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Discharge of filter bed material
INVENTIONSINFILTRATIONANDSEPARATION Abstracts of recent British Patents Cleaning a gas filter In p a t e n t GB 2 2 6 9 1 1 9 Pall Corporation describes filter elements in a housing. They are used to filter particles from waste gas before it is discharged from a radioactive w a s t e processing plant. When the elements are clogged they are cleaned by a reverse flow of liquid, delivered t h r o u g h a valve while venting off the gas, until the housing is full of liquid. Compressed air is t h e n delivered t h r o u g h a valve above the liquid, and a drain valve is opened, to force the liquid t h r o u g h the filter elements and out of the housing. Elements are HEPA- or ULPArated, and preferably of sintered metal fibres. The backwash liquid may be w a t e r with or w i t h o u t surfactant, caustic soda, nitric acid or an organic solvent, and helps to remove small particles by neutralising electrostatic forces holding t h e m in the filter element pores. The liquid and air are b o t h delivered to the housing t h r o u g h filters which are rated at least as finely pored as t h e elements. Used b a c k w a s h liquid is collected for f u r t h e r t r e a t m e n t . Several housings may operate in parallel, and be cleaned in sequence.
Water bath air filter In p a t e n t G B 2 2 6 9 1 1 8 C. M a c d o n a l d describes a w a t e r b a t h air filter with a d e m o u n t a b l e filtration bowl, so t h a t it can be filled with w a t e r and also emptied and cleaned quite easily. It is m o u n t e d on top of the power unit, which is designed to d r a w air t h r o u g h a suction tube. This tube is placed inside the fluted suction tube of the w a t e r bowl, and the two are sealed together by a r u b b e r seal a r o u n d the base of the tube. When the unit is switched on, a fan draws air in t h r o u g h the connected suction tubes, t h u s lowering the air p r e s s u r e in the air filtration bowl cavity. This drop in p r e s s u r e causes air to be drawn in t h r o u g h the w a t e r from outside the air filtration bowl. This air is cleaned by the fact t h a t if anything in the air is soluble in w a t e r it would be dissolved, anything heavier t h a n w a t e r would sink, and anything else would be t r a p p e d by the w a t e r ' s n a t u r a l surface tension. Bubbles which p a s s t h r o u g h the w a t e r are diffused by baffles placed in the top of the unit. This prevents s p l a s h e s of w a t e r fi'om entering into the suction tube and into the suction c h a m b e r of the p o w e r unit. Air is expelled t h r o u g h vents placed a r o u n d the suction c h a m b e r o p p o s i t e a n d a d j a c e n t to the suction fan blades.
Discharge of filter bed material In p a t e n t GB 2 2 6 9 3 2 8 H&G Process Contracting Ltd describes the discharge of filter bed material. After being used to filter water, g r a n u l a r activated carbon is discharged from a filter t a n k t h r o u g h a pipe in the form of a slurry, which is diluted with w a t e r drawn from an a n n u l a r enclosure a r o u n d a filtered w a t e r drainage nozzle.
Filtration & Separation
November 1994
Thus water taken from the enclosure h a s been filtered inwards and then outwards, t h r o u g h different p a r t s of t h e nozzle's filtering wall, and is t h e n delivered to the pipe t h r o u g h a jet directed at its open end or t h r o u g h holes in its circumference.
Screw compressor with oil/gas separation In p a t e n t GB 2 2 6 9 1 2 0 Thermo King Corporation describes a screw c o m p r e s s o r with a m e a n s of separating the oil and gas. A first stage of oil separation occurs where the gas flows from a cavity in the u p s t r e a m p a r t of a housing t h r o u g h a restricted outlet into the d o w n s t r e a m part. The s e p a r a t e d oil is drained off via a side passage. An a n n u l a r perforated steel filter encloses an internal housing, and is closed at one end by a wall which carries a wire m e s h filter pad. The outlet directs the gas onto the pad, and the wall then constrains it to flow t h r o u g h the pad and subsequently o u t w a r d s t h r o u g h the filter. The p a d and filter coalesce the oil, which drains into a sump, for recycling to a nozzle at the suction port, while the gas leaves via a n o t h e r port.
