Injection pump apparatus

Abstract

A pump monitoring and flow control system that provides direct indication and control of discharge flow on gas driven positive displacement or diaphragm injection-type pumps. The device uses a “tell-tale” check valve that drives a proximity switch each time the tell-tale valve, installed as the output check valve on a standard injection pump, opens with discharge flow. The proximity switch in turn signals the monitoring system which computes the volume of chemical injected and controls the injection pump gas motor to provide the required volume of injected fluid. Additionally the system can alarm if injection flow is interrupted.

Description

TECHNICAL FIELD OF THE INVENTION

This invention relates to the process and oil industries and to chemical injection; in particular the device relates to gas driven positive displacement or diaphragm injection-type pumps providing a means for monitoring and controlling the output flow.

BACKGROUND OF THE INVENTION

In the oil, gas, petrochemical, water treatment, and environmental protection industries there is an absolute necessity to treat many flowing liquids on a continuous basis with various chemicals. For example, a few of these chemicals are corrosion inhibitors, emulsifiers, scale inhibitors, antifreeze, bactericides, and others. Many of the flowing liquids are flowing under pressure within pipelines and require a high-pressure means of injecting the chemicals. In many cases, the quantity of injected chemical is somewhat critical and must be adjusted from time-to-time to conform to the flow rate within the pipeline.

Many injection sites for chemicals are remote from maintenance personnel, which create a dilemma since the injector pumps are, by nature, prone to unexpected failure. In the oil and gas industry for instance, an interruption of chemical treatment can mean the shut-in of a well or freeze-up of a transmission line. Such events can cost many tens-of-thousands of dollars.

Currently, the best method of protecting against injector pump failure is through a daily visit by pump maintenance personnel (known as a pumper). Many chemical injection locations are at oil well pumping sites that may be remote from the pumper by a hundred miles or more. Offshore production requires a boat and crew to assist the pumper in making his rounds to dozens of unmanned platforms. This type of service is very costly. Even with daily visits by a pumper, there is no assurance that the pump will not fail within minutes after the inspection is completed.

Typically, pump failures are caused by malfunctions of the suction or delivery check valve, packing leakage, mechanical drive failure, chemical supply blockage, electrical or gas interruption to the drive motor, or piping failures, just to name a few.

For the past fifty years or more, there has been a serious problem in the industry due to the inability to constantly monitor the flow rate of the chemical injection pumps. The problem has always been how to detect, measure, and possibly adjust the flow rate of a chemical injector from a distant location.

With the development of reliable cellular telephone service, it is now possible to provide communication between the pumper and the pump installation, both onshore and offshore, with the ordinary cellular telephone (or other SCADA—supervisory control and data acquisition system). If a simple and inexpensive method of automatically monitoring of injection flow rates was available, the monitoring system would transmit an appropriate signal to the maintenance personnel through the cellular system or SCADA system, and industry could save millions of dollars each year.

There have been many attempts made to monitor flow rates of chemical pumps and transmit this data, but none have been successful. Typically, these systems are so expensive and complicated that more problems are created than solved. The most common technique is by sensing the pressure in the output of the injection pump. There are several techniques, well known in the industry, to monitor pressure ranging from simple “snap-like” devices (high-normal-low pressure switches) to pressure transducers/transmitters. pressure transmitter system may be found in the disclosure by Smith et al. (U.S. Pat. No. 5,654,504) that, although the application is not for an injection pump, dislcoses a Downhole Pump Monitoring System that supervises a pump by using a pressure transmitter to determine if the pump is operating.

Yoder et. al. (U.S. Pat. Nos. 6,135,719 and 6,135,724) disclose a more typical injection pump system. Here a complex feedback control scheme is used to meter and monitor a series of chemical injection pumps by means of position control on the stroke control unit.

The problem of a simple tall-tale device has been resolved by the MG & G pump company who manufactures and markets their “Automatic Check Valve” known as an ACV. The same company also manufactures and markets chemical injection pumps as described in U.S. Pat. No. 3,500,753to Greene entitled “Injection Pump Apparatus” and has offered this device for some 30 years to the industry. The injection pump apparatus is rugged and has become an industry standard; however, as pump parts wear the quantity of fluid injected per stroke tends to wander and in some cases stop. Thus a need remains for a small, locally controlled chemical injection system that can adjust chemical injection rates in a set ratio and be reliable and consistent.

SUMMARY OF THE INVENTION

The present invention is a monitoring and control system for use with chemical injection comprising:

• • an indicating check valve or ACV;
  • a dual stroke pneumatic piston driver;
  • a solenoid valve; and
  • control means.

