Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS AND PLANT FOR INCINERATING WASTE WITH
PREHEATING OF THE LATTER
The invention relates to a method for incinerating
household or industrial waste in a reactor with
preheating of the waste by a steam circuit the steam
for which comes from the steam expansion turbine (TRV).
The oh jPr_.t of t_1'1P i n~ranf- i nn i c tn nhtai^. ..ltl-:in the
incinerator complete combustion without any unburnt
matter, without any troublesome residue, without
releasing gas into the atmosphere, in order to protect
the environment from any pollution.
Another object of the invention is to recuperate the
thermal energy released, to convert it into electrical
energy, and to reuse some of this energy within the
plant itself. The amount of electrical energy
recuperated is approaching 75%, excluding the energy
reinjected into the plant.
These objects are achieved by the invention which
consists in a process for incinerating household or
industrial waste in a combustion reactor, characterized
in that:
- the combustion is carried out under pressure and
with the addition of pure oxygen to the reactor,
and in the absence of nitrogen,
- the steam from the expansion turbine is tapped off
to preheat the waste before it enters the reactor,
- then the remaining gases are condensed in order to
recuperate them.
Furthermore, the method is characterized in that the
oxygen needed for combustion is produced by separating
the nitrogen and oxygen from the air, the nitrogen thus
produced being used in particular to cool the gases
resulting from the combustion of the waste, and the
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oxygen being injected into the reactor at at least one
point.
The method as defined allows better destruction of
dioxins, unburnt matter, compounds of nitrates,
carbonates and phosphates which give rise to oxides
A plant according to the invention, in order to
imnlPment. thP nrn~acc~ ;~ -haracterized in that it
comprises:
- a feed hopper (TA) having at its inlet and at its
outlet a shutter and comprising means;
- a feed screw capable of preheating the waste using
steam tapped from the expansion turbine (TRV);
- an intermediate hopper able to collect the waste
reheated in the feed hopper and introduce it into
the top of the reactor, and
- a reactor equipped with three burners, these being
a main burner (BP), an auxiliary burner (BA) and a
catalytic burner (BC) positioned near the
combustion gases outlet, each of these three
burners being fed with fuel by the fuel line (3)
and with pure oxygen by an oxygen production
circuit (5), the core of the reactor comprises a
cathode wall based on metals of the tungsten or
tantalum type, chosen for their refractory nature.
As a preference, the oxygen is produced by separating
air into nitrogen and oxygen.
The invention will be better understood with the aid of
the description which follows, given with reference to
the following attached figures:
- figure 1: an overview of a waste incineration
plant according to the invention,
- figure 2: a diagram of the water vaporization
circuit of the plant,
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- figure 3: a detailed diagram of the feed hopper
and of the feed screw according to the invention.
Reference is made first of all to figure 1 which shows
a plant in its entirety, this plant essentially
comprising:
- an inr.inPratinn linP I
--- --------------- ----~ -,
- a steam circuit 2,
- a fuel feed line 3,
- a nitrogen circuit 4,
- an oxygen circuit.
Incineration line (1).
Trucks containing the waste that is to be destroyed are
unloaded under gravity into a feed hopper (TA) the
outlet of which is equipped with a shutter (OF1).
A feed screw (VA) receives the waste from the feed
hopper (TA) and conveys it and tips it into an
intermediate hopper (TI) via an inlet situated at the
top of said hopper (TI) and equipped with a shutter
(0F2) .
The feed screw (VA) also allows the waste to be
preheated as will be explained later on. The
intermediate hopper (TI) has a central bottom outlet
equipped with a shutter (0F3) and via which it loads
the waste under gravity into an inlet chute opening
onto an opening shutter (0F4) of a combustion reactor
(RC) and at the top thereof.
