US20160223196A1

US20160223196A1 - Crude Oil Spray Combustor

Info

Publication number: US20160223196A1
Application number: US15/013,274
Authority: US
Inventors: Steven G. Tuttle
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 2015-02-02
Filing date: 2016-02-02
Publication date: 2016-08-04

Abstract

The disclosure describes a combustor suitable for burning emulsified crude oil and seawater, a flow-blurring atomizer positioned at first end configured for introducing atomized crude oil spray into an interior of the combustor. A shroud or combustion duct surrounds a portion of a burning plume of atomized crude oil. The shroud is connected to a base at the first end and is open at the opposite second end. Dilution holes extend through the base and/or the shroud, allow the aspiration and entrainment of air into the plume, and assist in the flame anchoring and propagation, and reduce the amount of soot produced by burning the emulsified oil. At least one ignition port directs an ignition flame or plasma toward the atomized crude oil spray. One or more abrupt expansions at the nozzle or at the shroud sidewalls form toroidal recirculation zones surrounding the atomized crude oil spray.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a non-provisional application under 35 USC 119(e) of, and claims the benefit of U.S. Provisional Application 62/110,890 filed on Feb. 2, 2015, the entire disclosure of which incorporated herein.

BACKGROUND

1. Technical Field
The disclosure is related to combustion systems, and more particularly, is related to portable burners for in-situ burning of crude oil and other fuels.
2. Related Technology
Oil spills in the marine environment can cause major environmental problems. The spilled oil and the resulting oil/water emulsions can be difficult to clean up. One method is to burn the oil in place, generally known as “in situ burning”.
In-situ burning with a mechanically atomized and swirled burner is discussed in Buist, I. A., “Disposal of Spilled Hibernia Crude Oils and Emulsions: In-Situ Burning and the “Swirlfire” Burner,” 12th Arctic and Marine Oil Spill Program Technical Seminar, Environment Canada, 1989. Flare burners for in-situ burning are discussed in Tebeau, P. et al., “Technology Assessment and Concept Evaluation for Alternative Approaches to In-Situ Burning of Oil Spills in the Marine Environment,” Final Project Report for U.S. Minerals Management Service, Sept. 1998 and in Tebeau, P. A., “Alternative Approaches to In Situ Burning Operations,” In Situ Burning of Oil Spills Workshop, Building and Fire Research Laboratory, National Institute of Standards and Technology, 1998.
Expro Group flame burners operated on oil platforms require large oil pumps and air compressors that operate at about 1500 psig, and are suitable for operation on large ships, off-shore oil platforms, and land-based oil extraction and processing facilities. Large combustion systems are not suitable for small fishing boats and small oil skimmers.
Some burner designs are also disclosed in U.S. Pat. No. 5,295,817 to Young, U.S. Pat. No. 5,472,341 to Meeks, U.S. Pat. No. 6,237,512 to Inoue, U.S. Pat. No. 7,677,882 to Harless, U.S. Patent No 8,550,812 to Moneyhun et al.

BRIEF SUMMARY

The disclosure describes a combustor suitable for burning emulsified crude oil and seawater, a flow-blurring atomizer positioned at first end configured for introducing atomized crude oil spray into an interior of the combustor. A shroud or combustion duct surrounds a portion of a burning plume of atomized crude oil. The shroud is connected to a base at the first end and is open at the opposite second end. Dilution holes extend through the base and/or the shroud, allow the aspiration and entrainment of air into the plume, assist in the flame anchoring and propagation, and reduce the amount of soot produced by burning the emulsified oil. At least one ignition port directs an ignition flame or plasma toward the atomized crude oil spray. One or more abrupt expansions at the nozzle or at the shroud sidewalls form toroidal recirculation zones surrounding the atomized crude oil spray.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present disclosure can be better understood with reference to the following diagrams. The drawings are not necessarily to scale. Instead, emphasis is placed upon clearly illustrating certain features of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1A-1D illustrate a burner for use in a combustion system for burning emulsified crude oil.

