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Sysoiev Pavel

Sysoiev Pavel

Faculty: Physical and Metallurgical

Speciality: Heat-Transfer Physics

Scientific adviser: Anatoli Tuyahov

About author
Rotary kilns are widely distributed at various businesses in all industrialized countries.

The most widespread technological application of this type of equipment is received in non-ferrous metallurgy.

In this industry, rotary kilns used for sintering of bauxite and nepheline slurry calcination of the hydrate of aluminum oxide, calcination of cement clinker (for complex processing of nepheline in the alumina, cement, soda, potash), firing bauxite ore leach cake (tubular leach), and as reaction units in the production ftoralyuminiya and for other purposes.

The title reflects the name of the furnace is usually implemented in its manufacturing process. So, for example, distinguish Waltz oven used for rolling cakes of zinc production, furnaces for sintering of bauxite, alumina calcination, roasting of mercury-containing materials, as well as kiln drying of various intermediate products of steel production.

In other industries (chemistry, metallurgy, construction and refractory materials, etc.), rotary kilns - one of the main types of heating equipment in large-scale production for the heat treatment of loose, less lumpy materials. If the performance of the first furnace in 1932 - year of the first domestic aluminum - was 9.6 t / h, then at present the performance of individual instances of furnaces is about 100 t / h clinker and other materials.

Widespread use of rotary kilns due to the low sensitivity to particle size of processed raw materials, the possibility of heating the material without contact with the coolant, while fuel consumption in their per unit of finished product is usually higher than in shaft furnaces and multi-fluidized bed. Bring the unit cost of fuel to the cost of blast furnace can be achieved by lowering the temperature of exhaust fumes, achieved an extension housing the furnace and the installation of the device to heat transfer in the zone of moderate temperatures, and return to oven heat-treated material is unloaded from the air supplied for combustion . In order to increase the thermal efficiency of the furnace along with the development of new built-in heat exchangers in recent years, much attention is paid to pechestroenii zapechnym remote heat exchangers for heat recovery from flue gases and heated in the furnace feed materials. As zapechnyh heat exchangers in some countries the use of multi-stage dust collectors, cyclones and counter-pipes, as well as interlayer heat exchangers.

Sensitive to the grain composition of the material outrigger exchangers considerably complicate debugging and maintenance of furnace systems, so they are widely distributed yet mostly during the firing of construction materials (cement, limestone), ie in large-scale industries, which justified a significant finishing work in such heat exchangers. In these industries is also justified as an improvement of more fuel in one of the remote heat exchangers (to increase the degree of pre-firing of raw materials). Such a solution can significantly improve performance furnace installation. Role of the rotary kiln in this case is reduced to performing the functions the device for generating a high flue gas and excerpts of the material at high temperature.

For chemical and other industries, where most often used oven up to 20-40 m, as a remote heat exchanger appropriate to use a rotary dryer, which is not inferior to the universality of the rotary kiln. Along with the use of a rotary furnace installations dryers widely installation, which includes several rotating kiln. For example, the Eastern Institute of refractory industry was proposed plant for treatment of granular material in the form of three successive rotating drums. The first movement of material along the drum is used to preheat the flue gases, the second - for the firing and the third - as a heat exchanger for heating the air before feeding it to the combustion heat of the burnt material.

On energy grounds tubular rotary kiln are furnaces, heat exchangers with a variable length of heat treatment work. At the site where the fuel combustion temperature and combustion products reaches 1550-1650 ° C by radiation regime of the furnace. As you move the combustion products along the length of the oven they are cooled to a few hundred degrees and the mode of heat of the furnace is gradually becoming a convective. Specific distribution of the furnace zone with convective and radiative modes depends on the type and process parameters.