For preference, the hopper (TI) is pressurized at a
temperature close to 900 C to accelerate the reforming
of and removal of halides from the POPs in order to
facilitate the expulsion of waste to the combustion
reactor. Advantageously, the pressurizing will be
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performed by introducing a mass of steam at high
pressure and high temperature in excess of 1000 C into
the hopper (TI) via at least one appropriate orifice.
This gaseous mass at high pressure will have the
advantage of fluidizing the mass of waste present in
the hopper TI and as a result of making it easier to
cause it to flow to the combustion reactor (RC) . In
order to prevent any leak of gaseous mass from the
intermediatP hnnnar tn thA hnnncr Tn ..,riio said
a.. rr..i1... .,tA.l.u
intermediate hopper is being filled, the orifice via
which the gaseous mass is introduced will be associated
with a remote-controlled valve. This valve will be in
the position of closing off the orifice when the hopper
loading hatch is in the open position and will be in
the position in which the orifice is open when the
loading hatch of the intermediate hopper is in the
closed position.
It will be possible to use several hoppers each in turn
communicating with the feed hopper and each in turn
communicating with the reactor RC. This arrangement
will allow one intermediate hopper to be filled from
the feed hopper when the other or one of the other
hopper(s) is in the process of unloading into the
reactor (RC).
It will be possible to incorporate, after the feed
hopper, a tank that will allow the waste to be mixed
with an additive based on sodium hydroxide or on
potassium hydroxide in order, at temperatures close to
200 C, to neutralize acids in a first phase and the
halides bound up in the inorganic molecules.
Halides present in the POPs (persistent organic
pollutants) will be eliminated or fixed using alkali
metal hydroxides in the intermediate hopper at
temperatures close to 1000 C.
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The combustion of waste produces fly ash and gases. The
fly ash drops to the bottom of the reactor (RC) and
then into a bottom ash hopper (TC) situated under the
reactor (RC) . This bottom ash hopper conveys the fly
ash to an ash cooling recuperator (RCE) via a shutter
(OF5). The recuperator RCE mixes the fly ash with water
and initiates reactions between the oxides and the
water to form soluble hydroxides. Next, the insoluble
flv ash i.R tlnY1P!-i intn a triirlr which takes -. ;`
....~.... ~u~.cl~ away
(1c).
All the fly ash, except for the air pollution control
residue (APCR) will be processed using water at
temperatures of between 200 and 400 C, at the outlet
from the reactor. No additional energy is needed to
obtain these temperatures because the dilution of
alkali metal oxides is exothermal.
A processing circuit enables soluble waste to be
separated from insoluble waste, the insoluble waste
being sent for sedimentation and some of the soluble
content will crystallize and be able to be reused. The
soluble part will be reintroduced into the feed hopper
following the separation of the salts of the halides,
and of the sulfates of potassium and of sodium.
The combustion reactor (RC) is equipped with refractory
bricks for good thermal insulation and a cathode wall
based on tungsten or tantalum at the heart of the
reactor ensures that the waste is burnt at very high
temperatures ranging between 1500-3000 C, and is so
using three burners (BP, BA, BC) fed with fuel and with
oxygen and respectively:
- a main burner (BP) positioned at the base of the
combustion reactor (RC),
- an auxiliary burner (BA) positioned in the middle
part of the combustion reactor (RC),
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- a catalytic burner (BC) positioned at the upper
part of the reactor and near the outlet of the
gases, combustion gases 5 completing and
optimizing the combustion.
The primary and auxiliary burners operate with an
excess of oxygen at a rate of reaction 10 to 20 times
higher than the habitual speed of combustion reactions.
The reactor (RC) is designed to operate at constant
high pressure and constant high temperature, and its
inlets and outlets therefore consist of hatches that
constitute heat shields and provide sealing.
The combustion reactor will preferably be a thermal
oxidation reactor (TOR).
The hoppers also operate under pressure and consist of
air locks with their inlet and outlet shutters.
Safety valves CE1 and CE2 are also provided in the
reactor and in the intermediate hopper.
