Perancangan Tangki Penyimpan dan Menara Distilasi

Process Equipment Design: 3 CR Codes such as: ASTM=American Society of Mechanical Engineers; API=American Petroleum Institute

Brownell, L.E., and Young, E. H., 1959, “Process Equipment Design: Vessel Design”, Wiley Eastern Limited, New Delhi 1. Vessel/Shell Factors influencing the design of vessels a. Selection of the type of Vessel Type of vessel that is suited for particular service b. The most common types of vessels based on their geometry are: i. Open tanks ii. Flat bottomed, vertical cylinder tanks iii. Vertical cylindrical and horizontal vessels with formed heads iv. Spherical or modified spherical vessels Vessels in each these classifications are widely used as storage vessels and as processing vessels for fluids c. Primary factors that must be considered as follows i. Function and location of vessel ii. The nature of the fluid iii. Operating pressure and temperature iv. Volume of storage or capacity for processing

Coulson, J.M., and Richardson, J.F., 1983, Chemical Engineering Volume 6 (SI Units) Design, Pergamon Press, Oxford p. 622, Chapter 13; Mechanical Design of Process Equipment The basic data needed by the specialist designer will be: a. b. c. d. e. f. g.

Vessel function Process materials and services Operating and design temperature and pressure Materials of construction Vessel dimensions and orientation Type of vessel heads to be used Openings and connections required

h. Specification of heating and cooling jackets or coils i. Type of agitator j. Specification of internal fittings Classification of pressure vessels are divided into two classes: thin walled vessels with a thickness ratio of less than 1:10; and thick walled above this ratio

General design considerations: pressure vessels a. Design pressure Pdesign = (1.5-1.1) Poperating ; If hydrostatic pressure in the base of the column should be added to the operating pressure, if significant b. Design temperature The strength of metals decreases with increasing temperature, so the maximum allowable design will depend on the material temperature c. Materials Carbon and alloy steels for pressure vessel construction are covered by the following British Standards: BS 1501, plate etc. d. Design stress (nominal design strength) For design purposes it is necessary to decide a value of the maximum allowable stress that can be accepted in the material construction. For materials not subject to high temperature the design stress is based on the yield stress or the tensile strength of the material at design temperature e. Welded joint efficiency, and construction categories The strength of a welded joint will depend on the type of joints and the quality of the welding. The soundness of welds is checked by visual inspection and non-destructive testing (radiography) f. Corrosion allowance Most design codes and standards specify a minimum allowance of 1.0 mm. For carbon and low-alloy where severe corrosion is not expected, a minimum allowance of 2.0 mm should be used; where more severe conditions are anticipated this should be increased to 4.0 mm. g. Design loads A structure must be designed to resist gross plastic deformation and collapse under all conditions of loading. Major loads 1. Design pressure including any significant static head of liquid; 2. Maximum weight of the vessel and contents, under operating conditions;

3. Maximum weight of the vessel and contents under hydraulic test conditions 4. Wind loads 5. Earthquake loads 6. Load supported by, or reacting on, the vessel Subsidiary loads 1. Local stresses caused by supports, internal structures and connecting pipes; 2. Shock loads caused by water hammer, or by surging of the vessel contents; 3. Bending moments caused by eccentricity of centre of the working pressure relative to the neutral axis of the vessel; 4. Stresses due to temperature differences and differences in the coefficient expansion of materials; 5. Loads caused by fluctuations in temperature and pressure h. Minimum practical wall thickness (Including the corrosion allowance, 2 mm) Vessel diameter (m) Minimum thickness (mm) 1 5 1 to 2 7 2 to 2.5 9 2.5 to 3.0 10 3.0 to 3.5 12

The design of thin-walled vessels under internal pressure a. Cylinder Shells P (D ) t = i i ; BS 5500 dengan f , Pi , J dan Di are design 2 Jf − Pi stress, internal pressure, joint factor and internal diameter, respectively. b. Spherical shells Pi ( Di ) t= ; BS 5500 4 Jf − 1.2 Pi c. Heads and closures i. Flat plates and formed heads

ii. Hemispherical heads iii. Ellipsoidal heads iv. Torispherical heads d. Typical shell shapes

