Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 16B083
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Treatment of Acidic Organic and Alkaline Inorqanic Wastes
BACKGROUND_OF~ T~E~ I~VEN~'ION
Modern industrial processes create a wide range of
i unuseable waste products. In addition, large amounts of refuse
of various kinds from domestic households and institutions are
generated. All of these waste materials require non-polluting
disposal or destruction. A number of disposal techniques are
known but these techniques mainly have application to specific
types of waste. Municipal refuse, for example, may be
comminuted, separated into useful and waste components and the
waste components destroyed by combustion, the ash residue being
disposed of as landfill. Acid wastes ~rom industrial processes
may be neutralized with caustic and the neukral product disposed
of in waterways. Alkaline wastes may be slmilarly neutralized
and discharged into waterways. Toxic wastes and other hazardous
sludges may be encapsulated into a structural material, for
example, a fly ash/hydrated lime mixture and the resultant
product disposed of in landEill. The problem face~ by industry
and by municipalities has been to devise waste treatment or
waste disposal methods which produce non-polluting, small volume
effluents, making use of facilities which are economic to
construct and operate and which are capable of treating more
than one type of waste product.
SUMMARY OF THE INVENTION
The present invention relates to the destruction of
organic wastes by substantially complete combustion to produce
an acid gas effluent and to treat the acid gas
effluent with waste alkaline liquids or slurries~ In particularr
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the presen-t invention contemplates the complete destruction of
combustible organic wastes without the release to atmosphere of
any harmful by-product gases or vapors. In addition, the hot,
gaseous products of combustion are employed -to desiccate a flow
of liquid or slurry alkaline waste.
A large number of organic wastes are produced in
technologically advanced societies and include, for example,
waste hydrocarbon oils and solvents from metal ~abrication,
expended hydraulic oils, oil refinery wastes, paints and plastics
industry wastes and the like. Similarly, large amounts of
alkaline liquid arld slurry waste products are generated in metal
descaling, lime treatment processes, sugar ~anufacture, textile
treatment, chemical processes and the like. Typically, organic
wastes are disposed of by combustion, the products of the
combustion being discharged to the environment sometimes after
appropriate cleansing or neutralization. Alkaline wastes are
typically neutralized by acid and/or are solidified or admixed
with flyash or similar material and disposed of in landfill.
The present invention provides a method for simultaneously
treating alkaline waste liquid or slurry and combustible organic
waste, which method comprises the steps of:
ta) combusting organic wastes in a combustion reactor
to produce a gaseous effluent containing molecules, which in
the presence of water, produce strong acids,
(b) directing a flow of dissolved or slurried aqueous
alkaline waste to a dryer reactor,
(c) directing the said gaseous effluent to the said
dryer reactor wherein the said acidic gaseous effluent is caused
to react with the said alkaline waste to precipitate and
simultaneously desiccate the said alkaline waster while the
said acidic gaseous effluent is substantially neutralized~
(d) directing the said precipitate and the said
neutralized acid gas effluent from the said dryer reactor to a
solids collection station, and
(e) separating said neutralized gas from the said
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precipitate fox discharge to the a-tmosphere while the
precipitate is collected for disposal.
DESCRIPTION OF THE DRAWING
. .
The drawing is a block flow diagram showing the method
of the invention-
DESCRIPTION OF T~IE PREFER~ED EMBODIMENT
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The method of the invention is suitable for treatment
of substantially all organic matter whether solid or liquid.
