Method and system for storing and hydraulically-pressurizing compressed natural gas (CNG) at an automotive re-fuel station

A system for delivering natural gas, from a moveable transport or pipeline, is off-loaded at an automotive re-fueling station, or other end-user facility, into one or more storage vessels equipped with internal flexible bladders. The pressure of the gas, stored inside the bladders, will be increased to levels sufficient for re-filling automotive on-board storage tanks, or other end uses, by pumping a hydraulic fluid in the annulus between the bladder and the walls of the steel storage vessels, thereby collapsing the flexible bladder and squeezing gas out to an on-board storage tank. The use of a hydraulic pump, instead of a more-expensive compressor, to pressurize the gas, results in significant cost savings which reduces the overall cost of CNG at the station, making CNG (the "preferred alternative fuel") less expensive than gasoline and/or diesel, which will enable CNG to replace gasoline and/or diesel as the primary fuel for automobiles, trucks, and busses.

BACKGROUND OF THE INVENTION 
1. Field of the invention 
The present invention relates generally to a method and a system for 
storing natural gas at an automotive re-fuel station for the purpose of 
re-fueling automobiles, busses, and trucks, and storage at other end user 
facilities. More particularily, it relates to such a method and system 
especially adapted to the economics involved with equipment used to 
increase the pressure of the stored natural gas from the pressure at which 
it was delivered to the re-fuel facility, to the pressure necessary to 
fill on-board storage tanks in the automobiles, trucks, and busses. The 
present invention relates, specifically, to the use of a flexible bladder, 
inside a steel vessel, to receive and store natural gas at a re-fuel site. 
In order to increase the pressure of the stored gas, a hydraulic fluid is 
pumped into the annulus between the outer walls of the bladder and the 
inner walls of the steel tank. With continued pumping, pressure in the 
annulus will exceed the gas pressure inside the bladder and the bladder 
collapses in size which results in the gas inside the reduced-size 
container (the bladder) being elevated to a higher pressure. The 
higher-pressured gas can then be transferred to a re-fill island on demand 
to fill on-board storage tanks. Without the presence of an internal 
flexible bladder, the storage vessel would have to be un-loaded with the 
assistance of an expensive compressor, which would increase the cost of 
compressed natural gas at the re-fuel station and make it more difficult 
for natural gas (the "preferred alternative fuel") to compete with 
gasoline and/or diesel as the primary fuel for automobiles, busses, and 
trucks. 
2. Description of the prior art 
The conventional manner of providing compressed natural gas to automobiles, 
trucks, and busses, is to bring the gas to the station site, by truck, or 
pipeline, and transfer the gas to storage vessels (usually one or more 
municipal code approved ASME vessels specifically designed for storage of 
hazardous gases). Since the gas will not flow, by gravity, the transfer 
from the delivery vehicle (or pipeline) into storage vessels must be 
accomplished by use of one or more multi-stage compressors. Once the gas 
is in storage, it must be further compressed to increase the pressure up 
to the level necessary to fill on-board storage tanks in automobiles, 
trucks, and busses. While the conventional method and system has proven 
successful in many instances, the economic costs are so expensive as to 
make the use of natural gas non-competitive with conventional fuels such 
as gasoline and diesel. 
The present invention is intended to solve the need for a more-economical 
method of storing and pressurizing natural gas so that the delivered cost 
of compressed natural gas (CNG) is substantially less than conventional 
gasoline and/or diesel fuels. The desired economics are possible due to 
the elimination of multi-stage compressors to un-load the gas from 
delivery vessels, and to pressurize the gas up to levels to re-fill 
on-board storage tanks. In this invention, the physical work of 
pressurizing the gas will be accomplished by pumping a hydraulic fluid in 
the annulus between the bladder and the steel walls of the storage vessel. 
The hydraulic pump - collapsing bladder work will replace the physical 
work of a multi-stage compressor, at a substantial cost savings. 
The flexible bladder is a one-piece cylinder liner which, when filled with 
gas will inflate substantially to the interior walls of the steel tubes 
which are 20 inches in diameter and 22 feet in length, made of rubberized 
nylon, or by choice, some other member of the elastomer family of 
synthetic rubbers, compatible with natural gas, fresh water/anti-freeze 
mix, or mineral hydraulic oil, with one domed end, the end open attached 
(bonded) to the face of a flange attached to the steel tube. 