Ellipse

Cylinder

Cone Cylinder

Hemispherical Typical vessel shapes

Stresses in Thin Shells Based on Membrane Theory

Rase and Barrow

Rase and Barrow_3 Pada leeward side vessel, beban angin dan dead weight mengakibatkan terjadinya compression internal pressure (longitudinal stress) mengakibatkan terjadinya tension, sehingga berlawanan dengan compression

S = Sw + S0 − S p

(R_14)

Allowable stress untuk buckling sama dengan stress karena beban angin dan dead weight

SB = Sw + S0

(R_16)

56

Rase and Barrow_4 Donell memberikan persamaan empiris sebagai berikut:

S

B

⎡ ⎢ 0 , 6 ⎛⎜ t ⎞⎟ − 1 0 7 ⎛⎜ ⎢ ⎝ R ⎠ ⎝ = E ⎢ ⎛ E ⎢ 1 + 0,004 ⎜ ⎜ S ⎢ y ⎝ ⎣

⎤ R ⎞ ⎥ ⎟ t ⎠ ⎥ ⎥ ⎞ ⎥ ⎟⎟ ⎥ ⎠ ⎦

(R_17)

57

Rase and Barrow_5 Jorgensen, menyerderhanakan rumus (R_4) untuk baja karbon (usual carbon steel) (R_18)

S

B

= 2 x1 0

6

⎛ t ⎞ ⎜ ⎟ ⎝ D ⎠

58

Rase and Barrow_6 Windward allowable stress

t=

2 Pw h 2 PDm W − + π D ' S π Dm S 4 S

Leeward allowable stress

t=

2 Pw h 2 PDm W + − π D ' S π Dm S 4S

Buckling stress Circumferential stress API_ASME CODE: ASME CODE

t=

2 Pw h 2 W + π D ' S B π Dm S B

t= t =

PD1 +c 2 SE − P

P D1 +c 2 S E − 0, 6 P 59

Brownell, L.E., and Young, E. H., 1959, “Process Equipment Design: Vessel Design”, Wiley Eastern Limited, New Delhi Flat Bottomed Cylindrical Vessels

Optimum tank proportions Vessel (bejana (bejana))

Perbandingan diameter (D terhadap tinggi (H) terletak diantara dua nilai: – Batas bawah untuk: untuk: (D/H) optimum

( cost of shell,bottom, roofs per unit area) ≠ f (D, H) Hal ini terjadi bila tangki volumnya kecil, kecil, hanya elastic stability dan corrosion allowance yang mengendalikan tebal shell

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Vessel (bejana (bejana)) –Batas atas untuk:(D/H) untuk:(D/H) optimum

Bila tebal shell sebagai fungsi d, H (

t = f ( D, H )

),

dan unit area costs of the bottom dan roofs tidak tergantung pada D dan H

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Vessel (bejana (bejana))

Misalkan: D diameter dalam tangki, tangki, ft H tinggi tangki dalam, dalam, ft V volum tangki dalam, dalam, ft3 Volum tangki tertentu, tertentu, sehingga H merupakan fungsi D

V =

π D2 H 4

atau

H =

4V D 2π

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Vessel (bejana (bejana))

Bila: A1=luas shell, ft2, A2=luas bottom (projected area), ft2, C1= annual cost of fabricated shell, $/ft2 C2= annual cost of fabricated bottom, $/ft2 C3= annual cost of fabricated roof, $/ft2 C4= annual cost of installed foundation under the vessel, $/ft2bottom C5= annual cost of land in the tank area chargeable to the tank area, $/ft2 bottom C= total annual cost of the vessel, $/year 2/21/2013

86

Vessel (bejana (bejana))

C=

4VC1 D

+

π D2 4

( C2 + C3 + C4 + C5 )

Jika tebal tangki

t ≠ f ( D, H )

dC 4VC1 π D =− 2 + ( C2 + C3 + C4 + C5 ) = 0 dD D 2

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Vessel (bejana (bejana)) D = 2H

C1

(C 2 + C3 + C 4 + C5 )

, persam aan untuk t ≠ f ( D , H )

Tebal tidak merupakan fungsi D dan H

t ≠ f ( D, H )

