US3829275A

US3829275A - Smokeless gas flare

Info

Publication number: US3829275A
Application number: US00192453A
Authority: US
Inventors: J Stranahan; J Hollier; H Deloney
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1971-10-26
Filing date: 1971-10-26
Publication date: 1974-08-13
Anticipated expiration: 1991-08-13
Also published as: JPS5127496B2; CA974872A; DE2252166A1; BE790605A; GB1405147A; JPS4851337A

Abstract

A method and at least one steam aspirating gas flare for carrying out the method are disclosed for smokeless burning of undesired gas. The flare includes a steam control valve responsive to a new very low gas flow detector utilizing a knockout drum water seal, a by-pass line with an orifice run, and a water level switch for supplying an empirically set fixed flow of steam to the flare for ensuring a smokeless flame prior to the gas flow rate reaching a measurable rate. A full range flare including all other gas flows includes also several steam flow valves, each valve being empirically set to provide the proper steam-to-gas ratios throughout its respective range responsive to several corresponding gas flow detectors for ensuring a smokeless flare as the flare gas flow varies from the immeasurable ranges through the measurable ranges of the detectors.

Description

United States Patent 1 Stranahan et al.

[111 3,829,275 Aug. 13, 1974 SMOKELESS GAS FLARE [75] Inventors: John J. Stranahan, Port Arthur;

John C. L. Hollier, Nederland; Huch C. Deloney, Houston, all of Tex.

Primary Examiner-William F. ODea Assistant ExaminerWilliam C. Anderson Attorney, Agent, or Firm-T. H. Whaley; C. G. Ries [5 7] ABSTRACT A method and at least one steam aspirating gas flare for carrying out the method are disclosed for smokeless buming of undesired gas.

The flare includes a steam control valve responsive to a new very low gas flow detector utilizing a knockout drum water seal, a by-pass line with an orifice run, and a water level switch for supplying an empirically set fixed flow of steam to the flare for ensuring a smokeless flame prior to the gas flow rate reaching a measurable rate. A full range flare. including all other gas flows includes also several steam flow valves, each valve being empirically set to provide the proper steam-to-gas ratios throughout its respective range responsive to several corresponding gas flow detectors for ensuring a smokeless flare as the flare gas flow varies from the immeasurable ranges through the measurable ranges of the detectors.

3 Claims, 2 Drawing Figures PATENTS) SHEET 2 BF 2 SMOKELESS GAS FLARE BACKGROUND OF THE INVENTION The government requires the burning of all excess gases being admitted to the atmosphere. The collection of these gases is normally put into a flare line which is equipped with a pilot light to ensure the burning of all gases.

Recent regulations require that this burning be smokeless in order to reduce air pollution.

Because of the wide range of gas flow going to a given flare (from miminum to maximum) the velocity of gas flow in the gas line is so low at times that the conventional differential flow measuring meters are not adequate to cover the full range.

Since the present method for making flares smokeless is by the use of steam for asiprating or pumping air to aid in getting the proper air-to-gas ratio for burning the gas, it is most economical to use only the necessary amount of steam to accomplish this, which means it is thus most desirable to have equipment that measures gas flow and controls steam flow at the exact precise rate to prevent smoking.

OBJECTS OF THE INVENTION A primary object of this invention is to provide a method for burning unwanted gas at all operating ranges without polluting the air with smoke.

Another primary object of this invention is to provide at least one mechanism for carrying out the disclosed method for smokeless burning of gas.

A further object of this invention is to provide a smokeless flare that operates with gases having a flow rate well below that rate that can be measured by the conventional gas flow rate pitot venturi detector.

A still further object of this invention is to provide a smokeless flare that operates over all design ranges of gas flow.

Still another object of this invention is to maintain a flare smokeless with a minimum amount of steam usage. 7

Another object of this invention is to provide a smokeless flare that is easy to operate, is of simple configuration, and is economical to form and assemble.

Other objects and various advantages of the disclosed smokeless flare will be apparent from the following detailed description together with the accompanying drawings, submitted for purposes of illustration only, and not intended to define the scope of the invention, reference being had for that purpose to the subjoined claims.

The drawings diagrammatically illustrate by way of example, not by way of limitation, a smokeless flare.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a smokeless flare with parts in section; and FIG. 2 is a schematic enlarged view of a modified very low gas flow rate detection system.

