Ships – Building – Freighters
Reexamination Certificate
2001-05-25
2003-04-01
Sotelo, Jesus D. (Department: 3617)
Ships
Building
Freighters
C210S764000
Reexamination Certificate
active
06539884
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally concerns the simultaneous control of both (i) gaseous emissions, and, in the event of rupture, (ii) spillage, from the loaded tanks of oil tankers.
The present invention particularly concerns the control of both the (i) pressure, and the (ii) constituent components, of ullage space gases in the tanks of oil tankers to the ends of eliminating or abating both (i) gaseous emission of volatile organic compounds (VOCs), and (ii) spillage of oil upon the occasion of rupture, from the tanks.
2. Description of the Prior Art
The transport of crude oil in tankers holds the potential for polluting the environment both from (i) gaseous emissions and (ii) oil spills. The present invention will be seen to deal with abating both aspects of pollution from oil tankers.
2.1 General Description of the Problem
As reported in the article “Volatile organic compounds in oil tankers to be used for propulsion” appearing in Alexander's Gas & Oil Connections, Volume 3, issue #12 for Friday, Apr. 17, 1998, (<http://www.gasandoil.com/goc/reports.rex81660.htm>) during the loading and unloading of crude oil, large quantities of its light components (Volatile Organic Compounds or VOCs) evaporate. Evaporation also occurs during the voyage when the oil splashes around in the cargo tanks.
The tanks are filled with inert gas to prevent the vapors from exploding, the inert gas normally consisting of cleaned combustion gas with an oxygen content below 5% (and hence primarily of nitrogen). To keep the pressure in the storage tanks below 0.14 bar gauge (a typical contemporary design value) the VOC is discharged to the atmosphere through a pipe from the crude oil tanks. The discharged gas, “a mixture of hydrocarbons and inert gas”, represents a substantial loss of energy as well as an environmental problem. The non-methane part of the VOC released to the atmosphere reacts in sunlight with nitrogen oxide and may create a toxic ground-level ozone and smog layer detrimental to human health and the environment. Ozone and smog attack mucous membranes (in the eyes and lungs), crops and forests.
2.2 Magnitude of the Problem
As reported in the article “Evaporation of VOCs during voyage less than expected” appearing in Alexander's Gas & Oil Connections, Volume 3, issue #2 for Thursday, Jan. 22, 1998, (<http://www.gasandoil.com/goc/reports.rex80420.htm>), Minton Treharne & Davies (MTD), an analytical and technical consultancy bureau, believes that crude oil cargo loss through evaporation on a typical voyage from the Persian Gulf to north-west Europe is much less than has been indicated in some quarters. MTD disputes suggestions that the VOC (volatile organic compounds) release from a 300,000 dwt VLCC fully-laden with Iranian light crude typically amounts to 0.6% over the course of a passage to Europe. It believes the figure is closer to just 0.01%-0.02%, contesting the projections of cargo loss by engine designer MAN B&W that has referred to measurements which have reportedly pointed to losses of around 0.6% of total cargo volume in this way.
MTD finds that crude oil originating in the Persian Gulf represents a different scenario than applications where crude oil is delivered to a vessel more or less directly from the well, without extensive treatment since Persian Gulf crude has been de-gassified prior to storage in shore tanks, and thus prior to loading into tankers. MTD says the Institute of Petroleum-s PM-L-4A marine loss database panel has correlated crude oil shipment information for many years. Analysis of the voyage data indicates that comparison between the net bill of lading and net outturn figures show a continual decrease in loss from 0.34% in 1989, to 0.25% in 1994 and 0.22% in 1996. Being that the ships and routes are essentially the same, MTD offers no explanation for the differing statistics, nor represents that any systemic decrease is occurring. The range is probably indicative of simple uncertainty.
Overall evaporation loss from all phases of the voyage, including loading and discharge, would therefore seem to be considerably less than the 0.6% figure. While it is appreciated that the majority of evaporative losses occur during loading and discharge operations, especially in the presence of crude oil washing, the total loss is to the order of 0.13%, or nearly five times less than reported, says MTD.
A study undertaken by Exxon and reported by Captain R. C. Uhlin at an IP meeting in London in 1984, according to MTD, indicated that the total loss due to evaporation was 0.13%, of which 0.033% occurred during loading, 0.079% during discharge, and 0.015% on passage.
Being that (i) there is uncertainty in the correct figure, and (ii) many important oil transport passages are longer than passage from the Persian Gulf to Rotterdam, this specification takes the nominal loss of VOCs from oil cargo during the transit portion of the voyage (only) to be of the order of a range from 0.15% to 0.26% by volume.
2.3 Background Regarding Control of the Spillage of Oil From Oil Tankers
The material of this section is substantially derived from the web site of the assignee of the present invention—MH Systems, Inc.—at <www.mhsystemscorp.com>.
Crude oil spills such as the Exxon Valdez incident off the Alaskan coast ignited public concern for the marine environment and prompted congressional legislation to prevent such tragic disasters. The U.S. Government quickly signed into law the Oil Pollution Act of 1990.
This law mandates the installation of double hulls on all new American tankers over 5,000 tons, and phasing out all single hull tankers by the year 2015. This is a costly proposition. Speculation exists among the marine community whether double hulls are the best and only viable solution.
The American Underpressure System (AUPS) presents an alternative. AUPS is the subject of U.S. Pat. No. 5,156,109 for a System to reduce spillage of oil due to rupture of ship's tank, and U.S. Pat. No. 5,092,259 for Inert gas control in a system to reduce spillage of oil due to rupture of ship's tank. It is also the subject of related U.S. Pat. No. 5,343,822 for Emergency transfer of oil from a ruptured ship's tank to a receiving vessel or container, particularly during the maintenance of an underpressure in the tank; U.S. Pat. No. 5,323,724 for a Closed vapor control system for the ullage spaces of an oil tanker, including during a continuous maintenance of an ullage space underpressure; and U.S. Pat. No. 5,285,745 for System to reduce spillage of oil due to rupture of the tanks of unmanned barges. All patents are to the selfsame inventor Mo Husain who is one of the co-inventors of the present invention. The contents of all related predecessor patents are incorporated herein by reference.
The AUPS is retrofittable on existing tankers, and has the similar spill avoidance capability as that of a double hull tanker during accidental rupture of the hull.
The American Underpressure System (AUPS) is a dynamic, state-of-the-art, spill avoidance system which creates a slight vacuum (two to four pounds per square inch) in each cargo tank. This vacuum, assisted by the outside hydrostatic pressure of the surrounding water, prevents or minimizes cargo loss in the event of hull rupture. In case of a bottom rupture caused by grounding, nearly all of the cargo can be protected. In the case of side hull damage, cargo below the level of the damage will be lost, while the cargo above the side hull rupture will be protected.
This system can be used in conjunction with existing inert gas systems that are mandatory on most tankers to prevent explosions.
The AUPS consists essentially of exhaust blowers with their isolation and control valves tapping into the inert gas system. A negative pressure of inert gas is created in the ullage space—the volume of gas above the oil. This negative pressure or underpressure is continuously adjusted and prevents oil from spilling if the tanker is ruptured. Stated simply, the oil is held in th
Hunter Henry
Husain Mo
Fuess & Davidenas
MH Systems Corporation
Sotelo Jesus D.
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