SU855031A1 - Method of annealing pellets on conveyer machines - Google Patents

Description

one

1 The invention relates to the preparation of metallurgical raw materials in the steel industry.

Methods are known for heating mountain calcined conveyor machines with a combined gaseous fuel combustion system, including separate supply of gaseous fuel and combustion air, from mixing, burning in the mountain space and directly in the layer of pellets. According to these methods, the intensification of heat and mass transfer processes in the layer is carried out by eliminating flare gas into part of the burning zone, introducing the entire gas-air mixture stream into pellets and burning this mixture in the middle and lower layer combustion zone l.

The disadvantages of these methods are: the need to organize a special zone of extinguishing the surface of a layer of pellets (by supplying cold air) in front of the zone of layer burning of fuel to eliminate the possibility of ignition of the fuel above the layer, resulting in an increase in the length of the kiln conveyor machines; need for location

devices for burning gas in the layer directly in the furnace space of the machines, which leads to a significant reduction in their mechanical stability; the presence of different types of fuel-burning equipment on roasting machines, which complicates its operation; the need to use natural gas in the process and the lack of availability of non-deficient cheap solid fuels. Thus, the application of these methods significantly complicates the design of the firing equipment and causes a decrease in the specific productivity of the firing machines. These deficiencies are eliminated by the simultaneous burning of gaseous (above the layer) and solid (in the layer of oats) fuels.

 The closest to the invention according to the technical essence is the method of heating calcined conveyor machines with a combined combustion system 25 or various types of gaseous and solid fuels, including separate supply of gaseous and solid fuels and combustion air, their mixing, burning in gdrnovy space of gaseous fuel, and burning solid fuel directly in the layer of pellets. According to this method, a mixture of gaseous fuel and air is burned in the furnace, and solid fuel is fed to the kiln carts (consecutively coal, layer of ore-coal granules) by layer-by-layer material stacking Thus, in the high-temperature zones, the fuel is simultaneously burned above the layer and in the layer of material 2. The disadvantages of this method are: layering of the material, which is currently the implementation of the impediment 1 in serial equipment but since it requires a special path for supplying solid fuel ; the need to separate solid fuel into two streams: an independent flow of fuel and fuel that is rolled into pellets, as a result of which the charge preparation system is significantly complicated, and the requirements for the degree of grinding of coal rolled into pellets are complicated; the impossibility of increasing and regulating the reaction rates of heat and mass transfer on all horizons of the layer of material / impossibility of the operation of the kiln kiln machines on a mixture of various (including solid) fuels. The purpose of the invention is to intensify the process of heat and mass transfer in the layer and reduce the consumption of scarce types of fuel. The aim of the goal is achieved by the fact that according to the method, through odd and even rows of opposing fuel-burning devices, a mixture of solid and gaseous fuels is introduced and burned in a furnace in the heat ratio, respectively, 1: (1.4-2.7) and 1: (2.0 -3.5), while 10-50% of solid fuel is burned in the hearth, and 5090% directly in the layer of pellets, the material residence time between adjacent odd-numbered fuel burners is 2-4 minutes. The use of cheap solid fuels in the production of pellets is a major national economic task. At the same time, the solution of this problem should be accompanied by an improvement in the pellet firing process. The proposed solution combines the use of cheap types of solid fuels with increased productivity of the equipment being fired and improves the quality of the finished products. , is partially burned in the hearth as a gas suspension in a mixture with natural gas and is burned (due to unburned large particles of fuel) directly in the material layer, the burning fuel particles enter the material layer along with the hot flow of heat-transfer gas. Combustion of fine particles of solid fuel (particle size up to 0.3 mm) is completed in the furnace space of the machine due to the oxygen of the furnace gases. Larger particles ignite in the furnace, with the flow of heat-transfer gas get into the layer of pellets and burn in it. It has been established that when changing the mode of combustion of fuel in the furnace from the burner to the burner, i.e. when creating a pulsating mode of burning fuel along the length of the machine, all heat and mass transfer processes are intensified. For this, the combustion mode of the fuel of odd and even rows of burners is set different from each other. In this case, the total amount of fuel in terms of heat in each row of burners is the same (i.e., the heat distribution along the machine corresponds to the flow chart), but in odd rows (first along the material) the gaseous fuel is supplied in a slightly smaller amount (to increase the proportion of solid fuel supplied to the layer at the beginning of the process) than to even rows of burners. At the same time, a change from row to row of the ratio of different types of fuel leads to a change in the parameters of its combustion, both in the hearth of the roasting machine and in the layer of pellets. As a result, controlled pulsations of the burning torch and pulsations of the heat treatment mode of individual horizons of the pellet layer, i.e. controlled intensification of heat and mass transfer processes in the pellet layer is carried out. The most effective pulsation mode of heat treatment of pellets becomes when the ratio of the heat to solid and gaseous fuels in odd and even rows of burners is 1: 1.42, 7 and 1: 2.0-3.0, respectively. The supply of gaseous fuel in an odd number of burners in an amount less than 1.4 of the amount of solid fuel worsens the process of igniting the heat-air mixture, which is undesirable. The supply of gaseous fuel in an odd number of burners in an amount greater than 2.7 from the amount of solid fuel reduces the amplitude of oscillations (pulsations) of the process of heat treatment of the pellet layer and the intensification of the process of calcining the pellets is ineffective. The supply of gaseous fuel to even rows of burners in an amount less than 2.0 of the amount of solid fuel also reduces the amplitude of the pulsations of the heat treatment process of the pellet layer and is undesirable. The supply of gaseous fuel in an even number of burners in an amount greater than 3.5 of the amount of solid fuel leads to a decrease in the solid fuel combusted in the charge layer and, consequently, to underburning of the lower horizons of pellets.

