Your SlideShare is downloading. ×
Thiet bi loc la
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×

Saving this for later?

Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime - even offline.

Text the download link to your phone

Standard text messaging rates apply

Thiet bi loc la

535
views

Published on


0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
535
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
0
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. The Vertical Pressure Leaf Filter – Thiết bị lọc lá áp lực kiểu thẳng đứng Description Vertical Pressure Leaf Filters are quite similar to the Horizontal Plate Filters except for the orientation of the filter elements which are vertical rather than horizontal. They are applied for the polishing slurries with very low solids content of 1-5% or for cake filtration with a solids concentration of 20-25%.
  • 2. Thiết bị lọc lá áp lực kiểu thẳng đứng hoàn toàn giống với Thiết bị lọc đĩa kiểu nằm ngang, chỉ khác việc bố trí các tấm lọc theo chiều thẳng đứng chứ không phải nằm ngang. Chúng được sử dụng cho việc làm sạch các dung dịch với với hàm lượng chất rắn rất thấp từ 1 – 5% hay cho bã lọc với nồng độ chất rắn 20 – 25%. Just like the Horizontal Plate Filter the Vertical Leaf Filters are also very well suited for handling flammable, toxic and corrosive materials since they are autoclaved and designed for hazardous environments when high pressure and safe operation are required. Likewise, they may be readily jacketed for applications whenever hot or cold temperatures are to be preserved. These features are not possible on Filterpresses which require the opening of plates to the atmosphere and shifting them one by one to allow cake discharge at the end of each cycle. Cũng giống như Thiết bị lọc đĩa kiểu nằm ngang, TB lọc lá rất thích hợp với các loại nguyên liệu có bản chất dễ bắt cháy, độc hại và ăn mòn khi chúng được đưa vào nồi hấp và thiết kế cho các môi trường độc hại yêu cầu áp suất cao và an toàn lao động. Tương tự như vậy, người ta có thể dễ dàng bao bọc thiết bị khi cần giữ ở nhiệt độ cao hay thấp. Những tính năng này không có trên thiết bị lọc ép vì cần cần mở các tấm đĩa lọc để lưu thông không khí và tháo rời từng cái một để loại bỏ các cặn rắn ở cuối mỗi chu kì lọc. The largest Leaf Filters in horizontal vessels have a filtration area of 300 m2 and vertical vessels 100 m2 both designed for an operating pressure of 6 bar (see below the section on The Vessel). The Leaves Slurry Feed Filtrate Leaf Screen Spacers The slurry is pumped under pressure into a vessel that is fitted with a stack of vertical leaves that serve as filter elements. Each leaf has a centrally located neck at its bottom which is inserted into a manifold that collects the filtrate. The leaf is constructed with ribs on both sides to allow free flow of filtrate towards the neck and is covered with coarse mesh screens that support the finer woven metal screens or filter cloth that retain the cake. The space between the leaves
  • 3. may vary from 30-100 mm depending on the cake formation properties and the ability of the vacuum to hold a thick and heavy cake to the vertical leaf surface. The space is set by the filtrate necks of the leaves at the bottom end and with spacers at the top end brackets. For fast filtering slurries the space may be doubled by removing every second plate so consequently the cake space doubles but the filtration area is cut in half. The Vessel There are two types of vessel configuration: • Vertical vessels • Horizontal vessels In most of the fine chemicals processes the leaves are fitted into vertical vessels whilst horizontal vessels are used in the heavier process industries such as the preparation of sulfur in phosphoric acid plants. The leaves inside horizontal tanks may be positioned either along the tank axis or perpendicular to the axis. In order to utilize the tank volume for maximum filtration area the width of the leaves is graduated so they fit to the circular contour of the tank. This also reduces the slurry heel volume that surrounds the leaves. The vessels are fitted with highly
  • 4. secured cake discharge openings to ensure safe sealing of the tank under pressure. The cake that accumulates on the leaves may be discharged as a wet thickened sludge or as a dry cake. For wet cakes the vessel will normally have a small outlet that is fitted with a valve whilst for dry cakes the opening is large and the closure locks up electrically or hydraulically with a bayonet wedge. The head cover of vertical vessels is often pivoted so that it is swung away to allow the upwards removal of the leaves in the stack. It is good practice to design a special rig that will support a leaf that is removed from the vessel. Special quick opening bolts are fitted around the cover so that tightness is secured during operation but enable easy opening when access to the stack is required. Cake Discharge One of the advantages of the Vertical Leaf Filter when compared to the Horizontal Plate Filter is when cakes depart easily from the filtering medium. In such cases it is not necessary to incorporate means to assist discharge since gravity will release the cake and let it drop towards the discharge opening. For such cakes that do not discharge readily a special mechanism that vibrates the entire stack is incorporated and this will in most instances release the cake. However, with this method care must be taken so that the cake does not bridge between the two adjacent plates since this will impair cake
