Abstract:
A continuous on-line combustion-type carbon analyzer for water applications is provided. The analyzer receives a continuous stream of sample and carbon dioxide-free gas. The analyzer includes control components to limit sample flow into a combustion furnace such that excessive pressures and thermal stresses are minimized. The sample specimen is oxidized within the combustion furnace and the oxidized sample is conveyed to a detector that provides a continuous read-out of carbon quantity in the sample stream.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is related to carbon analysis. More specifically, the present invention is related to a system for continuously measuring carbon content in an aqueous sample stream in substantially real-time.  
         BACKGROUND OF THE INVENTION  
         [0002]    Analysis of both organic and inorganic carbon content provides valuable information for a number of water processing applications. For example, such information can provide valuable insight regarding the efficacy of raw water management during waste water processing, monitoring of cooling water, cleaning water, purified water, as well as a monitoring of waste water effluent. Many pollutants and other undesirable substances generally contain at least some form of carbon. Thus, monitoring carbon content can provide an indication of the presence and quantitative nature of such substances. Such information can be a valuable diagnostic tool for monitoring, or otherwise controlling water treatment and processing facilities.  
           [0003]    In general, there are two primary types of carbon analysis that are currently performed. The goal of both such types of analysis is to fully oxidize all carbon present in the sample into carbon dioxide and subsequently detect the relative amount of carbon dioxide. A common method in which carbon dioxide is detected is using a non-dispersive infrared (NDIR) detector. The two types of analyses differ in how oxidation is effected.  
           [0004]    The first type of carbon analysis is known as low-temperature analysis and generally is performed at temperatures at or below 100° C. One example of such low temperature oxidation is the utilization of ultraviolet irradiation to bombard the sample, and with sufficient exposure, oxidize all dissolved organics into CO 2 . Carbon dioxide, in this case, can also be detected by measuring a change in conductivity of the sample. Another type of low-temperature carbon analysis utilizes a heated persulfate solution. In general, a sample is mixed with a quantity of persulfate solution and heated to approximately 100° C. After a pre-selected interval, the resulting CO 2  is purged out by a carrier gas and detected by an non-dispersive infrared (NDIR) sensor. Both of the above analyses generally require significant time in order to realize complete oxidation of the sample. A third low-temperature technique combines the above two techniques and uses a persulfate solution in addition to UV radiation. Thus, the sample is simultaneously exposed to persulfate and UV radiation. The resulting carbon dioxide is purged out by a carrier gas and detected by an NDIR sensor. Oxidation is more vigorous than the above methods and thus provides faster analysis.  
           [0005]    One of the drawbacks of low-temperature analyses, also know as wet-chemical oxidation, is that particulate matter is somewhat difficult to deal with. Particulates, by their nature, are usually more difficult to oxidize and some organics may escape exposure to UV agents by being positioned within the interstitial spaces of the particles.  
           [0006]    High-temperature techniques, also known as combustion techniques, generally expose the specimen to a high-temperature. Additionally, it is common to use a catalyst in order to facilitate more effective oxidation. One particular combustion technique utilizes a platinum-based catalyst and a combustion temperature in excess of approximately 680° C. Carbon-containing specimens are fully oxidized to carbon dioxide under the above conditions. The resultant carbon dioxide is provided to a detector, generally an NDIR detector, for further analysis. High-temperature carbon analysis provides an advantage in that oxidation can be effected relatively quickly compared to low-temperature techniques. Further, specimens that are difficult to oxidize via low-temperature techniques are readily oxidizable with high-temperature techniques.  
           [0007]    One of the difficulties of using high-temperature analyses, or combustion techniques, for carbon analysis is the relatively severe temperature changes that the sample undergoes during processing. A relatively small amount of liquid sample can become a significant amount of steam and carbon dioxide. Additionally, the thermal shock upon the combustion chamber can be significant as a specimen is introduced at a relatively low temperature and quickly heated by the combustion chamber to combustion temperatures. In general, therefore, combustion techniques are performed in a batch mode. In such a system, a pre-selected amount of sample is conveyed to the combustion chamber to ensure that the thermal mass and resultant gas and steam do no overly stress the system. However, batch-processing introduces a temporal lag that can adversely effect real-time control of water processing.  
           [0008]    One device that appears to provide on-line measurement of carbon content in water is commercially available from Shimadzu products under the trade designation TOC-4000. The product information for this device provides for a measurement cycle of approximately four minutes thus indicating a batch process that is performed successively. As stated above, batch processing introduces a temporal lag for real-time control of data processes. Additionally, the output from a detector in such a system would include undesirable peaks rendering data proximate the peak unusable. Therefore, there is a continuing need for a real-time carbon analyzer for water processing applications.  
         SUMMARY OF THE INVENTION  
         [0009]    A continuous on-line combustion-type carbon analyzer for water applications is provided. The analyzer receives a continuous stream of sample and carbon dioxide-free gas. The analyzer includes control components to limit sample flow into a combustion furnace such that excessive pressures and thermal stresses are minimized. The sample specimen is oxidized within the combustion furnace and the oxidized sample is conveyed to a detector that provides a continuous read-out of carbon quantity in the sample stream. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1. is a diagrammatic view of an on-line continuous combustion-type carbon analyzer for water applications.  
         [0011]    [0011]FIG. 2 is a chart illustrating measured CO 2  for various water specimens. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0012]    [0012]FIG. 1 is a diagrammatic view of an on-line continuous carbon analyzer for water applications in accordance with an embodiment of the present invention. System  100  receives blank water (water containing no carbon whatsoever)  102  at port  104 ; standard “calibration” water  106  at port  108 ; and a sample stream  110  at port  112 . Blank water  102  and Calibration water  106  are used to determine system response to known quantities, such that systemic errors can be corrected. System  100  also receives carbon dioxide-free air at port  114 . System  100  drains undesirable components out drain  116  and provides a continuous carbon readout from sensor  118 .  
