rrr
`
`rrF rnpv
`
`AFWAL-TR-88-2081
`
`JET FUEL DEOXYGENATION
`
`S. Darrah
`
`Geo-Centers, Inc.
`7 Wells Avenue
`Newton Centre, MA 02159
`
`October 1988
`
`CD
`
`Ln
`
`0N
`
`Interim Report for Period March 1987 - July 1988
`
`Approved for Public Release; Distribution Unlimited
`
`DTIC
`ELECTE
`E
`
`AERO PROPULSION LABORATORY
`AIR FORCE WRIGHT AERONAUTICAL LABORATORIES
`AIR FORCE SYSTEMS COMMAND
`WRIGHT-PATTERSON AIR FORCE BASE, OHIO
`
`45433-6563
`
`GE-1015.001
`
`

`
`NOTICE
`
`When Government drawings, specifications, or other data are used for any purpose
`other than in connection with a definitely related Government procurement operation,
`the United States Government thereby incurs no responsibility nor any obligation
`whatsoever; and the fact that the government may have formulated, furnished, or in
`any way supplied the said drawings, specifications, or other data, is not to be re-
`garded by implication or otherwise as in any manner licensing the holder or any
`other person or corporation, or conveying any rights or permission to manufacture
`use, or sell any patented invention that may in any way be related thereto.
`
`This report has been reviewed by the Office of Public Affairs (ASD/PA) and is
`releasable to the National Technical Information Service (NTIS).
`At NTIS,
`it will
`be available to the general public, including foreign nations.
`
`This technical report has been reviewed and is approved for publication.
`
`CHARES R.
`RTEL
`Project Engineer
`Fuels Branch
`
`FOR THE COMMANDER
`
`CHARLES L. DELANEY, Chie
`Fuels Branch
`Fuels and Lubrication Division
`
`BENITO P. BOTTERI, Assistant Chief
`Fuels and Lubrication Division
`Aero Propulsion & Power Laboratory
`
`If your address has changed, if you wish to be removed from our mailing list, or
`if the addressee is no longer employed by your organization please notify AFWAL/POSF,
`W-PAFB, OH 45433 to help us maintain a current mailing list .
`
`Copies of this report should not be returned unless return is required by security
`considerations, contractual obligations, or notice on a specific document.
`
`GE-1015.002
`
`

`
`UNCLASSIFIED
`SECURITY CLASSIFICATION OF THIS PAGE
`
`REPORT DOCUMENTATION PAGE
`Ia. REPORT SECURIrY CLASSIFICATION
`lb. RESTRICTIVE MARKINGS
`Unclassified
`2a. SECURITY CLASSIFICATION AUTHORITY
`
`Form Approved
`OOMBNo. 0704-o01
`
`3. DISTRIBUTION /AVAILABILITY OF REPORT
`Approved for public release; distribution
`unlimited
`S. MONITORING ORGANIZATION REPORT NUMBER(S)
`
`6b. OFFICE SYMBOL
`(if applicable)
`
`AFWAL-TR-88-2081
`7a. NAME OF MONITORING ORGANIZATION
`Aero Propulsion Laboratory (POSF)
`Air Force Wright Aeronautical Labs, AFSC
`7b. ADDRESS (City, State, and ZIP Code)
`
`2b. DECLASSIFICATION /DOWNGRADING SCHEDULE
`
`4. PERFORMING ORGANIZATION REPORT NUMBER(S)
`
`*
`
`GC-TR-88-1416-013
`6a. NAME OF PERFORMING ORGANIZATION
`
`Geo-Centers, Inc.
`6c. ADDRESS (City, State, and ZIP Code)
`7 Wells Avenue
`Newton Centre MA 02159
`
`Wright-Patterson AFB OH 45433-6563
`
`9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER
`
`F33615-84-C-2412
`10. SOURCE OF FUNDING NUMBERS
`PROJECT
`PROGRAM
`NO.
`ELEMENT NO.
`61101F
`
`30805
`3
`
`TASK
`NO.
`
`0
`
`WORK UNIT
`ACCESSION NO.
`46
`
`$a. NAME OF FUNDINGISPONSORING
`ORGANIZATION
`Aero Propulsion Laboratory
`Sc. ADDRESS (City, State, and ZIP Code)
`Air Force Wright Aeronautical Laboratories
`Wright-Patterson AFB OH 45433-6563
`
`8b. OFFICE SYMBOL
`(If applicable)
`AFWAL/POSF
`
`'
`
`___________________________
`
`11. TITLE (Include Security Classification)
`
`Jet Fuel Deoxygenation
`-12. P RSONAL AUTHOR(S)
`S Darrah
`I ~
`13o. TYPE OF REPORT
`Interim
`16. SUPPLEMENTARY NOTATION
`
`rMFROM Mar 87/
`13b. TIME COVERED
`Oo
`
`14. DATE OF REPORT (Year, Month, Day)
`"ju 8 1988 October
`
`15. PAGE COUNT
`26
`
`"
`
`17.
`
`COSATI CODES
`J21~~~
`SUB-GROUP
`GROUP
`05
`
`18.
`
`JECT TERMS (Continue on reverse If necessary and identify by block number)
`~~ t4J Fuels)
`-
`'
`iM:w
`FIELD
`Deoxygenation,
`"-
`W[ J21
`,
`ABSTRACT (Continue on reverse if necessary and identify by block number)
`This program was initiated to identify and characterize methods of deoxygenating quantities
`of jet fuel to improve fuel thermal stability. Three methods, chemical getters, molecular
`sieves and nitrogen sparging, were evaluated in our laboratory. In the case of nitrogen
`sparging, additional results were obtained by comparing laboratory experimental results
`with the output from ULLAGE, a computer based mathematical model. Each method was shown
`to reduce the oxygen content of jet fuel. Economic and system considerations favor
`nitrogen sparging for large quantities of fuel.
`
`-
`
`21. ABSTRACT SECURITY CLASSIFICATION
`0T' OTIC USERS IUnclassified
`22b. TELEPHONE (Include Area Code)
`
`Previous etions are obsolete.
`
`22c OFFICE SYMBOL
`1AFWAI/POSFU
`3UNCLASSIFIED
`SECURITY CLASSIFICATION OF THIS PAGE
`
`2 2
`
`0. DISTRIBUTION/AVAILABILITY OF ABSTRACT
`0] SAME AS RPT.
`&I]UNCLASSIFIED'UNLIMITED
`22m. NAME OF RESPONSIBLE INDIVIDUAL
`CHRLS
`.
`,513-255-7431
`A(RTEL
`DO Form 1473, JUN 86
`
`GE-1015.003
`
`

