Training Services
Pumps n Introduction
= Pump Curves - Head versus Capacity - WSH - EBciency
u Single-Stage Centrifugal Pwmp Design - Pump Components
- Shaft SeaXing
Pumps
(continued) m Reliability
Fan Laws a Hydraalics 8 Pump Control 8
i.
r Sdessh p s r h p Selection and PerEomance r Doizble Suction, Mujti-Stage, and Sundyne funips
"
pd46"S"
phq?!
This is a typical pump curve. The pump curve gives information on how the pump will perform, the NPSH required by the pump, and the impeller size m g e for the casing. AH p m p manufacturer's c m e s are similar so, if you can read one nnanufiictwer's curve, you can read anybodys.
0
400
800 1200 I W Gallons Per Minme
2000
2400
Head-capacity curve. Once this curve is established based on the impeller diameter and speed, the pump wig1 always operate on this curve. Note how the curve rises as the Row goes down. This is a charactexistic of d l centrifugal pumps.
Single Stage Centrifagal Pump Mechanical Seal
Shaft f Sleeve
~ k l i n ~Deflector Met Ring
L '
0 3 Levef BoHe
Single stage centrifugd pump. As the centrifugil force of the impeller throws the fluid out towards the cstsing, the velocity of the fluid goes up. -4s the fluid leaves the p m p , this velociQ energy is changed to pressure energy.
I L
Identical Pumps Handling Liquids of Dgferent Specific
CrasoEioc. S.G. = 0.75
Waxer, S.G. = f .O
Brine, S.G = 1.2
Pump perfomance is measured in feet or meters of head. Head i s the height of the column that the pump cm move the fluid. Pump head is a function of impeller diameter and sped. It is not a function of the density or specific gravity of &e pumped fluid. Here are three identical. pumps pumping out of three identical tanks. Note that the head or column height is identical even though the specific gravity of the Ruid is different.
Galbns Per ,Minute
'
Each pump casing size can handle more than one size impeller. This pump casing can handle impeller diameters between 9 and J 1 inches. Also, the impeller can be trimmed to any size between 9 and 11 inches to meet the sated opemxing point. The impeller diaeter does not have to be a whale inch size.
0
L2
-
.E;
z cr?
2
o
400
aw
1200 ISOO 2000 ~rl.00 CaXlons Per Minute
The pump m e also gives the NPSH required by the pump. Note how %he ,WE required curve rises with increasing flow.
B
A
Puhc Along Liquid Pit&
The fluid loses pressure in the pump before the pressure starts to rise. As the fluid enters the pump, these are entrance and friction losses. As the ffaid enters the rotating impeller, $here are turbulence and friction Iosses at the vane tips. If this pmssure drop is enough to drop the pressure of the fluid below its vapor pressure point, flashing will occur. This phenomena, called caviation, will quickly destroy an impeller and a pump. The h?SH ava3lable must be greater than the WSH required.
The NPSH avaifable is a function of the pumping sysxem. WSW available is the pressure at the pump suction minus the fluid vapor presswe. Xt is the pressure thaz can be lost in the pump inlet area before Washing or catritaeon begins. For a bubble point or vapor pressure point fluid, the &iSH avaitfabje is gained with vessel. elevation.
0
300
800 1200 1600 Galtoas Per &ate
2000
2400
The pump curve shows the efficiency of tfxe pump at any operating point. Note that the efficiencies rise with rising Bow to the best efficiency point (BEP), and then quickly drop off. Optimum pump operation is at or near best efficiency point.
0
- \
I d -
0
400
800 lGZOO 1600 Gallons Per Minute
2000
2300
Pwnp curves also show the FP requirement for the pump. Do not use these curves. CAU3UX,AE W. These FP c w e s only appfy if the specific gravity of the fluid is 1.0. Also, it i s difficult to get a good, accurate reading. EEP is a simple calculation shown later in this talk.
Pump Selection Y
60 Cycle C m n t 3550rlmn
Singk Sxcion 35% r/min
I
I
Two Sage Prmss Uoubit. Suction S550 r h n
Double Sumon
Pump Cap~ciry,gpm
This chart shows the approximate head-capacity ranges of single stage fuX1 and half speed pumps, doable suction pumps, and two and &ti-stage pumps. Low Bow, high head applications are Sundynes.
AE API pumps today are centerline mounted. The centerline mounx allows the pump casing to p w both up and down as the casing hears up. This keeps the shaft in the horizontal plane and helps prevents seal leaks and shaft mis-alignment.
Impellers
All API pumps today have closed impellers with covers or shrouds on both sides of the vanes. This gives the fluid a more defined path through the pump and raises efficiency. The flow splitter in the outlet or double volute equalizes the radial forces around the impeller and minimizes the load on the radial bearings.
Single Suetion Enclosed Impeller
Single suction enclosed impefier.
Siagle Suction impeller
Large single suction impeller. Note tee impeller vanes at the inlet md outIet, This is a half speed impeller. Full speed impellers are only allowed up to 15 inches in diameter to control tip speeds,
Suction Specific Speed
J.
PV*P
S = rpm ( g ~ r n/)frvPSItr)3J4 ~
-
r Can range between 3000 20000
'
The suction specific speed relates rpm, gpm, and NPSH required. UOP limits the suction specific speed to 11000. If a pump manufacturer w a s to reduce the NPSH required of a certain pump, he can increase the impeller eye m a to reduce fiction drop and reduce IWSW required. This increased eye area increases the internal circulation in rhe suction area of the pump. This can buitd up heat which can also flash the fluid and reduce pump reliability. This also reduces the sable operating range of the pump. As the flow is reduced, the p m p becomes less efficient and more heat is built up in the pump. At higher suction,. specific speeds this can promute cavitation.
Model 3735 High TmperatuteMigh Pressure Process Pumps Heavy Duty Design Features to Meet the Total Range of Process Indu:stries Intpetier Wearing Rings
Sealing Renewable Stuffing Box Refiability Froat Bushing
b
t
1
Y
Duaf
IWfficient Voiate Mechanical Casing Sealcooijng
,- Heavy Cast
Large Cooling Jacket
This is a single stage (one impeller), single suction (one entry into the impeller), overhung (impeller is cantilevered on one set of bearings) pump. This is c d k d a Process pump. The metdfwgy is as follows: Casing Impeller Shaft Wearing rings Throat bushing Throttle bushing
Carbon Steel Carbon Steel <50Q°F,11-13% Cr >50O0F Carbon Steel 11-1.396 Cr il-13%Cr Bronze or non-sparking m a h a 3
1 Single Stage Overhung Pump
Single stage, single suction, overhung p m p . Note the vent connection on the top of the casing.
Single Stage Pump
Single stage, single suction, overhung pump. This pump is self-venting as the dischsge is at the high point of the casing. This design is typic$.
Before there were mechanical seals, pumps were sealed by "stuffing" an absorbent material caned packing wound Ehe shaft. Since the process fluid had to lubricate &e surface between the stu%h,a and the shaft, the packing had to leak, typically a b u t 200 cchr for a new application. Over time, &e packing would become sitmated with fluid and the leakage would increase until the pump had to be shut down m d &e packing replaced. Today, UOP does not specify any pumps with packing.
Single Mechanical Seal I
Single mechanical seal. Mlost A H pumps today have single mechanical seals. The single mechanical pusher type seal has two members, a rotating member md a stationary member. The main sealing takes place due to the friction between the rotating seal face and the stationary seal face. Since the pumped fluid lubricated this seal face, the si-qle mechanical seal does leak. Typical leak rates are about 2 ccfhr or about f 00 p p of emissions in the air sumunding the se& As the seal faces wear, springs in the rotating member keep a t i a t fit between %he two seal faces. O-rings prevent X&age between the seal and the shaft and between she seal and the pump casing.
Connection B (refer io appropriate \xiliary seal piping m g e m c n t )
Connection A (refer to appropriate primary seal piping arrangement)
Seal Box
Seal
End Plate
Sleeve -.-w-
Rotatiag
Seal .Member
/
sealing device
Single mechanical seal. Used for most non-hazardous services.
