Design of Compressor Suction Scrubbers_Noijen_Clinton

Copyright of Shell Global Solutions International B.V.

Design of Compressor Suction

Scrubbers

Or

“Don’t wreck the expensive compressor with cheap

scrubbers or with inadequate engineering”

TEKNA-Conference

Norway, 26-27 September 2012

Hans Nooijen, GSNL-PTD/TRD Paul Clinton, GSNL-PTU/EKUW

Principal Technologist Distillation Principal Concept Engineer


DEFINITIONS AND CAUTIONARY NOTE

2

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future results are contained in Shell's 20-F for the year ended 31 December 2011 (available at www.shell.com/investor and www.sec.gov ). These factors also should be

considered by the reader. Each forward looking statement speaks only as of the date of this announcement, 22 February 2012. Neither Shell nor any of its subsidiaries nor

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SEC by calling 1-800-SEC-0330.


CONTENTS

1. What is the problem?

2. It’s an old problem and it’s an ongoing problem

3. Why do we get it wrong?

4. Examples of getting it wrong.

5. How should we get it right?

10/2/2012 3


WHAT’S THE PROBLEM?

1

4 10/2/2012


WHAT IS THE PROBLEM?

Inadequate separation upstream of compressors results in:

Liquids entering the compressor

Dissolved and entrained solids entering the compressor

Effect on the compressor:

Erosion

Deposition of solids

Eventual consequences:

Reduction of compression efficiency = loss of performance

Rotor imbalance - more unscheduled maintenance

Possible catastrophic failure

5 10/2/2012


IT’S:

An old problem

A current problem

An ongoing problem

2

6 10/2/2012


Case 1 Lift Gas Compressors Performance Check K-614

The second stage discharge pressure is higher than

expected. The high pressure trip has been reached

and the machine keeps tripping.

The problem has been getting worse and it is

suspected that carry-over is fouling the machine up.

This would have its greatest effect in the third stage

where the clearances are smaller.

27 May 1984

COMPRESSOR FOULING - IT’S AN OLD PROBLEM

10/2/2012 7


The liquid being drained from the casing drain resembled heavy crude

rather than condensate.

GS.06.50099 Case 1 Visit Report : COMPRI & Smart Fields Scouting Study

CASE 1 IN 2006

10/2/2012 8


CASE 2

10/2/2012 9


Salt

deposits

CASE 3

10/2/2012 10


CASE 4 - FOULED DIFFUSER

10/2/2012 11


CASE 5 - 1ST STAGE COMPRESSOR INLET EYE

10/2/2012 12


CASE 6 COMPRESSOR - EROSION

10/2/2012 13


When machine

was opened,

these pools of

liquid were found

in it.

CASE 7 CATASTROPHIC FAILURE

10/2/2012 14


CASE 7 - PIECE BROKEN OFF IMPELLER

10/2/2012 15


CASE 7 - BROKEN SEAL

10/2/2012 16


WHY DO WE GET IT WRONG?

3

17 10/2/2012


WHY DO WE GET IT WRONG?

Ignorance - not thinking about our design and not understanding

what is happening in our own process

Not following established good practice

Delegating design responsibility

Lack of attention to detail

No close supervision of contractors

Package unit & vendor guarantee mentality

Concept of “Industry standard”

Attempt to save money

10/2/2012 18


HOW DOES A COMPRESSOR SUCTION SCRUBBER

WORK?

Vessel

Provides larger flow area to

reduce flow velocity

For gas dominated two phase

flow, vertical vessel makes best

use of available area

If high proportion of liquid, need

pre-separation

Control volume for separated

liquid

19 10/2/2012

Inlet nozzle & pipe

Avoids severe maldistribution of

two phase flow across pipe area

Provides non slugging flow

regime

If mist flow be careful - if very

small droplet size, difficult to

separate

Inlet device

Makes coarse gas/liquid

separation

Distributes gas flow across vessel

area

Avoids re-entrainment of droplets

Demisting internals

Remove liquids by various means

Merge small droplets into bigger

droplets

Catch the droplets (cyclones, flow

direction change, etc

Return removed liquid to bottom

of vessel

Outlet nozzle & pipe

Avoids channeling of flow in the

demister


What is wrong with this PFS?

