CARRERA PIETRO (IT)
WO1993016017A1 | 1993-08-19 |
DE4315323A1 | 1994-11-10 | |||
FR2391164A1 | 1978-12-15 | |||
GB1066158A | 1967-04-19 | |||
DE4208390A1 | 1993-09-23 |
1. | A plant for the biological treatment of solid organic waste, which is fed into a treatment tank, characterized in that the tank has a horizontal bottom and in that the screw propellers stir and pish forward the organic mass, which inflows and outflows continuously, remaining continuously immersed inside the mass and, therefore, always operating, without any idle phase, moving forward and then back, according to a direction which is at right angles compared to the direction of movement of the organic mass. A plant according to claim 1, characterized in that the axis of the screw propellers is inclined according to a convenient angle, preferably between 10° and 50°, compared to its vertical, which serves the purpose of achieving the desired advance of the organic mass. A plant according to the preceding claims, characterized in that the organic mass is moved from the inflowing side of the treatment tank, across longitudinal zones divided by furrows, and resembling long proximate lengthwise heaps, which at each cycle are gradually advance toward the outflowing side of the treatment tank, according to a speed such as to guarantee that each particle of the organic mass remains inside the tank for an equal time. A plant according to claims 1 and 3, characterized in that the organic mass, before outflowing from the treatment tank is accumulated, for a short while, at the outflowing wall of the tank .where a special device applied to the bridge gradually extracts it, regardless of the operation of the screw propellers, and batches it, so as to obtain a perfectly regular outflow, thus simplifying all the subsequent operations concerning the organic mass. A plant according to claims 1 and 4, characterized in that the pitch of the furrows / 1 changes, so that the bottom section of the screw propellers may adequately plough through the lower layers of the organic mass, so as to prevent the formation, on the bottom of the tank, of a hardened layer of waste matter impermeable to air. |
2. | 6A plant according to claims 1, 3 and 5, characterized in that, according to the preferred embodiment, the screw propellers are slightly slanted, so that their bottom sections may adequately plough through the bottom layers of the waste matter according to two diverse longitudinal directions, thus forming two furrows on the bottom of the tank and facilitating the removal of any deposits. |
3. | 7A plant according to claims 1, 2 and 3, characterized in that by adequately increasing the distance between the furrows, in the directions from the outflowing end to the inflowing end of the treatment tank, it is possible to compensate the reduction of the organic mass, due to evaporation and other chemical reactions. |
4. | 8A plant according to claim 1, characterized in that the screw propellers are provided with a bladed device which, by contrasting with the fixed counterblades rigidly attached to the trolley, cut the threads and rags contained in the organic mass and which may wrap themselves around the screw propellers, gradually moving upwards, as a consequence of the rotatory movement. |
5. | 9A plant according to one or more of the preceding claims, characterized in that the air required for the biological process is blown in from the bottom of the tank, through pipes laid on the bottom of the tank and grouped into zones, accordind to the different quantities of air required 10A plant according to claim 10, characterized in that the pipes laid on the bottom of the tank have perforated sections at predetermined intervals and that these sectors are suitably protected, so as to prevent the entry of the organic mass into the pipes. |
6. | 11A plant according to claim 10, characterized in that both the pipes laid on the bottom of the tank and their protections are covered with a layer of material which is permeable to air, to avoid any contact with the organic mass. |
7. | 12A plant according to claims 10, 11 , characterized in that each pipe laid on the bottom of the tank is provided with a conduit for draining the condensation, which is then discharged into one or more common manifolds. |
8. | 13A plant according to claims 9, 10, 11 and 12, characterized in that by blowing air through the organic mass the heat generated by the biological reactions is transferred and exchanged, inside a heat exchanger, to the fresh air circulated by the ventilation system inside the building, thus preheating it and considerably increasing its capacity to absorb the vapour developed by the exothermic reaction and dispersed inside the building. |
9. | 14A plant accordmg to claim 13, characterized in that the absorbtion of the calories produced by the biological process, and their use to preheat the air entering the ventilation circuit, considerably enhances the system's enviromental impact, since it makes the absorbtion of the odour much easier, through the condensation generated inside the heat exchangers, thus considerably reducing the quantity of air requiring deodorization. |
Biological Waste Treatment Plant
Technical field
The present invention relates to a biological waste treatment plant
Background of the Prior Art
An enormous amount of organic waste is produced daily, by the human food chain, in
agriculture and by the agro-industrial sector. This organic waste accounts for a large part
of solid urban waste, it is one of the main components of sewage and constitutes the residue
of the agro-industry and other industries.
