Abstract:
A fixed and/or stationary modular unit consists of a hydraulic fluid tank and a pressurization pump. A compressed gas transportation system consists of a set of cylinders. Each cylinder has a charging port and a dispensing port. A valve is connected at the dispensing port of each cylinder. Each of the valves at the dispensing ports of the cylinders are connected to one another. After an idle period of dispensing activity, the valves on the dispensing ports of the cylinders are opened and compressed gas is bled from one of the cylinders into at least one of the other cylinders in the set until the at least one of the other cylinders reaches a desired dispensing pressure. Hydraulic fluid is pumped from the tank into the cylinder being bled from to maintain a substantially constant pressure within the cylinder.

Description:
[0001]    This application claims priority to provisional application 61/095,682, filed Sep. 10, 2008. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention is a method of boosting the pressure in a compressed gas cylinder while dispensing from another with hydraulic pressurization equipment in order to maintain a constant cylinder pressure throughout the gas dispensing operation. 
       BACKGROUND OF THE INVENTION 
       [0003]    Compressed natural gas (CNG) is any natural gas that has been processed and treated for transportation, in bottles or cylinders, at ambient temperature and at a pressure approaching the minimum compressibility factor. 
         [0004]    Natural gas is colorless, odorless, and lighter than air, and it easily dissipates into the atmosphere when it leaks. It burns with a flame that is almost invisible, and it has to be raised to a temperature above 620° C. in order to ignite. By way of comparison, it should be noted that alcohol ignites at 200° C. and gasoline at 300° C. For safety reasons, natural gas is odorized with sulfur for marketing purposes. 
         [0005]    Natural gas is an alternative to oil and therefore, it has great strategic importance, since it is a fossil fuel found in porous subsurface rock. It usually has low levels of pollutants, similar to nitrogen, carbon dioxide, water and sulfur compounds that remain in a gaseous state at atmospheric pressure and ambient temperature. Compressed natural gas is stored at a pressure of 220 bars or 3190 psi and is transported in trailers of varying volumetric capacity, depending on legislation and customer/project requirements. 
         [0006]    The principal advantage of using natural gas is the preservation of the environment. In addition to economic benefits, it is a non-polluting fuel and it burns cleanly, so its combustion products that are released into the atmosphere do not need to be treated. 
         [0007]    The great need to transport and store natural gas has contributed to increasing gas research around the world. Various methods have been proposed for storing and transporting compressed gases, such as natural gas, in pressurized vessels for overland transportation. The gas is typically stored and transported at high pressure and low temperature to maximize the amount of gas contained in each gas storage system. For example, compressed gas must be in a dense single-fluid state characterized as a very dense gas with no liquid. 
         [0008]    CNG is typically transported over land in tanker trucks or tank wagons. Tankers have storage containers such as pressurized metal vessels. These storage vessels have high burst strengths and withstand the ambient temperature at which CNG is stored. 
         [0009]    Storage vessels or cylinders are filled with compressed gas, typically using a compressor. A byproduct of the compression of the gas is heat, which ultimately raises the temperature of the gas in the cylinder. When a cylinder is filled to a specific pressure at a charging facility, for example 220 bar, that pressure will drop as the heat dissipates and the cylinder cools. When a series of cylinders reaches a dispensing location, the temperature of the cylinders has dropped, and as a result, the pressure of the cylinders has also dropped. Before gas can be dispensed from these cylinders, the gas pressure must be increased to the desired dispensing pressure, for example, 220 bar. 
         [0010]    A new technique is necessary in order to ensure minimal delay in charging a cylinder to a desired dispensing pressure once it arrives at a dispensing location. The following technique may solve one or more of these problems. The present technique exceeds the deficiencies described by providing hydraulic pressurization equipment that is capable of servicing the motor vehicles efficiently while maintaining a substantially constant desired pressure at all times. A system is utilized to boost the pressure in a cylinder while dispensing from another. 
       SUMMARY OF THE INVENTION  
       [0011]    A fixed and/or stationary modular unit consists of a hydraulic fluid tank, a pressurization pump, and a compressed gas transportation system consisting of a set of cylinders. Each cylinder has two ports, a hydraulic fluid charging port and a gas dispensing port, with actuated valves positioned at each port. A valve is connected at the dispensing port of each cylinders with the valves at the dispensing ports of each cylinder also being connected to one another. 
         [0012]    Gas is dispensed from the dispensing port of the cylinder by opening the valve at the dispensing port. The dispensing activity is monitored until a specified idle period has been met. The valves at the dispensing ports of at least two of the cylinders are opened and compressed gas is bled from one cylinder to another cylinder or plurality of cylinders. A pressure sensor monitors the pressure of the cylinder that compressed gas is being bled from and indicates when the pressure inside the cylinder has dropped. The valve connected to the incoming hydraulic fluid line is opened and hydraulic fluid is pumped from the tank into the cylinder to maintain a substantially constant desired pressure within the cylinder. Compressed gas is bled from one cylinder to another cylinder or plurality of cylinders until the other cylinder or plurality of cylinders have reached the desired dispensing pressure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic of a compressed gas filling system It illustrates the operation of the hydraulic pressurization equipment (HPU) connected to an over-the-road semi trailer. 
