Download or read book Pressure Dependence of Aluminum Ignition in Gaseous Oxygen and Possible Ignition Mechanisms in Brazed Aluminum Heat Exchangers written by Etienne Werlen and published by . This book was released on 2012 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt: The ignition of aluminum foils in gaseous oxygen was experimentally tested using a diode laser as the energy source, which provided a well-controlled, accurate, and reproducible method of ignition. The tests were conducted under different conditions in terms of oxygen pressure, oxygen purity, aluminum thickness, and gas velocity. The aluminum foils tested were between 0.2 mm and 0.45 mm thick, a range typical of fins contained in brazed aluminum heat exchangers (BAHXs) used in air separation units (ASUs). The experimental apparatus was composed of a pressure vessel in which a single aluminum test sample was placed. The vessel contained an optical window that allowed a short laser pulse of known power to be applied to the aluminum sample. The energy dose was systematically varied in order to identify the threshold ignition energy, defined as the point at which the probability of aluminum combustion with propagation beyond the laser spot was 50 %. The experimental results show that O2 pressure has no significant effect on the ignition energy of aluminum over the pressure range tested (10 bar to 120 bar). This conclusion holds for both standard commercial grade purity O2 (99.8 %) and high purity O2 (99.99 %), as well as for gas velocities higher than typically encountered in ASU BAHXs. Heat conduction calculations indicate that aluminum ignition occurs when the laser spot temperature reaches the melting point of the passivating oxide layer (about 2200 K to 2300 K). The heat conduction model accurately explains the dependence of the ignition energy on the aluminum sample thickness. These test results have been used in assessing the risk of ignition of BAHXs used in high pressure oxygen service in ASUs.

Download or read book Promoted Ignition Combustion Tests of Brazed Aluminum Heat Exchanger Samples in Cold Supercritical Oxygen written by James White and published by . This book was released on 2016 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: A common practice in the industrial gas industry is to produce product oxygen by boiling pressurized liquid oxygen in a heat exchanger. Multistream brazed aluminum heat exchangers (BAHX) typically are used as oxygen product vaporizers. This method inherently exposes liquid and gaseous oxygen to aluminum material. Customer demands continue to increase the product oxygen pressure requirements, and it is recognized that higher pressures could increase the severity of an aluminum/oxygen combustion event. A series of experimental programs were conducted from 1993 to 1995 to evaluate the safe use of BAHX for boiling oxygen at elevated pressures to 6,996 kPa. The present experimental study is a companion test program that was conducted from 2010 to 2012 to evaluate BAHX promoted combustion response in cold supercritical oxygen to 15,602 kPa. Promoted combustion experiments were conducted with miniature headered BAHX samples. Two types of samples were tested. The first were approximately 3.3 kg, having a thinner parting sheet thickness, and the second approximately 3.9 kg, having thicker parting sheets. The oxygen passages contained commercial purity cold supercritical oxygen having a pressure ranging from 10,197 to 15,603 kPa and the adjacent passages contained cold supercritical air ("inert" fluid) at pressures ranging from 10,440 to 15,170 kPa. Tests were conducted with the air passage pressure both higher and lower than the oxygen passage pressure. Nichrome wire was used to ignite a hydrocarbon promoter located within an oxygen passage, simulating a promoted ignition-combustion event. The experiments provided insights into the combustion mitigation behavior of BAHX used for producing high-pressure product oxygen via pumped liquid oxygen (LOX) gasification. Data are applicable in supporting the safe use of BAHX for high-pressure oxygen service.

Download or read book Flammability and Sensitivity of Materials in Oxygen enriched Atmospheres written by Ting C. Chou and published by ASTM International. This book was released on 1997 with total page 491 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Chemical Abstracts written by and published by . This book was released on 2002 with total page 2540 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Promoted Ignition Combustion Tests of Brazed Aluminum Heat Exchanger Samples in Gaseous and Liquid Oxygen Environments written by R. Zawierucha and published by . This book was released on 2000 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt: Most air separation plants employ compressors to increase oxygen pressure for customer usage. An alternative approach is to extract liquid oxygen from the separation column, which is pumped to higher pressure and then boiled in a heat exchanger to directly provide an elevated pressure gaseous oxygen product. Brazed aluminum heat exchangers (BAHX) are normally utilized as the product oxygen vaporizers.

