US3397547A - Avoidance of explosion hazards in air fractionation by halogenated hydrocarbon additin - Google Patents

Avoidance of explosion hazards in air fractionation by halogenated hydrocarbon additin Download PDF

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US3397547A
US3397547A US690684A US69068467A US3397547A US 3397547 A US3397547 A US 3397547A US 690684 A US690684 A US 690684A US 69068467 A US69068467 A US 69068467A US 3397547 A US3397547 A US 3397547A
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oxygen
liquid
ethane
passageway
concentration
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Erb Ezra
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Union Carbide Corp
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Union Carbide Corp
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04763—Start-up or control of the process; Details of the apparatus used
    • F25J3/04769—Operation, control and regulation of the process; Instrumentation within the process
    • F25J3/04854—Safety aspects of operation
    • F25J3/0486—Safety aspects of operation of vaporisers for oxygen enriched liquids, e.g. purging of liquids
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
    • F25J3/04406—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system
    • F25J3/04412—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system in a classical double column flowsheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure column
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J5/00—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants
    • F25J5/002—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants for continuously recuperating cold, i.e. in a so-called recuperative heat exchanger
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J5/00—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants
    • F25J5/002—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants for continuously recuperating cold, i.e. in a so-called recuperative heat exchanger
    • F25J5/005—Arrangements of cold exchangers or cold accumulators in separation or liquefaction plants for continuously recuperating cold, i.e. in a so-called recuperative heat exchanger in a reboiler-condenser, e.g. within a column
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/02—Bath type boiler-condenser using thermo-siphon effect, e.g. with natural or forced circulation or pool boiling, i.e. core-in-kettle heat exchanger
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2250/00—Details related to the use of reboiler-condensers
    • F25J2250/04—Down-flowing type boiler-condenser, i.e. with evaporation of a falling liquid film
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/10—Mathematical formulae, modeling, plot or curves; Design methods
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2290/00—Other details not covered by groups F25J2200/00 - F25J2280/00
    • F25J2290/90—Details about safety operation of the installation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S62/00—Refrigeration
    • Y10S62/916—Explosion reduction

