FR2654021A1 - FLYING ASH VITRIFICATION PROCESS AND DEVICE FOR ITS IMPLEMENTATION. - Google Patents

Abstract

The fly ash vitrification process according to the invention consists of: heating the fly ash regardless of its origin so as to reach their fluidity point at temperatures between 1150 ° C and 1450 ° C; - the destruction of these at very high temperatures (which can reach 2000 ° C) allowing the transformation of harmful products into plasma; - Abrupt cooling of the liquefied product to ambient temperature to ensure bursting leading to spraying so as to obtain grains whose particle size allows a good casting rate. The device for the implementation comprises in combination - means 1 for routing the fly ash; - a melting chamber 4, comprising heating means 5 to reach a temperature above 1450 ° C; - a solidification chamber 12 comprising cooling means allowing precipitation of the liquefied product; - Means for recovering 14 and evacuating 16 the vitrified ashes; a unit 19 for treating the combustion gases before they are discharged into the atmosphere.

Description

The present invention relates to a vitrification process of

  fly ash and a device for its implementation.

  It is usual, to treat industrial and household waste to eliminate them in an incineration network, and to use the combustion of a fossil material, such as coal, as energy in thermal power plants. Such solutions have the disadvantage, in the case of thermal power plants and the incineration of household waste, to lead to two main types of solid residues: machefers, or fireplace ashes that are melted or softened particles in the hearth that agglomerate and fall to the base of the combustion chamber

  fly ash which is very fine particles, trans-

  carried by the fumes and captured before being discharged into the atmosphere by

  various mechanical and / or electrostatic filtration processes.

  Fly ash, originating in France from the incineration of 17 million tonnes of household waste, represents 250 000 tonnes and is a powdery product consisting of very fine particles with a density ranging from 1900 to 2400 kg / m 3 and whose finesse, measured

  by a Blaine permeabilimeter ranges between 2200 and 4000 cm 3 / g.

  The size of these particles is between 0.5 JD and 200 gV with a percentage distribution, depending on the type of capture or filtration process, of the type: from 50 to 70% have a size less than 50 pu of 50 at 80% have a size between 50 and 80 from 10 to 25% are larger than 80 The great fineness of these particles poses a problem for their storage, and this, in particular because of the dissipation of these products and

  very high risk of their dispersion.

  The study of the chemical composition of these ashes, including

  The crude product content is 1% to 2%, and the solubility of 30 to 40% has been shown to include components such as Ca (OH) 2 50% Ca (CO 3) 10% Ca C 2 10% Ca SO 3 0.3% Ca F 2 0.1% Carbon traces Cl 4 to 6% Cd 0.04% Cu: 0.15 to 0.20% Fe 3 to 8% Mn: 0.2% Ni: 0, 02% Pb: 0.3 to 0.4% Zn 2 to 3% Hg: traces Dioxin traces the presence of such highly soluble metal salts, easily drivable by rainwater, is an important source of pollution

  soil and groundwater.

  This risk is all the greater, as very often, these ashes

  are mixed with machefers produced by incineration, the

  seems to be evacuated and stored without any special precautions.

  Fly ash produced by coal-fired power plants can be evaluated annually at 300 000 tonnes in France. Their particle size is similar to that of fly ash.

  from the incineration of household waste.

  The chemical analysis of these ashes has established that they generally consist of: Si O 2 42 to 45%

AI 203 22 to 32%

  Fe 203 + Ti O 2 4 at 15% Ca O 1 at 8% Mg O 1 at 3%

K 20 2 to 5%

  Na 2 0.5% to 1% So 3: 0.2 to 2% Carbon 2 to 8% Traces of Pb, Mn, B, Mb Although such a chemical composition is different from that

  fly ash from household garbage incineration plants

  and therefore does not present the same drawbacks of pollution and toxicity, their great fineness makes them comparable to cement powder, which poses the same problems for their handling and storage as those encountered by the fly ash from incineration plants. In addition, the improvement of the means of measurement is likely to show evidence of toxic elements present at low doses, as well as the use of fuel from

  new deposits, more or less diversified, can lead to

  other harmful compounds in the combustion residues.

  To overcome these drawbacks, since these fly ash are not admissible in certain landfills because of their solubility and their content of heavy metals, it is known to subject them to

  pre-treatment before depositing therein.

  This pre-treatment has a twofold objective, on the one hand to give cohesion to this powdery material, in order to facilitate its transport to its disposal in a landfill, and, on the other hand, to render inert or to extract the

  often toxic metals they contain.

