Abstract:
A system and method of injecting a chemical into a high pressure process stream without pumps or other active components. The system utilizes the differential pressure created by resistive losses of downstream components within a high pressure process stream. A bypass side stream is taken from an upstream pressure location and returned to the downstream side of the resistive inline process component. The chemical solution vessel is pressurized by the higher side of the pressure differential. The solution then passes through a flow controlling capillary tube exiting on the lower pressure differential side into the bypass stream. The high flow rate chemically diluted bypass stream then returns to the process stream at the lower differential process stream tie-in. The chemical solution is isolated from the process water pressuring the vessel by a movable separating device preventing mixing of the two fluids. The vessel can also be pressurized by gas.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    This invention relates to a method and process for injecting a chemical solution into a flowing, pressurized fluid stream. 
       BACKGROUND 
       [0002]    In various industries such as the power generation industry, there is a need to inject chemical solutions into flowing process streams at elevated pressures and temperatures for various purposes. In particular, it is necessary to inject solutions of noble metal containing chemicals, such as Na 2 Pt(OH) 6 , into the feedwater piping of boiling water nuclear reactors to aid in inhibiting intergranular stress corrosion cracking of susceptible structural materials in the reactor vessel in the presence of hydrogen. 
         [0003]    As reported by Hettiarachchi and Diaz, the noble metal chemical solution Na 2 Pt(OH) 6  is added to the feedwater piping of boiling water nuclear reactors over a 10 day period. Such 10 day injection periods are repeated during each subsequent yearly fuel cycle. For boiling water nuclear reactors with longer fuel cycles, the 10 day applications are conducted on an annual basis. The total mass of noble metal injected annually is also limited to a fixed value by an industry consensus standard described by Garcia et al. Because of a phenomenon known as “crack flanking”, described by Andresen and Kim, it is advantageous to inject the noble metal chemical over the entire operating period of a fuel cycle, not just during an annual 10 day period. Active metering pumps used for these 10 day injections, such as positive displacement pumps, have experienced maintenance problems due to interaction with the noble metal chemicals such as Na 2 Pt(OH) 6  and are not optimum for long term injection. 
         [0004]    A boiling water nuclear reactor that follows the industry consensus recommendation will typically add between 200 and 1, 200 gm of Pt (as Na 2 Pt(OH) 6 ) each calendar year, depending on plant specific features such as fuel surface area and power rating. If the addition is made continuously at a constant rate over 365 days, the addition rate will vary between 3.8×10 4  and 2.3×10 −3  gm (Pt)/min. If the feedstock is a 1% solution of Na 2 Pt(OH) 6 , the addition rate will be between 0.038 and 0.23 ml/minute (cc/m). The resulting concentration of Pt in the feedwater would be on the order of 10 parts per trillion. Accordingly, there has been a need in the nuclear industry for a chemical injection system that does not employ active pumps and is capable of adding small, metered amounts of noble metal chemicals, such as Na 2 Pt(OH) 6 , into the feedwater during the entire fuel cycle. 
         [0005]    U.S. Pat. No. 8,054,933 (Tran et al) describes a method of injecting chemicals into flowing nuclear reactor water streams teaching the use of positive displacement pumps, a process computer, various valves, chemical storage tanks, weighing scales and a source of deionized water. While this system is useful in injecting chemicals over short periods of time, it is quite complicated and not necessarily suited for trouble free injection of dilute solutions over longer periods of time. 
