CONSTRUCTIVE DESIGN AND FEATURES OF THE PROCESSES IN THE ROASTING SHAFT FURNACES BY USING GASEOUS FUEL

The article analyzes shaft furnaces for lime production. According to the method of firing, shaft furnaces are of bulk type, semi-gas type, gaseous and liquid fuels. The disadvantages of the operation of the main modern kilns during lime burning have been established. The main aggregates for high-tonnage lime production are mine lime kilns, in which blast furnace coke or anthracite, or high-quality coals are used as fuel. Generally, lean fuels are used in industries where, together with the technological cycle, carbon dioxide is used, which are contained in flue gases with a concentration of 36−40%mass. The data on the operation of six furnaces on the territory of Ukraine at the enterprises showed that gas shaft furnaces of cylindrical and slotted type with a straight-lining profile were widely used. The parameters of such furnaces are productivity from 100 to 250 tons per day, shaft diameter from 3.2 to 5.4 m, and height 6−8 furnace diameters. Most often, they use heating systems with central and two rows of peripheral injection burners without protrusion. The most critical part of all furnaces is the distribution of gas flow rates over the cross-section of the furnace shaft and the depth of radial penetration of the gas flow into the material layer. Calculations of τ1 and τП were carried out in the following way: for τ1, the temperature range of the medium was chosen from 1300 to 250−300 °С, τox − the temperature range for the material was chosen from 1000 to 100 °С and the density of the product was taken into account at the degree of decomposition of limestone 98% (=1700 kg/m3). In the preheating zone, the limiting stage is the supply of heat from the gas to the lump material, and at the same time can be taken equal to ⁓400−450 kJ/(m2∙h∙К) and τ1 is estimated as 0.8÷1 hour. The total residence time of the material in the furnace (in the heating zone and in the firing zone) is estimated at 1.4÷1.5 hours. The average speed of material movement in the cylindrical part of the furnace is estimated as 0.004 m/s, which makes it possible to consider the filtering layer conditionally stationary. These characteristics affect the quality of limestone and the uniformity of limestone firing that was the basis for the design of roasting shaft kilns using gaseous fuel.

Technological prerequisites for the energy efficiency increase of the engine cylinder bore processing

An example of the rationalization of the current technology for manufacturing a cylinder of a small-sized diesel engine at PA “TULAMASHZAVOD” from a cast iron is given. It is shown that lowpower obsolete equipment leads to an increase in the number of technological operations and equipment used. However, even if all the generally accepted technological recommendations are followed, only 80% of the parts meet the requirements for the required parameters of accuracy and quality of the cylinder bore surface. Studies have found that the main reasons for insufficient quality are the presence of residual stresses in the casting, which cannot be removed during artificial aging, as well as insufficient accuracy and rigidity of metal cutting equipment at turning and boring operations. The use of more powerful and accurate modern equipment is theoretically and experimentally justified, which, due to increased refinement, allows reducing the number of machining operations. Replacement of artificial thermal aging by natural, combined with the replacement of shaft furnaces for heat treatment of workpieces with chamber furnaces of lower power and higher capacity, reduce energy consumption for the manufacturing by almost 4 times.

Using of Enriched Air Blast While Operation of Shaft Furnaces at LLC “Mednogorsk Copper-Sulfur Plant”

In this article we consider the practices of blast smelting of copper-bearing charge with oxygen enriched air blast at Mednogorsk Copper-Sulfur Plant. The degree of air blast enrichment with oxygen has been increased from 30% to 36%, and productivity has raised by 20.1%. The copper content in matte has made up 33.0-35.3%, in dump slag – to 0.5% Cu. We have provided the mass and heat balances of the smelting. We have demonstrated the influence of air blast oxygen enrichment degree on productivity of blast smelting, solid fuel consumption, contents and quantity of smelting products. Keywords: blast smelting, air blast, oxygen enriched, enrichment degree, furnace capacity, specific smelting rate, matte, anthracite

OPTIMIZATION OF CEMENTATION TECHNOLOGY OF TRACK LINK SLEEVES IN THE ATMOSPHERE METHANE-AIR MIXTURE

New three- and four-cycle experimental cementation regimes for a layer thickness of up to 4.0 mm in an atmosphere of natural gas with air additives have been developed. Rational schemes for adding air to the atmosphere of methane for carburizing in shaft furnaces at different thicknesses of the hardened layer have been determined. Industrial testing of new modes has shown the possibility of reducing the total duration of the cementation process by 25%; significant reduction in energy consumption for heating furnaces and reduction of natural gas consumption for one carburizing mode by 35%.

