Compressor Performance: Aerodynamics for the User

194 Pages·2001·61.31 MB·English

by  Theodore Gresh

Compressor Performance:
Aerodynamics for the User
by Theodore Gresh

• ISBN: 0750673427
• Pub. Date: March 2001
• Publisher: Elsevier Science & Technology Books
Preface
This text has been designed to be used primarily by equipment The concepts and procedures presented in the following
users, as a guide in selecting, monitoring, and enhancing pages, while generally in line with EUiott Company Policy
the aerodynamic performance of various types of com- and Industry Standards, include opinions belonging solely
pressors. Some basic theory is included as an aid in helping to me. Conforming to guidelines in this text therefore does
field personnel to better understand the aerodynamics of not mean compliance with Elliott Company, API, or other
compressors so that performance enhancements and trouble industry standards. The methods presented are meant to be
resolution can be more readily realized. As much as possible, guidelines used for day-to-day performance trending or as
I have attempted to stick to the "business end" of the the first step in selection, trouble-shooting, or retrofitting
applicable aerodynamic principles. equipment. For potential wawanty cases, customer and vendor
This book is the result of various books, articles, notes, must agree on a specific test procedure before proceeding.
seminars, and personal experience that I have collected over For an "out of warranty" problem the field engineer is best
the years working in the field of compressor aerodynamics. advised to get some help from the equipment manufacturer,
As it is such a "collection," references have been used after some initial analysis is completed.
extensively as noted. M. T. Gresh
VII el
stnemgdelwonkcA
A special thanks to Elliott Company for the support in this Don Rudisel, Ron Aungier, John Beaty, Bob Spigarelli, Paul
endeavor and permission to print the various drawings and Gallick, Bill Hohlweg, Katsuhiko Yamanaka, Dennis
articles used throughout this book. Thanks also to GHH, Maffessanti, Ross Hackel, and my wife, Lynn.
,rezluS Carrier, General Electric Co., Ebara, Demag, Ingersol The talents of Frank Weidler, Gerry Brunson and Tom
Rand, DuPont, Gulf Publishing, and Natural Gas Processors Humphrey are displayed throughout this book in the various
Suppliers Association for technical data provided. drawings they created for .em
Thanks also to all the people who have personally helped Most crucial, though, to the development of this book
by offering their technical support and encouraging has been the excellent cooperation and typing skills of Kathy
comments, with special thanks to Marc Sassos, Dave Galster, Lazur.
ix
slobmyS
A Area, ft e q Heat transfer ft-lb force/lb mass
a Speed of sound, ft/sec R Gas constant (1544/MW)
BHP Brake or shaft horsepower Re Reynolds number
C Discharge coefficient pr Pressure ratio )IP12P(
% Specific heat at constant pressure, BTU/Ib mole ~ s Entropy, BTU/~
r Specific heat at constant volume, BTU/Ib mole ~ SHP Shaft horsepower
D Pipe diameter, inches T Absolute temperature
d Throat, or impeller diameter, inches (~ = ~ + 459.6)
E Voltage cT Critical temperature (~
E Velocity of approach factor RT Reduced temperature (TITc)
Eft Efficiency t Temperature (~
Fa Orifice meter thermal expansion factor U Tip speed, FPS
cg Gravitational constant u Internal energy, ft-lb force/lb mass
V velocity (ft/sec)
32.2 fi-lb mass
Specific volume (ft3/lb mass)
lb force-see 2 v
GHP Gas horsepower W Work ft-lbs force
lb mass
Head ft-lbs force y
H Flow meter expansion factor
lb mass Ya
Adiabatic expansion factor
HP Horsepower Z Compressibility factor
h Enthalpy (BTU/Ib mass) z Vertical height
wh Differential pressure, inches water
1 Amperage GREEK LETTERS
K Flow meter flow coefficient
Throat (or orifice) to pipe diameter ratio
k Adiabatic exponent (%1c0 fl
Efficiency
MW Molecular weight /7
Work coefficient
Weight flow (lb/min) 7
M Mach number, V/a /Iat' AHbesaodl ute coefficient viscosity lb-sec/ft 2
N Speed, RPM
,N Specific speed V' Kinematic viscosity ft2/sec
Density lb/ft 3
n Polytropic exponent P
Flow coefficient
P Static pressure (psia)
cP Critical pressure (psia)
SUBSCRIPTS
rP Reduced pressure
Pr Total pressure, psia ad Adiabatic process (Had)
oP Stagnation pressure, psia p Polytropic process (Hp)
vP Velocity pressure S Standard conditionsmusually 14.7 psia, 60~ dry
PF Power factor air
Q Flow rate ft3/min 1 Inlet conditions (Pl)(Ql)(tl)
,Q Flow rate fta/sec 2 Discharge conditions (Tz)(Pa)
Table of Contents