         [0006]    U.S. Pat. No. 2,266,981 (Miller) discloses a method and apparatus for injecting chemicals into a natural gas pipeline operating at elevated pressures that does not use a pump. The apparatus teaches a fluid supply for storing the chemical to be injected, a pressure feed tank for pressurizing and injecting the chemical into the pipeline and a series of lines, manual valves and gauges for controlling the flow of chemicals from the supply tank into the feed tank and ultimately into the pipeline using gravity. The natural gas line pressurizes the pressure feed tank to the same pressure as the gas in the pipeline and gravity allows the solution in the pressurized tank to flow into the gas pipeline. This arrangement would not work in adding low flow rates of chemicals into a flowing water filed pipe; as the pressurizing gas above the liquid in the feed tank would eventually become saturated. Degassing of the feed solution within the flow restrictor (valve, capillary) would occur and alter the rate of injection precision. An active flow rate control is required to maintain a constant injection rate as the change in height of the feed solution drains the tank. U.S. Pat. No. 6,779,548 (McKeary) teaches a similar method as U.S. Pat. No. 2,266,981 (Miller) but adds a system for automatically controlling the quantity of chemical injected into a pressurized gas system by employing two tanks, one pressurized and one not pressurized. While this system could work well adding liquid to a gas process stream, it will not control a liquid addition to a liquid stream to the accuracy and precision required for very low flow rates required in Pt injection nuclear applications. Similar problems will occur as with U.S. Pat. No. 2,266,981 (Miller) 
         [0007]    All injection patents researched for this application have some sort of active displacement component, do not account for dilution of the primary injection solution, have cover gas pressurization (that saturate the chemical injection solution), have active flow controls, or cannot yield very low flow rates (sub ccm) continuously over very long periods (months-year) without intervention. 
       SUMMARY OF THE INVENTION 
       [0008]    A reliable method of injecting small, accurate amounts of a chemical solution into a flowing process stream over long periods of time without the use of pumps is desired by some industries. Described herein is such a chemical injection system and method that uses the pressure drop in a process line as the motive force acting on a variable volume reservoir coupled with a passive, calibrated capillary tubing element to accurately control and meter the additions of a chemical into a liquid process stream at a location of lower pressure within the same line. The system is located in the process line where resistive components create pressure losses as the process fluid passes through, such as before and after a heat exchanger. The amount of solution injected by the system is determined by one control valve and a differential pressure meter measuring the fluid pressure differential location immediately before and immediately after the capillary tubing element. A method is also described in which a pressurized gas, rather than the higher pressure location of the process stream, provides the motive force acting on the variable volume reservoir. In both cases, a bypass stream taken from a high pressure portion of the process stream and introduced into a lower pressure location of the process stream is integral to the invention. The overall advantage of the process is to continuously and passively add metered amounts of a chemical solution in amounts as low as or lower than 0.01 milliliters per minute over periods of over 12 to 24 months. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic representation of the first embodiment of a method of passive injection of a chemical solution into a liquid process stream in accordance with the present invention. 
           [0010]      FIG. 2  is a schematic representation of the second embodiment of a method of passive injection of a chemical solution into a liquid process stream in accordance with the present invention. It is similar to the method of  FIG. 1 , but that the bellows separator arrangement between lines  10  and  19  in  FIG. 1  is replaced with the piston separator arrangement shown in  FIG. 2 . 
           [0011]      FIG. 3  is a schematic representation of the third embodiment of a method of passive injection of a chemical solution into a liquid process stream in accordance with the present invention. It is similar to the method of  FIG. 1 , but that the bellows separator arrangement between lines  10  and  19  is replaced with the membrane separator arrangement shown in  FIG. 3 . 
           [0012]      FIG. 4  is a schematic representation of the fourth embodiment of a method of passive injection of a chemical solution into a liquid process stream in accordance with the present invention as shown in  FIGS. 1 through 4 , but locates the metering capillary at the entrance to the pressure vessel between lines  9  and  10  rather than at the exit of the pressure vessel, between line  19  and valve  22 . 
           [0013]      FIG. 5  is a schematic representation of the fifth embodiment of a method of passive injection of a chemical solution into a liquid process stream in accordance with the present invention. It is similar to the method in  FIGS. 1 through 3 , but replaces the liquid pressurization source at location  7  with a gas pressurization source. 
