Abstract:
The invention is a method and apparatus for delivering large volumes of nitrogen gas, air, or other gas at high pressures from banks of high pressure cylinders and releasing that gas at the rate required by the operation. Not only can higher flow rates be achieved, but the absence of motors or engines can be an advantage in hazardous areas and can increase the reliability of the delivery of the gas. In addition, as compared to using liquid nitrogen, which typically must be delivered from a remote air separation plant, these banks of cylinders can then be recharged with gas by portable compressors or nitrogen generators.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to the field of methods and apparatus for the delivery of compressed gas for, inter alia, industrial or pipeline uses. 
   2. Description of the Prior Art 
   Nitrogen, air or other gas is used to service pipelines, tanks, or other items for the purpose of performing maintenance or some other operations. Typically dry air, nitrogen, or other gas is used, for example, to inert or dry pipelines  16  ( FIG. 1 ), or to propel pigs for cleaning or inspecting pipelines  16 . This dry air or nitrogen usually comes from either large motor or engine driven compressors  1  ( FIG. 1 ), from nitrogen gas generators  1 , which have a limited flow rate capability, or from liquid nitrogen which must be delivered to the site in sufficient quantities for the operation and then be pumped and vaporized with motor or engine driven pumps and heating equipment at the rate required by the application at hand. Nitrogen is the preferred gas to use for these applications due to its inherent nature of being relatively inert and very dry. 
   Time and cost are two major factors in determining what process to use in performing any of the operations. The fastest way to perform any of the operations is to obtain the highest flow rate of gas possible. In the current state of the art, this usually means using liquid nitrogen, which is the most expensive, equipment intensive and logistically difficult means. 
   The use of liquid nitrogen has been the preferred method of delivering gas for these applications because very high flow rates can be achieved at pressure required. When this method is used, the amount of gas must be estimated so that sufficient liquid nitrogen is available to complete the job. The disadvantages of this approach are the expense and logistics required for the supply and transportation of the liquid nitrogen, and the special equipment required to pump and vaporize the cryogenic medium. 
   The use of electric motor or engine driven compressors  1  to deliver the required gas (plus a nitrogen generator if necessary), although capable of delivering unlimited amounts of gas at a relatively low cost, is limited as to the rate at which the gas can be delivered and therefore increases the time required to perform the job. 
   Many of the operations that require a gas supply take place in hazardous locations (NEC Class 1 Division 2, or Zone 1 or 2) where the use of engines or electric motors  1  is discouraged, restricted, or require extensive safety provisions. In these cases both the use of the liquid nitrogen equipment and the compressors  1  present a potential problem that can usually only be remedied with expensive modifications to the equipment, or by using special equipment. 
   BRIEF SUMMARY OF THE INVENTION 
   The preferred embodiment of the invention is a method and apparatus for combining the advantages of the high flow rates that can be achieved using liquid nitrogen systems, with the lower cost and longer term operational capabilities of the compressors and nitrogen generators. The illustrated embodiment of the invention is a means for supplying high flow rates of gas by releasing the gas from one or more high pressure gas storage containers  10  (often known as “tube trailers” or “tube containers”). These gas storage containers  10  are arrays of high pressure cylinders that are interconnected with a manifold and are equipped with special valves that permit the high flow rates required by the operations. Multiples of these high pressure storage containers can be used for any single operation, with full containers replacing depleted containers  10  during the operation to maintain a sustained flow rate. Depleted containers  10  can be recharged by a nitrogen generator system  1  to achieve a longer operation and to meet the total volume requirement. The recharging can be performed off the hazardous site as discussed earlier. 
   An added benefit of this invention is that this procedure requires no power, in the form of gas or diesel engines or electric motors  1 , at the operation site. The absence of motors or engines  1  can be an advantage in hazardous areas and can increase the reliability of the delivery of the gas. 
   In addition, as compared to using liquid nitrogen, which typically must be delivered from a remote air separation plant, these banks of cylinders  10  can then be recharged with gas by portable compressors or nitrogen generators  1 . 
   Although the present invention still requires an estimate of the gas required, the cylinder banks  10  can be recharged with portable compressors and/or nitrogen generators  1  at or near the job site, albeit at a lower rate than is being delivered. 
   Considerably higher rates can be achieved with the present invention than with electric motor or engine driven compressors. The invention is normally operated with only low voltage control signals to control and record the flow of the gas, or can be operated with no power at all. 
