Comparison among Vacuum belt filter, Vacuum Disc/Drum filter and Filter
press
"Sl "Description "Horizontal Vacuum Belt "Vacuum Disc/Drum Filter "Filter Presses "
"No " "Filter " " "
"1 "Filtration area " "25-30% higher than HBF for "30% higher than drum/disc "
" "required " "similar throughput "filters for similar "
" " " " "throughput "
"2 "Area "Available in larger areas "No. of filters shall be "No. of filters shall be "
" " " "increased if filtration area "increased if filtration area "
" " " "requirement is more "requirement is more and it is"
" " " " "30% more than Disc/Drum "
" " " " "filters "
"3 "Area increase for"Possible by increasing the "Not Possible. New filter is "Not Possible. New filter is "
" "expanded capacity"length of the filter with "required. "required "
" "for "addition of vacuum boxes " " "
" "future " " " "
"4 "Filtration Rates "Higher "Lower "Lower "
"5 "Power Consumption"Higher "Higher by 15-20% than HBF "Higher by 35% than HBF "
"6 "Consumable Cloths"Once in 5-6 months "Once in 3-4 months "Once in 2 months "
"7 "Availability "Continuous operation and "Continuous "Batch operation, requires at "
" " "hence no stand by equipment"Operation, "least 40% more capacity in "
" " "required, "Equipment availability is less"multiple units, "
" " "Equipment availability is "than 80% "Equipment availability is "
" " "above 95% " "less than 75% "
"8 "Operational "< 5% of Capital cost per "< 10 % of Capital cost ">20% of Capital cost per "
" "Spares "annum "warranty time "annum "
"9 "Height of "3-4.5 m "6.5 to 10.5 m "6 m "
" "Installation " " " "
"10 "Civil work "Building is not required "Building is required "Building is required "
"11 "Discharge width "Discharge width is 400mm "200 mm "Discharge width is 2mtr "
" " " " "requires extra wide conveying"
" " " " "system "
"12 "Capital Cost "Capital costs are low "At least 50% more than Vacuum "At least 50% more than Vacuum"
" " " "Belt filter "Belt filter "
"13 "Washing Fluid "Water - Continuous "Water - continuous "Water - batch wise "
"14 "Particle Settling"All particles settling on "Coarse particles will settle "Fine solids in filtrate are "
" " "filter "at the bottom of feeder box "higher than HBF because of "
" " " "and causes overflow of feed. "high pressure feed "
"15 "Solids in "1-1.5 gpl, Fines shall be "40-50 gpl "2-3 gpl "
" "Filtrate "captured on top of the cake" " "
"16 "Process "Gravity Assisted feeding & "Should work against gravity "Should work against gravity "
" " "filtration " " "
"17 "Cake Moisture " "2-4% higher than HBF "2-3% lesser than HBF "
CURRENT FILTRATION TRENDS
With the introduction of belt filters as reliable operating units into the
process industry, there has been a distinct trend to move away from the
traditional rotary type filter towards the more serviceable belt filter.
Many Companies have replaced Drum and Disc filters with Belt filters.
Westcliff, Australia
Replaced drum filters with 2X100 m2 HBF for Fine coal dewatering
application. The main motivation was the reduction of energy costs and
maintenance cost
Oaky Creek, Xstrata Coal mine, Queensland
Replaced 2 x drum filters to horizontal belt filters , Installed another 2
x horizontal belt filters on their expansion modules.
Hindustan Zinc Limited – Debari (India)
Replaced three drum filters with single 40 m2 HBF for Jarosite filtration
CMP (Chile)
Replaced disc filters with a belt filter on de-watering magnetite pellet
feed fines. The main motivation was the reduction of energy costs.
Mantos Blancos (Chile)
Replaced Disc Filters with a number of Belt Filters on tailings and
concentrates dewatering at very low operating costs.
Foskor (South Africa)
Replaced discs with belt filters on Copper Concentrate, Phosphate
Concentrate, Baddellyite Concentrate.
Codelco - División Chuquicamata (Chile)
Operates a 50 m2 belt filter alongside disc and pressure filters on
concentrate dewatering.
Listed below are typical operating results.
" "DISC FILTER "BELT FILTER "
"CAPACITY (t/m2 .day) "6 - 8 "18 "
"AVAILABILITY "80 % "95 % "
"CAKE MOISTURE (% w/w) "15 - 17 % "13 - 14% "
San Esteban (Chile)
Replace disc filter with a belt filter. The justification for the belt
filter was based on lower moistures achieved by the belt filter and lower
energy costs.
On the basis of this installation San Esteban purchased a second Belt
filter for a second plant.
