high quality briquetting systems increase efficiency and yield - recycling magazine
Aluminium chips are produced throughout the entire product creation process; during the surface treatment of cast bolts and rolling ingots, during profile, plate and sheet production as well as the machining of components. Depending on whether they are produced by milling, turning, grinding or sawing, the chips, which are often wet, vary in form and properties; wool-like, spiral, rough, fine etc. What they all have in common is: they will be re-melted, whether in a Remelter or a Refiner. This phase describes both: The end and the new beginning of the eternal Aluminium-Recycling-Cycle.
But what are the key considerations in detail? Loose chips have a large volume at low weight; so they display low bulk weight, typically lying between 140 to 250 kg/m3. This effects significant costs for storage as well as transport, both internally and externally.
In order to react against this, the chips must be pressed. This is where the applied technology is of high importance. RUFs machines can compress to a level of 2,200 to 2,400 kg/m3 (and in individual cases these figures may be exceeded) when required. As a comparison: the density of solid aluminium lies, on average, at 2,700 kg/m3.
Chips are created in Rolling mills through the milling off of the casting surface. So-called edge trimming shavings are also created during the machining of sheets, coils or foils. Briquetting applies for either form. When the company has an affiliated melting works, the pressed aluminium will be conveyed directly there (highest added value). Otherwise they will be stored and sold on the scrap market.
On account of the high density when compared to loose chips, storage and transport costs are reduced by the use of briquettes. Furthermore, briquettes achieve higher sales revenue because they are better suited to the melting process.
Pressing plants produce chips primarily through reprofiling and sawing of casted round bolts as well as finished extruded sections. As very few of these types of companies are affiliated with a melting works, storage and transport costs are extra significant.
Another factor above all in achieving higher sales revenues is that Stamping/pressing plants dispose of single origin chips with a clearly defined composition. This means they can be used as alloying additions during the melting process, which is very much in-demand in the melting plants as it means they have to purchase less, very expensive, alloying elements and aggregates.
Machining companies are to be found in many branches like e.g. in the Automobile industry, Aerospace and Mechanical engineering. Handling chips is daily business for these companies, and it has the association of a waste product of machining. The advantages of briquetting regarding storage and transport costs also exist here, just like the optimisation of sales revenues, because of the volume reduction of the chips after briquetting by a factor of between six and twenty. Furthermore, there is another important factor in this area of application: the recovery of cooling lubricants, emulsions or oil.
RUFs systems are equipped with an integrated catchment device for fluids. This ensures that your storage area remains clean, which is very much in alignment with orderly production processes and environmental protection in practice. Personnel costs are reduced and work safety levels are increased when the machine works automatically and only the conveyance of chips or briquettes requires service personnel.
Remelters and Refiners are smelters, which are differentiated by e.g. the products they manufacture. Remelters mostly produce wrought alloys as wire, bolts and rolling ingots. Refiners produce casting alloys in the form of ingots. Both utilise chips, amongst others. The difference between using loose chips or briquetted aluminium for remelting is, in both cases, significant.
Because under the effect of flames, the light material burns-off very quickly instead of melting. And as the relation between surface area and density is particularly big with chips, a lot of material is lost through this burn-off. Moreover, the large exposed aluminium surface area of the chips mean a high tendency to oxide formation. This leads to further losses in the melting furnace in the form of dross.
A further problem factor in the melting of aluminium: when the liquid metal comes into direct contact with other liquids such as cooling lubricants, an almost explosive reaction takes place. Therefore, the factor of residual moisture is important.
Loose chips often have a moisture content of 20 per cent and more. If they are not briquetted, the chips must go through a centrifuge and further drying systems in order to remove the residual moisture. In contrast briquetting is significantly more economically effective, especially when high quality systems are used. An appropriately high pressing power reduces the moisture content down to between three and five per cent. If the briquettes are subsequently stored in a dry place this reduces to values fewer than two per cent. And the briquettes can be safely and efficiently melted.
Because of burn-off and oxidation, loose chips cannot be used in some melting furnaces or only after very cost intensive treatment. The melting process of loose chips in a rotary drum furnace requires the addition of salt. The inherent problem here is: the left over salt slag has to be disposed of or undergo re-treatment, which is very expensive.
Hearth type melting furnaces can also be equipped with so-called Vortex-installations, which can be operated with electromagnetic or mechanical pumps. This leads to the chips being stirred into the molten mass. This functions pretty well, but it requires a lot of effort. And apart from the purchase costs, the installation needs space, regular maintenance and there are also extra personnel and operating costs involved, particularly due to the high wear factor.