Download or read book Metals Abstracts written by and published by . This book was released on 1998-04 with total page 1176 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Ignition Phenomena of Bulk Aluminum Alloy as a Function of Oxygen Pressure written by K. Nguyen and published by . This book was released on 1984 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental study was undertaken to investigate the ignition phenomena of 6061 aluminum alloy as a function of oxygen pressure. Cylindrical aluminum alloy specimens were ignited in a pure oxygen environment by a focused cw CO2 laser beam. To study the effect of oxygen pressure on the surface temperature at ignition of 6061 aluminum alloy, the experiments were conducted at oxygen pressures ranging from 0.084 to 2.413 MPa. The temperature history of the entire upper surface of the specimen and of a 0.5 mm diameter spot located initially at the center of the specimen top surface was recorded by using a commercial two-color ratio pyrometer and a fast-response, narrow-band, two-color pyrometer. Mass, brightness, and interior temperatures, for certain experiments were also recorded throughout the experiment. The results show that the surface temperatures at ignition of the alloy obtained from the temperature curves are below the melting temperature of the aluminum oxide and are slightly dependent on oxygen pressure. The data indicate that the ignition mechanism is complex and probably composed of several phenomena acting both separately and in conjunction with each other.

Download or read book Promoted Ignition Combustion Behavior of Tubular Aluminum Samples in Liquid and Gaseous Oxygen Environments written by R. Zawierucha and published by . This book was released on 2003 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: Past literature has reported on the occurrence of violent energy releases (VER) involving either high surface area aluminum structured packing or brazed aluminum heat exchanger (BAHX) samples subjected to promoted ignition-combustion testing in liquid oxygen (LOX) environments. In each of these situations, both the aluminum packing samples and the BAHX specimens contained relatively thin sections of aluminum. The aluminum thickness ranged from 0.2 to 0.25 mm for the aluminum packing and the fin portion of "thin fin" BAHXs. Other "thick fin" BAHXs tested had nominal fin thicknesses ranging from 0.41 mm to 0.46 mm. Similar flammability data have not been reported for thick wall (4.1 mm), 3003 tubular aluminum heat exchanger material which may be used in LOX applications. The impetus for this program was to study the promoted-ignition combustion behavior of thick wall, tubular aluminum samples in various LOX environments using both a localized hydrocarbon promoter and uniformly dispersed hydrocarbon film. Tests were also conducted in various gaseous oxygen (GOX) environments using uniformly dispersed hydrocarbon films.

Download or read book Sealed Aluminum Cavity Reactions When Submerged in Pure O2 Reboiler Sump written by Stephen J. Wieder and published by . This book was released on 2009 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aluminum has a long history of safe service in cryogenic air separation units; however, there have been some rare instances of aluminum/O2 reactions. Aluminum ignition and propagation depends strongly on the oxygen purity, oxygen pressure, aluminum geometry, and type and energy of igniter. Over the years, the industry has experienced a particular type of aluminum/O2 reaction: cavity incidents. These incidents are characterized by the presence of a sealed cavity that is created when welding two metal items together. Such a sealed cavity can lead to aluminum ignition under certain specific conditions: (1) The sealed cavity is submerged in a bath of liquid oxygen. Over a long period of time, liquid cryogen can enter the sealed cavity through slight imperfections in the weld. (2) The sealed cavity is warmed over a short period of time, typically a few hours. (3) The liquid oxygen vaporizes, and the pressure inside the cavity builds to very high levels (potentially over 50 bars). (4) Ignition occurs in the high pressure, high purity oxygen environment, and the resulting aluminum/oxygen reaction burns through the relatively thick cavity walls. (5) The oxygen and reaction products exit the cavity through the hole, lowering the pressure and extinguishing the reaction. This paper discusses two such incidents, which have occurred since 2001. Both incidents took place in brazed aluminum heat exchanger (BAHX) reboiler support beam systems. In both cases, the BAHX reboiler was damaged, leading to a process leak, which required that the plant be repaired. In one case, the damage occurred while warming a plant. In the second case, the damage occurred during normal operation. This second case does not appear to follow the sequence of events outlined above; however, evidence is presented to support the scenario that the cavity incident occurred during a previous warming of the plant. This initial damage then impaired the normal operation of the reboiler, leading to a second hydrocarbon related reaction during normal operation. The paper discusses the potential ignition mechanisms, probable causes of the incidents, and methods to prevent future re-occurrences.

