Process Engineering Equipment Handbook Episode 1 Part 7 pdf

C-140 Expanders turboexpanders offer full arc admission, high efficiency, and robust design with a separate blade carrier, and are available with adjustable stator blades for first stage

FIG C-137 Single-stage turbocompressors with this OEM incorporate eight frame sizes, for suction volumes from 5000 to 250,000 m 3 /h (Source: Sulzer-Burckhardt.)

FIG C-138 TURBAIR™ vacuum blowers offer compact design, several different vacuum levels, low water consumption, the best possible matching to performance requirements, a flat characteristic over a wide working range, an economical vacuum system, good reliability, and low maintenance costs One application was specially developed for extracting water from paper, board, and pulp machines of all sizes (Source: Sulzer-Burckhardt.)

FIG C-139 TURBAIR vacuum blowers with this OEM incorporate five frame sizes to cover practical vacuum requirements (Source: Sulzer-Burckhardt.)

FIG C-140 Expanders (turboexpanders) offer full arc admission, high efficiency, and robust design with a separate blade carrier, and are available with adjustable stator blades for first stage Applications include nitric acid plants and power recovery (Source: Sulzer-Burckhardt.)

FIG C-141 Turboexpanders with this OEM incorporate eight frame sizes, with rotor diameters ranging from 31 to 80 cm Materials are selected to suit the specific application (Source: Sulzer-Burckhardt.)

Type AV. Compressors with adjustable stator blades on all or only some stages at

the inlet (VARAX) (see Fig C-131)

Each type range consists of 12 geometrically graduated sizes with rotor diametersextending from 40 to 140 cm This completely covers a suction volume range of70,000 to 1,250,000 m3

/h (See Fig C-143.)The required compressor size and number of stages, together with thecorresponding standardized overall length, are selected according to the suctionvolume and the thermodynamic head

Type A (FIXAX). The A-type FIXAX compressor is generally used whenever thedriver is a steam turbine, a split-shaft gas turbine, or a variable-frequency high-speed synchronous motor

The required operating points can be attained by speed variation, and there isbasically no need for adjustable stator blades Fixed-blade machines are alsoselected for installations where only minor flow variations are required, or if themass flow is adapted by variation of the suction pressure, as in aerodynamic testfacilities, for example

Type AV (VARAX). The AV series with adjustable stator blades permits a large stableoperating range at constant speed It is therefore used for constant-speed electricmotor drive Nevertheless, this type is being increasingly preferred for steamturbines and single-shaft gas turbines as well In this particular case, the statorblade control either facilitates operation with limited speed control range (increasedreliability of operation for certain turbine types) or, in combination with the speed control, provides an additional extension of the operating range and animprovement of the overall efficiency at part load Furthermore, it offers theadvantage of quick adaptation of the compressor to changed operating conditionswithout acceleration of the set—a characteristic that is of great interest for theperiodic charging of air heaters in blast-furnace blowing plants Many axialcompressors are fitted with adjustable stator blades

Stator blade setting with electric servomotor. For a great number of processes, thereference value of pressure or mass flow is selected at the process control panel andtransmitted to the compressor servomotor In this case this servomotor is of theelectric type with the additional possibility of manual adjustment of the stator blades

Stator blade control with hydraulic servomotor. If the process calls for automaticpressure or mass flow control, the stator blade adjusting mechanism will beoperated by a synchronized pair of hydraulic servomotors

With the exception of the stator blades and their adjusting mechanism, the samestandardized construction elements are used for both FIXAX and VARAX types

Performance data. Figures C-144 through C-149 (note type designation) facilitatethe selection of the

Relative humidity of the air or gas j1(%)

The following factors and symbols are also used for the calculation:

FIG C-142 Axial compressor, type AV 100–16, during erection Two identical steam-turbine–driven machines are supplying air to the blast furnace of a British steel works Suction volume 560,000 Nm 3 /h, discharge pressure 6.2 bar, power input 52,000 kW each (Source: Sulzer-Burckhardt.)

