Upload
ashik-jacob-oommen
View
224
Download
0
Embed Size (px)
Citation preview
8/17/2019 Control of Compressor
1/35
N A M E : A S H I K J A C O B O O M M E N
R O L L : 0 3
E N . N O : R 6 7 0 2 1 1 0 0 3
S A P : 5 0 0 0 1 5 1 1 1
M . T E C H P R O C E S S D E S I G N E N G I N E E R I N G
Control of Compressors
8/17/2019 Control of Compressor
2/35
Contents
Introduction
Types of Compressors
Polytropic Head
Compressor PerformanceProcess Symbols
Control in Turbo-Machines
Control in Reciprocating MachinesOther Control Parameters
Anti-Surge Control
Conclusion
8/17/2019 Control of Compressor
3/35
Introduction
Compressors are gas handling machines
Performs the function of increasing gas pressure
!one by Confinement or by "inetic energy con#ersion
Ma$or tic%et items in the capital cost of a chemical orpetroleum plant
&g ' (arge centrifugal compressor )ith a gas turbine is anin#estment of many millions
8/17/2019 Control of Compressor
4/35
Types of Compressors
Compressors
Positi#e!isplacement
Rotary*lo)ers
ReciprocatingCompressors
Turbo-machines
A+ial
CentrifugalCompressors
8/17/2019 Control of Compressor
5/35
The range of flo) capacities and discharge pressures
that different compressor design can handle
8/17/2019 Control of Compressor
6/35
Polytropic Head
Performance of Compressor e+pressed in terms ofPolytropic head
,here p . Polytropic &fficiency
/ . Adiabatic Inde+ Pd.!ischarge Pressure
Ps . Suction Pressure
0s . Compressibility 1actor
− −=
−
11
1
γη
γ
s
d s s
p p
p
P
P
MW
RT Z H
γ
γ η
8/17/2019 Control of Compressor
7/35
Compressor Performance
Compressor performance cur#esshould strictly be plots ofpolytropic head Hp againstSuction flo)
Performance cur#e of acentrifugal compressor terminates before the flo) reaches 2ero
At too lo) a flo)3 the compressor )ill 4surge5
6pper limit of Performance cur#eis 4Stone)all5
8/17/2019 Control of Compressor
8/35
Process Symbols
8/17/2019 Control of Compressor
9/35
Control in Turbo-Machines
8/17/2019 Control of Compressor
10/35
Introduction
The pressure dropthrough the processincreases in proportion tothe s7uare of the flo)
The e+it of the process isconstant so that )e canadd the process cur#e to
the compressorperformance cur#e
Compressor operated )here the t)o line cross
8/17/2019 Control of Compressor
11/35
To ad$ust the flo)3 either the process cur#e or thecompressor cur#e has to mo#e
Also has to remo#e the conditions that the discharge andthe process inlet pressures are e7ual or that the flo)s aree7ual
There are different schemes that are possible forcontrolling the flo) They are as follo)s '
!ischarge Throttling
Suction Throttling Speed Control
8ariable inlet 9uide 8anes
Recycle Manipulation
8/17/2019 Control of Compressor
12/35
!ischarge Throttling
Placing a control #al#e bet)een the compressorand the process
The pressure are nolonger e7ual
Process cur#e )ill mo#e
as )e change the #al#eopening
8/17/2019 Control of Compressor
13/35
!ue to the non-linear beha#ior of both thecompressor and the process3 the relationship bet)eenthe flo) and #al#e Pressure drop is highly non-linear
*ut since )e are e+pending energy to raise thepressure of the gas to partially reduce it again acrossthe #al#e3 the scheme is not energy efficient
Range is limited since the process cur#e approachesthe end of the compressor cur#e as )e close the #al#e3resulting in 4Surge5
8/17/2019 Control of Compressor
14/35
Suction Throttling
Control #al#e is relocated tothe suction of the compressor
The compressor cur#e mo#es )hen )e change the suction
pressure
More energy efficient thanSuction throttling due to
in#ol#ement of lo)erpressures
Has greater range becausesurge point reduces as suction
pressure is reduced
8/17/2019 Control of Compressor
15/35
It is possible for the suction pressure to fall belo)the atmospheric pressure
Any lea%s in the pipe-)or% )ould permit air to enterinto the compressor
If compressing a flammable gas3 )ill result in
e+plosion inside the machine
8/17/2019 Control of Compressor
16/35
Speed Control
6sed if the compressor isof #ariable speed type
*y changing the speed )e
mo#e from onecompressor cur#e toanother
This is energy efficient
Ho)e#er #ariablefre7uency dri#es :81!; forlarge electric motors arecostly
8/17/2019 Control of Compressor
17/35
8ariable Inlet guide #anes
6ses a set of ad$ustableguide #anes on the inletto one or more of thecompressor stages
Con#erts the inlet gasfor)ard momentum intorotational momentum
Angle of the guide #anesis ad$ustable
8/17/2019 Control of Compressor
18/35
Pre-rotation increases the compressor efficiencypermitting it to deli#er a greater flo) at the samedischarge pressure
