SOLIDS PUMPING APPARATUS

Abstract: A pump for feeding granular material into a pressurized zone. The pump employs a feed screw (14) having flights (32) rotatable in cylinder (12). The screw flights and cylinder are tapered at the discharge end. Such pumps, while capable of sealing against a reasonable back pressure, require high power consumption. Power consumption is reduced by providing a significantly greater clearance (38) between the screw flights (36) and the cylinder in the tapered zone (43) than the clearance (40) between the flights (32) and cylinder (12) in the nontapered zone.

Description: SOLIDS PUMPING APPARATUS BACKGROUND OF THE INVENTION This invention relates to + he feeding of particulate matter i ^o a high pressure zone, and in par + icular + o a screw feed appara+us frequen t ly known as a solids pump. There are occasions such as in t roducing pulverized coal into a high pressure air stream where it is necessary to pump "' ■ he coal to this high pressure level. This has been done with screw pumps where a helical member having fligh t s is ro+a + ed within a cylinder, and + he coal is supplied + o the upstream end of +his cylinder. These pumps operate at high speed (over 900 rpm). In some cases a reducing pi+ch is used so + ha + +he coal is compac+ed as it travels through + he cylinder, becoming sufficien t ly compacted + hat the high pressure air canno+ leak back through *he coal. In other cases a reducing nozzle is located a + the outle + end so tha+ + he coal is compac + ed as it pushes through + he nozzle thereby forming a seal at + hat Ioca*ion. Those pumps we have been able A o find which are capable of sealing agains + a reasonable back pressure have suffered from the disadvan t age of high power consump t ion. SUMMARY OF THE INVENTION Accordingly, it is an objec + o ou;~ inven t ion + o pump par t iculate or granular solids i to a hich pressure zone without back leakage of gases and i^h a rela t ively low power consump t i n. An apparatus for feeding a granular ma t erial into a pressurized zo e has a s+a + ϊonary hollow cylinder i^h a OMPI frus+oconical reducing nozzle located at + he discharge end. Means for feeding the granular material in+o the cylinder s loca t ed at +he upstream end. A rotary feed screw is !oca+ed within the cylinder and has helical ligh + s which have a decreasing pitch towards the discharge end. This feed screw is rota t ed at high speed within + he cylinder. At +he discharge end *he ou t side diame t er of the lights have a taper which is preferably equal + o but possibly grea+er than the taper of the nozzle. The helical feed screw is located in a position slightly withdrawn from the discharge end so +ha+ the radial clearance between the tapered flights and the nozzle is signifϊcan+ly grea+er than + he radial clearance between the uniform OD fligh + s and the bore cf + he cylinder. The tapered f !ϊgh + s extend i to but no + com le t ely through the nozzle. A coluπnal plug preferably cylindrical is cen t rally loca + ed wi t hin + he nozzle and a t tached + o + he end of +he feed screw. The optimum Ieng + h of """he tapered por + ϊon of the fligh+s appears + o be between -40 end 60 percent of the inside diame t er of the cylinder. Successful operation has been experienced with the radial clearance between +he fligh + s and the nozzle being greater than twice "^he clearance be t ween +he uniform OD fligh+s and ""-he bore, while even be* + er performance has been experienced when -"-his re^io exceeds four. The cylindrical plug is loca t ed i t i -"-he nozzle by making it an extension of + he feed screw shaf-*-. It is believed + ha + bes+ opera + ion is ob + ained if the ^ape of + he I i gh + s equals + ha + of "*"he nozzle and +ha + fur t hermore + he clearance be+ween -'-he +apered fligh+s and + he nozzle should exceed +hree times +he larges " particle size of + he ma t eriel being pumped. The knowledge of superior performance of our inven÷ion flows from + es÷ resul t s. The theory underlying the superior performance is based on specu la + ion. Tes + s were being run ■ <_■ de t ermine an op+imur. coal plug "*"hickness. The screw shaft was once wi t hdrawn as a s or^cu* me t hod for obtaining a thicker plug, end + he supe^ic- resu! + s were fϊrs + no + iced- OMPI . _ BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a general arrangement of the pump assembly; and Figure 2 