APCS filling liquid ammonia into railway tanks

Introduction

The purpose of this diploma project was to develop a system for controlling the process of pouring liquid ammonia into railway tanks.

The degree project consists of the following stages.

At the first stage, they described the process and analyzed the process as a control object.

At the second stage, they reviewed the existing control and management system.

At the moment, the "START" system is used as control and regulation systems, the main means of control and regulation are pneumatic primary and secondary devices. Their use has a number of drawbacks:

• by instruments located on the control room, the operator cannot monitor several parameters at the same time, and simultaneously monitor the operation of process equipment and actuators;

• In case of mechanical damage to the instruments, the correct operation of the process is impossible;

• When ambient air temperature decreases, breakdowns of pulse lines, air cables and failure of measuring parts of instruments are possible;

• With manual process control, the slightest confusion of a person and his untimely impact on the process can lead to various serious consequences;

• Current devices for accounting for raw materials, products and energy resources do not provide the possibility of automated calculation of economic indicators.

The diploma project envisages reconstruction of the liquid ammonia filling rack I&C. Elimination of the above drawbacks by introducing a centralized ACS based on microprocessor devices, creating an operator's AWS, introducing new devices, replacing positional regulation with continuous. Automation leads to an improvement in the main indicators of production efficiency: an increase in quantity, an improvement in quality and a decrease in the cost of production, and an increase in labor productivity. The introduction of automatic devices ensures high quality of products, reduction of scrap and waste, reduction of raw materials and energy costs, reduction of the number of main workers, reduction of capital costs for the construction of buildings (production is organized in the open air), extension of the time between repairs of equipment.

The introduction of special automatic devices contributes to the accident-free operation of the equipment, eliminates cases of injuries, prevents pollution of the atmospheric air and reservoirs by industrial waste. Also, the system will allow the economic and management services to receive operational data on the volume of raw materials consumption and output, therefore, the need for BCU (bureau of control and accounting) processing data from cartograms does not fall.

In automated production, a person switches to creative work - analyzing control results, compiling tasks and programs for automatic devices, adjusting complex automatic devices, etc. To service units equipped with complex automation systems, specialists with a high level of knowledge are required. With the improvement of the qualifications and cultural level of workers, the line between physical and mental labor is erased.

APCS analysis of liquid ammonia filling into railway tanks

1.1 Process Description

Liquid ammonia filling rack is designed to ship liquid ammonia to railway tanks for further transportation to the consumer. Liquid ammonia is supplied to the filling rack from the distribution header, in which the mass flow rate of ammonia is taken into account, liquid ammonia is supplied through filters, for its purification from oil impurities contained in it. Ammonia gas released during the pressurization of railway tanks and during the filling with liquid ammonia is sent to separate liquefaction. The pressure drop between ammonia gas lines AMG82 and AMG82a is maintained automatically by a control valve. If the pressure in the ammonia gas header is reduced to an emergency stop, all shut-offs on the ammonia gas lines AMG81 are automatically closed. In case of emergency emptying of tanks, liquid ammonia can be sent to the drain tank.

The ammonia compression and isothermal storage unit is designed to receive liquid ammonia from the AM76 unit into the isothermal storage of item 1 with a capacity of 10,000 m3 (filling 80 percent) and store it in it.

It is also intended for the delivery of liquid ammonia to the carbamide workshops, for the recovery of cold into the ammonia production of the AM76 unit and for pouring into railway tanks.

The ammonia content in the air in the compression room and in the plant area around the collapse of the isothermal storage is controlled by gas analyzers QRA501, 503, 504, QIA505, 506, 507, 508, indicating that the MPC (20 mg/m3) in the unit CPU is exceeded.

The TRA125 in the CPU indicates that the flame of the 7 flare has faded. The LRA423 device in the CPU signals the excess of the allowable level in the flare separator of item 7a.

1.2 Process Diagram Description

1.2.1 Reception of liquid ammonia from AM76 unit in the position storage and storage in it

Liquid ammonia from ammonia unit AM76 is supplied via AMZH1 line to ammonia compression and isothermal storage unit. Reception of liquid ammonia to the lower part of isothermal storage of position 1 is carried out through electric gate of position MOV10, cutoff of position EmV601. The temperature of liquid ammonia entering the lower part of the storage should be from minus 34 to minus 30 ° С, which is controlled by instruments of position TRSA102, TJR-132-1.

