Patent Publication Number: US-3880177-A

Title: Method for transporting waxy hydrocarbon mixtures

Description:
United &#34;Stag &#39;3 Kersch I 7 A3 METHOD FOR TRANSPORTING WAXY HYDROCARBON MIXTURES Keith M. Kersch, Littleton, C010.  
 [73] Assignee: Marathon Oil Company, Findlay,  
 Ohio  
  221 Filed: June 17, 1974 211 Appl. No.: 479,949  
 [75] Inventor:  
 [56] References Cited UNITED STATES PATENTS 9/1969 Wantanabc 264/9 4/1974 Merrill 137/13 Primary E.\-aminer-Alan Cohan Attorney, Agent, or Firm-Joseph C. Herring; Richard C. Willson, Jr.; Jack L. Hummel &amp;  
 [ Apr. 29, 1975 [57] ABSTRACT Waxy hydrocarbon mixtures are transported, e.g., in a pipeline, by fractionating the mixture into at least a relatively low pour point fraction and a relatively high pour point fraction, congealing the high pour point fraction by introducing and dispersing it through nozzles into the bottom of a water column having a highly saline solution in the bottom thereof, the saline solution is 550F. below the temperature of the high pour point fraction, permitting the particles of the dispersed fraction to float up through the column where they come in contact with water at a sufficiently low temperature to substantially solidify the particles, and thereafter separating the congealed particles and slurrying them in at least a portion of the low pour point fraction and transporting the slurry. The hot saline solution, e&#39;.g., an aqueous potassium alum solution, is preferably at saturation conditions and the water above the hot saline solution is at least 80F. less than the average temperature of the saline solution and less than the pour point of the high pour point fraction.  
 20 Claims, No Drawings METHOD FOR TRANSPORTING WAXY HYDROCARBON MIXTURES BACKGROUND OF THE INVENTION 1. Field of the Invention Waxy&#34; hydrocarbon mixtures are fractionated into at least a fluid fraction and a wax fraction. The wax fraction is congealed into small wax particles and then slurried into the fluid fraction to obtain a pumpable slurry.  
 2. Description of the Prior Art Pumping viscous hydrocarbon mixtures at tempera tures below the pour point is very difficult. Many methods have been tried to improve the pumpability, e.g., heat transfer methods, chemical agents to improve fluidity of the mixture, pour point depressants, diluents, etc.; but, these methods have generally not been commercially acceptable. In addition, the oil has been dispersed in water to form a water-external emulsion and the combination pumped at temperatures below the pour point of the crude oil.  
 Patents representative of the art include:  
  In a process taught in U.S. Pat. No. 271,080, Kells separates wax from crude oil by dispersing it, through nozzles, into the bottom of a tower wherein the oil is countercurrently contacted with refrigerated salt water. The wax is congealed as it floats to the top of the tower and is recovered in granular form.  
  British Pat. No. 282,994 teaches making pellets of wax by introducing a stream of molten wax into a liquid at a temperature higher than the melting point of the wax to form droplets of the wax; thereafter it passes the wax through the liquid at a lower temperature than the first liquid and then passes the wax into a liquid at a sufficiently low temperature to congeal the wax.  
  U.S. Pat. No. 346,448 teaches the separation of wax from hot paraffin distillate by gradually cooling it first in fresh water, then in saline water, and thereafter in brine at 20 to -lF.  
  Oberfell et al. in U.S. Pat. No. 2,526,966 teaches the transportation of viscous crude oils by removing the light hydrocarbons, hydrogenating the residue to increase the fluidity thereof and then combining teh hydrogenated product and the light hydrocarbons and pumping the mixture.  
  U.S. Pat. No. 3,234,122 teaches transporting waxy crudes by first precipitating the wax in the form of large discrete crystals and thereafter transporting the crude oil containing the crystals. The crystals are formed by first heating the crude oil to 200F. and then cooling it at lF./min to 60F.  
  Scott et al. in U.S. Pat. No. 3,269,401 teaches a process wherein the pumpability of waxy crude oils is improved by dissolving in the oil, at superatmospheric pressure and above its pour point, gases such as N CO flue gas, and hydrocarbons containing up to 3 carbon atoms. The gas becomes associated in some way with the wax crystals and prevents the precipitated wax from agglomerating to form strong wax structures.  
