Oil and Gas Process - Distributed Control System( DCS)

Dear friends, welcome to Infos, welcome to another video from oil and gas training. In this video, we are discussing about a new subject. In fact, it is not a new subject, it is a part of a control system, distributed control system. You may be remember my instrumentation module, control valve module, normal valve module. So, we have already studied various instruments using in the field and the signal, how the signal, the communication between the control room operator and the field instruments, how the control system is working. Some information we have already studied in our previous various videos. In this video, we are discussing about the total control system using, how to control efficiently and effectively in a process control, in a process plant. Welcome to this video, distribution, distributed control system or DCS. A distributed control system, DCS is a digital automated industrial control system that uses geographically distributed control loops throughout the factory. You can see here, the first in the bottom layer the field instruments, in the middle layer there is PLCs and other control panels are there in near the field, it is normally called LER, local equipment room and in the third layer, in the top side, we have graphical user interface and or HMI, human machine interface is there, that is the control room. So, we will discuss in three, the constructional details and features and what are the different type of DCS, how it is working, etcetera, etcetera, we will study in this video. So, that DCS is a digital automated control system that uses geographically distributed control loops throughout a factory or machine or control area. The goal of a DCS is to control industrial process, industrial processes to increase their safety, cost effectiveness and reliability, this is very important for DCS. Before DCS, earlier manual control system was there, when the science and technology is improving and the various new systems, control system, how to control the process plant, minimize the risk, hazards condition and effectively increase the effectiveness of the plant. So, that is why a DCS or electronic type control system or more important process instrumentation systems came to the plant and it is using for the increase their safety, cost effectiveness and reliability. A control system is a set of mechanical or electronic devices that regulate other devices or systems through the use of control loop. So, control loop already we have discussed that one in our previous instrumentation video. Control loops are systems composed of all the hardware and software control functions needed for measurements and adjustments of individual process. Control systems are a central part of a industrial process automation system, it is clear that. The DCS is a system of sensors, controllers and associated computers that are distributed throughout the plant. So, sensors and field instruments in the bottom layer you can see, various field instruments like switches are there, control valve is there, sensors are there, transmitters are there, shutdown valves are there, various other instruments are there. So, controllers means mainly programmable logical control or PLCs are there and like communication bus bar is there, communication link is there and the controllers itself have some computers are there, etcetera, etcetera. So, many instruments and the control system software, etcetera are included in DCS. Each of these elements serves a unique purpose of such data acquisition, data collection and acquisition you can say better, process control as well as data storage and graphical display. So, main area of serve purpose is data acquisition, process control as well as data storage and graphical display. These individual elements communicate with a centralized computer through the plants local area network often referred as a control network, we can say a total control network. As the central brain of the plant, the DCS makes automated decisions based on the production trends, it sees them in a real time throughout the plant. So, it can take some automatic decision based on the set point or predefined set point or predefined logic, it can take some automatic action without interference or intervene or without the involvement of operator. As an example, the DCS at a power plant might automatically increase steam generation capacity of multiple turbine in order to keep up with changing demand for electricity during hot summer days and then decrease it as it as outdoor temperature cool overnight and demand decrease. Simple example, when the DCS system is increasing the temperature or production capacity or production in the steam turbine when the summer time and the winter time it is reducing or decreasing. So, these are simple example how DCS is automatically taking some decision, it is not actually automatically taking decision, it is a predefined values and set points are there. So, according to that one it is action is taking place, whereas a PLC could adjust a single unit operation, the DCS can make adjustment of each of a plant may interact in unit operation. So, PLC we will discuss in detail, PLC is also part of DCS, so that we will discuss, but PLC has some difference, do not compare PLC is not equal to DCS, but PLC and DCS together joining in a family for a control system, so we will discuss PLC in a separate session. DCS are used across the process plant industries to supervise complex production processes, they are more widely deployed at large continuous manufacturing plant such as those in the oil and gas industry, it is very clear. With the help of a DCS, these and other manufacturers can efficiently coordinate adjustments in a top down fashion using a centralized network of computers and the other control system. Instructions from the DCS are deployed throughout the plant and fed into individual controllers, clear. So, from the control room, the instruction going to controllers and controllers to the field and reverse also from the field to control, local control room, then to CCR, central control room. When configured appropriately, the DCS can improve safety while also enhancing production efficiency. These two points are very important, improve safety or minimize the risk and hazards and enhancing production efficiency. How does a DCS distributor control system work? DCS are made up of control elements distributed