US2625298A - Fire prevention system for fuel tanks - Google Patents

Description

Jan. 13, 1953 E L AL 2,625,298

FIRE PREVENTION SYSTEM FOR FUEL TANKS Filed April 15, 1949 s Sheets-Sheet 1 INVENTORS IKE/4M Z. HEAL? 6% 105; .z canal/05;

Jan. 13,;1953 F. 1.. HEALY ETAL FIRE PREVENTION SYSTEM FOR FUEL TANKS 3 Sheets-Sheet 2 Filed April 15, 1949 I INVENTORS min Z J.

H L J. Z J

Jan. 13, 1953 F. HEALY ETAL 2,625,298

FIRE PREVENTION SYSTEM FOR FUEL TANKS Filed April 15, 1949 3 Sheets-Sheet 5 KIIWEWZU Izzy! 4 INVENTORS Patented Jan. 13, 1953 TAN FrankLrHealy, Dongan Hills, and John J. Con

nors,.Brooklyn,'N. Y., assignors'. to Todd Shipyards Corporation, a corporation of New York Application April15, 1949, Serial lye-87,662 6 Claims. (01. 220-88) 1 This invention relates" to gas inertion systems and apparatus. Tanks, reservoirs .or chambers used for the reception or storage of inflammable liquids, such as oil or gasoline, when empty-or only partially fi1led,- contain atmospheres which are frequently explosive. Under such conditions I there is great danger in introducing an open flame into such chambers as'may occur if repairs are to be made thereinfbywelding or burning. For example, if the oil storage tanks" of an oil tanker require to be repaired, great caremust be observed-to see that the fumes left in the oil tanks after withdrawal of the oil do not accumulate in the air in such proportion as to' explode' when the welding torch isused- Many accidents have resulted from suchicauses.

It has been proposed'to avoid danger of explosion by introducing carbon dioxide orlother inert gas into the chamber in such quantity. as to reduce the oxygen content'ofv-the atmosphere to a point where explosion cannot take place. Where the chambers in which-the atmosphereis to be inerted are very large, as for example in. the case of the storagetanks of a tanker, ,the quantity of inert gas which must be introduced is very great and the process of 'inerting, therefore, excessively costly, unless a very cheap source of the inert diluent gas can be provided.

In accordance with the'present invention-4a,

system of gas inertion is utilized which comprises introducing into the chamber inwhichthe atmosphere is to be inerted, purified products of combustion, such as flue gases from a boiler or oil burner or exhaust'gases from aninternal com bustion engine. Such gases consist; largely of nitrogen and carbon dioxide and if the proper amount of such gases is introduced asto reduce the oxygen concentration in the atmosphere in the chamber sufficiently, then the atmosphere will benon-explosive. As the proportion of nitrogen in the flue gases greatly exceeds, the

amount of carbon dioxide, the flue gases are much superior f or inertion purposes to carbon dioxide alone. For example, if there is water present in the tank or chamber tobe inerted, much carbon dioxide may be;dis'solved and will'therefore be ineffectiveindisplacing oxygen from the atmosphere. Furthermore, the carbon dioxide is much heavier than' the atmosphere so that it tends-to settle to the lower part of the chamber where there may be unnecessary concentration while the upper parts'of the'chamber still contain higher than the safeproportion of oxygen.

This makes" it 'difilcult to "determine whenas'afe' inertion of the chamber has been "reached as' 'a 2 mere'quantitative measurement of the amount of carbon dioxide introduced into. the chamber cannot beQrelied'upon. Nitrogen isnot subject to these disadvantages of carbon dioxide and therefore makes a morev efiective inerting medium while at the same time b'ein cheaper.

Difiiculty, however, has been experienced in using flue gases or products'of combustion for the reason that such gases almost always contain substantial amounts of sulphur dioxide, resulting' from combustion of the sulphur content of the oil oriothenfuel. The presence of sulphur dioxide renders thegaseshighly corrosive of the metal ofiwhich the'tank -i are] constructed. Removal of the-sulphur dioxide is therefore required if th be successfully used. If the sulphu acted so as to form carb'oi d; v o advantageous as increasing the'carbondio I content of the inerting gases. H

In order to assure that the oxygen content of the inerting gases"-has sired degree,'it is ra 'e to provide carbon dioxide indicator, record control devices suitably associated 'withthe-source of the flue gases and apparatus for supplyin them to the tanksto be'inerted. The amount of carbon di- For example, the fiue gasesmay be withdrawn from the flue ofth'e main power plant of the vessel; alternatively, a separate auxiliary boiler, system may be utilized, the fiue gases ofwhich are used for inertingtheatmo'sphere while the steam produced is utilized for providing the power to force the gases through the purifying filterand into the tank to be inerted and to operate the necessary auxiliaries. In some instances, instead of providing an auxiliaryiboiler plant, a special oil burning unit maybe provided to produce sufficient flue gases for thepurpose.