Suction volume (actual) V.1(m3/s)

Design features. The basic design offers (see Fig C-150):

 Cast casing and separate blade carrier

 Casing supported by means of pendulum supports (minimum expansion forces)

or feet with keyways for the smaller frame sizes

 Solid or hollow rotors, smooth-running characteristics with integrated balancingpistons

 Blading with optimal aerodynamic characteristics—with good efficiency andspecific capacity, low stressing, favorable control characteristics

 Blade vibrations minimized; blade profiles and blade fixation are designed accordingly

 Adjustable stator blades—of standard design—for optimum flow control

 Maintenance-free, oil-free stator blade adjusting mechanism that is also protectedagainst the ingress of contaminants

 Various bearing options

 Various shaft seal options

Casings, bearing pedestals. Depending on the type of gas and the design pressure, thecasings are made of gray cast iron, nodular cast iron, or cast steel The cast designincorporates a rigid construction, effective noise attenuation, and aerodynamicallyfavorable layout of the respective ducting The suction and delivery branches areusually routed vertically downward In cases where, due to the composition of thegas and/or the pressure level, steel casings are mandatory, a welded construction

FIG C-143 Type designation (Source: Sulzer-Burckhardt.)

FIG.C-145 Determination of the discharge temperature t2 (Source: Sulzer-Burckhardt.)

FIG C-146 Performance data for type A (FIXAX) (Source: Sulzer-Burckhardt.)

FIG C-147 Performance data for type AV (VARAX) (Source: Sulzer-Burckhardt.)

and C-147

Fig C-147 Fig C-146

Fig C-144

Fig C-145

Performance data [type A (FIG C-148), type AV (FIG C-149)] for selection and performance calculation of an axial

compressor (Source: Sulzer-Burckhardt.)

can be specified The suction branch may then be axial, or both suction anddischarge may be routed upward or downward In the vertical central plane, thecasing is aligned by two keyways; it is equipped with four supporting feet It is fixed

at one end in the axial direction by one pair of feet The other pair of feet of largeframe sizes rests on pendulum supports with spherical contact surfaces As a result

of this, the casing can take up the thermal expansion in both the axial and lateraldirection without difficulty This feature is particularly advantageous in the case of

FIG C-150 Longitudinal and cross-sectional view of an AV compressor (Source: Sulzer-Burckhardt.)

light steel foundations, as may be found, for instance, on an offshore platform Onsmall frame sizes the pendulum supports are replaced by sliding keyways.

Blade carrier, casing inserts. The blade carrier inserted in the casing is centered onboth the suction and discharge side, and is able to expand freely in the axialdirection The diffusor and the gland inserts are also fitted as separate parts in thecasing

The double-casing design with outer casing and blade carrier offers variousadvantages:

 Rigid casing construction; the clearances in the blade duct are not influenceddirectly by external pipe forces

 Simple fitting of the blades and assembly of the casing parts; the top half of thecasing can be raised without dismantling the blade-adjusting mechanism

 Possibility of fitting different blade carriers, for adapting the blade duct and thusthe compressor characteristics to greatly changed operating conditions

 Optimal protection of the adjusting mechanism in the space between the casingand blade carrier; the space is kept under suction pressure to safeguard theadjusting mechanism against condensation and corrosion attack

Rotor. The rotors are usually of forged solid design In the case of larger machines

or if the moment of inertia must be minimized to limit the power requirement whenrunning up with an electric motor, welded hollow rotors may be used Integratedbalancing pistons at both ends of the rotor facilitate an equalization of the axialthrust The careful balancing of the rotor at full speed results in highly smoothrunning characteristics If necessary, balancing can also be effected in the casing.The labyrinth strips are caulked in the rotor

Blading. Blading with a high degree of reaction, i.e., the increase in pressure takesplace exclusively in the impellers, is employed for the compression of lighter gasessuch as helium or hydrogen

For all other applications, such as the compression of air, blading with a lowerpercentage reaction is adopted The increase in pressure is distributed to the rotorand stator blades This enables the following design advantages to be realized:

 Higher efficiency with lower aerodynamic loading

 Widest possible control range with high part-load efficiency at constant speed

 Largest possible suction volume at given speed

 Increased reliability of operation due to larger radial blade clearances and theomission of guide vane sealings

 Steeper pressure volume characteristics, especially suitable for capacity control,for the parallel operation of different compressors, for refrigeration processes, andfor exact adjustment of the blow-off line

The rotor and stator blades are normally made of 13 percent chrome steel andmachined When handling highly contaminated aggressive air or corrosive gases,alloys with higher chromium and nickel content may be used The rotor blades haverhomboidal roots and are firmly braced in an exactly defined position in theperipheral grooves of the rotor This is of particular importance for their vibration-wise design The fixed stator blades are provided with a rectangular foot Theadjustable stator blades are made in one piece with a cylindrical shaft The latter

is seated in a bearing bush in the blade carrier The high damping characteristics

of this seating arrangement practically eliminate the potential for high vibrationamplitudes associated with the stator blades

Stator blade adjusting mechanism for the AV types. The adjusting mechanism is located

in an annular space between casing and blade carrier, and is thus well protectedagainst contaminants and moisture It is maintenance-free and does not requireany lubrication (See Figs C-151 and C-152.)

