Method and apparatus for drying sludge using movable plates

A method and apparatus for dewatering and drying sludge. A pair of upper and lower members form a closed chamber into which sludge is poured. Sidewalls of the upper member are pressed against the lower member to seal the chamber. Compressed air supplied at a pressure P.sub.1 to a continuous groove in the lower edge of the sidewalls flows across the sloped inside surfaces of the sidewalls and supplements air supplied to the chamber at a somewhat lower pressure level P.sub.2, the combined pressures P.sub.1 and P.sub.2 in said chamber forcing liquid from said sludge through porous media in the bottom of the chamber. Air from the continuous groove aids in releasing the dried sludge from the chamber when the upper and lower members are separated.

This invention relates to apparatus for removing liquids from and at least 
partially drying sludge materials so that they can be more readily used or 
disposed. 
BACKGROUND OF THE INVENTION 
In many industrial processes, waste materials in the form of a sludge are 
collected at a constant rate. At some point the accumulated sludge must be 
periodically disposed of or refined, particularly if the sludge contains 
deleterious substances. An example of this sludge accumulation problem 
occurs in many industrial plants and municipal treatment plants. In such 
installations, the accumulation of sludge occurs at a relatively high 
rate, often contains hazardous waste products and therefore must be 
disposed of in specially constructed waste dumps. Often, the acceptable 
dump sites for such sludge are located at substantial distances from the 
accumulation sites. Therefore, if the sludge can be dried or if the major 
percentage of liquid in the sludge can be removed, the cost of 
transporting the residual dried sludge and the volume of sludge required 
to be disposed of in a dump site can be greatly reduced. The present 
invention provides an apparatus that helps to solve this problem. 
Accordingly, one object of the present invention is to provide an apparatus 
that will remove the liquid from sludge materials and convert it to an 
essentially dry form that can either be reused or more easily transported 
to a dump site. 
Another object of the invention is to provide an apparatus for drying 
sludge materials comprised of a pair of plates that can be brought 
together to form a chamber for receiving the raw sludge material, a groove 
in the sidewall of one plate and source of air pressure connected to the 
groove so that air will flow from it inwardly and upwardly along the 
inside surfaces of the plate sidewalls, thereby sealing the chamber for 
the sludge and increasing the internal pressure that causes liquid to be 
removed from it. 
Another object of the invention is to provide a method for removing 
moisture or liquid from sludge to dry it into a cake form and also to 
remove from it deleterious and hazardous waste products. 
Still another object of the invention is to provide a separable plate-type 
apparatus for drying sludge wherein a pair of plate members form a drying 
chamber and are sealed by a peripheral groove connected to an air pressure 
source that also prevents the sludge from adhering to the plate sidewalls 
when the plates are separated. 
SUMMARY OF THE INVENTION 
In accordance with the principles of the invention, an apparatus similar to 
plate-type filter is provided comprised of at least one pair of upper and 
lower rigid plates which are movable together to form a sealed chamber. 
The lower plate has perforations and supports a layer of porous media such 
as a filter paper. The upper plate has sidewalls that engage the media and 
form the receiving chamber. With the plates held together by an 
appropriate mechanism, a quantity of sludge to be dried is supplied to the 
chamber. The drying process commences when air at a pressure P.sub.12 is 
supplied to the chamber above the sludge. This pressure forces liquid from 
the sludge which passes through the porous media and the perforations in 
the lower plate to a suitable liquid collection system. During the drying 
process, as the pressure P.sub.12 is applied, additional air at a somewhat 
higher pressure P.sub.11 is supplied through a sidewall inlet to a 
continuous groove in the lower edge of the upper plate sidewalls. This air 
under pressure P.sub.11 provides several advantageous results. First of 
all, it seals the periphery of the upper plate by preventing any liquid 
inside the closed chamber from passing under the surrounding wall. 
Secondly, it creates a flow of air inwardly into the chamber which forms a 
separating layer on the inside walls of the chamber that keeps the drying 
cake therein from building up against and adhering to the chamber walls. 
In cases where the sludge may contain heavy concentrations of unwanted or 
hazardous products, the same charge of sludge may be washed or recycled by 
supplying additional quantities of water to the chamber before the final 
drying cycle is completed. The unwanted products are thus removed from the 
solids of the sludge and are carried away by the water removed therefrom. 
Other objects, advantages and features of the invention will become 
apparent from the following detailed description thereof presented in 
conjunction with the accompanying drawing.