Tubular rotary furnace, except for receiving the spread of small ovens for drying sulfide raw materials, work in a countercurrent mode. Loaded into the furnace charge may have varying degrees of moisture, until the pulp containing up to 40% water. She served in the top (tail) of the oven and slowly moves toward the gases resulting from combustion of fuel at the head of the unit. From the drum recyclable products in the form of sinter or hot powdered material comes in a special refrigerator, and gaseous products of combustion along with the process gases are directed in the dust cleaning system. Depending on the type of recycled material for heating the tubular rotary kiln can be used: natural gas, fuel oil and solid fuel in the form of coke breeze or coal dust. Combustion burners typically use "pipe in pipe, nozzle or a special coal-fired burner.

 

  Motion of the layer charge in rotary kilns

In a rotary kiln to distinguish between internal and external movement of the mixture layer. Internal motion of the mixture layer define the following parameters: residence time of material in the zone (translational velocity), the variance of this time for various parts of the charge, the internal heat transfer, including the uniformity of the temperature field over the cross layer segregation of material in size, shape and density of the particles. These parameters are important for technology as well as for heat transfer, which is limited by internal heat exchange.

Despite the large number of experimental and theoretical work, many questions of internal motion of the layer remains unclear and therefore do not have a mathematical description. On several issues, researchers have different views, in particular, and about the mechanism peresypnogo layer motion, it would seem the most studied.

 

TYPES AND PURPOSE OF ROTARY KILNS

 Oven with a rotating drum of general purpose

The furnace is designed for various termotehnologicheskih processes with granular and liquid materials that can have contact with flue gases. Each particular process is carried out in a furnace with certain diameter and length, lined, speed and temperature.

In the kiln complex includes: stove with sliding bolt, loading and unloading chambers and drive mechanism rotating drum, fan, dedusting system, exhauster, air, gas and dymoprovody; chimney.

Oven with a rotating drum continuous form of a cylindrical welded body, which with the help of shoes fixed braces. Housing (drum) furnace based bandage on support rollers of the stations (base, base with a focus on, hard-core).

Inside the drum is lined with heat-or acid-proof brick, brand is chosen depending on the thermal regime of the furnace and processes.

To move the material toward discharge oven set at a slight angle to the horizontal.

 Muffle furnace with a rotating drum

The furnace is designed to produce semi-finished products of green ultramarine calcined kaolin.

In the kiln complex includes: muffle furnace with a rotating drum, loading and unloading chambers, two inserts for coolant fans to supply air exhauster; chimney.

The furnace consists of the following main components: a cylindrical drum, loading mechanism furnace chamber for the flue gases; chambers for feeding coolant furnaces, handling resistant devices drive mechanism.

Reaction chamber, where by firing a charge, a cylindrical drum with an outer diameter of 2500 mm, made of welded steel plate 22 mm thick. At the end of the drum is narrowed to a diameter of 1450 mm, the thickness of its walls reach up to 28 mm. The total length of the drum - 48 m. At the end of the drum has an internal projection 50 mm, which predotvrashaet horizontal displacement of the lining toward the unloading. Drum set with a bias toward unloading 64:1000. In order for firing the charge took place without contact with the coolant and the drum does not warp under high temperatures, lining made of shaped refractory blocks.

Internal muffle, which is firing and movement of charge, formed in 1912 carborundum blocks having a trapezoidal shape with internal flue channels of the same shape. The outer wall of the carborundum blocks overlap 12 solid trapezoidal blocks of lightweight fireclay. In between these blocks are set chamotte interlocking blocks. The refractory lining is placed on the asbestos sheet 10 mm thick that serve as thermal insulation of the drum.

The end of the drum lined with chamotte lightweight 113 mm thick on the asbestos sheet with a thickness of 6 mm.

 

 Furnace for the production of mineral salts

In the chemical industry, rotary kilns used for thermal, chemical, and combined treatment of various bulk and Komkova materials. By design, they are divided into flaming and muffle. The fuel for them to use natural gas, natural gas and fuel oil.

Muffle furnace double-seat with the length of the drum up to 22 m and a drum diameter up to 2,2 m (Berdichevsky Plant "Progress"), are designed for flow and countercurrent motion of the coolant and the material being processed.

