AMANDUS KAHL Wood and Straw Pelleting Plants for Waste tyres AMANDUS KAHL Pelleting Plants for Demestic Waste Complete Feed Mills Plants and Machines :: Company Information

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What are pellets and how do they differ from briquettes or granulate?

Different processes are used for compaction, i.e. for pressing powdery, pasty or lumpy products into uniform bodies. Depending on the process applied and the shape, the final product is called granulate, pellet, or briquette. A clear definition of terms is not available, but the following could be determined:

Product: Granulate / Pellet / Briquette

Size: 0.5 - 3 mm / 2 - 30 mm / 30 - 60 mm

Shape: undefined, but not powdery / cylindrical / geometrically defined

In general, one of the following two methods is applied for compacting:

1.) Agglomeration by agitation

In this case the adhesion of the particles is not reached by mechanical pressure acting from the outside, but by moving the product adding moisture and by subsequent drying.

This process is not appropriate for the compaction of saw dust and wood shavings.

2.) Agglomeration by compression

A process, where the adhesion of the particles is promoted by forces acting from the outside. By means of suitable pelleting elements the product is compacted to such an extent that agglomerates of sufficient solidity are produced.

Within the processes of agglomeration by compression, "pelleting" always proves to be the best if larger product quantities have to be processed under economic aspects. This applies particularly to products which do not have strong natural adhesive powers and do not allow the addition of binders.

KAHL pelleting presses are built in a basic design:

As a flat die press, where the pan grinder rollers rotate on a horizontally arranged die and the product is pressed downwards through the die holes (Figure 1).

Pelleting process and pelleting elements

The pan grinder rollers and the dies are the most important elements in the pelleting process.

Compaction takes place in the open effective bores of the die. The product is fed to the press vertically from above and is uniformly distributed into the pelleting chamber. A product layer is formed on the surface of the die. The rollers run over this layer and compact it.

The pressure is continuously increasing whilst the product is being rolled towards the effective bores, thereby pushing the product plug in the bores slightly forward. To achieve this, the frictional force within the effective bores must not exceed the effective pressure created by the rollers. On the other hand, the frictional force must be high enough to cause a sufficient compaction of the product to a solid agglomerate (Figure 2).

A small layer of product is forced into the effective bores which is united to a pellet by means of the pressure and the adhesive powers of the product. The individual layers of product form endless strands in the bores which are cut at the lower side of the die to the desired pellet length by means of rotating knives.

As for the pan grinder rollers, a large outer diameter and a solid bearing are required. The profile of the running surface can be varied, but this does not have such an influence as the execution of the die. Kahl presses are used with rollers of up to 450 mm in diameter and 192 mm in width. The profiles of the running surfaces are available in grooved, perforated, and corrugated design.

The pan grinder head rotates at a speed of approximately 60 rpm. For this reason the running speed and thus the noise level of the flat die press are very low. Nevertheless the number of rollers ensure a high roll-over frequency of the product which is necessary for achieving a high throughput.

The respective design of the die is very important. The ratio between the diameter of the bores and the length of the effective bores is called "pelleting ratio". Together with the product properties it determines the frictional force produced. So the pelleting ratio must be exactly adapted to the product, in order to reach optimum results concerning pellet quality and throughput of the machine. It must be taken into account that the ratio of pellet surface to volume changes with decreasing pellet diameter.

For this reason dies which are manufactured for pelleting compound feed, dried beet pulp, or other products, cannot be used for compacting wood.

Another important parameter of the dies is the number of holes and thus the "open perforated surface" available which has a direct effect on the throughput of the press together with the drive power.

Hydraulic system of the press

Today a hydraulic system for the exact adjustment of the rollers - also during operation of the press is "state-of-the-art".

By means of the product layer on the die a gap is produced between rollers and die which has an important influence on compaction. For this reason it is desirable to be able to modify this gap also during production and to check the operating state of the press by means of the product pressure against the pan grinder rollers.

Our hydraulic system is a proven accessory which offers these possibilities to the press operator. The process can be monitored and optimized during operation. On top of it, the hydraulic system is provided with an integrated pressure relief valve as safety device if foreign particles get into the press (Figure 3).

