A kiln is a thermally insulated chamber, or oven An oven is an enclosed compartment for heating, baking or drying. It is most commonly used in cooking and pottery. Ovens used in pottery are also known as kilns. An oven used for heating or for industrial processes is called a furnace or industrial oven. In modern times the oven is used to cook and heat food in many households across the globe, in which a controlled temperature regime is produced. Kilns are used to harden, burn, or dry materials. Specific uses include:
- To dry green lumber Lumber or timber is wood that is used in any of its stages from felling through readiness for use as structural material for construction, or wood pulp for paper production so that the lumber can be used immediately
- Drying wood Wood is a hard, fibrous tissue found in many plants. It has been used for centuries for both fuel and as a construction material for several types of living areas such as houses. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression. In the strict sense wood is produced as for use as firewood
- Heating wood to the point of pyrolysis Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen. Pyrolysis typically occurs under pressure and at operating temperatures above 430 °C . In practice it is not possible to achieve a completely oxygen-free atmosphere. Because some oxygen is present in any pyrolysis system, a small to produce charcoal Charcoal is the dark grey residue consisting of impure carbon obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood, sugar, bone char, or other substances in the absence of oxygen . The resulting soft, brittle, lightweight, black, porous
- For annealing, fusing and deforming glass Glass is an amorphous solid material. Glasses are typically brittle, and often optically transparent. Glass is commonly used for windows, bottles, and eyewear; examples of glassy materials include soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovy-glass, and aluminium oxynitride. The term glass developed in the late Roman, or fusing metallic oxide paints to the surface of glass
- For cremation Cremation is the process of reducing dead bodies to basic chemical compounds in the form of gases and bone fragments. This is accomplished through high temperatures and vaporization (at high temperature)
- Drying of tobacco Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as an organic pesticide and, in the form of nicotine tartrate, it is used in some medicines. It is most commonly used as a recreational drug, and is a valuable cash crop for countries such as Cuba, China and United States leaves
- Firing of material, such as clay Clay is a naturally occurring material composed primarily of fine-grained minerals. Clay deposits are mostly composed of clay minerals, a subtype of phyllosilicate minerals, which impart plasticity and harden when fired or dried; they also may contain variable amounts of water trapped in the mineral structure by polar attraction. Organic materials, to form ceramics A ceramic is an inorganic, non-metallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous . Because most common ceramics are crystalline, the definition of ceramic is often restricted to inorganic crystalline materials, as opposed to the non-
- Drying malted barley for brewing Brewing is the production of beer through steeping a starch source in water and then fermenting with yeast. Brewing has taken place since around the 6th millennium BC, and archeological evidence suggests that this technique was used in ancient Egypt. Descriptions of various beer recipes can be found in Sumerian writings, some of the oldest known
- Drying hops Hops are the female flower clusters , of a hop species, Humulus lupulus. They are used primarily as a flavoring and stability agent in beer, to which they impart a bitter, tangy flavor, though hops are also used for various purposes in other beverages and herbal medicine. Hops were cultivated continuously around the 8th or 9th century AD in for brewing (known as a hop kiln or oast house An oast, oast house or hop kiln is a building designed for kilning hops as part of the brewing process. They can be found in most hop-growing (and former hop-growing) areas and are often good examples of vernacular architecture. Many redundant oasts have been converted into houses)
- Smelting Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores. Smelting uses heat and a chemical reducing agent to change the oxidation state of the metal ore; the reducing agent is commonly a source of carbon ore to extract metal
- Heating limestone Limestone is a sedimentary rock composed largely of the mineral calcite . Like most other sedimentary rocks, limestones are composed of grains; however, most grains in limestone are skeletal fragments of marine organisms such as coral or foraminifera. Other carbonate grains comprising limestones are ooids, peloids, intraclasts, and extraclasts with clay to make cement In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed rock with burnt lime as binder. The
- Heating lime to make quicklime Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic and alkaline crystalline solid at room temperature or calcium oxide Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic and alkaline crystalline solid at room temperature
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Ceramic kilns
Kilns are an essential part of the manufacture of all ceramics, which, by definition, require heat treatment, often at high temperature. During this process, chemical and physical reactions occur which cause the material to be permanently altered. In the case of pottery, clay materials are shaped, dried and then fired in a kiln. The final characteristics are determined by the composition and preparation of the clay body, by the temperature at which it is fired, and by the glazes Glaze is a layer or coating of a vitreous substance which has been fired to fuse to a ceramic object to color, decorate, strengthen or waterproof it that may be used. Although modern kilns often have sophisticated electrical systems to control the firing temperatures, pyrometric devices Pyrometric devices gauge heatwork when firing materials inside a kiln. Pyrometric devices do not measure temperature, but can report temperature equivalents. The intention of the device is to give visually communicate any activity within the ware. In principle, a pyrometric device relates the amount of heat work on ware to a measurable shrinkage have been used to provide visual indication of the firing regime since around 1000 AD.
