Agitating – Mortar mixer type – With heating or drying
Reexamination Certificate
2000-01-14
2002-11-12
Drodge, Joseph W. (Department: 1723)
Agitating
Mortar mixer type
With heating or drying
C034S135000, C034S137000, C432S111000, C096S297000, C096S232000, C096S233000, C096S364000
Reexamination Certificate
active
06478461
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a transportable hot-mix asphalt manufacturing system and method, and more specifically, to a hot-mix manufacturing system that is relatively compact and transportable to sites where the hot-mix asphalt is to be manufactured. The present invention also relates to compact pollution control systems and pollution control methods for a hot-mix asphalt manufacturing system.
While techniques and systems for manufacturing hot-mix asphalt are generally known, typically the systems used to manufacture the hot-mix asphalt include large, cumbersome components that must remain stationary and that are not easily disassembled and/or transported should it become necessary to manufacture the hot-mix asphalt at another location. An example of such large, cumbersome components is the typical conventional rotary dryer and its associated pollution control equipment.
Asphalt plants with rotary dryers are well-known in the art. Such asphalt plants, however, tend to suffer from at least one of several disadvantages. Among the disadvantages are that: 1) they are excessively, complex, large or bulky and cannot be transported easily to a location where the hot-mix asphalt is needed, 2) they use excessively expensive, complicated, and/or large pollution control devices (some of which require frequent maintenance and monitoring), and/or 3) they are not compatible with recycled asphalt products (RAP) or cannot accept commingled RAP and virgin asphalt aggregates.
Conventional rotary dryers typically use cyclones, knock-out boxes, large bag houses, and/or other space-consuming pollution control devices to process the emissions from the rotary dryers. Still other rotary dryers use expensive and/or complicated thermal oxidizers, indirect heating systems where the RAP aggregate is not exposed to the heated air, or a second rotary dryer into which the polluted exhaust gases are inserted and diluted or burned. Notably, thermal oxidizer-based systems tend to be very expensive, bulky, and have large operating costs because of their high energy requirements. Indirect heating systems tend to be thermodynamically inefficient, expensive to build, and very limited in production rates. Systems that depend on a second rotary dryer disadvantageously prevent one rotary dryer from being used without another.
The space-consuming pollution control devices typically are not easy to disassemble and transport. Often transportation of such devices requires a significant amount of disassembly and/or unusual transportation equipment and techniques. The combined weight and/or size of a typical rotary dryer and its associated pollution control devices usually exceeds the size and/or weight restrictions of wide-load trucking in the United States. It therefore is difficult, if not impossible, to transport such systems using fewer than three truckloads, and without any complicated and time-consuming disassembly of the rotary dryer and its associated pollution control equipment.
There is consequently a need in the art for a hot-mix asphalt manufacturing system, such as a rotary dryer and its associated pollution control equipment, that can be transported in fewer than three truck loads, without complicated disassembly of the manufacturing system. Since wide-load trucking requires official permits, escorts, and can be performed only within certain regulatory limits, the use of wide-load trucking tends to be far more expensive, time-consuming, and less practical than conventional trucking. Conventional trucking (i.e., trucking without escorts and without wide-load designations) can be performed, according to U.S. regulations, when the load is no larger than 8 feet, 6 inches wide by 13 feet, 6 inches high by 53 feet long. The need for a transportable hot-mix asphalt manufacturing system therefore further extends to one that, without complicated disassembly of the manufacturing system, does not require loads that exceed the dimensional limits of conventional trucking, and preferably one that can be transported in fewer than three such conventional truck-loads.
If a rotary dryer is capable of handling recycled asphalt product (RAP), it typically will be configured with an external combustion chamber to protect the contents of the dryer's drum from the combustion process that is used to generate heat. The cumulative length of the rotary dryer therefore typically includes the length of the dryer's rotatable drum plus the length of the external combustion chamber. The additional length contributed by the combustion chamber usually precludes the rotary dryer from being transported using conventional trucking in a single truck-load. The aforementioned need to provide a readily transportable hot-mix manufacturing system therefore extends to one that has a rotary dryer with a combustion chamber does not contribute significantly, if at all, to the length of the rotary dryer.
While there are some pollution control devices that are more compact, less expensive, and/or less maintenance intensive than the pollution control devices typically found on a conventional rotary dryer, such devices generally have not found, their way into the rotary dryer industry. Presumably, this is because of perceived incompatibilities with the emissions from the typical rotary dryer. Plate collectors, for example, though they are fairly compact and inexpensive, are not used as pollution control equipment in the typical rotary dryer. It is generally perceived that plate collectors would be overburdened and/or clogged by the particulates in the exhaust gas of the typical rotary dryer. This is especially so if the plate collector is to be located in the recirculated exhaust gas stream of a rotary dryer. It is generally perceived that excessive maintenance and/or replacement of the plate collectors would be necessary if such collectors were used to remove particulate from the recirculated exhaust gas stream.
While plate collectors can be cleaned by continuously spraying them with water, such “wet” processing generally is not used in the context of rotary dryers because the emissions from such rotary dryers typically are treated in bag houses or using other fabric-based filters. Such bag-houses and other fabric-based filters typically are incompatible with condensed water. When such fabric-based filters are used, it is typically necessary that any moisture in the filtered emissions remain in the vapor state.
Likewise, fiber bed filters are not generally used to treat the pollution from the typical hot-mix rotary dryer. Presumably, this is, in part, because of the temperature limitations imposed by the use of such fiber bed filters. The typical fiber bed filter is not compatible with hot emissions that exceed a temperature of about 120 degrees F. It is not unusual for the emission temperature from a rotary dryer to exceed 200 degrees F. Since the emissions from the typical hot-mix rotary dryer far exceed the 120-degree temperature limitation, the general perception in the industry of hot-mix manufacturing is that fiber bed filters are not suitable for use as pollution control equipment in a hot-mix rotary dryer.
While some fiber bed filters have been provided with evaporative cooling systems, whereby water is sprayed through the emissions and evaporates to draw heat away from the emissions, the use of such fiber bed filters in the asphalt industry generally has been limited to treatment of relatively low-moisture asphalt emissions (e.g., emissions from shingle manufacturing and asphalt storage facilities) having a much lower moisture content than the emissions from the typical hot-mix rotary dryer. While evaporative cooling can be effective with low-moisture emissions, such evaporative cooling techniques alone generally are not effective in the context of the moisture-saturated emissions from the typical rotary dryer. In particular, the typical emissions from the rotary dryer can accept little, if any, additional moisture. Fiber bed filters therefore, even if augmented to include evaporative cooling systems, g
Cecil Terry K.
Drodge Joseph W.
RAP Technologies, Inc.
Schweitzer Cornman Gross & Bondell LLP
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