METHOD OF MAINTAINING A GAS FLARE SMOKELESS The invention comprises a method for maintaining a gas flare smokeless when the gas flow is less than that which the conventional flow meter can measure. The method comprises (1) to detect gas that is flowing at the very low rate, and (2) admitting a constant empirically determined amount of steam to the flare for ensuring a smokeless flame at all very low rates below a predetermined measurable rate prior to the gas rate reaching a rate greater than the predetermined measurable rate. The second method added to the above method for maintaining an all range flare smokeless including when the gas flow is sufficient enough to be easily measured incorporates the added steps (3) to detect one of three gas flow rate ranges, low, intermediate, and high which the gas is in, (4) empirically setting each of three steam flow controllers, one for each flow rate range to provide a smokeless flame over its gas flow rate range, and (5 admitting steam to the flare responsive to the corresponding steam flow controllers for providing a smokeless flare additionally over the DESCRIPTION OF THE FIRST EMBODIMENT The invention disclosed herein, the scope of which being defined in the appended claims is not limited in its application to details of construction and arrangement of parts shown and described, since the invention is capable of other embodiments and of being practiced or carried out in various other ways. Also it is to be understood that the phraseology or terminology em ployed herein is for the purpose of description and not of limitation.

FIG. 1 discloses a steam aspirating gas flare 10 designed for maintaining a smokeless flame. The flare control system comprises two portions, one portion for very low gas flow rates in which the rate is too low for accurate measuring and a second portion for all other varying flow rates.

VERY LOW GAS RATE FLARE CONTROL 7 PORTION The very low gas flow rate portion of the flare 10, FIG. 1, comprises a very low flow rate detection system 13 and a steam control system 14 for providing an empirically set amount of steam to the flare for all gas flows that are so low as to be detectable but immeasurable.

The very low flow rate detection system 13 comprises a water seal or knockout drum 15, a main gas line 16, to the drum, a bypass line 17 including a flow element 19 therein to the drum, and a gas flow transmitter 20. Flow element 19 may be an orifice plate, flow nozzle, etc. Knockout drum l5 prevents flame back-travel in main gas line 16.

All gas flows to the knockout drum 15 through the two

parallel lines

16 and 17,

outlets

21 and 22 of the respective lines being submerged beneath the surface 23 of the water 24 in the drum. In actual use, while the main line 16 may be a 24 inch diameter pipe, the bypass line 17 may be only a 6 inch pipe. With the bypass line outlet extending below the surface about 8 inches, for example, the bottom of the main line outlet is submerged at least another 8 inches deeper in the water than the bypass line outlet. The result is that gas flows through the bypass line instead of the main line when pressure in the line is greater than 8 inches of water but less than 16 inches of water, causing a differential pressure across flow element 19 which is measured and transmitted by gas flow transmitter 20. This very low flow rate is not detectable nor measurable by the conventional pitot venturi detector 25. Transmitter 20 then signals the steam controller 31 for injecting the empirically set amount of aspirating steam to the flare, which aspiration maintains the proper air-to-gas ratio for ensuring a smokeless flame.

More specifically the flow element 19 detects the very low flow through the bypass line 17, and gas flow transmitter 20 emits a signal which actuates a pressure switch 26 for energizing timer 27. The flow transmitter 20 preferably of the differential type flow rate meter has an output air pressure proportional to the gas flow in the bypass lineThis air pressure range, for example, may be 3 psi to 15 psi which represents to 100 percent flow of gas. Solenoid valve 28 is openedby timer 27 for supplying a fixed air pressure to a high pressure selector relay 29.

In order to prevent the system from injecting steam spasmodically at low gas flow rates, the timer maintains the steam flow rate up for a set period of time, such as 1.5 minutes after the gas flow stops.

High pressure selector relay 29, in response to the fixed air pressure from solenoid valve 28 and which air pressure is higher than the pressure reading from a square root extractor 30 transmits a signal to reset a steam flow controller 31 at an empirical value which controls the steam flow. This metered amount of steam will keep the flare smokeless over the very low flow range as determined by the limits set in flow transmitter 20. This flow control system comprises a cascade type steam flow controller 31, flow transmitter 32, very low steam flow control valve 34, and a flow element 33, such as but not limited to a flow meter with an orifice type flow element.

The empirically determined steam rate for this very low gas flow rate detected by flow element 19 is that which is found to keep the flare smokeless at the upper limit of gas flow in this very low flow range. This steamto-gas ratio may be set between 1 to 0.1 and 1 to 10, depending on the particular gas, I to 1 being the most common approximate ratio utilized.