Based on our above experiences we strongly suggest Horizontal Belt Filters
for fine coal filtration interms of high through put, Low Operating and
Maintenance cost compared to any other type of filters.
BELT FILTERS vs. DISC & DRUM FILTERS
Experience has shown the Vacuum Belt Filter to be a very cost-effective
method for solids dewatering,
particularly when compared to rotary disc or drum vacuum filters.
Summarised below are the main advantages of the belt filter. To understand
these benefits it is useful to be familiar with the Filtration Equation.
HIGH FILTRATION RATES
Belt Filtration rates are generally 3 to 10 times greater than those
achieved on rotary filters. The principle reasons for this are: -
1. Filtration in assisted by sedimentation of
coarser particles onto the filter cloth; The
fine product on top of the coarse material controls the
rate of flow of liquid through the cake. With a bootfeed
type filter (Disc/Drum) vacuum draws the finer
particles immediately to the filter cloth which then do
not allow more coarser material to be drawn up.
In both cases RC remains the same, but the belt
filter will have a thicker cake = more tph.
2. The coarse particles that settle first form an
effective pre-coat preventing the blinding of the filter
cloth by fines. Thus RT is lower on the Belt Filter =
more tph.
3. Belt Filter design allows the filter cloth to separate
from the rubber carrier belt at the discharge end.
Thus, after cake discharge water sprays wash the cloth.
This minimises blinding of the cloth by fines
and RT is lower = more tph.
Compressed air cleaning of cloths (disc filter) does not remove fines as
effectively as water.
4. Filtrate on the Belt Filter drains under gravity along the belt grooves,
to the vacuum box and into the receiver. Movement of filtrate on boot-feed
filters is against gravity, and vacuum is used to lift slugs of filtrate in
the vacuum lines. Thus, dP at the disc/drum filter cloth is lower when
compared to
Belt filters.
5. A Belt Filter has no separation between the feed and drying zones; Thus
a larger area of the filter (up to 70%) can be under liquid. This allows
for thicker filter cakes (higher tph). Boot-fed filters have only
20 - 30 % feed zones.
DRIER FILTER CAKES
When compared to boot-feed type filters, belt filters generally achieve 1%
to 5% better moisture. This can be attributed to :
RT is lower. A cloth that is not blinded allows more airflow, hence
lower moistures.
dP is higher through gravity assisted filtration and filtrate
drainage.
Cake discharge is assisted only by gravity. On a disc filter the cake
blow stage filtrate is blown back into the cake at discharge by the
compressed air.
Elimination of the filter boot overflow reduces the recirculation of
fines (lower RC) giving improved cake moisture.
LOW OPERATING COSTS
Belt Filter users have noted lower operating costs compared to disc filters
& Filter presses. The reasons are: -
Higher throughput per m2 of filter area means less installed filter
area.
Lower installed m2 means less vacuum requirements (lower kW).
Minimal compressed air requirements. The belt filter does not need
compressed air to effect cake discharge.
No feed agitation is required, as there is no filter feed boot. No
maintenance required for boot agitator glands.
Longer cloth life because of the cloth wash.
Less operator attendance is necessary, as variations in feed rates do
not require filter adjustment.
LOW MAINTENANCE COSTS
Generally maintenance costs are in the region of 2% of capital cost per
annum. Wear on the Delkor Belt
filter is confined to two areas: -
1. One is the replaceable continuous wear belt 50 mm wide, which forms the
vacuum seal: (Wear belts
can be expected to last 4500 hours, they are easily replaceable, the
replacement operation lasting 1 hour.)
2. Filter cloth life is usually 3 to 5 times longer than on disc filters.
3. The main component of the belt filter is the rubber carrier belt, which
has a life of 10 years. Operating
experience has shown carrier belts to operate without a mechanical
failure in fifteen years.
INCREASE OF FILTRATION AREA TO MEET INCREASED THROUGHPUT
1. Belt filters can be retrofitted to increase the filtration area to
meet the plant demands to increase the throughput in future. we have
executed this efficiently for Sterlite industries, Tuticorin to
increase the filter area from 64 m2 to 82 m2
2. Disc/drum filters and filter presses cannot be retrofitted to increase
the area. New filter is required to meet the increased plant
capacities
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FILTRATION EQUATION
WHERE
FR = Filtration Rate (or tph treated)
A = Filtration Area
dP= Pressure Drop (Vacuum level)
v= Liquid Viscosity (Temperature /Dissolved Solid content)
RT= Resistance to filtration of the Filter Cloth (permeability / blinding)
RC= Resistance to filtration of the Filter Cake (Porosity / Fines content)
