Patent Application
20210381175
The present invention relates generally to the production of asphalt concrete using aggregate materials that may include a high proportion of recycled materials. More particularly, the present invention relates to a method and apparatus for making asphalt concrete from aggregate materials including a relatively high percentage of recycled asphalt product (“RAP”) and/or recycled asphalt shingles (“RAS”).
Production facilities for making asphalt concrete to be used as a paving composition are well-known. Feed materials for these facilities include aggregate materials and asphalt cement. The aggregate materials may be provided in the form of virgin aggregate materials and/or RAP and/or RAS (collectively, “Asphalt Cement Components” or “ACC”). If ACC is included in the feed materials, these components will also provide an additional source of asphalt cement.
Some conventional asphalt concrete production plants employ a rotating dryer drum or pre-dryer in which virgin aggregate materials or ACC are introduced. A burner is located at one end of the drum and the input feed materials are moved along the drum through the heated gases generated by the burner in either parallel flow or counter-current flow to an outlet. A separate mixer that is external to the dryer, such as a rotating drum mixer or a pugmill, is employed to combine the aggregate materials with liquid asphalt cement. Another type of asphalt concrete production plant employs a dryer that dries and heats the aggregate material and also mixes it with asphalt cement. One such type of dryer is the DOUBLE BARREL® brand dryer that is sold by Astec, Inc. of Chattanooga, Tenn. This dryer includes a generally cylindrical fixed outer drum and a heating chamber located within a generally cylindrical inner drum that is adapted to rotate with respect to the outer drum. A burner at one end of the inner drum heats aggregate material by direct exposure to the hot gases generated, and the heated aggregate material is discharged from the inner drum into the outer drum where it is mixed with asphalt cement and/or with ACC. If substantial quantities of ACC are introduced into the DOUBLE BARREL® brand dryer, a mixer, such as a pugmill or mixing drum, may also be employed to add and incorporate additional asphalt cement into the mixture.
Because some conventional systems expose liquid asphalt cement or ACC materials to the high-temperature gases used for drying and heating the aggregate materials and to the steam generated in the drying process, emissions of smoke and volatile organic compounds (“VOCs”) are stripped from the light oil fractions of the ACC. In order to prevent these emissions from being discharged to the atmosphere, it has been deemed desirable, when only virgin aggregate materials are used, to either direct the emissions into the burner for incineration, or to filter the emissions from the plant exhaust gases and condense them for disposal. In addition, exposure of high proportions of ACC materials to the high temperatures from the drying and heating of aggregate materials combined with oxygen causes oxidation of the liquid asphalt in the ACC, which degrades the asphalt cement component and any pavement materials made with it. This reduces the number of applications for which high-ACC percentage asphalt concrete is considered suitable. Finally, conventional equipment that is used to make high ACC percentage asphalt concrete, particularly those without a pre-dryer, are operated at a lower production rate than when the same equipment is used to make asphalt concrete with only small amounts of ACC or with all virgin aggregate materials or when a pre-dryer is utilized.
With initial reference to
The batch plant 100 also includes stairs 124, which are frequently used by personnel to access various sections of the batch tower 112 during asphalt production, for inspections and maintenance of the batch tower, etc. As shown by the above discussion, certain ACC batch plants utilize pre-dryers, such as pre-dryer 104, to assist in the drying and heating process of ACC. These dryers are often direct-fired rotary dryers that are dedicated exclusively to heating and drying ACC. They are typically located at the top of the batch tower while, at the same time, a second conventional aggregate dryer, such as dryer 102, is located on ground level for drying and heating virgin aggregate. ACC pre-dryers require frequent maintenance. One reason for this maintenance is that the interior of these pre-dryers can accumulate large amounts of ACC fines and oxidized asphalt as a result of the direct firing process. The ACC fines and oxidized asphalt can catch on fire if not removed regularly. Additionally, ACC fines tend to become trapped in recirculation patterns around the burner and to stick to and foul the burner. This, again, requires periodic removal. This type of maintenance must be carried out manually by personnel at the top of the batch tower. However, due to the elevated location of the pre-dryer at the top of the batch tower, access for inspection, maintenance, etc. is labor intensive, requiring frequent trips up and down the stairs 124, and can be quite difficult. It would be much easier to carry out this type of maintenance work at ground level.
What is needed, therefore, is a method and apparatus for producing asphalt concrete from aggregate materials include a high percentage of ACC that utilizes a single dryer to dry and heat both virgin aggregate as well as blends of ACC and virgin aggregate, and does not utilize a second separate pre-dryer that is dedicated only to heating and drying ACC. It would also be desirable if the single dryer were located at ground level to facilitate periodic maintenance.