Since the guide #anes are present inside the compressor3ad$usting them changes the geometry of the machineitself
Another family of compressor cur#es )ill e+ist for eachguide #ane angle3 each )ith a different surge point
Mechanically guide-#anes are more comple+ and morecostly to maintain
8/17/2019 Control of Compressor
19/35
Recycle Manipulation
Partially recycling gasthrough the compressor
Thereby remo#ing thecondition that flo) throughthe machine must e7ual tothe flo) through the process
Offers the greatest range
since the surge point is ne#erapproached
Ho)e#er3 costly to install
and operate
8/17/2019 Control of Compressor
20/35
In reality3 the system is more comple+ than dra)n
1or e+ample3 the recycle must be cooled
It is the least energy efficient approach
It can ho)e#er be used to increase the range of theother schemes described3 by recycling $ust enough toa#oid the surge
8/17/2019 Control of Compressor
21/35
Control in ReciprocatingMachines
8/17/2019 Control of Compressor
22/35
Introduction
Reciprocatingcompressor is a constant
#olume3 #ariabledischarge pressure
machine
The #olumetricinefficiency is a result of
the clearance bet)eenthe piston end and thecylinder end on thedischarge stro%e
8/17/2019 Control of Compressor
23/35
Schemes used for the turbo-machines can also beapplied for reciprocating machines
Suction throttling reduces the suction pressure and soless gas enters the cylinder and less gas )ill bedischarged
!ischarge throttling has little effect on the flo)
Some other methods of capacity control is listed as
follo)s ' On-Off Control
Constant Speed unloading
Speed Control
8/17/2019 Control of Compressor
24/35
On-Off Control
If the compressor )astes po)er )hen run continuously3 thecapacity can be controlled by starting or by stopping themotor
&+ample sho)s an air mi+ blender uses a rapid series of high-
pressure air blasts )hen the mi+er becomes fullThe high pressure air for this purpose is stored in the recie#er
8/17/2019 Control of Compressor
25/35
Constant Speed (oading and6nloading
The dri#er operates continuously3 at constant speed
One #aries the capacity in discrete steps by holding thesuction #al#es open on the discharge stro%e or openingclearance poc%ets in the cylinder
The most common scheme are the three and the fi#e-
step unloading techni7ues
The large number of steps sa#es the horsepo)er becauseit more closely matches the compressor output to
demand
8/17/2019 Control of Compressor
26/35
ThreeS!e" #$%&'()$* +),eS!e" #$%&'()$*
Capacity increment are 3 ?=> pr => ofma+imum flo)
Method is accomplished by the use of #al#e
unloading in the double acting piston Three steps include Suction3 !ischarge and
*lo)do)n Capacity increment are 3 @?> 3 ?=>3 ?> or =>
At 3 both the suction #al#es and theclearance poc%et are closed
1i#e Steps include Suction3 !ischarge3*lo)do)n 3 *ypass and Purge
8/17/2019 Control of Compressor
27/35
8/17/2019 Control of Compressor
28/35
8/17/2019 Control of Compressor
29/35
Other Control Parameters
Control of Au+iliary items on the compressorPac%age '
Oil3 )ater and gas temperature
Oil3 )ater and scrubber li7uid le#el
1uel and starting gas pressures
Control of Compressor safety Safety shutdo)n controls to be pro#ided in case of harmful
temperatures3 pressures3 speed 3 #ibration 3 engine load and li7uidle#els
8/17/2019 Control of Compressor
30/35
Anti-Surge Control
Ob$ecti#e is to minimi2ethe recycling )ithoutdamaging the machine
To do this3 )e need to
predict that surge isabout to occur
Comple+ity of surgea#oidance depends much
on the machine and itsduty
&+ample is as sho)n onside
8/17/2019 Control of Compressor
31/35
This scheme causes therecycle to open if thedischarge pressure ise+ceeding the Suctionpressure
Pressure must changesignificantly as surge isapproached
*etter for SteepCompressor Cur#es
8/17/2019 Control of Compressor
32/35
Anti-Surge Controller
8/17/2019 Control of Compressor
33/35
Conclusion
Control of compressors plays a ma$or role in achemical industry
Temperature control can also be ta%en intoconsideration
8/17/2019 Control of Compressor
34/35
References
4 A Real time Approach to Process Control 43 Second &ditionB ,illiamS#rce%3 !onaldPMahoney3 *rentRoung3 Dohn ,iley and Sons (td
4 Process Control a Practical Approach5BMy%e "ingB Dohn ,iley and Sons (td
4Compressor Handbook53BPaulCHanlonBMc-9ra) Hill
Publishers
“Industrial Engineer’s Handbook: Process Control” B Third&ditionB *ela9(ipta%B Chilton *oo% Company
8/17/2019 Control of Compressor
35/35
THANK YOU!!!