Abstract:
A chemical treatment system that injects a dosage chemical solution into a process. A condition of the process is sensed by a sensor, communicated to a controller and used as a basis for varying in real time the dosage of the chemical solution. The sensor, the controller, a pump and the process are disposed in a closed control loop. The controller controls the operation of the pump (speed, duty cycle and the like) to vary the dosage based on the sensed condition, which is disclosed as a corrosion and/or scale of an element of the process, although other conditions can control the dosage as well.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to a system and method for chemical treatment of a process. 
       BACKGROUND OF THE INVENTION 
       [0002]    Chemical treatment management systems are used in chemical and refinery plants for major operational areas such as process units, cooling water systems, steam generating systems and wastewater systems and other systems. The chemical treatments are used for corrosion and scale control (corrosion and scale inhibiting chemicals), bio-control (biocides and disinfectants), pH control (pH adjusters), foaming control (anti-foaming and defoamers), emulsion control (emulsion breakers), solids control (coagulants and flocculants) and others. 
         [0003]    Most chemical treatment systems are small stand-alone systems monitored by outside operators. These systems are often neglected by operators and are looked after by the chemical treatment vendor on a periodic basis.  FIG. 1  shows a process  20  that receives chemical treatment from a typical chemical injection system  30 . System  30  includes a skid-mounted chemical storage tank or drum  32  with a fill line  34 , a drain line  36  and a sight glass  38  for visual inspection of drum inventory. The drum inventory contains a solution of the chemicals for the treatment of process  20 . A chemical injection pump  40  with a calibration tube  42  pumps a desired treatment dosage from drum  32  via an injection valve  44  for insertion into process  20 . System  30  is operated almost entirely manually making it prone to operator error and neglect. Significant incidents have been reported such as inadvertent discharge of the entire drum inventory to the process sewer or cooling tower basin, excess dosage to process  20  that caused high chemical concentrations in process water draws. All of these incidents resulted in additional costs and harm to the plant&#39;s wastewater treatment system. 
         [0004]    Low inventory can cause the loss of treatment with its associated cost in terms of increased corrosion, reduced throughput caused by foaming, etc. Expedited delivery of additional chemicals can add substantially to the cost of chemical treatment. High inventories typically indicate the loss of dosing over time. 
         [0005]    There is a need for a chemical treatment system and method for a process that overcome the above mentioned problems. 
         [0006]    There is a need for a chemical treatment system and method that overcome the above mentioned problems for the control of corrosion and scale. 
       SUMMARY OF THE INVENTION 
       [0007]    A chemical treatment system of the present invention injects a chemical solution into a process. The chemical treatment system comprises a chemical tank containing the chemical solution. A pump is disposed to provide a dosage of the chemical solution from the tank to the process. A sensor and a controller are disposed in a closed loop with the process and the pump to vary in real time the dosage of the chemical solution provided by the pump based on a condition of the process sensed by the sensor and communicated to the controller. 
         [0008]    In one embodiment of the chemical treatment system of the present invention, the dosage is determined by a speed of the pump. The controller provides a speed control signal proportional to the condition to the pump. 
         [0009]    In another embodiment of the chemical treatment system of the present invention, the controller correlates a current value and a previous value of the sensed condition to determine a variance upon which a change is made to the dosage. 
         [0010]    In another embodiment of the chemical treatment system of the present invention, the sensor is in wireless communication with the controller. 
         [0011]    In another embodiment of the chemical treatment system of the present invention, the condition is a corrosion condition. The chemical solution contains a corrosion inhibitor. 
         [0012]    In another embodiment of the chemical treatment system of the present invention, the condition is at least one of a corrosion rate and a pitting condition. 
         [0013]    In another embodiment of the chemical treatment system of the present invention, the dosage is controlled in a linear region of a curve of corrosion rate vs. dosage. 
         [0014]    In another embodiment of the chemical treatment system of the present invention, the dosage is also controlled in at least one non-linear region of the curve. 
         [0015]    In another embodiment of the chemical treatment system of the present invention, the sensor communicates a plurality of parameters of the condition to the controller for control of the dosage based on the plurality of parameters. 
         [0016]    In another embodiment of the chemical treatment system of the present invention, the plurality of parameters comprises a corrosion rate and a pitting condition. 
         [0017]    In another embodiment of the chemical treatment system of the present invention, the sensor is one of a plurality of sensors that sense a plurality of conditions of the process and communicates the plurality of conditions to the controller for control of the dosage based on the plurality of conditions. 
         [0018]    A method of the present invention injects a chemical solution into a process. The method comprises providing a dosage of the chemical solution to the process using a pump to pump the chemical solution from a tank to the process, and sensing a condition of the process, and varying the dosage in real time based on the sensed condition by varying the operation of the pump. 
         [0019]    In one embodiment of the method of the present invention, the condition is sensed by a sensor and communicated to a controller, and where the controller controls the pump to vary the dosage based on the sensed condition. 
