GB2458974A

GB2458974A - Aggregate dryer and process for drying aggregate

Info

Publication number: GB2458974A
Application number: GB0814930A
Authority: GB
Inventors: Terry Lagan
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-03-31
Filing date: 2008-08-15
Publication date: 2009-10-07
Anticipated expiration: 2028-08-15
Also published as: IES20080668A2; GB2458974B; IE20080669A1; GB0814930D0

Abstract

An aggregate dryer 1 comprises a rotatable cylindrical dryer drum 2 having an inlet feed chute 5 and an outlet delivery chute 6, and a stationary burner assembly 7 mounted adjacent to the outlet of the drum for delivery of combustion gases in contra flow to aggregate in the drum. The dryer comprises an inlet section 8 having a number of spirally arranged infeed channels 11 formed by inwardly extending walls 12 for delivery of the aggregate along the inlet section. A wear surface is formed between the infeed channels for retention and abrasion of the aggregate as it is delivered along the inlet section. The dryer further comprises an intermediate heating section 9 having a plurality of circumferentially arranged finger lifters 14 and a final heating section 10 having a plurality of circumferentially arranged combustion lifters 30. A number of discharge buckets 40 are provided for delivery of the aggregate to the outlet delivery chute. In use, the dryer allows efficient drying and heating of the aggregate while avoiding excessive wear of the dryer drum. In a further aspect, a process for drying aggregate is disclosed.

Description

"An aggregate dryer and process for drying aggregate"

Introduction

The present invention relates to an aggregate dryer comprising a rotatable cylindrical dryer drum having a proximal feed chute forming an inlet and a distal delivery chute forming an outlet. The invention further relates to a process for drying aggregate.

Examples of aggregate dryers are described in UK Patent No. 1 385 812 and US Patent Nos. 2,815,940 and 4,300,837. The dryers disclosed in these documents also comprise a stationary burner assembly mounted adjacent the outlet of the drum for delivery of combustion gases in contra flow to aggregate in the drum and various types of lifters which are attached to and rotate around the interior side wall of the drum. These lifters carry some of the aggregate along a portion of the drum until the aggregate falls from the lifters into the interior of the drum where it contacts the combustion gases. The problem with dryers of this type is that it can be difficult to ensure that all of the aggregate is efficiently dried and heated while also preventing the aggregate falling into the hot flames of the combustion gases and thus burning.

A further problem with dryers of this type is that the dryer drums can be quite easily damaged by the aggregate, and in particular the drum can be abraded by the aggregate as it is forced against the interior wall of the drum or damaged by hot aggregate. Additionally because of the weight of aggregate being handled and the general size of the dryers, a considerable amount of power for rotation is required. A balance in design has therefore to be struck between the robustness of the dryer and in particular the ability of the interior surface of the dryer to resist wear, while at the same time, balancing this resistance to wear and general robustness with weight.

Thus, the wear on the interior surfaces of the dryer and of the various equipment mounted in the dryer is a major cause of concern.

The present invention is directed towards providing efficient drying and heating of the aggregate while avoiding excessive wear in the dryer drum, without having to provide excessively heavy equipment.

Statements of Invention

According to the invention, there is provided an aggregate dryer comprising: a rotatable cylindrical dryer drum having a proximal feed chute forming an inlet and a distal delivery chute forming an outlet; a stationary burner assembly mounted adjacent the outlet of the drum for delivery of combustion gases in contra flow to aggregate in the drum; an inlet section having a number of spirally arranged infeed channels formed by inwardly extending walls for delivery of the aggregate along the inlet section, and a wear surface formed between the irifeed channels for retention and abrasion of the aggregate as it is delivered along the inlet section; an intermediate heating section having a plurality of spaced-apart lifters circumferentially arranged around the inside of the drum for transporting the aggregate around the interior of the drum and distributing the aggregate into the interior of the drum for heating by the combustion gases; a final heating section comprising a number of spaced-apart combustion lifters circumferentially arranged around the inside of the drum for lateral delivery of aggregate along the final heating section; and a plurality of discharge buckets for delivery of aggregate to the distal delivery chute.