FIG. 1E illustrates air entry into the burner through the shroud and recirculation zones.

FIG. 2A-2B are cross sectional views of a low pressure spray atomizer positioned within the base of the burner.

FIG. 3A and 3B illustrate another example of a burner for use in a crude oil burning system.

Additional details will be apparent from the following Detailed Description.

DETAILED DESCRIPTION

Overview

The following detailed description refers to the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the following description to refer to the same or similar elements. While embodiments of the disclosure may be described, modifications, adaptations, and other implementations are possible. For example, substitutions, additions, or modifications may be made to the elements illustrated in the drawings, and the methods described herein may be modified by substituting, reordering, or adding stages to the disclosed methods. Accordingly, the following detailed description does not limit the disclosure. Instead, the proper scope of the disclosure is defined by the appended claims.
The system described herein is a combustor useful for in-situ burning of crude oil, emulsified crude oil, and waste liquid. The system provides low-pressure atomization and combustion of these liquids. Because the system can operate at low liquid and air pressures (e.g., between about 10 psig and 100 psig), the system can use small pumps and compressors, and can be carried on fishing boats and other small watercraft typically deployed for spill remediation. The US
Navy's spill response community, for example, can clean up oil spills using vessels of opportunity such as barges, utility boats, or fishing boats, with various skimming systems including vessel of opportunity skimming systems, the Marco class V skimmer, or other oil skimmers, supplemented with oil containment booms, oil storage tanks and bladders, towing vessels, and other equipment.