   Thus the invention is defined as an apparatus for providing delivery of compressed gas to an application comprising at least one bank of compressed gas cylinders for storing gas at a pressure equal to or exceeding a predetermined delivery pressure; and a valve for controlling flow of gas from the bank to the application. 
   The apparatus further comprises a flowmeter coupled to the valve for monitoring flow of gas from the bank to the application. The flowmeter is preferably coupled to the valve downstream from the valve. The bank comprises a plurality of compressed gas cylinders coupled in parallel, coupled in series or as a cascaded system. 
   In another embodiment the apparatus further comprises a plurality of banks of gas cylinders. A corresponding plurality of valves are coupled to the plurality of banks of gas cylinders. A corresponding plurality of flowmeters are coupled to and downstream from the plurality of valves. 
   In still another embodiment the plurality of banks are divided into at least two sets of banks, each set having at least one bank of gas cylinders. At least one valve is coupled to each set of banks, a flowmeter is coupled to each valve, and at least two check valves are coupled to and downstream from the valves to permit selective detachment and coupling of each set of banks to the application. 
   The invention must also be understood to include the method of delivering compressed gas to an application or pipeline according the a method of operation using the above defined embodiments. 
   While the apparatus and method has or will be described for the sake of grammatical fluidity with functional explanations, it is to be expressly understood that the claims, unless expressly formulated under 35 USC 112, are not to be construed as necessarily limited in any way by the construction of “means” or “steps” limitations, but are to be accorded the full scope of the meaning and equivalents of the definition provided by the claims under the judicial doctrine of equivalents, and in the case where the claims are expressly formulated under 35 USC 112 are to be accorded full statutory equivalents under 35 USC 112. The invention can be better visualized by turning now to the following drawings wherein like elements are referenced by like numerals. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram which symbolically depicts a single bank of compressed gas cylinders coupled to a valve and flowmeter to deliver gas to an application or pipeline according to the invention. 
       FIG. 2  is a diagram of the invention wherein a plurality of banks of cylinders are employed. 
       FIG. 3  is a diagram of the invention of the embodiment of  FIG. 2  where the plurality of banks employ a common flowmeter. 
       FIG. 4  is a diagram of the invention wherein a plurality of banks of cylinders are employed in at least two sets in which one set is used and then exhausted with the second set then coupled to the application or pipeline to take up the gas delivery after the first set of banks are depleted. 
   

   The invention and its various embodiments can now be better understood by turning to the following detailed description of the preferred embodiments which are presented as illustrated examples of the invention defined in the claims. It is expressly understood that the invention as defined by the claims may be broader than the illustrated embodiments described below. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a diagrammatic depiction of a bank of high pressure cylinders  10  for storing the required gas at a pressure sufficiently higher than the required delivery pressure in the pipeline  16  or other application, so as to be able to maintain as high a flow rate as possible during delivery. Such a flow rate is substantially higher than that if the compressor/generator  1  were used to directly send gas to the pipeline  16 . The bank may be mounted on a transportable skid that can be loaded onto and off of a truck, barge, train car or aircraft. Alternatively, the bank can be integrally combined with the vehicle to provide a self-propelled unit. In general, while the delivery pressure can be understood to vary widely over the spectrum of all possible applications, for most pipeline deliveries a pressure in the range of approximately 100 to 500 psi is adequate. In addition the volume of gas which can be stored in a bank is highly variable according to the number and nature of gas cylinders ganged together to comprise the bank. Normally DOT cylinders would be used with maximum pressure capabilities of 2400 psig (3T-2400 tube) or 2850 psig (3T-2850 tube). The volume of each container depends on the length and number of tubes used. Other DOT and DOT exempt cylinders of various sizes may be used with pressures up to 5000 psig, arrayed into a bank of cylinders to make up a single container. However, container volumes in the range of 70,000 cubic feet to more than 185,000 cubic feet at 2400 psi or 2850 psi and at 70° F. are typical. The compressed gas is released from the bank of cylinders  10  through one or more valves  12  that serve to control the pressure and/or the flow rate of the delivered gas. A flow meter  14  may be included to monitor and/or record the flow rate and total flow of the delivered gas. The gas is delivered to the pipeline  16  or to another process or application. 
   The valve  12  may be incorporated as part of the bank of high pressure cylinders  10  or on a separate small skid with the flowmeter  14 . The flowmeter  14  is preferably located downstream of the valve  12 . The flowmeter  14  can be incorporated as part of the bank of high pressure cylinders  10  or on a separate small skid. 
