AU2016289602A1

AU2016289602A1 - Process and plant for roasting of dry ore particles in a fluidized bed

Info

Publication number: AU2016289602A1
Application number: AU2016289602A
Authority: AU
Inventors: Alexandros Charitos; Jochen Güntner; Jörg HAMMERSCHMIDT; Jean Claude Hein; Solmaz SÜKRÜ
Original assignee: Outotec Finland Oy
Current assignee: Outotec Finland Oy
Priority date: 2015-07-03
Filing date: 2016-06-23
Publication date: 2018-02-01
Anticipated expiration: 2036-06-23
Also published as: CL2017003360A1; WO2017005501A1; PL424587A1; PL233905B1; DE102015110772A1; AU2016289602B2

Abstract

The above invention relates to a process for the roasting of ore particles containing carbon and/or sulfur, wherein the particles are fed into the reactor for roasting. Anoxygen containing gas is introduced, wherein the particles are roasted in a fluidized bed at a temperature of 500 to 1000°C for at least 10 sec and whereby the roasted particles are withdrawn from the reactor. The particles have a water content of maximal 2 wt.-% and are injected pneumatically into the fluidized bed.

Description

Process and plant for roasting of dry ore particles in a fluidized bed

The invention refers to a process for the roasting of ore particles containing carbon and/or sulfur, whereby the particles are fed into the reactor for roasting, wherein oxygen is introduced, wherein the particles are fluidized in fluidized bed at a temperature of 500 to 1000 °C for at least 10 sec and wherein the roasting particles are withdrawn from the reactor. Furthermore, the present invention also relates to a plant suitable for carrying out the process.

Roasting is a step of the processing of certain ores. More specifically, roasting is a metallurgical process involving gas-solid reactions at elevated temperatures with the goal of separating of the metal compounds. Often before roasting, the ore has already been treated in beneficiation plants, like for example by froth floatation. But also grinded whole ore can be treated.

In roasting, the ores concentrate is treated with very hot air. The process is generally applied to minerals containing sulfur and/or carbon. During roasting, the sulfide and/or carbonates and/or org. carbon is/are converted to an oxide and sulfur is released as sulfur dioxide and org. carbon to cabon dixide or cabon monoxide. For the ores CU2S (chalcocite) and ZnS (sphalerite) balanced equation for the roasting are:

Organic carbon is converted according to the following equation:

A typical roasting process is described in document DE 976 145 A1, wherein a typical roaster is described. Therein, ore particles are fed into a fluidized bed reactor, which is built as such, that its cross-section is enlarged from the bottom up whereby particles of each diameter can be fluidized.

Document DE 3 300 609 deals with a process for particle roasting, wherein an excess of an oxidation gas is used in a fluidized bed reactor.

Document DE 907 417 describes a process for the reduction of Fe2C>3 to Fe3C>4 by using carbon as an oxidizing agent.

Also document DE 101 0 646 teaches with the reduction of Fe2C>3, whereby three fluidized bed systems are used, which are built on top of each other.

Document CH 538 655 describes a fluidized bed to convert manganese or magnesium sulfate in the cross bonding oxide. As it is typical for roasting processes, the educts are fed into the reactor from above.

In all these processes, the ore concentrate is fed with a water content of 5 to 12 wt.-%. During roasting, the moisture is evaporated and the resulting steam is passed through various consumers or used to make electricity in a generator. The concentrate of the moisture of 5 to 12 wt.-% is normally carried into the roaster with a slinger belt over a bed in the roaster.

Feeding dry concentrate with high energy content, would save the additional necessary energy cost to evaporate the contained water. However, it is not possible to feed the dry material with a slinger belt. Feeding material over the belt would lead to the effect that a high amount of material would fly into the free board over the fluidized bed. Therein, the solids would react, being overheated and forming agglomerates with themselves on the top of the roaster. As a result, not only clumps would be built up, but also the top of the roaster with bricks etc. would be overheated.

From other fluidized bed processes, a direct feeding is known. For example, document DE 3 534 419 C1 describes the gasification of coal in a fluidized bed, whereby the coal is injected into the fluidized bed itself, where it is immediately gasified. Nearly the same process is also described in DE 10 2005 047583 B4.

However, in a roasting process a direct feeding of ore particles to the fluidized bed the skilled person expect an agglomeration directed at the feeding points, due to the high local ore concentration. Therefore, since nowadays it does not seem to be possible to feed the ore particles in a dry state into a roasting reactor.

Therefore, it is the object of the invention to provide a process in which ore particles may be fed in a dry stage into a fluidized bed reactor.