Single Mechanical Seal
Here is another view of the single mechanical seal. Note the yellow process fluid coming from rhe pump discharge to the process side seal face. The mbbing seat faces generate heat. If the pumped Ruid is at vapor pressure or bubble point and. heat is added, the fluid could Aash around the sea$and the seal faces codd b e their lubricant- Process fluid flows fron the discharge of the p m p &-ou& an usifice. The pmsswe is kept high enough momd the seal to stay above the vapor pressure point even though with the seal faces are adding heat.
Puller Croove
Solid &.eel W v e Lags
Welded Metal Betitows
Rotating Sestf
Carbon or Tungsten Carbide vs. SteIlite Sealing Faces
Stationary seat
]Bellows seals are specified for high temperature applications, above 5S0°F. Bellows seals have two members9 a rotating member and a stationary member, similar to &e pusher type seal.
f
Cap S
X*FICOZI
When the seal face wears on a bellows seal, the metal beljlows expands like an accordion. The o-rings bemeen the seal and the shaft do not move dong Ehe shaft as they do in a pusher type seal. Since the xing material starts to break down at higher temperatures, pusher type seak are temperame limited due to h e dynamic o-ring. Since the o-ring on the bellows seal is sattic, the bellows seal cca operate effecgvely at temperatures up to 800°F.
m ~1000 ppm (Most
m Comply wigh Regulations in Most Cases 8
3+ Years Life
Liquid Taadem Seals (Unpressarized Dual Seals)
= c50 ppm (Most
r Diesel Buffer Liquid 8
3+ Years Life
Tandem seals are now referred to as mpxessurized dual seals. The buffer between the two seals is vented to flare and is unpressurized. Leakage of process fluid is greatly reduced from the single mechanical seal. Any process fluid that leaks across &e inner seal is contained by the outer seal. Refease of process fluid to the atmosphere is under 10 ppm.
Unpressurized Dual Seals Connection C (refer to appropriate randem seal piping m n g e m n t )
fe Bushing (mechaaical seal
Seal Member
shing) or auxiliary s e a h g device
Unpressusized dud mechanicd sed. Used for following:
-
Light hydrocarbons - Vapor pressure over 30 psig
* 1 wt % Benzene 25 wt % C6-c9~O-CS
5 mol% H,S * Other environmentally hazardous materials
Buffer fluid is circulated from the seal pot to the buffer area and back to the seal pot with pumping rings on the shaft. Leakage of process fluid is into the buffer area. The seal pot has a pressure dann for Bashing fluids and a level aIann fur non-flashing,fluids to warn of an inner seal leak.
Photo_wph of actual API Plan 52.
'
Mufti-stage pump with unpressurized dual sears. Note the two seal pots the the API Plan 52.
Disc .tion Tube
Suction
Sealless canned motor pump. Zero fugitive emissions. The motor windings turn a magnet on the pump shaft across a containment barrier. The process fluid lubricate the bearings on the pump shaft and remove heat from the mom windings. Therefore, %hepump cannot be run dry (bearings will not be lubric&ed] or be fun blacked in (heat will not be removed from a e motor). UOP specifies insmmentation (alarm and shutdowns) to prevent pump damage En the event of mis-opefatiom.
Sealless canned pump. Yote the process fluid circulating from the pump discharge to the back end of the pump. The nuid rhen travels though the p m p , Iszbricafing the shaft bearings and removing heat from the motor windings. .
If &e process fluid is comsivc, ( E F acid) the bearing fluid could be from an external source. s&
Sedfess canned pump. For this type, the process fluid i s circulating back through the shaft instead of externally.
Magnetic Drive Pamp
Sedless magnetic drive pump. Magnets on the motor shaft twn mapets on the pump shaft across a contaiment barrier. This is an altemte design to the canned motor p m p . Process ffuid still Iubpicates the p u p sha& bearings. Zero fugitive emissions.
Magnoseal "
Standard Features
ASMWANSI 13'mensions Magnetic Coupiings to 100 IfP Engineered Composite andMetal Containment SkUs m Precision Cast SemiOpen Impeller Wear Resistant Silicon Carbide Bearing System i
Sealless magnetic (Mag) drive pump. Note that the magnetic couplings are good only to 100 HP.
Reliability and Maintenance What is ReliabiXitv? The main objective of reliability is to achieve the highest plant availability at the lowest possible cost in order to maximize prof~t,
The goal is t o achieve f i e World Ciuss target of 95+%plant availability!
Reliability and Maintenance Equipment - Centrifugal Compressors, Some pumps - Unspared - Continuous Monitoring System .Pumps, Reciprocating Compressors - Spared ; .Critical
-
Periodic Monitoring o f Vibration b t a CoIleci and Analyze
-
R o o t Cause Analysis
-
Reliability and Maintenance Equipment Specs and Standards Vendor Selection Design and Testing
Process Considerations Operations and Monitoring
Reliability and Maintenance 95% on-kne availability for pumps, 5 year MTBR
1. Reactive - Run to failure 2. Preventative - Time-based maintenance 3. Proactive - Condition-based mainhnance
t
Reliability and Maintenance Reactive
- Run %oFailure
1
Process Interruption m No Opportunity for Diagnosis Frequent failures r Other Pasts are Effected Replace Good PUT%
Reliability and Maintenance Pre'ventative
- Time-based
Maintenance
r N o UppurtuniSy for Diagnosis i deplace
600d parts
Reliability and Maintenance Proactive m
- Condition-based Maintenance
Repair Before Pump Fails
m Replace Only Bad Parts u Diagnostics and Root Cause Anavsis
Portable Vibration Monitor
.Reliabilityand Maintenance
Unbalance RPMx 1 Bent Shaft W M x I. or 2, Cavitation Random Misalignment R3PN x 1 and 2 Pardlel Angular Foundatioffi, Unsteac3y XUPM,
Steady Axial high Fluctuating
Radial High Axial
Reliability and Maintenance Prucuremerzt
EPC during vendor/contractor proposal review "I am concerned with 3 things: Price, price and price"
Reliability and Maintenance
1. Price 2. Functionality
Reliability and Maintenance Procurement
Main Air Blower quits Cost up to $500,0001day in lost production
1. Functionality 2. Reliability 3. Utilities 4.
Price
Reliability and Maintenance Procurement
Reliability and Maintenance Life Cycle Costs
i1
I
Reliability and Maintenance
E
Besi Psactices - Pump and Sys?ern Design Suction Specific Speed 4 11000 m L3/b4 < 60 (inches) -6brj~-k+ 1% m Design system for operation a t or near BEP m 5 faot NPSH margin M i n i m 5 pipe diameters shvtight pipe on r 1mtafl APX Flush ?Ian 23 if pumping temperatwe > 30O0F (14g0C)
Reliability and Maintenance ,
=
-
1
-
Best Practices Pump Operation
Do not start and stop often Do not nm pump dry Operate at or near BEP m V i i y iinhpect pump often (once per shift) r M;easummd record brati ions
Check cooling water and seal flush temps B Inspect and change bearing 0.2(3-6 months) r Do not "hose down'' pumps D
r
Report problems immed.iately Training
Reliability and Maintenance Best Pmtices - Pump Reliabifitv r Alignment
-
~8kee 8 Bearings w b b e oil Mudtoring - $rendanalysis
Reliability and Maintenance
I Reliable Reciprocating Compressor Design
,
Hf
i
i
Limit Piston Speed m Lianit 3Pis;tonRPM .' Limit CyHnder Size 8 L M t Discharge Temp (250°F) r Lubricate Cylinders = coat ~isttyxR U ~ m Vibration and Temperature Moni^tor FPD.%XWPD-M
Relkbility and Maintenance Reliable Centrifugal Compressor Design
I
!i
m
r r r r
Limit b4axi.m-
Impeller Yield Strength
~q as Seals
Report all Operating Cases Voting Type Sha*down An$i-surge c;oatrok (where required)
Affinity Relationships
Q = Capacity, gpm N
= Rotative Speed, rpm
H = Head, feet ]HIP
= Horsepower
D
= Impeller Diameter
Affinity relationships or fan laws.
