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This application note presents SEL logic devices, such as the SEL-2411 Programmable
Automation Controller (PAC), SEL-2440 Discrete Programmable Automation Controller
(DPAC), and SEL-3530 Real-Time Automation Controller (RTAC), as distributed control
solutions for one of the most fundamental sectors in the electrical generation industry—steam
The main objective of a steam control system is the safe and efficient transfer of energy from the
input fuel source into the output electric generator steam turbine.
In order to maximize the electrical generation process efficiency, the control system should
optimize the steam energy level before it is delivered to the next step in the conversion process.
After the energy from the steam is fully absorbed by the generator turbine, it can be returned to
the boiler in a fluid form to start the cycle again.
The system is a complex, multivariable, and interactive process. Parameters like the burner firing
rate, combustion air, feed water, steam temperature, and pressure must be closely monitored and
controlled. All variables can affect or be affected by each other.
The SEL solution uses control logic algorithms distributed into the SEL-2411 PAC and the
SEL-3530 RTAC. The SEL-3530 RTAC works as an interface with the SCADA (supervisory
control and data acquisition) system interacting with the SEL-2411 PAC for localized process
control and the SEL-2440 DPAC for interlocks and alarms
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Following configuration, the operation of the control system can be set to work as a boiler
follower. In this configuration, the main steam valve to the generator turbine can be directly
modulated by the SEL POWERMAX® power management and control system, based on the
electrical system power and frequency demands. The SEL-2411 PAC modulates the boiler
systems to maintain a constant steam pressure. Other configurations are possible by using
POWERMAX as a coordinated unit to modulate the boiler and steam valve in parallel.
The boiler combustion control is critical to guarantee an efficient use of fuel to produce the
required steam demand. This process must be executed safely to avoid any risks to personnel,
equipment, and the environment. A cross-limited combustion control implemented on the
SEL-2411 PAC modulates the air damper and fuel valves to obtain the correct mix for an efficient
combustion process,as shown in Figure 2.
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The thermodynamic cycle for the steam turbine is known as the Rankine cycle. This cycle is the basis for
conventional power generating stations and consists of a heat source (boiler) that converts water to high
pressure steam. In the steam cycle, water is first pumped to elevated pressure, which is medium to high
pressure,depending on the size of the unit and the temperature to which the steam is eventually heated. It
is then heated to the boiling temperature corresponding to the pressure, boiled (heated from liquid to
vapor), and then most frequently superheated (heated to a temperature above that of boiling). The
pressurized steam is expanded to lower pressure in a turbine, then exhausted either to a condenser at
vacuum conditions, or into an intermediate temperature steam distribution system that delivers the steam
to the industrial or commercial application. The condensate from the condenser or from the industrial
steam utilization system is returned to the feedwater pump for continuation of the cycle.
A schematic representation of a steam turbine power system is shown in Figure 4-1.
Figure 4-1. Boiler/Steam Turbine System
In the simple schematic shown, a fuel boiler produces steam which is expanded in the steam turbine to
produce power. When the system is designed for power generation only, such as in a large utility power
system, the steam is exhausted from the turbine at the lowest practical pressure, through the use of a
water-cooled condenser to extract the maximum amount of energy from the steam. In CHP plants or
district heating systems, the steam is exhausted from the steam turbine at a pressure high enough to be
used by the industrial process or the district heating system. In CHP configuration, there is no condenser
and the steam and condensate, after exiting the process, is returned to the boiler.
There are numerous options in the steam supply, pressure,temperature and extent, if any, for reheating
steam that has been partially expanded from high pressure. Steam systems vary from low pressure lines
used primarily for space heating and food preparation, to medium pressure and temperature used in
industrial processes and cogeneration, and to high pressure and temperature use in utility power
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generation. Generally, as the system gets larger the economics favor higher pressures and temperatures,
along with their associated heavier walled boiler tubes and more expensive alloys.
Steam turbines differ from reciprocating engines, internal combustion engines, and gas turbines in that the
fuel is burned in a piece of equipment, the boiler, which is separate from the power generation equipment.
The energy is transferred from the boiler to the steam turbine generator by an intermediate medium,
typically steam under pressure. As mentioned previously, this separation of functions enables steam
turbines to operate with an enormous variety of fuels. The topic of boiler fuels, their handling,
combustion and the cleanup of the effluents of such combustion is a separate and complex issue that is
addressed in the fuels and emissions sections of this report.
For sizes up to (approximately) 40 MW, horizontal industrial boilers are built. This enables them to be
shipped via rail car,with considerable cost savings and improved quality, as the cost and quality of
factory labor is usually both lower in cost and greater in quality than field labor. Large shop-assembled
boilers are typically capable of firing only gas or distillate oil, as there is inadequate residence time for
complete combustion of most solid and residual fuels in such designs. Large, field-erected industrial
boilers firing solid and residual fuels bear a resemblance to utility boilers except for the actual solid fuel
injection. Large boilers usually burn pulverized coal; however,intermediate and small boilers burning
coal or solid fuel employ various types of solids feeders.
