Air compressor powered by differential gas pressure

Abstract

A gas-driven air compressor system and a method for using it. No electricity, lubrication or cooling water is required. A high pressure gas used to drive the compressor may be recovered at a pressure high enough to be retain its economic value. In one preferred embodiment, the air compressor includes a gas-driven drive cylinder and an air-driven boost cylinder, interconnected by reciprocating drive and boost pistons. The drive piston supplies force to power the boost piston, which pulls in atmospheric air and discharges it at a higher pressure for use by pneumatically-operated controls and equipment. A four-way valve operating on differential gas pressure may be used to automatically actuate the reciprocating piston. Using the present invention, fugitive gas emissions, such as normally occur when using a separator to remove oil and water from a wellhead gas stream, may be avoided.

I claim: 
     
         1 . A gas-driven air compressor, comprising:
 a gas drive cylinder and an air compression cylinder interconnected by reciprocating gas drive and air compression pistons;   the drive piston supplying force powered by a first gas stream at a first pressure within the drive cylinder which exhausts to a second gas stream at a second pressure lower than the first pressure; and   the air compression piston moving under the force supplied by the drive piston, which movement induces air at atmospheric pressure to flow into the air compression cylinder and boosts the pressure of the air in the air compression cylinder to a higher pressure than atmospheric pressure.   
     
     
         2 . The air compressor of  claim 1 , further comprising a four-way valve actuating the reciprocating piston, the four-way valve operating on differential gas pressure. 
     
     
         3 . The air compressor of  claim 2 , wherein movement of the four-way valve is actuated by gas pilot pressure applied on each side of the valve. 
     
     
         4 . The air compressor of  claim 2 , wherein movement of the four-way valve is actuated by gas pilot pressure applied on one side of the valve. 
     
     
         5 . The air compressor of  claim 4 , wherein venting of the gas pilot pressure results in a spring actuating a side opposing the one side of the valve. 
     
     
         6 . The air compressor of  claim 2 , wherein movement of the four-way valve is actuated by gas pilot pressure applied to a first valve piston on one side of the valve. 
     
     
         7 . The air compressor of  claim 6 , wherein venting of the gas pilot pressure results in supply pressure actuating the valve by acting on a second valve piston on a side opposing the one side of the valve, wherein the second valve piston is smaller than the first valve piston. 
     
     
         8 . The air compressor of  claim 3 , wherein a return movement of the valve is actuated by venting the gas pilot pressure to a low pressure gas line. 
     
     
         9 . The air compressor of  claim 4 , wherein a return movement of the valve is actuated by venting the gas pilot pressure to a low gas pressure line. 
     
     
         10 . The air compressor of  claim 6 , wherein a return movement of the valve is actuated by venting the gas pilot pressure to a low gas pressure line. 
     
     
         11 . The air compressor of  claim 1 , further comprising a mechanically-actuated four-way valve actuating the reciprocating gas drive piston. 
     
     
         12 . The air compressor of  claim 1 , wherein the air compressor operates without the need for electricity, lubrication or cooling water. 
     
     
         13 . The air compressor of  claim 1 , wherein the air compression piston pulls air at atmospheric pressure into the air compression cylinder through an inlet check valve on a forward stroke of the air compression piston, and pushes air at an elevated pressure above atmospheric pressure out of the air compression cylinder through a discharge check valve on a reverse stroke of the air compression piston. 
     
     
         14 . The air compressor of  claim 1 , wherein the air compression piston pulls air at atmospheric pressure into the air compression cylinder through an inlet check valve on one side of the cylinder, while simultaneously pushing air at an elevated pressure above atmostpheric pressure out of the air compression cylinder on the other side of the piston through a discharge check valve on a forward stroke of the air compression piston, and repeats the process on a reverse stroke of the air compression piston. 
     
     
         15 . The air compressor of  claim 1 , wherein the first gas stream originates from a well head, and wherein the compressed air supplied from the air compressor is used to operate controls of a separator used to remove oil and water from the first gas stream. 
     
     
         16 . A method for using a gas-driven air compressor having a gas drive cylinder and an air compression cylinder interconnected by reciprocating gas drive and air compression pistons, comprising the steps of
 moving the drive piston using a first gas stream at a first pressure within the drive cylinder which exhausts to a second gas stream at a second pressure lower than the first pressure; and   the air compression piston moving under the force supplied by the drive piston, which movement induces air at atmospheric pressure to flow into the air compression cylinder, thereby boosting air within the air compression cylinder to a higher pressure than atmospheric pressure.   
     
     
         17 . The method of  claim 16 , wherein the first gas stream originates from a well head, and further comprising the step of using the compressed air supplied from the air compressor to operate controls of a separator used to remove oil and water from the first gas stream. 
     
     
         18 . The method of  claim 16 , wherein a four-way valve is provided in fluid communication with the reciprocating gas drive piston, and further comprising the step of actuating movement of the four-way valve using differential gas pressure between the first and second gas streams. 
     
     
         19 . The method of  claim 18 , further comprising the step of actuating movement of the four-way valve using gas pilot pressure applied on at least one side of the valve. 
     
     
         20 . The method of  claim 16 , further comprising the step of the air compression piston pulling air at atmospheric pressure into the air compression cylinder through an inlet check valve on a forward stroke of the air compression piston, and the air compression piston pushing air at an elevated pressure above atmospheric pressure out of the air compression cylinder through a discharge check valve on a reverse stroke of the air compression piston.