   For higher flow rates, multiple banks of cylinders  10   a  and  10   b  may be used simultaneously delivering the gas in parallel as diagrammatically depicted in  FIG. 2 . Two or more banks of high pressure cylinders  10   a ,  10   b  for storing the required gas at a pressure sufficiently higher than the required delivery pressure in the pipeline  16  so as to be able to maintain as high a flow rate as possible. The gas is released from the multiple banks of cylinders  10   a  and  10   b  through one or more valves  12   a  and  12   b  respectively that serve to control the pressure and/or the flow rate of the delivered gas. A flow meter  14   a  and  14   b  may be included to monitor and/or record the flow rate and total flow of the delivered gas through valves  12   a  and  12   b  respectively. The gas is delivered to the pipeline  16  or to another process or application. Valves  12   a  and  12   b  may be incorporated as part of each bank of high pressure cylinders  10   a  and  10   b  respectively or on a separate skid with flowmeters  14   a  and  14   b  respectively to control and measure the flow of gas from the multiple banks of cylinders  10   a  and  10   b . The flowmeters  14   a  and  14   b  are preferably located downstream of the valves  12   a  and  12   b . The flowmeters  14   a  and  14   b  can be incorporated as part of the bank of high pressure cylinders  10   a  and  10   b  respectively or a single flowmeter  14  can be used on a separate small skid to measure the combined flow of the multiple banks of cylinders  10   a  and  10   b  as shown diagrammatically in  FIG. 3 . In the same way the function of valves  12   a  and  12   b  could be combined into a single valve to service banks  10   a  and  10   b.    
   For long durations jobs, multiple banks  10   a  to  10   n , where n is an arbitrary number, may be used sequentially, with one or more banks  10   a ,  10   b , . . . delivering the gas while additional banks of cylinders . . .  10   n  are standing by ready to deliver when the operating bank(s)  10   a ,  10   b , . . . of cylinders become depleted of gas or the pressure gets too low to maintain the desired flow rate. The gas may be delivered through one or more check valves  18   a  and  18   b  located just before the delivery point into the process  16  so that the depleted bank(s)  10   a ,  10   b , . . . may be removed from the process while the replacement bank(s) . . .  10   n  continue the operation. The depleted banks of cylinders  10   a ,  10   b , . . . can then be replaced with a fully charged bank of cylinders . . .  10   n . The depleted banks of cylinders  10   a ,  10   b , . . . can then be removed or recharged as required for continued operation. A separate check valve  18   a ,  18   b  . . . may be provided for each bank  10   a ,  10   b , . . .  10   n  or check valve  18   a  may be coupled via a manifold to a first set of banks  10   a ,  10   b  . . . which will be depleted first and then check valve  18   b  may be coupled via a manifold to a second set of banks . . .  10   n  which will be used next. 
   Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. 
   Therefore, it must be understood that the illustrated embodiment has been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following claims. For example, notwithstanding the fact that the elements of a claim are set forth below in a certain combination, it must be expressly understood that the invention includes other combinations of fewer, more or different elements, which are disclosed in above even when not initially claimed in such combinations. 
   The words used in this specification to describe the invention and its various embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definition in this specification structure, material or acts beyond the scope of the commonly defined meanings. Thus if an element can be understood in the context of this specification as including more than one meaning, then its use in a claim must be understood as being generic to all possible meanings supported by the specification and by the word itself. 
   The definitions of the words or elements of the following claims are, therefore, defined in this specification to include not only the combination of elements which are literally set forth, but all equivalent structure, material or acts for performing substantially the same function in substantially the same way to obtain substantially the same result. In this sense it is therefore contemplated that an equivalent substitution of two or more elements may be made for any one of the elements in the claims below or that a single element may be substituted for two or more elements in a claim. Although elements may be described above as acting in certain combinations and even initially claimed as such, it is to be expressly understood that one or more elements from a claimed combination can in some cases be excised from the combination and that the claimed combination may be directed to a subcombination or variation of a subcombination. 
   Insubstantial changes from the claimed subject matter as viewed by a person with ordinary skill in the art, now known or later devised, are expressly contemplated as being equivalently within the scope of the claims. Therefore, obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements. 
   The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptionally equivalent, what can be obviously substituted and also what essentially incorporates the essential idea of the invention.