Electrolytic Cell With a Heat Exchanger

Abstract

This invention relates to electrolytic cells used for production of aluminium. The side walls ( 8 ) of the pot surrounding its crucible ( 4, 4′ ) include a part ( 13 ) made of a porous material over at least one fraction of their height and/or their thickness, to enable a heat transfer gas to circulate, the part ( 13 ) made of a porous material being connected to heat transfer gas inlet means ( 15 ) and outlet means ( 16 ), so as to make a heat exchanger in order to recover heat energy lost through the sides of the pot.

1 . Electrolytic pot for production of aluminium, comprising side walls having a heat exchanger through which a heat transfer gas can circulate, wherein the side walls of the pot comprise at least one part made of a porous material over at least a fraction of a height and a thickness of the side walls, to enable circulation of the heat transfer gas, each part made of a porous material being connected to heat transfer gas inlet means and outlet means. 
   
   
       2 . Electrolytic pot according to  claim 1 , wherein the porous material is in the form of a foam. 
   
   
       3 . Electrolytic pot according to  claim 1 , wherein the porous material is formed from a material chosen from metals, metal alloys and ceramics, with an intrinsic thermal conductivity greater than 5 W/m.K, and a mix or a combination of these materials. 
   
   
       4 . Electrolytic pot according to  claim 3 , wherein said ceramic contains a majority of at least one component selected from the group consisting of: silicon carbide, silicon nitride and aluminium nitride. 
   
   
       5 . Electrolytic pot according to  claim 3 , wherein the porous material is a ceramic foam containing at least 70% by weight of heat conducting ceramic. 
   
   
       6 . Electrolytic pot according to  claim 3 , wherein said metal or metal alloy has a thermal expansion coefficient of less than 25×10 −6  K −1 . 
   
   
       7 . Electrolytic pot according to  claim 1 , wherein the part made of a porous material has a porosity greater than 70%. 
   
   
       8 . Electrolytic pot according to  claim 1 , wherein the part made of a porous material is formed from one or more porous slabs. 
   
   
       9 . Electrolytic pot according to  claim 1 , wherein the part made of a porous material is between 5 and 50 mm thick. 
   
   
       10 . Electrolytic pot according to  claim 1 , wherein the side walls of the pot comprise at least one first part made of a dense material located on an inner side of the side walls, and at least one second part at least partly made of a porous material located between the first part and an outside shell of the pot. 
   
   
       11 . Electrolytic pot according to  claim 10 , wherein the dense material is a ceramic material containing at least 70% by weight of silicon carbide. 
   
   
       12 . Electrolytic pot according to  claim 10 , wherein the part made of dense material has a porosity of less than 20%. 
   
   
       13 . Electrolytic pot according to  claim 10 , wherein the first part made of dense material and the second part made of porous material are assembled using a refractory material. 
   
   
       14 . Electrolytic pot according to  claim 13 , the first and second parts of the side walls are assembled using glue, in the form of a suspension, comprising a mix of a mineral filler with an average size grading of less than 250 μm, a silicone resin and an organic solvent to solubilise the resin and control the rheology of the suspension. 
   
   
       15 . Electrolytic pot according to  claim 10 , wherein first part made of dense material is formed from several slabs with a monolithic structure. 
   
   
       16 . Electrolytic pot according to  claim 10 , wherein the side walls of the pot comprise a structure formed from monolithic slabs, made from a material with variable porosity in the direction of the thickness of said side walls. 
   
   
       17 . Electrolytic pot according to  claim 10 , wherein the dense part is between 10 and 100 mm thick. 
   
   
       18 . Electrolytic pot according to  claim 1 , wherein said part made of porous material extends substantially over the entire height of the side walls of the pot. 
   
   
       19 . Electrolytic pot according to  claim 1 , wherein said part made of porous material extends over a limited portion of the total height of the side walls of the pot. 
   
   
       20 . Electrolytic pot according to  claim 19 , wherein said part made of a porous material extends over a fraction of the order of one third to one half of the height of the side walls of the pot. 
   
   
       21 . Electrolyte pot according to  claim 19 , wherein said part made of a porous material overlaps an interface between a liquid aluminium layer and a molten salts bath. 
   
   
       22 . Electrolytic pot according to  claim 1 , wherein the porous material has at least one variable characteristic selected from the group consisting of: porosity, thickness and thermal conductivity characteristics, over the height of the porous part, so as to obtain successive zones in the direction of the height with different heat exchange characteristics. 
   
