Apparatus for aerating organic waste material

In a stationary upright cylindrically shaped container, organic waste materials are passed downwardly from an upper inlet opening to a lower outlet opening. At the same time air is passed in counterflow upwardly through the downwardly flowing body of waste materials being converted into compost. The air supply means at the lower end of the container are divided into sector-shaped parts, and the compost is conveyed to the outlet opening from each of the sectors of the body so that the moisture content of the material leaving each sector can be checked. Air is introduced, in turn, into the lower end of each sector within the container. The amount of air introduced into each sector is regulated in accordance with the moisture content of the material discharged from that sector.

SUMMARY OF THE INVENTION 
The present invention is directed to the aeration of organic waste 
materials for transforming them into compost. The materials are guided 
from the inlet in the form of a material column, downwardly through an 
upright stationary container which has a cylindrical cross-section, to an 
outlet in the bottom of the container. The treated waste materials are 
discharged through the centrally located outlet by a rotating discharge 
screw conveyor which moves the materials radially inwardly to the outlet. 
Air inlet openings are provided in the bottom of the container for 
admitting air for counterflow upwardly through the material column with 
the amount of air supplied being determined by a control device. 
In an apparatus for aerating organic waste materials, such as the one 
disclosed in German Offenlegungsschrift No. 2,541,070, it is known that in 
spite of a uniform air supply over the entire cross-section of the waste 
material in the container, the discharged treated material has, at times, 
a variable moisture content. Increasing the rate of air flow when the 
moisture content is found to exceed a certain level, until the desired 
moisture content is achieved, has the result, as experience has shown, 
that dry zones occur within the body of the material being treated and 
such zones are highly undesirable, since the digestion process stops in 
such zones. 
Therefore, the primary object of the present invention is to provide a new 
apparatus for aerating waste materials in digestion containers with the 
waste materials travelling downwardly through the container in the form of 
a body of material. The apparatus facilitates a simple and reliable supply 
of air into specific portions of the body of material, regulated with 
regard to the amount and the time per unit area involved. In other words, 
a variably controlled aeration is provided relative to the cross-section 
of the body of material moving downwardly through the digestion container. 
In accordance with the apparatus of the present invention, air inlet 
openings are arranged in groups relative to sector-shaped portions of the 
body of material. Each group of air inlet openings is arranged in an inlet 
duct and each duct is connected through a time switch to a common supply 
source. The period during which each sector is aerated is controlled 
depending on the moisture content of the digested material discharged from 
that sector. 
In a preferred embodiment of the present invention, the air inlet openings 
are distributed in four radially extending ducts spaced 90.degree. apart. 
The four inlet ducts are connected to a common feed ring which extends 
around the centrally located outlet from the container. The feed ring is 
connected to a supply pipe via an adjusting valve. 
Another feature of the present invention is the provision of an adjusting 
valve for each of the inlet ducts with each valve actuated by an 
electromotor. Each adjusting valve is connected to an associated time 
switch. The time switches are adjusted manually or through a control 
device connected to a moisture sensor which checks the moisture content of 
the digested material as it is discharged through the outlet opening. 
Although the air is introduced into individual sectors within the 
container, after the air passes through a certain material layer, it then 
flows throughout the entire body of the waste materials above the inlet 
sector. Accordingly, sector zones containing excessive moisture can be 
eliminated in a simple manner by varying the flow of air into a specific 
sector. In this way, particular sectors at the bottom of the body of waste 
materials can be more strongly aerated than the other sector zones. As a 
result, a so-called forced aeration can be achieved whereby the material 
being digested can be variably aerated based on the moisture conent of the 
material discharged from that sector. Thus, the desired aerating influence 
occurs only within the lower end of a particular sector Since the periods 
during which the adjusting valves are opened are arranged to overlap, a 
continuous flow of air through the body of waste materials is ensured. 
Another advantage of this aeration apparatus is that the maximum available 
aeration output can be used, for a short time, to aerate only one sector 
for eliminating excessively compacted wet zones of the waste materials 
which occur for a short time. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its use, reference 
should be had to the accompanying drawings and descriptive matter in which 
there are illustrated and described preferred embodiments of the invention 
.