Clay consists of fine-grained particles, that are relatively weak and porous. Clay is combined with other minerals to create a workable clay body. Part of the firing process includes sintering Sintering is a method for making objects from powder, by heating the material in a sintering furnace below its melting point until its particles adhere to each other. Sintering is traditionally used for manufacturing ceramic objects, and has also found uses in such fields as powder metallurgy. This process heats the clay until the particles partially melt and flow together, creating a strong, single mass, composed of a glassy phase interspersed with pores and crystalline material. Through firing, the pores are reduced in size, causing the material to shrink slightly. This crystalline material is a matrix of predominantly silicon Silicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon and aluminium Aluminium (UK: /ˌæljʉˈmɪniəm/ AL-yew-MIN-ee-əm) or aluminum (US: /əˈluːmɨnəm/ ( listen) ə-LOO-mi-nəm) is a silvery white member of the boron group of chemical elements. It has the symbol Al and its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the most abundant metal in the Earth's crust, oxides, and is very hard and strong, although usually somewhat brittle.
Types of kiln
In the broadest terms, there are two types of kiln, both sharing the same basic characteristics of being an insulated The term thermal insulation can refer to materials used to reduce the rate of heat transfer, or the methods and processes used to reduce heat transfer. Heat energy can be transferred by conduction, convection, radiation or by actual movement of material from one location to another. For the purposes of this discussion only the first three box with controlled inner temperature and atmosphere.
In using an intermittent kiln, the ware to be fired is loaded into the kiln. The kiln is sealed, and the internal temperature Historically, two equivalent concepts of temperature have developed, the thermodynamic description and a microscopic explanation based on statistical physics. Since thermodynamics deals entirely with macroscopic measurements, the thermodynamic definition of temperature, first stated by Lord Kelvin, is stated entirely in empirical, measurable increased according to a schedule. After the firing process is completed, both the kiln and the ware are cooled.
A continuous kiln, sometimes called a tunnel kiln, is a long structure in which only the central portion is directly heated. From the cool entrance, ware is slowly transported through the kiln, and its temperature is increased steadily as it approaches the central, hottest part of the kiln. From there, its transportation continues and the temperature is reduced until it exits the kiln at near room temperature. A continuous kiln is the most energy-efficient, because heat given off during cooling is recycled to pre-heat the incoming ware.
A special type of kiln, common in tableware and tile manufacture, is the roller-hearth kiln, in which ware placed on bats is carried through the kiln on rollers.
Kiln technology is very old. The development of the kiln from a simple earthen trench filled with pots and fuel, pit firing Pit firing is the oldest known method of firing clay. Unfired pots are nestled together in a pit in the ground and are then covered with burnable materials such as wood shavings, leaves, metal oxides, salts, sawdust and dried manure. The top of the pit may be protected with moist clay, shards, larger pieces of wood or metal baffles. The filled pit, to modern methods happened in stages. One improvement was to build a firing chamber around pots with baffles and a stoking hole, this allowed heat to be conserved and used more efficiently. The use of a chimney stack improves the air flow or draw of the kiln, thus burning the fuel more completely. Early examples of kilns found in Britain Great Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island. With a population of about 59.8 million people in mid-2009, it is the third most populated island on Earth. Great Britain is surrounded by over 1,000 smaller islands and islets. The island of include those made for the making of roof-tiles during the Roman Roman Britain was the part of the island of Great Britain controlled by the Roman Empire between AD 43 and about 410 occupation. These kilns were built up the side of a slope, such that a fire could be lit at the bottom and the heat would rise up into the kiln.
