A process of melting silicate raw materials includes the steps of using the tank exhaust gases to heat the combustion air, using the tank exhaust gases to preheat a mixture of raw materials, removing acid gaseous aggressive media from the tank exhaust gases, then using the tank exhaust gases to preheat the combination air. Because the acid gaseous aggressive media are removed from the tank exhaust gases before the tank exhaust gases are used to preheat the combustion air, more heat can be withdrawn from the tank exhaust gases than was heretofore possible, since there is no danger of acid condensation even when the tank exhaust gases are cooled to near ambient temperature.