DETAIL DESCRIPTION OF THE INVENTION 
In FIG. 1 in-ground foundation 10 supports a vertically extending container 
11 which is cylindrical in cross-section. The walls of the container 11 
are heat insulated. At its top, container 11 has a centrally arranged 
inlet opening 12 and at its bottom, it has a centrally arranged outlet 
opening 14. Rotary cylinder 15 is centrally located in the bottom of the 
container and extends through the opening 14. A discharge screw container 
16 extends radially outwardly from the cylinder 15 across the lower end of 
the container. Cylinder 15 is driven by a motor, not shown, and rotates 
via a gearing, also, not shown. The discharge screw conveyor is located 
closely above the bottom of the container 13 and rotates with the cylinder 
15 and is driven via a motor and gearing, not shown. 
When the container 11 is filled, a column or body of waste materials HW 
extends upwardly above the discharge screw conveyor 16, note FIG. 3. In 
its uppermost layer, the column of waste materials may consist of 
undigested garbage, sludge or similar organic wastes and, its lowermost 
layer consists of digested material. The digested material is removed by 
moving the discharge screw conveyor about the axis of the container and by 
revolving the screw conveyor for carrying the material inwardly to the 
outlet opening 14 from where it flows downwardly into outlet connection 
18. A charging device 19 is provided at the top of the container for 
discharging waste materials to be digested, into the inlet opening 12. As 
a result, the column of waste materials travels slowly downwardly through 
the container from its top to its bottom. 
As shown in FIGS. 1 and 2, four air inlet ducts BR.sub.1 -BR.sub.4 are 
located in the bottom of the container below the discharge screw conveyor 
16. The air inlet ducts are spaced 90.degree. apart and extend radially 
relative to the central axis of the container. Each air inlet duct 
BR.sub.1 -BR.sub.4 has a number of air inlet openings 21 spaced apart in 
the radial direction of the container 11. A standpipe St.sub.1 -St.sub.4 
is connected to each of the air inlet ducts and the lower ends of the 
standpipes are connected to a feed ring 23 extending around the rotary 
cylinder 15. Each standpipe has an adjusting valve SV.sub.1 -SV.sub.4 and 
each valve is actuated by an electromotor. Feed ring 23 is supplied with 
compressed air from a pressure blower 28 via a supply pipe 25 in which an 
adjusting valve 26 is provided operated by a motor. 
The lower end of the container 11 is divided by four angularly spaced 
radially extending partitions 29. Partitions 29 extend above the air inlet 
ducts and their upper ends are located below the discharge screw conveyor 
16. Partitions 29 divide the bottom of the column of waste materials HW 
into individual sectors a-d with each sector being filled with gravel K. 
Each sector is supplied with fresh air by one of the air inlet ducts. As 
indicated, the top ends of the partitions 29 terminate below the discharge 
screw conveyor so that it can rotate with the cylinder 15 around the 
bottom of the container above the divided sectors a-d. 
A suction line 30 is connected through the container cover 31 and extends 
downwardly to a suction blower 33 for removing the air-gas mixture 
emerging from the upper surface of the waste materials column in the 
container. The air-gas mixture is drawn off through the suction line and 
discharged into the atmosphere through filter 34 which is schematically 
illustrated in FIG. 3. Furthermore, a separate line ML is connected to the 
outlet suction line 30 for checking the CO.sub.2 content in the exhaust 
gas removed from the container. 
The operation of the described apparatus will now be explained with the aid 
of FIG. 3. 
Fresh air drawn in by the pressure blower 28 is conveyed into the container 
11 through adjusting valve 26, the feed ring 23, the standpipes St.sub.1 
-St.sub.4, and the air inlet ducts BR.sub.1 -BR.sub.4. Within the 
container 11, the fresh air flows upwardly through the body of waste 
materials HW. A partial vacuum is established above the body of material 
by the suction pump 33, and the air-gas mixture flowing out of the top of 
the body of waste materials is drawn off through suction line 30 and 
conveyed into the atmosphere. In dependence on, for example, the CO.sub.2 
content in the exhaust air-gas mixture and a given nominal value, the air 
flow through the body of waste materials is controlled in a predetermined 
manner by a control unit 38 which regulates the motor controlling the 
adjusting valve 26. 
The aeration of the body of waste materials is carried out successfully in 
sectors by means of the adjusting valves SV.sub.1 -SV.sub.4, each 
connected to an associated St.sub.1 -St.sub.4 standpipe. Each of the 
adjusting valves SV.sub.1 -SV.sub.4 is opened and closed for a 
predetermined period via a time switch ZS.sub.1 -ZS.sub.4. During 
operation, the switching on and off of the adjusting valves SV.sub.1 
-SV.sub.4 is carried out in sequence, that is, sector a, sector b, sector 
c, sector d, sector a and so on with each sector receiving air for the 
same time interval determined on the basis of empirical findings. 
Accordingly, by means of the control unit 38, the amount of air conveyed 
into the body of waste materials is determined on the basis of a 
predetermined nominal value and a measured actual value. After flowing 
into the gravel layer K, the air originally supplied into one of the 
sectors a-d, is distributed above the sector, that is above the partition 
walls 29, throughout the entire cross-section of the body of waste 
materials which slowly travels downwardly through the container. The air 
passes in counterflow upwardly through the body of waste materials and is 
drawn off from the top of the container in the manner mentioned above. 
A change in the adjustment of the time switches ZS.sub.1 -ZS.sub.4, that 
is, a change in the predetermined aeration time of the individual sectors, 
is, in the simplest case, carried out manually on the basis of the 
moisture content of the digested material discharged by the screw conveyor 
from a particular sector of the container for a given time. By mechanical 
indicating means, not shown, it can be determined over which of the 
sectors a-d the screw conveyor passes at a given time. For example, in 
FIG. 2 the screw conveyor 16 is located in or over the angular range of 
the sector b. Accordingly, to influence the moisture content of the 
material in that sector, if the moisture content varies from the 
predetermined content, the adjustment of the time switch ZS.sub.2 is 
changed. The time switch is returned to its original adjustment as soon as 
the moisture content in the sector returns to the predetermined value. 
Additionally, the adjustment of the time switches can be effected by a 
control unit based on the readings provided by a moisture sensor located 
in the outlet pipe from the outlet 14 in the bottom of the container. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the inventive principles, it 
will be understood that the invention may be embodied otherwise without 
departing from such principles.