Cleaner for drum type vacuum filter system

Apparatus for cleaning a drum type vacuum filter having a rotating drum and a porous belt wrapped around and rotating with the drum. Liquid in a slurry carried by the belt is withdrawn through the belt and through grids carried on the drum and openings in the drum surface by a vacuum within the drum. Small particles of solids in the slurry are also drawn through the belt and lodge in and clog the grids and drum surface openings. The cleaning apparatus is positioned in a space formed between the belt and the drum by the travel of the belt from the drum and the return of the belt to the drum. The cleaning apparatus has a spray header movable along the length of the drum and carrying a plurality of nozzles facing the drum surface and grids mounted thereon and is connected to a source of high pressure liquid which is sprayed by the nozzles on the drum openings and grids to clean the solids from them. The number of nozzles and size of the spray header is relatively small compared to the size of the drum so that a large amount of cleaning force is applied to a small drum surface area.

BACKGROUND OF THE INVENTION 
This invention relates to a continuous belt, drum type vacuum filter system 
and, in particular, to an improved apparatus for cleaning the drum surface 
and elements associated with the drum surface. 
A drum type vacuum filter basically consists of a cylindrical drum covered 
with a filtering material or fabric which rotates partially submerged in a 
tank containing a slurry comprising solids and a liquid. Where the vacuum 
filter is used in a sewage treatment plant, the slurry will be a sludge of 
solid wastes and water. As the drum and belt rotate, the slurry will 
adhere to the outer surface of the belt and be carried on the belt along 
the surface of the drum out of the tank. The drum has a plurality of 
openings in its cylindrical surface and a vacuum is applied internally of 
the drum to extract water from the slurry. In being drawn into the drum by 
the vacuum, the water passes through pores or spaces in the belt and 
through the drum surface openings, leaving the solids on the belt. As the 
drum and belt continue rotating, the belt passes off or extends from the 
drum over relatively small rollers to dislodge the solids and again 
returns to the drum and passes into the tank. In addition, a scraper blade 
is typically positioned against the belt to insure that the solids are 
removed from the belt. Also to assist in flow of the water from the slurry 
through the belt and into the drum, means such as grids carried on the 
cylindrical drum surface and maintaining the belt at a spacing from the 
drum surface are used. 
A serious problem with this type of filter system is that small particles 
of the solid in the slurry are drawn through the pores or openings in the 
belt and into the grid openings and the openings in the drum surface. 
These solid particles will plug the belt pores as well as the grid and 
drum surface openings so that the filter system becomes inoperative . The 
solid particles tend to harden in the grid and drum surface openings and 
become extremely difficult to remove. Cleaning of the grids and drum 
surface openings is quite difficult since most of the drum surface is 
covered by the belt. Moreover, attempting to clean the grids and the drum 
surface openings in the space formed by the drum and the extension and 
return of the belt from the drum is also quite difficult since the axial 
length of the drum and the width of the belt is considerable. For example, 
lengths of vacuum filter drums are typically between 20 and 30 feet. 
Solutions to the problem have included the placing of an elongated pipe or 
spray header running the full axial length of the drum in the space formed 
by the drum and the extension and return of the belt from the drum. Spray 
nozzles are located in the spray header along its full length to spray 
water against the drum surface or against the belt to provide a cleaning 
effect. This approach is very ineffective and is not believed to be 
practiced to any great extent on commercial vacuum drum filter systems. 
Steam cleaning methods are also used in which the belt is removed from the 
drum, a large enclosure is placed over the drum and the drum is subjected 
to steam until the solids clogging the drum surface openings and grid 
openings disintegrate. Disadvantages of this type of cleaning include the 
necessity of removing the belt, the expense and problem of a large 
enclosure over the drum and the cost of a boiler for providing steam. 