In the steam turbine, the steam is expanded to a lower pressure providing shaft power to drive a generator
or run a mechanical process.
There are two distinct designs for steam turbines – impulse and reaction turbines. The difference between
these two designs is shown in Figure 4-2. On impulse turbines, the steam jets are directed at the turbine's
bucket shaped rotor blades where the pressure exerted by the jets causes the rotor to rotate and the
velocity of the steam to reduce as it imparts its kinetic energy to the blades. The next series of fixed
blades reverses the direction of the steam before it passes to the second row of moving blades. In
Reaction turbines, the rotor blades of the reaction turbine are shaped more like airfoils, arranged such that
the cross section of the chambers formed between the fixed blades diminishes from the inlet side towards
the exhaust side of the blades. The chambers between the rotor blades essentially form nozzles so that as
the steam progresses through the chambers its velocity increases while at the
same time its pressure decreases, just as in the nozzles formed by the fixed blades. The
competitive merits of these designs are the subject of business competition, as both designs have
been sold successfully for well over 75 years
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Follow a drop of water from the source through the treatment process.Watermay be treated differently in
different communities depending on the quality of the water which enters the plant. Groundwater is located
underground and typically requires less treatment than water from lakes, rivers, and streams.
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is treating water to make it suitable to be used. Providing drinking water is one of the main uses
of water treatment.
Many factories also need very clean water to make steam or to make high quality products. Some
of this water has to be made very pure with almost no other chemicals dissolved in it.
Treating sewage so that it does not cause harm to the environment is another use of water
pharmaceutical central utility plants
often generate chilled water and steam
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year round to handle both process and
HVAC loads. In addition, simultaneous
heating and cooling are often required to main
tain both humidity and space temperature set
points in Good Manufacturing Practices (GMP)
spaces driving utility demands higher. Power
requirements can be substantial. Typical plant
design includes both chillers and boilers running
year round to meet demand. A heat pump (heat
recovery chiller) may be installed to allow for re
covery of the waste heat off the chiller condenser
water to generate heating hot water for plant
heating in addition to generating useful Chilled
Water (CW). This will allow for the reduction of
loading on the chillers, steam boilers, cooling
tower fans, and cooling tower water makeup.
The installation of a heat pump was considered
and implemented as part of the original plant
design at the Novartis Flu Vaccine Facility in
Holly Springs, North Carolina
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Heat oil station
Thermal Oil Boilers
A thermal oil boiler fires through a helical coil and generates energy from the hot products of
combustion by heating the coil through radiation and convection. The coil heats thermal oil or
fluid that is pumped through the thermal oil boiler. The thermal oil heats coils in various types of
heat exchangers. Unlike a water or steam boiler, this heating process does not heavily pressurize
A thermal oil boiler is nearly always cheaper to operate and maintain than water boilers.
Unfortunately, due to the high pressure required to operate water and steam boilers, they can
become far more hazardous than thermal oil boilers.
Other noticeable advantages are the lack of corrosion, lime deposits and scale that are common
within heated water or steam boilers. This can raise the operating costs of a water boiler
considerably. You should also realize that thermal oil boilers don’t require makeup water or
efficiency draining steam traps.
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Thermal oil heaters can be delivered in horizontal execution (with low height), or in vertical
execution (occupying limited floor space). They are typically delivered complete, insulated and
equipped with burner, armatures, instrumentation, safeties and control panel - and with full
documentation including necessary certificates.
The heaters are made with winded-up coils made of seamless tubes. The thermal fluid is heated
during the flow through the tube coil. The heat is transferred to the fluid as radiant heat in the
combustion chamber, where the inner cylindrical tube coil and a flat tube coil forms the chamber
wall and the bottom respectively. Consequently refractory concrete can be avoided. The
combustion gasses are hereafter cooled in the outer convection part, as the gasses are led
between the space of the two tube coils and the outer boiler shell - in another two pass.
The thermal design with tube coils ensures a modest volume of the thermal fluid relative to the
size of the heater, and it also allows unlimited thermal expansion due to the high fluid
The heater and the thermal oil heating system should be designed and equipped according DIN
4754 and in EU the units will CE-marked accordingly. The pressure vessels parts are
consequently made according PED 97/23/CE.
The heaters are normally provided by international recognized and high quality burner brands -
for natural gas, light fuel oil, heavy fuel oil and combinations (dual fuel). Demands for special
burner designs can be meet and adapted in the heater design.
