Fundamentos De Compresores, Curvas Performance
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- Pages: 116
Centrifugal Compressors
© 2006 Dresser-Rand
Topics
Centrifugal Compressor Model
How a Centrifugal works / Energy Conversion
Centrifugal Flowpaths
Performance Curves
Operation Limits: Surge & Overload
Factors Affecting Compressor Performance
Operational Issues – Optimizing Compressor Efficiency © 2006 Dresser-Rand
Axially or Horizontally Split Compressor
© 2006 Dresser-Rand
Radially or Vertically Split Compressor
© 2006 Dresser-Rand
Radially Split with Shear Ring Heads Shear Ring
O-Rings
Retaining Ring © 2006 Dresser-Rand
Shear Rings & O-Rings
© 2006 Dresser-Rand
The Centrifugal Effect Centripetal Force Momentum Velocity & Direction
Centrifugal Reaction
© 2006 Dresser-Rand
Gas Velocity Increase V3 V2
V1
© 2006 Dresser-Rand
Gas Impeller Exit Angle Exit Path at Rated Flow Low Flow Exit Path Exit Path Due to Backward Curve Tangent Exit Path
•© 2004 © 2006 by Dresser-Rand
Centrifugal Action Cover
Blades
Disk
TIP OF THE IMPELLER High Velocity, Higher Pressure Gas Outlet EYE OF THE IMPELLER Low Velocity, Low Pressure Gas Inlet
© 2006 Dresser-Rand
Impellers Manufacturing • Cast • Riveted • Welded Two Piece Three Piece
Cover
Blades
Types • Open • Semi-Enclosed • Enclosed
Disk
Hub © 2006 Dresser-Rand
Polygon Fit Impeller Rotor Assembly
© 2006 Dresser-Rand
Centrifugal Action Diffusion Passage Diffusion Passage
Diffusion Passage
P2
P2 P1
P1 Shaft
Impeller
Impeller
© 2006 Dresser-Rand
Diffusion Passage Cross-Sectional Area Diffusion Passage
Diffusion Passage
© 2006 Dresser-Rand
Diffusion Passage Velocity Changes V1 V2
Diffusion Passage
Diffusion Passage
V2
V1
V1
V1 Shaft Impeller
Impeller
© 2006 Dresser-Rand
Pressure, Volume and Temperature
1 ft.
Gas = 1 ft.3 1 ft. 1 ft. © 2006 Dresser-Rand
Temperature and Molecule Energy Level Greater Temperature = Greater Energy = Higher Pressure
© 2006 Dresser-Rand
Pressure, Volume and Temperature
1 ft.
Gas = 1 ft.3 1 ft. 1 ft.
Add Heat © 2006 Dresser-Rand
What is a Stage of Compression? Centrifugal Stage
Return Bend
Return Bend
Diffuser Reduces Velocity Increases Static Pressure
Return Channel
Guide Vanes
Impeller Increases Velocity Increases Static Pressure
© 2006 Dresser-Rand
Centrifugal Compressor Stage
© 2006 Dresser-Rand
Energy Conversion
P4,V4,T4
P5,V1,T5
P3,V1,T3
P5,V1,T5 P2,V4,T2
P1,V1,T1
P3,V1,T3 © 2006 Dresser-Rand
Centrifugal Flowpaths P3
P5
P7
P9
Balance Piston P1
Straight Thru or Series Flow
© 2006 Dresser-Rand
Centrifugal Flowpaths SS In
P3
SS Out
P5
P7
P9
Balance Piston P1
Series Flow with Sidestreams
© 2006 Dresser-Rand
Centrifugal Flowpaths P7
P3 P5
P9
Balance Piston
P1
Compound Flow
© 2006 Dresser-Rand
Centrifugal Flowpaths P3
P5
P3
P1
P1
Parallel or Double Flow
© 2006 Dresser-Rand
Centrifugal Flowpaths P9
P5
D Wall
P1
D Wall
P5
Back to Back Flow with No Cooler
© 2006 Dresser-Rand
Back-to-Back Flow without a Cooler First Section Suction
Second Section Discharge
Second Section Inlet
Division Wall First Section Discharge
CrossOver
© 2006 Dresser-Rand
Centrifugal Flowpaths P9
P5
D Wall
P1
D Wall
P5
Back to Back Flow with a Cooler
© 2006 Dresser-Rand
Bridgeovers 1 2
3 4
5
1 2
3
6
7
8
9
10
4
5
6
7
Bridgeovers
© 2006 Dresser-Rand
Bridgeovers
Bridgeover © 2006 Dresser-Rand
Inlet Guides Fit to Diaphragm
Interstage Labyrinth Seal Grooves
© 2006 Dresser-Rand
Diaphragm Return Bend Diffusion Passage
Return Passage
© 2006 Dresser-Rand
Inlet Guide In Diaphragm
Outside Diameter of Impeller © 2006 Dresser-Rand
Interstage Seals Impeller
Function P3
P5
Diffuser Diaphragm
Shaft Interstage Laby Seals
Location
Labyrinth Seal
P1
Labyrinth Seal Shaft Spacer
Impeller
P4
Diaphragm
P2
Labyrinth Seal Labyrinth Seal
Shaft Spacer
P3 Impeller
© 2006 Dresser-Rand
Labyrinth Seals Seal Turbulence - Low Flow Seal Shaft Low Pressure
High Pressure Shaft
Seal with Worn Teeth
Low Pressure
Shaft Low Pressure
High Pressure
Laminar High Flow
High Pressure
Wet Gas Condensate Deposits
© 2006 Dresser-Rand
Hole Pattern Division Wall Seal with Swirl Brake
This design makes the seal insentive to preswirl even if the shunt is lost, which can occur during overload operation © 2006 Dresser-Rand
Performance Curves and Surge Control
© 2006 Dresser-Rand
Performance Curves
Head Concept
Basic Components
Fixed/Variable Speed
Surge/Overload
Effects on Performance
© 2006 Dresser-Rand
Head Concept Mechanical: The “work” (energy) developed to raise a weight of 1 pound by a distance of one (1) foot. Expressed in foot-pound (or equivalent Kgm or Nm);
Gas Compressors: “ work” done by the compressor / amount of gas. The head expressed in feet, is the height to which the gas could be lifted
© 2006 Dresser-Rand
Head Concept The height to which the gas is lifted depends on the velocity of the gas
For any given RPM, the head developed by the compressor is fairly constant, independent of the gas nature.
