RU2114056C1 - Device for controlling contact oxidation process - Google Patents

Abstract

FIELD: NITRIC ACID PRODUCTION. SUBSTANCE: device contains: pressure gradient, pressure, and temperature sensors in ammonia and air lines; ammonia- air mixture temperature sensor; barometric pressure, relative humidity, and atmosphere air temperature sensors; pressure sensor on the executive mechanism of the ammonia line control valve; compensation unit of input controlled disturbances in temperature, ammonia and air pressure, humidity, temperature and barometric pressure of atmosphere air, connected, through sensor and unit validity control unit, with square-root generation unit and ammonia concentration computation unit connected to concentration regulator; automatic structure and/or operation mode control unit connected with validity control unit and, through discrete signal input unit, with structure selector, and also with optimal process temperature selection cut-off device, with unit cutting off process temperature adjustment circuit from ammonia concentration regulator, with unit cutting off process temperature adjustment circuit from ammonia-air uptake ratio regulator, with internal regulator structure selection unit, with temperature regulator, and with operation mode selector. EFFECT: determined and stabilized optimal process temperature and improved reliability of device. 2 dwg

Description

 The invention relates to devices for controlling chemical-technological processes, and more particularly, to devices for controlling the process of contact oxidation of ammonia in the production of nitric acid.

 A device is known for controlling the process of contact oxidation of ammonia in the production of nitric acid, containing differential pressure sensors on the constricting elements of the gas pipelines of ammonia and air, a recording device with a software control unit, the input of which is connected to the differential pressure sensors and the temperature correction loop, and the output to the executive mechanism (A.S. USSR N 430053, class C 01 B 21/38, 1974).

 It is also known a device for controlling the process of contact oxidation of ammonia in the production of nitric acid, containing differential pressure sensors on the gas pipelines of ammonia and air, connected to the square root extraction unit, connected to the unit for calculating the concentration of ammonia in the ammonia-air mixture, connected to the regulator of the concentration of ammonia, input which is connected to a temperature sensor of the contact oxidation process, and the output to a control valve on the ammonia gas pipeline (AS USSR N 698918, class C 01 B 21/38, 1979).

 The known device does not allow to determine and stabilize the optimal temperature of the process of contact oxidation of ammonia to nitric oxide, ensuring the achievement of minimum costs for its implementation. In addition, it does not provide compensation for controlled input disturbances, which significantly reduces the quality of process temperature control. The known device also lacks the ability to automatically change its structure or mode of operation in case of failure of its constituent sensors or blocks, which reduces its reliability.

 The technical result of the present invention is to determine and stabilize the optimal temperature of the contact oxidation of ammonia, increasing the accuracy of its regulation and the reliability of the device.

 The specified technical result is achieved in that a device for controlling the process of contact oxidation of ammonia in the production of nitric acid, containing differential pressure sensors on the gas pipelines of ammonia and air connected to the square root extraction unit from the differential pressure, a temperature sensor of the contact oxidation process, an ammonia concentration calculation unit in an ammonia-air mixture, connected to a concentration regulator, a control valve on the ammonia gas pipeline, additionally contains sensors temperature and pressure on the gas pipelines of ammonia and air, a temperature sensor for ammonia-air mixture, sensors for barometric pressure, relative humidity and temperature of atmospheric air, a pressure sensor on the actuator of the control valve of the ammonia gas pipeline, a mode switch, an operator’s communication device with a microprocessor computer that includes blocks input and output of analog and discrete signals and a digital signal output unit, a read-only memory unit, which includes an extraction unit for the adratic root of the differential pressure values, which also performs the scaling function, a reliability control unit for sensors and device blocks, an input block for compensating input disturbances, a unit for calculating the concentration of ammonia in an ammonia-air mixture with its controller, a unit for disconnecting the correction circuit for the process temperature from the controller for ammonia concentration , unit for calculating the ratio of the flow rates of ammonia-air, regulator of the ratio of the rates of ammonia-air, block for disconnecting the correction circuit for the process temperature from p the regulator of the ratio of the flow rates of ammonia-air, the regulator of the correction circuit for the process temperature, the unit for calculating the optimal task for the process temperature and the unit for turning it off, the unit for receiving the task for the concentration of ammonia or the ratio of the flow rates of ammonia-air and the process temperature from the operator and transferring it to the corresponding regulators, block switching the structure of the internal controller, the unit for automatically changing the structure and / or operation mode of the device, while the inputs of the unit for calculating the optimal temperature task Through the square root extraction unit and through the analog signal input unit, they are connected to the indicated sensors, and the output through the optimum task shutdown unit is connected to the input of the temperature correction loop controller, the input of the compensation unit for input disturbances in temperature and pressure of ammonia and air, humidity, temperature and barometric pressure of atmospheric air, connected through the reliability control unit to the output of the square root extraction unit, and the output to the input of the computational unit ammonia concentration, the inputs of the unit for automatically changing the structure and / or operating mode of the device are connected respectively to the output of the unit for automatic reliability control and through the unit for inputting discrete signals with the adjusters of the structure or operating mode of the device of the operator’s communication device with the computer, and the outputs of the unit for automatically changing the structure and / or modes are connected respectively to the inputs of the shutdown blocks of the optimal task according to the process temperature, the shutdown of the correction loop for the process temperature from the regulator of the concentration of ammonia, disconnecting the correction loop for the process temperature from the regulator for the ratio of ammonia-air flow, switching the structure of the internal regulator to regulate the concentration of ammonia or the ratio of the flow of ammonia-air, as well as with the input of the regulator of the correction loop for temperature, the additional input of which is connected to the unit calculating the ratio of the flow rates of ammonia-air, and the additional output with its regulator through the corresponding shutdown unit, and the remaining output of the automatic an automatic change in the structure and / or mode through a discrete signal output unit is connected to a device operation mode switch, which is connected to a bypass panel for manual control of the position of the control valve actuator.

