FR2713509A1 - Continuous treatment of hot dust laden fumes - Google Patents

Abstract

Continuous treatment of hot fumes contg. dusts and coming from a thermal installation (1) consists of circulating the fumes in a treatment installation (3); dry treating the fumes and recovering a part of the dust contained in the fumes; wet treating of the fumes by spraying them with a liquid; recovering liquid contg. the dusts; and exhausting the dedusted and cooled fumes to atmos. Periodically and briefly the wet treatment is stopped and the part of recovered dusts are recycled and subjected to the wet treatment. The device and installation used to put this process into service are also claimed.

Description

 The present invention relates to a method and a device for the continuous treatment of hot smoke containing dust and originating from a thermal installation.

 The present invention also relates to an installation for treatment under low pressure of a liquid at high temperature, comprising such a device for treating smoke.

 Thermal installations which can be for example boilers, furnaces for incineration of residues, furnaces for calcination of pulverulent chemicals, furnaces for burning sulfur or phosphorus, or installations for treatment under low pressure at high temperature, for example molten metals and in particular steel, produce hot fumes generally composed of a mixture of gases, among which for example steam, and dust.

 Before being for example projected into the atmosphere, these hot fumes are generally treated in a treatment device which comprises several devices in which the hot fumes pass successively.

 Thus, the hot fumes are successively treated by a dry treatment apparatus and dedusted by a wet treatment apparatus.

 The hot fumes circulate in the various devices by means of compression or suction.

 The dry treatment apparatus also makes it possible to retain part of the dust contained in this smoke and is constituted for example by a cooler.

 In fact, the cooling of the flue gases is particularly important when the devices located downstream of the flue gas circulation flow cannot withstand high temperatures.

 This is the case when these fumes are sucked and not blown, because they must also pass through the suction means without thermally damaging them.

 This cooling can also be intended to recover calories.

 However, the dry treatment devices which retain part of the dust contained in the fumes must be periodically purged to avoid risks of clogging by dry dust which sty accumulates or to limit the fouling of the devices located downstream from the flow of the fumes , such as suction devices.

 For this purge, one generally proceeds to the opening of a purge valve or to the dismantling of a bottom disposed on the dry treatment apparatuses and, by the orifice thus opened, to the emptying of the accumulated dust.

 However, this purging process has serious drawbacks.

 Indeed, the opening of the purge valve leads to the direct rejection of hot fumes generated by the thermal installation, for example to the atmosphere, which can be incompatible with the environment.

 In addition, if the opening time of the purge valve is long, the thermal installation can be stopped for the duration of the purge, which can adversely affect productivity.

 Furthermore, the handling, packaging and transport of dry emptied dust presents a risk of scorching linked to their temperature which remains high and a risk for the environment in the event of flight during transfer or even storage operations.

 The object of the invention is to propose a method and a device for the continuous treatment of hot smoke containing dust which makes it possible to avoid prolonged shutdowns of the thermal installation and the risks of burns as well as damage to the environment. related to the purging of dry dust accumulated in the dry treatment apparatus of the dust treatment device.

The subject of the invention is therefore a process for the continuous treatment of hot smoke containing dust and coming from a thermal installation, process according to which
the smoke is put into circulation by suction or compression means in a treatment installation,
a dry smoke treatment is carried out and part of the dust contained in this smoke is recovered,
a wet treatment of the fumes is carried out by spraying said fumes with a liquid,
- the liquid containing the dust is recovered,
- the dust removed and cooled is discharged into the atmosphere, characterized in that, periodically and briefly, the wet treatment of the smoke is stopped, the part of the recovered dust is recycled using the suction or compression means and said wet treatment is carried out on the part of recovered dust.

 The subject of the invention is also a device for the continuous treatment of hot smoke containing dust and coming from a thermal installation, said device comprising means for compressing or extracting the smoke, at least one apparatus for dry treatment of flue gas connected by a pipe to the thermal installation and provided with a valve for purging dry dust recovered in said dry treatment device and at least one wet smoke treatment device connected by a pipe to said dry treatment device, characterized in that it comprises a pneumatic transport pipe for the dry dust collected in the dry treatment apparatus connecting said purge valve to said wet treatment apparatus.

