Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Other known processes (so-called wet combustion
or wet oxidation) involve combustion of aqueous sludges at
elevated temperatures and pressures in a reactor without
incineration (flamelessly) and without prior thickening of
the sludge, but below the critical temperature of the water.
Due to the prevailing thermodynamic conditions in these
processes no steam is formed in the reactor itself, and the
liquid reaction products are first expanded and then sub-
jected to phase separation in a separator connected to the
reactor, whereby the liquid reaction products are separated
from the combustion products and steam is recovered or
obtained. (See German Published Patent Applications St
2017/IVc/85c of December 8, 1955 (inventor: F.J. Zimmermann)
and DE-OS 26117340 of November 4, 1966 (inventor: L.A. Pradt),
and Meinck, "Industrial Waste Waters," 4th Edition, 1968,
pp. 143-144.)
However, in the above wet combustion processes,
the reconditioning of the resulting combustion products is
relatively expensive, and furthermore, in many cases the
products are subjected to a furthercostly aftertreatment
because of the hydrocarbons present resulting from the
combustion stage.
In German Published Patent Application DE-OS
2304273 published on August 1, 1974 (inventor: Dille et al.),
there is disclosed a process for the treatment of sulfide-
containing waste waters, wherein the waste waters are mixed
with a fuel and converted to synthesis gas at elevated tem-
peratures and pressures. Hot synthesis gas from the reactor
is quenched, washed and cracked or broken down into its
components.
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SUMMARY OF THE INVE~TIO~
An object of this invention is to provide a
process and an apparatus for oxidizing aqueous dispersion of
sewage sludges and the like which contain combustible or
oxidizable dry substances.
Another object of this invention is to provide
a process and an apparatus for oxidizing aqueous dispersions
of sewage sludges and the like, wherein heat energy obtained
from the oxidation of the sludges is almost entirely utilized
to supply the total thermal requirements for treatment of the
sludges including thickening, i.e. the total thermal treat-
ment of sludges is carried out solely with the heat energy
obtained from the oxidation of the sludges, without the
need for using additional fuels.
A further object of this invention is to pro-
vide a process and an apparatus for oxidizing aqueous dis-
persions of sewage sludges and the like wherein dissolved
salts contained in the untreated sludge are retained in
the residual water of the dehydrated sludge during the '
thermal treatment process.
In accordance with a broad aspect of the in-
vention, there is thus provided a process for the thermal
treatment of untreated aqueous sludges which contain com-
bustible matter, comprising thermally thickening the un-
treated sludge by heat exchange with oxidation products
obtained from oxidation of previously thickened sludge,
oxidizing the thickened ~ludge to generate ~as and steam
oxidation products by natural oxidation processes
carried out in the gas phase at temperatures above the
critical temperature of steam. Heat exchanging the
oxidation products with incoming untreated sludge to
thermally thicken,the untreated sludge, whereby the steam
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oxidation product is condensed, and separating and recovering
for further uses the phases of the oxidation products.
According to another broad aspect of the inven-
tion, there is provided in a process for the thermal
treatment of aqueous sludges, in particular of clarification
sludges, in which the sludge is thickened by indirect heat
exchange, using the combustion heat, and then oxidized by
being subjected to combustion at elevated temperatures. The
improvement wherein:
(a) the combustion takes place under excess
pressure in a pressure-tight furnace, in the gas phase at
temperaturesabove the critical temperature of steam,
(b) the sensible heat and heat of condensation
contained in the resulting pressurized mixture of steam
and combustion gas is coupled to following heat exchangers
and applied to preheating the combustion air, to pre-
heating the sludge, and to thickening the sludge; and
(c) the phases of combustion gas, steam and
condensate arising in the thermal thickening are separately
drawn off and supplied for a further utilization.
According to yet a further aspect of the in-
vention, there is provided an apparatus for the thermal
treatment of untreated aqueous sludges which contain com-
bustible matter, comprising thin layer evaporator means
connected to oxidation furnace means, the outer chamber
of the evaporator means being in communication with
oxidation products exiting from the furnace means whereby
sludge entering the inner chamber of the evaporator means
is thermally thickened by heat exchange with the oxidation
products, and the furnace means communicating with the
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inner chamber of the evaporator means for passage of the
thermally thickened sludge from the evaporator means to
the furnace means.
For a better understanding of the present
invention, together with other and further objects and
features thereof, reference is had to the following de-
tailed description of a preferred embodiment taken in con-
junction with the accompanying drawing.
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DETAILED DESCRIPTION OF THE INVEMTION
The process of this invent~on will be better understood
¦by way of example with reference to the accompanying drawing
which is a schematic depiction of the apparatus for carrying
out the process.
Sludge from a clarification plant with 95% water conten~
in line 24 is pumped by pump 16 through heat exchangers 14 and
17 and into a preliminary concentrator and/or sieve separator 1.
The sludge settles to the bottom of the concentrator, exits
through line 25 into a sludge disintegr,ator 20 and is pumped
therefrom in line 26 by pump 21 through a heat exchanger 18 and
into heating chamber 27 of a thin layer evaporator 2. The
thickened sludge containing 80% water exits from the evaporator
through line 28 and i8 pumped by pump 9 through heat exchanger
7, wherein it is heated to a temperature of about 200 C., and
passed into furnace 3, wherein it is oxidized, i.e. it is either
burned or carbonized at low temperature (degassed) or is gasified.
Ashes from the burned sludge are drawn off through exhaust line
4 and will be further described below.
