SINTEF 04/18/23

CONTROL OF VOC EMISSION FROM CRUDE OIL TANKERS

Otto M.Martens, MSc. Norwegian Marine Technology Research Institute (MARINTEK)Ole Oldervik, MSc. PhD. SINTEF Civil and Environmental EngineeringBengt Olav Neeraas, MSc. PhD. SINTEF Energy ResearchTerje Strøm, MSc. SINTEF Applied Chemistry

SINTEF 04/18/23

Results from study on reduction of VOC emission from Crude oil tankers

• Focus on shuttle tankers and FSO/ FPSO• Simulation of :

– evaporation rates for individual volatile compounds– gas emission rates– composition of emitted gas

• Reduced emission by combination of control techniques:

– sequential transfer of tank atmosphere (STTA)– reliquefaction of VOC– absorption of VOC in cargo oil

SINTEF 04/18/23

INTRODUCTION

• The VOC emission represents:– a loss of considerable monetary value– harmful consequences to the environment

• National goal of 30 % NMVOC emission• 50 % of emission in Norway from offshore loading• Actions taken:

– gas return and recovery plant at the Sture terminal– absorption plant on M/T “Anna Knutsen”– recondensation plant on M/T “Navion Viking”– several R&D projects and measurement series performed

• VOC diluted in inert gas creates a problem

SINTEF 04/18/23

The VOCON RESEARCH PROJECT

Sponsors- Statoil UBT/PRA

- Saga Petroleum ASA

- BP International Ltd

- Shell Expro

- Norsk Hydro

- Kværner Ship Equipment

- Aker Engineering,

- Umoe Technology Sandsli

- Bergesen DY AS

- Navion

- Norwegian Petroleum Directorate

- Det Norske Veritas

- Norwegian Council of Research

- Norwegian Maritime Directorate

- MARINTEK/SINTEF

Performed by SINTEF

Content :• Emission measurements

onboard• Developed emission

simulation program• Evaluated concepts for

VOC emission control– Required 75 % reduction of

NMVOC emission

SINTEF 04/18/23

The Simulation Program HCGas

• Typical components considered :

– C1, C2, C3, i-C4, n-C4, i-C5, n-C5, C6, C7, C8, C9, C10+, N2, CO2 , O2 • Transportation in liquid and gas phases by solving one dim

diffusion/ convection equation for each component• Local equilibrium at the free surface gives mass transfer of

each component between the phases• Mass continuity eq. for each tank and flow eq. for each pipe

used to compute flow• Loading and discharging rates specified• Temperature specified in liquid phase as f(time, space)• Temperature specified in gas phase as f(time, space) or

computed

SINTEF 04/18/23

Simulated cases

ST L

StoreT ransport

Case B: STL

ST T A

VOCrecovery

Shuttle

T ranspor t

Store

Case A: GBS

ST T A

VOCrecovery

Shuttle FPSO

Case C: FPSO

StoreT ransport

VOCrecovery

GasreturnST T A

Shuttle

Shuttle

StoreT ranspor t

FSO

Case D: FSO

VOCrecovery

GasreturnST T A

• 140300 m3 cargo capacity all ships

• shuttle tanker and STL loaded and discharged from 3 similar tank groups in series

• average sea condition offshore

• fairly volatile crude

• shuttle tanker– loading rate 2.2 m3/s– discharge rate 2.7 m3/s

SINTEF 04/18/23

SHUTTLE TANKER - BASE CASE

Figure 3 Gas flow out of tanks - Base Case

Time (h)0 2 4 6 8 10 12 14 16 18 20 22 24

Flo

w ou

t o

f ta

nk

s (

Nm3

/h)

0

2000

4000

6000

8000

10000

12000

14000

Figure 4 Composition of gas out of tanks - Base Case

Time (h)0 2 4 6 8 10 12 14 16 18 20 22 24V

olu

me

fra

cti

on

in

ga

s o

ut

of

tan

ks

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8C1

C2

C3

iC4

nC4

iC5

nC5

C6+

N2+O2

CO2

Figure 5 Relative composition of hydrocarbon gas

out of tanks - Base Case

Time (h)0 2 4 6 8 10 12 14 16 18 20 22 24

Re

l. f

rac

tio

n H

C i

n g

as

ou

t o

f ta

nks

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40rel C1

rel C2

rel C3

rel iC4

nC4

rel iC5

rel nC5

rel C6+

Figure 6 Volume fraction of hydrocarbon gas

emitted from tanks - Base Case

Time (h)0 2 4 6 8 10 12 14 16 18 20 22 24

Vo

lum

e f

ra

cti

on

HC

ga

s

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

SINTEF 04/18/23

SHUTTLE TANKER - BASE CASE

Figure 7 Molecular weight of hydrocarbon gas

emitted from tanks - Base Case

Time (h)0 2 4 6 8 10 12 14 16 18 20 22 24

Mo

lecu

lar w

eig

ht

(kg/k

mol)

40

42

44

46

48

50

52

54

56

58

60

Figure 8 Volume fraction hydrocarbon gas at

two levels inside the tank - Base Case

Time (h)0 2 4 6 8 10 12 14 16 18 20 22 24

AL

FA

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Top Tank 1 Half Height Tank 1 Top Tank 2 Half Height Tank 2 Top Tank 3 Half Height Tank 3

