1) As vast as the field of software engineering, a lot of research has been made that has seen numerous publications made on the application of various theories and concepts to the PLC software among them Petri nets and discrete event theory systems. Unfortunately, the impact of the research, publications, and application did is negligible on the practice of PLC programming as such findings have been found to be too sophisticated and challenging to be applied by most of the PLC programmers (Shenoi, 2015). Further work has been done to establish the applications of the principles of software engineering to the development of PLC software. Among such work include recognition of the design patterns through the use of an object-oriented approach as well as proposals on new high-level languages for the graphics. Despite a positive remark on the development, it is worth noting that the research of literature on such term as PLC software framework, PLC software architecture and scalable PLC software have not yielded any significant results (Badir, 2016). Instead, the search results obtained are found to be too complex and sophisticated to be applied in real life situation. This leaves a wide gap between academic and scholarly publications and industrial application and practice of Programmable Logic Controllers software.
It is not surprising that Programmable Logic Controllers are gaining more and more sophistication with time and the trend expected to increase. To most of the vendors, the term Programmable Automatic Controllers is being used as a form of degradation to the previous generations of Programmable Logic Controllers an instead make the current generation look more superior. In the ancient times, programming of the Programmable Logic Controllers was done by people who have very little or absolutely no background knowledge of computer programming (Furtado, 2013). This is contrary to the contemporary situation in which programming is conducted by experts in computer programming, having an elaborate and extensive understanding of the structures of data, the principles of object-oriented programming among other skills and experience. These experts are opportunistic of the capabilities that are provided by the latest Programmable Logic Controllers.
Contrary to most of the other types of software, Programmable Logic Controllers are seen and used as a troubleshooting tool by the end user. The troubleshooting individual, who is in most cases the electro-mechanical technician, has a limited range of skills in programming as they have numerous other responsibilities to deliver (Colombo, 2014). This is one of the fundamental points that is given priority during the development of Programmable Logic Controllers programs. A program is rated to be simple when it is easy to troubleshoot as compared to more sophisticated ones. A production line which is easiest to troubleshoot normally has the highest time up and hence perceived to be more profitable and efficient.
The oil refinery industry is one of the most important industries and sectors in the economy of any country following the range of valuable products that it produces. A lot of studies have been done with regards to the application of PLC systems in the operation of the boilers, treatment of wastewater among other functionalities (McCormack, 2016). The operations of the boiler are monitored through the use of controller PLC using communication cables which check the pressure and temperature levels as well as the flow.
2)
In automating an oil refinery, it is important to develop a PLC system that checks in the plant and aids in the reduction of the errors due to man. The PLC system is used to store instructions internally that are used in the implementation of various functions among them sequencing, timing, counting and arithmetic (Hathaway, 2014). These instructions control the different types of machine processes through the use of either digital or analog output/input modules. PLC systems are normally used in conjunction with SCADA systems which is a collection of telemetry and data acquisition. This system collects data through the use of a Remote Terminal Unit. The collected data is then carried by the PLC systems in conjunction with the Intelligent Electronic Devices back to the central site to allow for the execution of the required analysis and control after which the information is displayed on the operation screens (Badir, 2016). The most important parts of the SCADA system include the Master Station, the PLC system and the communication between the preceding components.
3)
The process of refining oil is composed of four main units among them crude oil storage unit, distillation unit, products storage unit and crude oil storage nit. In this case study, three GUIs units have been designed for the monitoring and control of the process of an oil refinery.
Crude oil storage unit
The GUI consists of:
Figure 1 is an illustration of the crude storage unit when (P-01) is running an illustration by the push button and the green indication. The push the buttons (P-01) and (P-03) are indicating red, an illustration that they are in the stop mode. It is only when these two pumps are in the running mode that the variable speed sliders P-01 and P-02 are activated. When there is a green indication on the line, it means there is a liquid flowing while a red indication shows no flow taking place. The presence of little crude oil in the tank TK-01 is indicated by the blue indication. A blue indication on valve MOV-01 indicates it is fully open while the red one on valve MOV-02 is an illustration that is fully closed (McCormack, 2016). For the purposes of navigation between the screens, the distillation and Home page push button are used. As can be seen in the diagram, differential pressure flow rate transmitter FT-01 indicates a reading of 58% while FT-02 indicates 0%.
Distillation Unit
The GUI consists of:
As shown in figure 3, the distillation unit P-04 is not operational as indicated by the push on the button of the P-04 and the red indication. The reading of FT-03A/B is at 0% hence there is no flow. The readings of the seven transmitters of temperature are at 27? as there is no flow (Furtado, 2013).