throughout a plant or factory. These control elements include computers, sensors and controllers, we already discussed. Each element serves a specific purpose such as data collection, data storage and process control. This is very important. Having the control system architecture distributed around the factory or plant that provides an effective control, efficiency and process quality strategy. This is also important, process quality strategy. Additionally, if a piece of DCS architecture fails, the plant can continue to operate. It is very, very important in case due to power failure or any other abnormal issues. In case DCS failure, a plant can continue to operate for a certain time, we can continue to operate without any further abnormal issue. That is also one advantage. For this reason, DCS are commonly found in industrial field and processing or manufacturing plant. A DCS is functionally similar to supervisory control and data acquisition SCADA. This also we have to discuss, we will discuss in detail in the coming videos. So, it is a SCADA also using for another control system for industrial control applications. You can look at to the picture in SCADA. Some more information. DCS is not equal to SCADA. SCADA and DCS are different, almost similar, but if they have difference, large difference is there in SCADA system and DCS system. SCADA systems are used in power plant, oil and gas operation, refining, telecommunication, transportation and water and waste water. All where DCS is using, SCADA can also use, but there is some difference is there. This is the one of the important and prime difference. They tended to be used in situations where the control center has more remote location. The location oil and gas, example a oil and gas production field is taking lot of remote locations are there and data coming from different remote location. In a refinery you are taking, a gas treatment plant you are taking, it is a only one plant or two plant or three plant you can configure or connect, interconnect that one. In that case DCS is best, but kilometers a plant, remote plant is scattered or distributed or it is remote, remotely located means then may be SCADA will be more suitable. You can see here the instrumentation input is coming from the field to remote terminal unit. Instead of local equipment room we call it as a remote terminal unit, it is same as a local equipment room, but it is each remote location we need a separate local equipment room, but to call as remote terminal unit. And from there and the communication to the HMI, human machine interface that is SCADA operator terminal, radio and the cellular telemetry technology is using for communication between LER and our RTU between and SCADA or between the field. So, some major difference is there in SCADA operation than DCS, so DCS is not similar to SCADA that is important one, we will concentrate DCS on in this video and SCADA and TLC we will concentrate or we will definitely we will make a another video. SCADA has some more information to provide as a overview, ask a SCADA system is a combination of hardware and software that enables the automation of industrial processes by capturing operational technology real time data, so SCADA we can define in this way. SCADA connect the sensors that monitor equipments like motors, pump and valves to an on site or a remote server and some overview is also included in this one to clear that one before going to DCS, PLC and SCADA. The primary difference between a PLC and SCADA is the technology for example, a PLC is a physical hardware where SCADA is a software, this is the very, very important information. PLC is a physical hardware whereas, SCADA is a software, this means that a PLC can picked up and physically inspected whereas, the SCADA works on a computer system and is comparable to that of an operating system like windows for example, so SCADA is a software. Software which connected to the PLC, so without PLC SCADA cannot work, so PLC is also included in the SCADA system in RTU, PLC is installed in the RTU or in the field itself also some more sometime PLC can installed, so PLC information coming to SCADA. How a DCS is structured, so this is our core information on this video, a distributor control system includes both software and the hardware element, see here both software PLC and software also included in DCS, this installation of most controllers locally keeps cost low. On-site automated control improves the reliability of this system and human oversight is enabled for central control functions and remote control options, so this is the and human oversight is enabled for central control function and remote control options. Individual processors have their own controllers with separate central processing unit CPU to, so other processor can continue if individual system fails that also possible, it is a separate different control systems are there in the each processor, so one fail also we can run or the other system will continue to work. The architectural design of a DCS system, number one an engineering workstation, this is a supervisory controller for the DCS as a whole, the whole the station typically includes configuration tools that let the user complete functions such as creating new loops and input and output point, IO point as well as configuring distributed device, around this area is called engineering station, this LER is called engineering station, some part may be in the CCR also included but core area is in the this area LER, local equipment room. An operating station mainly in the top area, human machine enterprise HMI, this station is used for operation, monitoring and control that is a operating station, where the panel operator is sitting, commonly called central control room or central control facility. A process control unit, this microprocessor based controller is designed for automatic and compound loop control, this is also part of LER. A communication system that is the data transfer, this system brings data from station to station and is important in distributor control system, typical network protocol used like Ethernet or PROFIBUS and device net using the communication. In a DCS architecture, sensors gather process information which is sent to a nearby IO module, IO module is located in LER, local equipment room. The data is moved to a process control unit as well, smart devices, some field replacer or digital smart devices, if used