Note: Descriptions are shown in the official language in which they were submitted.
METHOD AND FACILITY FOR THE SEMI-CONTINUOUS THERMAL HYDROLYSIS OF
SLUDGE
Field of the Invention
The invention relates to the field of the treatment of effluents constituted
by
or highly charged with fermentable organic matter and especially the treatment
of
sludge obtained from processes for the depollution of urban or industrial
waste-
water or sludges from the treatment of industrial or agricultural bio-wastes.
Here
below, these effluents are generally called "sludges".
Prior Art
At present, a part of the sludges produced by purification stations is
recycled
in the agricultural sector and another part is incinerated or treated in other
ways.
However, these sludges are increasingly being treated in specific sub-sectors.
Since the production of these sludges is increasingly great, it is indeed
necessary that they entail no danger to the environment and to human health.
In
fact, these sludges contain germs, some of which (coliform bacteria,
salmonella,
helminth eggs, etc.) are pathogenic. In addition, they are highly fermentable
and
cause the production of gases (amines, hydrogen sulfide, mercaptans, etc.)
which
cause olfactory nuisance. These considerations explain the need, in the above-
mentioned sludge treatment sub-sectors, to apply at least one step for
stabilizing
these sludges in order to obtain sludges that no longer evolve or evolve
slowly, both
biologically and at the physical/chemical level.
A major concern is to reduce the volume of these sludges and/or recycle
them in the form of biogas.
The methods proposed in the prior art to treat these sludges include thermal
hydrolysis which is considered to be a particularly promising method.
The thermal hydrolysis of sludges consists in treating them at a high
temperature and under pressure so as to make them hygienic (i.e. to greatly
reduce
their content in microorganisms, especially pathogenic microorganisms),
solubilize a
major part of the particulate matter and convert the organic matter that they
contain into easily soluble matter that is biodegradable (into volatile fatty
acids for
example).
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Such thermal hydrolysis of sludges could be planned upstream to or even
downstream from a step of anaerobic digestion.
A technique described in FR2820735 has been proposed for the hydrolysis of
sludges. This technique implements at least two reactors working in parallel.
In each
of these reactors, batches of sludges undergo a full cycle of thermal
hydrolysis. Each
of the cycles of thermal hydrolysis implemented in a reactor comprises steps
for
feeding the sludges to be treated in the reactor, injecting recovered steam
(flash
steam) therein in order to recover heat in the sludges, injecting live steam
therein in
order take them to a pressure P and a temperature T enabling hydrolysis,
keeping
.. them at this pressure P and at this temperature T for a certain period of
time,
bringing the sludges to a pressure close to atmospheric pressure by releasing
flash
steam that is recycled to pre-heat the sludges to be treated from the reactor
in
parallel, and draining the reactor of the sludges thus hydrolyzed.
According to this technique, it is planned that the cycle will be staggered in
time from one reactor to the next to use the flash steam produced from a
reactor to
inject it into the other reactor. Such an implementation makes it possible to
make
use of the flash steam produced in one of the reactors to feed the other
reactor with
steam.
Such a method can be implemented in facilities that are simple to use, the
steps of filling, hydrolysis, depressurizing and draining being carried out in
the same
reactor. The method thus minimizes the speed at which these facilities get
clogged,
minimizes odors when there is no passage of sludges from reactor to another
and
reduces live steam requirements.
It can be noted that, according to this technique, the injection of flash
steam
is done via a steam injector for injecting steam into the reactor sludge
blanket. Such
a configuration leads to major load losses, on the one hand because of the
configuration of the steam injector and on the other hand because of the
height of
the sludges in the reactor above the injector. In order to minimize these load
losses,
it is necessary in practice to use reactors having great height provided with
several
injectors distributed across this height. The steam can thus be distributed at
several
points in the sludge column through these different injectors. As a corollary,
the
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injectors must be equipped with as many passageways as there are levels of
steam
injection in order to ensure the maintenance of these injectors, and this
makes their
construction complex and increases their cost.
In order to limit steam consumption while at the same time improving the
efficiency of the thermal hydrolysis of the sludges, especially those with
high dry
content, another method of thermal hydrolysis has been proposed and is
described
in FR2990429. Such a method is carried out in at least two reactors working in
parallel, in each of which the sludges undergo a full thermal hydrolysis
cycle, said
cycle being staggered in time from one reactor to another to use the flash
steam
produced from one reactor to inject it into other reactor. The method
comprises a
step for extracting a part of the sludges contained in a thermal hydrolysis
reactor and
then reintroducing them into this reactor (i.e. this is a method in which a
part of the
content of a thermal hydrolysis reactor is recirculated within itself).
