Prospects for Coal Briquettes as a Substitute Fuel for Wood and ...

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APPENDIX A
COAL BRIQUETTING AND CARE3ONIZATION IPROCESSES
The particul ar steps of the coal briquetting process are described
below. Depending upon the qual ities of the coal used, not all of them
are always required. Howeverr the sequence described gives a general
impression of how coal briquetting and carbonization occurs.
JXE&LKQ* Crushing fs performed to obtain a fairly uniform particle
size for 1 ater pressing. In bi nderl ess briquettl ng the particl e sizes
are 4 mm and Smaller, with 60 percent below 1 mm. In briquetting with a
binder, they are much smaller: 93 percent less than 0.88 nm and 80
percent less than 0.5 mmC61 When fines are briquetted, crushing does
not need to be performed. Sizing occurs by screening? and is performed
to remove particles too large and sometimes those that have become too
small for optimal briquetting.
Drying. The extent of drying nemssary depends on the type of coalr
whether a binder is used or not, the type of binder -If one is used, the
amount of pressure applied, whether the coal undergoes some type of
pretreatment or not, and other parameters of the process. According to
Fabuss and Tatcan* binderless briquetting requires the coal to be dried
to 12 percent to 18 percent moistiJre content. (However, one process
reported by Ellison and Stanmore, which uses a hlgh temperature for
bi nderl ess briquetting and is perhaps an anomaly, requi res a molsture
content of only 1 percent.) In contrast, briquetting with a binder
rqui res the feed coal to have a lorr moisture content of 2 to 4 percent.
It should be noted that bfnderless briquetting is often successful for
certain coal typesl particularly lignites, while briquetting with
binders works for others.
Binw. If a binder is used, it is next added to the coal particles in
either solid or liquid form. The two are mixed in a tcpugtt or mixing
mill. There are two main classes of binders: organic and inorganic,
Among the organic binders there are two subtypes: (1) tars, pitches,
and asphalts, and (2) Industrial waste and byproduct binders.Cl21 To
the first group of organlc binders belong coal tar pitch, asphalt,
petrol eum bitumen, mal tha, producer-gas tar, coke-oven tar, coal-tar
creosote and similar products. To the second type of organic binders
belong 1 ignosul fonate (a waste product f rcm paper producti on) corn
starch, wheat starch, vegetable pulpr and rosin. Among the inorganic
bi nders are sodi um si1 lcateJ 1 ime, niagnesi a (magnesi urn oxide) dol orniter
cl ayJ brine, and cement.
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