A METHOD AND MEANS FOR INTRODUCING FINE PARTICULATE MATERIAL

Abstract: Method and means for introducing and mixing fine particulate material into a mixture of particulate material and binder to form a composite product such as asphaltic cement. The invention provides means for mixing the fine particulate material with a wetting agent such as a liquid binder to form a slurry prior to introducing the fine particulate material and binder to mixing apparatus in which further particulate material is added. This enables the dust nuisance and loss of fine particulate material to be reduced.

Description: "A METHOD AND MEANS FOR INTRODUCING FINE PARTICULATΞ MATERIAL" THIS INVENTION relates, to a method and means for introducing and mixing fine part±culate material to form a composite product such as asphaltic concrete or similar paving materials or the like. Drum type dryers and drier-mixers are well known and widely used in the production of hot mix asphalt or asphaltic concrete as it is alternatively known. Filler which commonly takes the form of flyash, limestone dust, crusher dust, or any other type of fine particulate material is added as the fines component of the mix. The existing methods of adding filler involve its introduction to the system as a dry powdered component either alone or with aggregate feed. In a drum type dryer or drier-mixer, the fines or filler become intermixed with the falling aggregate curtain. A significant proportion of this added filler ordinarily becomes suspended in the exhaust air stream from the drier-mixer and is lost to the .mix. Dust collectio plant is then required to capture this dust along with other fines from, the aggregate feed. In a pugmill or other type of mixer, the addition of a dry powdered filler as a separate component, or in combination with aggregate components is a source of dust generation which is to be avoided. An object of this invention is to provide a method of introducing filler material into mixing apparatus which will inhibit the filler material being captured in an air stream in the mixing apparatus or being dispersed into the atmosphere to thus form a source of waste or possible dust generation. According to one aspect, this invention relates to a method of introducing fine particulate material into mixing apparatus for forming a composite product including particulate material and binder said method including the steps of:- (.al introducing said fine particulate material and wetting agent into a mixing zone, (b) . mixing said fine particulate material with said wetting agent to form a slurry and, (c) feeding said slurry into said mixing apparatus. In step (a) the filler material may be introduced or discharged into the mixing zone in any suitable manner. Preferably, however, the filler material is fed by gravity into the mixing zone and this may be achieved from directly above the mixing zone by any suitable conduit. The filler material is suitably introduced into the mixing zone from a metering device so as to regulate the amount of filler fed into the mixing zone. in step (b) the binder material may be introduced or discharged into the mixing zone in any appropriate manner. Suitably, the binder material is introduced into the mixing zone simultaneous with the filler material. Suitably, if " a substantially vertical entry for the filler material is to be used a lateral entry may be utilized for the binder material although this is not essential. Preferably, the binder material is introduced into or adjacent the mixing zone so that the binder material may surround the incoming stream of filler material. Thus the binder material may be fed into or adjacent the mixing zone substantially tangentially to the incoming stream of filler material at spaced intervals about the periphery of a entry conduit which suitably tapers inwardly to an area of restricted cross section before communicating with the mixing zone. The binder material and filler material may be subject to agitation in the mixing zone and this may be accomplished in any suitable manner such as by agitators or rotating mixing paddles being provided in the mixing zone so that a slurry is formed before the resulting mixture is fed to the mixing apparatus. Preferably, the binder material is fed into the mixing zone in the liquid state and thus- depending upon the filler, it may be desirable to heat the mixing zone and/or entry conduit for the binder material so as to maintain same in the liquid state. In step (c) , the slurry pre-mix may be discharged under pressure from the mixing zone. This invention also includes within its scope apparatus for introducing and mixing fine particulate material to form a composite product including particulate material and binder, said apparatus including:- (a) a chamber assembly having a mixing chamber and agitation means operatively associated , therewith? (b) first entry means to said chamber assembly for introducing fine particulate material; (c) second entry means to said chamber assembly for introducing wetting agent, and, (d) exit means from said mixing chamber, said exit means being adapted for operative communication with said mixing apparatus . In order that the invention may be more readily understood and put into practical effect, reference is now made to a preferred embodiment of the invention which utilizes a liquid binder as the wetting agent illustrated with reference to the accompanying drawings, and wherein:- FIG 1; is a diagrammatic side view of mixing apparatus for producing say asphaltic concrete and, FIG 2; is a diagrammatic cross-sectional view of the primary mixing apparatus for mixing binder and filler material. As shown in the drawings, the mixing apparatus for producing say asphaltic concrete comprises an inclined rotary drum type drier-mixer 10, hereinafter referred to - 4 - as the type described, and having an inlet end 11 through which aggregate is introduced through a