Alternative Fuels (AF) and Secondary Fuels (SF)
Energy from waste
What are alternative fuels?
Alternative fuels or secondary fuels are fuels that are obtained from solid, liquid or gaseous waste. This waste undergoes different process levels depending on the purpose for which it is intended. Alternative fuels are produced, among other things, so recovered material (waste) which can no longer be recycled can be reused. The waste used for production comes from households, industry and commerce.
Alternative fuels as a solution
Today we are faced with two challenges: Firstly, the fact that households, industry and commerce are producing more and more waste, and secondly, the demand for energy from them is rising at the same time.
Another important factor is the trend with fossil fuels, because they are becoming scarcer and more expensive. In order to conserve natural fossil fuel resources, alternative fuels have become a real cost-effective choice.
Production of alternative fuels
Material preparation begins with pre-sorting the waste. Quality levels are set by the requirements of the customer involved. Because the better and more finely the waste is separated, the higher the quality of alternative fuel produced. Processing plants with our patented SPLITTER technology ensure ideal pre-treatment of the waste to be processed.
You too can benefit from our experience, from comprehensive advice and design development to after-sales service.
Production of alternative fuels
Materials for producing AF
Alternative fuels should only consist of 2D material (such as shredded film) and should not contain 3D material (such as stones, glass, pieces of wood, etc.). Plastics which have been pre-sorted from various types of waste are the material of choice for producing alternative fuels.
The following materials are suitable for the production of alternative fuels:
Household waste, commercial waste, bulky waste, production waste, mixed packaging, packaging waste
Alternative fuel energy values
When processing, a distinction is made between medium energy value (RDF – Refuse Derived Fuel) and high energy value (SRF – Solid Derived Fuel), which means the more materials with high energy value (e.g. film) are contained in the material, the higher the energy value.
- High energy: energy value often > 21 mJ/kg
- Medium energy: energy value often 12-16 mJ/kg
Preparing high energy AF: In order to obtain high energy AF, several levels with many sieving and separation processes are often required. Suitable materials for high-energy fuels are primarily lightweight packaging (household waste), production residues or pre-sorted material.
Processing of medium energy AF: Various types of waste such as domestic and commercial waste or bulky waste are also suitable for the production of medium energy AF . Since the need for medium energy AF is usually higher than the need for high energy material, different raw materials with high and low energy values are often mixed. In this way a medium energy value can be achieved and at the same time the entire amount of material can be processed.
As commercial waste often has a high energy value and bulky waste has a low energy value , the substances are often mixed to process all materials.
Where are alternative fuels used?
AF power plants
In an alternative fuel power plant (steam power plant) medium or high energy alternative fuels are used to generate heat and energy. In AF power plants, alternative fuel with a size of 80 mm up to approx. 200 mm can be burned.
Since the cement industry is a particularly energy-intensive sector , the use of alternative fuels is particularly advantageous here. High energy fluff is also very suitable because it burns in the air when it is "shot in" by the lance in the rotary kiln and does not cause any "false inclusions" in the clinker (molten rock in the rotary kiln).
High energy substitute fuel (also called fluff) is used in the rotary kiln. This fluff has a high energy value because, due to more intensive processing, it has gone through several stages and consists almost exclusively of pieces of film. 30% of alternative fuel is used in the rotary kiln and should therefore be high energy. Depending on the cement plant, high energy fluff of a size of up to 30 mm can be burned (between 2-20 tons per hour).
Medium energy AF is used in the calciner (tower). The requirement for medium energy AF in the cement plant is often up to 70% of the total amount of AF. Medium energy AF of a size between 80-100 mm can be burned in the calciner.
The SPLITTER stands at the beginning of the process chain
Thanks to its specific construction and working method, the SPLITTER is able to process large quantities of material as well as large (and uncut) pieces of material. In this way, the load and wear on the pieces of equipment downstream can be significantly reduced.
The SPLITTER as a process screen
Example of production of alternative fuel with the SPLITTER as a process screen
The SPLITTER can be used as a process screen directly after the shredder. Due to the roller track effect, the SPLITTER is able to separate film and 2D pieces in the upper grain category. 3D material, cubic and heavy material falls through the sieve and ends up in the lower grain category. This gives us the opportunity to create high energy alternative fuel from unsorted and pre-treated waste. 2D material such as film (e.g. from household recycling), which has a high energy value, come into the upper grain category. It can then be processed into high-quality fluff, instead of medium energy AF.
Even if your company does not plan to process upper grain material into high energy AF, it can be used efficiently and collected for further processing by another company that uses it to produce high energy alternative fuel.
The quality of the screening of medium and high energy material remains constant over the entire screening period due to the self-cleaning effect of the spirals.
- Upper grain SPLITTER: Further processing high energy
- Lower grain SPLITTER: Further processing medium energy
The SPLITTER as a pre-sorter
In Mediterranean countries in particular, there is no strict separation between organic waste, household waste etc., so rubbish often contains a lot of organic matter. Here, the SPLITTER sorts organics and minerals in the lower grain category and the valuable material for AF production can be separated into the upper grain category.
The stationary SPLITTER UNIT with its compact screen deck is particularly suitable as the first step in a process chain for processing solid waste such as lightweight packaging, commercial and domestic waste, metal scrap, slag, waste wood and much more.
The star screen at the end of the process chain
At the end of the process chain, the star screen is often used as a security screen/policing screen. This ensures that there is no clogging within the material before combustion and that any incorrect inclusions are in the clinker during the combustion. The star screen reliably sifts out unwanted long parts using the fingers of the star and the rotary movement. The star screen reliably ensures quality assurance in the process chain.
- SSF = Star Screen Fine: prepares high-energy alternative fuels up to 30 mm
- SSC = Star Screen Course:prepares medium-energy alternative fuel up to 80-100 mm
Advantages of using a star screen within the process chain:
- High throughput
- Quality assured commodity
- No need for secondary shredding
- Less energy consumption and wear on the shredder
Advantages for AF suppliers:
- The higher the quality of the commodity, the higher the profits. This also may mean better sales opportunities.
Advantages for cement producers:
- With your own star screen, lower quality commodities can also be accepted and the particular quality of the AF can be ensured.
The MULTISTAR 2-SE star screen system is an easily integrated solution thanks to its compact design. A modular system and options such as substructure, feed dosing container with feed and discharge belts, wind sifting etc. guarantees that your customer requirements are met precisely.
- Star screen: For exact fine sieving, safety screen, exact screen, policing screen
- SPLITTER: Pre-screening of coarse, bulky material to differentiate it for the process chain
- Flowerdisc: For clean input material that tends to twist or coil, mainly household waste
Every project and source material is different. Contact us for advice on the use of the different screen options.