Servomotors. Two types of servomotors are available, electric and hydraulic(Figs C-153 and C-154)

Automatic mass flow, volume or pressure control. The adjusting mechanism isoperated by means of two hydraulic servomotors that are affixed laterally to thecasing One of the servomotors is equipped with a positioning transmitter and thesecond operates hydraulically in parallel

The linear movement of the servomotor piston rods is transmitted directly to theadjusting cylinder by way of two ball and socket joints

Remote setting of reference value. One single electric servomotor is attachedlaterally to the bottom half of the casing Its driving shaft actuates a pivoted fork

FIG C-151 Adjustable stator blade, rotor blade, and fixed stator blade with intermediate piece (Source: Sulzer-Burckhardt.)

FIG C-152 Stator blade adjusting mechanism (Source: Sulzer-Burckhardt.)

positioned on either side of the casing in maintenance-free bearings This fork inturn moves the adjusting cylinder in the axial direction.

Adjusting cylinder. The adjusting cylinder of welded design can move in theaxial direction and is dry-seated There is no restriction of heat expansion in anydirection U-shaped guide rings are provided on the inner side in which theadjusting levers are engaged

Stator blades. The adjusting levers provided on the end of each stator bladeshaft are connected to the guide rings of the adjusting cylinder by means of pivotingsliders The axial movement of the cylinder is converted into a rotating movement

of the stator blades

The self-lubricating bearing bushes of the blade shafts are seated in the radialholes of the blade carrier O-ring packings prevent the ingress of contaminants intothe stator blade seating

Shaft seals. Labyrinth seals are used for the standard models The stainless steellabyrinth strips are caulked on the rotor and are replaceable In case of rubbing

FIG C-153 Electric servomotor (Source: Sulzer-Burckhardt.)

FIG C-154 Hydraulic servomotor (Source: Sulzer-Burckhardt.)

due to unbalance, the friction-induced heat is immediately passed to the massivestator, thus avoiding distortion of the rotor Gas-tight shaft seals and standstill sealscan be fitted for special requirements See Fig C-155.

Journal and axial bearings

Journal bearings. In the standard version, i.e., with the compressor rotor solidlycoupled and the rotor thrust transferred to the axial thrust bearing of the primemover or the gear, the bearing housings are equipped only with journal bearings.Two-lobe bearings are provided for the lower speed range; tilting pad journalbearings are generally used for the higher speeds of the smaller frame sizes forreasons of stability The slight curvature of the adjusting plates allows the bearings

to be set accurately on erection The bearings are firmly held in position by thebearing housing top half See Figs C-156 through C-158

Two-lobe bearings are suitable for both senses of rotation, while tilting padbearings are essentially for only one direction, although they can tolerate runningbackward with a somewhat reduced load capacity

Axial thrust bearings. If a flexible coupling is selected between driver and drivenmachine, the bearing housing can accommodate the necessary tilting pad thrustbearing The purpose of this bearing is to absorb the remaining thrust of themachine and any significant axial friction thrust of the coupling due to sharp

FIG C-156 Multisegment journal bearing with four tilting pads (Source: Sulzer-Burckhardt.)

due to unbalance, the friction-induced heat is immediately passed to the massivestator, thus avoiding distortion of the rotor Gas-tight shaft seals and standstill sealscan be fitted for special requirements See Fig C-155.

Journal and axial bearings

Journal bearings. In the standard version, i.e., with the compressor rotor solidlycoupled and the rotor thrust transferred to the axial thrust bearing of the primemover or the gear, the bearing housings are equipped only with journal bearings.Two-lobe bearings are provided for the lower speed range; tilting pad journalbearings are generally used for the higher speeds of the smaller frame sizes forreasons of stability The slight curvature of the adjusting plates allows the bearings

to be set accurately on erection The bearings are firmly held in position by thebearing housing top half See Figs C-156 through C-158

Two-lobe bearings are suitable for both senses of rotation, while tilting padbearings are essentially for only one direction, although they can tolerate runningbackward with a somewhat reduced load capacity

Axial thrust bearings. If a flexible coupling is selected between driver and drivenmachine, the bearing housing can accommodate the necessary tilting pad thrustbearing The purpose of this bearing is to absorb the remaining thrust of themachine and any significant axial friction thrust of the coupling due to sharp

FIG C-155 Labyrinth shaft seals (Source: Sulzer-Burckhardt.)