`
`FOREWORD
`
`This report documents work conducted under contract F33615-84-C-
`2412, Task No. 13, with Geo-Centers Inc. This contract is
`documented under project 3048, task 05, work unit 46. Funding for
`Task 13 was provided by Independent Laboratory In House Research
`funds (ILIR), work unit ILIRP705, program element 61101F. Dr
`Shirley Darrah, Geo-Centers Inc., was the principal investigator,
`and Mr Charles R. Martel, AFWAL/POSF, was the program manager.
`
`Accession For
`
`Ni tX 01Ac
`IDTIC TAB
`Unannounced
`Justifivatio
`
`By
`Distribution/
`Availability Codes
`vo1.and/or
`Special
`
`'Dist
`
`ift
`
`GE-1015.004
`
`

`
`ABSTRACT
`
`This program was initiated to identify and characterize
`methods of deoxygenating quantities of jet fuel to improve fuel
`thermal stability. Three methods, chemical getters, molecular
`sieves and nitrogen spurging, were evaluated in our laboratory.
`
`In the case of nitrogen sparging additional results were
`obtained by comparing laboratory experimental results with the
`output from ULLAGE, a computer based mathematical model. Each
`method was shown to reduce the oxygen content of jet fuel.
`
`Economic and system considerations favor nitrogen sparging for
`large quantities of fuel.
`
`iv
`
`GE-1015.005
`
`

`
`TABLE OF CONTENTS
`
`TABLE OF CONTENTS .
`
`..
`
`..
`
`.
`
`....
`
`..
`
`.
`
`..
`
`..
`
`...........................
`
`1 .0
`
`INTRODUCTION. .
`
`........
`
`.
`
`...
`
`.
`
`..
`
`........................
`
`2 .0
`
`CHEMICAL GETTrER.......................... ........
`
`........
`
`3 .0
`
`MOL.ECUJLAR SIEVES .....
`
`..
`
`.......
`
`.
`
`o .......
`o
`.
`...............
`
`4.0 NITROGEN SPARGING. ...
`
`.
`
`...
`
`..
`
`..
`
`.
`
`..
`
`............
`
`.. ..........
`
`5.0 CONCLUSIONS ....... ..
`
`..
`
`..
`
`..
`
`..
`
`.
`
`..........................
`
`PAGE
`
`v
`
`1I
`
`2
`
`5
`
`10
`
`21
`
`GE-1015.006
`
`

