SPECIALIST EQUIPMENT
SAFER SMELTING Manfred Rösch states the case for environmentally friendly taphole clay
n any discontinuous or batch pyro- metallurgic smelting process there is a requirement to close and open the taphole to tap the molten metal and slag out of the furnace. Te closing of the taphole is done by pushing a taphole clay (THC) into the taphole until after the molten metal and slag has stopped running out. Te objectives for the THC are: plugging the taphole safely until the next opening cycle to stop any unplanned metal tapping, which can result in a catastrophic furnace runout; easy opening of the taphole on the beginning of the taping cycle; and to maintain and possibly improve the integrity of the refractory structure of the taphole. Tese objectives should be met at the lowest cost possible and with the least environmental and health risk impact. Tere are various requirements and challenges for THC to meet the objectives. A dual-binder system is necessary to ensure strength in the THC as the temperature in the taphole varies considerably. Positive expansion is also needed, to ensure good adhesion and grip between the THC and the refractory. Other challenges include the elimination of toxic substances in the THC, and to prevent low temperature bonding of the THC to avoid mud-gun blockage. Finally, the THC itself needs to boast a reasonable shelf-life and, naturally, be the lowest price possible.
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THE PROBLEM For a long period of time conventional THCs consisted of anhydrous tar that acted as a binder. Although effective, tar has two main problems concerning the environment and health. Te first is that it releases volatile organic compounds (VOCs) into the atmosphere. Tese VOCs play a significant role in the creation of tropospheric (ground level) ozone and fine particulates, this in turn can also contribute to photochemical smog. Ground-level ozone gas has been shown to create a considerble amount of problems, which
Manufacturing taphole clay extrusion
can include chest pain, coughing, throat irritation and congestion. It can worsen bronchitis, emphysema, and asthma. Ground-level ozone can also reduce lung function and inflame the linings of the lungs. Repeated exposure may permanently scar lung tissue. Te same can be said for photochemical smog, which not only reduces visibility on days when atmospheric conditions are suitable, but also can irritate eyes and affect the respiratory system. Te other main problem with using tar in THC is that it contains benzo [a]
pyrene, which is a polycyclic aromatic hydrocarbon; this binds to DNA resulting in mutations and eventually cancer. It is therefore listed as a Group 1 (agent is carcinogenic to humans) carcinogen by IARC (International agency for research on cancer). Other research has also shown that benzo [a] pyrene exposure effects memory and learning in rats, as well as has an effect on the number of white blood cells, inhibiting some of them from differentiating into macrophages, the
Furnace: opening of taphole
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