Process Control Loops - Coursework Example

Process Control Loops By Engineering and Construction of Table of Contents Table of Contents 2 4 Introduction 5 Analysis 5 Figure 1: Relationship between the PV and Variability 6 The Control Loop 7 Figure 2: Functionality of the Loop 7 Types of Control loops 7 Open Loop Control 7 Application of the Open Control Loop in the oil and Gas Industry 8 Closed/ feed backward Control Loop 9 Application of the Closed Control Loop in the oil and gas refinery Process 10 Feed Forward Control Loop 11 Application of the feed forward Control Loop 12 Combined feed forward feed backward control 13 Application of the combined feed forward and feedback control loop 13 Reactor Tank Operator 14 Heat Exchanger 14 Conclusion 15 List of Reference 16 Table of Figures Figure 1: Relationship between the PV and Variability 6 Figure 2: Functionality of the Loop 7 Figure 3: Block Diagram of the Open Loop System 8 Figure 4: Open Loop duration versus the Integral 9 Figure 5: Functionality of a wireless Closed-Loop Control 10 Figure 6: Feed Forward Control Loop 11 Figure 7: Block Diagram of the Feed Forward Control Loop 12 Figure 8: Signal Block Diagram 13 Figure 9: Reactor Tank Operator 14 Figure 10: Heat Exchanger Process 15 Abstract This paper seeks to explore the functionality of various control loops relative to the manufacturing process in the industrial process. In this case, the oil and gas production process will be put into focus when explaining the attributes of these loops. The loops that will be dissected include open loop control, feed backward control, feed forward control and combined feed forward feed backward control. Further, the aspects of reduction variability, increase of efficiency and ensuring safety are given focus relative to the manufacturer’s point of view. In addition, the attributed instrumentation and signal diagrams will be used in explaining their applications in the production process and response to process disturbances. Keywords: Control loops, Process variance, Set Point, Load disturbance Introduction Process control refers to an engineering discipline, which deals with mechanisms, algorithms and architecture in a bid to maintain the output of a particular process within a given period. An example of this aspect can involve the control of the temperatures relative to the chemical reactor in order to sustain a consistent product output. This essay seeks to dissect various control loops relative to the applications in the chemical processes. A particular focus on the oil and petroleum form the basis of this essay. In addition, various kinds of response of the systems to disturbances will be evaluated relative to instrumentation and signal block diagrams. Analysis In most of the fluid processing industries sub-phases such as refining, handling and manipulating of these raw materials to have the products in the desired quality involves an accurate, demanding and hazardous process. It is imperative to note that, small variations in a process need to be accurately and constantly controlled to produce the needed end product in line with the least amount of raw materials and energy[5] .This process requires the process control technology tool to guide the producers to keep their activities running within the stipulated time limits. This enhances accurate limits to optimize the overall profitability, quality and security. These reasons of controlling the production process are widely perceived by manufacturers in terms of the following aspects Reduction of variability Increase efficiency Ensure safety The control loops ensures that the variability in the product is reduced to minimum and this enables production of a consistent and high quality product. In addition, variability reduction helps in saving money by reducing the necessity for the product padding in a bid to meet the particular product features. This relationship is illustrated in the graph below Figure 1: Relationship between the PV and Variability Source: GANSSLE, J. G., & BALL, S. R. (2008). Embedded systems. Amsterdam, Elsevier/Newnes On a similar note, part of the processes need to be sustained at a particular point to optimize the overall efficiency. Further, precise control loops helps in avoiding run-away process such as hyper-chemical reaction, which are detrimental. From the illustration, it is evident that any fluid process is attributed to both the process variable (PV) and the Set Point (SP). A process variable means a condition of a fluid whose potential can revolutionize the manufacturing process in some manner. On the other hand, the set point refers to specific value attributed to a process, which is needed to be sustained. This brings us to the various kinds of control loops and their functionality in process control relative to the oil and gas industry. The Control Loop A control loop refers to an action performed to restore the initial status. For instance, when a variable-temperature falls below the limit or required level for a process to go smoothly, an adjustment done to restore the level of temperature to the required one is called a control loop. Like in any other industry, a control loop performs three tasks in the oil and gas industry. They include measurement, comparison and adjustment. The following illustration indicates the functionality of a control loop with the three critical attributes in operation. Figure 2: Functionality of the Loop