Metal vapor-trapping system

A metal vapor-trapping system for trapping vapors of liquid metal from a gaseous mixture consisting of said vapors and another gas which comprises:

• a tank for holding a liquid metal heated to a prescribed temperature and a gaseous mixture consisting of vapors of said liquid metal and said another gas;
• a first conduit connected at one end to the gas outlet of the tank;
• a condensation device provided with a gas inlet connected to the other end of the first conduit, a gas outlet, and a liquid outlet, and provided with a plurality of packing members for progressively decreasing the temperature of said gaseous mixture from the gas inlet to the gas outlet and thereby trap substantially all of the metal vapors contained in the gaseous mixture by condensing the vapors into liquid;
• first temperature control means associated with said condensation device for controlling the temperature of said gaseous mixture such that even when cooled, the gaseous mixture has its temperature near the gas outlet maintained at a higher level than the solidification point of the liquid metal;
• a second conduit connected between the liquid outlet of said condensation device and said tank so as to return to the tank the metal vapors liquefied by condensation in said condensation device;
• a first valve provided on the second conduit for controlling the return flow of the liquefied metal vapors to the tank;
• a third conduit connected at one end to the gas outlet of said condensation device;
• a solidification device having a gas inlet connected to the other end of the third conduit, and a gas outlet, and provided with a plurality of filters for progressively decreasing the temperature of said gaseous mixture conducted from said condensation device and passing through said filters from said gas inlet toward said gas outlet;
• second temperature control means associated with said solidification device for controlling the temperature of said gaseous mixture and for reducing said temperature of said gaseous mixture to a lower temperature level than the solidification point of the liquefied metal so as to thereby solidify the small amount of metal vapors still remaining in the gaseous mixture, said solidified vapors being separated and deposited upon said filters within said solidification device;
• a fourth conduit connected at one end thereof to the gas outlet of the solidification device so as to conduct a gas substantially free from metal vapors which has been drawn out through the gas outlet;
• a second valve provided within the fourth conduit for controlling the flow of said gas free of said metal vapors through said conduit;
• a suction pump so driven as to conduct the gaseous mixture held in the tank to the condensation and solidification devices;
• a detection means for detecting the upper and lower limits reached by the amount of metal vapors liquefied by condensation and collected in the condensation device and, when either limit is reached, generating a signal denoting this event;
• a control signal generator connected to said detection means so as to be supplied with an output signal therefrom and so designed as to generate, upon receipt of an upper limit signal from the detection means, such a control signal as to close the second valve, deactivate the suction pump and thereafter open the first valve, thereby returning the liquid metal from the condensation device to the tank, and to generate, upon receipt of a lower limit signal from the detection means, such a control signal as to close the first valve and thereafter open the second valve and actuate the suction pump, thereby obstructing the return flow of the liquid metal from the condensation device to the tank.