Note: Descriptions are shown in the official language in which they were submitted.
2'~ X432 1
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A PROCESS FOR DISPOSING OF REFUSE WHICH INCLUDES
PATHOGENIC COMPONENTS
In its most general aspect the present invention relates
to a method for disposing of refuse which includes
pathogenic and/or toxic components.
More particularly this invention relates to a method for
the sterilisation and disposal of hospital refuse.
It is well known that the disposal of hospital refuse
currently constitutes a serious problem from an
environmental point of view. In fact, because of its
pathogenic germ content such refuse cannot be disposed of
via the usual discharge means authorised for the so-
called urban refuse.
On the other hand the extremely varied nature of the
composition of such refuse makes its disposal by
incinerator means equally problematic.
As well as artificial, synthetic or vegetable fibre
material (such as gauzes or cloths), fo:r example sheets
of the so-called one-time use type, such refuse contains
rubber, metal and plastics materials as well as
disinfectant residues and residues of. other medical
substances widely utilised in hospitals.
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These components (in particular the. plastics and
disinfectants) often contain fluorinated compounds which
have a well known tendency to generate compounds of the
tetrachlorodibenzodioxin type following treatments at
high temperature, such as are utilised in incinerators.
The risk and the noxious nature of. these latter
compounds, commonly called dioxins, is well known and
constitutes the main reason why the use of incinerators
for the disposal of hospital refuse is not acceptable.
For the reasons explained above the nece:asity of finding
a method of disposal of hospital refuse which overcomes
the problems of the environmental impact caused by the
1!~ use of incinerators is currently very strongly felt.
In order, on the one hand, to overcome the disadvantages
related to the use of incineration insta:Llations and, on
the other hand, to overcome the risk of allowing the
survival of pathogenic germs which are a:Lways present in
hospital refuse, methods have been proposed which provide
for the sterilisation of the hospital refuse before being
sent to the normal urban refuse discharge.
2!~ In one of these methods the sterilisation is effected by
subjecting successive charges of refuse to respective
heat treatments in rotating drums in a discontinuous
manner.
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This method has, however, the disadvantage of a high fire
risk because of the presence of cellul.osic fibres and
solvents in the materials to be treated.
This fire risk is not even eliminated by working in the
absence of oxygen in that the peroxide groups present in
the rubbers as a consequence of the vulcanisation process
can act to support combustion in place: of atmospheric
oxygen.
Moreover, in this batch process the individual charges of
refuse have a significant mass such that the heat
treatment is necessarily non-uniform and consequently the
complete sterilisation throughout the whole mass of the
material is not guaranteed.
To overcome the recognised disadvantages of the batch
process (the treatment of successive loads of large mass)
attempts have been made to sterilise hospital refuse by
utilising a technalogy based on the use of microwaves;
even in this case there are serious problems related to
the safety of the installation.
Micrometric waves at high energy (microwa.ves) utilised in
such installations can in fact be extremely dangerous,
for example as a result of uncontrollable and
unpredictable reflection phenomena due to the presence
of, for example, metal objects in the refuse to be
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treated. Because they require very strict safety
measures and highly specialised personnel such
installations involve very high management costs and
notwithstanding this do not always gave satisfactory
results.
The problem on which the present invent: ion is based is
that of making available a method for the disposal of
hospital refuse which can satisfy current. requirements as
1.0 explained more fully above, whilst contemporaneously
overcoming the disadvantages discussed with reference to
the prior art.
The technical solution of this problem is to subject
small quantities of hospital refuse maintained in a
highly turbulent state and constituting a substantially
continuous flow of material to a sterilising heat
treatment.
According to this idea the said technical problem is
resolved according to the present invention by a method
for disposal of hospital refuse and the like
characterised by the fact that it comprises the steps of
- grinding hospital refuse to obtain a comminuted
material which can be pumped;
- sterilisation heat treatment of the said
comminuted material disposed in a thin layer and
maintained in a highly turbulent condition
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- cooling of the said sterilised com~minuted material
and disposal thereof by discharge.
