SU1553519A1 - Method of controlling the process of thermal treatment of phosphorite pellets - Google Patents

Abstract

The invention relates to the field of controlling the process of preparing phosphate raw materials for electric distillation, in particular to methods of controlling the heat treatment of pellets obtained from finely divided phosphate raw materials, can be used in the chemical industry and allows increasing the yield of pellets. In accordance with the invention, the method consists in monitoring and controlling the cooling process of phosphate pellets, and as an indirect parameter, the difference in dust content at the exit of the burning zones and the first cooling zone, which should be at the level of the allowable value, is used. The temperature correction (cooling rate) of the first cooling zone is adjusted depending on the PH value of the calcined pellets. If the difference exceeds the allowable value, the cooling rate in the second cooling zone is adjusted by changing the flow of hot gas. 2 Il. 1 tab.

Description

The invention relates to automating the process of preparing phosphate raw materials for electric dressing, in particular the process of heat treatment of phosphate pellets, and can be used in the chemical industry.

The aim of the invention is to increase the yield of pellets.

Fig. 1 shows a block diagram of a device implementing this control method; Fig. 2 is a diagram of the gas streams supplied to the cooling zones of the firing machine.

The block diagram of the device comprises (Fig. 1) a conveyor 1, a burning machine 2, a drive 3 of the conveyor, a temperature sensor 4, a comparison unit 5 with an amplifier, a temperature setting unit 6, a control unit 7, a ratio setting unit 8, a comparison unit 9, a flow meter 10 , divider 11, actuators 12 and 13, pH measurement unit 14, comparison unit 15, control unit 16, landing unit 17, comparison unit 18, prohibition unit 19, actuator 20, sampling &

ЈЈ

nicknames 21 and 22, calculation block 23, comparison block 24 and block :; 25 controls

The method is carried out as follows.

In block 14, the pH value of the suspension prepared from roasted pellets is measured, and their strength is determined; in comparison block 15, the actual and predetermined pellet strength is compared, the output of block 15 through an amplifier is connected to a control unit 16 according to a specific program, i.e. changes the speed of movement of the pallet (signals Fq and F) or the dosage of raw pellets (signal Fg) „

If it is impossible to apply these control actions, change the temperature mode in the burning zone (signal F5).

At the same time, signals from the amplifier output (- & G) are fed to the input of the temperature setting unit 17 in the first cooling zone.

The inputs of the comparator unit 18 are connected to the output of the setting device 17 and the temperature sensor (not shown), and the outputs through the amplifier are connected to the actuator 20 (supply of the heat transfer medium to the first cooling zone), and if the temperature is higher than the specified one, then a deviation signal (+ D.T) passes to block 20, and if the temperature is lower than the set one, then the signal (- & T) passes to block 20 only through block 19, only if there is no signal f on blocking input 19 of block 19, which is formed at the output of control loop dustiness. The dust control coefficient consists of samplers 21 and 22, which measure the discharge concentration, respectively, at the exit of the burning zone and the first cooling zone.

In block 23, the difference between the readings of both samplers is calculated, which is compared in block 24 of comparison with a predetermined (reference) value. If the dust content is greater than the predetermined value, the Fg signal for correcting the temperature mode of the second cooling zone appears at the output of the amplifier and it (multiplied) the prohibition signal (Ј), which is fed to the prohibiting input of the prohibition unit 19.

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Consider the implementation of the method on the example of the work of the calcining conveyor machine. From the disc granules of the torus through the conveyor-laying system, the raw pellets are fed to the conveyor 1 of the roasting machine 2. The initial feeding is done so that the height of the pellet layer on the pallet is 200 mm. The advance speed of the pallet is set by drive 3, for example, 18 p / h .

Then the material enters the roasting machine, where it successively undergoes heat treatment according to the stages: drying, heating, roasting and cooling. The stages of drying and cooling are divided into separate subranges. So the drying zone has three subzones, and in each subzone they establish their own temperature and aerodynamic regime, i.e. drying temperature, filtration rate and flow direction of the coolant.

The temperature regime depending on the specific zone is maintained by changing the ratio between natural gas and air or the amount of coolant.

Let the initial setting of 8 set the ratio of the amount of secondary air to natural gas 1: 1,15. From the temperature sensor 4 (consider the burning zone, but the temperature control system is in each zone and works in a known manner) a signal proportional to the actual value, for example 1200 ° C, enters the comparison unit 5, where it is compared with the signal proportional to a predetermined temperature, for example 1170 ° s At the output of the comparator unit, the error signal + DT appears, which, through an amplifier, enters the control unit 7, which represents a two-position controller. The regulator 7 outputs to the control system of the supply of the heat transfer medium, in particular to the setting point 8, the signal F4, which changes the specified ratio from 1: 1.15 to 1: 1.12. Signals proportional to the actual consumption of air and natural gas are received by an arithmetic unit (block 11), made according to the splitter circuit. In this block, the actual ratio between the components of the heat carrier is determined.

The body, which is compared in block 9 of comparison with a predetermined value (1: 1.12), and in case of deviation, the signal goes to the actuator 13 (control valve), which changes the flow of natural gas.