Air filter In p a t e n t GB 2 2 6 9 5 4 7 Toyo Boseki KK describes an air cleaning filter. It comprises a layer of water-repellent fibrous fabric and a layer of bundles of w a t e r - a b s o r b e n t fibres, with the former layer having an air permeability of not less t h a n 100 cm3/cm 2. The latter layer is located u p s t r e a m of the f o r m e r layer. The filter is s u i t a b l e for removing salt particles for ventilation air, even u n d e r h u m i d conditions. The second layer may be in the form of s p u n lace, or parallel or woven threads, with each t h r e a d comprising several filaments. The first layer may comprise nonwoven polymeric fibres or waterproofed glass-fibre paper.
Transfer of granular materials from filters In p a t e n t GB 2 2 6 9 5 4 5 PWT Projects Ltd d e s c r i b e s a g r a n u l a r m e d i u m filter. It comprises a tank for holding the granular medium, and h a s a floor sloping to a sump, with the floor divided by u p r i g h t walls into a n u m b e r of channels running' substantially in the direction of the slope of the floor. Each channel is individually flushable, by supplying water to a corresponding spray pipe above its u p p e r end, to flush the m e d i u m towards the s u m p w h e n it is being discharged from the tank.
Rotary filters using filter aid In p a t e n t GB 2 2 6 9 5 4 6 Andritz-Patentverwaltungs-Gesellschaft mbH describes rotary filters using filter aid. Two rotary filters are connected in series, to recover solids from the w a s t e w a t e r from a p a p e r machine. Both filters are supplied with clean filter aid from an inlet, which divides and leads into the
u p s t r e a m side of each filter via valves controlled by consistency m e a s u r e m e n t s . The filters may be multiple disc or d r u m units, different zones of which p r o d u c e filtrates of different qualities. The cleanest filtrate from the second filter is recycled to its u p s t r e a m side to dilute the incoming water, while the more turbid filtrate is fed to the second filter. The cleanest filtrate from the third filter is discharged, while the moderately clean w a t e r is recycled to cakewashing nozzles in both filters, while the dirtiest is recycled to the inlet side of the second filter.
Process for making ceramic membrane filters In p a t e n t GB 2 2 7 3 6 7 2 t h e UK Atomic Energy Authority describes ceramic membrane filters which are p r e p a r e d by impregn a t i n g a p o r o u s s u p p o r t w i t h a first p r e c u r s o r liquid, The impregnated s u p p o r t is then treated with a second liquid to cause the m e m b r a n e to be deposited in or onto the support.
Sintered metal filter sheet In p a t e n t GB 2 2 6 9 7 6 3 Pall Corporation describes a sintered metal filter sheet m a d e by s u s p e n d i n g metal particulates in a liquid containing a stabilising and binding agent, filtering the stable s u s p e n s i o n to leave a wet cake which is then dried, compressed a n d sintered to produce the metal filter sheet. This s h e e t m a y be g r a d e d by filtering successive s u s p e n s i o n s of different particle sizes a n d / o r shapes. The sheet exhibits a u n i f o r m p o r e s t r u c t u r e in every p l a n e normal to the direction of flow, which is d e m o n s t r a t e d by its bubble p o i n t ratio (BPR) being a b o u t 1.2 or less. The BPR is the ratio between the p r e s s u r e required to force air t h r o u g h the sheet into an alcohol b a t h at 645,835 c m 3 / m i n / m 2 a n d t h e p r e s s u r e r e q u i r e d to p r o d u c e t h e first bubble, after correcting the first figure by subtracting the air resistance of the sheet itself.
