Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to the treatment of soiled
and waste materials from hospitals and oth~r sources of
biomedical waste materials.
Proper disposal of medical waste materials from
hospitals and other sources has become a matter of
increasing concern in recent years. A most effective way
of disposing of such materials has been incineration, but
it is difficult to ensure that incineration facilities
operate and many do not produce a sufficiently steady
supply to permit cost effective and efficient incineration
with proper controls to avoid discharge of harmful
emissions.
Most hospitals have steam laundries for the
laundering and recycling of soiled material such as bed
linen, gowns, etc. which can be reused. Such facilities
require a supply of low pressure steam, usually obtained
from a central heating plant.
It is known in large incineration plants to use a
waste boiler to recover heat from waste gases from the
incinerator, steam from the boiler being utilized to drive
a turbine yenerator producing electricity or used to
provide other steam requirements such as supplementing the
steam requirements of a hospital.
Typical examples of modern incinerators are
described in a brochure published by Ecolaire Canada Ltd.
entitled "Institutional-Industrial-Municipal Incineration
and Energy Recovery Systems". This brochure suggests at
page 10 that a hospital can supplement its steam supply for
laundry and heating purposes by heat recovery from an
incinerator.
Typical examples of turbine generators are described
in a brochure "Elliott Turbine - Generators" published by
Elliott Company.
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It is an object of the present invention to provide
safer and more efficient handling of soiled medical and
other and waste materials from hospitals and other sources
of biomedical waste. We have determined that, by
centralizing the incineration of medical wastes from a
group of hospitals and other facilities producing solid
waste in a given area and centralizing the laundry
facilities for the hospitals and possibly other institu-
tions at the same site, not only can the expected economics
of scale associated with centralization be achieved, but a
more efficient thermal cycle can be utilized to achieve
greater energy savings. Furthermore, handling facilities
~`or soiled materials can be automated to a greater extent,
thus reducing the risk to operating personnel, and reducing
the numher of persons exposed to risk.
According to the invention, there is provided a
method for the centralized treatment of soiled launderable
and waste materials from a group of hospitals and other
sources of biomedical and biomedically tainted materials,
comprising:
a) separately conveying to a treatment site both
materials which can be recycled by laundering and materials
which must be destroyed;
b) incinerating said materials to be destroyed in a
two stage inc:ineration process, in a first stage of which
the materials are combusted under oxygen deficit condi-
tions, and volatile constituents are separated from solid
residues, and in a second stage of which the volatile
constituents are combusted under oxygen surplus condi-
tions,
c) passing waste gas from said second incinerationstage through a waste heat boiler to generate high pressure
steam;
d) reducing the pressure of said steam whilst
recovering energy therefrom by passing it through a steam
turbine coupled to an electrical generator, so as to
provide low pressure steam; and
e) using said low pressure steam to steam launder
said materials which can be recycled by laundering.
The invention also extends to apparatus for carrying
out the above method~
It will be noted that waste heat fxom the inciner-
ator is used to generate high pressure steam which is used
to generate electricity, exhaust steam from ~he turbine
being utilized to operate the laundry, thus enabling more
effective energy recovery than when low pressure steam is
generated directly.
Further features of the invention will become ap-
parent from the following description of a presently
preferred embodiment of the invention.
In the drawings:
Figure l is a schematic diagram of a centralized
plant in accordance with the invention or the treatment of
soiled and waste materials from a group of hospitals; and
Figure 2 is a flow diagram illustrating the operation
of an exemplary embodiment of the invention.
Referring to Figure 1, waste material from a group
of hospitals is trucked to a treatment site, and the bulk
of it, compr:ising relatively low risk general waste, is
discharged into a hopper 2, from which it is fed into a
first chamber 4 of an incinerator 6 by a ram feeder 8 at a
rate such as to maintain a reasonably constant thermal
input to the system, whilst air or a mixture of air and
steam is fed to the chamber at a rate such that complete
combustion cannot take place. A second hopper 3, feeding
directly into the chamber 4, is provided for the disposal
of high risk or waste which will only form a minor portion
of the waste material received.