In the event of a firing temperature deviation, for example 1120 ° C, at the output of block 7 there is a signal F2 to increase the supply of natural gas by changing the predetermined ratio between the secondary air and natural gas, i.e. in block 8, a ratio of 1: 1.18 is set, which in block 9 of comparison is compared with the actual ratio and, since it is less than the specified ratio (1: 1.15), the control valve 13 receives an appropriate signal to increase the supply of natural gas .

Thus, testing of disturbances along the channel — temperature control is carried out by known methods.

The quality control of the calcined pellets is carried out as follows. After the calcination, 0.5 kg of pellets (piece, etc.) are taken, crushed and abraded, hydrated in 1 liter of distilled water at room temperature and constant stirring for 15 minutes. .

All these operations are carried out in block 14, the pH of the resulting suspension is measured with a pH meter. In Comparison Unit 15, the actual pH value is compared with a predetermined value or not. The respective strength values of the pellets are compared. The set value depends on the composition of the initial pelletized mixture and is in the range of 7-9.5.

The relationship between the pH of the calcined pellets and their mechanical strength was established.

The specific pH setpoint with which the actual value obtained is compared depends on a number of factors, so you can get it directly by heat treating the phosphate flour at the firing temperature, i.e. at 1150-1180 ° C, or using graphs obtained for different composition of raw materials and the content of the optimal fraction — 0.074 mm in the fosmuck.

Let ore containing COj be received for pelletizing. in it 7%, with

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the alkali metal oxide holding is 0.7 and the fraction yield is 0.074 - 70%. Based on the dependencies obtained, the target pH of the calcined pellets should be in the range of 7.0 - 8.0.

Therefore, in comparison unit 15, the actual pH value 9 is compared with

given pH 8.

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The optimum strength is pellets of 180 kg / cm2 and higher, and at pH 9 it is slightly lower and corresponds to 130-140 kg / cm2.

At the output of the comparator unit 15, an error signal appears corresponding to a pH of 1.0, i.e. the strength is lower than the set one, which is fed through the amplifier to the control unit 16. Depending on the magnitude of the deviation of the pH value (i.e., the strength of the pellets) at the output of the block 16, a signal F is generated - to decrease the speed of the pallet, i.e. to increase the residence time of the pellets in the burning zone, if the quality of the pellets is below the norm} signal F - to increase the speed of movement of the pallets, if the strength of the pellets is more than 200 kg / cm2 (with deviation of LRN 1), i.e. reduction of the residence time of the pellets in the burning zone.

The limiting factors for these two effects are, respectively, the minimum and maximum allowable speed of movement of the pallets.

In this case, when the quality of the pellets is rejected, a signal F6 is generated to change the amount of raw pellets, but only downwards, i.e. with insufficient pellet strength, therefore the limiting factor for this signal is the optimal performance of the roasting machine.

If the strength of the pellets is below normal, and the effects of F and F6 cannot be applied, then at the output of block 16 a signal F5 is generated - to change the firing temperature mode, i.e. temperature increase.

At the output of the control unit 16, if the quality of the burned pellets deviates from the norm, there is only one signal Ґ $ or. Usually, the burning rate of calcined pellets is initially set on the assumption that the heat treatment process proceeds normally, therefore it is usually taken in the first stage of cooling such a temperature so that the cooling rate in zone I is 100 ° C / min, in zone II - 40 ° C / min In this case, in zone II, cooling is carried out by maintaining the COOT charge between hot air with a temperature of 180 ° C and secondary air with a temperature of 250 ° C within 1: 2 (see Fig. 2).

In this example, the quality (strength) of burned. Coils is less than normal and there is a large mismatch of pH 1; therefore, the cooling rate in zone I should be reduced from the initial set speed of 100 C / min to 70 ° C / min. Since the strength of the calcined pellets is insufficient, a high state of cooling results in a shock state, the pellets crack, and the yield of fines increases.

The signal for the adjustment of the task to the unit 17 for setting the temperature mode of the cooling zone I comes directly from the phase-sensitive amplifier of the unit 15.

The desired temperature is maintained in a known manner by varying the amount of gas having a temperature of 350 ° C and entering through the exhauster into zone I. Regulation is carried out by a controller that includes a temperature sensor (not shown), unit 18 compared with the output amplifier, moreover, if the cooling rate is lower than the set one (- & T), then the signal to the executive unit 20 is received only if there is no signal at the inhibiting input of the prohibition unit.

This is due to the fact that if at a reduced cooling rate the amount of dust produced is greater than the acceptable value, then when the cooling rate is restored, it still becomes larger and the yield of pellets will decrease.

Dust control, therefore, is an additional control over the correct choice of cooling mode and is carried out as follows.

Simultaneously with the sampling of burnt pellets at the exit zone

firing, a sample of the flue gas is taken and the dust content is determined in it (block 21). Then, at the exit of the cooling zone I, the dust content in the flue gases is measured (block 22).

Let, for example, after the burning zone, the dust content in the exhaust gases was 0.55 g / Nm3, and after the cooling zone I - 0.80 g / Nm3.