In accordance with a further characteristic of the
invention, the said sterilisation heat treatment is
effected by making the said comminuted material flow in
a continuous thin and turbulent layer in contact with a
heated wall.
Advantageously the method of this invent=ion is put into
practice by utilising sterilisation apparatus comprising
a cylindrical tubular body provided with a heating
jacket, an inlet opening for the material to be treated
and a discharge opening for treated material, and a
paddle rotor rotatably supported in the cylindrical body
and driven to rotate at 200 - 1.500 revolutions per
minute.
Such apparatus will be identified hereafter in the
description and irr the subsequent claims with the term
"turbosteriliser".
By utilising such apparatus the method of disposing of
hospital refuse according to th.e present invention
comprises the steps of:
- comminuting the said hospital refuse to obtain a
pumpable comminuted material,
- supply of a continuous flow of this material to
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the inlet of a turbosteriliser having cylindrical
internal walls heated to a temperature of 300 - 500°C and
in which the paddle rotor is rotated at a speed lying
between 400 and 1500 revolutions per minute,
- centrifuging of the said comminuted material to
form a thin tubular layer which flows in contact with the
said heated wall towards the said discharge aperture with
contemporaneous sterilisation of the comminuted material,
- cooling and recovery of the sterilised and
comminuted material and subsequently de:Livering it to a
discharge outlet.
Contemporaneously with the heat steri:Lisation cf the
comminuted material maintained in a dynamic thin layer it
is dried by the removal in the form of steam of the
moisture originally contained in it, as well as the
removal of all the substances which evaporate at the
sterilisation temperature reached.
In accordance with a further characteristic of this
invention the steam generated during the sterilisation
heat treatment of the comminuted materi<~l is recovered,
subjected to a further sterilisation at nigh pressure and
condensed to be subsequently reincorporated into the
sterilised comminuted material, with which it is
delivered to the discharge.
Advantageously the condensed steam and sterilised
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comminuted material are intimately mixed and
simultaneously cooled to obtain a paste which is
subsequently subjected to compaction and briquetting and
then discharged.
The advantages and the characteristics of this invention
will become more apparent from the following description
of an embodiment of a process for continuous
sterilisation of hospital refuse, made from hereon with
reference to the attached drawings by way of indication
only.
Figure 1 is a schematic representation of apparatus for
performing the process of the invention;
Figure 2 is a schematic representation of the
apparatus used to perform a variant in the said process;
and
Figure 3 schematically illustrates a complete
installation for disposal of refuse containing pathogens,
2~ including the apparatus necessary for performing the
process of the invention.
With reference to Figure 1 the apparatus utilised for the
process according to the invention for continuous
sterilisation of hospital refuse comprises first
apparatus A which hereinafter in the description will be
called a turboster:iliser, second apparatus R hereinafter
called a turbocooler, a high pressure steriliser SP and
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a condenser C.
The turbosteriliser A essentially compri;ses a cylindrical
tubular body 1 preferably disposed with its axis
horizontal, closed at its opposite ends 2,3 and provided
coaxially with a heating jacket 4 intended to receive
appropriate heating means, for example an electrical
resistance, a diathermic fluid or oil, or the like.
1.0 The tubular body 1 is provided with an inlet aperture 5
for comminuted material obtained by finely comminuting
hospital refuse, and a discharge apex-ture 6 for the
treated comminuted material.
1.5 This aperture 6 is in communication via <~ duct 7 with the
inlet aperture 5' of the turbocooler R .
Rotatably supported in the tubular body 1 is a paddle
rotor 9. The paddle 10 of this rotor are disposed
20 helically and are orientated to centrifuge the comminuted
material against the internal wall of i=he tubular body
itself and simultaneously to convey this material towards
the discharge aperture 6. A motor 13 is provided to
drive the paddle :rotor at a speed vari<~ble from 400 to
25 1500 revolutions per minute.
The turbocooler R essentially comprises a cylindrical
tubular body 1', preferably disposed with its axis
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horizontal, closed at its opposite ends 2'3' and provided
with a coaxial cooling jacket 4' :intended to be
traversed, for example, by a refrigerant liquid.
