RU2073640C1 - Method of automatically operating contact apparatus in sulfuric acid production - Google Patents

Abstract

FIELD: nonferrous metallurgy. SUBSTANCE: invention deals with producing sulfuric acid from sulfur-containing off-gases from periodically operated plants. One measures sulfur dioxide concentration before contact apparatus, calculates average value, and compares this with threshold value. If the latter is exceeded, temperature at the outlet of catalyst layers is assigned on the level of lower process limits. If average sulfur dioxide concentration is below its threshold value, the aforementioned temperature is assigned on the level of upper process limits. This temperature is adjusted by varying input of cold part of initial gas mixture into heat exchangers of contact layers. EFFECT: enhanced efficiency of process. 1 dwg, 3 tbl

Description

 The invention relates to the field of non-ferrous metallurgy and can be used to control the process of producing sulfuric acid from waste sulfur-containing gases.

 A known method of producing sulfur trioxide by oxidation of sulfur dioxide (a.s. N 301985), in which sulfur dioxide is oxidized with atmospheric oxygen at an elevated temperature in an adiabatic reactor with several catalyst beds using temperature stabilization of the reaction mixture. In order to increase the productivity of the process, the highest permissible temperature of the reaction mixture at the outlet of the first catalyst layer is stabilized by changing the temperature of the reaction mixture at the entrance to the first layer or by changing the amount of reaction mixture entering the first layer, or both at the same time.

In common with the claimed invention is that, in an analog, the temperature at the outlet of the first layer is stabilized by changing the temperature of the reaction mixture at the entrance to the first layer. This method is applicable only for high concentrations of SO ₂ in the input stream, since the temperature at the inlet to the layer is controlled by adding cold air at a temperature of 30 ^° C in front of the first layer. The known method only stabilizes the temperature at the outlet of the first layer. Such control is acceptable only when the intensity and frequency of disturbances in the concentration of SO ₂ and gas flow are small, which does not correspond to the operating conditions of sulfuric acid plants operating on waste gases from non-ferrous metallurgy.

The closest in technical essence and the achieved result is a method for controlling a sulfuric acid production contact apparatus [1] in which the temperature at the outlet of the first catalyst layer is stabilized by influencing the temperature in the catalyst layer by controlling the supply of the cold part of the initial gas mixture to the input of the contact apparatus. The total flow rate of the feed gas mixture, its temperature and the concentration of sulfur dioxide in the feed gas mixture are measured. The total flow rate of the feed gas mixture is stabilized and the temperature of the feed gas mixture is controlled by changing the supply of the cold part of the feed gas mixture to the input of the contact apparatus with correction according to the concentration of sulfur dioxide in the feed gas mixture and the temperature in the catalyst layer, and when controlling the temperature in the catalyst layer, correction the total flow rate of the original gas mixture. Common between the prototype and the claimed invention is that they stabilize the temperature at the outlet of the first layer by changing the supply of the cold part of the source gas mixture to the input of the contact apparatus. However, under conditions of sharp (from 1 to 8%) fluctuations in the concentration of sulfur dioxide in gases, the frequency of which is of the order of 3 • 10 ^-2 Hz, the inability to measure the concentration of sulfur dioxide in front of the layers, it is impossible to stabilize the gas flow rate and temperature at the outlet of all layers by the method prototype for the disposal of exhaust gases of periodically operating units of pyrometallurgical shops.

The claimed invention is aimed at solving the following problem. Under conditions of sharp (from 1 to 8) fluctuations in the concentration of sulfur dioxide in gases, the frequency of which is of the order of 3 • 10 ^-2 Hz (for example, in periods of time when the converters are removed from the blast every 5-10 minutes), it is necessary to increase the degree of contacting contact apparatus for sulfuric acid production. When implementing the invention, a technical result can be obtained: slowing down the aging of the catalyst, stabilizing its activity in the contact apparatus under conditions of sharp and frequent changes in the input concentration of sulfur dioxide.

 To solve this problem, measure the concentration of sulfur dioxide in gases at the inlet to the contact apparatus, control the temperature at the inlet and outlet of the catalyst layers. If the concentration of sulfur dioxide is exceeded, the threshold value for the task at the exit temperature of the contact layers is set at the level of the lower technological boundaries. In this case, under conditions of sharp fluctuations in the concentration of sulfur dioxide, sintering of the catalyst mass and a decrease in its activity will not occur. If the average concentration of sulfur dioxide is below a threshold value, then the temperature task at the output of the contact layers is set at the level of the upper technological boundaries. In this case, the heat content of the contact apparatus is maintained at the highest possible level, and acid condensation does not form on the surface of the catalyst, which leads to the formation of a crust on the catalyst and a violation of the stability of the activity of the catalyst.

