SU1381182A1 - Method of controlling thermal treatment of phosphorite pellets - Google Patents

Abstract

The invention is intended to control the heat treatment process of phosphate pellets. The aim of the invention is to reduce the fluorine content in the gases leaving the burning zone. To control the process, the moisture content of the heat transfer fluid at the inlet and outlet zones, determined by a predetermined temperature interval, is additionally measured. The residual moisture in the pellets is determined by the difference in moisture content. Fluorine content is predicted, compared to the allowable value and, if the value is exceeded, the residence time of the pellets in the heat treatment zone is increased and the burning temperature is reduced at the same time. The fluorine content in the waste gases of the burning zone is measured, and when the permissible value is exceeded, the temperature of the exhaust gases from the drying zone is reduced by decreasing the temperature of the heat carrier or by increasing the layer of raw materials. 2 Il. (L

Description

113

The invention relates to the preparation of phosphate raw materials for the electric distillation of phosphorus, in particular, to methods of controlling the process of heat treatment of phosphate pellets obtained from fine phosphate raw materials.

The purpose of the invention is to reduce the fluorine content in the waste from the burning zone with gases.

The method is carried out as follows.

According to the heat treatment control method, the following additions are introduced: residual moisture determination

at the exit of the temperature zone of 300-600 ° C, according to the relationship between the residual benign content and the fluorine concentration in the exhaust gases, the lee value is predicted, compared with the maximum allowable fluorine content, in case of a large deviation, a signal is given at the same time to increase the residence time of the pellets in the temperature zone ZOO-bool C and for the adjustment of the firing temperature, i.e. its decrease, if it is greater than 1160 ° C, measures the actual fluorine concentration in the flue gases of the burning zone and corrects the regulatory actions.

FIG. Figure 1 shows a block-SZ device for carrying out the proposed method; in fig. 2 - depending

The gap is between the residual humidity in the zone with a temperature of 300-600 ° C, which corresponds to the hydrolysis zone of fluorine and precedes the zone of active emission of fluorine, and the concentration of fluorine in the exhaust gases of the burning zone at its different temperature.

The residual moisture content at the outlet of the zone with a temperature of 300-600 C can be determined by an indirect parameter, for example, by the difference in moisture content of the coolant and the moisture content of the pellets at the outlet of the drying zone.

The maximum permissible concentration of fluorine in the waste gases from the burning zone is determined on the basis that the waste gas from the burning zone returns to the sushi zone of the raw pellets as a heat carrier, some of the fluorine is captured, then some of the gas is emitted into the atmosphere and the rest is used as the heat carrier in other zones. Based on lengthy experiments with

0 5 0

five

0

five

0

five

by changing the height of the pellet layer within 300-400 mm, it has been established that the fluorine content in the exhaust gases from the burning zone when passing it through the layer of raw pellets decreases by 40-50%. The maximum permissible concentration of fluorine in the exhaust gases,. emitted into the atmosphere is 23 mg / nm, therefore the maximum permissible concentration of fluorine in the exhaust gases of the burning zone is taken as 40 mg / nm. The fluorine content in phosphate pellets entering the phosphorus electric sublimation is not limited.

An increase in the residence time of the pellets in the temperature zone of 300-600 ° C contributes to the reduction of moisture and the release of fluorine from the oxipia.

Additional adjustment of the heat treatment mode with an okpia is carried out (if necessary) according to the actual concentration of fluorine in the exhaust gases from the burning zone.

The block diagram of the device for the implementation of the proposed method (FIG. 1) consists of a conveyor 1, on which raw cells are placed from a heating unit, a firing machine 2 having drying zones (C), heating (P), firing (0), recovery (P), a zone with a temperature of 300-600 ° С (highlighted with shading) is especially highlighted; temperature controller (Fig. 1 shows one, but their number depends on the number of individual zones), including temperature sensor 3, unit 4 comparing the actual and set temperature with the amplifier, temperature setpoint 5, control unit 6, the outputs of which are connected to the inputs block 7 of the ratio controlling the flow of air and natural gas through the respective actuators 8 and 9, sensors 10 and 11 of the initial and final humidity of the coolant, i.e. on entering and leaving the temperature zone 300-600 s, computing device 12, in which the residual moisture content in phosphate pellets is determined, block 13 for determining the predicted fluorine concentration in the waste gases of the burning zone, block 14 comparing the predicted and specified values of fluorine content the amplifier, the first output of which through the block 15 of the ban is connected to the setpoint firing temperature, the second output - with the drive

moving the conveyor, sampler 16 with a pH meter (pH) of the suspension, block 17 comparing the actual pH value with the optimal value with an amplifier, the outputs of which are connected to the corresponding pellet quality control unit 18, the outputs of which are connected to the drive 19 of the KOH fan and the firing temperature setter , a fluorine content sensor 20 in the waste gases from the burning zone, a unit 21 comparing the actual and predetermined fluorine content with an amplifier, the output of which is connected to block 1 or 5.