Examples

FIG. 1A-1D show a combustor or burner 100 useful for burning crude oil, emulsified crude oil, and waste liquid fuel. The combustor 100 includes an air-assisted atomizer 120 designed for high viscosity fluids at low pressure. In this example, the atomizer 120 is a flow blurring atomizer. The atomizer receives oil via an oil inlet line 160 and receives compressed air via an inlet line 150, and discharges a crude oil spray into the combustor duct. The combustor duct is formed of a base or bulkhead 140 and a shroud 110. The combustor components are formed of materials that tolerate the high temperatures, such as, for example, metals and ceramics.
In the example shown in FIG. 1A-1D, the atomizer 120 is located in the center of a base 140, which is generally circular and flat. In this example, the shroud or combustion duct 110 has a circular cross sectional area that increases from the base 140 to the far end 111, with the shroud sidewall taking on the shape of a truncated cone. The shape of the shroud above the base can be a truncated cone. In operation, the shroud surrounds a portion of the burning plume, which extends past the far end 111 of the shroud.
The shroud 110 includes a plurality of dilution holes 112, 113 that can extend over the length of the shroud (from the base to the far end) or over a lesser part of the shroud. Dilution holes 141 can also be located in the base itself, in the region surrounding the atomizer. The size and position of the holes can be selected to produce a desired combustion effect. In this example, holes in the shroud 113 near the base are larger than the holes 141 through the base 140, and the holes 112 near the far end 111 of the shroud 110 are larger than the holes 113 near the base. The dilution holes allow the aspiration and entrainment of air into the plume and assist in the flame anchoring and propagation, and reduce the amount of soot produced by burning the emulsified oil. The dilution holes through the base allow a limited amount of air to mix with recirculated combustion products without quenching combustion. The dilution holes illustrated in FIG. 1A-1D are circular in shape, although they may be of other shape, for example, oval, square, triangular, or slot shaped. The size and number of the dilution holes should be sufficient to allow entrainment of surrounding air, but not so large as to prevent the shroud from shielding the plume from the wind.
As seen in FIG. 1D, ports 130, 131, 132, and 133 are positioned in the base. In operation, the ports introduce ignition and flame holding jets into the combustor and direct the jets toward the atomized crude oil spray. The ports are located symmetrically around the atomizer 120, and are positioned at a common distance from the atomizer. However, the design is not limited to four symmetrical ports located in the base. It may also be suitable to have more, or fewer ports, and to have ports located in the shroud sidewall, or in both the shroud sidewall and the base.
The shroud allows the spray plume flames to anchor by shielding the plume from any wind while reflecting radiant heat back to the plume and preventing errant droplets from falling to the ground. These droplets cling to the inside surface of the shroud, where they evaporate and burn, providing additional heat to the plume.
The notional cross sectional view of the combustion system shown in FIG. 1E shows a broad, sudden expansion 170 around the nozzle exit that provides a region for the formation of a toroidal recirculation zone where the flame anchors and then propagates along the length of the plume. The abrupt expansion at the nozzle together with the wall of the shroud create a toroidal recirculation zone 171 surrounding the atomized crude oil spray. FIG. 1E also shows air 180 entering the dilution holes in the shroud.
The width of the shroud at the base is determined based on the ignition and evaporation time scales. If the shroud is too wide, the atomized liquid fuel within the shroud will cool too much to ignite. If the shroud is too narrow, the atomized liquid fuel will not remain airborne within the shroud long enough to ignite.
FIG. 2A and 2B illustrate a flow blurring atomizer 120 in more detail. An oil line or “liquid feed tube” 210 is positioned in the center of a cylindrical atomizer body 250. The atomizer body includes an outer cylinder that surrounds the oil line, with the space between the oil line and the outer cylinder defining an axial air flow passage. The shape of the exit orifice through the atomizer body end forms a nozzle 253. The end of the liquid feed tube 210 is sharpened, and directs the crude oil 220 to the atomizer nozzle 253. The liquid feed tube 210 has an inner diameter D equal to the diameter of the exit orifice 251, with the sharpened outlet end 211 being spaced apart from the exit orifice at an offset distance H. The atomizer body has an end 254 that is closed except for an exit orifice 251 aligned with the outlet of the liquid feed tube, and an inner surface 252. A lateral cylindrical passageway 240 is formed by the gap between the tube end 211 and the exit orifice 251. Referring next to FIG. 2B, air flows through axially through the air passageway that surrounds the liquid feed tube and deflected inward by the inner surface 252 of the end 254 of the atomizer body 250 inward across the oil flow stream as the oil 220 exits the liquid feed tube 210. The atomizing air 241 atomizes the stream of oil 220 leaving the liquid feed tube 210.
The nozzle outlet is approximately flush with the surface of the base, as shown in FIG. 2A. However, the nozzle may be positioned with its outlet slightly above or below the surface of the base.
Although details of the design shown in FIG. 2A and 2B can vary, a flow-blurring atomizer is one that has a liquid feed tube with an exit end that is spaced apart from a nozzle. The smallest diameter of the exit nozzle 251 is approximately equal to that of the fuel tube. The nozzle surface flares out, so the larger diameter faces the inside of the combustor. The atomizer is configured such that air flows laterally inward toward the fluid flow leaving the liquid feed tube, atomizing the liquid. In this example, the material of the combustor base that surrounds the nozzle redirects the axial air flow inward toward the oil flow stream.
