Search This Blog

Friday, May 5, 2023

Centralia mine fire

From Wikipedia, the free encyclopedia
A small part of the Centralia mine fire after being exposed during excavation in 1969
 
View of smoke rising through a fissure in the ground in the closed-off area of former Pennsylvania Route 61. The melted snow, which covered the ground around it, shows areas where heat is escaping from the ground below.

The Centralia mine fire is a coal-seam fire that has been burning in the labyrinth of abandoned coal mines underneath the borough of Centralia, Pennsylvania, United States, since at least May 27, 1962. Its original cause and start date are still a matter of debate. It is burning in underground coal mines at depths of up to 300 ft (90 m) over an 8 mi (13 km) stretch of 3,700 acres (15 km2). At its current rate, it could continue to burn for over 250 years. It has caused most of the town to be abandoned: by 2017, the population had dwindled to 5 residents from around 1,500 at the time the fire is believed to have started, and most of the buildings have been razed.

Background

On May 7, 1962, the Centralia Council met to discuss the approaching Memorial Day and how the town would go about cleaning up the Centralia landfill, which was introduced earlier that year. The 300-foot-wide, 75-foot-long (91 m × 23 m) pit was made up of a 50-foot-deep (15 m) strip mine that had been cleared by Edward Whitney in 1935, and came very close to the northeast corner of Odd Fellows Cemetery. There were eight illegal dumps spread about Centralia, and the council's intention in creating the landfill was to stop the illegal dumping, as new state regulations had forced the town to close an earlier dump west of St. Ignatius Cemetery. Trustees at the cemetery were opposed to the landfill's proximity to the cemetery, but recognized the illegal dumping elsewhere as a serious problem and envisioned that the new pit would resolve it.

Pennsylvania had passed a precautionary law in 1956 to regulate landfill use in strip mines, as landfills were known to cause destructive mine fires. The law required a permit and regular inspection for a municipality to use such a pit. George Segaritus, a regional landfill inspector who worked for the Department of Mines and Mineral Industries (DMMI), became concerned about the pit when he noticed holes in the walls and floor, as such mines often cut through older mines underneath. Segaritus informed Joseph Tighe, a Centralia councilman, that the pit would require filling with an incombustible material.

Fire

The Buck Vein Outcrop
 
A plume of smoke wafts from the ground.
 
A DEP monitoring hole
 
A DEP underground reading of 187 °F (86 °C)

This was a world where no human could live, hotter than the planet Mercury, its atmosphere as poisonous as Saturn's. At the heart of the fire, temperatures easily exceeded 1,000 degrees Fahrenheit [540 degrees Celsius]. Lethal clouds of carbon monoxide and other gases swirled through the rock chambers.

— David DeKok, Unseen Danger: A Tragedy of People, Government, and the Centralia Mine Fire (University of Pennsylvania Press, 1986)

Plan and execution

The town council arranged for cleanup of the strip mine dump, but council minutes do not describe the proposed procedure. DeKok surmises that the process—setting it on fire—was not specified because state law prohibited dump fires. Nonetheless, the Centralia council set a date and hired five members of the volunteer firefighter company to clean up the landfill.

A fire was ignited to clean the dump on May 27, 1962, and water was used to douse the visible flames that night. However, flames were seen once more on May 29. Using hoses hooked up from Locust Avenue, another attempt was made to douse the fire that night. Another flare-up in the following week (June 4) caused the Centralia Fire Company to once again douse it with hoses. A bulldozer stirred up the garbage so that firemen could douse concealed layers of the burning waste. A few days later, a hole as wide as 15 ft (4.6 m) and several feet high was found in the base of the north wall of the pit. Garbage had concealed the hole and prevented it from being filled with incombustible material. It is possible that this hole led to the mine fire, as it provided a pathway to the labyrinth of old mines under the borough. Evidence indicates that, despite these efforts to douse the fire, the landfill continued to burn; on July 2, Monsignor William J. Burke complained about foul odors from the smoldering trash and coal reaching St. Ignatius Church. Even then, the Centralia council still allowed the dumping of garbage into the pit.

Clarence "Mooch" Kashner, the president of the Independent Miners, Breakermen, and Truckers union, came at the invitation of a council member to inspect the situation in Centralia. Kashner evaluated the events and called Gordon Smith, an engineer of the Department of Mines and Mineral Industries (DMMI) office in Pottsville. Smith told the town that he could dig out the smoldering material using a steam shovel for $175. A call was placed to Art Joyce, a mine inspector from Mount Carmel, who brought gas detection equipment for use on the swirling wisps of smoke now emanating from ground fissures in the north wall of the landfill pit. Tests concluded that the gases seeping from the large hole in the pit wall and from cracks in the north wall contained carbon monoxide concentrations typical of coal-mine fires.

Escalation

The Centralia Council sent a letter to the Lehigh Valley Coal Company (LVCC) as formal notice of the fire. It is speculated that the town council decided that hiding the true origin of the fire would serve better than alerting the LVCC of the truth, which would most likely end in receiving no help from them. In the letter, the borough described the starting of a fire "of unknown origin during a period of unusually hot weather".

Preceding an August 6 meeting at the fire site which would include officials from the LVCC and the Susquehanna Coal Company, Deputy Secretary of Mines James Shober Sr. expected that the representatives would inform him they could not afford mounting a project that would stop the mine fire. Therefore, Shober announced that he expected the state to finance the cost of digging out the fire, which was at that time around $30,000 (roughly equivalent to $269,000 in 2021). Another offer was made at the meeting, proposed by Centralia strip mine operator Alonzo Sanchez, who told members of council that he would dig out the mine fire free of charge as long as he could claim any coal he recovered without paying royalties to the Lehigh Valley Coal Company. Part of Sanchez's plan was to do exploratory drilling to estimate the scope of the mine fire, which was most likely why Sanchez's offer was rejected at the meeting. The drilling would have delayed the project, not to mention the legal problems with mining rights.

