LU88210A1 - Removal of solid residues from gas purification unit - using a fluidised bed formed by purge gases to separate toxic gases and water allowing pneumatic transport of residual solids - Google Patents

Abstract

Removal of solid residues, granular or powdered from a gas purification installation, partic. that of a furnace by: (a) discharge of solid residues from purification installation (10) to at least one prim. sealed vessel (18) via discharge pipe (12); (b) isolation of vessel (18) by sealing discharge pipe (12); (c) passage of at least one purge gas across residues to form fluidised bed (22); (d) controlled evacuation of purge gas; and (e) progressive evacuation of residues and transport by suspension in gas under pressure. At least one prim. purge gas is inert and at least one purge gas is a reheated gas with low humidity, e.g. dried air. Purge gases pressurise vessel (18) and flow is maintained constant. On evacuation, purge gases pass across separators to remove solids. Appts. comprises: (a) a sealed vessel (18) fed with residues from purification installation (10) via discharge pipe (12) with gas tight valve (16); (b) a fluidisation surface (20) supplied (42) with gas producing a static, resp. fluidised bed (22) of the solids; (c) a decompression pipe (24) with valve (26); and (d) an evacuation unit (64) for solids with valve (66) connected to a pneumatic conveyor (68). The gas supply unit (42) has a cooler (50), a water separator (52) and a reheater (56). Alternative versions employ either: (a) two vessels (18) in parallel, operating alternately, one filling and purging and the second emptying. In this case the pressure of the prim vessel to be filled is maintained close to that of the purification unit (10), or (b) two vessels (18) connected to one another via a gas tight pipe with associated valve, the second vessel being connected to the pneumatic conveyor.

Description

The present invention relates to a method and an installation for the evacuation of solid, granular or pulverulent residues, from a gas purification installation, including blast furnace gas. \

Gas purification installations, in particular blast furnace gases, are known in which solid, granular or pulverulent pollutants are separated from the gas phase using dry separators such as, for example, dust bags, cyclones, bag filters and electrostatic precipitators. These solid residues are collected in hoppers installed directly below the dry separators.

Until now, these hoppers, which must be emptied regularly, discharge, by means of extraction equipment freely the solid residues, either directly in wagons or vats of trucks, or simply on a pile under the hoppers to then be loaded by mechanical shovels on wagons or trucks. The trucks then evacuate the solid residues to an intermediate storage area. It will be noted that the solid residues separated from the blast furnace gases mainly consist of iron and coke dust which under certain conditions can be advantageously recycled in an agglomeration installation. The operation of evacuating solid residues from the filter hoppers is, in the current state of the art, essentially a batch handling operation which has major disadvantages. First of all, the free dumping of powdery solid residues is a very dusty operation, which undoubtedly leads to problems from the point of view of workplace health and environmental protection. Subsequently, the discharge into the open air of the solid residues also uncontrollably releases toxic gases and vapors which are entrained by the solid residues outside the gas purification installation during the discharge of the hoppers. These gases and vapors released in an uncontrolled manner undoubtedly represent a significant safety problem. Finally, the solid residues must be loaded by mechanical shovels on wagons or trucks which transport them to an N intermediate storage area to, if necessary, be subjected to an additional handling operation before recycling.

It is obvious that this discontinuous handling of solid residues is an unsanitary, polluting and costly practice. In addition, the disposal method described above has the disadvantage that we do not know how to exploit, in a recycling operation, the significant heat energy still contained in the solid residues at the outlet of the water treatment plant. gas.

One could naturally think of using continuous transport systems for granular or powdery products known per se, in particular open mechanical conveyors (for example conveyor belts), mechanical conveyors integrated in closed conduits (for example Archimedes screws ) and pneumatic conveyors. A priori, however, the aforementioned systems seem to create more problems than they solve. Open conveyors in no way eliminate the pollution, health and safety problems associated with the dust, gases and vapors released during the handling of solid residues. Mechanical conveyors integrated in closed conduits could, as sealed systems, solve the problem of release of dust, gas and vapors but, for cost reasons, it is however hardly possible to use such systems over longer distances. As for pneumatic conveyors, they are unreliable because they risk clogging when the solid residues are wet, leading to major cleaning work before they can be restarted again. However, in the case of blast furnace gases, it is necessary to provide, inside the gas purification installation, for certain operating regimes of the blast furnace, a partial condensation of the water vapor contained in gases, which naturally wets the solid residues collected in the hopper of the filter. This humidification of solid residues can also be due to an operation of adjusting the temperature of the blast furnace gases upstream of the filter, which is carried out by an injection of water. It should also be considered that any transport system by closed mechanical conveyor or by pneumatic conveyor will present serious risks of explosion if the gases entrained by the solid residues include combustible gases. The object of the present invention is to provide, for the evacuation of solid, granular or pulverulent residues, from a gas purification installation, in particular from blast furnace gas, a reliable process for the continuous evacuation of these solid residues mistletoe controls risks from the point of view of safety, health and pollution and whose operation is not called into question when the solid residues to be removed are wet.

