Many binders have been proposed and used to
produce hard coal briquettes. A review of binders published in 1969 by Waters3
is shown in Appendix 1. The properties required of a binder are:
(a) Produces a strong briquette.
(b) Produces a waterproof briquette.
(c) Does not detract from the quality of
the coal.
(d) Does not interfere with the use of the
coal.
(e) Is environmentally acceptable.
(f) Is economically viable.
The binders enjoying most success in the
production of hard coal briquettes have been:
Pitch
Bitumen
Lignosulphonates
Molasses
Starch
Pitch is highly carcinogenic and has
largely been replaced by Bitumen.
Lignosulphonate, although at one time
extensively used, is being replaced by Molasses as a result of environmental
concern.
Molasses is modified for use as a binder by
the addition of either lime or Phosphoric Acid.
Starch, Molasses and Lignosulphonates must
be treated at 200 to 300 degrees centigrade to develop the required strength
and weather resistance.
All of the binders are expensive and are
difficult to justify economically for use in South Africa.
Newly developed resin binders are showing
promise. These are cold curing binders, often supplied in two parts, which when
mixed together set chemically to form a strong weatherproof briquette.
Anthracite briquettes are being made in this manner in the U.K. and sold under
the name of Thermac. The cold curing binder is supplied by Du Pont and is a
by-product from their nylon plant at Wilton, Middlesborough.
Almost all binders used commercially
require that the total moisture of the feed is reduced to in the order of 10%
in order to produce an acceptable briquette.
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