increased temperature. Similar to carbon electrodes, production of graphite last
about 2 weeks; however, in order to meet standard, peak temperature is monitored
and controlled to improve its physical and electrical properties. After this, the
finished graphite is unpacked and air-cooled at room temperature and some of its
properties, like density, are improved by impregnating with coal tar pitch or petroleum oil. Though, this may equally be done before the production of graphite.
Handling and machinability, particularly, with conventional woodworking or metalworking tools, are also improved by quenching the impregnated graphite with
water.
Required quantities of calcined carbon filler, binders, and additives are weighed
and mixed together in a heated mixer, which turns the mixture to a “green” aggregate
with time. This aggregate is the compressed mold or extrude and may be air-cooled
or water quenched to solid form. The solidified green aggregate is often packed in
sand, coke granules, or charcoal where it is held to distribute heat uniformly, absorb
excess far or pitch binder, and prevent possible oxidation of the mixture during the
early stage of baking process. The baking process is carried out in a furnace, which
may be gas or oil fired, at a temperature of about 1000
C; however, the process
continues for week after the furnace temperature has been reduced to 400
C. The
baked carbon products are collected and processed further through cleaning, shaping, and surface grinding with diamond wheel to give a good finishing.
Wastewater Characterization
Generally, water generated in the production plants for carbon and graphite can be
categorized as contact water, used predominantly in the post-extrusion quench, postimpregnation quench, machining, and scrubbing. Water is used for cooling, dust
control, and wet grinding in the carbon electrode plants, while it is used for
wet-scrubbing in the graphite production plant. Depending on the size of the
manufacturing plant of this subcategory, water use in some verified plants ranges,
approximately, from 302,000 to 2,650,000 L/day and is mainly employed as contact
water for scrubbing. Major pollutants generated in this subcategory can be classified
as classical pollutants (suspended solids, oil and grease, etc) and toxic pollutants
(metals, inorganics, organics, and pesticides). In the study of wastewater characterization of plant 36173 used in the carbon and graphite manufacturing subcategory,
Table 4.6 presents wastewater characterization in the plant.
Elsewhere [6] the results of the quantification of wastewater generated in the
extrusion quench, impregnation quench, machining, and scrubbing streams are given
in Table 4.7. Some pollutants that were not detected in the wastewater streams are
equally listed in Table 4.8.
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O. S. Amuda et al.
about 2 weeks; however, in order to meet standard, peak temperature is monitored
and controlled to improve its physical and electrical properties. After this, the
finished graphite is unpacked and air-cooled at room temperature and some of its
properties, like density, are improved by impregnating with coal tar pitch or petroleum oil. Though, this may equally be done before the production of graphite.
Handling and machinability, particularly, with conventional woodworking or metalworking tools, are also improved by quenching the impregnated graphite with
water.
Required quantities of calcined carbon filler, binders, and additives are weighed
and mixed together in a heated mixer, which turns the mixture to a “green” aggregate
with time. This aggregate is the compressed mold or extrude and may be air-cooled
or water quenched to solid form. The solidified green aggregate is often packed in
sand, coke granules, or charcoal where it is held to distribute heat uniformly, absorb
excess far or pitch binder, and prevent possible oxidation of the mixture during the
early stage of baking process. The baking process is carried out in a furnace, which
may be gas or oil fired, at a temperature of about 1000
C; however, the process
continues for week after the furnace temperature has been reduced to 400
C. The
baked carbon products are collected and processed further through cleaning, shaping, and surface grinding with diamond wheel to give a good finishing.
Wastewater Characterization
Generally, water generated in the production plants for carbon and graphite can be
categorized as contact water, used predominantly in the post-extrusion quench, postimpregnation quench, machining, and scrubbing. Water is used for cooling, dust
control, and wet grinding in the carbon electrode plants, while it is used for
wet-scrubbing in the graphite production plant. Depending on the size of the
manufacturing plant of this subcategory, water use in some verified plants ranges,
approximately, from 302,000 to 2,650,000 L/day and is mainly employed as contact
water for scrubbing. Major pollutants generated in this subcategory can be classified
as classical pollutants (suspended solids, oil and grease, etc) and toxic pollutants
(metals, inorganics, organics, and pesticides). In the study of wastewater characterization of plant 36173 used in the carbon and graphite manufacturing subcategory,
Table 4.6 presents wastewater characterization in the plant.
Elsewhere [6] the results of the quantification of wastewater generated in the
extrusion quench, impregnation quench, machining, and scrubbing streams are given
in Table 4.7. Some pollutants that were not detected in the wastewater streams are
equally listed in Table 4.8.
122
O. S. Amuda et al.