A-82 Air Filtration; Air Inlet Filtration for Gas Turbines
FIG. A-74 Filter with water eliminator. (Source: Altair Filters International Limited.)
FIG. A-75 Pressure loss versus volume flow rate filter characteristic. (Source: Altair Filters
International Limited.)
semirigid construction, together with the fact that each pocket is divided into
smaller segments by means of a semipermeable “shelving” system, ensures the best
possible profile throughout all operating conditions. This produces an extremely
uniform flow distribution, leading to improved dust-holding capacity and
eliminating the likelihood of localized dust breakthrough.
Air Pollution Control A-83
Dynamic water eliminator
This feature conducts water and salt removal. The vanes, which are constructed
from corrosion-resistant marine grade aluminum (other materials are available),
are produced with a profile that allows the maximum removal of salt and water,
yet produces an extremely low pressure loss. This optimal profile has been achieved
by the very latest design methods, and in particular by utilizing a Computational
Fluid Dynamics (CFD) flow modeling system. Hydra also incorporates a unique and
novel method of separating water droplets from the air stream, and this has led to
improvements in bulk water removal compared with conventional methods.
Reference and Additional Reading
1. Tatge, R. B., Gordon, C. R., and Conkey, R. S., “Gas Turbine Inlet Filtration in Marine Environments,”
ASME Report 80-GT-174.
Typical Specifications for Range of Air Filters
This range includes panels and bags as well as high-efficiency, high-velocity systems
and air/water separators.
Filter holding frames are constructed in mild or stainless steel, designed to
provide quick and easy removal from upstream, downstream, or sides of ducting,
without the use of springs or clips of any kind. Filter housings, ducting, louvres,
dampers, and silencers can also be designed and fabricated, providing a total system
capability.

are produced with a profile that allows the maximum removal of salt and water,
yet produces an extremely low pressure loss. This optimal profile has been achieved
by the very latest design methods, and in particular by utilizing a Computational
Fluid Dynamics (CFD) flow modeling system. Hydra also incorporates a unique and
novel method of separating water droplets from the air stream, and this has led to
improvements in bulk water removal compared with conventional methods.
Reference and Additional Reading
1. Tatge, R. B., Gordon, C. R., and Conkey, R. S., “Gas Turbine Inlet Filtration in Marine Environments,”
ASME Report 80-GT-174.
Typical Specifications for Range of Air Filters
This range includes panels and bags as well as high-efficiency, high-velocity systems
and air/water separators.
Filter holding frames are constructed in mild or stainless steel, designed to
provide quick and easy removal from upstream, downstream, or sides of ducting,
without the use of springs or clips of any kind. Filter housings, ducting, louvres,
dampers, and silencers can also be designed and fabricated, providing a total system
capability.
Air Pollution Control*
The main methods of combating and controlling air pollution include:
᭿
Electrostatic precipitators (for particulates)
᭿
Fabric filters (for dust and particulates)
᭿
Flue gas desulfurization (for SO
x
removal)
᭿
SCR DeNO
x

refinement. Several of the improvements have been implemented to minimize
energy consumption. Originally, it took about 1 MW of power to operate an ESP in
a large coal-fired power station. Pulsed energization is a means to cut energy
consumption substantially while simultaneously improving separation efficiency.
Two systems for this purpose have been developed: the Semipulse Concept (SPC)
with millisecond pulses, and the Multipulse Concept (MPC) with microsecond
pulses. (See Fig. A-78.)
Since their introduction in 1983, more than 3500 SPC and MPC units have been
supplied. SPC can be easily installed in existing plants, while MPC involves a
higher investment and is generally considered for retrofits and new plants.
The savings for high-resistivity dust can be substantial. Energy consumption
after installation of SPC or MPC is typically between 10 and 20% of the original.
At the same time, dust emissions are reduced to 25–50%.
Upgrading or retrofitting with pulsed energization is often the solution when a
utility wants to switch to low-sulfur coals, which often produce dust of higher
FIG. A-77 A typical electrostatic precipitator. (Source: Alstom.)
resistivity. It also gives a utility a wider choice of coals that can easily be valued in
money terms.
Semipulse and Multipulse offer an inexpensive route not only by improving
energy and separation efficiency, but also by requiring a minimum of supervision
and maintenance.
Fabric Filters
Fabric filters are used for cleaning large flows of flue gases from coal-fired power
plants and municipal waste incinerators. (See Fig. A-79.)
The fabric filter has gained a wide market, due to its versatility for a large
number of dust and process types and its ability to capture all particles, not only
those that can be charged electrically (as in ESPs). (See Fig. A-80.)
Another reason for the recent success of fabric filters is that they operate by
passing the dust-laden gas through a dust cake that is constantly being built up
with the support of the fabric. This enables the removal of a large portion of the