  To do this, a Swiss process aims to solidify these ashes by adding cement and to inerter by stabilizing the p H using adjuvants of known type acting as a buffer This solution is economical but requires a prior washing of ashes before mixing with cement so as to eliminate any trace of chloride which prevents its solidification It is then necessary to carry out a water treatment

  in order to avoid any possibility of pollution.

  However, given the high content of these heavy metal ashes, such as lead or zinc, which due to the highly alkaline p H are in the form of readily soluble hydrocomplexes, the risk of pollution of these substances by migration is very important, and this same

  after solidification with cement.

  Moreover, other processes are aimed at conditioning these ashes by storage in plastic bags by bagging, before their disposal in a specific cell in a controlled discharge of urban residues of these bags coated with lime Whatever the mode of treatment chosen, these residues must be compacted in a cell or in a well-defined part of the discharge, in order to form a homogeneous and weak mass

  surface that does not come into contact with biodegradable substances.

  Indeed, the mixture, with household waste, causes variations of p H tending to solubilize the metal salts, which facilitates the

  mobility of toxic substances such as dioxin.

  The present invention aims to overcome these disadvantages by providing a method of vitrification of fly ash and a device

  for its implementation which allow an increase in the granulo-

  emits ashes, thus avoiding the dissipation into the atmosphere and the dispersion in the soil thereof, while guaranteeing the insolubility of the components which remain stable over time, confined in the vitrified particles, and relieving the constraints of handling of storage or

recycling of such compounds.

  In addition, this process promotes the reduction of the amount of waste by the elimination of residual carbon and the combustion and

  high temperature destruction of toxic products.

  To this end, the process according to the invention consists in heating the fly ash irrespective of their origin and so as to reach their point of fluidity at temperatures between 1150 ° C. and 1450 ° C. the destruction thereof at very high temperatures (which can reach 20000 C) to transform into plasma harmful products the sudden cooling of the liquefied product at room temperature to ensure a burst leading to a spray so as to obtain grains whose particle size allows a good flow rate

casting.

  According to an alternative embodiment, the second step of the process consists in treating the ashes by adding flux so as to maintain and to confine in the vitrified residue the harmful components to the

  lowest possible temperature (below 1450 C).

  Thus, these adjuvants serve on the one hand to ensure the cohesion of the products, and on the other hand, plays the role of fluxing so as to allow liquefaction at temperatures below the melting temperature of the "pure" product, thus avoiding the transfer of harmful products into the combustion gases. The invention also relates to a device for the implementation

process.

  According to a simple embodiment of the invention this device comprises in combination: means for routing the fly ash a melting chamber, comprising heating means, to reach a temperature above 14500 C.

  a solidification chamber comprising cooling means

  drainage allowing the precipitation of the liquefied product

  means for recovering and evacuating vitrified ashes

  a flue gas treatment unit prior to their

evacuation into the atmosphere.

  According to one embodiment of this device, the melting takes place inside the melting chamber in a furnace allowing the use of either a direct heating by fossil fuel of the coal or gas type, or by electric arcs. or electrical resistors, either

indirect heating.

  Advantageously, the use of direct heating allows the

  fly ash to directly undergo the liquefaction operation.

  According to another embodiment of the method, the indirect heating can be obtained either by the use of fossil fuel of the coal or fuel or gas type, or by arcs or resistors

  electric, either by the use of burners.

  In the current state of the art, the electric arcs or the electric resistances make it possible to obtain, thanks to their simplicity of implementation, a temperature range which ensures a good operation of the

  device and optimum quality of liquefied fly ash.

  Advantageously, the burners used are of the plume torch type

  electroburner or conventional gas burner.

  Plasma torches are of real interest only for

  temperatures above 2000 ° C.

  Electrobrulers generally combining a gas burner or an arcing flame doping are of interest to them.

  stable temperature above 1600 VC.

  Finally, conventional burners are generally sufficient for this type of vitrification, insofar as they provide a temperature

stable between 14501 C and 1500 'C.

  Advantageously, the use of such burners is an easy adjustment of combustion, which makes it possible to minimize the volume of gas produced. However, the use of a conventional heating method is feasible provided to provide an adaptation of the burners In the case of pulverized coal, this adaptation of the melting bag is then constituted by a cyclone type boiler. Whatever the origin of the heat source, it is intended to allow the obtaining of the temperature necessary for the fusion of the fly ash, with the adjustment adapted to the product and likely to ensure a temperature margin allowing to guarantee optimum quality of

product.