At the time, state mine inspectors were in the Centralia-area mines almost daily to check for lethal levels of carbon monoxide. Lethal levels were found on August 9, and all Centralia-area mines were closed the next day.

Early remediation attempts

First excavation project

Pressed at an August 12 meeting of the United Mine Works of America in Centralia, Secretary of Mines Lewis Evans sent a letter to the group on August 15 that claimed he had authorized a project to deal with the mine fire, and that bids for the project would be opened on August 17. Two days later, the contract was awarded to Bridy, Inc., a company near Mount Carmel, for an estimated $20,000 (roughly equivalent to $179,000 in 2021). Work on the project began August 22.

The Department of Mines and Mineral Industries (DMMI), who originally believed Bridy would need only to excavate 24,000 cu yd (18,000 m3) of earth, informed them that they were forbidden from doing any exploratory drilling in order to find the perimeter of the fire or how deep it was, and that they were to strictly follow plans drawn up by the engineers who did not believe that the fire was very big or active. The size and location of the fire was, instead, estimated based on the amount of steam issuing from the landfill rock.

Bridy, following the engineering team plan, began by digging on the northern perimeter of the dump pit rim and excavated about 200 ft (61 m) outward to expand the perimeter. However, the project was ultimately ineffective due to multiple factors. Intentional breaching of the subterranean mine chambers allowed large amounts of oxygen to rush in, greatly worsening the fire. Steve Kisela, a bulldozer operator in Bridy's project, said that the project was ineffective because the inrush of air helped the fire to move ahead of the excavation point by the time the section was drilled and blasted. Bridy was also using a 2.5 cu yd (1.9 m3) shovel, which was considered small for the project.

Furthermore, the state only permitted Bridy's team to work weekday shifts which were eight hours long and only occurred during the day time; commonly referred to as "first shift" in the mining industry. At one point, work was at a standstill for five days during the Labor Day weekend in early September. Finally, the fire was traveling in a northward direction which caused the fire to move deeper into the coal seam. This, combined with the work restrictions and inadequate equipment, greatly increased the excavation cost. Bridy had excavated 58,580 cu yd (44,790 m3) of earth by the time the project ran out of money and ended on October 29, 1962.

Second excavation project

On October 29, just prior to the termination of the Bridy project, a new project was proposed that involved flushing the mine fire. Crushed rock would be mixed with water and pumped into Centralia's mines ahead of the expected fire expansion. The project was estimated to cost $40,000 (roughly equivalent to $358,000 in 2021). Bids were opened on November 1, and the project was awarded to K&H Excavating with a low bid of $28,400 (roughly equivalent to $254,000 in 2021).

Drilling was conducted through holes spaced 20 ft (6.1 m) apart in a semicircular pattern along the edge of the landfill. However, this project was also ineffective due to multiple factors. Centralia experienced an unusually heavy period of snowfall and unseasonably low temperatures during the project. Winter weather caused the water supply lines to freeze. Furthermore, the rock-grinding machine froze during a windy blizzard. Both problems inhibited timely mixture and administration of the crushed-rock slurry. The DMMI also worried that the 10,000 cu yd (7,600 m3) of flushing material would not be enough to fill the mines, thus preventing the bore holes from filling completely. Partially filled boreholes would provide an escape route for the fire, rendering the project ineffective.

These problems quickly depleted funds. In response, Secretary Evans approved an additional $14,000 (roughly equivalent to $125,000 in 2021) to fund this project. Funding for the project ran out on March 15, 1963, with a total cost of $42,420 (roughly equivalent to $380,000 in 2021).

On April 11, steam issuing from additional openings in the ground indicated that the fire had spread eastward as far as 700 ft (210 m), and that the project had failed.

Third project

A three-option proposal was drawn up soon after that, although the project would be delayed until after the new fiscal year beginning July 1, 1963. The first option, costing $277,490, consisted of entrenching the fire and back-filling the trench with incombustible material. The second, costing $151,714, offered a smaller trench in an incomplete circle, followed by the completion of the circle with a flush barrier. The third plan was a "total and concerted flushing project" larger than the second project's flushing and costing $82,300. The state abandoned this project in 1963.

Later remediation projects

David DeKok began reporting on the mine fire for The News-Item in Shamokin beginning in late 1976. Between 1976 and 1986, he wrote over 500 articles about the mine fire. In 1979, locals became aware of the scale of the problem when a gas-station owner, then-mayor John Coddington, inserted a dipstick into one of his underground tanks to check the fuel level. When he withdrew it, it seemed hot. He lowered a thermometer into the tank on a string and was shocked to discover that the temperature of the gasoline in the tank was 172 °F (77.8 °C).

Beginning in 1980, adverse health effects were reported by several people due to byproducts of the fire: carbon monoxide, carbon dioxide, and low oxygen levels. Statewide attention to the fire began to increase, culminating in 1981 when a 12-year-old resident named Todd Domboski fell into a sinkhole 4 ft (1.2 m) wide by 150 ft (46 m) deep that suddenly opened beneath his feet in a backyard. He clung to a tree root until his cousin, 14-year-old Eric Wolfgang, saved his life by pulling him out of the hole. The plume of hot steam billowing from the hole was measured as containing a lethal level of carbon monoxide.

Possible origins

A number of competing hypotheses have arisen about the source of the Centralia mine fire. Some of them claim that the mine fire started before May 27, 1962. David DeKok says that the borough's deliberate burning of trash on May 27 to clean up the landfill in the former strip mine ignited a coal seam via an unsealed opening in the trash pit, which allowed the fire to enter the labyrinth of abandoned coal mines beneath Centralia.

