US2780921A - Gas distribution systems for a multiplicity of tanks containing liquefied hydrocarbons - Google Patents

Description

Feb. 12, 1957 w. L. MORRISON 2,780,921

GAS DISTRIBUTION SYSTEMS FOR A MULTIPLICITY OF TANKS CONTAINING LIQUEFIED HYDROCARBONS Filed on. 27, 1955 Pahkr 5 ('arfer flziorfieys States atent "55cc 2,780,92 l Patented Feb. 1.2, 1957 Willard L. Morrison, Lake Forest, Ill.,-assignor, by mesne assignments, to The :Union Stock Yard and Transit Company :of Chicago, Chicago, 1111., a corporation :of Illinois Application October 27, 1953, Serial No. 388,575

1 Claim. (Cl. 62-1) :My invention :relates to improvements in gas distribution systems which include -a multiplicity of tanks -in tended to contain liquefied hydrocarbon at pressures but slightly above atmospheric and at temperatures far below the freezing point of water.

The principal object of my invention is to provide an arrangement whereby gaseous hydrocarbon may be drawn :from a plurality of tanks each containing liquefied hydrocarbon. iThe liquefied hydrocarbon as it evaporates is discharged from one or -a plurality of tanks to any suitable point of use without the danger of any reduction o'f pressure below atmospheric in any one of the tanks.

I have illustrated my invention by showingaplurality .of tanks on .a plurality of barges connected in .tow with .a tow boat which uses some of the ,gas evaporated from .the tanks as fuel. 'Only a small proportion of the gas will be thus used, the great bulk of the liquefied gas lbe'ing .conveyed "from a source point .at which the :gas is liquefied to a point at which the liquefied gas in large quantities is vaporized and discharged from the tanks for use.

.Each of the tanks will contain a large quantity of liquefied hydrocarbon at temperatures far ,below the freezing point of water and therefore far below them- 'bient temperature, the temperature of the liquefaction of methane, for example, being approximately -258 F. To prevent too rapid evaporation or boiling off of gas from the liquid as a result of entrance of ambient heat the tanks will be insulated. Since it is desired to transport this liquid gas at approximately atmospheric pressure, insulation must be suflicient to allow only a very small amount of evaporation of the gas.

The insulation may be so eiiective that just enough gas is evaporated or boiled oil to furnish the power to operate the tow. Under these circumstances, with a mul tiplicity of separate tanks, each supplying some of the gas which is discharged or drawn from the tanks to be later increased in pressure for injection into the engine, there is the possibility that the evaporation rate in one or more tanks may be less than the demand rate. If this happens, it is essential that such tank or tanks or the whole system be automatically cut off from the engine so that the pressure in the tank or tanks never falls below atmospheric pressure.

This is necessary because while no danger of explosion exists with a tank full of pure hydrocarbon, liquid and gas, very great danger would result if air were allowed to enter the tank and mix with the gas to form an explosive mixture.

If the pressure in any one of the tanks or anywhere in the system as a result of the demand should fall below atmospheric, there would be great danger that air might enter the system.

I propose to interpose between each tank and the gas supply main, between the gas supply main on each barge and the engine injection or feed system, separate valves which, when the pressure on the upstream side of the valve falls -below the safety point, will automatically close. .:No further gas will be withdrawn from the upstream side of the 'valve until evaporation has built up the pressure to a point at which there is no danger of 5 air='entrance.

Depending on the size and other characteristics of the system, the safe point below which pressure in the tank or system must not fall may vary from -a few :ounces, to a few pounds gauge and of course pressure above or 'below such safety point must not be exceeded.

Means will be provided, forming no part of the present invention, to permit excess gas to be dissipated, flared, blown o'if, or otherwise safely disposed of. The tanks are designed to carry the liquid at approximately 'atrn'ospher ic pressure. This invention .deals not with the pressure relief phase but with the necessity of insuring thatthe'pressure in 'no one of the tanks and the pressure in no part of the system -falls below atmospheric. Usually the pressure 'below which the tan'k or pipe will be :cut off will in the interest of sa'fet-y 'be slightly above atmospheric.

Other objects will appear from time to time "throughout the specification andclairns.

My invention is illustrated more or less diagrammatically in the accompanying drawings, 'wherein Fi'gure is a diagrammatic plan view or a "tow;

' Figure 2 is a section through a valve adapted 'to close the -supply of gas when the pressure on'the upstream side falls below' the safety minimum.

Like parts are indicated by like characters throughout the-specification and drawings.

Referring to Figure l, 1 is a tow boat. Barges are indicated at 2. 3 is -a pilot boat at the front end of the two. The tow boat carries internal combustion engines 4, driving propellers S. The pilot boat carries combustion engine 6, driving through suitable gearing, steering propellers 7. '8 'is an injector pump --which'diseharges gas fuel to eacho'f the engines through the ducts 9 con'trol1ed by'governor valves 10. *Engines are preferably of ith'e dual ful, 'oil and gas burriing diesel type and it is necessary to inject the gas into the engines at several pounds above atmospheric.