   
       23 . Electrolyte pot according to  claim 1 , wherein the heat transfer gas inlet means and outlet means are located at the top and at the bottom of each part made of a porous material. 
   
   
       24 . Electrolytic pot according to  claim 23 , wherein the heat transfer gas inlet means and outlet means are located near the top portion and bottom portion of the side walls of the pot. 
   
   
       25 . Electrolytic pot according to  claim 22 , wherein the pot further includes at least one additional inlet and one additional outlet for the heat transfer gas located at an intermediate height. 
   
   
       26 . Electrolytic pot according to  claim 25 , wherein at least one of the additional inlet and the additional outlet for the heat transfer gas is located at the transition between two successive zones. 
   
   
       27 . Electrolytic pot according to  claim 1 , wherein heat transfer gas inlet and outlet means are distributed over the horizontal dimension of a part made of a porous material of the side walls of the pot. 
   
   
       28 . Electrolytic pot according to  claim 27 , wherein the inlet and the outlet are arranged at the two horizontally opposite ends of the part made of a porous material. 
   
   
       29 . Electrolytic pot according to  claim 1 , wherein the heat transfer gas inlet has orifices located above the liquid level in the pot, near the top of the shell. 
   
   
       30 . Electrolytic pot according to  claim 1 , wherein at least one side manifold is connected to a plurality of heat transfer gas outlets. 
   
   
       31 . Electrolytic pot according to  claim 30 , wherein each side of the pot is equipped with at least one side manifold, all manifolds being connected to a common suction unit. 
   
   
       32 . Electrolytic pot according to  claim 1 , wherein the through cross-section of at least one of the heat transfer gas inlet and outlet orifices is made adjustable using flaps. 
   
   
       33 . Electrolytic pot according to  claim 1 , wherein the heat transfer gas used is air, and wherein the air inlets are open to the surrounding atmosphere. 
   
   
       34 . Electrolytic pot according to  claim 1 , wherein the heat transfer gas used is selected from the group consisting of:
 air, an inert gas, and a mix of air and inert gas, and wherein the heat transfer gas is recycled through a distribution network bringing air or gas drawn off at the outlet orifices to the inlet orifices.   
   
   
       35 . Electrolytic pot according to  claim 34 , wherein the pot combines embodiments without air recycling and with air recycling, using direct air inlet valves located at different points in the distribution network. 
   
   
       36 . Electrolytic pot according to  claim 35 , wherein the pot further comprises isolating valves configured to isolate the different portions of the distribution network from each other. 
   
   
       37 . Electrolytic pot according to  claim 1 , wherein thermal insulation is provided between the part made of a porous material and the shell of the pot. 
   
   
       38 . Electrolytic pot according to  claim 37 , wherein the thermal insulation is a fibrous material. 
   
   
       39 . Electrolytic pot according to  claim 37 , wherein the insulation forms a substantially vertical layer, with a thickness of between 10 and 100 mm. 
   
   
       40 . Electrolytic pot according to  claim 1 , wherein the pot is connected to a suction system that can circulate a heat transfer gas by depression in each part made of a porous material. 
   
   
       41 . Electrolytic pot according to  claim 1 , wherein the side walls of the pot also comprise at least one conduit through which the heat transfer gas can be circulated along a preferred path towards the bottom of the porous part or from the top of the porous part, to enable a uniform and substantially vertical circulation velocity of the heat transfer gas. 
   
   
       42 . Electrolytic pot according to  claim 1 , wherein each porous part is assembled in the form of a module. 
   
   
       43 . Electrolytic pot according to  claim 42 , wherein said module comprises at least one first porous section with a first porosity and a second porous section with a second porosity arranged so as to be located above the first porous section in said side walls of the pot, the first porosity being greater than the second porosity, a first horizontal conduit through which the heat transfer gas flow can be distributed along the first porous section and a second horizontal conduit to collect the heat transfer gas from the second porous section. 
   
   
       44 . Electrolytic pot according to  claim 43 , wherein said module comprises an inlet to allow heat transfer gas to enter and an outlet for extraction of the heat transfer gas, and in that the inlet and the outlet are located in a portion of the module configured to be in the top part of said heat exchanger. 
   
   
       45 . Electrolytic cell comprising a pot according to  claim 1 . 
   
   
       46 . Industrial aluminium production plant comprising a plurality of electrolytic pots according to  claim 1 , connected through manifolds to a heat transfer gas circuit directed towards energy recovery means, comprising at least one of a heat exchanger and an electricity generator.