The flow varies proportionaI to the speed variation md the head varies pfoportionaI to the square of the speed. These laws explain why high flows and low heads are achieved wjth law speed p m g s and low flows and high heads ate achieved with high speed (Sundym) pumps.
d
I
BHP =
GP.M x Head x $13. CR - Ib / nin x Head 3960 x E g 33,000 x E#
- GPM
x PSI 1714 x Efl
When using pump curves for 60 cycle and the pumps wi3I be in a m n t y with 50 cycle power, &e Row, head, md NPSH required must be corrected before a pump can be selected,
Horsepower in Field Measure imp draw of motor Watts = b p s x Volts BHP=1.73 x Amps x VoRs x motor eff x motor power factor i
746
Motor eff = 0.95 (Approx) Motor power factor = 0.90 (Approx) For si~gfephase mot& don't mdtip3y by 1.73 (3y")
Horsepower in Field Power Factor Power factor is the ratio between the KW and the KVA drawn by an electricat load where the KW is the actual load power and the KVA is the apparent load power. Xt is a measure of how effectively the current is being converted into usem work output and more partZculariy is a good indicawr of the effect:of the load cmsent on &e eMicienty of the supply system*
I
Horsepower in Field
i
ExayXe ~ n r ~ s30' = Volts = 360 BKP = 1.73 ( 30) (360) (0.95) (090)/746 i
GPM = 300 P2 = 170
BHP = 21.4
Eff = (300) (1'70-95)/(1714)(21.(t)
Head = psi *2.31/S.G.
System Resistance Curve
Flow, gpm
IPP.WDR
q3 ~ s i g=i &&
I
30 psig mH a >
200 GPM, 33 % Flow 0 5 psi
1.5 psi
0.5 psi
I
1 psi
1 psi
7 70 psig
System Resistance Curve
R U Wgpm ~
E P W
System Resistance Curve
Pump Performance Curve
F~ow, gpm
IP&203Wpn78
Twu Centrifgal Pumps in Parallel
Capacity gpm
When pumps s e operated in parallel, the combined performance curve is obtaiaed by adding horizontally the capacities of the same heads. it is preferred that the head-capacity curves rise to shtrtoff: If the curves droop and if the second pump comes on-line at low flow, the pruryi, cuufd "hunt" between two flows at ate s m e head.
Two Centr?ugaIPumps in Series
Capacity gpm tPDWDBi P D M Y
For series opesation, the combined performance curve is abtained by adding vertically the heads at the same capacities. Note that the maximum suction pressme of the &wnswem p a p is the shutoff pressure of the upstream PUW'.
Typical Mo.tor/Motor Spare Pump Amgemeat Discharge
9
Typically, there are nxro pumps insQlled, one operating and one spare. If a pump goes out of service, an operator has to corne out and srart up the spare pump. Pumps are typiaEy started with the &scharee valve closed or pinched open. The bast amount, of starting torque req&red by the motor to stm the pump is with the discharge valve closed.
Typical Motor-Auto Cut-In Turbine Spare Pamp Arrangement Discharge .-----.-----.-:
i
!
I
h 7
"I I
i
Slow Roll
,EZY-P~SS
/
Control
Exhaust Steam 3.5 Kg/m2g
Critical service pumps are on mtomaric start. Examples of critical service pumps are Boiler Feedwater, Surface Condenser Condensate, Compressor Lube Oil, and HI? Add pumps. If a critical service pump goes out of service, equipment, personnel, or caalysr codd be damaged before an operator corxld get the spare p m p in opedon. Therefore, the spare pump must come on-line automaticidly when the operating p a p goes down,
Rolling Element (Ball)Bearings Radjd
Vent
Double Axial Thrust Bearings
Rolling Element Bearings
Ring Oil Bearing Lubrication
Rolling Element Bearings
r Per APX 610 Minimum Requirements
r 23M0 horn (3 yrs) at rated capacity m 16000 hours (2 yrs) at nzax radial & axial loads
Bearings Enemies rr Wrong 02 level Wa$er
a Sotids
Bearings Oil Level 8 Just Right - Half
way up bottom bearing Too Low - Inadequate Lubrication f" -!+bq Too High - Excessive Heat -+ k9 +& w-*Q
Per SKI", oil has useful life of 30 yrs @ 30°C (80°F) Cug in half for every 10°C ( 18"F)rise .rr At 100°C (2E°F) usefuf life is 90 days 8
Bearings Water Where Does It Come From?
i-
fCiq,.&, a House Cleaning Seal Gland Quench Aspiration N Open Oil Cans m Other
A h
bai.
?LAC)
Bearings Water What Are Problems? ifitting and
Corresion increase fatigue
Free a t d e X.f, camas hydrogen exnbnittlexnent acce~eralhgfatigue Water/oil emulsion is poor fabricant rt
01002% H 2 0 can reduce bearing life 48%
Bearings Solids Where Do They Come From? Seal Cage and Bearing Box Seal Wear m Oil Flinger Ring r,Soofids in contamhated 02 1 Air borne partides m Entrodaced during assembly
Oil Mist
Wrong 03 Ievds, water eontamination, solid abrasion all go away with oil mist lubrication
I
Pure Oil Mist
Pure Oil M-ist
Pure Oil M'st Engineered for large Process units: rn Serve up to 80 Pumps with Drivers Required Maimum of 30 SCFM of Air m Consume Less than 2 Gallons of Oil per Day ..,justifying use of Synthetic Oils for Mzulimm Benefits r I pm oil per 200,000 parts a b
Oil Mist Benefits a The Proper Amount of Clean Oil is Applied
Continuously a Clean Oace Thfough Lubrication B e a ~ Housings g are Pressurized Preventing External Contamination m Internal Metal Surfaces are Always Coated 114th oil which Prevents Corrosion (Important For Stand-by E q n i p a t ) n L,, Bearing Life $3Extended by a Factw of 6 Source: Texas A&M Unrivemity Research
Oil Mist BeneJits
m
m m
r
~ekringfdures reduced up to 90% Dirt particles are not delivered to the bearings Dirt pantides do not accumulate in the oil sump W y r particles are carried away hearings operate 18 to 27°F cooler Bearings see onjly fresh oil Seal failures m y be reduced up to 30%
Double Suction
Single stage, double suction between bearing pump.
.-
+*-fLdv2.te .an
irdJfl
6. 6y.f
\p,-.lha%
*"/pep
Single Stage Double Stlction
Single stage, double suction pump. Note the between bearing design.
Two Stage Single Suction Between Bearing
Two stage, single suction pump.
HofizontaEly (axially) spiit multi-stage pump.
8 Stage Centrtyugal P a q Opposed linpellers
Mechanical
Wear
Cross
Seal Quench 7
Discharge J
~ z & sOver f m 4th Stage Discharge to 5& Stage Suction
Inside of hurizontal11ysplit mufti-stage pump. The impeXlers are opposed to each other. The first stage is on the far left of &e pump. The fluid travels to f$e left for the first four stages. m e r the fourth stage, the fluid crossed over ta the far right and travels to fhe right for the 5th through 8th stages. This is to balance the axid thrust on the bearings.
1
Horizontally Split Multi-Stage
Six stage, axidly split pump. Note the cf.ossover piping internal to the casing.
Double Case Ceatr~ugalPamps
Radially split multi-stee pump. Radially split .multi-stage pumps are more expensive and take longer to repair &an axidly split multi-stage pumps. The axidZy split rnuki-stage pump has a large casing split. Therefore, to reduce &e possibility of process fluid Je&age, APT 610 does not allow the use of axidly split muki-stage pimps if the panping temperature is over 400°F,the discharge pressure is over 1450 psig or the specific gravity is under 0.7.
