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1 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
PROCESS COMPRESSOR CLEANING
CASE STUDY
GENERAL EQUIPMENT INFORMATION
Location: Refinery
Name: Cracked Gas Compressor
Type: Centrifugal compressor, horizontally-split, back-to-back arrangement
Sections: 2 (Low Pressure / High Pressure)
Stages: 8 (4 x Low Pressure / 4 x High Pressure)
Driver: E-motor with gearbox (fixed speed)
2 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
OPERATION HISTORY
The customer is experiencing severe fouling of a Cracked Gas Compressor. Both LP and HP sections
are affected (LP section to a lesser extent). The fouling adversely affects compressor performance
resulting in reduced plant throughput and increased power consumption.
Before installation of the Rochem on-line cleaning system, the plant had to be shut down to enable
manual cleaning of the compressor internals. The associated costs were estimated at USD4.8M per
event!
Rotor Assembly (HP Section) 1st Stage Diffuser (HP Section)
Top Cover (HP Section)
3 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
CURRENT SITUATION
In 2015, the customer installed an on-line cleaning system supplied by Rochem.
Scope of Supply
• Injection nozzle (LP and HP)
• Double block-and-bleed valve
• Hose assembly
• Wash delivery skid
• Rochem FYREWASH® F1 Chemical
• Full design study and calculations
• Performance analysis.
For a typical system arrangement and nozzle installation see figure 1 and 2.
Fig.1. System Arrangement (typical)
4 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
Fig.2. Nozzle Installation in Suction Line (typical)
Both LP and HP sections are cleaned on an as-and-when needed basis with Rochem FYREWASH® F1
(for product data see attachment A).
The Rochem FYREWASH® F1 is mixed with four parts of demineralized water (total quantity 125 liters
per section).
The nozzles by which the Rochem FYREWASH® F1 solution is being injected in the process gas stream
are installed in the suction lines of the LP and HP section upstream of the corresponding compressor
suction nozzles (see figure 3 and 4).
Fig.3. LP Nozzle
5 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
Fig.4. HP Nozzle
The design and location of the LP and HP nozzles has been optimized by using Computational Fluid
Dynamic modelling (CFD) (see figure 5).
Fig.5. CFD of Fluid Flow Showing Flush Mounted Nozzle
6 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
PERFORMANCE ANALYSIS
A third on-line cleaning operation was performed in June 2017. The on-line cleaning of the LP and HP
section took approx. 2 hours and was witnessed by Rochem staff.
The various process operating conditions were recorded during the on-line cleaning operation and no
abnormalities (vibration, noise) have been observed.
A compressor performance analysis of the HP section has been performed covering the period just
prior, during, and just after on-line cleaning.
To provide a basis for comparison, the compressor predicted performance curves, including operating
conditions, have been entered into the calculation model.
Site test data collected during 5-minute intervals prior, during, and after on-line cleaning have been
used for the performance calculations.
7 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
Head
A decay in compressor performance due to fouling will generally result in a performance curve shifting
downwards and towards reduced flow.
This effect can clearly be observed in figure 6 where the orange and green dots represent the process
operating conditions before and after the on-line cleaning operation. The orange dots represent the
fouled compressor, i.e. reduced polytropic head1 and flow. The green dots represent the clean
compressor, i.e. polytropic head and flow as per (or close to) original design.
The yellow dots represent the intermediate period during which actual on-line cleaning took place
and are – to a certain extent – erratic in nature.
The process system may also be suffering from fouling, i.e. the system resistance could have increased.
Since the compressor is no longer capable to provide the required head, more head may be required
by the process system.
The polytropic head increased by approx. 28% after on-line cleaning (from 25,500 to 32,750 ft) (see
figure 7).
Fig.6. Polytropic Head vs Volume Flow (HP Section)
1 Polytropic head. Polytropic head is the reversible work required to compress a unit mass of gas by a polytropic process
from the inlet total pressure and temperature to the discharge total pressure and temperature.
