Flare loads

Elevated Flares See Flares for a general definition. The elevated flare, by the use of steam injection and effective tip design, operates as a smokeless combustion device. Flaring generally is of low luminosity up to about 20 % of maximum flaring load. Steam injection tends to introduce a source of noise to the operation, and a compromise between smoke elimination and noise is usually necessary. When adequately elevated (by means of a stack) this type of flare displays the best dispersion characteristics for malodorous and toxic combustion products. Visual and noise pollution often creates nuisance problems. Capital and operating costs tend to be high, and an appreciable plant area can be rendered unavailable for plant operations and equipment because of excessive radiant heat. 

General choice for total flare load, or as overcapacity flare In coniunction with multi)et flare. Generally the only acceptable flare where producu of combustion or partial combustion are toxic or malodorous. 

A trial and error estimate is made for determining the diameter of the flare header based upon the maximum relieving flare load and considering the back pressure limitation of 10 percent for conventional valves and 40 percent for balanced type valves. Note, however, a single main header in most cases turns out to be too large to be economically feasible. Line sizing procedures are discussed in detail in the next subsection. 

Example The maximum flare load of a system is 1,000,000 Ibs/hr of vapor. The pressure at the base of the flare stack is 2 psig, the average molecular weight of the vapor is 50, at a temperature of 200°F at the combined header to the flare stack. The distance from the drum to the stack is 500 ft. The line consists of two 90° welding elbows and an orifice for a flow controller. The total pressure drop at the knock-out drum is 0.5 psi. Determine the pressure at the inlet of the knock-out drum. 

Determine the stack height required to give a heat intensity of 1500 Btu/hr/ft2 at a distance of 410 ft from the base of the flare. The flare diameter is 4 ft, the flare load is 970,000 lb/hr, and the molecular weight of the vapor is 44. 

Enclosed ground flares are most commonly used as a supplement to an elevated) flare on the same relief system. The primary reason for an enclosed ground flare is to reduce the visual impact of flared gas combustion on a nearby community. They are often used when it is desirable that all or part of a flare load be disposed of in a way that causes the minimum of disturbance to the immediate locality. They offer many advantages in comparison to elevated flares there is no smoke, no visible flame, no odor, no objectionable noise, and no thermal radiation (heat shield) problems. Enclosed ground flares are typically used for normal process flow (continuous) flaring, but with recent technical advances they are now also used for emergency flaring (AIChE-CCPS, 1998). 

Less common and unusual projectiles, such as exploding bullets saboted subcaliber bullets flare loads wax, rubber, plastic, and wooden bullets frangible bullets tear gas bullets and canisters baton rounds flechette cartridges poisoned bullets multiple loads shot loads for pistols and revolvers and other special purpose projectile types, are known and are occasionally encountered in forensic casework. 

The barium light uses the BaO spectrum and the sodium lights, I and II, use the strong spectrum spreading on both sides of the NaD lines. The burning data are shown as a summarized standard in the case of flares loaded at a high pressure. The barium light produces a white flame. 

Figure 6-3. Circles of 1,500 and 3,000 Btu/hr. sq. ft. heat intensity for one 48-inch flare stack height, 200 feet flare load. 970,000 Ib./hr. molecular weight. 44.

Nomographs can be used to solve typical stack height and heat intensity problems. To find the heat intensity q in Btu per hour square foot if y is known, first obtain X from Figure 6-5. Then with the value of X and the values of the flare load (in pounds per hour) and molecular weight, read q in Figure 6-6a. 

Overpressure and thermal protection of heat exchangers Continuous monitoring of pressure and temperature on this equipment Provkion of safety interlocks in fault tolerant mode S1L3 interlock system for flare load mitigation... 

HIPS are critical safety systems, essentially replacing pressure relief and/ or flare systems. These systems are used to provide overpressure protection and/or flare load mitigation for process equipment, pipelines, wellhead flowlines, gas manifolds, or other special purpose applications. Technically HIPS is a safety instrumented function that consists of a set of components, such as sensors, logic solvers, and final control elements (e.g., valves), arranged for the purpose of taking the process to a safe state when predetermined conditions are violated. The HIPS shall operate independently and be completely separate from the basic process control system (BPCS). 

Spacing of elevated flares from process equipment or facility boundary depends on the flare stack height, flare load, and the allowable radiant heat intensity for personnel, public, and equipment. 

Vessel V-001 is protected by a PRV. To reduce the flare load, the PRV has been designed only for a fire contingency, and it is expected that block discharge will not be a design contingency for the inlet separator. 

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. 

Use for base load or partial flaring ratas if noise and visual pollution are critical. 

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 subheaders in each process area similarly will have two levels of flare headers. The line sizing of each level of subheader in an individual area will depend upon the maximum simultaneous flow in that particular area. Thus the line sizing criterion of a subheader may be the largest single flow due to a blocked outlet condition. This flow may not necessarily be the controlling load for the flare stack. 

After the total number of flare headers has been established, it may be necessary to recheck the vapor load in individual headers since introduction of a separate header may allow subtraction of the flow quantity from the low-pressure header to which it was added initially. 

As flow rate to the compressor increases, the suction pressure rises until the volume of gas at actual conditions of temperature and pressure compressed by the cylinder equals the volume required by the cylinder. A flare valve is needed to keep the suction pressure from rising too high and overpressuring the suction cylinder, creating too high a rod load or increasing the horsepower requirements beyond the capability of the driver (see Chapter 11 for further discussion). 

A speed controller does not ehminate the need for a recycle valve, flare valve, or suction throttling valve, but it will minimize their use. The recycle valve and suction throttling valve add arbitrary loads to the compressor and thus increase fuel usage. The flare valve leads to a direct waste of reservoir fluids and tlius loss of income. For this reason, engine speed control is rec-... 

In the pyrot area, paraffin is widely used in the manuf of book and wooden matches, as a protective coating to counteract possible surface deterioration of metal powders, as a lubricant and waterproofing agent for the interior surfaces of kraft paper flare and signal cases, and as a binder which tends to fill interstices between particles on press loading (Ref 7, pp 69, 71, 302 316)... 

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