can also send the data to a process control unit directly. The data is then further processed and analyzed to produce an output result, the processed output is based on control logic used, predefined set point, predefined logical value which is the part of a program that control program operation, that I send it to a moving actuator to the control valve or actuator or motor to start or stop or etcetera, using another bus and then the commissioning process occurs. This is where instrument and control systems are verified and documented and where the control logic and implementations are transferred to an engineering station for the operator to be. So, operator we can view here and command here, edit here something, he can monitor and control, the operator send the control action to operator station. These devices in this process can be divided into the following five levels, various level of operation we can summarize, level 0 consist fielded devices like sensors, transmitters and other control element in this area, the field area. Level 1 is the I O module and processors in this area, level 2 is the supervisory computers that collect data from processor node that also part of LER, level 3 focuses on the production control level, monitor production here and level 4 is includes production scheduling part of the CCR and pre-programmed planning and scheduling operation. What are the challenges, advantages and challenges of a DCS? Distributor control system provide following benefit, number 1 complex structures, so different type of complex structures they can manage, unlike comparable programmable logical control PLCs, a DCS can assess large amount of information in a complex environment, this is very important. System redundancy, if a processor fail, the redundancy provided in the DCS ensures that only one section of the planned processes is interrupted, so other system will be normal and it will continue until the issue solved. Scalability, more controller processing can be added whenever needed, this is very important, adding more I O modules to a controller also extend I O's, input output devices, so that scalability is there in DCS system. Security also very important, security and cyber security capabilities are enabled at the higher engineer level and operator level. Some downside of the technology includes situation where failure of the one controller acts more than one. DCS versus PLC, some overviews, I have added some overviews on both, PLCs are another type of industrial control technology, they are small modular computers with customized instruction for performing a particular task, that is very important, they are small modular computers and customized instruction for performing a particular task, like a DCS, PLCs are using in ICS industrial control system for a variety of industry. A PLC controls individual devices, while a DCS can control multiple machines or process in a plant and while PLCs are designed to replace mechanical devices like mechanical device, DCS are able to control entire factories and process plant with many interconnection system. So, this is a, the picture is provided here is a typical PLC system, input is there and control system, control unit is there, CPU you can get and output device is there and you can interconnect with using a computer, HMI device is also there. DCS installation system somewhat information is also available for review on your study in a central whole DCS system, how it is structured using a pictorial representation. Number one is field you can see in this bottom area and somewhat in the, this area also in the field devices, transmitters, control valve, switches, marshalling boxes are installed in the plant or field you can say to measure each type of process variable such as pressure, level, temperature and flow and a dedicated transmitter is installed, many transmitters are installed in the field. These transmitters, transmitters are installed on the pipeline, vessel or rotating equipment and LER is the field information is gathering in the LER and some decision making process is taking place in LER as well and communication is sending to operator station as well also. So, LER is very important, LER is local equipment room, LER is situated in the plant in a safe area mainly DCS in LER contains. So, DCS is also involved in LER as well, the following marshalling cabinet intrinsically safe and non intrinsically safe, IS barrier, IS barrier cabinet from transmitter inputs and outputs. So, IO module, input output modules to control valves both are there, input module and output module. Input module is coming from the field, output module is going to the field. DCS cabinet analog input output, digital and digital input output card, multifunction process card may more card. Optical fiber cables that is a communication cable redundant, two pairs working together. CCR central control room, CCR is operated by the panel operator who is responsible for monitoring and vary the parameter and production and initiate shutdown as appropriate for the production and the safety of the plant. So, from this information you can see three categories, the three important parts are there in a DCS system, field instrument, LER instruments and the central control room facility. We will just to have a detailed look of this three information in more information available that is let us discuss that one field devices, transmitter sensors, transmitter sense the process variable then convert into a process into a meaningful output such as 4 to 20 milli amps when we are using a digital or electronic transmitter. Pneumatic transmitters are also there, but now a days most of the plant modern plants are using a digital or we can say electronic transmitter. So, it produces 4 to 20 milli amps equivalent to the field information. Such LER such signals pass through the marshalling box installed in the field to the marshalling cabinet installed in the LER. This information as information are very clear to control such a process variable dedicated control valves are installed in the plant. So, in the field there is another control valves are also there. The plant in the pipeline control valves receive 4 to 20 milli amp signal from the controllers installed in the LER through the marshalling cabinet then through the marshalling box installed in the field. So, control valves receive in the signal from the controller from LER through some other supporting