  According to a feature of the device, the vitrification is done inside a solidification chamber in a tray of a hydraulic ashtray. According to another advantageous feature of the device, the tray comprises an orifice arranged to receive a water supply conduit

and one too full.

  Advantageously, the overflow and the water supply allow

  attempt to maintain a constant level to compensate for evaporation or various losses, as well as to obtain a temperature of about 500 C which favors the good granulometry of the liquid ashes, in the form of a magma, which undergo a burst leading to their spraying due to

their brutal cooling.

  According to one characteristic of the invention, vitrified grains and

  obtained have a thickness of a few millimeters.

  Advantageously, such a size is obtained thanks to the independent or simultaneous adjustment of the temperature of the melting chamber and the

  flow rate of the casting of the liquefied product.

  According to another characteristic of the invention, the ashes are brought by distributors adapted to powdery products of the type

raclette chains.

  These ashes are then dumped into the fusion pocket by

  via an injection system.

  According to another characteristic of the invention, the injection system

  This is a pusher mechanism that allows you to achieve a perfect

  sealing of the melting pocket.

  The casting of the product is then done in a chamber coated with

  refractory type molten electro block or silica.

  According to a preferred embodiment, the installation can contain

  lateral burners, the technique of which depends on the temperature

  chée. According to one characteristic, the evacuation, at the outlet of the mechanical extractor ashtray vitrified ash, can be done either by

  hydraulic or by a vibrating table conveyor.

  Thus, the ashes are brought to a storage facility.

  or evacuation to a means of transport.

  According to another characteristic of the invention, the treatment unit

  It includes cleaning and decanting means which ensure cleaning of the flue gas before it is released into the atmosphere. This minimizes the release of toxic gas from the atmosphere.

the burning of fly ash.

  Anyway, the invention will be well understood using the

  description which follows, with reference to the appended schematic drawing,

  single figure represents an embodiment of the device for setting

implementation of the method.

  The fly ash vitrification unit shown in drawing comprises a melting chamber 2, a solidification chamber 12,

  means of transport 1 of the fly ash, and means of recovery

  14 and evacuation 16 of vitrified ash.

  The fly ash is conveyed via a conveyor 1, suitable for pulverulent products, of the type raclette chain, to

  the inlet of a closed chamber constituting the melting chamber 2.

  An injector, of the pusher mechanism type, not shown in the figure, being able to move by translation by known means along a horizontal axis, allows their introduction into the combustion chamber 4 by an adapted opening 3 located on the upper part of the combustion chamber A burner 5, of known type, inserted in the chamber of

  4 is fed by an external combustion inlet duct 6

  tible and in power supply.

  A fan 7, located outside the melting chamber 2 via an auxiliary circuit 8 to air, cools the burner The fly ash carried by gravitation fall in the bottom of the combustion chamber 4 They are there liquefied in the form of magma and drive out into a truncated well of casting 9 arranged in the bottom of the chamber 4 against one of these internal faces This liquid magma then arrives in a tank substantially filled with water,

  of a hydraulic ash box II of the solidification chamber 12.

  This tank 10 has in its upper part a first opening 12 arranged to receive the arrival of a conduit water supply and in its middle part a second opening 13 for a overflow conduit which leads to an evacuation circuit in non-water

shown in the figure.

  The liquid magma, in contact with the water cools suddenly, by vitrifying, then is deposited in the bottom of the tank 10 in the form of grains of vitrified ash A mechanical extractor 14 of the known type placed in the bottom thereof conveys these vitrified ashes to a decanting unit 15 of the known type. After passing through them, these vitrified ashes are carried away by a conveyor 16, of the table conveyor type.

  vibrating, up to means of transport 17.

  An external combustion gas outlet duct 18 placed at the top of the melting chamber allows the evacuation of the fumes to a unit

  evacuation and settling 19.

  A water conduit 20 provides its feed and opens into a tank 21 where the particles are deposited in the bottom by gravitation At the outlet thereof, the particles are taken by a conveyor 12 to the decanting unit 15 before be transported with vitrified ashes

by means of transport 17.

  The fumes, after purification and filtration, are evacuated

  the atmosphere by a chimney 23 placed at the exit of the unit 19.

  The process of vitrification of fly ash is proceeding as

described below.

  Fly ash, regardless of its origin, is brought into the combustion chamber 2 via a conveyor 1 They are introduced into the melting chamber 4 through an opening 3

  thanks to an injection system.