           [0014]      FIG. 6  is plot of capillary tubing flow rates versus pressure drop calculated with Poiseuille&#39;s Law for internal diameters of 0.005″ and 0.007″ and lengths of 30″ and 60″. The dashed lines within the plot are the results of the calculations using Poiseuille&#39;s Law. A calibration measurement was conducted on a 0.005″ by 60″ capillary tube and is shown also on  FIG. 6  as the solid plotted line. The correlation between the calculated 0.005″×60″ rate and measured rate at 50 psig indicates that the application of capillary flow control is valid. 
           [0015]      FIG. 7  is a schematic representation of an optional exit embodiment of a method of passive injection of a chemical solution into two liquid process streams in accordance with the present invention. The arrangement shown in the  FIG. 7  would replace the hardware downstream of the differential conductivity meter  26  in  FIGS. 1 through 5  to allow for the injection into two process streams. 
           [0016]      FIG. 8  is a schematic representation of an optional exit embodiment of a method of passive injection of a chemical solution into one process streams in accordance with the present invention. The arrangement shown in the  FIG. 8  would replace the hardware downstream of the differential conductivity meter  26  in  FIGS. 1 through 5  to allow for the injection into one or two process streams. The flow metering orifice  29  and/or  41  is replaced with a flow controlling sized orifice  45  and the differential pressure gauge  30  is replaced with a pressure gauge  46 . 
           [0017]      FIG. 9  is a schematic representation of the optional eight embodiment of a method of passive injection of a chemical solution into a process stream in accordance with the present invention. Whereas the schematic in  FIG. 1  has only one chemical subsystem between location tees  7  and  23 , embodiment eight adds a second chemical subsystem attached at location  7  and  23 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The system and method according to the present invention will be described in the context of injection of Na 2 Pt(OH) 6  into the feedwater of a boiling water nuclear reactor. This is done for purposes of illustration only and is not intended in a limiting sense. The system and method of the present invention are equally suitable for use in other industries in which low flow rates of chemicals must be dispensed with a high level of accuracy without any active components, such as metering pumps. 
       First Through Fourth Embodiments—Structure 
       [0019]    Referring to  FIG. 1 , a first embodiment of a method for passive injection of a chemical solution into a high pressure process stream system in accordance with the present invention generally includes the basic concepts that follow. The main process stream, to which the chemical is to be injected is represented by the dashed lines located on the right side of  FIG. 1 , called the feedwater system, is not a part of the embodiment. The injection system is comprised of a bypass stream line  24  and a chemical injection branch  19 . The high flow (1 to 10 liters/min) bypass loop starts at the system inlet  1  and consists of a heat exchanger  2  (which is cooled by service water  3 ), an isolation valve  6 , a capillary pressure control valve  25 , a bypass flow control vale  28 , a bypass flow element  29 , a second isolation valve  31  and ends via line  32  which enters a tee junction into the feedwater. There are four monitoring devices in the bypass loop, a temperature indicator  4  and a pressure gauge  5  located immediately downstream of the heat exchanger, a differential conductivity meter  26  (with inputs immediately before and after the tee junction  23  between valves  25  and  28 ), and a differential pressure meter  30  located with inputs before and after the bypass flow metering orifice  29 . The chemical injection branch consists of a line teed off the bypass loop immediately downstream of isolation valve  6  at tee junction  7  followed by an isolation valve  8  feeding a pressurizing fluid stream  9  into a pressure vessel  13  through line  10 . The resulting pressurized fluid  14  acts against the bellows separator  15  forcing the chemical solution  16  out of the pressure vessel through line  19  then through a capillary solution flow control segment  20  through an isolation valve  22  into the feedwater bypass loop at the tee junction  23 . The valves  17  and  12  are used for solution fill and vent/drain via the solution fill line  18  and the fill vent/drain line  11  respectively. A capillary differential pressure gauge  21  is located with inputs at both ends of the capillary solution control tubing  20 . The key design components are: the chemical  16  separation  15  from the pressuring fluid  14  to prevent dilution, a very low chemical flow rate control capillary flow device  20 , a high bypass flow rate through line  24  and utilization of the pressure drop as the main process passes through inline components. 