`
`FIGURES
`
`LIST OF FIGURES
`
`1
`
`2
`
`3
`
`4
`
`5
`
`6
`
`7
`
`8
`
`Percent oxygen removed from JP-5 with type 3A molecular
`sieves ................................................
`
`Deoxygenation of JP-5 with 99.999% N2 sparging gas at
`different flow rates .................................
`
`Deoxygenation of JP-5 with 99.5% N2 sparging gas at
`different flow rates ..................................
`
`Deoxygenation of JP-5 with 0.1 liter/min of 99.999% N2
`sparging gas at different temperatures ................
`
`Deoxygenation of 1 liter of JP-5 at 220 C with 99.999% N2
`at various flow rates and 95% efficiency ..............
`
`Deoxygenation of 10,000 gallons of JP-5 at 600 C and
`various fuel flow rates. Scrub gas is 99.95% N2 at 0.4
`lb/min and 95% efficiency .............................
`
`Deoxygneation of 10,000 gallons of JP-5 at 60°F and
`100 gal/min fuel flow. Scrub gas if 99.5% N2 at various
`flow rates and 95% efficiency ..........................
`
`Deoxygenation of 10,000 gallons of JP-4 at 60°F and
`various fuel flow rates. Scrub gas is 99.95% N2 at
`0.5 lb/min and 95% efficiency ..........................
`
`PAGE
`
`7
`
`12
`
`13
`
`14
`
`16
`
`18
`
`19
`
`20
`
`vi
`
`GE-1015.007
`
`

`
`1.0 INTRODUCTION
`
`The thermal stability of jet fuels has been a problem of
`increasing importance to both commercial and military users for
`many years. With the development of higher speed aircraft, which
`have higher temperature engines, the thermal stability of fuel is
`becoming increasingly critical. Thermal instability refers to the
`propensity of the fuel to form carbonaceous deposits on hot metal
`surfaces. This effect is a function of fuel components (especially
`trace contaminants), the composition of the metal surface and
`temperature.
`
`In aircraft, fuel thermal instability can cause problems in
`three major areas.
`The first two, deposits on fuel injection
`nozzles and metering valves, directly and perhaps catastrophically
`affect engine performance. The third, deposits on walls of heat
`exchangers, reduces the efficiency of heat transfer to fuel which
`is used as a coolant. The latter effect is becoming more important
`as higher Mach number aircraft are developed, which increasingly
`rely on fuel as a coolant of airframe and engine components.
`
`A major contributor to the thermal decomposition of fuels is
`dissolved molecular oxygen. When heated, oxygen readily forms free
`radicals which initiate and propagate autoxidation reactions of
`hydrocarbons. When the concentration of dissolved molecular oxygen
`is reduced to levels of lppm, this mechanism of decomposition
`becomes unimportant, and the pyrolysis of the fuel itself is the
`dominant mechanism. Pyrolysis, however, occurs at much higher
`temperatures than autoxidation. Thus, by decreasing the oxygen
`concentration to lppm, the fuel can be subjected to higher
`temperatures before thermal decomposition occurs.
`
`GE-1015.008
`
`

`
`GEO-CENTERS, INC. has conducted a program to identify and
`evaluate methods of deoxygenating jet fuels. These methods were
`considered for potential application to either a ground-based, fuel
`preconditioning and servicing system or to an on-board, aircraft
`fuel system.
`
`In evaluating methods of deoxygenation, several technical
`factors must be considered.
`Kinetics and thermodynamics must
`strongly favor oxygen removal to affect a low oxygen concentration
`in a short time. It is important that no new contaminants be
`introduced into the fuel and that no beneficial components be
`removed. In addition, safety considerations involving the fire
`hazard of exothermic reactions, toxicity of materials including the
`input stream and waste products, and the disposal of waste products
`must eventually be addressed. Economic factors, including the
`costs of materials, equipment and manpower, will eventually
`determine the viability of building large scale deoxygenation
`facilities. While we are mindful of safety and economic implica-
`tions of each method examined, the thrust of this effort has been
`directed to technical feasibility issues.
`
`2.0 CHFMTCAL GETTERS
`
`Chemical methods were the first approach evaluated during this
`program. Among the chemical methods, "getters", metals or alloys
`with chemically active surfaces, appeared attractive be cause they
`react with oxygen to form insoluble oxides. They have been widely
`used in the semiconductor and nuclear fuels industries. Many of
`these are transition metals which were deemed unacceptable for this
`application because of the potential for catalyzing reactions in
`fuel. Barium metal, however, is a commonly used getter and looked
`
`2
`
`GE-1015.009
`
`