 In FIG. 1 shows a diagram of a device for controlling the process of contact oxidation of ammonia in the production of nitric acid; in FIG. 2 is a diagram of a microprocessor calculator included in this device.

 The circuit of FIG. 1 contains a mixer 1, a contact apparatus 2 for the oxidation of ammonia, sensors 3, 4, 5 of the differential pressure of air complete with a constricting device, an air pressure sensor 6, an air temperature sensor 7 complete with a thermocouple, a barometric pressure sensor 8, a relative atmospheric humidity sensor 9 air, air temperature sensor 10 complete with a thermometer, ammonia differential pressure sensors 11, 12, 13 complete with constricting device, ammonia pressure sensor 14, ammonia temperature sensor 15 complete with thermocouple, sensor 16 temperature of the ammonia-air mixture complete with a thermocouple, a contact oxidation process temperature sensor 17 complete with a thermocouple, an actuator of the control valve 18 mechanism on the ammonia gas pipeline, a pressure sensor 19 on the valve, an electro-pneumatic converter 20, a remote control and manual drive mode switch 21 , bypass panel 22 manual control, microprocessor-based computer 23, a device 24 for communication between the operator and the computer.

 The circuit of FIG. 2 comprises an analog signal input unit 25, an analog signal output unit 26, discrete signal input unit 27, digital signal output unit 28, a digital signal output unit 29, a processor 30, a timer 31, a random access memory unit 32, a microprocessor computer interface line 33, a unit 34 permanent memory, block 35 square root extraction, also performing the function of scaling, block 36 control the reliability of the sensors and device blocks, block 37 compensation of input controlled disturbances, block 38 calculating the concentration of am ammonia in the ammonia-air mixture, block 39 for disconnecting the external correction loop for the process temperature from the internal controller 40 for ammonia concentration in a cascade control circuit, controller 40 for ammonia concentration, controller 41 for the ratio of ammonia-air flow rates, block 42 for calculating the ratio of ammonia-air flow rates, block 43 disconnecting the external correction loop for the temperature of the process from the internal regulator of the ratio of ammonia-air, block 44 receiving the task by concentration or ratio from the operator and transmitting it accordingly to the internal controller, block 45 for switching the structure of the internal controller, block 46 for switching off the optimal task for the process temperature, block 47 for receiving the task for the process temperature to the temperature control loop controller from the operator, temperature controller 48 for the temperature correction loop, block 49 for calculating the optimal task for the process temperature , block 50 automatically changes the structure and / or mode of operation of the device.