Definitions

  • This invention relates to the avoidance of explosion hazards in low temperature air fractionation plants, and more particularly to the hazards resulting from the accumulation of ethane ⁇ as an atmospheric air impurity in an obstructed heat exchanger passageway.
  • the prior art has employed various methods for controlling this explosion hazard, including (1) air feed stream purication means such as hydrocarbon scrubbers or adsorption traps, (2) periodic drainage of a portion of the oxygen-enriched liquid from the bottom of the condenser-reboiler to reduce the total quantity of explosive hydrocarbon material therein, and (3) by oxygen recirculation systems which selectively remove most of the dangerous hydrocarbons from the oxygen-enriched liquid by adsorption in regenerable traps.
  • air feed stream purication means such as hydrocarbon scrubbers or adsorption traps
  • periodic drainage of a portion of the oxygen-enriched liquid from the bottom of the condenser-reboiler to reduce the total quantity of explosive hydrocarbon material therein and (3) by oxygen recirculation systems which selectively remove most of the dangerous hydrocarbons from the oxygen-enriched liquid by adsorption in regenerable traps.
  • oxygen recirculation systems which selectively remove most of the dangerous hydrocarbons from the oxygen-enriched liquid by adsorption in regenerable traps.
  • An object of this invention is to provide an improved method for avoiding the explosion hazards in low temperature air fractionation plants.
  • Another object is to provide such a method which is effective against accumulation of the weakly adsorbed ethane impurity contained in the air feed and which builds up in the oxygen-enriched liquid reboiler.
  • Still another object is to provide an improved method which is not characterized by high contamination of the oxygen-enriched product stream, excessive consumption of ⁇ diluent and high power costs from increased air feed inlet pressure.
  • FIG. 1 is a longitudinal cross-section of a normally operating oxygen-enriched liquid reboiler passageway (without obstruction), utilizing the primary principle of recirculation wherein the liquid body enters the lower end;
  • FIG. 2 is a longitudinal cross-section of an alternative, normally operating oxygen-enriched liquid reboiler passageway (without obstruction) wherein the liquid body enters the upper end;
  • FIG. 3 is a longitudinal cross-section of the FIG. l passageway with an obstruction therein;
  • FIG, 4 is a graph showing the concentration of monochlorotriiluoromethane diluent required to avoid an explosion hazard for various ethane concentrations and various temperature differences across the obstructed passageway of FIG. 3;
  • FIG. 5 is a schematic drawing of a nitrogen condenseroxygen reboiler operating according to the present inven1 tion.
  • One aspect of this invention relates t0 an atmospheric ⁇ air fractionating operation wherein the air feed containing high boiling point hydrocarbon impurities including ethane is cooled, partially freed of these impurities other than ethane, and partially condensed.
  • the 'mixture is fractionated in the usual manner into a nitrogen-rich vapor and an oxygen-enriched liquid body containing the impurity.
  • the liquid body flows into one end of a multiplicity of passagewaysl having a vertical component for partial vaporization therein by heat exchange with a warmer fluid thermally associated with the passageways and establishing a temperature difference of below about 3.5 C.
  • the oxygen-enriched iluid is discharged from the opposite end of the passageways.
  • Oxygen-enriched liquid is provided at the upper end of the passageways, and an obstruction forms in at least one passageway intermediate the upper end lower ends thereof.
  • the specific novelty relates to the improvement of avoiding an explosive ethane-oxygen mixture in the obstructed passageway due to ethane accumulation immediately above the obstruction by adding an inert soluble low volatility diluent.
  • This diluent is added in a concentration below about 1,000 parts per million relative to the oxygenenriched liquid body, and in sufficient quantity to raise the boiling point yof the ethane-enriched, oxygen-containing liquid immediately above the obstruction sufliciently to eliminate boiling of the liquid before its ethane concentration attains 4.0 mol percent.
  • the diluent is a member selected from the group consisting of monochlorotriuoromethane and' tetrauoromethane.
  • FIG. l illustrates a normally operating oxygen-reboiler passageway 10, at least the lower part of which is lled with liquid from the oxygen-enriched pool 11 beneath the lower end of the passageway.
  • Pool 11 is forced into the passageway lower end by the hydrostatic head, and is partially evaporated by heat exchange with a warmer Huid 12 in the space 13 thermally associated with passageway 10.
  • This fluid may for example be cold nitrogen-rich vapor from the higher pressure rectication section of the column, which is condensed by the heat exchange. Since nitrogen is more volatile than oxygen at atmospheric pressure, (their respective boiling points are 196 C.
  • the nitrogen-rich cold gas entering space 13 may be at 75 p.s.i.g. and 178 C., and the pool 11 may contain 99.5 percent oxygen at 181 C. and 5 p.s.i.g.
  • Partial vaporization of liquid in passageway produces a low density two-phase mixture 14 which rises rapidly and is ejected from the upper end into chamber 15.
