Flare Stack Diffuser Tips.
In the oil and gas industry there are conditions that require the venting or combustion of waste gases from the production process. Combustion of the waste gases is done through devices called flare stacks. These flare stacks are elevated pipes standing vertically in the air to combust the waste gas at an elevation that is safe for toxic gas dispersion of unburnt gases and high enough that the flare does not ignite ground-level flammable items or present a high risk to the personnel operating the facilities. The conditions in which flare stacks operate are very harsh and challenging. Temperatures may range from extreme cold to extreme heat in a very short time. Flaring at the flare tip may cause materials to deteriorate due to the presence of high temperatures, hydrogen sulphide, windy, wet and/or oily conditions. Inefficient flare tips can cause issues such as increased carbon footprints, increased smoke production and incomplete combustion of waste gases. Flare stacks have to provide reliable ignition, cross-lighting and flame stability to ensure complete combustion of waste gases at both high and low flow rates.
Radial slot air assisted flare stack tips utilize high velocity air which mixes with the diffused waste gas stream to support complete combustion. A problem with existing designs is maintaining ignition of all the individual slots at flows less than the maximum design case. When these low flows are combined with a crosswind the individual slots on the upwind side can be snuffed out by the wind and will fail to reignite allowing the release of unburnt gas. A cause of this ignition failure can be a wall of air wedged between gas streams being released by the radial slots. In some cases, modifications of the radial systems such as the addition of a ring burner and flame retention tabs are required to compensate for this deficiency.
Radial slot style tips may release air in a wedge shape that lowers the amount of air being supplied to the core while at the same time the gas is becoming more concentrated as you move towards the center of the flare. The radial slot style tips also generally have a capped core which results in the fuel/air mixture being pulled down into the center of the stream further concentrating the excess gas in the core of the flare. This can cause incomplete combustion which results in soot formation which presents itself as dark orange flames and smoke in the center of tips built with this design. This incomplete combustion also releases unburnt greenhouse gases or gases that pose health risks to people and livestock in the area.
There is provided a flare stack diffuser tip for use with a flare stack having a waste gas conduit. The flare stack diffuser tip uses continuous diffuser rings to introduce the waste gas into the air stream. There is a minimum of one ring, additional rings are added as required by the assist air requirements of the waste gas composition to be combusted. There are one or more radial transfer spokes configured to connect to the waste gas conduit to receive waste gas. These spokes have a flame bridge built on the top of them when two or more concentric rings are required. This flame bridge is positioned below the flare tip ignition system and performs the critical role of cross-lighting the rings by ensuring all waste gas release points are contiguous. The one or more radial transfer spokes are in fluid connection with the concentric diffuser rings.
Using an uninterrupted ring ensures all released waste gas will be ignited and burnt without the extra complexity or burning of additional fuel gas that the ring burner utilized in radial slot style tips can require to maintain stable ignition and cross-lighting of the individual slots.
In various embodiments, there may be included any one or more of the following features. The radial transfer spokes define an open core permitting air flow through a central opening defined by a concentric diffuser ring. The one or more radial transfer spokes each extend upwardly and outwardly at an upper end of the flare stack waste gas conduit to define the open core. When two or more concentric diffuser rings are used they define air flow passageways between them. The air flow passageways connect to the open core. As the waste gas conduit increases in diameter the quantity of radial transfer spokes increases. The radial transfer spokes will be equally angularly-spaced from each other. Multiple waste gas streams can be configured in a single tip. An example of this would be a three concentric ring tip that would use an inner and outer ring to dispose of waste gas A while an intermediate ring would dispose of waste gas B. Waste streams A and B will exit a single tip but will never be combined. Another application for this configuration is to have the inner and outer rings dispose of low BTU waste gas while the intermediate ring burns fuel gas to sufficiently raise the combustion temperature of waste gas A so it burns completely. A multi-ring tip may employ fuel gas driven flame bridges in applications where the flare is not operating with a continuous purge gas flow.
These and other aspects of the device and method are set out in the claims.
Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which:
Connected to the concentric diffuser rings 12 are radial transfer spokes 30 configured to connect to the waste gas conduit of the flare stack to receive waste gas. The radial transfer spokes 30 are in fluid connection with the concentric diffuser rings 12. As shown in
The radial transfer spokes 30 define an open core 28 permitting air flow through a central opening defined by the concentric diffuser rings 12. As shown in
The concentric diffuser rings 12 have a plurality of diffuser tabs 16 at the top. As shown in
As shown in
As shown in
As shown in
The flare stack diffuser tip allows for reliable and consistent cross lighting performance. In some embodiments, this prevents the release of unburnt hydrocarbons due to poor cross lighting performance of existing designs and eliminates the burning of extra hydrocarbons by not needing a ring burner to function.
