The furnace is designed to operate with a normal top pressure of 2.5bar. When a slip or channel occurs on the furnace, the gas pressure may rise considerably above this value and may exceed the design maximum pressure for the system which is 3.0 bar. Furthermore, a pulse of higher pressure gas will enter the low pressure system and could affect the operation of the gasholder and the flare stack.
To prevent the development of high gas pressure that could lead to further danger or plant damage, the furnace is equipped with three bleeders to vent off gas in the event of an emergency. This results in a short term release of blast furnace gas to atmosphere accompanied by noise and a small release of particulate matter to atmosphere and environment.
The bleeders taken together have sufficient capacity to vent all gas arising from the furnace operating at full production. In practice, the bleeders are set to open in sequence around a rising pressure to minimise the release of gas to atmosphere and at the same time continue the supply of some gas into the work’s gas system.
Procedure
When operating with a top pressure of 2.5 bar, the bleeder trip set point on the bleeder nominated to open first should be set to 2.65 bar (i.e. 0.15bar above top pressure). The other bleeders should be set to open 2.7 bar (0.2bar above top pressure) and 2.75bar (0.25 bar above top pressure)
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