With the advent of the industrial age Industrialisation is the process of social and economic change that transforms a human group from a pre-industrial society into an industrial one. It is a part of a wider modernisation process, where social change and economic development are closely related with technological innovation, particularly with the development of large-scale energy and, kilns were designed to utilize electricity and more refined fuels, including natural gas Natural gas is a gas consisting primarily of methane. It is found associated with other fossil fuels, in coal beds, as methane clathrates, and is created by methanogenic organisms in marshes, bogs, and landfills. It is an important fuel source, a major feedstock for fertilizers, and a potent greenhouse gas and propane Propane is a three-carbon alkane, normally a gas, but compressible to a transportable liquid. It is derived from other petroleum products during oil or natural gas processing. It is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves and residential central heating. The majority of large, industrial pottery kilns now use natural gas, as it is generally clean, efficient and easy to control. Modern kilns can be fitted with computerized controls, allowing for refined adjustments during the firing cycle. A user may choose to control the rate of temperature climb or ramp, hold or soak the temperature at any given point, or control the rate of cooling. Both electric and gas kilns are common for smaller scale production in industry and craft, handmade and sculptural work.
- Anagama kiln - the Asian Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.6% of the Earth's total surface area and with approximately 4 billion people, it hosts 60% of the world's current human population. During the 20th century Asia's population nearly quadrupled anagama kiln The anagama kiln is an ancient type of pottery kiln brought to Japan from China via Korea in the 5th century has been used since medieval times and is considered the oldest style of production kiln, brought to Japan Japan is an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south. The characters that make up Japan's name mean "sun-origin", which is why Japan is from China China is seen variously as an ancient civilization extending over a large area in East Asia, a nation and/or a multinational entity via Korea Korea (Korean: 한국 Hanguk [hanɡuːk] or 조선 Joseon [tɕosʌn] – South and North Korea, respectively ) is a territory of East Asia that was formerly unified under one state, but now divided into two separate states and a region in northeastern Asia. Located on the Korean Peninsula, it is bordered by China to the northwest, Russia to the in the 5th century. This kiln usually consists of one long firing chamber, pierced with smaller stacking ports on one side, with a firebox at one end and a flue at the other. Firing time can vary from one day to several weeks. Traditional anagama kilns are also built on a slope to allow for a better draft.
- Bottle kiln - a type of intermittent kiln, usually coal-fired, formerly used in the firing of pottery; such a kiln was surrounded by a tall brick hovel or cone, of typical bottle shape.
- Catenary arch kiln, typically used for the firing of pottery using salt Salt is a mineral that is composed primarily of sodium chloride. It is essential for animal life in small quantities, but is harmful to animals and plants in excess. Salt flavor is one of the basic tastes, making salt one of the oldest, most ubiquitous food seasonings. Salting is an important method of food preservation, these by their form (a catenary In physics and geometry, the catenary is the curve that an idealised hanging chain or cable assumes when supported at its ends and acted on only by its own weight. The curve is the graph of the hyperbolic cosine function, and has a U-like shape, superficially similar in appearance to a parabola . Its surface of revolution, the catenoid, is a arch) tend to retain their shape over repeated heating and cooling cycles, whereas other types require extensive metalwork supports.
- Electric kilns - kilns operated by electricity Electricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning and static electricity, but in addition, less familiar concepts, such as the electromagnetic field and electromagnetic induction were developed in the 20th century, primarily for smaller scale use such as in schools, universities, and hobby centers. The atmosphere in most designs of electric kiln is rich in oxygen Oxygen (pronounced /ˈɒksɨdʒɨn/, OK-si-jin, from the Greek roots ὀξύς (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter), is the element with atomic number 8 and represented by the symbol O. It is a member of the chalcogen group on the periodic table, and is a highly, as there is no open flame to consume oxygen molecules, however reducing conditions can be created with appropriate gas input.
- Feller kiln brought contemporary design to wood firing by re-using the unburnt gas from the chimney in order to heat the air up before entering the firebox. This leads to an even shorter firing cycle and less wood consumption. This design requires external ventilation to prevent the in-chimney radiator from melting, being typically in metal. The result is a very efficient wood kiln firing one cubic meter of ceramics with one cubic meter of wood.
