Dual pressure flare

A smokeless burner apparatus for single structure flare systems which is capable of simultaneously burning emergency dumped gases from high and low pressure sources with minimal energy requirements for the low pressure gas combustion.

BACKGROUND OF THE INVENTION 
It is well known in the art that flaring of low pressure hydrocarbon gases 
having a molecular weight ratio of hydrogen to carbon less than 0.30 tends 
to produce smoke as a result of incomplete combustion and the formation of 
free carbon. The release of free carbon to the atmosphere creates a dark 
smoke plume which is unsightly and a matter of poor ecological practice. 
Of the various means devised for coping with said smoke generation, two 
methods have gained primary attention. The first method involves the 
introduction of a smoke suppressant, typically steam or water, to the 
combustion zone. The water, in vapor phase, reacts with the hydrocarbon by 
familiar and well-known endothermal reactions. The second method relates 
to the use of air-powered flares which provide turbulent mixing of air 
with the hydrocarbon gas for complete smokeless combustion. 
The flaring of high pressure hydrocarbon gases is different, however, and 
does not require additional energy as the relatively high pressure of the 
gas, upon release, provides sufficient kinetic energy for the system to 
operate smokelessly. Since the flaring of low pressure gas requires 
additional energy to be imparted to the system, and, whereas the flaring 
of high pressure gas does not require additional energy, separate flare 
systems are normally used for the different pressure waste gases, because 
lower pressure gas obviously cannot be vented to relief lines carrying gas 
at a higher pressure. This results in high capital and maintenance costs, 
the disadvantages of which are apparent. 
SUMMARY OF THE INVENTION 
The present invention contemplates a flaring means particularly designed to 
overcome the aforementioned disadvantages, and it is a primary object of 
this invention to provide a means for single flare structure smokeless 
flaring of smoke-prone combustible waste gases which are emergency dumped 
by separate relief lines from sources of high and low pressure gas. 
It is a further object of this invention to provide a single relief line 
flaring system to a single flare for operations where high pressure and 
low pressure venting does not occur simultaneously. 
It is a further object of this invention to achieve economy in the 
simultaneous flaring of both high and low pressure gases in a single flare 
structure by use of the energy of the high pressure gas to provide the 
required turbulent air and gas mixture for complete combustion for the 
high-pressure gases as discharged for burning. 
These and other objects are realized by the incorporation of high pressure 
and low pressure burner apparatus in a single flaring structure. If the 
process being relieved does not require the simultaneous venting of high 
and low pressure gases, the dual pressure burner apparatus may be served 
by a single relief line. The economy achieved by using a single relief 
line instead of separate relief lines for the high and low pressure gas 
sources is readily apparent. A pressure control means is attached to the 
relief line to sense pressure and permit gas flow to the high pressure 
burner apparatus above predetermined pressures. 
If simultaneous venting of high and low pressure gases is required by 
process conditions, it has been discovered that both gases may be flared 
simultaneously in the same stack without interference with the stable and 
smokeless operation of the flare. Furthermore, while the flaring of the 
low pressure gas requires fan or blower supplied air, the simultaneous 
combustion of low and high pressure gas minimizes the additional energy 
requirements due to the aspiration or air induction created by the 
discharge of the high pressure gas.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings in detail and in particular to FIG. 1, reference 
character 10 generally indicates a dual pressure burner apparatus 
concentrically located within air duct 12, which is normally the flare 
stack proper. As will become apparent later, the flare stack serves as a 
conduit for forced or induced air circulation to the low pressure gas 
discharge apertures. Spider hub 14 is comprised of a housing having a 
chamber therein for receiving low pressure gas from below (not shown) and 
having a plurality of spaced apertures through said housing in open 
communication with the chamber. Hollow spider arms 16 are affixed to said 
housing in open communication with the chamber and extend radially from 
the housing. Each spider arm is closed at the outer end and has a 
plurality of spaced apertures 18 laterally disposed along both sides 
thereof to direct the low pressure gas towards air space 24. A high 
pressure gas supply housing 20, providing a second chamber and having a 
plurality of outlets through said housing in open communication with the 
chamber is disposed circumferentially around spider hub 14, beneath spider 
arms 16. Hollow supply ducts 22 are secured to the high pressure housing 
in open communication with the housing outlets and with burner tips 26. 
High pressure gas enters the chamber provided by housing 20 from below 
(not shown) and passes through the chamber to burner tips 26 via supply 
ducts 22. As shown in FIG. 1, the burner tips 24 are disposed between 
pairs of adjacent spider arms 16 at a common radial distance from the 
center of the spider hub. A second arrangement is shown in FIG. 2 wherein 
the burner tips 26 are located at separate radial distance. FIG. 3 
discloses a third arrangement wherein a portion of the high pressure gas 
supply ducts 22 extend through the walls of the flare stack to serve high 
pressure burner tips outside the walls thereof as well as burner tips 
located inside the flare stack walls. 
FIG. 4 shows a cross section of FIG. 3 taken along section A--A thereof. As 
indicated in said figure, high pressure gas is admitted to the high 
pressure gas supply housing 20 through line 30, and low pressure gas is 
supplied to the spider hub by line 32. The spaced apertures in the low 
pressure gas housing previously mentioned are indicated herein generally 
by reference figure 36. An inlet 38 is provided for the introduction of 
water or steam to the stack beneath the burners for further smoke 
suppression if needed. During the simultaneous combustion of high and low 
pressure gas, air is aspirated as inducted through the inside of the flare 
stack 34 towards the top thereof, thus aiding the supplying of air for the 
low pressure gas. 
FIG. 5 represents the invention as contemplated for use in a single relief 
line flare system. As previously noted, a single relief line 40 can serve 
only those processes which do not require simultaneous venting of high and 
low pressure gas. Valve 42 is pressure controlled to open whenever the 
pressure of the relief line exceeds a predetermined pressure, thus 
admitting gas to the high pressure gas supply housing as well as the low 
pressure housing. Blower 44 provides air for the smokeless burning of the 
low pressure gas. 
While the invention has been described with a certain degree of 
particularity, it is manifest that many changes may be made in the details 
of construction and the arrangement of components. It is understood that 
the invention is not to be limited to the specific embodiments set forth 
herein by way of exemplifying the invention, but the invention is to be 
limited only by the scope of the attached claim or claims, including the 
full range of equivalency to which each element or step thereof is 
entitled.