The flow blurring atomizer is believed to operate by forming a turbulent, high shear stagnation zone at the surface of the liquid. As the liquid flows out of the liquid feed tube, the air cross streams fragment the liquid surface, then entrain and carry the atomized liquid out of the nozzle. The flow blurring atomizer relies on high speed air, rather than high pressure air. This allows the system to use an air compressor that produces low pressure, moderate flow air to effectively atomize the crude oil.
In contrast, air blast and effervescent atomizers rely on a high pressure air source. Effervescent atomizers have been considered for use in the emulsified crude oil combustion system discussed herein. However, effervescent atomizers demonstrated a very high pressure drop across the nozzle orifice, resulting in a very low flow rate. To overcome the high pressure drop across the nozzle and resulting low flow rate, very high fluid and air pressure would be required, which would increase the size and weight of the pumps, air compressors, and associated infrastructure. As a result, flow blurring atomizers, with their low pressure drop, operate at lower air and fluid pressures, and are considered more suitable for such portable combustion systems.
Additional details of some flow-blurring atomizers are disclosed in Gañan-Calvo, A. M.,
“Enhanced liquid atomization: From flow-focusing to flow blurring”, Applied Physics Letters, Vol. 86, No. 21, 2005, and in Simmons, B. M. and Agrawal, A. K., “Flow-Blurring Atomization for Low-Emission Combustion of Liquid Biofuels”, Combustion Science and Technology, Vol. 184, No. 5, 2012, pp. 660-675, the disclosure of each of which is incorporated herein in its entirety.
Referring again to FIG. 1A-1D, ignition and flame holding jets composed of hot plasma gas, enter the combustor via the ports 130, 131, 132, and 133. The ignition and flame holding jets evaporate and ignite the base of the jet to initiate combustion, and evaporates and ionizes the emulsified crude oil. A plasma torch (not shown) generates the hot plasma. The plasma torch requires a supply of air and a source of electricity, and because the plasma torch does not require another fuel source (e.g., propane), it is well suited for a portable shipboard or remote combustion system.
In other applications in which other fuel sources are available, it may be suitable to use a different flame-ignition system, for example, a propane-based flame ignition system.
FIGS. 3A and 3B illustrate a combustor 300 with another shroud and port configuration. In this example, the combustion duct or shroud 310 is formed of a smaller diameter cylindrical duct section 312 and a larger diameter cylindrical duct section 311, joined together by an annular shroud member that extends outward from the small diameter section 312 to the larger diameter section 311. The shroud shape has a first abrupt expansion 371 around the atomizer 320, and a second abrupt expansion 370 where the first and second duct sections 311, 312 meet. The abrupt expansions 370, 371 produce toroidal recirculation zones 360, 361 around the spray plume, as seen in FIG. 3B.
The sections could also be joined together by bending one of the cylindrical sections 312, 311 inward or outward so it is in direct contact with the other duct section. It may also be suitable to form the shroud as a single unitary component, or the shroud and base as a single unitary component.
In this example, two ignition ports 331 and 332 are located in the base or bulkhead 340. However, it may also be suitable to position ignition ports in the smaller diameter cylindrical shroud section 312. The ports direct the ignition and flame-holding jets toward the base of the atomized crude oil spray plume. Many dilution through- holes 313 and 314 extend through both of the shroud sections 311, 312 to allow aspiration and entrainment of air into the plume and to assist in the flame anchoring and propagation. As discussed above, number, size, and shape of the dilution holes should be sufficient to allow entrainment of surrounding air, but not so large as to prevent the shroud from shielding the plume from the wind.
As in the example shown in FIG. 1, air inlet 350 and an oil inlet line 360 provide air and emulsified crude oil or other liquid fuel to the flow-blurring atomizer 320. The flow blurring atomizer and nozzle configuration is as described above in the discussion related to FIG. 1A-1D.
In operation, a system with a 1 in-diameter (25 mm) nozzle will support combustion with the air and oil flow rates of 0.128 kg/s (0.282 lbm/s) air, and 8.0 L/min (2.11 gal/min) oil, using a burner with a first stage burner with a diameter of 800 mm and a length of 800 mm, and a second stage with a diameter of 1000 mm in diameter and a length of 1000 mm.
It may also be suitable to add one or more additional shroud sections above the larger diameter cylindrical shroud section, to shield more of the plume from the wind and to add toroidal recirculation zones at the abrupt expansions at the joints between the shroud sections. It may also be suitable to include dilution holes through the base 340 in addition to the holes through the shroud.
It is noted that effervescent atomizers have also been considered for use in the emulsified crude oil combustion systems described herein. However, effervescent atomizers demonstrate a very high pressure drop across the nozzle orifice. To overcome the high pressure drop across the nozzle and resulting low flow rate, very high fluid and air pressure are required, which increases the size and weight of the pumps, air compressors, and associated infrastructure. In contrast, flow blurring atomizers, with their low pressure drop, operate at lower air and fluid pressures, and are considered more suitable for such portable combustion systems.
In operation, the burner shown in FIG. 1A-1D or 3A-3B is typically oriented vertically, with the atomizer at the bottom and the far end of the shroud at the top. The crude oil/seawater emulsion is pumped via a pump and hose from a storage tank or bladder into the atomizer. In The oil/water emulsion can be collected by an oil skimmer, such as the US Navy's Class V oil skimmer. Compressed air is introduced through the air inlet line into the atomizer. The abrupt expansion around the atomizer at the base of the shroud produces a toroidal recirculation zone around the spray plume.