Joan Quigley argues in her 2007 book The Day the Earth Caved In that the fire had in fact started the previous day, when a trash hauler dumped hot ash or coal discarded from coal burners into the open trash pit. She noted that borough council minutes from June 4, 1962, referred to two fires at the dump, and that five firefighters had submitted bills for "fighting the fire at the landfill area". The borough, by law, was responsible for installing a fire-resistant clay barrier between each layer of trash in the landfill, but fell behind schedule, leaving the barrier incomplete. This allowed the hot coals to penetrate the vein of coal underneath the pit and light the subsequent subterranean fire. In addition to the council minutes, Quigley cites "interviews with volunteer firemen, the former fire chief, borough officials, and several eyewitnesses" as her sources.

Another hypothesis is that the fire was burning long before the alleged trash dump fire. According to local legend, the Bast Colliery coal fire of 1932, set alight by an explosion, was never fully extinguished. In 1962, it reached the landfill area. Those who adhere to the Bast Theory believe that the dump fire is a separate fire unrelated to the Centralia mine fire. One man who disagrees is Frank Jurgill Sr., who claims he operated a bootleg mine with his brother in the vicinity of the landfill between 1960 and 1962. He says that if the Bast Colliery fire had never been put out, he and his brother would have been in it and killed by the gases. Based on this and due to contrary evidence, few hold this position, and it is given little credibility.

Centralia councilman Joseph Tighe proposed a different hypothesis: that Centralia's coal fire was actually started by an adjacent coal-seam fire that had been burning west of Centralia's. His belief is that the adjacent fire was at one time partially excavated, but it nonetheless set alight the landfill on May 27.

Another hypothesis arose from the letter sent to the Lehigh Valley Coal Company by the Centralia Council in the days after the mine fire was noticed. The letter describes "a fire of unknown origin [starting] on or about June 25, 1962, during a period of unusually hot weather". This may make a reference to the hypothesis of spontaneous combustion being the reason for the start of the landfill fire, a hypothesis accepted for many years by state and federal officials.

Aftermath

The location at which the former roadbed of Pennsylvania Route 61 terminates due to the mine fire.
 
As the joining row homes were demolished, the buttresses were constructed to support the walls of the remaining homes.

In 1984, Wilkes-Barre Representative Frank Harrison proposed legislation, which was approved by Congress which allocated more than $42 million for relocation efforts (equivalent to $110 million in 2021) Most of the residents accepted buyout offers and dispersed far away from the area. (Data from the 1990 United States Census shows that the nearby towns continued to lose population at the same rate as previous decades, suggesting the Centralians did not locate there.) A few families opted to stay despite urgings from Pennsylvania officials.

In 1992, Pennsylvania governor Bob Casey invoked eminent domain on all properties in the borough, condemning all the buildings within. A subsequent legal effort by residents to have the decision reversed failed. In 2002, the U.S. Postal Service revoked Centralia's ZIP code, 17927.

In 2009, Governor Ed Rendell began the formal eviction of Centralia residents. By early 2010, only 5 occupied homes remained, with the residents determined to stay. In lawsuits, the remaining residents alleged that they were victims of "massive fraud", "motivated primarily by interests in what is conservatively estimated at hundreds of millions of dollars of some of the best anthracite coal in the world". In July 2012, the last handful of residents in Centralia lost their appeal of a court decision upholding eminent domain proceedings and was ordered again to leave. State and local officials reached an agreement with the seven remaining residents on October 29, 2013, allowing them to live out their lives there, after which the rights of their properties will be taken through eminent domain.

The Centralia mine fire also extended beneath the town of Byrnesville, a few miles to the south. The town had to be abandoned and leveled.

The Centralia area has now grown to be a tourist attraction. Visitors come to see the smoke and/or steam on Centralia's empty streets and the abandoned portion of PA Route 61, popularly referred to as the Graffiti Highway.

As of April 2020, efforts began to cover up Graffiti Highway by the private owner of the road. The abandoned highway was covered with dirt in April 2020, generally blocking public access to the road.

Increased air pressure induced by the heat from the mine fires has interacted with heavy rainfalls in the area that rush into the abandoned mines to form Pennsylvania's only geyser, the Big Mine Run Geyser, which erupts on private property in nearby Ashland. The geyser has been kept open as a means of flood control.

The fire and its effects were featured in 2013 on America Declassified on the Travel Channel, and on Radiolab's Cities episode.

The Silent Hill video game series draws on these events, although the film is based in West Virginia.

Smelting

From Wikipedia, the free encyclopedia
 
Electric phosphate smelting furnace in a TVA chemical plant (1942)

Smelting is a process of applying heat to an ore, to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a chemical- reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal base behind. The reducing agent is commonly a fossil fuel source of carbon, such as coke—or, in earlier times, charcoal. The oxygen in the ore binds to carbon at high temperatures as the chemical potential energy of the bonds in carbon dioxide (CO2) is lower than the bonds in the ore.

The carbon source acts as a chemical reactant to remove oxygen from the ore, yielding the purified metal element as a product. The carbon source is oxidized in two stages. First, carbon (C) combusts with oxygen (O2) in the air to produce carbon monoxide (CO). Second, the carbon monoxide reacts with the ore (e.g. Fe2O3) and removes one of its oxygen atoms, releasing carbon dioxide (CO2). After successive interactions with carbon monoxide, all of the oxygen in the ore will be removed, leaving the raw metal element (e.g. Fe). As most ores are impure, it is often necessary to use flux, such as limestone (or dolomite), to remove the accompanying rock gangue as slag. This calcination reaction also frequently emits carbon dioxide.

Smelting most prominently takes place in a blast furnace to produce pig iron, which is converted into steel.

Plants for the electrolytic reduction of aluminium are also referred to as aluminium smelters.