Technological possibilities of using natural gas in shaft furnaces for limestone roasting

One of the ways to improve the technology of limestone roasting in shaft furnaces is associated with improvement of conditions of combustion with natural gas when burning it directly in the layer. To implement this technology, it is necessary to ensure the development of two parallel processes: preparatory, in which the initial gas-air mixture is formed and heated to the ignition temperature, and the main one, during which a layer of combustion of gaseous fuel occurs. At air-blast tuyere feed and at coaxial jet supply of gaseous fuel under increased pressure when there are gas permeable nozzles in the path, a more powerful gas flow (natural gas) flows out of the nozzle at high speed into the external environment. It creates conditions for air flow ejection. Inside the annular space between the streams, a combustion zone is formed, on the inner and outer side of which there are circulating vortices directed along the axis of the jet to the nozzle. It improves stability of the gas-air mixture ignition. The considerable range of turbulent jets (at elevated pressures of the gaseous medium), as well as the possibility of sufficient complete mixing in the boundary layer, opens up the possibility of forming a gas-air mixture of a given composition along the front of the flare process, the movement of gas jets. To ignite the gas flow in the layer, it is necessary to ensure its preheating at least to a temperature of 800 – 1050 °C using a heat source located near its entrance. Energy efficiency of this direction is confirmed by experimental studies on a shaft furnace with a working space with diameter of 3 m. According to the results of experimental sounding of the heated zone of a limestone shaft furnace (in the mode of layer burning of natural gas), regularities were established in changing the temperature field of the burning layer with the formation of maximum temperature of 1200 °C at a distance of 200 mm from the nozzle section. The depth of formation of the combustion zone was limited to the level of 110 mm with the spread of the region of high temperatures over a distance of up to 1000 mm. Technological possibility of forming a region of high temperatures of 1100 – 1600 °C with a length of the high-temperature zone up to 2000 mm was established.

BUILDING MATERIALS BASED ON LIMESTONE DUST AND FINELY DISPERSED LIMESTONE

The paper presents research on the development of building materials with low CO2 emissions based on industrial man-made materials. The optimal recipe-technological parameters for the production of materials based on lime dust generated by mechanical deposition in cyclones and bag filters of shaft furnaces, as well as finely divided marble-like limestone with a fraction of up to 5 mm were determined. Studies have shown that it is possible to obtain a building material with compressive strength of more than 40 MPa from this recycled material by forced carbonization for three hours. Moreover, to obtain such strength indicators, the optimal content of lime dust in the raw materials is in the range of 35-40% wt. when the water content of the mixture is 6-7% wt. The carbonized material obtained at the indicated technological parameters will have an average density of 1.95-2.0 g / cm3 and water absorption by weight of not more than 12%. Accordingly, the data obtained make it possible to judge the possibility of obtaining high-quality construction products with physico-mechanical, physico-chemical, hydrophysical, and other properties sufficient for building materials.

On the possibility of using lime dust for the production of building materials of forced carbonate hardening

The paper presents research on the development of building materials with low level of CO2 emissions based on technogenic recycled materials. The paper addresses the determination of optimal formulation and technological parameters of obtaining materials based on lime dust generated by mechanical deposition in cyclones and bag filters of shaft furnaces, as well as finely dispersed marble limestone with a fraction of up to 5 mm. Studies have shown that it is possible to obtain carbonized material with compressive strength of more than 40 MPa from this recycled material by forced carbonization used during three hours. Moreover, to obtain such numbers, the optimal content of lime dust in raw materials should be in the range of 35-40% wt. when the water content of the mixture is 6-7% wt. The carbonized material obtained with the indicated technological parameters will have an average density of 1.95-2.0 g/cm3 and water absorption by weight of not more than 12%.