Source: GANSSLE, J. G., & BALL, S. R. (2008). Embedded systems. Amsterdam, Elsevier/Newnes Types of Control loops Open Loop Control In the case of an open loop control, its existence is attributed to a situation where the variable relative to a process is not evaluated, and an action is not executed in a rejoinder to a feedback attributed to the state of the process variable. However, it takes place about the variable states. An example of this situation is the opening of a water valve to add a water cooling effect aimed at averting the process fluid from going to elevated temperature levels [5]. This is based on a predetermined interval irrespective of the real temperature relative to the process fluid. Consider the following illustration, which indicates the various components of an open control loop. These systems are cheap and easy to comprehend however; the attributed efficiency is so low that it tends to zero. Figure 3: Block Diagram of the Open Loop System Source: http://www.daenotes.com/electronics/industrial-electronics/process-control The open control loop is controlled by the feeding of the system process with an input in a bid to sustain the output at the preferred level. In this case, the set point acts as a command. Application of the Open Control Loop in the oil and Gas Industry In the Industrial process of production and refining oil and gas, the open control loop is applied from the input of the raw material through the real process up to the production of the product. The concept of the DCS (distributed control system) is applied. This concept is attributed to the necessity of gathering data in real time, particularly on high bandwidth. The concept extends to the use of pneumatic control systems, which are far beyond a small cell area of a refinery. This concept enables automated information feeding as input and gives direction on the oil refinery process to the end [5]. The DCS is immensely attributed to the integral action of instrumentation, which returns the PV to the SP. This process is attained as long as the action of the proportional mode is repetitive relative to the existence of an error. It is imperative to note that, the open loop analysis is set on the integral (reset) action, which is defined by repeats per minute and minutes per repeat as indicated in the graph below. Figure 4: Open Loop duration versus the Integral Source: GANSSLE, J. G., & BALL, S. R. (2008). Embedded systems. Amsterdam, Elsevier/Newnes The above illustration is a representation of the response of control systems to disturbances that cause errors like in the case under consideration of oil and gas refinery process. Closed/ feed backward Control Loop The existence of a closed control loop is dependent on a measurable process variable, which is comparable to a particular set point. In this case, an action is taken to make correction to any deviation that may arise during the process progression. In this case, a closed-loop transfer function is applicable. Sometimes this type is called the single input –single output (SISO) approach. This type of loop is also called a feedback control system due to its ability to use the principle of the open loop system as its forward pathway [4]. Application of the Closed Control Loop in the oil and gas refinery Process The increasing demand of oil and gas products has necessitated enhancement of technologically designed and execution of large manufacturing and processing plants over far-flung areas attributed to hostile milieu conditions and demanding logistics. This has contributed to the adoption of wiring sensor network (WSN) instead of the traditional cabling has fully revolutionized the machine interconnection to a platform of closed loop control performance. It is imperative to note that, the installation of WSN is immensely attributed to the reduced costs in revamping and expansion among others [4]. The diagram below illustrates the functionality of a wireless closed-loop control in a refinery industry. Figure 5: Functionality of a wireless Closed-Loop Control Source: GANSSLE, J. G., & BALL, S. R. (2008). Embedded systems. Amsterdam, Elsevier/Newnes As indicated in the illustration, the Wireless networking is seen as efficient for less time-critical evaluating task such as leakage and machine state screening. In this case, humans act as the loop. Feed Forward Control Loop This kind of control loop involves the use of a path or a component, which is within a control system that sends a controlling signal from an external source or a signal from an external command, which necessitates loading somewhere in the external milieu. In essence, the feed forward control loop engages both the external and internal milieu in coordinating a particular process [3]. It is notable that a system such as the feed forward control loop, which has only a feed-forward conduct, only responds to its control signal in pre-determined approach in such way that there is no respond relative to the load’s reactivity. In this case, the load is taken as one of the components of the external milieu. In addition, the control variable adjustment attributed to the feed-forward control system is not based on errors. It is entirely dependent on the knowledge relative to the process. This knowledge is in most cases represented in a mathematical model relative to the process in terms of measurements and disturbances [3]. In the case of the responding to a threat, the