The hydraulic fluid is a matter of choice and can be either a 
water/anti-freeze mix or a mineral hydraulic oil. 
The present invention is particularily designed for more-economical storage 
and pressurization of natural gas utilizing a hydraulic pump instead of a 
gas compressor. While primarily designed to reduce the delivered price of 
compressed natural gas to re-fuel automobiles, busses, and trucks, the 
invention can also serve as a more-economical method of storing and 
pressurizing natural gas for other end-uses, such as for fork-lift trucks, 
airport luggage and passenger transports, and generally any other method 
of transportation involving gasoline and/or diesel fuels. 
SUMMARY OF THE INVENTION 
In the method and system of the invention, a terminal is built at a 
re-fueling station which consists of un-loading conduits, control 
mechanisms, and measuring devices for three storage vessels, each with an 
internal flexible, bladder, together with a hydraulic pump, motor, and 
surge tank. Start-up operations of the system will commence with the 
arrival of natural gas, by moveable transport or pipeline, at the re-fuel 
station. The off-loading conduit from the transport will be connected to 
the gas-entry conduits connected to valves at the openings to the bladders 
inside the steel storage vessels. By opening the valves on the delivery 
vehicle and the valves on the bladder, gas from the the delivery vehicle 
will flow to the storage vessel until pressures equalize. After pressure 
equalization, additional volumes of gas will be transferred into the 
bladders of the storage vessels by use of a hydraulic pump on the delivery 
vessel to collapse internal bladders inside the steel tubes on the 
transport vehicle, and squeeze the gas out into storage vessels. The 
inventor of the hydraulic method of un-loading gas from the delivery 
vehicle by the hydraulic pump method is also the inventor in this 
application. When the transport vessels have been emptied, as above, or 
the maximum storage gas has been delivered, the storage tanks will be 
disconnected from the transport vehicle which is then free to move to 
another location, or return to a pipeline for re-filling. 
Once the three storage tanks have been re-filled from the transport 
vehicle, the hydraulic pump on the storage skid will be activated to 
pressurize a hydraulic fluid, in a closed system, from a surge tank to the 
individual storage vessels, through individual conduits, to control valves 
on flanges leading to the annular space between the steel vessel's outer 
walls and the outside of the flexible bladder inside the steel vessel. 
Continued operation of the hydraulic pump will increase the pressure of 
the gas in all three storage vessels as needed for a cascade delivery 
system. In order to effect the cascade delivery system, three distinct 
banks, i.e., the "high bank", the "medium bank", and the "low bank" with 
pressures inside the bladders of the three vesses of approximately 4000 
psi, 3200 psi, and 2400 psi, respectively. When the operating pressures in 
each vessel have been obtained, the entry valves will be closed and the 
exit valves will be opened on demand from a sales dispenser. As the 
low-bank pressure decreases, and the on-board tank pressure increases, the 
flow rate to the sales vehicle decreases. At a pre-determined minimum flow 
rate, a logic controller will sequence the flow to the medium bank. 
Similarily, the sales vehicle will be filled from the medium bank until a 
pre-determined flow rate is reached, at which point the flow is sequenced 
to the high bank to complete the fill. As the bank pressures are 
decreased, a switch activated by the low or high bank, would open a 
control valve on the hydraulic fluid distribution conduit to permit 
pressurized hydraulic fluid to enter the annulus of the high bank storage 
vessel to raise the pressure of the gas in the bladder back to 
approximately 4000 psi to insure that the high bank is replenished first, 
then the medium bank raised back to approximately 3200 psi, and lastly, 
the low bank to approximately 2400 psi. Volumes of gas dispensed from each 
bank would be measured by conventional flow meters which will indicate; 
when it is time to re-fill the storage vessels. 