According to other features of the invention
the pipe connecting said dry treatment device and said wet treatment device is provided with a cut-off valve,
the suction means comprise steam ejectors, at least one of which is located downstream of said dry treatment apparatus and upstream of said wet treatment apparatus on the smoke circuit,
- said dry treatment apparatus is a cooler,
- Said wet treatment apparatus is a condenser or a washer or a condenser and a washer.

 The invention also relates to an installation for treatment under low pressure of a liquid at high temperature, such as for example a molten metal, characterized in that it comprises a device for continuous treatment of fumes as mentioned above.

The characteristics and advantages of the invention will appear during the description which follows, given solely by way of example and made with reference to the accompanying drawings, in which
- Fig. 1 is a schematic view of a thermal installation and an installation for treating hot smoke for implementing the method according to the invention,
- Fig. 2 is a schematic view of a thermal installation for treating a vacuum of liquid steel and of an installation for treating hot smoke for implementing the method according to the invention.

 In Fig. 1, there is shown schematically a thermal installation 1, for example of incineration of waste, supplied with air by a compression means such as for example a fan 2, and an installation 3 for treating hot smoke from the thermal installation 1 .

 The thermal installation 1 comprises, in a conventional manner, burners, fuel supply circuits, waste supply and ash extraction circuits, as well as a combustion chamber, not shown in FIG. 1.

 The hot smoke treatment installation 3 is connected to the thermal installation by a pipe 4 and comprises successively and in the direction of circulation of said hot smoke; a dry treatment apparatus 5, a wet treatment apparatus 6 connected to said dry treatment apparatus 5 by a pipe 8, and a chimney 7 connected to said wet treatment apparatus 6 by a pipe 9.

 Line 8 connecting said dry treatment apparatus 5 and wet treatment apparatus 6 to one another is equipped with a cut-off valve 10.

 The dry treatment apparatus 5 is formed by a cylindrical enclosure 5a with a double envelope, the axis of which is arranged vertically and the lower part of which closes with a neck 5b and a neck 5b with an inclined bottom 5d.

 The enclosure 5a is cooled by circulation of water in its double envelope.

 On the other hand, the cylindrical enclosure 5a is separated into several parts by at least one vertical partition 5e disposed substantially opposite the entry of the pipe 4 into said enclosure 5a and largely above the neck 5b.

 The lower end of the neck 5c opens onto the inlet of a purge valve 11.

 The outlet of this purge valve 11 is connected by a pneumatic conveying line 12 to a secondary inlet 13 of the wet treatment apparatus 6.

 The wet treatment apparatus 6 is formed by a cylindrical enclosure 6a whose axis is arranged vertically and whose lower part ends in a neck 6b and a neck 6c.

 The upper part 6d of the cylindrical enclosure 6a supports a spray device 14 opening into said cylindrical enclosure 6a.

This water spraying device 14 is connected to means for supplying treatment liquid, not shown,
The neck 6c leads to means for continuous treatment of liquid residues, not shown, which include means for separating the sludge, for example by decantation.

 Referring to FIG. 1, we will now describe the operation of the processing device according to the invention.

 When the fan 2 and the thermal installation 1 are in operation, the hot fumes from this thermal installation cause fine incineration dust to fly off in the main pipe 4.

 Still under the pressure exerted by the fan 2, the hot fumes containing the fine dust penetrate into the dry treatment apparatus 5, where they are, simultaneously, partially dusted dry and cooled.

 Indeed, the enclosure 5a is cooled by circulation of water in its double envelope and a significant proportion of dry dust is entrained in the fumes and is deposited at the bottom 5d of the enclosure 5a.

 The partition 5e reinforces the effectiveness of this double dusting and cooling action by lengthening the residence time of the fumes inside the enclosure 5a.