  Scott in U.S. Pat. No. 3,292,647 teaches pipelining waxy crude oils by first shearing the crude at a temperature below its pour point to break down the wax and form a fine dispersion, then he combines a gas, e.g., N CO and natural gas, with the sheared crude to prevent regrowth of the wax crystals and thereafter pumps the composition.  
  Dorsey in U.S. Pat. No. 3,321,426 teaches forming freeflowing wax particles by agitating molten wax in a nonsolvent (water) at a temperature above the melting point of the wax and thereafter cooling the mixture and separating the congealed pellets of wax. Agitation is effected by shearing the wax as it is extruded into the nonsolvent.  
  Kane in U.S. Pat. No. 3,425,429 teaches transporting viscous crude oils by forming an oil-in-water emulsion and pumping the emulsion. The water within the emulsion contains a nonionic surfactant.  
  Watanabe in U.S. Pat. No. 3,468,986 teaches forming spherical particles of wax by melting the wax, then dispersing it in a nonsolvent liquid (e.g., water) maintained at a temperature above the solidification temperature of the wax and thereafter cooling the dispersion to solidify the dispersed droplets. The particles can be coated with finely divided solids such as calcium carbonate, etc. Watanabe teaches that it is known in the art to disperse waxy particles by molding, prilling, spray drying, extruding, etc.  
  Simon et al in U.S. Pat. No. 3,487,844 teaches transporting viscous crude oils by admixing water containing a base and an emulsifying agent to obtain an oil-inwater emulsion and thereafter pipelines the emulsion. The emulsion contains 50-70 percent oil and 30-50 percent water.  
  Titus in U.S. Pat. No. 3,527,692 teaches transporting crushed oil shale -325 mesh size) in a solvent such as crude oil, retorted shale oil, or fractions thereof.  
  This technology, except for heat transfer systems, e.g., heat exchangers to heat the crude oil, and crude oil-water suspension systems, has generally proven to be commercially unattractive where the crude oil contains relatively large concentrations of wax.  
 SUMMARY OF THE INVENTION Waxy hydrocarbon mixtures can be transported by fractionating the mixture into at least a low pour point fraction (liquid fraction) and a high pour point fraction (wax fraction), dispersing the wax fraction in molten form into a column having a hot, dense, relatively static liquid in the bottom thereof and a lower density, colder liquid in the top thereof. The hot dense liquid facilitates the formation of substantially spherical wax particles that have minimum surface area and the cold, less dense liquid is of sufficiently low temperature to substantially congeal the dispersed wax particles as they float to the top of the column. These different density liquids permit a stable temperature gradient to be established in the column. The liquids are preferably water and the hot water is made more dense than the cold water by dissolving a material that has a high solubility in hot water and a low solubility in cold water. The congealed particles are separated from the liquid and slurried in the low pour point fraction and transported, preferably in a pipeline.  
 PREFERRED EMBODIMENTS OF THE INVENTION Waxy hydrocarbon mixtures having a pour point below the seasonably ambient temperature of the transportation system, e.g., a pipeline, are particularly applicable with this invention. Waxy hydrocarbon mixtures used herein as mixtures which contain wax defined as the precipitant which forms after one part of hydrocarbon mixture is dissolved in 10 parts of methyl ethyl ketone at about 80C. and the mixture cooled to -25C. Some asphaltenes can be tolerated. Examples of such mixtures include crude oil, shale oil. tar sand oil, fuel oil, gas oil, and like hydrocarbon mixtures or mixtures of two or more of the same type ordifferent hydrocarbon mixtures. Crude oils are particularly useful with this invention, especially the waxy&#34; crude oils. Examples of the latter include crude oils which exhibit a waxy gel appearance at seasonably ambient temperatures and which contain about one to about 80 percent wax, and preferably those which have an average pour point above the average minimum temperature of the transportation system. Specific examples of average pour points of waxy crude oils useful with this invention include about l to about 200F., and preferably about 0 to about 150F. and more preferably about 75 to about l50F.  
  The hydrocarbon mixture is first fractionated into at least liquid and wax fractions. The wax fraction is about 1 to about 80 percent and preferably about 5 to about 70 percent and more preferably about to about 60 percent by weight of. the original hydrocarbon mixture. It is to be understood that fractions other than liquid fraction and the wax fraction can be obtained from the hydrocarbon mixture and that these fractions canbe used in other process streams in a typical refinery, etc., or in conjunction with this process.  
