A. A. Shumilin

Firing Shchelkov and Dankov dolomites in rotary kilns with oxygen-enriched air

ConclusionsAs a result of enriching the air with oxygen to 23.5–24.9% during the firing of dolomite in a rotary kiln, the flame temperature is increased to 1900–1980°C, that is, by 150–185°C; the burnt dolomite, if the raw materials meet the requirements of ChMTU 8-22-67, satisfy the requirements of ChMTU 8-21-67 in terms of chemical composition and apparent density; the specific consumption of raw materials is 16–20% less, the specific yield is 40–50% greater, and the specific consumption of standard fuel is 10–14% less. The consumption of additional oxygen is 150–175 m3/ton of burnt dolomite.

Firing roof refractories by setting products of a single grade

ConclusionsA study was made of the firing process in a high-temperature tunnel kiln set with roof refractories of one and two grades. The firing loss when the products were placed in 3–4 rows (on edge) is slight but sharply increases in the two lower rows of the lattice setting using products of a single grade. The setting of the roof refractories over the height should consist of no more than four rows (on edge) which with a kiln channel height of 1.1 m is possible by using a setting of periclase-spinel refractories with an undersetting of chrome-magnesite products.The firing of the roof refractories should be done in a 7-column setting using products of two grades with a column thickness of 0.23 m and a length of 2.6 m.The possibility of using lattice settings in specialized kilns with a low channel height should be considered separately.

The ratio of zone lengths in high-temperature tunnel kilns

ConclusionsThe ratios of the heating zone lengths existing in high-temperature tunnel kilns for firing magnesia refractories are not optimal. There are reserves for improving the operation of the kilns by optimizing the ratio of the zone lengths.The operation of the preheat zone in a high-temperature tunnel kiln is characterized by perfect heat-exchange and the presence of a reserve section. This zone can be reduced without damage to the furnace operation, as a result of which it is possible to elongate the cooling zone.Further treatment of the question of optimization of the ratio of zone lengths in a high-temperature tunnel kiln should be continued in the new kiln design developed by the All-Union Institute of Refractories, which is equipped with burner assemblies from the 19th position.

Firing Savinsk magnesite in rotary kilns

ConclusionsSavinsk magnesite (lump and briquetted from the concentrate) can be thoroughly fired in rotary kilns of different sizes at a flame temperature of 1700–1750°C. The porosity of the powder is proportional to the size of the charge of raw material. During the firing of lump magnesite of all grades and briquette from ground concentrate it is possible to obtain powder with a porosity of 5–7%. When magnesite is being fired in a rotary kiln with a preparatory grid and when the raw materials charged amount to 1.5–2.0 times greater than when firing is done without the grid, a moderate-porosity powder is obtained. Thus, the fitting of a preparatory grid may increase the output of the furnace, and improve the quality of the product. During the firing of Savinsk lump and briquetted magnesite in rotary kilns in semiindustrial and industrial conditions, there is no bear formation, ringing, or crust formation on the lining of the furnace.

Determining the coefficients of air consumption from volumetric analysis of flue gases during the breakdown of material being calcined

ConclusionsA formula is proposed for determining the quantity of carbon dioxide evolved from material being burnt (dolomite, magnesite, or limestone) per 1 kg or 1 Nm3 for fuel, and also a formula for determining the coefficient of air consumption during the combustion of any fuel in the presence or absence, within the combustion products, of gases from the material being broken down (CO2).

Use of oxygen for burning fuel in rotary kilns

ConclusionsPreheating mazut oil up to 100°C and using hot producer gas with a temperature of 300°C, and also preheating air to 250°C may provide an increase in the furnace temperature of approximately 10%. Enriching the air used for combustion with oxygen is an effective method of boosting the combustion temperature in rotary furnaces.With an increase in the oxygen content in the oxidizing agent of from 21 to 30% in practice the combustion temperature of natural gas, using cold air, rises from 1570 to 2000°C. This temperature will be adequate for the thorough sintering of raw pure magnesite.

Shaft heat exchange in rotary furnaces for firing fireclays

ConclusionsThe shaft heat exchanger fitted to a rotary furnace firing fireclays is an effective means of improving the basic technical factors of the equipment.The gases should be piped from the shaft at low velocities and this can be done by increasing the area of the extractors.The shaft heat exchanger can operate with lump and briquetted clays of various sorts, and the firing of briquetted material increases the efficiency of the furnace. Roller-presses for obtaining small (less than 70 mm) briquettes are needed.The gas distribution over the cross section of the shaft is important in the operation of shaft heat exchangers and depends on the design of the units for feeding and withdrawing the gases.The use of the test shaft heat exchanger increased the output of a rotary furnace by 30% and reduced the specific fuel consumption for firing the clay by 25% and the dust removal by 20%.

Firing Dankov dolomites in a rotary furnace

SummaryCalcination of Dankov dolomites in a rotary furnace by the dry method is possible without the use of fluxing additions.Samples of dolomite from the top and bottom benches of the pit are calcined practically identically.The calcined dolomite in chemical composition and properties is suitable as metallurgical powder.

Combined grinding and drying of refractory clays in a shaft mill

ConclusionsThe shaft mill is suitable for combined grinding and drying of refractory clays with different moisture contents, including frozen clays.The product of combined grinding and drying in a shaft mill, in regard to grain-size composition and moisture content, corresponds to the technological norms. The grain-size composition and moisture content of the power are easily regulated.Operating costs with combined grinding and drying of refractory clays in a shaft mill are about 25% less than when drying in a drying drum and grinding in a disintegrator.The dimensions and capital costs of the installation with a shaft mill are less than for a unit with a drying drum and disintegrator.

Firing refractory material in rotary kilns with external heat exchangers

ConclusionsThe use of external heat exchangers with rotary kilns is of great advantage when firing refractory material, on account of which they should be used more extensively.The construction of large-size rotary kilns which do not have external heat exchangers means that their technical-economic operation characteristics will be poor.These characteristics can be improved and productivity can be stepped up by building on external heat exchangers.Drum coolers show poorer technical-economic characteristics than grate coolers. Hence when designing and constructing rotary kilns in the refractory industry, the installation of improved coolers should be envisaged.