User:A09/Čermak

The Čermak-Špirek furnace, also known as the Idrija mercury roasting furnace, is a type of roasting furnace used in the extraction of mercury. The first furnaces of this kind were installed in Idrija mercury mine in Idrija in 1886 as part of smeltery modernization, and in the middle of the 20th century, there were six such furnaces in Idrija. Čermak-Špirek II, manufactured in 1888, has been restored and is now located in the building of the CUDHg Smelting Plant. The Smelting Plant is part of the UNESCO World Heritage Site Idrija and Almaden and is the only remaining example of this type of furnace.

Development
Extracting mercury from ore is a complex process that demands specialized technology and techniques. Between 1873 and 1886, Joseph Čermak, a mining councillor from Bohemia, and Vincenc Špirek, a smelting master, developed this technology as part of the intensive modernization of smeltery, which based on Idrija shaft furnaces. Their invention significantly progressed smelting technology. Čermak later installed such furnaces in Italy, Almaden (Spain), and Algeria. Čermak received an order from Emperor Franz Joseph for his invention, while Špirek went to Tuscany on an invitation from the Italians and became wealthy. The smelting furnace surpassed the previously installed Spanish furnaces in Idrija, arousing the interest of the Almadén mercury mine, which later also ordered the installation of Čermak furnaces. Representatives from Almadén were amazed at the size of the furnace, the investments the Idrija mine has made, and the amount of fuel the mine consumes.

History
The Čermak-Špirek furnace partially replaced furnaces with horizontal flaming, increasing the daily ore processing capacity (from 10 tons per day to 50, later 110 tons per day). The first furnace was built in 1886, three more were added in the years 1888, 1912, and 1914, with two smaller ones added in 1916. Until 1912, the furnaces used wood as fuel, but after World War II, they were all equipped with gas heating. On February 18 1945, during a rocket attack by the South African Air Force, many smelting facilities were damaged, destroying Čermak-Špirek I. In 1954, furnaces II, III, and IV were reconstructed, and in 1961, furnace VI ceased operation. Furnaces III and IV stopped operating in 1968, and Furnace II ceased operation on September 24, 1974. Between June and July 2002, the last remaining furnace, Čermak-Špirek II, was dismantled, its parts stored under a rotary kiln. After the smelting plant was closed, Čermak-Špirek II stood under a wooden roof in the Gostol company's area. Restoration of the Čermak-Špirek II began in 2021 and finished in 2023. Čermak-Špirek II is now placed in the right wing of the Idrija Mercury Smelting Plant.

Roasting of mercury ore
The larger furnaces had a capacity of 105–110 tons of ore per day and were placed on reinforced concrete platforms in the production hall to the south of the smelting plant. The large furnaces measured 8.7 meters in length, 6.7 meters in width, and 3.5 meters in height. The furnaces had four shafts, and ten rows of refractory bricks were staggered like shingles on the inside. Granules of cinnabar with up to 40 mm slid down these bricks. The granules were shoved into through the open shafts at the top. A combination of a sealing layer of ore and a pressure difference of about 4.9 Pa prevented excessive evaporation of mercurial fumes. Initially, the furnaces used biomass as fuel, but after World War II, all furnaces had gas heating. The furnace's exterior was surrounded by cast iron to prevent mercury leakage and had holes to observe the roasting process. A discharge chute was on the furnace's bottom, through which the smelter emptied the burned remnants every hour and 20 minutes into a railway wagon. Ore's remnants were disposed of on the banks of the Idrijca river.

Condensation of mercury vapours
A fan next to the furnace drew mercury vapours into water-cooled condensers. These condensers were initially made of cast iron and later of stone. A pump supplied water to them. Vapours at a temperature of 200–300 °C, cooled down to between 20 and 50 °C inside of the condenser. The liquid mercury collected on the walls of the tubes, and during condensation, it sank into a water-filled trough under the condenser. These troughs had sloping bottoms. A gas pipe led smoke into the central condensation chamber, where a fan sent it through the chimney on a hill above the smeltery. Cleaning these pipes was done once a year and was one of the most toxic tasks in the mine due to the corrosiveness of the exhaust fumes. A new central condensation chamber with pressurized condensation was introduced in 1961.