FYI
Berikut adalah jawaban dari Alvin Alfiyansah, Technip Indonesia yang dititipkan ke saya....
JAWABAN
Mungkin yang harus diketahui selain parameter yang diperlukan utk mendesign internal vessel tersebut adalah aplikasinya.
Untuk process apa ....serta apakah itu termasuk inlet diverter atau outlet internal application...., yang tentu saja akan juga berpengaruh pada material yang akan dipakai. Semoga aja ngga dimarahin teman2 vendor karena mendahului untuk hal ini, atau mungkin ada yang lebih dapat mengkoreksi dan menambahinya.
OK let's discuss one by one, di-sandwich pakai bahasa gado-gado, males sich... :
1. Inlet Diverter - impingement separator (at inlet vessel)
Beberapa tipe yang ada antara lain :
- deflector baffle yang bisa berbentuk hemispherical dish, flat plate, piece of angle iron, metal cone, or just about any shape. Prinsipnya utk memisahkan gas & liquid karena adanya perubahan yang tiba dari aliran deras sang fluida dan kecepatannya (nah, sudah tahu kan parameter yang dipakai selain ada pengaruh momentum dan gravity). Advantages-nya : create less disturbance than flat plates or angle irons, cutting down on reentrainment or emulsification problems.
- cyclone inlet , menggunakan prinsip centrifugal force dibanding mechanical agitation to disengage the oil and gas seperti pada deflector baffle. Jenis inlet diverter ini mungkin punya a cyclonic chimney, atau menggunakan a tangential-fluid race around the walls of the vessel. Cyclonic inlets generally create a fluid velocity of about 20 ft/s around a chimney whose diameter is perhaps 2/3 that of the vessel diameter. Spiral fins, or helices, are also sometimes used in the last few feet of inlet piping, particularly in the Middle East.
- wave breaker, biasanya perlu di-instal pada sebuah horizontal vessel yang panjang. Cuma vertical baffles yang span the gas-liquid interface perpendicular to arah aliran, untuk mencegah waves karena liquid surges.
- Defoaming Plates . Foam bisa terjadi pada gas-oil interface ketika gas bubbles terbebaskan dari certain liquid mixtures. Stabilisasi liquid ini dapat dengan tambahan chemicals pada upstream inlet separator. Often, a more effective solution, since refineries sometimes object to defoamer chemicals in crude oil, is to force the foam to pass through a series of inclined parallel plates or tubes, this leads to the coalescence of the foam bubbles.
2. Outlet impingement separator (... pada outlet vessel biasanya)
-Vortex Breaker, bisa berbentuk slotted pipe, crossed plates. Gunanya mencegah terjadinya pusaran ketika liquid control valve terbuka,
A vortex could suck some gas out of the vapor space and re-entrain it in the liquid outlet.
- Mist Eliminator, bentuk2 umum yang biasa dipakai adalah wire mesh pads, vanes, and arch plates.
======read this for more information ===========
Wire mesh pads are made of finely woven mats of stainless steel wire wrapped into a tightly packed cylinder. The liquid droplets impinge on the matted wires and coalesce. The effectiveness of wire mesh depends largely on whether or not the gas is traveling at the proper velocity. If the velocity is too high, the liquids knocked out will be reentrained. If the velocity is too low, the vapor will just drift through the mesh element without the droplets impinging and coalescing. Rule of thumb, ketika menggunakan two wire mesh pads sekaligus, the first pad used as coalescer biasanya punya free space area setengah dari mesh pad kedua.
The construction of a wire mesh mist eliminator is often specified by a certain thickness (usually 3 to 7 inches) and mesh density (usually 10 to 12 pounds per cubic foot). Experience has indicated that a properly sized wire mesh eliminator can remove 99% of 10-micron and larger droplets. Although wire mesh eliminators are inexpensive they become plugged more easily than the other types.
Vane-type mist eliminators force the gas flow to become laminar between corrugated parallel plates. Droplets impinge on the plate surfaces, where they coalesce and fall to the liquid-collection section of the vessel. Vane-type eliminators are sized by their manufacturers to assure both laminar flow and a certain minimum pressure drop. hati2 jangan sampai pressure drop across vane melebihi its height above the liquid level, if downcomer pipe is used.
Arch plates are designed to function essentially in the same method as the vanes. The plates are formed as concentric cylinders, sometimes corrugated, on which the gas impinges and coalesces
==========================================
Design parameter utk mist eliminator : V = K 1/2^((rho.liquid - rho vapor)/rho.vapor)) , dimana v = design velocity, dan K = capacity factor (m/s) yang bergantung pada beberapa faktor misalnya liquid viscosity, surface tension, entrainment loading, kandungan dissolved and suspended solids, dan operating pressure. Standard guideline K = 0.107 m/s. Operating pressure drop negligible antara 1"WC dan pada high vacuum application = 0.1" WC.
Efficiency bisa didapat dari increase pad thickness, changing wire diameter, atau closeness of the weave. Wire mesh yang biasa dgunakan jatuh pada range : diameter (0.076-0.28 mm), void volume (92%-99.4%), density (48-529 kg/m3), surface area (64-1970 m2/m3).
Biasanya, jenis inlet impingement yang memakai gaya centrifugal membutuhkan kecepatan alir yang lebih besar utk memecah ke dalam smaller droplet dibandingkan impingement lain.
Sebagai tambahan informasi internal diverter diatas biasanya dipakai utk two-phase separator. Untuk three-phase separator mungkin saja ada additional components yakni coalescing plates and sand jet.
Sumber contekan :
1. IHRDC self learning information, 2003. Basically, it is from Surface Production Operations Book vol 1, Maurice Stewart & Ken Arnold.
2. Gas Conditioning & Processing Vol 2, JM Campbell, 1994.
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