PROCESS EQUIPMENT DESIGN

II. DESIGN OF STORAGE TANKFocus on: liquid material storage tank

Important physical properties of liquid to take into account in storage tank design:- Volatility, i.e.: non-volatile liquid (Tb > Tb water), volatile liquid (Tb < Tb water), more volatile liquid (condensed gases)

Volatility of liquid can be known from Antoine equation This property will determine operating conditions including temperature (T) and pressure (P)

Important physical property of liquid:Corrosion capacity: The ability of liquid material to cause corrosionThe materials are divided: corrosive (easy to cause corrosion); non-corrosive (hard to cause corrosion)

This property will determine types of material construction of tank

Types of Storage TankBased on operating pressure (P):Atmospheric tank (vertical cylindrical tank): to keep non-volatile materials as well as volatile ones at atmospheric pressure,

Pressured tank (vessel): to keep more-volatile materials at P > 1 atm

Design of Atmospheric TankDesigned items include:Operating conditions (P, T)Main dimensions: height (H), diameter (D), thickness of shell plate (ts), thickness of roof/head plate (th), thickness of bottom plate (tb)

Design of Atmospheric TankOperating Conditions ..Pressure: As its name the operating pressure (P) = atmospheric (1 atm)

Temperature: - Environment temperature (for non-volatile &volatile materials having boiling points above or same as the environment temperature)- Boiling point (for volatile materials having boiling points below the environment temperature) If operating T is below the environment temperature, to minimize evaporation due to heat transfer from the environment: the tank is insulated; if not enough, the tank is equipped with refrigeration system

Design of Atmospheric TankOperating Conditions ..

If the liquid material consists of several liquid components or a liquid mixture and is considered as an ideal solution, the boiling point of the liquid mixture can be determined from bubble point equation, as follows:

where y, x = mole fractions in vapor and liquid phases, respectively K = equilibrium constant

Design of Atmospheric TankTank Dimensions ..

Design equation of tank volume:

V = volume of tank = design capacityVf = volume of liquid material that will be stored.. = over design (20-40%)

Design of Atmospheric TankTank Dimensions ..D / H optimum = yielding minimum annual costSmall tank:

Criteria of small tank: If the value D*(H 1) 1720 (for butt welded shell)If the value D*(H 1) 1515 (for lap welded shell) Diameter of tank 45 ftThickness of shell plate inVolume of tank 71.534 ft3

Design of Atmospheric TankTank Dimensions ..D / H optimum Large tank:

c1 = annual cost of fabricated shell, cost/area or massc2 = annual cost of fabricated bottom, cost/area or massc3 = annual cost of fabricated roof, cost/area or massc4 = annual cost of foundation, cost/area or massc5 = annual cost of land, cost/area or mass

Design of Atmospheric TankTank Dimensions ..Thickness of shell plate:

D = diameter of tank = joint/welding efficiency = strength of material constructionc = corrosion allowable = 0,125 in

P is usually approached with hydrostatic pressure at 1 ft above tank bottom, P = . g/gc. (H 1)

Design of Atmospheric TankTank Dimensions ..

Thickness of bottom plate:

D = diameter of tank = joint/welding efficiency = strength of material constructionc = corrosion allowable = 0,125 in

Design of Atmospheric TankTank Dimensions ..Thickness of roof plate:

D = diameter of tank = joint/welding efficiency = strength of material constructionc = corrosion allowable = 0,125 in = slope angle of roofP = design pressure = 1,. x operating P (atmospheric)

Design of Atmospheric TankTank Dimensions ..Standard plate thickness:

3/16, , 5/16, 3/8, 7/16, , 9/16

5/8, , 7/8, 1, 1 1/8, 1 , 1 3/8, 1 , 1 5/8, 1 , 2, ect.

Design of Pressured Tank (Vessel)Operating Conditions (P, T)

Vessel is used to especially store more volatile materials where in normal (surrounding) conditions they exist in the state of gas. To ensure the materials are kept in liquid phase, the operating pressure must be high, and the operating temperature is maximum at its boiling point

In conclusion, P operation > atmospheric T operation

Design of Pressured Tank (Vessel) For elliptical dished head 2:1, volume of vessel:

V = design capacity = volume of tankVf = volume of liquid material to be keptD = diameter of tankL = length of tank

Design of Pressured Tank (Vessel)Main Dimensions (L/D) optimumFor ts 2, L/D = 6

For ts > 2, L/D = 8

Perancangan Menara Distilasi Dari jumlah stage:1 stage: flash distillation, untuk memisahkan komponen2 yang beda tingkat volatilitasnya tinggi, biasanya di awal

Cascade distillation: multi stage distillation

Dari kontinyuitas proses:Distilasi batchDistilasi kontinyu

Perancangan Flash Distillation Pers. Perancangan:

Atau:

Perancangan Flash Distillation Prinsip2 Perancangan: Jika P, T dirancang, maka V, L dan komposisi masing-masing terhitungJika P dan salah satu hasil dirancang, maka T dan hasil lain terhitungJika T dan salah satu hasil dirancang, maka P dan hasil lain terhitung

Perancangan Cascade Distillaion Jumlah sequence:

Sequence optimum:

Perancangan Cascade Distillation Sequence optimum cara empirik:Pasangan komponen yang mempunyai relative volatility kecil (mendekati 1) atau azeotrop dipisahkan terakhir, atau komponen yang memp. relative volatility terbesar dipisahkan duluKomponen paling ringan dipisahkan duluKomponen yang paling banyak jumlahnya di umpan, dipisahkan duluDiusahakan pemisahan menghasilkan near-equimolar split

Perancangan Cascade Distillation Perancangan distribusi komponenKomponen kunci: light component (LK), heavy component (HK), komponen yan menjadi target pemisaanDistributed component: ada di hasil atas maupun bawah Non-distributed component: hanya ada di salah satu hasil

Perancangan Cascade Distillation Perancangan Kondisi OperasiKondisi Operasi AtasMemperhatikan hal-hal berikut:Data kondisi kritis (terutama suhu kritis dan tekanan kritis)

Suhu operasi atas MD sebisa mungkin

Perancangan Cascade Distillation Perancangan Kondisi OperasiKondisi Operasi AtasMemperhatikan hal-hal berikut:Site plant condition (kondisi utilitas pendingin sekitar pabrik)

Perancangan Cascade Distillation Perancangan Kondisi OperasiKondisi Operasi AtasDiusahakan sebisa mungkin menggunakan kondenser total

Kondenser Total:Jika T operasi atas MD dirancang, maka P operasi dihitung:Dengan pers. RaoultDengan pers. bubble point

Jika P operasi atas MD dirancang, maka T operasi dihitung:- Dengan pers. bubble point

Perancangan Cascade Distillation Perancangan Kondisi OperasiKondisi Operasi AtasJika kondenser parsial:Jika T operasi atas MD dirancang, maka P operasi dihitung:Dengan pers. dew point

Jika P operasi atas MD dirancang, maka T operasi dihitung:- Dengan pers. dew point

Perancangan Cascade Distillation Perancangan Kondisi OperasiKondisi Operasi BawahJika kondisi operasi atas sudah dirancang, P operasi bawah dapat ditentukan dari:Asumsi P sepanjang menara tetap atau tidak ada pressure dropJika ada pressure drop, maka P bottom = P top + pressure drop (tekanan bawah > tekanan atas)

T bottom dihitung dengan pers. bubble pointPada prinsipnya perancangan kondisi operasi MD juga bisa dimulai dari bagian bottom MD, baru top MD