Introduction Refinery flares are special burners used to destroy unavoidable emissions of hydrocarbon and other combustible gases. It is necessary to burn such gases in order to (a) prevent deleterious effects on people@ animals. and plants as discussed in Chapters 2@ 7@ 10@ 14@ and 16 and (b) comply with federal@ state@ and municipal regulations as covered in Chapter 3. The methods available to prevent such emissions or to recover them before they escape are described in Chapters 7@ 14@ and 16. While these processes can be very efficient@ there are always small residual emissions which must be destroyed. In most cases the gases can be burned in a flare. but some gases may require the special incinerators discussed in Chapters 14 and 16. In addition to these small emissions@ the refinery flare must be capable of handling very large releases of hydrocarbons which exceed the capacity of the system for control and recovery. Such releases can occur in emergencies resulting from the failure of equipment or from fires. Basically a flare system consists of piping to collect the gases@ devices to remove entrained liquid@ and a terminal burner operating in the open with no provision to recover heat or to treat the combustion products. A typical refinery flare system is illustrated in Figure 15-1. The system consists of the following elements: I. Flare header from the process units 2. Knockout drums to remove and store condensable and entrained liquids 3. Proprietary seal. drum. or purge gas to prevent flashback 4. Flare stack to raise the burner to the desired height 5. Gas pilots and an igniter 6. Steam injection for smokeless flaring. Several types of flares are available. but all must operate safely and efficiently under widely varying con- 15-1 ditions. The flow of waste gas can range from almost zero@ when the only discharges are leakages from relief valves. to very large quantities in emergencies. Further@ the required capacity of the flare varies with (a) the crude throughout@ (b) the complexity of refining@ and (c) the capacity of the recovery system. Klooster [1]* provides the values in Table 15-1 for the maximum flaring rates from typical process units in a 250@000 barrel per day refinery. This table compares the maximum predicted rates from a minimum cost flaring system with those from a system designed for maximum recovery and minimum flare loss. It is difficult to design a single flare to handle efficiently such extreme variations in flow@ so many systems have two flares. One flare is designed to provide smokeless combustion for the normal flow@ the other is activated to handle excess flow resulting from an emergency. There also may be flares designed to serve single specialized units. * See reference list at end of text.
API PUBL 931 C15-1977 history
1977API PUBL 931 C15-1977 MANUAL ON DISPOSAL OF REFINERY WASTES VOLUME ON ATMOSPHERIC EMISSIONS CHAPTER 15-FLARES