Process

Copper smelter, Chelyabinsk Oblast, Russia
 
Electrolytic cells at an aluminum smelter in Saint-Jean-de-Maurienne, France

Smelting involves more than just melting the metal out of its ore. Most ores are the chemical compound of the metal and other elements, such as oxygen (as an oxide), sulfur (as a sulfide), or carbon and oxygen together (as a carbonate). To extract the metal, workers must make these compounds undergo a chemical reaction. Smelting, therefore, consists of using suitable reducing substances that combine with those oxidizing elements to free the metal.

Roasting

In the case of sulfides and carbonates, a process called "roasting" removes the unwanted carbon or sulfur, leaving an oxide, which can be directly reduced. Roasting is usually carried out in an oxidizing environment. A few practical examples:

  • Malachite, a common ore of copper is primarily copper carbonate hydroxide Cu2(CO3)(OH)2. This mineral undergoes thermal decomposition to 2CuO, CO2, and H2O in several stages between 250 °C and 350 °C. The carbon dioxide and water are expelled into the atmosphere, leaving copper(II) oxide, which can be directly reduced to copper as described in the following section titled Reduction.
  • Galena, the most common mineral of lead, is primarily lead sulfide (PbS). The sulfide is oxidized to a sulfite (PbSO3), which thermally decomposes into lead oxide and sulfur dioxide gas (PbO and SO2). The sulfur dioxide is expelled (like the carbon dioxide in the previous example), and the lead oxide is reduced as below.

Reduction

Reduction is the final, high-temperature step in smelting, in which the oxide becomes the elemental metal. A reducing environment (often provided by carbon monoxide, made by incomplete combustion in an air-starved furnace) pulls the final oxygen atoms from the raw metal. The required temperature varies both in absolute terms and in terms of the melting point of the base metal. Examples:

  • Iron oxide becomes metallic iron at roughly 1250 °C (2282 °F or 1523.15 K), almost 300 degrees below iron's melting point of 1538 °C (2800.4 °F or 1811.15 K).
  • Mercuric oxide becomes vaporous mercury near 550 °C (1022 °F or 823.15 K), almost 600 degrees above mercury's melting point of -38 °C (-36.4 °F or 235.15 K). Flux and slag can provide a secondary service after the reduction step is complete: they provide a molten cover on the purified metal, preventing contact with oxygen while still hot enough to readily oxidize. This prevents impurities from forming in the metal.

Fluxes

Metal workers use fluxes in smelting for several purposes, chief among them catalyzing the desired reactions and chemically binding to unwanted impurities or reaction products. Calcium oxide, in the form of lime, was often used for this purpose, since it could react with the carbon dioxide and sulfur dioxide produced during roasting and smelting to keep them out of the working environment.

History

Of the seven metals known in antiquity, only gold occurs regularly in its native form in the natural environment. The others – copper, lead, silver, tin, iron, and mercury – occur primarily as minerals, though copper is occasionally found in its native state in commercially significant quantities. These minerals are primarily carbonates, sulfides, or oxides of the metal, mixed with other components such as silica and alumina. Roasting the carbonate and sulfide minerals in the air converts them to oxides. The oxides, in turn, are smelted into the metal. Carbon monoxide was (and is) the reducing agent of choice for smelting. It is easily produced during the heating process, and as a gas comes into intimate contact with the ore.

In the Old World, humans learned to smelt metals in prehistoric times, more than 8000 years ago. The discovery and use of the "useful" metals – copper and bronze at first, then iron a few millennia later – had an enormous impact on human society. The impact was so pervasive that scholars traditionally divide ancient history into Stone Age, Bronze Age, and Iron Age.

In the Americas, pre-Inca civilizations of the central Andes in Peru had mastered the smelting of copper and silver at least six centuries before the first Europeans arrived in the 16th century, while never mastering the smelting of metals such as iron for use with weapon craft.

Tin and lead

In the Old World, the first metals smelted were tin and lead. The earliest known cast lead beads were found in the Çatalhöyük site in Anatolia (Turkey), and dated from about 6500 BC, but the metal may have been known earlier.

Since the discovery happened several millennia before the invention of writing, there is no written record of how it was made. However, tin and lead can be smelted by placing the ores in a wood fire, leaving the possibility that the discovery may have occurred by accident.

Lead is a common metal, but its discovery had relatively little impact in the ancient world. It is too soft to use for structural elements or weapons, though its high density relative to other metals makes it ideal for sling projectiles. However, since it was easy to cast and shape, workers in the classical world of Ancient Greece and Ancient Rome used it extensively to pipe and store water. They also used it as a mortar in stone buildings.

Tin was much less common than lead and is only marginally harder, and had even less impact by itself.

Copper and bronze

Casting bronze ding-tripods, from the Chinese Tiangong Kaiwu encyclopedia of Song Yingxing, published in 1637.

After tin and lead, the next metal smelted appears to have been copper. How the discovery came about is debated. Campfires are about 200 °C short of the temperature needed, so some propose that the first smelting of copper may have occurred in pottery kilns. (The development of copper smelting in the Andes, which is believed to have occurred independently of the Old World, may have occurred in the same way.)

The earliest current evidence of copper smelting, dating from between 5500 BC and 5000 BC, has been found in Pločnik and Belovode, Serbia. A mace head found in Turkey and dated to 5000 BC, once thought to be the oldest evidence, now appears to be hammered, native copper.

Combining copper with tin and/or arsenic in the right proportions produces bronze, an alloy that is significantly harder than copper. The first copper/arsenic bronzes date from 4200 BC from Asia Minor. The Inca bronze alloys were also of this type. Arsenic is often an impurity in copper ores, so the discovery could have been made by accident. Eventually, arsenic-bearing minerals were intentionally added during smelting.

Copper–tin bronzes, harder and more durable, were developed around 3500 BC, also in Asia Minor.

