GB2131708A - Recycling bituminous aggregate - Google Patents

Abstract

A machine for recycling old road metal comprises a cylindrical barrel (18) rotated about an axis inclined at a small-angle to the horizontal, the barrel (18) having internal flights (34) extending parallel to its axis, the flights (34) being spaced from the band wall by a distance D. Thus road metal lumps fed into one end (26) are rotated and tumbled in passing to the opposite end and the discharge opening (42), the tumbling breaking down the lumps until they are of sufficient size to slide between the flights (34) and the barrel wall and so be discharged. A burner (28 Fig. 1) fires into the material inlet end (26) of the barrel (18) to heat the aggregate as it passes along the barrel and flame and gas are exhausted at the opposite end of the barrel preferably through a vortex extractor system (70,72). <IMAGE>

Description

SPECIFICATION Recycling bituminous aggregate This invention relates to the preparation of bituminous coated aggregate for road repairs and similar operations, especially in small quantities.

Several different systems are possible and indeed in use at the present time.

The required material can be prepared in a fixed installation for example a local authority depot, and the installation might be constructed as in the proposals contained in British Patent 1443424 or 1385812 for example. Material prepared in the installation is delivered to site. Since the plasticity of the mixture is due, at least in part, to the temperature of the tar, the material may be unsatisfactory or even unworkable if the journey is long and the weather cold: moreover it may be difficult to judge the required quantity and hence over supply and wastage is likely.

To overcome the problems of cooling and quantity prediction, an alternative system uses a mobile preparation plant which can be towed to the site to supply hot plastic material in the required quantity. Mobile plants have been proposed for example in BP. 1443829 and 1385812.

All of the mentioned proposals are suitable for use with what might be called new stone and new pitch. The stone can be assumed to have been crushed to the appropriate particle size and probably sieved to reduce unwanted fine and dust content and for example in BP. 1442829 is preheated before being mixed with preheated and in fact liquefied bitumen prior to mixing the two together. Clearly, careful control of ingredients, temperature and mixing can lead to satisfactory results.

But many road repair operations involve removing the existing road material as quickly as possible, for example in order to get at a leaking gas or water pipe, and the old material, which may be assumed to be a satisfactory mix of the materials, is available perhaps in large lumps. If it is not re-used it has to be taken away. It has therefore been proposed for example in BP.

2013097 to provide a portable apparatus for recycling old material. Although the end product from such apparatus may be similar to the end product from the previously mentioned apparatus using "new" material-assuming that the materials in both cases were of the same standards, the recycling process is inherently different from the process for treating new material. Many of the complications for dealing with dust and for controlling the water content of the stone become unnecessary, but completely different problems are introduced by the fact that the material to be recycled is likely to be in much larger pieces than new material. Because it has already been coated, the control of the heating becomes so much more critical.Whereas the uncoated aggregate in a new material plant might be overheated without damage, the result with the coated material is likely to be production of volatiles and combustion of the same, and with normal bituminous materials the end result is clouds of dense smoke. But mere temperature limitation is also insufficient and other problems are due to the possibly large size of the lumps introduced in recycling material.

The object of the present invention is to overcome these problems, and to provide an improved portable apparatus for preparing recycled material.

In accordance with the invention considered broadly a process for recycling old road metal and the like comprising bituminous coated aggregate in large lumps comprises feeding the material unidirectionally and with gravitational assistance along a rotating barrel, tumbling oversize material by the provision of flights in the barrel and separating sized material by spaces between the flights and barrel before discharging sized material, and heating the material by a fuel fired burner directed along the barrel in the same direction as material movement and discharging exhaust products at the material discharge end of the barrel.

Preferably flame and combustion products from the burner are caused to sweep along the barrel an reverse before passing to exhaust.

Exhaust flow may be fan assisted or encouraged by a vortex throat in the exhaust system.

The invention further consists in apparatus for carrying out the process.