According to the present invention, this objective is achieved by a process characterized by unloading at least part of said solid residues in at least one first closed vessel located in the immediate vicinity of the purification installation, isolating this first closed vessel with respect to the gas purification installation when the unloading operation is completed, a passage of at least one purge gas under pressure through said solid residues contained in this first closed vessel so as to create a static bed fluidized respectively, said solid residues in this first closed vessel and a controlled evacuation of this purge gas, followed by an evacuation of the solid products by pneumatic transport, suspended in a gas under pressure.

According to the proposed method, said solid residues to be removed from the gas purification installation are first discharged into a first closed vessel. This first closed vessel is then isolated from the gas purification installation and a purge gas is blown under pressure into N said solid residues in order to create in said first closed vessel a static or fluidized bed of said solid residues. In this way the gases and vapors trapped between the solid particles are released and mix with the purge gas. The latter is then evacuated in a controlled manner together with the gases and vapors entrained by said solid residues outside of said first closed vessel.

It will be noted that the particles in suspension in the static or fluidized bed offer a very large contact surface with the purge gas. In this way it is possible to carry out, if necessary, an optimal transfer of heat energy from the gaseous medium to the solid residues. This heat exchange provides the latent heat necessary for the evaporation of volatile substances, such as water, which permeate the solid residues. The proposed method therefore makes it possible to carry out effectively not only a controlled elimination of the gaseous substances entrained by the solid residues, but also a drying of the wet solid residues and a controlled elimination of the vapors thus produced. At the end of the purging operation, we therefore find ourselves in the presence of solid residues ideally prepared to be transported by a pneumatic conveyor suspended in a second pressurized gas. In fact, the solid residues are separated from all the toxic and / or explosive gases possibly entrained by the solid residues outside the gas purification installation during their discharge. In addition, the solid residues have, where appropriate, been effectively dried in the static or fluidized bed and no longer present a risk of agglutinating in the wet state. Finally, the solid particles, granular or powdery, no longer form a compact mass, but are already at least partially in suspension in a gas.

As regards toxic, explosive and / or polluting gases and vapors, separated from said solid residues and diluted in an adequate purge gas, they can be evacuated in a controlled manner outside said first enclosure, either to a place where they can be released without risk to humans and / or the environment, or to a post-treatment facility for these gas mixtures.

With the purge gas, an overpressure is advantageously created in said first closed vessel. In fact, for the same mass flow rate of the purge gas, the higher this overpressure, the lower the speed of the gas in the fluidized bed, the more homogeneous the fluidization obtained and the lower the risk of entrainment of solid particles. Or in other words, for an imposed limit speed of the purge gas in the fluidized bed, the increase in pressure in the first closed vessel makes it possible to increase the mass flow rate of the purge gas. Note that this overpressure in said first closed cup can reach a few bars.

The first purge gas blown into said solid residues is advantageously an inert gas. In this way, any risk of explosion is effectively eliminated from the start of the process.

If the solid residues are wet, which could lead to agglutination of the solid particles during pneumatic transport, the purge gas is advantageously a heated gas, having a very low relative humidity, eg dried and heated air.

The flow rate of the purge gas is preferably kept constant in order to be able to keep the purge time constant.

The purge gas is advantageously removed through separators retaining the solid particles. However, it could also be reinjected into said gas purification installation upstream of the latter's solid particle separator.

If one wishes to obtain continuous operation of the pneumatic conveyor, without interruption during the N loading and purging operations of said first closed vessel, one can for example work with a second closed vessel installed downstream of said first closed vessel. In this case the solid residues are discharged, after the passage of the purge gas or gases, in said second closed vessel where they are at least partially kept in suspension in a gas under pressure, to be evacuated by pneumatic transport from this second closed vessel, which constitutes a sort of buffer tank for the pneumatic conveyor.

Alternatively, it is also possible to provide a second closed cup identical to the first and installed in parallel with the latter. The second closed vessel is loaded and the solid residues are purged and / or dried, when in the second closed vessel the solid residues are removed by pneumatic transport and vice versa.

It will be noted that continuous operation of the pneumatic conveyor can be advantageous from the point of view of optimization of the pneumatic transport energy and from the point of view of the final use of solid residues.