(what is missing?)

wells Flowlines

(5 - 10 km long)

manifold Production separator compressor

A clue:

Now the second

stage is shown

Suction

scrubber was

missing

Production separators are only

bulk separators, just like slug

catchers.

UNDERSTANDING BEGINS AT THE PFS

20 10/2/2012


PEFS

Production

separator

What instruction is missing from these

PEFSs?

To compressor

PEFS

Compression

From separator

To second

compression train,

see PEFS xyz

Slope, do

not pocket

Slope, do

not pocket

Slope, do

not pocket

Instructions to avoid slug formation!

UNDERSTANDING CONTINUES TO PEFS

10/2/2012 21

Copyright of Shell Global Solutions International B.V. 10/2/2012 22

RUNNING PIPING TO COMPRESSORS - PLAN VIEW

Piping dept don’t know about slugs and the

capabilities of your separators.

If you don’t instruct otherwise they will run the

pipes in the most convenient way:

At grade

Underground

Distance can be > 100 m

Well flowlines

Compression train

Compression train


RUNNING PIPING TO COMPRESSORS - ELEVATION

VIEW

10/2/2012 23

Suction scrubbers are not

slugcatchers.

When a slug hits the suction scrubber,

a significant proportion will leave in the

gas and enter the compressor.

Production

separator

Suction

scru

bber

Worst case is starting another

compressor. The equilibrium hold up

changes and a huge slug can be

generated.

High carryover to compressor

LZHH may be reached on running

machines - which will trip.

This gas pipe is now similar to a two phase

cross country pipeline. And it also has

slugs:

Terrain induced

Flow rate induced

A half full 100m long 30 inch pipe holds 7

m3 of liquid!


LZHH

LZLL

Clearance for

access

Range for

control By the time you have

engineered the drain pot,

how high must the pipe be

elevated?

Definitely higher than it

used to be!

I CAN SOLVE THAT WITH A DRAIN POT!

10/2/2012 24


Liquid removal by dip tube or

occasional blowdown are

desperate measures for

constructed plant. They should not

be engineered into a new design.

IF YOU CANNOT ELIMINATE SLUGS, ONLY PROPER

SOLUTION IS A SLUGCATCHER

10/2/2012 25

To suction scrubber

slugcatcher Long pipe

The slugcatcher will eliminate slugs.

Underground slugcatchers are nice for the

hydraulics, but very difficult for

maintenance and safety. (don’t do it)

Don’t forget that the compressor will still

require a suction scrubber.


Slope, do

not pocket

Note 1. No bends in horizontal plane, valves or swages allowed within 10 pipe diameters of inlet nozzle

Note 2. No bends in horizontal plane, valves or swages allowed within 2 pipe diameters of outlet nozzle

Note 1

Note 2

Inlet nozzle v2

requirement usually

needs larger pipe size.

Outlet nozzle v2

requirement usually

needs larger pipe

size.

Inlet nozzle

straight length

requirement.

Outlet nozzle

straight length

requirement.

SUCTION SCRUBBER INLET & OUTLET PIPING

10/2/2012 26


DEVIATION FROM SEPARATOR DEP

10/2/2012 27

Vendor Special

Exciting new technology

Smaller vessel

Cheaper!

CFD based design

Great list of installed units

(but have you spoken to

them?)

DEP Separator

Established technology

Based on many actual

field tests across Shell

Group

Deviation Control

Not applying the DEP requires approval to deviate from Shell practice.

You are not authorized to make this decision.

Why Gamble?

Taking a gamble on a cheaper scrubber is just not worth the risk of compressor damage.


Please remember that all these examples were engineered -

by engineers - it wasn’t an accident.

EXAMPLES OF GETTING IT WRONG

4

28 10/2/2012


The root cause failure report for K 0611 highlighted (utilizing thermo-graphic photos)

that the liquid suction header for the inlet scrubber was half filled with liquids (low

section of the header). This is the suction header to inlet scrubber V-0610.

CASE 1 IN 2006

10/2/2012 29


Long underground lines from flow

station

CASE 8

10/2/2012 30


What basis is there for believing that

this proprietary separator will work?

