Process Engineering Equipment Handbook Episode 1 Part 3 pdf

Air Pollution Control A-83Dynamic water eliminator This feature conducts water and salt removal.. Air Pollution Control* The main methods of combating and controlling air pollution inclu

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 intosmaller segments by means of a semipermeable “shelving” system, ensures the bestpossible profile throughout all operating conditions This produces an extremelyuniform flow distribution, leading to improved dust-holding capacity andeliminating 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 constructedfrom 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 ComputationalFluid Dynamics (CFD) flow modeling system Hydra also incorporates a unique andnovel method of separating water droplets from the air stream, and this has led toimprovements 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 systemsand air/water separators

Filter holding frames are constructed in mild or stainless steel, designed toprovide 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 systemcapability

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 SOxremoval)

 SCR DeNOx(for NOxremoval)

 Absorbers (for environmental toxins)

 End-product–handling systems (for solid and liquid wastes)

 Combined unit systems (for some or all of the previous items)

FIG A-76 Efficiency versus pressure loss filter characteristic (Source: Altair Filters International Limited.)

* Source: Alstom Adapted with permission.

Air Pollution Control A-83

Dynamic water eliminator

This feature conducts water and salt removal The vanes, which are constructedfrom 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 ComputationalFluid Dynamics (CFD) flow modeling system Hydra also incorporates a unique andnovel method of separating water droplets from the air stream, and this has led toimprovements 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 systemsand air/water separators

Filter holding frames are constructed in mild or stainless steel, designed toprovide 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 systemcapability

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 SOxremoval)

 SCR DeNOx(for NOxremoval)

 Absorbers (for environmental toxins)

 End-product–handling systems (for solid and liquid wastes)

 Combined unit systems (for some or all of the previous items)

FIG A-76 Efficiency versus pressure loss filter characteristic (Source: Altair Filters International Limited.)

* Source: Alstom Adapted with permission.

A-84 Air Pollution Control

Electrostatic Precipitators

In combustion processes, the largest quantities of heavy metals and dioxins arefound in the fly ash, or can be contained there by technical means It is thereforeessential to increase even further the very high precipitation efficiencies that arealready being achieved There are two types of ESPs, wet and dry, for collecting particles (See Fig A-77.)

New and retrofit systems are used Retrofitting with new spiral electrodes, arapping system, and pulsed energization pay immediate dividends in the form ofimproved abatement efficiency and lower power consumption

Semipulse ® and Multipulse ® for enhanced separation and energy efficiency

The rather uncomplicated process of charging dust by means of a high-voltage DCsystem, which makes dust stick against collector plates, has undergone high-techrefinement Several of the improvements have been implemented to minimizeenergy 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 energyconsumption 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 microsecondpulses (See Fig A-78.)

Since their introduction in 1983, more than 3500 SPC and MPC units have beensupplied SPC can be easily installed in existing plants, while MPC involves ahigher investment and is generally considered for retrofits and new plants

The savings for high-resistivity dust can be substantial Energy consumptionafter 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 autility 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 inmoney terms.

Semipulse and Multipulse offer an inexpensive route not only by improvingenergy and separation efficiency, but also by requiring a minimum of supervisionand maintenance

Another reason for the recent success of fabric filters is that they operate bypassing the dust-laden gas through a dust cake that is constantly being built upwith the support of the fabric This enables the removal of a large portion of thefinest particles, a feature that is becoming increasingly important as more stringent emission controls are required (See Fig A-81.)

With the fine particles, several heavy metals can be trapped in the dust cake,together with sulfur dioxide, if lime is introduced in the flue gas

This manufacturer/information source supplies two different kinds of fabricfilters: the high-ratio and low-ratio type, denominated by the air-to-cloth ratio

A major difference between the two filter types is the cleaning system The high-ratio fabric filter is cleaned by the Optipulse®

cleaning system (see following text).

Air Pollution Control A-85

In the Semipulse system, pulsing is achieved by controlling the conventional T/R set of the precipitator In the Multipulse system, special T/R equipment produces intensive bursts of short pulses.

FIG A-78 Pulse systems in precipitators (Source: Alstom.)

In the low-ratio filter, gas enters the filter bags from the inside, then outward.The filter bags are cleaned “off-line” using either the reverse gas flow, reverse gas with high-energy sound horns, or a cleaning system of the deflate or shakemechanism type (See Fig A-82.)