Head is depending upon: • Compressor geometry (i.e. no of stages, impeller diameters) • Compressor speed
Z: Compressibility Factor R: Gas Constant = 1545 / MW Ts: Suction Temperature (°R)
M:
r: Pressure Ratio (Pd / Ps) M: Polytrophic Exponent © 2006 Dresser-Rand
Head Concept – Example
© 2006 Dresser-Rand
Compressor Performance Curves illustrates the operating range and flexibility of a given compressor
% Head, Pressure, Pressure Ratio
120% Surge Region
110%
Design Point
100%
105% 100% 95% 90%
90% Speed Lines
80%
85%
70%
Overload Region
60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Compressor Performance Curves There are two types of curves that are generally required, section and overall:
• section refers to an impeller or sequence of impellers between two nozzles such that there is no pressure drop or temp reduction between impellers
• overall refers to a complete compressor or compressor train Note: a back-to-back unit with a crossover may often be considered a two-section compressor; but with respect to performance curves, it is a single section since no pressure drop or cooling is introduced between the impellers
For single section compressors, the section curves and overall curves are one in the same
© 2006 Dresser-Rand
Design Point is the point at which usual operation is expected and optimum efficiency is . It is the point at which the vendor certifies that performance is within the tolerance % Head, Pressure, Pressure Ratio
120% 110%
Design Point
100% 90% 80% 70% 60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Rated Point is intersection on the 100 % speed line corresponding to the highest flow of any operating point
% Head, Pressure, Pressure Ratio
120% 110%
Rated Point
100% 90% 80% 70% 60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Stability: the percent of change in capacity between the rated (design point) capacity and surge (limit) point, all at constant speed, is measured as the stability of the centrifugal compressor. Indicates the capability of the centrifugal compressor to operate at less than design flow
% Head, Pressure, Pressure Ratio
120% 110%
Design Point
100% % Stability
90% 80% 70% 60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Turndown: the percent of change in capacity between the rated
% Head, Pressure, Pressure Ratio
(Design point) capacity and the surge (limit) point, all at constant head or pressure is measured as turndown of the centrifugal compressor. Indicates the capability of the centrifugal compressor to operate at less than design flow 120% 110%
Design Point
100% 90% % Turndown
80% 70% 60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Rise to Surge: the percent of change in discharge pressure between the rated point and surge limit at constant speed. High RTS means the compressor can accommodate a modest increase in discharge pressure with a little change in flow
% Head, Pressure, Pressure Ratio
120% 110%
Design Point
% RTS
100% 90% 80% 70% 60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Surge Phenomenon At any given speed, there is minimum flow, below which, the compressor cannot be operated in a stable condition. This minimum flow value is called “surge “ point.
Surge is oscillation of the entire flow of the compressor system and this oscillation can be detrimental to the machine.
Compressor surge may be evidenced by the following: a) Excessive rotor vibration b) Increasingly higher process gas temp c) Rapid changes in axial thrust d) Sudden changes in load e) Audible sounds (if surge is severe) © 2006 Dresser-Rand
Surge Description
Resistance to Flow Causes Pressure to Rise Which Causes Flow to Decrease
Sudden Reversal of Flow Slams Thrust Disc Against
% Head, Pressure, Pressure Ratio
120% 110%
Inactive Thrust Bearing
Surge Region
Design Point
100% 90% 80% 70% 60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Surge Description
Resistance to Flow Causes Pressure to Rise Which Causes Flow to Decrease
Sudden Reversal of Flow Slams Thrust Disc Against
% Head, Pressure, Pressure Ratio
120% 110%
Inactive Thrust Bearing
Surge Region
Design Point
100%
Pressure Builds along the Design Curve Back to the Design Point
90% 80% Pressure Ratio Drops Low Enough
70%
for Flow to Instantaneously Build Back to the Design Curve
60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Surge Control System Input Signals Required 1 - Suction Flow 2 - Suction Pressure 3 - Discharge Pressure Suction
2
Flow Element
Flow Transmitter FT
Recycle Valve
1
Pressure PT Pressure PT Transmitter Transmitter 3 PC SP U
I/P
Discharge
G D A AC G E B I I OO B T C MCH
Surge Control In the PLC
© 2006 Dresser-Rand
Surge Control on Performance Curves Operating Point
Control Line
Surge Line 120%
Pressure Ratio
110% 100% 90% 80% 70% 60% 60%
80%
90%
100%
120%
Suction Flow © 2006 Dresser-Rand
Surge Control System Input Signals Required 1 - Suction Flow 2 - Suction Pressure 3 - Discharge Pressure Suction
2
Flow Element
Flow Transmitter FT
Recycle Valve
1
Pressure PT Pressure PT Transmitter Transmitter 3 PC SP U
I/P
Discharge
G D A AC G E B I I OO B T C MCH
Surge Control In the PLC
© 2006 Dresser-Rand
Surge Control on Performance Curves Operating Point
Control Line
Surge Line
Backup Line
120%
Pressure Ratio
110% 100% 90% 80% 70% 60% 60%
80%
90%
100%
120%
Suction Flow © 2006 Dresser-Rand
Surge Control Surge Controller Performance Map
© 2006 Dresser-Rand
Suction
Flow Element
To Vent
FT
Blow Off Valve
PC SP U
I/P
PT
PT
Discharge
G D A AC G E B I I OO B T C MCH
Surge Control In the PLC
© 2006 Dresser-Rand
Cooler Suction
Flow Element
Flow FT Transmitter Recycle Valve
Pressure PT Pressure PT Transmitter Transmitter PC SP U
I/P
Discharge
G D A AC G E B I I OO B T C MCH
Surge Control In the PLC
© 2006 Dresser-Rand
Surge – Damage of Compressor Internals High axial displacement
Deformation due to high temperature © 2006 Dresser-Rand
Surge The frequency of the surge cycle varies inversely with the volume of the system
If the check valve is located near compressor discharge nozzle, the frequency will be much higher than of a system with a large volume in the discharge upstream of the check valve
The higher frequency of the surge, the intensity will be lower (i.e. few cycles / minute up to more than 20 cycles / sec)
The intensity of the surge increases with gas density , pressure and lower temperature
© 2006 Dresser-Rand
Surge - Effects of Gas Composition Best Efficiency point E% Heavy Gas (propane, propylene) Medium Gas (air, nitrogen, natural gas) Light Gas (Hydrogen reach gases, i.e. hydrocarbon processing plants)
Surge points
Q © 2006 Dresser-Rand
Surge - Effects of Gas Composition Observations made in respect to the heavy gas:
The flow at surge is higher;
The stage produces more head than corresponding to medium gas / light gas
The right side of the curve turns downward (approaches stonewall) more rapidly
The curve is flatter in the opening stage (small RTS)
© 2006 Dresser-Rand
External Causes and Effects of Surge
Restriction in suction or discharge of system
Process changes in pressure, temperatures, or gas MW
Internal plugging of flow passages of compressor (fouling)
Inadvertent loss of speed
Instrument or control valve malfunction
Operator error
Misdistribution of load in parallel operation
Improper assembly of compressor (impeller overlap)
© 2006 Dresser-Rand
Restriction in Suction / Discharge
© 2006 Dresser-Rand
Parallel Operation Typically, for parallel operation, the flow is not split evenly and one section or compressor handles more flow than the other, but both sections are required to make the same pressure ratio
Careful analysis of the pressure ratio curves is required to insure satisfactory operation and suitable overall range
“similar pressure ratio curves” • At the design flow, section (1) is much more flow than of section (2)
• If the total flow is reduced 10%, the compressor slows down to maintain the same pressure ratio
• The flow to each section is reduced 10% (dashed line) since the pressure ratio curves have a approximately the same rise © 2006 Dresser-Rand
“different pressure ratio curves” (section 2 pressure ratio curve is steeper than section 1) • If the total flow is reduced 10% the compressor slows down to maintain pressure ratio • Section (1) reduces more than 10% ( about 12.5% - the dashed line) since its curve is shallower • Section (2) reduces less than 10% (about 5% - dashed line) since its curve is steeper • The two sections are now operating at significantly different portions of the curve and are now handling a different percentage of the total flow than they were at the design point.