A further ram expels ash from the first chamber into
a water filled ash pit from which it may be recovered for
disposal, whilst gases from th~ first chamber are passed
to a second combustion chamber 10 in which excess addition-
al combustion air is added so as to complete combustion.
Gas burners are provided in the first and second chambers
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to enable optimum operating temperatures to be attained
during start up and maintained during operation. Further
details of typical operation and control of such an in-
cinerator are to be found in the Ecolaire brochure to
which reference is made above.
Waste gases from the incinerator are passed to a
waste heat boiler 12 generating steam at relatively high
pressure, typically 600 psig, and this steam is fed to a
steam turbine 14 coupled to an electrical generator 16.
Exhaust steam from the turbine is piped to the laundry
described further below. Çases from the waste heat boiler
are passed through a scrubber and absorption column 18 and
are exhausted to a stack 20 by a fan 21 through a bag
house (not shown). These gas cleaning stages are conven-
tionally engineered to meet applicable environmentalstandards and their design forms no part of the present
inventlon .
In the laundry, soiled materials are shipped to the
plant in laundry carts 22, whose contents are weighed at a
weigh station 24 and charged into a washing machine 26,
using water heated by or condensed from exhaust steam from
the turbine. After preliminary water extraction, the
materials are sorted in a sorting station 28 and if not
requiring ironing are tumble dried in a steam heated tumble
dryer 30 and a steam heated finish dryer 32, whereafter
they are folded at a folding station 34, and wrapped at a
wrapping station 36. Items requiring ironing are passed
through a steam heated ironing machine 37 to the folding
or wrapping station. The tumble dryer may be provided
with a heat reclaim wheel 31 in order to improve its
thermal efficiency.
Ir the meanwhile, the carts 22 are passed through a
steam cleaning station 38, and receive wrapped laundry
from the wrapping machine ready for return to their
original source.
A simplified flow diagram for an exemplary installa-
tion of the apparatus is shown in Figure 2. This assumes
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an input of 2000 tons/per year of bio-medical wasted to
the incinerator 6, which for the purposes of this example
is presumed to operate 12 hours per day, 5 days per week,
equivalent to about 640 lbs/hour. The flue gases pass
through the waste heat boiler 12, generating about 4700
lbs/hour of high pressure steam which is applied to the
turbine 14 driving the generator 16 to produce about 120
kw of electric power, and about 4000 lb/hour of low pres-
sure steam for use in the laundry 40. Condensate from
the various steam heaters used in the laundry 40 is
recycled to a water treatment plant 42 together with make
up water to provide a feed of about 9 gallons per minute
to the waste heat boiler 12. About 16 gallons per minute
of make up water, which may contain chemicals such as
alkali to neutralize acid gas components, are fed to the
gas scrubber, whilst about 1 gallon per minute of residue
is fed to the ash pit together with ash from the inciner-
ator 6. The laundry will process about 1200 pounds of
material (bed linen, etc.) per hour.
It should of course be understood that all of the
above figures are exemplary only and approximate. A fair
degree of flexibility in operation is obtainable for
equipment of a given size and rating both by varying the
rate of throughput of waste materia], and by adjusting the
hours of operation of the apparatus. It is believed that
the electrical output of the system should in a typical
installation approximately equal the electrical require-
ment. It is also desirable to provide for any net surplus
to be returned to the supply grid. An external electrical
supply will certainly be necessary during startup of the
apparatus and when the apparatus is not in operation, as
will an uninterruptable emergency supply to maintain proper
control of operation of the incinerator in the event of a
power outage. A gas or other fuel supply to the
incinerator is also rec~uired for startup, and supplying
the burners which maintain correct combustion conditions
in the two chambers during operation.
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Although the apparatus and method described is
dependent upon having a group of hospitals as its major
source of material to be treated, it can advantageously
also handle supplementary bio-medical wastes from other
sources such as laboratories, as well as laundry from
other institutions. Furthermore, municipal and other
wastes may be processed if this will assist in efficient
operation.