 The fumes thus cooled and partially dedusted then penetrate into the enclosure 6a of the wet treatment apparatus 6 via the pipe 8 through the cut-off valve 10.

 In this enclosure 6a, the fumes are sprayed by the device 14 supplied with treatment liquid, for example water.

 The fine spray droplets cause a large proportion of dust still contained in the fumes and dissolve or react with certain gases contained in these fumes.

 These droplets are then collected at the bottom of the enclosure 6a in the neck 6b and the neck 6c to form residual liquids.

 The wet treatment apparatus 6 thus has a double action of dusting and physicochemical treatment of the fumes.

 The residual liquids, generally aqueous, are then treated continuously, in particular by decantation, before being partially recycled.

 The settling sludge, which contains dust entrained during the wet treatment of the smoke, is for example stored for several months before being removed without any particular risk in terms of handling and transport.

 The dedusted, cooled and treated fumes are then entrained towards the chimney 7 by the main pipe 9.

 Furthermore, the dust 7 accumulates in the bottom 5d of the enclosure 5a of the dry treatment apparatus 5.

 So that this accumulation in the neck 5b and the neck 5c does not end up obstructing the enclosure 5a and impairing its effectiveness, this enclosure 5a is purged by closing the cut-off valve 10 and opening the purge valve 11 without stopping the fan 2.

 The pressure is then exerted against the dry dust accumulated in the bottom of the enclosure 5a which rushes into the pneumatic conveyor line 12 towards the secondary inlet 13 of the enclosure 6a of the wet treatment apparatus 6 in operation.

 In this wet treatment apparatus 6, the dry dust is then dispersed in the droplets and the residual liquids which are generally aqueous.

 They are thus found in the settling sludge like the dust normally extracted by the wet treatment apparatus 6.

 When all of the dry dust accumulated in the enclosure 5a of the dry treatment apparatus 5 is discharged, the purging is stopped by opening the cut-off valve 10 and closing the purge valve 11.

 This purge operation can be repeated frequently and therefore its duration is very short.

 Thanks to this process, the handling and transport of dry and hot dust is totally avoided, which is advantageous for safety and the environment.

 As the purge operation of the enclosure 5a of the dry treatment apparatus 5 is very brief, it is generally not necessary to interrupt the operation of the thermal installation 1 which is advantageous in terms of productivity .

 Finally, there is no risk of exhaust fumes to the atmosphere before treatment, even at the purge valve 11 of the dry treatment apparatus 5, which represents the best guarantee of protection for the environment.

 Of course, the thermal installation can be a boiler, an oven for calcining chemicals, for example a rotary oven, an oven for burning other products, for example sulfur or phosphorus, or any other device producing hot fumes. .

 Referring to FIG. 2 we will now describe another embodiment of the method according to the invention, which applies in particular to the case where the fumes are sucked and no longer compressed.

The device shown schematically in the
Fig. 2 comprises a thermal installation 20 for vacuum treatment of liquid steel, a treatment installation 3 for hot smoke, suction means formed by a pump 21 and a chimney 7.

 The thermal installation 1 is a conventional liquid steel treatment installation under vacuum.

 This thermal installation 1 comprises for example a cylindrical vacuum enclosure 20a with a vertical axis, the bottom of which is provided with two cylindrical plungers, respectively 22 and 23, hollow and made of refractory materials.

 A gas injection pipe 20b communicates with one of the plungers, such as for example the plunger 22.

 The upper part of the envelope 20a communicates with the treatment installation 3 for hot smoke by a main pipe 4.

 The hot smoke treatment installation 3 successively comprises and in the direction of circulation of the smoke, a dry treatment apparatus 5, a steam ejector 24 connected to the dry treatment apparatus 5 by a line 8, an apparatus wet treatment 6 connected by a pipe 25 to the steam ejector 24 and also connected to the pump 21 by a pipe 9.

 The main line 8 is provided with a cut-off valve 10.

 The dry treatment apparatus 5 is identical to that of the installation described above.

