Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
  • B01D53/06—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with moving adsorbents, e.g. rotating beds
  • B01D53/08—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography with moving adsorbents, e.g. rotating beds according to the "moving bed" method
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
  • B01D46/30—Particle separators, e.g. dust precipitators, using loose filtering material
  • B01D46/32—Particle separators, e.g. dust precipitators, using loose filtering material the material moving during filtering
  • B01D46/34—Particle separators, e.g. dust precipitators, using loose filtering material the material moving during filtering not horizontally, e.g. using shoots
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2257/00—Components to be removed
  • B01D2257/30—Sulfur compounds
  • B01D2257/302—Sulfur oxides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2259/00—Type of treatment
  • B01D2259/40—Further details for adsorption processes and devices
  • B01D2259/40003—Methods relating to valve switching
  • B01D2259/40005—Methods relating to valve switching using rotary valves
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2259/00—Type of treatment
  • B01D2259/40—Further details for adsorption processes and devices
  • B01D2259/40011—Methods relating to the process cycle in pressure or temperature swing adsorption
  • B01D2259/40077—Direction of flow
  • B01D2259/40081—Counter-current
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2259/00—Type of treatment
  • B01D2259/45—Gas separation or purification devices adapted for specific applications
  • B01D2259/455—Gas separation or purification devices adapted for specific applications for transportable use

Definitions

• the present invention relates to a fume-filtration system having a moving bed of stone chippings serving both as a dust remover and as a neutraliser for the oxides of sulphur in the fumes.
• Filtration systems have been known for some time which make use of moving beds of inert granular material instead of cyclones or textile filters whose effectiveness and useful life are limited and also instead of expensive and bulky scrubbers in thermal power plants.
• the temperature of the fumes is correlated with the vapour content in such a way that some of the water vapour condenses and activates the reaction of the /12659 PC17EP96/03940
• EP-A-0 321 914 describes a similar cross flow filter system which allows very hot fumes, up to 1200°C, to be cleansed of solid particles carried in them by means of a moving bed of basalt, in such a way that the fumes, already purified, traverse heat recovery devices.
• Filtration systems have also been proposed in which the inert filter material is a component of a product of a process which requires combustion and in which fumes are produced.
• Italian Patent No. 1 188 668 describes a system for the preparation of a bituminous conglomerate in which the fumes and dust given off by the process are filtered by a moving bed of stone chippings which constitute a component of the conglomerate.
• the fumes enter and leave the moving bed through a natural sloping interface where there is no relative sliding between the inert material and the retaining grill but only the formation of a natural slope with reduced mechanical forces between the granules of the inert material so that the formation of dust is minimised.
• the formation of dust due to the movement of the bed of aggregate is completely eliminated in a modular structure with several filter elements, with beds which move intermitantly in alternate phases in tandem in the sense that, whilst one or more modules are in active operation, their filter beds being steady in order to filter the fumes, another module, excluded from the path of the fumes, is subjected to complete or partial renewal of its moving bed.
• the system is constituted by a plurality of filter modules so as to provide a plant whose potential can vary within wide limits by the combination of different numbers of modules while, at the same time, ensuring a uniform flow distribution between the modules as well as a uniformly distributed, or at least controlled, rate of flow of the aggregate materials between the various modules.
• the modular structure as well as allowing economy of scale, also allows the production of small components which can be transported by road and minimises the operations needed to set up the plant at the work site.
• the present invention provides a filtration system with modules operating in 12659 PCI7EP96/03940
• a pneumatic system for recycling the chippings employs a proportion of the fumes to be filtered as the carrier fluid.
• FIG. 1 is a partially exploded perspective view of a first preferred embodiment of the moving-bed fume-filtration system according to the present invention
• FIG. 2 is a sectional view, taken on the line I-
• FIG. 3 is a sectional view of a first variant of the filtration module;
• FIG. 4 shows in section a second variant of the filtration module;
• Figure 5 is a perspective view of a second preferred embodiment of the filtration system of the present invention.
• FIG. 6 is a perspective view of an assembly of a third preferred embodiment of a fume-filtration system according to the present invention with pneumatic recycling of the stone chippings.
• a filtration system formed in accordance with the present invention includes a plurality of filter modules 1, 2, 3, 4, 5.