       First Embodiment—Operation 
       [0020]    Embodiment one in  FIG. 1  incorporates common features of this injection system seen also in embodiments two through four herein. They are:
       a. the bypass stream  24  developed from a higher pressure process stream location  1 , for example at the process feedwater pump exit, to a lower pressure process stream location further downstream  32 , such as after a pressure loss through a process component such as a heat exchanger and flow nozzle. The bypass water is first conditioned by a heat exchanger  2  with service water  3  or optional cooling water on the secondary side. Valves  6  and  31  are used to isolate the injection system when necessary. The flow rate in the bypass stream line  24  is affected by the restrictions in the bypass stream including the heat exchanger  2 , the isolation valves  6  and  31 , the capillary pressure control valve  25 , the bypass flow control valve  28 , and the flow meter orifice  29 . The major control restrictions are the capillary pressure control valve  25  and the bypass stream control valves  28 . The desired flow rate at line  32  is controlled and monitored with a calibrated flow metering orifice  29  and its associated differential pressure gauge  30 .   b. the second common feature of these injection systems is the chemical solution injection subsystem tee junction  7  through tee junction  23  (which contains the pressure vessel  13  and the capillary flow restrictor  20 ) that controls the rate of chemical injected into the bypass stream. The pressure vessel is pressurized with the liquid obtained from the bypass stream at tee junction  7 . A separator  15  inside the pressure vessel prevents the pressurizing fluid  14  from mixing with the chemical solution  16  located on the other side of the separator. The separator  15  moves within the pressure vessel  13  such that the pressure on both sides is the same, that is, both the pressuring fluid  14  and chemical solution  16  are at the same pressure. Valve  25  controls the pressure drop across the capillary flow control device  20  since the pressure at line  19  is the same as at location line  24  and the capillary exit pressure and valve exit pressure are the same at tee junction  23 . The chemical solution  16  from the chemical solution subsystem at tee junction  7  through tee junction  23  is diluted as it flows into the bypass stream at tee junction  23 . The transit time of the chemical solution from tee junction  23  to the feedwater injection tap through line  32  is minimized by the high bypass flow rate, thus minimizing the potential of premature Na 2 Pt(OH) 6  thermal degradation and Pt deposition in undesired locations. To provide the low flow rates required for Na 2 Pt(OH) 6  chemical additions to boiling water nuclear reactor applications, a capillary solution flow control device  20  made of small diameter capillary tubing is located at either the exit of pressure vessel  13  in  FIG. 1  through  FIG. 3 , or at the entrance of pressure vessel  13  in  FIG. 4 . To verify the proper flow rate is being accomplished, a differential pressure measurement  21  is made across the capillary tube  20  and compared to the capillary calibration behavior for the particular capillary being used. An example of a capillary verification behavior chart is shown in  FIG. 6 . Poiseuille&#39;s Law was used to calculate the flow rate of water at different pressure drops, tubing lengths (30″ and 60″) and tubing internal diameters (0.005″ and 0.007″). A tube of 0.005″ internal diameter by 60″ long was tested for flow versus pressure drop. The measured values are plotted (solid line) and compared to a Poiseuille&#39;s Law calculation (dotted line) and compare very well in  FIG. 6 . Poiseuille&#39;s Law for flow is proportional to the length and to the fourth power of the radius. Other capillary diameters and lengths are plotted in  FIG. 6  as dotted lines. This plot indicates the potential flow rates of chemical solution required over the expected process stream flow rates (0.03 ccm to 0.25 ccm) are easily accomplished with capillary tubing. Other flow rates can be accomplished with smaller or larger capillary internal diameters and lengths.       
 
         [0023]    In addition to the normal chemical injection operation of the system, there are two other procedures necessary: 1) the initial start-up of the system and 2) subsequent refilling of the vessel after an operational period. Both procedures require the chemical injection subsystem be isolated from the bypass stream by closing valves  8  and  22 . Both procedures require ambient pressure conditions. The initial start-up will require filling pressuring fluid volume  13  with high purity water via valve  12  and fill line  11  and then the chemical solution volume  16  with the chemical solution to be added utilizing solution fill line  18  and valve  17 . Once the two volumes are completely full (no air gaps), the fill  17  and vent isolation  12  valves can be closed. 
