Feedstocks and Briquette Production

It is possible to add material to aid combustion of briquettes, such as waxes, sodium nitrate, and so on, during manufacture to give a more acceptable product. Also clay as a binder, silica, and so on can be mixed with the fines to reduce the cost of the briquette. This lowers the calorific value and is merely a form of adnlteration for which the nser pays, thongh claims may be made that burning is improved. 

Lower grades of coal may also be carbonized for nse in charcoal. Crashed coal is first dried and then heated to abont 590°C (1100°F) to drive off the volatile components. After being air-cooled, it is stored nntil needed. 

Charcoal and minor ingredients such as the starch binder are fed in the proper proportions into a paddle mixer, where they are thoroughly blended. At this point, the material has abont a 35% moistnre content, giving it a consistency somewhat like damp topsoil. 

The blended material is dropped into a press consisting of two opposing rollers containing briquette-sized indentations. Because of the moisture content, the binding agent, the temperatnre (about 40°C or 105°F), and the pressure from the rollers, the briquettes hold their shape as they drop out the bottom of the press. 

The briquettes drop onto a conveyor, which carries them through a single-pass dryer that heats them to about 135°C (275°F) for 3-4 h, reducing their moistnre content to aronnd 5%. Briqnettes can be produced at a rate of 2,200-20,000 lb (1-9 metric tons) per hour. The briquettes are either bagged immediately or stored in silos to await the next schednled packaging rnn. 

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