chute 12 or other suitable means from conveying apparatus 13, and conveying means 14 through which a pre ^ mix slurry of binder and filler is introduced part-way along the drum, as at 15. The pre-mix slurry is delivered from- the primary mixing . apparatus 16 which is more fully illustrated in FIG 2. The mixer 10 further includes a combustion chamber and burner assembly 17 which supply hot air through the rotary drum 18, to an air expansion housing 19 at the down-stream end of the drum 18 at which there is provided the product outlet 20 through which the final mixture is gravitationally discharged. In conventional manner the rotary drum 18 is provided with spaced inwardly extending blades around its internal surface whereby the aggregate or other coarse particulate material to be dried and mixed is introduced thereto, is alternately lifted up and dropped by the .blades as it advances operatively along the * drum from the inlet end to the outlet end. The induced hot air draft drys the wet aggregate as it passes along the first portion of the drum 18 whereafter, according to this embodiment the pre-mixed slurry of fines or filler and binder, suitabl liquid asphalt, is introduced into the drum 18 at 15 and is then alternately lifted up and droped by the blades to throughly mix with the dried aggregate and comingle to form the desired product. Of course, the aggregate and the slurry are metered to achieve the desired result. Referring to FIG 2, it will be seen that the primary mixing apparatus 16 is in the form of an enclosed bousing which comprises a downwardly tapering lead-in portion 21 and a lower open topped mixing chamber 22 which houses a rotaty assembly 23 supported at the lower end of a shaft 25 which passes upwardly and sealably through the top of the housing 26 and is driven by drive means such as the electric motor 27, In this embodiment, the filler in the form of fine dry particulate material is introduced through conduit means 28 which passes obliquely through the side of the housing to terminate at an open end 29 disposed concentrically about the drive shaft 19 and directly above the rotor assembly 23. The binder, say asphalt is introduced under pressure from air inlet pipe 30 arranged substantially tangentially to the cylindrical upper portion 31 of the housing so that it is fed around the inside wall thereof to encircle the outlet 29 and material issuing therefrom and so combine with the filler as it enters the mixing chamber 23. Both materials are gravitationally fed to the mixing chamber in which they are mixed into a slurry form prior to being discharged through the discharge outlet 32. Suitably, the rate of rotation of the rotor 23 and the Supply of materials are controlled so that there will not be a build-up of material above the rotor 23. The filler binder slurry is discharged from the rotor 23 through the outlet pipe 32 and thence via the transfer means, suitably conduit 14 to the drier- mixer 10. It is preferred that the primary mixing apparatu 16 be supported above the inlet to the rotary drum 18 so that material in the conveying means 14 feed gravitationall to the outlet 15. Of course, the lead-in portion 21 and other necessary portions of the equipment including the inlet conduit 28 may be provided with heating coils or are heated by other suitable means to maintain the binder, suitably asphalt, in a liquid state. Additionally, if desired, the means for introducing the filler and binder into the mixing chamber could be varied such as by for example, by intro¬ ducing the binder in the form of a spray through an inlet in the transition piece 33 immediately above the mixing chamber 23. It will be seen that in the primary mixing chamber the filler is mixed with the binder to form a slurry in a housing which is not subject to a substantial air draught therethrough so that the fine filler material is not picked up and carried away as is the case with conventional drum type drier-mixer means in which a substantial amount of filler is introduced into an enclosed housing and can exit therefrom only in the form of a slurry so that there is minimal wastage of filler in the method of the present invention. Also since the filler is introduced to the rotary mixing drum 10 in the form of a slurry it will not be, at that stage, carried away with the hot air draught passing through the drum and substantially all filler will be mixed with the aggregrate and binder to form a compos- ition desirably free of voids since the particle sizes can be accurately gauged to ensure that the final compos¬ ition includes the correςt amount of particles of varying sizes and binder. Of course, other binders as appropriate may be ulitized and the binders themselves may be in liquid or powdered form, but a liquid carrier or other suitable wetting agent must be introduced in the pre-mixing stage so that the fine particulate material or filler enters the mixing means for forming the desired product in the form of a slurry. The wetting agent may, of course, be the binder itself as described above or a further process fluid introduced into the pre-mixing stage. It will be seen that by utilizing the present invention the dust nuisance normally associated with formation of composite products including fine particulate material will be alleviated and that pre-mixing of fines with binder to form a slurry will provide good wetting of the fines in the product. Additionally, it is often necessary to add emulsifiers or other active ingredients such as solvents, extenders or retardan s and they can be advantageously added at the pre-mix stage with the filler slurry. While the above has been given by way of illustrative example, it will of course, be realised that all such modifications and variations to the inventio as would be apparent to persons skilled in the art and deemed to fall within the broad scope and ambit of the . invention as is defined by the appended claims.

