Flare capacity requirements

They are effective as a means of reducing flare capacity requirements. 

Air Flow - The capacity of a multijet flare to induce air flow must be calculated, to make sure that it is adequate to meet the maximum air flow requirement for smokeless combustion. (W, of Equation 4 below must be > W, of Equation 5). The term air flow capacity refers to the primary air flow rate which will be induced around each jet, and may be estimated from the following equation ... 

The value of W calculated from the gas composition or from Equation 5 should be considered to be a minimum requirement. A multijet flare should be designed with a calculated air capacity as high as possible, as limited by practical limitations of economics and geometry. 

For a flare stack to function properly and to handle the capacity that may be required, the flows under emergency conditions from each of the potential sources must be carefully evaluated. These include, but may not be limited to, pressure relief valves and rupture disks, process blowdown for startup, shutdown, upset conditions, and plant... 

W = required vapor capacity in pounds per hour, or any flow rate in pounds per hour, vapor relief rate to flare stack, Ibs/hr W(. = charge weight of explosive, lb Wj. = effective charge weight, pounds of TNT for estimating surface burst effects in free air W, = required steam capacity flow or rate in pounds per hour, or other flow rate, Ib/hr Whe = hydrocarbon to be flared, Ibs/hr Wtnt equivalent charge weight of TNT, lb Wl = liquid flow rate, gal per min (gpm)... 

At the John Zink Company (Tulsa, OK), various flare designs are tested comprehensively to determine performance parameters such as flame stability, flame length, smokeless capacity, purge rate required, blower horsepower, or steam requirements for assisted flares, tip longevity, radiation, and noise. All relevant data are recorded for each test in a single record. The data acquisition system consists of three computers (see Figure 28.9) ... 

Steam-assisted flares are similar to air-assisted flares in that additional air is entrained into the flare to increase the smokeless capacity [54]. In steam-assisted flares, sfeam is used to entrain air into the flare, in addition to the ambient air surrounding the flare that is entrained into the flame. Figure 28.25 shows a series of photos of a steam-assisted flare as the steam flow goes from zero to the required flow rate for smokeless operahon. 

A facility s flare relief system analysis is required to ensure that relief capacity from the revamp project does not exceed the existing relief system design capacity. Proper checks need to be performed at substation facilities for installing switch gears, variable speed drives (VSDs) and other OSBL systems. If not properly evaluated, OSBL system limitations can escalate revamp project cost to such an extent that the whole project may become unattractive. A 20-30% escalation in the project cost is not uncommon if existing OSBLs are not properly evaluated in conceptual design. 

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