FIG C-156 Multisegment journal bearing with four tilting pads (Source: Sulzer-Burckhardt.)

temporary differential expansion between rotor and casing To provide easy accessand reduce the overhang, it is preferably mounted on the free shaft end.

The tilting pads are supported on load-equalizing segments that allow angularity

of the shaft up to 0.3 percent

Because the tilting pads are supported eccentrically, thrust bearings are suitablefor only one direction but tolerate a reversed rotation at a reduced load capacity

Solid coupling. It is this OEM’s normal practice to make extensive use of solidcouplings allowing the use of only one axial thrust bearing for single- or multiple-casing arrangements

An intermediate shaft, flexible enough to allow for considerable misalignment, isinserted between the two shaft ends of the machines to be coupled together (Fig.C-159) In case of motor-driven units, the normal technique is to use single helicalgears provided with thrust collars on the pinion shaft, as shown in Figs C-160 andC-161 The thrust collars not only neutralize the axial thrust created by themeshing of the teeth cut at an angle to the axis of the shaft, but also transmit

FIG C-157 Two-lobe journal bearing (Source: Sulzer-Burckhardt.)

FIG C-158 Kingsbury-type thrust bearing with self-equalizing pads with directed lubrication (Source: Sulzer-Burckhardt.)

the unbalanced axial thrust of the high-speed rotor train to the thrust bearing onthe low-speed wheel shaft Good gear meshing requires parallelity of gear andpinion shaft and automatically ensures parallelity of the contact surfaces of thrustcollar and wheel rim The slight tapering of the thrust collars is responsible for theformation of a wedge-type oil film creating a pressure zone spread out on anenlarged surface with a pressure distribution very similar to that of a standard oil-lubricated journal bearing.

The relative motion between the two contact surfaces of the thrust collar system

is a combination of rolling and sliding and takes place near the pitch circle diameter,resulting in a very small relative velocity The thrust transmission is thereforeconducted with minimal mechanical losses The considerably reduced losses of the single thrust bearing on the low-speed shaft as compared with the high losses

of individual thrust bearings on the high-speed train lead to a substantial powersaving This low-speed bearing can also be more amply dimensioned to provide amuch higher overload capacity

For direct turbine-driven compressor trains, the thrust bearing is usually located

in the turbine Also in this case solid couplings with flexible intermediate shafts aremuch preferred

This coupling arrangment avoids heavy overhung gear couplings that are usuallyresponsible for not clearly defined lower critical speeds and for the phenomena oftorque lock leading to additional loading of the axial thrust bearing The resultingaxial friction forces can become quite substantial if insufficient attention is given

to the cleanliness of the lubricating oil

Centrifugal compressors

Centrifugal compressors made by this information source are available for thecompression of various gases within a flow range of about 0.6 to 60 m3

/s andpressures up to 700 bar They are used in the most varied applications, mainly in

FIG C-159 The solid quill-shaft coupling conforms to API 671 standard and consists of the quill shaft and the two hubs hydraulically fitted onto the shaft ends of the connected machines On each coupling side, an equal number of tie bolts for axial fixation and tapered dowel pins for torque transmission and centering ensure a clearly defined connection Balancing as a complete assembled unit and correlative marking enable removal and remounting of this intermediate shaft with the connected rotors remaining in place, without affecting the balancing quality and vibration behavior of the complete string (Source: Sulzer-Burckhardt.)

the fields of process engineering, chemical industry, and mineral ore processing, aswell as oil and gas production See Fig C-127.

Units made by this information source have power inputs varying between a fewhundred kilowatts and nearly 40 MW

To minimize design lead time and ensure economical manufacturing and stocking

of the major components, the range of these compressors has been standardized to

an optimum extent The constant geometrical ratio between the frame sizes allowscompressors to be assembled to different specifications with the minimum inventory

of component parts, diminishing the investment on spare parts It also permitscomparison and forecast of performance and stresses within the series of framesizes Figure C-162 shows a section through a centrifugal axially split compressor

Type range. The standardized range of horizontally split casing types (see Fig C-131) extends to eight frame sizes for this OEM source including three pressureranges for each frame size up to 70 bar and is designed for appropriate turndown

FIG C-160 Method of axial thrust transfer in a single helical gear with thrust collar (Source: Sulzer-Burckhardt.)