For purifying"t1ie 'gases,scrubbers or filtering means are provided and preferably also desiccating units for'drying the gasesbefore' introduction into the chamber into which the atmosphere is 'to' be inertedi For the removalof sulphur dioxide very satisfactory results are obtained by. using a scrubbing tank or towercontaining a body of broken" limestone. Sprays 'or jets are provided at the topo'f the receptacle or tower so as to spray water down over the limestone. As the flue gases 'passupwardly'through .ebeengreduoed to the dethe fragments of wet, broken stone, the sulphur dioxide in the gases is efiectually washed out, most of it combining with the calcium carbonate so as to form additional carbon dioxide passing on" with the flue gases and calcium sulphite which dissolves in wash water. After the gases have passed through the scrubber, they are preferably passed through desiccating chambers to remove as much of the moisture from the gases as possible. Such desiccating chambers may be of any suitable construction and any desired desiccant may be employed. For example, they may contain trays of calcium chloride or the like. Means for regenerating the desiccant may also be utilized, for example, heating coils heated by the hot liquid withdrawn from the scrubber. A plurality of desiccating chambers is preferably provided which may be used alternately, the desiccant in one chamber being regenerated while another chamber is being utilized.

The use of scrubbers and desiccating chambers through which the flue gases are passed, provides effective spark arresters, preventing sparks from the boilers or combustion chambers reaching the explosive atmosphere in the chambers being ina sulphur dioxide content has been about 043%.

Since both nitrogen and carbon dioxide are inert gases and 3% oxygen is not sufiicient to support combustion, this combination of gases is an effective inerting medium once the corrosive element, sulphur dioxide, has been removed. With the system of the present invention, the sulphur content has been reduced to less than .010%, an amount which is not harmful to the steel of which the tanks are constructed.

In the accompanying drawings,- three systems for application of the present invention are illustrated. It will be understood that various modifications and changes may be resorted to as found most convenient and applicable to the particular installations to be made.

In the accompanying drawings:

Figure 1 is a diagrammatic illustration of an oil tanker which is provided with a system for withdrawing flue gases from the main stack and utilizing the same for inerting the atmosphere in the oil storage tanks of the vessel;

Figure 2 is a diagrammatic or schematic representation of a system utilizing gases withdrawn from the main stack of the propulsion power plant of a tanker;

Figure 3 is a similar representation of a system utilizing a special oil burner for producing products of combustion for inerting purposes; and

Figure 4 is a similar view, showing a system employing an auxiliary boiler to provide the inert gases, the boiler being utilized to supply steam for operating the various auxiliaries.

Referring to Figure 1, 10 represents the hull of a tanker, showing the steam boiler and propelling turbine installation, indicated generally by the numeral l2. The flue gases pass out through the stack [4 to the funnel It. The oil storage tanks are indicated at ll.

Referring particularly to Figure 2, an offtake pipe l8 having a mouthpiece 20 curved so as to face the direction of flow of the flue gases, is in troduced into the stack [4 and a. proportion of the gases are withdrawn by a centrifugal blower 22 driven by an electric motor or other prime mover 24. The gases are discharged into the bottom of a scrubbing chamber or tower 26 which contains a body 28 of coarse broken pieces of limestone, marble or the like, through which the gases may readily pass. In the top of the scrubber, a multiplicity of jets or spray heads 30 are provided which are supplied by a pipe or pipes 32 through which water is pumped by a pump 34 driven by a motor 38. The water passes down over the limestone, washes the sulphur dioxide from the flue gases, and a large part of the sulphur is converted to calcium acid sulphite, which is soluble in water and passes ofi at the bottom of the scrubber through the discharge pipe 38. The reaction is generally as follows:

CaCO3+2H20+2SO2+ CO2+H20+ Ca (HSOs) 2 The CO2 formed by this reaction passes oil? with the flue gas and increases the carbon dioxide content thereof.