• Section (1) is nearing surge. Further reduction in flow would force section one into surge
• The difference in the curve shape results in a reduced overall range for parallel operation © 2006 Dresser-Rand
Impeller Overlap with Diffuser
© 2006 Dresser-Rand
Impeller Overlap with Diffuser
Positive overlap
Nominal
Non Desirable
Limited
Desired
Limited
© 2006 Dresser-Rand
Impeller Overlap with Diffuser
It is preferable that no impeller shall have negative overlap
The negative overlap is limited to 5% of the impeller tip
© 2006 Dresser-Rand
Overload
% Head, Pressure, Pressure Ratio
120% Surge Region
110%
Design Point
100%
105% 100% 95% 90%
90% Speed Lines
80%
85%
70%
Overload Region
60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Choke Limit Choke is the maximum flow that a centrifugal compressor can handle at a given speed. At that point, the compressor is unable to produce any net overall pressure ratio.
The maximum flow region of the compressor performance curve is where the gas speeds approach Mach 1
Gas compression is no longer occurring in the compression channels. This region of the curve, as it becomes almost vertical at the choke limit, is also know as “Stonewall”
Stonewall is usually not detrimental to the compressor, it simply limits the maximum flow. If choke occurs at an off design condition, the maximum volume flow can be increased by increasing the rotational speed
© 2006 Dresser-Rand
Performance Curves – Inlet Gas Condition Effects
© 2006 Dresser-Rand
Performance Curves – Inlet Gas Condition Effects
© 2006 Dresser-Rand
Factors Affecting Compressor Performance MW & Head - If MW increases, the head for a given ratio will decrease in direct proportion
Temp & Head - If the Ts increases, the head for a given ratio will increase in direct proportion
Zave & Head - If the average compressibility increases, the head will increase in direct proportion
N and Head - If speed increases, the head will increase in direct proportion
BHP and Head - If Head increases, the BHP will increase in direct proportion
Flow and Speed - If the speed increases, the flow will increase in direct proportion
© 2006 Dresser-Rand
Factors Affecting Compressor Performance N & BHP - If the speed increases, the BHP will increase in proportion to the cube of the speed. (Because flow increases directly as speed and head increases as the square of the speed and BHP is the product of head X mass flow)
Density - The only thing a compressor impeller sees is inlet capacity. Thus to get more capacity out of an existing compressor it is necessary to change the density of the inlet by: • decreasing the suction temperature • increasing the suction pressure • increasing the MW of the gas
© 2006 Dresser-Rand
Compressor Off - Design Performance Performance curves for axial and centrifugal compressors are usually based on constant inlet conditions (Ps, Ts, MW). In actual service, these compressors rarely see these base curve conditions exactly
If the field inlet conditions deviate more then 5% from the curve inlet conditions then the field data can not be accurately plotted on the curve without converting the field data to curve conditions
To properly evaluate the compressor (running off design), the performance parameters shall be corrected to the design conditions
© 2006 Dresser-Rand
Allowable Variance for Inlet TZ / MW for Acceptable Head Curve Accuracy
© 2006 Dresser-Rand
Operation Limitations Compressor Driver Power Process © 2006 Dresser-Rand
Compressor Operation IssuesEfficiency Drop
Internal recycle Un-tuned Surge Control System Leakage via by-pass valve(s) in process Compressor operated out of “guaranteed performance envelope” Impeller & Diaphragm erosion Fouling
© 2006 Dresser-Rand
Internal Recycle – Gap at the diaphragm / guides splits
© 2006 Dresser-Rand
Internal Recycle – Gap at the diaphragm / guides splits
© 2006 Dresser-Rand
Labyrinth Leakage Leakage proportional to: • ∆P • Clearance • Diameter •1 / (No.Laby Teeth)0.5 Eye laby leakage is approx. 10 times spacer laby leakage
Eye Laby Leakage Spacer Laby Leakage © 2006 Dresser-Rand
Internal Recycle – Labyrinth Clearance
Process labyrinths can be plugged by wet particles in the gas flow
© 2006 Dresser-Rand
Internal Recycle – Labyrinth Clearance Shaft Spacer
Impeller Cover
© 2006 Dresser-Rand
Internal Recycle – Labyrinth Clearance
Impeller Cover
© 2006 Dresser-Rand
PEEK Labyrinth
© 2006 Dresser-Rand
PEEK Physical Properties GRADE
Arlon CP Torlon 4340 Fluorosint 500
COEF. THERMAL EXPNSION (F) 17 x 10 /-6 18.8
TENSILE STRENGTH (PSI)
ELONGATION (%)
SPECIFIC GRAVITY
11,080 12,900
2.0 6.6
1.45 1.44
19.4
1,100
10.0
2.32
© 2006 Dresser-Rand
Un- tuned Surge Control System
Recycle valve shall be calibrated at every planned S/D
• • •
fast opening ( < 1 sec) total travel 0-100 %; 4 – 20 mA mechanical stop to coincide with 100 % close
Valve positioner shall match the command
FT instrument shall be calibrated at every planned S/D
Flow calculation block – correct constants, correct range
© 2006 Dresser-Rand
Fouling … is the deposit and the non –uniform accumulation of debris in the gas
Occurs due to carry over of liquids and debris from the inlet suction scrubber
Polymerization may occur in wet gas and cracked gas compressors applications if the temperature exceeds the critical point beyond the polymerization process occurs (235 F)
Fouling build up occurs usually on the impeller hub and shroud. There is also a build up on the blades ( on the pressure side)
© 2006 Dresser-Rand
Fouling
IGV partially clogged
1st stage impeller – hard deposits
© 2006 Dresser-Rand
Fouling Effects – Charge Gas
3M7 – Eroded Sleeves © 2006 Dresser-Rand
Fouling Effects
April 25 '99
NPC Thai Fouling
Abrasive Scoring due to Fouling
9
© 2006 Dresser-Rand
Fouling Effects – Charge Gas
3M7 - Deterioration of stage clearances © 2006 Dresser-Rand
Fouling Deposit Characterization
Scientifically characterization of the fouling deposits can provide clear information about the actual cause(s) of the problem(s) . Key deposit characterization includes:
1)
Elemental Analysis - Chemical Composition (C, H, O, N, S)
2)
Electron Microscopy Morphology – Microstructure composition analysis components (asphaltene, oil, coke, and inorganic)
3)
TGA (thermo gravimetric analyzer) - Thermal fractionation into components
4)
EDS (x-ray) Electron Dispersive Spectroscopy - Inorganic elements
5)
X-RAY Diffraction - Inorganic compounds
© 2006 Dresser-Rand
Techniques to Prevent Fouling Condition monitoring, both aerodynamic and mechanical parameters
Process control
Online solvent injection
Coatings of Impellers and Diaphragms
© 2006 Dresser-Rand
Fouling - Condition Monitoring (aerodynamic and mechanical parameters)
Monitor and trend the information regarding process conditions • MW • Pressure • Temperature
Vibration monitoring • On line system • Off line system © 2006 Dresser-Rand
Condition Monitoring Calculate and trend the compressor polytrophic efficiency using the reference point (i.e. after overhaul, revamp)
k − 1 log(Pd Ps ) ηp = ⋅ k log(Td Ts ) K – isentropic coefficient; Cp , Cv – specific heat at constant pressure / volume
© 2006 Dresser-Rand
Condition Monitoring – DR RECON Online System
© 2006 Dresser-Rand
Fouling - Process Control
Accurate control of process conditions can prevent fouling ( for applications where polymers can be formed) Temperature control is the most important factor for preventing polymer formations (i.e. Ethylene cracked gas, Fluid catalytic cracker off-gas FSS) Critical temperature above fouling occurs varies with each process, compressor, application Monitoring of process is required to establish the temperature threshold for each case
© 2006 Dresser-Rand
Fouling – Online Fluid Injection ..
