Indirect Heating Asphalt Plant for 100% RAP Recycling
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Solution Overview
Problem
Existing asphalt mixing plants face limitations such as incomplete combustion, poor mixing quality, dust generation, and a maximum RAP recycling ratio of less than 50%, leading to inefficient production and environmental pollution.
Innovation Solution
The introduction of an indirect heating system with a rotating inner drum and stationary outer housing, combined with helically aligned segmented screw flights and a surface combustion burner, enables 100% RAP recycling by achieving frictional shear mixing and convectional heating, eliminating dust generation, and ensuring complete fuel combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional oil burner is used to heat aggregates in the mixing drum, then heating function is provided, but incomplete combustion occurs causing air pollutant emissions
Solution Approach 1:
The patent replaces the conventional oil burner system with a surface combustion burner that operates on the principle of complete combustion. The burner design incorporates a special combustion chamber and air-fuel mixing system that ensures complete fuel consumption, eliminating incomplete combustion products and air pollutant emissions while maintaining effective aggregate heating.
Solution Approach 2:
The surface combustion burner uses enhanced oxygen supply and optimized air-fuel ratio control to accelerate complete combustion of the fuel. The combustion chamber design promotes thorough oxidation of fuel molecules, converting them completely to CO2 and H2O, thereby preventing the formation of harmful incomplete combustion products.
2Ease of operation
If simple tumbling mixing is used in the mixing zone, then mixing function is provided, but poor mixing quality results
Solution Approach 1:
The patent introduces a dynamic mixing mechanism where the mixing drum rotates at controlled speeds to create tumbling motion of aggregates. This dynamic action, combined with the sequential addition of RAP and asphalt binder, ensures thorough mixing and uniform distribution of materials, significantly improving HMA mix quality compared to static mixing methods.
Solution Approach 2:
The mixing process operates continuously with constant drum rotation and continuous material flow. The tumbling action persists throughout the mixing zone, ensuring that all aggregates receive adequate mixing action. This continuous dynamic mixing eliminates dead zones and ensures uniform mix quality throughout the entire batch.
3Quantity of substance
If RAP is added in the mixing zone with conventional heating, then RAP recycling is achieved, but insufficient heating time and energy cause early pavement damage
Solution Approach 1:
The patent implements preliminary heating of RAP aggregates before they enter the final mixing zone. The mixing drum design includes a heated zone that pre-heats RAP materials, reducing the thermal shock when cold RAP is added to hot virgin aggregates. This preliminary action ensures RAP reaches optimal temperature for bonding, preventing early pavement failures.
Solution Approach 2:
The system controls and optimizes temperature parameters throughout the mixing process. By maintaining precise temperature control of both virgin aggregates and RAP, and by controlling the addition rate and timing of asphalt binder, the process ensures complete coating and proper bonding. This parameter optimization allows high RAP content (up to 100%) while maintaining pavement durability.
4Use of energy by moving object
If direct heating of aggregates is used in the mixing drum, then heating efficiency is improved, but dust generation occurs requiring dust collectors
Solution Approach 1:
The patent introduces hot air as an intermediary medium for heat transfer. Instead of direct flame contact with aggregates, the oil burner heats air, and this hot air circulates through the mixing drum to heat aggregates indirectly. This intermediary approach maintains high heating efficiency while preventing dust generation from direct flame exposure, eliminating the need for dust collectors.
5Temperature
If the maximum RAP recycling ratio is limited to less than 50%, then heat exchange requirements are met, but recycling efficiency is reduced
Solution Approach 1:
The patent fundamentally changes the thermal parameters of the mixing process by implementing a heated mixing drum and controlled temperature zones. This allows cold RAP to be effectively heated to the required mixing temperature even at 100% RAP content. The temperature parameter control ensures uniform heat distribution throughout the mix, maintaining mix temperature uniformity while maximizing recycling efficiency.
Solution Approach 2:
The continuous rotation of the heated mixing drum provides uninterrupted heating action to all RAP materials throughout the mixing zone. This continuous thermal processing ensures that even 100% RAP mixes reach uniform temperature and proper bonding conditions, eliminating the need to limit RAP content for heat exchange reasons.
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 solution allows for the production of high-quality 100% RAP-recycled HMA with reduced environmental pollution, increased RAP recycling ratio, and efficient material transfer, mixing, and heating, while saving fuel and reducing production costs.
Implementation Method 1
a surface combustion burner for heating located at the inside of the inner drum to make indirect heating
Implementation Method 2
heating caused by friction of the materials with the segmented screw flights and convectional heating of the materials by rotation of the inner drum
Implementation Method 3
helically aligned segmented screw flights and directional flights both fixed on the outside surface of the rotating inner drum creates frictional shear force on materials in the channel when the inner drum rotates
Implementation Method 4
convectional heating of the materials by rotation of the inner drum
Implementation Method 5
a surface combustion burner for heating located at the inside of the inner drum to make indirect heating and complete combustion of fuel
Data Source
AI summary
A hot mix asphalt (HMA) or warm mix asphalt (WMA) plant features material transfer by shear action of segmented screws and directional flights standing on an inner drum. Indirect convective material heating is initiated by a heating source located inside of the inner drum. Material mixing, heating, melting, and uniform coating, all take place as a single simultaneous process. As the result of processing, regular HMA (or WMA) or up to 100% RAP (or ARS) recycled HMA (or WMA) can be produced. Many heat sources, such as a conventional oil burner and the surface combustion burner, may also be utilized in the plant. The plant may be combined with paving units for an integrated, mobile paving system.