SUMMARY

The combustion system described herein can reliably ignite and burn emulsified oil. A prototype system demonstrated stable combustion of an oil/water emulsion with a seawater content range of 0 to 50%, providing nearly complete combustion of both heavy and light components of the crude oil, with little or no unevaporated or unburned spray. The shroud protects the plume from the wind, and the holes through the shroud provide additional air, reducing soot. The prototype combustion system produced approximately 30% less soot and CO than burning the crude oil/seawater emulsions with surface pool fires. The low air and oil pressure requirements permit low power compressors and pumps with a minimal infrastructure footprint. This allows a combustion system to be skid mounted and carried on a vessel of opportunity (e.g., a fishing vessel) to assist in disposal of emulsified crude oil. The system size and capacity can be scaled up or down for larger or smaller vessels, respectively. This technology can be a scalable, effective, and fieldable remediation method for benthic spills or crude oil that is too emulsified for traditional in situ burning.
While the specification includes examples, the disclosure's scope is indicated by the following claims. Furthermore, while the specification has been described in language specific to structural features and/or methods, the claims are not limited to the features and methods described above. Rather, the specific features and methods described above are disclosed as examples that illustrate aspects of the disclosure.

Claims

What is claimed as new and desired to be protected by Letters Patent of the United States is:

1. A combustor suitable for burning emulsified crude oil and seawater or other liquid fuel, comprising:

a base at a first end;

a flow blurring atomizer positioned at the first end configured for introducing atomized crude oil spray into an interior of the combustor;

a shroud configured to surround a portion of a burning plume of atomized crude oil, the shroud connected to the base at the first end, the shroud being open at an opposite second end,

at least one of the shroud or the base having a plurality of dilution holes therethrough for introducing diluent air; and

a port configured to direct an ignition flame or plasma toward the atomized crude oil spray.

2. The combustor according to claim 1, wherein the shroud has a cylindrical cross section.

3. The combustor according to claim 1, wherein the shroud is shaped as a truncated cone with a smaller end of the truncated cone connected to the base.

4. The combustor according to claim 1, wherein the at least one port is a plurality of ports arranged symmetrically in the base surrounding the atomizer.

5. The combustor according to claim 1, wherein the at least one port includes a plurality of ports arranged in the shroud.

6. The combustor according to claim 1, wherein the at least one port is a plurality of ports arranged in the base and a plurality of ports arranged in the shroud.

7. The combustor according to claim 1, wherein the plurality of dilution holes therethrough for introducing diluent air include holes of at least two different diameters, with larger holes positioned farther from the base and smaller holes positioned closer to the base.

8. The combustor according to claim 7, wherein the plurality of dilution holes therethrough includes holes through the base surrounding the atomizer.

9. The combustor according to claim 1, wherein the flow-blurring atomizer has a liquid feed tube with an exit end, a nozzle spaced apart from the exit end of the liquid feed tube, the nozzle being tapered outward with a smallest diameter end of the nozzle facing the liquid feed tube and a larger diameter end of the nozzle facing the inside of the combustor.

10. The combustor according to claim 9, wherein the smallest diameter end of the nozzle has a diameter approximately equal to the inner diameter of the exit end of the liquid flow tube.