The device operates as follows. The ammonia-air mixture obtained in the mixer 1 by mixing the flows of ammonia and air is supplied to the contact apparatus 2, in which nitrous gases are formed. The signals from the sensors 3-17 and 19 are fed to the input of the block 25 of the microprocessor calculator 23. These input signals are converted to digital code by the processor 30 and the interface line 33, at predetermined time intervals generated by the timer 31, are transferred to the memory block 32, in which are processed by the corresponding units 35 ^o C38, 42, 49, by the regulators 40, 41, 48 of the device, which are part of the permanent memory unit 34, depending on each specific configuration of the connections between these units, determined by the units switching 39, 43, 46 and switching 45, which are controlled from the block 50, which changes the structure or through blocks 28, 21 - operation mode (automatic or manual) of the device.

Along with continuous, discrete signals are also sent to the microprocessor calculator 23 through the block 27 from the operator’s communication device 24 with the calculator: to the input of the block 50 about the desired structure or operating mode of the device, to the input of block 49 about the results of laboratory analyzes of the degree of conversion of ammonia and losses platinum catalyst β _pt for adaptation of the corresponding mathematical models, to the input of block 47 - about the desired task of the temperature of the contact oxidation process to the controller 48 of the temperature correction loop, to the input of block 44 - about the desired the task according to the concentration of ammonia to the regulator 40 or the ratio of the costs of ammonia-air to the regulator 41, and the signals about the change in the task from the operator are processed by the corresponding named blocks depending on the structure of the control device, changed by the block 50.

 The basic structure of the device (structure 1), set by block 50, is such that blocks 35-38, 40, 47, 49, regulators 40, 48 operate, ensuring the optimal temperature of the contact oxidation process.

 The converted values of the input signals stored in the block 32 of the RAM are initially processed by the block 35, which performs the extraction of the square root of the differential pressure values obtained from sensors 3-5 and 11-13 and scaling of all variables to convert them to physical units.

 Then, the block 35 starts the operation of the block 36, which controls the reliability of the sensors and the health of the main units of the device and prepares the initial information for the operation of the block 49, which calculates the optimal task by the process temperature, which starts first when the main structure of the system is turned on, and then when the air changes by a value exceeding a predetermined error.

где
β $\genfrac{}{}{0ex}{}{\text{T}}{\text{NH3}}$ - теоретический расходный коэффициент по аммиаку на производство 1 т HNO₃;
Y - степень конверсии аммиака в оксид азота;
Y_A - среднестатическое значение степени абсорбции;
β_pt - расходный коэффициент по платиноидному катализатору;
Ц_NH3, Ц_pt - цена 1 т аммиака и 1 г платины соответственно, причем β_pt и Y являются функциями от Tк.о.Block 49 uses the information obtained to determine the conditions for its start-up and the adaptation of mathematical models of the degree of conversion of Y and the loss of the platinum catalyst β _pt , calculates the optimal contact temperature Tk.o. from the temperature of the contact oxidation process, determining it from the condition of minimum total costs associated with ammonia losses and platinum catalyst, at each given air flow rate by minimizing the following objective function:

Where
β $\genfrac{}{}{0ex}{}{\text{T}}{\text{NH3}}$ - theoretical ammonia consumption coefficient for the production of 1 t of HNO ₃ ;
Y is the degree of conversion of ammonia to nitric oxide;
Y _A is the average statistical value of the degree of absorption;
β _pt is the consumption coefficient for the platinum catalyst;
Ts _NH3 , Ts _pt - the price of 1 ton of ammonia and 1 g of platinum, respectively, and β _pt and Y are functions of Tk.o.

 The obtained optimum value of the temperature of the contact oxidation process Tk.o., which, through block 46, is supplied as a reference to the input of the controller 48 of the temperature correction circuit, which is external in the cascade temperature control circuit Tk.o.

 Blocks 36, 37, 38 provide further processing of the input information for the controller 40 of the concentration of ammonia, which is an internal controller in a cascade temperature control circuit.

 Block 36 performs the following: compares each variable with allowable limits in magnitude and rate of change, identifying failed sensors, identifies faulty sensors for differential pressure of ammonia 3, 4, 5 and air 11, 12, 13 using redundancy of information and averages their readings, performs filtering of input variables, checks the operability of block 25 by evaluating the correctness of its conversion of a predetermined "reference" signal, checks the operability of the block 26 output of analog signals using the signal back due to pressure to the control valve 18 from the sensor 19.