The problem is how to treat this wast, so as to prevent its entering the sewerage, and to
reutilize it.
Aerobic decomposition by means of micro-organism (composting) is undoubtedly a very
efficient and economic technique. The biological treatment plants currently known
generally operate by feeding the organic matter, either continuously or discontinuously,
into treatment tanks of various shapes, where it is stirred by mechanical means, so as to
achieve a state of homogenization, and moved forward, so as to make room for the
inflowing waste matter; furthemore, the treated matter is kept well aerated, so as to ensure
that the micro-organism which perform the biological process, are kept well supplied with
the necessary amount of oxygen.
Various waste treatment plants are known which operate according to the above
mentioned technique, however, they all feature drawbacks which limit their efficiency.
For instance, Swedish patent 7306001-4, deposited on 27-4-1974 by Johnson Construction
Company AB, provides for a treatment tank with a sloping base, above which are
suspended one or more sets of screw propellers, pivoted around a horizontal axis attached
to a roller bridge, which are dipped inside the mass and move across the entire length of
the treatment tank, from the inflow wall to the outflow wall, thus mixing and pushing the
mass forward to make space for new waste matter. When the screw propellers reach the outflow
wall they are turned around their hinges, pulled out of the mass and then moved back to
the inflow wall, where they are once again dipped into the mass and begin a new cycle. The
air for the micro-organisms performing the biological process is pumped through the screw
propellers themselves, which are hollow inside. This kind of system features various serious
drawbacks, such as a loss of about 50% of the working time for the idle return of the screw
propellers across the treatment tank after each process cycle, the non-uniform progress of
the mass from the inflow side of the treatment tank to the outflow, due to the necessary extraction and re-immersion of the screw propellers inside the mass, and the prerequisite
of a treatment tank with a heavily sloping base, to help the mass in its progress, since
otherwise it would exercise too strong a resistence against the screw propellers,
jeopardising the correct operation of the system's mechanical parts. This loss of time
translates into a reduction of the treating capacity, while the non-uniform progress of the
mass, as well as the variation, in the order of 50%, of the time required by the waste matter
to achieve a sufficient degree of maturation, may completely alter the outcome, which is
measured as the degree of maturation and is closely linked to the time spent in the
treatment tank by the totality of particles composing the mass, and other parameters, such
as mixing and aeration.
Italian patent 23342 of 18-10-1983, deposited by Secit SpA, provides for a technique similar
to the one described in the Swedish patent,
whereby the screw propellers advance in the same direction as the mass, while in this case the screw propellers are removed from the mass by means of traslation along their axis,
perpendicularly to the base of the tank, and the aeration of the mass takes place through
protected pipes laid on the bottom of the treatment tank.
With the exception of the non-uniform advance of the mass, which defect is remedied by
the extraction and re-immersion of the screw propellers, which translate along their axes,
no remedy is found for the other drawbacks of the Swedish patent, on the contrary, to
these one must add the further disadvantage of having to provide for a building large
enough to house the entire plant, which is quite tall, so as to enable the lifting of the screw
propellers.
Since all plants of this kind must be adequately sealed from the outside, for obvious reasons
of environmental impact, a higher building, besides entailing higher construction costs, also
requires higher operating costs, due to the larger amounts of air to be circulated within the
building and then deodorized, since the number of change of air per hour must remain
equal.