Download or read book Flame Spreading and Violent Energy Release VER Processes of Aluminum Tubing in Liquid and Gaseous Oxygen Environments written by JH. Sturges and published by . This book was released on 2000 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work is motivated by the need for a fundamental understanding of the unintentional combustion of aluminum heat exchange equipment used in liquid oxygen (LOX) service; in which combustion can be quite energetic and cause severe damage. The promoted ignition, flame spreading, and combustion phenomena of aluminum tubing filled with LOX, surrounded by a shell of gaseous oxygen (GOX), were systematically observed and recorded. Parameters studied include the tube- and shell-side pressures, GOX and LOX flow rates, and GOX quality (the mass fraction of GOX in the two-phase flow inside the tube sample). Results from high-speed movie films indicate that under certain operating conditions, a transition from a "normal" (much slower) burning mode to an extremely rapid and violent burning mode occurs. This transition was shown to occur in some cases after a period of delay and in other cases immediately after the onset of ignition. The "Violent Energy Release," or VER burning mode, is characterized by an extremely high flame spreading rate (1-2 orders of magnitude higher than the flame propagation rate in a purely GOX environment), a high luminosity flame-zone, and a very rapid rate of heat release. Within the range of initial conditions tested, the major parameters that tend to enhance the degree of violence of aluminum combustion in a LOX/GOX environment include increasing initial pressure and decreasing GOX quality (higher LOX fraction). A burning regime map showing the threshold boundaries between conditions of no self-sustained flame propagation, "normal" burning, and VER burning mode is presented. It was found that the threshold boundaries between the different regimes of burning are essentially determined by the tube-side conditions. In addition a detailed insight into the controlling mechanisms of the VER reaction has been obtained, and a physical description of the transition mechanism is presented.

Download or read book Ignition Testing by Fracture of Oil and Particle Contaminated Aluminum Pipes in High Pressure Oxygen at Ambient and Elevated Temperature written by Matthias Meilinger and published by . This book was released on 2012 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aluminum and its alloys are the preferred material in air separation units (ASUs) and are submitted to strict cleanliness requirements to avoid combustion reactions in oxygen. Linde Engineering Division has investigated the role of particle contamination for the ignition of aluminum pipes in high pressure oxygen. Tests were carried out with oil coated aluminum pipes in combination with a particle contamination. Accumulations of following particle types were tested: molecular sieve 13X, filter deposits (rust), perlite, quartz sand, and aluminum swarf. The contaminated pipes were pressurized with oxygen up to 150 bar and fractured in a hydraulic apparatus. The conditions and probability of an ignition reaction compared with oiled pipes without particles were of interest. Additionally, similar high pressure tests with a mixture of liquid and gaseous oxygen were performed. A combination of oil and particles enhanced the probability of an ignition at elevated temperatures. The results indicated that temperature is the dominating factor for an oil ignition, not the oxygen pressure. At room temperature, an oil/aluminum ignition could never be initiated. The results give a good understanding regarding the mechanism of an aluminum ignition and help to clarify causes of damage in the ASU industry.

Download or read book Flammability Tests of Miniature Brazed Aluminum Heat Exchangers in Liquid Oxygen written by JF. Million and published by . This book was released on 1997 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: Most air separation plants currently in use employ compressors to increase oxygen pressure for customer usage. An alternative approach is to extract liquid oxygen from the separation column which is pumped to higher pressure and then boiled in a heat exchanger to directly provide an elevated pressure gaseous oxygen product. Brazed aluminum heat exchangers (BAHX) are normally utilized as the product oxygen vaporizers. The process results in substantial contact between high pressure liquid oxygen and aluminum material. The increased use of BAHXs to produce pressurized oxygen as an alternative to the use of oxygen compressors led to a series of experimental programs pertinent to the safe use of BAHXs for boiling oxygen at elevated pressures.