- Microwave assisted firing - this technique combine microwave Microwaves are electromagnetic waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF (millimeter waves), and various sources use different boundaries. In all cases, microwave includes the entire SHF band ( energy with more conventional energy sources such as radiant gas or electric heating in order to process ceramic materials to the required high temperatures. Microwave-assisted firing offers significant economic benefits.
- Noborigama kiln - the Noborigama is an evolution from Anagama design as a multi-chamber kiln, usually built on a slope, where wood is stacked from the front firebox at first, then only through the side-stoking holes with the benefit of having air heated up to 600 ºC from the front firebox, enabling more efficient firings.
- Sèvres kiln was invented in Sèvres, France and enabled to reach efficiently high-temperature (1280 ºC) in order to have fully water-proof ceramic bodies and easy to obtain glazes. It features a down-draft design that enabled to reach high temperature in shorter time, even with wood-firing.
- Top-hat kiln - an intermittent kiln of a type sometimes used in the firing of pottery. The ware is set on a refractory hearth, or plinth, over which a box-shaped cover is then lowered.
Wood-drying kiln
A variety of wood drying Typically when burning wood it is best to dry it. Moisture effects the burning process leading to unburnt hydrocarbons going up the chimmney. Though if a 50% wet log is burnt at high temperature, with good heat extraction from the exhaust gas leading to a 100C exhaust temperature, only about 5% of the energy of the log is wasted evaporating and kiln technologies exist today: conventional, dehumidification, solar, vacuum and radio frequency.
Conventional wood dry kilns (Rasmussen, 1988) are either package-type (sideloader) or track-type (tram) construction. Most hardwood lumber kilns are sideloader kilns in which fork trucks are used to load lumber packages into the kiln. Most softwood lumber kilns are track types in which lumber packages are loaded on kiln/track cars for loading the kiln.
Modern high-temperature, high-air-velocity conventional kilns can typically dry 1-inch-thick (25 mm) green lumber in 10 hours down to a moisture content of 18%. However, 1-inch-thick green Red Oak requires about 28 days to dry down to a moisture content of 8%.
Heat is typically introduced via steam running through fin/tube heat exchangers controlled by on/off pneumatic valves. Less common are proportional pneumatic valves or even various electrical actuators. Humidity is removed via a system of vents, the specific layout of which are usually particular to a given manufacturer. In general, cool dry air is introduced at one end of the kiln while warm moist air is expelled at the other. Hardwood conventional kilns also require the introduction of humidity via either steam spray or cold water misting systems to keep the relative humidity inside the kiln from dropping too low during the drying cycle. Fan directions are typically reversed periodically to ensure even drying of larger kiln charges.
Most softwood lumber kilns operate below 240 °F (116 °C) temperature. Hardwood lumber kiln drying schedules typically keep the dry bulb temperature below 180 °F (82 °C). Difficult-to-dry species might not exceed 140 degrees F.
Dehumidification kilns are very similar to conventional kilns in basic construction. Drying times are usually comparable. Heat is primarily supplied by an integral dehumidification unit which also serves to remove humidity. Auxiliary heat is often provided early in the schedule where the heat required may exceed the heat generated by the DH unit.
Solar kilns are conventional kilns, typically built by hobbyists to keep initial investment costs low. Heat is provided via solar radiation, while internal air circulation is typically passive.
Newer wood drying technologies have included the use of reduced atmospheric pressure to attempt to speed up the drying process. A variety of vacuum technologies exist, varying primarily in the method heat is introduced into the wood charge. Hot water platten vacuum kilns use aluminum heating plates with the water circulating within as the heat source, and typically operate at significantly reduced absolute pressure. Discontinuous and SSV (super-heated steam) use atmosphere to introduce heat into the kiln charge. Discontinuous technology allows the entire kiln charge to come up to full atmospheric pressure, the air in the chamber is then heated, and finally vacuum is pulled. SSV run at partial atmospheres (typically around 1/3 of full atmospheric pressure) in a hybrid of vacuum and conventional kiln technology (SSV kilns are significantly more popular in Europe where the locally harvested wood is easier to dry versus species found in North America). RF/V (radio frequency + vacuum) kilns use microwave radiation to heat the kiln charge, and typically have the highest operating cost due to the heat of vaporization being provided by electricity rather than local fossil fuel or waste wood sources.