It will be seen that the scrubbing tower containing the limestone and having the water sprays at the top thereof will act effectively to cool the gases suificiently and will also act as a spark arrester, preventing any possibility of sparks or flames from the stack passing beyond the scrubber.

It is desirable to dry the inerted gases before introducing them into the tanks in which the atmosphere is to be inerted. For this purpose, a system of desiccating chambers may be provided, such chambers being indicated at 40, the inlets to the chambers being controlled by valves 42. A plurality of chambers are preferably provided so that one can be used while the others are being regenerated or supplied with fresh desiccating material. Any suitable means for drying the gases may be employed. For example, the desiccating chambers may be provided with a plurality of trays 44 for holding any of the well known desiccating materials, such for example as calcium chloride. Means may be provided for regenerating the desiccating material in one or more of the desiccating chambers while another chamber is being used. For example, the inner walls of the chambers may carry pipe coils 46 through which steam or hot water may be passed so as to heat the chamber not in use and drive the moisture oil from the desiccant. The Water from the scrubber discharge pipe 38, for example, may be passed through the coil 46 as the water from the scrubber has been raised to a substantial temperature by its contact with the hot flue gases. The purified and dried flue gases coming from the desiccating chambers are led through a pipe 48 to the oil storage tanks I! (Figure 1) which are to be inerted.

In order to ensure that only gas in which the oxygen content has been sufiiciently reduced by combustion is supplied, a continuous CO2 gas analyzer 60 is preferably used, this being connected by a duct 62 arranged to extract a sample of a gas from the ofitake pipe 18 or from any other suitable location in the system. The

analyzer 60 may be visually observed and the system properly controlled by the operator, but preferably, automatic controls are operated from the analyzer. These controls desirably act upon a motor speed controller 64 to which they are connected by a conductor 66, such controller governing the speed of the blower operating motor 24, and upon the oil burner or other source of the flue gases through conductor 6.8. In this way. the character of the combustion canb'ei regulated so as to produce the optimum condition for production of a and corresponding reduction of free oxygen and the speed of the blower may be varied or theblower stopped ifthe conditionsfor production of COz-areunsatisfactory. Any-suitabletype of CO2- analyzer may beused, such; for instance, as thethermalcondiictivity type rthe automaticOrsattype.- A type which has been found successful'is the Hayes recorder:

In Figure 3, a self-eontaine'd system fdr'siipplying inert gas is shownin which the gas is provided by combustion of oil consumed by a burner 19 in a combustion chamber 12. The combustion chamber may be provided withsuitable cooling and insulating means indicated generally by the jacket 14. Oil is supplied to the oil burner through a pipe 16 controlled by valve 73 actuated from the CO2 analyzer 60. The gas is forced through the system by a blower 22 operated by motor 24, the controller 64 of which is actuated from the analyzer 60 as in the construction previously described. In all other respects the system may be the same as that shown in Figure 2.

In Figure 4, another self-contained system is provided in which a small boiler 80 is utilized in the firebox 82 of which oil is burned at a: burner 85. The supply of oil to this is controlled by a valve 86 actuated from the gas analyzer 60. The fine gases from the boiler pass through a. stack 88 to a scrubber 26 which may be similar to that already described, and after passing the scrubber, the gases pass through a desiccating chamber or chambers 40. In the stack .88 an economizer 50 may be located for heating the boiler feed water and also a coil 92, through which water may be forced by the pump 94 tothe sprays 30, in the top of the scrubber 26. Steam from the boiler passing through the pipe 96 may be used to operate the pump 94, a fuel pump it, and a steam turbine N12 for driving the forced draft blower I04 supplying air to the oil burner 84. The speed of the forced draft blower may be controlled by the valve I06 in the pipe leading from the steam pipe 96 to the turbine I92. Steam from the pipe 96 may also be used to operate the boiler feed pump [08 which draws water from the hot well H0 and passes itthrough the economizer 90 to the boiler. Steam from the pipe is also used to operate the circulating pump N2 of a condenser I [6 in which any surplus steam from the boiler may be condensed.

Steam or hot condenser water may be used forreactivating the desiccators if desired.