Heated ammonia is supplied via AMZH21 line to warm ammonia collector AMZH20, from where it can be sent:

• along the AMZH80 line for filling railway tanks;

• AMZH26 for carbamide production;

• via AMZH25 line to fill the AM76 unit system;

• via AMZH11 line to isothermal storage of item 1 for cooling after repair;

• via AMZH37 line to fill liquefaction compartment in line receivers of position 14 and position 66;

• via AMZH23 line to the evaporator at 16.

Between lines AMZH80 and AMZH25 there is a jumper AMZH25a for receiving warm ammonia from unit AM76 to railway tanks.

Liquid ammonia is supplied to AMZH20 header:

• via AMZH25 line from AM76 unit;

• via AMZH29 line from the drain tank of item 9;

• via AMZH64 line from line receiver position 66.

1.2.2 Filling of liquid ammonia into railway tanks

Liquid ammonia is poured into railway tanks on a double-sided rack with 12 filling points (trusses) on each side. Warm ammonia from AMZH20 header or cold ammonia from AMZH5 header via AMZH80 line through MOV103 electrical valve and pressure regulator valve before PCV1284 is supplied to liquid ammonia filling rack.

To bring the quality of commercial ammonia to grade A, a system is provided for cleaning it from oil, mechanical impurities, which consists of a pre-filter of position 24/1 (cleaning ammonia from mechanical impurities) and a coalescer of position 24/2 with built-in filtering elements coagulating oil from liquid ammonia. The oil collected in the coalescer of 24/2 flows into the vertical settler of the coalescer and is withdrawn from there as it accumulates into the drain vessel of 9. When the oil level in the sump rises to 240 mm, the position isolator LCV408 on the drain line opens and the oil flows into the tank at 9. To prevent liquid ammonia from leaking into the E-9 tank at 100 mm oil level in the sump, the shut-off valve is closed.

In case of satisfactory analysis of commercial ammonia at the inlet to the liquid ammonia storage or during repair of the purification system, liquid ammonia goes to the liquid ammonia filling rack, bypassing the filters of item 24/1.2.

To protect the pipeline from overpressure in it, a safety valve with a discharge to the AMZH10 line is installed on the AMZH80 line.

Between the lines AMZH80 and AMZH26, after the filters of position 24/1.2, a jumper AMZH26a is provided to deliver liquid ammonia purified from oil to the carbamide workshop to object 1506.

1.2.3 Liquid ammonia evaporators

The liquid ammonia evaporators of 16/1.2, one of which is working and the other is standby, serve to produce gaseous ammonia for further use in the testing of railway tanks, the transfer of liquid ammonia from railway tanks, the drain tank of 9, the receivers of 15, 67 and the purging of the isothermal storage of 1 after repair before filling it with liquid ammonia.

1.2.4 High pressure nitrogen supply

High-pressure nitrogen (ADG) is supplied to the unit for operation of position EmV601 and EmV602 cutoff devices, for pressure testing of railway tanks and transfer of liquid ammonia from them to the tank of position 9.

Depending on the command by the button from the CPU board, the electrically charged solenoid valve section of position EmV601 (EmV602) opens or closes and nitrogen enters the upper or lower compartment of the cutoff cylinder, pushing its rod before opening or before closing.

In case of termination of high-pressure nitrogen supply from the network, the receiver of the 28 position will ensure the shutoff devices operation for 1 hour.

Safety valves shall be installed after the valve of position PCV296 in order to avoid excess nitrogen pressure on the lines to the cutoff valves before and after the valve of position PCV264 and on the line of nitrogen supply to the railway tanks and to the tank of position 9.

1.2.5 Collection of liquid ammonia during emptying of devices and pipelines

Liquid ammonia from the units and pipelines of the unit during preparation for repair via the common header DR1, as well as from the separator of position 23 and from bypass valves via the line DR-4 is sent to the drain tank of position 9.

Liquid ammonia is transferred from the tank of item 9 to the AMZH20 warm ammonia distribution header or via the AMZH82 line to the NOS to the railway tank. If an emergency discharge of a railway tank is required, liquid ammonia may be transferred via AMZH82 to the tank of item 9.

