Seven million tons of municipal waste can be processed into about three million tons of alternative fuels with a caloric value of abt. 17,500 KJ/kg. They are used as an important energy source in the following sectors:
- Iron extraction
- Power stations
- Production of the synthesis gas methanol
- Cement industry
The production of alternative fuels contributes to the conservation of the resources of fossil fuels.
Modern waste management means to minimise or even better prevent the production of waste in the community. Furthermore, dangerous substances in the waste must be eliminated in order to exclude risks to humans, animals, and the environment.
To achieve this aim, several concepts for the recycling of waste materials such as feedstock and energy recovery of waste are being pursued by politics and industry. In recent years, the production of alternative fuels and their use have become an important topic in the sector of waste technology, not least due to the pricing of primary energy sources on the world market. Due to the requirements of the various combustion systems, in particular the production of sophisticated and high-quality alternative fuels is a challenge for waste management companies and machine suppliers.
Depending on the customers’ requirements, alternative fuels in the form of pellets or fluff are produced. The central part of the processing plant is the flat die press. By means of the flat die press, the waste materials are more or less strongly compacted depending on the quality requirements. At the same time, in particular the light frac - tions with a high calorific value are homogenized. The slightly compacted or slightly pelleted material is also called fluff.
The pelleting elements such as pan grinder rollers (A) and die (B) exert a combined shearing and cutting impact on the product to be processed.
Example of a plant design for alternative fuel conditioning The waste materials pass through the process steps intake, processing, drying, sifting and conditioning.
- Primary crushing
- Screening into several fractions
- Separation of ferrous and non-ferrous metals,
- If necessary, drying for stabilising the waste and to increase the calorific value
- Classification and separation of the light and heavy fraction
- Post-treatment of the heavy fraction
- Production of pellets/fluff from the light fraction
- Dedusting and treatment of the exhaust air
If fluff is produced, after treatment using the flat die press, the material is conveyed for example into a press container for loading.
If pellets are produced, the pellets are cooled, screened and inter- mediately stored in silos prior to loading/discharge by truck
Plant example with flat die presses:
The pre-crushed material is fed into a scraper conveyor (2) for distribution to the flat die presses if several pelleting presses are required.
Outlet slides as well as the actual propor tioning elements (3) consisting of proportioning wheels and screws are mounted below the scraper conveyor. The speed of the respective proportioning element is controlled by a frequency converter depending on the current
consumption of the press motor. It is a load-dependent control system to ensure an optimum throughput.
The flat die presses (4) are placed in parallel, with the presses being operated in a so-called „overflow“.
The product which is not drawn-in by the proportioning elements is conveyed by the scraper conveyor and intermediately stored on a buffer belt (1) from which it is returned to the pelleting plant. Thus temporary production fluctuations in the upstream and downstream line can be
If stable pellets are produced, they are subsequently cooled in the cooler (5) prior to loading. If fluff is produced, a cooler is usually not required.