Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B08—CLEANING
  • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
  • B08B9/00—Cleaning hollow articles by methods or apparatus specially adapted thereto 
  • B08B9/08—Cleaning containers, e.g. tanks
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B08—CLEANING
  • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
  • B08B3/00—Cleaning by methods involving the use or presence of liquid or steam
  • B08B3/04—Cleaning involving contact with liquid
  • B08B3/08—Cleaning involving contact with liquid the liquid having chemical or dissolving effect
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B08—CLEANING
  • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
  • B08B9/00—Cleaning hollow articles by methods or apparatus specially adapted thereto 
  • B08B9/08—Cleaning containers, e.g. tanks
  • B08B9/093—Cleaning containers, e.g. tanks by the force of jets or sprays
  • B08B9/0936—Cleaning containers, e.g. tanks by the force of jets or sprays using rotating jets

Definitions

• a typical cargo tank might measure, for example, 30 feet by 30 feet and have a height of 40 feet.
• large surfaces may be relatively smooth and accessible, there are inevitably inwardly extending reinforcing members, frequently with overhanging portions which provide inaccessible surfaces which are extremely difiicult to clean.
• the chemical to be employed in the new method is a type previously used for the cleaning of machinery, the cleaning up of oil spillages on floors and the like, and similar marine and industrial housekeeping in areas which tend to become contaminated with petroleum products and sludge. It comprises a mixture of a highly aromatic petroleum fraction, and a completely miscible emulsifying agent which is capable of producing oil-in-water emulsions. Particularly effective as emulsifying agents are the liquid nonionic surfactants.
• the aromatic fraction should be a mixed methyl-naphthalene type fraction (including mono-, diand poly-methyl-naphthalene) boiling within the range 350'700 F., and having a flash point above 150 F.
• composition should contain about to 94% by volume of aromatic fraction and 6 to 20% by volume of emulsifying agent. Within this range the preferred amount of emulsifying agent will depend upon the nature of the cleaning operation and the intended manner of disposal of collected residues. Thus, while compositions containing to 94% by volume of aromatic fraction, and 6 to 10% by volume of emulsifying agent are generally preferred, somewhat greater proportions of emulsifying agent may sometimes be desirable to provide complete emulsification of the petroleum residues.
• the emulsifying agents for use in the cleaning compositions can be selected from a wide variety of commercially available surfactants which form oil-in-Water emulsions and are miscible with the aromatic petroleum fractions.
• Suitable nonionic surfactants include those in which hydrophobic moieties are condensed with a lower alkylene oxide to form hydrophilic oxyalkylene chains.
• Hydrophobic moieties can be provided by fatty alcohols, alkyl phenols, such as nonyl phenol, octyl phenol, and the like, by polypropylene glycols, and other relatively high molecular weight compounds having free hydroxyl groups.
• condensing such an alcoholic compound with a lower alkylene oxide, such as ethylene oxide has a solubilizing effect which increases with the length of the ethylene oxide chain; but also has a viscosity increasing effect as the molecular weight of the resulting condensates is increased, with the higher molecular weight condensates becoming pastes, or even solids.
• those surfactants should be selected which are liquid and highly water soluble, as well as being miscible with the petroleum fractions.
• a preferred aromatic fraction for use in the cleaning composition is a mixed methylnaphthalene fraction having a boiling range of about 400 to 550 F.; and with this methylnaphthalene fraction preferred surfactants include octyl phenol and nonyl phenol ethylene oxide condensates containing about 9 to 10 mols ethylene oxide per mol of alkyl phenol.
• Such a composition is a transparent liquid of very low viscosity, and generally light amber in color, and has a flash point in excess of 175 F.
• the chemical, or cleaning composition above described is applied as uniformly as possible to all oil and sludge coated surfaces in an enclosure at the rate of about 50 to 80 gallons per thousand tons of tank capacity.
• selection of the optimum amount will depend generally on the nature and thickness of deposits to be removed, and the amount of additional surface Within the tank by reason of beams, bays, and other braces protruding from the walls.
