Laggan & Tormore Gas Plant: 18 Months of Operation Results of a New Produced Water Treatment

Patrick Baldoni-Andrey Total Cathy Fuchs Suez

AGENDA

• Background • Process Overview • Operating results • Conclusions

Laggan & Tormore – Shetland Gas Plant (UK)

The Shetland Gas Plant (SGP) is a 500 MMSCFD capacity gas plant located at

Sullom Voe. It receives reservoir fluids, via twin 143km multiphase flow

lines, directly from the Laggan-Tormore fields which are located 125km

north-west of the Shetland Islands (North Sea) in approximately 600m water

depth.

The produced water is fed to the Effluent Water Treatment Plant (EWTP) for

processing prior to being discharged to Yell Sound via a 3.75km pipeline. Slug

Catcher

Incoming gas

Condensates separation

Gas to processing / export

Condensates to BP Sullom Voe

MEG processing

Lean MEG to subsea production

Produced Water

SGP MEG regeneration effluent source

rich MEG

effluent

pretreatment vessel

particle filter

MEG regeneration column

side stream MEG reclamation unit

MEG reflux drum

lean MEG

brine slurry

SGP EWTP Pegasus process

effluent discharge to sea

Oil separator

•insoluble hydrocarbon removal

Stripping

•BTEX removal

•no waste product

•fuel gas reused in the LP gas system

Polishing

•residual hydrocarbon removal

•biofilter wash water treatment

Biofilter

•soluble organic removal

SGP EWTP – Deoiling since start up

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

03-2016 04-2016 05-2016 06-2016 07-2016 08-2016 09-2016 10-2016 11-2016 12-2016 01-2017 02-2017 03-2017 04-2017 05-2017 06-2017 07-2017 08-2017 09-2017

Oil

(m

g/l

)

Effluent Feed Flotation Unit Outlet

Effect of upstream improvement

Effect of temperature increase

SGP EWTP – physical BTEX removal

0

200

400

600

800

1000

1200

To

tal

BT

EX

(m

g/l

)

Feed effluent Stripping outlet

64%

26%

5% 1% 4%

Feed BTEX composition

62%

24%

9% 2% 5%

Stripped effluent BTEX composition

Benzene Toluene m- & p-Xylene Ethyl Benzene o-Xylene

No significant change in proportions of individual components Stripping equally effective for removing different BTEX components

SGP EWTP – Optimizing chemical dosing to improve TSS removal

0

20

40

60

80

100

120

140

03-2016 04-2016 05-2016 06-2016 07-2016 08-2016 09-2016 10-2016 11-2016 12-2016 01-2017 02-2017 03-2017 04-2017 05-2017 06-2017 07-2017 08-2017 09-2017

TS

S (

mg

/l)

Flotation Unit Outlet

Coagulant #1

Flocculant #1

Coagulant #1

Flocculant #2

Coagulant #1

Flocculant #3

Coagulant #2

Flocculant #3

SGP EWTP – COD reduction upstream of the biological treatment

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

03-2016 04-2016 05-2016 06-2016 07-2016 08-2016 09-2016 10-2016 11-2016 12-2016 01-2017 02-2017 03-2017 04-2017 05-2017 06-2017 07-2017 08-2017 09-2017

CO

D (

mg

/l)

Effluent Feed Flotation Unit Outlet

MEG regeneration

•Optimize operation

EWTP

•Improve chemical dosing

Biological treatment

•Less load

SGP EWTP – biological treatment performance

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

03-2

016

04-2

016

05-2

016

06-2

016

07-2

016

08-2

016

09-2

016

10-2

016

11-2

016

12-2

016

01-2

017

02-2

017

03-2

017

04-2

017

05-2

017

06-2

017

07-2

017

08-2

017

09-2

017

CO

D (

mg

/l)

COD removal

Biofilter feed Biofilter out

0

5

10

15

20

25

30

35

40

45

CO

D (

mg

/l)

Phenol removal

Biofilter feed Biofilter out

Upstream optimization

Better pretreatment

Better biological

performance

Better removal of components such as Phenol

Visual indication of performance across the EWTP

Conclusions

• First 18 months of operation have shown the importance of: • Optimizing the upstream process to control load to the effluent

treatment • Getting the chemical selection right • Maintaining stable operation of the EWTP

• Once the above issues were addressed good compliance with the plant’s discharge permit was achieved

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