The tubular body 1' is provided with an inlet opening 5'
for the material treated in the turbosteriliser A and a
cooled material discharge opening 6'
A paddle rotor 9' is rotatably supported in the tubular
body 1', the paddles 10' of which are disposed helically
and are oriented to centrifuge and simultaneously convey
the material subject to treatment towards the outlet.
A motor 13' is provided for driving the rotor 9' at a
speed variable from 400 to 100 revolutions per minute.
The high pressure steriliser SP is of conventional type
and is in communication with the turbosteriliser A via a
suction-blower unit. 8 and, on the opposite side, with the
condenser C. This latter, which is of conventional type,
is in turn in contact with the turbocooler R through a
pump P.
Advantageously the delivery duct of the pump P is in
2~ communication with the interior of the turbocooler R via
a liquid inlet aperture 11 provided close to the inlet
opening 5' for the sterilised comminuted material coming
from the turboster:iliser A.
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With reference to Figure 2, in which all the same
components as those already described have the same
reference numerals, the apparatus used in a variant of
the method of the invention includes a stabiliser S
5 maintained at a temperature lying between 100 and 300°C,
which acts to determine the time for which the product
leaving the turbosteriliser A remains at high
temperature.
10 With reference to Figure 3, the installation for disposal
of pathogen-containing refuse comprises, in addition to
the apparatus already illustrated in. the preceding
Figures, an indicated with the same reference numerals,
a mill of conventional type, for example a multiple mill,
the output product of which is continuously fed to the
turbosteriliser A.
According to the method of this invent_Lon the hospital
refuse is subjected wholly (that is to say all of the
components of which it is composed) to a forced grinding
in an appropriate mill until it reache:~ an appropriate
grain size such that it can be pumped or conveyed in a
screw conveyor; in general, and pr~sferably, these
components, after comminution, have an almost powder-like
consistency, with a moisture content variable from 5 to
30o by weight.
A continuous flow of the various different comminuted
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components thus obtained is fed continuously to the
turbosteriliser A (through the inlet aperture 5 thereof)
from the input of which it is taken and mechanically
"worked" by the paddles of the rotor 9, which are
maintained at an appropriate speed of rotation.
The speed of rotation of this paddle rotor 9 is chosen in
such a way that from the inlet of the turbosteriliser A
the comminuted material is centrifuged against the hot
internal wall of the turbosteriliser itself and
accelerated (with respect to the speed of flow at the
inlet) towards the outlet so as to be "transformed" from
a solid vein flow into a thin tubular .Layer dynamic in
substantial contact with the hot wall of the
turbosteriliser, dynamic in that it is continuously
displaced towards the outlet opening; the comminuted
material is maintained in a highly turbulent state within
the said thin tubular layer by the mechanical action of
the paddles of the rotor.
It is thus apparent that all of the individual particles
of comminuted material are indiscriminately brought into
contact with the hot wall of the turbosteriliser for a
very large but indefinite number of times, thereby
undergoing a corresponding number of heat. exchanges, just
as corresponding heat exchanges are experienced by the
remaining particles of the thin layer. Consequently the
sterilisation heat treatment is guaranteed for each
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particle of this thin layer contrary to what occurs in
the bulk treatment of hospital refuse in the prior art.
It has been established that wall temperatures of between
200 and 500°C, and preferably between 350 and 400°C, are
more than sufficient for a total sterilisation of
hospital refuse thus treated.
It is to be noted that simultaneously with the
sterilisation, drying of the (originally wet) r_omminuted
material also takes place with the gene=ration of steam;
this steam is more than sufficient to render the material
itself non-flammable, thereby eliminating any possible
risk of fire.
To this end a flow of steam or inert gas can
advantageously be introduced into the turbosteriliser.
The vapours generated within the turbosl=eriliser, which
include steam and substances which evaporate at the
sterilisation temperature used, are recovered, for
example sucked out from the turbodrier itself and
subjected to a sterilisation at high pressure, preferably
10/12 atmospheres, and to condensation.
