Briquetting Solutions

Almost 50 years later economic pressure joined forces with technological progress to give substance to Easby’s vision. The coal briquetting process as it ultimately evolved in the United States consisted of first drying the coal, then crushing and screening it; mixing the dry coal with about 6% molten asphalt binder, briquetting this mixture in roll type briquette machines and finally cooling the briquettes on a conveyor before loading them into cars or diverting them to stockpile. Over 6 million tons of coal briquettes were produced annually in the United States before the process was doomed by cheap oil and gas just after World War II.

The briquettes made by this process were used primarily for domestic heating and many attempts were made to eliminate the asphalt binder, as the smoke from the binder was the major objection to the product.

The briquetting of coal today is of more than historic interest. Coal is briquetted as an initial step in the production of activated carbon. There is growing interest in briquetting coal to reclaim stockpiles of abandoned screenings. Coal that has been crushed for conveying by pipe line or crushed for cleaning to remove sulfur and ash cannot readily be shipped without reagglomerating it to a larger size. Coal smaller than one-quarter inch cannot be used without agglomeration in some of the processes for synthetic fuels. Briquetting is used in the production of form coke and has advantages in the production of metallurgical grade coke as well.

Coal, which launched a major briquetting industry in the first half of this century, may well come full circle in the second.

Many other materials are briquetted with binders. Iron and chromite ore are briquetted with a binder consisting of lime and molasses. Fluorite also is briquetted with lime and molasses binder as well as with sodium silicate. Portland cement is used as a binder for bauxite and the lignosulfonate binders which are a residue of the paper industry are used for copper ores and for magnesite. In glass batch mixes, water and soda ash form a binder for the silica sand.

Binders are divided by their function into matrix type binders, film type and chemical binders. Some examples of each of these are listed below:

2 Component Plastics such as the epoxies

Matrix type binders embed the particles into a substantially continuous binder phase. The properties of the briquettes, therefore, are largely determined by the properties of the binder.

Film type binders are like glues and usually depend upon the evaporation of water or some solvent to develop their strength.

Solvent type binders are sometimes used, even though the material can be briquetted with pressure alone, as lower pressures can be employed and briquettes with a more porous structure can be made this way.

Chemical binders can be either film or matrix type. The chemical binders used for foundry sands are good examples of the film type binders.

Briquettes made with binders are usually pressed at low pressure. When briquettes are made without binders, however, the success of the process depends upon crushing or plastically deforming the particles to bring them closely together. It is not surprising that many crystalline organic components can be briquetted with pressure alone. The forces that bind these crystals together are neither strong nor specific, so it is necessary only to squeeze the individual crystals into close contact.

K.R. Komarek Inc. can advise or assist your company in the design of a complete briquetting or compacting system. In most all cases we can suggest or supply the important ancillary equipment related to the briquetting or compaction machine. Properly designed systems should take into account material flow, mixing, feeding, product handling and controls systems. Let the experience engineering staff at K.R. Komarek Inc help you with important design areas.

Continuous Strips
Continuous bars and strips can also be rolled from particulate materials with roll type briquette machines. If the rolls are arranged one above the other, as in a rolling mill, the strips will issue from the machine horizontally, where they can be fed into a roller hearth, or other furnace, for subsequent processing. Portland cement, sponge iron, coke, metals and alloys, sintered ores, dusts from steel making and other metallurgical processes, and many other products can be made or processed in this way. Dust losses can be reduced and thermal efficiencies can possibly be increased. No application for this technique outside the metals industry appears to be practiced commercially at this time, but with our growing concern about ecology and the conservation of energy and materials, a fresh look at established industrial processes does not seem to be amiss.

The Briquetting Machines
Roll type briquette machines apply pressures to particles by squeezing them between two rolls rotating in opposite directions. Cavities or indentations cut into the surfaces of the rolls form the briquettes.

Characteristics of Roll Type machines
In early briquette machines, the axes of the rolls were always horizontal and their centers were fixed in the frame. A simple feed box or hopper mounted above the rolls held the material to be briquetted and it flowed from there into the rolls by gravity.

Modern briquette machines usually have only one roll in a fixed position in the frame. The other roll is moveable, but is restrained by hydraulic cylinders. The rolls may be arranged horizontally or side by side in the frame, or they may be arranged vertically or one above the other as in rolling mills. The rolls additionally may be located symmetrically between the bearings or they may be mounted outside the bearings at the end of cantilevered shafts. Each of these four arrangements has certain unique properties. Other features of the machines as well can be varied to satisfy special process conditions. Six characteristics in all determine the behavior of roll type briquette machines.