Oxidation gases and steam as a mixture exit from the
furnace through line 29 and pass through heat exchanger 5, line 8,
heat exchanger 7, line 30, filter 10, and line 31 into outer
heating chamber 11 of exaporator 2, wherein the gases and steam
indirectly heat the sludge in the inner, thin layer heating
cham~er 27, whereby the steam is condensed and the combustion
gases exit through line 32, pass through a filter 12, and enter
into an expansion engine 13. The filter 10 in line 8 removes
ashes, dust and particles from the gas-steam mixture.
The gas and steam, at a temperature of about 1000 C.,
leaving furnace 3 through line 29 into heat exchanger 5 release
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part of their heat to combustion air, oxygen, or any other
oxygen-air mixture entering in line 38. The combustion air is
thereby preheated to about 800 C. and is blown into furnace 3
from line 39.
The combustion gases after having passed through the
outer chamber of evaporator 2, filter 12, and engine 13 can be
utilized as combustion or synthesis gases.
The condensed steam in outer chamber 11 of the evaporator,
which still has a temperature of about 170 C. and a superpressure
of about 20 bar, is withdrawn through line 33, passed into heat
exchanger 14 to preheat the entering sludge, and is subsequently
expanded in an expansion engine 15 and diverted.
The sludge in inner thin layer chamber 27 of evaporator 11
boils at a temperature of about 150 C. and about 3 bar super-
pressure. The steam produced exists through line 34 into lines
35 and 36. From line 35, the steam passes into heat exchanger
18, which heats the sludge passing through line 26 before the
sludge enters the evaporator 2. From line 36, the steam passes
through lines 37 and 23. From line 37, the steam passes into
heat exchanger 17 which heats the sludge passing through line 24
before it enters the preliminary concentrator 1. From line 23,
excess steam is drawn off for other uses. After the steam has
passed through heat exchangers 17 and 18, the steam is sub-
sequently expanded as steam or condensate in expansion engines
1~ and 22, respectively, and diverted.
In the above process wherein the sludge is preheated with
the products of the combustion thereof, dissolved matter in the
sludge ~ater, e.g., albumen, is eliminated, whereby few or no
precipitants are required for removal of the dissolved matter.
However, advantageously, materials to bond pollutants in the
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sludge, such as sulfur and he~v~ metals, in particular, can be
added during treatment of the sludge in order to render the
ashes directly depositabIe andlor to produce clean gases
emitting from the furnace 3.
The salts originally dissolved in the sludge water and
remaining in the residual water of the thermally thickened
sludge contribute to a higher salt concentration therein and
some salts, i.e. sodium a~d magnesium compounds, act as dissolu-
tion agents, and therefore greatly reduces or entirely eliminates
the need for the addition of dissolving agents.
The various salts which are contained in the original
untreated sludgP are still present in the ashes drawn off by
exhaust line 4. These various soluble salts in the ashes are
particularly suitable for use as agricultural fertilizer. If
dissolution agents are added to the sludge before or during
oxidation, the phosphates or other fertilizer compounds in the
ashes are rendered more water or citric acid soluble, and as such
are more readily accepted by agricultural plants. In addition,
other salts contained in the residual water of the sludge can
2Q effect dissolution.
In the above described process, the invention is charac-
terized by the fact that the inner chamber 27 of the thin layer
evaporator 2 is connected on one side to the entering sludge and
on the other side to the sludge entry of furnace 3, and that the
gas side of the furnace is in communication with the outer
chamber 11 of the evaporator.
It is to be understood that oxidation in the process of
this invention other than combustion can also include low
temperatu~e carbonization or gasification. Thus, in gasification,
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the sludge having a water content of about 80% can be burned in
furnace 3 at a pressure of about 20 bar and a temperature of
about lOOQ C. resulting in the formation of gases, steam and
ashes. In this regard, the furnace 3 is constructed to be
pressure resiætant and can be a muffle furnace, slag tap furnace,
blast furnace, or a fluidized bed furnace of sand or granulated
ashes.
In the oxidation part of the process, conventional fuels,
waste oil or general waste materials can be added to optimize
the process on the one hand while on the other hand disposing .
of waste materials in an economical manner or in aiding in its
recycling. Thus, it is conceivable to subject fuels, waste
oil, used tires, garbage or other general waste materials, if
necessary, subsequent to preliminary or pretreatment thereof,
partly or entirely to the process of the invention. More
significantly, however, than the above variations of the process,
is the fact that there is a total combustion possible o~ the
excess oxygen.
The process of the invention is also chara~terized and
.produces an eusential.advantage in that the thermal energy
requirements for the individual steps of the thermal treatment
of the sludge is energy entirely regained from energy which is
released from oxidizing the sludge in the furnace and, further- :.
more, that this energy is then utilized in its entirety by con-
densing the steam contained in the gas-steam mixture obtained
from the furnace.
In the thermal thickening of the sludge, it is preferable
to carry out the process in several stages whereby the steam
produced during thickening in one step is used for thickening
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f the s1udge in a previous step, and the steam w~ich ls the
product of the thickening is cooled or condensed-in heat exchange
with the sludge to be heated. In addition, because the condensed
steam still contains residual heat, it may further be used for
thermal treatment of the sludge by heat exchange. Energy can
even be recovered from the gases still under pressure by the use
of expansion engines.
It is to be understood that the concept of the invention
is not limited to the specific embodiment set forth above, but
can also comprise treatment plants for various sludges such as
industrial sludges containing matter combustible in its dry state
or in a slurry, or to sludges to which combustible matter is
added.
