Desain Kolom Pemisah Distilasi

Ada beberapa macam pemilihan kolom pemisah distilasi yaitu :

1. Packed Tower

Dipilih packed tower karena :

• Utk liquid korosif, karena alat lebih murah
• Membutuhkan tahanan liquid yg rendah karena densitasnya yg besar
• Memberikan pressure drop per tahap kesetimbangan yg rendah
• Utk diameter kolom yg kecil

Packed Tower

Syarat packing yang bagus adalah :

• Bulk density kecil (tdk terlalu membebani kolom)
• Luas yg terbasahi besar
• Volume rongga besar (mengurangi pressure drop)
• Sifat pembasahan baik
• Tahan korosi
• Memiliki struktur yg kuat utk menahan beban tumpukan
• Murah

Macam - macam bentuk packing :

Rasching ring

Berl saddle

Pall ring

• sederhana : rasching ring, harga lebih murah tapi efisiensi lebih rendah, sering chanelling
• sedang : pall ring, batas flooding tinggi dan distribusi liquid baik
• tinggi : berl saddle, mahal, bed seragam, batas flooding tinggi dan pressure drop rendah

Pemilihan bahan packing :

• Keramik, utk liquid yg bersifat korosif
• Plastik, cocok utk temperatur sedang dan tidak cocok utk pelarut organik
• Logam, utk kondisi operasi yg tdk stabil

Be selected packed tower due to :

• For corrosive liquid, due to cheaper instrument than others
• Requires low liquid resistance due to large density
• Provide low pressure drop per equilibrium stages
• For small column diameter

The requirement of quality packing are :

• Small bulk density (not loading column)
• Large of wetted area
• Large of hole volume (reducing pressure drop)
• Good wetting properties
• Corrosive resistant
• Has a strong structure to hold the piles load
• Cheap

Selection of packing material due to :

• Ceramic, for corrosive liquid
• Plastic, suitable for moderate temperature and unsuitable for organic solvent
• Metal, for unstable operating condition"

      2. Tray / Plate Column /  Sieve Tray

• Kapasitas tinggi
• Efisiensi tinggi
• Pressure drop sedang
• Biaya instalasi dan perawatan murah

Tray Tower

• Korosi rendah

Jumlah tahapan plate disusun berdasarkan :

• Tingginya kesulitan pemisahan zat yg akan dipisahkan
• Perhitungan neraca massa dan kesetimbangan

Dipilih jenis ini bukan packed tower karena :

• Bisa menangani laju alir liquid dan gas yang besar
• Pembersihan mudah karena bisa dipasang manhole
• Lebih mudah utk pengambilan produk melalui samping
• Desain plate lebih terjamin efisiensi kerjanya

"2. Tray / Plate Column / Sieve Tray
A number of plate stages are shaped according to :

• Height of difficulty separation of substances that will be separated
• Calculation of mass balance and equilibrium

Be selected this type not packed tower due to :

• Able handling large liquid and gas flow rate
• Easy maintenance due can be installed manhole
• Easier to taking product through side stream
• Working efficient of plate design is more secure"
  

      2. Bubble Cap Tower
Spesifikasinya adalah :

• Kapasitas sedang sampai tinggi
• Efisiensi sedang sampai tinggi
• Biaya instalasi dan perawatan lebih mahal
• Laju alir rendah karena pressure drop tinggi

Bubble Cap Tray

• Korosi tinggi 

    

• The capacity is moderat until high 
• Efficiency is moderat until high
• Installation cost and maintenance are more expensive than others
• Low flow rate due to high pressure drop
• High corrosion"

Sistem Bubble Cap

Sistem Aliran Liquid (Downcomer & Downflow)

Istilah-istilah yg biasanya muncul adalah :