This object substantially is solved by the invention as defined in claim 1. Thereby, the particles are fed into the roasting reactor. Further, an oxygen containing gas is introduced, which is preferably used as fluidizing gas. The particles are fluidized inside of the reactor in a fluidized bed at a temperature of 500 to 1000 °C for at least 10 sec. An average retention time in a normal fluidized bed reactor is in the range of 20 to 50 minutes. After that, the roasted particles are withdrawn from the reactor. Naturally, the roasting gases are removed from the reactor at the top of the reactor.

It is the basic idea of the invention, that the particles have a surface water content of maximal 2 wt.-%, preferred maximal 1 wt.-% and are injected pneumatically into the fluidized bed. Therefore, the material can react in the bed as requested, since next to the outlet of the feeding line, the particle concentration is diluted due to the pneumatic gas. As a result, the energy consumption is reduced since no water has to be evaporated.

The ratio between pneumatic gas and particle weight would be in maximum 10 kg solids per kg of pneumatic gas.

Preferably, the org. carbon content is between 0 and 8 wt.-% and/or the metal sulfide - sulfur content is between 3 and 55 wt.-%. In this range, the yield of the reaction is as high as possible.

Typically, the average diameter of the particle is between 0,001 and 10 mm, preferred 0,001 and 2 mm. In this range, the particles can be fluidized in typical fluidized bed reactors.

In a preferred embodiment of the invention the design of the fluidized bed is a bubbling fluid bed. Bubbling system takes place when the inlet gas velocity of the fluidized gas is slightly greater than the minimum fluidizing velocity. This contributes to a small expansion in the bed. Small bubbles tend to become adapted in the dense phase where it is injected into a stationary, therefore nonbubbling bed. Subsequently, when the gas flow in the dense phase increases, large bubbles tend to rise. If the bubbles are larger than the critical size, the bed will start to expand in an amount which is the same as a volume of the injected bubble. Using a bubbling fluidized bed, a more uniform temperature profile is created in the bed, which is why the reaction temperature can be lowered. Lowering the temperature will lead to a small risk of agglomeration, which is positive for injection of the particles directly into the bed.

Roasting reactions are exothermic reactions. Therefore, a fluidized bed has to be cooled. Preferably, the fluidized bed is cooled via at least one cooling device, like cooling coils or cooling plates which sticks into the bed.

In a preferred embodiment of the invention, the particles are injected inside of one cooling device, like between two cooling plates or inside of a cooling coil. It is also possible to inject the particle with a distance of 50 cm or less, preferably 25 cm or less, most preferably 15 cm or less to the cooling device. This offers the possibility to inject the particles in a region, where the temperature is locally lower than the average temperature of the fluidized bed. Therefore, the risk of agglomeration can be lowered further.

It is also preferred to use an inert gas like nitrogen as the gas for the pneumatic injection. Thereby, clumping can be reduced since not only the local particle concentration but also to the local oxygen concentration is lowered.

The particles are introduced via at least one nozzle, whereby the average velocity of the particles in the nozzle(s) is between 10 and 60 m s'1.

Furthermore, the invention also comprises an apparatus for roasting of ore particles containing org. carbon and/or sulfide-sulfur with the features of claim 8. Such an apparatus comprises a fluidized bed reactor for performing the roasting process. The fluidized bed reactor features at least one feeding line to introduce ore particles containing org. carbon and/or sulfide-sulfur, one oxygen line to have oxygen containing gas stream and an outlet line to remove the roasted particles from the reactor. According to the invention, the feeding line features a pneumatic delivery system and has at least one opening which is positioned such during operation that the particles are directly fed inside of the fluidized bed. This offers the possibility to feed dry particles which would otherwise flow in the freeboard of the roaster, where they react, create agglomeration and heat up the reactor's top.

To cool the fluidized bed and withdraw the heat caused by exothermic roasting reactions, at least one cooling device is installed such that during operation it sticks into the fluidized bed of the fluidized bed reactor.

Preferably, the cooling device features at least two cooling plates and/or at least one cooling coil.

To prevent the fresh fed particles from agglomeration, in a most preferred embodiment the outlet of the feeding line ends between the cooling plates and/or inside of the cooling coil. It is also possible that the outlet is situated with a distance of 50 cm or less, preferably 25 cm or less, most preferably 15 cm or less to the cooling device. Thereby, the local temperature at the feeding position is lowered, which is why the activation energy needed for an agglomeration is not reached.

It also lies within the scope of the invention to add an additional cooling of the feeding line or at least the outlet of the feeding line to reduce the risk of clumping further.

The reactor can be configured such that the feeding line features at least four outlets which are evenly distributed in the reactor.