The advantage of this particular dryer arrangement and in particular the specific construction of the various lifters is that it ensures efficient heating and drying of the aggregate while also minimising any burning of the aggregate. Additionally the dryer drum is protected by the wear surface provided on the interior of the drum wall.

In one embodiment of the invention, each lifter is a finger lifter and comprises a shelf which extends inwardly from the drum sidewall, and a number of fingers which project upwardly at an innermost end of the shelf.

In this embodiment of the invention, each finger comprises a supporting web for reinforcement of that finger. The supporting web thus prevents any collapse of the fingers due to them being abraded or weakened from the rubbing action of the aggregate on the fingers and also allows further retention of aggregate within the lifter.

Ideally, the wear surface is formed from a plurality of juxtaposed angle iron ribs extending between the walls forming the infeed channels. The angle iron ribs are particularly advantageous as they protect the interior of the drum from abrasion by the aggregate as it passes through the drum thus reducing the typical high wear rates on the drum sidewall.

In another embodiment of the invention, each combustion lifter comprises an elongate panel spaced-apart from the drum sidewall having a trailing edge which engages the drum sidewall, and an outwardly bent leading edge spaced-apart from the drum sidewall leaving a gap, an end wall at one end and an opening at the other end.

In this embodiment of the invention, the combustion lifters are arranged in a first and a second row; such that in the first row the opening is provided at the proximal end of the lifter and the end wall is at the distal end; and in the second row the end wall is at the proximal end of the lifter and the opening is provided at the distal end.

The advantage of the combustion lifters is that they catch and keep the heated aggregate around the drum sidewall, thus keeping the aggregate out of the flame of the burner which could overheat and damage it. The combustion lifters also effectively form a band of aggregate on the inside of the drum wall which helps insulate the drum sidewall from excessive heat which could cause expansion and cracking of the drum sidewall and bearing arrangement. There is also a fuel saving as less heat is lost through the drum sidewall due to the increased insulation effect.

Ideally, the dryer further comprises a canopy which extends over and protects the burner assembly.

According to the invention, there is also provided a process for drying aggregate; the process comprising: delivering aggregate through a proximal feed chute into a rotatable cylindrical dryer drum of an aggregate dryer; delivering combustion gases in contra flow to the aggregate in the drum by means of a stationary burner assembly mounted adjacent an outlet of the drum; delivering aggregate along an inlet section of the drum, by means of a number of spirally arranged infeed channels formed by inwardly extending walls, and retaining and abrading the aggregate as it is delivered along the inlet section by means of a wear surface formed between the infeed channels; transporting the aggregate around the interior of the drum by means of a plurality of spaced-apart lifters circumferentially arranged around the inside of an intermediate heating section of the drum and distributing the aggregate into the interior of the drum for heating by the combustion gases; delivering the aggregate laterally along a final heating section of the drum by means of a number of spaced-apart combustion lifters circumferentially arranged around the inside of the final heating section of the drum; and delivering aggregate to a distal delivery chute by means of a plurality of discharge buckets.

In one embodiment of the invention, the process further includes transporting the aggregate around the interior of the drum by means of a plurality of spaced-apart finger lifters, wherein each finger lifter comprises a shelf which extends inwardly from the drum sidewall, and a number of fingers which project upwardly at an innermost end of the shelf.

Ideally, the process includes retaining and abrading aggregate by means of a plurality of juxtaposed angle iron ribs which form the wear surface and extend between the walls which form the infeed channels.

In another embodiment of the invention, the process includes: delivering aggregate into a first row of combustions lifters through an opening provided at a proximal end of the combustion lifters and/or a gap formed between an outwardly bent leading edge of the combustion lifters and the drum side wall; lifting the aggregate up and around the top of the drum by means of the first row of combustion lifters; allowing the aggregate to fall out of the first row of combustion lifters through the gap; delivering the aggregate into a second row of combustion lifters through a gap provided between an outwardly bent leading edge of the combustion lifters and the drum sidewall; and delivering the aggregate from a second row of combustion lifters to a plurality of discharge buckets through an opening provided at a distal end wall of the second row of combustion lifters.