Such a method does not however give full satisfaction. Indeed, it lengthens
the time spans of the cycles and therefore entails increases in the size of
the facilities
that implement it. In addition, it introduces flash steam into the non-
preheated
sludges, and this does not favor the thermal transfer of steam towards the
sludges.
In practice, it is necessary to maintain a leftover quantity (a basic residual
quantity)
of hot sludges in each thermal hydrolysis reactor, these sludges representing
about
10% of the volume of the reactor and limit the filling of these reactors.
Under heat,
the reactors cannot be filled beyond 70% of their volume capacity. Finally,
the dry
content of the sludges that can be treated by this process remains in practice
limited
to 18% of dry matter.
Although these techniques implement cycles of treatment by thermal
hydrolysis of batches of sludges using several thermal hydrolysis reactors,
they also
provide for a feeding with sludges to be treated and for a draining of the
sludges that
can be continuous. They are thus called semi-continuous methods or again
"serial
continuous" methods. These methods ensure that each batch of sludges undergoes
a given thermal hydrolysis time.
There also is a known method in the prior art, according to FR3010403, for
the treatment of sludges by thermal hydrolysis which is an entirely continuous
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method. This method includes the steps for injecting recovered steam into the
sludges and mixing them with these sludges by means of a primary dynamic mixer-
injector device in order to obtain a uniform primary mixture; injecting and
mixing live
steam into this primary uniform mixture by means of a secondary dynamic mixer-
injector device so as to obtain a uniform secondary mixture; conveying the
uniform
secondary mixture to a pressurized tubular reactor and prompting the flow,
essentially a plug flow, of this secondary uniform mixture into said reactor
for a
residence time that is sufficient and at a temperature that is sufficient to
enable the
thermal hydrolysis of the organic matter present in this secondary uniform
mixture;
producing said recovered steam within means for the production of recovered
steam
from said secondary uniform mixture obtained at exit of said tubular reactor;
cooling
said uniform secondary mixture at its exit from said means for the production
of
recovered steam at a temperature enabling the subsequent digestion of the
hydrolyzed organic matter that it contains.
Such a technique, which is very promising, however implies the need to
sometimes install several treatment lines to meet the demand for sludge
treatment.
All the techniques described here above have the advantage of implementing
recovered steam produced by depressurization of a thermal hydrolysis reactor.
The
piping and pumps provided for this purpose are, however, subject to pressure
and
temperature constraints that necessitate maintenance and supervision and can
ultimately make them fragile. They therefore make the structure of the
facilities and
their maintenance somewhat complex.
Goals of the invention
It is a goal of the invention to propose a method for the semi-continuous
thermal hydrolysis of sludges, offering an alternative to the known prior-art
methods
art described here above.
It is a goal of the present invention thus to describe such a method that has
the advantages of:
- treating
the sludges by thermal hydrolysis in batches (i.e. without risks of
migration of particles from one batch to another) while at the same time
being capable of being implemented in facilities that receive sludges to be
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hydrolyzed continuously and that remove the hydrolyzed sludges also
continuously;
- ensuring that each particle of the sludge undergoes thermal hydrolysis
during a sufficient pre-determined time.
It is another goal of the invention to propose such a method that can be
implemented in facilities that are less complex to make than those used for
the
methods of the prior art. In particular, it is the goal of the invention to
describe a
facility which, for substantially equal treatment capacity, has fewer
passageways,
fewer pipes, fewer valves and a smaller footprint than facilities implementing
the
semi-continuous methods of the prior art described here above.
It is a goal of the present invention especially to disclose such a method
capable of being implemented in at least certain embodiments, in facilities
that do
not implement steam injectors in the hydrolysis thermal reactor.