The use of the terms “a”, “an”, “the” and similar terms in the context of describing the invention are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising”, “having”, “including” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The terms “substantially”, “generally” and other words of degree are relative modifiers intended to indicate permissible variation from the characteristic so modified. The use of such terms in describing a physical or functional characteristic of the invention is not intended to limit such characteristic to the absolute value which the term modifies, but rather to provide an approximation of the value of such physical or functional characteristic. All methods described herein can be performed in any suitable order unless otherwise specified herein or clearly indicated by context.
Terms concerning attachments, coupling and the like, such as “connected” and “interconnected”, refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both moveable and rigid attachments or relationships, unless otherwise specified herein or clearly indicated by context as having a different relationship. The term “operatively connected” is such an attachment, coupling or connection that allows the pertinent structures to operate as intended by virtue of that relationship.
The use of any and all examples or exemplary language (e.g., “such as” and “preferably”) herein is intended merely to better illuminate the invention and the preferred embodiments thereof, and not to place a limitation on the scope of the invention. Nothing in the specification should be construed as indicating any element as essential to the practice of the invention unless so stated with specificity.
Various terms are specifically defined herein. These terms are to be given their broadest possible construction consistent with such definitions, as follows:
The term “asphalt cement components percentage” and “ACC percentage” and similar terms refer to the proportion, by weight, of asphalt cement components (i.e., ACC) provided in an asphalt concrete blend as a percentage of the entire asphalt concrete blend.
The term “aggregate materials” and similar terms refer to crushed stone and other particulate materials that are used in the production of asphalt concrete, such as, for example, crushed limestone and other types of crushed stone, crushed Portland cement concrete, shredded or comminuted mineral and cellulosic fibers, RAP, RAS, gravel, sand, lime and other particulate additives. The term “virgin aggregate materials” refers to aggregate materials that do not include asphalt cement. The term “aggregate mix” refers to a mixture of virgin aggregate and RAP and/or RAS.
The term “asphalt concrete” and similar terms refer to a bituminous paving mixture that is produced, using asphalt cement and/or RAP and/or RAS and any of various aggregate materials, in an asphalt dryer or other asphalt concrete production plant.
The term “asphalt cement” and similar terms refer to a bituminous material that may be used in combination with aggregate materials in the production of asphalt concrete. Asphalt cement acts as the binder for various aggregate materials in the production of asphalt concrete.
As used herein, the term “baghouse” refers to any structure adapted to trap solids that have temporarily combined with gases.
As used herein, the term “burner” refers to any device adapted to produce a burner flame which may be used to dry and heat virgin aggregates, RAP, RAS and the like in connection with the production of asphalt concrete blends.
The term “direct dryer”, “direct fired dryer” and similar terms refer to a dryer or dryer device having a burner, generally located at one end, which device is adapted to move input feed materials to be heated or dried along the device through the heated gases generated by the burner in either parallel flow or counter-current flow to an outlet. “Direct” drying or heating of materials is carried out by moving such materials directly through a burner flame or heated gases generated by a burner.
The term “high” and “Hi”, when used to refer to the percentage of ACC, RAP, or RAS provided in a given asphalt concrete blend (e.g., Hi-RAP), means that the blend, as a whole, is comprised of a minimum of 25% of ACC, RAP, or RAS.
The term “indirect dryer”, “indirectly heated pre-dryer” and similar terms refer to a dryer or dryer device which is adapted to dry or heat input feed materials without such materials coming into direct contact with a burner flame or heated gases generated by a burner. “Indirect” drying or heating of materials is carried out without such materials coming into direct contact with a burner flame or heated gases generated by a burner.
As used herein, the terms “liquid asphalt cement” and “liquid AC” and “AC” refer to a substance or material used in combination with virgin aggregates, RAP, RAS and the like in connection with the production of asphalt concrete blends. More particularly, the terms “liquid asphalt cement” and “liquid AC” and “AC” refer to any substance or material that has the characteristic of forming a cohesive relationship between virgin aggregates, RAP, RAS and the like for the purpose of producing asphalt concrete blends.
As used herein, the term “pugmill” refers to any device adapted to combine materials such as virgin aggregates, RAP, RAS, liquid asphalt cement and the like to produce asphalt concrete blends.
The terms “recycled asphalt product”, “RAP” and similar terms refer to a comminuted or crushed product containing aggregate materials bound together by asphalt cement. RAP typically comprises crushed or comminuted recycled asphalt paving materials.