The shutters OF1 to OF5 can be actuated by motors
external to the elements to which they are fitted. The
motors will be of any known type. Without implying any
limitation, they could consist of remote-controlled
electric, hydraulic or pneumatic cylinder actuators.
The combustion gases are capped from the outlet (la) at
the top of the reactor (RC) and sent through a pipe
(SGC) to a particulate filter (PF) and then into heat
exchangers ECT1, ECT2 toward an expansion turbine
(TRGC).
The expansion turbine (TRGC) is advantageously
associated with an electric energy generator (GE3) and
so some of the heat energy of the combustion gases is
thus converted into electricity.
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The water vapor is condensed and the gaseous oxides are
removed (lb) to (CGC). Some of the water from CV2 is
reintroduced into the compressor (7), having passed
through an osmotic filter.
Steam circuit (2)
Arl~~antanr~ni~.gl y~ cnma nf thc rpndenSed ;.lat r Can be
recuperated and vaporized into the form of high-
pressure and high-temperature dry steam to form the
high-pressure gaseous mass introduced into the
intermediate hopper. Thus, upon leaving the condenser
(CVl) the water will be bled to a heat exchanger 6
where it is vaporized into the form of high-pressure
dry steam. Advantageously, the heat exchanger may
consist of a tube bundle in thermal contact with the
reactor (RC) to recuperate some of the heat given off
by the latter, thereby stabilizing the temperature
inside the reactor, this heat being used to vaporize
the water and most of the steam being directed to an
expansion turbine (TRV), another proportion of it being
injected into a pipe (TI).
The steam leaving the TRV is introduced into a
preheating device (SP) incorporated into an endless
feed screw (VA) provided between the feed hopper (TA)
and the intermediate hopper (TI) . This feed screw (TA)
comprises a longitudinal shaft (2d) on which a screw
thread (2c) is mounted. A drive member of any known
type will be coupled to the shaft of the screw.
The preheating device (SP) is preferably, but
nonlimitingly, that of figure 3 which consists of a
screw thread (2c) in the form of a box with a gas inlet
downstream to the screw and a gas outlet upstream to
the screw, the gas outlet being between the screw
thread and the inlet shutter (OOF1) . The upstream and
downstream inlets are each formed of a blind axial
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drilling made in the shaft (2d) at a corresponding end
and of a radial drilling made in said shaft and
opening, at one end, into the blind axial drilling and
into the box form that the screw thread (2c) exhibits.
The steam is injected axially into the start of the
screw thread and heats up the waste as it travels along
the screw thread, then leaves the thread to be sent to
a first condenser (CV1), having passed through a
compressor 7:
As a preference, a compressor 7 may be positioned
upstream of the exchanger 6 to pressurize the water and
create at this point a back pressure that prevents the
reflux of steam to the condenser (CV1).
It may be pointed out that the circulation of steam
through the screw is countercurrent with respect to the
progress of the waste carried by this screw.
The condensers (CV1, CV2, CGC) are of the conventional
type with tube-type heat exchangers through which a
refrigerant from an evaporator-type refrigeration
device (EFF) passes.
The tapped-off combustion gases are gases which are
oxidized and stabilized without dioxin and without
unburnt matter in the duct SGC. Some of their heat
energy is converted into electrical energy in a
generator associated with the turbine (TRGC) and most
of the energy is used to heat up the nitrogen.
Following cooling using nitrogen, the combustion gases
are conveyed to ECTl and ECT2. These gases are
condensed and then introduced into the turbine TRGC
which converts the energy of the combustion gases back
into electrical energy. Following expansion, the gases
are separated from the steam, because the latter
condenses.
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This water circuit (ld) also contains at least one
means (for example using osmosis filtration) of
inerting the water that has been condensed in the
condenser (CV2).
Fuel line (3)
To feed fuel along a line (3), provision is made for
the fuel to be taken from a tank (RCA) and injeCted
under high pressure into each of the three burners,
namely the main burner (BP), the auxiliary burner (BA)
and the catalytic burner (BC).