Preface
Acknowledgments
Symbols
Pt. I Theory
Ch. 1 Introduction to Aerodynamics 3
Ch. 2 Thermodynamics 11
Ch. 3 Aerodynamic Components 23
Ch. 4 Compressor Characteristics 33
Pt. II Application
Ch. 5 Equipment Selection 45
Ch. 6 Operation 55
Ch. 7 Field Performance Testing 67
Ch. 8 Troubleshooting 87
Ch. 9 Flow Meters 97
Ch. 10 Multi-section Compressors 103
Pt. III Reference Material
App. A Properties 121
App. B Mollier Diagrams 127
App. C Conversion Tables 169
App. D Permissible Deviations and Fluctuations 187
App. E Thermal Expansion Factor 189
App. F: Surge Identification 191
App. G: Glossary of Terms 193
References 197
Additional Reading 198
Compressor and Steam Turbine Performance Software 199
Index 201
1
INTRODUCTION TO AERODYNAMICS
~ own through the years, human needs and With the advent of the Iron Age, which
serised have required a continued began around 1000 s.c., no longer were simple
evolution of more and more sophisticated drafting techniques adequate. A much higher
fluid-handling apparatus. nI general, fluid hearth temperature required a pressurized air
handling involves two problems, fluid blast. Small foot- and hand-operated bellows
transportation and fluid pressurization. were used in the small hearths of the farrier and
Ancient man saw most concerned with liquid blacksmith. Five hundred years ago immense
transport and storage. Of primary concern saw bellows were used in Germany to supply the air
irrigation for agricultural purposes and transport of required for large furnaces. These were
water to .seitic ultimately supplemented by piston pumps.
ehT Bronze Age, which began about 3000 .8 ,.c ,yadoT rotary compressors are used almost
brought with it the requirement of smsinahcem ylevisulcxe for this purpose.
for enhancing air supply to hearth .secamuf ehT Industrial Revolution and, most ,yltnecer
Air saw first introduced in hearths by crude the ecapS Age, have produced an exponential
drafts and simple fanning. With time, innovation growth in the advancement of turbomachinery,
brought improved air supply .secived Hearths from the simple squirrel cage fan in a car's
were oriented to capture the prevailing winds, heater to the liquid fuel pumps used on the
and chimneys were added to help draw more ecaps shuttle .senigne
air to the .secanruf
FLUID MECHANICS AND THERMODYNAMICS came the aerodynamic scientists Kutta, Joukowsky, Von
Karman, noV Mises, Prandtl, Lamb, Struhal, Tiejens, Stodola,
Little heed was paid to the various fluid properties in the
Dryden, Parsons, and Paulson. With the advent of flight,
design of compression devices until the 19th century. Until
these men developed theories on boundary layer, vortex
this period, only a slight density and temperature change
shedding, aeroelastic phenomena, and other necessary tools
was encountered at the reduced compression ratios used in
used in the design of present-day turbomachinery 1.
air pumps. The designer had a large margin of error possible
since he was at liberty to "tinker" and adjust the apparatus
STSRIF
at the job site until it was perfected. nI most instances both
the building and design were done at the job site. In Alexandria, Egypt, about 130 A.D., a priest scientist named
Concepts of flow, energy, work, heat, and momentum, Hero employed aerothermo principles to generate steam
which eluded the grasp of the early Greek philosophers and and drive a small reaction turbine.
later the Roman engineers, gradually began to be understood Although the fluid mechanics of a compressor and turbine
and deterpretni under the impetus of the Renaissance scientists are much the same, knowledge of fluid mechanics is much
da Vinci, Galileo, Newton, Bernoulli, Euler, St. Venant, more crucial for the design of a compressor than for a .enibrut
Stokes, and Navier. The mathematical tools to describe and A turbine, with its flow usually going from a high to a low
solve problems were wrought by Liebniz, Newton, De pressure, will always work. With reasonable design, it will
Moivre, Descartes, Legendre, and others. Watt, Stephenson, work at a respectable efficiency. A compressor, conversely,
Carnot, Clausins, and Thurston through their applied efforts ylralucitrap an axial compressor, will not produce any pressure
on the steam locomotive developed technical, mechanical, rise at all unless properly designed. Consequently, very little
and thermodynamic solutions which have contributed to activity was seen in the field of compressor design until the
the compression equipment of our century. The science of 18th century.
heat transfer, thermodynamics, and energy conservation was In 1705 Denis Papin published full descriptions of the
developed by Maxwell, Thurston, Otto, Helmholtz, Steffan, centrifugal blowers and pumps he had developed; however,
Boltzmann, Rayleigh, Rankine, Mach, and Plank. In the the efficiency of these machines is unknown 2, 3.
wake of the Wright Brothers' first flight ta Kitty Hawk John Barber designed and patented a gas turbine engine
4 THEORY
in England in 1791. The engine was designed to operate on fluid through the process. The purpose may also include a
a constant pressure cycle using gas from wood or coal as desired temperature rise to enhance the chemical reaction
fuel [4]. in the process.
In 1851, Henry Gifford flew from Paris to Trappes in Devices that develop less than 5.0 psig, or that effect a
the first successful aircraft propulsion device, a propeller- 7% density increase from inlet to discharge, are classified
