INCINERATION FURNACE FOR PASTY PRODUCTS, IN PARTICULAR
SLUDGE FROM PURIFYING STATIONS
The present invention relates to a furnace for pasty
5 products, in particular sludge from purifying stations,
with a bed of granular material which is fluidized by
injection of a gaseous fluid, the furnace being of the
type comprising at least two nozzles for injection of
pasty products into the bed, which nozzles are supplied
10 respectively by a duct which is provided with a valve,
and is connected to the discharge of a single pump, and
a pipe for discharge of the combustion gases.
During combustion of pasty products in a fluidized bed
15 furnace, the most efficient injection is that obtained
by pumping which discharges directly into the bed of
granular material. Indeed, the pasty products are then
finely distributed in the bed of granular material, and
the combustion is the most efficient and the most
20 complete. The product is injected by means of a limited
number of nozzles inside the bed. However, this type of
injection can give rise to a plurality of problems:
firstly, an injection nozzle can become clogged without
this clogging being observed quickly, and secondly,
25 this clogging can give rise to carbonization of the
sludge at the orifice, and permanent clogging of the
injection nozzle.
These problems are present particularly when the pasty
30 products injected are very viscous, in particular in
the case of sludge from purifying stations.
A plurality of solutions have been proposed in order to
eliminate these problems.
35
A first solution consists of cyclical closure of each
of the injection nozzles of the furnace which are
supplied by a single pump: this pump thrusts the
products into the furnace alternately by means of a set
of valves, through a single one of the nozzles. The
pasty products, in particular the sludge, are forced to
exit via this nozzle, which leads to it being
unclogged.
5
This solution has a plurality of disadvantages. It
requires putting into place of automatic guillotine
valves which function frequently, and will be become
worn relatively quickly. In addition, this solution
10 gives rise to a high loss of load in order to make all
of the product pass permanently into a single nozzle,
resulting in oversizing of the pump.
Another solution consists of using one pump per
15 injection nozzle. In this case, the injection is
perfectly controlled by putting a flowmeter into place
on each pump. However this solution is expensive since
the pressurized pumps have a high cost.
20 The objective of the invention is in particular to
propose an incineration furnace which permits control
of the injection of the pasty products, and unclogging
of the nozzles when necessary, for a moderate cost.
25 According to the invention, a furnace for incineration
of pasty products, in particular sludge from purifying
stations, with a bed of granular material which is
fluidized by injection of a gaseous fluid, of the type
previously defined, is characterized in that the
30 furnace comprises at least two temperature sensors
which are arranged above the bed of granular material,
each temperature sensor being situated in an area which
is associated with at least one injection nozzle, and
means which are sensitive to a temperature difference
35 between the sensors, which, when the temperature
difference exceeds a predetermined value, can detect
the clogging of at least one nozzle.
Advantageously, the means which are sensitive to the
temperature difference between the sensors can cut off
the supply of sludge to the nozzle(s) associated with
the temperature sensor which is indicating a
5 temperature which is higher than that provided by the
other sensor.
Preferably, the sensitive means comprise an automaton
which .can command the cutting off of the supply of
10 pasty products, in particular of sludge, to the
nozzle (s) associated with the temperature sensor which
is indicating a temperature which is higher, in
particular by at least 1O0C, than that provided by the
other sensor.
15
The bed of granular material can be configured
imaginarily into angular sectors, in particular with an
equal size, and at least one injection nozzle is
associated with each angular sector.
20
Advantageously, each temperature sensor is arranged
vertically above an injection nozzle, or the median
area of a group of nozzles associated with the sensor.
25 As a variant, each temperature sensor can be arranged
in a part of the area associated with each nozzle or
group of nozzles.
Each temperature sensor can be located at a distance of
30 between 0.1 and 2 m above the bed of granular material,
with all of the sensors constituting a first series.
Preferably, each temperature sensor of this first
series is at a distance of 0.5 m above the bed of
granular material.
3 5
The furnace can comprise a second series of temperature
sensors situated above the first series of temperature
sensors. Each temperature sensor of the second series
can be at a distance of between 1.5 and 8 m above the
bed of granular material. Advantageously, each
temperature sensor of the second series is at a
distance of approximately 2 m above the bed of granular
material.
5
The furnace can comprise two diametrically opposite
injection nozzles, each nozzle being surmounted by a
temperature sensor.
