Enclosed ground flares conceal the flame and provide smokeless operation without steam injection. By eliminating steam, one source of noise is completely removed. Combustion noise is also reduced by using many small burners and many small individual flames. The combustor is lined with an acoustically absorbent high-temperature ceramics to reduce the combustion noise. The combustion air inlet is acoustically shrouded and baffled to reduce noise outside the unit. The main disadvantages of ground flares are the larger ground area required and high initial cost. However, they provide the best overall control of noise and combustion problems and offer best solution for performance and reliability.
A refinery may have both elevated and ground flares (Figure 10-6). In this case, safe disposal of a normal load is achieved by knocking down the heavy ends and condensables in the flare knockout drum and burning the gases in an elevated stack. A controlled amount of steam is used to ensure smokeless burning. A water seal is used to prevent flame flashback.
In emergency loads, the high rate of gas flowing through the common header causes the flow to be partly diverted to a ground flare and, after passing through a ground flare water seal, are burned off in the ground flare.
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