Solid organic wastes such as plastic material, resins, fibres,
and the like may require pre-combustion preparation such as by
comminution by well-known methods. Lean liquid organics not
having sufficient fuel value for self-sustained combustion require
the addition of a secondary fuel such as fuel oil or they may be
blended with richer organic liquid wastes. The alkaline waste
capable of treatment by the method of the invention may requixe
screening, water dilution or agitation prior to gaseous
neutralization. Both types of waste, prior to treatment are
usefully held in storage reservoirs and their pre-treatment
composition determined by chemical/physical analyses~
The method of the invention is diagrammatically shown
in the drawing. An alkaline waste which may comprise, inter alia,
high calcium lime, magnesia, sodium hydroxide and the like in the
form of an aqueous solution or slurry is held in an alkaline waste
reservoir Erom which it can be delivered by pump (not shown) to
the dryer reactor. Organic liquid waste which may comprise, for
example, oil refinery discharge, is held in a liquids reservoir
from which it can be delivered by pump (not shown) to a com-
bustion reactor or incinerator. Organic solid waste comprising,
for example, plastics residue, is held in a reservoir for delivery
3Q to the combustion reactor by, for example, mechanical or pneumatic
conveyor (not shown). Upon combustion, the organic waste is
converted into an acidic gaseous mixture containing, ~or example,
hydrogen chloride, sulfur dioxide, nitric oxides, carbon dioxide,
nitrogen, oxygen, water vapor plus trace amounts of other gases,
and some aerosols. Some small amounts o~ additional solids,
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mainly incombustible mineral ash, ma~ also be produced
The hot gases from the combustion reactor are preferably, but
not essentially; cooled to a temperature of about ~50C. in
a cooler before being introduced into the dryer reactor where
they are brought into contact with the incoming flow of alkaline
waste. Care must be taken to maintain the temperature o~ the gas
above its dew point, that is, the temperature at which the
components of the gas are converted to a vapor or li~uid. The
rate offlow of alkaline waste liquid or slurry to the dryer
reactor is based upon its alkaline content and is maintained
so that the alkaline component of the waste liquid is in
stoichiometric excess of the acid component of the combustion
gases. The hot, acidic combustion gases react with the fluid
alkaline waste within the dryer reactor to produce a salt
precipitate and water as follows, for example:
NaOH + HCl > NaCl ~ HOH
or
Mg(H2) ~ H2S~ MgS04 + 2HOH
Simultaneously, the aqueous component of the alkaline waste is
driven off as water vapor. In the dryer, the combus~ion gases
are effectively cooled during the reaction with the liquid or
slurry alkaline waste resulting in a substantial reduction in
gas volume with a consequent reduction in the rate of flow of
the effluent gases. Additionally, the lowering of the
temperature of the gaseous dryer e~fluent permits the use of
a variety of solids collecting or filtering devices which would
otherwise not be possible with gases at near combustion
temperatures. The solid products of the reaction which form
when the excess water is evaporated within the dryer reactor
consist of a mixture of metal salts, e.g. chlorides, sulfates,
carbonates and the like, in the form of small particles or dust.
The heavier solid products precipitate to the bottom of the dryer
reactor and are removed for subsequent disposal. The lighter
solid products are carried by the unreacted combustio~ gases,
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e.g., carbon dioxide, nitrogen, oxyyen, water vapor, to a solids
collector such as a baghouse, where the solids are removed from
the gas stream by filtration, centri~uye or cyclone or similar
means and thereafter packaged or compressed for landfill disposal.
The harmless gases are vented to atmosphere.
The apparatus used to practise the method o~ the
invention is substantially conventional apparatus such as is
used in standard chemical or engineering processes. The com-
bustion reactor or incinerator may be, for example, a rotary
kiln, for organic sludges or a semi-suspension or mass-burning
refuse incincera-tor, etc. The combustion gas cooler, when used,
can be for example, an economizer or an air-to-air heat
exchanger. The dryer reactor can be a spray dryer of the high-
pressure nozzle or rotating disc atomizer type. The solids
collection apparatus is preferably a baghouse type collector,
for example, a pulse-jet type. The various reservoirs, piping,
pumps~ ducts, fans, stacks and auxiliary apparatus are conven-
tional in design or modified as necessary and the material o~
construction is selected for the particular process conditions
encountered.
EXAMPLE
A waste treatment facility o~ the present invention was
utilized to process liquid organic wastes ~mixed oil refinery
waste) and alkaline wastes ~lime treatment process waste liquor~
as follows. Organic waste was fed by pump to a stationary
incinerator at a rate of 250 liters per minute where it was
burned to produce an exhaust gas effluent at 700C. The exhaust
gas was cooled to 450C in an air-to-air heat exchanger and
directed into a spray dryer reactor. Approximately 85.1 liters
per minute of alkaline waste liquor was sprayed into the dryer
reactor where it reacted with and cooled the combustion gas
effluent to 200C. Greater than 80% of HCl and 50% of SO2 were
removed from the gas effluent in the spray dryer. The
substantially neutralized gas effluent was directed to a
baghouse for particulate remo~al. The particulate material
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recovered from the spray dryer and baghouse amounted to 20.1
kilograms per minute of operation or abou~ 38.6 cubic meters
per day at a density of 750 kilograms/per meter3. On an annual
basis, 142,000 cubic meters per year of combined organic and
alkaline waste is reduced in volume by 91.3% to 12,300 meters3
of dry particulate, suitable for landfill.
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