Combustion tips are available from a number of makers. They are designed to provide smokeless flaring up to some fraction of the maximum relief capacity of the relief system. Steam injection, when available, is used to suppress smoke with required steam pressures from 75 to 150 psig. Lower pressure steam can be used if the steam piping and injectors are designed for it. High pressure (15 psig) relief gas or air can be substituted for steam in some special designs. See “Flares at Producing Sites” on page 1200-72 for a discussion of flares at producing sites where steam is rarely available.
Combustion tips with smokeless capacities up to one million pounds per hour are available. Few process plants, however, have sufficient excess steam to supply the flare during a major release; and furthermore, during a major upset, extra steam is often required by the process units.
Combustion tips are made of stainless steel in diameters up to 6 feet. The tips and the piping are flanged so that they can be removed from the flare stack. The design depends upon the supplier selected. The Company has had good experience with two designs: Flaregas and John Zink.
The Flaregas design uses a large number of special Coanda nozzles which promote thorough mixing of air and steam with the relief gas prior to burning. Steam is distributed to the nozzles by a steam chest. As the steam flows through the nozzles into the mixing chamber, it draws air along with it. Figure 1200-42 shows a flare tip with Coanda nozzles. Figure 1200-43 shows the Coanda nozzle.
The other design, John Zink, uses a number of internal pipes to distribute the steam-air mixture across the combustion zone. This design also utilizes a separate central steam injector and an outer steam ring to give three stages of smokeless combustion capacity. Each of the three injection systems has its own controls. The outer ring is very noisy and is used only in a major release where additional smokeless capacity is required with the sacrifice of noise control. Figure 1200-44 shows a flare tip with internal steam piping.
With the exception of the outer ring, both designs are equally noisy.