A universal criterion for estimating the service life of the refractory lining in heat-powered units is proposed. An algorithm for optimum choice of the design and thermal engineering properties of multilayer heat-insulating linings is discussed.The state of the fuel and power complex in the early 21st century in Russia and countries of the former Soviet Union dictates implementing a stringent engineering policy in the area of fuel resources, in particular, calcination technologies. Because of the low market cost of energy resources, of late predominant in the Russian Federation, the domestic industry has so far shown little interest in reducing the power supply per unit product. Still, the trends towards a leveling of prices of power resources in the internal and world markets makes the reduction of energy expenditures and, consequently, enhancing competitiveness of domestic products on the world market, an issue of urgent concern.Modern calcination processes are implemented through curtailing the consumption part of the heat balance of a particular furnace or a heat-powered unit. The use of modular high-temperature heat-insulating lightweight materials (MHTLWM) makes it possible to reduce heat losses through the refractory lining of the working chamber of a heat-powered unit to an acceptable level of about 250 W/m 2 [1]. The MHTLWM is thus a set of space-oriented multilayer refractory heat-insulating materials assembled into a module and aimed at solving a multifunctional engineering task in a particular heat-powered unit. The development of a lining for MHTLWM-based furnace and heat-powered units is a challenging task which involves a compromise between the requirements, not infrequently contradictory, placed on the refractories' service [2].It is practically impossible to functionally harmonize parameters for a lining made of a uniform material [3]; a way out of this situation is to use a multilayer refractory lining. In developing such a structure, the designer should take into account a number of parameters, such as: (i) the cost of refractory materials available from domestic and foreign manufacturers; (ii) operating temperature for a particular refractory; (iii) heat conductivity, heat capacity, coefficient of linear thermal expansion (CLTE), and mechanical strength of the lining materials; (iv) resistance of refractories to thermochemical attack of the hot-furnace space; (v) environmental requirements placed on the chemical composition of the refractory; (vi) temperature drop at the layer interface and the associated therewith change in heat conductivity of the material; and (vii) resistance of the hot layer of the lining to abrasive attack of the dust-and-gas furnace space.In this work, we have estimated the MHTLWM service life in terms of a criterion with a value of K = 1.0 which parametrizes the loss of basic operational properties (heat capacity, heat conductivity, and mechanical strength). This criterion has been derived using research data from the literature [2, 4 -7], statistical results of obser...

A system has been developed for choosing the parameters of gas and air flows for tunnel furnaces for various purposes. An algorithm has been devised for controlling a system for selecting the hot air from the cooling zone for the dryer and for differential transfer of atmospheric air through special throttle packings in the cooling zone in order to reduce the level of thermal shock on components and normalize the gas-dynamic parameters of the working channel.During the last 50 years there have been no major changes in the design of tunnel furnaces as regards the working channel geometry and the organization of the gas and air flows in the working channel and outside it. While there have been changes in the design of the lining for the walls, roof, and floor of the wagons and in the range of heat-insulating materials used, which are qualitative changes designed to reduce heat losses, raise the thermal stability, and reduce the mass and heat capacity of the lining, there has been a more conservative approach to the organization and optimization of gas and air flows. In particular, there are only long-standing localized and distributed modes of admitting atmospheric air through the corresponding inlets to the cooling zone, the existing schemes do not eliminate the conflict between the balance of the gas and air flows with existing controls.It is impossible to provide good and economical firing modes without allowing for the optimal organization of the heat and mass transfer. The decomposition of the model may be considered as approach for minimizing its complexity, i.e., solving the following minimization [1]:in which L Ä * is the minimal complexity of the decomposed system, D the operational decomposition, and G D the set of all acceptable decomposition operations for the given system. To compensate the nonlinearity in the redistributed heat fluxes, as is evident from the equations, it is necessary to introduce into the cooling system a mechanism for differentiated atmospheric air supply. There are heat-engineering parameters of a tunnel furnace such as the uniform temperature background over a vertical section and asymmetry in the temperature pattern between the left and right sides of the working channel, which cannot be optimized without allowance for the gas-dynamic curve (hydraulic curve) for the working channel and the zero-point coordinates. This complicated task cannot be resolved without developing a special algorithm (Fig. 1) and using a carefully considered set of instruments in the parameter control. In particular, one needs a furnace design with effector mechanisms, systems for handling the gas and air flows, and throttle slide valves, together with a special mathematical model (Fig. 2) for processing the information signals from the sensors and acting on the thermal processes by means of the effector mechanisms based on rotating slide valves handling the volumes of gas and air flows within and outside the furnace [2]. Figure 2 shows the structural scheme, where the block Constant 3 has the value 50°C ...