  • 5. discharge. There are instances when the cake is disposed to ponds or repulped for further treatment and in these cases special oscillating high impact jet headers sweep the medium surface and sluice the cake through the discharge outlet. These headers also serve to wash the filtering medium and dislodge particles that clog the metal screen or cloth. Selection Criteria Vertical Leaf Filters are best selected in the following instances: • When minimum floor space for large filtration areas is required. • When the liquids are volatile and may not be subjected to vacuum. • When there is a risk of environmental hazard from toxic, flammable or volatile cakes specially secured discharge mechanisms may be incorporated. • When high filtrate clarity is required for polishing applications. • When handling saturated brines that require elevated temperatures the tank may be steam jacketed. • When the cake may be discharged either dry or as a thickened slurry. They should be selected with care: • When the cake is thick and heavy and the pressure is not sufficient to hold it on the leaf. • When coarse mesh screens are used the filtration step must be preceded with a precoat to retain cakes with fine particles. Precoating with a thin layer of diatomite or perlite is not a simple operation and should be avoided whenever possible. Advantages • The cloth or woven mesh screens that cover the leaves of horizontal tanks may be accessed easily once the stack is pulled out of the vessel. This allows thorough washing of the medium with high impact jets manually in case that the cake bridges between the leaves. On vertical tanks the head cover must be unbolted and removed in order to access the leaf stack. • Mechanically simple since there are no complex sealing glands or bearings.
  • 6. Disadvantages • High headroom is required for dismantling the leaves on vertical vessels. • Large floor space is required for discharging the cake on horizontal vessels. • The emptying of the vessel in between cake filtration, washing and drying requires close monitoring of the pressure inside the vessel to ensure that the cake holds on to the candles. Operational Sequence The operation of a Vertical Pressure Leaf Filter is labor intensive and requires a complex manipulation of valves so present day installations are in most cases fully automated.
  • 7. Precoating The precoating stage is done only in the following cases: • When the contaminants are gelatinous and sticky the precoat layer forms a barrier that avoids cloth blinding. Likewise the interface between the precoat and the cloth departs readily so the cake discharges leaving a clean cloth. • When a clear filtrate is required immediately after the filtration cycle commences otherwise recirculation must be employed until a clear filtrate is obtained. Filtration Once the precoating stage is completed the process slurry is pumped into the filter, the forming cake is retained on the leaves and the filtrate flows to further processing. When the solids are fine and slow to filter a body-aid is added to the feed slurry in order to enhance cake permeability. However, it should be kept in mind that the addition of body- aid increases the solids concentration in the feed so it occupies additional volume between the leaves and increases the amount of cake for disposal. Likewise, for all those applications when the cake is the product, precoat and filter-aid may not be used since they mix and discharge together with the cake. Please refer to the section on Pressure
  • 8. Maintenance The Vertical Pressure Leaf Filter requires attention on a regular basis to safety devices and automation features that accompany modern filters. The space above the filter should have a hoisting device and sufficient headroom to lift each leaf and move it horizontally to a location adjacent to the filter tank. It is recommended to have a special rig that will hold the leaf for maintenance. Space must also be allocated for the cover which may be either hinged or removed. The major components that require attention are: • The filter tank must conform to an Unfired Pressure Vessel code, such as ASME, and checked periodically as required by the safety regulations. • The pressure relief valve that is located on the top of the tank must be checked for emergency functioning. • The "o"-rings that seal between the leaves necks and the filtrate collecting manifolds. • The large diameter caulking gasket of the dished top head cover. The ends must be cut in an angle to ensure a perfect seal. • The hinged head cover locking bolts. • The cleanliness of the filtrate sight glass that monitor on-line or visually enables inspection of the filtrate clarity. • The interlock that disables opening the cake discharge when the vessel is still under pressure. • The maintenance hoist above the filter must pull out the leaves vertically so that they will not hit the tank wall. • The condition of the filter medium, cloth or mesh screen, must be done periodically to ensure that they are not damaged. • The vent on top of the head must be checked for free evacuation of air. • The filter must not be overfilled with cake since this causes the leaves to bend so they must be checked periodically.
  • 9. The Horizontal Plate Pressure Filter - Thiết bị lọc lá kiểu đứng Description Horizontal Plate Pressure Filters were commonly applied to the fine chemical process industries such as antibiotics, pesticides or pigments when the load of impure insoluble is low and polishing is required to obtain high product clarity. However, in recent years they may be seen more and more in heavier industries such as fertilizers or precious metals when the product is the cake and efficient washing and low moistures are required.
