Method and device for the heat treatment of granular solids

Abstract

A method for the heat treatment of granular solids includes initially introducing solids into a first reactor configured as a flash reactor or fluidized bed reactor where they are brought into contact with hot gases at temperatures in the range 500 C. to 1500 C. Next, the solids are passed through a residence time reactor in which they are fluidized. The residence time reactor is configured in a manner such that it has various regions which are separated from one another, from which the solid can be withdrawn in a manner such that it is provided with a variety of residence times in the residence time reactor.

Claims

1. A method for the heat treatment of granular solids, wherein the solids are initially introduced into a first reactor configured as a flash reactor or fluidized bed reactor where they are brought into contact with hot gases at temperatures in the range of 500C to 1500 C., and wherein the solids are then guided through a residence time reactor in which they are fluidized with a fluidizing gas, wherein the residence time reactor is configured in a manner such that it is provided with various mutually separated regions from which the solid is separately removed in a manner such that it has a residence time in the residence time reactor which is of a variable duration, wherein removal from the various regions of the residence time reactor is carried out in a manner such that not all of the regions are fluidized, wherein the fluidized regions are fluidically connected in succession, whereby specific downstream regions are no longer fluidized with a fluidizing gas and therefore actively removed and wherein each region has its own removal device.

2. The method as claimed in claim 1, wherein solid is actively removed from at least one region.

3. The method as claimed in claim 1, wherein the first reactor is provided with a circulating fluidized bed.

4. The method as claimed in claim 1, wherein the air is used as the fluidizing gas in the residence time reactor.

5. The method as claimed in claim 1, wherein the residence time in the first reactor is in the range 0.1 sec to 15 min.

6. The method as claimed in claim 1, wherein the residence time in the residence time reactor is in the range 10 to 600 min.

7. The method as claimed in claim 1, wherein lithium carbonate is produced and/or the temperature in both reactors is in the range 750 C. to 1500 C.

8. A device for the heat treatment of finely granulated solids, comprising a first reactor for performing a method according to claim 1, which is configured as a flash reactor or as a fluidized bed reactor, and a second reactor, which is configured as a residence time reactor, wherein at least a portion of the residence time reactor is divided into a plurality of regions by means of partitions which are separately fluidized and which have separate outlets.

9. The device as claimed in claim 8, wherein the individual regions are disposed with respect to each other in the manner of steps.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a process flow diagram of the method in accordance with the invention, and

(2) FIG. 2 shows a diagrammatic representation of the reactor in accordance with the invention.

DETAILED DESCRIPTION

(3) The solid is supplied to a storage container 11 via line 10, from which it is mixed via line 12 into line 13 and then is fed into an electrostatic precipitator 14 via the line 13. The granular solid is transported from the electrostatic precipitator 14 into the first preheating stage 20 via line 15.

(4) Hot gas is withdrawn from the first preheating stage 20 via the line 13 and supplied together, as is known, with the solid via the line 13 to the electrostatic precipitator 14, in which a first preheat and a separation of the solid from the gas are carried out. Next, the gas is sent to a compressor 17 via line 16 and from there for waste gas purification, not shown, via line 18.

(5) The solid is transported from the first preheating stage 20 into the second preheating stage 22 via line 21. The hot gas from the preheating stage 22 is recycled to the first preheating stage 20 via line 23 as a counter-current in order to optimize the energy efficiency of the method.

(6) The solid is supplied via line 24 to a seal pot 30 with a discharge device, from which it is passed via line 31 to the first reactor 40 configured as a circulating fluidized bed; in addition, the material is discharged via line 53 to the downstream second reactor 50.

(7) This first reactor 40 is supplied with fuel via line 41. Furthermore, for fluidization, what is known as primary air is introduced via line 42 into the bottom of the reactor 40. In order to form a circulating fluidized bed, secondary air is also required, which is introduced via line 43.

(8) Hot waste gas is withdrawn from the first reactor via line 44 and introduced into the second preheater 22 in order to use the energy contained therein for preheating. The solid is supplied to the metering device 30 via line 45, from which it enters the residence time reactor 50. Furthermore, a line 51, which transports fluidization air to the residence time reactor 50 in order to fluidize the solid, branches off from the primary air supply line 42. Line 52 constitutes the first possibility for introducing the additional fuel, which then is already mixed with the fluidization air in the line 51. In addition or alternatively, the fuel may also be introduced via a separate system, as indicated by line 56, directly into the residence time reactor 50. Because of the partitions 50a and 50b, the residence time reactor is divided into three chambers from which the solid can be separately withdrawn via the lines 54a, 54b and 54c.

(9) The solid is finally withdrawn via line 54. In this regard, a sealpot as described in DE 10 2007 009 758 may be envisaged. The hot air from the residence time reactor 50 is mixed with line 44 via line 55 and from here it is returned to the second preheating stage 22.

(10) FIG. 2 shows the residence time reactor 50 in accordance with the invention. Because of partitions 501a, 501b, 501c and 501d, the individual regions 500a, 500b, 500c, 500d and 500e of the residence time reactor 50 are separated from each other in a manner such that they are now only partially fluidically linked together. In this regard, the walls 501a and 501c are configured in a manner such that a fluidic connection exists in the lower region of the reactor, whereas the walls 500b and 500d allow a fluidic connection exclusively in the upper region, wherein the overall arrangement of the walls must be such that in operation, the fluidized beds in the individual regions 500a, 500b, 500c, 500d and 500e are fluidically connected together, i.e. solid can move from one region to the next.

(11) The individual regions 500a, 500b, 500c, 500d and 500e are thus designed in a manner such that region 500a, regions 500b and 500c and regions 500d and 500e form steps; a different type of step arrangement is also possible. It only needs to be ensured that directly connected regions are always at the same or a lower level than the previously traversed regions, so that the solid and blockages can pass through the individual regions in succession.

(12) The individual regions 500a, 500b, 500c, 500d and 500e may be fluidized separately via individual lines 510a, 510b, 510c, 510d and 510e. Preferably, these lines contain individual regulating or control devices to supply the fluidization air.

(13) Furthermore, each region 500a, 500b, 500c, 500d and 500e has its own removal device 540a, 540b, 540c, 540d and 540e, via which solid can be separately removed from each of the regions 500a, 500b, 500c, 500d and 500e. The solid removed actively by means of the removal devices 540a, 540b, 540c, 540d and 540e and/or passively by means of lack of fluidization is then removed via a line 540. In this regard, the dotted lines represent what is known as an air slide.

Example

(14) An example of an application is calcining of spodumene ores in order to convert -spodumene into -spodumene. The process requires a high temperature of more than 1050 C. and a sufficient residence time of more than 30 minutes in order to convert sufficient of -phase into -phase. The use of the fluidized bed is advantageous compared with the rotary kiln which is otherwise employed, because precise temperature control is required in order to avoid overheating the minerals and thus to prevent dead burning. The residence time reactor is thus connected downstream of the fluidized bed reactor and in this manner enables the limited residence time in the reactor to be extended to the desired residence time of 40 minutes, for example.

LIST OF REFERENCE NUMERALS

(15) 10 line 11 solid storage container 12,13, 13 line 14 electrostatic precipitator 15, 16 line 17 compressor 18 line 20 first preheating stage 21 line 22 second preheating stage 23-25 line 30 metering device 31 line 40 reactor with circulating fluidized bed 41-46 line 50 residence time reactor 50a, 50b partition 51-55 line 500a-500e region 501a-501d partition 510a-510e line 540a-540e removal device