Thus, for very low gas flow unmeasurable by conventional instruments, the very low gas flow rate detection system 13 provides a predetermined, measured, and fixed flow rate of steam to the flare for maintaining a smokeless flame.

PREFERRED VERY LOW GAS RATE FLARE CONTROL PORTION The preferred very low flow rate detection system 13a, FIG. 2, comprises a knockout drum 15a at the end of a main gas line 16a and a by-pass line 17a, the latter having an orifice run 18a, and the knockout drum having a liquid level switch 11 for activating the timer 27, FIG. 1, for opening the steam very low flow control valve 34.

More particularly, switch 11, FIG. 2, is a conventional liquid level switch having liquid inlets 12a and 12b at depths of 8 inches and [8 inches, respectively, for example, in the main line 16a. Thus any depth of water level between 8 inches and 18 inches in pipe 160 caused by the main line pressure is at least detected, and, if possible measured and at the preferred predetermined depth as a depth of 8 inches for example, the liquid level switch 11 is activated for transmitting an electric signal over a suitable electrical connection 11a to the timer 27,.FIG. l, for actuation of the very low flow control valve. Accordingly, a very low gas flow is detected and a predetermined, measured, and fixed flow rate of steam is supplied to the flare 10 for maintaining a smokeless flame. While liquid switch upper inlet 12a is positioned in the main supply line 16a, lower inlet 12b may be positioned in any suitable under water location in the knockout drum 15a below the level of inlet 12a. While the details are not illustrated in FIG. 2, the knockout drum 15a, like knockout drum 15, FIG. 1, is connected to the conventional pitot venturi detector 25 (not shown) similar to how knockout drum 15, FIG. 1, is connected.

VARYING GAS FLOW RATE SMOKELESS FLARE PORTION The other portion of the flare control system provides the proper amount of steam flow to the flare 10, F IG. 1, to ensure a smokeless flame by utilizing two additional steam

flow control valves

35 and 36 in combination with valve 34.

There is not a constant steam-to-gas ratio that will provide a smokeless flame over the full measurable operating range of flare gas flow. Thus, variable steam control valve 34 is controlled by steam controller 31 to provide a smokeless flame or smokeless flare over the low range of gas that can be detected by low range flow transmitter 39 over and above the empirically set amount required by the very low gas flow rate detection system 13 described above.

In operation, when the gas flow from main line 16 becomes great enough to expel! the 8 or 10 inch difference of water from knockout drum 15 of FIG. 1 or of FIG. 2, respectively, this higher and measurable gas flow to and through gas flow rate detector 25 is perceived and a low range meter as the differential pressure transmitter 39 responsive to the detector sends a signal to open the steam flow valve Wider, as via pneumatic lines, for example.

First on the pneumatic line from the low range differential pressure transmitter 39 is ratio relay 40 which multiplies its input signal by a number, as between .5 and 1.7, for example, actuating square root extractor 30 for transmitting a signal to high pressure selector relay 29 greater than the very low pressure indicating signal from solenoid valve 28. Relay 29 then transmits a signal to open steam flow control valve 34 even wider.

Steam flow controller 31 controls steam flow control valve 34 in response to pitot detector 25 as it responds to gas flow to theflare in order to provide the proper steam-to-gas mixture ratio in the flare to ensure a smokeless flare.

Likewise, intermediate range differential pressure transmitter 41, responsive to gas flow rate detector 25 transmits all medium or intermediate gas flow rate signals to its steam control valve 35 via its intermediate range high limit relay 42, steam flow controller 37, steam flow meter 43, and flow element 44.

Also, high range steam flow control valve 36 controls the proper amount of steam to the flare to ensure smokeless burning of the various gas flows through the gas flow detector 25 in the high range as transmitted by the high range differential pressure transmitter 45. This control system comprises a high limit relay 46, a cascade type flow controller 38, flow transmitter 47, high flow control valve 36, and a flow element 48.

Each of the low, intermediate, and high range

differential pressure transmitters

39, 41, and 45 varies the amount of stream in its respective range to insure smokeless burning while there is overlap at the extremities of each range to ensure continuous and uninterrupted flow control.

This system also provides a higher proportion of steam-to-gas to the aspirating gas flare at the low gas flow velocities than at the higher gas flow velocities. The square root extractor 30 increases the relative steam flow at low gas flow rates.

