Certain elements in the structure of coke ovens are subject to the constant action of low or high temperatures in service; other parts, together with physicochemical and mechanical action, are subjected to the influence of sharp temperature variations.With an overall working period of 25-30 yr for the entire furnace, various parts are destroyed prematurely and require preventitive repairs even in the first years of service.Such elements include the outer roof and hearth bricks, the heads, and the extreme verticals of the coking chamber.It is established that the main factor influencing the rapid destruction of these structural elements is their deep cooling during the discharge of the coke and after the loading of the coal batch, and also the mechanical action of certain production operations.The destruction of the dinas in the heads and the outer verticals occurs due to the following. As a rule, small cracks first appear in various top, wall, outer hearth, and roof refractories. Then there occurs partial scaling of the surface layers of the structure, attached generally to the corners, edges and the resulting cracks of the various bricks.During subsequent heating and cooling scaling progresses, spreading not only deep down, but embracing a large part of the surface of the separating wall.According to [i], particularly rapid destruction in the zone of the first verticals is observed in the coke batteries of the PK-2K system, while in the central part of the furnace chamber there is no such damage.After charging the coal batch into the furnace chamber the surface layer of the structure is cooled to 600~[2]. According to [3], dealing with a study of the temperature fields in the structure, the temperature opposite the first heating channels in the first 5 min is sharply reduced from i010 to 200~ and then after i0 min it again rises to 650~ This indicates that the surface of the structure in the zone of the outer verticals, although briefly, is located in conditions of reverse low-temperature changes: u-quartz $ B-quartz and a-cristobalite ~ B-cristobalite with a volume effect of expansion or contraction equal to 0.82% (at 573~ for quartz and 2.8% (in the range 270-170~ for cristobalite.The deep cooling of the surface layers of the structure in the zone of the outer verticals is also helped by the rapid steam formation as a result of the evaporation of water brought in with the coal batch (moisture content 7-9%*). The moisture of the batch migrates to the lower, less heated courses of the separating wall, and into the zone of the outer verticals [4]; this causes embrittlement of the structure and a reduction in the original strength of the dinas [5].During the last 30 years no positive results have been obtained with attempts to increase the durability of the structure of the outer verticals.Different points of view have emerged about the causes of the formation of cracks and scaling.Some researchers have maintained that the formation of cracks and scaling is due to the size of the bricks and their low strength.In t...
An increase in the air temperature in blast furnace hot-blast stoves increases the severity of the operating conditions of the refractories in the lining and especially in the checkers, which are subjected to heating from all sides and loading for a long time. In connection with this, during recent years investigations have been conducted on improving the quality of refractories and the development of new and more resistant parts for the high temperature zones of hot-blast stoves. Most complex are the service conditions of refractories in the lower portion of the combustion chamber, where the refractory lining is subjected to the action of high temperatures and sharp temperature shocks. In the upper portion of the combustion chamber and the checkers, dinas refractories are being used successfully [1]. For the lower portion of the combustion chamber heat resistant refractories stable at temperatures up to 1500~ are necessary [2], such as mullite--c o rund tun.A new method for mullite--corundum refractories [3] has been introduced in Zaporozh'e Refractory Plant. For the production of chamotte briquets with not less than 77.5 wt.% A12Oa, a mixture consisting of alumina and Polngi kaolin is used. The briquets are prepared by the plastic method and fired in a rotating kiln. The water absorption of the chamotte is 3-5?0. The briquets are ground and a mixture is prepared consisting of the 3-0.5 mm coarse-grained fraction and a mixture of combined ground chamotte and Pologi kaolin (content of particles finer than 0.088 mm, 90%). The parts are formed on SM-1085 presses.The apparent density of the green part varies from 2.60 to 2.65 g/cm a. The parts are fired in a tunnel kiln at 1630~ in four positions with six pushes of the cars in a shift. The characteristics of the refractories are shown in Table 1.Experimental mullite--corundum parts I and II were prepared from chamotte obtained by firing briquets in batch kilns with a firing time of 70 h and a hold at 1700~ of 6 h. The briquets were prepared by the plastic method from alumina and kaolins of the Pologi (parts I) and Novoselitsa (parts II) deposits. The water absorption of the chamottes (78 wt.% A12Oa) varied within limits of 1.4-1.7 and 2-3?0, respectively.
A wide range of refractories is used in the USSR and abroad for building the stoves of blast furnaces. Fireclay, dinas, and high alumina articles are commonplace. Information exists on the use of corundum, magnesite, and forsterite bricks for this purpose.
An increase in blast temperature is one of the basic directions in reducing coke consumption and increasing blast-furnace productivity~ It is known that each IO0~ increase in blast temperature reduces the specific coke consumption by 12-15 kg per ton of iron melted.Production experience has shown that the most effective is differentiated use of refractories in different zones of hot blast stoves. At present chamotte, kaolin, mullite--corundum, and dinas refractories are used.In the 12th Five-Year Plan the variety of refractories for hot blast furnaces will be significantly broadened as the result of introduction of production in new and existing shops of fused and sintered mullite and corundum parts and also effective magnesia, dinas, and chamotte refractories and various thermal insulation materials and ramming mixtures (Tables ! and 2).In the service of hot blast stoves the most effective operation of them may be obtained with a systematic improvement in the lining design, the creation of favorable service conditions of the refractories, and an increase in their quality.Experience confirms that only with simultaneous work in these directions may the desired final result be reached.The different service conditions of refractories in hot blast stoves requires a differentiated approach to their use with a simultaneous improvement in quality~ For many years hot blast stoves have been built with internal combustion chambers with the use of chamotte refractories, which operate successfully with a blast temperature up to 1000=C. With an increase in blast temperature to II00~ kaolin and high-alumina refractories with a content basically of 62-72% AI=O~ are widely used. However, the use of these parts does not provide sufficient life of the equipment [I, 2], which required further development of investigations for development of more resistant refractories, primarily of dinas, corundum, and mullite--corundum ones [3][4][5].An investigation of the condition of hot blast stoves in a number of steel plants showed that individual portions of the lining of the combustion chamber, the walls, and the crown and of the upper part of the checkers were in unsatisfactory condition.Checkerwork of chamotte and high-alumina refractories was subjected to intense deformation (about 5-8%) and in some rows the chamotte parts were deformed up to 12%. The open porosity of such refractories dropped from 20-24% to 12-14% and the apparent density increased to 2~ g/cm3~For the purpose of studying the creep of refractories at various temperatures, loads, and holds investigations were made of production and experimental refractories.From the data presented (Fig. i) it may be seen that the deformation of chamotte refractories at 1200~ with a load of 0.2 MPa is about 2.8% with a hold of I00 h. Under these conditions mullite refractories deform less (about 1.1%) but more than kaolin parts (about 0.6%). This may be explained by the fact that kaolin refractories are produced from pure kaolin raw material, which is distinguished by a high weight share ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.