The Optipulse ® cleaning concept

(Optipulse is a trademark for a proprietary design of this information source.)Pulse-jet fabric filters operate with dust-laden gas approaching the filter elementsfrom the outside, depositing the particles on the fibers of a depth-filtering medium.The clean gas leaves the open end of the filter element, which is typically oftubular design with a diameter of 120–150 mm (5–6 in) An internal wire cagesupports 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 arapid pulse of air The removed dust cake is transported by gravity toward the dusthopper

The effectiveness of the cleaning depends on the character of the pressure pulse.Optipulse produces a forceful pulse by an optimized geometry of the pneumaticsystem delivering the pulse (see Fig A-84):

 The pulse air is injected in the filter element, without dissipation of energy in alarge 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 setstandards for SO2 emissions and committed themselves to large reductions ofnational 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

A-88 Air Pollution Control

FIG A-81 Air filter elements (Source: Alstom.)

FIG A-82 Low-ratio fabric filter installation at Nevada Power, United States (Source: Alstom.)

FIG A-83 Installation of filter elements in an Optipulse fabric filter (Source: Alstom.)

Air Pollution Control A-89

FIG A-84 Operating principles of the Optipulse pulse cleaning system (Source: Alstom.)

FIG A-85 Wet/dry flue gas FGD plant, including fabric filters, after two coal-fired boilers at TWS Dampfkraftwerk, Stuttgart, Germany (Source: Alstom.)

Three common technologies for FGD

1 The wet/dry lime spray drying process offers low capital costs and an easily disposable/reusable end product for small and medium-sized plants (See Figs.A-85 and A-86.)

2 The open spray tower lime/limestone wet FGD process offers low operating costsand proven production of commercial grade gypsum (See Figs A-87 and A-88.)

3 The seawater process offers low operating costs and fully eliminates disposalproblems of end products at plants with access to suitable and sufficient amounts

of seawater (See Figs A-89 and A-90.)

SCR DeNO x Technology

Catalysts solve pollution problems

The SCR (selective catalytic reduction) technique was transferred to Europe fromJapan, where it was first developed

The reduction of nitrogen oxides with ammonia, which occurs spontaneously athigh temperature [about 950°C (1750°F)], can be achieved at a manageabletemperature after the boiler with the aid of a catalyst (See Fig A-91.)

For NOxreduction, the catalyst is usually an active phase of vanadium pentoxideand tungsten trioxide on a carrier of titanium Other types of catalysts areavailable, however

The ideal catalytic reactor is made up of catalyst elements that are assembled inmodules 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

eliminator above the spray nozzlebanks.

Secondary oxidation is normally achieved through introduction of oxygen at the bottom of the slurry tank.

With oxidation, the reaction product, after dewatering, will

be gypsum.

FIG A-87 Wet FGD plant (Source: Alstom.)

FIG A-88 Wet FGD plant with one single absorber installed after a 700-MW coal-fired boiler at Asnæsværket utility in Kalundborg, Denmark The plant produces commercial quality gypsum (Joint venture Alstom and Deutsche Babcock Anlagen.) (Source: Alstom.)

A-91

The wet FGD process can utilize the alkalinity of seawater to absorb SO2 in the flue gas Absorption takes place in a once through packed bed absorber.

The effluent is aerated in a seawater treatment plant and mixed with cooling water from the condensers before disposal

at sea.

FIG A-90 Basic operation of seawater FGD (Source: Alstom.)

FIG A-89 Seawater FGD plant at Tata Industries, India (Source: Alstom.)

A-92

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 Thisallows 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 andsimple, there are a few issues that require special attention One such issue is gasdistribution at the inlet of the reactor In the case of high dust it is of the utmostimportance that the gas is properly distributed to avoid catalyst erosion problems.The reactor is equipped with guide vanes and distributor plates to ensure even gasdistribution under all operating conditions (See Fig A-95.)

Another important issue is ammonia slip, which must be kept to a minimum forseveral reasons

If the gas still contains sulfuric gases, i.e., in the high dust case, ammonia slipwill react with sulfur trioxide to form ammonia bisulfate when cooled in the air

FIG A-93 SCR reactor of the high-dust type (Source: Alstom.)