The present invention also provides a device for the evacuation of solid, granular or pulverulent residues, from a gas purification installation, in particular from blast furnace gas, characterized by a first closed vessel forming a pressure container, a loading line connected between said gas purification installation and said first closed vessel, a gas-tight isolation member integrated in said loading line, a fluidization surface arranged in said first closed vessel so as to be able to inject gas through said solid residues from the bottom to the top, at least one gas supply source connected to said insufflation surface and dimensioned to deliver a gas with a flow and a pressure sufficient to create and maintain a static bed, respectively a fluidized bed, said solid residues above said insufflation surface, a gas evacuation pipe connected to said closed vessel N and provided with an isolation member, a pipe for discharging solid residues connected to said closed vessel and provided with an isolation member, a pneumatic conveyor connected in leaktight manner to said pipe for discharging solid residues.

It will be noted that the overpressure in said first closed vessel is advantageously kept constant using two Laval nozzles, one of which is placed between the fluidization surface and the gas supply source, and the other is integrated in the gas evacuation pipe.

Preferential examples of implementation of the proposed method and device are described, by way of example only, based on the appended figures, in which: Figure 1 is a block diagram of an installation allowing the implementation the proposed process; - Figure 2 is a first alternative embodiment; - Figure 3 is a second alternative embodiment.

In FIG. 1, the reference 10 identifies a hopper installed below a solid particle separator (not shown) of a blast furnace gas purification installation. This hopper 10 receives the solid residues separated by the separator of the blast furnace gas. Note that these blast furnace gases include toxic gases such as CO, SO2 and more or less significant amounts of water vapor. Solid residues mainly consist of coke dust, coal and iron ores and consequently constitute a raw material normally recyclable in an agglomeration installation.

A discharge line 12, fitted upstream of a closure member 14 for solid residues and downstream of a gas-tight isolation valve 16, connects the hopper 10 to a closed vessel 18. The closed vessel 18 constitutes a thermally insulated pressure vessel V into which the discharge line 12 opens at its upper part. At its lower part, the vessel 18 is equipped with a fluidization device 20 making it possible to inject a gas from below, through the solid residues discharged into the closed vessel. The fluidization device 22 is for example constituted by a peripheral surface permeable to gases and delimiting on the lower part of the vessel 18 the space for storing solid residues. From the upper part of the closed vessel also leaves a purge line 24, which is provided with a gas-tight isolation valve 26. This purge line 24 is advantageously connected to a solid particle separator, for example a bag filter 28. A hopper 29 below the filter 28 is discharged through a discharge line 30, provided with an isolation valve 32 gas tight, in the vessel 18. The purge gases filtered by the filter 28 are evacuated through evacuation pipes 34, 36, each provided with an isolation valve 38, 40 gas tight. A Laval nozzle 27, integrated in the purge pipe 24 makes it possible to carry out these purge and drying operations at high pressures, therefore increasing the mass flow rate of the purge gas without entraining the solids.

A gas supply source is generally identified by the reference 42. In the case shown in FIG. 1, this supply source comprises a supply line 44 for an inert gas, for example nitrogen and a installation for generating dry air,

generally identified by the reference 46. This air generator 46 comprises for example an air compressor 48, an air cooler 50, followed by a water separator 52, optionally an additional air dryer 54 for post-drying of the air and of an air heater 56. The air generator 46 consequently makes it possible to create a flow of pressurized air whose relative humidity is very low. NA through the isolation valves 58 and 60 it is known to connect either the inert gas line 44 or the air generator 46 to the fluidization device 20. The gas supply to the fluidization device 20 is preferably done by a supersonic flow through a Laval 62 nozzle, which makes it possible to fix the gas flow rate at a well-determined value. The lower end of the vessel 18 opens into a fluidization elbow 64, which itself opens through an isolation valve 66 in a pneumatic conveying line 68. The fluidization elbow 64, the upper part of the vessel 18, as well that a postfluidization station 70 are supplied with gas by a pipe 74 connected to the gas supply source 42.

The operation of the device described in the foregoing can be summarized as follows:

The discharge line 12 makes it possible, by opening the isolation valve 16 then the closure member 14, to discharge by gravity said solid residues from the hoppers 10 into the closed vessel 18. When the closed vessel is filled to a certain height, which is detected by a level detector 80, the shutter member 14 is closed first, interrupting the discharge flow before closing the gas-tight isolation valve 16. When loading the vessel 18 at least one of the purge valves 36 and 38 and the isolation valve 26 are open in order to allow the gaseous content of the vessel 18 to be evacuated.