Let the heat treatment be carried out on an OK-1-18 calcining conveyor machine. The consumption of raw pellets is set in such a way that the layer height on the pallet of conveyor 1 would be l / 400 mm. The conveyor speed was selected 18 pallets / h using drive 19, then raw pellets go to roasting machine 2, where they pass through three stages of drying with gaseous coolant fed through a layer of pellets, and in the first and third stages from top to bottom ( through the layer), and in the second stage - from the bottom up (blowing through the layer). The filtration rate is maintained respectively in stages of 0.3-0.5; 1.45-1.55 and 1.3-1.4 m / s, and the residence time is respectively 1-2, 13-14 and 3-4 min, the temperature of the heat carrier is maintained at the first stage of 180-200, at the third - 200220 ° C. Temperature mode for a separate

drying stages, in the heating zone

and roasting support in a similar way. A thermocouple or resistance thermometer is used as the temperature sensor 3. In block 4 of the comparison, signals are compared that correspond to the actual temperature and are set (by block 5) for the monitored zone. If the temperature deviates from the set, i.e. more (less) than specified, the error signal from the amplifier enters the control unit 6, where a signal is generated to restore the normal mode F, or F, and F, to decrease the temperature of the heat carrier or its flow (depending on the choice of regulating effect), and F 1 - to increase the temperature of the heat, and j

p 25., Q: 35

40

50 55 45

detractor or its expense. These signals through the flow control unit or the unit 7 of the ratio of the components of the coolant flow to the actuators (valves, valves, etc.).

ZOO-BOO C temperature zone is located at the end of the zone and in the heating zone (from 2 to 4 vacuum chambers). In this zone, the moisture in the pellets is monitored, since the concentration of fluorine compounds in the exhaust gases depends on the change in moisture. To do this, in the sensors 10 and 11, the moisture content of the coolant is measured at the inlet and outlet of the special zone, respectively. The computing device 12 determines the residual moisture in the cells, for which signals are also received in the block that are proportional to the flow rate of the coolant, the weight of the pellets and the moisture content in them. The following equation is realized in the computing device:

 ,

WOCTQ

where W is the residual moisture content,%; } Q - moisture content of pellets

at the entrance of the zone 300-600 C,%; - the difference of moisture content

no heat carrier,%; Q - consumption of pellets, t / h; (have coolant flow,

nm / h

After calculating the residual moisture in the sample is 1.5%, then in block 13, which can be made in the form of a display, which shows a graph of fluorine content in exhaust gases from residual moisture and calcining temperature, the predicted fluorine content is determined . It is possible to perform this block as a computation block that implements an equation relating the moisture content of the pellets to the fluorine content of the exhaust gases. For this, a signal is received in block 13, which is proportional to the set firing temperature. From the graph (Fig. 2), based on a given calcining temperature of 1180 ° C, the predicted fluorine content in the exhaust gases is determined at a given calcining temperature of 75 mg / nm. In the comparison unit, the predicted fluorine content (75 mg / nm) is compared with the target value (40 mg / nm) and, since it is greater than the target value (4Cp 35 mg / nm), the signal proportional to this value is amplified by the amplifier and simultaneously enters firing temperature setter F (reduction of the set firing temperature to 1160 ° C), and the FJ signal (to decrease the conveyor movement speed) to block 19 and the movement speed decreases from 18 to 17 pallets / h, thereby increasing 11826

firing temperature), which comes from the firing temperature sensor. At the exit of the roasting zone, the actual fluorine content in the exhaust gas (block 20), which is 44 mg / nm, is measured. In comparison block 21, proportional to it, is compared with that proportional to given Q (40 mg / nm), as a result the amplifier of the comparator unit 21, the FT signal does not appear, since its deadband is equal to ff + 5 mg / nm, i.e. if actually

The residence time of the phosphate rocks was greater than the fluorine content.

