Reciprocating Compressor System with Liquid Pumping Capability

Abstract

A reciprocating-type piston compressor that can operate at very low speed (<300 rpm) with the ability to pump liquids. It can be configured with one or more double-acting cylinders. A variable speed drive can be used to adjust the operating speed of the compressor to control system torque requirements throughout the compression cycle.

What is claimed is: 
     
         1 . A reciprocating compressor system with liquid pumping capability, the system comprising:
 a low inertia reciprocating piston compressor further comprising at least one intake valve and at least one discharge valve;   an intake flow line operatively coupled to the at least one intake valve;   an output flow line operatively coupled to the at least one discharge valve;   a compressor drive unit operatively coupled to the compressor, the compressor drive unit configured to operate the compressor; and   a suction pressure transducer operatively coupled to the intake flow line and further operatively coupled to the compressor drive unit, the suction pressure transducer configured to measure suction pressure within the intake flow line and to generate a suction pressure data signal, the compressor drive unit configured to control speed of operation of the compressor in response to the suction pressure data signal.   
     
     
         2 . The system as set forth in  claim 1 , wherein the compressor comprises at least one double-acting cylinder. 
     
     
         3 . The system as set forth in  claim 1 , wherein one or both of the at least one intake valve and the at least one discharge valve comprises a check valve. 
     
     
         4 . The system as set forth in  claim 1 , wherein the compressor comprises at least one substantially horizontal cylinder wherein the at least one intake valve is disposed on a top surface thereof, and the at least one discharge valve is disposed on a bottom surface thereof. 
     
     
         5 . The system as set forth in  claim 1 , wherein the compressor drive unit comprises a motor operatively coupled to a speed reducer, wherein the speed reducer is operatively coupled to the compressor. 
     
     
         6 . The system as set forth in  claim 5 , wherein the motor comprises an electric motor. 
     
     
         7 . The system as set forth in  claim 6 , further comprising a variable frequency drive (“VFD”) unit configured for controlling speed of operation of the electric motor, wherein the VFD unit is configured for operating the electric motor in a constant torque mode at motor speeds between 0 to 1800 revolutions per minute (“RPM”) and in a constant horsepower mode at motor speeds between 1800 to 3600 RPM. 
     
     
         8 . The system as set forth in  claim 7 , wherein the VFD unit is configured to slow the speed of the electric motor when a liquid is drawn into the at least one intake valve. 
     
     
         9 . The system as set forth in  claim 7 , further comprising a controller operatively coupled to the suction pressure transducer and to the VFD, the controller configured to generate and transmit a VFD control signal to the VFD, the VFD control signal configured for controlling the speed of the electric motor in response to the suction pressure data signal. 
     
     
         10 . The system as set forth in  claim 9 , wherein the controller is configured to compare a current suction pressure reading with a historical suction pressure reading and to generate a slug protection speed limit control signal if the historical suction pressure reading is greater than the current suction pressure reading by a predetermined liquid warning threshold. 
     
     
         11 . The system as set forth in  claim 9 , wherein the controller further comprises input controls configured for one or both of setting and controlling pressure limits and temperature limits of the system. 
     
     
         12 . The system as set forth in  claim 9 , wherein the controller comprises a programmable logic controller. 
     
     
         13 . A method for compressing gas and pumping liquids, the method comprising the steps of:
 providing a reciprocating compressor system with liquid pumping capability, the system comprising:
 a low inertia reciprocating piston compressor further comprising at least one intake valve and at least one discharge valve, 
 an intake flow line operatively coupled to the at least one intake valve, 
 an output flow line operatively coupled to the at least one discharge valve, 
 a compressor drive unit operatively coupled to the compressor, the compressor drive unit configured to operate the compressor, and 
 a suction pressure transducer operatively coupled to the intake flow line and further operatively coupled to the compressor drive unit, the suction pressure transducer configured to measure suction pressure within the intake flow line and to generate a suction pressure data signal, the compressor drive unit configured to control speed of operation of the compressor in response to the suction pressure data signal; 
   drawing in gas through the intake flow line and compressing the gas with the compressor;   measuring the suction pressure in the intake flow line to produce a current suction pressure reading;   comparing a historical suction pressure reading to the current suction pressure reading; and   slowing the speed of operation of the compressor if the historical suction pressure reading is greater than the current suction pressure reading by a predetermined liquid warning threshold.   
     
     
         14 . The method as set forth in  claim 13 , further comprising slowing the compressor when a liquid is drawn into the at least one intake valve. 
     
     
         15 . The method as set forth in  claim 13 , wherein the compressor comprises at least one double-acting cylinder. 
     
     
         16 . The method as set forth in  claim 13 , wherein one or both of the at least one intake valve and the at least one discharge valve comprises a check valve. 
     
     
         17 . The method as set forth in  claim 13 , wherein the compressor comprises at least one substantially horizontal cylinder wherein the least one intake valve is disposed on a top surface thereof, and the at least one discharge valve is disposed on a bottom surface thereof. 
     
     
         18 . The method as set forth in  claim 13 , wherein the compressor drive unit comprises a motor operatively coupled to a speed reducer, wherein the speed reducer is operatively coupled to the compressor. 
     
     
         19 . The method as set forth in  claim 18 , wherein the motor comprises an electric motor. 
     
     
         20 . The method as set forth in  claim 19 , wherein the system further comprises a variable frequency drive (“VFD”) unit configured for controlling speed of operation of the electric motor, wherein the VFD unit is configured for operating the electric motor in a constant torque mode at motor speeds between 0 to 1800 revolutions per minute (“RPM”) and in a constant horsepower mode at motor speeds between 1800 to 3600 RPM. 
     
     
         21 . The method as set forth in  claim 20 , wherein the system further comprises a controller operatively coupled to the suction pressure transducer and to the VFD, the controller configured to generate and transmit a VFD control signal to the VFD, the VFD control signal configured for controlling the speed of the electric motor in response to the suction pressure data signal. 
     
     
         22 . The method as set forth in  claim 21 , wherein the controller is configured to compare the current suction pressure reading with the historical suction pressure reading and to generate the slug protection speed limit control signal if the historical suction pressure reading is greater than the current suction pressure reading by the predetermined liquid warning threshold. 
     
     
         23 . The method as set forth in  claim 21 , wherein the controller comprises a programmable logic controller.