 The lower end of the neck 5c of the enclosure 5a opens onto the inlet of a purge valve 11 and the outlet of this purge valve 11 is connected by a pneumatic conveying line 12 to a secondary inlet 13 of the enclosure 6a of the wet treatment apparatus 6.

 The steam ejector 24 is a device of conventional type intended to increase the smoke suction rate on the treatment circuit and to further lower the pressure upstream, in particular in the enclosure of the thermal installation 1 .

 This steam ejector is supplied by means of producing steam under pressure, not shown.

 The wet treatment apparatus 6 is identical to that of the installation described above.

 The water spraying device 14 here comprises several spraying ramps.

 The neck 6c of the enclosure 6a of the wet treatment apparatus 6 leads to means for continuous treatment of liquid residues, comprising means for separating sludge, for example by decantation.

These means are not shown on the
Fig. 2.

 The pump 21 is with a liquid ring and the chimney 7 is connected to the extraction orifice of the pump 21 by a pipe 19.

The treatment facility shown in
Fig. 2 operates as follows.

 A pocket 30 containing liquid steel is brought under the thermal installation 1 for the vacuum treatment of the steel contained in said pocket 30.

 The vacuum steel processing operation lasts about 30 minutes.

 When the pump 21, the steam ejector 24 are in operation, and the plungers 22 and 23 are partially immersed in the liquid steel, the enclosure 20a is under low pressure and the liquid steel enters it.

 This steel is circulated between the two plungers 22 and 23 by injecting a gas through the pipe 20b at the plunger 22.

 On the surface of the liquid steel maintained under low pressure in the enclosure 20a, extremely hot fumes are released, which contain said gas injected by the plunger 22, dissolved gases and impurities extracted from the liquid steel.

 These fumes also contain dust, which results in particular from condensation or the reaction of gases between them.

 Under the action of the suction means constituted by the steam ejector 24 and the pump 21, the hot fumes penetrate into the enclosure 5a of the dry treatment apparatus 5 where they are simultaneously partially dusted dry and cooled .

 A large proportion of dry dust entrained in this smoke is deposited at the bottom 5d of the enclosure 5a and the smoke thus cooled is no longer liable to damage the devices located downstream on the circuit and in particular the steam ejector 24.

 The cooled and partially dusted fumes are then sucked in by the steam ejector 24 through the main line 8 through the cut-off valve 10 and they emerge from said steam ejector 24 with steam coming from the normal operation of this device. .

 To maintain the low pressure, it is then necessary to condense this vapor.

 These fumes, which contain water vapor, then enter the enclosure 6a of the wet treatment means 10 via the pipe 25 where they are sprayed by the device 14 supplied with cold water.

 The fine spray droplets cause a significant proportion of dust still contained in the fumes and cause the condensation of the water vapor contained in these fumes.

 The droplets are then collected at the bottom of the enclosure 6a of the wet treatment apparatus 6 in the neck 6b and the neck 6c to form residual water.

 This wet treatment apparatus 6 therefore has a double action of dusting and condensation.

 The residual water is then treated continuously, in particular by decantation and cooled before being partially recycled.

 The settling sludge which contains the dust entrained during the wet treatment of the fumes is for example stored for several months before being discharged without any particular risk in terms of handling and transport.

 The fumes thus dedusted and cooled are then sucked by the pump 21 and discharged to the atmosphere by the chimney 7.

 Furthermore, the dry dust accumulates at the bottom 5d of the enclosure 5a of the dry treatment apparatus 5.

 Indeed, it has been found, for example, that approximately half of the dust was retained at this level.

 In order to avoid entrainment of dust in the devices located downstream and in particular in the steam ejector 24 where they could damage it, the enclosure 5a is purged by closing the cut-off valve 10 and opening the purge valve 11 without stopping the pump 21 or the steam ejector 24.

 The dry dust accumulated in the bottom of the enclosure 5a is thus sucked into the pneumatic conveying line 12 towards the secondary inlet 13 of the enclosure 6a of the wet treatment apparatus 6 in operation.

