Design av demistere for høytrykksanvendelsehøytrykksanvendelse

S j t k l i 2009Separasjonsteknologi 2009

September 30 2009September 30, 2009Presenter: Dag Kvamsdal

Overview todays presentationOverview todays presentation

• Quick overview of demisters• Quick overview of demisters• Typical separation performance requirement of

demisters• Operational envelope for scrubbers today• Operational envelope for scrubbers today• Testing of demisters in laboratory• What will affect the demister performance• Status on CFD calculations• Status on CFD calculations• Natco Norway focus for new development of

demisters and scrubber internals

Demisters in a process systemDemisters in a process system

Primary Separators

Gas scrubbers

Contactor towers

Demisters used in scrubbers and separatorsE lExamples

Vanepack

Demisting cyclones

Separators

Demisting cyclonesDemisting cyclones

ScrubberSingle stage scrubber

Two types of demisters discussedAxial flow cyclones and vane packs

Vane packVane pack

Suited for low-mid pressure application p essu e app ca oand low gas loading

Axial flow cyclones

Suited for high pressure demisting

Separation efficiency scrubberUsing Natco Norway correlationsg y

eff

[%]

Sep

Efficiency demister

0 % 20 % 40 % 60 % 80 % 100 % 120 %

Relative flow rate

li id

gasgasuk

ρρρ−

=

ep e

ff [%

]

gasliquid ρρ

Se

Efficiency bulk separation vesselK-value [m/s]

Required separation efficencyExample; Achieve 0.1 gal/MMSCF

Demister section

Process conditions Year 2011Operating pressure [bara] 25 1

Example case

section99.73 %

Operating pressure [bara] 25.1Operating temperature [ºC] 105Gas actual flow rate [Am³/h] 25263Gas actual density [kg/m³] 22.5Gas actual viscosity [cP] 0.01

I l t ti

y [ ]Hydrocarbon liquid flow rate [Am³/h] 22.71Oil actual density [kg/m³] 881Hydrocarbon surface tension [N/m] 0.021Oil actual viscosity [cP] 13.0200

Inlet section and vessel combined88.97 %

Water flow rate [Am³/h] 0.0Water actual density [kg/m³] 991.5Water actual viscosity [cP] 0.6Liquid fraction [vol%] 0.09 %

Overall efficiency: 99.97 %

Efficiency limitations for scrubbersOperational envelope LCO<0.1 gal/MMSCF

The scrubbers using inlet vanes will have a limitation around k=0.15 m/s to 0.20 m/s due to the rapid increase in liquid to

the demister section from the bulk section of the vessel

2 0 %

the demister section from the bulk section of the vessel

1 5 %

2.0 %

n

> 0.1 gal/MMSCF

1.0 %

1.5 %

ume fraction

0.5 %Liqu

id volu

Increasing Pressure

0.0 %k‐value [m/s]

< 0.1 gal/MMSCF

k value [m/s]

Options for demister testingThe Natco axial flow cyclone has been tested at the following labs

Ai t l b t N t L b t R l fl id l b tAir water laboratory

Functional testing of a

Natco Laboratory

Testing of individual

Real fluid laboratory

For instance StatoilHydro K-full axial flow cyclone box

demisters and demister sections

lab.

Real fluids, Full size test

Test pressure 1-5 bargModel fluids and possibility to run gas densities of 60 kg/m3

,sections and up to 150 bar

densities of 60 kg/m

Testing high pressure demistersReal world vs laboratory conditions

1 10 100

Real world Gas density [kg/m3]

Real world S rface tension [kg/m3]1 10 100

Surface tension [kg/m3]

10-3 10-110-2 100 101

ScrubbersDemisters Diameter [m]10-3 10-110-2 100 101

Ai tAir water

Natco Norway Laboratoryy y

Separation efficiency for a demisterDifferences from lab to real conditions axial flow cyclones

99.0 %

99.5 %

100.0 % Test data

Test data from air water gives 100%

97.0 %

97.5 %

98.0 %

98.5 %

Efficiency

Real fluids

Test data from air water gives 100% separation efficiency, nothing to learn!