How smiths learned to produce copper/tin bronzes is unknown. The first such bronzes may have been a lucky accident from tin-contaminated copper ores. However, by 2000 BC, people were mining tin on purpose to produce bronze—which is remarkable as tin is a semi-rare metal, and even a rich cassiterite ore only has 5% tin. However early peoples learned about tin, they understood how to use it to make bronze by 2000 BC.

The discovery of copper and bronze manufacture had a significant impact on the history of the Old World. Metals were hard enough to make weapons that were heavier, stronger, and more resistant to impact damage than wood, bone, or stone equivalents. For several millennia, bronze was the material of choice for weapons such as swords, daggers, battle axes, and spear and arrow points, as well as protective gear such as shields, helmets, greaves (metal shin guards), and other body armor. Bronze also supplanted stone, wood, and organic materials in tools and household utensils—such as chisels, saws, adzes, nails, blade shears, knives, sewing needles and pins, jugs, cooking pots and cauldrons, mirrors, and horse harnesses. Tin and copper also contributed to the establishment of trade networks that spanned large areas of Europe and Asia and had a major effect on the distribution of wealth among individuals and nations.

Early iron smelting

The earlist Iron smelting was in Lejja, Nigeria. They have carbon-dated slag blocks to 2000 BCE. In a village square in Lejja, located about 15 kilometers south of the university town of Nsukka in southeastern Nigeria, lies what appears to be the oldest iron-smelting site in the world. Arranged in crescent shapes with mounds in the middle across a wide sitting area at Otobo Ejuona, as the arena is known, are hundreds of bits of smelting debris, or slags, recently carbon-dated to about 2000 BCE by a team of archaeologists and other experts from the University of Nigeria, Nsukka and Oxford University in the United Kingdom.

Evidence of iron smelting in Lejja Intensive smelting of iron took place at the site of Lejja, in south east Nigeria during prehistoric periods. This statement is substantiated by the extensive iron smelting debris left behind in Lejja. The debris could point not only to an extensive iron smelting period in the history of the site, but could even represent the remains of a once thriving industry. Iron smelting often involved the community as a whole, and its effects were usually far reaching; from changing the status and living standards of the smelters to the actual development of some African cultures 

The earliest evidence for iron-making is a small number of iron fragments with the appropriate amounts of carbon admixture found in the Proto-Hittite layers at Kaman-Kalehöyük and dated to 2200–2000 BCE. Souckova-Siegolová (2001) shows that iron implements were made in Central Anatolia in very limited quantities around 1800 BCE and were in general use by elites, though not by commoners, during the New Hittite Empire (∼1400–1200 BCE).

Archaeologists have found indications of iron working in Ancient Egypt, somewhere between the Third Intermediate Period and 23rd Dynasty (ca. 1100–750 BCE). Significantly though, they have found no evidence of iron ore smelting in any (pre-modern) period. In addition, very early instances of carbon steel were in production around 2000 years ago (around the first-century CE.) in northwest Tanzania, based on complex preheating principles. These discoveries are significant for the history of metallurgy.

Most early processes in Europe and Africa involved smelting iron ore in a bloomery, where the temperature is kept low enough so that the iron does not melt. This produces a spongy mass of iron called a bloom, which then must be consolidated with a hammer to produce wrought iron. The earliest evidence to date for the bloomery smelting of iron is found at Tell Hammeh, Jordan, and dates to 930 BCE (C14 dating).

Later iron smelting

From the medieval period, an indirect process began to replace the direct reduction in bloomeries. This used a blast furnace to make pig iron, which then had to undergo a further process to make forgeable bar iron. Processes for the second stage include fining in a finery forge. In the 13th century duringHigh Middle Ages the blast furnace was introduced by China who had been using it since as early as 200 b.c during the Qin dynasty. Puddling was also Introduced in the Industrial Revolution.

Both processes are now obsolete, and wrought iron is now rarely made. Instead, mild steel is produced from a Bessemer converter or by other means including smelting reduction processes such as the Corex Process.

Base metals

Cowles Syndicate of Ohio in Stoke-upon-Trent England, late 1880s. British Aluminium used the process of Paul Héroult about this time.

The ores of base metals are often sulfides. In recent centuries, reverberatory furnaces have been used to keep the charge being smelted separately from the fuel. Traditionally, they were used for the first step of smelting: forming two liquids, one an oxide slag containing most of the impurities, and the other a sulfide matte containing the valuable metal sulfide and some impurities. Such "reverb" furnaces are today about 40 meters long, 3 meters high, and 10 meters wide. Fuel is burned at one end to melt the dry sulfide concentrates (usually after partial roasting) which are fed through openings in the roof of the furnace. The slag floats over the heavier matte and is removed and discarded or recycled. The sulfide matte is then sent to the converter. The precise details of the process vary from one furnace to another depending on the mineralogy of the ore body.

While reverberatory furnaces produced slags containing very little copper, they were relatively energy inefficient and off-gassed a low concentration of sulfur dioxide that was difficult to capture; a new generation of copper smelting technologies has supplanted them. More recent furnaces exploit bath smelting, top-jetting lance smelting, flash smelting, and blast furnaces. Some examples of bath smelters include the Noranda furnace, the Isasmelt furnace, the Teniente reactor, the Vunyukov smelter, and the SKS technology. Top-jetting lance smelters include the Mitsubishi smelting reactor. Flash smelters account for over 50% of the world's copper smelters. There are many more varieties of smelting processes, including the Kivset, Ausmelt, Tamano, EAF, and BF.

Environmental and occupational health impacts

Smelting has serious effects on the environment, producing wastewater and slag and releasing such toxic metals as copper, silver, iron, cobalt, and selenium into the atmosphere. Smelters also release gaseous sulfur dioxide, contributing to acid rain, which acidifies soil and water.

