US3893003A

US3893003A - Method for reducing the strength of electrostatic fields in an oil tanker

Info

Publication number: US3893003A
Application number: US390803A
Authority: US
Inventors: Julian H Dancy
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1973-08-23
Filing date: 1973-08-23
Publication date: 1975-07-01
Anticipated expiration: 1992-07-01

Abstract

The method permits an electrostatic field strength in a substantially empty hold of a tanker to be reduced safely during washing of the hold. The method provides a supply of water to a predetermined location in the hold of the tanker where it is converted to a mist and distributed throughout the hold of the tanker. As the water is converted to a mist, the water acquires a charge opposite in polarity to the polarity of the initial electrostatic field caused by the charged mist generated by the washing process. The added mist is distributed throughout the hold, mixing with the charged washing mist, so that the net strength of the electrostatic field is substantially less than that of the initial electrostatic field.

Description

United States Patent 11 1 Dancy 1 1 METHOD FOR REDUCING THE STRENGTH OF ELECTROSTATIC FIELDS IN AN OIL TANKER [75] Inventor: Julian H. Dancy, Richmond, Va.

|73| Assignee: Texaco Inc., New York, NY.

[22] Filed: Aug. 23, 1973 211 Appl. No; 390,803

152] U.S. Cl 317/2 R; 134/22 R; 239/3 I51] int. Cl. HOSf 3/00 [58] Field of Search 239/3. 15; 244/1 A;

317/2 R, 2 D, 2 E; 134/10, 22 R, 24; 118/621, 629, 627

[56] References Cited UNITED STATES PATENTS 632185 8/1899 Jones .1 317/2 R X 2.065.462 12/1936 Olsson 3,164,747 1/1965 Yahnke 3,188.238 6/1965 Lyon 3,384,446 5/1968 Ziems et a1. 239/3 X PUMP FILTER REG 1 July 1,1975

3.802.625 4/1974 Buser et ul 239/15 Primary Examiner-R0bert S. Ward, Jr.

Assistant Examiner-Randolph A. Reese Attorney, Agent, or FirmT. H. Whaley; C. G. Ries;

Ronald G. Gillespie [57] ABSTRACT The method permits an electrostatic field strength in a substantially empty hold of a tanker to be reduced safely during washing of the hold. The method provides a supply of water to a predetermined location in the hold of the tanker where it is converted to a mist and distributed throughout the hold of the tanker. As the water is converted to a mist, the water acquires a charge opposite in polarity to the polarity of the initial electrostatic field caused by the charged mist gener' ated by the washing process. The added mist is distributed throughout the hold. mixing with the charged washing mist, so that the net strength of the electrostatic field is substantially less than that of the initial electrostatic field.

12 Claims, 2 Drawing Figures AIR F'LTER SUPPLY OF TANKER METHOD FOR REDUCING THE STRENGTH OF ELECTROSTATIC FIELDS IN AN OIL TANKER BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method for reducing the strength of an electrostatic field.

SUMMARY OF THE INVENTION The method reduces the strength of an electrostatic field in a substantially enclosed volume. The method comprises providing a liquid at a predetermined pressure at a predetermined location in the enclosed volume in a manner so that the liquid acquires a charge opposite in polarity to the polarity of the electrostatic field. The charged liquid is converted to droplets so as to provide a mist. The mist is distributed throughout the enclosed volume so that the net strength of the electrostatic field is substantially less than the original strength of the electrostatic field.

The objects and advantages of the invention will appear more fully hereinafter from the consideration of the detailed description which follows, taken together with the accompanying drawings wherein one embodiment of the aforementioned invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration purposes only and are not to be construed as defining the limits of the invention.

DESCRIPTION OF THE DRAWINGS FIG. 1 depicts apparatus for performing a method, in accordance with the present invention, for substantially reducing the strength of an electrostatic field in a hold of a tanker.

FIG. 2 is a detailed drawing of nozzle shown in FIG. 1.