Then the valve 60 is opened in order to supply the fluidization device 20 with a constant flow of inert gas. This gas flow is blown from below through the solid residues to create a static bed or fluidized bed of solid particles. It remains to note that the fluidization obtained in the vessel 18 will not necessarily be homogeneous, which is however without major disadvantage. What matters is that as few compact blocks of solid residues as possible remain which have not passed through the inert gas.

The inert gas, entraining the gases and vapors contained in the vessel 18 and trapped in the solid residues, is evacuated through the line 24, and the filter 28 in one of the purge lines 34 or 36. In the filter 28 the mixture of gas is separated from entrained solid particles. As the flow of inert gas which is established in the closed vessel 18 is constant, it can be estimated that after a predetermined period of time the elimination of gaseous substances and vapors is almost entirely complete.

The valve 58 is then gradually opened and the valve 60 is closed in parallel, until the static or fluidized bed is maintained entirely by a flow of hot and dried air produced by the air generator 46. This flow of hot dry air replaces the flow of inert gas as purge gas and causes in the static or fluidized bed 22 an evaporation of the water possibly impregnating the solid particles, in order to evacuate this water in vapor phase through one of the conduits 34, 36. It will be noted that the representation of two pipes 34 and 36 indicates that there is for example the possibility of evacuating the purge air at a place other than the inert purge gas. Instead of using preheated air, the inert gas could of course also be preheated, which is made possible by bypass 61.

The degree of drying of the solid residues in the vessel 18 can be continuously monitored, for example by means of relative humidity and temperature measurements carried out on the air flow rate at the outlet at 82 and on the flow rate d air at the inlet at 84. When the solid residues are sufficiently dry to avoid any risk of agglutination of the solid particles, the main purge valve 26 and the purge gas supply valve 62 are closed. The valve 66 at the inlet of the pneumatic conveyor and one of the valves 75, 76 or 77 are open. The air generator 46 now flows into line 74. In the fluidization bend N there is a flow of fluidized solid residues towards the pneumatic transport line 68. A complementary fluidization of this flow is made possible by the 'introduction into 70 and 71 of air taken from line 74. A line 72, connected to line 74, makes it possible to maintain in the upper part of the vessel 18 the pressure necessary to ensure the flow of solid residues in the elbow fluidization 64.

Of course, it is also possible to inject a preventive flow of inert gas into the pneumatic conveying line 68, when an explosive mixture of fuel dust and air is to be feared in the latter. This is for example the case just after the opening of the valve 66, when the density of solid particles in suspension in the air is still low. After establishment of the fluidized regime flow in the conveyor 68, the risk of dust explosion is reduced, however, since the proportion of combustible dust is much too high compared to the oxygen contained in the transport air. In this stage of the process, an explosion of dust in the conveyor 68 is no longer to be feared and the inert gas can be replaced entirely by air.

When the vessel 18 is completely drained, the isolation valves 66 and 75 or 76 or 77 are closed. The valve 26 and at least one of the purge valves 38, 40 are open. After decompression, the valve 32 is opened to discharge the content of the hopper 29 from the filter 28 through the pipe 30 into the vessel 18 and the operations are repeated as described in the foregoing.

FIG. 2 shows a first variant embodiment which makes it possible to operate the pneumatic transport 68 ′, without interruptions due to the loading and purging operations of the closed vessel. In this embodiment, the closed vessel 18 ′ is equipped in a similar manner to the vessel 18 in FIG. 1 (all the equipment is not shown in FIG. 2). The difference between the installation of Figure 1 and the installation of Figure 2 is essentially located at the connection of the vessel 18 'to the conveyor 68'. This connection is no longer made through a fluidization bend, but through a buffer tank 100 which also constitutes a pressure tank. The latter is equipped at its base with a conventional fluidization device which feeds the pneumatic conveyor 68 '. The valves 104 and 106 make it possible to isolate the buffer tank 100 from the vessel 18 ′ during the loading and purging operations which take place therein. It will be noted that during the discharge of the vessel 18 'in the buffer tank 100, the operation of the conveyor 68' must not be interrupted.