DESIGNMAX NORMAL
MIN NORMAL
5
10
15
20
25
30
35
3 4 5 6 7 8
PO
LYTR
OP
IC H
EAD
(FT
)
Tho
usa
nd
s
INLET FLOW (CFM)
Thousands
Polytropic Head vs Volume FlowHP Section
8 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
Fig.7. Polytropic Head (HP Section)
25
26
27
28
29
30
31
32
33
34
35
1:00 PM 2:00 PM 3:00 PM 4:00 PM
PO
LYTR
OP
IC H
EAD
(FT
)
Tho
usa
nd
s
TIME (HR/MIN)
Polytropic HeadHP Section
9 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
Efficiency
Fouling will reduce the compressor efficiency, because of the increased frictional losses and internal
recirculation. The capacity of the compressor will also reduce, because of increased resistance. Hence,
the efficiency curve will also shift downwards and towards reduced flow.
This effect can clearly be observed in figure 8. The orange dots represent the fouled compressor, i.e.
reduced polytropic efficiency2 and flow. The green dots represent the clean compressor, i.e. polytropic
efficiency and flow as per (or close to) original design.
The yellow dots represent the intermediate period during which actual on-line cleaning took place
and are – to a certain extent – erratic in nature.
The green dots are located on (or close to) the original design curves and indicate that the efficiency
curves are not influenced by the system resistance and only represent the compressor performance
as such.
Fig.8. Polytropic Efficiency vs Volume Flow (HP Section)
2 Polytropic efficiency. The polytropic efficiency is the ratio of the polytropic head to the gas work input.
DESIGN
MAX NORMAL
MIN NORMAL
0.0
20.0
40.0
60.0
80.0
100.0
3 4 5 6 7 8
PO
LYTR
OP
IC E
FFIC
IEN
CY
(%)
INLET FLOW (CFM)
Thousands
Polytropic Efficiency vs Volume FlowHP Section
10 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
Because of fouling, the polytropic efficiency has dropped to unacceptable levels.
Fig.9. Polytropic Efficiency (HP Section)
After on-line cleaning, a dramatic improvement in polytropic efficiency has been observed (from 62
to 82%) thereby restoring original design conditions (see figure 9).
50.0
55.0
60.0
65.0
70.0
75.0
80.0
85.0
90.0
95.0
100.0
1:00 PM 2:00 PM 3:00 PM 4:00 PM
PO
LYTR
OP
IC E
FFIC
IEN
CY
(%)
TIME (HR/MIN)
Polytropic EfficiencyHP Section
11 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
Pressure
The compressor discharge pressure is controlled by the process control system and maintained at a
constant pressure level of 245 psia (see figure 10 and 11).
Fig.10. Discharge Pressure vs Mass Flow (HP Section)
The green dots represent the clean compressor and are located slightly below the predicted
performance curves. This can be explained by the fact that the actual molecular weight of the gas is
lower than original design.
Fig.11. Discharge Pressure (HP Section)
DESIGN
MAX NORMALMIN NORMAL
125
175
225
275
325
100 120 140 160 180 200 220 240 260 280
DIS
CH
AR
GE
PR
ESSU
RE
(PSI
A)
FLOW (LB/HR)
Thousands
Discharge Pressure vs Mass FlowHP Section
240
241
242
243
244
245
246
247
248
249
250
1:00 PM 2:00 PM 3:00 PM 4:00 PM
DIS
CH
AR
GE
PR
ESSU
RE
(PSI
A)
TIME (HR/MIN)
Discharge PressureHP Section
12 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
The on-line cleaning operation started around 2:05 PM. From figure 11 it appears that the average
discharge pressure before on-line cleaning was slightly higher than after on-line cleaning.
The on-line cleaning operation resulted in an increased capacity and head. By maintaining the
discharge pressure at a constant level, a sharp decline in suction pressure has been observed (see
figure 12).
Fig.12. Suction Pressure (HP Section)
The pressure ratio improved from 2.0 to 2.5 after the on-line cleaning operation (see figure 13).
