Final Control Element. FCE may be referred as actuator such as valve, gate, motor or relay. It enables an operator of a plant to achieve a desired process variable

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A final control element (FCE) is a mechanical device that changes a process physically which in response to the change the setpoint of the process control system. It is driven by a controller to carried out its control mechanism and are located in the process line. There are great differences between the FCEs where their accessories that cause each of them to have their own characteristics of function to adapt to a particular process dynamic. In designing a control system, two of the most essential characteristics that must be take into account are linearity and the speed of response. If a FCE is nonlinear, it will affect the stability of the system as the linearity of the process does.

FCE may be referred as actuator such as valve, gate, motor or relay. It enables an operator of a plant to achieve a desired process variable output by manipulated the setpoint of the process variable. In other words the valve must move to a certain position that represented by the value of controller. The faster and more accurate the valve follow the dictates the better the performance of the valve.

In past, FCE is functioned together with electric actuator and a squirrel-cage motor, which they are suffered from several operation limitations. The commonly used of pneumatic actuators suffer from overshot performance and high maintenance costs. The insufficient of technologies has cause poor control and process output variability to the process. Usually these situations gone unnoticed as they are not directly apparent. Therefore, in the selection of a FCE, the actuator should have the characteristics that enable valve to perform well in order for the control system to function as designed.

However, current technologies have focused on improve the performance of the process control. This can mean that FCE has been improved to more precise and consistent in their performance. in order to improve the performance of the process control, the major step is to improve the FCE performance, where the beck electric actuator provide the necessary control that many FCE, especially valve depends on.

The most common FCE in industrial control system is control valve which is used to control fluid flow in pipeline. In petrochemical industry, control valve has known on its well performance in adjust the flow of the fluid in the production process. Energy costs is the major operating expense in petrochemical plants, so, poor valve control can lead to low plant profits.

Therefore, valves such as gate valve with electric actuator and that with manual actuator, gate valve with pneumatic membrane actuator and pressure relief valve play an important role in ensure the optimum process conditions is achieved during the benzene distillation. Gate valve is most often used to cut off very thick liquid such as benzene using its sharp gates. The different operation of actuators on the valve will depends on the materials conditions that they faced in the pipeline. Meanwhile, pressure relief valve used in petrochemical industry, such as benzene distillation process to release stored gas in the equipment to maintain an optimal level of pressure in the equipment. As improper management of benzene may cause adverse effect to human health and environment because of its evaporates quickly when exposed to air.  



2.1        Final Control Element

Final control element (FCE) is a mechanical device that physically changes the operating condition of the process in response to a change the setpoint of the control system. It is driven by a controller and carried out the control mechanism produced by actuator. The FCE that commonly used in industry are valves. FCE is an important part in the process control system where it allows desired process output to achieved by manipulate the process variable towards the setpoint (Harold Becks & Sons, 2017). The valve must move to a position represent by the value of the controller output. However, many people mistakenly consider that valve is not really important in the performance of the control system.  The concept of thinking that the valve will not always move to the exact correct position required by the controller output as it may be varied by other physical factors in the practical condition. Actually, I (integral) in controller will always eliminate the error so that when the valve does not get to the right position, it will vary its output to match with the valve position (Michael Brown, 2001). FCE is usually being referred as output device of a control system as it carries out the action after receive instruction from controller. FCE regulate the process condition by using energy which usually from electricity, air pressure or hydraulic pressure. There are a great variety between the FCEs which differentiate by accessories and having their own characteristics to adapt to a particular process dynamic (Next A Schlumberger, 2002).

2.1.1        Gate Valve with Electric Actuator

Gate valve (also known as knife valve or slide valve) can be widely used in all type of applications and it available for both on ground and underground applications. Gate valve is designed to be fully closed and fully open performance. they are usually installed in pipelines as an isolating valve, rather than as control valve or regulating valve. Gate valve is linear motion valve which a flat element cuts into the flow stream to shut-off the process flow (Engineering 360, 2005). Gate valve can be applied effectively in cut off slurry. It also involves in viscous liquid such as light grease, honey and cream. However, gate valve is limited by low pressure application and low effectiveness when operated at process that requires cleanliness and sanitary conditions. It performs excellently as a shutoff valve anywhere needed. Gate valve also designed to reduce pressure drop across the valve in the fully opened position to allow fluid to flow completely. The direction of fluid flow does not change, diameter of fluid passes is the same as the that of pipe (Cameron,2011). In petrochemical industry, the main type of valves are API 600 (cast body carbon), API 603 (cast body stainless), AP 602 (forged body gate valve) and pressure seal gate valve. Knife gate valve is manufactured according to Technical Association of the Pulp and Paper Industry (TAPPI) standards (Lugano,2018).  

2.1.2        Gate Valve with Manual Actuator

Manually operated gate valve has long working lifespan, but it is robust. A manual actuator operates hand levers, gear actuators, chainwheel actuators handwheel pedestals, stem extensions or handwheels to move the stem of the valve. Manual actuator is operated by hand therefore depends on human power adjust it. It has simple design construction and using of corrosion resistant aluminium which die with optional heavy duty actuator to ensure positive operation and media control. Meanwhile, manual actuated valve is inexpensive, which typically self-contained and easy to operate. It does not require any other equipment such as electric motor to work with. However, there are also some limitation on the manual actuator in which it does not suitable to operate with large valve. This is because the large valve will require much larger human force to move the actuator which is impossible to operate by human. Other than that, manual operated valve also not available for the condition that need valve to be located in remote, toxic or hostile environment. However, the some of the operate automatically will have equipped with handwheel that allow manual operation. The automatic operating ability will be closed so that the valve is no longer obey the remote signals.

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2.1.3        Gate Valve with Pneumatic Membrane Actuator

Pneumatic gate valve, also known as air control valve operates by converting the energy from compressed air into mechanical motion. The motion can be either rotatory or linear, depending on the type of the actuator. There are some type of the pneumatic actuators such as tie rod cylinders, rotatory actuators, grippers, vacuum generators and others. It is one of an array component that used in control the pressure, rate and volume of air that move through he pneumatic system. There are various type of pneumatic valves can be found in the heart of ...

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