Ammonia gas for transfer is supplied to the tank of station 9 from AMG14 header via AMG16 line.

The container of the station 9 is provided with an outer coil for heating the liquid ammonia therein. The coolant is steam. Steam condensate is diverted to BTs3.

1.2.6 Air supply for instrumentation

In case of termination of instrument air supply from the network, four air collectors of 27 items will ensure uninterrupted operation of the automation for 1 hour.

Decrease of instrument air pressure in the common manifold to 0.25 MPa (2.5 kgf/cm2) by the device of position PIA298 and in the manifold behind the CPU panel to 0.14 MPa (1.4 kgf/cm2) by the device of position PIA274 notifies the sound and light alarm in the CPU.

The instrument air pressure at the NOS is controlled by the PCV232 self-regulating valve.

1.3 Analysis of existing BC

At the moment, the "START" system is used in the control system, which includes:

• Primary pneumatic transducers for measuring pressure of WFP 2, flow rate of 13DD11, UBP level;

• secondary display and recording devices with control station (PV10.2E).

And also, pneumatic PIDs of PR-3.31, pneumatic actuators, primary temperature converters of THA, secondary instruments for temperature measurement with KSP3 control station. These are pneumatic primary and secondary devices. Their use has a number of drawbacks:

• by instruments located on the control room, the operator cannot monitor several parameters at the same time, and simultaneously monitor the operation of process equipment and actuators;

• In case of mechanical damage to the instruments, the correct operation of the process is impossible;

• When ambient air temperature decreases, breakdowns of pulse lines, air cables and failure of measuring parts of instruments are possible;

• With manual process control, the slightest confusion of a person and his untimely impact on the process can lead to various serious consequences;

Current devices for accounting for raw materials, products and energy resources do not provide the possibility of automated calculation of economic indicators.

1.4 Description of existing APCS functional diagram

Shipment of marketable liquid ammonia to railway tanks is carried out on a double-sided rack with 24 filling points.

Liquid ammonia is supplied to the filling rack from AMZh-20 distributing number-lecturer via AMZh81 line or from position 3 pump directly via AMZh80 line under pressure from 1.4 to 2.0MPa. on the line, the cis-tern is filled with liquid ammonia at 416.

The ammonia supply is automatically stopped by closing the EMV618 on the liquid ammonia supply line to the tank.

It is also provided to close the cutoff EMV618 when the pressure of position 235 in the line AMZh - 80 at the entrance to the railway tank decreases .

Special part

2.1 Selection and justification of control and monitoring system structure

Reconstruction of APCS on liquid ammonia filling rack consists in creation of multi-level APCS consisting of lower (field), controller and operator levels.

At the lower level, sensor equipment is used to collect primary information about the progress of the monitored process, as well as actuators for direct control of the process.

The controller layer provides:

• collection and primary processing of data from sensor equipment;

• mathematical processing of the initial process data;

• Logic and software management;

• process alarm;

• preliminary archiving of calculation and initial data

To organize the controller layer, general or special purpose controllers are used, the consolidation of which is possible on the basis of the RS232C/485 interface using the Bell202 or Modbus protocol with an exchange rate of up to 19.6 Kbot.

The operator level is designed for visualization of the controlled process, archives management, operational intervention in the process and reporting.

The reconstruction of the existing ACS consists of the following main components:

• introduction of additional temperature, level and pressure sensors for collection and remote transmission of data on process parameters;

• Installation of new intelligent flowmeters to collect and process information on raw material and product consumption;

• introduction of logic programmable controllers for automated control of level, pressure and temperature on the liquid ammonia filling rack;

• creation of WS operator of liquid ammonia storage unit;

• Replacement of discrete actuators and regulators with continuous actuators and regulators.

Additionally, a system for monitoring the leakage of toxic gases and linking it to the existing ventilation system is provided.

To obtain the necessary information about the process parameters in real time, centralized display of this information, and process control in the project, the following sensors are used - primary transducers.

2.1.1 Temperature sensors

Thermoelectric converter TCM 50M - 055 with a range of measured temperature -50... 50 С, which provides continuous conversion of the value of the measured parameter into a unified current signal 420mA .