The drawing shows a diagram of an installation that implements a method of automatic control of the contact apparatus. The installation contains catalyst layers 1, 2, 3, heat exchangers 4, 5, 6, mixing units 7, 8, 9 of the initial gas mixture with a heated gas mixture, temperature sensors 10, 11, 12, 13, 14, 15 at the inlet and outlet contact layers, computing devices 16, 17, 18, 19 for calculating the task of the temperature at the output and input of the contact layers, digital controllers 20, 21, 22 and actuators 23, 24, 25 connected to the control chokes, gas analyzer 25. The installation works in the following way. The signal about the concentration of sulfur dioxide in the initial gas mixture in front of the contact apparatus is supplied to the computing device 19, which compares the concentration value with the threshold value and, if the threshold value is exceeded, issues to the computing devices 16, 17, 18 a task for the temperature at the output of the contact layers at the lower level technological boundaries, and if the concentration of sulfur dioxide is less than the threshold value, then at the level of the upper technological boundaries. Computing devices 16, 17, 18 determine the magnitude of the deviation of the temperatures at the output of the contact layers from the specified values by mathematical expression
ΔT _out.i = T _out.i -T _out.i ,
where T _o.i is the temperature at the output of the i-th layer;
T _ozdzi i setpoint temperature at the output of the i-th layer. Then, the computing devices 16, 17, 18 calculate the correction value of the task by the temperature at the output of the i-th layer inversely with the deviation of the temperature at the output of each of the layers 1, 2, 3 from the set values according to the mathematical expression
ΔT _{inlet ii} = - k _i • ΔT _out.i ,
where k _{i is the} coefficient of proportionality for the i-th layer.

After that, the value of the new, adjusted task by the temperature at the input of each of the layers 1, 2, 3 is calculated by the mathematical expression
T _{input i} = T _{input (i-1)} + ΔT _{input i} ,
where T _{int. (i-1)} previous task on the temperature at the entrance of the i-th layer, ^o C.

The calculation of the task according to the temperature at the input of the layers is supplied to the digital controllers 20, 21, 22, which calculate the magnitude and sign of the control pulses for the actuators 23, 24, 25 by mathematical expression
Δτ _i = k _2i • (T _{input i} -T _{input Ii} ),
where Δτ _{i the} duration of the control pulse, sec;
k _2i constant coefficient, sec / ^o C.

Then, the digital controllers 19, 20, 21 turn on the actuators 23, 24, 25 in accordance with the Δτ _i value and turn the throttle valves, which change the proportion of the cold part of the initial gas mixture entering the heat exchangers from the mixing units 7, 8, 9.

Example
The experiment was carried out on a 3-layer contact apparatus in the sulfuric acid workshop of the Severonickel plant. Gas was continuously supplied from the furnaces of the compressor station of the refining shop and periodically from the converters of the smelting and smelting shops. By the beginning of the experiment, the following regulatory parameters were on the contact apparatus:
The concentration of sulfur dioxide at the entrance to the contact apparatus of 4.2%
Gas consumption 45 thousand m ³ / hour
A specific feature of the technological situation was that gas was not supplied to the contact apparatus from continuously operating KS furnaces; therefore, the sulfur dioxide concentration in front of the contact apparatus changed sharply with an amplitude of 3 to 4% at intervals of 5-10 minutes. Under such conditions, the apparatchik could not promptly set the tasks for the temperature at the exit of the contact layers with sufficient accuracy. The degree of contact at this time was about 95.8%. The initial values of the temperatures at the inlet and outlet of the contact layers are shown in Table 1. By the time the experiment began, the average concentration of sulfur dioxide was changing and amounted to 4.6%. The gas flow through the contact apparatus remained at the same level 45 thousand m ³ / hour. Management has been switched to automatic mode. The threshold value was set at 4.5%. Computing device 19 issued tasks at the output of contact devices at the level of lower technological boundaries. After 16 minutes, the contacting process was characterized by the operating parameters shown in Table 2. Then, the average concentration of sulfur dioxide in the gas changed and after 1 hour was 3.8%. The gas flow through the contact apparatus was 45 thousand m ³ / h. The task of the temperature at the exit from the layers by the computing device 19 was set at the level of upper technological limitations. The values of the operational parameters of the contacting process are given in table 3. The degree of contacting during the experiment was 96.4%
Thus, in the conditions of sharp and frequent changes in the concentrations of sulfur dioxide in the gases in front of the contact apparatus, process control by the present method allows to increase the degree of contacting of the contact apparatus.

Claims (1)

A method for automatically controlling a contact apparatus for sulfuric acid production, including controlling the temperature at the inlet and outlet of the first catalyst layer by changing the supply of the cold part of the initial gas mixture to the input of the contact apparatus, characterized in that the temperature target at the outlet of all catalyst layers is set depending on the deviation of the average concentration value sulfur dioxide in gases at the entrance to the contact apparatus from a threshold value, while if the concentration of sulfur dioxide is higher than the threshold value, the reference temperature is set at a lower process limit, and if lower, the process at the upper limit then further define the temperature deviation from the nominal value at the output of the mathematical expression layer
ΔT _out.i = T _out.i -T _out.i ,
where T _o.i is the temperature at the output of the i-th layer;
T _ozdzi i setpoint temperature at the output of the i-th layer,
determine the correction value of the task according to the temperature at the input of the i-th layer inversely to the deviation of the temperature at the output of the i-layer from the set value by mathematical expression
ΔT _{inlet ii} = - K _i • ΔT _out.i ,
where K _{i is} the proportionality coefficient for the i-th layer, then the task on the temperature at the input of the i-th layer is changed by the value of the calculated correction.

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