Technology has been developed in NK-Teplokhimmontazh for heat insulating objects of aluminosilicate composition with high thermal shock resistance. Industrial tests have been performed and series production of objects has been assimilated. Material is recommended for use in furnaces of both continuous and batch operation.Currently saving energy is one of the most important tasks of the majority of countries in the world. A reduction in the reserve of non-renewable sources of energy, such as coal, oil, gas, and worsening of the ecological situation in the world, has led to the situation that solution of the problem is at the state level. It is apparent that an important role in resolving the problem of saving energy and economy of thermal energy is effective heat insulation.Recently particular interest has developed in high-temperature materials with a fibrous structure, since they exhibit valuable properties suitably distinguishing them from other materials. Fiber material have a quite broad range of density, low thermal conductivity and much higher thermal shock resistance than dense and cellular ceramics.The lining of heating units during operation is subject to rapid heating and cooling, as a result of which between the surface and inner part of refractory material there is a temperature drop. It is well known that if during a rise in temperature material thermal conductivity does not manage to change at the rate of an increase in temperature, then the temperature at the surface exceeds that of its inner part. During a reduction in temperature the reverse occurs. With an uneven temperature distribution in the material due to different thermal expansion of the high-temperature and low-temperature parts a stress arises that is called thermal. If the thermal expansion coefficient has a positive value, then in the high-temperature part a compressive stress arises, and in the low-temperature part it is tensile. If the thermal stress reaches the material breaking stress (strength), then the material fails. The interconnection between the high-and lowtemperature parts of a material is a conceptually complex picture.Thermal shock is the most widespread form of wear for refractory objects during service. It is possible to indicate the four main factors, each of which individually provides a refractory with high thermal shock resistance: low elasticity modulus; low LTEC; high refractory matrix thermal conductivity; rational binder composition, cementing the granular component of a refractory mix of an object and its structure.A binder is an essential factor governing refractory object thermal shock resistance. Data from numerous thermal shock resistance tests show that normal magnesite objects do not exhibit thermal shock resistance; magnesite objects based on a forsterite binder also lack thermal shock resistance. Conversely, magnesite objects based on a spinel binder exhibit quite high thermal shock resistance. It is well known that introduction into a coarse grained ceramic material (matrix) of fiber materials makes ...

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The company has developed a technology for making alumosilicate heat insulating components (lightweight) with ethyl silicate binder. Industrial tests have been performed and regular production has been initiated.Heat insulating components are widely used in industry to reduce heat losses and improve the efficiency of heating plant. Light-weight thermal insulating refractories are made in Russia by traditional technologies, and their physicochemical parameters match GOST 5040. Recently, a demand has arisen for a wider range of heat-insulating refractory components characterized by various compositions, densities, strengths, and thermal conductivities. This has been due to a considerable extent for repairs to heating plant lined with imported materials. During the last 15 years, this company has accumulated much experience in that area. Materials we have made, including heat insulating ones, have been used at the Lebeda GOK Company for the GBZh-1 and GBZh-2 plants, at Mikhailov GOK Company for repairing firing machines, and at Novolipetsk Metallurgical Corporation for lining a plant for hot zinc coating and so on.In the production of alumosilicate heat-insulating components, much use is made of methods involving the use of additives that burn up and ones that produce foam. When one makes such components by traditional methods with burn-up additives, the minimum possible apparent density is 1.0 g/cm 3 . Components with lower apparent density (down to 0.4 g/cm 3 ) are obtained by the foaming method.The foam method has two major shortcomings. Firstly, mechanical processing is required, and secondly, the drying process is very critical. Mechanical processing requires the use of grinding machines and a dust-extraction system, which increase the capital cost for this type of product. Also, it becomes necessary to employ more staff. There is also the question of reusing or recycling trimmings, which constitute 25 -35% of a component. These shortcomings certainly raise the cost of the product. Components made by the foam method have low apparent density and thermal conductivity, but the maximum temperature of use is also low. For example, the maximum working temperatures for ShL-0.4 and ShTL-0.6 components are 1150°C, and for MKRL-0.8, 1250°C.When additives that burn up are used, the components are made preferentially by the plastic shaping method, which also has shortcomings. The dimensions of parts made from plastic masses are reduced considerably on drying and firing (linear shrinkage 2 -5% for each of these operations), which leads often to cracking and deformation.It is better to use a semidry forming method. Components made from semidry masses (water content 3 -10%) hardly shrink at all on drying, while on firing the shrinkage barely exceeds 1%, so the components are more accurate in shape and size. The traditional technology for making heat-insulating refractory components has a section concerned with semidry forming, but it has not been widely used [1]. The semidry method has been used in making lightweight firebri...