supports the filter element against the pressure caused by the gas flow. (See Fig.
A-83.)
Periodically, the dust cake is cleaned off by expanding the filter element with a
rapid pulse of air. The removed dust cake is transported by gravity toward the dust
hopper.
The effectiveness of the cleaning depends on the character of the pressure pulse.
Optipulse produces a forceful pulse by an optimized geometry of the pneumatic
system delivering the pulse (see Fig. A-84):
᭿
The pulse air is injected in the filter element, without dissipation of energy in a
large volume of flue gas, through injection nozzles optimally selected in relation
to filter element size.
᭿
The area of all nozzles on the header serving one row of filter elements is matched
to the area of a large, pilot-operated, fast-opening supply valve.
Flue Gas Desulfurization (FGD)
Today, flue gas desulfurization is a well-established method to fight global
environmental impairment such as acid rain. Most industrial countries have set
standards for SO
2
emissions and committed themselves to large reductions of
national emissions in international agreements.
There are several different types of FGD technologies for a wide range of
applications.
A-86 Air Pollution Control
FIG.
A-79 Fabric filter installation in a metallurgical plant, Höganäs, Sweden (left).
(Source: Alstom.)
FIG. A-80 Typical filter product range. (Source: Altair Filters International Limited.)
A-87

x
reduction, the catalyst is usually an active phase of vanadium pentoxide
and tungsten trioxide on a carrier of titanium. Other types of catalysts are
available, however.
The ideal catalytic reactor is made up of catalyst elements that are assembled in
modules usually 1 ¥ 1 ¥ 2 meters in size. A reactor normally has three to four layers
of catalyst modules.
Three positions of the reactor are possible in the treatment chain (see Fig.
A-92):
A-90 Air Pollution Control
The reactor in the W/D FGD plant
utilizes a spinning disk or a two-fluid
nozzle for atomization of lime slurry.
The reaction between absorbent and
acid gas components takes place
mainly in the wet phase. The process is
regulated in such a way that the
reaction product becomes dry and can
be collected in a conventional dust
collector.
FIG. A-86 Basic principles of wet/dry FGD installation. (Source: Alstom.)
In a wet FGD plant, line or
linestone slurry is sprayed
through nozzles into the gas flow.
The mixture of slurry and reaction
products is gathered at the bottom
of the absorber-tower and
recycled through the spray-
nozzles. An important element in
the wet FGD process is the mist

FIG. A-91 The reduction of nitrogen oxides with ammonia is achieved at a manageable temperature
by the use of a catalyst. (Source: Alstom.)
FIG. A-92 Flow diagrams for different DeNO
x
process systems. (Source: Alstom.)
A-93
A-94 Air Pollution Control
1. High dust system. The reactor is placed before the air preheater, and operates
directly in the dust-laden and acidic gas that leaves the boiler. This system
dominates the fossil fuel boiler market today. (See Fig. A-93.)
2. Low dust system. The reactor is placed after the hot electrostatic precipitator
but before the air preheater, which is possible, for example, in the case of
waste incineration or, in the case of a gas turbine, in the heat recovery
boiler.
3. Tail end system. The reactor is placed after particulate control and after sulfur
dioxide and/or hydrochloric acid removal in the flue gas cleaning train. This
allows for the use of a much more compact catalyst reactor. The tail end solution
is used when the particulates or gases are harmful to the catalyst. (See Fig.
A-94.)
SCR reactor design
Although design and operation of an SCR reactor is fairly straightforward and
simple, there are a few issues that require special attention. One such issue is gas
distribution at the inlet of the reactor. In the case of high dust it is of the utmost
importance that the gas is properly distributed to avoid catalyst erosion problems.
The reactor is equipped with guide vanes and distributor plates to ensure even gas
distribution under all operating conditions. (See Fig. A-95.)
Another important issue is ammonia slip, which must be kept to a minimum for
several reasons.
If the gas still contains sulfuric gases, i.e., in the high dust case, ammonia slip
will react with sulfur trioxide to form ammonia bisulfate when cooled in the air

temperatures for various applications.
Absorbers for Environmental Toxins
The dioxin and heavy metal problem
This refers to the entrapment of dioxins in dry scrubbers. The experiments in this
field were first conducted in gas cleaning systems for waste-to-energy plants, where
dioxin emissions are a major problem. The emission control system described
combines the dual effect of chemically enhanced adsorption/absorption and
filtration.
The fabric filter is also very effective for controlling heavy metals, due to its
capacity for filtering submicron particles. The combination of dioxin and heavy
metal abatement has been especially important for the environmental acceptance
of waste-to-energy plants. This manufacturer has developed the TCR (Total
Cleaning and Recycling) concept for complete control of flue gases from waste-to-
energy installations.
More than 50 Filsorption plants have been installed in Europe and the United
States. These plants repeatedly measure dioxin emissions below 0.1 ng/Nm
3
. (See
Fig. A-96.)
The latest development is the Filsorption
®
II system, which introduces a mixture
of lime and coke in a safe blend to enhance abatement of organic emissions,
primarily dioxins, heavy metals, and acidic gases.
Filtration and chemisorption (Filsorption
®
II)
Filsorption is short for filtration and chemisorption, indicating the dual duty of the
system. The Filsorption II system is primarily aimed at the control of organic
emissions such as dioxins. The system also offers control of mercury, acidic gases,