         [0024]    The refill procedure is simpler since there should be no air pockets after the initial operating period. The liquid pressuring fluid  14  only needs to be vented via valve  12  while the chemical solution is transferred into the upper chamber  16  until the separator  15  is fully extended. Once the chemical solution chamber  16  is full the fill  17  and vent  12  valves should be closed. 
         [0025]    After the initial filling or after subsequent refills, the isolation valves  8  and  22  of the injection subsystem can be opened slowly. If the bypass stream is flowing, the chemical solution will start to flow. If the bypass stream is off-line, as soon as the system is placed into service the chemical solution will start to flow. 
         [0026]    To place the system into service, start with valves  6 ,  25 ,  28  and  29  closed. Start the service water flow  3  to the heat exchanger  2  then fully open the isolation valves  6  and  31 . Slowly open the capillary flow control vale  25  and bypass flow control valve  28  while maintaining a vigil of the temperature  4  exiting the inlet heat exchanger. Open both flow control valves  25  and  28  until the desired capillary differential pressure  21  and bypass differential pressure  30  are obtained. Some iteration of the valve positions may be required, since the two control points and flow rates are not independent. Using the desired chemical solution flow rate, the desired capillary differential pressure gauge value is determined from the correct capillary diameter/length line from a plot like that shown in  FIG. 6 . 
         [0027]    After a period of time, the measured differential conductivity  26  should indicate that chemical is being injected. The downstream conductivity value, after tee junction  23 , should be higher than the bypass water, after valve  25 . The measured difference can be corroborated by knowing the solution chemical ionic properties, the chemical solution injection rate and the bypass flow rate. A monitoring delay time is necessary to allow the temperature and flow transients to dissipate. 
       Second Embodiment—Structure 
       [0028]    Referring to  FIG. 2  shows the second embodiment of the invention identical to that in  FIG. 1  except that between line  10  and line  19 , where the bellows separator is replaced by a floating piston separator  33  using O-ring seals  34 . The vessel design would be changed to accommodate the piston seal movement against the vessel walls. The pressurizing fluid  14 , the chemical solution  16 , the vent/drain line  11 , valve  12 , solution fill line  18  and fill valve  17  would remain schematically the same. 
       Second Embodiment—Operation 
       [0029]    All of the operation procedures for the second embodiment, shown in  FIG. 2 , are the same as the operation procedures for the first embodiment. The separation device is a floating piston  33  with one or more O-ring type seals  34 . The piston seal cavity and O-ring size would be manufactured to allow for a low friction sliding motion. The vessel  13  walls would be manufactured to accommodate for near zero bypass of the pressurizing fluid  14  mixing with the chemical solution  16 . The floating piston  33  accomplishes the same objective as the bellows separator  15  in  FIG. 1 , separating the pressurizing fluid from the chemical solution. In some situations the use of the floating piston would be advantageous. 
       Third Embodiment—structure 
       [0030]    Referring to  FIG. 3  shows the third embodiment of the invention identical to that in  FIG. 1  except that between line  10  and line  19  whereas the bellows separator is replaced by a flexible membrane separator  35 . The vessel design would be changed to accommodate for sealing the flexible membrane  35  sandwiched between two flanges in the middle of the vessel. The pressurizing fluid  14 , the chemical solution  16 , the vent /drain valve line  11 , valve  12 , solution fill line  18  and fill valve  17  remain schematically the same. 
       Third Embodiment—Operation 
       [0031]    All of the operation procedures for the third embodiment, shown in  FIG. 3 , are the same as the operation procedures for the first embodiment. The separation device is a flexible membrane  35  which is stretchable to accommodate the volume of chemical for one operating period. The flexible membrane accomplishes the same objective as the bellows separator  15  in  FIG. 1 , separating the pressurizing fluid from the chemical solution. In some situations the use of the flexible membrane would be advantageous. 