2.1.2 Pressure sensors

To measure the pressure on the pouring rack, I propose to use the Sapphir22DI primary pressure converter, which ensures the continuous conversion of the measured parameter value to a unified current signal of 420mA.

On the filling rack at position 235 I propose to install pressure switch RD - 80 with discrete output signal.

2.1.3 Level sensors

Hydrostatic pressure sensor (level) ROS 501I provides non-intermittent conversion of measured parameter value into unified current signal 420mA, is installed directly on the flange of the device in which the level is measured, has built-in microprocessor converter due to which it has advantage over similar sensors with analog converter in metrological, functional, operational parameters.

On the filling rack, the maximum level in the railway tank of item 424 is signaled by the POS 501I level relay with a discrete output signal.

2.1.4 Flow sensors

To obtain data on the flow rate of liquid ammonia and steam, the following flow converters are used in the project.

Vortex acoustic flow converter Metran300PR, measurement limit 0.18... 700 m3/h, output signal - unified current 420mA. This converter uses the principle of ultrasonic detection of vortices formed in the liquid flow when it flows around a prism located across the flow. The advantage of this converter is the possibility of verification in place without dismantling, a large interval between tests, self-diagnostics. It is installed on the AMZH1 pipeline at the entrance to the isothermal storage of item 301.

FisherRosemount Model 8800 Intelligent Vortex Flowmeter, 420mA output. Uses the principle of determining the frequency of vortices formed in the flow of the measured medium when circulating a body of a special shape, which is directly proportional to the speed of the moving medium. This transmitter, thanks to digital technology, allows the flowmeter to ensure maximum accuracy and reliability of measurements.

2.1.5 Data collection and processing devices

A group of programmable modular controllers is used as the main AML (data collection and processing device) in the project. You can install a single, module-based Advantech controller with a different number of expansion modules (analog and discrete I/O modules). Controller is designed for collection, initial processing and preliminary archiving of information on consumed and released energy resources, such as water, gas, steam.

The PC performs the following process functions:

• regulation of filling level in the railway tank according to the specified control law;

• regulation of pressure in railway tanks by closing the shutoff devices of item 635 on the liquid ammonia supply line;

• conversion and output of process parameter information using RS232/485 interface to operator station.

Small, programmable Advantech controllers are used in small automation systems. They feature high processor performance, high I/O, 100240V AC power supply, and 24V DC sensors.

Advantages of small PCs:

• A significant number of entry/exit points (up to 24 points), with small occupied dimensions, allows you to reduce the size of panels where the parameters of the occupied space are important;

• A variety of expansion modules and add-on modules that give the user the flexibility of larger controller platforms. With up to seven discrete I/O expansion modules (corresponding configuration with 17 I/O points) and add-on modules such as a digital display, memory frame, real-time clock frame, and additional communication ports with RS485 or RS232C interfaces, you can increase the capabilities of the small-size Advantech controller with I/O points;

• To connect expansion modules to the controller, several connection options are offered, such as removable screw terminal blocks and spring connectors, providing a simple, fast and safe connection;

• The use of display and embedded memory allows you to configure, transfer and back up applications. The digital display can be used as a tool for local display and configuration. EEPROM memory modules allow you to reserve and transfer programs to any compact P;

• The software allows simple programming using instructions of the Instroction List language or graphics objects of the Ladder language;

• Compact controllers have two analog potentiometers located on the front panel. Potentiometer values are stored in system words and updated after each program cycle.

• For the possibility of connection to the sensor controller with analog output signals and control of actuators, the project provides for the connection of additional modules for expansion of analog input/output. Two TWD AMI 2HT modules (2 inputs and 1 high output) are connected to the controller. For the control controllers of the shutoff operation, the connection of the discrete input/output module TWD DRA 16RT is provided, expanding the number of discrete outputs of the controller to 26 pieces.

In addition to the controller, the RS485 TWD NAC485D adapter (for communication with the operator station through an additional port) and the TWD XCP ODC digital display are connected.

Programming of the controller is carried out using software, through the built-in serial port miniDIN type RS485

To create an operator's AWS for the installation of LMS on the basis of an IBM compatible PC, the project provides for the use of a SCADA system based on Cascade ACS software. This product is based on open and standard technologies today and offers a complete set of easy-to-use graphical functions for visualization systems.