Mrclti-Stage Pump with Balancing Drum
Suction
Inside a radially split multi-stage p m p . Note that the impellers are all facing the same direction. This is because the design of she forged, barrel type casing does not allow for the cross over piping. To bdance the axial thrusts, a balance d m atmched to a line at suction pressure is installed on the discharge side. This drum absorbs the axial thrust. Also, this enables both seals to sed against suction pressure.
RadtizlZy Split Multi-Stage
Six stage radial1y spjitjt pump. Note the double suction suction erst stage for
reduced -WSH. Also note .the balance piston discharge.
Mbdel LiMV21 Sundyne Process Pump Power linit
Gearbox
Integral Centrifugal Separator Diffuser
Mechanicai Seal
Pump Casing
Sundyne pump. This is a high speed, integrally geared pump used for low flow, high head appXica~ions. Sundyne is the only manufacturer having good success with this design of p m q . This pump is built to MI 610 standards. It can achieve high heads using high speed rather than multiple impellers.
Sundyne with single gem between motor shafl and impeller shaft. This type gear box is good to 50 hp.
Purchasing Pumps Technical Evalaation Does it meet flow and head? Check completed API data sheets line by line. Does it meet the spec? 96 of BEP
Parchasing Pumps Technical Evaluation 5.
Suction Specific Speed
6.
Seals
7.
Materials
8-
Efficiency
9
Exceptions to Specs and Standards
lo.
Experience
PROBLEMS
"
Problem I I
I
Liquid is at bubble point. Friction loss is 2 psig. (6 feet) npsha = (26 - 3) - 6 = 17 feet
Two existing pumps (operating and spare) Byron Jackson 4 x 6 x 13
Present pump duty
Flow Head npshr Sp Gr Temperature 60 Cycle
600 gpm 500 ft 14 ft 0.80 150°F
New conditions require flow to be increased to 780 gpm. Now need 18 R npsh. What can be done?
j$ L (curve attached)
PROBLEM I - MSWER
Methods to increase available npsh: I
Raise minimum liquid level Modify piping to reduce friction loss Reduce pump centerline elevation Operate both pumps in parallel Purchase new pump with lower npsh required Cool vessel liquid to reduce vapor pressure Note that increasing flow will increase friction loss in piping about 1 psig or 3 feet.
Problem I11
1.
Make the best pump selection fiom the attached curves.
4 x 6 ~ -
P/IM/J;~:@&
2.
TOC
How many stages?
6 3.
What is the efficiency?
4.
What is the horsepower?
d + F
*% s/fjQ--
C
3F 5.
What is the required npsh? d\lfS"tW\>
1 2 FJc
X
%
---. Effective FEE. 65
WGp
w/lP hternational, hc. Pwnp Divisim
Byron Jacksonm Pumps
United Centrifugalm Pumps
Senion Paoe
1-130 1.730-4s
Effective FEB. 65
r
Byron
United
Pumps
Pumps
Page
1-730-47
Effective FEB. 65
,
wGP w/IPInternational,Inc. Pump Division
Byron Jackson@ Pumps
United CentrifugalN Pumps
Section 1-730 Page 1-730-49
'
Effective May 65 Supersedes February 6!
WGInY BWIIP ~niernatbnal,IN. Pmp Division
Byron Jacksona Pumps
United centrifugalm Pumps
Section 73 0 Page 1-730-51
Section 1-73 , I
PumpDivlslon
Byron
United
Pumps
Pumps ..
Effective February 65 Effective February 65
wqIF
BWN) lntemtional, inc Pllmp oivision
Byron Jackson@ Pumps
United Centrifugal" Pumps
Se~ti0n 730 Page 1-730-53
Effective Februarv 65 J
w*p
m p Internatbnal, Inc. Pump Oivision
Byron Jackson* Pumps
United CentrifugaP Pumps
Sectia n 73 0 Page 1-730-55
Best pump selection - 4 x 6 x 9D 2604-2 Stages
I
- 7
Efficiency
- 80%
Horsepower
- 750HP
Required npsh
- 17 feet
Types of Co~npressors
- ., , Posjtive Displacement 0
(Centrifugal)
I
.<
%
Reciprocating
-
As with pumps, there are dynamic md positive displacement compressors.
Compfessor $law is measuted in ACFM, Actual Cubic Feet per Minute, or inlet Ms/hr. ACT34 is the flow rate at atmospheric conditions (standard) correcxed for inlet gempernure and pxessme.
Compressors r Basic Theory
Hardware i i
Case studies
3
Large, 10 cylinder reciprocating compressor.
Receiver
cieAnce Volume
1
Discharge
Iniet
Reciprocating Cornpressor Compression Cycfe Compression (1 -2) The piston compresses the gas inside the cylinder. When the pressure exceeds the suction pressure, the inlet valves close so the gas cannot escape h c k to the suction side. The piston continues to compress the gas until the discha-ge pressure is reached. At this point, the discharge vdves open.
Ex haust (2-3) The piston continues in its forward stroke, pushing the gas out at discharge pressure.
Expansion 1
f
Discharge
Pressure
k-)
Stroke
,-A
1
I
.
.:,..0 '
Inlet
Expansion (3-4) The piston completes its forward stroke. Some gas is left inside the cylinder. The piston moves back toward the crankcase. The gas inside the cylinder expands and the pressure drops. When the presswe inside the cylinder drops below discharge pressure, the discharge valves cXose. When the gas &ups bdow suction pressure, the suction valves open.
I
.f
Receiver Pressure
Discharge Inlet
Iritake (4-1) As the piston .travels back toward the crankcase, the cylinder continues to fiE with gas.
Compressor Valves The compressor valves are nothing more than check valves designed to open or close based on the differeaiaf pressure across the vafve. Since most of the maintenmce of reciprocating .compressors have to do with the valves, there 'has been much research and imprmmenw; in vdve types and mdexids. Channel valves have been used fox- a long time. ' h e channels move up and down 300-500dxnes a nziau%ead&nst the valve sptings. If any liquid gets between the channel md spring, the spring could break as liquid is inconrpressjble, h is important that the gas is kept clean and dry.
Ring valve. T d a y the i n s are made out of a high temperawre themzopliassic, PEEK.
Plate valve with PEEK plate.
Poppet vaive with PEEK poppets. One size poppet fits
valve sizes.
Two Stage Compression
Volume
-
Staging Reciprocating compressors have a discharge temperature constraint. Due so mechanical considerations, the discharge temperature of a gas compressor should not exceed 27S°F. Discharge temperamre is a function of compression ratio and sucGozl temperature. X f the process demands a compression ratio resulting in an unacceptable discharge temperature, the compression can be staged. The compressor shown above has a suction pressure of 15 psia and a discharge pressme of 115 psia. This coxnpsession ratio of 7.7 will resub in an unacceptably high discharge temperature. Therefore, the compression is divided into two stages with intercoofing. The first-stase cylinder(& raise the pressme up to 40 psia. The gas is then cooled back down to XOO°F. The second-stage cylinder(s) then raise the pressure up FO If5 psia. At no time does the gas temperature exceed limitations. Staging also saves power consu3nption. Cooling the gas after partial compression to a temperature equal to the original intake temperature reduces the power required in the second stage. (HP is a function of m a s flow times differential head. Head is a function of temperature.) Occasional!y. even if discharge temperature is not a consideration, intercooling is used to save power. The power savings has to offset the utility consumption of the intercooler.
Reciprocating Compressor Control r Saction Valve Unfoaders
r Cyfinder Pockets w Bypass
Capacity is controlled with suction valve unfoadefs, cylinder cIearance pockexs, and bypass.
Finger Type Unlouder
Unloaders hold fie suction valves open so no compression can take place. If one side of a double acting cylinder is unloaded, the capacity goes down by 50% for that cylinder. A one cylinder cornpressor can unload to 50% and 0% capacity. A two cylinder compressor can unload to 75%, 50%-25% and 0%. A four cylinder compre~j,sorcan unIoad in steps of 12.5% and so on.