Accordingly a reliable and efficient steam control system resultsfor measuring, metering, and supplying the proper amount of steam to the flare for maintaining the proper air-to-gas ratio and resultant smokeless flare in all ranges of gas flow from the immeasurable, but detectable, flow to the maximum flow.

In practice, while no method is provided herefor differentiating between high and low molecular weight hydrocarbons, a steam rate of about .35 pounds of steam per pound of hydrocarbon is the minimum to allow for the heaviest hydrocarbons.

Accordingly, through the three steam control valves responsive to the three ranges of gas flow as detected by the gas flow rate detector, the proper proportion of steam-to-gas is maintained and a smokeless flare results through all ranges of flare gas flow in the measurable ranges.

STEAM CONTROL SYSTEM By the use of the above described steam systems in conjunction with the gas metering components disclosed above, all of the steam or the total steam is ratioed to all gas or the total gas in the low, intermediate, and high ranges with a minimum of instrumentation.

This feature of the invention amounts to a parallel arrangement of the valves in the main steam supply line 50 for supplying steam to steam aspirating gas flare 10. Valve 36 is on the main steam supply line 24, valve 35 is on a bypass line 24a around valve 36, and valve 34 is on a bypass line 24b around valve 35.

Each of the valves has a steam controller and a flow meter in addition to the orifice runs. Steam flow controller 31, flow meter 32, and flow element 33 control the steam flow through control valve 34 over and above the empirical setting for very low immeasurable gas flow rates for control in the low range of measurable gas flow. Steam flow controller 37, flow meter 43, and flow element 44 control the steam flow through control valve 35 for the intermediate range of gas flow. Steam flow controller 38, flow meter 47, and flow element 48 control the steam flow through control valve 36 for the high range of gas flow. A heat-up by-pass line 49 may be utilized for permitting a small constant flow of steam to flow for maintaining the steam pipes at operating temperatures and conditions.

Thus, it will be seen that the instant gas flare for covering the full operating ranges of gas flow provides a smokeless flame in a manner which meets each of the objects set forth above While a method and two portions of a gas flare for carrying out the method of the invention have been disclosed in the accompanying specification and drawing, it will be evident that various other methods and modifications are possible in the arrangement and construction of the disclosed smokeless flare without departing from the scope of the invention, and it is accordingly desired to comprehend within the purview of this invention such methods and modifications as may be considered to fall within the scope of the appended claims.

We claim:

1. A gas flare having means for mixing steam with gas for maintaining the gas flare smokeless over a wide range of gas flow rates of a first range of very low and immeasurable flow rate, a second range of low flow rate, a third intermediate range, and a fourth high range comprising,

a. first means for electrically detecting a gas flow in said first range of a very low and immeasurable flow rate,

b. second means for detecting a gas flow in said second range having an empirical setting for said second range,

'c. third means for detecting a gas flow in said third range having an empirical setting for said third range,

d. fourth means for detecting a gas flow in said fourth range having an empirical setting for said fourth range,

e. means responsive to said first electrically detecting means for controlling the steam-to-gas flow ratio to a fixed empirically determined steam flow rate to ensure a smokeless flame throughout said first range,

f. means responsive to said second detecting means for controlling the steam-to-gas flow ratio to a value that provides a smokeless flame throughout said second range,

g. means responsive to said third detecting means for controlling the steam-to-gas flow ratio to a value that provides a smokeless flame in said third range, and

h. means responsive to said fourth detecting means for controlling the steam-to-gas flow ratio to a value that provides a smokeless flame in said fourth range.

2. A smokeless gas flare utilizing aspirating steam for mixing air with gas for burning over varying flow rate ranges of very low and immeasurable range, low range, intermediate range, and high range of gas flow comprisa. means for electronically detecting gas in said very low and immeasurable gas flow rate range,

b. means for detecting gas in said low gas flow rate range,

c. means for detecting gas in said intermediate gas flow rate range,

d. means for detecting gas in said high gas flow rate range,

e. means for controlling aspirating steam flow to said gas flare for each of said ranges,

f. said aspirating steam flow control means for said very low gas flow rate range being means for providing a fixed empirically determined steam flow rate to said flare, and

g. each of said steam flow controlling means being responsive to its respective detecting means for its range for maintaining a smokeless flame in the flare as the gas flow rate varies between the very low immeasurable, low, intermediate, and high ranges.