DETAILED DESCRIPTION OF EMBODIMENT 
With reference to the drawing, FIG. 1 shows diagrammatically an apparatus 
10 for dewatering or drying sludge such as may be produced during various 
manufacturing processes or from municipal waste plants. In either case, 
the sludge material extracted usually accumulates at a high rate and often 
contains hazardous or toxic chemicals. This requires that the sludge, when 
accumulated, be transported to specified dump sites. If water can be 
removed from the sludge, it will be lighter and more manageable and thus 
less costly to move. Moreover, if toxic substances can be removed, the 
choice of dump sites for the dried residue can be greatly expanded. 
In general, the apparatus comprises a pair of upper and lower plate members 
12 and 14 which are movable together and apart during cycles of the 
apparatus by a suitable mechanism (not shown). Such a mechanical 
arrangement for manipulating these plate members may be similar to that 
shown in my U.S. Pat. No. 4,289,615 showing a plate-type filter system. 
In the present apparatus, a carrier sheet 16 of porous material such as a 
paper-type filter media is supplied from a roll and extends across the 
lower plate member. A suitable means (not shown) for advancing the carrier 
sheet is provided. 
The lower plate member 12 is provided with a pattern of recesses 18 in the 
upper surface which serve to receive, collect and remove the liquid from 
the sludge which is forced out of it. 
The upper plate member 14 has a transverse portion 20 having the same shape 
and size as the lower plate member and downwardly extending sidewalls and 
end walls 24. When the two plates are pressed together, as shown in FIG. 
2, the sidewalls and end walls form an enclosed chamber 26. An opening 28 
with a suitable closure is provided in the transverse portion of the upper 
plate member through which sludge can be poured or pumped to partially 
fill the chamber 26. 
As shown in FIG. 2, the lower edge 30 of the sidewalls and end walls of the 
upper plate member has a generally flat surface which is provided with a 
single continuous open groove 32. In one sidewall, a branching passage 34 
extends upward from the groove 32 and then outwardly to connect with a 
conduit 36. This latter conduit is connected through a valve 38 to a first 
source 40 of air pressure (P.sub.1). 
From a second source 42, air at a pressure P.sub.2 is supplied through a 
valve 44 and an inlet conduit 46 in the transverse portion of the upper 
plate member 12 to the chamber 26. This latter source of pressure fills 
the chamber and presses the sludge 48 against the paper media 16 below, 
thereby extracting water from the sludge. As shown in FIG. 2, the pressure 
P.sub.1 from the first source 40 travels through the inlet conduit 36, the 
sidewall passage 34 and into the sealing groove 32. Upon reaching the 
sealing groove, some of the air therefrom escapes outwardly, as indicated 
by the arrows 50. However, an equal or larger amount of P.sub.1 air flows 
inwardly from the sealing groove 32 (as indicated by the arrows 52), and 
as it does, it passes around the inner corner of the sidewalls and up 
along their inside surfaces 54. This flow of air thus constantly cleans 
the inner sidewall surfaces and prevents the sludge from adhering to these 
surfaces as it dries. The pressure P.sub.1 is always adjusted to be 
somewhat greater than the other pressure P.sub.2, so the flow of P.sub.1 
air up along the wall surfaces is assured. 
A typical sequence of events or steps for drying a quantity of sludge using 
the apparatus 10, according to the invention, is illustrated in FIGS. 3-5. 
In FIG. 3, the drier plates are together and the chamber 26 formed between 
them is being filled with undried sludge through the opening 28 in the 
upper plate member. In FIG. 4, the plates have been pressed tightly 
together and pressure from the two air sources is being applied, the 
pressure P.sub.1 seals the periphery of the chamber 26 and "washes" the 
inner surfaces of the sidewalls, as previously described. The resulting 
total pressure P.sub.1 and P.sub.2 in the chamber continues to exert 
pressure against the body of sludge 48, thereby forcing water from it 
which passes through the porous media 16 and into the accumulating 
recesses 18 of the lower plate 14, which ultimately feed through an outlet 
passage 56 into a receiving receptacle 58. 
After a period of time during which the sludge is subjected to a 
predetermined quantity of drying air, the plates 12 and 14 are separated 
after the chamber pressure has been reduced. 
The paper media 16 carrying the now dried cake of sludge 48 is advanced, so 
that the cake can be broken up and removed to a storage or dump site. 
Since the sludge at this point has solidified to a cake and is almost 
totally free of moisture, its density is minimized and also in many 
instances any toxic substances were also removed with the water. Thus, the 
resulting sludge product is not only easier and lighter to handle, but in 
many instances it no longer is classified as a hazardous waste. 
In situations where the sludge being processed is more apt to contain toxic 
substances, the same body of sludge within the chamber may be subjected to 
one or more "washing" cycles by supplying a charge of water before the air 
pressure is applied. The added water helps to separate the toxic products 
from the sludge which are then trapped in the water that passes through 
the carrier media 16 and is recovered. For particularly hazardous sludge 
products, as many as three or four water cycles may be used. 
To those skilled in the art to which this invention relates, many changes 
in construction and widely differing embodiments and applications of the 
invention will suggest themselves without departing from the spirit and 
scope of the invention. The disclosures and the descriptions herein are 
purely illustrative and are not intended to be in any sense limiting.