FIG A-94 This coal-fired 550-MWe/900-MWth combined heat and power plant is located centrally in the town of Västerås, Sweden Alstom has gradually extended its flue gas treatment system, which today comprises ESP, FGD, and SCR units for full emission control (Source: Alstom.)

FIG A-95 Stadtwerke München Süd, Germany, has installed a CDAS (Conditioned Dry Absorption System), as well as a tail-end-type SCR unit, at its 300,000-tons-a-year waste-to-energy plant (Source: Alstom.)

A-95

A-96 Air Pollution Control

preheater This formation will take place on the dust particles and make the fly ashunsuitable for direct use in concrete manufacturing

The ammonia will also end up in the effluent from a downstream FGD plant, requiring effluent treatment

The SCR plant is therefore equipped with a control system of the “feed trim back” type In this system, ammonia is injected before the catalyst in relation

forward-to both the measured NO content after the reacforward-tor and the amount of NO present

in the gas fed into the reactor

Catalyst activity will inevitably decrease with time The mechanisms that control

the rate of deactivation are mainly: (i) sintering of the microsurface due to elevated temperatures, (ii) poisoning of the active metal atoms or molecules through a permanent bond or reaction with, for example, alkali metals, and (iii) blocking of

pores by, for example, ammonia bisulfite or dust

The reactor is equipped with a spare layer that can be charged when the efficiency

of the catalyst has dropped below a certain level When the activity drops further,the catalyst has to be replaced

The obvious advantages with the tail end system, with favorable conditionsregarding all three deactivation parameters, are offset only by the cost of bringingthe gas temperature back to the elevated operation temperature of the catalyst.This manufacturer is also conducting research to find catalysts with lower operationtemperatures 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 thisfield were first conducted in gas cleaning systems for waste-to-energy plants, wheredioxin emissions are a major problem The emission control system describedcombines the dual effect of chemically enhanced adsorption/absorption andfiltration

The fabric filter is also very effective for controlling heavy metals, due to itscapacity for filtering submicron particles The combination of dioxin and heavymetal abatement has been especially important for the environmental acceptance

of waste-to-energy plants This manufacturer has developed the TCR (TotalCleaning 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 UnitedStates These plants repeatedly measure dioxin emissions below 0.1 ng/Nm3 (SeeFig 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 thesystem The Filsorption II system is primarily aimed at the control of organicemissions such as dioxins The system also offers control of mercury, acidic gases,and particulate emissions Filsorption is an “absolute filter” for securing very lowemission levels

The system includes a storage and injection system for the chemically active

Air Pollution Control A-97

FIG A-96 Hazardous waste incineration plant with Alstom Filsorption system, Cleanaway Ltd., Ellesmere Port, UK (Source: Alstom.)

sorbent The sorbent is normally a mixture of coke and lime, mixed to a safe blend.This is a significant advantage of this system, which reduces risks for operatingpersonnel

The fabric filter collects the particulate matter that escapes the upstream particulate control units along with the injected sorbents and reaction products.The fabric filter also acts as a chemical reactor for lime with SO2, SO3, HCl, andHF

The ash collected in the filter is discharged for final handling or recirculation back

to the combustion unit to destroy its organic contents The contaminated reactionproduct requires a dust-free handling system This information source provides

an underpressure conveying system to prevent potentially hazardous ash fromcontaminating the working area

The Filsorption system can be used for treatment of gases containing dioxins andheavy metals from other types of industrial processes besides waste-to-energyinstallations (See Figs A-97 to A-103.)

End-Products Handling Systems

The often substantial amounts of solid or liquid wastes resulting from emissioncontrol systems require careful and efficient handling systems within the plantitself, as well as environmentally sound methods of treatment, recycling or disposal.Ash-handling technology needs various types of solids handling, including bottomash submerged drag chain conveyors, wet impounded hoppers, economizer andpyrites 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 densephase technology

Cost-efficient methods are developed to utilize the solid waste products A number

of commercial operations have already been established such as commercial gradegypsum 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 variousunits The example illustrated is the TCR system This system is designed to cleanflue gas from waste incineration and produce certain recyclable end products

In a similar manner, units are combined to form complete flue gas treatmenttrains in modern power plants

Such treatment trains could combine DeNOxand wet FGD units in, for example,

a large coal-fired power plant with an ESP for full emission control of the flue gases.Because emissions of heavy metals such as mercury and cadmium are commonproblems associated with coal firing, Filsorption units may be utilized to curb suchemissions

Also industrial application often contains several unit operations for full emissioncontrol A steel process plant, for example, has many emission sources that allrequire a separate solution

TCR

The TCR system contains basically three unit operations: (i) Filpac, (ii) Wetpac, and (iii) Catpac.