11 are gas supply mains extending along each of the barges. Each of the gas storage tanks 12 is connected to the supply main through a valve 13. The supply mains on each barge are connected by flexible couplings 14 and a similar flexible coupling 14 is interposed between each end of the supply main system and the tow and steering boats. Manually actuated shut ofi valves 15 at each end of the supply main 11 on each barge provide means to positively close the mains when desired. Adjacent each end of each supply main 11 is a valve 13 of the same type as that interposed between each tank and the supply main.

As gas is evaporated in each of the tanks by ambient heat the gas escapes through the valve 13 to the main and the gas from all the tanks will normally flow along the main toward the injector pump which draws gas from the main and compresses it for engine supply. It is not desired that the pressure of the gas in the tanks or of the gas in the supply main be high enough to satisfy the need for relatively high pressure in the gas supplied to the engine so that normally the pump 8 will draw gas from the main thus assisting the flow of gas induced by the pressure slightly above atmospheric resultant from evaporation of the liquid. There will thus normally be in the supply system gas at slightly above atmospheric pressure just as there will normally be in each tank pressure slightly above atmospheric.

Referring now to Figure 2, which discloses a suitable type of control valve, duct 16 communicates with one of the tanks. Duct 17 communicates with the supply side and hold the valve 19 off its seat. pressure in the passages 16, 17, the valve chamber and main. 18 is a valve seat. 19 is a valve interposed between ducts 16 and 17. Duct 16 is on the upstream side of the seat and duct 17 on the downstream side. As the pressure in duct 16 is above the pressure, in duct 17, valve 19 will be opened by the differential pressure and gas will flow from the tank through 16, pass the valve 19 through 17 to the main 11. That is the normal situation for operation.

The valve 19 is carried by a valve stem 20 encircled by Sylphon type bellows 21. This bellows is exposed to atmospheric pressure and atmospheric pressure tends as applied through the bellows to seat the valve 19 on the seat 18. The valve is unseated against this pressure by the pressure in duct 16 but if the pressure in the duct 16 falls below the predetermined minimum, it will not be sufiicient to overcome the pressure applied to the valve 19 from the stem 20 through the Sylphon bellows 21 and valve 19 will close and remain closed until the pressure on the upstream side of the valve reaches the desired safety point. Thus, the compressor 8 cannot draw gas from any tank or from the system when the pressure is below the safe point.

.spect to the stem 20 that when pressure of gas flowing from 16 past 19 through 17 remains above the prede- ,.termined safe minimum pressure, the pressure maintained in the chamber within the bellows 21 around the stem 20 is sufiicient to overcome air pressure from the out- However, when the Sylphon falls below the save minimum, then atmospheric air pressure applied to the outside of the Sylphon bellows causes the valve 19 to seat, preventing flow through the passage 16 and the lower the pressure in 17 falls the greater the differential pressure between the outside and the inside of the bellows and the more securely is the valve 19 held on its seat 18.

The valve must close whenever the pressure of the gas in the system falls to atmospheric pressure and preferably the valve will close even though the pressure of .the gas in the system is still slightly above atmospheric.

The essential thing is that no matter what happens, no

They

matter what the circumstances are the engine injection apparatus or any other apparatus drawing gas from the system must never be allowed to draw a vacuum or pressure below atmospheric in the gas line because if that should happen, any leak would permit entrance of air into the system with danger of resultant formation of an explosive mixture in the gas line or in the gas tanks.

If the apparatus is so set that the valve closes even at a point slightly above atmospheric pressure, then slight variation or slight inaccuracy will not permit pressure in the gas line below atmospheric.

A leak in the system when the pressure is above atmospheric will merely result in loss of gas or discharge to the outer air which is much less dangerous than entrance of air into the gas line.

I claim:

The combination of a plurality of containers each at least partially filled with liquefied methane maintained at substantially atmospheric pressure and at about minus 258 F. and thus always subject to a certain degree of vaporization because of heat transfer through the Walls of the containers, a delivery manifold, separate connections from each of said containers to said delivery manifold, and a valve in each such connection adapted to shut off such connection during such times but only during such times when the boil-01f rate in the container associated therewith is reduced to a value insufiicient to maintain a predetermined pressure in such container.

References Cited in the file of this patent UNITED STATES PATENTS 1,140,250 Cabot May 18, 1915 1,389,245 Gaertner Aug. 30, 1921 1,393,544 Knight Oct. 11, 1921 1,703,570 Borck Feb. 26, 1929 2,096,785 Carter Oct. 26, 1937 2,329,363 Thomas Sept. 14, 1943 2,550,886 Thompson May 1, 1951 2,562,511 Schowalter July 31, 1951 2,606,108 Ensign Aug. 5, 1952 2,624,290 McLean Jan. 6, 1953 2,645,906 Ryan July 21, 1953 2,658,737 Nutter Nov. 10, 1953

Images