Nitrogen circuit (4)
A bank of air compressors (BCA) compresses the
atmospheric air from one bar to about 300 bar, this air
being cooled after each compression stage in heat
exchangers using the refrigerant conveyed along a pipe
(4a) from the refrigeration device (EFF) already
mentioned.
A turbocompressor (TCA) expands the air from 300 bar to
about 50 bar, this expansion being accompanied by a
cooling of the air from -43 (approximately, on leaving
the heat exchanger of the final compression stage) down
to -134 approximately, thus allowing the gaseous
nitrogen to be separated from the liquefied oxygen
inside an air expansion vessel (BDA).
The same turbocompressor (TCA) recompresses the gaseous
nitrogen from about 50 bar to about 280 bar, liquefies
some of it in RAL and sends the remainder of the
gaseous nitrogen to a nitrogen tank RAG.
The nitrogen is then sent from the tank (RAG) to a heat
exchanger (CFF2) where it is heated back up to about
61 C then sent into the tube-type heat exchangers ECTl,
ECT2 in order to cool the combustion gases to 200 C.
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The nitrogen is heated back up to about 900 C
countercurrent to the combustion gases. The nitrogen is
then sent into the nitrogen recuperation turbine (TRA)
associated with an electric generator GE3. In this way,
the nitrogen is used to recuperate heat energy, which
energy becomes converted into electrical energy by the
generator GE3.
The n i trnrrcn cor~~r~t; nn ; t th + 1 ~ t
~ 1- .,.,L....l .....~.,, ..--.. ~~. u~ ii~S ]uo~ uccii
described by way of nonlimiting example is intended to
avoid the encumbrance associated with nitrogen the
atmospheric air content of which is 78%, and associated
with the production of unwanted NOx.
Oxygen circuit (5)
A paramagnetic separator separates the liquid oxygen
from the gaseous nitrogen leaving the expansion vessel
BDA.
The liquid oxygen is sent to a liquid oxygen tank
(ROL). Following storage, it is preheated in an
exchanger CFF2 from -134' to approximately 0 at which
it turns into a gas and is directed to the reactor RC
to feed each of the three burners (BP, BA, BC).
The oxygen feed to the burners encourages complete
combustion of the waste.
An additional catalytic burner (not depicted), also fed
with oxygen, also allows dioxin molecules to be broken
down and the elimination of any unburnt matter.
The means just described for separating the air into
oxygen and nitrogen is used in preference for high-
capacity incinerators according to the invention.
For incinerators according to the invention, but which
are of low capacity, it may be preferable to use air
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separators operating using membrane filters to separate
the oxygen and the nitrogen, this type of separator
making it possible to obtain the oxygen and the
nitrogen directly in gaseous form.
The advantages afforded by this novel type of
incinerator are as follows:
- to in`,iiicrutc tiie same amount of waste, t11C vVlulcle
of the incinerator is markedly lower than that of
the incinerators currently in use,
- the use of oxygen in place of air reduces the
volume of oxidizer by the 79% of nitrogen
contained in atmospheric air. High-pressure
operation within the incinerator speeds up the
rate of combustion of waste in the presence of
oxygen, the absence of nitrogen allowing direct
contact with the oxidizer,
- the recuperation of the nitrogen from the
separation of air makes it possible in high-
capacity incinerators to produce energy using the
recuperation turbines coupled to an electric
generator,
- because the incinerator operates under pressure,
the combustion gases produce energy through the
use of recuperation turbines each coupled to an
electric generator,
- given the operating characteristics of this novel
type of incinerator, the investment required to
incinerate the same amount of waste is lower than
that required with present-day incinerators,
- the closed-circuit operation achieved thanks to
the recirculation of the oxidized gases avoids any
discharge of gas into the atmosphere,
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- the plant can incinerate all kinds of waste
including asbestos and drilling sludge for
example.
