-level furnace

Info

Publication number: WO2001031070A1
Application number: PCT/EP2000/010138
Authority: WO
Inventors: Romain Frieden; Patrick Hutmacher; Pascal Ferretti; Stephan Schons
Original assignee: Paul Wurth S.A.
Priority date: 1999-10-25
Filing date: 2000-10-16
Publication date: 2001-05-03
Also published as: AU7788000A; LU90463B1

Abstract

The invention relates to a multiple level furnace which has several superposed, unsupported levels, and a rotatable shaft with several arms which extend beyond the levels and which are positioned in such a way that they transfer fine-grained or powdered material through the multiple-level furnace from the top to the bottom. Said material is conveyed from the inside to the outside in a spiral shape on one level and then onto the respective level below through gravity feed openings before being conveyed from the outside to the inside in a spiral shape and onto the respective level below through gravity feed openings. The invention is characterised in that at least one arm has a gravity feed pipe on the different levels for conveying the material to the next level down, respectively.

Description

deck oven

The present invention relates to a deck oven and a method for the thermal treatment of fine-grained or powdery material in a deck oven.

Deck oven are used e.g. B. in the drying of fine-grained or powdery Mateπal, in the pyrometallic treatment of residues and in the direct reduction of iron ore. From DE 1 225 673 z. B. such a method for drying reduction of fine iron ore in a deck oven known.

The furnace masonry of such a deck furnace is surrounded by a sheet metal jacket. Arms are rotatably arranged on the respective floors. The arms are equipped with stirring teeth or crusher which have the task of conveying the material on a spiral path either from the inside out or from the outside in so that it falls through the drop openings provided on the outer or inner circumference of the floor to the next lower floor can and in this way traverses the deck oven from top to bottom.

The gases, on the other hand, flow from bottom to top through the deck oven at a relatively high speed, thereby removing large amounts of dust from the deck oven. The exhaust gases are dedusted and the dusts are returned to the deck oven. The finer the material to be treated, the greater the amount of dust discharged.

The object of the invention is to provide a deck oven in which the discharge of fine-grained or powdery material is reduced together with the exhaust gases.

This object is achieved according to the invention by a deck oven which has a plurality of superimposed, self-supporting floors, a rotatable shaft with a plurality of arms which project above the floors and are designed such that they transfer fine-grained or powdery material from top to bottom through the deck oven, the material on one level spiral

ERSATZBLAH (RULE 26) from the inside to the outside and from there through drop openings to the floor below and then spirally from outside to inside and from there through drop openings to the floor below. The deck oven is characterized in that on different floors at least one arm has a downpipe through which the material is conveyed to the respective lower floor.

In the deck oven according to the invention, the material flow is therefore separated from the gas flow. The arms are designed in such a way that the material only falls through the drop opening (s) onto the floor below, under which the arm (arms) with the downpipe is (are) located. The arms that convey the material through the drop openings to the floor below rotate synchronously with the arms of the floor below with the correspondingly attached downspouts, so that the material falls through the downpipes onto the floor. Under the drop opening through which straight material falls, there is a downpipe which largely prevents the gas flowing upwards from flowing through this drop opening and entraining dust. The gas flows much more up through the other openings that are not covered by the downpipe. As a result, far less fine-grained or powdery material is carried with the exhaust gases from the tiered oven.

However, it is not necessary to equip all floors with such downpipes. Often it is sufficient to equip the upper floors to prevent larger amounts of dust from being removed from the deck oven.

In the context of the present invention, fine-grained or powdery material means material that has a relatively large proportion of material that has a fine granulometry. The material does not have to have a uniform grain size distribution.

Preferably, no arm is equipped with a downpipe on the first floor, since the material is introduced into the deck oven through a fixed opening. According to another aspect of the invention, a method for the thermal treatment of fine-grained or powdery material in a deck oven is presented, which has several superimposed, self-supporting floors, a rotatable shaft with several arms that project above the floors and are arranged so that they the material Transfer from top to bottom through the deck oven, whereby the material is transported spirally on one floor from the inside to the outside and from there through drop openings to the floor below and then spirally from outside to inside and from there through drop openings to the floor below are transported and a gas stream is passed from bottom to top through the deck oven. The process is characterized in that the material flow is separated from the gas flow.

