Tiêu đề Plate and Frame Filter Press.pdf ✅

PANKAJ GAJARE | Dept. of Pharmaceutics, PES’s RTBCOP, PONDA B. PHARM | SEM-III | SEPT-2020- JAN-2021 | Plate and Frame Filter Press Principle: The mechanism of this filter is surface filtration. The slurry enters the frame by pressure and flows through the filter medium. The filtrate is collected on the plates and sent to the outlet. A number of frames and plates are used so that surface area increases and consequently large volumes of slurry can be processed simultaneously with or without washing. Construction: The construction of a plate and frame filter press is shown in the Fig. 3. The filter press is made of two types of units, plates and frames. The components of this filter are as follows. (i) Frame: It maintains the slurry reservoir and has inlet (eye) for slurry. (ii) Filter medium: It is for solid retention. (iii)Plate: This equipment along with section-supports the filter medium, receives the filtrate and has outlet (eye). (iv) Assembly of plate and frame filter press.
PANKAJ GAJARE Fig.3: Frame and Press Filter Plate and frame are usually made of aluminium alloy. Sometimes these are also coated for protection against corrosive chemicals and made suitable for steam sterilization. Frame contains an open space inside wherein the slurry reservoir is maintained for filtration and an inlet to receive the slurry. The plate has a studded or grooved surface to support the filter cloth and an outlet. The filter medium (usually cloth) is fitted between plate and frame. Frames of different thicknesses are available and frame with optimum thickness is chosen. Selection is mainly based upon the thickness of the cake formed during filtration. Plate, filter medium, frame, filter medium and plate are arranged in the sequence as shown in Fig. 3 and clamped in a supporting structure. A number of plates and frames
PANKAJ GAJARE are used to have a large surface area. These filtration units are operated in parallel. Channels for the slurry inlet and filtrate outlet can be arranged by fitting inlet to the plates and frames, these join together to form a channel. In some types, only one inlet channel is formed, while each plate is having individual outlets controlled by valves. Working: Working can be divided into two steps 1. Filtration operation Frame- marked by 2 dots Plate – marked by 1 dot • Slurry enters the frame from the feed channel and passes through the filter medium on the surface of the plate • The solid forms a filter cake and remain in the frame • The thickness of the cake is half of the frame thickness, because on each side of frame filtration occurs • Thus, two filter cakes are formed, which meet eventually in the centre of the frame • The filtrate drains between the projections of the surface of the plate and escape from the outlet • As filtration proceeds, the resistance of the cake increases and filtration rate decrease • At a certain point process is stopped and press is emptied and cycle is restarted. 2. Washing of cake (if desirable) • When washing of cake is also required modified plate and frame filter is used. • For this purpose, an additional channel is included called as washing plate and are identified by 3 dots.
PANKAJ GAJARE • In the half of the washing plate, there is a connection from wash water cannel to the surface of plate. • The sequence of arrangement of plates and frames can be represented by dots as 1.2.3.2.1.2.3.2.1 so on (between 1 and 1, 2.3.2 must be arranged. The steps of the filtration are as follows: (i) Slurry enters the plates and filtration proceeds in the ordinary way until the frames are filled with cake. (ii) To wash the filter cake, the outlets of the washing plates are closed. (iii)Wash water is pumped into the washing channel. The water enters through the inlets on to the surface of the washing plates. (iv) Water passes through the filter cloth and enters frame which contains the cake. The water washes the cake, passes through the filter cloth and enters the plate down the surface. (v) Finally washed water escapes through the outlet of that plate. Fig. 4: Filtration Operation with Wash Water Facility Thus, provision of special washing plates makes it possible for the wash-water to flow over the entire surface of washing plate that makes the uniform resistance of cake to the flow and the entire cake is washed efficiently. The water wash is efficient only when the frames are full with filter cake. If the cake does not fill the frame completely the wash water causes the cake to break on the washing plate side of the frame and the washing will be less effective. It is essential to allow the frames
PANKAJ GAJARE become completely filled with the cake. This helps in emptying the frames as well as in washing the cake correctly. Special Provisions: A provision of glass tube (sight glass) to observe contamination can be made at the outlet on each plate. This permits the inspection of quality of the filtrate. The filtrate goes through the control valve to an outlet channel. The filtration process from each plate can be seen. In the case of a broken cloth, the faulty plate can be isolated and filtration can be continued with one plate less. A provision of filter sheets composed of asbestos and cellulose capable of retaining bacteria can be used for sterile filtration with whole filter press and filter medium previously sterilized. Usually steam is passed through the assembled unit for sterilization. The examples include collection of precipitated antitoxin, removal of precipitated proteins from insulin liquors and removal of cell broth from the fermentation medium. Heating/cooling coils can be incorporated in the press for the filtration of viscous liquids. Advantages: i. Simple in operation, convenient in maintenance, and safe in operation with multiple safety devices. Variety of materials such as cast iron (for handling common substances), bronze (for smaller units), stainless steel (to avoid contamination), hard rubber or plastics (to avoid metal) and wood (for lightness) can be used. ii. It provides a large filtering area in a relatively small floor space. iii. It is versatile equipment whose capacity can be varied according to the thickness and the number of frames used. Surface area can be increased by employing chambers up to 60. iv. This press has sturdy construction that makes use of pressure difference of 2000 kilopascals to be used. v. Cake washing is very efficient. vi. Operation and maintenance is low as it has no moving parts and the filter cloths can be easily renewable. vii. The presence of all external joints makes plate to be isolated in case of if any leaks and the contamination of the filtrate can be avoided. (viii) It produces dry cake in the form of slab.