It is the principal object of the present invention to provide a method and 
system for economically storing and transferring compressed natural gas 
(CNG) at an automotive re-fuel station, or other end-user site, without 
the use of multi-stage compressors. The key to obtaining this objective is 
to modify an approved storage vessel by inserting a flexible bladder, the 
same size as the internal walls of the storage vessel, which will maintain 
separation of the gas and a hydraulic fluid which is injected into the 
annulus to collapse the bladder and increase the pressure of the gas 
sufficient for it to flow to the sales conduits. The desired object will 
be obtained by utilizing a hydraulic pump system to pressurize a closed 
hydraulic system to pressures above the pressure of the gas inside the 
bladder. As the pressurized fluid is injected into the annulus between the 
bladder and the steel walls of the storage vessel, the pressure 
differential will compact the bladder, reducing the internal volume, with 
a resultant increase in pressure of the gas inside the bladder. The 
resultant increase in pressure will have been obtained without the use of 
a conventional gas compressor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In U.S. patent application Ser. No. 08/454,531, now U.S. Pat. No. 
5,603,360, filed by the same inventor of this invention, there is 
disclosed a method and system for transporting natural gas, from a gas 
pipeline, to a compressed natural gas (CNG) re-fuel station, inside a 
flexible bladder, and to discharge the transported gas into storage at a 
CNG re-fuel station with the aid of a hydraulic pump instead of an 
expensive compressor. 
It should be noted that the present invention utilizes the same 
bladder-squeeze technique for storage and transfer of stored gas to a 
dispenser to re-fuel automobiles, trucks, and busses, as that disclosed in 
patent application Ser. No. 08/454,531, now U.S. Pat. No. 5,603,360. While 
the prior patent application deals primarily with bladder-equipped 
high-pressure steel tubes approved by the Department of Transportation 
(DOT) for use in over-the-road transportation of natural gas, this present 
invention relates solely to the use of bladder-equipped high-pressure 
storage vessels, manufactured in accordance with ASME standards for 
storage of natural gas in municipal areas. Also included is a method and 
system of pressurizing the gas inside the bladders which are inside the 
steel vessesl, to levels sufficient to re-fuel on-board storage tanks in 
automobiles, trucks, and busses, all to be accomplished with a hydraulic 
fluid system instead of conventional gas compressors. 
In the present distribution method, natural gas is received at a re-fuel 
station in a moveable transport vehicle, or from a nearby pipeline, where 
it is off-loaded for storage. The basic storage unit consists of three 
bladder-equipped ASME pressure vessels which will be operated, in a 
cascade arrangement of low-bank, medium-bank, and high-bank whereby CNG 
under various pressures will be made available to a re-fueling dispenser 
from the appropriate bank until the on-board storage tank on the 
re-fueling vehicle is completely full. Increasing the pressure of the gas 
inside the bladders, as gas is withdrawn for sales, will be accomplished 
by injection of a hydraulic fluid in the annulus between the bladder and 
the steel walls of the storage vessel, which will increase the pressure in 
the confined area and collapse the bladder, which will result in the same 
amount of gas being confined in a smaller container, resulting in an 
increased pressure of the gas. 
The basic storage unit, three ASME storage vessels, together with the 
necessary gas filling and dispensing conduits, control valves, safety 
valves, together with the hydraulic pump, motor, surge tank, regulating 
valves, all mounted on a single skid, constitute a typical 
storage-pressurization unit for a typical CNG re-fueling station. If sales 
volumes dictate, additional modules of three storage vessels could be 
added. 
The method and system are especially effective for storing and pressurizing 
natural gas at compressed natural gas (CNG) re-fueling stations. However, 
it is understood that the present method and system can also be utilized 
to satisfy other end-user needs such as furnishing CNG as fuel for 
gas-fired boilers, engines, turbines, and for emergency supplies of gas in 
the event of a supply interruption, or for use as temporary storage and 
pressurization of natural gas from isolated gas wells for transport to gas 
pipelines. In each instance, the loading and un-loading method and system 
will function in the same manner and the vessels can be evacuated by a 
hydraulic fluid system rather than an expensive compressor. 
Given this explanation, it is understood that where storage and 
pressurization at a CNG re-fuel facility are referred to herein, it might 
instead refer to an end-user facility of some other function which has a 
need, short-term or permanent, for the same type storage and 
pressurization equipment. 