injecting a small amount of solvent to reduce the friction coefficient of the blade and impeller surface (maintain the surface wet) thus preventing the fouling to build up on the surface The injection shall be done from the start (new equipment / overhauled) , if not the fouling deposit could be dislodged and moved downstream (blockage)
Injection objective is to prevent fouling accumulations, not to provide on line cleaning of the impeller / blade
Non continuous solvent injection program will allow the impeller / blade to dry and promote fouling
© 2006 Dresser-Rand
Fouling – Online Fluid Injection
Critical factors that ensure fouling will not form: • Type of injection spray nozzles • Location of the spray nozzles • Selection of solvent Solvent vapor pressure and internal comp temperatures is necessary to determine if stage or section solvent injection is applicable Typically amount of solvent injection is 1-2 % of total mass flow. Excessive injection could erode leading edge blade tips, causing impeller fatigue © 2006 Dresser-Rand
Online Fluid Injection
Solvent injection:
• Purpose is to maintain a wet surface to prevent fouling material sticking (typically Naphtha based solvent) • Injected at suction pipe of each section (Spool piece) • Injected at compressor return bends regardless gas temperature • 0.5 to 1.0% of total gas weight flow at each section is effective, but not exceed 3% of total gas weight flow
H2O injection:
• Purpose is to reduce gas temperature ( by evaporation of water) • Injected at return bends where discharge gas temperature is high • Demi water (boiler feed water), with low oxygen content is recommended. Filters to be installed at upstream of spray nozzle to prevent clogging
© 2006 Dresser-Rand
Fluid Injection at Suction Nozzle
© 2006 Dresser-Rand
Fluid Injection at Return Bend
© 2006 Dresser-Rand
Online Fluid Injection F
Flowmeter
Water Injection Nozzle
Solvent Injection Tank (Optional)
Water Injection Connecting Piping (By Customer) Optional Solvent Injection Nozzle Optional Solvent Injection Connecting Piping (By Customer)
PG Pressure Gauge
Valve BFW Pump (By Customer)
H2O Tank
>20 kg/cm2
BFW PUMP F
F PG
PG
F
F
PG
PG
F
F PG
PG
“A”
Stg 1
Stg 2
Sect 1
Stg 3
Stg 1
4M7-6
Stg 2
Stg 3
F
F
“A”
PG
Sect 2
PG
“B”
PG
F PG
F PG
Stg Stg Stg Stg 2 3 4 1
2M9-7
Sect 4
“B” F
F PG
PG
Stg Stg Stg 1 2 3
Sect 3
F
F
F PG
F PG
F PG
PG
© 2006 Dresser-Rand
Coatings - Purpose Prevent the base metal from external attack Protect the blades against oxidation, corrosion, and cracking problems Extend the life of the impeller (protect the blades by being sacrificial by allowing coating to be restripped and recoated) Improve surface smoothness in order to reduce: • friction in lieu of solvent injection • erosion on compressor blades
© 2006 Dresser-Rand
Engineered Coatings – “Cold Coatings” ….
A Sacrificial Barrier Coating System with a Base
Coat and Multiple Topcoats
Benefits: a) Protection
• Corrosion • Fouling • Erosion
b) Improved Operation
• Smoother Surface Finish • Improved Resistance to Fouling • Improved Efficiency • Improved Reliability © 2006 Dresser-Rand
D-R Corrosion / Antifoulant Coating System EEC-C1 Hard Top Seal Coat
Sacrificial Base Coat
© 2006 Dresser-Rand
D-R Anti-foulant Coating System EEC-A2 &A3
PTFE Top Coat Barrier Coat
Sacrificial Base Coat
© 2006 Dresser-Rand
Anti-Foulant Coating
EEC - A2
EEC - A3
© 2006 Dresser-Rand
Engineered Coatings – Thermal Coatings A metallic particle spray overlay applied by a High Velocity Oxy Fuel (HVOF) Process
Benefits:
• Dimensional Restoration • Protection • Wear • Erosion
• Improved Wear Characteristics • Improved Reliability © 2006 Dresser-Rand
Engineered Coatings – Thermal Coatings A metallic particle spray overlay applied by a High Velocity Oxy Fuel (HVOF) Process
Benefits:
• Dimensional Restoration • Protection • Wear • Erosion
• Improved Wear Characteristics • Improved Reliability © 2006 Dresser-Rand
HVOF Applied EEC - TC Coatings Piston Rods
Impellers
Rotor Shafts
© 2006 Dresser-Rand
Coatings - SermaLon® Coating The SermaLon coating system consists of:
• Al-filled chromate/phosphate bond coat;
• Intermediate high temperature polymeric inhibitive coating
• PTFE impregnated topcoat (provides a barrier against corrosion and excellent resistance to fouling) The coating system provides excellent protection to 403 and 410 stainless substrates when exposed to corrosive steam conditions or low pH wet chloride environments
© 2006 Dresser-Rand
Coatings - SermaLon® Coating Advantages Smooth surface finish and PTFE impregnated topcoat contribute to performance recovery and reduced fouling rate
Excellent bond strength
High resistance to corrosion fatigue
Applications Centrifugal compressors exposed to wet chlorides or excessive fouling
Steam turbine components exposed to corrosive steam;