One presently preferred embodiment of the invention is now described by way of example only and with reference to the accompanying drawings wherein: Figure 1 is an elevation of a portable apparatus for recycling old road material; Figure 2 is a plan view of the same; Figure 3 is an end elevation from the input end; Figure 4 is a sectional plan of the drum forming part of the apparatus, on an enlarged scale; and Figures 5-8 are sections further enlarged, on the lines 5-5, 6-6, 7-7, and 8-8 of Figure 4.

Turning now to Figure 1, the apparatus is mounted on road wheels 10 with chocks or jacks 12 to immobilise the apparatus when it has been taken to a required site, and with an appropriate towing hitch 14 and other fittings as commonly provided on road trailers for convenience, safety or to meet road vehicle construction regulations.

The wheeled chassis is provided with a system of support rollers 16 (Figures 1 and 3) which axially and angularly locate a drum or barrel 18 for rotation about a fixed axis 20, Figure 1 which is intended to be inclined at a small angle to the horizontal. To this end, a jack or jacks at one end of the chassis may be telescopic and adjustable in length so that the axis of the barrel can be varied.

This also allows for the vehicle being parked on an incline. Any convenient motor system may be used to rotate the barrel at an appropriate speed, for example from a small gas or petrol engine 22 mounted on the chassis and driving the barrel via a gear system or via a chain or toothed belt system 24. The barrel is cylindrical.

One end of the barrel, which is the upper end in use, has an annular end plate 26 and the internal aperture provides an entry port for flame from the burner 28, for additional combustion air, and for material to be recycled. The burner is mounted on the chassis to fire into the aperture preferably as illustrated along an axis which is below the rotational axis of the barrel and to one side of the same, this axis being offset from a vertical plane containing the rotational axis in the same direction as that of rotation of the barrel.

A material inlet chute or hopper 30 is provided adjacent the annulus and includes an outlet gate 32 parallel to the plane of the annulus, and the gate can be swung out of the way e.g. lifted by lever 34, Figure 3, to allow material to discharge through the aperture. This allows batch loading.

The barrel is generally cylindrical (see Figure 4) and over a major portion of its length, commencing a short distance from the inlet end and extending to the other end, extend a plurality of flights 34. Each of these lies in a radial plane of the barrel, that is to say they are not skewed or spiralled about the barrel along their length, and they are equispaced angularly. Typically eight such flights will be provided, but the number will depend upon the diameter of the barrel.

The flights have a radially outer edge spaced from the inner wall of the barrel by a predetermined dimension D which is related to the required particle size. For example if a nominal one inch (2.5 cm) (maximum) particle size is required, the radially outer edge of each flight is effectively spaced from the barrel wall by a minimum of that one inch (2.5 cm), and so on.

This spacing may be achieved by mounting pins supporting the flights, or one end of each flight may be fixed to the discharge end wall of the barrel and the inlet end of each flight to a bracket.

The radially inner edge of each flight converges towards the rotational axis by a small extent. For example the flights might be two inch (5 cm) wide (in the radial dimension) at the inlet end 36 and 4 inches (10 cm) at the outlet end 38, in a barrel length of say 6 feet.

The portion of the barrel length which is not occupied by the flights is the reiatively short portion adjacent the inlet and is provided with breaker strips 40 which conveniently extend colinearly with the flights between the same and the inlet end wall, but which are not spaced from the barrel.

The object of the flight and breaker strip construction is that when material falls from the chute into the barrel it impacts against one or more of the breaker strips during a portion of barrel rotation and this may commence the breakup of the lumps into smaller pieces. Due to the inclination of the barrel axis the pieces gradually progress along the length of the barrel and due to the rotation the pieces are tumbled by the flights. That is to say the material resting at the lowermost part of the barrel between a pair of flights is lifted up by the trailing one of these flights in barrel rotation and eventually falls over the radially inner edge of that flight to land on a lower flight or at the lowermost part of the barrel, and so on.Particles which are reduced to a dimension less than the clearance between the outer edge of the flight and the barrel are not subject to this tumbling but tend to slide on the inner surface of the barrel during its rotation passing below the flights. The intention is that as the material progresses along the barrel more and more of the material slides and less and less of it tumbles, but, because of the increase in height of the flight along the barrel, material which does not slide but is tumbled, will be taken around the barrel for a greater distance before falling, so as to suffer a greater impact when it does fall. Hence the more difficultly reduced material is subject to the greater stress.