• the dosage of chemical can also be expressed as about to 9 gallons per thousand square feet of surface to be cleaned. In practice, however, it is more practical to relate the dosage to the tank capacity, since this figure will be readily available to operating personnel.
• the application of chemical to contaminated tank surfaces can be accomplished by an operating team of 2 or 3 men entering the tank with hoses and spraying all surfaces as uniformly as possible.
• This method of application permits complete wetting and coating of deposits in inaccessible placesbehind beams and bulkheads, and the like but is subject to variation in the care exerted by the workmen in reaching all areas.
• Careful hand spraying of chemical on inner contaminated surfaces of a tank having a capacity of 800 to 1,000 tons can be accomplished within a period of about one hour to one and one-half hours.
• the tank is allowed to stand to permit a 2 to 6 hour, and preferably a 2 to 4 hour, residence time of the chemical on the tank deposits. During this period the chemical has a chance to thoroughly penetrate the deposit reacting upon and softening even the caked sludge formed in repeated carrying of cargoes, such as residual fuel oil.
• washing the treated tank with either heated or unheated sea water dislodges virtually all of the softened deposits, leaving the walls substantially free of any petroleum residue.
• the washing can be done with hand hoses, requiring a workcrew of 2 to 3 men, or can be done with mechanical washing equipment, the operation in either instance requiring about 1 hours for a 1,000 ton tank.
• the residence time of 2 to 6 hours, and preferably 2 to 4 hours, should be adhered to for optimum results with the new method, as the subsequent rinsing or washing operation tends to be prolonged with a longer residence period.
• Tanks have been found to rinse clean, however, even when washing is done two or three days after the cleaning material has been applied.
• a prefered adaptation of the new tank cleaning method which further reduces cleaning time and costs while eliminating this unpleasant operation of hand application of cleaning material, and the chances of human error in the hand application, involves the generation within the tank of a dispersion of cleaning material in the form of a wet fog.
• wet fog is used to designate a particle size of about 10 to 40 microns. This compares, for example, to a dry fog having a particle size of about 2 to 5 microns, and a misty rain having a particle size of about 50 to microns.
• the particle size of the sprayed material can be within the range of about 5 to 50 microns, provided that the bulk of the material is in the wet fog range of 10 to 40 microns. To better visualize the significance of particle size, attention is directed to the following tabulation:
• the cleaning material when it is realized that the cleaning material is applied at the rate of about 50 to 80 gallons per thousand tons of tank capacity, it will be apparent that the spraying of a wet fog will distribute the cleaning material as a continuous film of appreciable thickness on all inner tank surfaces. It should be noted in this connection, that the cleaning material penetrates rapidly into oil and sludge deposits, thereby minimizing accumulation at the surface of the deposits and runoff of the impinging cleaning material.
• a wet fog of the type suitable for use in the present method can be accomplished with commercially available spray equipment, preferably involving the use of pneumatic atomizing nozzles providing a wide and dense spray pattern, to which cleaning agent and atomizing air are feed at separately and properly controlled pressures to give the desired particle size distribution.
• Suitable nozzles can be obtained from various suppliers, but particularly good results have been obtained wtih Spray Setup No. 29, produced by Spraying Systems Company of Bellwood, Ill., and utilizing their fluid nozzle No. 60100 and air nozzle No. 1406-52-70, which provides a wide angle round spray pattern.
• a preferred apparatus has been an elongated unit with a cluster of nozzles at each end which may be passed through the openings for mechanical washing apparatus, standard on most oil tankers, and the like, and which can then be suspended at different heights within a tank from its midpoint.
• a unit approximately 6 feet long with a total of nozzles, 4 angularly disposed, and 1 axially disposed at each end of the unit have been found to provide excellent spray distribution, and a practical feed rate at the desired operating pressures, permitting discharge of a 1% to 2 times as much cleaning material as previously indicated.
• the rinsing or washing operation is carried out in the manner previously described after a residence time of the cleaning material of about 2 to 6 hours, and preferably 2 to 4 hours. Whether the washing is done by means of hand hoses, or by mechanical washing apparatus, the cleaning results are excellent, generally surpassing to some extent, the results obtained when the cleaning material is applied by hand. This is understandable, since the wet fog application of cleaning material provides a uniformity of contact with contaminated surfaces which is difiicult to achieve with hand application.