The Filpac stage (shown here is the Filsorption II process) is used for separation

of submicron particles, heavy metals, and toxic hydrocarbons by a combination offiltering, “sorption,” and chemical reaction

The Wetpac®

process is an absorption stage collecting the acid gas componentsand producing recyclable products, such as hydrochloric acid, chloride, and sulfatecompounds

A-100 Air Pollution Control

FIG A-101 Schematic for end-products handling for boiler fixed plant (Source: Alstom.)

Air Purification; Air Sterilization A-101

Catpac is used to reduce nitrogen oxides but may also incinerate hydrocarbons

or dioxins

With the TCR approach we combine well-proven unit operations into modularlybuilt and fully optimized APC solutions for true eco-engineering

Reference and Additional Reading

1 Soares, C M., Environmental Technology and Economics: Sustainable Development in Industry,

Butterworth-Heinemann, 1999.

Air Purification; Air Sterilization

Certain specialized processes require air that is a great deal cleaner than outlined

in the previous section on air pollution control Examples include food processingand pharmaceuticals production The detailed methodology needs to be worked outwith 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 0.1mm; 1 to 5 mm iscommon).

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.)

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, forinstance, to balance a pump in situ in the plant, if their readings with theirvibration analysis equipment confirm that this is what needs to be done For morecritical items, such as process compressors, this process is best done in the overhaulfacility 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 thatwas capable of handling the rotor in question

Most balancing of rotating machinery rotors or components of rotors (such asturbine wheels and so forth) is done in a balancing machine at speeds in theneighborhood of 1800 to 2000 r/min in atmospheric conditions In certain rareinstances, balancing at these speeds does not remove the imbalance (that wascausing rotor vibration in the first place) As a last resort, the process engineer mayhave to specify onspeed balancing of this rotor This needs to be done in a vacuumchamber and is expensive Also, there are very few suitable vacuum test facilities

in the world Before getting into this additional expense, the process engineer isprobably well advised to consult a rotating machinery engineer

Balancing Problems, Troubleshooting (Turbomachinery)

(see Condition Monitoring)

Batteries (see Cells)

Bearings* (see also Lubrication)

Bearings permit relative motion to occur between two machine elements Two types

of relative motion are possible, rolling or sliding, each of which depends upon thedesign of the mechanical bearing element Thus bearings are classified into twogeneral types: the rolling-contact type (rolling) and the sliding-contact bearing design

in which the bearing elements are separated by a film of oil (sliding) Both can bedesigned to accommodate axial and/or radial loads Each has a wide variety of typesand designs to fit a wide variation in uses The selection of a bearing type for application

to a particular situation involves a performance evaluation and cost consideration.There is ample literature available to determine the relative merits of each type.This subsection will provide a general overview of the types of bearings presentlyencountered in the equipment covered in this edition Changes take placefrequently because many scientists and engineers work constantly to improve thestate of the art in bearing design

B-1

* Source: Demag Delaval, USA.

Rolling-Contact Bearings

Rolling-contact bearings include ball bearings, roller bearings, and needle bearings.Within each category several variations have been developed for specificapplications Variations in the amounts of radial and thrust load capabilities alsoexist between specific types Self-aligning ball or roller bearings, by virtue of theirspherically ground outer race, can tolerate misalignment of the shaft or housing.Rolling-contact bearings consist of four principal components: an outer race, aninner 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 stationaryhousing The facing surfaces of the inner and outer rings are grooved to conform tothe rolling-element shape The rolling elements (with separator) accurately spacethe 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 andthrust bearings Journal bearings support radial loads imparted by the rotatingshaft and may also be required to arrest or eliminate hydraulic instabilities thatmay be encountered in lightly loaded high-speed machinery The thrust bearingsare used for loads parallel to the shaft and may be required to support the fullweight 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 bearingsB-2 Bearings

FIG B-1 Nomenclature of a ball bearing (Source: Demag Delaval.)