         [0020]    In another embodiment of the method of the present invention, the process, the sensor, the controller and the pump are disposed in a closed control loop. 
         [0021]    In another embodiment of the method of the present invention, the dosage is determined by a speed of the pump. The controller provides a speed control signal proportional to the condition to the pump. 
         [0022]    In another embodiment of the method of the present invention, the controller correlates a current value and a previous value of the sensed condition to determine a variance upon which a change is made to the dosage. 
         [0023]    In another embodiment of the method of the present invention, the sensor is in wireless communication with the controller. 
         [0024]    In another embodiment of the method of the present invention, the condition is a corrosion condition. The chemical solution contains a corrosion inhibitor. 
         [0025]    In another embodiment of the method of the present invention, the condition is at least one of a corrosion rate and a pitting condition. 
         [0026]    In another embodiment of the method of the present invention, the dosage is controlled in a linear region of a curve of corrosion rate vs. dosage. 
         [0027]    In another embodiment of the method of the present invention, the dosage is also controlled in at least one non-linear region of the curve. 
         [0028]    In another embodiment of the method of the present invention, the sensor communicates a plurality of parameters of the condition to the controller for control of the dosage based on the plurality of parameters. 
         [0029]    In another embodiment of the method of the present invention, the plurality of parameters comprises a corrosion rate and a pitting condition. 
         [0030]    In another embodiment of the method of the present invention, the sensor is one of a plurality of sensors that sense a plurality of conditions of the process and communicates the plurality of conditions to the controller for control of the dosage based on the plurality of conditions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference characters denote like elements of structure and: 
           [0032]      FIG. 1  is a diagram of a prior art chemical treatment system; 
           [0033]      FIG. 2  is a diagram of a chemical treatment system of the present invention; and 
           [0034]      FIG. 3  is a graph that depicts corrosion rate as a function of treatment dosage for the chemical treatment management system of  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0035]    Referring to  FIG. 2 , a chemical treatment system  130  of the present invention is disposed to control chemical treatment of a process  20 . Chemical treatment system  130  includes components that are the same as components included in  FIG. 1  and that bear like reference numerals. 
         [0036]    Chemical treatment system  130  comprises a vessel, shown as a skid-mounted drum  32  with a fill line  34 , a drain line  36 , a calibration tube  42  and a sight glass  38  for visual inspection of drum inventory. In a preferred embodiment a corrosion inhibitor is supplied to drum  34  via fill line  34 . The corrosion inhibitor may vary from one process to another. 
         [0037]    Chemical treatment system  130  further comprises a corrosion sensor  162  disposed to sense corrosion and/or scaling in process  20  and to supply an output signal that is a function of the corrosion rate. Corrosion sensor  162  may be any suitable corrosion sensor. For example, corrosion sensor  162  may be a SmartCet™ probe, SmartCet™ being a trademark of Honeywell International, Inc. 
         [0038]    Chemical treatment system  130  further comprises a chemical injection pump  140  and a controller  150  that are connected in a closed loop with corrosion sensor  162  to control dosage injection of the chemical inhibitor into process  20 . Controller  150  may be any suitable controller. Controller  150 , for example, may be a Profit Controller® device, or Profit Loop™ controller available from Honeywell International Inc. Profit Controller is a registered trademark of and Profit Loop is a trademark of Honeywell International Inc. 
         [0039]    Chemical injection pump  140  is a variable speed pump having a variable speed drive that is controlled automatically by controller  150  to pump a desired dosage of the corrosion inhibitor via a line  156  and an injection valve  44  for insertion into process  20 . For example, the corrosion inhibitor is injected into a wastewater system (not shown) in process  20 . That is, the desired dosage is a flow rate that is determined by the speed of chemical injection pump  140 . 
         [0040]    Chemical treatment system  130  further comprises a pulsation dampener  145 , an over pressure protection valve  164  and a pressure indicator  166 , each being coupled to line  156 . Pulsation dampener  145  dampens pulsation from chemical injection pump  145 . 
         [0041]    Corrosion sensor  162 , for example, provides an output signal that is proportional to a corrosion rate that occurs to an element (e.g., a vessel, a pipe, etc.) in process  20 . Controller  150  uses the output signal from corrosion sensor  162  to generate an output or dosage control signal that controls the speed of chemical injection pump  140 . For some pumps, the controller output signal is a 4 to 20 milli-amperes current pulse signal. For other pumps, the output signal may differ. Thus, chemical storage tank or drum  32 , chemical injection pump  140 , injector valve  44 , process  20 , corrosion sensor  162  and controller  150  are disposed in a closed loop control to meter the chemical inhibitor solution from chemical storage tank  32  to process  20  in a dosage flow rate based on the corrosion rate detected by corrosion sensor  162 . Controller  150  correlates or compares the current value of the corrosion signal with its value at a previous correlation time. If greater, the dosage is increased by increasing the pump speed. If less, the dosage is decreased by decreasing the pump speed. If there is no change, the current pump speed is maintained. 
