US 2839339 A
Description (OCR text may contain errors)
June 17, 1958 l. w. MILLS 2,839,339
PROCESS AND APPARATUS FGR ELEVATING GRANULAR SOLIDS Filed Aug. 17, 1956 Elecfricul lnsulmion Electnc Power Supply Voliage Regulator Electrical Charqmg Means 23 Electrical lnsuiafim INVEN TOR. IVOR W. MILLS Wk, 9 @Qm TORNEY PROCESS AND APPARATUS FOR ELEVATING GRANULAR SOLIDS Ivor W. Mills, Glenolden, Pa., assignor to Sun Oil Conn pany, Philadelphia, Pa., a corporation of New Jersey Application August 17, 1956, Serial No. 604,805
9 Claims. (Cl. 302-66) This invention relates to process and apparatus for elevating granular solids by means of a lifting gas.
It is known in the art to elevate granular solids by suspending such solids in a lifting gas under pressure, and conveying the suspension upwardly through an elongated confined lifting zone or zones to a disengaging zone in which space for expansion of the lifting gas is provided in order that the granular solids may be dis engaged from the lifting gas and dropped into a lower portion of the disengaging zone. Such lifting operations are beneficially applied in various processes, including for example processes in which granular solids are circulated repeatedly through a system comprising a downflow path and an upfiow path provided by the corn fined lifting zone or zones.
In such lifting operations, a serious problem which is frequently encountered is excessive attrition of the granular solids during the lifting operation. The total solids in a solids circulation system at agiven time may comprise for example a major proportion of particles having sizes greater than 20 mesh (U. S. sieve series), and
often greater than 8 mesh. A certain amount of attrition of the solids to produce very fine solid particles inevitably occurs, but it is desirable to minimize the formation of fines as much as possible, since excessive formation of fines results in high rates of loss of solids from the system and other undesirable effects.
The attrition resulting from particles striking the wall of the lift conduit is a particularly significant factor in the total attrition occurring in a solids circulation system, and the present invention is primarily directed to reducing the amount of attrition occurring from this cause.
According to the invention, attrition is reduced by employing electrical charges to maintain a cushioning layer of fine solids adjacent the wall of the lift conduit.
Such fines may be for example less than mesh in size, vand are generally produced by the attrition which occurs on the particles, so that the fines are attracted to the lift conduit wall and have a greater concentration in the region adjacent the lift conduit wall than in conventional operation where electricalv charges are not employed in the manner according to the invention.
The layer of fines adjacent the lift conduit wall provides a cushion to prevent the large particles from striking the lift conduit wall in the manner which occurs in conventional operation, or to reduce the force with which the large particles strike the wall. The high concentration of fines near the lift conduit wall also provides benefits in inhibiting the tendency for larger particles to fall back downwardly in the lift conduit in the region adjacent the wall. In ordinary operation, since the velocity of lifting gas and solids is greater near the axis of the lift conduit than it is in the peripheral portions of the lift conduit, there is a tendency for large particles to fall downwardly in the peripheral regions where the supporting velocity of lifting gas is less. This tendency is counteracted according to the invention, since greater support for the large particles near the peripheral por-. tions of the lift conduit is provided by the larger concentration of fine particles in those regions, the fine particles having a significant supporting effect.
According to the invention, the concentration of fines near the lift conduit wall is higher than in prior art operation, and in one embodiment of the invention, there is also a stationary or substantially stationary layer of fine particles which are held against the lift conduit wall by the electrical charges involved. In the latter case, a particularly suitable cushion is provided to prevent excessive attrition of large particles upon striking the lift conduit wall.
In pneumatic lifting operations of granular solids, particularly where fine granular solids are involved, electrical charges are spontaneously produced on the particles by contact with other particles and the lift conduit wall. Also, electrical charges, opposite in sign to those on the particies, are spontaneously produced by contact of the solids with the lift conduit wall. In conventional lifting operations, however, the charges are dissipated from the lift conduit wall, since the latter is grounded, and the charges do not build up to a sufficient level to produce. the, beneficial effects according to the invention. According to the invention, means are provided for main-. fairing an electrical charge on the lift conduit Wall, which charge is sufficient to provide substantial deviation of fine solids from their normal course through theliftconduit.
In one embodiment of the invention, sufiicient electrical charges are maintained on the lift conduit wall by insulating the. lift conduit from the rest of the apparatus, so that the charge is permitted to build up to a desired level. The voltage generated can be regulated by means of a voltage regulator of conventional design, by means of which voltage above the desired amount can be dissipated.
in some instances at least, it is not necessary to employ external means for producing an electrical charge on the lift conduit wall, but such means can be employed if necessary, a voltage regulator also being used if necessary to control the intensity of the electrical charge on the lift conduit wall.
In another embodiment of the invention, a non-conwhich can be used. In the case of a nonconducting ma-. terial, the electrical charge can build up to a desired level without dissipating the charge, since the material does not conduct the charges sufficiently for them to be dissipated.