Other methods include manual cleaning which requires removal of the belt 
and the grids from the drum and manually cleaning the drum openings and 
the grids. Methods such as soaking the grids in any of a variety of 
cleaning baths and/or subjecting the grids and the drum surface to 
ultrasonic devices may also be utilized. The disadvantages of these 
methods also include the necessity of removing the belt and removing the 
grids. It can be appreciated that the foregoing described cleaning methods 
require the drum filter to be taken out of operation for a considerable 
length of time. Also, the amount of manual labor in removing the belt and 
cleaning the grids and drum surface is substantial. Further, removing the 
belts from the drum deteriorates the belts to the extent that they 
typically cannot be put back into service. The belts are quite expensive 
and the inability to continue their use adds a large expense to the 
operation of the sewage treatment plant. 
SUMMARY OF THE INVENTION 
The principal object of the present invention is to provide a cleaner for a 
drum type vacuum filter system which eliminates the aforementioned defects 
and problems of presently known apparatus and methods. 
Another object of the present invention is to provide in a drum type vacuum 
filter system having a filter belt rotating with a drum, apparatus for 
using high pressure liquid to effectively clean the drum surface and 
openings therein and elements such as grids positioned between the drum 
and belt and carried on the drum surface without removing the belt or 
grids from the drum. 
A further object of the present invention is to provide, in a drum type 
vacuum filter system having a filter belt rotating with the drum and 
extending from and returning to the drum along a portion of the belt 
length, apparatus for using high pressure liquid to clean the surface of 
the drum and openings therein and grids carried on the drum surface, which 
fit in the space between the drum and the portion of the belt extending 
from the drum and which permits concentration of high pressure liquid 
spray on a limited surface area of the drum to maximize the cleaning 
force. 
A still further object of the present invention is to provide, in a drum 
type vacuum filter system having a belt rotating with the drum and 
extending from and returning to the drum along a portion of the belt 
length, cleaning apparatus for the drum surface and elements positioned on 
the drum surface which is movable within the space between the drum and 
the portion of the belt extending from the drum along the entire axial 
length of the drum. 
Another object of the present invention is to provide, in a drum type 
vacuum filter system having a belt rotating with the drum and extending 
from the drum along a portion of the belt length, cleaning apparatus for 
the drum surface and elements carried on the drum surface having a drive 
means which does not extend substantially beyond the width of the drum. 
In a drum type vacuum filter, the belt which is positioned around the drum 
is a porous filter cloth having a desired mesh size. However, other types 
of filter material may be used, for example, string type filter material 
may be used in which the filter belt comprises a large number of cords or 
strings positioned closely together around the drum along the drum's axial 
length. Although the mesh size of the filter belt may be quite small, 
small particles of solids in the slurry are nevertheless drawn through the 
belt and the grids mounted on the drum and separating the belt from the 
drum and thence through the vacuum openings in the drum. The solid 
particles adhere to the grid openings and the vacuum openings in the drum 
and eventually clog the openings until the vacuum is no longer effective 
to draw liquid out of the slurry. The present invention permits highly 
effective cleaning of the drum openings and grids openings by positioning 
a movable spray header connected to a source of high pressure liquid in 
the space between the extended belt and the drum surface immediately 
opposite the drum surface. The spray header carries a plurality of nozzles 
and is relatively small compared to the axial length of the drum and the 
drum surface area which is to be cleaned. When connected to the high 
pressure liquid source, the small size of the spray header and the small 
area against which spray from the header is applied permits a very large 
force to be applied to the drum surface area which is extremely effective 
in cleaning the drum grids and drum openings in a relatively short length 
of time. The spray header is mounted on a support member that extends the 
axial length of the drum and the spray header is movable along 
substantially the full length of the support member to clean the entire 
surface of the drum as the latter rotates. The high pressure liquid is 
supplied to the spray header by a flexible hose which can be extended into 
or drawn out of the space in which the spray header is located. Drive 
means for the spray header may be either manual or a suitable motor source 
and may be located substantially entirely within the space between the 
extended belt and drum surface. 