Product feeding and shearing effect

The product to be compacted is fed into the press by a suitable feeding screw, depending on the load. Due to the large press interior there is sufficient space for voluminous products, too. Forced feeding, which might cause blockages, is not required.

Individually adjusted scrapers serve for a uniform product distribution on the die.

In case of products with a high content of crude fibres such as wood the flat die press is equipped with cylindrical rollers which cause a shearing effect when running on the circular path of the die. This desired effect produces a twisting and primary crushing of the product on the die, so that it can be pelleted more easily.

Particularities of pelleting wood

Prerequisites for optimum operation are continuous product feeding into the press and a homogeneous, sufficiently pre-crushed product. The moisture should be kept very constant at a range of 12 - 15 %.

Due to the large volume reduction when compacting wood and wood shavings, particularly sawdust from about 100 to 600 kg/m³, the capacity of the machine, i.e. the press interior, must be as large as possible. Further requirements made by the wood industry are a robust machine construction and a high availability of the plant in order to meet the required operational safety.

A sufficiently high throughput with the lowest possible specific energy consumption and a good pellet quality are further requirements, along with the aim to reach a long service life of the wear parts.

In comparison with other products wood does not have strong adhesive powers like starch-containing feed, for example. The antifriction properties are not very distinct, either. As a result a high frictional force is quickly produced in the effective bores, which also is necessary for compacting this product with its low own binding forces.

It is noteworthy that there are differences concerning the processing of different kinds of wood which depend to a large extent on the resin content. In case of hard wood, such as beech or oak, pelleting presses for shaping wood pellets require higher pressure forces than for soft wood and conifers. The pressure forces lead to the "specific energy consumption", which is between 40 and 60 kWh/t in case of wood processing.

Due to the high frictional resistance and the low adhesive powers of some kinds of wood preconditioning, i.e. pretreatment of the product before the actual pelleting process, is very important.

The product moisture, temperature, and crushing degree play an important part. In order to increase the moisture content of the product, water should be added partly in form of steam and the moistened wood should be given sufficient retention time for letting the moisture penetrate into the product.

For this reason an ideal plant is provided with a crushing system, e.g. a suitable hammer mill, a continuous mixer for the addition of steam and water, and a long-term conditioner for the retention time before pelleting (Figure 4).

Particularly for the pelletization of wood the company Amandus Kahl has developed pelleting presses with reinforced bearings and further construction details which meet the requirements made by the wood industry.

Pan grinder mill

AMANDUS KAHL has gone back to the well-known pan grinding tradition. The established KAHL flat die pelleting press, which is based on this principle, has been further developed to a "dieplate pan grinder mill". On the occasion of the trade fair "BioEnergy Europe 2008" in Hanover the pan grinder mill won the Innovation Award 2009 of the Deutscher Landwirtschaftsverlag DLV (German agricultural publishing house).

Wet and dry biomass or wood chips can be crushed without problems and the capacity of the pan grinder mill even increases with the moisture of the raw material. Very wet wood does not cause any difficulties. The pan grinder mill reaches capacities of a few 100 kg/h up to 40 t/h and can replace the hammer mill, depending on the raw material.

Advantages over the hammer mill are the quiet operation even at full load, the low space requirement and the minimum energy consumption. Besides, it can be used without dedusting systems, cyclones, filters and exhaust air plants and free from ATEX requirements.

Co-firing in power plants is the newest application of defibered wet biomass. In a two-stage process, the biomass is defibered to particle sizes < 2 mm and then directly injected with the coal dust into the combustion zone. The fresh, defibered wood chips are not dried or pelleted, so that the energy consumption can be reduced drastically.

New Recycling Methods for Old Tyres

In the European Union more than 2.5 million tons of waste tyres are produced annually, from this amount almost 600,000 tons in Germany. About 270,000 tons are used as RDF in cement factories and power stations.

As the limited petroleum resources are dwindling and the energy yield is low compared with the energy required for the production of tyres, thermal utilisation of end-of-life tyres neither makes sense ecologically nor economically. Under these premises, material recycling of the main components is the better alternative.