© 2006 Dresser-Rand
www.dresser-rand.com [email protected] © 2006 Dresser-Rand
© 2006 Dresser-Rand
Topics
Centrifugal Compressor Model
How a Centrifugal works / Energy Conversion
Centrifugal Flowpaths
Performance Curves
Operation Limits: Surge & Overload
Factors Affecting Compressor Performance
Operational Issues – Optimizing Compressor Efficiency © 2006 Dresser-Rand
Axially or Horizontally Split Compressor
© 2006 Dresser-Rand
Radially or Vertically Split Compressor
© 2006 Dresser-Rand
Radially Split with Shear Ring Heads Shear Ring
O-Rings
Retaining Ring © 2006 Dresser-Rand
Shear Rings & O-Rings
© 2006 Dresser-Rand
The Centrifugal Effect Centripetal Force Momentum Velocity & Direction
Centrifugal Reaction
© 2006 Dresser-Rand
Gas Velocity Increase V3 V2
V1
© 2006 Dresser-Rand
Gas Impeller Exit Angle Exit Path at Rated Flow Low Flow Exit Path Exit Path Due to Backward Curve Tangent Exit Path
•© 2004 © 2006 by Dresser-Rand
Centrifugal Action Cover
Blades
Disk
TIP OF THE IMPELLER High Velocity, Higher Pressure Gas Outlet EYE OF THE IMPELLER Low Velocity, Low Pressure Gas Inlet
© 2006 Dresser-Rand
Impellers Manufacturing • Cast • Riveted • Welded Two Piece Three Piece
Cover
Blades
Types • Open • Semi-Enclosed • Enclosed
Disk
Hub © 2006 Dresser-Rand
Polygon Fit Impeller Rotor Assembly
© 2006 Dresser-Rand
Centrifugal Action Diffusion Passage Diffusion Passage
Diffusion Passage
P2
P2 P1
P1 Shaft
Impeller
Impeller
© 2006 Dresser-Rand
Diffusion Passage Cross-Sectional Area Diffusion Passage
Diffusion Passage
© 2006 Dresser-Rand
Diffusion Passage Velocity Changes V1 V2
Diffusion Passage
Diffusion Passage
V2
V1
V1
V1 Shaft Impeller
Impeller
© 2006 Dresser-Rand
Pressure, Volume and Temperature
1 ft.
Gas = 1 ft.3 1 ft. 1 ft. © 2006 Dresser-Rand
Temperature and Molecule Energy Level Greater Temperature = Greater Energy = Higher Pressure
© 2006 Dresser-Rand
Pressure, Volume and Temperature
1 ft.
Gas = 1 ft.3 1 ft. 1 ft.
Add Heat © 2006 Dresser-Rand
What is a Stage of Compression? Centrifugal Stage
Return Bend
Return Bend
Diffuser Reduces Velocity Increases Static Pressure
Return Channel
Guide Vanes
Impeller Increases Velocity Increases Static Pressure
© 2006 Dresser-Rand
Centrifugal Compressor Stage
© 2006 Dresser-Rand
Energy Conversion
P4,V4,T4
P5,V1,T5
P3,V1,T3
P5,V1,T5 P2,V4,T2
P1,V1,T1
P3,V1,T3 © 2006 Dresser-Rand
Centrifugal Flowpaths P3
P5
P7
P9
Balance Piston P1
Straight Thru or Series Flow
© 2006 Dresser-Rand
Centrifugal Flowpaths SS In
P3
SS Out
P5
P7
P9
Balance Piston P1
Series Flow with Sidestreams
© 2006 Dresser-Rand
Centrifugal Flowpaths P7
P3 P5
P9
Balance Piston
P1
Compound Flow
© 2006 Dresser-Rand
Centrifugal Flowpaths P3
P5
P3
P1
P1
Parallel or Double Flow
© 2006 Dresser-Rand
Centrifugal Flowpaths P9
P5
D Wall
P1
D Wall
P5
Back to Back Flow with No Cooler
© 2006 Dresser-Rand
Back-to-Back Flow without a Cooler First Section Suction
Second Section Discharge
Second Section Inlet
Division Wall First Section Discharge
CrossOver
© 2006 Dresser-Rand
Centrifugal Flowpaths P9
P5
D Wall
P1
D Wall
P5
Back to Back Flow with a Cooler
© 2006 Dresser-Rand
Bridgeovers 1 2
3 4
5
1 2
3
6
7
8
9
10
4
5
6
7
Bridgeovers
© 2006 Dresser-Rand
Bridgeovers
Bridgeover © 2006 Dresser-Rand
Inlet Guides Fit to Diaphragm
Interstage Labyrinth Seal Grooves
© 2006 Dresser-Rand
Diaphragm Return Bend Diffusion Passage
Return Passage
© 2006 Dresser-Rand
Inlet Guide In Diaphragm
Outside Diameter of Impeller © 2006 Dresser-Rand
Interstage Seals Impeller
Function P3
P5
Diffuser Diaphragm
Shaft Interstage Laby Seals
Location
Labyrinth Seal
P1
Labyrinth Seal Shaft Spacer
Impeller
P4
Diaphragm
P2
Labyrinth Seal Labyrinth Seal
Shaft Spacer
P3 Impeller
© 2006 Dresser-Rand
Labyrinth Seals Seal Turbulence - Low Flow Seal Shaft Low Pressure
High Pressure Shaft
Seal with Worn Teeth
Low Pressure
Shaft Low Pressure
High Pressure
Laminar High Flow
High Pressure
Wet Gas Condensate Deposits
© 2006 Dresser-Rand
Hole Pattern Division Wall Seal with Swirl Brake
This design makes the seal insentive to preswirl even if the shunt is lost, which can occur during overload operation © 2006 Dresser-Rand
Performance Curves and Surge Control
© 2006 Dresser-Rand
Performance Curves
Head Concept
Basic Components
Fixed/Variable Speed
Surge/Overload
Effects on Performance
© 2006 Dresser-Rand
Head Concept Mechanical: The “work” (energy) developed to raise a weight of 1 pound by a distance of one (1) foot. Expressed in foot-pound (or equivalent Kgm or Nm);
Gas Compressors: “ work” done by the compressor / amount of gas. The head expressed in feet, is the height to which the gas could be lifted
© 2006 Dresser-Rand
Head Concept The height to which the gas is lifted depends on the velocity of the gas
For any given RPM, the head developed by the compressor is fairly constant, independent of the gas nature.
