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Nowaday’s demand for power generation is increasing. Therefore control system requirements are also increasing. In this paper boiler is operated using many control strategies so that resultant operation will be practically implemented for industrial purpose. In this experiment the electrically heated boiler and pipe in pipe type heat exchanger is used. Electrically heated boilers make use of electric current running through a heating element to create heat, to boil water into high-temperature and high-pressure steam. To test better Controllability pipe in pipe type counter current heat exchanger. During first phase the installation, calibration and testing for all transmitters and actuators are completed. By making a system available to programming logic controllers, distributed control system as well as to simulation softwares phase. Multiple control ends are achieved. Pilot plants are controlled using user friendly frontends. In this different control strategies are used such as PLC,DCS, MATLAB as well as virtual PLC and DCS with local controllers without any compromise in safety.
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Automation is the use of machines, control systems and information technologies to optimize productivity in the production of goods and services. Beyond that possible with current human labor levels so as to realize economies of scale, and realize predictable quality levels. In the present world of rapid technological changes there is an urgent demand for the very best quality products . The automation and simulation of this project is being done with the help of PLC. Programmable logic controllers have been an integral part of factory automation as well as industrial process control. As we know power demands are increasing unit operations should be handled with good amount of efficiency and control to save energy and enhance production quality and quantity. Controllers like Programmable Logic Controllers, Distributed Control Systems and simulation tools and test control strategies are available to control pilot plants. We have comparative studies of different class of control strategies and different class of controllers. We are having two pilot plants boiler and heat exchanger. The boiler is an electrical boiler operated at 3.5bar pressure at 1350C temperature giving steam of 30kg=hr. This Steam is utilized in Heat Exchanger which is of pipe in pipe type and operated in counter current flow of fluids .Both pilot plants are well equipped with transmitters and actuators of industry grade. The boiler drum contains water which is electrically heated with a PWM controller and generates steam at 4 bar and 144C. The water for heating is pumped from a boiler feed water tank using a positive displacement pump.
The boiler drum made up contains water which is electrically heated with a PWM controller and generates steam at 4 bar and 144C. The water for heating is pumped from a boiler feed water tank using a positive displacement pump. The steam generated Flows towards the heat exchanger through an equal percentage globe valve which controls the steam flow. The heat exchanger being of tubular counter flow type, water to be heated is pumped from a cold water tank from the other end using a centrifugal pump. The condensate formed in the heat exchanger during heat transfer is collected in a separate condensate tank. The hot water is collected in hot water tank which also be either mixed in the cold water tank or can be added partially/fully to the feed to the boiler to change the feed water temperature.
Boiler and Heat exchanger
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A boiler is a closed vessel usually made of stainless steel in which water or other fluid is heated. Electric steam boilers use resistance- or immersion-type heating elements.
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact. There are two primary classifications of heat exchangers according to their flow arrangement. In parallel flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. In counter flow heat exchangers the fluids enter the exchanger from opposite ends.
Sensors and transmitters
The transducer measures a process variable while the transmitter transmits the data to the controller as a 4-20 mA current signal.
The final control element adjusts the amount of energy/mass that goes into or out from process as commanded by the controller.
Following are the final control elements used in the plant:
a. Positive displacement pump for feeding boiler feed water : The speed of the motor and in turn feed flow is changed using variable frequency drive.
b. Centrifugal pump for feeding cold water to heat exchanger: The speed of the motor and in turn feed flow is changed using variable frequency drive.
c. Equal percentage globe control valve for manipulating steam flow current signal from controller is converted to pneumatic signal using an I/P converter which decides the valve opening.
d. Solenoid valve which has 2 positions (open or close): Opening of the valve allows mixing of hot water with the cold water feed for heat exchanger as well as changing the boiler feed water temperature.
These components ensure process safety which generally refers to the prevention of unintentional releases of chemicals, energy, or other potentially dangerous materials (including steam) during the course of process that can have a serious effect to the plant and environment. Process safety involves, for example, the prevention of leaks, spills, equipment malfunction, over-pressures, over-temperatures, corrosion, metal fatigue and other similar conditions.
Following instruments are included to keep process variables under safe limit as well as provide alarms interlocks to automatically take necessary action:
a. Pressure switch and temperature switch : Shuts o_ the boiler if drum pressure/temperature exceeds 4 bar/144 deg C .
b. Low level switches: For the boiler drum this switch, shuts off the heater if there is no water in the drum. For other tanks these switches are used to avoid dry running of pumps if there is nothing to pump in the tanks.
c. High level switches provided to the cold water and hot water tanks to avoid overflow of liquid.
Variable tag and input output range of devices with unit
Above figure shows how networking is done so that user can have multiple options to control. Local PLC provide two serial ports (one with RS232 and other RS232/485) and Ethernet port utilizing MODBUS and Ethernet IP protocols. As shown in Fig.4 we communicate PC where MATLAB and server for VPLC and VDCS resides with MODBUS RTU with RS232 serial protocol.DCS is communicated through MODBUS RTU with RS485 as make of local PLC and DCS are different and we aim to have daisy chaining for other pilot plants. As contrologix PLC is connected with Ethernet IP protocol and communicated through messaging.
To provide a solution, ideas are tested and verified on pilot plants as they represent a down scaled version of industrial process plants. According to this practice, pilot plants are experimented for various control strategies and a solution is given to professional world in order to implement that specific strategy to industry grade process plants. One step ahead of this, we make pilot plants available to control from variety of controllers like Programmable Logic Controllers, Distributed Control Systems and simulation tools and test control strategies. We can have comparative studies not only in class of control strategies but also in class of different controllers. Acknowledgment I am very thankful of Prof. S. D. Agashe for his ideas and guidance. Without his motivation and guidance this work would have been impossible. He always answered my questions and helped me out when I was stuck with a problem.
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