• EXAMPLE I A tanker having 20 wing tanks of approximately 1,000 ton capacity and 10 center tanks of approximately 2,000 ton capacity had been carrying Bunker C oil and was now needed for higher grade cargo. Hot mechanical washing for extended periods of time, followed by hand hosing operations, failed to remove the heavy residue on the inner tank surfaces. Subsequent attempts to dissolve the residues by carrying cargoes of crude oil were unsuccessful. At this point, the captain agreed to conduct a test with applicants new cleaning method.
• Cargo Tanks Condition Floor Bulkheads, Frames, etc.
• the spray assemblage in a tank which may be, for example, to feet deep, it is preferable to spray the cleaning material in three stagesfirst, at a point about 4 to 5 feet from the bottom of the tank; second, at approximately the mid-point; and finally, at a point about 6 feet from the top of the tank-discharging at each level about /3 of the total amount of cleaning material desired.
• the number of drops in a particular tank will depend upon the length and width of the tank.
• a conventional tanker for example, where the side or wing tanks are generally elongated lengthwise of the ship and normally equipped with 2 openings for mechanical washing apparatus, it is practical to make 2 drops with the atomizing units.
• a liquid cleaning material consisting of 92 parts by volume of a mixed methylnaphthalene fraction having a boiling range of 400 to 550 F. and 8 parts by volume of a nonyl phenol ethylene oxide condensate containing 9 to 10 mols of ethylene oxide per mol of nonyl phenol supplied in 55 gallon drums, was then hand sprayed on inner tank surfaces using a 3-man crew per tankone spraying, one handling the hoses in the tank, and a safety man on deck tending the pump and equipment.
• the cleaning material was applied at the rate of 55 gallons per 1,000 ton tank, except in two instances (the dirty No. 4 wing tanks) where 82 gallons were used.
• a waiting period of 2 to 4 hours (or longer) was allowed to elapse, and the crew then again entered the tank to wash down the inner surfaces with cold sea water.
• the deposits were easily Washed from the tank surfaces, becoming emulsified in the water collecting at the bottom of the tank, which was pumped out and discharged into the ocean.
• the time required to rinse a tank varied from about 1% hours to about 4 hours depending on the tank size and the resi- 7 dence time of the chemical. When rinsing started within about 6 hours after application of chemical, it could generally be completed in about 1 /2 to 2 hours; but even when rinsing took place 2, 3, or 4 days after application of chemical, it could generally be completed in 3 to 4 hours.
• EXAMPLE II A ship quite similar to that described in Example I was made available for testing a modification of the new cleaning method. This ship had 9 center tanks of approximately 1,900 tons cargo capacity each and 18 wing tanks of approximately 880 tons capacity each. Twenty-six tanks of 31,040 tons cargo capacity were to be cleaned, one center tank being clean. The prior cargo had been crude oil, and in a five-day trip from New York to Port Arthur, Tex., it was desired to prepare the tanks for loading of No. 2 oil.
• wing tanks In the wing tanks two atomizing units were operated simultaneously, at three levels-i.e., 4 feet from the bottom, mid-point, and 6 feet from the top of the tankspraying approximately 15 minutes in each position. In two, very dirty, wing tanks 82 gallons of cleaning material were sprayed as a wet fog, while all other wing tanks received gallons of chemical.
• center tanks received similar treatment except that to drops were made with the spray heads, first in one diagonal position, and then in the opposed diagonal position. In all center tanks, the amount of chemical used was 55 gallons per drop, or 110 gallons per tank.
• the rinsing was done with cold sea water fed through the Butterworth tank cleaning apparatus operated 30 minutes each at three levels in the tank. Three tanks were mechanically washed simultaneously following the order of chemical application, so that the residence time was at least two hours, but less than 6 hours. In this way, the rinsing was completed in 21 hours with two men handling the operation and shifting of hoses for the Butterworth apparatus (approximately 42 man-hours). In two wing tanks which had only one opening for inserting mechanical washing apparatus, slight hand rinsing was needed to complete the washing off of fore and aft ends which the jets of the Butterworth apparatus did not completely reach. All other tanks, however, were rinsed clean by the Butterworth apparatus.