As shown in
Embodiments of the flare stack diffuser tips may provide for extra cross lighting and flame stability which in turn may provide for a much higher turn down rate so the tip can handle a larger volume of gas flows without compromising its performance under low flow conditions. Embodiments of the flare stack diffuser tip may also provide higher combustion efficiency, and better mixing due to a more laminar flow. By using a more laminar flow, the mixing can be controlled to a higher degree. A balanced flow may also be achieved due to consistent and tuneable spacing of flow passages as well as the ability to tune the size of the gas port formed by the diffusion tabs 16.
The flare stack diffuser tip alternates air and gas streams in concentric rings. This provides a more uniform mixture in a low pressure flare application. The air to gas ratio is consistent and controlled throughout the mixed streams. The flare stack diffuser tip has the open core 28 allowing the air stream to flow into it to keep the flows balanced. Embodiments of the flare stack diffuser tip provide reduced carbon footprints and reduced operating and construction costs in relation to convention designs of flare tips.
In some embodiments, the cross lighting performance eliminates the need for a ring burner which lowers the carbon foot print by eliminating the need to burn extra gas and all of the materials used to construct the ring burner and flame retention tabs.
A smaller tip size can be used due to better mixing conditions and the precise air/fuel gas ratios provided by the consistent ring spacing. With a smaller tip comes a reduction in air supply requirements which translates directly into lower energy usage. Benefits in flare tip design can also create benefits to the main structure of the flare stack. A smaller tip may allow the rest of the flare to be proportionately smaller which may result in fewer construction materials and less weight to transport so the carbon footprint is reduced.
The amount of space available for air to arrive in the core of the flare may be adjusted to improve the performance of the flare tip.
In some cases, replaceable tabs may be used for the diffuser tabs of the diffuser tip. The diffuser tab is considered a wear/sacrificial area of the tip. The diffuser tabs may be made from various materials, including ceramics, such as silicon nitride when extreme conditions require it. In some less extreme applications using replaceable diffuser tabs, the tabs may be made from a different material from the remainder of the flare stack diffuser tip. For example, the replaceable diffuser tabs may comprise SAE 310 stainless steel while other parts of the diffuser tip comprise SAE 316 and SAE 304 stainless steel.
Replaceable diffuser tabs may permit tips to be made with more expensive materials than may otherwise be economically viable. Making them replaceable enables the use of higher grade materials only where required. In addition, where one or more of the replaceable diffuser tabs experiences greater deterioration during use than other replaceable diffuser tabs, those particular diffuser tabs can be replaced. This allows the user to avoid having to replace the whole flare stack diffuser tip when only a part of a tip has deteriorated.
The ports where gas exits the tip may be various shapes other than just square or rectangular openings. In some embodiments, the ports may be triangular which may allow for tuning the air/gas mixture depending on the molecular weight of the gas and the flow rates so it is optimized for each application.
In this document, although the word ‘gas’ is used to describe waste gas to be combusted, the term is intended to include any mix of fluids, including those that includes entrained liquid. The flare stack tip may be used for combustion waste fluids from industrial plants such as petroleum refineries, chemical plants and natural gas processing plants or at oil or gas extraction sites.
Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims. For example, although the radial transfer spokes are shown in this document as having a rectangular shape extending radially outward, the transfer spokes can have many different shapes and sizes as long as they extend sufficiently in the radial direction to connect between concentric diffuser rings. The radial transfer spokes could be spiral, rounded or any other shape. The concentric diffuser rings do not need to be circular in shape. In the embodiments shown in
In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite articles “a” and “an” before a claim feature do not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims.
Number | Date | Country | Kind |
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3088318 | Jul 2020 | CA | national |
This application is a continuation of and claims priority to U.S. Non-Provisional patent application Ser. No. 17/388,513, filed on Jul. 29, 2021, which in turn claims the benefit of Canadian Provisional Patent Application Serial No. 3088318, filed on Jul. 29, 2020, the disclosures of which are incorporated by reference herein in their entireties.
Number | Date | Country | |
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Parent | 17388513 | Jul 2021 | US |
Child | 18751820 | US |