Summary of the Invention
These goals, as well as others that shall appear here below, are achieved by
means of the invention which relates to a method for the thermal hydrolysis of
sludges characterized in that it comprises:
the pressurizing of sludges to be treated at a reference pressure of 2 bar a
to 16 bar
a,
the injection of live steam into said pressurized sludges so as to carry the
temperature of these sludges to 120 C to 200 C,
the application to said pressurized and heated sludges of a cycle of thermal
hydrolysis treatment comprising the steps consisting of:
a) conveying a batch of heated and pressurized sludges into a reaction space,
b) maintaining said batch of sludges in said reaction space for a duration
sufficient for its thermal hydrolysis,
c) draining said reaction space of said batch of sludges,
the cooling of said hydrolyzed sludges,
the depressurizing of said hydrolyzed sludges,
the removal of said hydrolyzed sludges,
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the application to said sludges of a cycle of thermal hydrolysis treatment
that is
conducted in parallel in at least three reaction spaces, in each of which a
succession
of treatment cycles is implemented, each of said reaction spaces being
dedicated to
the treatment of distinct batches of sludges, said steps a), b) and c) of said
treatment
cycles being staggered in time from one reaction space to the other,
a gas atmosphere common to at least three reaction spaces being prepared and
the
pressure prevailing in said common gas atmosphere being measured and kept
essentially constant at said reference pressure.
The method according to the invention therefore proposes not to isolate the
.. gas atmospheres in the different reaction spaces. Thus, the common gas
atmosphere serves as a chamber for re-balancing the pressures of these
reaction
spaces during the steps of a) filling one reaction space and c) draining
another
reaction space. In practice, the draining of one reaction space enables the
concomitant filling of another reaction space.
In order to prepare such a gas atmosphere common to all the reaction
spaces, it is possible to do away with the implementation of valves isolating
the gas
atmosphere of each reaction space. This simplifies the design and construction
or at
least the use of facilities for implementing such a method.
Besides, the injection of live steam upstream to the reaction spaces makes
.. the use of live steam injectors not indispensable. It is thus possible to
reduce the
number of passageways serving these reaction spaces and enable the facility
and
maintenance of such injectors.
It can also be noted that the method according to the invention does not
implement any depressurizing of sludges within reaction spaces. Indeed, the
sludges
are depressurized after having undergone a processing cycle in one of these
spaces
and after having been drained from this cycle.
Preferably, the method according to the invention comprises a step for
adjusting the pressure prevailing in said common gas atmosphere, said step for
adjusting the pressure comprising the injection of a gas into said common gas
atmosphere when said pressure prevailing in this gas atmosphere is below a
predetermined lower threshold and/or the removal of a part of the gas present
in
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said common gas atmosphere when said pressure prevailing in it is above a
predetermined upper threshold.
The upper and lower pressure thresholds will be determined around said
reference pressure desired for the thermal hydrolysis of sludges, itself
varying as a
function of the nature and/or composition of the sludges to be treated.
It will be noted that the gas in question could advantageously be live steam.
It could also be another gas, such as an inert gas, nitrogen (N2), carbon
dioxide (CO2),
or air especially.
In either case, means will be provided for injecting this gas into said common
gas atmosphere.
Although, said step for adjusting the pressure prevailing in the common gas
atmosphere could be done manually, using measurements of pressure made, this
adjustment will preferably be implemented automatically.
Equally preferably, the injection of live steam into said pressurized sludges
is
.. done so as to carry said sludges to a temperature of 140 C to 180 C. This
temperature of thermal hydrolysis could be chosen as a function especially of
the
nature of the sludges and of the final purpose of the method (hygienization or
sanitization, solubilization etc.).
Equally preferably, said reference pressure will range from 3.5 bar a to 10
bar
a.
Equally, according to an advantageous variant, the injection of live steam is
done using means included in the group constituted by dynamic mixer-injector
devices and inline steam injection heaters. It will be noted that the
following are the
meanings of some of the terms used in the present description:
- Dynamic mixer-injector: any mixer constituted by a chamber receiving a steam
injector and means used to cause a stirring operation, using motor-driven
mechanical elements, of the different phases entering this chamber in order to
obtain a uniform mixture at output; such motor-driven mechanical elements can
for
example be constituted by blades or screws moved by a rotor or any other type
of
.. mixture also moved by a rotor; advantageously, the chamber is cylindrical
and
provided with rotary blades having appropriate geometry mounted on a shaft
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rotating at a rotation speed preferably ranging from 200 rpm to 4000 rpm,
corresponding to a speed of 1 m/s to 94 m/s;
- In-line steam injection heater: any means for injecting or distributing
steam in a
network of tubes without motor-driven mechanical stirring.