 In the event of a failure of a sensor or unit of the device, the unit 36 also generates discrete signals of its malfunction and switches on the unit 50, which automatically changes the structure or operation mode of the device in accordance with the situation, and then turns on the unit 37.

 Block 37 compensates for the previously listed input disturbances, minimizing possible temperature deviations of the contact oxidation process and thereby increasing the accuracy of its regulation, namely: it corrects the consumption of ammonia and air by their temperature and pressure, as well as by barometric pressure; determines the flow rate of dry air, subtracting from the flow rate of moist air a value equal to the amount of water vapor calculated from the known relative humidity and outdoor temperature; turns on block 38.

Вычисленное текущее значение концентрации Q_NH3 вместе с заданием по концентрации аммиака, которое является выходом внешнего цифрового ПИ - регулятора 48 контура коррекции по температуре, поступают, причем последнее - через блок 39 на вход внутреннего цифрового ПИ - регулятора 40 концентрации аммиака, выход которого через блоки 45, 26, преобразователь 20 и переключатель 21 поступает на исполнительный механизм регулирующего клапана 18. Регулятор 40 производит также выравнивание задания концентрации с переменной при переходе с нижеописанных структур III, V, VI на структуры I, II, IV для обеспечения безударного перехода. Выравнивание задания и переменной по температуре Тк.о. производит регулятор 48.Block 38 calculates the concentration Q _{NH3 of} ammonia in the ammonia-air mixture from the flow rates of ammonia F _NH3 and dry air F $\genfrac{}{}{0ex}{}{\text{c}}{\text{b3}}$ obtained in block 37:

The calculated current value of the concentration Q _NH3 along with the reference on the concentration of ammonia, which is the output of the external digital PI - controller 48 of the temperature correction loop, is received, the latter through block 39 to the input of the internal digital PI - controller 40 of the ammonia concentration, the output of which through the blocks 45, 26, the converter 20 and the switch 21 is supplied to the actuator of the control valve 18. The controller 40 also aligns the concentration task with a variable when switching from the structure described below III, V, VI to the structures I, II, IV to provide a bumpless transfer. Alignment of the task and the variable in temperature Tk.o. produces a regulator 48.

 Structure II occurs when operational personnel refuse to maintain the optimum temperature Tk. about. , due to production needs. At the same time, the corresponding command is issued from the device 24 to the input of the block 50 through the block 27, which, acting on the block 46, disconnects the output of the block 49 from the input of the controller 48 of the temperature correction loop and instead connects the output of block 47 to receive the temperature task Tk. . from the operator. Otherwise, structure II is identical to structure I.

 Structure III occurs when some of the sensors fail, for example 6, 7 or 14, 15 or others, when the differential sensors 3, 4, 5 and 11, 12, 13 (at least 2 of 3) remain in operation, as well as the process temperature sensor 17 contact oxidation. In this case, it is no longer possible to calculate the concentration of ammonia, because the relative error of its calculation becomes very large up to 10% or more. Therefore, block 50 turns off optimization block 49, calculation blocks 37, 39 and ammonia concentration regulator 40 and connects, acting on shutdown blocks 46, 45, 43, respectively, temperature receiving unit 47 from the operator and calculation block 42 and regulator 41 - ratios ammonia air. In this case, the regulator 41 aligns the task according to the ratio of ammonia-air with a variable during the transition from structures I, II, IV, VI to structure III to ensure shock-freeness. Upon transition to this structure from structures IV-VI, controller 48 also aligns the task with temperature Tk.o. With this structure, cascade control of the temperature of the contact oxidation process is also provided by the external controller 48 of the correction circuit together with the internal controller 41 of the ammonia-air ratio.

 Structure IV arises from structure I when the temperature sensor 17 of the contact oxidation process fails. In this case, the block 50, acting on the block 39, disconnects the regulator 48 from the input of the regulator 40 and connects to its input the block 44 for receiving the task in concentration from the operator. In this case, the concentration of ammonia in the mixture is regulated, which makes it possible to indirectly stabilize the temperatures of the contact oxidation process, although with less accuracy than when working with structures I-III.

 The structure V arises from structure III also in the event of a sensor 17 failure. In this case, the block 50, acting on the block 43, disconnects the regulator 48 from the input of the regulator 41 and connects the last block 44 to the input of the last one to receive the task in relation to the operator. In this embodiment, the ammonia-air ratio is regulated, which also allows you to indirectly stabilize the temperature of the contact oxidation process, but with even less accuracy than during the operation of structure IV.