The present invention uses the indicating check valve to provide a measurement of the quantity of flow and couples the indicting check valve to a pneumatic (gas or air) operated positive displacement pump driver via a local electronic controller.

The inlet of the pump draws injection fluid and the outlet of the pump passes through the indicating check valve and into the process stream. The check valve signal (an on/off signal or count) is passed to a local electronic controller (typically a Programmable Logic Controller—PLC). The local electronic controller is also coupled to the solenoid valve that operates the dual stroke pump driver. The electronic controller is programmed so that converts counts per unit time coming from the indicating check valve to volume per unit time of injected fluid.

The controller is given the “ratio” of injection fluid to process stream fluid better known as the setpoint. This value may be passed by a local device (such as a programmer) or by a distant device over a SCADA scheme.

The controller then opens and closes the solenoid valve on the pump over a sufficient period of time driving the dual stroke pump to push a quantity of fluid into the stream. The number of times that the check valve pulses determines the quantity of fluid injected. When the controller is satisfied with the quantity, the solenoid valve is closed and the dual stroke pump returns to its starting position. This process is repeated indefinitely. Alternatively, the electronic controller can be programmed to modulate the solenoid more slowly or more rapidly in order to inject the required fluid per unit time.

Any failure is immediately detected by the automatic check valve and the controller will alarm. That alarm may be local or passed to the SCADA system.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure One shows an injection pump driven by a dual stroke driver utilizing the prior art pneumatic driver motor with an standard output check valve on the injection pump and a regulator valve controlling the inlet gas supply to the gas driver motor.

Figure Two shows the instant invention utilizing a pneumatic driver motor and an injection pump with an automatic check valve on the injection pump outlet and a solenoid valve controlling the inlet supply to the pneumatic driver motor.

Figure Three shows the system electronic connections.

Figure Four shows the improved pneumatic driver motor of the instant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The prior art (Greene apparatus) is shown in FIG. 1. A complete description of the operation of the Greene apparatus appears in U.S. Pat. No. 3,500,753 which is incorporated in its entirety by reference. As shown in FIG. 1, the prior art comprises a standard chemical injection pump driven by the Pneumatic Driver mechanism described in the Greene disclosure. The essential parts of the Greene apparatus are the gas motor housing, 1, the venting assembly, 50, and the regulator, 40. The injection pump, 2, utilizes a standard output check valve, 30.

The instant invention is shown in FIG. 2. The complete system comprises a pneumatic driver motor, 1, (essentially dual stroke piston) driving a chemical injection pump, 2, which is coupled to an Automatic Check Valve, 3, connected to the outlet port, 11, of the injection pump. Driving pressure is supplied to the motor, 1 by a 3-way solenoid valve, 4.

The principal behind the motor using a dual stroke pump is shown in FIG. 4. Supply air or gas (fluid) enters the driver through ports 7 and 8. There is a significant difference in piston area seen by the fluid entering the two ports. Fluid that enters though port 7 sees area 5; whereas, fluid entering port 8 sees area 6. Because of the large difference in area, the fluid entering port 7 will drive the piston down even though the same pressure appears at port 8. Thus, the dual stroke piston is biased in the upward direction; however, the bias is readily overcome because of the area differences.

The 3-way solenoid valve, 4 controls air or gas entering or leaving port 7. When the valve is activated gas pressure is placed at port 7. When the valve is deactivated, gas is vented from port 7. Thus, the solenoid valve operates the dual stroke gas motor in much the same manner as the Greene device except that the internal vent mechanism, 50, and the gas regulator, 40, are both eliminated. (A single stroke piston could be used with a return spring pressing against area 6 thereby providing bias; however, springs are known to fail.)

FIG. 3 shows the complete apparatus. An electronic controller, 10, which may be a programmable logic controller (PLC), serves to operate the solenoid valve, 4 based on pulses supplied by the ACV, 3. The ACV, as explained, is a check valve that provides the equivalent to a contact closure whenever the valve opens. Since the volume of the injection pump chamber is known, then it is a simple mathematical relationship to calculate the volume of injection fluid delivered each time the ACV opens (and closes).

The electronic controller (preferably a PLC), accepts the pulse signal from the ACV and computes volume per unit time. Based on the required injection rate or setpoint (set by the ratio of injection fluid to process fluid—process fluid being the fluid into which chemicals must be injected), the controller will activate the solenoid valve driving the dual stroke piston within the gas driver motor and therefore powering the chemical injection pump. Based on required injection rate per unit time, the controller will modulate the 3-way solenoid sufficiently to obtain the required injection rate.