The discharge system comprises a port 42 in the barrel at the end opposite to the inlet, and with a simple grid 44 over that port (see Figures 5 and 6) forming a sieve to prevent particles larger than the grid size passing through.

A door is provided for closing (or opening) the port 42. The door 44, see Figure 2 and 5 is generally rectangular and guided at its edges parallel to the drum axis in channels 46 fixed to the drum exterior. The door mounts a cam follower 48 which projects generally radially outwardly away from the drum axis.

It will be appreciated that during rotation of the drum, the port and the closing gate rotate with the drum.

A skeleton framework 50 (Figure 2) encloses the drum, and is used to mount guard panels to avoid operator's accidentally coming into contact with the exterior of the drum, particularly when the same is hot, although an insulating jacket 52, Figure 4, over much of the area of the drum minimises risks of burning. The framework is used to pivot a cam handle 54 which projects laterally so that its extremity 56 can be operator displaced from the full line position to the chain line position of Figure 2. It will be appreciated that the handle 54 does not rotate with the drum.In the illustrated position (Figure 2) the cam follower moves in the direction of the arrow B in the figure and encounters the edge 58 of the cam once in each revolution of the drum and this serves to maintain the follower in the same position measured axially of the drum and hence keeps the door 44 in the illustrated and closed position. To open the door, the cam is moved to the chain line position of Figure 2 and then the opposite edge 60 is encountered by the cam follower in its rotation with the drum and this displaces the door to the open position. Hence as the drum continues to rotate, the door is open and any material which can fall through the grid can fall through the door opening to fall onto the discharge chute in chain dot line with the reference 62 Figure 1. Hence some treated material will fall through on each rotation but only whilst the grid is in the lower portion of its arcuate path.

Although discharge particle size is affected by the flight/barrel wall clearance, a further factor in this direction is the size of the grid apertures, and it is preferred to make the grid interchangable to enable for exaple fine material, or mixtures of fine and coarse materials to be discharged.

The combustion products exhaust system may include a baffle system causing at least one exhaust gas reversal, e.g. it comprises a deflection cone 70, Figure 4, located generally on the axis of the barrel and having its apex towards the barrel inlet and its base towards the outlet. The cone is supported on a circular exhaust duct 72 of smaller diameter than the base of the cone, and with interposed struts 74 to physically support the part, so that exhaust gas can enter into the cone when travelling in the opposite direction to that in which the burner fires.In this preferred embodiment, the cone base is integral with a cylindrical skirt 74 acting as an extension of the cone and concentrically located to the exhaust duct and gas must flow along the cylindrical space in said reverse direction before entering the cone and undergoing a further 1 80O direction change to flow along the exhaust duct to and through the end wall of the barrel.

The arrows on Figure 4 show the direction of flow of combustion products from the burner to exhaust.

The cone is held in place on a central bolt 74 carried by a diametrically extending strap extending across the end of the duct 72. To prevent the cone being unscrewed as a result of relative movement between it and the duct, due to impact by material tumbling in the barrel, a key 80 is provided for example welded to the duct 72 and angularly fixing the cone 70 thereto.

