OCR Text |
Show Controls Adequate control instrumentation (Fig. 4) helps operate the unit efficiently, effectively and safely. To insure a reducing atmosphere in the reduction furnace, combustibles analyzers measuring CO and H2 are used. The combustibles controller modulates the amount of combustion air to the first stage to maintain the desired level of combustibles. Temperature in the reduction furnace is controlled by modulating the fuel gas supply. For exothermic wastes, water, steam or recycled flue gas may be injected into the reduction furnace to maintain a cenain operating temperature. Operating temperature in the second stage or the quench section is maintained by modulating the flow of the cooling medium (water, steam or recycled flue gas) to the quench section. An oxygen analyzer measures the oxygen content of the flue gas exiting the final stage and is used to modulate re-oxidation air flow. Temperature in the re-oxidation furnace is generally allowed to float within a range of 1800 to 2000-F. Because the rise in temperature experienced between the quench section and the re-oxidation furnace is proportional to the combustibles level in the flue gas exiting the reduction furnace, it has been used as a measure of combustibles concentration in the reduction fmnace. This eliminates the use of expensive and maintenance-prone analyzers. FUEL I~.t---... BURNER Figure 4 - Controls 6 QUENCH MEDIUM RE-OXJ AIR RE-OXIDA 11 ON FURNACE |