NGL-Recovery Expander-Compressor Commissioning

(Case Study)( y)

By Nabil Madani,

Sr. Rotating Equipment EngineerSr. Rotating Equipment Engineer

Outline

o Commissioning Background

o Description of the NGL Process.

o Description of the NGL expanders-compressors.

o Initial startup issues, troubleshooting and solutions:

• 0% IGV speed overshoot.

• Decrease of the Bearing housing temperature.

o Recommendations.o

Commissioning Background

o Late 2008, 1st LNG Mega-Train (7.8 MT/Y) commissioning and start-up started at Qatargas Train-4 facilities.

o The majority of the Machinery commissioning was divided into three phases :

• Driver solo run (Uncoupled run), except for expanders-compressors.

• Coupled commissioning run (Air run and safe-fluid run), except for expanders-compressors.

• Normal run (Startup for duty).

o January 2009, 1st NGL expander-compressor was started.

NGL Unit Process Description

Lean NG (Unit-OUT)

Natural Gas (Unit-IN)

G, -

44de

gC

ASV

60 B

arG

28 BarG, 22 degC

1deg

C

etha

nize

r

35 B

arG

, 4

Seal Gas (External)

E C De-

M

30 BarG 77degC

Magnetic Bearing

JT

Simplified NGL Recovery Process P&ID

30 BarG, -77degCNGL

(Unit-OUT)

NGL Expander-Compressor Description

SGM

M

MM

PTPDC

M

MM

PDT

M M MM

PT

EXPANDER COMPRESSOR

Simplified Expander-Compressor Cross Sectional Drawing

PTPT

Pre-startup Checks

o NGL Expanders-Compressors were delivered with a dummy Mechanical Center Section (MCS), the duty MCS was packaged inside a preservation container under N2.

o The following adjustments and clearances were set during the duty MCS installation:

• Expander and Compressor wheels clearances.

• Inlet Guide Vanes Close clearance (0% IGV) and Open clearance (100% IGV).

• Actuator stoppers (Close/Open) and stroke adjustment.

o Controls tuning and final assembly checks.

o All the adjustments and clearances were recorded.

0% IGV Speed Overshoot

30.0

40.0

11000

12000

Max Continuous Speed (10400 RPM)

Over-speed Trip (11200 RPM)

906219.5

0 0

10.0

20.0

8000

9000

10000Max. Continuous Speed (10400 RPM)

-20.0

-10.0

0.0

6000

7000

8000

eg C

RPM

SpeedOulet Temperature

-40.0

-30.0

4000

5000

DeR

De-Methanizer Temperature @ Startup (- 37 DegC)

Excepted Start-up Speed Range

-70.0

-60.0

-50.0

1000

2000

3000p p p g

-73.1-80.0

70.0

0

1000

0 30 60 90 120

150

180

210

240

270

300

330

360

390

420

450

Seconds

IGV Mechanism

IGV Mechanism (Illustration Video Only)

IGV Mechanism

Fixed Pivot Holder Shifting (Illustration Video Only)

0% IGV Speed Overshoot

Solution:

o Addition of two dowel pins between the holder and the support preventing rotational movements.

Facts:

o Expander speed reached 87% of the total speed range at 0% IGV.

o Outlet temperature dropped from 19 to -73 deg C within 7 mn.

o There is no contractual limitation in either the speed or the outlet conditions when starting the machines with the IGV at 0%.

o API-617 Chapter 4 “Expanders Compressors” do not limit speed or the outlet conditions with the IGV at 0%.

Bearing Temperature Decrease

30.0

40.0

4500

5000

10.0

20.0

3500

4000

SpeedExpander Thrust Bearing Temperature

-10.0

0.0

2500

3000

eg C

RPM

Expander Thrust Bearing TemperatureExpander Journal Bearing Temperature

-30.0

-20.0

1500

2000

DeR

-50.0

-40.0

500

1000

-60.00

0 30 60 90 120

150

180

210

240

270

300

330

360

390

420

450

480

510

540

570

600

630

660

690

720

750

780

Seconds

Bearing Temperature Decrease

SGM

M

MM

PTPDC

M

MM

PDIPDT PDI

M M MM

PT

EXPANDER COMPRESSOR

Simplified Expander-Compressor Cross Sectional Drawing

PTPT

Bearing Temperature Decrease

Solution:

o Operating procedure and an Extra Delta Pressure transmitter were added to monitor the Delta pressure across the bearing housing during pressurization.

Facts:

o Operations Procedures developed during the construction phase (machine already manufactured) extracted from the Vendor instructions.

o Vendor instructions limited to the package boundaries .

o HAZOP performed for the NGL unit, not specific to expanders.

Recommendations

o Consider maximum speed or expander process p p poutlet limitations at 0% IGV during the engineering

hphase.

o Operations involvement during the early stage of p g y gthe machine engineering.

o Specific Operational review and start-up HAZOP for systems involving expanders.for systems involving expanders.

Thank youThank you …