DESCRIPTION OF THE INVENTION In recent years several mammoth oil tankers have experienced explosions. The most probable cause of the explosions has been traced to the existence of an electrostatic field in a substantially empty hold of a tanker, when tank washing activities are carried out, and a subsequent electrical discharge caused by that field occurs in the presence of an explosive atmosphere. The method of the present invention combines a mist, having an electrostatic opposite polarity, with the initial field to substantially reduce the net strength of the electrostatic field and the mist to a level such that a subsequent field-caused electrical discharge, if any, will not cause an explosion.

Referring now to FIG. 1, there is shown a field reduction system. A manifold 1, having nozzles 3, is lowered into the hold of a tanker, through one of several openings generally available to a predetermined depth. For large holds several manifolds with nozzles may be used simultaneously at different locations in the holds. A nozzle 3 is shown in greater detail in FIG. 2. A pump 7 pumps sea water or fresh water through a filter 9 which filters out particles which may clog nozzles 3. Filter 9 may be of the type manufactured by Dayton Electric as their part number 1P635.

A regulator 14 reduces the pressure of the water from filter 9 to a predetermined pressure conducive to providing a mist when the water is discharged from nozzles 3. By way of example, the pressure of the water provided by regulator 14 may be within the range of 15 to 30 psi.

Referring also to FIG. 2, the water leaving each nozzle 3 is initially a fine stream 17 of water before breaking into droplets 18, forming a mist. Due to the presence of a strong electrostatic field, water stream 17 is inductively charged to an opposite polarity from that of the field. As stream 17 separates into droplets 18, each droplet 18 has trapped its charge so that it is charged opposite to that of the field.

Each nozzle 3 provides air not only to help generate the mist but also to move the mist away from nozzle 3. When the mist is not moved away, the collection of charged droplets l8 acts as a space charge to reduce the charging of water stream 17 until very little opposite charge is being induced in water stream 17.

Referring again to FIG. 1, a supply 28 of air provides air to a conventional type air filter 29, which filters out particles from the air to prevent clogging of nozzles 3. The air pressure is not critical and, as such, no regulator is required. Generally, the tanker has a compressed air line which may be used as supply 28. The air from filter 29 is provided to manifold l, by way of hose 35, which in turn provides the air to each nozzle 3.

Referring now to FIGS. I and 2, each nozzle 3 has an inner tubing 37, connected to a hose 39, partially en closed by outer tubing 38 and a T-fitting 40. Tubing 37 has an inner diameter selected to facilitate the creation of a mist. Tubing 37 may, by way of example, be Vs-inch diameter brass tubing. Tubing 38 may be /4-inch diam eter brass tubing, having one end soldered to fitting 40 and the other end rolled to create an orifice 44 with respect to tubing 37 so that compressed air in between

tubings

37 and 38, as hereinafter explained, leaves through the orifice 44. Tubing 37 is separated from tubing 38 by spacers 45.

Tubing 37 projects a predetermined distance from tubing 38, as shown in FIG. 2. The projection is used to increase the efficiency of the induction of the charge in water stream 17. If tubing 37 did not project out of tubing 38, the electrostatic field would induce a charge on tubing 38 taking away from the induced charge of water stream 17.

Fitting 40 has a threaded end which is perpendicular to the longitudinal axis of

tubings

37 and 38; each nozzle 3 is threaded into manifold l by using at threaded end. The air in manifold 1 enters fitting 40 through the threaded end and leaves by way of orifice 44. The remaining end of fitting 40, not yet discussed, is welded to tubing 37 so that air can only leave through orifice 44. Another fitting 48 connects hose 39 to the lastmentioned end of fitting 44 so that water in hose 39 enters tubing 37. Hoses 39 are connected to manifold blocks 50 in groups of threes. Block 50 is connected to tube 15 and facilitates the passage of water from tube 15 to each nozzle 3 through a corresponding hose 39.