is a detai I at the discharge end of the pump. DESCRIPTION OF THE PREFERRED EMBODIMENT An inlet hopper 10 is arranged to supply a granular material such as pulverized coal "*Ό + he ups + ream side of a stationary cylinder 12. A ro t ary feed screw 14 is concentrically and rota + ably mounted within the cylinder. The screw is canti levered from radial bearing 16 and thrust bearing 18 with an adjus+ab.le leng t h join* 20 loca+ed between the bearings. Drive motor 22 rotates the screw a 4 " a high speed such as 1250 rpm. Seal 24, preferably of the air injec + ion type, seals the shaft 26 as i 4- passes through the upstream end of the cylindrical housing. At the downstream end o + he housing an air header 28 supplies air into a nozzle mixing chamber 30 for the purpose of en t raining +he coal in a stream of air. The air pressure as used here, in chamber 30, is in the order of two o three atmospheres. In order +o ob+a?n effective sealing, the granular ma+erϊal must contain a reasonable amount of fines. The screw 14 has helical fligh t s 32 welded +here + o with a decreasing pitch as + he fligh + s proceed + owards the discharge end. With the high speed of ro + a + ion of the screw it is believed A hat the coal flowing within the screw forms an annular band so tha + the space be t ween + he f I igh + s is not full. As the pitch decreases the mass is compacted and + he air forced back +o a vent (no + shown) loca + ed in + he ups t ream end. A frus+oco ica I reducing nozzle 34 is bol+ed +o +he discharge end of cylinder 12. This nozzle forms an angle with respect to + he cylinder of approxi a t ely 6 degrees. The tapered f I i gh + s 36 at the downstream end of the screw have a tapered reducing outside diame + er at an angle ma t ching + ha* of the nozzle. It is believed + hat en ancle slich + ly grea t er +han + ha+ of -"-he nozzle would also perform sa t isfac t ori ly. The feed screw is no* fully ins + alled in + o + he nozzle bu + is wi÷hdrawn Ό.. ?I and loca+ed wi+h?n the nozzle such tha + the clearance 38 between the +apered f(igh+s and *he nozzles is significan t ly greater than the clearance 40 between • '-he constant OD flights and the bore of the cylinder 12. In - u he specific embodimen t with a 4 inch bore through cylinder 12, the radial clearance 40 was 0.009 inches while the radial clearance 38 was tested a + 0.125 and 0.250 inches. Satisfactory opera t ion is expected wϊ + h + he clearance 38 being twice the clearance 40, and superior operation is expected where the clearance 38 is just over four times +he clearance 40. The tapered fllgh + s 36 should extend within the nozzle 34 bu+ should no+ pass comple + e!y therethrough. An unperturbed zone 42 is required to permi+ +he for a+ion of an undisturbed coal plug which will effec t ively resist the backward flow of pressurized gas. The longi t udinal leng t h 43 of +he + apered f ligh + s 36 was varied during, experiments. I + was found tha+ in +he 4 Inch bore """he best resul + s were ob t ained be+ween 1 1/2 and 2 1/2 inches. Accordingly, the leng+h of +he + apered portion of the screw is preferably between 40 and 60 percent of the Inside diame + er of the cylinder 12. It is also believed, because of +he +heory set for+h later, tha* *he radial clearance between + he tapered flights and the nozzle should be greater + han + hree times + he largest par+icle size of + he ma+erϊa! being pumped. A columnar plug 44 in + he form of a cylinder is fastened o -"-he end of shaft 26. It extends concen+rical ly with the nozzle +hrough e+ Ieas + a por t ion of the nozzle beyond the tapered flights. The annular space between + he plug and the nozzle is comple + ely free and undisturbed, thereby per i+ting a plug of a coal to be formed in this area to resist reverse gas leakage. The annular shape of + his plug gives it more s + renσ*h ^ha e disc-shaped plug would have, and +he forming of + he plug is facilϊ+a + ed in ligh + of +he high speed of ro+a*ion of -""he shaf+ and + he higher concen+raΗon of coal OMFI on +he ou+er edges of the f ligh + s, par+icularly at low solids pump loadings. Tes + s were carried ou+ on a coal pump for pumping 3000 pounds per hour of coal i + o an a+mosphere wherein +he discharge pressure was up to two to three a t mospheres. In all cases, *he cylinder had a 4 inch ID; and +he fligh t s which were of cons + an+ ou+side diame + er had a radial clearance with