As used herein, the term "slurry" is intended to mean any admixture of 
liquids and solids from which it is desired to remove the liquids. For 
example, slurries which can have liquid removed from them by a drum type 
vacuum filter include sludges treated at sewage treatment plants, other 
types of wastewater containing solids, and wood pulp or paper mashes being 
processed at paper producing mills.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIGS. 1 and 2 of the drawings, a drum type vacuum filter 
system is shown as having a frame 2 and a drum 4 rotatably mounted on the 
frame 2. A porous filter belt 6 is positioned around the drum 4 for 
rotation with the drum and the belt 6 extends from the drum to pass around 
the rollers 8, 10, and 12 and return again to the drum 4. The portion of 
the belt 6 extending and returning from the drum 4 forms a space 7 between 
the belt 6 and drum 4. The rollers 8, 10 and 12 support the filter belt 6 
in the desired position and at least one of the rollers is movable to 
permit adjustment of tension on the filter belt 6. 
The frame 2 includes a tank 14 containing a slurry 16 from which liquid is 
to be removed by the filter system. The filter belt 6 and the drum 4 
rotate through the tank 14 and pick up the slurry 16 as shown in FIG. 1. A 
vacuum is applied internally of the drum 4 which causes air at atmospheric 
pressure to be drawn through the plurality of openings 18 in the drum 
cylindrical surface 20. A plurality of grids 22 each having a plurality of 
honeycomb openings 24 in communication with the openings 18 in the drum 
surface 20 are mounted on the drum surface 20. The grids 22 serve to 
maintain the belt 6 spaced from the drum surface 20 so that liquids from 
the slurry 16 will readily flow through the belt 6 and into the drum 
openings 18. The grids 22 may be made of any suitable material, however, 
they are preferably made of a high durability material such as nylon. 
Other means may be used to maintain separation between the belt 6 and the 
drum surface 20 such as ribs projecting from the surface of the belt 6 
facing the drum surface 20. However, grids such as disclosed herein are 
quite effective and are used in many commercial drum type vacuum filters. 
As previously stated, the vacuum within the drum 4 draws liquid from the 
slurry 16 through the filter belt 6 and, in view of the position of the 
grids 22 between the belt 6 and the drum surface 20, through the openings 
24 in the grids 22 and finally into the drum 4 through openings 18. The 
liquid drawn from the slurry 16 into the drum 4 may be pumped from the 
drum by any suitable means (not shown). As the liquid is drawn into the 
drum 4, small particles of solids in the slurry 16 are also drawn through 
the filter belt 6, the grid openings 24 and the drum surface openings 20. 
The solids tend to lodge in the belt and the openings such that ultimately 
the openings will become plugged and the filtering system will become 
ineffective. 
After the liquid is withdrawn from the slurry 16, the solids portion of the 
slurry continues on the belt 6 as it passes from the drum 4. As the belt 6 
moves around the roller 8, some of the solids will fall from the belt 6 
into solids tank 26. Any solids that continue to adhere to the belt 6 
after it moves around roller 8 are removed by scraper 28. 
Referring now to FIGS. 1, 2 and 3, a cleaner apparatus 30 is shown mounted 
on the frame 2. The cleaner apparatus 30 includes support member 32 
affixed to the frame 2, a support bracket 34 slideably mounted on the 
support member 32 for movement along the length of the support member 32 
within the space 7, and means such as cotter pins 36 projecting through 
the support bracket 34 for retaining the latter on the support member 32. 
A spray header 38 is rigidly affixed to the support bracket 34 and 
contains a plurality of orifices or nozzles 40 facing and spaced from the 
drum surface 20. The spray header 38 is thus movable with the bracket 34 
on the support member 32 along the drum surface 20 over the full axial 
length of the drum 4. The spray header 38 is connected by means of a hose 
42 to a pressurized liquid supply source 44. The pressurized liquid is 
typically high pressure water, however, the water may also carry chemicals 
or other materials for facilitating cleaning of the drum surface 20 and 
the grids 22. A drive means 46 for the spray header 38 is connected to a 
tab 48 on support bracket 34 and comprises one or more rods 50 which may 
be threaded together and to the tab 48 and used to push the spray header 
38 across the surface of the drum 20. While the spray header 38 is near 
the end of the drum 4, only one rod may be used. As the spray header 38 is 
moved towards the opposite end of the drum 4, additional rods 50 may be 
threaded together to permit continued movement of the spray header 38 
along the axial length of the drum 4. Hose support hooks 52 are carried on 
the rods 50 for supporting the hose 42 with the space 7 so that the hose 
42 does not interfere with the movement of the belt 6. As the spray header 
38 is moved along the surface of the drum 20 by the drive means 46, the 
hose 42 may be inserted into or removed from the hooks 52 as needed. 