Manifold 1 may be a length of brass pipe having tapped holes at predetermined intervals to facilitate the mounting of nozzles 3. The design of manifold l is determined by the volume to be filled with mist. Manifold 1 carries I5 nozzles 3, mounted in groups of threes. The direction of discharge of nozzles 3, about the longitudinal axis of manifold l, for one group is opposite to the direction of discharge for an adjacent group of nozzles 3 to reduce the rotational effect imparted to manifold l by the discharging water from nozzles 3. Nozzles 3 are specially arranged with manifold 1 so as to achieve the maximum distribution of the mist.

The combined strength of the electrostatic field of the initial mist and the sprayed mist is substantially less than the strength of the electrostatic field of the initial mist alone.

The method of the present invention as heretofore described provides a mist in the presence of an electrostatic field in such a manner that the mist assumes an opposite polarity to the polarity of the electrostatic field. The net strength of the electrostatic field is reduced to a safe value, thus eliminating the probability of an explosion due to accidental electrical discharge caused by the electrostatic field.

What is claimed is:

l. A method for reducing the strength of an electrostatic field in a substantially empty enclosed volume, which comprises the following steps of providing a supply of liquid at a predetermined pressure at a predetermined location in the substantially enclosed volume, converting the liquid to droplets to provide a mist, utilizing the electrostatic field to charge the droplets during the converting step to an opposite polarity to the polarity of the electrostatic field, and distributing the oppositely charged mist throughout the substantially enclosed volume so that the net strength of the electrostatic field is substantially reduced.

2. A method as described in claim 1 which further comprises converting the liquid to mists at different locations, and blowing the mist away from each location.

3. A method as described in claim 2 in which the converting step includes providing the liquid through an orifice of a predetermined size, and the blowing step includes providing an air current, having a predetermined direction of flow, through a corresponding orifice in such a manner as to carry the mist away from the orifice.

4. A method as described in claim 3 in which the converting steps include converting the liquid to droplets having a size of 30 microns or less.

5. A method as described in claim 4 in which the predetermined liquid pressure may be within a range of [5 to 30 pounds per square inch.

6. A method as described in claim 5 which further comprises continuing the aforementioned steps when the net strength of the electrostatic field is not less than a predetermined strength, and terminating the method when the net strength of the electrostatic field is less than a predetermined strength.

7. A method for reducing the strength of an electrostatic field in a substantially empty hold in an oil tanker which comprises the following steps of providing a supply of liquid at a predetermined pressure and a predetermined location in the substantially empty hold of the tanker, converting the liquid to droplets to provide a mist, utilizing the electrostatic field to charge the droplets during the converting step to an opposite polarity to the polarity of the electrostatic field and distributing the oppositely charged mist throughout the hold so that the net strength of the electrostatic field is substantially less than the strength of the initial electrostatic field.

8. A method as described in claim 7 which further comprises converting the liquid to mist at different locations in the hold, amd blowing the mist away from each location.

9. A method as described in claim 7 in which the converting step includes providing liquid through an orifice at each location of a predetermined size and a blowing step includes providing the air current, having a predetermined direction of flow, through a corresponding orifice in such a manner as to carry the mist away from the orifice.

10. A method as described in claim 9 in which the converting step includes converting the liquid to droplets having a size of 30 microns or less.

ll. A method as described in claim 10 in which the predetermined liquid pressure may be within the range of l5 to 30 pounds per square inch.

12. A method as described in claim 11 which further comprises continuing the aforementioned steps for a predetermined time interval.

t l i I. l

Claims

1. A method for reducing the strength of an electrostatic field in a substantially empty enclosed volume, which comprises the following steps of providing a supply of liquid at a predetermined pressure at a predetermined location in the substantially enclosed volume, converting the liquid to droplets to provide a mist, utilizing the electrostatic field to charge the droplets during the converting step to an opposite polarity to the polarity of the electrostatic field, and distributing the oppositely charged mist throughout the substantially enclosed volume so that the net strength of the electrostatic field is substantially reduced.

5. A method as described in claim 4 in which the predetermined liquid pressure may be within a range of 15 to 30 pounds per square inch.

11. A method as described in claim 10 in which the predetermined liquid pressure may be within the range of 15 to 30 pounds per square inch.