external command takes charge and is always available to ascertain that the load impact on the system output is known before acting. Consider the following illustration indicting the feed forward control loop. Figure 6: Feed Forward Control Loop Source: GANSSLE, J. G., & BALL, S. R. (2008). Embedded systems. Amsterdam, Elsevier/Newnes In essence, the feed forward control loop functions on the theory of data from the outside or outlet of a process that is being fed in return to the input of the same process aimed at a corrective action. Consider the following block diagram, which simplifies this process. Figure 7: Block Diagram of the Feed Forward Control Loop Source: GANSSLE, J. G., & BALL, S. R. (2008). Embedded systems. Amsterdam, Elsevier/Newnes Application of the feed forward Control Loop The feed forward control loop is attributed to the use of a command from an external source, which sends a signal to an internal system. In the case of the oil and gas industry process, the feed forward control process is used to facilitate communication from the monitoring room to the production facility or tanks, which are located very far away in areas, which are either inaccessible or vulnerable to security issues. This technique is integrated with the concept of the DCS (distributed control system) [2]. This concept is attributed to the necessity of gathering data in real time, particularly on high bandwidth. The concept extends to the use of pneumatic control systems, which are far beyond a small cell area of a refinery. This concept enables automated information feeding as input and gives direction on the oil refinery process to the end. Combined feed forward feed backward control This loop represents the combination of the feedback and feed forward control loops. This implies that the combined approach will have both the features of feedback and feed forward. In essence, the combined loop functions on the theory of data from the outside or outlet of a process that is being fed in return to the input of the same process aimed at a corrective action and also on the principle of the open loop system as its forward pathway [2]. The principle of open loop system enhances an action to be taken to make correction to any deviation that may arise during the process progression. Consider the following illustration of the loop in a tank activity. Figure 8: Signal Block Diagram Source: DORF, R. C., & BISHOP, R. H. (2001). Modern control systems. Upper Saddle River, NJ, Prentice Hall Application of the combined feed forward and feedback control loop This approach uses both the applications that are attributed to the feed forward and feedback control loops. On essence, this approach applies the concept of the DCS (distributed control system) to gather data in real time and by extension; the concept uses pneumatic control systems, which are far beyond a small cell area of a refinery [1]. This technique is used to feed a continuously stirred tank reactor which functions under a reactor temperature control as illustrated in the following figure. Reactor Tank Operator The process is as illustrated in the figure below. The Combined feed forward and feedback is used in inletting and out letting the requisite raw materials under particular temperatures. The technique is applied in regulating the temperatures relative to the process. Figure 9: Reactor Tank Operator Source: DORF, R. C., & BISHOP, R. H. (2001). Modern control systems. Upper Saddle River, NJ, Prentice Hall Where FFC-Feed forward Controller, FT-Flow Transmitter, TC-Temperature Controller, Temperature Transmitter In addition, the approach uses wiring sensor network (WSN) instead of the traditional cabling to revolutionize the machine interconnection to a platform of closed loop control performance. Heat Exchanger The combined feed forward feedback compensators are applied in controlling temperature relative to a chemical reactor. This happens through a heat exchanger. The chemical reactor is referred as a stirring tank. In this process the tank liquid need to be sustained at a constant temperature. This is done by adjusting the quantity of steam that is supplied to the heat exchanger. This happens through the control valve. The primary source of disturbance in this case is attributed to the variations relative to the inlet flow. Consider the following illustration which indicates this process. Figure 10: Heat Exchanger Process Source: http://in.mathworks.com/help/control/examples/temperature-control-in-a-heat-exchanger.html Conclusion The aspect of control loop systems has revolutionized with time and today most process are automated and well connected with the modern technology such as the wiring sensor network (WSN), which has increased performance, efficiency, and safety. In addition, these methods have helped in reducing costs of operation. List of Reference BROWN, G. S., & CAMPBELL, D. P. (1998). Principles of servomechanisms; dynamics and synthesis of closed-loop control systems. New York, J. Wiley. DORF, R. C., & BISHOP, R. H. (2001). Modern control systems. Upper Saddle River, NJ, Prentice Hall. GANSSLE, J. G., & BALL, S. R. (2008). Embedded systems. Amsterdam, Elsevier/Newnes. http://site.ebrary.com/id/10378878. MCMILLAN, G. K. (1993). Tuning and control loop performance. Research Triangle Park, N.C., Instrument Society of America PHELAN, R. M. (1997). Automatic control systems. Ithaca, N.Y., Cornell University Press. Read More