Definition: "a method of mining sulphur by pumping superheated water down into the deposit, thereby melting it so that it can be pumped to the surface."
Frasch process was the most used process for sulphur extrusion through the 20th century. It was invented by Herman Frasch, (the German-born American chemist) to bypass the quicksand which was preventing the mining of sulphur in the caprock of salt dome in the sulphur mine in Lousiana. The first successful execution of this process was done in 1894, when first molten sulphur was brought to the surface.
The Frasch process includes the uses of three concentric steel pipes, one inside other. These pipes are bored underground to the sulphur deposits. Then water, which is heated to a temperature above the melting point of sulphur (165-170°C or 340°F), is injected under pressure through the outer pipe. This superheated water cause the melting of sulphur at approx. 115.21°C. After then, compressed air is pumped down with high pressure through the innermost central pipe which forces the sulphur to the surface through middle pipe. Here is the video explaining the complete process-
sulphur produced through Frasch process are found very pure, usually 99.5% to 99.8%.
Having many advantages, this process was so expensive, as high quantity of fuel was needed for superheating water. In 1901, Spindletop oil field in Texas was discovered which provided cheap fuel oil and Frasch process commercialized in 1903 in Lousisiana.
When elemental sulphur was produced through conventional mining methods, Italy played the role of leading producer of sulphur. Still industrial demands can't be fulfill with all elemental sulphur and pyrites. After, Frasch process started the economic production of sulphur, US became the leading producer. In 1974, 8 million tons sulphur was produced from 12 mines, using Frasch process.
Being very expensive processing and due to the limited sulphur deposits, this process was replaced with other sulphur producing methods like recovery from gas and patrol.