How it Started
In 1848 a Patent was granted to William Easby for a METHOD OF CONVERTING FINE COAL INTO SOLID LUMPS. In his application Easby made only one claim, "The formation of small particles of any variety of coal into solid lumps by pressure". In an equally brief description of the process he mentions, "The utility and advantage of the discovery are that by this process an article of small value and almost worthless can be converted into a valuable article of fuel for steamers, forges, culinary and other purposes thus saving what is now lost."
Easby in his few words had patented the entire coal briquetting industry and had as well stated the rationale for its existence.
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.
Briquetting with Binders
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.
Briquetting without 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.
Complete System Design