Italian patent of 7-8-1987 in the name of Sorain Cecchini SpA describes a technique
whereby the organic matter is contained inside a preferably sloped treatment tank and one
or more sets of slanted screw propellers, suspended from a sliding bridge parallel to the
tank base, stir and move the mass, not by pushing it but by pulling it toward the outflow, in
order to reduce the stress exercised by the mass on the screw propellers.
In this case, the screw propellers move in an opposite direction compared to the mass, but
this plant too features the drawback of their idle return run, as well as the overturning of
the screw propellers at the end of the cycle and their re-immersion into the mass, thus
featuring the same drawbacks as the previous invention.
Disclosure of invention
The present invention relates to a biological waste treatment plant aimed to remedy the
drawbacks affecting the above mentioned inventions and to allow economies, with regard
to both the initial investment and operating costs.
The main objects of the present invention are: to eliminate of the dead time due to the idle return of the screw propellers;
to use horizontal treatment tanks and industrial pavings, without having to incorporate
any channels of pipes;
to guarantee a regular and uniform progress of the treated mass, thanks to the use of a
simple and easily adjustable system; to ensure the continuous and proportioned outflow of the mass from the tank, without the
need of any effluent clearing pockets; to guarantee the self-cleaning of the screw propellers, with the continuous elimination,
while operating, of the threads and rags which inevitably get wrapped round the screws;
to maintain a constant height of the mass in the tank, so as to compensate the reduction of
volume due to evaporation and to other chemical processes, by adopting simple measures;
to continuously remove of the dense and hardened layers of matter, which may accumulate
on the bottom of the tank, if they are not stirred by the screw propellers for a long time;
to ensure the forced aeration of the organic mass, so as to minimize condensation inside the building housing the biological treatment tank;
to recover the heat produced by the biological processing cycle and use it to heat the
ventilated air circulating inside the building, in the colder and damper season, thus
reducing humidity, with considerable benefits from the point of view of the enviromental imact.
The present invention is based on the principle that the waste matter to be treated is stirred
and moved exactly as if it were done manually, thus creating a close succession of heaps, by
means of mechanical tools such as screw propellers.
Accordmg to the present invention, the treatment tank is a horizontal rectangular tank into
which the organic solid waste is fed, either continuously or discontinuously, along one of
the longer walls, by means of conveyor belts or any other mechanical means, the processed
matter outflowing on the opposite side.
According to the preferred embodiment of this invention, above the tank there is a bridge
with a trolley to which two screw propellers are attached, in a slightly slanted position,
with the tips pointing towards the inflowing side. The screw propellers are lowered into the
mass near the inflowing side of the treatment tank and are then moved longitudinally
across the entire length of the tank by the bridge. Due to their inclination, the screw
propellers plough through the mass forming longitudinal furrows and expelling from the
treatment tank a volume of waste matter equal to the volume of the furrow.
According to this technique, the waste matter is cut longitudinally, thus separating a first
heap, which then flows out over the tank wall. After this first furrow has been made and
reached the treatment tank wall, the set of screw propellers remains inside the waste
matter and moves along the bridge to the inflowing wall, where it starts ploughing a new
furrow, thus making another heap, and so on, through a succession of furrows, until it
reaches the inflowing of the tank, where the screw propellers engage the fresh organic
matter and create the empty space for the inflowing waste matter. At this point the set of
screw propellers, having completed the cycle, usually at the end of the day, returns to the
starting point, where it remains immersed inside the matter, although it is possible to
remove it, if necessary, since it is attached to the bridge by means of a hinge.
The succession of heaps ensures the regular advance of the waste matter at each passing of
the screw propellers; at the same time the heaps are very close the one to the other,
separated only by a superficial furrow, thus achieving a high degree of optimization of the
treatment tank volume.