 Structure VI occurs in the event of a failure of blocks 25 and 26, or of a sensor 19 and a converter 20. The device, acting on the switch 21 of the operating mode, disconnects the analog output of the block 25 of the microprocessor calculator 23 from the actuator of the control valve 18. The pressure on the actuator and provides the ability to connect to its input bypass panel 22 manual control from the operator.

 All changes in the structure, the inaccuracy of the sensors and blocks of the device are reflected by the block 50 on the signal boards and the display of the device 24.

 The display also reflects digital information issued through block 29 by all the blocks and controllers that process the input information, namely 35-38, 40-42, 44, 47-49, 42. 44, 49 and 41, 48, respectively.

Maintaining the optimum temperature of the contact oxidation of ammonia process can reduce the loss of ammonia and a platinum catalyst and provide a more economical process. Improving the accuracy of regulation of this temperature provides more accurate stabilization of the operating mode of the contact oxidation unit and subsequent units of the nitric acid aggregate. The maximum error in the temperature of the contact oxidation process is 1-2 ^o C.

 Improving the reliability of the device allows you to reduce the likelihood of unscheduled shutdowns of nitric acid units due to its failure and to increase the reliability of the units as a whole.

Claims (1)

 A device for controlling the process of contact oxidation of ammonia in the production of nitric acid, comprising a differential pressure sensor on the ammonia and air pipelines connected to a square root extraction unit from the differential pressure values, a contact oxidation process temperature sensor, a unit for calculating the concentration of ammonia in the ammonia-air mixture, connected with a concentration regulator, a control valve on the ammonia gas pipeline, characterized in that it further comprises temperature and pressure sensors for gas ammonia and air wires, ammonia-air mixture temperature sensor, barometric pressure, relative humidity and atmospheric air temperature sensors, pressure sensor on the actuator of the ammonia gas control valve, operating mode switch, operator’s communication device with a microprocessor computer that includes analog input and output blocks and discrete signals and a digital signal output unit, a read-only memory unit, which includes a square root extraction unit from ne pressure drop, which also performs the scaling function, the reliability control block of sensors and device blocks, the input compensation block of controlled disturbances, the unit for calculating the concentration of ammonia in the ammonia-air mixture with its regulator, the unit for disconnecting the process temperature correction loop from the ammonia concentration regulator, the unit for calculating the ratio ammonia - air flow rate, ammonia - air flow rate ratio regulator, process temperature correction circuit shutdown unit from flow rate regulator ammonia - air, regulator of the correction loop for the process temperature, unit for calculating the optimal task for the process temperature and its shutdown unit, unit for receiving the task for ammonia concentration or the ratio of ammonia-air consumption and process temperature from the operator and transferring it to the respective regulators, structure switching unit an internal controller, a unit for automatically changing the structure and / or operating mode of the device, while the inputs of the unit for calculating the optimal task for the process temperature through the unit from treatment of the square root and the input block of analog signals are connected to the indicated sensors, and the output through the shutdown block of the optimal task is connected to the input of the temperature correction loop controller, the input of the compensation block of input controlled disturbances in temperature and pressure of ammonia and air, humidity, temperature and barometric pressure air is connected through the reliability control unit to the output of the square root extraction unit, and the output to the input of the ammonia concentration calculation unit, inputs b locks of automatic change of the structure and / or operating mode of the device are connected respectively to the output of the automatic reliability control unit and through the input unit of discrete signals with the adjusters of the structure or operation mode of the device of the operator’s communication device with the computer, and the outputs of the automatic change of structure and / or mode are connected the inputs of the shutdown block of the optimal task for the process temperature, the shutdown of the correction loop for the process temperature from the ammonia concentration regulator disconnecting the correction loop for the temperature of the process from the regulator of the ratio of the flow rate of ammonia - air, switching the structure of the internal regulator to control the concentration of ammonia or the ratio of the flow rate of ammonia - air, and also with the input of the regulator of the circuit of the correction for temperature, the additional input of which is connected to the unit for calculating the flow of ammonia - air, and an additional output with its regulator through the corresponding shutdown unit, and the remaining output of the unit for automatically changing the structure and / or mode through a discrete signal output unit it is connected to the device operation mode switch, which is connected to the bypass panel for manual control of the position of the control valve actuator.

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