       Fourth Embodiment—Structure 
       [0032]    Referring to  FIG. 4  shows the fourth embodiment similar to that shown in  FIG. 1  except that the capillary solution flow control  20  is located just after  9  and before the pressure vessel  13 . The capillary differential pressure gauge  21  has input lines located between isolation valve  8 , on line  9 , and between the capillary output on line  10  at the entrance of the pressure vessel  13 . The pressurizing fluid  14 , the pressure vessel  13 , the chemical solution  16 , the vent/drain line  11 , valve  12 , solution fill line  18  and fill valve  17  remain schematically the same. 
       Fourth Embodiment—Operation 
       [0033]    All of the operation procedures for the fourth embodiment, shown in  FIG. 4 , are the same as the operation procedures for the first embodiment. The only difference being the location of the capillary flow control device  20  at the entrance of the pressure vessel. The fourth embodiment utilizes the principals of hydrodynamics and incompressible liquids. Since the pressure vessel  13  is filled with liquids, for both the pressuring fluid  14  and chemical solution  16 , the flow rate entering the vessel equals the flow rate out of the vessel. This embodiment can also be utilized in embodiments one, two and three without any procedural changes. 
       Fifth Embodiment—Structure 
       [0034]    Referring to  FIG. 5 , the fifth embodiment is similar to that in  FIG. 1  except that a high pressure gas supply  36 , rather than the water from the bypass loop  24 , is used to pressurize the pressure vessel  13  in volume  14 . The gas pressure is controlled by the pressure regulator  37 , which includes a pressure gauge  38 . The gas pressurizing fluid enters the pressure vessel  13  through line  10 . 
       Fifth Embodiment—Operation 
       [0035]    The fifth embodiment, shown in  FIG. 5 , changes the source of vessel pressurization to that of a high pressure gas supply instead of the liquid supplied by the bypass stream  24 , shown in  FIGS. 1 through 3  at junction tee  7 . This change also alters the chemical supply subsystem isolation during the initial filling and subsequent refilling procedures. Embodiment five will not work with embodiment four, where the capillary flow control  20  is in line  10  at the vessel  13  entrance. 
         [0036]    The initial and subsequent filling of the vessel is accomplished by closing the high pressure gas supply at valve  39  and the chemical injection valve  22 . With valve  12  in the open position the chemical solution is added via line  18  through the open valve  17 . When sufficient chemical solution has been added to the chemical solution reservoir  16 , valve  17  and valve  12  are closed. The pressure regulator  37  is then set to the desired initial gas pressure on gauge  38 . Valve  39  is then opened. Valve  22 , where the chemical solution is injected into the bypass stream, is then opened. If not already open, valves  1  and  32  are opened. The capillary pressure control valve  25  is set to wide open (in embodiment five there is no initial need to adjust the capillary pressure control valve  25  to obtain the desired chemical solution flow rate). The desired capillary differential pressure gauge value  21  is obtained by adjusting the pressure regulator  37  to obtain the desired differential pressure across the capillary flow device  20 . The downstream pressure of the capillary flow control device is the pressure measured at pressure indicator  5 . Thus the differential pressure drop across the capillary flow control device  20  is the difference between pressure gauge  38  and pressure gauge  5 .The bypass flow control valve  28  is used to set the bypass stream flow rate. 
       Sixth Embodiment—Structure 
       [0037]    Referring to  FIG. 7 , the sixth embodiment is applicable to embodiments 1 through 5 of this invention, wherein the components after the differential conductivity cell  26  tie into line  27 , items  28  through  32  are duplicated with items  40  through  44  as shown in  FIG. 7 , allowing controlled injection into two feedwater lines. 
