Flares location

Elevated Flare Location, Spacing and Height - Ijocation, spacing and height of elevated flares are a function of permissible radiant heat densities, possible burning liquid fall-out, and pollution considerations. Design requirements are as follows ... 

Flare location and height must be such as to meet all applicable standards of noise level and atmospheric pollution by combustion products. 

During typical plant design, the flare location has to be carefully examined. All wind velocities and directions should be considered in the design. Some experts suggest that flares should be located downwind while others propose they should be upwind of the facility. This is based on the assumption that a flare may overflow with liquids or un-ignited gas may occur and therefore the flare should be downwind so these materials would not disperse on the facility, while vice versa, an upwind location would allow gases to travel downwind onto the plant and be ignited in the process. 

Flare noise (roar of combustion) is the most serious because it is elevated and the sound carries. The flare can be located at a remote distance from the operating unit or surrounding community. Noise of steam injection into the burner can be reduced by using multiple no22les. Furnace noise from air intake, fuel systems, and combustion blower forced draft/induced draft (FD/ID) fans can be reduced by acoustics. The plot plan should be evaluated for noise generation and to find the means of alleviating or moving noise to a less sensitive area. 

Flow Nozzles A simple form of flow nozzle is shown in Fig. 10-17. It consists essentially of a short cylinder with a flared approach section. The approach cross section is preferably elliptical in shape but may be conical. Recommended contours for long-radius flow nozzles are given in ASME PTC, op. cit., p. 13. In general, the length of the straight portion of the throat is about one-h f throat diameter, the upstream pressure tap is located about one pipe diameter from the nozzle inlet face, and the downstream pressure tap about one-half pipe diameter from the inlet face. For subsonic flow, the pressures at points 2 and 3 will be practically identical. If a conical inlet is preferred, the inlet and throat geometry specified for a Herschel-type venturi meter can be used, omitting the expansion section. 

In offsite locations, thermal expansion PR valves may discharge to a flare header upstream of a knockout drum, if available, or to the equipment (e.g., a tank) on the opposite side of one of the blocking-in valves, or to the atmosphere. Atmospheric discharges must be at grade level in a safe location... 

Routing of Flare Header through Process Areas - Flare headers in process areas should be routed to avoid locations of particularly high fire risk, such as over pumps, near furnaces, etc. The headers and subheaders should also be laid out and provided with isolating CSO valves and spectacle blinds, unless prohibited by local codes, such that it is not necessary for flare lines to remain in service in units which are shut down separately. Blowdown and water disengaging drums should be spaced from process areas. 

The vapor outlet may be discharged either to the atmosphere or to a flare. Atmospheric discharge may be considered, provided that a safe location can be achieved, as defined by the following ... 

In this section we shall discuss flare spacing, location and height. Spacing, location and height of flares are determined by consideration of the following factors ... 

Flares should be located to limit the maximum ground level, heat density to 1.6 kW/m at any property line. The minimum distance from the base of the flare stack to the property line should be 60 m. 

Recommended nominal steam rates at 60 m/s exit velocity for a typical flare tip are shown in Figure 2. At lower velocities, higher steam ratios are required. Typical steam control consists of a flow ratio controller with adjustable ratio set point, related to flare gas flow. The ratio adjustment, located in the control house, provides for the higher steam ratios necessary at low flaring rates. 

In the consideration of elevated flare pilots and igniters, proprietary flare tips are normally provided with the manufacturer s recommended igniter and pilot system. Usually, one to four pilots are used depending on the flare tip type and diameter. The forced air supply type of igniter system (described below) is normally preferred. Controls should be located at a distance from the base of the... 

Pilots and Igniters - Duplicate continuous gas pilots are required at each side of the flare, corresponding to the split burner grid layout. Selection of pilot and igniter systems follows the guidelines described below, and the controls should be located 15 m to 30 m from the windbreaker. 

Pilots and Igniters - Two gas-fired pilots with igniters are installed adjacent to the inlet distributor. The igniter assembly and pilot gas valves must be located remote from the flare for protection of personnel and equipment. This restricts igniter selection to the forced air supply type. Location of these components should be such that the calculated radiant heat density at maximum load does not exceed permissible levels for personnel exposure. Because of the potential hazard of release of unignited hydrocarbons at ground level, a flame scanner (suitably shielded and aircooled and cotmected to an alarm in the control house), is provided for each pilot. 

The drum is usually equipped with steam injection if required for winterizing or cold releases. Refer to Figure 7 for some of the details. If winterizing is necessary, then the steam should be temperature-controlled in order to maintain the seal water temperature at 4 to 10 C. It is important to note that the drum should be located at a minimum safe distance from the flare. 

Maximum value of K at design flare release at any location where personnel have access e.g., at grade below the flare, or on a service platform on a nearby tower. Exposure must be limited to a few (approx, six) seconds, sufficient for escape only. On towers or other elevated strucmres, ladders must be provided on the side away from the flare, so that the tower or strucmre can provide some degree of shielding. 

If provided, thermocouples shall be protected by inconel sheathing and shall terminate in a steel or cast iron juntion box located four (4) feet above grade at the base of the flare stack. 

Relieving vapors from various pressure-relief and depressuring valves in the system must be collected in individual flare headers that should be appropriately located near each process area. Subheaders must be interconnected to a main flare header which feeds to a knock- out drum and disposal system. Condensates that are carried over by vapors are separated in the knock-out drum. The vapors that exit the vessel go to the flare stack where they are burned. 

The equivalent length of the main flare header is then calculated from the flare stack to the last safety valve, taking into consideration the straight length of the pipe and approximate equivalent lengths for bends, etc. If the achial location of the flare stack is not known by that time, it maybe assumed to be 500 ft from the last piece of equipment. Later on, even if it varies from 500 ft, it will not affect the pressure drop calculation at all compared with the entire length of the pipe. 

Often, the blowdown valve is routed to a closed flare system, which services other relief valves in the facility to ensure drat all the gas is vented or flared at a safe location. In such instances, a separate manual blow -down valve piped directly to atmosphere, with nothing else lied in, is also needed. After the compressor is shut down and safely blown down through the flare system, the normal blowdown valve must be closed to block any gas that may enter the flare system from other relief valves. The manual blowdown valve to atmosphere protects the operators from small leaks into the compressor during maintenance operations. 

Diffusion Flame. Wlien the fuel and oxidizer are initially unmixed and then mix in a thin region where the flame is located, the flame is called a diffusion flame (Figure 2). The word diffusion is used to describe the flame because the fuel and oxidizer are mixed on the molecular level by the random thermal motion of the molecules. An example of a diffusion flame is a candle flame or flares at an oil refinei y. 

Other energy sector concerns are methane emissions from unburned fuel, and from natural gas leaks at various stages of natural gas production, transmission and distribution. The curtailment of venting and flaring stranded gas (remotely located natural gas sources that are not economical to produce liquefied natural gas or methanol), and more efficient use of natural gas have significantly reduced atmospheric release. But growth in natural gas production and consumption may reverse this trend. Methane has... 

Prevailing wind locate hazardous vents, burning flares, waste burning pits, waste settling ponds down-wind of plant proper. 

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