driven dirigible balloon powered by a steam engine [5]. as fans or blowers. Above this level, the devices are referred
In 1872, Dr. Stolze patented a gas turbine which was to as compressors. Due to the low density change, fan
eventually built and operated. The engine employed a multi- equations assume constant density, thus simplifying the
stage axial-flow compressor and a multi-stage turbine with calculations [7, 8].
both mounted on the same shaft. Heat was supplied to the Pumps are very similar to compressors but deal primarily
air by means of a furnace located between the compressor with incompressible hydraulic fluids, whereas compressors
and turbine [4]. generally deal with compressible gaseous fluids.
Around the same period, Parsons and Delaval developed
a reaction steam turbine, for the purpose of driving blowers TYPES OF COMPRESSORS
and generators. Although Parsons also used this device in
The two basic types of compressors are positive displacement
reverse to serve as a compressor, the efficiency was low--
and dynamic.
around 60%. Sir Charles Parsons' 1884 patent also made
reference to the gast urbine engine and provided for cooling
EVITISOP DISPLACEMENT ROSSERPMOC
to the turbine blades [ 1-3].
The first United States patent covering a gas turbine The positive displacement compressor functions by means
was by Charles Curtis (inventor of the Curtis steam turbine) of entrapping a volume of gas and reducing that volume, as
in June of 1895 [3]. in the common bicycle pump, and the screw compressor
In Dr. 1905, Alfred J. Buchi of Switzerland first suggested shown in Figure 1.1. The general characteristics of the positive
the turbocharger for enhancing the output of internal displacement compressor are constant flow and variable
combustion engines. He later went on to patent his ideas in pressure ratio (for a given speed).
1915 and to organize the Buchi Syndicate in 1927 for the Positive displacement compressors include
purpose of developing his systems [3].
It was not until January ,61 1930, that Frank Wittle, an (cid:12)9 piston compressor
officer in Great Britain's Royal Airforce, developed and
(cid:12)9 screw compressor
patented a practical design for an aircraft gas turbine engine.
(cid:12)9 vane compressor
However, the British Air Ministry dismissed the design,
finding it impractical [3, 6]. (cid:12)9 lobe compressor
A few years later in 1934, a German named Hans yon
Ohain began development of an engine of similar design. In DYNAMIC ROSSERPMOC
1936 he joined forces with Ernst Heinkel, an airplane
The dynamic compressor depends on motion to transfer
manufacturer. Progress was good and an aircraft with yon
Ohain's engine was successfully flown in August, 1939.
Von Ohain's HESSA Engine had a centrifugal compressor
and a mixed-flow expander [2, 6].
Meanwhile, Wittle had obtained some money from the
British AirM inistry to develop his engine. In May 1941, an
aircraft with Wittle's jet engine was successfully flown.
Wittle's W2/700 Turbojet Engine, which consisted of an
axial compressor, a single-stage centrifugal compressor, and
an axial expander, was eventually developed into the Rolls-
Royce Welland in England and also the General Electric
J33 in the United States [3, 6].
DEFINITION OF COMPRESSOR
A compressor is a device that transfers energy to a gaseous
fluid for the purpose of raising the pressure of the fluid as Figure 1.1. Positive compressor. displacement ysetruoC( of NAM
in the case where the compressor is the prime mover of the ).HHG
INTRODUCTION TO AERODYNAMICS 5
energy from the compressor rotor to the process gas. The pressure process gas. This type of compressor is commonly
characteristics of compression vary depending on the type used for vacuum applications.
of dynamic compressor and on the type of gas being Centrifugal Compressor A centrifugal compressor acts
compressed. The flow is continuous. There are no valves on a gas by means of blades on a rotating impeller. The
and there is no "containment" of the gas, as in a positive rotary motion of the gas results in an outward velocity due
displacement compressor. Compression depends on the to centrifugal forces. The tangential component of this out-
dynamic interaction between the mechanism and the gas. ward velocity is then transformed to pressure by means of
Dynamic compressors include a diffuser.
Figure 2.1 is typical of a single-stage centrifugal compres-
(cid:12)9 ejector sor. A high-pressure multi-stage compressor is shown in
Figure 1.3.
(cid:12)9 centrifugal compressor
Axial Compressor An axial compressor imparts
(cid:12)9 axial compressor momentum to a gas by means of a cascade of airfoils. The
lift and drag coefficients of the airfoil shape determine the
Ejector An ejector is a very simple device which uses compressor characteristics. Figure 1.4 shows a typical axial
a high-pressure jet stream to compress gas. The momentum compressor. An axial compressor incorporated in a turbo-
of the high-pressure jet stream is transferred to the low- charger is shown in Figure 1.5.
! ....... I ....
teln~ elzzoN !:~.~-
24 --4PI 300o ! I
...................... i~ .... :.i ~ , ..... ~ i ~ ,/:'_'~--.
i i ..i .. ......................
.........................................................
Figure 1.2. Centrifugal compressor. ysetruoC( of arabE ).noitaroproC
CO ~ O c m "O .1 C e'- 2 e-" ID a CD E m I 8 E 0 L_
(cid:12)9
Q I TI
i~
l
I ! I ! i I
0