High level of asphalt recycling
The Benninghoven granulator is a specialized recycling plant designed to match the demands of the asphalt industry. It delivers the highest level of production efficiently with minimum fines and dust content, reducing wear rates and operational cost.
The use of Asphalt Recycling is not only subject to economic constraints but also to the statutory provisions for waste management in order to save our valuable resources. These targets are focused in many publications and reports, and primarily manifested in the technical delivery conditions directives for granulated asphalt (TL AG).
There is no mention of any grinding criteria or method that significantly influences the quantity or quality of the granulate which then has a direct impact of the additions for reclaimed asphalt into the Asphalt Plant.
Partly proposed in the directives were measures to avoid the degradation of granulate sizes. In the second part it is stated that the grinding process is unavoidable.
However, according to previous experience, it can be assumed that the grinding process still occurs when utilizing machines such as impactors.
These well known crushers are primarily developed for material such as hard rock and concrete demolition. Therefore a high energy input is inevitable for the crushing process.
This type of process leads to fragmentation of the aggregates within the reclaimed asphalt and a huge amount of fines is unavoidable. This alters the grading curve compared to the original material.
To obtain the required aggregate size of the end product large quantities of virgin rock must be added.
From a mathematical standpoint this limits the addition of asphalt granulate.
Fine grained material in the crushed asphalt absorbs large quantities of water when it is stored in the uncovered stockpiles. This additional water needs to be evaporated in another process.
High fines can also cause problems within Asphalt mixing plants (recycling drum in particular). Requiring regular cleaning which is costly and labour intensive. This is another very important aspect that should be taken into consideration.
The first concept impact crusher for reclaimed asphalt was launched more than twenty years ago to fulfill the criteria mentioned above. Unfortunately this machine had some disadvantages by the design, especially being sensitive to the iron components that are frequently found in feed material.
Benninghoven has constantly continued the research and development for this improved technology. In developing the machine, the main criteria for the Benninghoven R&D team was to design a highly efficient granulator capable of breaking reclaimed asphalt blocks and planings down to a perfect recyclable size without reducing the original stone content. Another most important issue was to develop a machine which can handle trapped steel without damaging the machine.
Primary granulator (BRG 1.300/2.000)
After the pre granulated material is transported onto the conveyor belt a magnetic separator collects all steel items contained within the RAP.
Single or double deck screen
The material is then screened and separated in to the different fractions. Oversize material is fed into the double rotor granulator to produce the final grading.
Secondary Rotor granulator (BZG 1200)
The Single rotor granulator combines with a secondary double rotor granulator in order to achieve the final Grading.
The machine is designed in various versions, fully mobile (4-axle trailer), skid mounted transportable or stationary version.
Another impressive feature is the short set-up time for the mobile plant of 1 h max. On hard-surfaced sites, the crusher can be started up after just 30 min. This very short set-up time means that even relatively small quantities of material can processed economically.
With the two selected crushing stages, the unit is designed primarily to satisfy the requirements of the asphalt industry for the production of ever smaller product sizes, without increasing the percentage of unwanted fines.
Principle of Operation
The primary crusher of the granulator is fed directly by a wheel loaders.
The length of the feed slabs can be up to 1,800 mm.
Hydraulically powered arms press the material onto the single rotating grinding rotor; where the cutting teeth act against the adjustable crusher camber bar to break down the feed materials.
The speed of the shaft is controlled electronically and ensures a consistent feed regardless of the material type (broken asphalt, milled material or mixture of both)
If the feed material contains iron components, the spring-mounted breaker bar will allow the material to pass without causing major damage.
The iron contaminants fall onto the discharge belt and are then removed by an over belt magnetic separator.
The drive of the milling drum is designed to enable trouble-free start-up of the machine even with a full feed hopper. The variable speed of the milling drum allows the machine to run at an optimized high production rate.
The material pre-crushed to around 0/60 mm, is transferred onto a feed belt and after passing the over belt magnet continues onto a high-capacity vibrating screen which sizes the finished product.
The screened material is collected by a conveyor belt (0-8mm and 8-22mm) positioned under the vibrating screen.
The oversize from the screen is recrushed in the twin shaft BZG 1200 rotor granulator.
One of the two counter rotating rollers of the secondary granulator is spring loaded.
The required final size is obtained by variable adjustment of the gap between this and the fixed roller. A space-saving recirculation of the recrushed material to the high-capacity screen ensures that the finished product only contains the required size.
As a consequence of the Benninghoven crushing technology, the crusher tools only briefly come into contact with the material feed, the entire plant therefore operates with very low wear and tear.
Moreover the material is handled gently so that the original grain structure of the aggregates is not destroyed during processing of the asphalt and only limited grit and dust are produced.
(Diagram 2: dry screening process) shows the comparison of the material size between an impact crusher and a Benninghoven Granulator analyzed in an independent laboratory.
This diagram shows clearly, that the granulator produces a significantly larger proportion of 16-22 mm material. Almost 45 %.
The focus of the impact crusher (red) demonstrates a larger proportion of 1-4 mm material. This indicates that grain degradation can be avoided to a large extent by the use of the granulator
It is important to point out that these analysis are the results of a dry screening process. This explains the high percentage of 16-22 mm material.
Comparing the results to the Benninghoven Granulator in various laboratory tests it is proven that hardly any original stone sizes are destroyed and only a low fines content is generated. This is totally different to the results using a hammer mill crusher system.
With regard to the particle size distribution, almost 100 % of RC granulate can be integrated. Concerning the grain structure, up to 90 % crushed material from the granulator can be added.
The Benninghoven Granulator ensures that the following requirements have been met:
- Recycling Management and Waste Act demands a high quality recycling of broken asphalt
- The technical delivery conditions directives for granulated asphalt (TL AG)
- The economic viability requires low moisture asphalt granulate and low crushing operation cost
- Highest possible addition of RAP to the Asphalt Plant.
Most Asphalt plants in Germany now dose the recycling material by various cold feed bins in order to match the recipe and therefore increase the recycling content within the mix.