The smelter in Flin Flon, Canada was one of the largest point sources of mercury in North America in the 20th century. Even after smelter releases were drastically reduced, landscape re-emission continued to be a major regional source of mercury. Lakes will likely receive mercury contamination from the smelter for decades, from both re-emissions returning as rainwater and leaching of metals from the soil.

Air pollution

Air pollutants generated by aluminium smelters include carbonyl sulfide, hydrogen fluoride, polycyclic compounds, lead, nickel, manganese, polychlorinated biphenyls, and mercury. Copper smelter emissions include arsenic, beryllium, cadmium, chromium, lead, manganese, and nickel. Lead smelters typically emit arsenic, antimony, cadmium and various lead compounds.

Wastewater

Wastewater pollutants discharged by iron and steel mills includes gasification products such as benzene, naphthalene, anthracene, cyanide, ammonia, phenols and cresols, together with a range of more complex organic compounds known collectively as polycyclic aromatic hydrocarbons (PAH). Treatment technologies include recycling of wastewater; settling basins, clarifiers and filtration systems for solids removal; oil skimmers and filtration; chemical precipitation and filtration for dissolved metals; carbon adsorption and biological oxidation for organic pollutants; and evaporation.

Pollutants generated by other types of smelters varies with the base metal ore. For example, aluminum smelters typically generate fluoride, benzo(a)pyrene, antimony and nickel, as well as aluminum. Copper smelters typically discharge cadmium, lead, zinc, arsenic and nickel, in addition to copper. Lead smelters may discharge antimony, asbestos, cadmium, copper and zinc, in addition to lead.

Health impacts

Labourers working in the smelting industry have reported respiratory illnesses inhibiting their ability to perform the physical tasks demanded by their jobs.

Regulations

In the United States, the Environmental Protection Agency has published pollution control regulations for smelters.

Coke (fuel)

From Wikipedia, the free encyclopedia
Raw coke

Coke is a grey, hard, and porous coal-based fuel with a high carbon content and few impurities, made by heating coal or oil in the absence of air—a destructive distillation process. It is an important industrial product, used mainly in iron ore smelting, but also as a fuel in stoves and forges when air pollution is a concern.

The unqualified term "coke" usually refers to the product derived from low-ash and low-sulphur bituminous coal by a process called coking. A similar product called petroleum coke, or pet coke, is obtained from crude oil in oil refineries. Coke may also be formed naturally by geologic processes.

History

China

Many Historical sources dating to the 4th century describe the production of coke in ancient China. The Chinese first used coke for heating and cooking no later than the 9th century. By the first decades of the 11th century, Chinese ironworkers in the Yellow River valley began to fuel their furnaces with coke, solving their fuel problem in that tree-sparse region.

China is the largest producer and exporter of coke today. China produces 60% of the world's coke. Concerns about air pollution have motivated technological changes in the coke industry by elimination of outdated coking technologies that are not energy-efficient.

Britain

In 1589, a patent was granted to Thomas Proctor and William Peterson for making iron and steel and melting lead with "earth-coal, sea-coal, turf, and peat". The patent contains a distinct allusion to the preparation of coal by "cooking". In 1590, a patent was granted to the Dean of York to "purify pit-coal and free it from its offensive smell". In 1620, a patent was granted to a company composed of William St. John and other knights, mentioning the use of coke in smelting ores and manufacturing metals. In 1627, a patent was granted to Sir John Hacket and Octavius de Strada for a method of rendering sea-coal and pit-coal as useful as charcoal for burning in houses, without offence by smell or smoke.

In 1603, Hugh Plat suggested that coal might be charred in a manner analogous to the way charcoal is produced from wood. This process was not employed until 1642, when coke was used for roasting malt in Derbyshire; previously, brewers had used wood, as uncoked coal cannot be used in brewing because its sulphurous fumes would impart a foul taste to the beer. It was considered an improvement in quality, and brought about an "alteration which all England admired"—the coke process allowed for a lighter roast of the malt, leading to the creation of what by the end of the 17th century was called pale ale.

The original blast furnaces at Blists Hill, Madeley

In 1709, Abraham Darby I established a coke-fired blast furnace to produce cast iron. Coke's superior crushing strength allowed blast furnaces to become taller and larger. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution. Before this time, iron-making used large quantities of charcoal, produced by burning wood. As the coppicing of forests became unable to meet the demand, the substitution of coke for charcoal became common in Great Britain, and coke was manufactured by burning coal in heaps on the ground so that only the outer layer burned, leaving the interior of the pile in a carbonized state. In the late 18th century, brick beehive ovens were developed, which allowed more control over the burning process.

In 1768, John Wilkinson built a more practical oven for converting coal into coke. Wilkinson improved the process by building the coal heaps around a low central chimney built of loose bricks and with openings for the combustion gases to enter, resulting in a higher yield of better coke. With greater skill in the firing, covering and quenching of the heaps, yields were increased from about 33% to 65% by the middle of the 19th century. The Scottish iron industry expanded rapidly in the second quarter of the 19th century, through the adoption of the hot-blast process in its coalfields.

In 1802, a battery of beehive ovens was set up near Sheffield, to coke the Silkstone coal seam for use in crucible steel melting. By 1870, there were 14,000 beehive ovens in operation on the West Durham coalfields, producing 4,000,000 long tons of coke per year. As a measure of the expansion of coke making, the requirements of the iron industry in Britain were about 1,000,000 tons per year in the early 1850s, rising to about 7,000,000 tons by 1880. Of these, about 5,000,000 tons were produced in Durham county, 1,000,000 tons in the South Wales coalfield, and 1,000,000 tons in Yorkshire and Derbyshire.