  • the vaporized portion 16 then preferably passes through a series of rectication stages for counterow against descending liquid, and further oxygen-enrichment.
  • the unvaporized part of the mixture emerging from the upper end of passageway 10 is preferably withdrawn through conduit 17, directed through an adsorption trap for further removal of adsorbable air impurities, and returned to oxygen-enriched liquid pool 11.
  • this unvaporized part of the liquid falls downwardly onto the header sheet 18 connecting adjacent passageways. Part of this falling liquid is capable of flowing backwardly by gravity through any passageway in which boiling does not occur.
  • Another possible source of oxygen-enriched liquid for backward flow downwardly through passageway 11 is liquid draining from the rectication stages above (not illustrated).
  • the oxygen-enriched liquid pool 11 is over the oxygen reboiler passageway header sheet 18, so that the liquid enters the upper end of passageway 10 and the two-phase mixture formed therein ows downwardly.
  • This mixture is ejected from the passageway lower end into chamber 19.
  • the oxygen-enriched vapor portion is withdrawn through conduit 20 and the unvaporized portion is withdrawn through bottom conduit 21.
  • the liquid portion is preferably pumped through an adsorption trap for further removal of air impurities and returned to pool 11 in chamber 15 at the top end of passageway 10.
  • FIG. 3 illustrates the phenomenon occurring when a solid obstruction 22 is formed in the FIG. 1 passageway and the present invention is used to avoid an explosive mixture from the resultant ethane accumulation.
  • the passageway 10 must have a vertical component or projection for the ethane accumulation to occur. That is, the passageway is either vertical or inclined less than 90 degrees from the vertical alignment, so that oxygen-enriched liquid enters the upper end thereof and descends by gravity through the passageway until stopped by obstruction 22.
  • the oxygen-enriched liquid and the vapor formed from the heat introduced to this liquid through the walls of passageway 10 ow concurrently, i.e. in the same direction.
  • This direction can be either upward (FIG. 1) or downward (FIG. 2).
  • the two phases ow countercurrently, i.e. in opposite directions.
  • only a minor part of the oxygen-enriched liquid is vaporized whereas in the obstructed passageway a major fraction of the liquid is vaporized.
  • oxygen-enriched liquid containing perhaps 15 p.p.m. ethane in chamber 15 drains downwardly through the upper end of obstructed passageway 10 and is rectied against the vapors rising through the passageway section 23 above obstruction 22.
  • Ethane is less volatile than oxygen, and thus tends to accumulate in the passageway section 24 immediately above the obstruction 22. That is, passageway upper section 23 tends to act as a wetted wall tower or stripping column.
  • the ethane depleted oxygen vapor also containing still lower boiling components such as nitrogen rises from the passageway upper end through chamber 15 as stream 16.
  • the boiling oxygen-enriched liquid in passageway upper section 23 also contains other components which have higher boiling points than oxygen and are inert (non-explosive), they assist the ethane in reducing the AT.
  • Xenon is such a component, and the normal xenon content in atmospheric air aids in reducing the AT before 4% ethane concentration in the oxygen-enriched boiling liquid is reached.
  • an inert diluent selected from the group consisting of monoohlorotriuorornethane and tetrafluoromethane is introduced to the liquid Ibody in a concentration below about 1000 p.p.m. relative to the oxygen-enriched liquid body.
  • This inert diluent may for example be introduced to the liquid on passageway closure means 18 through conduit 25, and thus passes downwardly through the passageway upper section 23 with the oxygen-enriched liquid.
  • the inert diluent may be introduced with any stream entering the rectification equipment.
  • Each of these diluents is (l) non-explosive in admixture with oxygen, (2) soluble in liquid oxygen to the extent of greater than 10 mol percent under prevailing operating conditions, and (3) less volatile than oxygen.
  • halogenated hydrocarbons are not suitable for use as the diluent of this invention because of poor solubility in liquid oxygen at prevailing conditions, i.e. less than 10 mol percent. Another reason why other lhalogenated hydrocarbons are not suitable is their relatively high freezing points and their tendency to freeze in the ⁇ feed conduit to the cold fractionating equipment. These low solubility compounds would also accelerate passageway obstruction if added in concentrations exceeding their solubility limits.
  • the inert diluent-containing-oxygen-enriched liquid descending in passageway upper section 23 is rectied by the rising oxygen-rich vapors, and the higher boiling soluble diluent is progressively concentrated in the lower end 24 of upper section 23 along with ethane.
  • the boiling point of this liquid increases by virtue of the increasing concentrations of inert soluble diluent, ethane and xenon (if present), and the decreasing oxygen concentration.
  • the resulting small liquid pool 26 accumulates in section 24 immediately above obstruction 22. It has been found that the boiling point of liquid pool 26 rises suiciently to eliminate boiling thereof before the ethane concentration reaches 4%.