The Cascade Automatic Control and Data Acquisition (SCADA) software includes basic packages for creating supervisor monitoring and control applications, as well as additional elements (options) that improve the functions of these packages for such special applications as statistical process management or integration with databases. There are four different product baselines depending on the size of the real-time database available and the maximum number of process input/output parameters (tags). In a broad sense, the functionality of all these options is the same for all variants of the basic operating system. This simplifies application migration from one platform to another. Currently, Cascade Self-Propelled Guns is designed to work under the operating systems Windows NT, Windows 95 and 98. A full set of ACS cascades options is possible under Windows NT. A limited number of options are available under Windows 95 and 98. There is no Cascade automatic control system version for OS/2.

Cascade-ACS is a multi-user SC¼ real-time application server for automation of production and technological processes. It allows you to collect critical information from numerous devices and devices of an industrial facility and then distribute it throughout the enterprise (organization).

Cascade-ACS provides such critical features of the SCDONBASS system as retrospective data, signaling and statistical process management. In addition, the Cascade ACS database, updated by change, provides unique scalability - there are applications that process more than 2 million tags.

Cascade ACS visualization functions are used for:

• reading variable values from the PLC and displaying these variables on the screen;

• control and monitoring of systems with process control;

• archiving to the database of PLC variable values or internal control system variables;

• Built-in software data processing.

The PLC is connected via the Modbus bus and is connected via the RS 485B interface in multipoint mode.

2.2 Functions performed by control monitoring system

2.2.1 Main information functions of the rack APCS system

liquid ammonia filling

APCS system of liquid ammonia filling rack is designed for:

• implementation of functions of automatic control and measurement of process parameters (tele-measurement, tele-signaling) and control of process equipment (tele-control) of the workshop;

• organization of process metering points for ammonia shipped to the consumer;

• accumulation and storage of operational and technological information in the internal database;

• visualization of process parameters (signals of TI, the CU, the alarm and precautionary system - on an automated workplace of the operator; telesignation of shutoff devices position - on manual control units);

2.2.2 Main functions of APCS of liquid ammonia filling rack for information collection

APCS of liquid ammonia filling rack provides implementation of the following main functions for information collection;

• interrogation of discrete signals about the state of process equipment directly or via local automation systems of filling trusses;

• survey of analog sensors of tele-measurement directly or via local automation systems of filling trusses: pressure, temperature, etc.;

• survey of current values of process parameters calculated by local automation systems of filling trusses: ammonia consumption.

2.2.3 Main functions of APCS of liquid ammonia filling rack for information presentation

APCS of liquid ammonia filling rack provides implementation of the following main functions for information presentation:

• display of process parameters, warning and alarm values, display of shutoff valves status on the operator's AWS screen;

• display on manual control units (BRU) of signalling about condition of shutoff devices and integrity of solenoid circuits;

• display of information on the system operation when performing automatic functions of liquid ammonia filling rack protection on the operator's AWS screen;

2.2.4 Main functions of APCS of liquid ammonia filling rack for information processing

APCS of liquid ammonia filling rack provides implementation of the following main functions for information processing:

• identification and recording of emergency and warning events based on the state of process equipment;

• Detection and recording of emergency and warning events when the values of tele-measurements exceed the corresponding set limits (installations);

• calculation of ammonia flow values (technical accounting of ammonia flow);

• monitoring and control of liquid ammonia filling rack subsystems;

• Define the current process

• ESD monitoring and control.

2.2.5 Main functions of APCS of liquid ammonia filling rack for information archiving

APCS of liquid ammonia filling rack provides implementation of the following main functions for information archiving:

• within 30 days, the history of changes in the values ​ ​ of the following parameters is preserved (data archive):

telemetry:

• pressure in liquid ammonia lines;

• pressure in ammonia gas lines; Telesignalization:

• emergency and preventive;

• change of position of cutoff devices with control mode mark (local/remote);

• abnormal situations during operation of the pressure control system;

• abnormal situations in ammonia flow calculations; design parameters:

• daily ammonia consumption;

• for 360 days all events recorded by the system are saved: emergency, warning and other messages (event archive).