Independent of which furnace technology is implemented, the melting process functions at its best with highly compressed briquettes. What is decisive is the density of the briquettes, which lies between 2,200 and 2,400 kg/m3. The density of liquid aluminium is, on average, around 2.350 kg/m3, depending on the alloy. Therefore the briquettes hardly float at all, which means burn-off and oxide formation are reduced to the minimum. This is the reason why Refiners generally report a yield at least two per cent higher. Some have confirmed five to seven per cent more metal yield.
the principle of biomass briquetting and bio briquette process
Biomass briquetting is to briquette and carbonize the scattered, light, difficult to store cellulose biomass, turn it to a kind of fuel. Biomass briquetting can increase capacity and calorific value of biomass, improve combustion performance, make the bio waste become a kind of commodity energy source. This conversion technology is increasingly accepted by people around the world now.
Briquette was first developed by the British mechanical engineering research institute. Their raw material is peat. Then the technology was used to process lignite and clean coal, and was gradually developed to use for the waste in the paper mills. In the 1930s, the United States began to design the screw type briquette machine. At the same time, modern piston briquetting machines were invented and promoted in Sweden and Germany, the piston briquette with sawdust as raw materials were competitive in the market all along the time.
Wood processing plants in Western European countries and the United States have proposed the use of wood for energy self-sufficiency. Therefore, biomass compressed fuels have developed rapidly and have become an industry in countries such as Western Europe and Japan. Some countries in India and Southeast Asia also had paid considerable attention to the research and application of this technology. By 1984, 172 factories in Japan had produced biomass briquettes with a total output of 260,000 tons/year.
The loose biomass material, when subjected to a certain external pressure, will decrease the volume and increase the density. The raw material particles undergo successive stages of rearranging position, mechanical deformation and plastic rheology.
When the water content is about 10%, although it is necessary to apply a large pressure to form it, since the non-elastic or viscoelastic fiber molecules are entangled and twisted together, after removing the external pressure, it is generally impossible to restore the original shape and it becomes a firm structure briquette.
Take the lignin as an example, when the briquetting temperature reaches its softening point, plastic deformation occurs, thereby bonding the raw fibers closely together and maintaining the established shape.
When the lignin content of the raw material is low, it is necessary to add an appropriate proportion of binder, such as clay, starch, waste paper, etc., in order to make the briquette with a dense structure and fixed shape.
After adding the binder, there will be an adsorption layer on the surface of the biological particles, which will cause a gravitational force between the particles by the van der Waals force. When the external force is applied, the particles can also generate an electrostatic attraction between the particles, resulting in particles a chain structure.
For example, in the particle briquetting process, if the particles of the raw material are too large, the material must be crushed in the briquetting machine before entering the forming hole, so that the briquetting machine consumes a large amount of power.
In the briquetting process, the briquetting machine can also perform a certain crushing operation, but it is not as efficient as a crusher. So it is much important to crush the raw material in a crusher.
It is not necessary to crush all the materials when briquetting. For example, when hot briquetting is carried out using sawdust or rice husk as raw materials, foreign matter of a large size is often removed from the raw materials, and briquetting can be performed without crushing.
However, for large-scale agricultural and forestry wastes such as wood chips, bark, and plant straws, crushing operations are required. Crushing is often performed twice or more, and a drying process can be inserted in the middle of the crushing process to increase the crushing effect.
Therefore, after the biomass is crushed, a drying process is required, the optimum humidity usually is 10% to 15, and the piston type briquetting machine can be appropriately higher (16% to 20%) because the processing process is intermittent.
By the drying operation, the water content of the raw material is reduced to the extent required for briquetting. The dryers used in conjunction with the biomass briquetting machine mainly are rotary drum dryer and vertical type air flow dryer.
The main driving force of the machine is affected by the friction force and the density and diameter of the briquette. The influence of the friction is the angle (half the opening angle of the mold) and the mold temperature. The larger the angle, the greater the friction, the higher the density of the material, and the greater the total power. Therefore, the design of the angle is a key factor. It has different requirements depending on the diameter, density and material type.
For example, a screw briquetting machine, the structural size is relatively determined, and the heating temperature should be based on the structure of the machine so that the temperature is kept within a reasonable range. If the temperature is too low, the raw material is difficult to briquette, and the energy consumption will be increased. When the temperature is increased, the energy consumption of the motor is reduced, but the briquetting pressure is also reduced, so that the briquette density becomes small, which will cause crackle or even fracture. When the heating system works on this type of briquetter, the temperature is usually controlled between 150C to 300C, and the corresponding adjustments are made depending on the raw materials.
In the briquetting process, the raw material also can be used without the external heat source, on the pistion briquetting process, due to the mutual friction between the raw material and the machine parts, the raw material is also heated, and reaches a temperature of about 100 C, the lignin contained in the raw material can also be softened then and acts as a binder.
The inner diameter of the sleeve for shape retention must be slightly larger than the diameter of the smallest part of the briquetting molding, in order to eliminate the partial stress of the finished biomass briquette.
The port of the sleeve is designed to adjust the shape retention capacity. If the briquetting diameter is much smaller than the shape of the sleeve mold, the biomass will expand rapidly and cause cracks. On the contrary, if it is too small, the stress will not be eliminated, after the briquette output from the sleeve, it will suddenly crack or smash because of the sudden drop in temperature.