41 018 of the Deutsche Reichsbahn climbing the famous Schiefe Ebene, 2016

In the first years of steam locomotives, coke was the normal fuel. This resulted from an early piece of environmental legislation; any proposed locomotive had to "consume its own smoke". This was not technically possible to achieve until the firebox arch came into use, but burning coke, with its low smoke emissions, was considered to meet the requirement. This rule was quietly dropped, and cheaper coal became the normal fuel, as railways gained acceptance among the public. The smoke plume produced by a travelling locomotive seems now to be a mark of a steam railway, and so preserved for posterity.

So-called "gas works" produced coke by heating coal in enclosed chambers. The flammable gas that was given off was stored in gas holders, to be used domestically and industrially for cooking, heating and lighting. The gas was commonly known as "town gas" since underground networks of pipes ran through most towns. It was replaced by "natural gas" (initially from the North Sea oil and gas fields) in the decade after 1967. Other byproducts of coke production included tar and ammonia, while the coke was used instead of coal in cooking ranges and to provide heat in domestic premises before the advent of central heating.

United States

Illustration of coal mining and coke burning from 1879

In the US, the first use of coke in an iron furnace occurred around 1817 at Isaac Meason's Plumsock puddling furnace and rolling mill in Fayette County, Pennsylvania. In the late 19th century, the coalfields of western Pennsylvania provided a rich source of raw material for coking. In 1885, the Rochester and Pittsburgh Coal and Iron Company constructed the world's longest string of coke ovens in Walston, Pennsylvania, with 475 ovens over a length of 2 km (1.25 miles). Their output reached 22,000 tons per month. The Minersville Coke Ovens in Huntingdon County, Pennsylvania, were listed on the National Register of Historic Places in 1991.

Between 1870 and 1905, the number of beehive ovens in the US increased from approximately 200 to nearly 31,000, which produced nearly 18,000,000 tons of coke in the Pittsburgh area alone.[16] One observer boasted that if loaded into a train, "the year's production would make up a train so long that the engine in front of it would go to San Francisco and come back to Connellsville before the caboose had gotten started out of the Connellsville yards!" The number of beehive ovens in Pittsburgh peaked in 1910 at almost 48,000.

Although it made a top-quality fuel, coking poisoned the surrounding landscape. After 1900, the serious environmental damage of beehive coking attracted national notice, although the damage had plagued the district for decades. "The smoke and gas from some ovens destroy all vegetation around the small mining communities", noted W. J. Lauck of the U.S. Immigration Commission in 1911. Passing through the region on train, University of Wisconsin president Charles Van Hise saw "long rows of beehive ovens from which flame is bursting and dense clouds of smoke issuing, making the sky dark. By night the scene is rendered indescribably vivid by these numerous burning pits. The beehive ovens make the entire region of coke manufacture one of dulled sky: cheerless and unhealthful."

Production

Industrial coke furnaces

A coke oven at a smokeless fuel plant, Abercwmboi, South Wales, 1976

The industrial production of coke from coal is called coking. The coal is baked in an airless kiln, a "coke furnace" or "coking oven", at temperatures as high as 2,000 °C (3,600 °F) but usually around 1,000–1,100 °C (1,800–2,000 °F). This process vaporises or decomposes organic substances in the coal, driving off volatile and liquid products, including water, such as coal gas and coal tar. Coke is the non-volatile residue of the decomposition, the cemented-together carbon and mineral residue of the original coal particles in the form of a hard and somewhat glassy solid.

Additional byproducts of the coking are coal tar pitch, ammonia (NH3), hydrogen sulphide (SH2), pyridine, hydrogen cyanide and carbon based material. Some facilities have "by-product" coking ovens in which the volatile decomposition products are collected, purified and separated for use in other industries, as fuel or chemical feedstocks. Otherwise the volatile byproducts are burned to heat the coking ovens. This is an older method, but is still being used for new construction.

Sources

Bituminous coal must meet a set of criteria for use as coking coal, determined by particular coal assay techniques. These include moisture content, ash content, sulphur content, volatile content, tar, and plasticity. This blending is targeted at producing a coke of appropriate strength (generally measured by coke strength after reaction), while losing an appropriate amount of mass. Other blending considerations include ensuring the coke doesn't swell too much during production and destroy the coke oven through excessive wall pressures.

The greater the volatile matter in coal, the more by-product can be produced. It is generally considered that levels of 26–29% of volatile matter in the coal blend are good for coking purposes. Thus different types of coal are proportionally blended to reach acceptable levels of volatility before the coking process begins. If the range of coal types is too great, the resulting coke is of widely varying strength and ash content, and is usually unsaleable, although in some cases it may be sold as an ordinary heating fuel. As the coke has lost its volatile matter, it cannot be coked again.

Coking coal is different from thermal coal, but arises from the same basic coal-forming process. Coking coal has different macerals from thermal coal, i.e. different forms of the compressed and fossilized vegetative matter that comprise the coal. The different macerals arise from different mixtures of the plant species, and variations of the conditions under which the coal has formed. Coking coal is graded according to its ash percentage-by-weight after burning:

  • Steel Grade I (Ash content not exceeding 15%)
  • Steel Grade II (Exceeding 15% but not exceeding 18%)
  • Washery Grade I (Exceeding 18% but not exceeding 21%)
  • Washery Grade II (Exceeding 21% but not exceeding 24%)
  • Washery Grade III (Exceeding 24% but not exceeding 28%)
  • Washery Grade IV (Exceeding 28% but not exceeding 35%)

The "hearth" process

The "hearth" process of coke-making, using lump coal, was akin to that of charcoal-burning; instead of a heap of prepared wood, covered with twigs, leaves and earth, there was a heap of coals, covered with coke dust. The hearth process continued to be used in many areas during the first half of the 19th century, but two events greatly lessened its importance. These were the invention of the hot blast in iron-smelting and the introduction of the beehive coke oven. The use of a blast of hot air, instead of cold air, in the smelting furnace was first introduced by Neilson in Scotland in 1828. The hearth process of making coke from coal is a very lengthy process.

