SU1357380A1 - Method of roasting chalkstone in mine furnace - Google Patents

Description

This invention relates to calcining limestone in a shaft furnace.

The purpose of the invention is to improve the quality of the finished product and reduce fuel consumption.

The method is carried out as follows.

Piece raw materials are loaded into the shaft slit furnace from above. The limestone in the kiln successively passes through the heating, calcining, cooling zones and is discharged from the bottom of the kiln. In the lower part of the cooling zone, all the air required for burning the gaseous fuel is supplied at a flow rate of 1.0-1.1. The air rises over the kiln shaft and cools the calcined material.

From the top of the cooling zone, all the air enters through the bottom row of holes in the walls of the oven chamber. The chambers are located on the outer side of the long walls of the furnace and have two rows of holes connecting the chambers to the furnace shaft. The distance between the holes in the chambers is chosen so that the resistance to movement of air in the material layer is many times more resistance. chambers. This leads to the fact that all the air without the aid of liquid-flow agents comes from the furnace shaft into the chambers.

The temperature of the air coming from the furnace shaft to the chambers is 600 °, the need to cool the calcined product from 1000-1250 ° C in the burning zone of the material prior to unloading from the furnace is determined by the heat balance.

, The gaseous fuel enters the lower part of the chambers, mixes with the hot air and burns out completely. The temperature of the product of combustion of natural gas reaches 2200-2300 ° C. Combustion products with such a temperature are directed to the calcination of limestone. The optimal calcination temperature for limestone is in the range from 1000 to. The lower temperature limit is determined by the rate and completeness of the calcination of limestone. Calcification of limestone at a temperature below 1000 ° C is characterized by a low rate of dissociation of limestone and a low degree of decomposition. So, if limestone dissociation rate at 950 ° C is taken as a unit, then at 050 ° C, it increases by 1.8 times, at 1150 ° C, by 4 times. The upper temperature limit of 1250 ° C is determined by the start of sintering processes (formation of silicates, aluminates and calcium ferrites), as well as recrystallization of calcium oxide, which reduces the content of active calcium oxide in the final product.

The calcination temperature is also determined by the physical nature of the limestone. } 1p firing limestone with a bulk weight of 1300-2000 kg / m requires a temperature of 1000-1150 0, and for firing limestone with a bulk weight of 2000-2800 kg / m 1150-1250 ° C. Thus, carried out the process of roasting of raw materials in the temperature range of 1000-1 250 C, you can use limestone with different physical properties and get the finished product of higher quality.

To reduce the temperature of the combustion products of the gaseous fuel, they are mixed in the combustion chambers with 40-70% (vol.) Waste: from the furnace gases. At the same time, using 40% of the exhaust gases of the total amount of gases allows to obtain a temperature of the gas mixture equal to, and using 70% of the exhaust gases 1 is 1000 C. When fuel is added to the combustion products, less than 40% of the gases leaving the furnace, the temperature of the gas mixture higher than optimal, which leads to image-. calcium silicates, aluminates and ferrites and recrystallization of calcium oxide. If more than 70% of the waste gases are added, the temperature of the mixture is below the optimum, which, with a constant furnace productivity, leads to a decrease in the rate and completeness of lime dissociation. Thus, the use of waste gases with exorbitant amounts (40-70%) reduces the quality of the finished product.

The gaseous mixture obtained through the upper windows Kg1mer enters the furnace shaft into the layer of calcined material and, lifting up, gives off heat to the material. The gases from the furnace are removed with smoke exhausters. Part of. they are directed to the upper part of the chambers to reduce the temperature of the combustion products of the gaseous fuel.

Primer p. In a shaft furnace with a length of 6 m, a width of 1.6 m, and a height of 22 m, limestone is loaded to with a size of pieces of 50–100 mm. The material is lowered, from top to bottom, through heating, calcining and cooling zones, and is discharged from the furnace with a discharge device. The productivity of the kiln is maintained at different lime temperatures, equal to 100 tons of lime per day. Air is cooled from below the kiln to cool lime in the amount of 3450-5560. After cooling of the day of lime, all air with the temperature of a BOO-OOO C is removed from the layer of material into the chambers, where 540-547 natural gas is supplied (at STOML

The coefficient of air consumption is -t5 known in the table.

From the table, we see that when calcining limestone according to the proposed method, in the temperature range JOOO-1250 ° C (tests 3-6), a finished product of higher quality is obtained in comparison with the known (experiment 1). The degree of decomposition of limestone from 96% increases to 96.2-97.3%. The content of active calcium oxide in the finished product also increases to 86.4-88.7% instead of 86.1% by a known method. However, limestone roasting at

em 1.0-1.1). Natural gas is mixed with hot air in the free space of the chambers and burned. Combustion products are mixed in chambers with 30-80% of gases from the furnace, having a temperature of about 200 ° C. The resulting mixture of gases with a temperature of 920 is sent to the kiln in the burning zone of lime. The mixture of gases due to the vacuum created by the smoke exhauster on the furnace top passes through a limestone column and heats it.

The results of calcining limestone by the proposed method in comparison with

in one case (test 7),

a decrease in the degree of decomposition of limestone to 95.8% instead of (96%) and a decrease in the content of active calcium oxide in the finished product to 85.7% (instead of 86.1). In another case (experiment 2)

the content of active calcium oxide decreases to 84.9%.

Using the total amount of air for burning fuel (experiments 2-7) instead of 30% according to the known method

sob (test 1) heated to BOO-OOO C instead of 150 ° C by a known method, and also mixing air with natural gas and burning the latter in free space of chambers instead of a layer of calcined material (known) increases the fuel utilization rate by reducing chemical underburning .

At the same time, the consumption of natural gas per 1 ton of lime is reduced from 139.4 m (test 1) to 129.8-130.5 m (tests 2-7)

or 5.6-6.9%.

Claims (1)

Invention Formula The method of burning limestone in a shaft furnace, including the supply of air Editor N. Bobkova Compiled by A. Kulabukhova Tehred M. Morgental Proofreader V. But ha 5940/21 Circulation 588. Subscription VNSh-SHI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, Projecto st., 4 , Ci to cool the mat of trial, exhausting heated air for mixing with gaseous fuel and burning it at an air flow rate of 1.0-1.1, characterized in that, in order to improve the quality of the finished product and reduce fuel consumption, all heated The upper part of the cooling zone of the material is mixed with gaseous fuel outside the furnace; after burning the fuel, 40-70% waste gas from the furnace gas is supplied to the combustion product formation zone and the resulting mixture with a temperature of 1000-1250 ° C is fed to the firing zone.