Such equipment makes it possible to obtain essentially homogenous sludges
at exit. The residence time of these sludges in such equipment is very short:
1
second to a maximum of 5 minutes. The dynamic injector/mixer devices can, in
addition, be used to lower the viscosity of the sludges and thus favor their
mixing
with steam.
Advantageously, the method comprises a step for the pre-heating of said
incoming sludges upstream to the injection of live steam.
Equally advantageously, the cooling of the hydrolyzed sludges produces
recovered steam and the method comprises the mixing of recovered steam with
said
incoming sludges for their pre-heating.
Preferably, the recovered steam is injected into said sludges upstream to said
step for injecting live steam through at least one means included in the group
constituted by dynamic mixer-injector devices, inline steam injection heater
and
pulper-mixer devices
It will be noted that in the present description the term "pulper/mixer" is
understood to mean any mixer constituted by a mixing vessel with a steam
injection
heater integrated into the vessel or a recirculation loop, the stirring means
of which
are mechanical and internal (blades, submerged pumps etc.) or external (a pump
in a
recirculation loop).
Preferably, each of said steps a), b) and c) of said cycle has a duration
ranging
from 10 mn to 120 mn, advantageously from 15 mn to 30 mn. According to the
invention, said steps a), b) and c) are conducted concomitantly in said at
least three
reaction spaces.
It will be noted that in the context of the present invention, the method
according to this invention could implement more than three reaction spaces.
Advantageously, said batch of sludges to be treated has a dry content of 10%
to 40% by weight of dry matter. In order to show the desired dry content for
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treatment through the method according to the invention, the sludges to be
treated
could be preliminarily diluted, especially with hot water.
The invention also relates to any facility characterized in that it comprises:
means for conveying sludges;
means for pressurizing said sludges;
means for conveying live steam and means for mixing said live steam with said
sludges;
means for distributing batches of sludges from said mixing means alternately
into at
least three reaction spaces for the thermal hydrolysis of said sludges;
means for removing said batches of hydrolyzed sludges alternately from each of
said
at least reaction spaces to means for cooling and means for depressurizing
said
hydrolyzed sludges;
means for removing depressurized hydrolyzed sludges;
said at least three reaction spaces having a common gas atmosphere and said
common gas atmosphere being provided with means for removing gas and means
for measuring the pressure prevailing therein.
The common gas atmosphere with which the facility is provided enables the
pressures in the different reaction spaces to be balanced with the reference
pressure
desired for thermal hydrolysis. The means for measuring pressure in this gas
atmosphere are used to supervise the maintaining of this pressure at the right
level.
The means for removing gas, apart from removing non-condensable gases, for
their
part are used to lower this pressure if the pressure thus measured is
excessively
high.
According to one variant, said means for mixing said live steam with said
.. sludges include at least one dynamic mixer/injector (as defined here above)
and/or
at least one inline steam injection heater (as defined here above) connected
to said
live steam inlet means.
According to one variant, said gas atmosphere common to the reaction
spaces is provided with not only gas-removal means but also gas-injection
means.
Thus, the pressure measured in said common gas atmosphere is below a lower
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threshold. A gas can be injected enabling this pressure to be made to rise to
the
height of the reference pressure.
According to one variant of the invention, said reaction spaces are each
demarcated by a reactor structure.
In such an example, the common gas atmosphere is advantageously
constituted by a set of upper parts of the reactor structures not filled with
sludges
and by all the pipes going from each reactor structure to said gas-removal
means.
According to another variant, said reaction spaces are grouped together in a
single reactor structure, each of said reaction spaces constituting a
compartment of
said single reactor structure. This reactor structure could be cylindrical and
the
compartments could advantageously take the form of a cylinder portion. Such a
configuration of reaction spaces optimizes the footprint of the reactor
structure.
In such an example, said common gas atmosphere is advantageously
constituted by a space provided in the upper part of the reactor common to the
compartments forming it and by all the pipes going from each reactor structure
to
said gas-removal means.
Equally, according to one variant of the invention, the facility comprises a
standby vessel sized to receive at least one batch of sludges and means for
dispensing batches of sludges from said at least one dynamic mixer-injector
device or
inline steam injection heater or pulper-mixer towards said standby vessel Such
a
standby vessel could be used for the application of one or more batches of
sludges of
the thermal hydrolysis processing cycles during periods when one of the
reaction
spaces will be under maintenance. In
practice, the reaction space under
maintenance will then be isolated by the closing off of a set of valves and
this
standby vessel will be used by the opening of another set of valves.