Download or read book Ignition of Metals and Alloys in Gaseous Oxygen by Frictional Heating written by FJ. Benz and published by . This book was released on 1986 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: The ignition of metals and alloys have been investigated by rotating the end of a hollow cylinder against an identical stationery cylinder on a common axis (frictional heating) in gaseous oxygen. A ranking criterion that measures the resistance of metals and alloys to ignition is discussed. It consists of the power per unit area required for ignition, conveniently expressed as the product of contact pressure P and average linear velocity ̄v. Data are presented that demonstrate that materials that are high in nickel and copper require greater Pv products for ignition (more resistant to ignition) than materials that are high in iron. Aluminum and titanium alloys are shown to require the lowest Pv products for ignition. The effects of varying surface velocity, contact pressure, coefficient of friction, and oxygen pressure on P ̄v products required for ignition are discussed. The results indicate that P ̄v product required for ignition increases as surface velocity increases, as contact pressure decreases, and as the coefficient of friction decreases. Increasing oxygen pressure will cause the P ̄v product required for ignition to decrease at low pressures and increase at high pressures. In some cases, the relative ranking of materials based on P ̄v products will also change as conditions are varied.

Download or read book High Temperature Spectroscopic Measurements of Aluminum Combustion in a Heterogeneous Shock Tube written by Patrick T. Lynch and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Aluminum is an important energetic material that burns with a variety of oxidizers with a high reaction enthalpy. It is a top performer for energy density if oxidizer mass is considered as well as the fuel. Because of this, it is often used as an energetic additive in anaerobic conditions because it reacts in what typically are products of primary fuels and oxidizers and further increases chamber temperatures in solid rocket motors or blast overpressure in enhanced blast weapons. Despite decades of research, gaps still exist in the knowledge of how aluminum burns, especially with the recent trend of using smaller particles (10 micron and below). While aluminum is a very energetic material, its rate of oxidation is relatively low, and efforts are made to not only increase the heat release rate of particles reacting with oxidizer, but also to increase peak combustion temperature. Experimental studies were performed measuring the combustion characteristics of aluminum in the heterogeneous shock tube. The heterogeneous shock tube provides unmatched control of temperature, pressure, oxidizer concentration, etc., in which to test energetic materials of different particle sizes. The burning time diameter exponent, n as in t_b ~ d^n, in aluminum particle combustion was measured to be as low as, or lower than 0.3, in conditions in the transition regime between kinetic and diffusion limited particles. This anomalous result, as well as observed increases of burn time with pressure when using water vapor as an oxidizer had been attributed to a pressure dependence on ignition of particles in these conditions or broad overlapping size distributions. Both theories were tested and rejected. Furthermore, an acrylic end section was implemented on the shock tube which provides complete optical access to the final 61 cm of the shock tube. This optical access allowed high speed images (50k fps) of the particle motion, ignition, and combustion. Results are presented which give a more complete understanding of burntime variability in the heterogeneous shock tube, owing to the contribution of initially wall-bound particles vs. those that are in the free stream upon the passage of the incident shock, bright clusters of rapidly moving burning particles, and non-uniform cloud distributions in the tube, all previously undifferentiated by shock tube burntime methods. Absorption spectroscopy was used to probe the ground state of Aluminum monoxide (AlO), a gas phase combustion intermediate, and Al vapor in order to quantify the amount of Al and AlO present under conditions where these species were not observed in emission previously, notably in most conditions with nano-aluminum particles. At least three regimes of combustion were observed for nano-aluminum combustion. At temperatures above 2000 K, particles burn with AlO and Al vapor present. Between 1500 K and 2000 K, particles burn with Al vapor present, but without detectable AlO. Between 1200 K and 1500 K, particles burn without either vapor phase component present. These results had important implications for two proposed mechanisms for nano-aluminum ignition and combustion. Optical measurements of the peak combustion temperature from AlO consistently measure near 3200 K in micro-Al combustion, even though higher temperatures are seen near larger particles. One proposed limiting factor was the volatilization temperature of alumina. The reference literature is divided on this temperature, which previously was measured with large extrapolations. The volatilization temperature was measured by measuring the extinction cross-section of nano- and micro-alumina at non-resonant wavelengths at different ambient temperatures. The volatilization temperature at 1 atm appears to be at least as high as 4000 K and does not appear to be a limiting temperature in micro-Al combustion Finally, two other sets of measurements were made to support high temperature measurements of aluminum combustion, especially in the optically thick conditions commonly observed in propellant plumes or explosive fireballs. The first was a measurement of the alumina emissivity spectral dependence, which is absolutely necessary to make pyrometric measurements. A significant temperature dependence was observed in the emissivity spectral dependence. Additionally, spatially resolved fiber optic emission probing was used in the optically thick fireballs from aluminized explosives. Using the probes allowed observations inside the fireball and avoided biases from temperature inhomogeneity and ambient air interactions in these explosive fireballs.