Filter in vacuum cleaner In p a t e n t GB 2 2 7 3 8 9 0 R. Hamilton describes a rotary filter element in a street v a c u u m cleaner. Ducting defines a filtering station, where debris is removed from the air by the element. There is an intermediate cleaning station, where debris falls from the element or is removed by a fixed nozzle or scraper. At a reverse flow station at least some of the filtered air is directed t h r o u g h the filter element to complete its cleaning. The air may then flow to a n o t h e r filter to c a p t u r e small particles removed by the r e v e r s e flow. T h e d e b r i s falls i n t o a collector, and is compressed and bagged for disposal.
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Water bath air filter In p a t e n t G B 2 2 6 9 1 1 8 C. M a c d o n a l d describes a w a t e r b a t h air filter with a d e m o u n t a b l e filtration bowl, so t h a t it can be filled with w a t e r and also emptied and cleaned quite easily. It is m o u n t e d on top of the power unit, which is designed to d r a w air t h r o u g h a suction tube. This tube is placed inside the fluted suction tube of the w a t e r bowl, and the two are sealed together by a r u b b e r seal a r o u n d the base of the tube. When the unit is switched on, a fan draws air in t h r o u g h the connected suction tubes, t h u s lowering the air p r e s s u r e in the air filtration bowl cavity. This drop in p r e s s u r e causes air to be drawn in t h r o u g h the w a t e r from outside the air filtration bowl. This air is cleaned by the fact t h a t if anything in the air is soluble in w a t e r it would be dissolved, anything heavier t h a n w a t e r would sink, and anything else would be t r a p p e d by the w a t e r ' s n a t u r a l surface tension. Bubbles which p a s s t h r o u g h the w a t e r are diffused by baffles placed in the top of the unit. This prevents s p l a s h e s of w a t e r fi'om entering into the suction tube and into the suction c h a m b e r of the p o w e r unit. Air is expelled t h r o u g h vents placed a r o u n d the suction c h a m b e r o p p o s i t e a n d a d j a c e n t to the suction fan blades.
Discharge of filter bed material In p a t e n t GB 2 2 6 9 3 2 8 H&G Process Contracting Ltd describes the discharge of filter bed material. After being used to filter water, g r a n u l a r activated carbon is discharged from a filter t a n k t h r o u g h a pipe in the form of a slurry, which is diluted with w a t e r drawn from an a n n u l a r enclosure a r o u n d a filtered w a t e r drainage nozzle.
Filtration & Separation
November 1994
Thus water taken from the enclosure h a s been filtered inwards and then outwards, t h r o u g h different p a r t s of t h e nozzle's filtering wall, and is t h e n delivered to the pipe t h r o u g h a jet directed at its open end or t h r o u g h holes in its circumference.
Screw compressor with oil/gas separation In p a t e n t GB 2 2 6 9 1 2 0 Thermo King Corporation describes a screw c o m p r e s s o r with a m e a n s of separating the oil and gas. A first stage of oil separation occurs where the gas flows from a cavity in the u p s t r e a m p a r t of a housing t h r o u g h a restricted outlet into the d o w n s t r e a m part. The s e p a r a t e d oil is drained off via a side passage. An a n n u l a r perforated steel filter encloses an internal housing, and is closed at one end by a wall which carries a wire m e s h filter pad. The outlet directs the gas onto the pad, and the wall then constrains it to flow t h r o u g h the pad and subsequently o u t w a r d s t h r o u g h the filter. The p a d and filter coalesce the oil, which drains into a sump, for recycling to a nozzle at the suction port, while the gas leaves via a n o t h e r port.
Air filter In p a t e n t GB 2 2 6 9 5 4 7 Toyo Boseki KK describes an air cleaning filter. It comprises a layer of water-repellent fibrous fabric and a layer of bundles of w a t e r - a b s o r b e n t fibres, with the former layer having an air permeability of not less t h a n 100 cm3/cm 2. The latter layer is located u p s t r e a m of the f o r m e r layer. The filter is s u i t a b l e for removing salt particles for ventilation air, even u n d e r h u m i d conditions. The second layer may be in the form of s p u n lace, or parallel or woven threads, with each t h r e a d comprising several filaments. The first layer may comprise nonwoven polymeric fibres or waterproofed glass-fibre paper.