  • the practice of this invention actually eliminates the explosion hazard by preventing the ethane concentration from attaining the hazardous level.
  • This is in contrast to many previously employed and ineifective methods in which the hydrocarbon concentration in the liquid oxygen body is monitored, and apprporiate measures are taken when the ethane concentration increases.
  • the present invention recognizes that the explosion hazard does not usually occur in the bulk liquid oxygen but rather in an undetectable obstructed passageway in which boiling ethane-containing oxygen-enriched liquid is accumulating.
  • the present invention does not by itself eliminate the problem of explosion hazards due to hydrocarbon buildup in an obstructed liquid oxygen-enriched passageway.
  • Other means such as adsonption traps must be provided to remove the bulk of the acetylene in the air feed. Without such other means acetylene will lreadily concentrate in the oxygen-enriched liquid (even without passageway obstruction) to about 1.2 p.p.m. or higher. ln an obstructed passageway acetylene need concentrate inthe oxygen-enriched liquid to only a yfew p.p.m. to begin formin-g an easily detonated solid phase.
  • This invention does not desensitize the oxygen-enriched liquid provided at the upper end of the obstructed passageway or the oxygen-enriched liquid body entering the lower end of this passageway. That is, a concentration of less than about 1000 p.p.m. soluble diluent is far below the concentration necessary to significantly aiect the explosive propensity or characteristic of ethane, oxygen-enriched liquid. A diluent concentration of at least 5000 p.p.m. (0.5%) and preferably at least 20% is necessary to desensitize a body of oxygen-enriched liquid.
  • the specific concentration of inert soluble diluent needed to avoid an explosion hazard in an oxygen-enriched liquid boiler-heat exchanger with an obstructed passageway depends not only on the ethane concentration of this liquid, but also on the temperature difference between the boiling liquid and the warmer heat exchanging lluid.
  • a minimum required ratio exists between the total inert diluent material (e.g. monochlorotriuorometh-ane and atmospheric xenon) and the ethane present, so that for increased amounts of ethane in oxygen-enriched liquid an increased amount of externally introduced inert diluent material will be needed.
  • a relatively large AT will require a larger concentration of diluent to raise the boiling point of the oxygen-enriched liquid suiciently to overcome this AT, eliminate boiling and further ethane concentration to the 4% level.
  • FIG. 4 is a family of curves for various AT values between 1.5 C. and 3.5 C., the monochlorotritiuoromethane concentration being plotted as the abscissa and the ethane concentration as the ordinate.
  • the curves indicate the concentration of monochlorotriuoromethane needed in substantially pure liquid oxygen to eliminate the temperature difference and boiling of liquid oxygen at a certain ethane concentration in this liquid. For example, if the temperature difference is 2.0 C. and the boiling liquid oxygen has an ethane concentration of 200 p.p.m., a mono- Y chlorotrifluoromethane concentration of 600 p.p.m. is needed in this liquid to eliminate the boiling.
  • the monochlorotriuorometh-ane concentration should be about 800 p.p.m.
  • tetrauoromethane is employed as the inert diluent, except that relatively more diluent is needed because of its lower boiling point and higher relative volatility with respect to oxygen (see Table A).
  • the boiling liquid contains significant quantities of nitrogen, e.'g. 50% O2, with the balance N2 and atmospheric inerts.
  • FIG. 5 illustrates a liquid oxygen boiling-nitrogen vapor condensing heat exchanger 30 comprising a series of oxygen passageways 31 in alternating sequence with nitrogen passageways 32 and bonded thereto for heat exchange by solid conduction between the passageway walls.
  • Each oxygen passageway 31 is thermally associated with, and separates adjacent nitrogen passageways in a sandwich-type assembly.
  • the nitrogen passageways are manifolded together (by means not illustrated) at both the upper inlet end in communication with inlet conduit 33, and the lower discharge end in communication with the discharge conduit 34.
  • the oxygen passageways 31 are open at both their lower and upper ends, the former communicating with bottom chamber 35 having liquid oxygen inlet means comprising downcomer 36 from a series of rectication stages.
  • the oxygen passageway upper ends are joined by nitrogen passageway closure means 18 forming the base of upper chamber 15.
  • the inert soluble diluent is introduced to 4bottom chamber 3S through conduit 37 and control valve 38 therein.
  • Liquid oxygen at about -181 C. and 5 p.s.i.g. is forced by hydrostatic head through the lower end of passageways 31 to a level preferably at least two-thirds of the distance between the lower and upper end.
  • Cold nitrogen vapor at about 178 C. and 75 p.s.i.g. is introduced through inlet conduit 33 at the upper end of the heat exchanger 30 and flows downwardly through passageways 32.
  • Heat is transferred from the nitrogen vapor to the oxygen liquid through the thermally associated ⁇ passageways 31 and 32, by the temperature difference of 3 C. for boiling of the oxygen liquid and condensation of the nitrogen vapor, the latter being withdrawn through discharge conduit 34.