       Sixth Embodiment—Operation 
       [0038]    All five of the embodiments in  FIGS. 1 through 5  show a single exit variable bypass flow control valve  28 , a single bypass flow metering orifice  29 , a single differential pressure gauge  30  and a single isolation valve  31  for a single chemical addition point into one process stream pipe through line  32 . Embodiment six, shown in  FIG. 7 , shows a multiple exit approach that can be incorporated into each of the embodiments one through five. Embodiment six only changes the procedures in embodiments one through five because of adjustments associated with two flow control valves  28  and  40  instead of one are required. The operation of the second exit flow path is the same as for the single path approach. The bypass stream flow rate may have to be increased to accomplish similar attributes of lowering the transit times and maintaining high velocities to lower the potential of premature platinum chemical thermal degradation. All other procedures within the embodiments one through five are applicable. 
       Seventh Embodiment—Structure 
       [0039]    Referring to  FIG. 8 , the seventh embodiment is applicable to embodiments one through five of this invention, wherein the components from the differential conductivity cell  26  tie in to line  27 , item  28  is removed, the flow metering orifice  29  is replaced with a flow controlling orifice  45  and the differential pressure gauge  30  is replaced with a pressure gauge  46 . 
       Seventh Embodiment—Operation 
       [0040]    Embodiments one through five have a bypass flow control valve  28 , a flow meting orifice  29 , a differential pressure meter  30  and an isolation valve  31 . The seventh embodiment replaces the flow metering orifice  29  (small pressure drop) and flow control valve  28  with a controlling orifice  45 , sized to specifically control the desired flow rate for the bypass. The flow regulating valve  28  is removed. The differential pressure gauge  30  is changed to a pressure gauge  46 . Whereas the bypass flow rate was controlled by the valve  28 , with a flow metering system (orifice  29  and differential pressure measurement  30 ), embodiment seven incorporates an orifice that is sized for the pressure drop developed across the components in the main process stream between locations  1  and  32  minus the pressure drop across valve  25 . 
         [0041]    Embodiment six has two exit paths which duplicate the same exit hardware for a second feedwater injection stream, items  40 ,  41 ,  42 , and  43 . In  FIG. 7 , these parallel stream items are replaced with duplicate items as shown and described above for the single stream in embodiment seven. 
       Eighth Embodiment—Structure 
       [0042]    Referring to  FIG. 9 , the eight embodiment is applicable to embodiment one of this invention as an additional chemical second subsystem between lines  7  and  23 . Duplicate components of items  8  through  22  (designated as  8   a  through  22   a ) are attached at tee junctions  7  and  23  respectively. 
         [0043]    Similar chemical injection subsystem components in embodiments two through five can be employed as an additional second subsystem and attached to tee junctions  7  and  23  in their respective  FIGS. 2 through 5 . 
       Eighth Embodiment—Operations 
       [0044]    The operations of the eighth embodiment is the same as in the embodiments one through five except when isolating one or both of the two subsystems. In general only one of the subsystems would be in operation at a time, although both could be in use at the same time. Two subsystems would allow for continuous chemical injection during refilling operations of the other. Two subsystems would also allow for significantly different injection rates by varying the capillary size (internal diameter and length) on the optional second subsystem. 
       CITATION LIST 
     Patent Literature 
       [0045]    U.S. Pat. No. 8,054,933 (Tran et al) 
         [0046]    U.S. Pat. No. 2,266,981 (Miller) 
         [0047]    U.S. Pat. No. 6,779,548 (McKeary) 
       Non Patent Literature 
       [0048]    S. Hettiarachchi and T. P. Diaz, The On-Line NobleChem™ Application Experience In An Operating BWR, International Conference on Water Chemistry of Nuclear Reactor Systems, Jeju Island, South Korea, Oct. 23-26, 2006 
         [0049]    S. E. Garcia, J. F. Giannelli and M. L. Jarvis, “BWR Chemistry Control Status: A Summary of Industry Chemistry Status Relative to the BWR Water Chemistry Guidelines”, Nuclear Plant Chemistry Conference 2010”, Quebec City, Canada, October 2010 
         [0050]    P. L. Andresen and Y. J. Kim, “Developments in SCC Mitigation by Electrocatalysis,” 15th International Conference on Environmental Degradation of Materials in Nuclear Power Systems-—Water Reactors, Colorado Springs, Colo., Aug. 7-11, 2011