Reset this site with frames
|
|
THE FLARE SYSTEMPRESSURES |
|
|
In any pressurized system, a flow will try to proceed from the high pressure toward the low pressure. Thus, because of the buildup of pressure associated with operating excess, the gases in the plant will flow naturally into the flare system if a clear passage into the header is available. This is assured by opening a valve on the relevant tank or vessel and allowing the outflow of the unwanted gases. In normal service, some valves are opened by the plant operators and others open automatically when the pressure inside the vessel goes beyond a safe or pre-defined limit. In the flowing condition, the pressure measured in the header reduces continuously from the vessel to the outlet of the flare and is self adjusting, being always just enough to push the amount of gas provided out through the flare. This self-adjusting aspect of the pressure causes it to be known as "back-pressure" because the pressure "backs-up" against the flow. The size of the flare and the flare header are carefully selected by the design engineer to ensure that the pipes are large enough to allow the maximum possible flow without causing a serious restriction and thus ensure that the greatest possible "back-pressure" is never greater than the lowest required pressure downstream of any relief valve which will still permit a full design flow condition. The use of the available pressure to drive the flow avoids any need to use mechanical devices such as pumps or blowers to move the gas. Mechanical means to boost pressure are used only in a few specific circumstances where there is no naturally occurring pressure to move the gas. Use of available pressure also permits the flare system to function safely even in the event of a power failure or loss of some similar utility which would represent a complication if a mechanical blower were used. More on pressure drops |
|