FLASH DRUM DESIGN

ChE 4253 - Design IChE 4253 - Design I

Vertical vessel Horizontal Vessel

FLASH DRUM DESIGN

ChE 4253 - Design IChE 4253 - Design I

Installed Units

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ChE 4253 - Design IChE 4253 - Design I

Deflectors, and Diffusers

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ChE 4253 - Design IChE 4253 - Design I

Demisters

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ChE 4253 - Design IChE 4253 - Design I

Control Schemes

FLASH DRUM DESIGN

ChE 4253 - Design IChE 4253 - Design I

Dimensions to decide

DhVhLhf

FLASH DRUM DESIGN

ChE 4253 - Design IChE 4253 - Design I

Calculations to make

Ratchford Rice Equation (look for it!!)

F L V= +

i i iFz Lx Vy= +

i i iy K x=

1ii

x =∑1i

iy =∑

1 ( 1)

1 ( 1)

ii

i

i ii

i

zxV KF

K zyV KF

⎧ =⎪ ⎡ ⎤+ −⎪ ⎣ ⎦⇒ ⇒⎨⎪ =⎪ ⎡ ⎤+ −⎣ ⎦⎩

FLASH DRUM DESIGN

ChE 4253 - Design IChE 4253 - Design I

Dimensions to decide

D related to vapor velocity. hV related to vapor velocity. hL related to level control hf related to flooding

FLASH DRUM DESIGN

ChE 4253 - Design IChE 4253 - Design I

D related to vapor velocity.

Permitted velocity

Where do these come from ?

( )L Vperm

V

v K ρ ρρ−

=

2 3 4ln (ln ) (ln ) (ln )lv lv lv lvA B F C F d F E FK e + + + +=

1.8774780.8145800.1870740.0145230.001015

ABCDE

= −= −= −= −= −

L Llv

V V

WFW

ρρ

=

FLASH DRUM DESIGN

ChE 4253 - Design IChE 4253 - Design I

D related to vapor velocity.

Stokes

drag

gravity-Buoyancy

( )L Vperm

V

v K ρ ρρ−

⇒ =

6vis d dF R vπμ=

34( )3g L V dF g Rρ ρ π= −

( )2 2 31 4( )2 3drag vis drag g D D V d L V dF F F F C R v g Rπ ρ ρ ρ π+ ≈ = ⇒ = −

visF dragF

gF

212drag D V dF C A vρ=

83

d

D

gRKC

=drag visF F>>

FLASH DRUM DESIGN

ChE 4253 - Design IChE 4253 - Design I

Dimensional analysis for drag: Force is dependent on velocity, cross sectional area, density and viscosity.

Two nondimensional numbers:

Therefore

Thus is a function of the particle Reynolds number.

/Re dv A πμ

= 212

dragD

V d

FC

Avρ=

(Re, ) 0b Df C =2

(Re)12

DD c

V d

FC fAvρ

= =

DC8

3 (Re)c

dgRKf

=

( , , , , ) 0a drag d Vf F v A ρ μ =

FLASH DRUM DESIGN

ChE 4253 - Design IChE 4253 - Design I

But, what should be used? The criteria is that 5% of the liquid

is entrained.

Thus

; were obtained

fitting experimental data.

Therefore

Demisters should take care of 4% (or less) of the 5%.

L Llv

V V

WFW

ρρ

=

4 4D

perm V

VD Avπ π ρ

= =

2 3 4ln (ln ) (ln ) (ln )lv lv lv lvA B F C F d F E FK e + + + +=

dR

FLASH DRUM DESIGN

ChE 4253 - Design IChE 4253 - Design I

Who came up with this rule and why?

What is so magic about 3 ft? (Room for demister?)

Again, why 2ft? (Residence Time, Failure Analysis,Other Control issues?)

or ~2 minutes residence time.

Finally: Nozzle size

136"2Vh diameter of feedline= +

112"2fh diameter of feedline= +

V f LL h h h= + +

2

4

poolL

Vh

Dπ=

FLASH DRUM DESIGN

ChE 4253 - Design IChE 4253 - Design I

Final considerations

IF 3 increase Vpool (Why???)

IF 5 Use horizontal drum (Why???)

Different design protocol: Why?

LD<

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