Ovens two-, three-and Four-designed for countercurrent movement of the coolant and the material being processed.

Oven with a rotating drum continuous form of a cylindrical welded body, which with the help of shoes fixed trusses, barrel (drum), the furnace is supported on support rollers shrouding the appropriate stations.

 

Rotary kilns ferrous and nonferrous metallurgy

 The use of rotary furnaces in nonferrous metallurgy

Tubular (drums), rotary kilns are widely used in nonferrous metallurgy. On concentrators are used for drying concentrates. In metallurgy, light metals, they are used for drying and dehydration of aluminum ore, bauxite for the sintering of the charge and for the calcination of alumina. In these nickel metallurgy furnace used for drying the nickel ore roasting ores and matte, and metallurgy of zinc and lead - for the processing of various intermediates and waste (rolling). Tube furnaces are also used in metallurgy Tin metallurgy secondary non-ferrous metals for the process of drying, roasting and sublimation. Short tube furnaces used for melting and refining of metals, such as secondary copper.

Tubular rotary furnace can be divided into several groups. The first group includes the furnace for sintering, calcination, sintering and sublimation. This is a furnace with the highest ratio of length to diameter (20 to 30). On the temperature regime in this group include the furnace operating at medium and high temperatures in the hot zone (up to 1600 ° C).

The second group can be attributed to dehydration of the furnace materials containing hydrates, and for drying. The ratio of length and diameter of these furnaces occupy a middle position (5 to 15). The temperature in the hot zone of the furnace does not exceed 500-900 ° C.

In furnaces of these two groups have a direct-flow, and countercurrent motion of gases and heated materials.

The third group includes the furnace for melting and sublimation. This is a short kiln with a length to diameter ratio of 1 to 3. On the temperature regime they correspond to the furnaces of the first group, but are characterized by a uniform temperature in the workspace.

The fourth group includes the heating furnace.

 Rotary kiln for sintering aluminum ores

The main element of the furnace is a steel drum in length from 5 to 100 m and a diameter from 2,0 to 3,8 m, lined with high alumina and fireclay bricks based on the rollers. To promote the material the drum has a bias towards the horizon of 4-6%. The drum rotates at a rate of about 1 rpm. The furnace operates on the principle of counterflow. Blend dry or wet as a slurry with a moisture content of 40-42% goes into the drum through its terminal part (cold end) and moves slowly toward the head of the (hot end) towards the gas. From the drum product sintering - the spectrum - are poured into the refrigerator, underneath the oven and are also the drum up to 30 m and diameter 2,5 m, cooled by moving towards the air or water, which irrigates the refrigerator on top. When cooled cake with air, the last prosasyvaetsya a refrigerator fan, feed on the hot air to the burners.

For the heating furnace used gas, fuel oil, coal dust. Nozzle or burner located at the head of the drum. Flue gases from the drum comes in a dust chamber and electrostatic precipitators to capture carried away from the furnace dust particles charge and through the exhauster is sent either in a chimney, or to the scrubber separation of carbonization.

Due to the fact that the weight of the drum is very significant (with a length of 70 m it is lined with about 400 tons), the supporting device are crucial node in the design of the furnace. They consist of rollers on which the drum is supported by bandages. Ties are pushed onto the drum, forming a local support unbroken ring. The width of the tie - 400 to 600 mm. Each bandage is based on two rollers. Drum rotation rollers due to the friction of the tires rotate with it.

Hot end of the furnace is in the fuel or unloading head which is usually set is rolled back. The front of the fuel head there are openings for burners or injectors. To the head abuts the mouth of the channel through which to pour the spectrum in the refrigerator.

Cold end of the furnace is in a boot box. Download the dry mixture produced by the pipe passing through the loading box furnace. Feeding the furnace pulp can be made either by filling or by the method of atomization, through special nozzles which each furnace installed 03/04 pieces. Pulp is fed to the injectors pump pressure 5-6 atm.