95.5 %

96.0 %

96.5 %

97.0 %Model fluids

Air waterModel fluids gives reduced efficiency and it is possible to evaluate the geometry

50 % 70 % 90 % 110 %

Flow [‐]

g y

Real fluids gives considerably lower efficiency

Flow mechanisms in a demisterAffecting the separation Affecting the separation

Droplet break up

Droplet transportation

Wall interaction

Collisions / Coalescence

CFD challenge for demister equipmentg q p

• Why cannot CFD replace testing all together• Limited computer capacity allows sets an upper limitation of the length scales

that can be resolved• CFD can only resolve the length < 1000 nodes in 3 dimension total nodes 10003

= 109

Equipment

The challenge of CFD; it is all about scales

Equipment

TurbulenceDroplets Length [m]

10-6 10-410-5 10-3 10-2 10-1 10-0

CFD resolvedCFD resolvedCFD resolvedCFD resolved

g [ ]

CFD ability to capture the flow field

RANS calculations

Time averaged solution that in many ways do y ynot visualize the real

flow pattern in the vanepack

LES calculations

Able to calculate the main flow structures and the general flow pattern qualitative

correct

Calculation 15 000 CPU h iCPU hours using 7 000 000 cells

Multiphase flowIncluding; droplet break up, coalescence and wall film model

Flow in a vanepack as filmed in the laboratoryp y

G d it 60 k / 3Gas density 60 kg/m3

Flow in the vanepack slow motionFlow in the vanepack slow motion

Gas density 60 kg/m3

Efficiency vane packAs tested in the Natco laboratory

99 %

100 %

Vane pack efficiency

High efficiency for k < 0 1 m/s for all96 %

97 %

98 %

99 %

ncy

High efficiency for k < 0.1 m/s for all gas densities up to 60 kg/m3

Falls below 99% when k>0 15 m/s92 %

93 %

94 %

95 %

Efficie

Increasing density

Falls below 99% when k>0.15 m/s90 %

91 %

K‐value [m/s]

Vane pack efficiency 96 %

98 %

100 %

Vane pack efficiency compared to axial flow

cyclones90 %

92 %

94 %

ion efficiency Vane pack

Cyclones

The axial flow cyclones can handle considerably higher flow without loss

of performance82 %

84 %

86 %

88 %

Separat

80 %

82 %

K‐value [m/s]

Development of scrubber internalsDevelopment of scrubber internals

• Under development• Under development– New generation of axial flow cyclones

• Should achive 10 times or more better performance than the existing axial flow cyclonesI t t f t i li l ti ll hi h• Important for one stage inline solutions as well as high pressure scrubbers

New scrubber inlet section– New scrubber inlet section• Should give 99% or better efficiency for a k-value in the

vessel of 0 25 m/svessel of 0.25 m/s.

Next generation axial flow cyclonesOperational envelope LCO<0.1 gal/MMSCF

Improved axial flow cyclones where the efficiency is improved with a factor of 10 compared with

existing cyclonesexisting cyclonesThe maximum k value to achieve 0.1 gal/MMSCF

will be as shown

2.0 %

n

> 0.1 gal/MMSCF

1.0 %

1.5 %

ume fraction

0.5 %

Liqu

id volu

Increasing Pressure

0.0 %k‐value [m/s]

< 0.1 gal/MMSCF

Design of Gas ScrubbersInlet devices

g

Inlet Vane Diffuser Swirl InletInlet Cyclone Distributor Statoil’s SPINLET

Efficiency for new type inletEfficiency for new type inlet

Key for further scrubber development is to manage to remove 99% or more of the droplet in

the vessel before demister up to k 0 25the vessel before demister up to k ~ 0.25

1.5 %

2.0 %

n

> 0.1 gal/MMSCF

1.0 %

1.5 %

lume fraction

0.5 %Liqu

id vol

Increasing Pressure

0.0 %k‐value [m/s]

< 0.1 gal/MMSCF