Slagging bottom

More recent results with fixed bed units at Westfield have demonstrated the operation of a slagging bottom instead of a grate. 

Chemically speaking, slag (bottom ash) and fly ash are composed of metal... 

HYCOL Process (16,17). The HYCOL process is similar to the Destec (Dow) process in its use of a two-stage entrained-flow gasifier. The char that the lower-temperature top stage produces recycles to the hotter (slagging) bottom stage. The key difference is that the HYCOL gasifier is dry fed, whereas the Destec gasifier is water slurry fed. 

In the early 1990s, Ohio Edison completed a four-day scrap tire test bum of cofiring whole scrap tires and pulverized coal [34, 35]. Testing was done at the Toronto Plant, located in Toronto, Ohio. This facility is a 162 MWn plant with three generating units still in service. TDF testing was done in Unit 5, a 42 MWn B W pulverized coal-fired wet slag bottom boiler. The boiler was modified to accept whole scrap tires. 

High calcium fly ash and granulated blast furnace slag are cementitious. Low calcium fly ash is termed a normal pozzolan. Condensed silica fume and rice husk ash are highly pozzolanic. Slowly cooled blast furnace slag, bottom ash, and field burnt rice husk ash are weak pozzolans. 

Reaction (13.4) is exothermic and reversible, and begins at about 700 K by Le Chatelier s Principle, more iron is produced higher up the furnace (cooler) than below (hotter). In the hotter region (around 900 K), reaction (13.5) occurs irreversibly, and the iron(II) oxide formed is reduced by the coke [reaction (13.6)] further down. The limestone forms calcium oxide which fuses with earthy material in the ore to give a slag of calcium silicate this floats on the molten iron (which falls to the bottom of the furnace) and can bo run off at intervals. The iron is run off and solidified as pigs —boat-shaped pieces about 40 cm long. 

Normally ca 50% of the coal ash is removed from the bottom of the gasifier as a quenched slag. The balance is carried overhead in the gas as droplets which are solidified when the gas is cooled with a water spray. A fluxing agent is added, if required, to the coal to lower the ash fusion temperature and increase the molten slag viscosity. 

In 1986 Britannia Refined Metals (Northfleet, U.K.) introduced technology for the treatment of Parkes cmst, a triple alloy of Ag, Zn, Pb, which by 1992 had been adopted by seven lead refineries (22). The technology consists of a three-stage process in which the silver-rich cmst is first Hquated to reduce its lead content, then placed in a sealed furnace where the 2inc is removed by vacuum distillation and, finally, the silver—lead metal is treated in a bottom blown oxygen cupel (BBOC) to produce a Htharge slag and dorn metal. 

Fig. 15. Bottom blown oxygen cupel (BBOC) in positions for (a) blowing oxygen and (b) tapping slag.

Blast furnaces are charged through the top with coke, flux (usually iron metal and siUca), and scrap while air is iajected through tuyeres continuously at the bottom just above the black copper. The coke (100 kg/1 slag) bums to maintain furnace temperatures of 1200°C, provides the reductant, and maintains an open border. A charge of 10 t/h is typical. The furnace produces a molten black copper that contains about 80% copper. The 2iac, lead, and... 

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