PROCESS AND PLANT FOR INCINERATING WASTE WITH PREHEATING OF THE LATTER

Abstract

The invention relates to a process for incinerating domestic or industrial waste, in a reactor. The combustion is carried out under pressure and with a supply of pure oxygen in the reactor. In the absence of nitrogen, the vapors resulting from the steam expansion turbine are withdrawn in order to preheat the waste before entry thereof into the reactor, then the remaining gases are condensed with a view to the recovery thereof. A plant carrying out the process mainly includes an incineration line, a vapor circuit, a fuel supply line, a nitrogen circuit and an oxygen circuit.

Description

CROSS-REFERENCE TO RELATED U.S. APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

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).

2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98

The object of the invention is to obtain within 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.

BRIEF SUMMARY OF THE INVENTION

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 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 implement the process, is characterized 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.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will be better understood with the aid of the description which follows, given with reference to the following attached figures.

FIG. 1 is a schematic view of an overview of a waste incineration plant according to the invention.

FIG. 2 is a schematic view of a diagram of the water vaporization circuit of the plant.

FIG. 3 is a detailed schematic view of a diagram of the feed hopper and of the feed screw according to the invention.

Reference is made first of all to FIG. 1 which shows a plant in its entirety, this plant essentially comprising:

• • an incineration line 1,
  • a steam circuit 2,
  • a fuel feed line 3,
  • a nitrogen circuit 4, and
  • an oxygen circuit.

DETAILED DESCRIPTION OF THE INVENTION

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 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 intermediate hopper to the hopper TA while said 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.

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 (0F5). 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 fly ash is tipped into a truck which takes it 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),
  • 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 (1a) 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.

The water vapor is condensed and the gaseous oxides are removed (1b) to (CGC). Some of the water from CV2 is reintroduced into the compressor (7), having passed through an osmotic filter.

Steam Circuit (2)

Advantageously, some of the condensed water 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 (CV1) 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 FIG. 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 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 ECT1 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.

This water circuit (1d) 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 ECT1, ECT2 in order to cool the combustion gases to 200° C. 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 nitrogen separation circuit that has just been 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 maybe preferable to use air 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 incinerate the same amount of waste, the volume 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,
  • the plant can incinerate all kinds of waste including asbestos and drilling sludge for example.

Claims

1. A process for incinerating household or industrial waste in a reactor, characterized in that , said process comprising the steps of: combusting waste under pressure and with addition of pure oxygen to the reactor, and in the absence of nitrogen;tapping off steam from an expansion turbine to preheat the waste before the waste enters the reactor; andcondensing remaining gases in order to recuperate the remaining gases.

2. The method as claimed in claim 1, wherein the oxygen needed for combustion is produced by separating the nitrogen and oxygen from the air, the nitrogen thus produced being used to cool the gases resulting from the combustion of the waste, and the oxygen being injected into the reactor at at least one point.

3. A plant for incinerating household or industrial waste, said plant comprising: a reactor with at least one burner fed by a fuel feed line;a feed hopper having a shutter at an inlet and outlet thereof and comprising means for preheating the waste using steam tapped from an expansion turbine;an intermediate hopper to collect the waste preheated in the feed hopper, introducing the preheated waste into the top of the reactor; anda reactor equipped with three burners, the three burners being comprised of a main burner, an auxiliary burner and a catalytic burner positioned near the combustion gases outlet, each of the three burners being fed with fuel by the fuel line and with pure oxygen by an oxygen production circuit.

4. The plant as claimed in the preceding claim, characterized in that the claim 3, wherein said means for reheating the waste comprises a screw thread 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 at the other end between the screw thread and the inlet shutter.

5. The plant as claimed in claim 3, further comprising: a steam circuit attached to the walls of the reactor.

6. The plant as claimed in claim 5, wherein the steam recovery circuit comprises at least one condenser.

7. The plant as claimed in claim 3, further comprising: an air separator operating using membrane filters to separate the oxygen and the nitrogen.

8. The plant as claimed in claim 3, further comprising: an air separator being comprised of a bank of air compressors and a turbocompressor, separating gaseous nitrogen from liquefied oxygen.

9. The plant as claimed in claim 8, wherein oxygen production circuit comprises, after the air separator and the turbocompressor, an expansion vessel, a liquid oxygen storage tank, an exchanger, wherein the oxygen is gasified to be fed to each of the three burners.

10. The plant as claimed in claim 8, further comprising: after the air separator and the turbocompressor, an expansion vessel, a nitrogen tank, three heat exchangers, and a tube-type heat exchanger and a nitrogen recuperation turbine.

11. The plant as claimed in claim 5, wherein the expansion turbine is associated with an electric generator.

12. The plant as claimed in claim 3, wherein the hopper is pressurized to facilitate the expulsion of waste to the combustion reactor.

13. The plant as claimed in claim 12, wherein pressurizing of the intermediate hopper is performed by introducing a gaseous mass under high pressure into said hopper via at least one appropriate orifice.

14. The plant as claimed in claim 13, wherein an orifice via which the gaseous mass is introduced into the intermediate hopper is associated with a remote-controlled valve in order to prevent any leakage of gaseous mass from the intermediate hopper to the hopper while said intermediate hopper is being filled.

15. The plant as claimed in claim 12, wherein the gaseous mass is high-pressure dry steam.

16. The plant as claimed in claim 4, wherein gases leaving the screw thread of the screw are sent to a first condenser is to condense the, condensing water vapor contained in the combustion gases, having passed through a compressor.

17. The plant as claimed in claim 15, wherein water condensate leaving the condenser is bled off to a heat exchanger, the water condensate being vaporized to the form of high-pressure dry steam.

18. The plant as claimed in claim 17, wherein the heat exchanger of comprises a tube bundle in thermal contact with the reactor to recuperate some of the heat given off thereby, this heat being used to vaporize the water.

19. The plant as claimed in claim 18, further comprising: a compressor positioned upstream of the exchanger to pressurize the water and to create at this point a back pressure which prevents the reflux of steam toward the condenser.

20. The plant as claimed in claim 3, wherein, after cooling using nitrogen, the combustion gases are conveyed and condensed then introduced into the turbine, and wherein, after expansion, the gases become separated from the condensed water.