DE2942223A1 - METHOD AND DEVICE FOR REMOVING SOLIDS FROM GASES - Google Patents

Description

It is known that finely divided solids suspended in a gas can be removed from the gas by passing the gas through a bed of granular solid material (Perry's Chemical Engineers' Handbook , 4th Edition, McGraw-Hill, at 20-74 and 20-75 shown). A method and apparatus for removing finely divided solids from a gas by passing a feed gas containing finely divided solids through a downwardly moving mass of granular solid material is described in U.S. Patent 4,017,278. The method and the corresponding device described in the latter publication are currently in commercial use in a number of operating plants.

The current interest in preventing air pollution has to ever stricter requirements with regard to the solids content of Gases emanating from commercial facilities.

The method and apparatus of US Pat. No. 4,017,278 are disclosed in U.S. Patent No. 4,017,278 Removal of solids from effluent gases from plants has been found to be satisfactory, however, it has been found that when the injected gas contains a significant proportion of very finely divided solids in the inlet; d. H. below 1 to 2 microns then the effectiveness tends to be the device, expressed as a percentage of total solids, which are removed from the injected gas to fall off. These Reduction in effectiveness is due to the fact that the very finely divided solid particles are more difficult to remove and a greater proportion of them manage to pass through the granular bed without being removed. A fallback to the use of finely divided granular material in the beds, or the use of thicker beds with the coarser material increases the effectiveness and can do the desired reduction in the amount of finely divided

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Solids contained in the released gas reach, but resorting to one of these options to achieve this result results in a higher pressure drop when the injected gas through the bed and therefore more energy is required to move the injected gas through the unit. When thicker beds of granular material are used, not only does the pressure drop increase, but the facility must also be larger to take into account the increased stress on the granular material.

Consideration has already been given to charging the finely divided solids in the gas fed in by means of a high-voltage charger such as is used in electric precipitation (Perry's Chemical Engineering Handbooks at 20-82 and following), the gas fed in, which the now contains charged, finely divided solids carried along, is passed through the granular bed of solids. The metal structure that encloses the bed of granular solids is electrically grounded and holds the charged particles in place. This concept actually reduces the residual solids content of the gas to sufficiently low levels to meet the tough requirements for maximum solids content, but this result is achieved by using only the inlet side of the bed of granular solids while filtration through the deep Bed is not exploited, and also at the expense of the very substantial expense of adding the high voltage, high energy electric precipitator-type charger in the process flow line and the past and present difficulties in operating such chargers resulting from the construction of a result in a strong accumulation of solids on the conductor surfaces.

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Brief description of the invention

The efficiency of removing finely divided solids from the Gas by passing an injected gas containing such finely divided solids across a downward moving one Bed made of electrically poorly conductive material is achieved in that an electrically conductive bed inside the moving bed Element or elements are arranged to which a voltage in the range of about 2,000 to 50,000 volts is applied. The electrically conductive element or these elements is or are constructed in such a way and have such a size and shape that there are no results in significant obstruction to the movement of the bed of solid material or the flow of the injected gas through the material. Exercise the downward movement of the bed of solid granular material a continuous cleaning effect on the surface of the electric conductive element, so that it continuously during the entire inflow period with practically the effectiveness of a completely clean conductor is working. The electrical consumption is very low and all solid material that is removed from the gas leaves the system with the solid contact material, from which it is then removed before the solid contact material is recirculated.

Detailed description of the invention In the drawing show:

Figure 1 is a side view of a very simple form of granulate bed separator with an electrically conductive element which is arranged in the granulate bed;

FIG. 2 shows a plan view of the separator according to FIG. 1;

FIG. 3 shows a side view of a granulate separator accordingly

the granulate bed separator according to US Pat. No. 4,017,278, in which, however, an electrically conductive element within the granulate bed is arranged.

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Figure 4 shows a section along the line 4-4 through the

Granulate bed separator according to FIG. 3; and

Figure 5 shows an arrangement of the electrically conductive element, the

arranged in the granulate bed according to FIGS is.

Referring to Figure 1, an elongated, hollow column 1 is generally square or rectangular cross-section with a mass of granular,

solid contact material filled. Solid contact material is filled into the column through the solid inlet opening 3 and through the solids outlet port 4 withdrawn from the column. The solid contact material moves downward through the column by gravity at a linear rate ranging from 0.5 to 40 feet per hour (0.15 up to 12 m per hour). The downward movement of the solid contact material can be intermittent if desired. The flow rate of the solid contact material is controlled by the rate at which the solid contact material is withdrawn through the solids outlet port 4 and the actual rate of movement varies with the amount of the finely divided Solid matter contained in the feed gas entering the column, the rate being greater as the amount of contained finely divided solid material is high.