The value of the invention for CNG re-fuel station storage and 
pressurization needs flows from several features thereof. First of all, by 
eliminating the need for compressors to evacuate natural gas from the 
pressure vessels, the savings from the initial costs and operating costs 
will enable compressed natural gas to be more competitive with gasoline 
and/or diesel as the preferred fluid for automobiles, trucks, and busses. 
Farther, the method and system of the invention provide for the safe and 
effective handling of the natural gas fuel, at re-fuel stations and other 
end-user facilities, utilizing relatively-untrained personnel who will be 
receiving, storing, pressurizing, and evacuating the storage vessels 
utilizing hydraulic fluid instead of high-pressure gas compressors. 
Referring now to the drawings, FIG. 1 is a basic, three-vessel storage and 
pressurization unit, skid-mounted for installation in minimal surface 
areas generally available at CNG re-fuel stations, or other end-user 
sites. The skid-mounted unit, indicated at (1), contains three 
high-pressure cylinders (2) which are especially constructed to satisfy 
municipal codes for construction and operation of high-pressure vessels 
for storage of compressed natural gas in municipalities. These vessels (2) 
are seamless steel tubes, of ASME SA-372 material, Type IV, with 
sufficient wall thickness to contain working pressures up to 4000 psi with 
a safety factor of 3 (per ASME specifications for Boiler and Pressure 
Vessel Code, Section VIII, Division 1), with threaded out-lets on each end 
(3) with internal diameters of approximately ten inches to accomodate the 
insertion of a flexible bladder (4) inside each cylinder (2). The bladder 
(4) is a or, e-piece tube of elastomer material of conventional design 
with an external surface area essentially the same as the internal surface 
area of the steel cylinder (2) into which it is inserted so that when 
natural gas is injected into the bladder (4), the bladder (4) will extend 
and conform to the shape of the interior of the steel tube (2). As the 
pressure of the stored gas in the bladder (4) increases, the pressure will 
be contained by the steel tubes (2) backing-up the bladder (4)material. 
On one end of the skid (1), generally at (5), is a natural gas loading and 
un-loading system consisting of conduits (32) and (13) respectively, entry 
control valves (6) and exit control valves (7) on each of the three 
storage vessels (2), a master control valve (8), one-half of a quick 
connect-disconnect coupling (9), conduits and couplings to connect the 
master valve (S) to the three entry valves (6), and couplings (10) to 
connect the entry valves (6) to the inner flange (11) which, together with 
the outer companion flange (12), provides entry access to the interior of 
the bladder (4) inside the steel storage vessels (2). Exit from the 
bladder (4) is accomplished by closing the entry valve (6) and opening the 
exit valve (7), which is connected by separate conduit (13) to a 
sequencing control apparatus whereby gas can be withdrawn from any one of 
the three storage vessels (2) to re-fueling dispensers or other end-uses. 
On the opposite end of the skid (1), generally at (15), is a natural gas 
pressurizing apparatus consisting of a hydraulic pump and prime-mover 
(16), surge tank (17) and a manifold means whereby hydraulic fluid is 
pumped through conduits (18) to entry control valves (19) on each end of 
the storage vessels (2), individually or simultaneously, to pressure-up 
the annulus (30) between the outer walls of the bladder (4) and the inner 
walls of the storage vessels (2). Exit from the annulus (30) is 
accomplished by closing the entry valve (19) and opening the exit control 
valve (20) which is connected by separate conduits to a common-return 
maniflod (21) which is connected to the surge tank (17). Also shown is a 
control valve (22) which can be used to connect the surge tank (17) to an 
auxilary hydraulic fluid tank or drain line. 
FIG. 2A is an enlarged view (top) of one of the three storage vessels of a 
typical natural gas storage unit. The upper view, generally at (23) is a 
cut-away view of a steel storage vessel (2), depicting the position of the 
flexible bladder (4) as it is inserted into the steel storage vessel (2) 
before the flanges (11) and (12) are bolted together with bolts (24). 
Entry into and exit from, the storage vessels (2) will be made through the 
threaded outlet (3), into which a threaded nipple (25) is attached which 
nipple (25) is attached to the inner flange (11). The bladder (4) is 
attached to the outer flange (12) by bonding to the face of the outer 
flange, shown generally at (26). The flanges, inner (11) and outer (12) 
are companion ring-gasket flanges, manufactured in accordance with API 
specifications for 4000 psi service. The ring-gasket (27) will effectuate 
the seal between the flanges when the flanges are bolted together. The 
open end of the bladder (4) will extend through the open ring-gasket (27) 
to the face of the outer flange (12) where it is bonded and sealed to 
effectuate the containment of natural gas inside the bladder (4). 