`
`attractive. Barium reacts readily with oxygen and water, but the
`reaction is not as exothermic as the reaction of other metals such
`as sodium. The relevant reactions of barium are:
`
`2Ba + 02 - 2BaO
`Ba + H 2 0 - BaO + H 2
`BaO + H 2 0 - Ba(OH) 2
`
`Laboratory experiments were performed to determine the
`effectiveness of this method.
`The initial experiments were
`conducted with JP-5 in a threeneck round bottom flask. Two of the
`necks contained stopcocks attached to ground glass joints. One
`stopcock was used to admit nitrogen gas while the other was used
`to vent the flask. The third neck held the probe for a Yellow
`Springs Instrument International, Inc. model 58 dissolved oxygen
`meter. One liter of JP-5 fuel was used. The barium metal was
`purchased in 6 mm diameter sticks (granulated barium metal is not
`currently available from laboratory suppliers). These sticks were
`cut into pieces approximately 6 mm in length. The barium was
`stored in oil under a nitrogen atmosphere in an attempt to prevent
`its surface from oxidizing. The JP-5 fuel was saturated with air
`prior to the experiment by bubbling air through it.
`
`In the first experiment, fuel and barium were stirred together
`in the flask under a nitrogen atmosphere. After 30 minutes, the
`oxygen concentration had decreased to 50% of the initial concentra-
`tion. It was observed, however, that this result could be obtained
`simply by stirring the fuel under a nitrogen atmosphere without the
`barium metal. The presence of white solid did indicate that some
`barium had reacted. Subsequent experiments were performed with air
`initially present and no nitrogen purging of the flask.
`
`3
`
`GE-1015.010
`
`

`
`In order to increase the exposed surface area of barium, the
`threenecked flask was replaced with a blender. The lid was sealed
`to the container to prevent air leakage after the deoxygenation
`process began. The system was simplified by using cyclohexane
`rather than JP-5. The cyclohexane was mixed with the pieces of
`barium in the blender until the barium was broken into very small
`particles. After 30 minutes, the oxygen concentration was 4% of
`the initial concentration. The absolute concentration of oxygen
`in the cyclohexane could not be determined by our measuring
`instrumentation which gives a relative indication, however,
`assuming the air saturated concentration to be 50 ppm then 4% would
`be 2 ppm. This value may well reflect the air-tightness of the
`blender rather than the limit of the deoxygenation capability of
`the barium. A white solid was observed in the liquid. At the
`conclusion of the experiment, solid barium metal remained in the
`container. The white solid was filtered from the liquid with
`Whatman No. 2V filter paper. This paper retains solids larger than
`8 microns in size. The filtered solution was observed to be clear
`and did not scatter light, thus indicating that all solid
`by-products had been removed by the filter. It was also observed
`that a coating of white solid remained on the walls of the
`container.
`
`Calculations of the quantity of barium metal required to
`stoichiometrically react with 10,000 gallons of fuel with 50 ppm
`oxygen yield a value of 35 lbs of barium. Additionally, twenty-two
`lbs of barium react with 70 ppm of water in 10,000 gallons of fuel.
`The actual quantity of barium metal required to react with both the
`oxygen and water is less than the total of these two values because
`barium oxide itself reacts with water. Barium sells commercially
`for approximately $20/lb which is in the range of economically
`feasibility.
`However, barium is costly enough that recycling
`technique should be explored for large throughput operations.
`
`4
`
`GE-1015.011
`
`

`
`3.0 MOLECULAR SIEVES
`
`The use of molecular sieves as deoxygenating agents was also
`investigated in this program. They are commonly used in industrial
`processes to remove water and contaminant gases. Molecular sieves
`have advantages over chemical means of deoxygenation in that they
`are nontoxic, nonflammable, and can be regenerated by physical
`means, thus avoiding disposal problems.
`
`Zeolite molecular sieves have pores of a uniform size which
`can adsorb small molecules such as oxygen, while excluding the
`larger molecules present in jet fuel. These materials have a high
`internal surface area available for adsorption due to the channels
`or pores which uniformly penetrate the entire volume of the solid.
`The available surface area is very much larger than the external
`surface of the adsorbert particles, which contributes only a small
`percentage of the total area. The particular sieves to be used are
`chosen by matching the size of the molecules to be occluded with
`the diameter of the channels.
`
`Initially, Type 3A sieves in 1/16 inch pellets were chosen.
`These were chosen because they occlude only molecules which are 3
`angstroms in size or smaller. Thus they should occlude oxygen in
`the channels but exclude the larger fuel molecules. The
`
`5
`
`GE-1015.012
`
`