The injected gas, which contains finely divided solid material, to be removed is admitted through gas inlet 5, which is provided with an enlarged, generally rectangular gas inlet opening 6 in FIG Connection. A part of the side wall of the column 1, which communicates with the enlarged inlet opening 6, is provided with slots, wherein the slot vanes are steeply inclined so that gas can enter through the slots, the escape of solid contact material however, this prevents it. The entering gas comes into contact with the granular solid contact material 2 and moves across the mass of solid contact material to the opposite one Wall of column 1 to reach. At this opposite one

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Wall is an enlarged gas outlet opening of generally rectangular cross-section in contact with the outer wall of the column 1, and the part of the wall of the column 1 which communicates with the gas outlet opening is provided with steeply covered slots, to prevent the gas from escaping, but to prevent solid contact material from escaping through the slots. Gas, which is almost completely free of suspended solid grain material, is withdrawn through the gas outlet line 8, which is in communication with the enlarged gas outlet opening 7. The configuration of the illustrated electrically conductive element is a conductor made up of a series of elongated, electrically conductive rods or tubes 9, which are in weld or screw connection with a metal rod 10, which with insulators 11 from the walls of the column 1 is supported and isolated from them; through the insulators 11, a high voltage electric current is introduced. The pillar 1 and all internal metal parts including the slotted parts of the inlet and outlet walls of the column 1 are electrically grounded. When the high voltage is applied to the electrically conductive element, a potential between the conductive element and the Inlet and outlet slots of the column 1 constructed. This potential creates an electric field that the finely divided solid that are contained in the gas fed in, on the moving bed of electrically poorly conductive material 2 and drifts on this. A certain part of the finely divided solids is attracted and held in place by the electrically conductive element. The continuous downward movement of the solid material in contact with the electrically conductive tubes 9 continuously moves any accumulation of solids from the surface of the conductive element, so that any build-up of an electrically resistive layer on the surface of the conductive element, which would accordingly reduce the generation of the electric field from the electrically conductive element and ultimately eliminate it.

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The path of least resistance for the injected gas is this Path between the enlarged inlet opening 6 and the enlarged outlet opening 7. The mass of contact material above the top Levels of the outlet opening 7 and below the bottom of the outlet opening is long enough to prevent any gas flow through the solids inlet opening 3 or through the solids outlet opening 4. A part of the gas can follow a curved path which rises slightly above and slightly below the outermost points of the outlet opening 7 or falls as the gas traverses the mass of contact material that Gas following the path of least resistance finds its way to the outlet opening 7 through the outlet conduit 8 and out of it.

In Fig. 2 is a plan view of the column is shown. The electric conductive element is shown as a number of tubular electrodes 9, in electrical contact with an electrically conductive rod 10 at intervals of about 2 to 12 inches (5 to 30 cm). Sufficient space remains between the electrodes 9, which are closest to the adjacent walls of the column 1, by a minimum Ensure voltage loss between the end electrodes and the walls of the column. The electrically conductive rod 10 is insulating the side walls of the column 1 supported.

FIG. 3 shows an apparatus for separating finely divided solids from gases which is generally similar to the apparatus according to US Pat. No. 4,017 is equivalent to. A cylindrical vessel 20, which is usually a shallow or has a frustoconical lid and a tapering frustoconical bottom, ar bottom has a solids outlet and at least one solids inlet port 22 at the top. Gas flow openings 23 and 24 are located at the top and on the side of the Vessel 20. The gas fed in, which contains suspended solids, can be introduced through the opening 24 and the clean gas withdrawn through the opening 23, or vice versa. A first cylinder wall 25 with a slotted surface and a smaller diameter

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than that of the vessel 20 is arranged concentrically in the vessel 20 and leaves an annular space 26 between the side wall of the vessel 20 and the wall 25. The cylindrical wall 25 is sealed at 28 at the upper end connected to the top of the vessel 20 to close the annular space 26 at the top. The annular space 26 is open at the bottom and stands with the frustoconical bottom of the vessel 20 in connection. One second cylindrical wall 29 with a diameter smaller than that of the first cylinder wall 25 and a slotted surface is arranged concentrically within the first cylinder wall 25, so that a Annular space is formed between the two cylinder walls, which is extends from the upper to the lower end of the vessel 20. The second cylinder wall 29 is with the gas flow opening 23 on the top of the Vessel in connection and extends generally beyond the top of the vessel 20, either as a chimney, from the treated gas the vessel leaves, or as an opening, through the gas to be treated is introduced. The lower end of the cylinder wall 29 is with the Mass of contact material in connection, which is arranged in the frustoconical bottom part of the vessel 20. A crowd out granular solid contact material 30 fills the annulus between the cylindrical walls 25 and 29 and the mass of solid contact material is in open communication with the solid outlet 21 at the bottom of the vessel. Solid contact material, which leaves the annular space between the walls 25 and 29 through the solid outlet opening 21, enters a solid separator 31, the is able to separate finely divided solids from the granular solid contact material. Suitable solid-state separators are Vibrating sieve separators, which can be either reciprocating or rotating sieves, whose openings are dimensioned so that the very finely divided materials which have been separated from the treated gas from the granular Solid contact material circulating through the system can be separated. The finely divided material that is fed by the Gas has been collected from the surface of the contact material