These signals are compared in comparison unit 23, and at its output a signal AZ appears, which is compared in block 24 with a predetermined value

UZ is set to the specified value. p 0.3 g / Nm3, since according to the regulations, the total pyepsez content in the exhaust gases from all zones should not exceed 1 g / Nm3.

Considering that the formation of dust mainly occurs in the drying zone ("60%) and cooling zones and depends on the strength of the pellets, these values are accepted.

Thus, in block 24, a proportional signal & ZCp ci.Z3a (, i.e., 0.25 with 0.30 g / Nm3) is compared, and since the dead zone (response) of the amplifier is proportional to +0.1 g / mme, then there is no signal at the output of block 24 and, accordingly, no signal Fg is output at block 25, i.e. the cooling mode is not corrected in the second zone.

Temperature control is performed as follows.

In block 18, the comparison compares the actual cooling rate in zone I, equal to 60 ° C / min, with the corrected setpoint of 70 ° C / min, and at its output a mismatch signal appears, which is proportional to - / UG 10 ° C / min and As the prohibiting input of the prohibition unit 19 is not a signal f, then the FT signal appears at the input of the actuator to increase the cooling rate in zone I, i.e. reduction of hot air with a temperature of 350 ° C through the corresponding smoke exhauster. The adjustment of the mode in the cooling zone is not carried out, since the deviation of the dust content is 0.05 g / mne. If the cooling rate in zone I is greater than the specified one, for example 80 ° C / min, then the output of block 18 is the error signal + UTP which directly goes to the input of the input 91

an additional mechanism 20 (signal F) to decrease the cooling rate, i.e. an increase in the supply of hot air to zone I.

If at the output of the dust control unit in the exhaust gases there is a mismatch signal + AZ, i.e. Dust content is greater than allowable after cooling zone I, for example, after the burning zone is 55 g / Nm3, and after the burning zone I - 0.95 g / Nm3, i.e. At the output of comparator 24, there will be a signal -J-AZ of 0.10 g / Nm3, then at the output of block 25 a signal P appears to correct the cooling mode in zone II, i.e. cooling rate in this zone is reduced. The perturbation is tested by changing the ratio between hot air with a temperature of 180 ° C and with air having a temperature of 25 ° C. The initial ratio between them, equal to 1: 2.0, will be changed to 1: 1.8.

In the table, several KQH specific examples of the method implementation are given, and Example 1 corresponds. the prototype.

Example 2 differs from Example 1 in adjusting the temperature in the cooling zone from 100 to 70 ° C / min. This made it possible to reduce the dust content at the exit of the cooling zone I from AZ 0.45 g / Nm3 to UZ 0.25 g / Nm3, and the yield of suitable pellets from 80.5 to 86.3%, despite the deviation of the firing temperature conditions and strength. pellets less optimal (140 instead of 180 kg / cm2).

In examples 3.6, the heat treatment parameters were close to optimal values, as evidenced by both the pH value and the & Z, found

shcha with below acceptable limits.

Example 4 shows that the firing mode is not quite optimal, as evidenced by its temperature of 1140 ° C, due to deviation of the dust content after the cooling zone of zone I

(& Z 42 g / Nm3) it can be seen that the cooling rate in zone I is higher, therefore it is necessary to reduce it to 70-80 ° C / min, which will reduce the formation of small-i and increase the yield of usable pellets from 88 to 92-94%.

In example 5, the heat treatment mode is close to optimal, but taking into account that the yield of pellets was

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92%, and the deviation of the dust content at the exit of the cooling zone I (& Z 0.26 g / Nm3) is close to the maximum permissible; it is advisable to reduce the cooling rate in zone II from 50 to 40 C / min, resulting in an increase in the yield from 92 up to 95.0%.

Thus, when using the proposed method, the yield of the coaters increases compared with the prototype by 5-6% (examples 1 and 2)

Claims (1)

Invention Formula The method of controlling the heat treatment process of phosphorus pellets in the roasting machine, including temperature control in the drying and roasting zones, B of the first, second and third cooling zones by changing the ratio of natural gas to air flow rates or heat carrier flow to these zones, adjusting the mechanical strength of the roasted pellets according to the pH of the suspension prepared from them, by changing the flow rate or the rate of movement of the raw material in the kiln, characterized in that, in order to increase the progress of suitable pellets, in addition, they measure the content at the exit of the burning zone and the first cooling zone, determine the difference between these measured values of the forest content dust, compare it with the setpoint. If the measured value of this difference is greater than the specified value, then the temperature in the second cooling zone is increased. When the measured pH value of the suspension is less than the specified value, the specified cooling rate in the first zone is determined by the pH value of the suspension, compare it with the measured value. the speed value is cooled in the first zone more than the specified value, then the temperature in the first cooling zone increases, if the measured value of the cooling rate in the first zone is less than th measured value and the difference value to you pypesoderzhani during firing zone and the first zone COOL - spinning is equal to or greater than a predetermined value, then reduce the temperature in the first cooling zone, when the flow rate or velocity of movement of the raw material into the burning the machine limits and when the measured pH value of the suspension is greater than a specified value, increase the temperature in the burning zone. . Cooling . 2 Dh U0 ° C