Treatment of materials by means of combustion processes for smelting furnaces for the manufacture of glass and non-ferrous metals; rental of combustion equipment for smelting furnaces for the manufacture of glass and non-ferrous metals; rental of heat exchangers for smelting furnaces for the manufacture of glass and non-ferrous metals; rental of installations for producing, purifying and recycling gases and gas mixtures for use in industry; production of gases and gas mixtures for use in indu...