The introduction of the required amount of solid fuel into the layer of pellets is ensured by adjusting its size in fractions of 0.3- and +0.3 mm. According to the firing technology over the charge layer, it is necessary to burn 10-50% of solid fuel (for this, the content in it is +0, 3 mm should be 95-60%. Combustion above the charge layer of less than 10% solid fuel is essentially impossible due to the natural presence in the fuel (after the mill) fraction class - 0.3 mm and partial combustion in the hearth mixture of larger fuel particles. a layer of charge more than 50% solid t Pliva impractical, ie, otherwise the amount of fuel combusted in the bed charge, is insufficient, and the lower layers nedoobzhigayuts layer.

When burning over a layer of pellets 10-50% of solid fuel in the layer burns 50-90% of its total amount. These limits are determined by the amount of fuel burned above the layer for the reasons given,

Pulsations of the heat treatment mode, which are round the machine, are determined not only by the amplitude of the pulsations, but also by their frequency. In this case, the frequency of the pulsations is determined by the residence time of the pellets between adjacent odd: even (even) rows of fuel-burning devices. Experimental data showed that this time should be 2-4 minutes. With a shorter pellet residence time between adjacent odd rows of burners (less than 2 minutes), the efficiency of intensification of heat and mass transfer processes in the layer is reduced, which is undesirable. With a longer residence time of the pellets (more than 4 minutes), areas with a lower temperature of the surface of the layer may be formed between the KciMH burners, which is unacceptable.

The essence of the invention is to create a pulsed mode along the length of the firing conveyor machine by heat treatment of a layer of pellets with a given amplitude and pulsation frequency. At the same time, the amplitude of the pulsations is determined by the different ratios of gaseous and solid fuels supplied to the burners, and the frequency is determined by the time spent between the adjacent odd (even) and r dgkmi burners.

Example: Raw iron ore pellets are loaded onto an annealing conveyor belt and subsequently subjected to drying, heating and high-temperature roasting, In the hearth of the heat-resistant zones of the roasting machines

gaseous and solid fuels, as well as combustion air as separate streams, are supplied through combined fuel-burning devices (providing for the simultaneous supply of gaseous and solid fuels as a gaseous fuel). it provides the required firing temperature mode, In odd rows of burners, a mixture of solid and gaseous fuels in a ratio of 1: 1.4-2.7, for example, at a ratio of 1: 2 and heat output of the burners 2.5 million kcal / h. Solid fuel is supplied to the burner.

178 kg / h (f 47 o | - I - the calorific value of fuel, kcal-kg and natural gas - 196 (with calorific value, gas capacity. 8500). A mixture of solid and gaseous fuels in an even ratio of 1: 2, 0-3.5. For example, at a ratio of 1: 3 with the specified parameters, solid fuel of 133 kg / h is supplied to the burner, 220 kg of natural gas. Natural gas and fuel consumption is established by means of regulating equipment (throttle valves, valves, and t, n, ),. are controlled by standard weight measuring instruments and are adjusted by dosing devices,

In the furnace burner, 10-50% of solid fuel is burned, and the rest of it (50-90%) is burned in the layer of pellets. To burn 10% solid fuel in the hearth, the amount of its fractions of class +0.3 mm is set equal to 95% (abs,). With an increase in the share of solid fuel burned in the furnace (specified by the process technology), the number of coarse fractions in the fuel is gradually increased. For burning 50% of solid fuel in the furnace, the amount of its fractions of class +0.3 mm is set to 60%. The degree of grinding of solid fuel (the ratio of coarse and fine fractions in it) is regulated by the operating mode of the grinding mills and is controlled by the dissemination of fuel before the burners.

With these parameters, the residence time of the material between adjacent odd rows of burners (ripple frequency) is set to 3, t) min (this time can vary from 2 to 4 min, depending on the firing mode). The pulsation frequency is controlled by the speed of movement of the firing carts and controlled by stationary instrumentation.

After firing, the pellets are cooled and sent to the finished product storage,

Claims (2)

The application of the proposed method makes it possible to increase the productivity of annealing conveyor machines by 5-7%, improve the quality of the finished product and ensure the possibility of partial replacement of natural gas with non-deficient solid fuels. The economic effect with such an improvement is 90 thousand rubles. per 1 million tons of pellets. The invention of the method of burning pellets on conveyor machines, including the separate supply of gaseous, solid fuels and combustion air / their mixture, burning in the space of gas-generating and partially solid fuel afterburning of solid fuel in the layer of pellets, which causes by the fact that, in order to intensify the processes of heat and mass exchange in the layer and reduce the consumption of scarce types of fuel, through an odd and even rows of opposite fuel burning devices, a mixture of solid and g zorago fuel in the ratio of heat, respectively, ltd, 4-2,7) and 1: (2.0-3.5), while 10-50% of solid fuel is burned in the hearth, 50-90% directly in the layer of pellets, time material stays between adjacent odd rows of fuel-burning devices for 2-4 minutes. Sources of information taken into account in the examination 1. A. Butkarev. and others. The graining of iron ores and cocentrates.-Sat. Institute Uralmechanobr, Metallurgists, 1978, 5. 2. The patent OilA 3383199, cl. 75-4, 1967.