Cleaner Production

The new process avoids these problems by gas-phase treatment using a fluidized bed of alumina particles (Figure 1.2). A mixture of air, ammonia, nitrogen, natural gas, pg (liquefied petroleum gas), and other gases are used as the fluidizing gas to carry out the heat treatment. The bed is heated by electricity or gas and quenching is also carried out in a fluidized bed.14

Fluidized beds have been used for some years in a variety of roles: heat exchange, gas absorption, chemical reaction, and combustion. In this case the mixture of gases produces the fluidizing

Flue gas

Flue gas

Heating medium Electric or gas

FIGURE 1.2 Fluidized bed. (From Wang, L.K. et al. Case Studies of Cleaner Production and Site Remediation, Training Manual DTT-5-4-95, United Nations Industrial Development Organization, Industrial Sectors and Environment Division, Vienna, Austria, April 1995.)

Heating medium Electric or gas

FIGURE 1.2 Fluidized bed. (From Wang, L.K. et al. Case Studies of Cleaner Production and Site Remediation, Training Manual DTT-5-4-95, United Nations Industrial Development Organization, Industrial Sectors and Environment Division, Vienna, Austria, April 1995.)

atmosphere for heat treatment of the material immersed in the fluidized bed. Hydrocarbon gases are used for carburizing, ammonia for nitriding, and nitrogen for neutral hardening. The hot exhaust gases are used for heat exchange.

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