ROTARY VACUUM FILTERBy:K.Kartik K.Sankeerth M.Pavan Kumar (CH05B012) (CH05B034) (CH05B056)

Sumit Kumar Amb (CH05B060)

VACUUM FILTERS

BATCH

CONTINUOUS

Nutsche

Leaf

Rotary drum

Rotary disc

Horizontal

Rotary vacuum drum filterWhat is a Rotary Drum Vacuum Filter? A rotary drum vacuum filter (RDVF) is a continuous filter wherein the solid constituent in a pulp or slurry is separated.

Mechanism:Separation is done by a porous filter cloth or other media rotated through the pulp or slurry, with vacuum applied to the inner surface to cause the solids to accumulate on the surface as a cake or layer through which the liquid is drawn.

ROTARY VACUUM DRUM

How does it work? work?The process cycle of the RDVF is continuous. Each revolution consists of cake formation, cake washing (if required), drying and cake discharge.

Rotary vacuum filter consists of a drum, vacuum pump, compressor, filters and pure water/solvent for cake wash

CAKE

DISCHARGE

There are various ways in which discharging can be done: (i) scraper discharge (ii) string discharge (iii) belt discharge (iv) roll discharge Normally a discharge device will be selected based on the process material characteristics and how readily it is released from the filtering media.

Hard plastic tips When good filtrate clarity is required, a layer of cake can be built up on the drum to the limits of the position of a fixed knife, which scraps out excess cake. Used if cake is 3mm thick.

Used for cake having cohesive strength. Strings are kept uniformly spaced using comb.

BELT DISCHARGE:The endless filter cloth passes over a series of rollers at the end of each filtration cycle. While away from the drum surface the cake is discharged and the filter cloth is washed, usually on both sides. At the discharging roll the belt is made to change direction suddenly and cake cannot keep up. So it breaks up and falls down.

Following cake discharge the cloth is washed and it goes through a series of high pressure sprays to remove any adhering solids. The liquid used for washing is collected in a separate trough. This makes it possible to wash the cloth after every cycle which increases filtration efficiency. The above process also helps in maintaining high degree of purity of cake.

Selection criteria:Scraper discharge is used: a) For fast filtering materials. b) For discharging granular or crystalline material. c) For discharging cakes in excess of 1/4" thick. d) For nonblinding cakes where cloth washing is not required.

The Roll discharge filter is usually fitted with a very tight filter medium to retain very small particles and is used: a) For discharging very thin, sticky (tacky) cakes. b) For discharging dilatent and thixotropic materials. c) For applications with very small particle sizes.

String discharge is used: a) For discharging cohesive cakes. b) For discharging gelatinous cakes.

Problems:The main problem with belt type discharge is misalignment. Misalignment is of 4 types: a) Edge misalignment b) Lateral misalignment c) Uneven stretching (also called Mooning) d) Wrinkling.

Edge misalignment occurs when one edges of belt becomes displaced longitudinally with respect to other edge. It also occurs due to poor belt fabrication or drum and roller misalignment. Lateral misalignment occurs when filter cake loading is uneven and is often caused by poor cake discharge and /or roller misalignment. Mooning is typified by a crescent shape occurring in the belt , hence the name.

Typical causes of mooning are high cake loading at centre of the belt and uneven washing. Wrinkling is caused by a combination of before said malfunctions.

Solutions:All misalignments problems originate from some form of cloth fault and are enhanced by poor filtering operations which follow. A single-width cloth having no longitudinal singlejoints will give fewest operational problems. This combined with effective tracking mechanism result in minimal stresses in the belt and ensure long belt operational life

Applications Based on Discharge Type

Scrapper dischargeFlue Gas Desulfurization Sludge Scrubber Sludges Inorganic Chemicals and Minerals Pigment Processing Plastics Resins (Polymers) Calcium Compounds Titanium Dioxide

Roll DischargeKaolin Clay Titanium Dioxide Pigments Ceramic Materials Magnesium Hydroxide

String DischargeStarch Fruit Juice Fermentation Broths Mineral Processing

Advantages:Continuous and automatic in operation. Design and operation variations cater for a wide range of suspensions. Cleaning operations. Low maintenance cost. Effective washing and dewatering. Wash filtrate separation is possible.

Disadvantages:High capital cost. Large area required. Limitations by vapour pressure of hot and volatile liquids. Cannot be use for explosive and inflammable gases. Not suitable for quick settling slurries.

Bibliography SOLID LIQUID SEPARATION by Ladislav Svarovsky www.sciencedirect.com www.solidliquid-separation.com www.solidliquid www.steadfastequipment.com/