Brief Description of the Drawings

The invention will now be more clearly understood from the following description of some embodiments thereof given by way of example only with reference to the accompanying drawings, in which: Fig. I is a schematic sectional elevational view of the aggregate dryer according to the invention; Fig. 2 is a detail perspective view showing an inlet portion of the aggregate dryer; Fig. 3 is a detail perspective view of one finger lifter; Fig. 4 is a detail elevational view of one finger lifter; Fig. 5 is a detail perspective view of one finger lifter; Fig. 6 is a detail perspective view of the combustion lifters; Fig. 7 is a side elevational view of one combustion lifter; Fig. 8 is a side elevational view of another combustion lifter; and Fig. 9 is a detail perspective view showing a final heating section of the aggregate dryer.

Detailed Description of the Invention

Referring to Fig. 1, there is provided a dryer indicated generally by reference numeral 1. The dryer 1 comprises a rotatable c,1indrical dryer drum 2. A pair of spaced-apart metal bands 3 are mounted on an exterior of the drum 2. Each band 3 is supported on a pair of rollers 4 and at least one pair of the rollers 4 is driven to rotate the drum 2.

The drum 2 has a proximal feed chute 5 forming an inlet and a distal delivery chute 6 forming an outlet. A stationary burner assembly 7 is mounted adjacent the outlet end of the drum 2. The burner 7 is operable for heating air and delivering combustion gases into the drum 2 which heats aggregate as it passes through the drum 2 between the inlet and the outlet. The drum 2 is inclined downwardly slightly between the inlet and outlet so the aggregate will naturally feed under gravity therebetween.

The drum 2 has an inlet section 8, an intermediate heating section 9 and a final heating section 10.

The inlet section 8 has a number of spirally arranged infeed channels 11 formed by inwardly extending walls 12 which project from the inside surface of the drum 2. A plurality of juxtaposed angle iron ribs 13 extend between the walls 12. The infeed channels 11 feed aggregate quickly from the proximal feed chute 5 along the inlet section 8 to the intermediate heating section 9. The ribs 13 also protect the interior of the drum 2 from abrasion by the aggregate as it passes through the drum 2. Some of the aggregate will lodge between the ribs 13 to form a protective layer on the inside of the drum 2 so the incoming aggregate is effectively abrading against itself as it moves along the drum 2.

The aggregate is then passed into the intermediate heating section 9 where a number of spaced-apart finger lifters 14 are arranged around the inside circumference of this section 9 of the drum 2. These finger lifters 14 lift up aggregate as the drum 2 rotates and transports the aggregate around the interior of the drum 2 and distributes the aggregate into the interior of the drum 2 for heating by the combustion gases within the drum 2. Essentially this forms a curtain or "waterfall" of aggregate across the gas stream for good heat transfer to the aggregate. A number of the angle iron ribs 13 are also located between the finger lifters 14 to form a further protective layer in this section 9 of the drum 2.

The inlet section 8 is shown in more detail in Fig 2. There is also shown in Fig. 2 a portion of the intermediate heating section 9 with the finger lifters 14. The finger lifters 14 are shown in more detail in Fig. 3. These essentially comprise a shelf 20 which extends inwardly from the drum sidewall, and a number of fingers 21 which project upwardly at an innermost end of the shelf 20. Each of the fingers 21 also comprise a supporting web 22 which reinforces and prevents collapse of that finger 21. Each of the finger lifters 14 is mounted by associated mounting brackets 23 on the drum sidewall to which they are bolted so they can be easily replaced if necessary. The finger lifters 14 are shown in further detail in Figs. 4 and 5.

Referring again to Fig. 1, the aggregate after passing through the intermediate heating section 9 is then delivered into the final heating section 10 where a number of spaced-apart combustion lifters 30 are arranged around the inside surface of the drum 2 for lateral delivery of aggregate along this section 10. These combustion lifters 30 catch and keep the heated aggregate around the drum sidewall thus effectively forming a band of aggregate on the inside of the drum wall which helps insulate the drum sidewall from excessive heat of the combustion gases and burner 7.