         [0042]    Corrosion sensor  162  could also, or alternatively, provide an output signal that is proportional to pitting of a surface of an element in process  20 . Since pitting is indicative of an advanced state of corrosion, controller  150  may be programmed to respond to the pitting signal to change the pump speed by larger increments. For example, if a normal incremental speed change of X is made in response to the corrosion signal, then in response to the pitting signal the speed change increment is larger by as much as 10× or more. 
         [0043]    Corrosion sensor  162  can also provide an output B-value, known as the Stern Geary Constant. The B-value may optionally be used by controller  150  as a disturbance variable to adjust the dosage of the chemical solution (and/or pressure, temperature, flow) by fine adjustment of the speed of chemical injection pump  140 , thereby controlling the output or conditions of process  20  to reduce corrosion rate, pH, and/or overall cost per unit of the product of process  20 . 
         [0044]    Chemical injection pump  140  may be any variable speed pump, such as any off-shelf injection pump that is controllable by an input signal to vary pump speed or flow rate. The pump size, impeller and manufacturer may vary from process to process as well as the chemical being injected. Alternatively, chemical injection pump  140  may simply be a manual metering pump with its micrometer screw adjustment replaced by an electronic actuator that would be controlled by controller  150 . This would allow automatic flow rate adjustment in response to an output signal from controller  150 . 
         [0045]    Corrosion sensor  162  preferably has a wireless transmitter  161  that transmits its output signal(s) to controller  150 . Controller  150  has a wireless transceiver that receives the transmitted signals from wireless transmitter  161 . Alternatively wireless transmitter  161  and/or wireless transceiver  152  can be independent units that are in wired communication with corrosion sensor  162  and controller  150 , respectively. The wireless communication between corrosion sensor  162  and controller  150  together with the closed loop control provide a real time control as distinguished from the manually controlled system described in the Background of the Invention. 
         [0046]    Referring to  FIG. 3 , a graph  200  depicts a curve  201  of corrosion rate as a function of corrosion inhibitor dosage. Curve  201  comprises a linear region or range  206  subtended by non-linear ranges  203  and  205 . A dosage  202  is a minimum dosage, less than which no reduction in corrosion rate occurs. A dosage  204  is a maximum dosage, greater than which no reduction in corrosion rate occurs. Between dosages  202  and  204  is controllable region or range  206  that is reasonably linear with dosage rate. Regions  208  are transition regions. Controller  150  performs a correlation that allows dosages in the controllable or linear range  206  as well as in the non-linear ranges  203  and  205 . 
         [0047]    The objective of closed loop control is to maintain the measured corrosion rate at a specified value or within a range. If the corrosion rate is specified as a range (for example, range  206 ), then an economic objective function can be formulated as a minimum cost function as shown by the following equation: 
         [0000]      Cost T +COR*Cost COR +INH*Cost INH    
       Where: 
       [0000]    
       
         Cost T  is the total cost, USDollars/Time 
         COR is the corrosion rate, Length/Time 
         Cost COR  is the cost of corrosion, USDollars/Length 
         INH is the inhibitor rate, Volume/Time 
         Cost INH  is the cost of the inhibitor, USDollars/Volume 
       
     
         [0053]    The economic objective serves to optimize inhibitor dosage rate by minimizing corrosion rate and minimizing total cost. There is a trade off the cost of the inhibitor against the equipment life. The tendency is for the objective function to maximize dosage in order to minimize corrosion rate. On the other hand, when corrosion is in a stage in which pitting occurs, the pitting signal output of corrosion sensor  162  may be used to provide a large dosage increase as compared to a normal dosage increase. 
         [0054]    Additional sensors  158  of other functionalities may optionally be provided to monitor other conditions of process  20 . An output signal from one of the additional sensors  158  can be used in combination with or in place of the output signal of corrosion sensor  162  as an input to controller  150 . If controller  150  has multiple inputs, the output signals of additional sensors  158  and corrosion sensor  162  can be used in any desired combination to produce the signal that controls the pump speed. Additional sensors  158  preferably include wireless transmitters to transmit their output signals to controller  150 . 
         [0055]    Additional sensors  158  may sense other conditions of process  20 . For example, in a wastewater system these conditions may include process measurements such as flow rate of the wastewater, temperature, and pressure (e.g., pressure in the tanks, piping and other pressure vessels that make up the process system). Other sensed conditions may include ph, biocide concentration, oxygen scavenger concentration and others. 
         [0056]    Calibration of pump  140  can be performed by hand or with a tool. The calibration results can be entered into controller  150  by any suitable input device, such as a handheld device with wired or wireless communication. 
         [0057]    The present invention having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as defined in the appended claims.