Plate Size
Once the cubic foot capacity of a filter press has been determined the next step is, the proper selection of the size of the filter plates, frame, components and any accessories. This will allow you to see exactly where the cu. ft. capacity fits in relation to the volume of each size press. For example a 5 cu. ft. can be sized as a 470 mm, a 630 mm and also an 800 mm. The size selected is determined by the amount of expandability desired. After the plate size is selected, there are many options from which to choose. The following information is a summary of what needs to be considered in order to make the proper selection, Please read each section in turn and note your requirements.
Plate Construction
Select the type of filter plate material. The standard material is an industrial grade polypropylene. An optional FDA approved food grade polypropylene material, or a high temperature glass filled polypropylene material are also available. Special materials are also available such as Carbon Steel , Stainless steel and Kynar.
Plate Style
The standard is a 100 psi recessed gasketed plate with EPDM seals. Viton seals are available as an option. Also available are non-gasketed plates with quick removal latex edged cloths, where the cloth acts as the gasket. The Non gasketed plates allow for easier change out of the filter cloth, are lower in cost, but are not completely liquid tight during the processing stage. Special membrane squeeze plates have the ability to expand after the chambers are full to 'squeeze' additional process liquid out of the filter cake. A 'mixed stack' of plates will be provided where every other plate will be a special membrane squeeze plate
Optional Backing Plate
If a shorter cycle is desired, when running low volume applications for example, the capacity of the filter press can be temporarily reduced. This is done by moving the follower (tail) plate forward in the plate stack. The backing or 'blank plate' is then placed behind the follower plate acting as extra support. The follower plate will not flex or break when used in this manner.
Plate and Press Pressure Rating
The 100 psi design is standard for most dewatering applications and will produce a cake with approximately 30-35% solids. A 225 psi design can be used to provide an increased yield per cycle and depending on the application can increase the solids in the cake to 50% or more.
Cake Thickness
The 32 mm cake thickness is standard. Options include 25, 38 and 50 mm cake thickness. 25 mm would be used for high viscosity (slimy) materials and 50 mm would be used for easily filtered material.
Cloth Type
ErtelAlsop can provide filter cloths in many different materials, weaves, thread styles, and air permeability values resulting in a wide array of performance characteristics. If possible ErtelAlsop would like to receive samples of the process liquid to conduct filterability tests for cloth selection. If testing is not possible then we will furnish our standard polypropylene filter cloth, a monofilament x multifilament, Sateen weave with a CFM<1.0.
Frame Design
All ErtelAlsop frame configurations are sidebar design. Frames can be designed in Carbon Steel or Stainless Steel.
Volume of Plates/Expansion Spacer
All filter presses are available with optional removable expansion spacer. On presses ordered with a spacer, the first number denotes current plate capacity. The second number in the nomenclature is the maximum capacity the frame will allow.
Discharge/Air Blow-down Piping
The discharge/air blow-down piping is available in either manual or in automatic operation. An optional core blow-down is available to purge the center feed line of residual fluid. Available materials of construction are schedule 80 CPVC, or schedule 40 Stainless Steel.
Feed Style'
The feed style can vary for special applications such as pharmaceuticals and some type of food processing. Center feed is standard, however a choice of any corner feed is available.
Automation versus Manual Operation
Manual or semi automatic operation requires input from an operator to start and operation of the filter press, including opening and closing, blow down, plate shifting etc. Fully automated presses require initial start up of operation and then close fill, blow-down, plate shift, discharge and cloth wash is automated. Restarting the press cycle still requires operator input.
Unlike other devices used in the industrial field (tape press, centrifuge, etc.), the filter press has the characteristic of being a discontinuous machine, i.e., during the filtration phase a finite volume of sludge or more generally of fluid is processed dehydrate.
Already from this difference, it has no real basis to talk about the hourly flow rate processed, but we should talk about the flow rate per filtration phase.
