Kilns intermittent

The older types of intermittent kilns have mainly been replaced by the tunnel type. Piece ware is placed on grates of a suspended conveyer. The gas kilns are provided with muffles but in view of the low temperatures (780—900 °C), electric kilns with metal heating elements are preferred. The kilns are frequently constructed in U form (reversing types). 

All intermittent kilns are thermally inefficient because there is little heat recovery in the preheating and cooling zones. In addition, much of the volatile matter in the fuel distils out of the kiln as smoke rather than burning. Judging the amount of fuel required to calcine a charge of limestone is based partly on previous experience and partly by poking rods into the charge to assess the amount of unburned limestone. 

Bottle Oven. 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. 

Box Kiln. A relatively small industrial intermittent kiln of box-like shape Boxing. The placing of biscuit hollow-ware, e.g. cups, rim to rim one on another this helps to prevent distortion during firing. 

Dutch Bond. Brickwork with alternate header and stretcher courses and alternate stretchers in vertical alignment. Dutch Kiln. An early type of up-draught intermittent kiln for the firing of bricks it had a number of small chimneys in the roof. 

Newcastle Kiln. A type of intermittent kiln formerly popular in the Newcastle-on-Tyne area. In its original form it is a rectangular kiln with two or three fireboxes at one end and openings for the exhaustion of waste gases at the base of the other end-wall, which incorporates a chimney. In a later design the kiln is of double length, there are fireboxes at each end, and the waste gases are removed from the centre of the kiln. 

Periodic Kiln. See intermittent kiln. Peripheral Speed. The rate of movement of a point on the edge of a rotating disk or cylinder it is the product of the circumference and the rate of revolution. The peripheral speed is of importance, for example, in the operation of abrasive wheels and ball mills. 

Rectangular Kiln. An intermittent kiln, rectangular in plan, with fireboxes at intervals along the two long sides. Such kilns find limited use in the heavy-clay and refractories industries. 

Stack Kiln. An old type of up-draught intermittent kiln for the firing of bricks. It was usually round, the feature of the kiln being the brick cone built on top of the kiln waste gases passed into this cone, and thence to the atmosphere, through openings in the kiln crown. 

Straightening Kilns. Electric intermittent kilns have been used specifically for straightening distorted ware, especially earthenware. 

Suffolk Kiln. An early type of rectangular up-draught intermittent kiln. The fireboxes were below the kiln floor which was perforated for the upward passage of the hot gases the waste gases escaped through openings in the kiln crown. 

Top-Blown Converter. See converter. Top-fired Kiln. A kiln with the burners in the roof, rather than in the walls, or fired by feeding coal or oil through apertures in the roof. The typical kiln of this type is the Hoffmann annular kiln, but the Monnier kiln provides an example of a topfired car-tunnel kiln. 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 boxshaped cover is then lowered. 

Up-cast. Local term in England for positive pressure in the atmosphere of some zones of an annular kiln the term is applied to the hot products of combustion that escape through any open feed caps in these zones. Up-draught Kiln. An intermittent kiln in which the combustion gases pass from the fireboxes through the setting and thence through one or more chimneys in the roof. Such kilns are inefficient and are now obsolete. 

The lime, cooled somewhat by the entering air in the lower parts of the shaft kiln, is discharged intermittently and slaked to calcium hydroxide with... 

Spinning-cup atomisers are used ia some plants to provide finer atomisation, allowiag smaller burner chambers and easier turndown, but with the burden of added rotating equipment. Rotary kiln burners were once popular to bum lower quaHty sulfur, but few are stiU ia operation. Spray burners can be operated intermittently and used at higher rates than rotary burners. 

When radiating and receiving surfaces are not in parallel, as in rotary-kiln devices, and the solids burden bed may be only intermittently exposed and/or agitated, the calculation and procedures become very complex, with photometric methods of optics requiring consideration. The following equation for heat transfer, which allows for convective effects, is commonly used by designers of high-temperature furnaces ... 

During the schedule automatic controls (or manual operator) intermittently adjust the dry and wet-bulb temperatures so that the kiln eonditions correspond to the next stage of the schedule and so on until the sehedule is complete. The wet-bulb depression must be controlled accurately as it has a disproportionate effeet on the severity of the schedule, compared to any drift in both dry and wet-bulb temperatures (Table 8.2). If the wet-bulb depression is too great, the rate of drying will be too fast, and the lumber may suffer degrade. 

Intermittent mixed-feed kilns are similar in general design, but, instead of additional fuel being added on to the hearth, it is added in layers while the kiln is being charged with limestone. 

The sand-bed oven is a closed, long kiln with a bottom consisting of screen plates. These screens support a bed of sand that is fluidized by intermittent blowing of steam, air, recycle gas, or inert gas. The briquettes in the kiln are heated by the hot sand and travel from the feed point to the extraction point where they pass the screen and are separated from the sand. 

Holes (in electrical conductivity). The absence of an electron from a compound or crystal structure leaves a hole. Holes move through the crystal or compound under the action of an electric field, in the opposite direction to that taken by electrons. They thus behave much like electrons, but carrying positive charge. Holey Boy. A type of perforated floor in intermittent downdraught kilns firing salt-glazed pipes. 

Kassel Kiln. An old type of intermittent, rectangular, fuel-fired kiln which diminished in cross-section towards the end leading to the chimney it originated in the Kassel district of Germany. Kavalier Glass. An early type of chemically resistant glass characterized by its high potash content it was first made... 

Shuttle Kiln. An intermittent bogie kiln consisting of a box-like structure with doors at each end and accommodating kiln cars (usually two in number). Pottery-ware is set on the refractory decks of the cars which are then pushed along rails into the kiln, displacing two other cars of fired ware from the kiln. The fired ware is taken from the displaced cars which are then re-set with more ware to be fired. The shuttle movement of the kiln cars is is then repeated (cf. bogie kiln). 

Waste-heat Dryer. A dryer for clayware that derives its heat from the cooling ware in the kilns. Such dryers are common in the brick industry and, even though the fuel consumption in the kilns may be slightly increased, this method of heat utilization results in an overall economy in fuel. Hot-floors, chamber dryers or tunnel dryers can be operated on this principle and the necessary heat can be derived from intermittent, annular or tunnel kilns. 

Wicket. A wall built of refractories to close an opening into a kiln or furnace it is of a temporary nature, serving as a door, for example, in intermittent or annular kilns. 

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