All thermal oil heaters must be carefully checked, controlled and function tested prior to dispatch
from the workshop and are delivered with a full set of documentation comprising drawings,
diagrams, data sheets, specifications, part list and instruction manuals.
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Considering all above, it is therefore strongly recommended that the chosen brand is from a
experienced and well reputated manufacturer. Do never compromise in quality, it can be both
fatal and expensive
Heat ventilation and air conditioning system
One of the most important decisions regarding a new
home is the type of heating and cooling system
to install. Equally critical is the heating and c
ooling contractor selected,
as the operating efficiency
of a system depends as much on proper installati
on as it does on the performance rating. Keys to
obtaining the design efficiency of
a system in the field include:
Sizing and selecting the system for the heati
ng, cooling, and dehumidification load of the
home being built
Correct design of the ductwork or piping
Proper installation and charging of the HVAC unit
Insulating and sealing al
l ductwork or piping
An HVAC designer will recommend different types of air conditioning systems for different
applications. The most commonly used.
The choice of which air conditioner system to use depends upon a number of factors including
how large the area is to be cooled, the total heat generated inside the enclosed area, etc. An
HVAC designer would consider all the related parameters and suggest the system most suitable
for your space.
Split Air Conditioner
The split air conditioner comprises of two parts: the outdoor unit and the indoor unit. The
outdoor unit, fitted outside the room, houses components like the compressor, condenser and
expansion valve. The indoor unit comprises the evaporator or cooling coil and the cooling fan.
For this unit you don’t have to make any slot in the wall of the room. Further, present day split
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units have aesthetic appeal and do not take up as much space as a window unit. A split air
conditioner can be used to cool one or two rooms.
Packaged Air Conditioner
An HVAC designer will suggest this type of air conditioner if you want to cool more than two
rooms or a larger space at your home or office. There are two possible arrangements with the
package unit. In the first one, all the components, namely the compressor, condenser (which can
be air cooled or water cooled), expansion valve and evaporator are housed in a single box. The
cooled air is thrown by the high capacity blower, and it flows through the ducts laid through
various rooms. In the second arrangement, the compressor and condenser are housed in one
casing. The compressed gas passes through individual units, comprised of the expansion valve
and cooling coil, located in various rooms.
Central Air Conditioning System
Central air conditioning is used for cooling big buildings, houses, offices, entire hotels, gyms,
movie theaters, factories etc. If the whole building is to be air conditioned, HVAC engineers find
that putting individual units in each of the rooms is very expensive making this a better option. A
central air conditioning system is comprised of a huge compressor that has the capacity to
produce hundreds of tons of air conditioning. Cooling big halls, malls, huge spaces, galleries etc
is usually only feasible with central conditioning units.
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The potato cannon uses the basic principle behind any reciprocating internal combustion
engine: If you put a tiny amount of high-energy fuel (like gasoline) in a small, enclosed space
and ignite it, an incredible amount of energy is released in the form of expanding gas. You can
use that energy to propel a potato 150 metres. In this case, the energy is translated into potato
motion. You can also use it for more interesting purposes. For example, if you can create a
cycle that allows you to set off explosions like this hundreds of times per minute, and if you can
harness that energy in a useful way, what you have is the core of a car engine! Almost all cars
currently use what is called a four-stroke combustion cycle to convert petroleum into motion.
The four-stroke approach is also known as the Otto cycle, in honour of Nikolaus Otto, who
invented it in 1867. The four strokes are
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You can see in Figure 2 that a device called a piston replaces the potato in the potato cannon.
The piston is connected to the crankshaft by a connecting rod. As the crankshaft revolves, it has
the effect of "resetting the cannon." Here's what happens as the engine goes through its cycle:
• The piston starts at the top, the intake valve opens, and the piston moves down to let the
engine take in a cylinder-full of air and petroleum. This is the intake stroke. Only the tiniest drop
of petroleum needs to be mixed into the air for this to work;
• Then the piston moves back up to compress this fuel/air mixture. Compression makes the
explosion more powerful; and
• When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the
petroleum. The petroleum charge in the cylinder explodes, driving the piston down. Once the
piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder
to go out the tailpipe.
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Now the engine is ready for the next cycle, so it intakes another charge of air and gas. The
motion that comes out of an internal combustion engine is rotational, while the motion produced
by a potato cannon is linear (straight line). In an engine the linear motion of the pistons is
converted into rotational motion by the crankshaft. The rotational motion is nice because we
plan to turn (rotate) the car's wheels with it anyway
Basic Engine Parts
The core of the engine is the cylinder, with the piston moving up and down inside the cylinder.
The engine described above has one cylinder. That is typical of most lawn mowers, but most
cars have more than one cylinder (four, six and eight cylinders are common). In a multi-cylinder
engine, the cylinders usually are arranged in one of three ways: inline, V or flat (also known as
horizontally opposed or boxer), as shown in the following figures.