By gauging the pitch of the furrows, by means of a computer and relative programme, it is
possible to maintain the mass at a constant level, since it would otherwise diminish, due to
the effects of evaporation and other chemical reactions, while the slanting of the screw
propellers ensure the advance of the mass at the desired speed, thus making sure that it
remains inside the treatment tank for a suitable period of time.
By means of the computer and suitable programme, and of the slanted screw propellers, it
is possible to ensure the cyclic,thus furrowing of the entire mass, right down to the lowest layers preventing the matter from stagnating, since after a while it would become hard and
impermeable to air.
According to the present invention, blades are attached to the upper part of the screw
propeller stems so that, by the contrast with other fixed blades it is possible to cut any
threads and rags contained in the mass and which may wrap around the revolving parts,
eventually reaching the upper part of the screw propellers, thus avoiding any laborious
manual cleaning operations, which would require the stopping of the plant.
Furthermore, since the set of screw propellers, when forming the first furrow, would
determine the outflow from tank of the entire equivalent of a daily cycle, in a relatively
short period of time, thus requiring a large pocket to receive it before the subsequent
treatments, accordmg to the present invention, the outflowing side of the tank is provided
with a platform, along its entire length, where on the waste matter is temporarily held
while an extractor-batcher on the edge of the bridge gradually removes and batches the
treated waste matter throughout the forward and backward movement of the bridge, while
the furrowing takes place inside the treatment tank. This results in a regular and easily
adjustable outflow, capable of directly supplying the following mechanism without the need of any pockets.
Further advantages may be obtained, with regard not only to the biological process, but
also to the enviromental impact, by means of a special forced aeration system from the
bottom of the treatment tank and the recovery of the heat generated by the biological
process, thus enabling the pre-heating of the air for circulation inside the building, as well as the considerable reduction of the quantity of air, with enormous benefits for the
subsequent deodorization of the surroundings.
Brief description of the drawings
In order to explain the invention in question more clearly, a more detailed structural and
functional description of the preferred embodiment will now be given, with reference to the
accompanying drawings, in which:
Figure 1 shows a cross section of the treatment tank;
Figure 2 shows the plan of the tank;
Figure 3 shows a preferred angle of the screw propellers;
Figure 4 shows the thread cutting device;
Figure 5 shows two embodiments of the extracting device;
Figure 6 shows the aeration system;
Figure 7 shows a cross-section of the tank and of the building housing it.
Detailed description of the preferred embodiment
Referring to the figures, and in particular to figure 1, the organic mass (2) is fed into the
treatment tank (1), preferably in a continuous manner, by means of a conveyor belt (3), or
similar device. Above the tank (1) is a bridge (5) along which runs a trolley (6), to which is
attached a set of one or more screw propellers (7), characterized in that they (i) rotate
around their own axes and move from one end of the tank (1) to the opposite end, carried
by the bridge (5); (ii) move along the bridge (5) across the tank (1), from one end to the opposite end; (iii) may be overturned by rotating around their rotation axis (8), thus
enabling their extraction from the organic mass, if necessary.
Figure 2 shows a plan of the tank with the direction of movement of the screw propellers,
from the starting point (9) up to the end point (10), according to a fret-like movement, indicated with a dotted line. At the end of the movement from the ehd point (10) to the
starting point (9), the screw propellers are preferably extracted from the organic mass (2)
by rotating them around their axis (8), and this operation, as previously mentioned, occurs
at the end of the processing cycle, which normally lasts one day, since, according to the
preferred embodiment, the organic mass is mixed once a day. The overturning of the screw
propellers (7) is useful mainly to enable the bridge (5) to move away from the treatment
tank (1), for the purpose of maintenance, or to be moved over another tank, since the same
The preferred embodiment comprises two screw propellers (7), placed alongside one other, longitudinally, one of which traces yhe furrow while the other one finishes the work. The
entire run of the screw propellers is active and their fret-like movement is guided by a computer, whose programme provides for a number of different cycles, which differ for
small variations of the fret-like movement, so that the bottom end of the screw propellers
trace ever changing furrows, compared to the previous cycle, to make sure that the organic
mass is ploughed through its entire height.