  Fractionation can be by any process which separates the hydrocarbon mixture into high and low pour point fractions. Optionally, a part of the wax fraction can be cracked and/or hydrogenated during fractionation or before congelation.  
  The molten wax is preferably about 0 to about 175F. and more preferably about to about 150F. and most preferably about 50 to about lF. above its melting point (as defined by inverse cooling curve&#34; in Characterization of Petroleum Waxes, S.W. Ferris, Chapter 1 of The Proceeding of the ASTM TAPPI Symposium on Petroleum Waxes, Feb. 18-21, l963, Special Technical Association Publication, STAP, No. 2) as it is dispersed into the column. Also, it is preferred that the temperature of the molten wax be high enough that there is substantially. no crystalline structure (including hydrocarbons other than wax) within the molten wax and that maximum durability or integrity of the resulting wax particles, while dispersed in the slurry be obtained. If the wax fraction has not been cooled to a temperature below the above preferred temperature range since coming from the distillation column, it can be introduced directly into the column and still obtain durable wax particles.  
 Cooling The molten wax is cooled in two stages. First, the wax is dispersed into a hot, dense wax immiscible liquid (coolant) at a temperature which relatively slowly cools the wax while interfacial tension forms smooth, substantially round, preferably shperical, dispersed wax particles. Then, the particles are passed into a colder, less dense liquid (colder coolant) to substantially complete the solidification of the particles.  
  The hot, dense coolant should have a temperature above the pour point of the wax, but below the wax temperature. Preferably the coolant is at least about 5 to about. 150F. and preferably about 10 to about 100F. and more preferably about 20 to about 80F. below the molten wax temperature as it is dispersed into the column. Examples of useful temperature include at least ]40F. and preferably about lF. when the coolant is water.  
  Superior results are obtained through the use of substantially concentrically arranged nozzles wherein the wax is injected or extruded into the coolant through a central orifice preferably about 0.025 to about 0.5 inch and more preferably about 0.050 to about 0.100 inch in diameter. The coolant can be introduced through an annular nozzle so that it flows cocurrent and concentric to the wax. Velocity of the wax and coolant is preferably within the laminar flow region. Different flow rates can cause turbulence, reduce the size of the particle and roughen the surface of the particle.  
  The cooled wax particles should have an average di ameter of about 0.05 or less to about 20 or more mm. and preferably about 0.1 to about 10 mm. and more preferably about 1 to about 8 mm. The particles are preferably spherical, but can be elongated and can be of either substantially uniform or random diameter sizes.  
  The wax particles then come in contact with the colder, less dense, wax immiscible liquid (colder coolant) to obtain a substantially solidified particle. The colder coolant can be about ambient temperature and is preferably about 3 to about F. below the solidification temperature of the wax. The particles follow a sufficiently long flow path to substantially solidify the wax droplets.  
  Temperature change from the hot, dense coolant to the colder, less dense coolant can be controlled by regulating either heat input or output in the column by heat exchangers, or the temperatures of the materials introduced into column. The temperature change can be a gradual change or a combination of a gradual change in the bottom of the column and an abrupt change in the top of the column, or any desired modification thereof. However, it is necessary that the temperature change of the coolants be sufficient to cool the average temperature of the wax particle below the average pour point of the wax.  
  The coolant and the colder coolant should be more dense than the wax particle and can be any liquid that is substantially immiscible with the wax at the dispersing temperature but which have different densities. The density differential between the coolant and the colder coolant should be at least about 0.2 g/cc and preferably at least about 0.4 g/cc. Also, the compositions of these different density coolants should permit a stable temperature gradient to be maintained in the column, i.e., preferably the compositions should not facilitate mixing. Examples of coolants include organic materials such as halogenated hydrocarbons but preferably the coolants are water containing water-soluble, density imparting agents which obtain the above properties.  
  Examples of water-soluble agents are salts such as potassium alum, potassium metaphosphate, aluminum acetate, fluoride compounds such as strontium fluoride, like materials, and mixtures thereof. Concentration of the salt within the hot water is preferably at saturation conditions; however, lesser concentrations are useful. The concentration of the salt can be in excess of saturation (i.e., in a free crystalline state), this permits solubilization of salt that might be removed from the hot water by the colder water and/orwax particles as they pass through the hot water. Solubility of the salt is desirably much greater in the hot water than it is in cold water. The salt can be added periodically to the column by methods known in the art. Combinations of two or more salts in the hot and/or colder water layers are useful. The colder, less dense coolant should have a low solubility for a given salt while the hot, dense coolant should have a high solubility for the same salt. This permits a more stable temperature gradient to be established and also permits better segregation of the hot dense coolant from the colder, less dense coolant.  