The paragraphs above describe the preferred mode for the instant invention which provides an improved injection apparatus driven by a pneumatic motor. This mode improves the Greene driver by reducing the complexity (removes the venting assembly) and provides internal feedback that the actual injection pump/driver are functioning utilizing the ACV style check valve on the outlet of the injection pump. It should be noted that this mode provides a fixed injection flow into the process stream.

The preferred mode may be modified to provide a constant injection ratio based on the flow of process fluid into which injection is required. A standard flowmeter should be added to the process line which measures process flow using standard techniques. Based on the process flow and the required injection rate (set by the ratio), the controller will activate the solenoid valve driving the dual stroke piston gas driver and therefore the chemical injection pump. Thus, by carefully programming an algorithm in the local controller (PLC)—the system can deliver a more or less fluid resulting in a constant injection flow into the process. These algorithms are well known in the industry and may be readily programmed based on piston size, gas pressure, pump size, etc.

Finally, if the pump (or system) fails, the ACV, 3, will no longer indicate flow and the local controller will pass a system alarm.

The device has been described as a stand-alone unit; however, as implied the local controller may be part of a full SCADA or distributed control system with the control algorithm based in the SCADA or distributed control system. The device has been described for use with PD pumps, but will serve equally well with diaphragm pumps and other similar types of positive displacement pumps. Hence the term pump as used in the claims should be broadly construed.

Claims

1. An improved pneumatic motor for operating an injection pump of the type having a cylinder incorporating a moveable piston having two sides one side being connected to the injection pump and being biased towards one end of the cylinder and having a pressure regulator means and venting means incorporated within the cylinder and operated by the movement of the piston, and wherein the injection pump has an outlet check valve, wherein the improvement comprises:

(a) elimination of the venting means incorporated within the cylinder;

(b) replacement of the pressure regulator means with a 3-way electric solenoid valve, wherein said 3-way electric solenoid valve shifts to apply pressure to the non-biased side of the moveable piston or vents pressure from the non-biased side of the moveable piston;

(c) replacement of the outlet check valve with an indicating check valve incorporating means to indicate the open or closed position of said indicating check valve; and

(d) electronic control means for sensing said open position of said indicating check valve and for modulating said 3-way electric solenoid between applying pressure to or venting pressure from the non-biased side of the moveable piston dependent on a control algorithm internally stored in said electronic controller.

2. The improvement of claim 1, wherein the injection pump is connected to a process stream to which fluids are to be injected in a given ratio, and wherein said electronic control means accepts a setpoint indicative of the required given ratio and wherein said algorithm computes the required quantity of injected fluid per unit time and modulates said 3-way electric solenoid valve while sensing said open position of said indicating check valve thereby providing the correct quantity of injection fluid.

3. The improvement of claim 2, wherein the process stream quantity of flow is measured and provided to said electronic control means and wherein said algorithm modulates said 3-way solenoid valve thereby varying the injection fluid quantity proportionally to the process stream quantity thereby providing a given ratio of injection fluid to process stream fluid.

4. An apparatus and control system for injecting a given quantity of injection fluid into a stream containing a process fluid comprising:

(a) an injection pump having an inlet and outlet port;

(b) an indicating check valve connected to said outlet port, and wherein said inlet port is connected to a source of injection fluid and wherein said indicating check valve is in communication with the stream containing a process fluid and wherein said indicating check valve provides indication of the open or closed position thereof;

(c) a cylinder means incorporating a moveable piston having a first side and a second side, wherein said first side is larger in area than said second side, said piston having means mechanically coupling said piston to said injection pump;

(d) means for biasing said piston on said second side of said piston;

(e) means for supplying and venting pneumatic fluid under pressure to said first side of said piston;

(f) control means for operating said means for supplying and venting pneumatic fluid under pressure wherein said control means monitors said open position of said indicating check valve and operates said means for supplying and venting pneumatic pressure thereby operating said injection pump and causing the given quantity of injection fluid to enter the process stream.

5. The apparatus of claim 4 wherein a given ratio of injection fluid to process fluid is required and wherein said electronic control means accepts a setpoint indicative of the required ratio and wherein said algorithm computes the required quantity of injected fluid per unit time and modulates said 3-way electric solenoid valve while sensing said open position of said indicating check valve thereby providing the correct quantity of injection fluid in the required ratio.

6. The apparatus of claim 5, wherein the process stream quantity of flow is measured and provided to said electronic control means and wherein said algorithm modulates said 3-way solenoid valve thereby varying the injection fluid quantity proportionally to the process stream quantity thereby providing a given ratio of injection fluid to process stream fluid.

7. The improvement of claim 1 wherein said electronic control means is incorporated into a SCADA system.

8. The apparatus of claim 5 wherein said electronic control means is incorporated into a SCADA system.