The combustion lifters 30 are shown in more detail in Fig. 6. They essentially comprise an elongate panel 31 spaced-apart from the drum sidewall with an outwardly bent leading edge 32 and trailing edge 33. The leading edge 32 is spaced-apart from the drum sidewall leaving a gap 34 while the trailing edge 33 engages the drum sidewall. Thus, aggregate can enter through the gap 34 and collect within the combustion lifters 30. It will be noted also that one end wall 35 of each combustion lifter 30 is closed whereas an opening 36 is provided at the other end.

As shown in Fig. 1 the combustion lifters 30 are arranged in two rows. The distal end wall 35 of the first row of combustion lifters 30 is closed, whereas the proximal end wall 35 of the second row of combustion lifters 30 is closed. In this way aggregate coming from the intermediate heating section 9 can enter the opening 36 at the proximal end as well as the gap 34 in the first row of combustion lifters 30, whilst the closed end wall 35 at the distal end prevents the aggregate spilling out at that end.

The combustion lifter 30 lifts the aggregate up and around the top of the drum 2, and as the lifter 30 comes down the far side, the gap 34 faces downwardly and the aggregate can fall out of the gap 34. Because of the tilt of the drum 2, as the aggregate falls out of the first row of combustion lifters 30 it moves downwardly towards the second row of combustion lifters 30, where it can similarly enter through the gap 34 in the leading edge of each combustion lifter 30.

For the second row of combustion lifters 30, the proximal end wall 35 is closed to prevent any aggregate working back up the drum 2 whereas the distal end has an opening 36 to allow aggregate to discharge out from the gap 34 and the opening 36.

The combustion lifters 30 are shown in further detail in Figs. 7 and 8. Fig. 7 shows a side elevational view through the opening 36 of one the combustion lifters 30 from the first row. Fig. 8 shows a side elevational view of one of the combustion lifters 30 in the second row with the proximal end closed off by the end wall 35.

Referring now to Fig. 9. there is shown the final heating section 10 of the drum 2. The aggregate discharges from the gap 34 and the opening 36 of the second row of combustion lifters 30 into circumferentially spaced-apart discharge buckets 40 at the outlet end of the drum 2. These discharge buckets 40 feed heated aggregate from the final heating section 10 to the distal delivery chute 6. A canopy 41 extends over the burner assembly 7 to protect the burner assembly 7 from any falling aggregate. One side of this canopy 41 forms a portion of the distal delivery chute 6 for discharge of heated aggregate from the drum 2. As the discharge buckets 40 approach the top of the drum 2, they discharge aggregate out into the distal delivery chute 6.

In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms "include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.

The invention is not limited to the embodiment hereinbefore described, but may be varied in both construction and detail within the scope of the appended claims.