The material is advantageously passed through a different drop opening than the gas stream. The present invention can be used in a wide variety of processes for the treatment of fine-grained or powdery or dust-containing material, be it for drying or in the thermal treatment of solid material, thermal treatment being understood only to mean heating or else pyrometailic treatments. Pyrometailic treatments are, for example, reductions of various metal oxides, or recycling and separation of residues, the oxides being sequentially reduced and discharged from the deck oven either in gaseous form or as solid substances.

Multi-deck ovens are also suitable for the thermal treatment of residues containing heavy metals, e.g. Sludges from surface treatment, pickling and cleaning, metalization and tinning processes of metal parts.

In such processes, large quantities of residues containing heavy metals are produced in the form of sludge or dust. These residues occur, for example, when filtering the immersion baths and, in addition to large amounts of water, contain various metals such as zinc, nickel, molybdenum, coblad, copper, iron in the form of hydroxides, chlorides and sulfates. These sludges can get in Deck oven are treated and the different metals are separated and recycled ..

An embodiment of the invention will now be described below with reference to the accompanying figures. 1 shows a section through a deck oven,

Fig.2: part of a deck oven in axial section

3: a section through FIG. 2 according to A-A,

Fig.4: a section through Fig. 2 according to B-B.

Fig. 1 shows a section through a deck oven 10, which has several - in this case eleven - stacked floors 12. These self-supporting levels 12, as well as the jacket 14, cover 16 and the bottom 18 of the furnace are made of refractory material.

A vent 26 is provided in the lid 16 of the furnace 10, through which the gases can be evacuated from the furnace and an opening 28 through which the fine-grained or powdery material can be applied to the top floor.

This material is, for example, iron ore, filter dust of various origins, residues containing metal oxide, the lead, zinc, nickel and iron oxides, etc. included, etc. Multi-deck ovens are also suitable for treating sludge, which is first dried on the top floors of the multi-deck oven and then treated if necessary. This material can be mixed with reducing agents and other additives before or after it is placed in the deck oven.

In the middle of the furnace, a shaft 20 is attached, to which arms 22 are attached, which protrude above the respective floors.

The shaft has a ring gear and is supported in a track bearing. The sprocket is driven by a pinion. The drive movement for the pinion is transmitted by an electric motor via a reduction gear, a clutch and a drive shaft. The shaft 20 and the arms 22 are air-cooled and openings 24 are provided on the arms through which the air can flow into the interior of the furnace and can be used there for afterburning.

At least one inlet opening 30 is provided in the side walls of the furnace 10, usually in the upper third, through which reducing agents or other auxiliary substances can be introduced into the furnace. The reducing agents can be in gaseous form as well as in liquid or solid form. The reducing agents are carbon monoxide, hydrogen, natural gas, petroleum and petroleum derivatives, or solid carbon carriers, e.g. around lignite coke, petroleum coke, blast furnace dust, coal, or the like. The carbon carrier, which is introduced to a level further down in the furnace 10, is mixed there by the arms 22 with the heated, powdery material. Due to the high temperature and the presence of carbon monoxide, the oxides contained in the powdery material are gradually reduced during transport through the deck oven 10.

In the lower half of the side wall, nozzles 32 are provided for blowing in hot (350 ° C. to 500 ° C.), oxygen-containing gases, through which air or another oxygen-containing gas can be introduced into the furnace 10. Due to the high temperatures and the presence of oxygen, part of the carbon burns to carbon dioxide, which in turn reacts with the excess carbon and is converted to carbon monoxide. The carbon monoxide finally reduces the oxides. Since this reaction is predominantly endothermic, it makes sense to install burners 34 in the lower part of the furnace, which ensure a constant high temperature in the lowest levels of the furnace. Gas or coal dust burners can be used here.

These burners 34 can be fired with air for preheating and / or for additional heating with gas or coal dust. An additional reducing gas can be generated by the quantitative ratio between oxygen and fuel material, or afterburning of the process gases is achieved with excess air. In the case of coal dust combustion, an overflow in the burner shot of carbon monoxide. With external combustion chambers, it can be avoided that the ashes of the burned coal get into the furnace. The temperatures in the combustion chambers are chosen so that the slag can be drawn off in liquid form and can be disposed of in a glazed form. The production of carbon monoxide reduces the consumption of solid carbon carriers in the furnace 10 and thus also the ash content in the finished product.