Valid economic studies of different wood drying technologies are based on the total energy, capital, insurance/risk, environmental impacts, labor, maintenance, and product degrade costs for the task of removing water from the wood fiber. These costs (which can be a significant part of the entire plant costs)involve the differential impact of the presence of drying equipment in a specific plant. An example of this is that every piece of equipment (in a lumber manufacturing plant) from the green trimmer to the infeed system at the planer mill is the "drying system". Since thousands of different types of wood products manufacturing plants exist around the globe, and may be integrated (lumber, plywood, paper, etc.) or stand alone (lumber only), the true costs of the drying system can only be determined when comparing the total plant costs and risks with and without drying.
The total (harmful) air emissions produced by wood kilns, including their heat source, can be significant. Typically, the higher the temperature the kiln operates at, the larger amount of emissions are produced (per pound of water removed). This is especially true in the drying of thin veneers and high-temperature drying of softwoods.
See also
- Oven An oven is an enclosed compartment for heating, baking or drying. It is most commonly used in cooking and pottery. Ovens used in pottery are also known as kilns. An oven used for heating or for industrial processes is called a furnace or industrial oven. In modern times the oven is used to cook and heat food in many households across the globe
- Furnace A furnace is a device used for heating. The name derives from Latin fornax, oven. The earliest furnace was excavated at Balakot, a site of the Indus Valley Civilization, dating back to its mature phase . The furnace was most likely used for the manufacturing of ceramic objects
- Forge A forge is both the workplace and hearth of a smith or a blacksmith. The workplace is sometimes referred to as a smithy
- Cement kiln Cement kilns are used for the pyroprocessing stage of manufacture of Portland and other types of hydraulic cement, in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates. Over a billion tonnes of cement are made per year, and cement kilns are the heart of this production process: their capacity
- Lime kiln A lime kiln is a kiln used to produce quicklime by the calcination of limestone . The chemical equation for this reaction is:
- Oast house An oast, oast house or hop kiln is a building designed for kilning hops as part of the brewing process. They can be found in most hop-growing (and former hop-growing) areas and are often good examples of vernacular architecture. Many redundant oasts have been converted into houses
- Wood drying Typically when burning wood it is best to dry it. Moisture effects the burning process leading to unburnt hydrocarbons going up the chimmney. Though if a 50% wet log is burnt at high temperature, with good heat extraction from the exhaust gas leading to a 100C exhaust temperature, only about 5% of the energy of the log is wasted evaporating and
Gallery
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Brick and roof tile making kilns on a branch of the Mekong in the Delta region of Vietnam. |
Brickmaking kilns, Mekong delta. The cargo boat in the foreground is carrying the rice chaff which is the fuel for the firing. |
A wood fired pottery kiln in Hoi An Vietnam. |
Remains of a ceramics producing kiln just north of Sukothai, Thailand. |
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Same kiln as previous shot. Glazed pottery produced in this area's kilns, dated from around the 14th - 15th century AD |
A Catenary Arch kiln used for firing high temperature electron tube grade aluminium oxide ceramics |
Kiln from previous picture while being relocated |
A two-story porcelain kiln with furnaces á alandier in Sèvres Sèvres is a commune in the southwestern suburbs of Paris, France. It is located 9.9 km from the center of Paris, France circa 1880 |
External links
- Information about the history of bottle ovens (kilns) from Gladstone Pottery Museum in Stoke-on-Trent, UK.
- History of the Bottle Kiln (from thepotteries.org)
- How the Bottle Kiln Works (from thepotteries.org)
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sindh today
... boy who wants to play cricket and go to school, but is forced to work in a brick kiln , lost the best short film, live action Oscar to The New Tenants . ...
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There are 5 ports to load wood through one in front and two on each side one of the side ports is open and you can see one of the potters fueling the fire with wood and flames coming out This chimney is above the kiln and at night watching the flames out the top is dramatic The lit windows in the lower left are in the pottery studio the library windows in main building can
Fri, 08 Dec 2006 08:13:47 PST
This 3D real time model is of a cement kiln turning while monitored by an infrared linescanner. The model is radiometric which means that any ... youtube.com.
brandon phillips
hu, 24 Jun 2010 23:50:00 GM
I offered a small amount of advice for a . kiln. he was building based on my old wood . kiln. . He really took a liking to it and was intrigued with having a small . kiln. that could be filled and fired easily with one person. ...