Head is depending upon: • Compressor geometry (i.e. no of stages, impeller diameters) • Compressor speed
Z: Compressibility Factor R: Gas Constant = 1545 / MW Ts: Suction Temperature (°R)
M:
r: Pressure Ratio (Pd / Ps) M: Polytrophic Exponent © 2006 Dresser-Rand
Head Concept – Example
© 2006 Dresser-Rand
Compressor Performance Curves illustrates the operating range and flexibility of a given compressor
% Head, Pressure, Pressure Ratio
120% Surge Region
110%
Design Point
100%
105% 100% 95% 90%
90% Speed Lines
80%
85%
70%
Overload Region
60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Compressor Performance Curves There are two types of curves that are generally required, section and overall:
• section refers to an impeller or sequence of impellers between two nozzles such that there is no pressure drop or temp reduction between impellers
• overall refers to a complete compressor or compressor train Note: a back-to-back unit with a crossover may often be considered a two-section compressor; but with respect to performance curves, it is a single section since no pressure drop or cooling is introduced between the impellers
For single section compressors, the section curves and overall curves are one in the same
© 2006 Dresser-Rand
Design Point is the point at which usual operation is expected and optimum efficiency is . It is the point at which the vendor certifies that performance is within the tolerance % Head, Pressure, Pressure Ratio
120% 110%
Design Point
100% 90% 80% 70% 60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Rated Point is intersection on the 100 % speed line corresponding to the highest flow of any operating point
% Head, Pressure, Pressure Ratio
120% 110%
Rated Point
100% 90% 80% 70% 60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Stability: the percent of change in capacity between the rated (design point) capacity and surge (limit) point, all at constant speed, is measured as the stability of the centrifugal compressor. Indicates the capability of the centrifugal compressor to operate at less than design flow
% Head, Pressure, Pressure Ratio
120% 110%
Design Point
100% % Stability
90% 80% 70% 60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Turndown: the percent of change in capacity between the rated
% Head, Pressure, Pressure Ratio
(Design point) capacity and the surge (limit) point, all at constant head or pressure is measured as turndown of the centrifugal compressor. Indicates the capability of the centrifugal compressor to operate at less than design flow 120% 110%
Design Point
100% 90% % Turndown
80% 70% 60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Rise to Surge: the percent of change in discharge pressure between the rated point and surge limit at constant speed. High RTS means the compressor can accommodate a modest increase in discharge pressure with a little change in flow
% Head, Pressure, Pressure Ratio
120% 110%
Design Point
% RTS
100% 90% 80% 70% 60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Surge Phenomenon At any given speed, there is minimum flow, below which, the compressor cannot be operated in a stable condition. This minimum flow value is called “surge “ point.
Surge is oscillation of the entire flow of the compressor system and this oscillation can be detrimental to the machine.
Compressor surge may be evidenced by the following: a) Excessive rotor vibration b) Increasingly higher process gas temp c) Rapid changes in axial thrust d) Sudden changes in load e) Audible sounds (if surge is severe) © 2006 Dresser-Rand
Surge Description
Resistance to Flow Causes Pressure to Rise Which Causes Flow to Decrease
Sudden Reversal of Flow Slams Thrust Disc Against
% Head, Pressure, Pressure Ratio
120% 110%
Inactive Thrust Bearing
Surge Region
Design Point
100% 90% 80% 70% 60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Surge Description
Resistance to Flow Causes Pressure to Rise Which Causes Flow to Decrease
Sudden Reversal of Flow Slams Thrust Disc Against
% Head, Pressure, Pressure Ratio
120% 110%
Inactive Thrust Bearing
Surge Region
Design Point
100%
Pressure Builds along the Design Curve Back to the Design Point
90% 80% Pressure Ratio Drops Low Enough
70%
for Flow to Instantaneously Build Back to the Design Curve
60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Surge Control System Input Signals Required 1 - Suction Flow 2 - Suction Pressure 3 - Discharge Pressure Suction
2
Flow Element
Flow Transmitter FT
Recycle Valve
1
Pressure PT Pressure PT Transmitter Transmitter 3 PC SP U
I/P
Discharge
G D A AC G E B I I OO B T C MCH
Surge Control In the PLC
© 2006 Dresser-Rand
Surge Control on Performance Curves Operating Point
Control Line
Surge Line 120%
Pressure Ratio
110% 100% 90% 80% 70% 60% 60%
80%
90%
100%
120%
Suction Flow © 2006 Dresser-Rand
Surge Control System Input Signals Required 1 - Suction Flow 2 - Suction Pressure 3 - Discharge Pressure Suction
2
Flow Element
Flow Transmitter FT
Recycle Valve
1
Pressure PT Pressure PT Transmitter Transmitter 3 PC SP U
I/P
Discharge
G D A AC G E B I I OO B T C MCH
Surge Control In the PLC
© 2006 Dresser-Rand
Surge Control on Performance Curves Operating Point
Control Line
Surge Line
Backup Line
120%
Pressure Ratio
110% 100% 90% 80% 70% 60% 60%
80%
90%
100%
120%
Suction Flow © 2006 Dresser-Rand
Surge Control Surge Controller Performance Map
© 2006 Dresser-Rand
Suction
Flow Element
To Vent
FT
Blow Off Valve
PC SP U
I/P
PT
PT
Discharge
G D A AC G E B I I OO B T C MCH
Surge Control In the PLC
© 2006 Dresser-Rand
Cooler Suction
Flow Element
Flow FT Transmitter Recycle Valve
Pressure PT Pressure PT Transmitter Transmitter PC SP U
I/P
Discharge
G D A AC G E B I I OO B T C MCH
Surge Control In the PLC
© 2006 Dresser-Rand
Surge – Damage of Compressor Internals High axial displacement
Deformation due to high temperature © 2006 Dresser-Rand
Surge The frequency of the surge cycle varies inversely with the volume of the system
If the check valve is located near compressor discharge nozzle, the frequency will be much higher than of a system with a large volume in the discharge upstream of the check valve
The higher frequency of the surge, the intensity will be lower (i.e. few cycles / minute up to more than 20 cycles / sec)
The intensity of the surge increases with gas density , pressure and lower temperature
© 2006 Dresser-Rand
Surge - Effects of Gas Composition Best Efficiency point E% Heavy Gas (propane, propylene) Medium Gas (air, nitrogen, natural gas) Light Gas (Hydrogen reach gases, i.e. hydrocarbon processing plants)
Surge points
Q © 2006 Dresser-Rand
Surge - Effects of Gas Composition Observations made in respect to the heavy gas:
The flow at surge is higher;
The stage produces more head than corresponding to medium gas / light gas
The right side of the curve turns downward (approaches stonewall) more rapidly
The curve is flatter in the opening stage (small RTS)
© 2006 Dresser-Rand
External Causes and Effects of Surge
Restriction in suction or discharge of system
Process changes in pressure, temperatures, or gas MW
Internal plugging of flow passages of compressor (fouling)
Inadvertent loss of speed
Instrument or control valve malfunction
Operator error
Misdistribution of load in parallel operation
Improper assembly of compressor (impeller overlap)
© 2006 Dresser-Rand
Restriction in Suction / Discharge
© 2006 Dresser-Rand
Parallel Operation Typically, for parallel operation, the flow is not split evenly and one section or compressor handles more flow than the other, but both sections are required to make the same pressure ratio
Careful analysis of the pressure ratio curves is required to insure satisfactory operation and suitable overall range
“similar pressure ratio curves” • At the design flow, section (1) is much more flow than of section (2)
• If the total flow is reduced 10%, the compressor slows down to maintain the same pressure ratio
• The flow to each section is reduced 10% (dashed line) since the pressure ratio curves have a approximately the same rise © 2006 Dresser-Rand
“different pressure ratio curves” (section 2 pressure ratio curve is steeper than section 1) • If the total flow is reduced 10% the compressor slows down to maintain pressure ratio • Section (1) reduces more than 10% ( about 12.5% - the dashed line) since its curve is shallower • Section (2) reduces less than 10% (about 5% - dashed line) since its curve is steeper • The two sections are now operating at significantly different portions of the curve and are now handling a different percentage of the total flow than they were at the design point.