The lower view on FIG. 2B, generally at (28) depicts the position of the 
flexible bladder (4), after the flanges on each end (11) and (12) have 
been bolted together with bolts (24), and after the bladder (4) has been 
expanded to it's maximum size, i.e., to the inner walls of the storage 
vessel (2), by the injection of natural gas through entry control valve 
(6) with exit valve (7) remaining closed. Also depicted, generally at (29) 
on the end of the storage vessel opposite the gas entry apparatus, a 
portion of the hydraulic fluid system is shown. The entry valves (19) and 
the exit valves (20) indicate where hydraulic fluid can be pumped into the 
annulus between the bladder (4) and the inner walls of the storage vessel 
(2) to collapse the flexible bladder (4) which results in an increase in 
the pressure of the gas inside the bladder. Upon depletion of the gas 
inside the bladder (4) to a sales dispenser (14), the annulus pressure can 
be released back to the surge tank (17) and the gas filling process 
described above can be repeated. 
The present invention contemplates storing natural gas at several different 
pressure levels, and to have the capability to increase the pressure to 
levels desired to re-fuel automobiles, trucks, and busses in a cascade 
system, i.e., a portion of the refill is taken at one pressure level, 
additional gas taken at an intermediate level, and final fill taken from 
the top level. The method of the invention is to accomplish the storage 
and pressurization requirements without the use of expensive compressors, 
by creating a flexible storage vessel which can be evacuated using 
hydraulic fluid instead of gas compressors. 
The manner in which the storage and pressurization system functions to 
carry out the method is believed to be evident from the above description 
thereof. In order to load, or re-supply, a typical three-vessel storage,; 
natural gas from a pipeline is transported to the re-fuel station, 
sometimes by extending the pipeline itself, but most often by hauling in 
over-the-road transport vessels. Upon arrival at the re-fuel station, the 
delivery vehicle is placed in position to off-load by connecting the 
transport vessel to the storage unit (1) on FIG. 1, by connecting to the 
mating half of the quick connect dis-connect coupling (9). The master 
control valve (8) is then opened and gas from the transport can flow to 
all storage tanks where the pressure is less than that available from the 
transport, by opening the appropriate entry valve (6). At such time as the 
storage tanks have accepted all of the supply gas that the delivery v 
vehicle can deliver, the entry valves (6) will be closed and the master 
valve (8) will be closed. After the pressure in the delivery line has been 
bled off, the quick connect-disconnect coupling can be separated and the 
re-supply operation has been completed. 
Upon completion of the re-supply operation, the gas in storage inside the 
flexible bladders (4) at various pressures, can be delivered to the 
re-fuel dispensers from any of the three storage vessels as required. If 
the re-fuel station operator desires to re-fuel vehicles from a cascade 
system (a high-bank, a medium-bank, and a low-bank), the gas pressure in 
the three storage vessels can be changed utilizing the pressurization 
apparatus on the opposite end of the storage vessel, generally at (15), 
whereby the hydraulic pump (16) is activated to take hydraulic fluid 
suction from the surge tank (17); pressurize the fluid above the pressure 
of the gas inside the bladder (4) of the low-bank vessel and inject the 
hydraulic fluid, through control valve (19), into the annulus (30) between 
the bladder (4) and the steel walls (2). Increasing the pressure of the 
hydraulic fluid in the annulus (30) above the pressure inside the bladder 
(4) causes a partial collapse of the bladder (4) which will reduce the 
volume of the container in which the gas is stored, resulting in an 
increase in the pressure of the gas in the bladder (4). Injection is 
continued until the gas pressure in the low-bank vessel exceeds the 
pressure in the medium-bank and the high-bank, at which time the three 
vessels are in pressure equilibrium. Further increases inside the 
medium-bank, and the high-bank, can be achieved by repeating the same 
process in each vessel, or by pressurizing one vessel at a time and 
tranferring the higher pressure gas to another one of the banks. 