Figure 9 Mass of gas emitted from tanks - Base Case

Time (h)0 2 4 6 8 10 12 14 16 18 20 22 24

Ac

cu

mu

late

d m

as

s

(kg

)

0

25000

50000

75000

100000

125000

150000

175000

200000

Emitted VOC

Emitted IN

Emitted C1

SINTEF 04/18/23

SHUTTLE TANKER - STTA

• Emission of NMVOC:– base case 193000 kg– base case with STTA

169000 kg

• Compared to base case STTA gives:

– reduced flow rate– reduced emission– reduced running time and

better condition for recovery plant

Crude

STTAGas out

Figure 13 Volume fraction hydrocarbon gas emitted

from the tanks - Shuttle Tanker with STTA

Time (h)0 2 4 6 8 10 12 14 16 18 20 22 24

Vo

lum

e f

ra

cti

on

HC

ga

s

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

SINTEF 04/18/23

Shuttle Tanker with STTA and liquefaction plant

Case NMVOCemissionreduction(wt. %)

Reducedemisson

(ton NMVOC)

Maximumcompressor power

(kW)

Energyconsumption

(kWh)

Relative averageenergy

consumption (kWh/kgNMVOC)

Plantcomplexity

BaseCasewithoutSTTA.Recovery onshuttle

75 145 1 900 28 000 0.19 - VOC compressor.- Refrig.plant.- Requires drying of VOC/inert gas

BaseCase withSTTA.Recovery onshuttle

75 144 1 600 21 000(no operationthe first two

hours)

0.15 - VOC compressor.- Refrig. plant.- Requires drying of VOC/inert gas- STTA

L iq u id N M V O C

R e frig era tio np lan t

D ry erV O Cc o m p res so r

U n co n d e n se d g as

F ig u r e 1 1 . R e l iq u e f a c t io n p la n t in p r in c ip le .

Combi-nation

Endtemperature

(0C)

Endpressure

(bar)

RecoveredNMVOC

plant alone(wt %)

Totalcompr.power(kW)

a -20 7 71.4 1521b -30 5 72.6 1673c -40 3.5 74.0 2071

SINTEF 04/18/23

Shuttle Tanker with STTA and absorption plant

Case NMVOCemissionreduction (wt. %)

Reduced emisson(ton NMVOC)

Maximumcompressorpower (kW)

Energy consumptionincl. crude pump

(kWh)

Relative average energyconsumption(kWh/kgNMVOC)

Plantcomplexity

BaseCase withoutSTTA.Recovery onshuttle

75 145 1 500 22 905 0.16 - VOC compressor.- Crude pump.- Absorption column

BaseCase withSTTA.Recovery onshuttle

80 131 1 450 21 708 0.14 - VOC compressor.- Crude pump.- Absorption column- STTA

Figure 17. Schematic outline of absorption plant.

SINTEF 04/18/23

Gas Return from Shuttle Tanker to FSOwith STTA on shuttle tanker and liquefaction plant on FSO

Table 7. Calculated recovery rates

Comb Temp.[0C]

Pres.[bar]

NMVOCrecovery period 1[wt.%]

TotalNMVOCrecovery[wt.%]

a -20 7 87.4 77.1b 15 20 87.8 77.4

Figure 18 Flow out to the atmosphere from the FPSO/FSO and the Shuttle Tanker

Time (h)

0 12 24 36 48 60 72 84 96 108 120 132 144

Flo

w o

ut

to a

tmo

sp

he

re (N

m3 /

h)

0

2000

4000

6000

8000

10000

Figure 19 Volume fraction hydrocarbon gas out to the atmosphere from the FPSO/FSO and the Shuttle Tanker

Time (h)

0 12 24 36 48 60 72 84 96 108 120 132 144

Vo

lum

e fr

acti

on

HC

gas

0.00.10.20.30.40.50.60.70.80.91.0

0

1 0 0

2 0 0

3 0 0

4 0 0

5 0 0

0 5 0 1 0 0 1 5 0

T im e (h )

Sha

ft p

ower

(kW

),

Acc

.rec

. NM

VO

C (t

on)

0

1 0 0 0 0

2 0 0 0 0

3 0 0 0 0

4 0 0 0 0

5 0 0 0 0

Acc

.Ene

rgy

(kW

h)

P o w e r N M V O C

E n e rg y

F ig u re 2 0. P o w e r re q u irem en t, a cc um u latedre c ov ere d N M V O C a nd ac c um ulate d e ne rgy

c o n sum ptio n for c a se 2 .

SINTEF 04/18/23

CONCLUSIONS

• STTA combined with recovery plant reduces :– required peak power– energy consumption– process equipment dimensions (slightly)

• Economy of combination must be evaluated for each ship• Compared to absorption plant a reliquefaction plant :

– requires higher power– becomes more complex– produces VOC to be used as fuel

• Gas return to FSO requires small plant to satisfy specified reduction of NMVOC emission

• HCGas is a powerful tool for computing evaporation and emission from various crude types and cargo handling procedures