In the context of the present invention, the means for cooling the hydrolyzed
sludges could be planned in different shapes. Preferably, these means will be
chosen
from the group constituted by heat exchangers, means for diluting hydrolyzed
sludges with industrial-use water, means for injecting fresh sludges into said
hydrolyzed sludges, means for generating recovered steam.
CA 2992657 2018-11-19
When a heat exchange is implemented, it is possible to use an exchanger
comprising an inlet for the treatment for sludges to be heated and an inlet
for the
hydrolyzed sludges to be cooled. This type of heat exchanger is called a
sludge-
sludge heat exchanger.
When these cooling means include at least one heat exchanger, the heat
recovered through the heat exchanger could be used to heat buildings or for
other
treatment operations such as a digestion of the sludges.
The means for generating recovered steam could be constituted by a waste
steam boiler or could advantageously include a flash tank. It will be noted
that in the
.. present description the term 'flash tank' is understood to mean a tank in
which the
pressure of the hydrolyzed sludges is suddenly lowered, giving rise
concomitantly to
the cooling of the sludges and to the emission of steam under high pressure.
Such a
tank therefore constitutes both the cooling means and the depressurizing
means.
When the facility comprises means for generating recovered steam, it will
preferably include at least one piping for conveying said recovered steam
upstream
to said mixing means for mixing live steam with the sludges and means for
putting
said recovered steam into contact with said sludges to be treated. This
putting into
contact will then enable the preheating of the sludges at reduced cost. In
order to
favor this putting into contact, the plant will preferably include at least
one of the
means chosen from among a pulper-mixer, a dynamic mixer-injector device, an in-
line steam injector and a pulper-mixer device (as defined here above).
List of figures
The invention, as well as its different advantages will be understood more
easily from the following description of four non-exhaustive embodiments given
with
.. reference to the appended drawings of which:
figure 1 schematically represents a first embodiment of a facility according
to the
invention in which the reaction spaces are each demarcated by a reactor
structure;
figure 2 schematically represents a second embodiment of a facility according
to the
invention in which the reaction spaces are grouped together in a single
reactor
structure;
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figure 3 schematically represents a third embodiment of a facility according
to the
invention in which the reaction spaces are each demarcated by a reactor
structure,
the facility comprising in addition a standby vessel to ensure the maintenance
of the
reaction spaces;
figure 4 schematically represents a fourth embodiment of a facility according
to the
invention.
Description of embodiments
Referring to figure 1, the facility comprises sludge-conveying means 1
comprising a main piping having two bypasses la, lb. The main piping and its
bypasses are each equipped with, on the one hand, means 2, 2a, 2b for
pressurizing
the sludges, each including a pump, and on the other hand mixer means 4, 4a,
4b for
mixing the pressurized sludges with the live "water" steam each including a
dynamic
mixer-injector 18, 18a, 18b. It will noted that in other embodiments, the
mixing
means could include an inline steam dispenser or inline steam injection heater
(as
defined here above). Such distributors are especially commercially distributed
by the
ProSonix firm under the name "inline direct steam injection heater".
In order to enable the mixing of the pressurized sludges with the steam, the
facility comprises live steam conveying means 3 comprising a main piping
having two
bypasses 3a and 3b respectively serving the dynamic mixer-injectors 18, 18a,
18b.
These live steam conveying means 3 are connected to a steam production unit
(not
shown in figure 1).
The facility also comprises means of distribution 5 of batches of sludges from
said dynamic mixer-injectors 18, 18a, 18b in alternation in at least three
reaction
spaces 7a, 7b, 7c for the application of thermal hydrolysis cycles which shall
be
described here below in detail.
In this embodiment, each reaction space 7a, 7b, 7c is individualized by a
reactor structure 19a, 19b, 19c respectively. In other words, each reaction
space is
demarcated by the walls of a reactor independent of the other reactors
demarcating
the other reaction spaces.
The distribution means 5 comprise three distribution lines 5a, 5b, 5c each
equipped with a sludge feeder valve 6a, 6b, 6c respectively and enabling the
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distribution of the batches of pressurized sludges pressurized and heated in
alternation in the three reaction spaces 7a, 7b, 7c.