2.2.6 Main functions of APCS of liquid ammonia filling rack for control

APCS of liquid ammonia filling rack provides the following main control functions:

• control of two-position process facilities (Cutaways);

• automatic (according to the specified algorithm) and manual control of shutoff devices;

• automatic (according to the specified algorithm) and manual generation of the control signal for the pressure regulator.

2.3 Monitoring indication, recording, signalling,

ESD, regulation, archiving, visualization

The system for measurement, control and regulation of process parameters is designed for measurement and processing of signals coming from sensors installed on process equipment, generation of commands and actions on control and control objects, visualization of ongoing technological processes and a dialog interface with the operator.

• Monitoring of liquid ammonia filling process by automated control system and independent emergency protection system (hereinafter referred to as ESD) using microprocessor equipment;

• Constant monitoring of process parameters and mode control to maintain their regulated values;

• Registration of actuation and monitoring of serviceable condition of measuring instruments;

• Reducing the level of influence of the human factor and improving the safety of maintenance personnel when filling liquid ammonia;

• Visualization of process parameters and dialog interface with operator;

• Reduction of liquid and gaseous ammonia emissions into the environment;

• Accumulation and storage of operational process information in the internal database of APCS of liquid ammonia loading rack ensures implementation of the following main functions for information archiving:

• Within 30 days, the predistory of changing the values ​ ​ of the following parameters (data archive) of tele-measurement is preserved:

• Pressure in liquid ammonia lines;

• Pressure in ammonia gas lines; telesignalization:

• Emergency and preventive;

• Changes in position of shutoff devices with control mode mark;

• Abnormal situations during operation of the pressure control system;

• Abnormal situations when calculating ammonia consumption;

Design parameters:

• All events registered by the system are saved within 360 days;

• Daily ammonia flow rates;

• Emergency, warning and other messages.

The operation mode of the autonomous refuelling pod can be controlled by a button in place or from the operator's AWS with transmission to the operator's AWS of relevant information on the fact of switching on or off in place or from the operator's AWS. Refuelling pod unit is made in the form of separate module and serves for generation of control signals of protective closures of shutoff devices. ESD actuation is accompanied by actuation of alarm in place.

2.4 Control and monitoring algorithms

The database contains both system-independent executable code available only to the controller, and the source texts of technological programs written in the FBDU ST technology programming languages available to the user.

The main structural unit of constructing algorithms is a design module that describes the algorithm of a particular technological object or their combination. Inside the project module, unique blocks and diagrams are defined that are available only to this project and describe the functional elements of the algorithms. When creating algorithms, the built-in elements and functions regulated by the above standard and library blocks created by the user are also used. These features are available to all project modules.

Algorithmic software is designed to solve the following problems:

• Control of process parameters of liquid ammonia filling rack;

• Control and monitoring of shutoff valves;

• Technological accounting of ammonia shipped;

• Start-up, shutdown, control of ammonia shipment process from liquid ammonia filling rack.

Conclusion

In the course project, the RSA of the level of liquid ammonia filling into the railway tanks of the liquid ammonia storage unit was developed, which will ensure optimal accident-free process management, increased reliability due to the use of redundancy of the most important components of the system, effective ergonomic interaction with the operator.

The diploma project also considered the issue of reconstruction of ASU of liquid ammonia filling rack of workshop No. 54 of JSC "SNS"

The developed control system is based on the use of technical and software tools. A special advantage of the technique is that it covers all levels of automation, which avoids problems with compatibility, scaling and achieves a high level of speed, functionality and reliability.

The implementation of the system will ensure high quality of products, reduced costs for raw materials and energy carriers, reduced load on maintenance personnel, and reduced harmful emissions into the atmosphere.

Section 1 describes the process of receiving liquid ammonia from the AM76 unit to the isothermal storage of item 1; discharging liquid ammonia from the station 1 storage to the AMZH5 distribution manifold; condensation of liquid ammonia of the storage cycle; heating of liquid ammonia; Shipment of liquid ammonia to railway tanks.

Section 2 describes the current automatic control system, control parameters, position numbers, functional diagram of automatic control and regulation.

Section 3 Calculation of automatic control system for liquid ammonia filling into railway tanks includes calculation of automated continuous control system, description of control object and its dynamic characteristics.