CASE 1 K-614 SCRUBBER - VESSEL DATA SHEET

10/2/2012 31


Dresser stated that they were

unable to comply with 24”

manway requirements.

Customer (x) agreed for

vessels with no internals.

CASE 1 K-614 SCRUBBER - IT GETS EVEN WORSE

10/2/2012 32


PROPRIETARY SEPARATOR – CASE 9

10/2/2012 33

Flow evenly

distributed

across vane

pack?

Re-entrainment

of droplets?

Channelling

through vane

pack?

Inlet 12”

Outlet 12”

Vessel ID

= 750 mm


In September 2003 severe rotor damage of the Export compressor K-83502

occurred.

Liquid carryover from the suction scrubber vessel V-83502 was identified as a

possible cause of failure.

To quantify the level of liquid carryover and to determine the separation efficiency of

the scrubber V-83502, a dedicated isokinetic sampling campaign was carried out by

Shell Global Solution (SGSi-OGRD) over the period 10 to 12 October 2004.

The vendor guarantee specification for liquid in the off gas from this scrubber is

< 13 litres/MMsm3 (0.1 US gal/MMsft3). This translates to an actual liquid

concentration

of < 10 ppmw in the scrubber off gas.

Conclusions

The measurements from the isokinetic sampling showed an average liquid–in–gas

concentration of 0.19wt% with a separator liquid removal efficiency of 68%.

The vendor guarantee separator performance of 0.1 Usgal/MMsft3 (or 13

liters/MMsm3) carryover in the gas, which equates to a separation efficiency of

99.8%, is by far not being achieved.

Ref OG.04.50720

CASE 9 PROPRIETARY SEPARATOR - EVALUATION

10/2/2012 34


Bend in horizontal plane

violating 10D straight length

requirement.

V-1410

Propane

compressor

suction

scrubber

CASE 10 - INCORRECT INLET PIPING TO SUCTION

SCRUBBER

Case 10 Pre-start-up audit, July 2005

35 10/2/2012


HOW SHOULD WE GET IT RIGHT?

5

36 10/2/2012


HOW SHOULD WE GET IT RIGHT?

Understand the problem and how to avoid it.

Follow established good practice:

Use the Separator DEP

Eliminate slugs and keep them from re-forming

Pipework configuration correct

Don’t delegate design responsibility:

Put “high level” philosophical requirements in BOD & BDP

Ensure that our requirements are fulfilled:

Project spec contractor to correctly express our philosophical

requirements in the EPC bid document

EPC contractor to purchase accordingly

EPC contractor to construct accordingly 37 10/2/2012


Principal

(asset owner)

Design

contractor Vendor Fabricator

relationship

Who is making the decisions?

Who is truly providing the guarantee?

Where is the expertise?

Who really knows how the equipment will

perform?

Technical

advisor

rela

tio

nship

Is the process engineering expertise in the project at the Principal’s end or the other end?

There is no reason for the expertise not to be at the Principal’s

end.

That expertise should be you!

relationship relationship

RELATIONSHIPS & EXPERTISE

10/2/2012 38


THANK YOU FOR YOUR ATTENTION

39 10/2/2012


DEP 31.22.05.11-Gen. September 2002

In E&P Offshore service

Separator handling natural-flowing production from:

a) its own platform 1.2

b) another platform or well jacket in shallow water 1.3

c) another platform or well in deep water 1.4

Separator handling gas lifted production from:

a) its own platform 1.4

b) another platform or well jacket 1.5

In E&P Onshore service Separator handling natural flowing production, or gas plant inlet separator in:

a) flat or low rolling country 1.2

b) hilly country 1.3

Separator handling gas lifted production in:

a) flat or low rolling country 1.4

b) hilly country 1.5

In Refineries and Chemical plants: The design margin ranges typically from

1.15 to 1.25

SURGE FACTORS - For the production separator upstream of the compressor suction

scrubber

10/2/2012 40


CORROSION EROSION

10/2/2012 41


THRUST BEARING (BOTTOM) & SEAL

10/2/2012 42


RECIPROCATING COMPRESSOR OUTBOARD

DISCHARGE VALVE

10/2/2012 43

Documents

Design of Compressor Suction Scrubbers_Noijen_Clinton