respect t σ the bore of 0.018 Inches. In all tests +he cylinder had a 6° reducing nozzle a* the outlet end wi + h a 3.5 inch inside diameter. In -"-he Initial *est the pump had Iigh + s wϊ÷h a cons+an+ ou t side diame+er which s+opped before +he nozzle of +he cylinder. The shaft of the screw continued end ran completely through the nozzle. It was found that -"-he pump opera t ed satisfactori ly against discharge pressures up to 20 psig using over 16 horsepower when pumping 3000 pounds per hour. Effective sealing could no+ be ob+ained against pressure exceeding 20 psig. The power consumption ve ied linearly wi+h +he discharge pressure; end, accordingly, +hε pump used 0.8 horsepower per psi at 3000 pounds per hour coal flow. The screw was modified to ex + end """he fligh t s so tha+ +hey had a 4- +he end an ou t side diame+er +aper equal "*Ό +ha+ of +he nozzle. A series of ^es^s were run ex p ending *he leng+h 1, 1.5, 2.0, and 2.5 inches, respec + iveIγ. In -""his series of +es + s, the screw was lef+ a+ i + s fully Inser t ed posi t ion such + hat the clearence between + he + apered fligh t s and ^he nozzle was the seme as + he+ be + ween + he un+apered fligh t s and *he cylinder. Using the same shef 4 " speed of 1250 rp end the same coal feed ra^e of 3000 pounds per hour, + es A s were run over discharge pressures from 0 + o 35 psig. The power consumption in each of *hese tes + s was 0.7, 0.65, 0.3, end 0.3 horsepower per psi, respec + ive ly. I 4 - was, furthermore o^ed -"-he- the horsepower consu p+ion i^h respec 1 " +o a discharge pressure remained li ear. However, a 4- higher discha r ge pressures + he li ear rela t ionship las t ed for only one + o 'five minutes, af^er which i 4 - rose rapidly +o ar-d *he original horsepower consump t ion curve. For ins t ance, using -'-he 1 1/2 inch extension, this poin + occurred beyond 20 psig discharge pressure. At this time, on one test, the screw was retracted +o increase +he coal plug +hickness, ra + her + han follow +he usual 5 procedure of machi ing a shorter ex+ension. It was no + ed tha+ the power surge disappeared. To check ÷he possϊbϊli+y that the previous surge was caused by hea+ expansion of the shaft, it was re t urned to Its original position and cooled wl + h dry Ice. The power surge returned. 0 A series of tests were then run re + rac+ing the screw up *o 9/16 of an inch, + hereby providing a radial clearance . be + ween the tapered f!ϊgh+s and +he nozzle of up +o 0.25 inches. Power consumption was reduced from the original 0.8 horsepower per psi to 0.29 horsepower per psi when pumping 3000 5 pounds per hour, which was an overall reduc t ion of power of 63.5 percent. This was accomplished wi^h a 2.0 Inch extension of +he + apered fligh+s, and with wi t hdrawals of .125 + o 0.313 inches. This resul+ed In a radial clearance within + he nozzle of approxima÷ely .022 - .040 inches. It was found that +he 0 power surges occurring a + the high discharge pressures af + er a short period of opera+ϊon were el imϊna + ed. Increasing -*-he retraction from 0 + o 5/16 of an Inch with a 2 1/4 inch flight ex+ension increased the maximum obtainable steady-state discharge pressure, and very li++le 5 chance i power consump+ion occurred wi-*-h + h?s amoun+ of retraction. Retracting + he screw beyond + hϊs resulted in Increased power consump + ion. Tes+s were run wl+h +he +apered fligh t s ex+endϊng co ple+ely +hru the nozzle. The pump would not opera t e in that ;0 It would no+ seal. I* was also noted + ha 4 - the + apered flights seem + o cooperate with + he coal to form a bearing. The pump was quie + er when the coal was actually ormi g a seal and became noisy when sealing was lost. It is specula t ed -""ha 4 " In ÷he firs 4- modification wi+h 5 - fc he + apered fligh t s being immedia+ely edjecen* +he nozzle ÷hat the shearing force occurring on + he coel is e resul+ of movemen÷ of +he screw rela+ive +o the s^a^ionary discharge nozzle. Because of the close + olerance be t ween +he f 1 i gh+ and +he nozzle, only a +hin layer of coal would exϊs + ; and +he discharge nozzle would begin coking a + higher discharge pressures. The coking of + he coal would cause ex p ensive fric+ional forces in this area . This phenomenon would occur at higher discharge pressure because higher forces are involved, and + he discharge temperature normally increases with + he higher discharge pressure and the normal