Kasus khusus Tangki kecil (small tank) terbuka, terbuka, harga tanah dan fondasi diabaikan. diabaikan. Biasanya tebal shell sama dengan tebal bottom. Jika C3 = C4 = C5 = 0 dan ,

C1 = C2 didapat

D = 2H

Tangki kecil (small tank) tertutup harga tanah dan fondasi diabaikan, diabaikan, berarti nilai C4 = C5 = 0 dan, dan, C1 = C2 = C3 didapat

D=H 2/21/2013

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Vessel (bejana (bejana))

Jika tebal tangki

t = f ( D, H ) C1 = C6 ( H − 1) D

C=

4V ⎡⎣C6 ( H − 1) D ⎤⎦ D

H diganti dengan

+

π D2 4

( C2 + C3 + C4 + C5 )

H =

4V D 2π

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Vessel (bejana (bejana))

π D2 ⎛ 4V ⎞ 4 VC + − ( C2 + C3 + C4 + C5 ) 6 2 ⎟ 4 ⎝πD ⎠

C = 4VC6 ⎜

⎛ 32C6V 2 ⎞ 2π D dC = −⎜ −0+ ( C2 + C3 + C4 + C5 ) = 0 2 ⎟ 4 dD ⎝ πD ⎠ Didapat, hubungan diameter dengan tinggi tangki sebagai berikut

D = 4H

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C1

( C2 + C3 + C4 + C5 )

90

Vessel (bejana (bejana))

Tangki besar tertutup , atap dan shell harganya dua kali harga bottom, C1 = 2C2 = C3 dan C4 = C5 = 0 didapat D = 4H

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2C2

8 = H ( C2 + 2C3 + 0 + 0 ) 3

91

Vessel (bejana (bejana))

Shell design of small and medium sized vessels (production tanks) pp.43 B&Y. Vertical flat bottoms disebut production tanks. Tebal sama (single thickness). Ukuran optimum:d (diameter=H(tinggi (diameter=H(tinggi)) Lihat fig:3.7 dan tabel 3.3 (B&Y, pp.43pp.43-44) Tebal:3/16” or ¼”, lebar flat ≥60”

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Vessel (bejana (bejana))

Shell design of large storage tanks (pp.34 B&Y). Tanks bentuk silinder, silinder, great structure strength dan mudah dibuat Several types of stresses yang mungkin terjadi pada tangki bentuk silinder: silinder: Longitudinal stress internal pressure Circumferential stress internal pressure Residual weld stresses localized heating 2/21/2013

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Vessel (bejana (bejana))

Stresses superimposed loads seperti: wind, snow, and ice, auxiliary equipment, and impact loads Stresses karena thermal differences Others

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dijumpai didalam paraktek

94

Proportioning and head selection for cylindrical vessels with formed heads Chapter 5, p 76With ellipsoidal head with dimension diameter of 2:1. Δy

H y

x a D

a=2b Vessel (bejana (bejana))

Dimensi Vessel Tebal, Tebal, inches

L/D

3/16 sampai 2

6

2 sampai dengan 6

8

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b

Coulson, J.M., and Richardson, J.F., 1983, Chemical Engineering Volume 6 (SI Units) Design, Pergamon Press, Oxford p. 622, Chapter 13; Mechanical Design of Process Equipment 2. Separation Process/Separation Columns Distillation process Absorption Scrubber It will be emphasized on distillation processes due to basic features and many of the design methods also apply to other multistage processes such as stripping, absorption and extraction

The choice between packed and plate columns Liquid-vapor transfer operation dapat dilakukan pada : Packed or plate columns o Packed column: continuous contact o Plate column: stage wise contact Both system works in different modes Pemilihan menara didasarkan pada empat(4) faktor (Barker &Hakkers): 1. Factors that depend on the system, i.e. the component, 2. Factors that depend on the fluid flow movement, 3. Factors that depend upon the physical characteristics of the column and its internals, 4. Factors that depend upon the of operation I.

SYSTEM FACTORS 1. Scale: Diameter 2,5:1, dipilih a plate column 5. Semua faktor tersebut diatas harus dipertimbangkan dan untuk pemilihan akhir harus ada kompromi diantaranya. . IV. TIPE, UKURAN PACKING, DIAMETER MENARA DAN LIQUID DISTRIBUTOR 1. RASCHIG RINGS: ukuran packing