The sterilised and dry comminuted material at the output
of the turbosteriliser can be sent, after cooling, to a
conventional discharge.
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In accordance with a further characteristic of the
present invention this material is supplied to a
turbocooler into which the condensed steam mentioned
above is simultaneously supplied. In tree turbocooler an
intimate mixture between the conde~nsate and the
sterilised dry comminuted material takes place to obtain
a paste which, at the output of the said turbocooler, has
a consistency and a temperature allowing it to be easily
compacted and briquetted into the form of blocks. These
blocks are subsequently discharged or sent to other
destinations.
In a preferred embodiment of the invention the material
at the output of the turbosteriliser is sent to a
stabiliser S in which it is maintained at a temperature
lying between 100 and 300°C for a sufficient time, for
example 2-10 minutes to guarantee the total elimination
of sporogenic germs.
The said stabiliser can be constituted by a static
furnace with a t:Lmed discharge o:r, preferably, a low
speed screw conveyor system.
The high pressure sterilisation can be replaced by other
known sterilisation systems adapted for gases and
vapours, such as, for example, those based on ultra
violet rays.
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In Figure 3 is shown the arrangement. of a complete
installation for performing the method of the invention
which includes a mill, usually of the multiple acting
type able to comminute material of diverse consistency,
such as, for example, plastics, rubber, cellulose, glass
and steel and continuously to supply the turbosteriliser
A described above. The installation i:~ completed by a
high pressure steriliser SP, a condenser' C, a stabiliser
S, a turbocooler R and apparatus, not shown, for
compaction or briquetting of the product at the output of
the turbocooler R.
EXAMPLE
By utilising the apparatus shown and described above, and
following the method of the invention, the material
coming from the hospital refuse comminution step in the
form of a powder containing an average moisture of about
20o by weight, was continuously supplied into the
turbosteriliser A at a flow rate of 300kg per hour, in
co-current with a flow of saturated steam.
The wall temperature was controlled about the value of
350°C, whilst the speed of rotation of the paddle rotor
was maintained constantly at 850 revolutions per minute.
After about three minutes the flow of steam was
interrupted, whilst after a delay time of ten minutes
dried comminuted material was discharged from the
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turbosteriliser. This material, having a moisture
content of 1.5o by weight and a temperature of 130°C was
then fed continuously into the stabiliser S. The said
material was maintained at a temperature of 150°C for ten
5 minutes before being discharged and fed continuously into
the turbocooler R.
The vapours generated in the turbosteri:liser, aspirated
out from it were subjected to a pressure of twelve
10 atmospheres in the high pressure steriliser SP and
condensed in the condenser C.
The sterilised and stabilised comminuted material was
then intimately mixed with the sterile liquid condensate
15 coming from the condenser C in the turbocooler R.
The wall temperature in the turbocooler R was about 0°C,
whilst the speed of rotation of the paddle rotor was
maintained constantly at 650 revolutions per minute.
After a delay of about ten minutes a paste was discharged
from the turbocooler R which was subsequently sent to
compression in the compactor.
A micro biological examination conducted on samples taken
both from the output product from the turbocooler and the
product output from the turbosteriliser, after incubation
at 20° and at 37° respectively, both in aerobic and in
anaerobic conditions, detected absolutely no development
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of microbic forms.
The invention thus conceived can be subject to variations
and modifications, all lying within the ambit of
protection thereof. It remaining understood that the
critical fundamental condition of the method of this
invention for the continuous sterilisation of hospital
refuse is constituted by the heat trE=_atment of this
refuse reduced to comminuted material of appropriate
grain size in a thin and dynamic layer, many variations
can be introduced thereto even at the level of the
composition of the said comminuted material, such as the
chemical/physical quantities in play, and the structural
characteristics of the apparatus, all a.s a function of
the particular and contingent requirements which it is
intended to attribute to the final product, beyond those
specifically aimed at by the present invention. Thus,
for example, additives such as binding substances can be
added for the purpose of modifying the characteristics of
the final product.