 

 Rotating furnace

To melt large quantities of metal (10-12 m) in non-ferrous metal sometimes used in rotary kilns, which are the drum of the boiler steel, lined with refractory ramming mass of crushed quartz with clay. In the end walls of the furnace are holes: one wall of the hole for the burner, on the other side - opening for removal of combustion products. The furnace is on four casters, and with the drive mechanism during melting slowly rotates around its longitudinal axis (0.5 rpm).

Rotation can be done in both directions, which enables besides rotation, producing well and swinging metal. In addition to the mechanism for the rotation around the longitudinal axis of the furnace has a mechanism for rotation around the transverse axis. This allows you to attach the furnace tilt to load it through the burner opening. Release of metal and slag produced through the holes in the side wall. Melting furnace with a rotating space ensures good mixing of the metal during its melting and, besides, you can use to heat the metal heat accumulated by the upper parts of the masonry. However, these stoves have not been spread because of the complexity and cumbersome design.

 

 Rotary kilns OTHER

Other, less common, but are of interest to its design type of rotary kilns include: vacuum furnace filters, furnace plants for spraying sludge, small oven with peresypnymi silo and kiln calciner reactors shaft type for the preparation of raw mix for sintering in suspension state.

Vacuum filters are installed on the feed end of furnaces for the partial dehydration of sludge before it is put into the oven.

Often used for dewatering sludge is continuously active and less disc rotary vacuum filters. According to studies that were conducted Yuzhgiprotsementom, filtering can be subjected to almost all the sludge, seeking to reduce their moisture from 35-45% to 15-20%. During the firing of sludge, dehydrated to such an extent, reduced fuel consumption by 10-15% and approximately the same proportion, increasing productivity of the furnace.

Since the presence of vacuum filters humidity raw mixture entering the furnace, almost 2 times less than normal moisture content of sludge and, consequently, the evaporation of water it requires less consumption of heat from the furnace equipped with a vacuum filter, the gases from the elevated temperature. Using the heat of exhaust gas stoves in the recovery boiler or in any other way, we can further improve the efficiency of vacuum filters.

Depending on the physical properties of the slurry performance disk vacuum filter, referred to 1 m2 of its surface, is 200-400 kg in 1 h in dry matter. More efficiently, vacuum filters work when arriving at their sludge is preheated. When heated sludge from 20 to 60 ° C, the filter performance increases by 30-40%. She also increase by the introduction of a slurry in a small amount of additives such as milk of lime or portland cement.

Derived from cuttings "cracker" and testoobrazen Lipki. To make a "cracker" suitable for the transportation of estrus in the oven and moving along the oven, add to it a dry, trapped in the smoke chamber raw dust. Mixing of dust from the "biscuit" is produced in a screw-type mixer or by passage of material through the roller crusher. Dust is added in an amount such that the humidity "biscuit" when exiting the mixer was approximately 15% and its structure mass is a mixture of fine granules.

At the Krasnoyarsk cement plant, for example, mixing "biscuit" with the raw dust and feed the mixture into each of the rotary kiln size 3,6 (3,0) 3,6 x60 m used screws 630 mm in diameter. Screw-type feeder is made and the transport of dust to the mixing auger.

Mixed with dust, "cracker" in the inner cavity of the boot end of the kiln is fed by obliquely installed feed tube.

The main apparatus installation for vacuum filtration of sludge include vacuum filters, vacuum pumps, blowers and centrifugal pumps.

Operation of rotary kilns with a vacuum filter is associated with increased costs for labor, filter materials, mainly cotton cloth, and electricity.

Equipment rotary kilns vacuum filters complicates their design and operation and reduce utilization. Because of this furnace with a vacuum filters are of limited use as domestic and foreign cement factories.


Important Note
When writing this author's abstract, Master's work is not completed yet. Final completion: January 2012. Full text and materials on the subject can be obtained from the author and his manager after that date.