• the modules in the form of vertical containers of square cross-section, each terminating at its lower end in a discharge hopper which is dihedral in Figure 1 but may be pyramidal or conical, are juxtaposed in a direction of alignment perpendicular to the front and rear walls of the mutually juxtaposed modules.
• the upper regions of the modules are traversed, in the direction of alignment, by a feed-screw conveyor 6, shown in broken outline, housed in a suitable housing open towards the interiors of the modules.
• the screw conveyor is rotated by drive members 7 and its inlet 8 is connected to the outlet 9 of a rotary drum screen 16 housed in a container 10 preferably, but not necessarily, located over the modules 1, 2, 3, 4, 5. In this way much of the heat evolved by the modules is recovered in pre-heating the screened chippings.
• the screen is also rotated by drive members, not illustrated, which may also include the motor 7.
• the screw conveyor is supplied by the screen (not necessarily a rotary drum) with screened chippings, free from fine dust particles which are, instead, collected in the container 10 and discharged under gravity to a collection vessel, not visible.
• the chippings may be obtained from any type of rock available as long as it is not friable and may be chosen according to specific requirements of the plant.
• the rock is a carbonate, such as limestone or dolomite, because of the property that such rocks exhibit when hot and/or in the presence of vapour of reacting with sulphur dioxide and trioxide which are the most common pollutants in fumes, fixing them in the form of calcium sulphate.
• the chippings are supplied to the modules 1 to 5 and fill them to a predetermined level set by the position of the screw conveyor itself, the transport action of which, in known way, stops with the occlusion of the outlet opening.
• a rotary discharge valve arranged with its axis in the direction of alignment of the modules and rotated by drive members 11 so as to extract a quantity of chippings from the various modules at a controlled rate and to discharge them into a rotary screw conveyor 12 driven by drive members not illustrated.
• the screw 12 conveys the chippings discharged from the modules to the base of a conventional elevator, of screw or bucket type, which raises the chippings to its top 14 and empties them under gravity into an inlet duct 15 of the screen 16.
• the continuous cycle for the chippings thus described may include a reservoir, for example immediately upstream of the screen or the screw conveyor 6, with a flow-metering valve, as well as a line for introducing additional chippings which, in time, are exhausted through use.
• FIG. 2 is a section taken on the line I-I of Figure 1 showing one of the modules 2 and clearly shows the feed screw 6 housed in a suitable seat 17 which is open downwardly towards the interior of the module which is bounded by two parallel vertical sides 18, 19, a lid 20 and two inclined lower walls 21, 22 forming a conveying hopper which opens downwardly to the rotary valve 23.
• the chippings introduced into the filter module by the screw 6 fill the entire module, distributing themselves under gravity and as a result of friction between them so as to form inclined free surfaces 23, 24 extending close to the openings Pl, P2 between the walls 18, 21 and 19, 22 respectively.
• the chippings define an interface constituted by two free surfaces 25, 26 extending between the seat 17 and the walls 18, 19 respectively.
• deflectors such as 27, which provide local resistance to the fall of the chippings, whose rate of descent is very low and can be continuous or intermittent.
• the uncleansed fumes are introduced through the apertures Pl, P2 , pass through the entire column of chippings between the walls 18, 19 in counter-current with the flow of chippings, and leave the module through the apertures P3, P4.
• the concentration of dust and oxides gradually decreases from the bottom upwardly, both in the fumes and in the aggregate, and the bed of aggregate can exert its maximum filtering action.
• the quantity of particles (and oxides) retained can be considered proportional to the concentration of particles in the fumes and to the filtering activity of the bed, which decreases as a function of the quantity of particles already retained.
• the upper layers of the filter bed which are practically clean as they are renewed continually, can filter the fumes effectively even though the particle concentration in the fumes has been reduced to very small values.
• the quantity of dust transported by fumes leaving the module is therefore very small and can be further reduced by dampening the chippings immediately before their introduction into the modules or even by dampening the free surfaces 25, 26 by sprinkling. In particular operating conditions this dampening can also be advantageous to increase the capture of noxious, gaseous pollutants such as oxides and acids.
• the dampening can also result from the condensation of vapour in the fumes as a result of their cooling by release of heat to the filter bed if the working temperature of the filters is relatively low.
• a further important consideration is that, to penetrate the bed of chippings, the fume flow does not have to traverse retaining structures and deflector shuttering and is subject only to the pressure drop imposed by the reduction in section and the tortuousness of the labyrinth formed by the granular bed.
