Method and apparatus to condense magnesium vapor using a fluid-cooled heat exchanger
A system and method that uses a high-temperature condenser to collect magnesium produced by thermal reduction, electrolysis, or distillation. The condenser is a common heat exchanger design (shell/tube, plate/plate, etc.) and uses a heat transfer fluid to cool and condense magnesium gas, e.g., to 200-900° C. under vacuum or pressure conditions. Solid or liquid magnesium is collected in the condenser along with any by-products or impurities at a purity greater than 35 wt-% Mg. Magnesium is subsequently liberated from the condenser by raising the temperature of the system, lowering the pressure, or both, to induce a phase change in the metal, such as melting or distillation, for further purification to, e.g., >90 wt-% Mg.
1 . A method for condensing magnesium (Mg) metal from a gaseous stream, the method comprising:
feeding a magnesium-containing gaseous stream at a temperature of at least 650° C. into a heat exchanger;
cooling the magnesium-containing gaseous stream with a cooling heat transfer fluid not in direct communication with the magnesium-containing gaseous stream at a temperature of 200-650° C. to deposit magnesium metal on walls of the heat exchanger of at least 35 wt-% Mg; and
inducing a phase change in the deposited magnesium metal by raising the temperature of the heat exchanger using a heating heat transfer fluid of the same composition as the cooling heat transfer fluid, thus heating the magnesium metal to at least the boiling point of magnesium, to allow the magnesium metal to flow into another area for further processing.
2 . The method of claim 1 , wherein cooling the magnesium-containing gaseous stream in the heat exchanger deposits solid magnesium metal.
3 . The method of claim 1 , wherein the heat exchanger has a tube/shell configuration.
4 . The method of claim 1 , wherein the heat exchanger has a plate/plate configuration.
5 . The method of claim 1 , further comprising operably connecting the heat exchanger to a vacuum source.
6 . The method of claim 1 , wherein the heat exchanger is equipped with appropriate valves, pumps and tanks to replace the cooling heat transfer fluid with the heating heat transfer fluid.
7 . The method of claim 1 , wherein the magnesium-containing gaseous stream further comprises a non-condensable and non-oxidizing inert gas.
8 . The method of claim 1 , wherein the magnesium-containing gaseous stream further comprises carbon monoxide.
9 . The method of claim 1 , wherein the heat transfer fluid comprises at least one of molten metal, molten salt, high temperature oil, high pressure water, steam, and air.
10 . The method of claim 9 , wherein the molten metal is lead, tin, bismuth or mixture thereof.
11 . The method of claim 9 , wherein the molten salt is nitrate, chloride, fluoride, or mixture thereof.
12 . The method of claim 1 , further comprising obtaining the magnesium-containing gaseous stream via one or more of:
metallothermic reduction of magnesium oxide rich ores;
an electrolytic cell;
a distillation apparatus producing magnesium gas by distillation of crude magnesium metal; and
carbothermal reduction of magnesium oxide rich ore.
13 . The method of claim 1 , wherein the magnesium metal deposited on the walls of the heat exchanger comprises at least 99 wt-% Mg.
14 . The method of claim 1 , wherein a set of scrapers, brushes, and/or nozzles are positioned to remove deposits from the walls of the heat exchanger after the magnesium metal has been allowed to flow into the another area for further processing.
15 . The method of claim 1 , further comprising extracting heat from the cooling heat transfer fluid using a heat transfer medium.