Further developments, advantages and possible applications of the invention can also be taken from the following description of the drawings. All features described and/or illustrated for the subject matter of the invention per se or in any combination, independent of their inclusion in the claims or their back-references.

In the drawings:

Fig. 1 shows schematically an apparatus according to the invention and

Fig. 2 shows schematically a cross section of the reactor.

According to Fig. 1, the apparatus 10 features a feeding line 13 for injecting ore particles into the reactor 11. The feeding line 13 includes a pneumatic delivery system 12. To withdraw particles after roasting from the fluidized bed, an outlet line 16 is foreseen.

Oxidizing gas is introduced via oxygen line 15, whereby the oxidizing gas, preferably air, is also used as fluidizing gas, which is why it is introduced at the bottom of the reactor 11. After introducing, the fluidized gas has to be passed through a perforated base 20. During operation, a fluidized bed 21 is situated during operation above the perforated base 20.

Above the fluidized bed 21, the so called freeboard 22 is situated on the top of the reactor 11. From the freeboard 22, a line 30 is foreseen to withdraw the roasting gases. Line 30 ends in a cyclone 31, wherein the gas is separated from small particles carried out. The gases are passed from cyclone 31 via a line 32 to a, not-shown further gas cleaning while the particles separated in cyclone 31 are passed via a line 33 back into the reactor 11.

Inside of the fluidizing bed 21, cooling devices 17 in form of line cooling plates are installed such that during operation they are inside of the fluidized bed 21. The feeding line 13 leads into the middle of these cooling devices 17 and injects ore particles via an injection nozzle 14 between the cooling devices 17 designed as cooling plates. Therefore, the local temperature at the injection position is lowered to avoid agglomeration.

Fig. 2 shows a cross section of the reactor 10. Over feeding line 13, material is transported to the injection nozzles 14. All injection nozzles are positioned between two cooling devices 17 built as plates. Thereby, the injection position features a temperature of at least 3 °C, preferably 5 °C, most preferably more than 10 °C lower than the average reactor temperature to lower the risk of agglomeration.

To protect the cooling devices 17 and the infection nozzles 14 from damages by fluidized particles, the perforated base 20 is not perforated in the regions of the cooling devices 17 and the infection nozzles 14. As a result, no fluidizing gas is introduced in these regions.

Reference numerals 10 apparatus 11 reactor 12 pneumatic delivery system 13 feeding line 14 injection nozzle 15 oxygen line 16 outlet line 17 cooling device 20 perforated base 21 fluidized bed (during operation) 22 free board 30 line 31 cyclone 32,33 line

Claims

1. Process for the roasting of ore particles containing carbon and/or sulfur, wherein the particles are fed into the reactor for roasting, wherein an oxygen containing gas is introduced, wherein the particles are roasted in a fluidized bed at a temperature of 500 to 1000 °C for at least 10 sec and whereby the roasted particles are withdrawn from the reactor, characterized in that the particles have a water content of maximal 2 wt.-% and that the particles are injected pneumatically into the fluidized bed.

2. Process according to claim 1, characterized in that the carbon content is between 0 and 8 wt.-% and/or the sulfur content is between 3 and 55 wt.-%.

3. Process according to any of the preceding claims, characterized in that the average diameter of the particles is between 0,001 and 10 mm.

4. Process according to any of the preceding claims, characterized in that the fluidized bed is a bubbling fluid bed.

5. Process according to any of the preceding claims, characterized in that the fluidized bed is cooled via at least one cooling device.

6. Process according to any of the preceding claims, characterized in that the particles are injected inside of the cooling device or with a distance 50 cm or less to the cooling device.

7. Process according to any of the preceding claims, characterized in that the gas for the pneumatic injection is an inert gas.

8. Apparatus for roasting particles comprising a fluidized bed reactor with at least one feeding line (13) to introduce ore particles containing carbon and/or sulfur, one oxygen line (15) to add an oxygen containing gas stream and an outlet line (16) to withdraw the roasted particles, characterized in that the feeding line (13) features a pneumatic delivery system (12) and ends that the feeding line (13)in the fluidized bed (21) during operation.

9. Apparatus according to claim 8, characterized in that at least one cooling device (17) sticks into the fluidized bed (21) during operation.

10. Apparatus according to claim 9, characterized in that the cooling device (17) features at least two cooling plates and/or at least one cooling coil, wherein at least one outlet (14) of the feeding line (13) ends between the cooling plates and/or inside of the cooling coil.

11. Apparatus according to any of claims 8 to 10, characterized in that the feeding line (13) and/or at least one end of the feeding line (13) is partly cooled.

12. Apparatus according to any of claims 8 to 11, characterized in that the feeding line (13) features at least four outlets which are evenly distributed in the reactor (11).