The voltage to be maintained on the lift conduit wall will depend upon the various factors which are involved in the lifting operation, such as the nature of the solids, the rate of elevation of the solids, and other factors. In
the light of the present specification, a person skilled in.
the art candetermine the proper voltage to be used in a. lifting operation.
. The invention will be tothe'attached drawing, which is a schema-ticillustration of'apparatus suitable for use according to the invention.
Referring now to the drawing, a vessel 10, gas lift engager vessel 311, lift conduit 12, and disengaging vesa sel 13 are illustrated therein. Lift conduit 12 is con structed ofelectrical conducting material, e. g. steel, and
Patented June 17, 1958 further described with reference -maintained on the lift conduit wall.
. 6 s. nsulated rq nthe est of t e appa a us by elestr salinsulating means 14 and 15. Electric power supply 16 is connected to lift conduit 12 through voltage regerenator I'Lthe latter also-being connected to a ground 18. V
In operation granular solids are gravitated from dis engager 13 through line 19 intoivessel. lit, and are then removed through line 20 and introduced into engager 11. Liftinggas is introduced into engager lll'through line 21, and carries the solids upwardly through lift conduit 12 into disengager 13. Lifting gas is separated from solids. in disengager 13 and removed through line 22. The separated solids are gravitated through line 19 again into vessel 10.
Lines 19 and 20 and vessel It constitute a downflow pathfor granular solids. ,Any suitable operation or operations in which the solids participate can be carried out during passage through the downflow path. Thus,,for example, the solids can be contacted with gaseous or liquid materials in order to bring about a physical operation or a chemical reaction, the solids acting as an adsorbent or catalyst for example.
The wall of lift conduit 12 is maintained at'a suitable voltage by means of voltage regulator 17; if necessary, electric power supply l6 provides electrical potential to maintain the desired voltage. On the other hand, if sufficient potential is spontaneously generated in lift conduit 12, electric power supply 16 is not needed. f excessive voltage is spontaneously generated, the excess over that desired is removed to ground 18.
The charged lift conduit wall attracts charged articles to the wall andprovides a high concentration of fines near the Wall, with resulting reduced attrition of the large particle passing through the lift conduit. Because of their greater mass, the large particles, though theymay be electrically charged, are subject to less deviation from their normal course than the fine particles.
It is within the scope of the invention to impress an electric charge on the solids, by suitable means 23, prior to introduction into the lift conduit, e. g. while passing through conduit 20, for example, or while passing through a lower portion of lift conduit 12 (means not shown). This can. be accomplished by any suitable known means for electrically charging material passing through a conduit.
Suitable means not shown can be provided in conjunction with disengager 13 to remove the charge from the solids after they-have issued from lift conduit 12 and have been collected in disengager 13.
The following example illustrates the invention:
A mixture elf-granular solids at a temperature of about 200 F. is elevated through a cylindrical lift conduit having diameter of 8 inches and height of 70 feet. The solids elevated have the following approximate distribution of sizes:
The rate of elevation of solids through the lift conduit is 40 tons per hour, and the lifting gas rate is i900 standard cubic feet per minute. The apparatus and operation conform to those described in connection with the drawing, and an electrical potential of about 5000 volts is The fine solids are attracted to thelift conduit wall, the strength. of the attraction being inversely proportional to the size of the solids, .so that fraction 7 for example is more strongly attracted than fraction 6, fraction 6 more so than fraction. 5', and so forth. The fine solids become conccn-i trated in the region near the lift conduit wall, and the 4' tr tion o the arg Pa t les s. h reby r ed; the reduction in attrition makes it possible to maintain a suitably low concentration of fines in the system while removing less fine solids in the elutriating apparatus. Thus, economy of catalyst utilization is obtained, and detrimental effects produced by excessive concentration of fines in the system are avoided.
The process according to the invention is applicable generally to those particles which are capable of carrying and holding an electric charge. Determination of suitability of p .cular solids, in the light of the present specification, is within the ability of a person skilled in the art. Examples of suitable solids are silica gel, alumina, bauxite, clay, fullers earth, kieselguhr, silica-alumina compositions, etc.
An example of an operation to which the present in vcntion is applicable is the transportation of granular cracking catalyst as employed in the petroleumindustry in the Houdriflow process. involving the gravitaticnof granular catalyst in compact form through a cracking or reaction zone and'a catalyst regeneration zone in series, followed by pneumatic elevation of the cracking catalyst at a temperature of about 1600 F. to a disengaging vessel positioned above the reaction zone. This general scheme of operation is also applicable to other petroleum conversion processes, and also to processes outside the petroleum field.
The present invention can be applied to the elevation of granular solids at ordinary temperature without heating or at elevated temperatures. Since dissipation factor for electrical charges generally increases with increasing temperature, it may be necessary at elevated temperatures to provide special means for ii pressing electrical charges upon the particles, such as the charging means 23, and in some cases it may be necessary to provide such,
means at a location close to that where the desired attraction of fine solids to the wall. is to take place, in order that the charges will not become dissipated before having the desired effect.