3. A control system for supplying steam in precise amounts to a steam aspirating gas flare for maintaining a smokeless flame comprising,

a. a main steam supply line for being connected to said aspirating gas flare,

b. a first flow element for detecting flow rates in a high range and a first flow control valve in said main steam supply line,

c. a first by-pass line with a second flow element for detecting flow rates in an intermediate range and a second flow control valve therein connected to said main line around said first control valve,

d. a second by-pass line having a third flow element for detecting flow rates in a low range and a third flow control valve connected in said second bypass line around said second flow control valve,

e. a third flow element in said second by-pass line,

f. a very low and immeasurable flare gas flow rate electrical detection means connected to both said third flow element and said third flow control g. said third flow control valve being responsive to said very low and immeasurable flare gas flow ratevalve,

electrical detection means for passing a fixed empirically determined amount of steam to the aspirating gas flare for maintaining a smokeless flame,

h. said third flow control valve being responsive to said third flow element for varying the steam flow in said low range of flow rates,

. said second flow control valve being responsive to said second flow element for varying the steam flow in said intermediate range of low rates, and

j. said first flow control valve being responsive to said smokeless flame.

Claims

1. A gas flare having means for mixing steam with gas for maintaining the gas flare smokeless over a wide range of gas flow rates of a first range of very low and immeasurable flow rate, a second range of low flow rate, a third intermediate range, and a fourth high range comprising, a. first means for electrically detecting a gas flow in said first range of a very low and immeasurable flow rate, b. second means for detecting a gas flow in said second range having an empirical setting for said second range, c. third means for detecting a gas flow in said third range having an empirical setting for said third range, d. fourth means for detecting a gas flow in said fourth range having an empirical setting for said fourth range, e. means responsive to said first electrically detecting means for controlling the steam-to-gas flow ratio to a fixed empirically determined steam flow rate to ensure a smokeless flame throughout said first range, f. means responsive to said second detecting means for controlling the steam-to-gas flow ratio to a value that provides a smokeless flame throughout said second range, g. means responsive to said third detecting means for controlling the steam-to-gas flow ratio to a value that provides a smokeless flame in said third range, and h. means responsive to said fourth detecting means for controlling the steam-to-gas flow ratio to a value that provides a smokeless flame in said fourth range.

2. A smokeless gas flare utilizing aspirating steam for mixing air with gas for burning over varying flow rate ranges of very low and immeasurable range, low range, intermediate range, and high range of gas flow comprising, a. means for electroNically detecting gas in said very low and immeasurable gas flow rate range, b. means for detecting gas in said low gas flow rate range, c. means for detecting gas in said intermediate gas flow rate range, d. means for detecting gas in said high gas flow rate range, e. means for controlling aspirating steam flow to said gas flare for each of said ranges, f. said aspirating steam flow control means for said very low gas flow rate range being means for providing a fixed empirically determined steam flow rate to said flare, and g. each of said steam flow controlling means being responsive to its respective detecting means for its range for maintaining a smokeless flame in the flare as the gas flow rate varies between the very low immeasurable, low, intermediate, and high ranges.

3. A control system for supplying steam in precise amounts to a steam aspirating gas flare for maintaining a smokeless flame comprising, a. a main steam supply line for being connected to said aspirating gas flare, b. a first flow element for detecting flow rates in a high range and a first flow control valve in said main steam supply line, c. a first by-pass line with a second flow element for detecting flow rates in an intermediate range and a second flow control valve therein connected to said main line around said first control valve, d. a second by-pass line having a third flow element for detecting flow rates in a low range and a third flow control valve connected in said second by-pass line around said second flow control valve, e. a third flow element in said second by-pass line, f. a very low and immeasurable flare gas flow rate electrical detection means connected to both said third flow element and said third flow control valve, g. said third flow control valve being responsive to said very low and immeasurable flare gas flow rate electrical detection means for passing a fixed empirically determined amount of steam to the aspirating gas flare for maintaining a smokeless flame, h. said third flow control valve being responsive to said third flow element for varying the steam flow in said low range of flow rates, i. said second flow control valve being responsive to said second flow element for varying the steam flow in said intermediate range of low rates, and j. said first flow control valve being responsive to said first flow element for varying the steam flow in said high range of flow rates through said main steam supply line for providing a very precise and accurate steam flow control system for maintaining a smokeless flame.