Claims: Claims: 1. A method of introducing fine particulate material into mixing apparatus for forming a composite product including particulate material and binder said method including the steps of:-^ (a) introducing said fine particulate material and a wetting agent into a mixing zone, (.b) mixing said fine particulate material with said wetting agent to form a slurry and, (c) feeding said slurry into said mixing apparatus. 2. A method according to Claim 1, including the step of introducing a binder into said mixing zone, said binder constituting said wetting agent. 3. A method according to Claim 2, and wherein said binder is liquid only at an elevated temperature, the method further including the step of heating said mixing zone to an elevated temperature to maintain said binder in a liquid state. 4. A method according to Claim 3, including the step of providing a heated inlet means for said binder. 5. A method according to any one of the preceding claims, including the steps of:- (a) introducing said fine particulate material into said mixing zone above a mixing rotor supported therein, and (b) rotating said mixing rotor at a speed sufficient to mix said fine particulate material and said wetting agent into a slurry form and to discharge said slurry through an outlet associated with said mixing zone. 6. A method according to any one of the preceding claims and wherein said mixing apparatus is in the form of a rotary drum type drier-mixer of the type described, the method further including the step of introducing said slurry into said drum type drier-mixer at a position intermediate the inlet and outlet means of said drum type drier-mixer. 7. A method according to any one of the preceding claims, including the step of introducing said fine particulate material to said mixing zone in a substantiall vertical direction, and introducing said wetting agent to said mixing zone in a substantially lateral direction. 8. A method according to Claim 6, including the step of introducing said wetting agent into or adjacent the mixing zone so that said wetting agent surrounds the incom¬ ing particulate material. 9. Apparatus for carrying out the method of any one of the preceding claims, said apparatus including:- (a) a chamber assembly having a mixing chamber and agitation means operatively associated therewith? (b) first entry means to said chamber assembly for introducing fine particulate material; (c) second entry means to said chamber assembly for introducing wetting agent, and, (d) exit means from said mixing chamber, said exit means being adapted for operative communication with said mixing apparatus . 10. Apparatus according to Claim 9 wherein said agitation means is a rotor operatively supported within said mixing chamber. 11. Apparatus according to Claim 9 or Claim 10, wherei said rotor is rotatable about a substantially vertical axis and said chamber assembly includes a lead-in portion above said mixing chamber, the latter being an open topped chambe to expose said rotor to said fine particulate material and said wetting agent, said lead-in portion expanding upwardly from said mixing chamber and being operatively sealed at its upper end to prevent escape of said fine particulate material. - 10 - 12. Apparatus according to Claim 11, wherein said first entry means has a material outlet opening disposed directly above said rotor and said second entry means has an outlet opening disposed beneath said material outlet opening and spaced laterally therefrom. 13. Apparatus according to Claim 12, wherein said . upwardly expanding lead-in portion is in the form of a truncated cone and said second entry means is adapted to feed wetting agent substantially tangentially onto the inside surface of said lead-in portion whereby in use said wetting agent will move down and about the fine particulate material falling to said rotor. 14. Apparatus according to Claims 10-13, wherein said exit means is a port in said mixing chamber arranged such that the slurry formed in said mixing chamber is forced through said port by said rotor. 15. Apparatus according * to any one of Claims 9-14, wherein said exit means includes transfer means passing from said mixing chamber to a position intermediate the ends of a rotory drum type drier-mixer of the type described so as to introduce said slurry into said rotary drum type drier-mixer operatively downstream of the inlet for particulate material to be dried in said drier-mixer.

Inventors: DUNSTAN T
Applicants: DUNSTAN T, HOPGOOD DUNSTAN & PARTNERS PTY, HOPGOOD DUNSTAN & PARTNERS PTY LTD
Application year: 1981
Main classification: E01C19
IPC codes: E01C19