• the module of Figure 2 can have a depth perpendicular to the plane of the drawing, of the order of 4 m, a width of the column of granules of the order of 1.5 m, a height of the column of granules traversed by the fumes of the order of 1.5 and free inlet and outlet passage sections of the order of 3.2 2 (divided into two pairs of inlet and outlet openings) .
• the pressure drop is of the order of 15 mbar (150 mm of water column) and is exclusively due to the traversal of the bed.
• the filtering efficiency is extremely high, of the order of 99.9% and, in absolute terms, the solid particulate residue in the fumes is less than 20 mg per m 3 of fumes.
• the particulate residue is due essentially to the transport of inert dusts generated by the granules at the output interfaces of the filter bed whilst the unburnt pollutants in the fumes are retained upstream.
• modules operating in parallel make it possible, according to the number of modules installed, to provide higher potential, for example up to 15-20 m 3 per second or even more, by providing a greater number modules or more batteries of modules operating in parallel.
• Figure 1 shows, by way of example, five identical modules aligned in a battery.
• the flow of fumes is distributed between the modules by a first distributor duct 27 of variable cross-section with an inlet opening 28 and a plurality of outlets connected to the inlet openings 29, 30, 31, 32, 53 on one side of the various modules.
• a similar distributor 49 is provided on the opposite side of the battery of modules.
• a fume manifold 50 of variable cross-section is connected to the openings of each of the modules on one side thereof and conveys the filtered fumes towards a suction system represented as a centrifugal fan 51.
• a similar manifold 52 connected to the first is provided on the opposite side.
• Figure 3 shows in section, again on the line I-I of Figure 1, a variant of the filter module which achieves even more thorough filtration of the fumes by completely eliminating the transport in the fumes of dust formed at the output interfaces of the filter bed due to the movement of the granules constituting the bed.
• This variant can be used to advantage in modules operating at high temperatures in which the bed cannot be moistened.
• the module of Figure 3 differs from the module of Figure 2 in that it includes two pivoted shutters 33, 34 for closing the outlet openings of the module, controlled independently for each module, the shutter 33 being represented in its open position and the shutter 34 in its closed position.
• each of the modules (which, as illustrated in Figure 3, can be replaced by a transverse shutter 35) is also controlled by an actuator 36 independently of the others but coordinated with the closure of the fume shutters.
• the filter beds can be renewed intermittently and cyclically as each of the modules is temporarily excluded from the flow of fumes.
• the bed of another module from which the flow is excluded, can be entirely or partly, and therefore gradually renewed, giving time for the dust to settle before the fume flow is reintroduced into the module.
• the module excluded from the fume flow can be subjected to a reverse flow in order to transport the dust generated by the movement of the aggregate towards the lower part of the bed.
• the pivoted shutters 33, 34 can be shaped in such a way as to perform a dual action of closing the fume outlet openings and opening a passage 37 communicating with the external environment, the said opening 37 normally being closed.
• the fume pressure in the distributors such as 27, 29 of Figure 1, will be below ambient.
• Any dust formed at the interfaces 23, 24 is filtered by the other modules.
• the filter system is particularly suitable for high-temperature operation with an appropriate choice of material for the bed such as a mixture of, for example, basalt and a small proportion of additives, such as rock carbonates for de-sulphurising, and can be located upstream of the heat-exchangers to ensure their perfect efficiency by preventing the formation of dust deposits.
• material for the bed such as a mixture of, for example, basalt and a small proportion of additives, such as rock carbonates for de-sulphurising, and can be located upstream of the heat-exchangers to ensure their perfect efficiency by preventing the formation of dust deposits.
• Figure 4 shows, in section, a module 40 similar to those described but having an asymmetric section with a single inlet opening 38 on one side and a single outlet opening 39.
• the module 40 can be provided (like the other modules already described) with a plurality of accessories, such as a modulation/exclusion shutter 41 and, for specific applications, with sprinkler systems 44 or systems with adsorbent substances for treating the filter bed to promote the removal of the oxides of sulphur and other pollutants, such as electrostatic generators 42 immediately upstream of the filter bed for ionising the fumes (and hence the particles contained therein) and increasing the filter power of the bed in known manner (by electrostatic adhesion) , the bed moving continuously or intermittently, and also devices 43 for blowing steam into the hot fumes upstream of the filter column.