Referring to FIG. 4, another embodiment of the cleaner apparatus is shown 
in which elements which are substantially the same as those shown in the 
embodiment illustrated in FIG. 3 carry the same identifying numerals. The 
cleaner apparatus 30 shown in FIG. 4 utilizes a sprocket and chain drive 
means 54 mounted on the support member 56. The drive means 54 includes a 
rotatable shaft 58 mounted on the hollow end 60 of the support member 56 
and a second shaft 62 mounted through the hollow end 64 of the support 
member 56. Sprocket gears 70 and 72 are respectively affixed to the shafts 
58 and 62 within the ends 60 and 64. The shaft 58 is manually rotatable by 
means of a handle 66. A chain 68 is connected at both its ends to support 
bracket 74 and extends through the hollow length of the support member 56 
and passes around the sprocket gears 70 and 72. The support bracket 74 
carries the spray header 38 and is movable along substantially the full 
length of the support member 56 by rotation of the shaft 58 to drive the 
chain 68. A hose support tray 76 is mounted on the support member 56 by 
arms 78 to hold the hose 42 within the space 7. 
As previously discussed, the axial length of the drum of a drum type filter 
system is quite long and typically will have a length of between 20 and 30 
feet. The spray header 38 of the invention, however, has a length 
dimension parallel to the axis of the drum 4 which is quite small compared 
to the full axial drum length and relatively few spray orifices 40 
compared to stationary type spray headers which have sufficient orifices 
to simultaneously spray along the entire axial length of the drum. The 
dimensions of the spray pattern or area of the orifices 40 on the drum 
surface 20 is thus limited to a very small part of both the axial length 
of the drum and the circumferential length of the drum so that all of the 
force of the high pressure water is concentrated on a small, limited area. 
For example, a high degree of cleaning in a minimal amount of time can be 
attained by utilizing four spray orifices 40 having a focal distance from 
the drum surface 20 of 8 inches and an included spray angle for each 
orifice of 40.degree.. With a 25% spray overlap on the drum surface 20, 
the orifices would have a center-to-center spacing of 4.25 inches. The 
overall length of the spray header 38 would be three center-to-center 
spacing distances of 4.25 inches plus about 1.5 inches at both ends of the 
header for a total length of about 16 inches and a spray pattern width of 
approximately 18 inches. The spray pattern width is thus approximately 5% 
to 7% of the axial length of a drum 4 and preferably should not be greater 
than about 10% of the axial length of the drum. 
The allowable size of the orifices 40 and therefore the cleaning rate of 
the cleaner apparatus 30 is dictated by the volume and pressure of the 
water available from the supply source 44. It has been found, for example, 
that four orifices 40 each having a 0.062 diameter can be effectively used 
with a supply source capacity of 35 gallons per minute at 4,000 lbs. per 
square inch (psi) pressure. In general, it is preferable that the water 
supply pressure be between 4,000 and 5,000 psi and not less than 2,500 
psi. 
As may be appreciated from the aforegoing description, due to its 
movability along the surface 20 of the drum 4, the spray header 38 is 
controllable to clean any particular spot or area on the drum surface 20 
that may need special attention. As disclosed herein, the drive means may 
be manually operated and therefore controlled, however, mechanical or 
electrical drive means which may be either manually or automatically 
controlled may be also utilized. 
It may thus be seen that a cleaner apparatus for a drum type vacuum filter 
system has been invented which permits access to the drum surface and 
grids carried thereon without removing the belt or the grids from the 
drum. Furthermore, the cleaning apparatus according to the invention is 
far more effective than previously known washing systems and is 
controllable to permit cleaning where most needed. 
It will be understood that the foregoing description of the present 
invention is for purposes of illustration only, and that the various 
structural and operational features herein disclosed are susceptible to a 
number of modifications and changes, none of which entail any departure 
from the spirit and scope of the present invention as defined in the 
hereto appended claims. For example, in addition to the drive means 
previously described, the drive means may also be a screw type drive 
mechanism.