10 According to a variant, the furnace can comprise four
injection nozzles, two nozzles being allocated to a
first semicircular angular sector which is surmounted
by a first temperature sensor, and two other nozzles
being allocated to a second semicircular angular sector
15 which is surmounted by a second temperature sensor.
Each injection nozzle can be in the form of an inverted
"V", with narrowing of the cross-section of passage as
far as the exit, thus being able to create a loss of
20 load which is at least equal to the maximum difference
of loss of load between two lines of injection of pasty
products from the discharge of a single pump.
Other characteristics and advantages of the invention
25 will become apparent from the following description of
preferred embodiments, with reference to the appended
drablings which however do not have any limiting nature.
In these drawings:
30 Figure 1 is a diagram of a first embodiment of a
furnace according to the invention;
Figure 2 is a diagram on an enlarged scale of the area
of injection of the sludge of the furnace in figure 1;
35
Figure 3 is a schematic horizontal cross-section of
figure 1; and
Figure 4 is a view similar to figure 3 of another
embodiment of the invention.
Figure 1 shows a furnace 1 for incineration of pasty
5 products, in particular sludge from purifying stations,
with a fluidized bed of granular material, in
particular sand.
In its lower part, the furnace 1 comprises a wind box
10 2, above which a bed of sand 3 is arranged. The wind
box 2 is connected to the discharge of a blowing
apparatus, not represented, for blowing air through the
bed 3. Supply lines, not represented, permit passage of
the air from the air box to the bed of sand 3, in order
15 to ensure the fluidization of the sand. Above the bed
of sand there is a post-combustion area 4 which is
surmounted by an orifice and a duct 5 for exit of the
fumes .
20 Two injection nozzles 6 and 7 which are situated on
both sides of the bed of sand 3, and are preferably
diametrically opposite, permit injection of sludge to
be incinerated into the bed of sand 3. The supply to
the nozzles 6 and 7 is regulated by the opening and
25 closure of valves, respectively 8 and 9, and preferably
solenoid valves. The pressurized sludge is introduced
by means of ducts and a pump 10.
The turbulence of the bed of sand induced by the blown
30 air obtained from the wind box permits homogenous
mixing with the sludge obtained from the nozzles 6 and
7.
When an injection nozzle becomes clogged, a decrease in
35 the temperature of the bed assembly can be detected.
However, because of the homogeneity of the temperature
in the bed of sand 3 and its strong thermal buffer
effect (high calorific capacity of the mass of sand),
it is not possible to determine which nozzle is
clogged.
Unexpectedly, and although the temperature of the bed
5 is homogenous, it has been found that temperature
measurements carried out above the bed 3, preferably
vertically relative to the nozzles, rapidly show a
significant difference, of at least 1O0C, between the
higher temperature above a nozzle which is not clogged,
10 and the temperature above a clogged nozzle supplied by
the same pump as the other nozzle.
Temperature sensors, in particular thermocouples 11,
12, 13, 14 have been installed above the bed of sand,
15 vertically relative to the nozzles 6 and 7 (figures 1
and 3). This configuration makes it possible to detect
whether the pasty product has been well injected by
each nozzle concerned.
20 In the bed of sand, it is not possible to determine
clogging, since the turbulence in the bed caused by the
injection of air horizontally, which is transformed
into vertical movement, is very strong, and there is
real homogenization of the bed. The aforementioned
25 determination carried out above the bed of sand gives
reason to believe that the flow of air, which has
become vertical, depends to a large extent on what is
happening at its lower vertical level. In addition, the
combustion of the pasty substance takes place in two
30 stages, i.e. one part in the bed of sand, and another
part above it. It is the lack of homogeneity of this
second part which is detected.
A temperature measurement in the bed of sand 3 would
35 make it possible to detect the presence of a global
problem, if a significant temperature variation were
detected, but not to locate the problem accurately.
n0 designates the mean altitude of the upper surface of
the bed of sand 3. At a level nl situated above n0
there are arranged two thermocouples 11 and 12,
constituting a first series. The thermocouple 11 is
5 arranged vertically relative to the injection nozzle 6,
whereas the thermocouple 12 is arranged vertically
relative to the injection nozzle 7.
Level nl, the altitude at which the thermocouples 11
10 and 12 are located, is situated approximately 0.5 m
above the level n0 corresponding to the upper surface
of the bed of sand.