Clearance Pocket
In addition to suction valve unloaden, head end fixed cleaance pockets are also used for capacity controI. The head end of the cylinder has a pocket that can be opened. When opmed, the total cylinder clearance increases. On the intake part of the stroke, the gas thax fifills the clearance pocket expands and less gas enters fie cylinder. When the pocket is opened, the capacity DECREASB. Typically, the pocket is sized for 10% capacity. With the pockex closed. the compressor is at rated capacity of 110%nonnal pmcess requirement. with the pocket opened, the compressor is a XOO% process capacity. Variable capacity pockets are not recommended. The plunger in the variable pocket tends to leak, making the pocket useless.
Clearance Pocket
I
Here is a manual clearance pocket on the heid end of a cylinder.
Nore 2 compartment disrance piece, piston packing, piston sings, and rider rings. Also note clearance pocket on head end of cylinder.
Cut-away of tbe two cylinder compressor. Note how the connecting rod
between the crankshaft and the piston rod is connected to the piston sod at the crosshead. Tfne piston rod screws i ~ t the o crosshead. A pin attaches the connecting rod to the crosshead.
Single Cylinder Reciprocating Compressor 250 BHP Frame Rating
Single cylinder compressor. Double acting with one hlet md oudet vdve on each side. The box mounted on the f m e is the crankshaft driven cylinder ~ubxicatur.The oif lines from tbe f~brktit~r to the cyiinder can be seen. Typically, tfie packing box is dso lubricated by this lubricator.
Two Cylinder Balanced- Opposed Reciprocating Compressor 400 BHP Frame Rating
Two cylinder, two-stage compressor. The larger first-stage cylinder is an the right. The fist-stage cylinder has 92 valves total, the second-stage cylinder has four vdves total. Again, note the cylinder a d packing lubricator mounted on the crankcase-
Pump to Point Cylinder Lubricator
Two cylinder, two-stage compressor. The larger first-stage cyXinder i s on the right. The first-stage cylinder fits 12 valves roM. the second-stage cylinder has four vaEves t a d . Again, note &e cylinder and packing
lubricator mowted on the crankcase.
Cut-away of the two cylinder compressor. Note how the connecting rod between the crankshafi and tEre pistun rod is connected to the piston rod at the crosshead. The piston rod screws into the crosshead. A pin attaches the connecting rod to the crossbead.
Crankshaft
Cut-away of the two cylinder compressor. Note how the connecting rod between the crankshaft and the piston rod i s connected to the piston rod at the crosshead. The pism rod screws into the crosshead. A pin attaches the connecting rod ro the crosshead.
Connecting Rod
Cut-away of the two cylinder compressor. Xote how the connecting rod between the crankshaft and the piston rod is connected to the piston rod at
the crosshead. The piston rod screws into the crosshead. A pin attaches the connecting rod to the crosshead,
Cms Head
Cut-away of the two cylinder compressor. Note how the connecting rod between the crankshdt and the piston rod is connected to the piston rod at the crosshead. Tfae piston md screws into the crosshead. A pin attaches the connecting rod to the crosshead.
Cut-away of the two cyfinder compressor. Note how the connecting rod between the crankshaft and the piston rod is connected to the piston rod at the crosshead. The piston rod screws into the crosshead, A pin attaches the connecting rod to the crosshead.
Paeking Box
Cut-away of the two cylinder compressor. Note how the comecting rod between the crankshaft and the piston rod is connected to the piston rod at the crosshead. The piston rod screws into the crosshead. A pin attaches the connecting rod to the crosshead.
Four cylinder, two-stage compressor. The smaller second-stase cylinders are on the right.
Fow cyhder, two-stage, compressor in field. Note the suction pulsation bottles on top of the cylinders. There are also dischaage pulsation bottles under the cylinders. The pulsation butdes danpen the pulses caused by rhe reciprocating action of the pistons and ease the pulsations on the piping and fuu~dation,
'
Large, eight cylinder, two-stage compressor. The four first-stage cylinders are on the right. Note Be total number of valves. Each first stage cylinder has eight suction and eight discharge vafves. Each second-mge cylinder has six suction arnd six discharge valves. The total number of valves is 112! If one vdve bm&, the compressor is down.
Recip.rocating Compressor Piston Rod, Two Compariement Distance Piece
Two compartment distance piece and crosshead connecting piston rod to
connecting rod.
Reciprocating Compressor Frame Oil System Lubricator .
Crankcase wl& shaft driven f m e oil pump. Note the motor driven cylinder lubricators located on top of the crankcase.
ReeQroeah'ng Compressor Piston Piston Rings, Rider Rings
After the $-hour shop mechanical run, the piston nod is disconnected from the cross head and the piston is pulled .From the cyginder for inspection.
Note the piston and rider rings
Recerocating Compressor Advantages High Compression Ratios i Constant VolmeIWide Pressure Range m Molecdar Weight Flexibility r Fairly Basic Evolved Teclunology Mcieney $
A
Reciprocating Compressor Disadvantages r Foundation and Piping Requirements
r t
r
n r
Pufsatin;:Fiow Vulnerable to Dirt and Liquid Maintenance Plot Area Large Volumes Constraints Lurbsieticta:Contamhating Process Torsional Xmplia.bions
The foundation and piping have to be designed to handle the pulsating Bow. Niaintenance is higher than far centrif~tgafcompressors due to the parts with close clearances. Reciprocating compressors are typically spared. Reciprocating compressors take up a lot more space &an centrifugal compressozs. The cylinder lube oiE can con2runinare downstream catalyst or molecular sieve absorbents. A reciprocating compressor driven by a steam turbine though a speed reducing gear is not recommended. i
High presswe barze1 type centrifugal compressor.
Diaphaps guide the gas from the discharge of one impeller to the suction of the next impeller.
Recycle Gas Compressor 5 Stage CePttrifugZ Compressor
Five-stage centrifugal compfessos. Note the seal md lube oil piping connections. The labyrinth seals minimize the flow of gas back to a lower pressure impeller.
Compressor Impeller.
Stress Corrosion Crack
Riveted impeller. This is an old manufacturing technique, now obsolete. Today, most impellers are machined. The cover is $hen welded in place. The stronger wheds result in higher achievable perfonnif~ceper stage.
Stress Corrosion Crack
Riveted impeller. This is an old manufacturing technique, now obsolete. Today, most impellers are machined. The cover is %en welded in place. The stronger wheels resuft in higher achievable performance per stage.
Cen&i!ugal Compressor Control
=
Variablte Speed
r Suction Throttle Valve
Centrifusal compressors are controlled with variable speed or for a singXe speed driver, suction tkxottling.
CentrifugaE Compressor Typical Variable Speed Performance Curves
30
30
40
50
60
70
80
90
100 110 120 130
Percent Inlet Volume IPD21k14/CD45 cD.RCc-12
For a variable speed driver, steam tusbine, or variable speed motor, the compressor speed can be varied to meet the head requirements along the system resistance curve. Most variable speed compression trains can opesate between 70% md 105%of the design speed.
Centrifugal Compressor Typical Constant Speed Performance Curve
Percent Inlet Volume
When a compressor is motor driven, there is only one head-capacity curve. When operating at off-design cases, pressure must be thjrotzled over a conbraf valve.
Centrifugal Compressor Typical Constant Speed Performance Curve
The throztle valve can go upstream or downstream of the compressor. If the valve goes on the discharge, the voJurnetric Row rate, A m , is directly proportional to the mass flow, lbslh~. 808 Ibshr will be achieved at 80% ACEM. Note that a%80% ACFM, almost half the head pmduced by the compressor is ti~oa1edacross the control valve. Since HP is a Emction of mass fiow time heasl, almost half &e E l?requirement of the compsessox is wasted across the control valve.
Centri@gal Compressor Typical Constant Speed Performance Curve I
J'
Suction
I
n~
I
I
surge ~ i n e valve5 w
;
9
Percent Inlet VoEume
If the throttle valve is on the compressor suction, not only does the mass flow decrease as the vabe is dxrottjed, but the suction pressure also decreases. A C W is inversely proposticmal $0 suction pressure. With $he valve on the suction, 80% mass flow can be achieved at a b u t 90% ACI.'M. Compared to discharge throttling, less pressure is taken across the control valve and less WP is rqaired for the same mass flow. Therefore, most centrihgstl compressus with singie sped drivers have suetion throttle valves.
