Control of Boiler Operation using PLC – SCADA full report
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Over the years the demand for high quality, greater efficiency and automated machines has increased in the industrial sector of power plants. Power plants require continuous monitoring and inspection at frequent intervals. There are possibilities of errors at measuring and various stages involved with human workers and also the lack of few features of microcontrollers. Thus this paper takes a sincere attempt to explain the advantages the companies will face by implementing automation into them.
The boiler control which is the most important part of any power plant, and its automation is the precise effort of this paper.
In order to automate a power plant and minimize human intervention, there is a need to develop a SCADA (Supervisory Control and Data Acquisition) system that monitors the plant and helps reduce the errors caused by humans. While the SCADA is used to monitor the system, PLC (Programmable Logic Controller) is also used for the internal storage of instruction for the implementing function such as logic, sequencing, timing, counting and arithmetic to control through digital or analog input/ out put modules various types of machines processes.
Systems are used to monitor and control a plant or equipment in industries such as oil and gas refining, water and waste control and transportation.
II. DRAWBACK OF CONVENTIONAL SYSTEM
Errors due to the involvement of humans in the data collection and processing using complicated mathematical expressions.
In the coding process of this implementation with micro-controller, it requires a fast and efficient processing which on the other part depends on the length and sub-routines of the coding process.
III. CRITICAL CONTROL PARAMETERS IN BOILER
A. Level Control
Steam Drum level, De-aerator level and hot well level
B. Pressure Control
Force draft pressure, Induced draft pressure, Steam drum pressure, De-aerator pressure, Turbine inlet steam pressure, balanced draft pressure
C. Flow Control
Air flow, Steam flow, Water flow
D. Temperature Control
Steam drum temperature, Underbed boiler temperature, Turbine inlet steam temperature, Flue gas temperature.
In this, the Control and Automation are done by
• Human Errors subsequently affect quality of end
• Hard Wired Logic Control
• Bulky and complex wiring,
Electronics Control with Logic Gates
In this, Contactor and Relays together with timers
and counters were replaced with logic gates and
electronic timers in the control circuits.
• Reduced space requirements, energy saving, less
maintenance and hence greater reliability.
The Major Drawbacks
• Implementation of changes in the control logic as
well as reducing the project lead- time was not
Programmable Logic Controller
In this, instead of achieving desired control and
automation through physical wiring of control
devices, it is achieving through program say software.
Reduced Space, Energy saving, Easy trouble shooting, Error diagnostics programmer, Economical, Greater life and reliability,
At the beginning of each cycle the CPU brings in all the field input signals from the input signals from the module and store into internal memory as process of input signal. This internal memory of CPU is called as process input image (PII). User program (Application) will be available in CPU program memory. Once PII is read, CPU pointer moves in ladder program from left to right and from top to bottom. CPU takes status of input from PII and processes all the rungs in the user program. The result of user program scan is stored in the internal memory of CPU. This internal memory is called process output image or PIQ. At the end of the program run i.e., at the end of scanning cycle, the CPU transfers the signal states in the process image output to the output module and further to the field control.
I/O driver (SCADA) picks up PII and PIQ and transfers the image to database and this image is called driver image. This driver image available in SCADA database is used for graphical view of process monitoring from operator station (OS) in the central control room.
SCADA stands for Supervisory Control and Data Acquisition. As the name indicates, it is not a full control system, but rather focuses on the supervisory level .
What is SCADA? It is used to monitor and control plant or equipment. The control may be automatic or initiated by operator commands. The data acquisition is accomplished firstly by the RTU’s(Remote telemetry or terminal units) scanning the field inputs connected to the RTU (it may be also called a PLC – programmable logic controller.). This is usually at a fast rate. The central host will scan the PTU’s (usually at a slower rate). The data is processed to detect alarm conditions, and if an alarm is present, it will be displayed on special alarm lists.