Rolls
Briquette machine rolls are classified according to their construction as integral, solid or segmented. Integral rolls, as the name implies, are made integral with the shafts. These rolls usually have a band of stainless steel or some corrosion or abrasion resistant material welded to their circumference or working face. Since they have no joints or mating surfaces, integral rolls are frequently used for briquetting food or pharmaceutical products where cleanliness is of primary concern. Integral rolls can easily be steam heated or water cooled. They are not generally suitable for abrasive materials.

Solid rolls or tires are the most commonly used briquetting rolls and consist of replaceable rings keyed or shrink fitted to the shafts. The rolls are made from a variety of abrasion and corrosion resistant materials. Unlike integral rolls, which require some compromise in materials of construction, solid rolls and shafts can each be made from the most suitable material.

Segmented rolls are made in a series of sections or segments which are mechanically clamped to the shafts. The advantages of segmented rolls are obvious to anyone who has ever changed conventional rolls, so rolls of this type have been the subject of continuing investigation since the beginning of the briquetting industry. Segmented rolls are recommended for briquetting hot or abrasive materials and are made from materials suitable for such applications.

The mechanical construction of the rolls determines such important characteristics as reliability, ease of maintenance and cost of operation. The effect that the rolls will have upon materials passing through them, however, depends on their geometry.

Hydraulic System
In most briquette machines, the moveable roll is pressed against a fixed roll by hydraulic cylinders. Stops located between the bearing blocks prevent the rolls from coming in contact with each other. Material passing between the rolls attempts to spread them apart. The hydraulic cylinders resist this effort until the force exerted by the material exceeds that exerted by the cylinders. The moveable roll is then displaced and in turn displaces the pistons in the hydraulic cylinders until both efforts become equal. The oil displaced by the pistons is stored under pressure in a gas filled accumulator. It returns from there as needed to push the moveable roll back against the stops.

The hydraulic system acts like a spring. The initial force holding the rolls together can be adjusted by the pressure of the oil in the cylinders. The incremental force necessary to displace the moveable roll is also adjustable by the volume of the gas in the accumulator.

The success of the modern roll type briquette machine is due in no small part to this ability of the hydraulic system to match the slope of the force-displacement curve of the moveable roll to the requirements of the briquetting process.

Feeder
When roll type briquette machines were limited to compacting materials, which were mixed with binders, the simple gravity type feeder was usually adequate. Briquetting in this case is primarily a forming or molding process and little change in the density of the product occurs as it passes through the rolls. The pressure required for such applications is low and the virtue of simplicity frequently outweighs the advantages possible from more sophisticated control. Gravity type feeders consequently are still used for some purposes.

For dry or finely divided materials, screw or auger type feeders are commonly used. These feeders in addition to controlling the mass of material passing between the rolls, frequently have important secondary effects. They may precompress the material before it reaches the rolls. They may crush the particles to achieve a more favorable size consistency. There is speculation that the mobility of the particles in the feed screw allows the crystal axes to align themselves more favorably so as to produce better quality briquettes. Heating of the particles in the screw feeder may also have a significant effect. Whatever the mechanisms may be, briquettes of better quality frequently can be made by using a screw feeder.

Some typical shapes and sizes of briquettes and compacts that can be produced from ores, chemicals, plastics, solid fuels and metals with our two-roll machines. We will be pleased to advise you how your material can be formed into these or other shapes.

1. Chromite screenings with 2 1/4% molasses and 2% Ca(OH)2
2. Coke screenings with 8% coal tar pitch binder
3. Coal dust collector pressed with pressure alone
4. Sodium Chloride pressed with smooth rolls
5. Polyethylene scrap pressed with corrugated rolls and diced
6. Sodium Chloride pellets pressed at 100°C with pressure alone
7. Composite ore and coke briquette
8. Fluorite and lime pressed with pressure alone
9. Hematite screenings with lime-molasses binder
10. Minus 60 mesh coal pressed with pressure alone
11. Lead ore and sand with lime-molasses binder
12. Glass batch mix with 8% water
13. Magnesium oxide pressed with pressure alone
14. Chromite ore with lime-molasses binder
15. Midrex reduced pellet screenings with 1 1/2% Sodium Silicate and 1% Ca(OH)2 as binder
16. Nickel latterites with 10% water
17. Thermally de-oiled brass turnings pressed with pressure alone
18. Cast iron borings pressed at 650°C
19. Nickel metal powder with .2% acrysol binder pressed into continuous trip
20. Reduced iron screenings pressed into continuous strip with pressure alone