07 Aug RAP(Recycled Asphalt Pavement) System in Asphalt Plants.
Recycled asphalt pavement (RAP) is a particularly valuable material to the asphalt production industry and its value will continue to increase as the cost of virgin aggregate and bitumen rises. Producers who can supply high-quality mixes with RAP with minimum energy usage and minimum environmental impact will be best prepared to compete in future markets.
Batch plants are often converted to allow the use of more RAP. In these plants, the aggregate is superheated in the dryer and held within the hot-stone bin as an energy store for the drying and heating of the cold wet RAP. The recyclable material is fed directly into the pugmill with the superheated aggregate where the RAP quenches the aggregate, dries and achieves final mix temperature. Bitumen is then injected to coat the RAP/virgin aggregate mix.
As the percentage of RAP increases in batch plants, operators must consider the steam created as the RAP is heated by the hot virgin aggregate during the mixing process. Since steam is generated almost instantly upon mixing RAP with virgin aggregate, the large volumes of steam from wet recyclable material usually overwhelms batch plant scavenge systems. A RAP feed system that controls and extends the time of RAP introduction into the pugmill should be used to give the scavenge system more time to evacuate the steam. Keeping the recyclable material as dry as possible reduces the total volume of steam generated and also reduces drying cost.
Ashitech offers RAP systems(upto 40% RAP Addition) for Batchmix Plants for the models ABM-80,ABM-120,ABM-160 and ABM-180.
RAP dryers can be utilized to dry and warm the RAP, reducing the level of superheating of the virgin aggregate required when directly compared with cold wet RAP at given addition rates. These drums are often installed at high level adjacent to the batch tower to allow warm RAP to flow by gravity to the mixing process. However, these dryers can be particularly polluting as, without abatement, blue smoke generated by the drying process can escape the dryer and pass into and through the fabric filter. Light oils, which can be stripped from the bitumen contained within the RAP, can also pass into the filter, oil-soaking the bags and producing odour and visible emissions from the stack.