Natural gas compressing and refueling system and method

Abstract

A refueling system for natural gas users (e.g., natural gas vehicles) includes a two-stage compression system that compresses low-pressure gas in a natural gas supply line to compressed natural gas (CNG) pressure for use by a user. A single motor drives both a first stage rotary compressor and a rotary hydraulic pump that powers a second-stage liquid piston compressor. The motor, first stage compressor, and pump may be co-axially aligned. Booster vessels store compressed gas to augment the system's compressed gas delivery flow rate when desired. The booster vessels may be recharged with compressed gas when the system is not delivering gas to a user. Hydraulic liquid may be pumped into and out of the booster vessels during booster vessel discharge and recharge, respectively, to maintain a desired pressure within the vessels.

What is claimed is: 
     
         1 . A two-stage gas compression system configured to compress gas, the system comprising:
 a rotary power source having an output shaft;   a positive-displacement first stage rotary compressor having a first stage gas inlet and a first stage gas outlet, the first stage rotary compressor being operatively connected to the rotary power source to be driven by the output shaft;   a hydraulic pump operatively connected to the rotary power source to be driven by the output shaft, the pump having a hydraulic liquid inlet and a hydraulic liquid outlet; and   a positive-displacement second stage compressor having
 a second stage gas inlet fluidly connected to the first stage gas outlet, and 
 a second stage gas outlet configured to provide second stage compressed gas to a user, 
   wherein the second stage compressor operatively connects to the liquid outlet of the pump so as to be driven by pressurized liquid provided by the pump.   
     
     
         2 . The system of  claim 1 , wherein:
 the pump comprises a rotary hydraulic pump driven by a pump drive shaft that is driven by the output shaft;   the first stage rotary compressor comprises a compressor drive shaft that drives the compressor and is driven by the output shaft; and   the output shaft, pump drive shaft, and compressor drive shaft are co-axial with each other.   
     
     
         3 . The system of  claim 1 , wherein the first stage rotary compressor and hydraulic pump are commonly disposed within a sealed shell. 
     
     
         4 . The system of  claim 1 , wherein:
 the system is a home refueling system configured to compress natural gas from a residential natural gas supply and supply compressed natural gas to a compressed natural gas vehicle;   the system comprises a dispensing port operatively connected to the second stage gas outlet, the dispensing port being configured to connect to the compressed natural gas vehicle to provide second stage compressed gas to the vehicle; and   the first stage gas inlet is configured to receive gas at a base pressure level from a natural gas supply line of a residential natural gas supply.   
     
     
         5 . The system of  claim 1 , wherein the first stage compressor and the second stage compressor are configured such that the gas compression is near-isothermal. 
     
     
         6 . The system of  claim 1 , further comprising at least one atomized liquid injector connected to at least one of the compressors and configured to provide atomized liquid into the at least one of the compressors to cool the gas being compressed in the at least one of the compressors. 
     
     
         7 . The system of  claim 6 , wherein:
 the at least one of the compressors comprises the first stage compressor and the second stage compressor; and   the at least one atomized liquid injector comprises
 at least one first stage atomized liquid injector connected to the first stage compressor and configured to provide atomized liquid into the first stage compressor, and 
 at least one second stage atomized liquid injector connected to the second stage compressor and configured to provide atomized liquid into the second stage compressor. 
   
     
     
         8 . The system of  claim 1 , wherein the hydraulic fluid is an ionic liquid. 
     
     
         9 . The system of  claim 1 , wherein:
 the second stage compressor comprises a first hydraulic piston compressor;   the system further comprises a second positive-displacement hydraulic piston compressor having
 a second stage gas inlet fluidly connected to the first stage gas outlet, and 
 a second stage gas outlet configured to provide second stage compressed gas to the user; 
   the second hydraulic piston compressor operatively connects to the liquid outlet of the pump so as to be driven by pressurized liquid provided by the pump; and   the system further comprises a controller that is configured to operate the first hydraulic piston compressor out of phase from the second hydraulic piston compressor.   
     
     
         10 . A method of using a two-stage gas compression system to compress gas, the system comprising a rotary power source having an output shaft; a positive-displacement first stage rotary compressor having a first stage gas inlet and a first stage gas outlet, the first stage rotary compressor being operatively connected to the rotary power source to be driven by the output shaft; a hydraulic pump operatively connected to the rotary power source to be driven by the output shaft, the pump having a hydraulic liquid inlet and a hydraulic liquid outlet; and a positive-displacement second stage compressor having a second stage gas inlet fluidly connected to the first stage gas outlet, and a second stage gas outlet configured to provide second stage compressed gas to a user, wherein the second stage compressor operatively connects to the liquid outlet of the pump so as to be driven by pressurized liquid provided by the pump, the method comprising:
 receiving a gas at the first stage gas inlet;   operating the rotary power source, which causes the output shaft to drive the first stage compressor, thereby compressing the gas in the first stage compressor into first stage compressed gas;   causing the first stage compressed gas to flow from the first stage gas outlet into the second stage compressor via the second stage gas inlet;   operating the rotary power source, which causes the output shaft to drive the pump and pump hydraulic liquid into the second stage compressor, thereby compressing the first stage compressed gas disposed within the second stage compressor into second stage compressed gas; and   discharging the second stage compressed gas from the second stage compressor to a user.   
     
     
         11 . The method of  claim 10 , wherein the gas comprises natural gas. 
     
     
         12 . The method of  claim 10 , further comprising injecting atomized liquid into at least one of the compressors while the at least one of the compressors is compressing gas.