Download or read book Promoted Ignition Combustion Tests with Structured Aluminum Packings in Gaseous Oxygen with Argon Or Nitrogen Dilution at 0 1 and 0 6 MPa written by M. Meilinger and published by . This book was released on 2003 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: High-surface-area aluminum structured packings are finding a wide use in the cryogenic distillation of air. An experimental program was performed to determine the oxygen compatibility of commercial packings. In particular, the influence of pressure increase up to 0.6 MPa (6 bar absolute) and the effect of the replacement of nitrogen by argon as O2-diluting gas were investigated. Additionally, the impact of reducing the sheet thickness from 0.2 mm to 0.1 mm was tested.

Download or read book Ignition of Contaminated Aluminum by Impact in Liquid Oxygen Influence of Oxygen Purity written by Etienne Werlen and published by . This book was released on 2009 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: Impact tests in liquid oxygen and oxygen enriched liquids have been conducted on aluminum foils (0.2 mm thick) used for heat exchangers of air separation units (ASUs). Some adaptations to the ASTM Standard D2512, "Standard Test Method for Compatibility of Materials with Liquid Oxygen," have been done to ensure the good control of oxygen content in the cryogenic liquid and to get reproducible results in aluminum ignition with hydrocarbon coating. Modified striker pins with a cavity on the contact surface have been used. The vertical guiding and the centering of the striker pins have been ensured by using two machined guides. Test samples were three layers of aluminum foil, two corrugated and one flat, contaminated by various quantities of hexadecane. The criteria for the identification of aluminum ignition (positive tests) have been validated by performing Scanning electron microscope surface analysis on residuals of a few impact tests performed in copper cups. Criteria have also been defined to check that hexadecane combustion took place in negative tests. A sufficient number of tests have been performed to plot the probability of ignition of the aluminum samples as a function of the average thickness of hexadecane coating and as a function of the oxygen content in the cryogenic liquid varying from 50 % to above 99.95 %. The remaining part in the cryogenic liquid was nitrogen and 2.3 % argon except for one series of tests where the influence of the absence of argon could be identified. The results of these tests can be used to assess the risk of ignition of some aluminum exchangers or structures used in ASU.

Download or read book Surface Ignition of Aluminum in Oxygen written by B. Newton and published by . This book was released on 2006 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: Published reports of burning aluminum in oxygen using ASTM G 124-type testing demonstrated that aluminum alloys are difficult to ignite but once ignited are extremely flammable in terms of regression rate and energy release. The ignition resistance of aluminum is associated with its tenacious and protective oxide, which allows aluminum to safely contain high-pressure oxygen in certain applications. The ignitability of aluminum varies between alloys and surface treatments so a test method was developed to evaluate the ignitability of various aluminum surfaces. The test method uses a promoted ignition chamber consistent with ASTM G 124 testing; however, the test sample is configured in the shape of a coupon. Instead of promoting the sample with an electrically heated wire, a controlled electrical arc is generated by drawing an electrode away from the center of the coupon while passing current through the sample. The level of energy applied to the surface of the coupon is semi-quantifiable and kept constant between tests. Based on this semi-quantifiable amount of energy, an ignition pressure is established and the influence of alloy composition and surface treatments on aluminum is evaluated.