`
`experiments were performed in a one liter round bottom flask. The
`sieves were placed in the flask and activated by heating them while
`the flask was being evacuated. JP-5 jet fuel was then allowed into
`the flask. The small volume in the flask which was not occupied
`by the 1 liter of fuel was allowed to fill with air so that the
`system was under atmospheric pressure. The probe for the oxygen
`meter which had previously been calibrated on air-saturated fuel
`was inserted into the flask.
`The mixture was stirred until
`equilibrium was attained (the meter readings were constant).
`
`The results of these experiments are shown in Figure 1.
`Deoxygenation does occur and is a function of the quantity of
`sieves used. The efficiency of these particular sieves, however,
`is not sufficient for fuel deoxygenation because even at a ratio
`of 150g sieves/liter fuel a reduction of oxygen concentration by
`only 27% was obtained.
`
`Because oxygen molecules are near the limit of the Type 3A
`channels in size, experiments were also performed with Type 4A
`sieves in the form of 8-12 mesh beads. Although the larger size
`of the channels allow slightly larger molecules such as C02 to be
`occluded, it was hoped that they would be more efficient
`deoxygenating agents. As in the previous experiments, a 1 liter,
`three necked flask was used. The beads were activated by heating
`them under vacuum. After cooling, fuel was admitted to the flask
`and the mixture was stirred until equilibrium was obtained. The
`concentration of oxygen in the fuel relative to the concentration
`of oxygen in air saturated fuel was measured. The concentrations
`of oxygen in the gas space above the fuel and in the sieves were
`calculated.
`
`6
`
`GE-1015.013
`
`

`
`100
`50
`150
`200
`Grams molecular sieves/liter fuel
`
`100
`
`75
`
`50
`
`25
`
`0 Q
`
`)
`
`X0 4
`
`1
`
`a)
`04
`
`00
`
`0
`
`Figure 1. Percent oxygen removed from JP-5
`with Type 3A molecular sieves
`
`7
`
`GE-1015.014
`
`

`
`Since the flask is under vacuum when the fuel is admitted to
`it, gases boil out of the air saturated fuel as the flask is being
`filled. Therefore, the flask can not be completely filled with
`fuel.
`In order to evaluate the effect of this phenomenon,
`experiments were first performed simply with an evacuated flask
`and no sieves present. The total volume of the flask was actually
`1.215 liter. With no sieves present, the fuel occupied a volume
`of 1.15 liter. Assuming a concentration of 40 ppm in air saturated
`fuel, the fuel contained 46.1 mg of oxygen. When the flask was
`filled with fuel, 10 ml of air at atmospheric pressure which was
`in the tubing was also admitted into the Figure 1 flask.
`It
`contained 2.8 mg of oxygen. Thus, the total oxygen content of the
`flask was 48.9 mg. After equilibrium, the oxygen concentration in
`the flask was 31.0 ppm or a total content of 35.5 mg. From Henry's
`law and the ideal gas law, the gas phase contained 13.9 mg of
`oxygen. The total oxygen in the flask was 49.4 mg which agrees
`well with the calculation of the quantity of oxygen initially
`admitted to the flask.
`
`For the experiments with the sieves, the initial and final
`concentrations of oxygen in the fuel were measured with the oxygen
`meter. The oxygen contents of the gaseous and liquid phases were
`calculated by the same procedure used when no sieves were present.
`The oxygen content of the sieves was the difference between the
`initial and final contents of the gaseous and liquid phases. The
`results of the measurements and calculations are given in Table 1.
`Although the sieves do remove oxygen from the fuel, their efficien-
`cy is not good and in practice massive quantities would be
`required.
`
`8
`
`GE-1015.015
`
`

`
`TABLE 1. Results of Jet Fuel Deoxygenation Experiments
`Using Type 4A Molecular Sieves
`
`Wt. of sieves (g)
`
`Vol. of sieves (ml)
`
`0
`
`0
`
`50
`
`30
`
`100
`
`60
`
`150
`
`90
`
`Vol. of fuel (ml)
`
`1150
`
`1110
`
`1075
`
`1035
`
`Vol. of gas (ml)
`
`65
`
`75
`
`80
`
`90
`
`Initial 02 in fuel (mg) 46.1
`
`44.5
`
`42.9
`
`Initial total 02 (mg)
`
`48.9
`
`47.4
`
`Final 02 in fuel (mg)
`
`35.5
`
`30.2
`
`Final 02 in gas (mg)
`
`13.9
`
`14.1
`
`Final 02 in sieves
`
`0
`
`3.1
`
`45.8
`
`24.0
`
`12.3
`
`9.5
`
`41.3
`
`44.2
`
`17.8
`
`10.7
`
`15.7
`
`9
`
`GE-1015.016
`
`

