PROCESS AND PLANT FOR THERMAL DECOMPOSITION OF ALUMINIUM CHLORIDE HYDRATE INTO ALUMINIUM OXIDE

Abstract

A process and its relating plant for thermal conversion of aluminum chloride hydrate into aluminum oxide and gaseous hydrogen chloride. In a first step, aluminum chloride hydrate is fed into a decomposition reactor where it is heated to a temperature between 120 and 400° C. Afterwards, the partially decomposed aluminum chloride hydrate is finally calcined to aluminum oxide at a temperature between 850 and 1200° C. in a second reactor. The aluminum chloride hydrate is admixed with aluminum oxide in an intensive mixer with a mass ratio between 1:1 and 10:1 aluminum chloride hydrate to aluminum oxide for using a fluidized bed reactor as a decomposition reactor.

Claims

1.-16. (canceled)

17. A process for thermal conversion of aluminum chloride hydrate into aluminum oxide and gaseous hydrogen chloride by partially decomposing the aluminum chloride hydrate into a decomposition reactor by heating to a temperature between 120 and 400° C. and then calcining the partially decomposed aluminum chloride hydrate in the calcining reactor to aluminum oxide at a temperature between 850 and 1200° C., wherein the aluminum chloride hydrate is admixed with aluminum oxide in an intensive mixer with a mass ratio between 1:1 and 10:1 aluminum chloride hydrate to aluminum oxide and that the resulting mixture is fed into the decomposition reactor which is a fluidized bed reactor.

18. The process according to claim 17, wherein at least parts of the aluminum oxide from the calcination is recirculated into the decomposition.

19. The process according to claim 18, wherein the recirculated aluminum oxide features a temperature between 600 and 1100° C. into the decomposition reactor.

20. The process according to claim 17, wherein at least parts of the aluminum oxide from the decomposition is recirculated into the decomposition.

21. The process according to claim 20, wherein the recirculated aluminum oxide for the admixing in the mixer has a temperature below 100° C.

22. The process according to claim 17, wherein the aluminum chloride hydrate is passed through a lump breaker and/or a dryer before being fed into the mixer.

23. The process according to claim 17, wherein the calcination takes part in a fluidized bed/or a rotary kiln.

24. The process according to claim 17, wherein decomposition and/or calcination take/s in a circulating fluidized bed.

25. The process according to claim 17, wherein steam and/or air is added to the decomposition and/or air and/or a fuel is added to the calcination.

26. The process according to claim 17, wherein the off-gases are passed separately from the decomposition and the calcination to an off-gas treatment.

27. The process according to claim 26, wherein the off-gas treatment contains a quenching step and/or a scrubbing step and/or an absorption step.

28. The process according to claim 17, wherein the mixing is performed in a mixer with knifes and/or ploughshares and/or paddles.

29. The process according to claim 28, wherein the knifes rotate at least twice as fast as the ploughshares.

30. The process according to claim 17, wherein the residence time in the mixer is more than one minute.

Description

[0039] In the drawings:

[0040] FIG. 1 shows a process flow diagram of the method in accordance with the Invention.

[0041] FIG. 1 shows the principal design underlying the invention. Wet aluminium chloride hydrate is passed via conduit 111 into the mixer 110, where it is intensely mixed with aluminium oxide, which is introduce into the mixer 110 via conduit 112.

[0042] Afterwards the mixture of solids is passed through conduit 113 into a decomposition reactor 120, which is designed as a fluidized bed reactor. Further, its fluidization gas, preferably steam, is introduced via conduit 121.

[0043] The produced rich HCl gas, typically but not necessarily with an HCl content of above 30 vol.-% is passed via conduit 123 in an HCl absorption 140. This absorption stage 140 features preferably at least two stages, whereby conduit 123 is preferably con-nected to its first stage.

[0044] Via conduit 122, a product stream of the decomposition reactor 120, typically containing a mixture of already calcined Al.sub.2O.sub.3 and AlCl.sub.6.Math.6H.sub.2O, is passed into calcination reactor 130. Therein, often a gaseous fuel and/or liquid fuel is introduced via conduit 136 as energy source. Conduit 135 feeds an oxygen source into the calcination reactor 120. Via conduit 137, quench water is added. Via conduit 134 and 138, a cooling medium, preferably water, is recirculated in and out of the calcination reactor 130. The final calcined product Al.sub.2O.sub.3 is withdrawn via conduit 133 and further passed into at least one cooling stage 150 and further discharged via conduit 152.

[0045] Via conduit 132, a lean HCl gas, often but not limiting with an HCl content of less than 7 vol.-%. is passed into the HCl absorption 140, preferably its second stage.

[0046] If the absorption stage 140 is designed as a two-stage absorption, HCl solution withdrawn via conduit 141, while a first off-gas is withdrawn via conduit 142. Process water for the first stage is added via conduit 143 and withdrawn via conduit 144. Cooling water is injected by conduit 145 and withdrawn via conduit 146. From the second stage of the HCl absorption 140, an off-gas is withdrawn via conduit 147, while process water is added via conduit 148. Cooling water is recirculated via conduit 149 and 151.

[0047] For increasing energy efficiency, it is preferred that via conduit 131, parts from the calcination reactor 130 are passed into the decomposition reactor 120. Alternatively, but not shown, it is also possible to have only one withdrawing of Al.sub.2O.sub.3, from which a recycling stream into the decomposition reactor 120 is branched off.

[0048] In preferred embodiments of the invention, the aluminium oxide added into the mixer via conduit 112 is part of a product stream from a downward device. As one example amongst others, it is shown that parts of the product from the cooling stage 150 are withdrawn via a conduit 153 and fed into conduit 112.

[0049] Not shown in FIG. 1 but complementary or alternatively it is possible to withdrawn parts of the products form the decomposition reactor and/or the calcination reactor 130. It is also thinkable to have a branch-off in any conduit transporting an intermediate or the final product like conduit 122, conduit 131, conduit 133 and conduit 152. It is also possible to adjust the temperature of the recirculated stream by at least one additional and not shown cooler.

REFERENCE SIGNS

[0050] 110 mixer [0051] 111-113 conduit [0052] 120 decomposition reactor [0053] 121-123 conduit [0054] 130 calcination reactor [0055] 131-138 conduit [0056] 140 absorption stage [0057] 141-149 conduit [0058] 150 cooling stage [0059] 151-153 conduit