FIG C-161 Transfer of external forces (Source: Sulzer-Burckhardt.)

An appropriate selection of impellers and diffusers enables the compressor stages

to be matched to any specified operating data See Figs C-163 through C-167.The barrel-type design is suitable for discharge pressures of up to 700 bar It hasvertically split casing with end cover and autoclave cover and horizontally splitinternal casing for easy assembly and dismantling Option of intermediate nozzlesfor connecting to intercoolers or for side-stream intake or extraction The internalcomponents, including the horizontally split internal casing, autoclave cover,diaphragms, and rotor with bearings and seals, are assembled outside the barrelcasing; the internal clearances can then be checked exactly prior to final assembly

Compressor design: adaptability of standardized product range. The different ways ofadapting standard designs to varied operating conditions are described as follows:

Adapting to different specific flow conditions. The basic dimensions of thecomponents and parts of compressors such as casings, impellers, diffusers, andbearings are standardized by using a constant scale factor between the differentframe sizes As can be seen in Fig C-165, this factor is 1.25 for the casing sizes,1.12 for impeller diameters, and even smaller for certain dimensions of internalparts This system permits the assembly of various compressors complying to specified data by using a minimum number of predesigned parts Moreover, itensures accurate forecasting of performance interpolated from other frame sizes.The eight frame sizes cover a range between 0.5 and 60 m3

/s The range of higher

FIG C-162 Section through a horizontally split axial compressor (Source: Sulzer-Burckhardt.)

suction volumes above about 25 m3

/s and up to 350 m3

/s is covered by 12 frame sizes

of axial compressors, where a scale factor of 1.12 is used

Adapting to different specified pressures. This information source’s models (R,

RZ, and RS) can be equipped with casings made of gray cast iron, nodular cast iron,

or cast steel which, depending on the frame size, makes them suitable for standarddesign pressure classes of 6, 16, 25, 40, or 64 bar The RB, RBZ, and RBS casingsare invariably made of fabricated or cast steel to cover the standard pressure range

of up to 700 bar

Adapting to different process conditions. The process industry has an changing range of requirements concerning the arrangement of external casingnozzles, either when intercooling is needed to limit temperature during compression

ever-or intermediate inlets have to be provided fever-or side-streams The standard design isvery flexible in this respect

CENTRIFUGALS WITH HORIZONTALLY SPLIT CASINGS

 Series R: straight-through compressor without provision for intercooling

 Series RZ, RZ2: compressors with one or two pairs of intermediate nozzles forconnecting to one or two intercoolers

 Series RS, RS2: compressors with one or two intermediate inlet nozzles for one

or two side-streams

CENTRIFUGALS WITH VERTICALLY SPLIT CASINGS

 Series RB: straight-through compressor without provision for intercooling

 Series RBZ: compressor with one pair of intermediate nozzles for connection to

an intercooler

 Series RBS: compressor RB with additional inlet or outlet

FIG C-163 Selection chart for centrifugal compressors of the R and RZ series (Source: Sulzer-Burckhardt.)

FIG C-164 Typical series designations for centrifugal compressors (Source: Sulzer-Burckhardt.)

Building block system. Each compressor frame size exists in differentstandardized lengths to accommodate different numbers of stages With castcasings, adjustments of the pattern are made using a modular technique wherebyspacing rings are fitted between standardized pattern parts of the casing to alterthe length (Fig C-167).

When the head required is more than that practicable within one compressorbody, two or more casings can be connected in series to form a train

Design features Casing. Depending on the required pressure class and the type of gas, thehorizontally split casings of the series R, RZ, and RS are made of gray cast iron,nodular cast iron, or cast steel, unalloyed or alloyed See Fig C-168 for a sectionthrough a horizontally split centrifugal compressor and Fig C-169 for a sectionthrough a barrel centrifugal compressor All suction, intermediate, and dischargenozzles are normally facing downward to facilitate inspection without disturbingthe process pipe connections Optionally they can be arranged facing upward Inthe case of flammable or toxic gases, the horizontal division flange can be provided

is designed to accommodate three different impeller diameters and different impeller types (Source: Sulzer-Burckhardt.)

FIG C-166 Standard pressure classes (Source: Sulzer-Burckhardt.)