• Example II The total labor involved in this cleaning operation, after the initial mechanical washing, was approximately man-hours, only a small fraction of the labor required with the hand application and hand rinsing procedure of Example I.
• the overall time for chemical cleaning is substantially less in Example II than in Example I.
• Example II The results obtained in the very dirty tanks of Example II were quite satisfactory, indicating that the procedure of Example II has general applicability. Even if extreme conditions were to require supplemental hand rinsing, or even supplemental application of chemical and rinsing of troublesome areas, the prolonged dispersing of chemical as a wet fog and the mechanical cold water rinse with the Butterworth apparatus is preferred as the first, and major, cleaning operation.
• Example II Using the same cleaning material as described in Example I, this was applied by pressure atomizing as a wet fog using a multi-nozzle atomizing unit about 6 feet long, having at each end 4 angularly arranged and one axially arranged nozzles (the nozzles being Spraying Systems Company Spray Setup No. 29).
• the chemical was fed to the atomizing unit at a pressure l520 p.s.i. with air to the atomizing unit at 50 p.s.i.
• the cargo tanks as slop tanks to collect and store cleaning residue from all other tanks and to pump the residue to the storage tanks before emulsification was complete, i.e., with entrained lumps of sludge. Then after the ship is at sea, the stored residue can be discharged in two stages, first the emulsified portion, and then the additional emulsion formed by adding to residual sludge an appropriate amount of cleaning material and additional rinsing water.
• Such a storage use of one or two cargo tanks could, in some instances, be the most economical way of handling the disposal problem for in-port cleaning.
• the initial mechanical washing to wash and gas free cargo tanks is normally desirable for two reasons. It removes a substantial amount of loosely adhering deposits on the inner tank surfaces, thus minimizing the amount of deposit to be removed chemically. Furthermore, the collected oil deposits are of value as a fuel supplement, or for further processing at a refinery. It should be understood, however, that if time were a factor (and realizing that the mechanical washing ties up much of a ships water circulating system for 1 /2 to 2 days) the initial mechanical washing can be eliminated, and cleaning material can be applied by prolonged dispersion as a wet fog directly to unwashed tanks. In such event, cleaning material must be used in greater amount, i.e. 70 to 80, or more gallons per 1000 tons of tank capacity. Chemical application time and rinsing time would be slightly greater than in Example II above when thus handling larger quantities of chemical and cleaning residues, but the overall saving in time and man-power by eliminating the initial mechanical washing could offset or justify the added cost of cleaning material required.
• tanker cargo holds which may be of 1,000 to 2,000 ton and higher cargo capacity, involving the steps of applying a liquid chemical cleaning material to inner tank surfaces, allowing a residence time for optimum action of such cleaning material, and then washing with water to remove chemical and dislodged deposits from the tank surfaces;
• the improvement for providing uniform application of cleaning material to all inner tank surfaces including inaccessible surfaces of structural and support members that comprises generating a dispersion of said cleaning material within said tank in the form of a wet fog having a particle size predominantly within the 10 to 40 micron range.
• said surfactant is a C to C alkyl phenol ethylene oxide condensate containing about 9 to 10 mols of ethylene oxide per mol of alkyl phenol.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Cleaning In General (AREA)
• Cleaning By Liquid Or Steam (AREA)

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Citations (12)

• 1965
  • 1965-05-13 US US455630A patent/US3436263A/en not_active Expired - Lifetime
• 1966
  • 1966-04-13 GB GB16137/66A patent/GB1110437A/en not_active Expired
  • 1966-04-13 GB GB50891/67A patent/GB1110438A/en not_active Expired
  • 1966-05-12 NL NL6606534A patent/NL6606534A/xx unknown
  • 1966-05-12 DE DE19661517883 patent/DE1517883A1/de active Pending

Patent Citations (12)

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