  • 10. Slurry Inlet Filtrate Outlet Cake Outlet Air Vent Cake Scrapers Filtering Plates Scavange Plates Sight Glass Drive Shaft Hydraulic Drive To view the components move mouse pointer over the menu Horizontal Plate Filters are very well suited for handling flammable, toxic and corrosive materials since they are autoclaved and designed for hazardous environments when high pressure and safe operation are required. Likewise, they may be readily jacketed for applications whenever hot or cold temperatures are to be preserved. These features are not possible on Filterpresses which require the opening of plates to the atmosphere and shifting them one by one to allow cake discharge at the end of each cycle. The filter structure consists of a stack of plates attached to a hollow shaft which are mounted inside a pressure vessel with each plate covered with a suitable filter medium. The slurry is fed under pressure into the vessel and the cake, which is retained by the filter medium, forms on the top of each plate whilst the filtrate passes through the hollow shaft further to the process. Please refer to the Operational Sequence below which describes the filtration cycle in detail. Filter sizes may vary but generally the maximum is 60 m2 area and designed for a 6 bar operating pressure. The Plates Each circular plate in the stack is constructed with radial ribs that are welded to the bottom and support a horizontal coarse mesh screen which is covered with a finer woven metal screen or filter cloth to retain the cake. The bottom of the plate slopes towards the hollow central shaft which lets the filtrate flow freely through circumferential holes and further down the shaft to the filtrate outlet.
  • 11. The clearance between the plates is maintained by special spacers with "o" rings to positively seal between the slurry that surrounds the plates and the shaft that collects the filtrate. The height of the spacers determine the clearance for cake build-up and may be replaced to meet various process conditions. One of the obvious differences between polishing and cake filtration is the space between the plates. For polishing applications the clearances are about 20 mm as opposed to cake filtration applications where, depending on the percentage of solids and cake build-up properties, clearances may reach 100 mm. Hence, polishing filters accommodate more plates than cake filters so for the same vessel size more effective area is available with polishers. There are several applications, mainly in the pharmaceutical and paint industries, where special disposable filter paper is used to cover the plates on both sides so the filtration area is doubled. The Vessel The vessels of Horizontal Plate Filters are, as opposed to Vertical Leaf Filters, always constructed vertically to accommodate the plates stack. All have removable dished heads but there are two options for bottom design: • A conical bottom. • A dished bottom. The selection depends largely on the cake discharge arrangement as discussed later. The head of the larger vertical vessels is often pivoted so that it is swung away to allow the upwards removal of the plates stack. The layout should provide sufficient headroom for raising the stack over the vessel and additional floor space next to the filter for stack maintenance and replacement of damaged plates. It is good practice to design a special rig that will support the removed stack. The vessels at their bottoms are fitted with highly secured cake discharge openings to ensure safe sealing of the tank under pressure. Cake Discharge The concept of cake filtration, as opposed to polishing, was enabled by substantial improvements in the cake discharge mechanisms since such filters are operating on a short cycle time. There are two types of cake discharge mechanisms and both use centrifugal force to throw the cake against the cylindrical wall which then falls to the bottom of the tank:
  • 12. • The rotating disc stack. • The vibrating disc stack. The rotating type may be driven from either the top or the bottom whilst the vibrating type is always driven from the top. The removal of the tank head cover from top driven filters is generally more complex than those driven from the bottom. On the other hand bottom driven filters are more susceptible to slurry leaks. The position of the cake outlet depends on the construction of the tank bottom. There are two types available: • With a conical bottom and a central outlet. • With a dished bottom and a side outlet. Tanks with conical bottoms discharge cakes by gravity and those with dished bottoms have a spade that rakes and conveys the cake towards the outlet. Hence, the conical types require more headroom as compared to the dished type having the same filtration area. Conical tanks also have often an additional scavenging plate at the lower part of the cone to filter the residual slurry heel that remains below the main plates. The slurry heel that remains at the very bottom of the tank is removed through a special dip pipe to avoid discharging a wet cake. To facilitate better cake discharge there are designs with sloping plates. With this concept the cake, owing to the centrifugal force, flies off the plate in a horizontal trajectory without being dragged and subjected to the frictional radial shear over the surface as with conventional flat plates. The cake that accumulates on the plates may be discharged as a wet thickened sludge or as a dry cake. For wet cakes the vessel will normally have a small outlet that is fitted with a valve whilst for dry cakes the opening is large and the closure locks up electrically or hydraulically with a bayonet wedge. Selection Criteria Horizontal Plate Filters are best selected in the following instances:
  • 13. • When minimum floor space for large filtration areas is required. • When the liquids are volatile and may not be subjected to vacuum. • When there is a risk of environmental hazard from toxic, flammable or volatile cakes specially secured discharge mechanisms may be incorporated. • When high filtrate clarity is required for polishing applications. • When handling saturated brines that require elevated temperatures the tank may be steam jacketed. • When efficient washing is required. • When the cake is heavy and must be supported as opposed to a Vertical Leaf Filter where the cake forms on a vertical surface and may fall-off once the pressure drops. • When the cake may be discharged either dry or as a thickened slurry. They should be selected with care: • When the cake does not discharge readily accessing the filter medium between the plates for washing is difficult. • When coarse mesh screens are used the filtration step must be preceded with a precoat to retain cakes with fine particles. Precoating with a thin layer of diatomite or perlite is not a simple operation and should be avoided whenever possible. Advantages • The removal of the plate stack on bottom driven filters is simpler than on top driven machines since on the later the entire drive has to be removed to allow access to the stack. • Plates with the screens mounted on the topside, as opposed to two sided plates, provide good support for the forming cake and therefore are always used on applications with thick and heavy cakes. Disadvantages • High headroom is required for dismantling the entire plate stack. • The bearing of top and bottom driven filters, that supports the rotating plate stack and its sealing, is complex since it has to withstand the internal pressure and the side forces imposed by the mechanical drive. However, side loads on some machines are eliminated by the use of hydraulic motors. • The emptying of the vessel in between cake filtration, washing and drying requires close monitoring of the pressure inside the vessel to ensure that the cake holds on to the candles. Operational Sequence
  • 14. The operation of a Horizontal Plates Filter is labor intensive and requires a complex manipulation of valves so present day installations are in most cases fully automated.
  • 15. Precoating The precoating stage is done only in the following cases: • When the contaminants are gelatinous and sticky it forms a barrier that avoids cloth blinding. Likewise the interface between the precoat and the cloth departs readily so the cake discharges leaving a clean cloth. • When a clear filtrate is required immediately after the filtration cycle commences otherwise recirculation must be employed until a clear filtrate is obtained. Filtration Once the precoating stage is completed the process slurry is pumped into the filter, the forming cake is retained on the plates and the filtrate flows to further processing. When the solids are fine and slow to filter a body-aid is added to the feed slurry in order to enhance cake permeability. However, it should be kept in mind that the addition of body-aid increases the solids concentration in the feed so it occupies additional volume between the plates and increases the amount of cake for disposal. Likewise, for all those
  • 16. Maintenance The Horizontal Plate Filter requires attention on a regular basis to safety devices and automation features that accompany modern filters. The space above the filter should have a hoisting device and sufficient headroom to lift the entire disc stack and move it horizontally to a location adjacent to the filter tank. It is recommended to have a special rig that will hold the plate stack for maintenance since the bigger ones may reach a length 3 meters or more. Space must also be allocated for the cover which may be either if it is hinged or removed. The major components that require attention are: • The filter tank must conform to an Unfired Pressure Vessel code, such as ASME, and checked as required by the safety regulations. • The pressure relief valve that is located on the top of the tank. • The bearings, retainers, o-rings, gaskets and seals where the center shaft enters the vessel. This applies to both top and bottom driven stacks with the former being susceptible to air or gas leaks and the later to slurry leaks. • The large diameter caulking gasket of the dished top head cover. The ends must be cut in an angle to ensure a perfect seal. • The hinged head cover locking bolts. • The spacers' ring seals that press the entire plate stack together. • The cleanliness of the filtrate sight glass that monitor on- line or visually enables inspection of the filtrate clarity. • The interlock that disables stack spinning with a closed cake discharge outlet. • The interlock that disables opening the cake discharge when the vessel is still under pressure. • The maintenance hoist above the filter must pull out the entire stack vertically so that the plates will not hit the tank wall. Its exact positioning is also essential for bottom driven stacks since on many types there is no access to the bearings and gland seals from the bottom and the entire insertion is done from the top. • The condition of the filter medium, cloth or mesh screen, must be done periodically to ensure that they are not damaged. • The vent on top of the head must be checked for free evacuation of air. • The filter must not be overfilled with cake since this
  • 17. causes the plates to bend.