         [0013]    As described above, sample  110  is provided to sample inlet port  112  and is conveyed to sample flow controller  120 . Flow controller  120  is adjusted to provide a suitable flow of sample specimen to sample standard valve  122 . When sample standard valve  122  is suitably actuated, sample specimen is conveyed therethrough and provided to metering pump  124 . Metering pump  124  precisely controls the amount of sample specimen provided to furnace  126 . Careful selection of sample flow ensures that system  100  is not overly stressed. In one preferred embodiment, pump  124  is a metering pump and controller available from Eldex Laboratories, Inc of Napa, Calif. under the trade designation Model A-60-VS. Preferably, sample flow is set to between approximately 0.5 cc per minute and approximately 2.0 cc per minute. A flow rate of 0.5 cc per minute corresponds with a controller setting of approximately 230 generating 2 to 3 drops of sample specimen per pump cycle.  
         [0014]    Carbon dioxide-free air is received by system  100  at port  114 . The gas is filtered by filter  128  and provided to pressure regulator  130 . Regulator  130  is set to provide a suitable pressure on line  132  which pressure is indicated by gauge  134 . The pressurized gas is conveyed to primary oxygen/air controller  136  which is adjusted to provide a suitable flow therethrough. The adjusted flow is measured by primary oxygen/air flow meter  138  and conveyed on to furnace  126  through check valve  140 .  
         [0015]    Furnace  126  is maintained at an elevated temperature, such as 680° C., in order effect high-temperature oxidation. To maintain this elevated temperature, furnace  126  is thermally coupled to heating elements  142  that are controlled by temperature controller  144  based upon a measured temperature of furnace  126  by sensor  146 , which is preferably a thermocouple. Specimen  110  and pressurized gas are thus conveyed to combustion furnace  126  at furnace inlet  148 . A combustion tube  150  is coupled to inlet  148  and conveys the specimen and pressurized gas to outlet  152  after it has been heated and exposed to the combustion catalyst. Preferably, tube  150  is a precision ceramic combustion tube such as that commercially available from Mindrum Precision, Inc. of Rancho Cucamonga, Calif. Within combustion tube  150 , a quantity of quartz wool is preferably positioned in order to support catalyst pellets, such as platinum-based catalyst pellets. Preferably, one gram of quartz wool is disposed within combustion tube  150  as well as about 20.1 grams of catalyst pellets such as commercially available from Tekmar Company, of Cincinnati, Ohio. Additionally, 40 grams of quartz granules are also preferably positioned within combustion tube  150 . The heat of combustion tube  150  as well as the catalytic materials disposed therein cause the sample to combine with oxygen and generate steam and carbon dioxide. Additional particulate matter may also be heated and conveyed from outlet  152 . The heated materials are provided from outlet  152  to thermoelectric cooler  154 . Preferably, thermoelectric cooler  154  employs a Peltier device generating a low temperature based upon the well-known Peltier effect. In one preferred embodiment, cooler  154  is a commercially available thermoelectric gas chiller available under the trade designation Model 600, from Universal Analyzer Inc., in Nevada. As cooler  154  cools the heated materials, water and particulate matter condense and flow into drain line  156  which is coupled to drain pump  158  to pump such materials out drain port  116 . However, carbon dioxide does not flow into drain line  156 , but is instead conveyed along line  160  to detector  118 . Preferably, detector  118  is a known non-dispersive infrared detector that is capable of resolving 0 to 100 parts per million of CO 2 . In the embodiment just described, the read-out of detector  118  will correspond with total carbon. However, those skilled in the art will recognize that organic carbon can also be measured by first conveying the sample to a solution that reacts with inorganic carbon, such as, for example, a 20% phosphoric acid solution that reacts with inorganic carbon to form carbonate and bi-carbonate. This reaction can be used to separate the inorganic carbon from the sample stream prior to analysis thereby causing detector  118  to provide an indication of total organic carbon.  
         [0016]    [0016]FIG. 2 is a chart of detector  118  read-out for various solutions monitored over time. As can be seen, for the first approximately 70 minutes, a solution of HPLC grade water was conveyed through system  100  providing a relatively low read-out in the range of about 2 units. Thereafter, from approximately 70 minutes to approximately 140 minutes, a solution of an isopropanol water solution of approximately 100 ppmw was conveyed through system  100  and generated a reading of approximately 75 units. Thereafter, from approximately 140 minutes to approximately 210 minutes, a solution of de-ionized tap water was conveyed through system  100  and a reading of approximately 25 units was measured. Finally, from approximately 210 minutes through 280 minutes, Sparkletts drinking water was conveyed through system  100  and generated a reading of approximately 18 units.  
         [0017]    The system described above uses carefully selected components and component settings to generate a continuous flow that does not overly stress the system itself. Thus, the flow is small enough to inhibit excess pressure forming from the relatively significant expansion caused by heating an aqueous solution well past its boiling point. Further, providing the specimen at a relatively low temperature to a catalyst that is maintained at approximately 680° C. represents a significant thermal shock. However, the flow rates disclosed herein mitigate the thermal shock while providing suitable sample flow for useful measurements. As can be seen from the readings in FIG. 2, the output from detector  118  does not contain any large spikes that would be indicative of batch flow processing and substantial system stress.  
         [0018]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.