Claims

CLAIMS1. An aggregate dryer (1) comprising: a rotatable cylindrical dryer drum (2) having a proximal feed chute (5) forming an inlet and a distal delivery chute (6) forming an outlet; a stationary burner assembly (7) mounted adjacent the outlet of the drum (2) for delivery of combustion gases in contra flow to aggregate in the drum (2); an inlet section (8) having a number of spirally arranged infeed channels (11) formed by inwardly extending walls (12) for delivery of the aggregate along the inlet section (8), and a wear surface formed between the infeed channels for retention and abrasion of the aggregate as it is delivered along the inlet section (8); an intermediate heating section (9) having a plurality of spaced-apart lifters (14) circumferentially arranged around the inside of the drum (2) for transporting the aggregate around the interior of the drum (2) and distributing the aggregate into the interior of the drum (2) for heating by the combustion gases; a final heating section (10) comprising a number of spaced-apart combustion lifters (30) circumferentially arranged around the inside of the drum (2) for lateral delivery of aggregate along the final heating section (10); and a plurality of discharge buckets (40) for delivery of aggregate to the distal delivery chute (6).
2. An aggregate dryer (1) as claimed in claim 1, wherein each lifter (14) is a finger lifter and comprises a shelf (20) which extends inwardly from the drum sidewall, and a number of fingers (21) which project upwardly at an innermost end of the shelf (20).
3. An aggregate dryer (1) as claimed in claim 2, wherein each finger (21) comprises a supporting web (22) for reinforcement of that finger (21).
4. An aggregate dryer (1) as claimed in any preceding claim, wherein the wear surface is formed from a plurality of juxtaposed angle iron ribs (13) extending between the walls (12) forming the infeed channels (11).
5. An aggregate dryer (1) as claimed in any preceding claim, wherein each combustion lifter (30) comprises an elongate panel (31) spaced-apart from the drum sidewall having a trailing edge (33) which engages the drum sidewall, and an outwardly bent leading edge (32) spaced-apart from the drum sidewall leaving a gap (34), an end wall (35) at one end and an opening (36) at the other end.
6. An aggregate dryer (1) as claimed in claim 5, wherein the combustion lifters (30) are arranged in a first and a second row; such that in the first row the opening (36) is provided at the proximal end of the lifter (30) and the end wall (35) is at the distal end; and in the second row the end wall (35) is at the proximal end of the lifter (30) and the opening (36) is provided at the distal end.
7. An aggregate dryer (1) as claimed in any preceding claim, wherein the dryer (1) further comprises a canopy (41) which extends over and protects the burner assembly (7).
8. An aggregate dryer (1), substantially as hereinbefore described with reference to the accompanying drawings.
9. A process for drying aggregate; the process comprising: delivering aggregate through a proximal feed chute (5) into a rotatable cylindrical dryer drum (2) of an aggregate dryer (1); delivering combustion gases in contra flow to the aggregate in the drum (2) by means of a stationary burner assembly (7) mounted adjacent an outlet of the drum (2); delivering aggregate along an inlet section (8) of the drum (2), by means of a number of spirally arranged infeed channels (11) formed by inwardly extending walls (12), and retaining and abrading the aggregate as it is delivered along the inlet section (8) by means of a wear surface formed between the infeed channels (11); transporting the aggregate around the interior of the drum (2) by means of a plurality of spaced-apart lifters (14) circumferentially arranged around the inside of an intermediate heating section (9) of the drum (2) and distributing the aggregate into the interior of the drum (2) for heating by the combustion gases; delivering the aggregate laterally along a final heating section (10) of the drum (2) by means of a number of spaced-apart combustion lifters (30) circumferentially arranged around the inside of the final heating section (10) of the drum (2); and delivering aggregate to a distal delivery chute (6) by means of a plurality of discharge buckets (40).
10. A process for drying aggregate as claimed in claim 9, wherein the process further includes transporting the aggregate around the interior of the drum (2) by means of a plurality of spaced-apart finger lifters (14), wherein each finger lifter comprises a shelf (20) which extends inwardly from the drum sidewall, and a number of fingers (21) which project upwardly at an innermost end of the shelf (20).
11. A process as claimed in any of claims 9 or 10 wherein the process includes retaining and abrading aggregate by means of a plurality of juxtaposed angle iron ribs (13) which form the wear surface and extend between the waIls (12) which form the infeed channels (11).
12. A process as claimed in any of claims 9 to 11, wherein the process includes: delivering aggregate into a first row of combustions lifters (30) through an opening (36) provided at a proximal end of the combustion lifters (30) and/or a gap (34) formed between an outwardly bent leading edge (32) of the combustion lifters (30) and the drum side wall; lifting the aggregate up and around the top of the drum (2) by means of the first row of combustion lifters (30); allowing the aggregate to fall out of the first row of combustion lifters (30) through the gap (34); delivering the aggregate into a second row of combustion lifters (30) through a gap (34) provided between an outwardly bent leading edge (32) of the combustion lifters (30) and the drum sidewall; and delivering the aggregate from a second row of combustion lifters (30) to a plurality of discharge buckets (40) through an opening (36) provided at a distal end wall of the second row of combustion lifters (30).
13. A process for drying aggregate substantially as hereinbefore described with reference to the accompanying drawings.