Shaft kiln to coke (coal) and gas fuel

Rotary kilns 30-100 m long, 2.4 m in diameter, with a 3-4 ° tilt angle and rotation speed of 0.5-1.2 / min. Specific daily their productivity reaches 500-700 kg / m3 based on the amount of direct calcining drum. Performance increases with the furnaces of their length, and thus fuel consumption is reduced. There are various ways to reduce fuel consumption in the lime calcination in a rotary kiln. These measures are suitable for heat recovery of gases from the furnace at a temperature of 750-800 ° C. In particular, furnaces put heaters in that guide is intended for burning lump material. Hence, 500-8000S temperature it enters the rotary kiln, and from it in the refrigerator. With this method of operation of the furnace firing rate is reduced to firing at 4600-5030 kJ / kg of lime. As the fuel burned directly in the drum torch furnace, apply oil or gas. For the lime burning is not recommended to use solid pulverized fuel with a high ash content, since ash precipitates on limestone at high temperatures and forms a low-melting compounds, which form the accretion, disrupts the normal operation of the furnace. Limestone is the motion of the drum takes in sequence the drying zone, heating to a temperature of 1123-1153 K (850- 880 ° C), pre-firing and cooling. When firing dense limestone zone drying oven is not due to the low moisture content. The preheating zone is typically 50-70% of the furnace length, firing zone is 25-30%. The length can be adjusted by changing the length of the torch burning fuel. Further, from the lime burning zone enters the pre-cooling zone, which occupies usually about 5% of the furnace length. Finally cooling occurs in a special refrigerated. The air heated in the cooler to 573-673 K (300-400 ° C) cooled lime enters the furnace fuel combustion as a secondary air. Primary air is in an amount of 15-20% of its total flow is fed through a combustion burner. To accelerate the heat exchange in the heating zone is set Valium chain and metal heat exchangers. It is also possible to use external heat exchangers and the cyclone in the form of the lattice conveyor. Heat transfer takes place in rotary kilns by the radiation method, and in mine - by convection. In the rotary kilns - is associated with a greater heat transfer surface and the fact that 3-atomic gases (V2 = VCO2 + VH2O + VSO2} 3-atomic gases) capable of transmitting heat radiation well enough. Advantages of the rotary kiln as follows: when the length of 30-100 m and the diameter of 1,8-3 m output reaches 400 - 500 t / day, which is 2-4 times higher than that of shaft furnaces.. The second major technological advantage lime burning in rotary kilns - small time material flow from the loading point to the exit from the furnace, which provides process control efficiency. In addition, the rotary furnace provides a compact flowsheet allow you to automate the process and reduce the capital cost of construction of workshops. In the rotary kiln can be obtained by firing limestone of high quality at moderate to high enough temperatures. Due to the short residence time in the furnace material in danger of burnout are minimal. Thus lime considerably more homogeneous in composition and contains less impurities. Advantages of rotary kilns: 1) high quality lime; 2) the use of any raw material; 3) the use of any type of fuel; 4) obtaining any kind of lime (construction, metal). Disadvantages: 1) large metal; 2) large investments; 3) significant fuel consumption (compared with the silo); 4) high energy consumption (compared to mine). Summary. Rotary kilns let you receive myagkoobozhzhennuyu known for its high quality of fine-grained limestone of soft carbonate rocks (chalk, tuff, shell limestone), which can not be fired in blast furnaces because of the tendency of these materials to "freeze" in the mine, which leads to disruption of the burning technology. Firing lime shaft furnaces, gas-fired. to the fractional composition of raw material requirements. Fuel burners and their location within the furnace. Device furnaces, strengths and weaknesses of their work. Consider now the shaft lime kiln. Typologically they are divided into peresypnye, polugazovye and gas furnaces. Peresypnye and polugazovye furnace is currently being built on small enterprises and low productivity. We can say that the design data are outdated furnaces and lime produced does not meet modern standards.

These types of kilns thing of the past, and so it makes no sense to spend time analyzing their konstruktsii.Neskolko words about gas furnaces for lime burning. When baking in blast furnaces to natural gas quality lime significantly improved. Also, increased furnace productivity, and improved working conditions. Rationalization of production often resorts to transfer existing peresypnyh and polugazovyh shaft furnaces to gas fuel. In translating important to create conditions for the uniform distribution of gas across the cross section of the mine. In ovens with a diameter less than 1.8 m into the furnace gas is fed via the burner introduced in special openings in the furnace walls. A larger diameter made peripheral and central gas heating, while the slot-like cross-section of the mine - only peripheral flow on two levels and more. Central gas produced by a vertical core arranged diametrically or metal beams, water-cooled, with podbalochnymi burners. This allows you to enter an additional gaseous fuel in the mine area. Water cooled beam furnace operation difficult and cause loss of heat from the cooling water. To replace the spoil of the beam is necessary to stop and unload the oven. Therefore, instead of these beams cantilever mounted air-cooled tuyere burner that can be replaced without stopping the furnace. Workspace shaft furnace is divided into three zones - zone heating, firing and cooling the material. Zone heating furnace gas is 35% of the useful height of the shaft, thereby reducing the flue gas temperature to 300-3500S (without suction of cold air) and heat the particulate material in the end zone to a temperature 9000S. Exiting the heating zone furnace gases with the rational mode firing contain 24-26% carbon dioxide (CO2) and 3-4% oxygen (O2). firing zone occupies 40% of the useful height of the shaft. The firing zone the combustion of natural gas and the dissociation of limestone. Average gas in the burning zone temperature is maintained at 1100-1200 ° C temperature uniformity of the gas flow cross-section in the firing zone of the mine depends on the uniformity of distribution of gas and air on the shaft section and the mixing conditions. Since the conditions of mixing gas and air in the furnace are not ideal, it is necessary to apply an additional amount of air oven (20-30% above the stoichiometric flow rate), i.e. an excess air ratio is maintained in the range 1.2-1.3. Cooling zone occupies a quarter of the height of the mine of useful and serves to cool the lime to 80-1200S before entering on the unloading mechanism. At the bottom of the furnace under the unloading device mounted cooling lime silo capacity of 2-3 m3, allowing the material to cool further 50-800S and preheat air entering the bottom of a blast furnace. During operation of the furnace is extremely important uniform supply of gaseous fuel and preventing local overheating of the material. Otherwise, the process leads to a violation of spёkov ("goats", welded), which dramatically worsen the gas dynamics in the oven and can cause it to stop. Advantages shaft furnaces: 1) low metal; 2) moderate investments; 3) lower fuel consumption (compared with rotating); 3) Low power consumption (compared to rotating). Disadvantages: 1) high enough decarbonization of raw material (usually no more than 93-97%); 2) uneven baking, which increases with decreasing diameter and height furnaces; 3) relatively high demands on the homogeneity of raw material quality and particle size, and degree of soiling his clay impurities; 4) limited capacity (capacity of 100 t / d is critical for shaft furnaces because of the risk of neprozhzhennuyu central zone).