Transfer of granular materials from filters In p a t e n t GB 2 2 6 9 5 4 5 PWT Projects Ltd d e s c r i b e s a g r a n u l a r m e d i u m filter. It comprises a tank for holding the granular medium, and h a s a floor sloping to a sump, with the floor divided by u p r i g h t walls into a n u m b e r of channels running' substantially in the direction of the slope of the floor. Each channel is individually flushable, by supplying water to a corresponding spray pipe above its u p p e r end, to flush the m e d i u m towards the s u m p w h e n it is being discharged from the tank.
Rotary filters using filter aid In p a t e n t GB 2 2 6 9 5 4 6 Andritz-Patentverwaltungs-Gesellschaft mbH describes rotary filters using filter aid. Two rotary filters are connected in series, to recover solids from the w a s t e w a t e r from a p a p e r machine. Both filters are supplied with clean filter aid from an inlet, which divides and leads into the
u p s t r e a m side of each filter via valves controlled by consistency m e a s u r e m e n t s . The filters may be multiple disc or d r u m units, different zones of which p r o d u c e filtrates of different qualities. The cleanest filtrate from the second filter is recycled to its u p s t r e a m side to dilute the incoming water, while the more turbid filtrate is fed to the second filter. The cleanest filtrate from the third filter is discharged, while the moderately clean w a t e r is recycled to cakewashing nozzles in both filters, while the dirtiest is recycled to the inlet side of the second filter.
Process for making ceramic membrane filters In p a t e n t GB 2 2 7 3 6 7 2 t h e UK Atomic Energy Authority describes ceramic membrane filters which are p r e p a r e d by impregn a t i n g a p o r o u s s u p p o r t w i t h a first p r e c u r s o r liquid, The impregnated s u p p o r t is then treated with a second liquid to cause the m e m b r a n e to be deposited in or onto the support.
Sintered metal filter sheet In p a t e n t GB 2 2 6 9 7 6 3 Pall Corporation describes a sintered metal filter sheet m a d e by s u s p e n d i n g metal particulates in a liquid containing a stabilising and binding agent, filtering the stable s u s p e n s i o n to leave a wet cake which is then dried, compressed a n d sintered to produce the metal filter sheet. This s h e e t m a y be g r a d e d by filtering successive s u s p e n s i o n s of different particle sizes a n d / o r shapes. The sheet exhibits a u n i f o r m p o r e s t r u c t u r e in every p l a n e normal to the direction of flow, which is d e m o n s t r a t e d by its bubble p o i n t ratio (BPR) being a b o u t 1.2 or less. The BPR is the ratio between the p r e s s u r e required to force air t h r o u g h the sheet into an alcohol b a t h at 645,835 c m 3 / m i n / m 2 a n d t h e p r e s s u r e r e q u i r e d to p r o d u c e t h e first bubble, after correcting the first figure by subtracting the air resistance of the sheet itself.
Filter in vacuum cleaner In p a t e n t GB 2 2 7 3 8 9 0 R. Hamilton describes a rotary filter element in a street v a c u u m cleaner. Ducting defines a filtering station, where debris is removed from the air by the element. There is an intermediate cleaning station, where debris falls from the element or is removed by a fixed nozzle or scraper. At a reverse flow station at least some of the filtered air is directed t h r o u g h the filter element to complete its cleaning. The air may then flow to a n o t h e r filter to c a p t u r e small particles removed by the r e v e r s e flow. T h e d e b r i s falls i n t o a collector, and is compressed and bagged for disposal.
ilili! i!i !iii i !iii ii!i
iii!ii]
713