CONTROL OF BOILER OPERATION USING PLC-SCADA
ABSTRACT
The boiler is a fundamental part of almost all
industries. It varies in application from low pressure to high pressure. The
paper outlines the various stages of operation involved in the conversion of a
manually operated boiler towards a fully operated boiler. The initial phase of
the paper focuses on passing the inputs to the boiler at a required
temperature, so as to maintain a particular temperature in the boiler, and
shows the temperature/pressure relationship. To achieve desired steam pressure
(2Bar) at certain temperature, the Properties of Steam Table analysis is done.
A proper boiler design and modeling and safety precautions are taken into
consideration. Focusing on level, pressure, temperature parameters are
constantly monitored using SCADA screen which is connected to the PLC.
Keywords: Automation, PLC-SCADA, Boiler.
INTRODUCTION
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/output
modules various types of machines processes. Systems are used to monitor and
control a plant or equipment in industries such as telecommunications, water
and waste control, energy, oil and gas refining and transportation.
DRAWBACK OF CONVENTIONAL SYSTEM
Conventional equipment systems are prone to errors due to
the involvement of humans in the data collection and processing using
complicated mathematical expressions. Thus what we require is a system that
collects raw data, processes it and presents it in values which can be verified
and compared with the standard values.
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. Thus
it provides a real challenge with systems involving
TYPE OF BOILER
Electric boilers are noted for being clean, quiet, and
easy to install, and compact. Because there are no combustion considerations,
an electric boiler has minimal complexity (no fuels or fuel handling equipment)
with easily replaceable heating elements.
An electric boiler may be the perfect alternative to
supply low or high pressure steam or hot water where the customer is restricted
by emission regulations. In areas where the cost of electric power is minimal,
the electric boiler could be the best choice. Electric Boiler shows some good
signs such as-High efficiency, low maintenance, space factor, fuel limitations.
CRITICAL CONTROL PARAMETERS IN BOILER
Level Control:
Steam Drum level, High and Low
Level Pressure Control:
Steam drum pressure, Inner drum pressure
Flow Control:
Steam flow, Water flow
Temperature Control:
Steam drum temperature, under bed boiler temperature.
ALLEN BRADLEY PLC
Programmable Logic Controller or PLC is an intelligent
system of modules, which was introduced in the control, & instrumentation
industry for replacing relay based logic. Over a period of time, better I/O
handling capabilities and more programming elements have been added along with
improvement in communication.
A. PLC Working
Basics of a PLC function are continual
scanning of a program. The scanning process involves three basic steps.
Step 1: Testing input status
First the PLC checks each of its input with intention to
see which one has status on or off. In other words it checks whether a switch
or a sensor etc., is activated or not. The information that the processor thus
obtains through this step is stored in memory in order to be used in the
following steps.
Step 2: Programming execution
Here a PLC executes a program instruction by instruction
based on the program and based on the status of the input has obtained in the
preceding step, and appropriate action is taken. The action might be activation
of certain outputs and the results can be put off and stored in memory to be
retrieved later in the following steps.
Step 3: Checking and Correction of output status
Finally, a PLC checks up output signals and adjust it has
needed. Changes are performed based on the input status that had been read
during the first step and based on the result of the program execution in step
two following execution of step three PLC returns a beginning of the cycle and
continually repeats these steps. Scanning time = Time for performing step 1+
Time for performing step 2+ Time for performing step 3.
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.
B. Interfacing
C. Input-Output Configuration for PLC
1) Input Configuration:
Feed Pump
RTD Transmitter
Level Switch
Pressure Transmitter
2) Output Configuration:
Solenoid Valve for water inlet
Solenoid Valve for Steam Outlet
Heater
SCADA
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 RTUs 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
PTUs (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.
Its function is to control process equipment at the
remote site, acquire data from the equipment, and transfer the data back to the
central SCADA system.
Proficy software enables you to configure a system environment
that provides: Supervisory control, batch processing, data acquisition,
continuous control, and statistical process control for industrial
applications.
FLOWCHART
BOILER OPERATION
Water plays a major part in the generation of steam. Feed
water pump is switched ON by using feed water pump switch. In this, water
should be maintained at least at 50%.For sensing water level we use Low Level
Switch and High Level Switch, and connected to the Allen Bradley PLC. When the
level is lesser than or greater than 50%, PLC controller senses the level
change and sends the appropriate control signal to the feed water valve 1.
Thus, in spite of any changes in disturbance variable, the water level can be
maintained at 50% by proper scaling of PLC controller.
The
heat quantities and temperature/pressure relationships need to be taken into consideration,
for this Properties of Saturated Steam table is referred. Heaters are then made
on (Each of 1500 w) and water stats heating. For sensing temperature we use RTD
Two Wire Transmitter and are connected to the PLC. To certain temperature the
heating is carried out, until saturated steam temperature is not 130deg the
heating is carried out. Steam Pressure is building up as the temperature in the
cylindrical tank is increasing. Temperature and Pressure are continuously
monitored through sensors and signals are fed into PLC, and controlling action
is taken as per desired objective. When desired temperature and pressure gets
achieved the steam outlet valve is made on and flow of steam is regulated
through that same valve and simultaneously heaters is made off. If in case
pressure exceeds the specified value then safety valve gets open to remove
excess pressure generated. While heating water, level of water is continuously
monitored because low water level can burst heater coils.
When water is heated at atmospheric pressure, its temperature rises until
it reaches 212F, the highest temperature at which water can exist at this
pressure. Additional heat does not raise the temperature, but converts the
water to steam. The heat absorbed by the water in raising its temperature to
boiling point is called sensible heat or heat of saturated liquid. The heat
required to convert water at boiling point to steam at the same temperature is
called latent heat. The unit of heat in common use is the Btu which is the amount
of heat required to raise the temperature of one pound of water 1F at
atmospheric pressure. If water is heated under pressure, however, the boiling
point is higher than 212F, so the sensible heat required is greater. The higher
the pressure, the higher the boiling temperature and the higher the heat
content. If pressure is reduced, a certain amount of sensible heat is released.
This excess heat will be absorbed in the form of latent heat, causing part of
the water to flash into steam.
RESULT
CONCLUSION
The most important aspect of any power plant is the boiler control. Several
techniques can be implemented to control the boiler in power plant. The method
that has to be used relies on varied objectives like superior quality,
increased efficiency, high profit and other such points depending upon the
purpose of the company that implies it. With the prime objective of catering to
these necessities and the needs of the industrial sector, significance has been
given here to automation.
ACKNOWLEDGEMENT
I am grateful to Prof. Dr. A. D. Rahulkar and I
acknowledge with gratitude to my supervisor Prof Dr. A. D. Rahulkar, Department
of Instrumentation Engineering, and all staff members for his innovative
thinking, continuous guidance, genius role and encouragement throughout the
whole project period.
REFERENCES
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[6] Gary Dunning, “Introduction to programmable logic
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