  Inside this melting chamber 4, these ashes are heated by burners 5 adapted to reach their point of fluidity at temperatures between 11501 C and 14501 C and then are converted at a temperature of 20000 C in plasma to to destroy the

  harmful compounds they contain. This plasma is then cooled

  in a tank 10 of the hydraulic ash tray It in contact with water, this

  which allows a burst leading to a spray.

  An extractor 14 conveys these vitrified ashes fallen by

  gravitation in the bottom of the tank 10 to a settling unit 15.

  After the passage in this one they are led by a

  vibrating table conveyor 10 to means of transport 17.

  The fumes coming from the combustion of these ashes are captured at the outlet of the melting chamber 4 and are treated by a purification and settling unit 19. The particles derived from the latter are then conveyed to the unit of separation. decantation 15 before being conveyed

  with fly ash to means of transport 17.

  It goes without saying that the invention is not limited to the sole embodiment of this device for the implementation of this method of

  vitrification of fly ash which has been described above as an example

  ple, it embraces on the contrary all variants and

  application respecting the principle.

  Thus we will not depart from the scope of the invention, by the use of any type of brutal cooling liquefied ash in the form of magma or by the use of other types of direct heaters

  and indirect, used alone or in combination.

Claims (17)

  1 process for vitrification of fly ash characterized in that the invention consists in carrying out: the heating of fly ash irrespective of their origin so as to reach their point of fluidity at temperatures between 11501 C and 14501 C the destruction thereof very high temperatures (which can reach 20000 C) making it possible to transform into plasma the harmful products the brutal cooling of the liquefied product at ambient temperature to ensure a burst leading to a spraying for   obtain grains whose granulometry allows a good flow of casting.   2 Process according to claim 1, characterized in that the second step of the process consists in treating the ashes by adding flux so as to maintain and to confine in the vitrified residue the harmful components at the lowest possible temperature (less than 14500 C).   3. Method according to one of claims 1 or 2, characterized in that   that the brutal cooling takes place in a tank substantially filled with water.   4 Device for implementing the method characterized in that it comprises in combination: fly ash tracking means (1) a melting chamber (4) having heating means for reaching a temperature above 14501 C a solidification chamber (12) comprising cooling means for the precipitation of the liquefied product of the means for recovering (14) and evacuating (16) the vitrified ashes a flue gas treatment unit (19) prior to their evacuation into the atmosphere.   Device according to claim 4, characterized in that the melting is carried out inside the melting chamber (4) in a furnace for using a direct heating by fossil fuels of the type coal, fuel or gas.   6 Device according to claim 4, characterized in that the melting is carried out inside the melting chamber (4) in a fireplace there   allowing to use a direct heating by electric arcs.   7 Device according to Claim 4, characterized in that the fusion takes place inside the melting chamber (4) in a firebox   allowing to use a direct heating by electric resistances.   8 Device according to claim 4, characterized in that the fusion takes place inside the melting chamber (4) in a fireplace by indirect heating.   9 Device according to claim 8, characterized in that the indirect heating is obtained by the use of fossil fuel of the type coal, fuel or gas.   Device according to claim 8, characterized in that the   Indirect heating is achieved by the use of an electric arc.   11 Device according to claim 8, characterized in that the   indirect heating is achieved by the use of an electrical resistance.   Device according to claim 8, characterized in that the   Indirect heating is achieved by the use of suitable burners (5).   13 Device according to Claim 12, characterized in that the burners used are of the plasma torch, electroburner or burner type. conventional gas.   Device according to Claim 4, characterized in that the vitrification is carried out inside a solidification chamber (12)   in a tank (10) of a hydraulic ashtray (11).   Device according to claim 14, characterized in that the tank (10) comprises an orifice arranged to receive a duct   water supply (12) and overflow (13).   Device according to one of Claims 4, 14, 15, characterized   in that the vitrified grains obtained have a thickness of a few millimeters. Apparatus according to claim 4, characterized in that the fly ash is supplied by distributors (1) adapted to   pulverulent products (1) of the raclette chain type.   Device according to claim 4, characterized in that the   injection system is a push mechanism.   19 Device according to one of Claims 4 and 14, characterized   in that the discharge at the outlet of the mechanical extractor (14) of the ashtray   (11) vitrified ash is done hydraulically.   Device according to one of claims 4 and 14, characterized   in that the evacuation at the outlet of the mechanical evacuation of the ashtray (11) from the vitrified ashes is carried out by a table conveyor vibrating (16).   Device according to claim 4, characterized in that the treatment unit (19) comprises cleaning and settling means (19) which make it possible to ensure the cleaning of the combustion gas.   before being released into the atmosphere.