Nalawade Reshma S.
Electronic and Telecommunication
Now a day’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.
Keywords: Pilot Plant, Boiler, Heat exchanger, Programming logic controller.
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.10
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.9
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.
Fig.1 Block diagram of Boiler and Heat
Exchanger pilot plant
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.
generated Flows towards the heat exchanger through an equal percentage globe
valve which controls the steam flow.
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.
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
shows the working Automation of Boiler and heat Exchanger pilot plant in the
department of Instrumentation & Control College of Engineering Pune.
Fig: 2 Working
of Boiler and Heat Exchanger pilot Plant
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.
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
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
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
in different modes of controlling
Fig.4 Topology of communication
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
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.
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.