           [0014]      FIG. 2  is a flow chart of the operating steps of the system for pressurizing a compressed gas cylinder while dispensing from another. 
           [0015]      FIG. 3  is a schematic of an example of the system for pressurizing a compressed gas cylinder while dispensing from another. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]      FIG. 1  illustrates a compressed gas dispensing system consisting of a hydraulic pressurization unit (HPU)  10 , which is connected to an over-the-road compressed gas semi trailer  40 . 
         [0017]    As illustrated by  FIG. 1 , HPU  10  consists of a hydraulic fluid tank  11 , a hydraulic level gauge  13 , a particle filter  16 , a motor  21 , a coupling  23 , a pump  25 , a check valve  26 , a pressure sensor  27 , an outgoing fluid line  33 , and a fluid return line  91 . Additionally, HPU  10  consists of a capacity control sensor  93 , a photoelectric control sensor  95 , an incoming gas line  110 , a pressure sensor  111 , an actuated ball valve  112 , a hydraulic fluid separator  113 , a coalescing filter  115 , and an outgoing gas dispensing line  117 . An electric/electronic control panel (not visible), and programmable logic controller software complete HPU  10 . HPU  10  ensures that the compressed gas cylinders are charged to a specific pressure throughout the dispensing operation. In order to accomplish this, HPU  10  pumps hydraulic oil into the cylinders as gas is dispensed, in order to maintain a specific pressure. 
         [0018]      FIG. 1  also illustrates HPU  10  connected to an over-the-road compressed gas semi trailer  40  comprised of a gas cylinder module  39 , of which each module may consist of grouped sets of horizontal (tubular) cylinders (for example  61   a - d ), each with the same volume capacity. Cylinders carry compressed gas such as compressed natural gas (CNG), hydrogen, and other gases. Each module has a charging end  50  and a dispensing end  70 . Pressure gauges  41 ,  55 , and a set of valves consisting of manual ball valves  43 ,  57 , and actuated ball valves  51   a - d,    52   a - d  are connected at the charging end  50  of module  39 . The upstream connection from actuated ball valves  51   a - d  is connected to an incoming fluid line  37 . The upstream connection from actuated ball valves  52   a - d  is connected to a fluid return line  81 . 
         [0019]    A set of valves consisting of actuated ball valves  71   a - d,  a manual ball valve  75 , and a pressure relief valve  73  are connected at dispensing end  70  of cylinder module  39 . The downstream connection from actuated ball valves  71   a - d  is connected to an outgoing gas line  83 . The over-the-road semi trailer is charged with compressed gas at another location. 
         [0020]    Cylinders are filled with compressed gas, typically using a compressor. A byproduct of the compression of the gas is heat, which ultimately raises the temperature of the gas in the cylinder. When a cylinder is filled to a specific pressure at a charging facility, for example 220 bar, that pressure will drop as the heat dissipates and the cylinder cools. When a series of cylinders reaches a dispensing location, the temperature of the cylinders has dropped, and as a result, the pressure of the cylinders has also dropped. Before gas can be dispensed from these cylinders, the gas pressure must be increased to the desired dispensing pressure, for example, 220 bar. In order to ensure minimal delay in charging a cylinder to a desired pressure once it arrives at a dispensing location, a system is utilized to boost the pressure in a cylinder while dispensing from another, 
         [0021]    Once cylinder module  39  is filled with compressed gas, the gas is transported to a gas dispensing station where HPU  10  is installed. The over-the-road compressed gas semi trailer  40  is connected to HPU  10  with three hoses: an outgoing fluid hose  35 , a return fluid hose  85 , and a gas hose  87 . 
         [0022]    In order to dispense gas from cylinder module  39 , the start button on the control panel (not visible) is pushed and HPU  10  begins unloading gas from the first cylinder  61   a  in compressed gas module  39  on over-the-road semi trailer  40 . The electronic control panel (not visible) sends a signal to actuated ball valve  112  on HPU  10  and actuated ball valve  71   a  on dispensing end  70  of module  39 , causing the valves to open, allowing the gas in cylinder  61   a  to be dispensed. The gas dispensed from module  39  flows through outgoing gas line  83  and gas hose  87  until it reaches gas line  110  of HPU  10 . When the gas reaches line  110  of HPU  10 , the gas flows through pressure sensor  111 , actuated ball valve  112 , hydraulic fluid separator  113 , through coalescing filter  115 , through dispensing line  117 , and into gas line  120 . As the gas is dispensed from cylinder  61   a  of module  39 , pressure sensor  27 , located downstream of check valve  26 , senses the hydraulic pressure drop in cylinder  61   a.  When the pressure reaches a selected level, such as 210 bar or less, sensor  27  sends an electrical signal to the control panel (not visible). The control panel then sends a signal that simultaneously actuates motor  21  and opens actuated ball valve  51   a  on the charging end  50  of cylinder  61   a.    