  • the resulting oxygen liquidvapor mixture emerges from-the upper ends of passageways 31 and the vapor may be withdrawn as product through conduit 39 or passed upwardly through a series of rectification stages (not shown) in communication with upper chamber 15 for contact with a downwardly iiowing liquid.
  • the ethane concentration of the liquid oxygen pool 11 in bottom chamber 35 is monitored. This for example may be accomplished by liquid phase sampling conduit 40 communicating with analyzer 41, as for example comprising a gas chromatograph and ilame ionization detector. The concentration of the inert soluble diluent, introduced through conduit 37 and control valve 38, is monitored in the same manner.
  • an obstruction 22 forms in at least one oxygen passageway intermediate the lower and upper ends thereof and the liquid oxygen descending into this passageway is rectied by the rising vapors.
  • the ethane concentration of the liquid immediately above the obstruction increases.
  • the soluble inert diluent concentration in the upper section of obstructed passageway 10 is sufficient to eliminate the AT across this particular passageway and eliminate liquid oxygen boiling therein.
  • the remaining unobstructed passageways 31 continue to operate in the normal manner and are substantially unaffected by the inactivity of passageway 10.
  • the ethane and soluble inert diluent concentrations in the remaining passageways 31 will remain constant lbecause they are not dead-ended.
  • Percent *Diluent is n1onochlorotrifluoromethane.
  • oxygen-enriched liquid refers to a liquid containing more than the normal -concentration of oxygen in air, i.e. 21%.
  • the liquid accumulating in the kettle or lower end of a rectication column contains about 50% O2, and thus is an oxygen-enriched liquid.
  • This liquid is often boiled in a heat exchanger to extract heat from nitrogen vapor, and the liquid is further enriched in oxygen as it boils.
  • Rectification of the further enriched liquid in an obstructed passageway of the heat exchanger still further concentrates the oxygen along with ethane impurity from the atmosphere. This concentration is sufficient to create an explosive iluid, and the present invention may be etfectively employed to avoid this hazard.
  • higher pressure air may be at least partially condensed as the warmer fluid in heat exchange with the boiling oxygen-enriched liquid.
  • oxygen-enriched liquid is provided at the upper end of said passageways, and an obstruction forms in at least one passageway intermediate the ends thereof: the improvement of avoiding an explosive ethaneoxygen mixture in the obstructed passageway due to ethane accumulation immediately above them obstruction, by adding an inert soluble diluent to said oxygen-enriched liquid body at concentration below about 1000 parts per million relative to said oxygen-enriched liquid body and based on the temperature difference between the oxygenenriched liquid body and the said warm fluid associated therewith and the observed ethane concentration in the oxygen-enriched liquid body, the diluent addition being in sufficient quantity to increase the diluent to second higher concentration in ethane-enriched, oxygen-containing liquid immediately above the obstruction and raise the boiling point of such liquid sufficiently to eliminate boiling of the liquid before its ethane concentration attains 4.0 mol. percent, the said diluent being tetraiiuoromethane.
  • oxygen-enriched liquid is provided at the upper end of said passageways, and an obstruction forms in at least one passageway intermediate the ends thereof: the improvement of avoiding an explosive ethaneoxygen mixture in the obstructed passageway due to ethane accumulation immediately above the obstruction, by adding an inert soluble diluent of monochlorotrii'luoromethane to said oxygen-enriched liquid body at rst concentration below about 1000 parts per million relative to said oxygen-enriched liquid body and based on the temperature difference between the oxygen-enriched liquid body and the said warmer iluid associated therewith and the observed ethane concentration in the oxygenenriched liquid body and consistent with the chart illustrated in FIGURE 4, the diluent addition being in suicient quantity to increase the diluent to second higher concentration in the ethane-enriched, oxygen-containing liquid immediately above the obstruction and raise the boiling point of such liquid suciently to eliminate boiling of the liquid Ibefore its ethane concentration attains 4.0
  • oxygen-enriched liquid is provided at the upper end of said passageways, and ethane accumulates in at least one passageway: the improvement of avoiding an explosive ethane-oxygen mixture in the one passageway due to ethane accumulation, by adding an inert soluble diluent to said oxygenenriched liquid body at yconcentration below about 1000 parts per million relative to said oxygen-enriched liquid body and based on the temperature difference between the oxygen-enriched liquid body and the said warm fluid associated therewith and the observed ethane concentration in the oxygen-enriched liquid body, the diluent addition being in su'icient quantity to increase the diluent to second higher concentration in ethane-enriched, oxygen-containing liquid in said one passageway and raise the boiling point of such liquid sufficiently to eliminate yboiling of the liquid before its ethane concentration attains 4.0 mol. percent, the said diluent being tetrauoromethane.