The terms “recycled asphalt shingles”, “RAS” and similar terms generally refers to crushed, shredded or comminuted asphalt roofing shingles or asphalt cement-containing products other than RAP. However, throughout this specification, the term “RAP” or the term “ACC” (i.e., asphalt cement components) may be used to refer to either RAP or RAS, or both unless otherwise specifically noted.
As used herein, the term “scalping screen” refers to any device adapted to remove oversized materials such as trash, debris and the like from virgin aggregates, RAP, RAS and the like.
The above and other problems are addressed by a plant configured for the batch production of an asphalt concrete blend having a high percentage of ACC of at least 25% percent. The plant includes a single and only dryer for mixing and for carrying out all drying operations required in producing the asphalt concrete blend by the plant. The dryer is provided with a generally cylindrical fixed outer drum, a generally cylindrical rotating inner drum positioned inside of and configured to rotate within the outer drum, and a burner directing a flame in a generally axial direction into a heating chamber within the inner drum. A mixing chamber is formed between an outer surface of the inner drum and an internal surface of the outer drum that is in selective communication with the heating chamber to either prevent aggregate from passing from the heating chamber to the mixing chamber in a first mode of operation or to enable aggregate to pass from the heating chamber to the mixing chamber in a second mode of operation. A plurality of mixing paddles is located within the mixing chamber that are sized and configured to combine virgin aggregate and ACC and/or liquid asphalt cement within the mixing chamber. The dryer also includes an ACC chute through which ACC may be passed into the mixing chamber and an aggregate chute through which aggregate may be passed into the inner drum. In certain embodiments of the invention, the plant includes a frame that is sized and configured to mount the dryer at ground level and at an angled orientation in order to provide an upper end and a lower end that is vertically lower than the upper end. Preferably, the ACC chute is located at the lower end of the dryer and the aggregate chute is located at the upper end of the dryer. In certain embodiments of the invention, a slide gate is located on the dryer that is movable between a closed position, wherein the dryer operates in the first mode of operation and virgin aggregate exits the dryer after being dried and heated but without being mixed in the mixing chamber, and an open position, wherein the dryer operates in the second mode of operation and virgin aggregate passes from the inner drum through open slide gate and into the mixing chamber. In certain embodiments of the invention, the plant includes a source of liquid asphalt cement and a secondary mixer that is external to the dryer that is configured to receive virgin aggregate or aggregate mix from the single and only dryer, to receive liquid asphalt cement from the liquid asphalt cement source, and to combine the virgin aggregate or aggregate mix with liquid asphalt cement in forming the asphalt concrete blend.
The present disclosure also provides a method for producing an asphalt concrete blend that includes the steps of drying and heating aggregate in a single and only dryer without use of a pre-dryer and then combining asphalt cement with the aggregate such that the asphalt concrete blend has an asphalt cement components (ACC) percentage of at least 25% percent. In certain embodiments, the method includes the step of adding liquid asphalt to the aggregate, wherein all of the liquid asphalt of the asphalt concrete blend is added to the aggregate after the aggregate is dried and heated by the single and only dryer. In certain cases, the liquid asphalt is added in a mixer that is external to the dryer. In certain cases, the liquid asphalt is added in a batch tower that is external to the dryer. Preferably, the asphalt cement content of the asphalt concrete blend is provided by a maximum of 70% ACC. In certain embodiments, the asphalt concrete blend is comprised of ACC and liquid asphalt cement. In preferred embodiments, the aggregate is dried and heated via direct drying and heating in a first portion of the single and only dryer. Thereafter, the aggregate is combined with ACC to form an aggregate mix that is then heated via indirect heating in a second portion of the single and only dryer. Furthermore, in certain embodiments, the aggregate mix is then combined with liquid asphalt cement to form the final asphalt concrete blend.
The present disclosure also provides a method for producing asphalt concrete blends that includes the step of providing a dryer having a fixed outer drum, a rotating inner drum positioned inside of and configured to rotate within the outer drum, a burner directing a flame into a heating chamber within an interior of the inner drum, and a mixing chamber formed between an outer surface of the inner drum and an internal surface of the outer drum. A slide gate located on the dryer is movable between a closed position when the dryer operates in a first mode of operation, wherein aggregate located within the heating chamber is prevented from passing into the mixing chamber, and an open position when the dryer operates in a second mode of operation, wherein aggregate located within the heating chamber is permitted to pass into the mixing chamber. A plurality of mixing paddles located within the mixing chamber that are sized and configured to mix aggregate located within the mixing chamber. The method also includes the steps of heating and drying first aggregate within the heating chamber and then combining the first aggregate with asphalt cement to form a first asphalt concrete blend. Certain embodiments of the method further include the step of providing a mixer and, with the dryer in the first mode of operation, combining the first aggregate with the asphalt cement in the mixer to form the first asphalt concrete blend. According to certain embodiments of the invention, with the dryer in the second mode of operation, the first aggregate is combined with the asphalt cement in the mixing chamber to form the first asphalt concrete blend. In some embodiments, the asphalt cement includes ACC. In some embodiments, the asphalt cement is liquid asphalt cement. In certain of those cases, the method further includes the step of providing a mixer and combining the first asphalt concrete blend with liquid asphalt in the mixer to form a second asphalt concrete blend.
Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale so as to more clearly show the details, wherein like reference numerals represent like elements throughout the several views, and wherein:
This description of the preferred embodiments of the invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. The drawings are not necessarily to scale, and certain features of the invention may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness.
Referring now to
ACC is delivered from one or more ACC supply bins 218 (
Virgin aggregate is delivered from one or more aggregate supply bins 226 of a bin coldfeed system 228 into the inner drum 210 of dryer 202 after passing through a scalping screen 230, by belt conveyor 231 or other similar conveyance means, through chute 232 located at upper end 234 of the dryer, whereupon it is dried and heated. The ACC supply bins 218 and the aggregate supply bins 226 of the bin coldfeed system 228 are each preferably equipped with a variable speed feeder that can control the discharge of material from the bin onto conveyors 221, 231, respectively.
The interior of the inner drum 210 is functionally separated into a combustion zone located in the vicinity of burner flame 216 and a drying zone located between the combustion zone and the upper end 234 of dryer 202. Because upper end 234 of dryer 202 is elevated above lower end 214, the virgin aggregate delivered into the interior of the inner drum 210 through chute 232 will move towards the lower end and is dried and heated as the inner drum rotates. Preferably, inner drum 210 includes a plurality of V-flights (not shown), such as are described and shown in U.S. Pat. No. 8,863,404, on its inner surface to facilitate this heating and drying process. Combustion products and exhaust gases generated during the operation of dryer 202 rise out of the inner drum 210 through exhaust gas outlet 236 and are conveyed to baghouse 204 (
With continued reference to
On the other hand, when the slide gate 242 is in the open position, the plant 200 operates in a second mode of operation where an aggregate mix formed by combining virgin aggregate together with ACC may be produced within dryer 202. More particularly, virgin aggregate may pass from inner drum 210 through open slide gate 242 and into mixing chamber 224 to be mixed with heated ACC material located there to form an aggregate mix. Inner drum 210 supports a plurality of mixing paddles 248, which extend away from an outer surface of the inner drum into mixing chamber 224. ACC delivered into mixing chamber 224 through chute 222 is thoroughly mixed with the virgin aggregate by mixing paddles 248 to form an aggregate mix. In certain preferred embodiments, the aggregate mix is comprised of up to 70% ACC. Asphalt cement may be injected into the aggregate mix within the dryer 202. However, in certain preferred embodiments, no additional asphalt cement is injected into the aggregate mix inside of the dryer 202. Rather, as discussed below, additional asphalt cement is injected into the aggregate mix within a mixer, such as a pugmill or continuous rotary mixer 250 (shown in
In certain embodiments, the blend produced by the dryer 202 is the final asphalt concrete blend and no further processing is required. However, in other embodiments, the blend proceeds from the dryer 202 for further processing. For example, referring again to
Referring again to
Thus, it may be seen that methods, systems, assemblies, facilities, and combinations of components according to the present general inventive concept, as described above, allow for the production of asphalt concrete from aggregate materials including a high percentage of ACC while using only a single dryer or a single dryer and a single mixer for both virgin aggregate and ACC, without using a separate pre-dryer for heating and drying ACC. Additionally, embodiments of the present invention, as described above, allow for ground access to the dryer, thereby making the frequent and routine maintenance of the dryer much faster and much safer. Furthermore, various embodiments of the present invention avoid injecting liquid asphalt cement within the dryer in order to reduce the maintenance interval. Instead, liquid asphalt cement is injected within a pugmill within a batch tower or within a separate rotary mixer.
Although this description contains many specifics, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments thereof, as well as the best mode contemplated by the inventor of carrying out the invention. The invention, as described and claimed herein, is susceptible to various modifications and adaptations as would be appreciated by those having ordinary skill in the art to which the invention relates.
This application claims the benefit of U.S. Provisional Application No. 63/035,306 filed Jun. 5, 2020, and entitled HI-RECYCLE ASPHALT BATCH PLANT, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63035306 | Jun 2020 | US |
