PROCESS COMPRESSOR CLEANING CASE STUDY€¦ · CASE STUDY GENERAL EQUIPMENT INFORMATION Location: Refinery Name: Cracked Gas Compressor Type: Centrifugal compressor, horizontally-split,

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)


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)


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)


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


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


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.


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


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


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


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


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


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


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


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


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


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


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).


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….


ATTACHMENT A



ATTACHMENT B

Reference List:

Documents

PROCESS COMPRESSOR CLEANING CASE STUDY€¦ · CASE STUDY GENERAL EQUIPMENT INFORMATION Location: Refinery Name: Cracked Gas Compressor Type: Centrifugal compressor, horizontally-split,