• Section (1) is nearing surge. Further reduction in flow would force section one into surge
• The difference in the curve shape results in a reduced overall range for parallel operation © 2006 Dresser-Rand
Impeller Overlap with Diffuser
© 2006 Dresser-Rand
Impeller Overlap with Diffuser
Positive overlap
Nominal
Non Desirable
Limited
Desired
Limited
© 2006 Dresser-Rand
Impeller Overlap with Diffuser
It is preferable that no impeller shall have negative overlap
The negative overlap is limited to 5% of the impeller tip
© 2006 Dresser-Rand
Overload
% Head, Pressure, Pressure Ratio
120% Surge Region
110%
Design Point
100%
105% 100% 95% 90%
90% Speed Lines
80%
85%
70%
Overload Region
60% 60%
80%
90%
100%
120%
% Inlet Capacity or Flow
© 2006 Dresser-Rand
Choke Limit Choke is the maximum flow that a centrifugal compressor can handle at a given speed. At that point, the compressor is unable to produce any net overall pressure ratio.
The maximum flow region of the compressor performance curve is where the gas speeds approach Mach 1
Gas compression is no longer occurring in the compression channels. This region of the curve, as it becomes almost vertical at the choke limit, is also know as “Stonewall”
Stonewall is usually not detrimental to the compressor, it simply limits the maximum flow. If choke occurs at an off design condition, the maximum volume flow can be increased by increasing the rotational speed
© 2006 Dresser-Rand
Performance Curves – Inlet Gas Condition Effects
© 2006 Dresser-Rand
Performance Curves – Inlet Gas Condition Effects
© 2006 Dresser-Rand
Factors Affecting Compressor Performance MW & Head - If MW increases, the head for a given ratio will decrease in direct proportion
Temp & Head - If the Ts increases, the head for a given ratio will increase in direct proportion
Zave & Head - If the average compressibility increases, the head will increase in direct proportion
N and Head - If speed increases, the head will increase in direct proportion
BHP and Head - If Head increases, the BHP will increase in direct proportion
Flow and Speed - If the speed increases, the flow will increase in direct proportion
© 2006 Dresser-Rand
Factors Affecting Compressor Performance N & BHP - If the speed increases, the BHP will increase in proportion to the cube of the speed. (Because flow increases directly as speed and head increases as the square of the speed and BHP is the product of head X mass flow)
Density - The only thing a compressor impeller sees is inlet capacity. Thus to get more capacity out of an existing compressor it is necessary to change the density of the inlet by: • decreasing the suction temperature • increasing the suction pressure • increasing the MW of the gas
© 2006 Dresser-Rand
Compressor Off - Design Performance Performance curves for axial and centrifugal compressors are usually based on constant inlet conditions (Ps, Ts, MW). In actual service, these compressors rarely see these base curve conditions exactly
If the field inlet conditions deviate more then 5% from the curve inlet conditions then the field data can not be accurately plotted on the curve without converting the field data to curve conditions
To properly evaluate the compressor (running off design), the performance parameters shall be corrected to the design conditions
© 2006 Dresser-Rand
Allowable Variance for Inlet TZ / MW for Acceptable Head Curve Accuracy
© 2006 Dresser-Rand
Operation Limitations Compressor Driver Power Process © 2006 Dresser-Rand
Compressor Operation IssuesEfficiency Drop
Internal recycle Un-tuned Surge Control System Leakage via by-pass valve(s) in process Compressor operated out of “guaranteed performance envelope” Impeller & Diaphragm erosion Fouling
© 2006 Dresser-Rand
Internal Recycle – Gap at the diaphragm / guides splits
© 2006 Dresser-Rand
Internal Recycle – Gap at the diaphragm / guides splits
© 2006 Dresser-Rand
Labyrinth Leakage Leakage proportional to: • ∆P • Clearance • Diameter •1 / (No.Laby Teeth)0.5 Eye laby leakage is approx. 10 times spacer laby leakage
Eye Laby Leakage Spacer Laby Leakage © 2006 Dresser-Rand
Internal Recycle – Labyrinth Clearance
Process labyrinths can be plugged by wet particles in the gas flow
© 2006 Dresser-Rand
Internal Recycle – Labyrinth Clearance Shaft Spacer
Impeller Cover
© 2006 Dresser-Rand
Internal Recycle – Labyrinth Clearance
Impeller Cover
© 2006 Dresser-Rand
PEEK Labyrinth
© 2006 Dresser-Rand
PEEK Physical Properties GRADE
Arlon CP Torlon 4340 Fluorosint 500
COEF. THERMAL EXPNSION (F) 17 x 10 /-6 18.8
TENSILE STRENGTH (PSI)
ELONGATION (%)
SPECIFIC GRAVITY
11,080 12,900
2.0 6.6
1.45 1.44
19.4
1,100
10.0
2.32
© 2006 Dresser-Rand
Un- tuned Surge Control System
Recycle valve shall be calibrated at every planned S/D
• • •
fast opening ( < 1 sec) total travel 0-100 %; 4 – 20 mA mechanical stop to coincide with 100 % close
Valve positioner shall match the command
FT instrument shall be calibrated at every planned S/D
Flow calculation block – correct constants, correct range
© 2006 Dresser-Rand
Fouling … is the deposit and the non –uniform accumulation of debris in the gas
Occurs due to carry over of liquids and debris from the inlet suction scrubber
Polymerization may occur in wet gas and cracked gas compressors applications if the temperature exceeds the critical point beyond the polymerization process occurs (235 F)
Fouling build up occurs usually on the impeller hub and shroud. There is also a build up on the blades ( on the pressure side)
© 2006 Dresser-Rand
Fouling
IGV partially clogged
1st stage impeller – hard deposits
© 2006 Dresser-Rand
Fouling Effects – Charge Gas
3M7 – Eroded Sleeves © 2006 Dresser-Rand
Fouling Effects
April 25 '99
NPC Thai Fouling
Abrasive Scoring due to Fouling
9
© 2006 Dresser-Rand
Fouling Effects – Charge Gas
3M7 - Deterioration of stage clearances © 2006 Dresser-Rand
Fouling Deposit Characterization
Scientifically characterization of the fouling deposits can provide clear information about the actual cause(s) of the problem(s) . Key deposit characterization includes:
1)
Elemental Analysis - Chemical Composition (C, H, O, N, S)
2)
Electron Microscopy Morphology – Microstructure composition analysis components (asphaltene, oil, coke, and inorganic)
3)
TGA (thermo gravimetric analyzer) - Thermal fractionation into components
4)
EDS (x-ray) Electron Dispersive Spectroscopy - Inorganic elements
5)
X-RAY Diffraction - Inorganic compounds
© 2006 Dresser-Rand
Techniques to Prevent Fouling Condition monitoring, both aerodynamic and mechanical parameters
Process control
Online solvent injection
Coatings of Impellers and Diaphragms
© 2006 Dresser-Rand
Fouling - Condition Monitoring (aerodynamic and mechanical parameters)
Monitor and trend the information regarding process conditions • MW • Pressure • Temperature
Vibration monitoring • On line system • Off line system © 2006 Dresser-Rand
Condition Monitoring Calculate and trend the compressor polytrophic efficiency using the reference point (i.e. after overhaul, revamp)
k − 1 log(Pd Ps ) ηp = ⋅ k log(Td Ts ) K – isentropic coefficient; Cp , Cv – specific heat at constant pressure / volume
© 2006 Dresser-Rand
Condition Monitoring – DR RECON Online System
© 2006 Dresser-Rand
Fouling - Process Control
Accurate control of process conditions can prevent fouling ( for applications where polymers can be formed) Temperature control is the most important factor for preventing polymer formations (i.e. Ethylene cracked gas, Fluid catalytic cracker off-gas FSS) Critical temperature above fouling occurs varies with each process, compressor, application Monitoring of process is required to establish the temperature threshold for each case
© 2006 Dresser-Rand
Fouling – Online Fluid Injection ..