The rotary tube kiln

Structurally, the tubular furnace (. Fig 97) is riveted or welded sheet steel drum thickness of 20 - 70 mm, mounted on roller bearings angle 2 - 50 to the horizontal plane. To stiffen the drum along its length are welded several shells that are thicker than the shell itself. Inside the drum is lined with refractory brick. Sometimes, to increase the residence time in the furnace, the maximum temperature zone of the drum expanding. With the ends adjacent to the furnace so-called head, which usually make sliding. Appointment of the top of the head - removal of gases and dust removal chastichnoeih. A body of this head pipe passes to load the oven. The lower fuel-head set apparatus and a receiving bin, into which the finished product is discharged from the furnace.

Fig. 97. The tubular rotary kiln 1 - fuel burning device; 2 - lower head; 3 - shoe; 4 - shell is; 5 - Drum Corps; 6 - lining; 7 - loading chute; 8 - upper head; 9- bandage; 10 - the driving gear; 11 - ring gear; 12 - roller carriage

The most critical part of the installation are supporting devices (bandages, and rollers), whose purpose - to take the load and ensure smooth rotation of the furnace. The load from the drum on the rollers is transferred via shrouds. For small diameter tires are mounted on the drum by hot landing. The drums of large diameter in order to prevent axial displacement of their tires mounted on cast iron shoes with heads rotated in different directions (Fig. 98). Make bandages from cast steel grades 35HGSA, 2HGSL, ZOGSL.

Fig. 98. Planting rectangular band on the stove body: 1 - regulating lining; 2 - band; 3 - steel shoe; 4 - shell is

Fig. 99. Methods for fixing the ring gear: 1 - drum; 2 - a nave; 3 - ring gear; 4 - longitudinal spring; 5 - steel segment; 6 - Joint; 7 - leaf spring

 

Tubular small size rotary kilns have two legs, and furnaces of great length do multisupport. Span take up to 20 m.

The diameter of the rollers is 0.25 - 0.33 diameter band, width 40 - 80 mm greater than the width of the band. The material for the steel rollers are 20GSL, 30GSL. The axis of the rollers are made of structural steels 45 and 50. Grease all bearings are managed centrally. To bandages did not descend from the rollers and the length of exposure is not less than 75% of its nominal value, rollers unfurl in a horizontal plane relative to the axis of the furnace at an angle of 10 - 450 so that occurs when this resistance force did not allow the drum to slide a distance greater than the thermal elongation.

Widespread roller with ball bearings and welded trusses, which allowed to greatly improve the reliability of the mechanical part of the furnace units and reduce the cost of their maintenance and repair.

For axial loads mounted pressure rollers. They are arranged so that they touch the side surface of one of the bands. Typically, pressure rollers made conical, so that they rolled on the surface of the band without slipping.

The latest advanced designs kilns supports the scheme is built on the principle of constant parallelism of the axes of rollers and the longitudinal axis of the furnace. The parallel arrangement of rollers provides a longer life tires and rollers at mensheyih width. In this case, the drum is held hydraulic system stops, which includes high-pressure hydraulic pumps, horizontal jacks and pressure rollers in contact with the end surface of bandages. longitudinal movement of the furnace is controlled automatically. By moving the furnace turns on the hydraulic pump, forcing oil under the piston of the jack. Jack pushes up the oven as long as the band reaches the stopper and turn off the pump. When the oven starts again shifted downward displacement restrictor again includes the pump and the cycle repeats. Cycle time displacement 24 - 48 hours.

Drive oven is usually set at equal distances from the ends of the drum. It consists of a pair of gear (drive gear and the crown) and the gear motor. The ring gear are made of quality carbon steel. To ensure longevity of the ring gear, which requires replacement of a long stoppage of the furnace, they are made of a harder material than the small (drive). large gears assembled from several sectors.

There are two types of fastening the ring gear to the drum: a tough and resilient. Rigid fixation (Fig. 79 a) used for the units, which body temperature during operation varies little and, hence, no thermal stresses. For average furnace crown resiliently fastened on the longitudinal (Fig. 99 b) or to the tangential plates. A crown secured to the longitudinal springs which in turn are rigidly fixed to steel at the edges of segments welded to the drum. When tangential connection (. Figure 99, c) one ends of the flat steel springs are rigidly attached to the drum, and the other - to the crown hinges. In large furnaces carried articulation rim and drum with the help of rods.