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  Method of monitoring membrane cleaning processesThe Patent Description & Claims data below is from USPTO Patent Application 20060157090. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a divisional application of U.S. patent application Ser. No. 10/108,694, which was filed on Mar. 28, 2002. FIELD OF THE INVENTION [0002] This invention relates generally to membrane cleaning and, more particularly, to methods for monitoring and/or controlling the cleaning of membrane separation systems. BACKGROUND OF THE INVENTION [0003] Membrane separation, which uses a selective membrane, is a fairly recent addition to the industrial separation technology for processing of liquid streams, such as water purification. In membrane separation, constituents of the influent typically pass through the membrane as a result of a driving force(s) in one effluent stream, thus leaving behind some portion of the original constituents in a second stream. Membrane separations commonly used for water purification or other liquid processing include microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), electrodialysis, electrodeionization, pervaporation, membrane extraction, membrane distillation, membrane stripping, membrane aeration, and other processes. The driving force of the separation depends on the type of the membrane separation. Pressure-driven membrane filtration, also known as membrane filtration, includes microfiltration, ultrafiltration, nanofiltration and reverse osmosis, and uses pressure as a driving force, whereas the electrical driving force is used in electrodialysis and electrodeionization. Historically, membrane separation processes or systems were not considered cost effective for water treatment due to the adverse impacts that membrane scaling, membrane fouling, membrane degradation and the like had on the efficiency of removing solutes from aqueous water streams. However, advancements in technology have now made membrane separation a more commercially viable technology for treating aqueous feed streams suitable for use in industrial processes. [0004] During membrane separation, deposits of scale and foulants on the membrane can adversely impact the performance of the membrane. For example, in membrane filtration such foulants and scales can decrease the permeate flow for a given driving force, lowering the permeate quality (purity), increasing energy consumed to maintain a given permeate flow or the like. This can necessitate the cleaning of the membrane separation system in order to remove the scalants, foulants and the like from the membrane separation system. Thus, the performance of the membrane system in use can be enhanced. [0005] In general, the membrane cleaning process includes adding a suitable cleaning agent and circulating it within the membrane separation system. In this regard, the cleaning agent acts to remove scalants, foulants or the like that have deposited on surfaces of the membrane system, including the membrane itself. After the membrane system has been washed with the cleaning agent, the system is then, in general, flushed or rinsed to remove the cleaning agent along with other impurities that may remain in the system. [0006] Membrane cleaning processes usually consist of removing the membrane system from service, rinsing the membrane system (membranes, housings and associated piping) with high quality (preferably permeate quality) water, preparing a cleaning solution by adding the cleaner to a specified volume of permeate quality water, heating the cleaning solution, circulating the cleaning solution at low pressure through the membranes and back into the clean-in-place (CIP) tank thereby displacing the rinse water and diluting the cleaning solutions. The cleaning process further consists of alternately circulating the cleaning solution through the membrane system and soaking the membrane system in the cleaning solution. During the process the system may be rinsed and fresh cleaning solution applied as needed. Finally the system is rinsed with permeate quality water and either subjected to a second cleaning or placed back in service. [0007] Typically, the membrane cleaning process is maintained by evaluating a variety of different process conditions, particularly the pH of the system during cleaning. However, this type of monitoring is not very specific and/or selective to, for example, the concentration of the cleaning agent during cleaning. In this regard, fluctuations in the amount of cleaning agent may not be effectively identified. Thus, the amount of cleaning agent may not be effectively monitored and thereby controlled in order to enhance the performance of the cleaning process. [0008] Accordingly, a need exists to monitor and/or control the cleaning of membrane separation systems where conventional monitoring techniques lack the sensitivity, selectivity and/or accuracy necessary to adequately monitor one or more process parameters specific to the cleaning of membranes or systems in order to adequately evaluate the performance of the same. SUMMARY OF THE INVENTION [0009] The present invention provides methods and systems for monitoring and/or