Rated TD Turb
SCFL)
6 0 W
48
TD Disch TD Suct 48
48
ELECXEUC MOTORS
SSM
vsm
i
Gas turbines, Gas engines
STEAM TURBI1LXS Cond
Back Pressure
Mechanical Shafi Seal (TSO-Carbon Seal)
Sucfrnn G a Chantbcr
I. llvtatinif Carbon King 2. Robting Scsf King 3. SCz2ronary Slecvc
I ----" -"#------A 1-
7. C h and Contanimtcd Oit #>rain
i
h b'ta;ttrngBabbitt-FacedSteel Kin:: 9. Sea1f Y i ~ King r I*. &a! 08 Drab L* 1I. Sccontisry \Vi;'ia? Ring m ~ i n t h 12.
ikaring Oil Drain Lint
12. Gzaring Wiper Kin%
Like the pump seal, the contact type compressor seal has a rotating member and a stationary member. A floating carbon bushing is between the two members. Process gas leaks across the ltab*nth on the right side of the seal and fills ii gas chamber. This gas is at a lower pressure t h n the process because of &e pressure drop across the labyrinth. Seal oil is i.n.troduc& on &e bearing side of the seal faces. Most of &e oil goes around the seal back to the reservoizt The 03 pressure is maintained higher than the gas pressure in the gas chamber. The oil lubricates the sea3 and about 10 liters per day of oi2 leaks into the gas chamber. This sow: oil is drained. Note that most of the UOP processes contain some H,S or HCI. IE the sour oil is put back in the oil reservoir, the lube oil can become co&minated at b & n g or seal problems can result.
.
Liquid Film Sleeve Seal (TSO-Sleeve Seal)
i . .U.monar). &al S1csi.w
2. Kot3trag.%I.& Slt.~.v~.cvc 3 Spring 4. ,%a1 C~%:n;tr%s:trtion 9. tk.;l?rf%g Olf t>rsr;t [.me 6. and Cnn:.ztnmatcd Oil h r n 7. Ftaatrng fL~bbrtc-Fae~d St*.*! King S. .%A Oit ifran ttnc 9. Wrwr Km,: 30 %.srir$ Wiper Kinf
Bushing type seal. Oil leakage is greater &an contact type but: there i s no normal seal wear.
Thncst Bearing
'
'Rxust bearings are designed to withstand rhe axial forces on the shaft. The thrust pads are designed to pivot to the contour of %heshaft.
Thmst bearing. The bearing pads ride against the thmsr disc and absorb force in ei&ex axial drrection.
Journal Bearing
The journal hasings are d e s i ~ e to d withstand the radial forces on the shaft. The bearing pads can tilt to fit the contour of the shaft. Note the temperature mani tors on the back side of the pads.
\'
Compressor Lube Oil System
Centrifugal compressor bearings are rypicdly Iubricabd by an external pressurized oil system. Oil is sroted in a large reservoir. These we two pumps, one operating and one ;spare. On low oiI pressure, the spare p m p comes on-line autoxnatidly. The two pumps should be driven by diffetenr power supplies, w i e d l y dectt-ic mozor and steam twhine, to insme a supply of oil to the compressor. The spare pump must be motor driven. A stem turbine will rake $00kmg €0come on-line. Note &e twin coolers and fiIters. Also note Ffie three separate low oil pressure shutdown switches. t to The shutdown is two of three voting. Two of the switches ~ u s vote shutdown before the drives is tripped- This avoids spurious shutdowns and insures a shutdown i f one is needed-
Compressor Seal Oil System
E Xfe compsessor has an oil lubricated sed, the seal must be suppIied with pressurized oil. The sea9 oil system is very similar to the lube oiX system
Compressor Lube and Seal Oil System
There are many common components between the lube and seal oil systems, such as pumps, coolers, filters, ezc. Mmy compressors have combined lube and seal oil systems. Ody one reservoir and one sez of p e coolers, fiften, etc., is required. If the compressor has a high sztction pressure or contains a large pantity of EX2$ fNydromackip1g Units), the oil systems are kept separate. OtherwiseJ UOP specified combined lube sfnd seal oil S ~ & S SO only the lube oil system is system. Today, UUP specifies dry required.
Mechanical ShaJt Seal (TW-Carbon Seal)
1. R~tatiFt:!Carhon Rirtfi 2. I
3. Ststrmsv S$ccw 4. Spring Ketaincr 5 Snring
11. kcondclt): \\'ID?: HlnC I&-rin:b
I l w r i n g Oil I f r ~ i !].he i 13. licaring \\'ipcr Rin:: I?.
Like the pump seal, the contact type compresses: seal has a rotating mernber and a stationary member. A floating carbon bushing is between the two members. 3Psocess gas leaks across the fabyx5nf.h on the right side of the seal and fills a gas chamber. 33% gas is at a lower pressure than the process because of the pressure drop across the Tabykith. Seal oil is introduced on. the bearing side of the seal faces. Most of the oil goes wound the seal back to the reservoir. The oil pressme is maintained higher than the gas pressure in the gas chamber. The oil lubricates the seal and about 10 liters per day of oil leaks into &e gas chamber. 'This sum oil is drained. Note that most of the UOP processes contain some H2S or MC1. If the sour oil is put back in the oil reservoir, the lube oil can k o m e contaminated at bearing or seal problems can result.
Lipid Film Sleeve Seal (TSO-Sleeve S e a
Bushing type sed. 011 leakage is g e m than contact type but there i s no nonnd seal wear..
Dry Gas Seal Spiral Groove Arrangement
Rotation to Prim
Rotating face of dry gas s d . The se&ng face is attached to the compressor shaft and rotates against a solid stationary face. With rotation, gas is pumped from the 0.D. inward toward the root of the grooves where a sealing dam is defined. The sealing d m provides resistance to flow, increasing the pressme. The pressure genefated separates the carbon ring surface out of contact with the tungsten carbide x-ing by about 0.0001 to 0.UW inches. This allows less &an 2 c h of gas to leak across the wal faces.
Single Dry Gas Seal
SingIe dry gas seal cartridge.
Principle of Operation
Gas i s Compressed and Pressure is Increased
As the grooved face rotates with the shaft, gas is~pmpedtowards &e center and, after a few rotations, lift off occurs.
Design Comparisons
f
I t
Spiral Groove
Bidirec80natl Spiral Groove ipD.mD-GP CfMOc-21
Some seals are bidirectional. With the spiral groove design, the seals on. either side of the compressor shaft are minor images of each other. Idet side and ouder side seals are not interchangeable. The bidirectional grooved seal is syamesric so both seals on either end of the shaft are identical.
Dynamic Test Leakage fur a 4.937" L)iameter Seal 2.5
g
2.0
C
0 V)
V
a>
C35
5.5
a3 x
nr
@
A
1.0
0.5 0
1000
1,200
Pressure (pig) FD-2OWCD-65
COa0522
Typical seal leakage rates. As can be seen from the tests, leakage is primarily a function of speed and pressure. Nfolecular weight and temperature can d s o affect the leakage rate to a lesser degree.
Control System m Provjdes three main Xiunctions
-
IF&&-ation of buffer gas - Replation of buffer gas - Monitoring of seal performance r Ugem 1-1 indication;of fEtw amd seal performance m Design is simple $0 operate and user friendly with
minimnm maintenance requireme~&ts
The control system filters and regdates tho gas and monitor seal
performance.
Dry Gus Seal
'
To Rare
The seal buffer gas is typically process gas from the discharge of the compressor. The process gas is filtered and coalescecl, down to one micron liquid and three microns solids. Note that it is critical to supply the seals with a clean, dry baffer gas. The gas is injected on the process side of the seal about 20 psi above the conrpessos suction pressure. Most %hethe gas goes across a labyrinth back into the compressor. Under two cfm leaks across the seal. This gas is routed to 8are,
. Type 28
Seal Arrangements
Single Seal
Tandem Seal
Double Opposed Seal
Triple Seal
UOP specifies tandm dry gas seals for process gas applicadons.