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is shaken off in the solid separator 31, is through opening 32 deducted. Solid contact material leaving the solid separator 31 is conveyed to the top of the vessel 20 with an elevator 33 transported and back into the annular space between the cylinder walls 25 and 29 are introduced via the solids inlet line 22. An electrically conductive grid made up of a plurality of electrodes 34 consists, is arranged in the mass of solid contact material so that it is within the mass of contact material vertically downwards extends and lies between the cylinder walls 25 and 29. Electric Current is fed on line 35 through insulator 36 which isolates the electrical line from the vessel in contact with the Electrodes 34.

Figure 4 is a section through Figure 3 taken along line 4-4. One A number of electrodes 34 are attached to a conductive ring 37 by welding or screwing and extend from this ring through the Mass of solid contact material downwards.

Fig. 5 shows a grid arrangement with a plurality of electrodes 34, which are attached at the top to a conductive ring 37 by welding or screwing, and at the bottom of a ring 38 by welding or Screws are attached. The attachment of the electrodes to the two rings keeps them in a fixed position relative to the mass Contact material in which they are embedded. Support rods 39 extend from insulators 36 down to the ring 37 to which they are connected. The isolators 36 are attached to the top of the vessel and ensure a support for the support rods 39 with the ring and the attached electrodes.

Direct current or alternating current with a voltage in the range of 2,000 up to 50,000 V is applied to the electrodes. The material that forms the mass of granular solid contact material through which the injected gas happens should be electrically non-conductive or little

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be conductive and temperature stable at the temperature of the injected gas, preferably has rounded rather than angular surfaces to facilitate flow and prevent bridging, and the particles should be reasonably uniform in size. The particle sizes are preferably between about 2 mm in diameter and 12.5 mm in diameter. A mass of particles in which the largest particles, present in appreciable quantities, have diameters no more than 3 to 4 times the diameter of the smallest particles, present in appreciable quantities, becomes a reasonably uniform mass considered and shows good flow properties in the system. Coarse sea sand or fine gravel are cheap, readily available, and make excellent contact masses. A San Simeon sand containing 8% U.S. No. 6 sieve (3.3mm opening), 62 % U.S. No. 7 sieve (2.8mm opening), and 30 % U.S. No. 8 sieve (2.4 mm sieve opening) is a satisfactory coarse sea sand. Fine gravel composed of 66 % US No. 4 sieve (4.7 mm sieve opening) particles, 26% U.S. No. 5 sieve (4 mm opening) particles, the remainder only slightly larger than No. 4 and slightly smaller than No. 6 is a suitable fine gravel for use in the process. In the event that gas is to be treated at a very high temperature, ceramic or quartz beads and similar materials with low conductivity and higher resistance to temperature fractures than sand or gravel should be used as the solid contact material.

The downward flow rate of a solid contact material can be im Range from about 1/2 foot to 40 feet per hour (0.15 to 12 meters per hour), but is preferably in the range of about 3 to 10 feet per hour (0.9 to 3 meters per hour). The downward movement continuously scrubs the surface of the electrically conductive element .

The voltage applied can range from 2,000 to 50,000 V. A more complete removal of the very fine particles that are in the

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injected gas are included, is reached at higher voltages. For example, if no voltage at all is used in a commercial size unit as shown in Fig. 3, particles 1/2 µm in size are removed by 65% , and when a voltage of 10,000 V is applied to the electrodes set in the contact material, the distance increases of the small particles to 75 %, and at 20,000 V the removal is 95 % of the total material content of 1/2 pm.

The configuration of the electrically conductive element can be varied but the controlling characteristic for size and shape is that it is not the downward movement of the solid contact material may noticeably affect the transverse movement of the Feed gas through the mass of contact material. Rods or tubes about 1/2 to 1 inch (12 to 26 mm) in diameter are suitable, too Flat rods 1/4 in. (6 mm) thick and up to 2 in. (50 mm) wide can be used. It can also be a coarse cylindrical mesh can be used in place of the rods in the form of a device as shown in FIG.