  Design of the column can be constructed to facilitate confining the hot dense coolant to the bottom fo the column-this can be accomplished by known methods such as baffling, physical confinement of the hot dense coolant by temperature control, etc.  
  The colder coolant can flow cocurrent or countercurrent to the flow of the dispersed wax. It preferably enters at ambient or colder temperature. The colder coolant can be recycled through a heat exchanger to remove heat. Make-up water can be added when necessary.  
  It is to expected that the density imparting agent may adhere to the wax particles as the particles move through the column. lf desirablethe agent can be removed by washing the particles, preferably after they are separated from the colder coolant, and then recycling the agent back into the column.  
  Other additives can be added along with the density imparting agent to impart desired properties. For example, flocculating agents can be added to enlarge the crystals of the salts so that they will settle more rapidly when the water is oversaturated with the salt.  
  The temperature and density of the hot, dense coolant should be such that surface tension forces between the hot coolant and the molten wax facilitate obtaining minimum surface area of the dispersed wax particles. The column may be designed to permit heat input into the hot, dense coolant on a periodical or continual basis. However, the molten wax may be hot enough to supply sufficient heat to the hot, dense water to maintain the desired temperature conditions.  
  Solidification, as used herein, includes congealing, crystalization and making into a consistency like jelly. Preferably the solidified particle has at least a hard veneer on the wax particle. The interior of the particle can be fluid, but is preferably substantially solid.  
  A surfactant can be incorporated into the molten wax. Volume amounts of 0.001 to about 20 percent and preferably about 0.01 to about percent and more preferably about 0.1 to about 1 percent, by volume based on the fraction, are useful. Examples of useful surfactants include fatty acids, e.g., containing about 10 to about carbon atoms, and preferably the monovalent cation-containing salts thereof. Sorbitan monolaurate is an example of a useful surfactant. Preferably the surfactant is a petroleum sulfonate and more preferably one containing a monovalent cation, e.g., sodium or ammonium, and preferably having an average equivalent weight of about 200 to about 600, more preferably about 250 to about 500, and most preferably about 350 to about 420.  
  At the top of the column, the solidified wax particles are removed. This can be effected by removing the particles and the colder coolant and thereafter separating the particles by means known in the art, e.g., by mechanical means such as straining the coolant from the particles, etc.  
  In a preferred embodiment, the liquid fraction or a liquid hydrocarbon is introduced into the top of the column to physically remove the wax particles. In this case, an interface between the colder coolant and the liquid hydrocarbon is maintained at a point below the elevation in the column at which the particles are removed. The particles tend to accumulate at the interface.  
 Slurry Preparation The liquid hydrocarbon (this term is defined to include the liquid fraction) should be at least 5 and more preferably at least about 30 and most preferably at least about F. below the solution temperature of the solidified wax particles when the liquid hydrocarbon is slurried with the particles. Solution temperature is defined as that temperature at which a major portion of the particles are in solution in of the liquid hydrocarbon.  
  During the slurrying operation, the temperature of the liquid hydrocarbon is such that the resulting slurry temperature is preferably about 5 to about 10F. above and more preferably 0 to about 5F. above the minimum seasonably ambient temperature of the transportation system. Also, it is preferred that the temperature of the liquid hydrocarbon during slurrying is about 30F. and more preferably about 70F. below the solution temperature of the particles in the fraction.  
  The usual techniques and equipment for slurrying solids in liquids are useful in our process. However, the liquid hydrocarbon should be at least about 5 and more preferably at least about 30 and most preferably at least about 70F. below the solution temperature of the particles in the liquid hydrocarbon and have a pour point at least 1 and preferably at least 5F. and more preferably at least about 15F. below the average temperature of the transportation system.  
  Also, it is preferred that the temperature of the liquid hydrocarbon be low enough during the slurrying operation to provide a slurry temperature preferably about 10F. below to about 10F. above and more preferably at about the minimum seasonably ambient temperature of the transportation system.  