`
`4.0 NITROGEN SPARGING
`
`The deoxygenation of fuel by nitrogen sparging has also been
`evaluated during this program. Sparging is the method which has
`been used in laboratory studies on thermal stability of
`deoxygenated fuel.
`It has the advantage of not introducing
`possible contaminants or reactive materials to the fuel and also
`poses no disposal problem.
`
`Sparging is a physical process in which the composition of the
`atmosphere which is in contact with the fuel is changed. As the
`composition of the atmosphere changes, then the composition of the
`fuel must also change in order to maintain equilibrium. The
`relationship between the concentrations of oxygen in the two phases
`is give by Henry's Law:
`
`pj = xjkj
`
`where pj is the partial pressure of the solute (oxygen) in the
`vapor above the solution, xj is the mole fraction of the solute in
`the fuel and k. is a constant. Calculations using Henry's law show
`that fuel which contains 40 ppm oxygen when air saturated should
`contain 1 ppm oxygen when in equilibrium with an atmosphere which
`has no more than 0.5% oxygen.
`
`Experiments were performed to study the effect of fuel
`temperature and sparging gas concentration and flow rate on
`deoxygenation rate and final oxygen concentration. A three-neck
`round bottom flask containing 1 liter of JP-5 fuel was used. The
`fuel was first saturated with air and then deoxygenated by bubbling
`the sparging gas through the fuel with a glass tube with a fritted
`
`10
`
`GE-1015.017
`
`

`
`cylinder. The fuel was stirred during deoxygenation in order to
`maximize the efficiency of the deoxygenation and also to ensure
`proper response of the oxygen metpr. The two different gases used
`for sparging were a special mixture containing 99.5% N2 and 0.5%
`02 and "ultrapure" nitrogen, containing 99.999% N2.
`
`With the gas containing 99.5% N2 , a final concentration of
`2.5% of the air saturated oxygen concentration was obtained.
`Assuming the air saturated JP-5 contains 40 ppm of 02 then 2.5% of
`this value is 1 ppm. Figures 2 and 3 show graphically deoxygena-
`tion experiments with "ultrapure" and 99.5% N2 . Although, a 1 ppm
`level can be attained with either gas, the time of deoxygenation
`and volume of sparging gas required were significantly less for
`"ultrapure" N 2 rather than the 99.5% mixture. Thus, the 99.5%
`mixture is adequate to maintain fuel at the 1 ppm dissolved oxygen
`concentration, but higher purity nitrogen is more efficient for the
`initial deoxygenation process.
`In actual practice, different
`methods may be advantageous for purifying the nitrogen gas used at
`different steps of the fuel handling and storage process.
`
`In Figure 4, the effect of temperature is illustrated. The
`deoxygenation process is as expected from kinetics arguments slower
`at lower temperatures. Therefore, the range of temperatures to
`which the fuel could be subjected in the deoxygenation process must
`be considered in setting the requirements for the sparging system.
`
`Following these laboratory experiments, the application of
`nitrogen sparging to deoxygenation of full-scale systems was
`studied by performing calculations with the computer based
`mathematical model, ULLAGE. This model is described in the report
`
`11
`
`GE-1015.018
`
`

`
`@ 0. 1
`
`Vmnin
`
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`
`100
`
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`
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`cm
`
`cc:
`
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`
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`
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`
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`
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`
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`
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`o
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`20
`
`GE-1015.019
`
`

`
`Vmin
`
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`
`100
`
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`
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`
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`
`10
`
`20
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`30
`
`40
`
`50
`
`60
`
`IME (MINUTES)
`
`Figure 3. Deoxygenation of JP-5 with 99.5% N 2Sparging
`Gas at Different Flow Rates.
`
`13
`
`c 20
`
`0
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`z00
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`GE-1015.020
`
`

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`10
`
`20
`
`30
`
`40
`
`50
`
`60
`
`IME (MINUTES)
`
`Figure 4. Deoxygenation of JP-5 with 0.1 Itmin of 99.999%
`N2 Sparging Gas at Different Temperatures.
`
`14
`
`z00
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`0 c 20
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`0
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`GE-1015.021
`
`