• Downcomer : lubang tempat masuknya aliran dari atas berupa liquid (plate atas) ke plate bawah (kita memandang plate  bawah ini sbg acuan)
• Downflow : lubang tempat keluaran liquid dari plate atas (kita memandang sbg acuan) ke plate di bawahnya
• Entrainment : peristiwa liquid terangkut ke plate atasnya karena dorongan gas dari bawah yg berlebihan, disebabkan laju alir gas terlalu besar
• Flooding : menggenangnya liquid di plate karena kiriman liquid yg berlebihan dr plate atasnya, bisa disebabkan karena adanya entrainment, shg plate atas menerima kelebihan liquid
• Weeping : liquid yg ada pada plate jatuh bebas ke plate bawahnya karena tekanan gas dari bawah kurang, disebabkan karena laju alir gas kecil.
• Cap : penghalang / pengkontak antara liquid dan uap yang dipasang di setiap tray, bentuk seperti topi yg pinggirnya ada slot utk mengatur besar kecilnya gas yg keluar keatas
• Tray / Plate : lapisan atau level disetiap kolom, biasanya terbuat dari besi baja yg kuat menahan beban liquid atau cap
• Slot : tempat bukaan pada cap yg mempunyai macam-macam bentuk (trapesium, persegi, segitiga dll) yg berfungsi mengatur bukaan gas yg keluar ke atas shg liquid dan gas berkontak secara normal
• Enriching : bagian plate yg berada diatas tempat masukan feed
• Exhausting / Stripping : bagian plate yg berada dibawah tempat masukan feed
• Baffle : penghalang yg berada di tengah-tengah tray utk membuat aliran lebih lama berada di tray (penerapan hanya di reverse flow)
• Weir : penghalang yg dipasang di pinggir dari downflow utk membuat agar volume liquid yg tertampung di tray banyak, sehingga efektif terjadinya kontak antara liquid dan gas
• Cross Flow : aliran liquid datang dari atas (downcomer) lalu mengalir di sepanjang tray dan mengalir ke plate bawahnya di downflow. Disebut cross flow karena letak downcomer dan downflow di sisi berseberangan. Jarak yg dilewati liquid panjang shg efisiensi tinggi
• Reverse Flow :  aliran liquid datang dari atas (downcomer) lalu mengalir di sepanjang tray dan berbelok ke bagian tray sebelahnya karena adanya baffle lalu mengalir ke plate bawahnya di downflow. Disebut reverse flow karena letak downcomer dan downflow di sisi yg sama. Dapat digunakan utk menampung cap lebih banyak, L/V rendah, luas downcomer kecil
• Double Pass Flow:  aliran liquid datang dari atas dari 2 bagian downcomer (kiri kanan ) lalu mengumpul di tengah-tengah plate dan turun ke bawahnya. Digunakan utk beban liquid yg besar, L/V tinggi

Cross Flow

Reverse Flow

Double Pass Flow

• Downcomer : hole as place input flow from upper plate (liquid) to bottom plate (we know this as a reference)
• Downflow : hole as place output liquid from upper plate ( we know this as a reference) to the bottom plate
• Entrainment : occurrence liquid carry up to upper plate because excess gas pressure from bottom, caused by large gas flow rate
• Flooding : excess liquid in plate due to sending of excess liquid from upper plate, able due to entrainment so that upper plate give excess liquid
• Weeping : liquid in the plate free fall to the bottom plate due to low gas pressure from bottom, caused by small gas flow rate
• Cap : barrier / contacter between liquid and gas in every plate, form like a cap which edge there is slot to manage large small out gas to above
• Tray / Plate : layers or levels each column, commonly makes from stainless steel which strong to hold liquid load or cap
• Slot : opening at cap have varieties shape (trapezoidal, square, triangle etc) function to manage out gas throttle above so liquid and gas normal is contacted
• Enriching : part of plate have place above from feed hole
• Exhausting / Stripping :  part of plate have place under from feed hole 
• Baffle : barrier in the center tray to make flow longer in the tray (applicated only in reverse flow)
• Weir : barrier that is installed in the edge of downflow to make much liquid volume contained in the tray, so that effective is contacted between liquid and gas
• Cross Flow : liquid flow come from above (downcomer) then flow in the along the tray and flow to the under plate pass downflow. Called cross flow because position of downcomer and downflow is opposite. The distance liquid passing is long so high efficiency
• Reverse Flow : liquid flow come from above (downcomer) then flow along the plate and turn to side tray due to baffle then flow to under plate pass downflow. Called reverse flow because position of downcomer and downflow is same. Can be used to collect more cap, very low L/V and small downcomer area 
• Double Pass Flow: liquid flow come from 2 part downcomer (left right) then collect in the middle plate and downflow. Can be used to large liquid load and high L/V"