Alternative apparatuses and methods to determine chemical injection dose using a positive displacement pump

Abstract

An alternative method and apparatus for determining a chemical injection dose to a fluid system is provided. The method and apparatus uses a monitor and control system processor connected to a pressure sensor and a positive displacement pump. The monitor and control system processor determines a stroke of a positive displacement pump by measuring a low-pressure on the suction side of the pump and equates each low pressure point with a pump stroke (or the discharge of a piston volume for dual stroke pumps). The monitor and control system processor calculates the dose by multiplying the number of low-pressure points with the volume of the discharge.

What is claimed is: 
     
         1 . A method for calculating a chemical dose for a chemical injection system having a source tank and a positive displacement pump with a piston chamber having a chamber volume, without a proximity sensor, flow sensor, secondary vessel, or pump stroke sensor, the method comprising:
 receiving the chamber volume for the positive displacement pump at a monitor and control system processor;   receiving, at the monitor and control system processor, one or more signals from a pressure sensor wherein the one or more signals are indicative of the pressure in the source tank;   processing one or more signals, by the monitor and control system processor, such that a pressure drop below a low-pressure point generates a pump stroke signal;   counting, by the monitor and control system processor, each pump stroke signal to obtain a counted number of pump strokes; and   calculating, by the monitor and control system processor, a calculated total dose volume of fluid from the source tank injected into the fluid system by multiplying the received chamber volume by the counted number of pump strokes.   
     
     
         2 . The method of  claim 1 , comprising receiving at the monitor and control system processor a received total dose volume to be delivered by operation of the positive displacement pump. 
     
     
         3 . The method of  claim 2 , comprising turning the positive displacement pump on when the monitor and control system processor receives the total dose volume to be delivered and turning the positive displacement pump off when the calculated total dose volume equals or exceeds the received total dose volume. 
     
     
         4 . The method of  claim 2 , comprising receiving at the monitor and control system processor a time frame for delivery of the received total dose volume such that the monitor and control system processor controls causes the positive displacement pump to deliver the calculated total dose volume of the time frame. 
     
     
         5 . The method of  claim 2 , comprising receiving a temperature signal from a temperature sensor to sense temperature at the monitor and control system processor such that the monitor and control system processor adjusts the received total dose volume to compensate for changes in a temperature sensed by the temperature sensor. 
     
     
         6 . The method of  claim 1 , comprises determining the low-pressure point that generates the pump stroke signal by monitoring a pressure wave over at least one pump stroke to calibrate the low-pressure point. 
     
     
         7 . A method for determining that a positive displacement pump has delivered a volume of fluid from a fluid source into a fluid system, comprising:
 monitoring, by a pressure sensor, a pressure of the fluid source between the fluid source and the suction manifold of a positive displacement pump where the suction manifold comprises at least one suction side check valve;   generating, by the pressure sensor, a signal indicative of the pressure;   receiving, at a monitor and control system processor, the signal indicative of the pressure from the pressure sensor;   determining, by the monitor and control system processor, whether the signal indicative of the pressure indicates that the pressure is equal to a low pressure point;   accumulating a sum of low-pressure points, by the monitor and control system processor, indicative that the positive displacement pump has delivered the volume of fluid to the fluid system.   
     
     
         8 . The method of  claim 7 , wherein each low-pressure point of the accumulated sum of low-pressure points equals a single stroke of a single stroke positive displacement pump. 
     
     
         9 . The method of  claim 7 , wherein each low-pressure point of the accumulated sum equals the delivery of the volume of fluid and equals ½ of a single stroke of a dual stroke positive displacement pump. 
     
     
         10 . The method of  claim 7 , wherein generating the signal indicative of the pressure by the pressure sensor comprises digitizing the signal indicative of the pressure by the pressure sensor. 
     
     
         11 . The method of  claim 7 , comprising transmitting the signal indicative of the pressure from the pressure sensor to the monitor and control processor. 
     
     
         12 . The method of  claim 7 , wherein the monitor and control system processor digitizes the signal indicative of the pressure received from the pressure sensor. 
     
     
         13 . The method of  claim 7 , comprising receiving a temperature signal from a temperature sensor to sense temperature at the monitor and control system processor such that the monitor and control system processor adjusts the volume of fluid delivered to compensate for changes in the sensed temperature. 
     
     
         14 . A system for delivering a chemical dose from a chemical source tank to a fluid system, without a flow sensor, proximity sensor, or measuring a level change in the chemical source tank, comprising:
 a chemical source tank, the chemical source tank having one or more chemicals to be injected to the fluid system;   a positive displacement pump having a suction manifold and a discharge manifold, the suction manifold of the positive displacement pump being in fluid communication with the chemical source tank and the discharge manifold being in fluid communication with the fluid system, the positive displacement pump being configured to inject a chemical dose;   a pressure sensor to sense a pressure of the chemical source tank, the pressure senor being in fluid communication with the chemical source tank and located between the chemical source tank and the suction manifold; and   a monitor and control system processor operationally coupled to the pressure sensor to receive signals from the pressure sensor indicative of a pressure wave between the suction manifold and the chemical source tank when the positive displacement pump is in a suction cycle, wherein the monitor and control system processor counts a stroke of the positive displacement pump by counting a low-pressure point generated by the pressure wave, wherein the monitor and control system processor can determine the chemical dose delivered by multiplying a volume of chemical delivered multiplied by the counted low-pressure points.   
     
     
         15 . The system of  claim 14 , wherein the positive displacement pump is a single stroke positive displacement pump and each low-pressure point counts as a single pump stroke. 
     
     
         16 . The system of  claim 14 , wherein the positive displacement pump is a dual stroke positive displacement pump and two (2) low-pressure points counts as a single full pump stroke. 
     
     
         17 . The system of  claim 14 , wherein the monitor and control system processor is operationally coupled to the positive displacement pump to turn on the positive displacement pump to inject the chemical dose to the fluid system and to turn off the positive displacement pump when the positive displacement pump has injected the chemical dose. 
     
     
         18 . The system of  claim 14 , wherein the monitor and control system processor calibrates the low-pressure threshold to count the low-pressure point based on monitoring the low-pressure points of the pressure wave during one or more cycles of the positive displacement pump. 
     
     
         19 . The system of  claim 17 , comprising a chemical source tank level system wherein the chemical source tank level system is not used to determine the chemical dose.