Single &y gas seat. The grooved silcar rotor is attached to the shaft.
Tandem dry gas seal. Most of the gas which Eeaks across the primary seal is
vented to flare. Under 0.5 cfm leaks across the secondary seal. A nitrogen separation gas prevents the process gas from migrating to the lube oil in the bearing box. The gas that escapes across b& seals is routed to atmosphere outside the compressor shelter.
If zero fugitive emissions is &sired, rhe nitrogen separation gas can be routed between the two seal faces. This will force dl of the gas that teaks across the primary seal our the vent to flare, Only inert nitrogen will leak across the secondary seal to atmosphere.
d
Comparison of Wet Seal vs, Dry Gas Seal
I
I I
I
Sed oil consu&tjon Maintneance cost
I
Energy costs
1
Process gasj~&age
/ 1
Wet Oil Seals Pumps,~t:semoirs,filters traps. coofers. consoles 1-100gaXfonslday A major ex nditsue over equipment Ke SgaI R p e r loss: 10-30MP ZImt &ven pumps: 20-100 HP Gas Leakage: 25 scfm & higher
Dry Gas S d
I
None
j NO sea1 oil NegIigibIe
) Less than 2 scfm
Today dmost d1 process gas compressors axe specified with dry gas seaIs.
I
Dry Gas Seal Console
Dry Gas Seal Console
Compressor Dry Gas Seal System vet to
Rcl*Im&f
t
I
seal schematic. A 2 of 3 voting high-high pressure shutdown UOP dry is specified on each primary seal vent to shut down in the event of a primary seal leak. A low flow d m across the primary seal vent warns of a secondafy sed leak. If more gas is leaking across the secondq seal, less gas will be tmveEing out &e primary seal vent.
A Model of Sarge m Surge DelEi~ritioa Surge is self-osc~~ions of pressure and fbw, including a flow reverkaL Tlxe surge flow reversal is the only point of the curve when pressure and flow drop simulbneously.
Characteristic Curve of42 Typical C&rrtnjCugaZCompressor - BtoCin24lto50mSec - Cycle B to B at 0.33 to 3 Hertz
IPPZGWC076 CD-RW29
All centrifugal compressors can and surge. If the compressor rides up its curve due to rising discharge pressure or decreasing gas rno~ecalaxweight, the compressor will physically not be able to overcome the downsueam pressure requirements. Since gas is eompsessible, pressure and energy ~ $ 1 1 build up downs@eam. When the compressor curve reaches point B, the cornpressor will no Ionger be able to push the gas out the discharge. The gas will then reverse Bow through the compressor. Row & point C is negative. Now that the downstream presswe has been relieved through the compressor, the compressor cstn start pushing gas out the &sctnage again. When the pressure builds up and the compressor em no Xonger keep up with the demand, the gas once again goes back through the compressor to the suction. This can happen multiple .timesper second.
The Surge Phenomena 1 3
0
Rapid flow osciIfations
r Thmt reversals r Potentialdamage
6
w
e
1 (0
k
r Rapid pressure oscilfations with smess instabilitv 4
c.
r Rising tempmbres inside cowressar
T i m e
The consequences of surge are severe. The thrust reversds on the shaft wilI damage seals, bearings, md open up critical internal clearances. Since the same gas is passing throagh the compressor multiple t i m s a second, the temperatwe in the compressor rises rapidly.
Surge Description FXQWreverses -in20 to 50 milJiseconds Surge cycles at a rate of 113 to 3 hertz r Compressor vibrates 8
"CWJhoosbijng" noise
Trips may wcur I Conventioad btmrnents and hmm operators m y fail to rec~~anize surge
8
Some Stlrge Conseqrcences r Umbbie flow and pressure Damage h sequence with increasing severity to s 4 s , bearings, impeEEers, shaft r Increased seal c1eat.mces and leakage
r Lower energy efficiency i
Redaced compressor fife
PlatJorming Recycle Gas Circuit
This is a VOP Piatforming recycle gas circuit. Note that this i s a circulating loop circuit. The compressor discharges into the comprressor suction. There are no automatic conxols on compressor speed and no ausoxnazic control valves. Assuming no blockages occur in the exchangers or reactor, which will only happen slowly over time, there is nothing in tkis circuit &a%can put the cornpressor into sage. Therefore, UOP recycle gas circaits do not require anti-surge control.
FCC Muin Air Blower
a Regenerator
This is a FCC Main Air Blower. There are automatic valves which if not operating properly can put the blower into surge. Therefore, anti-surge equipment is specified-
Antisurge Controller Operation S e e limit Line (SU)
'
The anti-surge con.trolIes measures gas pressure, temperature, and flow a minimum of 40 ~ m e sper second. E the operating point hits &e surge controf line, the anti-surge co~trolfersmds a signal. to open the spillback valve. This allows tbe gas downstream of the comp~msoran alternate path around the compressor instead of back through fhe compressor. A margin7 b2, is left between the surge con&ol Ene and the actual surge line. This ensures that the spillback valve will open in time to prevent the compressor from surging.
Antisurge Controller Operation Surge Limit Line (SLL) APc 0
0
0 0
Surge Control Equarion: KA PC+ bX = APo minimum
! I
I
Aattslcrge ControIZer Operation S&ge
Limit Line (SLZ)
Antisurge Controller Recycle Trip Circait Operation swge ~ i n - i~t
i (SLL) e \
/
Recycle Trip Line (RTIL)
.----
Surge Control Line (SCL)
0
0 0
Activates open loop control m Reven& surge in all but $he most severe disturbance
APo
The surge controller is also progmmmed with a recycle trip h e . If the opera%ing point hits the surge control line, the spilgback valve opens slowly. Xt is not desirable for &e spillback valve %ogo wide open because catalyst in the circuit cadd be starved of hydrogen.
K -the opefating p i n t hits the recycle trip line, now the compressor is in danger of surging.. The spillback valve wiIl step open quickly to avoid surge.
Simple Antisurge System r Flow measured in suction
(@o)
Suction and discharge pressure transmitters for pressure differential calculation r Control strategy is proportional plus integral control to maniprrEate recycle valve I Increase flow through compressor and reduce discharge resistance when required to prevent surge
h a simple amisurge system, flow and pressure measurements on the suction and pressure measuremen%on the discharge me sent to rhe antisurge contro31er7 'LTXC. The U C controls the recycle valve which is nonnaEXy closed. If surge is approached, &e ZsyC opens the recycle valve.
FCC Axial Main Air Blower with CCC Performance Controller CCC Pctiomwicc Co~twl!c
6 8
2
t
,
,
*-_-------*L-..--.? -----"-----C----,
8
,
t t
I
.
'
This is an actual UOP FCC Main Air Blower P & XD. Note the flow, pressure, a d ternpermre measurements transmitted to the perfommce controfler which i s contxoIliag the flow of air to the regenerator. The performance controller is adjursting the axid air blower guide vanes or the tufbirte driver speed. The pdomance controller is also sendlag d&a to the antisurge c o n ~ l l e rwhicb , is controlling the normally closed snort valve. If the surge line i s appxoached, the antisurge contro1ler will open the snort valve md uncouple the performance controUer from the Emp.
Occasionafly, in a surge event? the pedommce contrler could actually push the compressor further towards swrge by speeding up or slowing down the compressor. With the antisurge and perfommce cortrroflers '?taiking'!"'to each other, this is pzvented fiom happening. 1
Purchasing Reciprocatiag Compressors Technical Evahatiovc 1.
2.
Scope of Supply (Per Spec and API 618)
,
Frame Loading
3.
No. of Cylinders
5.
Cylinder Diameter
P~crchasingReciprocating Compressors Technical Ifvaluation 6.
Piston Speed
7.
Piston R_PM
8.
Exceptions to specs and standards
9.
