The process is continuous in the furnace, where the feeding material is melted at 1.500 ºC to 1.580 ºC (depending on the raw material) and goes out by overflow. The feeding flow rate is 800 kg/h.
The combustion is made normally by natural gas (NG) with air. The flow rate of NG is 165 Nm3/h and the air has a 10 to 15% excess. Additionally, the air is preheated up to 600 ºC thanks to the energy recovery system installed in the flue gases (1.300 ºC – but a particle filter is needed beforehand). The energy recovery system has reached a maximum technology performance, and although some attempts to increase energy recovery have been done, it has not been successful. Currently, gases are thrown at high temperature to the atmosphere. Frit melting furnaces produce waste heat at 800-1000 ºC, gases that are loaded with dust and undergo treatment by dust collectors. Previously due to the high temperatures cooling is required. Waste exhausts consist on steel panels covered internally with insulating fibber.
Downstream the process, the melted material is thrown to a water tank, in which it becomes vitreous, necessary for the product features. This material is following milled to reach required particle size, which is between 200 and 600 micrometres. Heat consumption is given, depending on the material, before or after the milling process, to ensure complete drying of the product to continue the process.