Flare capacity

The most difficult task is to estimate the optimum design capacity of the flare. It is easy 

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

Flare capacity must always be available for emergency releases that may occur... 

A large-scale flare test facility (see Figure 28.1) will be used as an example to illustrate the concepts discussed in this chapter [37,38]. A significant maximum flaring capacity allows many flares to be tested at full-scale (see Figure 28.2). 

Examples of such problems include limitations on flare capacity or protection against exothermic reactions. Any decision to use instrument based systems rather than more traditional approaches such as relief valves will need to be supported by sound reasons that will stand up to regulatory authority challenge. 

Product quality specification Contractual agreements Capacity and availability Concurrent operations Monitoring and control Testing metering Standardisation Flaring and venting Waste disposal Utilities systems... 

Safety Systems. Major expenditures here include the flare system (the flare structures and large lines extending throughout the plant) and the iirevvater system (high-capacity pumps and extensive piping). Safety systems, fortunately, are usually given particular attention. At this study phase, the main thrust should be to check the completeness of licensor equipment lists for cost estimation purposes. 

Compounds considered carcinogenic that may be present in air emissions include benzene, butadiene, 1,2-dichloroethane, and vinyl chloride. A typical naphtha cracker at a petrochemical complex may release annually about 2,500 metric tons of alkenes, such as propylenes and ethylene, in producing 500,000 metric tons of ethylene. Boilers, process heaters, flares, and other process equipment (which in some cases may include catalyst regenerators) are responsible for the emission of PM (particulate matter), carbon monoxide, nitrogen oxides (200 tpy), based on 500,000 tpy of ethylene capacity, and sulfur oxides (600 tpy). 

In applying this rule, the capacity of the pressure relief system must also be sized to handle the quantity of fluid released at this pressure (together with other expected loads during this contingency), so that the built-up back pressure will not result in exceeding 1.5 times the design pressure. This additional load need not, however, be considered in calculations of flare and PR valve radiant heat levels. 

Restriction Orifice - In general a restriction orifice should not be used as a means of limiting the capacity of a pressurization path. In special cases, where large incentives apply (such as reducing die size of a flare system), a restriction orifice may be used, provided that all the following conditions are satisfied ... 

Normally an overcapacity line to an elevated flare is provided to handle the excess flow when the flaring rate exceeds the capacity of the multijet flare. The overcapacity flare is usually not equipped with steam injection, and smoke formation is accepted during infrequent operations. The overcapacity line and flare is designed to handle the entire maximum flow so that it can spare the multijet flare when the latter is shut down for maintenance. 

A butterfly valve in the line to the first stage seal drum limits the maximum flow to the first stage burner. The valve is set by observing the burners while flaring at design capacity. Once adjusted, the valve should be locked in position. 

V = Flare design capacity, m /h (for a flare system, actual and standard cubic meters are virtually equivalent). 

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 high-temperature system, a separate subheader may be run up to the point where the temperature drops down to the allowable limit of a less expensive material. It may then be connected to the main flare header (either low pressure or high pressure).To properly evaluate this a heat loss calculation is needed. As a rule of thumb a heat loss of 10 BTU/hr/ft may be assumed for a quick estimate for bare pipe. Consideration should also be given to the need for expansion joints. Main flare headers may be as large as 36 to 42 inches in diameter for a large-capacity plant. Expansion joints of such magnitudes may be so expensive as to call for a separate small header for the hot flare system. 

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... 

For non-smokeless flares (no steam injection) about 30% higher capacity can be allowed [59]. Therefore, the diameter of a non-smokeless flare stack is approximately (0.85) (diameter of the smokeless flare stack). 

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)... 

Increasing the wet gas compressor capacity and increasing duties through the gas plant can impact the flare system. 

Effects of performance changes, 201-203 Head curve for single pump, 198 Relations between head, horsepower, capacity and speed, 200 Temperature rise 207-209 Viscosity corrections, 203-207 Purging, flare stack systems, 535 Reciprocating pumps, 215—219 Flow patterns, 219 Specification form, 219 Relief areas, 437 External fires, 451, 453 Sizing, 434, 436... 

Test results ( , ) for several candidate materiaIs (Table III) are reported which span the range of energetic capacity. Those values which exceed the threshold are highly susoect and have been known to result in serious fires in the past. Mix No. 1, (M49A1, Trip Flare Mixture) is a "safe" mixture that is insensitive to electrical spark, impact, and friction. It does not have a fast bum rate on the Vee Block tester and it has a low pressure-rate-of-rise. 

A primary reason for use of an open field ground (matrix) flare is to reduce the visual impact of flared gas combustion in the manner of an enclosed ground flare. The open field ground (matrix) flare, however, has a significantly larger capacity than could be practically handled in a fumacelike structure, and the visual shielding is provided by tall fencing located some distance away from the burners themselves so that the fence encloses a small field. ... 

In sizing depressuring valves, it should be assumed that heater burners are shut-off, reboilers are shutdown, and normal flow in the vessel has ceased. Vapor depressuring valves should be designed such that the initial, instantaneous depressuring flow rates do not exceed the capacity of the closed pressure relief system and the flare. 

Relief/flare system. Investment may be reduced in relief drums by using a high-pressure and a low-pressure relief system instead of a single low-pressure relief system. Investment may also be lowered by designing relief drums by analysis of liquid dump capacity, and not by the droplet size criteria of API S21. 

The local annual production of Azerbaijan amounted to 4.5-6 bcm over the recent years. Because of limitations of the existing offshore pipelines capacity, more than half of the current gas production is reportedly flared or vented. The country s total demand is secured by imports of Russian natural gas (4-6 bcmp.a.). 

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