`
`AFWAL-TR-87-2060, "Volume I - Airplane Fuel Tank Ullage Computer
`Model".
`In this model, aircraft fuel tanks are simulated and
`conditions such as temperature and flow rates can be varied. The
`software was modified to calculate the concentration of oxygen
`dissolved in the fuel in ppm (mg oxygen/liter fuel) and to output
`this value as a function of time.
`
`Initially, the model was used to simulate the conditions which
`had been used in previous laboratory experiments. These conditions
`were 1 liter of JP-5 at 720F
`in a volume of 1.2 liter with a
`surface area of 0.102 ft. 2 Calculations were performed for 99.999%
`N2 at flow rates of .01 liter/min, 0.05 liter/min and 0.02
`liter/min with an efficiency of 0.96. Comparing Figure 2 with
`Figure 5 shows there is good agreement between the experimental
`and calculated results.
`
`Calculations were also performed to show the effect of
`temperature on deoxygenation. These res,.lts did not agree well
`with experiments. The calculated rates of deoxygenation showed an
`insignificant change with change in temperature unlike the
`laboratory experiments. The reason for this discrepancy is not
`understood at this time. However, the laboratory results shows a
`consistent temperature effect which leads us to believe that the
`computer model should be examined with respect to its handling of
`temperature parameters.
`
`The deoxygenation of fuel in storage tanks was next simulated.
`For the calculations, 10,000 gallons of fuel in a 1500 ft3 tank
`with 113 ft2 surface area was used.
`The calculations were
`performed for a variety of conditions including an empty tank being
`filled with fuel at various flow rates and a previously filled
`tank. The fuel and upper skin temperatures were varied as were the
`scrub flow rate, scrub gas concentration and scrub efficiency.
`
`15
`
`GE-1015.022
`
`

`
`061 0-006-MM1 02022-IL
`
`*A
`
`40*
`40 0
`
`A=0.10OVmin
`B =0.05 Vmin
`C = 0.02 Vmin
`
`* 0.1 Vmin
`0.05 Vmin
`*0.02
`Vmin
`
`0
`
`20
`1
`
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`0
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`GE-1015.023
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`

`
`The time and quantity of nitrogen required to deoxygenate a
`tank of fuel is highly dependent on the fuel flow rate. Figure 6
`shows oxygen concentration versus time for several flow rates plus
`for a previously filled tank. As can be seen, deoxygenating a
`previously filled tank is the least efficient process. At the
`given conditions of 600F, 0.4 lb/min scrub rate, 99.95% N2 and 95%
`efficiency, the 250 gal/min flow rate is most efficient because
`the tank is filled in forty minutes and a 1 ppm 02 level is reached
`after 62 minutes. At 100 gal/min the 1 ppm 02 concentration level
`is reached in less time, but the tank is not filled until 100
`minutes have elapsed. Therefore, more nitrogen is also required
`to maintain scrub conditions through the longer time interval.
`
`These results show that it is important to optimize the fuel
`flow and scrub flow rates in order to produce a tank of fuel
`deoxygenated to the 1 ppm oxygen level most efficiently. Although
`a fast fuel flow rate will fill the tank more quickly, a slower
`rate may actually produce deoxygenated fuel more quickly depending
`on the scrub flow rate. On the other hand, a fast scrub rate may
`result in excess nitrogen being used if the fuel flow rate is low.
`Figure 7 illustrates this by showing the deoxygenation of 10,000
`gallons of JP-5 with fuel flow rate of 100 gals/min. Scrub flow
`rates of 0.40 and 0.18 lbs/min were used. Although both produce
`the desired result in 100 minutes, the time required to fill the
`tank, the faster scrub flow required an excess of 32 lbs of
`nitrogen over the slower scrub rate.
`
`Other variables of the system were also tested in these
`calculations. Figure 8 shows the deoxygenation of JP-4 under the
`same conditions as the JP-5 shown in Figure 6. Because of the
`higher initial 02 concentration, the deoxygenation proceeds more
`
`17
`
`GE-1015.024
`
`

`
`A=full tank
`B =1000 gal/min
`C =500 gal/min
`250 gal/min
`D0
`E =100 gal/min
`
`60-
`
`50
`
`40 -
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`00
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`0
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`10 -
`
`A
`
`0
`
`10
`
`20
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`.30
`
`40
`TIME
`
`50
`f'.IINUTES)
`
`60
`
`70
`
`60
`
`90
`
`100
`
`Figure 6. Deoxygenation of 10.000 gals of JP-5 at 60*F and various fuel flow
`rates. Scrub gas is 99.95% N2 at 0.4 lb/min and 95% efficiency.
`
`18
`
`GE-1015.025
`
`