Openings 36 are provided in the side wall of the furnace at the level of the middle floors, through which hot gases can be removed from the furnace.

The addition of a gaseous reducing agent, e.g. Carbon monoxide or hydrogen through special nozzles 37 provided. The reduction of the ore can be completed in this atmosphere with an increased reduction potential. The treated material is then discharged through the outlet 39 in the bottom 18 of the furnace 10 together with the ashes of the reducing agents.

This furnace 10 allows various problem wastes such as e.g. Recycle dust and sludge contaminated by metals.

The dusts or sludges can thus be introduced into the deck oven 10 through the opening 28 in the lid 16. Metal oxide-containing dusts and sludges can be introduced into the furnace 10 together with the solid reducing agents through the inlet opening 28 or after the solid reducing agents through one or more openings in the side wall.

Some of the gases that flow upwards in the furnace can be sucked out of the furnace 10 through a suction nozzle in the side wall and can be blown back into the furnace 10 through an inlet. The gas with a relatively high content of reduced, evaporated metal can then be cleaned separately before it is possibly blown back into the deck oven. Fig. 2 shows part of a deck oven in axial section. Only the first three superimposed floors are shown on this figure.

The arms 22 are generally opposed, with four arms normally provided on each floor. A downpipe 42 is attached to one arm per floor, except on the first, which covers the drop openings 44 on the next higher floor.

The arms 22 are provided with stirring teeth 46 or craters which have the task of conveying the powdery material on a spiral path 48 either from the inside out or from the outside in so that it falls through the drop openings 44 provided on the outer or inner circumference of the floor can fall into the next lower floor and in this way pass through the deck oven from top to bottom (see also FIGS. 3 and 4).

During this time the powdery material is heated approximately 600 ° C to 1200 ° C. The stirring teeth 46 are arranged such that only one arm 22 per level conveys the powdery material through the drop openings 44. On the floor below, on the arm that rotates under the arm that transports the powdery material through the drop opening, a downpipe 42 is attached at the level of the drop openings 44. Due to the synchronous rotation of the two arms, the downpipe always covers the opening through the powdery material that trickles down onto the floor. The downpipe is designed so that only a small amount of gas can get up through the downpipe. Since the other drop openings are free, the gas will go up through these openings. Since hardly any gas moves up through the downpipe, hardly any powdery material is entrained. As a result, the dust concentration in the flue gases is much lower than in the conventional deck oven.

In the case of larger deck ovens, two or more downpipes can of course be provided on individual levels. In such a case, the corresponding ones Arms on the floor above are designed so that material is conveyed through the downpipes to the floor below.

Claims

1. deck oven, which has several superimposed, self-supporting floors, a rotatable shaft with several arms that protrude above the floors and are arranged so that they transfer fine-grained or powdered material from top to bottom through the deck oven, the material spiraling on one floor from are conveyed inside out and from there through drop openings to the respective lower level and then spirally conveyed from outside to inside and from there through drop openings to the lower level, characterized in that at least one arm has a down pipe on different levels, causing the material is transported to the lower floor.

2. deck oven according to claim 1, characterized in that the arms are designed so that above the floor on one arm equipped with a downpipe, each arm carries the material through the openings.

3. deck oven according to one of the preceding claims, characterized in that on different floors except the first floor at least one arm equipped with a downpipe.

4. Process for the thermal treatment of fine-grained or powdery material in a deck oven which has several superimposed, self-supporting levels, a rotatable shaft with several arms which project above the levels and are arranged in such a way that they pass the material from top to bottom through the Transfer the deck oven where the material is conveyed spirally from the inside to the outside and from there through drop openings to the floor below and then spirally from the outside to the inside and from there through drop openings to the floor below and with a gas flow from below passed upwards through the deck oven is characterized in that the material flow is separated from the gas flow. A method according to claim 4, characterized in that the material is passed through a different drop opening than the gas stream.