Material Recycling of Waste Tyres

In order to recycle the tyre materials, the tyres must be crushed and then separated completely into their components rubber, steel and textile fibres. Normally, the tyres are pre-crushed in slowly running two-shaft shredders or rotor-cutters and afterwards processed to crumb and powder of different granular sizes in a single- or multi-stage grinding process. The two following processes are possible:

· Cold grinding: In this process, also known as cryogenic grinding, the pre-crushed tyre chips are made brittle by liquid nitrogen (LN2), so that they can be ground more easily in the hammer mills. In case of cryogenic grinding, one phase normally suffices for reaching the requested separation of the components and obtaining a broad particle size spectrum of rubber crumb. A disadvantage of this technology is the high cost for the use of liquid nitrogen, since one to two tons of LN2 are required for one ton of waste tyres. Besides, the small surface of the glass-like broken crumb / rubber powder has a negative effect.

· Warm grinding: Warm grinding takes place at ambient room temperature. For this reason it is also called "ambient grinding". The tyre chips are crushed in fast running granulators or mills without being made brittle. By means of (cutting) granulators connected in series the product is reduced gradually to the requested granular size. The main disadvantages of warm grinding with granulators are the high energy demand due to the use of several crushing phases as well as the relatively high wear of the granulator knives causing high maintenance and wear parts costs.

The Alternative: Tyre Grinding with Flat - Die Granulation Presses

The process developed by Amandus Kahl GmbH at Reinbek for ambient grinding of waste tyres is an economic alternative to the aforementioned traditional grinding processes.

The supplied tyres are cut in a preliminary stage to a chip size of 50 to 100 mm. Via an intermediate buffer the chips are conveyed into the core component of the plant, the rubber grinding unit. Here the tyre chips are ground in a Kahl flat-die granulation press according to the pan grinder roller principle.

The tyre chips are ground between the cylindrical pan grinder rollers and the circular die designed as perforated plate. The shearing forces produced by the pan grinder rollers when rolling over the circular die as well as the pressing forces of up to 120 bar applied by an automatically regulable hydraulic system decompose the tyre parts and separate the different components. Unlike the traditional (cutting) granulators, the material is not reduced to small pieces by geometrically shaped cutting edges, but only by the shearing forces produced between the grinding tools and in the product. As a result, the wear of the grinding tools does not have any influence on the granulation result.

The granulation press, type 60-1250, with a drive power of 2 x 160 kW processes up to 4.5 t/h tyre chips with an input size of about 50 to 80 mm in case of truck tyres and about 100 to 150 mm in case of car tyres to a granular size of 0.4 – 20 mm. The effective throughput of the press depends on the requested granular size of the final product. When producing rubber crumb of less than 4 mm, the capacity of a single-stage grinding system is about 2.5 t/h. The respective oversize particles are mixed with the tyre chips in the buffer bin upstream the granulation press and ground again.

Typical Separation Result

· Steel: 15 to 20 %

· Rubber crumb

4 - 6 mm in size: 15 %

2 - 4 mm in size: 15 %

0 - 2 mm in size: 30 %

· Textile/rubber mixture: 15 to 20 %

Of course, the percentages can vary depending on the composition of the input material.

Conditioning of the Ground Product

After grinding, magnets separate the uncovered steel wires and steel/rubber compounds. In a first screening phase, fines smaller than 8 mm are separated and conveyed to the crumb cleaning system. The coarse fraction and the steel/rubber compounds are returned to the granulation press, the quantity of the returned material depending on the particle size spectrum of the requested product.

After granulation, the ground product is classified according to customer requirement and cleaned in fractions in a multi-stage sorting and sifting system. Metal separation is effected in magnetic drums, classification by means of screens. Final sifting for separation of textiles and minerals is realized by means of zigzag sifters and table separators. Depending on the requirements of the customer, the cleaned crumb can be packed in small or big bags. As alternative, it can also be stored in silos for bulk loading in tank trucks or containers.

