Partial pre-mix flare burner and method

Abstract

A flare burner that is particularly suitable for use in connection with ground flares and other types of flares in which it is important to control the height of the flame envelope created by the burner is provided. The flare burner includes a pre-mix zone including a pre-mix chamber into which air is entrained. A uniform mixture of fuel and air is formed in the pre-mix zone and caused to exit an air / fuel outlet in the top of the pre-mix chamber. In one embodiment, the amount of air in the fuel / air mixture that exits the air / fuel outlet is in excess of the stoichiometric amount of air required to support combustion of the fuel in the mixture. Fuel is injected around the perimeter of the air / fuel outlet, combustion is initiated and a flame envelope is created. By injecting a mixture of fuel and air that includes excess air into the center of the flame envelope, combustion of the central portion of the flame envelope is accelerated which allows more fuel to be flared with a given flame envelope height. The invention also includes a ground flare and a method of flaring fuel with a flare burner.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to flare apparatus and methods of flaring flammable waste gases and diverted fuel stock. In one embodiment, the invention relates to ground flare burners, ground flares and associated methods.[0002]Flare apparatus and methods are utilized to burn and dispose flammable waste gases and diverted fuel stock in a variety of applications. For example, flares are typically located at production facilities, refineries, processing plants and the like for disposing of flammable waste gases that are dumped and / or fuel stock streams that are diverted during venting, shut-downs, upsets or emergencies. The flaring of flammable waste gases and diverted fuel stock (hereinafter referred to as “fuel”) without producing smoke is usually desirable or even mandatory. Smokeless flaring is accomplished by assuring that non-oxidized soot does not form in a sufficient quantity to leave the flame. This is accomplished by assuring that a sufficien...

AI Technical Summary

Benefits of technology

[0010]In accordance with the invention, a flare burner is provided that is capable of combusting a high volume of fuel with a relatively short flame envelope. The decrease in the length of the flame envelope leads to many advantages. For example, the height of the surrounding enclosure of a ground flare can be decreased or the volume of the fuel that can be flared with an existing enclosure height can be increased.

[0014]The main fuel outlet is located in a position with respect to the top of the pre-mix chamber such that fuel can be injected from the main fuel outlet around the perimeter of the air / fuel outlet of the pre-mix chamber. In one embodiment, the main fuel outlet is spaced outwardly from the pre-mix chamber to provide a space between the exterior surface of the sidewall of the pre-mix chamber and the main fuel outlet. As discussed further below, this space allows fresh air to be entrained from below the burner to a point adjacent to the fuel ports disposed on an inner portion of the main fuel outlet. The enhanced mixing created by such entrainment can be important in certain applications, such as when heavy hydrocarbons or unsaturated fuels are being flared.

[0019]In order to enhance the entrainment of air caused by injecting fuel through the supplemental fuel inlet into the pre-mix zone, the interior surface of the pre-mix chamber can include a section that is a Coanda surface. The supplemental fuel inlet is located in a position with respect to the pre-mix chamber such that fuel can be injected from the supplemental fuel inlet onto the Coanda surface. The fuel tends to adhere to and follow the path of the Coanda surface and form into a relatively thin film which causes more air to be entrained into the pre-mix chamber and better mixing of the air with the fuel to occur in the pre-mix chamber.

[0020]The pre-mix chamber can have a length to inside hydraulic diameter ratio in the range of from about 0.25:1 to about 4:1. A unit with a pre-mix chamber having a length to inside hydraulic diameter ratio greater than 4:1 would function with an added benefit but would generally be cost prohibitive. In one embodiment, the pre-mix chamber has a length to inside hydraulic diameter ratio in the range of from about 1:1 to about 3:1. In another embodiment, the pre-mix chamber has a length to inside hydraulic diameter ratio of about 1:1 or less. A relatively short length of the pre-mix chamber can be advantageous in ground flare and other flare applications in which the length (or height) of the burner is important, or in applications in which highly reactive fuels might lead to internal burning. Also, in some configurations the fuel is injected from the supplemental fuel inlet under conditions (for example, a plurality of small jets; high pressure) that allow a uniform mixture of air and fuel to be achieved even when the pre-mix chamber has a very low length to inside hydraulic diameter ratio.

[0024]The amount of fuel introduced into the pre-mix zone is preferably in the range of from about 5% to about 50% of the total amount of fuel to be flared by the flare burner. Due to the injection of a pre-mixed fuel stream into a central portion of the flame envelope in accordance with the inventive method, the flame envelope includes combustion at its center as well as its outer surface. The resulting toroidal flame creates additional mixing and turbulence which results in more uniform and faster combustion of the flame envelope. As a result, the height of the flame envelope can be decreased or the volume of fuel that can be flared with a given flame envelope can be increased. Other advantages are achieved by the inventive flare burner and method as well.

[0025]It is, therefore, a general object of the present invention to provide a flare burner and associated method by which a high volume of fuel can be combusted in a relatively short and uniform flame envelope.

Problems solved by technology

On the other hand, such flares need to have the capacity to combust a large volume of fuel at any given time.

As a result, the enclosure can be costly to erect and maintain.

Unfortunately, due to the interaction of the individual fuel jets, the dense core of fuel formed at the center of the flame envelope makes it difficult to increase the flow rate of the fuel to support a larger capacity without causing the length of the flame envelope to increase and / or smoke to occur.

An increase in the length of the flame envelope often requires the enclosure surrounding the ground flare to be higher which can significantly increase the cost of the enclosure.

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