Fig.13. Pressure Ratio (HP Section)
95
100
105
110
115
120
125
1:00 PM 2:00 PM 3:00 PM 4:00 PM
SUC
TIO
N P
RES
SUR
E (P
SIA
)
TIME (HR/MIN)
Suction PressureHP Section
1.75
2.00
2.25
2.50
2.75
1:00 PM 2:00 PM 3:00 PM 4:00 PM
PR
ESSU
RE
RA
TIO
TIME (HR/MIN)
Pressure RatioHP Section
13 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
Flow
The capacity of the compressor has seen a significant improvement after the on-line cleaning
operation (see figure 14). The mass flow increased by approx. 10% after the on-line cleaning operation
(from 140,000 to 153,000 lb/hr).
Fig.14. Mass Flow (HP Section)
The volume flow increased by approx. 30% after the on-line cleaning operation (from 4,500 to 6,000
cfm) (see figure 15).
Fig.15. Volume Flow (HP Section)
135
140
145
150
155
1:00 PM 2:00 PM 3:00 PM 4:00 PM
FLO
W (
LB/H
R)
Tho
usa
nd
s
TIME (HR/MIN)
Mass FlowHP Section
4.0
4.5
5.0
5.5
6.0
6.5
1:00 PM 2:00 PM 3:00 PM 4:00 PM
INLE
T FL
OW
(C
FM)
Tho
usa
nd
s
TIME (HR/MIN)
Volume FlowHP Section
14 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
Temperature
Total work is directly related to enthalpy which in turn is related to temperature. Monitoring
temperature rise will be an indication of total work input.
If the temperature rise goes up for a given flow and speed then this will be an indication that the
efficiency of the compressor has gone down.
Both the inlet and discharge temperature have gone down after the on-line cleaning operation (see
figure 16).
Fig.16. Inlet / Discharge Temperature (HP Section)
Although the effect has been very small, the temperature rise has dropped slightly after the on-line
cleaning operation (see figure 17).
100
125
150
175
200
225
250
1:00 PM 2:00 PM 3:00 PM 4:00 PM
INLE
T /
DIS
CH
AR
GE
TEM
PER
ATU
RE
(°F)
TIME (HR/MIN)
Inlet / Discharge TemperatureHP Section
15 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
Fig.17. Temperature Rise (HP Section)
90
95
100
105
110
1:00 PM 2:00 PM 3:00 PM 4:00 PM
TEM
PER
ATU
RE
RIS
E (°
F)
TIME (HR/MIN)
Temperature RiseHP Section
16 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
Power
The operating point has changed towards higher flow and head. Because of this change in operating
point, the power consumption has increased accordingly (see figure 18).
Fig.18. Gas Horsepower vs Mass Flow (HP Section)
Since the polytropic efficiency has improved, the relative work input of the HP section has reduced.
MAX NORMALDESIGN
MIN NORMAL
2000
2500
3000
3500
4000
100 120 140 160 180 200 220 240 260
GA
S H
OR
SEP
OW
ER (
HP
)
FLOW (LB/HR)
Thousands
Gas Horsepower vs Mass FlowHP Section
17 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
SUMMARY OF RESULTS
From the previous observations it can be concluded that the on-line cleaning operation has been
very successful.
• The polytropic head increased by 28%
• The pressure ratio improved from 2.0 to 2.5
• The polytropic efficiency increased from 62 to 82%
• The relative work input has reduced
• The plant throughput increased by 10% (based on mass flow).
The customer is very happy with the on-line cleaning system and continues to work with Rochem to
further optimize the on-line cleaning regime (cleaning quantity, frequency, and sequence).
18 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
COST SAVINGS
The costs of fouling can be significant thereby adversely affecting plant profitability.
Because of on-line cleaning, the customer has reported cost savings of USD4.8M per event. These
costs can be attributed to:
• Reduced equipment availability and reliability
• Loss of revenue resulting from reduced plant throughput
• Plant outage costs resulting from unscheduled maintenance (on average 9 days per event)
• Direct and indirect equipment overhaul costs
• Manhour costs.
Given the fact that this has been the third on-line cleaning operation in a 2-year period, the customer
has potentially saved USD14.4M!
Thereby considering that the total costs of the Rochem on-line cleaning system and chemicals is just
a tiny fraction of this amount….
19 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
ATTACHMENT A
20 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
21 | P a g e P r o c e s s C o m p r e s s o r s _ C a s e S t u d y _ v 3 . d o c x
ATTACHMENT B
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