The modular system is designed for a plant capacity of 2.5 t/h per granulation press in three-shift operation. This corresponds to a throughput of up to 15,000 t/a for one line. By mounting several modules in parallel, the plant capacity can be increased almost at random.

Wide Range of Application for Products

Apart from the high purity degree of the rubber crumb and meal, the process also excels by the very pure steel fraction obtained as final product. With a maximum residual impurity of three percent rubber and textiles in the steel, for the first time prices of clearly more than 100 Euro/t can be reached with the steel fraction. These high-quality steels are used in blast furnaces for steel production or recently as additional concrete reinforcement for the construction of buildings.

The rubber crumb obtained by warm grinding has a much larger specific surface than the cold-ground crumb. Rubber crumb and meal are used in different fields of application. They are used as filler in the caoutchouc industry, for example. Thus material costs can be reduced and the production process simplified. With the addition of PU binders, the material can also be pressed to protection mats for playgrounds and sport venues surfaces. Another possibility is the addition to topsoil which improves the compaction and drainage behaviour of heavily trampled lawns. When adding plastic crumb, such as recycled thermoplastics, instead of PU binders, elastomer compounds can be produced in special extrusion processes. By means of extrusion or injection moulding, a large number of products can be produced from these materials. Warm-ground rubber meal is particularly appropriate for this purpose.

When added to asphalt, the asphalt properties for road construction are improved, as the rubber asphalt reduces noise emissions by up to nine decibel. Besides, the temperature stability of the road surface increases, so that the formation of lane grooves in summer and frost cracks in winter is reduced.The application possibilities, particularly for warm-ground crumb, are numerous. But they are only efficient when using an economic granulation process.

Advantages of the Technology

· Compact construction size

· Reduced machine expenditure due to single-stage grinding

· Prolonged life granulation tools, thus wear costs of 5 Euro/t

· High throughput

· Fast and simple tool change

· Automatic adjustment of the grinding gap by means of the hydraulic system

· Automatic lubrication

· Noise emission level below 85 dB(A)

· Production costs of about 40 €/t

	KAHL Pelleting of Compost Compost products continually require new markets. KAHL have developed a process for the production of fertiliser pellets from compost. This fertiliser has considerable advantages over conventional compost products: * higher nutrient content due to the addition of NKP * easy handling of the coated pellets KAHL manufacture complete plants which process the material from raw compost to packed pellets.
	KAHL Pelleting Technology The treatment of waste and residual materials is one of the most important issues of the future. Since the 1970s KAHL has dealt with plant technologies aiming at a reasonable and economic recovery. The sophisticated KAHL flat die pelleting presses are suitable for the production of fluff and pellets for thermal or material recovery. The pelleting presses are the central elements of many custom-made turn-key recycling plants built by us. We reasonably complete our flat die pelleting presses by plants for grinding, drying and cooling. We offer consultation and assistance from the start of the project until after-sales service. KAHL technology is suitable for * Waste tyres * Domestic waste * Industrial waste * Sewage sludge * Plastic waste * Wood waste * Waste paper
	Recycling Industry In the past few years the waste and recycling industry have recognized the advantages of the KAHL pelleting technique in comparison with processing methods used so far. Through practical experience gained with plants supplied and research and development KAHL has become a competent partner of the waste and recycling industry. Examples of products already successfully pelleted are: Household and industrial waste, waste paper, waste wood, sewage sludge, bio mass, coal dust, coal grit, peat, FGD gypsum, fly ash, plastic waste, filtering dust etc.
	Wood Pelleting Plants A high quality awareness establishes KAHL on the wood pellet market. For more than 30 years Kahl has dealt with this product and can offer a sophisticated process for the production of high-quality pellets with very good combustibility, now. * clean cut * low dust content * highly compacted Robust design and a high availability of the plant ensure economic operation. KAHL pelleting presses are available with a drive power of 3 kW to 500 kW and a throughput of 300 kg/h to 8 t/h. We offer our customers assistance in obtaining approval, planning, engineering, commissioning, and after-sales service. Our pilot plant is available to our customers for tests with their products.