Single Dryer for High-Recycle Asphalt with Indirect Heating
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Solution Overview
Problem
Conventional asphalt concrete production plants face challenges when using high percentages of recycled asphalt products (RAP) and shingles (RAS), including emissions of smoke and VOCs, oxidation of asphalt cement, and labor-intensive maintenance due to the use of separate pre-dryers for heating and drying, which limits the suitability and efficiency of high-ACC percentage asphalt concrete production.
Innovation Solution
A single dryer system is used for both virgin aggregate and blends of RAP/RAS, with a cylindrical fixed outer drum and a rotating inner drum, allowing for direct or indirect heating and mixing, and a slide gate for controlling the flow of materials, eliminating the need for a separate pre-dryer and facilitating ground-level maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a separate pre-dryer is used to heat ACC materials before the main dryer, then the drying efficiency is improved, but the device complexity and maintenance difficulty increase
Solution Approach 1:
The patent combines the pre-drying function and main drying function into a single dryer unit. The dryer includes a rotating drum with internal lifting bars that perform both pre-drying of ACC materials and main drying of aggregate materials in one integrated system, eliminating the need for separate pre-dryer equipment
Solution Approach 2:
The single dryer is designed to perform multiple functions: it can dry ACC materials (RAP/RAS) and virgin aggregate materials, and can operate in different modes (direct fire or indirect fire) depending on the material being processed. This multi-functional design replaces what would traditionally require separate specialized equipment
2Productivity
If ACC materials are exposed to high-temperature drying gases, then the drying speed is improved, but oxidation of asphalt cement occurs degrading the material
Solution Approach 1:
The patent implements dynamic control of the drying process by allowing the operator to select between direct fire mode (for virgin aggregate) and indirect fire mode (for ACC materials). The system dynamically adjusts the heating method based on the material being processed, preventing oxidation of asphalt cement in ACC while maintaining efficient drying
Solution Approach 2:
The patent changes the thermal processing parameters based on the material type. For ACC materials, it uses indirect heating through hot air circulation without direct flame contact, maintaining lower temperatures that prevent asphalt cement oxidation. For virgin aggregate, it uses direct high-temperature firing to maximize drying speed
3Productivity
If liquid asphalt cement is exposed to high-temperature gases and steam during drying, then the drying efficiency is improved, but emissions of smoke and VOCs increase
Solution Approach 1:
The patent converts the potential harm of high-temperature exposure into a benefit by using indirect heating for ACC materials. The hot air circulation system provides sufficient drying heat without direct flame contact, preventing the thermal degradation and VOC emissions that would occur with direct high-temperature exposure, while still achieving effective drying
4Adaptability or versatility
If a separate pre-dryer is used for ACC materials, then the processing capability is improved, but the maintenance becomes more labor-intensive
Solution Approach 1:
The patent merges the pre-dryer and main dryer into one integrated unit with a single rotating drum. This consolidation reduces the total number of components that require maintenance and allows all drying operations to be serviced from a single location, reducing labor-intensive maintenance while maintaining full processing capability for both ACC and virgin aggregate materials
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces emissions, prevents oxidation of asphalt cement, and simplifies maintenance by allowing the single dryer to be located at ground level, enhancing the production efficiency and safety of high-ACC percentage asphalt concrete.
Implementation Method 1
A burner at one end of the inner drum heats aggregate material by direct exposure to the hot gases generated
Implementation Method 2
the heated aggregate material is discharged from the inner drum into the outer drum where it is mixed with asphalt cement
Data Source
AI summary
A method for producing an asphalt concrete blend that includes the steps of drying and heating aggregate in a single and only dryer, preferably via direct heating, and without use of a pre-dryer. The aggregate is then combined with asphalt cement, preferably via indirect heating, such that the blend has an asphalt cement components (ACC) percentage of at least 25% percent to form an aggregate mix. Liquid asphalt cement may also be added to the aggregate mix. Preferably, the asphalt cement content of the final asphalt concrete blend is provided by a maximum of 70% ACC. In certain cases, the asphalt cement content of the asphalt concrete blend is comprised of ACC and liquid asphalt cement.