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tyshy in the temperature zone of 300-600 ° C since, under certain assumptions, the residence time of the pellets and the release of fluorine into the exhaust gases of this zone is related by the equation of the form20

45 mg / nm, the comparison amplifier 21 would work and, at its output, would adjust the signal F to adjust the temperature of the heat in the drying zone or increase the cell mass of the raw pellets (flow) The decrease in the heat-transfer temperature in the drying zone or the increase in the layered pellets helps to catch

C, 52, 5 10

 BUT

mg / nm

After the preheating zone, the pellets are transferred to the roasting zone, where they support -25 fluorine, since the exhaust gases

New set point temperature. At the exit from the burning zone, 0.5 kg of pellets are taken, crushed, hydrated, and the pH of the suspension is measured (in block 16, for example, a pH value of 8.3 is obtained). The signal proportional to this value is compared in block 17 with a signal proportional to the optimum pH value of 8.0, which corresponds to a strength of 180 kg / approx. Since the deviation from the optimal value (0.3) of pH (0.5) p, the amplifier of the comparison unit does not work and there are no signals at its output to restore the deflection FJ, FJ. This means that the quality

calcined pellets above the lower permissible limit (130 kg / ok) or less than 8.5 pH. If the pH of the suspension would be greater than 8.5, for example, 9.0, then at the output of the control unit 18 there would be a reducing effect Fj (on reducing the speed of movement of the conveyor 1). In the event that the speed of the pallet does not exceed the permissible value, for example 12 pallets / h, the signal FJ (to increase the firing temperature) is generated at the output of the control unit 18, which is fed to the set firing temperature setter. If the firing temperature is lower than 1160 ° C, a signal f appears at the prohibitory input of block 15, (to prohibit

some fluorine content was higher

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45 mg / nm, the amplifier of the comparison unit 21 would operate and at its output, if necessary, a correction signal F would be applied to adjust the temperature of the coolant in the drying zone or increase the height of the layer of raw pellets (flow). Reducing the temperature of the coolant in the drying zone or increasing the layer of raw pellets helps to catch 0

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five

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from the burning and cooling zones, containing acidic phosphorus compounds (PjOi), fluorine (HF and SiF), sulfur (50, SOj) and carbon dioxide, are fed to the process head, to the drying zone. The acidic components of the heat carrier gas are adsorbed by the surface alkaline layer of raw okappei and the chemical interaction of acid gases with alkali and alkaline earth metals occurs, resulting in the formation of phosphate compounds, sulfides, fluorides and secondary carbonates of alkali and alkaline earth metals, which contributes to increasing the stability of octopia from thermal damage, which allows (if necessary) to increase the temperature of the coolant in the drying zone and reduce the drying time.

An analysis of the gases leaving the drying zone showed that the fluorine content in it was 22 mg / nm, i.e. less MPC, so that part of the gas that is emitted into the atmosphere does not need additional cleaning.

Corrective action (lowering the temperature of the coolant in the drying zone) is always possible, but this increases the residence time in this zone. Increasing the height of a layer of raw materials is only possible if their consumption is not extremely high. 713

empty, i.e. it depends on the performance of the roaster. The choice of corrective action is carried out by the technologist, taking into account the situation.

The proposed method of controlling the release of fluorine in the heat treatment process is of great practical importance from the point of view of utilization of harmful sulfur, fluorine and phosphorus compounds emitted into the atmosphere, which reduces capital expenditures for a dust and gas treatment facility. In addition, as a result of preserving the fluorine compounds in the pellets, the process of their hardening and the process of electric sublimation of yellow phosphorus are improved.

Claims (1)

Invention Formula The method of controlling the heat treatment of phosphate pellets, including moving them through the zones of drying, heating, roasting and recovery of the kiln, temperature control over zones, comparing them with a given value and in case of deviation change the flow rate of the coolant, quality control of the kilns burned by the amount of hydrogen Suspension Indicator, From /    ||  C I Lam IX 28 Their spares, comparison with the optimal value and in case of deviation, the change in the speed of movement of the kiln conveyor, characterized in that, in order to reduce the fluorine content in the gases leaving the burning zone, the moisture content of the coolant at the inlet and outlet zones is determined According to the previously obtained dependence between it and the fluorine content in the exhaust gases of the burning zone, taking into account the predetermined temperature range, taking into account the predetermined temperature between them and the fluorine content The firing temperature is predicted, the fluorine content is predicted, compared to the allowable value and, if this value is exceeded, the residence time of the pellets in the treatment zone is increased and the burning temperature is also reduced within the allowable values, the actual fluorine content in the waste gases from the burning zone is measured when the permissible value is exceeded, the temperature of the exhaust gases from the drying zone is reduced by lowering the temperature of the heat carrier or increasing the layer of raw pellets. / Gr gas / wr to15 Fi9 2 to 7.