Beehive coke oven

Postcard depicting coke ovens and coal tipple in Pennsylvania

A fire brick chamber shaped like a dome is used, commonly known as a beehive oven. It is typically 4 meters (13.1 ft) wide and 2.5 meters (8.2 ft) high. The roof has a hole for charging the coal or other kindling from the top. The discharging hole is provided in the circumference of the lower part of the wall. In a coke oven battery, a number of ovens are built in a row with common walls between neighboring ovens. A battery consisted of a great many ovens, sometimes hundreds, in a row.

Coal is introduced from the top to produce an even layer of about 60 to 90 centimeters (24 to 35 in) deep. Air is supplied initially to ignite the coal. Carbonization starts and produces volatile matter, which burns inside the partially closed side door. Carbonization proceeds from top to bottom and is completed in two to three days. Heat is supplied by the burning volatile matter so no by-products are recovered. The exhaust gases are allowed to escape to the atmosphere. The hot coke is quenched with water and discharged, manually through the side door. The walls and roof retain enough heat to initiate carbonization of the next charge.

When coal was burned in a coke oven, the impurities of the coal not already driven off as gases accumulated to form slag, which was effectively a conglomeration of the removed impurities. Since it was not the desired coke product, slag was initially nothing more than an unwanted by-product and was discarded. Later, however, it was found to have many beneficial uses and has since been used as an ingredient in brick-making, mixed cement, granule-covered shingles, and even as a fertilizer.

Occupational safety

People can be exposed to coke oven emissions in the workplace by inhalation, skin contact, or eye contact. The Occupational Safety and Health Administration (OSHA) has set the legal limit for coke oven emissions exposure in the workplace as 0.150 mg/m3 benzene-soluble fraction over an eight-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 0.2 mg/m3 benzene-soluble fraction over an eight-hour workday.

Uses

Coke can be used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. The carbon monoxide produced by combustion of coke reduces iron oxide (hematite) to produce iron:

.

Coke is commonly used as fuel for blacksmithing.

Coke was used in Australia in the 1960s and early 1970s for house heating, and was incentivized for home use in the UK (so as to displace coal) after the 1956 Clean Air Act, which was passed in response to the Great Smog of London in 1952.

Since smoke-producing constituents are driven off during the coking of coal, coke forms a desirable fuel for stoves and furnaces in which conditions are not suitable for the complete burning of bituminous coal itself. Coke may be combusted producing little or no smoke, while bituminous coal would produce much smoke. Coke was widely used as a smokeless fuel substitute for coal in domestic heating following the creation of "smokeless zones" in the United Kingdom.

Highland Park distillery in Orkney roasts malted barley for use in their Scotch whisky in kilns burning a mixture of coke and peat.

Coke may be used to make synthesis gas, a mixture of carbon monoxide and hydrogen.

  • Syngas; water gas: a mixture of carbon monoxide and hydrogen, made by passing steam over red-hot coke (or any carbon-based char). Hydrocarbonate (gas) is identical, although it emerged in the late eighteenth century as an inhalation therapeutic developed by Thomas Beddoes and James Watt categorized under factitious airs
  • Producer gas; wood gas; generator gas; synthetic gas: a mixture of carbon monoxide, hydrogen, and nitrogen, made by passing air over red-hot coke (or any carbon-based char)
  • Coke oven gas generated from coke ovens is similar to Syngas with 60% hydrogen by volume. The hydrogen can be extracted from the coke oven gas economically for various uses (including steel production).

Phenolic byproducts

Wastewater from coking is highly toxic and carcinogenic. It contains phenolic, aromatic, heterocyclic, and polycyclic organics, and inorganics including cyanides, sulfides, ammonium and ammonia. Various methods for its treatment have been studied in recent years. The white rot fungus Phanerochaete chrysosporium can remove up to 80% of phenols from coking waste water.

Properties

Hanna furnaces of the Great Lakes Steel Corporation, Detroit. Coal tower atop coke ovens. November 1942

The bulk specific gravity of coke is typically around 0.77. It is highly porous. Both the chemical composition and physical properties are important to the usefulness of coke in blast furnaces. In terms of composition, low ash and sulphur content are desirable. Other important characteristics are the M10, M25, and M40 test crush indexes, which convey the strength of coke during transportation into the blast furnaces; depending on blast furnaces size, finely crushed coke pieces must not be allowed into the blast furnaces because they would impede the flow of gas through the charge of iron and coke. A related characteristic is the Coke Strength After Reaction (CSR) index; it represents coke's ability to withstand the violent conditions inside the blast furnace before turning into fine particles. Pieces of coke are denoted with the following terminology: “bell coke” (30 - 80 mm), “nut coke” (10 - 30 mm), “coke breeze” (< 10 mm).

The water content in coke is practically zero at the end of the coking process, but it is often water quenched so that it can be transported to the blast furnaces. The porous structure of coke absorbs some water, usually 3–6% of its mass. In more modern coke plants an advanced method of coke cooling uses air quenching.

Bituminous coal must meet a set of criteria for use as coking coal, determined by particular coal assay techniques.

Other processes

The solid residue remaining from refinement of petroleum by the "cracking" process is also a form of coke. Petroleum coke has many uses besides being a fuel, such as the manufacture of dry cells and of electrolytic and welding electrodes.

Gas works manufacturing syngas also produce coke as an end product, called gas house coke.

Fluid coking is a process which converts heavy residual crude into lighter products such as naphtha, kerosene, heating oil, and hydrocarbon gases. The "fluid" term refers to the fact that solid coke particles behave as a fluid solid in the continuous fluid coking process versus the older batch delayed-coking process where a solid mass of coke builds up in the coke drum over time.

Due to a lack of oil or high-quality coals in East Germany, scientists developed a process to turn low-quality lignite into coke called high temperature lignite coke.

Computing education

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Computing_education Elementar...