 This dry dust is then dispersed in the droplets and the residual water and is thus found in the settling sludge like the dust normally extracted by the wet treatment apparatus 6.

 When all of the dry dust accumulated in the enclosure 5a of the dry treatment apparatus 5 is discharged, the purge is stopped by opening the cut-off valve 10 and closing the cut-off valve 11.

 This purging operation is preferably carried out between each vacuum treatment of pockets of liquid steel, while the enclosure is no longer under low pressure.

 The purge operation therefore takes place "in masked time" while the vacuum treatment installation is inoperative.

 One of the advantages of this type of sequence lies in the fact that the suction of the dust is faster at the time of the purge. The duration of the purge operation is then only around five seconds for 10 to 50 kg of dry dust to be extracted.

 Thanks to the treatment method and device according to the invention, all the dust is collected in a single stream, namely the sludge from settling of residual water from the wet treatment apparatus 6, which facilitates operation and limits the costs.

 Therefore, handling and transport of dry and hot dust is totally avoided, which is particularly advantageous for safety and the environment.

 Thanks to the rapidity of the purge, for example by simply opening the bottom 5d of the enclosure 5a of the dry treatment apparatus 5, the purge operation lasts approximately 30 minutes.

 According to other variants within the framework of the invention, the vacuum treatment installation can be intended to treat molten metals other than steel or molten glasses, or be intended to crystallize solutions. and the smoke treatment and suction installation may include several steam ejectors and several pumps connected in series or in parallel.

 The dry treatment device can be a heat exchanger, an electrostatic filter, a cycloning device or any device where dry dust can accumulate and the wet treatment device can be a washing, atomizing tower. or any other smoke treatment device delivering residual liquids entraining part of the dust contained in this smoke.

 On the other hand, several devices, such as ejectors, may be located between the enclosure of the dry treatment device and the enclosure of the wet treatment device on the smoke circuit and several wet treatment devices. on the smoke circuit, of the same type or of different types.

Claims (8)

 1. Process for the continuous treatment of hot smoke containing dust from a thermal installation (1), process according to which  - the flue gases are circulated by suction or compression means in a treatment installation (3),  a dry smoke treatment is carried out and part of the dust contained in this smoke is recovered,  a wet treatment of the fumes is carried out by spraying said fumes with a liquid,  - the liquid containing the dust is recovered,  - the dust removed and cooled is discharged into the atmosphere, characterized in that, periodically and briefly, the wet treatment of the smoke is stopped, the part of the recovered dust is recycled using the suction or compression means and said wet treatment is carried out on said part of recovered dust.  2. Device for the continuous treatment of hot fumes containing dust and coming from a thermal installation (1), said device comprising means for compressing (2) or extracting (21) the fumes, at least one treatment device dry (5) smoke connected by a pipe (4) to the thermal installation (1) and provided with a purge valve (11) of the dry dust recovered in said dry treatment apparatus (5) and at least a wet smoke treatment device (6) connected by a pipe (8) to said dry treatment device (5), characterized in that it comprises a pipe (12) for pneumatically transporting the dry dust recovered in the dry treatment (5) connecting said purge valve (11) to said wet treatment apparatus (6).  3. Device according to claim 2, characterized in that the pipe (8) connecting said dry treatment device (5) and said wet treatment device (6) is provided with a cut-off valve (10).  4. Device according to claim 2 or 3, characterized in that the suction means (21) comprise steam ejectors (24) at least one of which is located downstream of said dry treatment device (5) and upstream of said wet treatment device (6) on the smoke circuit.  5. Device according to one of claims 2 to 4, characterized in that said dry treatment apparatus (5) is a cooler.  6. Device according to one of claims 2 to 4, characterized in that said wet treatment apparatus (6) is a condenser or a washer or a condenser and a washer.  7. Installation for treatment under low pressure of a high temperature liquid, characterized in that it comprises a device for continuous treatment of smoke according to any one of claims 2 to 6.  8. Low pressure treatment installation according to claim 7, characterized in that the high temperature liquids is a molten metal, in particular steel.