The efficient production of the cement

1. The processes of fragmentation, crushing and activation

        Portland cement – the product of the fine crushing of the clinker derived by a burning till the caking of raw mix which consists of carbonate components (limestone, chalk, shell rock, calc-tuff, marble, marl) and clayey componenets (clay, cinder, slime) and corrective ingredients. The best raw carbonate component is the lime marl which contains 75-80% CaCO3 and 20-25% of clay. More often on cement works there is used the limestone  – artificial blends: CаО –63-66%. KaО2 – 21–24%, Аl2О3 – 4–8%, Fe2O3 – 2–4%.

The production of the protland cement consists of 2 main stages:

  • the production of the clinker;
  • the crushing of the clinker with gypsum;

    70-80% of the cost of the portland cement is the cost of the clinker, and the production of the clinker is the estraction of raw materials, its crushing, the grinding of the raw blend till it is of the necessary composition, its blending and burning. The production of the portland cement itself from the klinker includes the crushing of the clinker, the preparation of mineral additives (the fragmentation and drying), the crushing of gypsum stones, the grinding of the clinker with active minaral additives, packing and warehousing.

    There exist 3 methods of the clinker production to produce raw blend of the necessary quality and composition with the minimum of power inputs: wet, dry and combined.

    By the wet method the fine crushing of the raw blend is carried out in the aqueous medium getting charges in the form of water suspension -  sludge (humidity 30 – 50%).

    By the dru method the raw charge is being prepared in the form of finely crushed dry powder. For that raw materials are dried before or during the process of grinding and delivered for burning in the form of a powder-like dry raw blend.

    By the combined method the raw blen is being prepeared (crushed) in the form of sludge either with the following dehydration using filters or a spray drier, or firstly it is dried and then crushed before the process of caking.

    The main drawback of the wet method is the evaporation of water (30 – 50% of the sludge mass). That increases the heat consumption for the water evaporation - 5,8 - 6,7 mega watt-second per kilogram, i.e. 30 – 40% more than by the dry method.

    The mai advantage of the dry method is the reduction of heat consumption for the burning of the clinker up to 3,4–4,2 mega watt-second per kilogram, reduction of furnace gases in 35 – 40%. That altogether provide with higher performance characteristics of the dry method. But performance capabilities of the dry method are limitted by the initial humudity of raw materials. That is important taking into consideration the fat that the crushing of materials in the existent mills can be carried on only under the humidity not more than 1%. That is why the crushing of the initial raw materials whcih have the humidity of 20-25% is characterised by the high  consumption of heat for drying.

    The high energy output, processing complexity and awkwardness of the process of the cement production are caused mainly by the fact that nearly 85% of electric power consumed for the production of cement, is used for the fragmentation and grinding of raw materials; at that 75% of electric power is used for grinding.

    The existent methods of fragmentation do not allow to grind viscous-plastic and wet materials and especially clays with the initial (natural) humidity. That is why by the wet method of clinker production some water is injected to gring the clay (the water later evaporates) or by the dry method the initial raw material is preliminary dried and then grinded, that also costs.

    Developed by us hardware of grinding and crushing-activation, and methods of dispersion allow to grind materials of a wide range of viscosity more efficiently. Using our methods, for example, clay powders can be obtained directly from the raw blend of its initial humidity, that increases the efficiency of the process. The plunger plant of "the hydrostatic shear dispersing extrusion" was initially developed for the processing of raw clay with the purpose of the sharp increase of its viscosity by the production of the building tile, and the centrifugal-dispersing mill-burner - for the atomization of clay and obtaining clay powder.

    These methods simplify the technology of the preparation of raw clinker materials and reduce the power inputs. This reduction is caused by a high efficiency of the developed methods of fragmentation-crushing, by the absence of costs for the evaporation of water from clay and by the fact that the suggested technology does not presupposes the equipment which can provide both with the dry and with the wet methods of the clay processing.

    The modified plunger miller is an efficient alternative for the fragmentation of raw clinker materials and crushing-activation of the clinker, with simple hardware-technological approach and power inputs of 30 mega watt-second per kilogram (considering that the existent technologies consume 90-110 mega watt-second per kilogram).

    The main characteristics of the portland cement (solidity, solidification rate, etc.) depend on the  dispersibility of particles and their inner structure (activation conditions) which are determined by the conditions of the process of crushing. At that the fine crushing of the clinker with gypsum and activized mineral admixtures is the final anf power-consuming procedure in the technology of the portland cement production. The comparative analysis of power inputs carried out by us showed that the standard technology of crushing using ball mills consumes 38 kilowatt-hour per tonn to crush the clinker up to the necessary size of particles (74 micromicron), while the suggested technology consumes 9 kilowatt-hour per tonn, i.e. charges for the crushing are reduced more than in 3 times. Besides, in the production of quality cement the fine crushing allows to save the power greatly.

    2. Systems for the deep dust-purification

    To satisfy the ecologycal requirements of dust- and gas-purification we suggest efficient technologycal systems to refine smoke fumes from the following ingridients with the efficiency of:

  • solid admixtures - 95-99%;
  • СО - 50–70%;
  • SO2 - 80–95%;
  • NхOх - 75–90%;
  • CхHх - 80-97%;

    The productivity of the system is from 10 thousand up to 1 million m3 per hour. These characteristics are provided with the usage of vortical scrubbers (gas cleaners) for the gas-purification, efficient vortical aerodynamic cyclone separators - for the refinement from solid admixtures and ionic filters - for the powder-like fractions.

    3. The system of the heat disposal

    The developed system for the utilization of heat on the basis of heat pumps allows to convert the heat which is discharged into the atmosphere into electric energy. In the technological process of the cement production this energy also provides with the reduction of production costs.

 

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