devices are there like I2P is there, postioner is there, so load valve is many information are there, but in general we can say control valve receive 4 to 20 milli amp signal from controller. So, that is important controller is a electronic controller. Control valves are mostly being pneumatic signal this is important and electro pneumatic converter called I2P or transducer is installed in the field that convert 4 to 20 milli amps signal to 3 to 15 PSI to pneumatic signal to the control valve positioner. So, this information is already we have discussed in detail in our various instrumentation module. I request you to watch that module we will get a detail information here is a overview of how it is working switches such as pressure level temperature and flow switches are using for in alarms producing alarms and trip conditions are installed for the process and they provide the pre alarm and shut down at the set value as necessary. So, these are also in the field information a transmitter plus controller plus control valve provide a close the control loop this is very important whereas, the switches provide the safe guard this is the very very important a control loop is there and safe guard system is there to the plant in the event of a failure of the control loop. Now let us discuss on a local equipment room LER is situated in the plant in a safe area mainly DCS in LER contains flow following these are the LER contains item marshalling cabinet intrinsically safe and a non intrinsically safe IS barrier cabinet from transmitter input and output to control valve DCS cabinet analog input output detail input output card multifunction process card may many more card optical fiber cables redundant two pair working together the DCS in LER is the heart of the DCS system. So, DCS in LER is the heart of the whole DCS system a controller situated here calculate the error between the set point received from CCR against the field transmitter signal and output is send it to the field control valve to correct the error signal digital signals from the switches are verified against the predefined logic this also doing in LER. There is a redundant optical fiber network data highway we can call between the LER and CCR a high data speed signal is transmitted through the optical fiber cable communication and in unidirectional both way from LER to CCR and CCR to LER field information is continuously a sent to the CCR for display and the demand signal set point set the CCR is received on the control memory. So, both way it is communicating field information continuously sending to CCR and set point and other information receiving from the CCR to take a necessary action a fault diagnostic is continuously monitored in the DCS in the event of total power failure at CCR still DCS in the LER will continue to monitor and control the process in case a power failure in CCR DCS in LER will help to continue the plant until the power failure issue or any abnormal issue to be resolved. If the power supply in the LER is fail the UPS uninterrupted power supply would support the required power supply to LER DCS in case there is a total power failure remote chance to the DCS in LER then the plant will totally shut down and all the ESDV emergency shutdown valves will go to the fail safe condition either to open or close example or inlet ESDV to the separator would close all when the ESDV would open and rotating equipment pump and compressor will shut down. CCR is the one more facility included in DCS system let us see what are the information available what are the facilities is included in DCS CCR system. CCR is operated by panel operator who is responsible for monitoring and vary the parameters of production and the parameters of production initiate shut down as appropriate for the production and the safety of the plant. So, he can see the plant layout in the plant layout he can see the overview by equipment wise like separator, heat exchanger, stripper, pump etcetera see the alarm see an alarm and alarm summary in a day wise hour wise any override done on the PLC metrics panel any override for the maintenance work inspection work etcetera that also he can see in the CCF operator. Trend of a loop over a real time graph he can see many trend and graph moreover can read the following for every loop the operator who is sitting there he can read the following every loop what process parameter pressure level temperature level etcetera ESDV control valve open or close he can always monitor whether the position of control valve and ESDV shut start of the equipment pump compressor run stop he can do various rotating equipment alarms he can see pre and shut down alarms in the time to time receiving with the audible and visual. So, he can see the alarms and he can take a necessary action can change of a controller on the following he can do some changes as well on a controller the set point raise or lower to manipulate the process variable he can change the set point in some extent he can do that one take auto and manual take the controller to manual in case of a shut down and start up is taking place or any abnormality coming that one or any maintenance activity he can make to auto and manual option in a controller. Close open control valve manually he can do a control valve to open and close due to some maintenance or start up or shut down he can do that one can initiate start. So, he can do some activity from field activity from control room pump he can start or stop turbine he can start or stop or compressor he can start ultimately he can start any rotating equipment like id fan or blower fan motors or something he can do the rotating equipment start stop according to the situation can initiate shut down of the plant in emergency coming and he can initiate a shut down from the plant partially he can shut down unit by unit or full also he can do a panel operator he can print or he can take some reports for the general reporting purpose for the higher management or the seniors for the performance to view the performance of the plant alarms he can print parameters also he can print the various parameters controlling on the plant status he can print history he can print. Thanks for watching this video we have discussed a DCS system in detail and PLC and SCADA only overview hopefully we can add more videos on control systems and SCADA PLC and DCS system in our coming videos thanks for watching this video have a good day.