injecting a small amount of solvent to reduce the friction coefficient of the blade and impeller surface (maintain the surface wet) thus preventing the fouling to build up on the surface The injection shall be done from the start (new equipment / overhauled) , if not the fouling deposit could be dislodged and moved downstream (blockage)
Injection objective is to prevent fouling accumulations, not to provide on line cleaning of the impeller / blade
Non continuous solvent injection program will allow the impeller / blade to dry and promote fouling
© 2006 Dresser-Rand
Fouling – Online Fluid Injection
Critical factors that ensure fouling will not form: • Type of injection spray nozzles • Location of the spray nozzles • Selection of solvent Solvent vapor pressure and internal comp temperatures is necessary to determine if stage or section solvent injection is applicable Typically amount of solvent injection is 1-2 % of total mass flow. Excessive injection could erode leading edge blade tips, causing impeller fatigue © 2006 Dresser-Rand
Online Fluid Injection
Solvent injection:
• Purpose is to maintain a wet surface to prevent fouling material sticking (typically Naphtha based solvent) • Injected at suction pipe of each section (Spool piece) • Injected at compressor return bends regardless gas temperature • 0.5 to 1.0% of total gas weight flow at each section is effective, but not exceed 3% of total gas weight flow
H2O injection:
• Purpose is to reduce gas temperature ( by evaporation of water) • Injected at return bends where discharge gas temperature is high • Demi water (boiler feed water), with low oxygen content is recommended. Filters to be installed at upstream of spray nozzle to prevent clogging
© 2006 Dresser-Rand
Fluid Injection at Suction Nozzle
© 2006 Dresser-Rand
Fluid Injection at Return Bend
© 2006 Dresser-Rand
Online Fluid Injection F
Flowmeter
Water Injection Nozzle
Solvent Injection Tank (Optional)
Water Injection Connecting Piping (By Customer) Optional Solvent Injection Nozzle Optional Solvent Injection Connecting Piping (By Customer)
PG Pressure Gauge
Valve BFW Pump (By Customer)
H2O Tank
>20 kg/cm2
BFW PUMP F
F PG
PG
F
F
PG
PG
F
F PG
PG
“A”
Stg 1
Stg 2
Sect 1
Stg 3
Stg 1
4M7-6
Stg 2
Stg 3
F
F
“A”
PG
Sect 2
PG
“B”
PG
F PG
F PG
Stg Stg Stg Stg 2 3 4 1
2M9-7
Sect 4
“B” F
F PG
PG
Stg Stg Stg 1 2 3
Sect 3
F
F
F PG
F PG
F PG
PG
© 2006 Dresser-Rand
Coatings - Purpose Prevent the base metal from external attack Protect the blades against oxidation, corrosion, and cracking problems Extend the life of the impeller (protect the blades by being sacrificial by allowing coating to be restripped and recoated) Improve surface smoothness in order to reduce: • friction in lieu of solvent injection • erosion on compressor blades
© 2006 Dresser-Rand
Engineered Coatings – “Cold Coatings” ….
A Sacrificial Barrier Coating System with a Base
Coat and Multiple Topcoats
Benefits: a) Protection
• Corrosion • Fouling • Erosion
b) Improved Operation
• Smoother Surface Finish • Improved Resistance to Fouling • Improved Efficiency • Improved Reliability © 2006 Dresser-Rand
D-R Corrosion / Antifoulant Coating System EEC-C1 Hard Top Seal Coat
Sacrificial Base Coat
© 2006 Dresser-Rand
D-R Anti-foulant Coating System EEC-A2 &A3
PTFE Top Coat Barrier Coat
Sacrificial Base Coat
© 2006 Dresser-Rand
Anti-Foulant Coating
EEC - A2
EEC - A3
© 2006 Dresser-Rand
Engineered Coatings – Thermal Coatings A metallic particle spray overlay applied by a High Velocity Oxy Fuel (HVOF) Process
Benefits:
• Dimensional Restoration • Protection • Wear • Erosion
• Improved Wear Characteristics • Improved Reliability © 2006 Dresser-Rand
Engineered Coatings – Thermal Coatings A metallic particle spray overlay applied by a High Velocity Oxy Fuel (HVOF) Process
Benefits:
• Dimensional Restoration • Protection • Wear • Erosion
• Improved Wear Characteristics • Improved Reliability © 2006 Dresser-Rand
HVOF Applied EEC - TC Coatings Piston Rods
Impellers
Rotor Shafts
© 2006 Dresser-Rand
Coatings - SermaLon® Coating The SermaLon coating system consists of:
• Al-filled chromate/phosphate bond coat;
• Intermediate high temperature polymeric inhibitive coating
• PTFE impregnated topcoat (provides a barrier against corrosion and excellent resistance to fouling) The coating system provides excellent protection to 403 and 410 stainless substrates when exposed to corrosive steam conditions or low pH wet chloride environments
© 2006 Dresser-Rand
Coatings - SermaLon® Coating Advantages Smooth surface finish and PTFE impregnated topcoat contribute to performance recovery and reduced fouling rate
Excellent bond strength
High resistance to corrosion fatigue
Applications Centrifugal compressors exposed to wet chlorides or excessive fouling
Steam turbine components exposed to corrosive steam;
© 2006 Dresser-Rand
www.dresser-rand.com [email protected] © 2006 Dresser-Rand
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