controlling the cleaning of membrane separation systems. In this regard, the detection of inert fluorescent tracers is utilized to evaluate and/or control a number of different process parameters unique to the cleaning of membrane separation, such as operational parameters, chemical parameters, mechanical parameters, the like and combinations thereof. The inert fluorescent tracer monitoring technique of the present invention can be performed with a high degree of sensitivity and selectivity with respect to the monitoring of process parameters specific to the cleaning of a membrane separation system. In this regard, the methods and systems of the present invention can be effectively utilized to optimize the performance of cleaning and, thus enhance the performance of the membrane separation process. Examples of such optimized performance include longer times between membrane cleanings, longer membrane life, verification of treatment chemical in the system, ability to operate at optimal recovery, and decreased energy costs due to better control of scaling, fouling and other system parameters. [0010] To this end, in an embodiment of the present invention, a method of monitoring a cleaning process capable of cleaning a membrane separation system is provided. The method includes the steps of providing an inert fluorescent tracer and a cleaning solution; adding the inert fluorescent tracer and the cleaning solution to the membrane separation system; providing a fluorometer to detect the fluorescent signal of the inert fluorescent tracer in the membrane separation system; and using the fluorometer to determine an amount of the inert fluorescent tracer in the membrane separation system during the cleaning process. [0011] In another embodiment, a method of cleaning a membrane separation system including a membrane capable of removing impurities from a feed stream is provided. The method includes the steps of providing an inert fluorescent tracer and a cleaning solution; flushing the membrane separation system; adding the inert fluorescent tracer and the cleaning solution to the membrane separation system; circulating the inert fluorescent tracer and the cleaning solution in the membrane separation system; rinsing the membrane separation system; providing a fluorometer to detect the fluorescent signal of the inert fluorescent tracer in the membrane separation system; using the fluorometer to measure an amount of the inert fluorescent tracer ranging from about 5 parts per trillion ("ppt") to about 1000 parts per million ("ppm"); and evaluating at least one process parameter specific to cleaning based on the amount of the inert fluorescent tracer that is measured. [0012] In yet another embodiment, a cleaning system capable of cleaning a membrane separation system adapted for use in an industrial process is provided. The cleaning system includes an inert fluorescent tracer and a cleaning solution added to the membrane separation system during cleaning; a detection device capable of fluorometrically measuring an amount of the inert fluorescent tracer ranging from about 5 ppt to about 1000 ppm during cleaning of the membrane separation system wherein the detection device is capable of producing a signal indicative of the amount of inert tracer that is measured; and a controller capable of processing the signal to monitor cleaning of the membrane separation system. [0013] It is, therefore, an advantage of the present invention to provide methods and systems that utilize inert fluorescent tracers to monitor and/or control the cleaning of membrane separation processes or systems. [0014] Another advantage of the present invention is to provide methods and systems that utilize measurable amounts of inert tracers to improve the operational efficiency of the cleaning of membrane separation processes or systems. [0015] A further advantage of the present invention is to provide methods and systems for monitoring parameters specific to the cleaning of membrane separation processes with selectivity, specificity and accuracy based on measurable amounts of inert tracers added during cleaning. [0016] Yet another advantage of the present invention is to provide methods and systems for monitoring and/or controlling the cleaning of membrane separation processes adaptable for use in industrial water systems. [0017] Still further an advantage of the present invention is to provide an improved performance specific to the cleaning of membrane separation processes or systems that utilize cross-flow and/or dead-end flow separation to remove impurities from a variety of suitable feed streams. [0018] The benefits of this invention include the accurate determination of the system volume of a membrane separation system including the housings and associated piping, the accurate dosing of cleaning chemicals during system cleaning, and the assessment of rinse times for the system. [0019] Additional features and advantages of the present invention are described in, and will be apparent in, the detailed description of the presently preferred embodiments. DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS Continue reading... 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