A second series of two thermocouples 13 and 14 is
15 situated at a level n2 above the level nl. The
thermocouple 13 is situated vertically relative to the
injection nozzle 6, whereas the thermocouple 14 is
situated vertically relative to the injection nozzle 7.
20 Level n2 is situated higher in the post-combustion
area.
Level n2 is situated approximately 2 m above level no.
25 Other thermocouples 15 and 16 are situated in the upper
part of the post-combustion area 4.
Finally, a thermocouple 17 is situated at the discharge
pipe 1.
30
The temperature sensors are connected to an automaton A
which constitutes means sensitive to the temperature
difference between the sensors. The measurements
obtained from the different thermocouples are processed
35 by the automaton A, which is connected to the solenoid
valves 8, 9, in order to control them.
In the case when a temperature difference greater than
a predetermined value, in particular 1O0C, is detected
between the temperature measured by the sensor 11 and
that measured by the sensor 12, the automaton A can
emit an alarm in order to indicate the probability of
clogging of one of the two injection nozzles.
5
The lowest temperature indicates the location of the
clogging.
Indeed, if there is no longer i.nt.roduction of the
10 product into a nozzle, the temperature will drop
rapidly, and therefore the temperature measured by the
sensor situated vertically relative to said nozzle will
be lower.
15 In the case of detection of clogging, for example if
the temperature measured by the thermocouple 11 is more
than 10°C lower than the temperature measured by the
thermocouple 12, which corresponds to clogging of the
injection nozzle 6, advantageously the automaton A
20 commands closure of the valve 9, such as to orient all
of the flow of sludge obtained from the pump 10 which
is common to the two nozzles 5, 6 towards the clogged
nozzle 6 alone, which will rapidly give rise to its
unclogging, without distracting globally from the flow
25 injected into the furnace.
At the end of a pre-parameterized time, the valve 9
will once again be opened in order to permit return to
normal functioning.
30
If the thermocouples 11 and 12 indicate persistence of
a temperature difference, and therefore clogging at the
end of the pre-parameterized time, a second unclogging
cycle is triggered.
35
In the case of malfunctioning, for example of one of
the thermocouples of the first row of thermocouples 11,
12, the second row of thermocouples 13 and 14 makes it
possible to switch to regulation of the automatic
unclogging using the thermocouples 13 and 14. It also
makes it possible to determine a second alarm level, if
the first row of thermocouples does not detect a
temperature difference, whereas the second row does
5 detect one.
The invention permits numerous possibilities, and in
particular is not limited to the control of two
injectors.
10
It is possible to use a larger number of injection
nozzles, each of the nozzles comprising at least one
thermocouple which is preferably situated vertically
above the bed of sand.
15
It is also possible to group the injection nozzles
according to angular sectors, with the assembly of the
injection nozzles of said sector being considered as a
single nozzle within the context of the unclogging
20 device according to the invention. The temperature
sensor which is associated with a sector is preferably
arranged in the median area of this sector.
Figure 4 illustrates the case when use is made of four
25 nozzles 6a, 6b, 7a, 7b, equally distributed on two
opposite semicircular sectors S1 and S2, the sectors S1
and 52 being surmounted by the thermocouples,
respectively 11 and 12.
30 In the case when the thermocouple 11 which is situated
vertically relative to the median area of the sector S1
detects a drop in temperature, and therefore clogging,
the valves 9a and 9b which supply the nozzles 7a and 7b
of the other sector 52 are temporarily closed, whereas
35 the valves 8a and 8b which supply the sector S1 are
kept open.
After a first predetermined period of time, if the
thermocouples do not indicate that the situation has
become normal once more, the valves 8a and 8b are
closed alternately in order to ensure the unclogging.
However, in the case of the four nozzles, it is
5 recommended to put four thermocouples strictly above
the nozzles, or at an angle of 45' (360/4/2) around the
nozzles, in order to control the action of each nozzle.
The furnace according to the invention also comprises
10 arrangements which make it possible to minimize the
risk of clogging of the nozzles.
This risk of clogging is substantially derived from the
fact that a small difference of loss of load on one of
15 the injection lines derived from the discharge from a
single pump gives rise to a drop in the flow in this
line. This drop in the flow gives rise to a light
deposit which increases the loss of load, thus
amplifying the drop in the flow, and ultimately leading
20 to clogging.