ly expec+ed linear increased power inpu+. By re+rac+ϊng + he screw rela + ive to the discharge nozzle, however, the shearing force created by the screw's movement is against a stationary or slowly moving finite boundary layer of coal. This continuous flow of coal and the reasonable boundary layer thickness avoids coking phenomenon and frictional drag experienced in the close clearance embodiment. Fur t hermore, +his arrangemen-*- would appear + o give a wider range of t hroughput capabi lity wi + hou 4 - experiencing high compresslve and concomitan 4 - fric + ional forces. As +he diame+er of the fligh + s wi + hin the nozzle is decreased, + he volume within them is decreasing, resul + ϊng In a compac+ϊon of +he coal. If because of +he high ro + a + ional speed + he flight is not full, i 4 " would result in an i ward movemen 4- of the coal particles + o fill the space between the fligh + s. On + he other hand, If the loading were relatively high such + hat fligh + s were already ful l, the pressure would tend +o Increase. Wi + h the rota + ϊng ligh+s ÷ending + o s + ir + he powdered mix+ure, i+ could flow ra+her fluently out + hrough + he clearance, thereby avoiding high forces and fric + ion due + o overcompac + ing of + he coaI . C FI

Claims: --- CLAI MS 1. An apparatus for feeding a granular ma + erial In + o a pressurized zone comprising: a sta + ϊonary hollow cylinder having a bore; a frus + oconical reducing nozzle located at a discharge end of said cylinder; meens for feeding + he granular material into said cylinder a + an upstream location of sald cylinder; a ro÷ary feeder screw conce + rlca I ly located within said cylinder and having helical flights + hereon, said flights having a decreasing pitch towards the discharge end; means for ro+a+ϊng said feed screw a÷ high speeds; said fligh + s having an OD only slightly less + han said bore through a majority of the length of said feed screw, and having a + apered decreasing OD a+ +he discharge end, the +eper being a + least as great as that of said nozzle; said feed screw being located wi÷hϊn said cylinder such tha + the radial clearance be + ween +he nozzle bore and +he tapered fligh+s is significan ly greater than that between + he bore of + he cylinder and + he flights + hrough +he majority of leng+h, end + he + apered flight extending through only a portion of said nozzle; and a columnar plug rota+ϊng with said screw and concentrically loca + ed wi + h said nozzle. 2. An apparatus as In Claim 1 wherein +he leng+h of the + apered portion of the Iigh+s is greater +han 40 percent of the inside diameter of the bore. 3. An appera + us as in Claim 2 wherein +he leng + h of +he tapered por + ion of the f I ϊgh + s is less + han 60 percen + of + he inside diame + er of +he bore. 4. An appara + us as in any one of Claims 1 through 3 wherein + he radial clearance of + he tapered flights w? + hin the nozzle is grea + er than + wo + imes + he cleerence of + he non- tapered flϊch + s within + he bore. 5. An eppera + us as in Claim 4 wherein + he clearance between + he + apered fligh+s and + he nozzle is grea + er +han four +imes + he clearance of + he non- + apered f ligh+s wi + hin +he bore. 6. An eppere + us es in any one of Claims 1 +hrouch 3 wherein said columnar plug is cylindrical. <* ■ c 7. An apparatus as In Claim 5 wherein said columnar plug is cy I indrical . 8. An appara + us as in any one of Claims 1 through 3 wherein the radial clearance between + he + apered flights and the nozzle Is grea + er +han + hree times + he lerges + particle size of the mε + erial t be fed. 9. An apparatus as in any one of Claims 1 through 3 wherein +he angle of + he +aper of +he f'ligh+s equals the angle of + aper of the nozzle. 10. An apparatus as in Claim 5 wherein the angle of +he taper of the flights equals the angle of + aper of + he nozzle. 11. An apparatus as in any one of Claims 1 through 3 wherein + he taper of the flfgh+s equals + he taper of the nozzle, and wherein said columnar plug is a cylindrical extension of said feed screw. 12. An appara+us -as in Claim 5 wherein +he angle of +he taper of +he f Iigh + s equals + he angle of + aper of + he nozzle. o.:?ι

Inventors: POTE BRUCE MACNEIL, SMITH DONALD ARTHUR
Applicants: COMBUSTION ENG, POTE BRUCE MACNEIL, SMITH DONALD ARTHUR, COMBUSTION ENG INC
Application year: 1981
Main classification: B65G53
IPC codes: B65G33, B65G53, F23H3