It is a feature of the invention that the exhaust system includes a vortex and this can be provided by careful proportioning of the total cross sectional area of gas ports into the cone i.e. the area of the annulus defined between skirt 74 and duct 72, minus the key 80, in relation to the cross sectional area of the exhaust duct supporting the cone, and again of the total cross sectional area of exhaust ports from the end wall. To this end the exhaust end wall may be a double wall comprising parallel plates of which the inner, that is the one nearest to the burner actually supports the exhaust duct, and the outer is vented to atmosphere, and in this case it will be the total cross sectional area of the exhausts to atmosphere which are to be taken into account in calculating the vortex.It will be appreciated that effectively the cross sectional area of the exhaust duct must be less than that of the cone and the double wall outlets individually. The effect of all this may be that the lower end wall is heated and insulated against heat loss by radiation to ambient atmosphere because of the exhaust gases flowing between the double walls, and if the material outlet is closely adjacent to the end wall, it is believed that this will give improved results and avoid premature chilling of prepared recycled material.Additionally, the gas flow pattern produced by this arrangement ensures that combustion products flow along substantially the whole length of the barrel before being drawn into the exhaust system, and this arrangement may be contrasted favourably with that in some prior proposals where the inlet and exhaust ports for combustion products are one and the same, and in which stagnant barrel atmosphere zones are likely particularly at positions more remote from the inlet.

If, instead of using the natural and vortex assisted gas flow, a fan is used, generally similar principles may be observed in relation to fan capacity being matched to cross sectional areas.

The fan system however may be found to be advantageous where an exhaust stack is desired to dissipate fumes well above the apparatus.

In the illustrated embodiment a single end wall 80 Figure 4 rather than double end wall is provided, and the ducts 72 opens through a central aperture in the end wall 80 to a space bounded by a parallel plate 82 held in spaced relationship by a series of equi-pitched bolts 84 and spacers 86, see also Figure 8. A stub axle 90 forming part of the system for supporting and journalling the barrel is fixed to the end plate 82 the cantilever load being taken by a series of radially extending webs 92 which permit gas flow therebetween to exhaust between the respective spacers. A final drive sprocket 94 in the drum drive system is also mounted on the same arrangement.

The burner may be supplied with gas or liquid fuel from reservoir tanks supported on plafforms shown in chain dot line with the reference 98 Figure 2 and the engine driving the drum may be a gas engine fed from the same source. This may make the apparatus totally independent of services, for use at any required roadside location.

Claims (9)

Claims

1. A process for recycling old road metal and the like including bituminous coated aggregate in large lumps comprises feeding the material unidirectionally and with gravitational assistance along a rotating barrel, tumbling over-size material by the provision of flights in the barrel and separating sized material by spaces between the flights and barrel before discharging sized material, and heating the material by a fuel fired burner directed along the barrel in the same direction as material movement and discharging exhaust products at the material discharge end of the barrel.

2. Apparatus for carrying out the process claimed in Claim 1 comprising a barrel arranged for rotation about an axis inclined to the horizontal, a plurality of flights provided in the barrel with spaces between the flights and barrel wall, a discharge port in the barrel wall, a fuel fired burner for directing combustion products along the barrel axially in the same way as the material movement, and an exhaust for combustion products at the opposite end of the barrel to the material and burner inlet.

3. Apparatus as claimed in Claim 2 including a baffle system for causing reversal of combustion products between the burner and the exhaust.

4. Apparatus as claimed in Claim 3 wherein an exhaust duct extends axially into the barrel from the opposite end to the material inlet and burner end and the duct is provided with a cone deflector having its apex directed towards said inlet end.

5. Apparatus as claimed in any of Claims 2 to 4 wherein the end wall of the drum through which exhaust takes place is double walled with gas flow between the two walls.

6. Apparatus as claimed in any of Claims 2 to 5 wherein a vortex is provided in the exhaust system.

7. Apparatus as claimed in any of claims 2 to 5 wherein an exhaust fan is provided to extract combustion products from the barrel.

8. Apparatus as claimed in any of Claims 2 to 5 or 7 wherein the exhaust opens into a chimney or stack extending above the apparatus.

9. Apparatus as claimed in any of Claims 2 to 8 wherein the flights taper from a minimum radial width adjacent the material inlet end of the barrel to a maximum radial width at the opposite end and the space between the radially outer edge of each flight and barrel wall is substantially constant along the length of the flights, the flights being equi-spaced about the barrel.