Power Requirement
la
Experience
Purchasing CentPz?$ugal Compressors Technical Evaluation scope of Supply
1.
2.
i-
Can it meet all,operatiagpoints (N2 start)
3.
Materials (Impeller yield strength)
4.
3Es proposal complete
5.
Does proposal meet APE 617 IPtT1oae'CP$O
Purchasing Centm~uggalCompressors Technical Evaluation 6.
Efficiency of various operating points
7.
Rotor: dynamic stability (How many wheels)
8.
Exceptions to specs and standards
10.
Experience similar casing sizes, rotor sizes, pressufes, Bows
TRAXNlNG P R O G U M - PROBLEMS A & 3 (Complete BBP Calculation Forms) TYPE
1 Date I BY
Page No.
COMPRESSORS
Project
f
XTEM NO.
I
t
/ SERVICE
1
PROBLEM A RECYCLE GAS
1
1
(Lubricated)
1
6.35
c1
1
Atmospheric
4-38
c2
D
PROBLEM B MAXN AIR BLOWER
m TYPE
ED-2004
I
MOTOR
uc)Ip
Air
I
1
TtR3I;NJE
Compressors-l
I
Subject: RECIPROCATING COMPRESSORS-BHP
For:
Sample Problem A
SYMBOL
-
and Suction Tmpemtufe
Date
/ BY
Subject: For:
CEhmFUGAL COMPRESSORS-BHP Sample Problem B
SYMBOL
tosses frictional Seal
Date
, BY
Compressor Palytropic Efpclency
Basic bhp/mmfi3/d
Compression W o
SpeciJic Gravity Cowectiun
1
PLATFORMXNG W T GAS - PROBLEM C
1
Gentxifugd compressor (condensing steam turbine driven) vs. 3-50% reciprocating compressors
(motor driven). Which is better?
Cost of 2 body compsessor, condensing steam turbine including oif console and g s seal console:
Spare compressor and tmbine rotors: $1,065,000 Cost of 2 stage (6 cylinder) reciprocating compressor: $3,327,000 Assumptions: Installation:
i
Centrifugal - 20% of compressor cost Reciprocating - 50% of compressor cost
Maisftenance: Centrifugal
- Ohp/y
Reciprocating - $35hp/yr
4
'
CEN'SJRWCAL COMPRESSORS
PROJECT N W E R
RECfPROCATLNG COMPRESSORS
PROSECT NZjmBER
SOLUTION
- PROBLEM A
Subject:
RECIPROCATING COMPRESSORS-BHP
Date
For:
Recycle Gas
By
SYMBOL Qb
Million SCFD
30.55
Ts
OR
580
ps
psia
243
pd
psia
387
r
Pd1p.s
1.59
k
C ~ / C ~
1.311
mol wi
Molecular Weight
7.6
SP gr
Specific Gravity
0.26 1.001
2s zd
1.003
=avg
1.002 ft3/min Q Suction
Qs
(sfd 1 ? ~ / d ) 7 4 . 7 ) ( ~ ~ ~ 1 ~ ) (1440)(pS1520) k-1 k
Td
( A)
1('
1433
0.237
(TS r
187°F
BHP/mm @ 14.4 psia and Suction Temperature
23
c)
sp gr Correction (Qb XI. 02 KTs ) 520
34.76
(D)
Add 5 pct if N.L.
---
(E)
Zavg
(F)
Gear Loss 3 pct (if Gear is u s e d )
BHP Req d
( A + BXCXDXE)(F)
(B) (
IPD-2004
3
I
1.002 906
UOP
Compressors-1
-
COMPRESSOR PROBLEM SOLUTIONS PROBLEM B
-) Centrifugal - Main Air Blower
A ft3/min =
std ft3/d 14.7 psia Ts" R x xminuteslday ps psia 520°R X zs
Aft 3/min = 34.54x106 x-14'7x555x1.0=26134fi3/min 63 Inlet 1440 14.4 520
Ib/min wt flow =
34.54 x 1D" 28.49 Ibllb mol = x 7440 379.48 std ft 3/lb mol
0.546 --
M
lb,min
- Beta = 1.590
Polflropic Head = ZavgRTs B = (1.0)(1545J28.49)(555)(1.590)=47846 ft Ib f/lb m
GHP =
Head x lblmin - (48376)(1800.8) = 3138 33000 x Eh (33000X0.832)
-
SOLUTION PROBLEM B (cont.)
Subject:
CENTRIFUGAL COMPRESSORS-BHP
Date
For:
Main Air Blower
By
SYMBOL Qb
Million SCFD
7s
"R
555
ps
psia
14.4
pd
psia
51.2
r
PdIPs
3.556
Molecular Weigh1 1545 mol wi
28.49
mol
wl
R
k
C~/Cv
Qs
ft3/min @ Suction (Qb Xmol wt) 546000
Iblmin wt flow
34.54
54.23 1.4 26 134 1800.8 1.o
2s
Zd
1.o
=avg
1.0
Eh
M
Polytropic Efficiency k-1 k k-1
k Eh
Beta Head Gas hp
0.832 0.2857 0.343
(r)M - 1
0.546
(rlM - I M
1.590
)@XTS
)(Beta)
47846
(Wt low X ~ e a d ) ( 3 3 0 0 0 ) ( ~) ~
3138
(zavg
l
Losses Frictional Seal
I pct of Gas hp
32
Gear
(If used) 3 pct of hp
-
Total bhp 7d
-
3170
MM
(TS
398
SOLUTION
- PROBLEM C Centrifugal
Reciprocating
Capital Cost
$5.32
$9.98
Installation
$0.85
$4.99
UtilitiesNear
$2.72
$2.44
Maintenance
0
$0.26
$8.89
$17.67
Total11st Year
Savings with centrifugal compressor - $8.78 million for first year
CENTRIFUGAL COMPRESSORS
PROJECT NUMBER
1st
2nd
Qb
Million SCFD
74.76
77.27
Ts
OR
566
555
ps
psia
49.35
107.81
pd
psia
115.06
243.50
r
Pd/Ps
2.33
2.26
MW
Mol. Wt.
10.3
9.9
R
1545/MW
150.0
156.1
k
CdCv
1.257
1.267
Qs
CFM @ Suct. QbxMW 546000
16832.556
7824.635
1409.14
1399.89
zs
1.ooo
1.002
zd
1.002
1.004
za v
1.001
1.003
Poly Eff.
0.83
0.81
k -7/k
0.204
0.21 1
k - l/k€h
0.246
0.260
0.232
0.236
Beta
( r ) -I M
0.941
0.908
Head
Zav R Ts Beta
79991.486
78840.783
GHP
wt Flow x Heaa
41 15.351
4129.01 7
7% of GHP
1.01
1.O1
3% of GHP
1
1
4156.504
4170.307
237.232
226.041
#/Min Wt. Flow
Eh
M
M
( r ) -1
M
33000 x Eh Losses Frict. Seal Gear
I
Total BHP Td
Ts( r )
RECIPROCATING COMPRESSORS
PROJECT NUMBER
1st
2nd
Qb
Million SCFD
37.38
38.64
Ts
OR
566
555
ps
psia
49.35
107.81
pd
psia
115.06
243.50
r
Pd/Ps
2.33
2.26
k
cp'cv
1.257
1.267
MW
Mol. Wt.
10.3
9.9
S.G.
Spec. Grav.
0.4
0.3
Zs
1.ooo
1.ooo
Zd
1.002
1.002
zave
1.001
1.001
8416.278
3905.014
0.204
0.21 1
212.948
198.960
Qs
CFM Suct k-l/k k-l/k
Td
r
Ts
6.4)
BHP/mm @ 14.4 psia & Suct T
41
41
(B)
Sp. Gr. Corr
3.5
3.5
(C)
Qb (1.02) Ts/520
41 -50
42.07
Add 5% if N.L.
1
1
(E)
Zav
1.001
1.001
(F)
Gear loss 3%
BHP Req'd
(A+B) (C) (D) (E) (F) (G)
(0)
1 1848.616
1
1873.790