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  • Engineering & Computer Science (AREA)
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  • Mechanical Engineering (AREA)
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  • General Engineering & Computer Science (AREA)
  • Separation By Low-Temperature Treatments (AREA)
US690684A 1965-05-17 1967-12-14 Avoidance of explosion hazards in air fractionation by halogenated hydrocarbon additin Expired - Lifetime US3397547A (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3720071A (en) * 1969-06-14 1973-03-13 Linde Ag Heat exchanger

Citations (5)

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US2541409A (en) * 1943-06-07 1951-02-13 Richard T Cornelius Gas fractionating apparatus and method
US2918801A (en) * 1955-10-10 1959-12-29 Union Carbide Corp Process and apparatus for separating gas mixtures
US3081157A (en) * 1958-09-19 1963-03-12 Little Inc A Liquid composition comprising liquid free oxygen and method of reducing the sensitivity of same
US3080724A (en) * 1958-09-19 1963-03-12 Little Inc A Reduction of explosion hazards in the separation of gaseous mixtures
US3124443A (en) * 1960-05-17 1964-03-10 Gas fractionating system

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2541409A (en) * 1943-06-07 1951-02-13 Richard T Cornelius Gas fractionating apparatus and method
US2918801A (en) * 1955-10-10 1959-12-29 Union Carbide Corp Process and apparatus for separating gas mixtures
US3081157A (en) * 1958-09-19 1963-03-12 Little Inc A Liquid composition comprising liquid free oxygen and method of reducing the sensitivity of same
US3080724A (en) * 1958-09-19 1963-03-12 Little Inc A Reduction of explosion hazards in the separation of gaseous mixtures
US3124443A (en) * 1960-05-17 1964-03-10 Gas fractionating system

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3720071A (en) * 1969-06-14 1973-03-13 Linde Ag Heat exchanger

Also Published As

Publication number Publication date
DE1551627A1 (de) 1970-04-23
NL6707500A (hu) 1968-12-02
FR1526618A (fr) 1968-05-24
BE726251A (hu) 1969-05-29
GB1103532A (en) 1968-02-14

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