         [0023]    Motor  21  suctions the hydraulic fluid from tank  11 , forcing it through particle filter  16  to pump  25 . Pump  25  forces the hydraulic fluid through check valve  26 , outgoing fluid line  33 , and outgoing fluid hose  35 , until it reaches incoming fluid line  37  of the over-the-road semi trailer  40 . The hydraulic fluid flows through actuated ball valve  51   a  and into cylinder  61   a,  forcing the gas from cylinder  61   a  out the dispensing end  70  of the module  39 . Once pressure sensor  27  senses the gas pressure has reached a selected pressure, such as 220 bar or 3190 psi, an electronic signal from the control panel (not visible) switches off motor  21 . Check valve  26  prevents hydraulic fluid from flowing back into tank  11 . 
         [0024]    As gas is being dispensed from cylinder  61   a,  the pressure in cylinder  61   b  is below the desired dispensing pressure due to the temperature drop and subsequent pressure drop experienced during transport of the cylinders from the charging station to the dispensing location. In order to charge cylinder  61   b  to the desired dispensing pressure, cylinder  61   b  is charged using a method comprised by the invention, and as outlined in the flow chart of  FIG. 2 . The method requires bleeding gas from one cylinder into another. For example, referring to  FIG. 3 , cylinder  61   a  is being dispensed from, and cylinder  61   b  will follow once cylinder  61   a  is exhausted. In order to ensure that cylinder  61   b  is at the desired pressure by the time cylinder  61   a  is depleted, the pressure in cylinder  61   b  is boosted at intervals by gas from cylinder  61   a.  The boosting is controlled by the control panel (not visible). The control panel monitors the dispensing activity of module  39 , and in particular cylinder  61   a.  When there has been a specified idle period in dispensing activity (i.e., actuated ball valve  112  is closed), the control panel sends a signal to actuated ball valves  71   a,    71   b,  which had been closed and now open. The control panel monitors the flow of gas from cylinder  61   a  to cylinder  61   b,  and sends a signal to actuated ball valves  71   a,    71   b  closing them after a specified amount of time. The amount of gas transferred from cylinder  61   a  to cylinder  61   b  is closely controlled and monitored by the control panel (not visible) to ensure that any pressure drop in cylinder  61   a  caused by the boosting of cylinder  61   b  is minimal. 
         [0025]    When pressure sensor  27  senses a drop in pressure in cylinder  61   a,  it sends a signal to the control panel, which then functions as previously discussed, causing hydraulic oil to be pumped into cylinder  61   a  until it reaches a desired pressure. The boosting process continues in this cycle, until pressure sensor  27  does not sense a drop in pressure when charging cylinder  61   b.  If no pressure drop is detected, boosting is complete and cylinder  61   b  has been charged to the desired pressure. The boosting of cylinder  61   b  is done in small increments over an extended amount of time in order to minimize pressure drop in cylinder  61   a,  and subsequently, to reduce charging time for cylinder  61   a.  After cylinder  61   b  has been charged to the desired pressure, the boosting process continues by boosting the pressure in the next available cylinder, for example cylinder  61   c.    
         [0026]    When cylinder  61   a  is depleted, and gas is dispensed from cylinder  61   b,  the boosting process continues with gas from cylinder  61   b  boosting the remaining cylinders in the series that have not yet been boosted to the desired pressure. The process illustrated above continues until all of the cylinders in a series are boosted to a desired pressure. 
         [0027]    The gas is dispensed and the dispensing process discussed above is repeated until cylinder  61   a  has been depleted. The hydraulic fluid is discharged from cylinder  61   a  as discussed in U.S. patent application Ser. No. 12/435,078, herein incorporated by reference. 
         [0028]    When the discharge of hydraulic fluid from cylinder  61   a  begins, the control panel begins unloading gas from cylinder  61   b  (beginning another cycle). The cycle is repeated for each cylinder in a module until the entire module has been exhausted. The number of cylinders in a module, and the number of modules depends solely on the volume of gas that needs to be transported and the manufacturing standards of the over-the-road semi trailer. 
         [0029]    The invention has significant advantages. The boosting system is a cost effective means of increasing the efficiency of the dispensing activity by minimizing delay times associated with charging a cylinder to a desired dispensing pressure. The boosting system allows for timely and efficient transition from one cylinder to another within a module. 
         [0030]    While the invention has been shown in only a few of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention. For example, compressed gas may simultaneously be dispensed from more than one cylinder. Additionally, compressed gas may be bled from more than one cylinder simultaneously, and more than one cylinder may be boosted to a desired dispensing pressure simultaneously.