  A liquid and/or gaseous diluent such as straight run gasoline, CO N reservoir condensate or light hydrocarbon can be admixed with the liquid hydrocoarbon before, during or after the slurrying operation. Any diluent is useful as long as it is miscible with the liquid hydrocarbon, has a pour point below the minimum temperature of the transportation system and does not readily solubilize the wax particles or cause any reaction to substantially increase the solubility of the wax particles in the liquid hydrocarbon. Crude oils can be used as the diluent, but preferably the crude oil has a wax concentration less than about 10 percent-the wax can be in crystalline form. Where a gaseous diluent is used, it is preferred that it be dissolved in the slurry at transportation condition to prevent cavitation of pumps.  
  Concentration of the wax particles in the slurry is preferably about 1 to about 60 percent or more and preferably about 5 to about 55 percent and most preferably about 20 to about 45 percent by weight. Transportation of the Slurry The temperature of the slurry during transportation is preferably below the solution temperature of the wax particles at substantially all times. The slurry can withstand temperatures higher than the solution temperature of the wax for short periods of time so long as substantial amounts of the wax particles are not reliquefied. But if the temperature does exceed the solution temperature, the slurry can still be effectively transported in a pipeline as long as the temperature does not cycle more than preferably about 35F. below the highest temperature reached by the slurry during transportation. Also, as long as the temperature is increasing during the pipelining, even above the solution temperature, there is no detrimental effect. However, when the temperature decreases to more than about 10F. below the highest transportation temperature, then large pressure drops occur.  
  Transportation system, as used herein, tanks, tank trucks, tank trailers, tank barges, ships or tankers, pipelines, pipelines and tank batteries, or holding tanks and combinations thereof. Preferably the transportation system is a pipeline or a pipeline plus tanks.  
  The slurry can be transported under laminar flow, transitional flow (e.g., Reynolds Nos. about 2,000 to about 4,000) or turbulent flow conditions in the conduit. It is preferably transported under laminar and transitional flow conditions-turbulency within the pipeline tends to break apart and solubilize the wax particlesv in the liquid hydrocarbon of the slurry.  
  The slurry is preferably transported in a conduit wherein the average maximum temperature of the conduit is below the average solution temperatureof the wax particle in the liquid hydrocarbon.  
  In addition, the average temperature of the conduit is desirably not below the average pour point of the liquid hydrocarbon and preferably is at least about 20F. and more preferably at least about 25F. above this pour point.  
  The wax particles can also be coated with solid materials or other agents to inhibit agglomeration and to permit higher slurry transportation temperatures.  
 Working Example The following example is presented to teach working embodiments of the invention. Unless otherwise speci fied, the percents are based on weight.  
 EXAMPLE A crude oil having an average pour point of ll5F. is distilled into a low pour point fraction (average pour point 17F.) and a high pour point fraction (average pour point 125F., melting point l80F.). The high,  
 pour point fraction is heated to and maintained at 230F. in a holding tank. The high pour point fraction is pumped at a rate of 3.5 lb/hr through a nozzle (6 inches long and 0.080 inch inside diameter) into the bottom of a glass column filled with water-temperature of the molten wax as it is dispersed into the column is 218F. The column has an inside diameter of 2 inches and is 36 inches long and has 4 inches (measured from the base of the nozzle) of hot, dense water (hot cool ant) at 145F. saturated with&#39;potassium alum; Above the layer of hot alum, there is 32 inches of water saturated with alum but at a temperature of about 80F. Water is withdrawn about one-eighth inch above the interface of the hot alum and is circulated through a cooling chamber and introduced back into the top of the column at about 70F. to congeal the hot wax being dispersed into the column. A heater is submerged into the hot alum to maintain the temperature at 145F. The wax is dispersed into the bottom of the column under laminar flow condition and is congealed by the time it reaches the top of the column. At the top, the congealed, spherical wax particles plus a portion of the water is removed; the water is separated, passed through a cooler and then into the top of the water column. Alum is periodically added through the top of the column and permitted to settle down into the hot alum solution to maintain the saturation conditions. The wax particles are slurried in the low pour point fraction to obtain a concentration of about &#34;30 percent of wax beads and the resulting slurry is pumped in a pipeline under conventional pressures without unusual pressure drops.  
  It is not intended that all equivalents obvious to those skilled in the art be incorporated within the scope of the invention as defined within the specification and appended claims.  