A solid-state gas separator as described in connection with FIG. 3 of Drawing is described, was modified so that an electrically conductive element according to FIG. 4 was used. The separator unit had a design capacity of 40,000 actual cubic feet each Minute (1,100 nr per minute) and was used to remove smoke from a power plant boiler that uses waste fuel to process was operated. The granular solid material used had U.S. No. 4 to No. 5 sieve size (4.8 to 4 mm sieve opening). The granular solid ring mass was 18 inches thick (46 cm) and a height of about 16 feet (4.9 m). The rate of flow of the mass of granular solid material down through the ring between cylinder walls 25 and 29 of Figure 3 was about 3 feet per hour (0.9 m per hour). 42 electrodes that are

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Tubes of one inch (25.4 mm diameter) were attached to a ring such as ring 37 of Figure 5 at 6 inch (15 cm) intervals and the resulting grid arrangement was in the annular mass arranged from granular material. A number of passes were then made carried out using the arrangement thus modified which was used to extract finely divided solid material from flue gases from a waste fuel fired boiler.

The following table shows the data obtained in a series of runs with the applied grid voltage varied between 0 and 20,000 volts. The various column headings in the table are (in the order of the table) gas flow in actual cubic feet per minute (equivalent to 0.028 m ^ per minute) at the outlet of the unit; Pressure drop through the unit, measured in inches of water column (corresponding to 2.4 mbar); Grid voltage in kilovolts; Grid current in mA; Incoming gas temperature in degrees Fahrenheit; Exiting gas temperature in degrees Fahrenheit; the front half content of finely divided solids in the feed gas, measured in grains per standard cubic foot dry, and the content of the outlet gas in grains per standard cubic foot dry, corrected to give the exhaust gas a uniform CO ^ content of 12% ( these measurements were carried out in accordance with EPA method no. 5 for determining the total solids content of a gas); % Opacity obtained by subjecting the exhaust gas to a test in a Lear-Siegler opacity meter; and finally, solids removal efficiency expressed as a percentage of total feed content.

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Run gas stream no. At the outlet (ACFM)

1
2
3
4th
5
6th
7th
8th
9
10

26220 25000 27100 26100 26000 26600 26900 25900 24900 25100

Pressure difference inches of water column

Grid grid input output voltage current temp. temp. kV mA OF OF Front half
gr / sdcf at 12 % CO ₂ opacity effective-

Inlet outlet % ^{speed %}

2.8 2.8 3.0 2.7 3.0 3.2 3.3 3.2 3.0

0 10 10 10 15 15 15 20 20

3 13

9 14

6.5 16-30 14

308

310 352 315 325 308 320 345 350 390

320 0.191 295 0.164 340 0.320 285 0.158 300 0.152 280 0.141 305 0.137 325 0.300 330 0.325 350 0.244

0.033 5-6 83 0.018 2 90 0.011 4th 97 0.014 2 90 0.009 1 94 0.008 1.2 97 0.010 1.0 92 0.014 1-5 95 0.012 1-3 96 0.057 12th 77

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Both direct current and alternating current are applied to the electrodes in the voltage ranges described have been applied. Direct current is equally effective, whether positive or negative. Alternating current results a noticeable improvement in solids removal but appears to be less effective than direct current.

From the data given in the table it is clear that the arrangement of electrodes in the mass of solid contact material and the application of a reasonably high voltage to the electrodes in one very significant increase in the efficiency of the total solid removal results. The precise way in which the arrangement is in the Device realizing these improved results is not completely clear, but the result itself is completely clear and very welcome.

As indicated, the applied voltages are generally in the range from 2,000 to 50,000 V, preferably in the range from 10,000 to 25,000 V. These areas are given quantitatively, but it should be mentioned that in a quantitative sense it is only necessary that the applied voltage should be sufficient to produce a marked improvement in solids removal efficiency.

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Claims (2)

Claims 1. Process for separating finely divided solid material which are contained in an injected gas stream, in which the stream with a downward moving mass of solid particles low electrical conductivity brought into contact is, characterized in that an electrically conductive element is arranged in the mass of solid particles to which one Voltage in the range of about 2,000 to 50,000 V is applied. 2. Apparatus for performing the method according to claim 1, with two gas-permeable walls, a gas inlet through which the gas is supplied to one of the two gas-permeable walls, one Gas outlet to which the gas is supplied from the other of the two gas-permeable walls, a contact material outlet at the lower end the space between the two gas-permeable walls, as well as solid contact material in this space, characterized in that an electrically conductive element within the space is supported and insulated from the walls, and that this electrically conductive element is down into the mass of solid contact material extends. D30020 / 0601 ORIGINAL INSPECTED