FIG. 3 represents a second alternative embodiment allowing a continuous supply of an end user to be carried out. This variant includes two identical 18 '' and 18 '' 'closed vessels, fitted in the same way as the closed vessel 18 shown in Figure 1 (these devices are not shown in Figure 3). A three-way valve 110 is mounted downstream of the shutter member 14 '' and makes it possible to orient the solid residues collected in the hopper 10 '', either through a pipe 12 '' in the closed vessel 18 ' '', or through a 12 '' 'pipe in the 18' 'closed cup. Each of the 12 '' and 12 '' 'lines has its own gas-tight isolation valve 16' 'and 16' ''. The closed vessel 18 '' is connected through a fluidization elbow 64 '', fitted with an isolation valve 66 '', to a first pneumatic conveyor 68 ''. The closed vessel 18 '' 'is connected through a fluidizing elbow 64' '', fitted with an isolation valve 66 '' ', to a second pneumatic conveyor 68' '' connected further to the conveyor 68 '' . It will be noted that the closed vessel 18 '' will flow into the conveyor 68 '',

"N when the loading and purging operations take place in the 18 '' 'conveyor and vice versa.

Claims (16)

1. Method for the evacuation of solid, granular or pulverulent residues, from a gas purification installation (10), in particular from blast furnace gas, characterized by an unloading of at least part of said solid residues in at least a first closed vessel (18), located in the immediate vicinity of the gas purification installation (10), an isolation of this first closed vessel (18) with respect to the gas purification installation ( 10) when the unloading operation is complete, a passage of at least one purge gas under pressure through said solid residues contained in this first closed vessel (18), so as to create a static, respectively fluidized bed (22 ), said solid residues in this first closed vessel (18), and a controlled evacuation of this purge gas, followed by an evacuation of the solid products by pneumatic transport (68) suspended in a gas under pressure. 2. Method according to claim 1, characterized in that one creates with the purge gas an overpressure in the first closed vessel (18). 3. Method according to claim 2, characterized in that a first purge gas consists of an inert gas. 4. Method according to any one of claims 1 to 3, characterized in that at least one purge gas is a heated gas having a very low relative humidity. 5. Method according to claim 4, characterized in that said heated gas is air previously dried. 6. Method according to any one of claims 1 to 5, characterized in that the purge gas flow rate is kept constant. 7. Method according to any one of claims 1 to 6, characterized in that the purge gas or gases are evacuated through solid particle separators (28). 8. Method according to any one of claims 1 to 7, characterized in that after the passage of the purge gas or gases, the solid residues are evacuated in at least a second closed vessel (100), in that this second closed vessel (100) is then isolated from the first closed vessel (18 '), and in that said solid products are removed by pneumatic transport (68') suspended in an N gas under pressure. 9. Method according to any one of claims 1 to 7, characterized in that the discharge of said solid residues is done alternately in at least two closed vessels (18 '' and 18 '' ') mounted in parallel, and in that the first closed vessel (18 '') is loaded respectively purged, when in the second closed vessel (18 '') said solid residues are removed by pneumatic transport (68 '' ') and vice versa. 10. Device for implementing the method according to claim 1 for the evacuation of solid, granular or pulverulent residues, from a gas purification installation (10), in particular from blast furnace gas, characterized by a first closed vessel (18) forming a pressure vessel, a loading line (12) connected between said gas purification installation (10) and said first closed vessel (18), an isolation member (16) sealed against gas integrated into said loading line (12), a fluidization surface (20) arranged in said first closed vessel (18) so as to be able to inject gas through said solid residues, at least one gas supply source ( 42) connected to said fluidization surface (20) and dimensioned to deliver a gas with sufficient flow and pressure to create and maintain a static bed (22), respectively a fluidized bed (22), of said solid residues above said surface fluidization (20), a gas discharge line (24) connected to said closed vessel (18) and provided with an isolation member (26), a discharge line (64) of solid residues connected to said vessel closed (18) and provided with an isolation member (66), N a pneumatic conveyor (68) connected in leaktight manner to said solid residue discharge pipe. 11. Device according to claim 10, characterized in that said gas evacuation pipe (24) opens into a filter (28) for solid particles. 12. Device according to claim 10 or 11, characterized in that said gas supply source (42) comprises a gas heater (56). 13. Device according to claim 12, characterized in that said gas supply source (42) comprises, upstream of the gas heater, a gas cooler (50) and a water separator (52). 14. Device according to any one of claims 10 to 13, characterized in that said first closed vessel (18) is connected to a second closed vessel (100) by a conduit provided with at least one isolation member sealed against gas (104, 106) and in that said second closed vessel (100) is tightly connected to said pneumatic conveyor (68 '). 15. Device according to any one of claims 10 to 13, characterized in that at least two devices (18 '', 18 '' ') are connected in parallel on the same gas treatment installation (10' '). 16. Device according to any one of claims 10 to 15, characterized in that the fluidization surface (20) is connected through a first Laval nozzle (62) to the gas supply source (12) and in that the gas discharge pipe (24) is provided with a second Laval nozzle (27).