All of the systems described provide purified and desiccated fiue gases having the desired low oxygen content which may be used for inerting'. the atmosphere in tanks or chambers which are to be repaired by the use of flame producing equipment. All of the systems provide an inerting gas which is of adequate purity to avoid ob-- jectionable corrosion and which may be pro-- duced in very large quantities at very small expense so as to enable tanks of great size, such, for example as the tanks on an oil tanker, to betreated.

While certain preferred embodiments of the invention have been illustated and described in detail, it is to be understood that changes may be made therein and the invention embodied in other structures. It is not, therefore, the inten-- tion to limit the patent to the specific construe- 6 tions illustrated, but to-coverthe invention tread; lyin whatever form'its principle 'mayT beuanzea.-

We claim: r

l. A system for iinjerting; the-atmosphere inempty cargo oil storage tanks-of arenxanaan a steam propulsion power plant-using oilas a fuel, which comprises means for withdrawing a ro: portion of the linegasesfrom the main power plant of thevessel; a scrubberfor extraction ofsulphur dioxide'fromsaid gases; a desiccator,- and means for forcing said gasest-hrough saidsciubber and desiccator to the tank in which theatmosphere is to beinertedi and a; device responsive to carbon dioxide concentration mane gases. forced through theapparatus foi controlling the conditions" of combustion of fuel in the vessel power plant and therate of feed of the gases to the tank to be treated.

2. In a gas inertion system, a fuel burner, means for withdrawing products of combustion from the fuel burner and forcing them to the chamber in which the atmosphere is to be inert-ed, means through which the gases are passed for removing a substantial proportion of any sulphur dioxide present in such products of combustion and converting such sulfur dioxide into carbon dioxide and a soluble sulfur salt, said carbon dioxide being mixed with the products of combustion so as to augment the supply of inerting gas, said sulfur dioxide removing means comprising a scrubbing chamber containing limestone in lump form and water sprays located in the upper portion of said chamber for spraying water upon said limestone, and a desiccator through which the gases are passed after leaving the scrubbing chamber.

3. In a gas inertion system, a fuel burner, a duct for carrying off at least a portion of the products of combustion from the fuel burner, a blower in said duct, a motor for driving said blower, a scrubber into which said blower discharges for scrubbing sulphur dioxide from said products of combustion, means for conducting the gases from the scrubber to the chamber in which the atmosphere is to be inerted, a carbon dioxide responsive control instrument connected with said duct, means for regulating the conditions of combustion of the fuel burner, and means for regulating the speed of the blower, both of said means being responsive to the action of the carbon dioxide control instrument.

4. In a gas inertion system, an oil burner, means for forcing oil thereto, a control valve for controlling the supply of oil to the burner, a forced draft blower for supplying air to the oil burner, a motor for actuating the same, a speed control device for said motor, a duct for leading the products of combustion from said oil burner to the chamber the atmosphere of which is to be inerted, a blower in said duct, a. motor for driving said blower, an automatic control instrument responsive to carbon dioxide concentrations in said duct, connections from said automatic control instrument to the means for controlling the oil feed and to both blower motor speed control devices, and a sulphur dioxide scrubber and a desiccator connected with said duct, through which the gases are passed on the way to the chamber to be treated.

5. In a gas inertion system, a fuel burner, the products of combustion of which provide an inerting gas containing sulphur dioxide, and means for purifying the gas before introduction into said chamber the atmosphere of which is to be inerted, said purifying means comprising a scrubber containing limestone, means for spraying water over said limestone, at least a portion of the sulfur dioxide in the inerting gas being thereby converted into carbon dioxide and a soluble sulfur salt, said carbon dioxide augmenting the supply of inerting gas, and a desiccator through which the gases are passed after leaving said scrubber. said desiccator comprising receptacles for holding a desiccating agent and having a regenerating coil therein, and means for forcing the hot wash water from the scrubber through said regenerating coil.

6. A system as claimed in claim 5, in which a pluralityof desiccators are arranged so that they may be used in alternation.

FRANK L. HEALY. JOHN J. CONNORS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,417,066 Howard May 23, 1922 1,482,125 Gaster Jan. 29, 1924 1,934,472 Allen et a1 Nov. 7, 1933 1,947,303 Morgan Feb. 13, 1934- 2,049,987 Willenborg Aug. 4, 1936 2,059,005 Lane Oct. 27, 1936 2,375,834 Walker May 15, 1945 FOREIGN PATENTS Number Country Date 20,667 Great Britain 1913

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