The facility further comprises means 8 for removing batches of hydrolyzed
sludges in alternation from each of the three reaction spaces 7a, 7b, 7c to
depressurizing means 10, 10a, 10b each comprising a pump.
These removal means 8 comprise three removal lines 8a, 8b, 8c each
equipped with a draining valve 9a, 9b, 9c enabling the distribution of the
batches of
hydrolyzed sludges respectively to the depressurizing means 10, 10a, 10b.
The facility also comprises removal means 11, 11a, 11b for removing the
hydrolyzed sludges. Each of the removal means 18comprise a piping.
A heat exchanger 20 is provided on these removal means in order to recover
and/or remove a part of the heat from the removed hydrolyzed sludges, the heat
being possibly re-routed towards a steam production unit or else used to heat
buildings or for another processing such as a digestion.
The installation also comprises a water system 21 used to dilute the sludges
at the exit from the reaction spaces.
The heat exchanger 20 and the water system 21 constitute means of cooling
hydrolyzed sludges. As specified here above, other means of cooling could be
used
in the context of the present invention such as especially an injection of
fresh
sludges.
In accordance with the present invention, the three reaction spaces 7a, 7b, 7c
demarcated by the walls of the reactors 19a, 19b, 19c respectively have a
common
gas atmosphere 12. This common gas atmosphere is provided with means 13 for
removing the gas present in it including a valve 14, and means 16 for
injecting a gas
in it including an injection lance and a valve 17. The common gas atmosphere
12 is
further provided with means 15 for measuring the pressure of the gas
prevailing in it.
It will be noted that the common gas atmosphere is represented
schematically in figure 1 as a set capping the three reactors 19a, 19b, 19c.
In
practice, it is constituted by the set of upper parts of the three reactors
19a, 19b, 19c
not filled with sludges and by the set of piping systems going from these
reactors up
to the valve 14.
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The working of this installation shall now be described. On this subject, it
will
be noted that, when the elements are represented in dotted lines, it means
that
their use is optional.
Sludges to be treated, possibly diluted and/or pre-heated, are raised to an
absolute pressure ranging from 2 bar to 16 bar, preferably 3.5 bar to 12 bar
using the
pumps 2, 2a, 2b and then heated to a temperature of 120 C to 200 C, preferably
140 C to 180 C through mixer-injector devices 18, 18a, 18b. Through such
equipment, the sludges are intimately mixed with the steam and their viscosity
is
lowered, thus facilitating their subsequent processing.
One batch of these sludges (i.e. a given volume) is then distributed through
the means 5 to one of the reaction spaces where they undergo a full cycle of
thermal
hydrolysis comprising the steps of:
a) routing the batch of heated and pressurized sludges into this reaction
space,
b) keeping said batch of sludges in said reaction space for a duration
sufficient
for its thermal hydrolysis,
c) draining said reaction space of said sludges through draining means.
Following this full cycle of thermal hydrolysis, the hydrolyzed sludges are
cooled (here through the heat exchanger 20 and the input of water by the water
system 21 and then possibly by other means in the context of other
embodiments),
and then depressurized through the depressurizing means and removed.
According to the invention, the cycles of thermal hydrolysis processing are
conducted in parallel with the three reaction spaces, the steps a), b) and c)
of these
cycles being staggered in time from one reaction space to the other.
According to such a cycle, a batch of pressurized and heated sludges is
conveyed during the step a), called a filling step, into the reaction space
7a. To this
end, the valve 6a serving the reaction space 7a is opened and the draining
valve 9a is
closed.
In this filling step a), the reactor 19a demarcating the reaction space 7a is
filled up to between 70% and 95% of its total volume capacity. The volume of
the
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interior of the reactor not occupied by the sludges is occupied by a gas
atmosphere
planned in the upper part of the reactor during the step a).
In the present example, this step a) lasts 20 minutes.
During a step b), called a thermal hydrolysis reaction step which, in this
example, also lasts 20 minutes, the thermal hydrolysis of the sludges takes
place,
while the supply valve 6a and draining valve 9a remain closed.
At the end of this step b), the valve 9a is open causing, during a step c),
the
draining of the content of the batch of hydrolyzed sludges contained in the
reaction
space 7a towards the heat exchange at 20 and then towards the depressurizing
means 10, 10a, 10b before they are removed through pipings of the removal
means
11, 11a, 11b. Upstream to the exchanger 20 and downstream from this exchanger
20, water is conveyed to take part in the cooling of the sludges hydrolyzed by
the
water system 21.