Other equipment located on the pressurization end of the skid (1) include 
the pressure gauges (31) on each of the three discharge conduits (18) from 
the hydraulic pump leading to entry valves (19) on each of the three 
storage vessels, and exit valves (20) which can be opened, with entry 
valve (19) closed, to route the hydraulic fluid back to the surge tank 
(17) through conduits (21). Also included is a valve (22) and a conduit 
(34) for use with temporary low-pressure lines to drain the hydraulic 
fluid or re-fill the hydraulic system. Also included is a pressure 
regulating valve (35) which permits re-circulating part of the hydraulic 
fluid back to the surge tank to maintain pressure, and to serve as a 
safety relief valve. 
Other equipment located on the gas-entry end of the skid (1), generally at 
(5), are the pressure gauges at the outlet-inlet of each storage vesse 
(31) which registers the pressure of the gas inside the bladder (4) at all 
times. Also included are individual exit valves (7) and individual 
conduits (18) from each storage vessel (2) to the dispensing unit. Also 
shown are the master valve (8) and the entry conduit (32), and the 
mating-half of a quick connect-disconnect coupling. The dispensing unit is 
a priority panel which directs, or priortizes, storage vessel deliveries 
to re-fuel vehicles. Priority panels, of conventional design, may vary as 
to mechanisms and functions but will serve to dispense to vehicles a 
measured amount of gas from the low-bank switch over, when instructed to 
do so from a logic sequencer, to the medium-bank, and top-off from the 
high-bank. Also indicated are safety valves (33) which are pre-set maximum 
pressure devices on each conduit (13) to the three storage vessels (a) 
which will prevent excessive pressure on the dispenser. 
It is believed apparent from the above how the present method and system of 
storing and pressurizing natural gas can be adapted for uses other than 
compressed natural gas (CNG) re-fuel stations. The method of the invention 
remains the same, i.e., the use of a flexible bladder inside a steel 
storage tank whereby gas inside the bladder may be increased in pressure 
by pumping hydraulic fluid in the annulus between the bladder and the 
steel walls, thereby collapsing the bladder and confining the gas in a 
smaller volume which increases the pressure. Other end-uses would be to 
store gas for fuel in areas removed from natural gas pipelines for 
industrial or municipal users provide gas for stand-by service in 
situations where curtailments of gas supply cannot be tolerated; provide 
gas for areas where transportation is restricted because of terrain or 
bodies of water; and many other uses where pressurization by a 
conventional gas compressor would be excessively expensive, such as 
on-board cylinders on fork-lift, airport baggage and passenger transports, 
and other such uses. 
The present method and system fulfills all of the objects set forth 
hereinabove for the invention, and make it the best possible way to 
economically store and pressurize natural gas at automotive re-fuel 
stations other uses. Thus the availability of natural gas, the 
environmentally-preferred fuel for automobiles, busses, and trucks, can be 
such that it can economically compete with gasoline and diesel for 
automotive fuel use. In addition, the increased use of natural gas as the 
primary fuel for automobiles, trucks, and busses will open further 
opportunities to reduce the amount of crude oil used to make gasoline, 
which, in turn will reduce the reliance on foreign crude oil as the 
primary source of domestic energy requirements. The reduced reliance on 
foreign oil imports could have a major favorable impact upon the United 
States Adverse balance-of-payments and a major beneficial effect on the 
U.S. budget and long-term debt. 
It should be noted that the present invention utilizes the concept of a 
system for transporting natural gas from a pipeline to a compressed 
natural gas automotive re-fuel station, as proposed by the same inventor 
in patent application Ser. No. 08/454,531, now U.S. Pat. No. 5,603,360 to 
contain natural gas inside a flexible bladder during transportation, or, 
in this invention, to store and pressurize natural gas utilizing a 
hydraulic pump system instead of a more-expensive gas compressor system. 
It is the pressurization method of this invention which makes the 
technique for storage of natural gas both effective and economically 
sound. 
Obviously, many modifications and variations of the invention are possible. 
Further, it is evident that the method and system as described herein 
meets the objects set forth hereinabove, and that the invention makes 
possible the storage and dispensing of natural gas at CNG re-fuel 
stations, and other end-uses.