Ash-handling technology needs various types of solids handling, including bottom
ash submerged drag chain conveyors, wet impounded hoppers, economizer and
pyrites systems, and pneumatic fly ash handling.
A-98 Air Pollution Control
FIG. A-98 Stabilized gypsum from a wet FGD plant. The end product is suitable for landfill use.
(Source: Alstom.)
The DEPAC
®
system illustrated is a pneumatic conveying system based on dense
phase technology.
Cost-efficient methods are developed to utilize the solid waste products. A number
of commercial operations have already been established such as commercial grade
gypsum for wallboard manufacturing and high-strength fill materials.
FIG. A-97 Schematic for filtration and chemisorption unit (Filsorption II). (Source: Alstom.)
Air Pollution Control A-99
FIG.
A-99 Group of silos for short-term storage of reagents and reaction products from an FGD
plant. (Source: Alstom.)
FIG. A-100 The heart of the Fläkt DEPAC system is the dust transmitter, in which the product is
fluidized by means of compressed air. (Source: Alstom.)
Combining Unit Operations
Total turnkey solutions for emission problems combine the operations of various
units. The example illustrated is the TCR system. This system is designed to clean
flue gas from waste incineration and produce certain recyclable end products.
In a similar manner, units are combined to form complete flue gas treatment
trains in modern power plants.
Such treatment trains could combine DeNO
x
and wet FGD units in, for example,
a large coal-fired power plant with an ESP for full emission control of the flue gases.

in the previous section on air pollution control. Examples include food processing
and pharmaceuticals production. The detailed methodology needs to be worked out
with equipment vendors, but basically it involves:
FIG. A-102 Combined NO
x
and FGD units. (Source: Alstom.)
1. Filtration (the end process may require removal down to 0.1 mm; 1 to 5 mm is
common).
2. Electrostatic precipitation (can remove up to 90% plus of the particles in the air).
3. Air washing (can remove between 50 and 80% plus of the microorganisms in the air).
4. Ultraviolet irradiation. Different microorganisms have different sensitivities.
5. Heat and compression. Heat helps the sterilization process. Compression
produces work, which, in turn, produces heat that also can contribute to
sterilization.
A-102 Air Purification; Air Sterilization
FIG. A-103 Unit for separating submicron particles, heavy metals, and toxic hydrocarbons. (Source: Alstom.)
B
Balancing; Onspeed Balancing of a Rotor
Balancing generally refers to the balancing of a turbomachinery rotor. Balancing
can, in some cases, be done in the field. Maintenance staff can be trained, for
instance, to balance a pump in situ in the plant, if their readings with their
vibration analysis equipment confirm that this is what needs to be done. For more
critical items, such as process compressors, this process is best done in the overhaul
facility of the original equipment manufacturer (OEM). The exception to this would
be if the end user had his or her own balance equipment and had trained staff that
was capable of handling the rotor in question.
Most balancing of rotating machinery rotors or components of rotors (such as
turbine wheels and so forth) is done in a balancing machine at speeds in the
neighborhood of 1800 to 2000 r/min in atmospheric conditions. In certain rare
instances, balancing at these speeds does not remove the imbalance (that was

Rolling-contact bearings consist of four principal components: an outer race, an
inner race, rolling elements, and a separator, or spacer, for the rolling elements.
The inner ring is mounted on the shaft. The outer ring securely fits in a stationary
housing. The facing surfaces of the inner and outer rings are grooved to conform to
the rolling-element shape. The rolling elements (with separator) accurately space
the inner and outer races and thus enable smooth relative motion to occur (see Fig.
B-1).
Sliding-Contact Bearings
Sliding-contact bearings are classified into two general types: journal bearings and
thrust bearings. Journal bearings support radial loads imparted by the rotating
shaft and may also be required to arrest or eliminate hydraulic instabilities that
may be encountered in lightly loaded high-speed machinery. The thrust bearings
are used for loads parallel to the shaft and may be required to support the full
weight of the rotor in cases of vertical machinery.
Journal Bearings
The common types of journal bearings are:
᭿
Plain journal bearings
᭿
Three-lobe journal bearings
᭿
Tilting-pad journal bearings
B-2 Bearings
FIG. B-1 Nomenclature of a ball bearing. (Source: Demag Delaval.)