• a modulation/exclusion shutter 41 and, for specific applications, with sprinkler systems 44 or systems with adsorbent substances for treating the filter bed to promote the removal of the oxides of sulphur and other pollutants
• electrostatic generators 42 immediately upstream of the filter bed for ionising the fumes (and hence the particles contained therein) and increasing the filter power of the bed in known manner (by
• FIG 5 is a perspective view of a second preferred embodiment of the filtration system of the present invention which differs from that shown in Figure 1 in that the rotary screen 101, housed in a sealed box 102, is disposed immediately downstream of the discharge screw conveyor 12 of the filter modules.
• the dust is deposited on the bottom of the container 102 from which it is removed by known means, for example, a screw conveyor and/or rotary valve.
• the screened chippings are discharged to the bottom of an elevator 103 which raises them and discharges them into a storage reservoir 104 with a discharge hopper which opens to the feed screw 105 of the filter modules.
• An oscillating valve 106 (or even a rotary valve) is suitably arranged immediately upstream of the reservoir 104 (or even downstream of it) to prevent unwanted air being sucked by the elevator into the filter modules.
• the elevator can also function as a washing tower for the chippings.
• Figure 6 is a perspective view of a third embodiment of the invention which differs from the preceding embodiments in that the chippings are recycled to the moving-bed filter modules by pneumatic means, with the use of the fumes themselves which are to be filtered as the transport medium.
• a high-power centrifugal fan 60 draws a relatively small proportion, of the order of 10%, of the fumes to be filtered from a duct 61 which delivers the fumes to a battery 62 of filter modules.
• This proportion of the fumes is conveyed through a duct 63 to a convergent duct portion 64 downstream of which a high-speed, low-pressure flow is established in a duct 65 into which the conveyor which receives the chippings from the modules discharges the chippings to be cleansed of dust and recycled.
• the speed of the fumes in the duct 65 is sufficiently high, of the order of 40-80 m/s, to entrain the chippings effectively and raise them through a column 66 which opens through an elbow 67 into a syphon chamber 68, of greater diameter, where the speed of the fumes falls significantly so that the chippings, no longer supported by the flow of fumes, fall under gravity into a storage reservoir 69, through an oscillating or rotary valve 70, whilst the finer dust and solid particles are carried away by the fumes.
• a metal mesh 71 may be located close to the head of the syphon for capturing any chippings larger than a predetermined limit should they reach the mesh due to inertia.
• the film of powder formed on the surfaces of the chippings becomes separated and the chippings collected are perfectly clean and are separated from the dust even better than by means of a screening operation.
• the diameter of the duct is gradually reduced so that the speed of the flow of fumes, rich in dust, increases.
• the fumes thus accelerated, enter a cyclone 72 of conventional type where a good proportion of the solid particles is captured and removed from the cyclone by known means, such as rotary valves and the like.
• the fumes, cleansed to the limits allowed by the efficiency of the cyclone, are drawn through a duct 73 by the fan 60 and from here returned to the duct 61 for delivery to the battery 62 of filter modules where, mixed with that proportion of the fumes not used for the pneumatic transport of the chippings, they are subject to much more thorough dust removal by the moving bed filter modules.
• the pneumatic recycling system operates with a fluid and transported chippings which are substantially at the same temperature so that heat is not extracted from the chippings and they are not subject to thermal stress which is a possible cause of fragmentation. Since the proportion of fumes used for recycling the chippings is modest and the fume velocity is extremely high, small-section ducts are employed which limits the heat-dissipation and which, in any case, can easily be insulated.
• the circuit for the recycling of the chippings operates at low pressure compared with the pressure in the duct 61 which, in turn, as already mentioned, is preferably below ambient pressure. Consequently, should there be any imperfect sealing of the joints between the various sections of the circuit, no fumes are emitted into the environment.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Analytical Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Filtering Of Dispersed Particles In Gases (AREA)

Applications Claiming Priority (3)

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• 1995
  • 1995-10-02 IT IT95MI002009A patent/IT1276807B1/it active IP Right Grant
• 1996
  • 1996-09-09 EP EP96931050A patent/EP0862490A1/en not_active Withdrawn
  • 1996-09-09 CA CA002233638A patent/CA2233638A1/en not_active Abandoned
  • 1996-09-09 WO PCT/EP1996/003940 patent/WO1997012659A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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