Figure 3 shows the preferred embodiment with regard to the operating position of the
screw propellers (7) which, although they both skim over the bottom of the tank, have a
split end section to guarantee a more effective ploughing of the lowest layers of the organic mass.
As previously mentioned, the system is also provided with a device for cutting the threads
and rags, shown in figure 4, which may get wrapped around the screw propellers and
which inevitably tend to move upwards.
The blades (11) attached to the stem of the screw propellers cut the threads and rags
wrapping around the screw stems during the rotation, and which would otherwise require
the machine to be stopped, thanks to the counter-blades attached to the screw trolley (6).
Figure 5 shows two different embodiments of the organic waste matter extracting and
batching device.
The first device comprises a circular mill (13) carried by a telescopic arm (14), while the
second comprises a screw feeder (15) supported on a telescopic arm (16).
Both these devices move integrally with the bridge (5) and briefly penetrate the organic
waste matter to be extacted each time the bridge reaches one end of the tank to change its
direction, in this manner, while the screw propellers (7) furrow through the organic mass
(2) inside the tank (1), the extraction and batching device completes the outflowing
operation, thus ensuring the removal a sufficient amount of the mass such as to make space
for the inflowing matter, when the screw propellers run the first leg of a new processing
cycle.
It is well known that the organic mass must be adequately aerated, so as to supply oxigen to
the micro-organisms performing the biological process.
According to the present invention, the forced aeration system shown in figure 6 is
achieved by blowing the air into the organic waste matter from the bottom of the tank. To
this purpose, the bottom of the tank is symbolically divided, lengthwise, into a certain
number of zones (2/6), according to the width of the tank; the zones correspond to various
phases of the biological process on trasformation of the organic mass, along entire length of
the tank, and requiring different amounts of air for each phase. Each of the zones is served
by a specific set of pipes (18), laid on the bottom of the tank and perforated so as to allow
the air to pass through.
Item (17) is one of the manifolds, located outside the tank, from which the pipes (18)
serving a specific zone of the tank originate. Item (19) indicates the protection covering the
perforated section of the pipes (18), to prevent any infiltration by the mass, which could
block the pipes. Each manifold is directly connected to a fan (23), capable of blowing or
sucking air into or from the bottom of the tank. When the air is sucked, since it is quite warm (40-55°), it is first made to pass through a set of heat exchangers (22), which transfer the heat to the fresh air before this is used for ventilating the building housing the tank.
This arrangement is very important in those areas affected by a cold and humid climate, or
in the wet season, since the preliminary heating of the air, by enhancing its water vapour
carrying capacity, considerably reduces condensation, while at the same time reducing the
amount of air required for ventilating the building. This is an enormous advantage, from
the point of view of the environmental impact, because the air which passes through the building is charged with the smell and needs to be deodorized before being expelled into
the atmosphere; however, since the deodorizing process cannot be 100% effective, the atmosphere; lesser the amount of air requiring treatment, the lesser its polluting effect.
Figure 7 shows a cross-section of the treatment tank and of the building housing it, showing
the cross-section of the pipes for the forced aeration of the organic mass. It shows the pipes
(18) with the perforated sections lying on the bottom of the tank, the protection (19)
• covering the perforated sections of the pipes, the conduit (20) connected to each pipe (18),
for collecting the condensation, and the layer of permeable material (21) placed over both
the pipes (18) and the protections (19), to prevent any contact with the organic mass.
The plant for the biological treatment of organic waste matter according to the present
invention, has been described and illustrated by way of example only and the preferred
embodiment may be modified, according to any practical and technical requirements
falling within the inventive scope of the present invention.
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