The step c) also lasts 20 minutes.
In the present embodiment, the steps a), b) and c) each have a duration of 20
minutes and constitute a 60-minute processing cycle.
This cycle is immediately repeated for one and then other batches of sludges
to be processed in the reaction space 7a. The operations for treating
different
batches of sludges therefore succeed one another in a succession of 60-minute
cycles during which these different batches of sludges travel in transit
through the
reaction space 7a.
Identical successions of processing cycles are implemented for other batches
of sludges by means of the reaction spaces 7b and 7c. The description of these
successions of cycles is identical to that made here above with reference to
the
reaction space 7a, except that it is the valves associated with the reaction
spaces 7b
and 7c that are actuated, namely:
- the sludge feeder valve 6b and the draining valve 9b for the treatment
cycle implemented in the reaction space 7h;
- the sludge feeder valve 6c and the draining valve 9c for the treatment
cycle implemented in the reaction space 7c.
CA 2992657 2018-11-19
According to the invention, the starting points of the cycles of these
different
successions of cycles are staggered in time so that the steps a) of a
succession of
cycles carried out in a first reaction space are concomitant with the steps b)
of
another succession of cycles conducted in a second reaction space and with the
steps c) of another succession of cycles conducted in a third reaction space.
In the present example, this staggering between the cycle starting points of
each succession of cycles is 20 minutes.
The feeding of sludges into the installation and the discharging of sludges
from the installation is thus continuous.
Through the common gas atmosphere 12, the pressure prevailing in the
different reaction spaces 7a, 7b, 7c is balanced in these spaces.
If the means 15 for measuring the pressure prevailing in the gas atmosphere
12 show that the pressure prevailing in this gas atmosphere 12 is above a pre-
determined upper threshold, the valve 14 can be open for a certain period of
time in
order to lower this pressure and bring it into the region of the reference
pressure.
If, on the contrary, these means 15 for measuring pressure prevailing in the
gas atmosphere 12 show that the pressure prevailing the gas atmosphere 12 is
below
a pre-determined lower threshold, the valve 17 can be open for a certain
period of
time to convey a gas (for example an inert gas or live steam) into this gas
atmosphere to increase this pressure and bring it to the reference pressure or
into
the region of this reference pressure.
The embodiment described with reference to figure 2 does not differ from
that made with reference to figure 1 except by the characteristic according to
which
the reaction spaces 7a, 7b, 7c are grouped into a single reactor structure 19
of which
they constitute portions and by the fact that the inline steam injection
heaters 22,
22a, 22b are used instead of the mixer-injector devices. In this embodiment,
the
common gas atmosphere is constituted by the upper part of the reactor. It will
be
noted that in this embodiment, the reactor has a vertical shape. In other
embodiments, it could however have a horizontal shape.
The embodiment described with reference to figure 3 does not differ from
that described with reference to figure 1 except by the characteristic
according to
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CA 2992657 2018-11-19
which a standby vessel 7d is provided to act as a reaction space during
maintenance
of one of the reaction spaces 7a, 7b and 7c. This vessel 7d can also be used
to
temporarily store sludges.
In the embodiment according to figure 4, the hydrolyzed sludges are
depressurized and cooled concomitantly in a flash tank 23 provided at the exit
from
the reaction spaces 7a, 7b and 7c. The cooling of the sludges is completed by
the
injection of water into the sludges exiting this flash tank through the water
system
21 before they are removed by a piping of removal means 11.
The flash steam emitted is routed via a piping 25 towards a pulper-mixer 24
also receiving the incoming sludges. Thus, the incoming sludges can be pre-
heated
to a temperature ranging for example from 50 to 100 C and preferably from 80
to
95 C. The pre-heated incoming sludges are then routed by a pipe 25a to mixing
means 4, 4a, 4b for mixing these sludges with live steam. The rest of the
installation
is compliant with the embodiment given with reference to figure 1.
It will be noted that, in other embodiments, the means for placing the
recovered steam into contact with the incoming sludges could include other
items of
equipment than a pulper-mixer. In particular, in this context it is possible
to envisage
the implementing of mixer-injector devices or inline steam injection heaters
as
described here above.
It will also be noted that, in other embodiments, the recovered steam
production means could be means other than a flash tank. In particular, it
could be a
simple waste steam boiler.
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