US2891607A - Flare stack steam control - Google Patents

Description

June 23, 1959, A. J. WEBSTER ET AL I 2,391,607

FLARE STACK STEAM CONTROL Filed Dec. 10, 1956 Ii I l, WW"

N G N INVENTORS ROBERT c. HUMPHREY ANTONE J. WEB TER MM ATTORNEYS United States Patent FLARE STACK STEAM CONTROL Antone J. Webster, Novato, and Robert C. Humphrey, Richmond, Calih, assignors, by mesne assignments, to California Research Corporation, San Francisco, Calif., a corporation of Delaware Application December 10, 1956, Serial No. 627,487

3 Claims. (Cl. 158-99) This invention relates to the disposal of variable quantities of waste gas such as are produced from petroleum refining operations, by burning the gas in such a manner as to make the least amount of smoke and objectionable odors and, specifically, refers to the control of steam to such a stack to facilitate the burning of such gas, particularly at low flow rates.

It is an object of this invention to provide means for disposing of waste gas in a manner consistent with the greatest safety and also to admit a controlled quantity of steam to the combustion zone.

A further object is to provide an improved apparatus for disposing of waste gas by burning, by means of which a controlled quantity of steam is admitted to the combustion zone at low gas flow rates and means are provided for admitting larger quantities of gas without aflecting the steam admission to the combustion zone.

These and other objects will be apparent from the following description and the attached drawing, which illustrates a preferred embodiment of the invention.

The drawing is a vertical and part sectional view of a flare stack illustrating an example of this invention as applied to disposal of waste gas from a petroleum processing plant.

In the drawing, reference number 10 designates a generally cylindrical chamber, from the top of which a vertical stack 11 projects upwardly to terminate at 12 in what may be designated a combustion zone. Chamber 10 is partly filled with water 13, the level of which is maintained substantially constant by means of an inverted siphon 14, and is indicated by a liquid level device 15. Desirably, a continuous supply of fuel gas is admitted to chamber 10 above the water level by means of a conduit 16. This provides a continued source of fuel for a flame at combustion zone 12, which may be initiated and main tained by the usual pilot flare or igniter (not shown).

Waste gas from a number of individual sources, for example, petroleum refining or processing units, is conveyed to an accumulator 17 by means of conduits 18, 19, and 20. Liquids which may be carried into accumulator 17 are removed as required through drain conduit 21, as their presence is shown by a liquid level indicator 22.

In this example, two conduits lead from the upper portion or gas space of accumulator 17 to the Water-sealed chamber 10. One of these, designated 23, is desirably the larger in diameter and projects inwardly and downwardly in chamber 10 to terminate at a desired distance or submergenee A below the level of the water therein. The second conduit similarly projects into chamber 10, but terminates at a smaller distance B below the water level. Intermediate the length of conduit 24 is a flow-responsive means, which, in this example, comprises an orifice plate 25, pressure connections 26 and 27, and a differential pressure-responsive controller 28. This means is connected by line 29 to control throttle valve 30 in steam line 31, the purpose of which will next be discussed.

It has been found that, with a flare stack of this type,

in which air is not admitted to the rich combustible gas until it reaches the combustion zone 12, there is a tendency for a variable and smoky flame to persist at low gas rates. If steam is admitted to this flame under such circumstances, it will be more rapidly and efliciently mixed with atmospheric air and will burn without objectionable smoke and obnoxious odors. Desirably, this mixing is obtained by means of a circular steam ring 32 surrounding zone 12 at the top of stack 11. Steam is admitted to supply line 31 from any suitable source, and its flow rate to ring 32 is controlled by throttle valve 30. By the use of this arrangement, the rate of flow of gas through conduit 24 from accumulator 17 to the chamber 10 is adapted to control the rate of steam flow to the combustion zone and, hence, obtain the desired objective. When only the pilot flare at zone 12 is in operation, the steam supply is shut ofl entirely. As the gas flow through conduit 24 increases, the flow-responsive controller 28 acts correspondingly to open the steam valve 30 up to the maximum flow rate for which conduit 24 is designed.

At low gas flow rates from accumulator 17, the higher submergence A of the outlet of conduit 23 in the water 13 of chamber 10 will prevent any gas flow through that conduit. Under these conditions, only the back pressure due to the smaller submergence B of conduit 24 will be imposed upon accumulator 17 and all of the flow from that accumulator will take place through conduit 24. If the gas flow into accumulator 17 through conduits 18, 19, and 20 becomes greater than can be handled by small conduit 24, the seal A of conduit 23 will be broken by the increased pressure in accumulator 17 and the excess gas will pass through that conduit. Thus, there are provided two passages for gas from accumulator 17 to cham ber 10, the one through conduit 24 at low gas flow rates, and the two conduits 23 and 24 in parallel at larger flow rates.

As stated above, it is usually necessary to control the ratio of steam to gas flow to combustion zone 12 only at the lower gas flow rates, so that the lack of steam control at the higher rates is immaterial.

In conclusion, it will be appreciated that this invention relates to the control of steam to a flare stack for the disposal of waste gases, particularly at low flow rates of such gases when the introduction of steam will improve the combustion characteristics, to prevent smoke and objectionable odors. Although a single example is given, it is apparent that numerous changes could be made without departing from the essential features of the invention, and all such changes and modifications that come within the scope of the appended claims are intended to be embraced thereby.

We claim:

1. A waste gas burner, comprising a vertical stack having a steam injector at its top to promote smokeless combustion of said gas, a steam supply conduit for said injector, a water seal chamber communicating with the bot tom of said stack, an accumulator for waste gases, a plurality of gas inlet conduits connecting said accumulator to said chamber, each having a separate outlet for admitting waste gas to said chamber at different levels below the surface of water therein so that those conduit outlets having the greater submergence will be sealed by water in said chamber to prevent gas flow through their respective conduits into said chamber whenever the gas inlet pressure in said conduits is insufiicient to displace the water from their outlets, flow-responsive means in that gas conduit having the least submergence, and flow control means in said steam supply conduit responsive to said gas flow-responsive means to vary the steam flow in accordance with variations in gas flow rates in said lastnamed gas conduit, said last-named conduit being ar- 3 ranged td"disch'arg'e'varying amounts of gas under inlet pressures less than those" required to admit gas to said chamber through any of the'other of said conduits.

2. A waste gas burner according to claim 1, with the additi'oii'oftneans for controlling the water level in said sealehamber' to maintain the subme'rgence of said condu'its substantially constant;

31 A waste gas burner according to claim 1, in which said flow-responsive means comprises means for causing a differential 'pressure'tha'ti's a fuliction'of gas fiowin'said conduit, and means responsive to said differential pressure for actuating said steam flow control means.

References Cited in the file of this patent UNITED STAT-ESPATENTS

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