In figure 4, P-04 is in the run mode with the variable speed slider being active. The crude oil is at vaporized state inside T-01. The indication at FV-03 is that it is 75% open. Temperature transmitter TT-01 reads 300?, the temperature of the crude oil, while TT-02 reads 700?, the temperature of the output crude oil. TT-03 is 30?, the temperature of the output gas coming from T-01 (JEROME, 2010). TT-04 reads 40? which is the temperature of Naphtha that has been output from T-01 while TT-05 reads 70?, the temperature of Gasoline. TT-06 is 120?, the temperature of kerosene and lastly TT-07 reads 200?C, the reading of the temperature of Diesel all of which output from T-01.
Dispatch/product storage unit
The GUI consists of:
Figure 5 is the product storage unit in a non-operational mode. The push buttons P-05… 09 have a red indicator illustrating they are in the stop mode. Still, the stop mode is illustrated by the LPG mastering station push button and the input field value which is zero (Badir, 2016).
The product storage in the run mode is illustrated in figure 6 in which the push buttons (P-05… 09) are all having a green indication and the LPG metering station push button also indicating the unit is in the run mode. The push buttons (LA-01… 04) and their associated pictures besides the loading arms are also indicative the products are in use. There are additional GUIs that have been designed in this case study: homepage, alarms and the trends GUIs (Arzen, 2014).
The home page GUI and the accompanying operation sequence diagram is shown in figure 7. Selection of a page from a drop-down list is made using the symbolic output/input field of the select page. Pressing the “Go” button activates this symbolic input/output field (Åström, 2013). The home page displays the operation sequence diagram of the crude oil in the storage unit or the pretreatment unit. Fast navigation is achieved through the use of the push buttons for the distillation units and the products storage units.
The design of the alarms is shown in figure 8 which shows the alarms when in operation while figure 9 illustrates the trends in the design of the GUI for both FT-01 and FT-02.
Conclusion
PLC systems are used in the process of an oil refinery and are designed for use in the monitoring and control of the system process. There are four main parts of the refinery process: distillation unit, a storage unit for crude oil, pretreatment unit for crude oil as well as the products storage unit. Monitoring and storage are the most significant advantages that come with the oil refinery process. The systems save time as well as enhancing the safety of the workers in the industry.
Programmable Logic Controllers (PLCs) are computers that are specifically designed and applied in the industry for the purposes of controlling and automation of the processes and the machinery used in the industry. Languages defined and specified in the International Electrotechnical Commission 61131-3 standards are the only languages used in the programming of Programmable Logic Controllers. The efficiency of production is directly influenced by the quality of the Programmable Logic Controller software that is used in its control and automation. An example can be observed in the case where a PLC software sequences an equipment in a way that was not intended and as per designed by the designer or equipment that are interlocked may remain in a state of wait for longer time than expected but the software will still manage to successfully produce products of the required quality in as much as time and energy will be wasted in the process of production.
References:
Arzen, K.-E. (2014). Computer Software Structures Integrating AI/KBS Systems in Process Control. London: Elsevier.
Åström, K. J. (2013). Computer-Controlled Systems: Theory and Design, Third Edition. New York: Courier Corporation.
Badir, A. B. (2016). Industrial Control Systems: Mathematical and Statistical Models and Techniques. Paris: CRC Press.
Colombo, A. W. (2014). Industrial Cloud-Based Cyber-Physical Systems: The IMC-AESOP Approach. Kansas: Springer Science & Business Media.
Furtado, J. C. (2013). Wireless Sensors in Industrial Time-Critical Environments. Manchester: Springer Science & Business Media.
Hathaway, M. (2014). Best Practices in Computer Network Defense: Incident Detection and Response. Oxoford: IOS Press.
JEROME, J. (2010). VIRTUAL INSTRUMENTATION USING LABVIEW. Cambridge: PHI Learning Pvt. Ltd.
King, R. P. (2012). Modeling and Simulation of Mineral Processing Systems. New York: Elsevier.
McCormack, R. L. (2016). Routledge Handbook of the Law of Armed Conflict. London: Routledge.
Shenoi, M. R. (2015). Critical Infrastructure Protection IX: 9th IFIP 11.10 International Conference, ICCIP 2015, Arlington, VA, USA, March 16-18, 2015, Revised Selected Papers. New York: Springer.
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