The electrical charging means representedat 23in the drawing can for example be a section of the solids transfer conduit which is insulated from the remainder of the conduit and upon which an electric potential is impressed by any suitable means of supplying electricalenergy. Thus, for example, the conduit section can be given a negative charge, which is transferred to solid particles upon contact of the latter with the wall of the conduit section. The charged particles in turn charge other particles upon contact therewith. The lift conduit wall, in this embodiment, can be given a positive charge, by suitable known means, whereby the negatively charged particles are attracted to' the lift conduit wall "duringpassage through lift conduit 12. In this embodiment, it is desirable that the conduit 20 and engager 11 have an insulating lining in order that the solids do not lose their charges during passage therethrough into lift conduit 12. Alternatively, conduit 20 and engager 11 can be given a negative charge, for example, and insulated from other apparatus, in order that solids contacting the walls of the conduit and engages will become negatively charged. it is also within the scope of the invention for a lower portion of lift conduit 12 to be insulated from, and have a charge opposite in sign from that of, an upper portion of lift conduit 12', in order that the solids acquire, for example, a negative charge while passing through the lower portion, and are attracted to the wall of the positively charged upper portion while passing therethrough.
The process and apparatus according to the invention are advantageous in that a cushioning layer of fine solids can be maintained on the lift conduit wall, which layer is.
continuously restored by the attraction of new particles tosthe wall to replace those particles which have lost their-charge and been swept away from the lift conduit wall hy the lifting gas, or otherwise removed from the wall. This. feature. provides an important advantage over, for example, a padding material secured to the inner lift conduit wall, such material being subject to rapid wear by contact with solid particles.
The invention claimed is:
1. Process for elevating granular solids having particle size greater than mesh wich comprises: suspending such solids in a lifting gas in an engaging zone; passing the suspension upwardly through a confined lifting zone in the presence of granular solids having particle size less than 20 mesh; discharging solids from said lifting zone into a disengaging zone; gravitating solids from said disengaging zone through a downfiow path to said engaging zone; and maintaining an electrical charge on the Wall of the lifting zone, which charge is opposite in sign to the electrical charge on the solids, whereby said solids having particles size less than 20 mesh are caused to deviate from their normal course of travel by the attractive force of the opposite charges and become more concentrated in the peripheral portions of the lifting zone than in the absence of such attractive force, said lifting zone h'aving substantially rectilinear axis and being substantially unconstricted throughout the region in which said charge is applied.
2. Process according to claim 1 wherein the first named solids have particle size greater than 8 mesh.
3. Process according to claim 1 wherein a predetermined voltage is maintained on the wall of the lifting zone by conducting away from the wall a controlled amount of the voltage generated by collisions of solids with the wall.
4. Process according to claim 1 wherein a predetermined voltage in maintained on the wall of the lifting zone by supplying electrical current to the wall in controlled amount from an external source.
5. Apparatus for elevating granular solids which comprises: a lift conduit; means for introducing granular solids and lifting gas into a lower portion of said lift conduit; receiving means for granular solids discharged from an upper portion of said lift conduit; means for gravitating solids from said receiving means through a downflow path to said means for introducing; and means for maintaining an electrical charge of controlled voltage on the wall of the lift conduit, thereby to exert a selective attractive force on the smaller sized, electrically charged solid particles passing upwardly through the lift conduit, said lift conduit having substantially rectilinear axis and being substantially unconstricted throughout the region in which said charge is applied.
6. Apparatus according to claim 5 wherein the inner surface of the entire lift conduit wall is an electrical conductor which is electrically insulated from other portions of the apparatus.
7. Apparatus according to claim 5 wherein the inner surface of the entire lift conduit wall is an electrical non conductor.
8. Process according to claim 1 wherein said charge is maintained substantially throughout the entire length of said lifting zone.
9. Process for elevating granular solids which comprises suspending granular solids having particle size greater than 8 mesh in a lifting gas in an engaging zone; passing the suspension upwardly through a confined lifting zone in the presence of granular solids having particle size less than mesh, the larger particles tending during such passage to fall in the peripheral portion of said lifting zone; discharging solids from said lifting zone into a disengaging zone; gravitating solids from such disengaging zone through a downflow path to said engaging zone, and maintaining an electrical charge on the wall of the lifting zone, which charge is opposite in sign to the electrical charges on the solids, whereby said solids having particle size less than 50 mesh are caused to deviate from their normal course of travel by the attractive force of the opposite charges and to become more concentrated in the peripheral portion of the lifting zone than in the absence of said attractive force and to counteract the tendency of said larger particles to fall in the peripheral portion, said lifting zone having substantially rectilinear axis and being substantially unconstricted throughout the region in which said charge is applied.
Ardern July 24, 1951 Garbo Dec. 11, 1951