 What is claimed is:  
  1. An improved process of transporting a waxy hydrocarbon mixture comprising fractionating the mixture into at least a high pour point fraction and a low pour point fraction, cgggealing at least a portion of the high pour point fraction by dispersing it as molten wax particles into the bottom of a column having a hot dense liquid in the bottom thereof and a colder, less dense liquid in the top thereof, permitting the wax particles to move to the top of the column, the colder, less dense liquid being at a sufficiently low temperature to substantially solidify the wax particles by the time they reach the top of the column, separating the solidified wax particles and slurrying at least a portion of the solidified particles in a liquid hydrocarbon comprised of at least a portion of the low pour point fraction and thereafter transporting the slurry.  
  2. The process of claim 1 wherein the hot dense liquid is at a temperature of at least l40F.  
  3. The process of claim 1 wherein the colder, less dense liquid is at a temperature less than about F.  
  4. The process of claim 1 wherein the coolants are water and the different densities of the hot dense water and the colder, less dense water are obtained by incorporating water soluble salt.in the water. I  
  5. The process of claim 4 wherein the salt is potassium alum, potassium metaphosphate, aluminum acetate, strontium fluoride or mixtures thereof.  
  6. The process of claim 1 wherein the temperature of the molten wax as it is introduced into the column is about 0 to about 175F. above its melting point.  
  7. The process of claim 1 wherein the temperature of the molten wax is about 20 to about 150F. above it melting point.  
  8. The process of claim 1 wherein the temperature of the molten wax is about 50 to about F. above its melting point.  
  9. The process of claim 1 wherein the hot, dense liquid is at least about 5 to about F. below the temperature of the molten wax as it is dispersed into the column.  
  10. The process of claim 1 wherein the molten wax as it is introduced into the column is under laminar flow.  
  l l. The process of claim 1 ,wherein the density differential of the hot, dense liquid compared to the colder, less dense liquid is at least about 0.4 g/cc.  
  12. The process of claim 11 wherein the density differential is at least about 0.2 to about 0.4 g/cc.  
  13. The process of claim 1 wherein the concentration of solidified wax particles in the liquid hydrocarbon is within the range of about 20 to about 45 percent by weight.  
  14. The process of claim 1 wherein at least a major portion of the wax particles is substantially solidified.  
  15. The process of claim 1 wherein the waxy hydrocarbon mixture has an average pour point within the range of about 75 to about 150F.  
  16. The process of claim 1 wherein a diluent miscible with the liquid hydrocarbon is admixed with the slurry to facilitate transportation.  
  17. The process of claim 1 wherein the diluent is a liquid crude oil containing less than 10 percent wax.  
  18. An improved process of transporting a waxy hydrocarbon mixture comprising fractionating the mixture into at least a high pour point fraction and a low pour point fraction, congealing at least a portion of the high pour point fraction by dispersing it as molten wax particles into the bottom of a column having a hot dense, saline water in the bottom thereof and a colder,  
 less dense water in the top thereof, permitting the wax particles to move to the top of the column, the colder, less dense water being at a sufficiently low temperature to substantially solidify the wax particles by the time they reach the top of the column, separating the solidified wax particles and slurrying at least a portion of the solidified particles in a liquid hydrocarbon comprised of at least a portion of the low pour point fraction and thereafter transporting the slurry.  
  19. The process of claim 18 wherein the hot dense, saline water is at about 5 to about F. below the temperature of the molten wax as it is dispersed into the column.  
  20. The process of claim 18 wherein the temperature of the molten wax as it is introduced into the column is about 0 to about F. above its melting point.  
 *zg g UNITED STATES PATENT OFFICE CERTIFICATE 0F QORRECTION Patent No. 3 880 177 ,Dated April 29 1975 Inventor(s) Keith M. Kersch It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:  
 Col. 1, line 44: Delete &#34;Teh&#34; and insert -The.  
 Col. 3 line 57: I Delete &#34;shperical&#34; and insert -&#39;--spherical-.  
 Col. 5, line 10: I Delete &#34;f0&#34; and insert --of-.  
 Col, 6, line 9: Add --about-- after &#34;least&#34;.  
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 1 Col. 8, line 11: 4 I Delete &#34;not&#34;.  
 Claim 7, line 2: Delete &#34;it and insert -its.,  
 En&#39;gned and Sealed this thirtieth D ay 0f September I 9 75 [SEAL] A ttest:  
 RUTH C. MASON C. MARSHALL DANN Altuung ()fjlver (&#39;mnmissimwr of Patents and Trademarks