Inline - The cylinders are arranged in a line in a single bank.
The spark plug supplies the spark that ignites the air/fuel mixture so that combustion can occur.
The spark must happen at just the right moment for things to work properly.
The intake and exhaust valves open at the proper time to let in air and fuel and to let out
Note that both valves are closed during compression and combustion so that the combustion
chamber is sealed.
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A piston is a cylindrical piece of metal that moves up and down inside the cylinder.
Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of
the cylinder. The rings serve two purposes:
• They prevent the fuel/air mixture and exhaust in the combustion chamber from leaking into the
sump during compression and combustion.
• They keep oil in the sump from leaking into the combustion area, where it would be burned
• Most cars that "burn oil" and have to have a quart added every 1,500 kilometres are burning it
because the engine is old and the rings no longer seal things properly.
The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its
angle can change as the piston moves and the crankshaft rotates.
The crankshaft turns the piston's up and down motion into circular motion just like a crank on a
The sump surrounds the crankshaft. It contains some amount of oil, which collects in the bottom
of the sump (the oil pan).
So you go out one morning and your engine will turn over but it won't start... What could be
wrong? Now that you know how an engine works, you can understand the basic things that can
keep an engine from running. Three fundamental things can happen: a bad fuel mix, lack of
compression or lack of spark. Beyond that, thousands of minor things can create problems, but
these are the "big three." Based on the simple engine we have been discussing, here is a quick
rundown on how these problems affect your engine:
Bad fuel mix
A bad fuel mix can occur in several ways:
• You are out of gas, so the engine is getting air but no fuel.
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• The air intake might be clogged, so there is fuel but not enough air.
• The fuel system might be supplying too much or too little fuel to the mix, meaning that
combustion does not occur properly.
• There might be an impurity in the fuel (like water in your gas tank) that makes the fuel not
Lack of compression
• If the charge of air and fuel cannot be compressed properly, the combustion process will not
work like it should. Lack of compression might occur for these reasons:
• Your piston rings are worn (allowing air/fuel to leak past the piston during compression).
• The intake or exhaust valves are not sealing properly, again allowing a leak during
• There is a hole in the cylinder.
• The most common "hole" in a cylinder occurs where the top of the cylinder (holding the valves
and spark plug and also known as the cylinder head) attaches to the cylinder itself. Generally,
the cylinder and the cylinder head bolt together with a thin gasket pressed between them to
ensure a good seal. If the gasket breaks down, small holes develop between the cylinder and
the cylinder head, and these holes cause leaks.
Lack of spark
The spark might be nonexistent or weak for a number of reasons:
• If your spark plug or the wire leading to it is worn out, the spark will be weak;
• If the wire is cut or missing, or if the system that sends a spark down the wire is not working
properly, there will be no spark; and
• If the spark occurs either too early or too late in the cycle (i.e. if the ignition timing is off), the
fuel will not ignite at the right time, and this can cause all sorts of problem.
Many other things can go wrong. For example:
• If the battery is dead, you cannot turn over the engine to start it;
• If the bearings that allow the crankshaft to turn freely are worn out, the crankshaft cannot turn
so the engine cannot run;
• If the valves do not open and close at the right time or at all, air cannot get in and exhaust
cannot get out, so the engine cannot run;
• If someone sticks a potato up your tailpipe, exhaust cannot exit the cylinder so the engine will
If you run out of oil, the piston cannot move up and down freely in the cylinder, and the engine
will seize; and
• In a properly running engine, all of these factors are within tolerance.
As you can see, an engine has a number of systems that help it do its job of converting fuel into
motion. We'll look at the different subsystems used in engines in the next few sections
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Engine Valve Trainand Ignition Systems
Most engine subsystems can be implemented using different technologies, and better
technologies can improve the performance of the engine. Let's look at all of the different
subsystems used in modern engines, beginning with the valve train. The valve train consists of
the valves and a mechanism that opens and closes them. The opening and closing system is
called a camshaft The camshaft has lobes on it that move the valves up and down.
Most modern engines have what are called overhead cams. This means that the camshaft is
located above the valves, as you see in Figure above. The cams on the shaft activate the valves
directly or through a very short linkage. Older engines used a camshaft located in the sump near
the crankshaft. Rods linked the cam below to valve lifters above the valves. This approach has
more moving parts and also causes more lag between the cam's activation of the valve and the
valve's subsequent motion. A timing belt or timing chain links the crankshaft to the camshaft so
that the valves are in sync with the pistons. The camshaft is geared to turn at one-half the rate of
the crankshaft. Many high-performance engines have four valves per cylinder (two for intake,
two for exhaust), and this arrangement requires two camshafts per bank of cylinders, hence the
phrase "dual overhead cams."
Thanks / mostafa Elmeshad