The sizing of the sludge filter press is done once the filterability characteristics of the sludge to be processed are known and on the basis of this data, the filtering volume that the machine must make available to dispose of a certain flow rate can be traced back.
The filterability characteristics of the sludge can vary greatly between one type and another and in general only a laboratory test can provide these data. Where it is not possible to carry out these tests (think for example of the case in which a plant is being designed) we rely on the experience of the manufacturer or we go by analogy with other similar cases.
There are cases in which the filtration lasts 3 or 4 hours (for example biological sludge), others in which inert materials or very heavy fluids are treated (for example lead pastel) in which the cycle is very fast (15/20 minutes) or still other cases in which in particular industrial processes of concentration the cycle can last even 7/8 hours and finally other shorter cycles 1.5-2 hours if we think for example of the cases of sludge containing aluminium hydroxides.
The filterability of the sludge is therefore the key data from which to start to arrive at the sizing of the filter press.
The other parameters that need to be considered for correct sizing are:
' Hourly flow rate of sludge to be processed
-% of dry solid contained in the sludge
' Density of the inlet sludge
-Amount of hours/day of operation of the filter press
' Desired degree of automation (automatic, manual)
With these data, it is possible to proceed with a mass balance to correctly size the filter press for the chosen process.
Let's see this example:
' Hourly inlet sludge flow rate: 1.25 m3/h
BRIGHT are exported all over the world and different industries with quality first. Our belief is to provide our customers with more and better high value-added products. Let's create a better future together.
-3% SS of solid substance in the sludge
-Inlet sludge density: 1.1 Kg/dmc
-Sludge production hours: 8 h/day
Qf in = 1.25 m3/h*8h/day = 10 m3/day ' daily flow rate of sludge to be disposed of.
Pf in = 10 mc/day*1.1 Kg/dmc = 10 mc/day* Kg/mc = Kg/day sludge
Of this sludge, the solid content is 3%
Pf SS = Kg/day * 3% = 330 Kg/day of sludge
While the remainder is liquid fraction.
Summing up:
Pf in = Kg/day of which: Pf SS = 330 Kg/day + Pf L = Kg/day.
Let's suppose that the output density of the sludge that can be obtained with the filtration process is 30%.
With a simple mass balance, we have that the solid content found in the previous step now represents 30% by mass (we find it again in the panel):
Pp out = 330 Kg/day / 30% = Kg/day
In summary, the panel (or cake) is made up as follows:
Pp out = Kg/day of which PSS = 330 Kg/day, while PL out = 770 Kg/day
If we assume (either by calculation or following experimental tests) that the density of the waste cake is equal to 1.4 Kg/dmc, we obtain the volume of the cake:
Kg/day / 1.4 Kg/dmc = 785.7 dmc/day
The filter press must dispose of a volume of cake equal to 785.7 dmc in one day.
Let's assume that the filtration system works for 8 h/day and that a filtration process (including filling, filtration, opening and various options) lasts 4 h:
nf = 8 h/day / 4h/filtered = 2 filtered/day
Vf = 785.7 dmc/2 = 392.85 dmc (volume of the filter press).
The volume of the sludge filter press must therefore be approximately 393 dmc.
At this point it is necessary to find the size and number of filter plates, keeping in mind the process in which this machine will be inserted.
These dimensional data must then be crossed with the degree of automation desired (semi-automatic ' fully automatic) and precisely the type of process and available options; but in general, the rough calculation that can be made for sizing the filter press is the one just shown.
However, the fundamental thing is to understand that the sizing of the sludge filter press is a mass balance.
In terms of calculation, I must always consider that the solid part of the incoming sludge will concentrate at the outlet, with a cake (also called cake) which will contain a higher percentage of suspended solids than the one at the inlet, while in the discharge of the filtrate I will tend to have only the liquid part.
Therefore, by adding the liquid part of the filtrate discharge to the liquid part contained in the cake, I will have to obtain the liquid part contained in the incoming sludge, while the solid part will be completely transferred to the residual cake.