`
`A = 0.18 lb/min
`B = 0.40 lb/min
`
`A
`
`60
`
`40
`
`30
`
`20-
`
`1 20
`
`*
`
`z (
`
`,)
`
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`
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`
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`
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`
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`20
`
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`30
`
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`
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`
`40
`TIME
`
`50
`(MINUTES)
`
`60
`
`70
`
`s0
`
`90
`
`100
`
`Figure 7. Deoxygenation of 10,000 gals of JP-5 at 60°F and 100 gal/min fuel flow.
`Scrub gas is 99.95% N 2 at various flow rates and 95% efficiency.
`
`19
`
`GE-1015.026
`
`

`
`A = ull tank
`B = 1000 gat/min
`C = 500 gal/min
`D0=250 gal/min
`E =100 gal/min
`
`A
`
`80-
`
`70
`
`c~50
`
`z <
`
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`
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`
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`z0
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`00
`
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`
`0
`
`10
`
`20
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`30
`
`50
`40
`TIME (MINUTES)
`
`60
`
`70
`
`so
`
`90
`
`100
`
`Figure 8. Deoxygenation of 10,000 gals of JP-4 at 60OF and various fuel flow
`rates. Scrub gas is 99.95% N2 at 0.4 lb/min and 95% efficiency.
`
`20
`
`GE-1015.027
`
`

`
`slowly. Simulations in which the temperature of the fuel or upper
`skin were varied showed a very slight, less than 1 percent, change
`in deoxygenation rate. As discussed above this conflicts with
`laboratory results. Also, simulations were performed with the vent
`valve set at an overpressure. In these cases, the deoxygenation
`was delayed until sufficient scrub gas was added to equal the
`overpressure and then the deoxygenation proceeded normally for the
`given conditions.
`
`9
`
`5.0 CONCLUSIONS
`
`Several methods of deoxygenating jet fuel have been considered
`and evaluated. These methods were based on both the chemical and
`physical properties of oxygen. The chemical methods suffer from
`several disadvantages. The best reducing agents are difficult to
`handle because they must be protected from air and often react so
`exothermically as to be a fire hazard. Also, good reducing agents
`are not easily regenerated after exposure to oxygen. The large
`volumes of fuel which must be deoxygenated then result in large
`quantities of used agents which must either be subjected to costly
`regeneration processes or disposed of in a safe manner.
`
`Molecular sieves do not suffer from these disadvantages
`because they are inert, nontoxic, nonflammable materials. Also,
`because they function by the physical process of adsorption rather
`than by chemical reaction, they are more easily regenerated. The
`adsorption of gases is an equilibrium process and by placing the
`sieves under vacuum, the gases can be removed. The disadvantage
`of sieves is that massive quantities of sieves will be required in
`order to deoxygenate jet fuel to the low oxygen concentrations
`required to improve thermal stability.
`
`21
`
`GE-1015.028
`
`

`
`Sparging fuel with nitrogen gas is also a physical process of
`removing oxygen
`involving an equilibrium between the fuel and
`the atmosphere surrounding it. As the oxygen concentration of the
`atmosphere is decreased, the oxygen concentration in the fuel also
`decreases in order to maintain the equilibrium. In this study, it
`was found that deoxygenation is best achieved by using high purity
`nitrogen and deoxygenating as fuel flows into a storage container.
`The fuel flow rate should be adjusted according to the scrub gas
`f low rate so that a 1 ppm oxygen level is attained in the time that
`it takes to fill the tank. It is very important that the proper
`relationship be maintained between the two flow rates in order to
`most efficiently obtain a full tank of deoxygenated fuel. It may
`even be more efficient to use a slower fuel flow rate in order to
`achieve this goal. The scrub gas should also be dispersed into
`small bubbles in order to present the maximum surface area to the
`fuel, resulting in maximum efficiency.
`
`Although high purity nitrogen is best for the deoxygenation
`process, gas which is 99.5% nitrogen is sufficient to maintain the
`deoxygenated fuel.
`This number is significant because it is
`achievable by processing air with hollow fiber membrane filters.
`Thus, these filters could be used to supply the atmosphere in
`storage tanks as well as to provide demand gas on the aircraft.
`This eliminates the need to provide prepurified nitrogen on the
`aircraft.
`Such systems are available commercially from Dow
`Chemical under the trademark GENERON or Permea Inc., a Monsanto
`Company under the trade name Prism Alpha Nitrogen Systems.
`
`*U.S.Government Printing Office: 1989 - 648-056/04168
`
`22
`
`GE-1015.029