In order to minimize this risk of clogging, according
to figure 2 injection nozzles 6, 7 are provided which
are each in the form of an inverted "V", and in
25 particular are frusto-conical, with narrowing of the
cross-section of passage as far as the exit. A nozzle
of this type is designed to create a loss of load which
is at least equal to the maximum difference of loss of
load between the two injection lines derived from the
30 same pump.
The loss of load created by the nozzles, corresponding
to 100% of the maximum possible difference of loss of
load between the two injection lines, makes it possible
35 to reduce the relative influence of said loss of load
between lines. This loss of load, which is created by
the form of the nozzles, makes it possible to cover
virtually 100% of the "non-homogeneities" of loss of
load.
The furnace according to the invention has numerous
advantages. It makes it possible firstly to minimize
the clogging of one of the injection nozzles, and
5 secondly to automate the unclogging of the nozzles if
dlogging occurs, without having to increase the number
of costly items of equipment such as the injection
pumps, or to oversize this equipment.
CLAIMS
1. A furnace (1) for incineration of pasty products,
or sludge, with a bed of granular material which
is fluidized by injection of a gaseous fluid, the
furnace comprising at least two nozzles (6, 7) for
injection of products into the bed, which nozzles
are supplied respectively by a duct which is
provided with a valve (8, 9 ) , and is connected to
the discharge of a single pump, and a pipe (5) for
discharge of the combustion gases, characterized
in that the furnace (1) comprises at least two
temperature sensors (11, 12) which are situated
above the bed of granular material (3), each
temperature sensor (11, 12) being situated in an
area which is associated with at least one
injection nozzle (6, 7), and means (A) which are
sensitive to a temperature difference between the
sensors (11, 12), which, when the temperature
difference exceeds a predetermined value, can
detect the clogging of at least one nozzle.
2. The furnace as claimed in claim 1, characterized
in that the means (A) which are sensitive to a
temperature difference between the sensors can cut
off the supply of sludge to the nozzle(s)
associated with the temperature sensor which is
indicating a temperature which is higher by at
least the predetermined value than that provided
3 0 by the other sensor.
3. The furnace as claimed in claim 1, characterized
in that the sensitive means comprise an automaton
(A) which can command the cutting off of the
supply of pasty products, in particular of sludge,
to the nozzle (s) associated with the temperature
sensor which is indicating a temperature which is
higher, in particular by at least 10°C, than that
provided by the other sensor.
4. The furnace as claimed in any one of the preceding
claims, characterized in that the bed of granular
material (3) is configured imaginarily into
angular sectors (Sl, SZ), in particular with an
equal size, at least one injection nozzle (6, 7)
being associated with each angular sector (S1,
52) .
10 5. The furnace as claimed in any one of the preceding
claims, characterized in that each temperature
sensor is arranged vertically above an injection
nozzle, or the median area of a group of nozzles
associated with the sensor.
15
6. The furnace as claimed in any one of claims 1 to
4, characterized in that each temperature sensor
is arranged in a part of the area associated with
each nozzle or group of nozzles.
7. The furnace as claimed in any one of the preceding
claims, characterized in that each temperature
sensor (11, 12) of a first series is located at a
distance of between 0.1 and 2 m above the bed of
sand (3).
8. The furnace as claimed in claim 7, characterized
in that each temperature sensor (11, 12) of the
first series is at a distance of 0.5 m above the
30 bed of sand (3) .
9. The furnace as claimed claim 7 or 8, characterized
in that the furnace (1) comprises a second series
of temperature sensors (13, 14) situated above the
first series of temperature sensors (11, 12).
10. The furnace as claimed in claim 9, characterized
in that each temperature sensor (13, 14) of the
second series is at a distance of between 1.5 and
8 m above the bed of sand (3).
11. The furnace as claimed in claim 10, characterized
5 in that each temperature sensor (13, 14) of the
second series is at a distance of 2 m above the
bed of sand (3).
12. The furnace as claimed in any one of claims 1 tb
11, characterized in that it comprises four
injection nozzles (6a, 6b, 7a, 7b), the nozzles
(6a, 6b) being allocated to a first sector (Sl)
which is surmounted by a first temperature sensor
(ll), and the nozzles (7a, 7b) being allocated to
a second sector (S2) which is surmounted by a
second temperature sensor (12).
13. The furnace as claimed in any one of the preceding claims, characterized in that the injection nozzles (6, 7) are each in the form of an inverted "V", with narrowing of the cross-section ofpassage as far as the exit, thus being able to create a loss of load which is at least equal to the maximum difference of loss of load between two injection lines.