COMBINATION TOD-TC ANALYSIS METHOD
United States Patent 3854877
An integrated instrument and modified technique are provided for measuring the total carbon content (TC) and total oxygen demand (TOD) concurrently on samples of aqueous solutions or dispersions. Further, a method is provided for measuring the extent of other oxidation reactions such as nitrification occurring in processes such as the bio-oxidation of wastes.
US Patent References:
Method and apparatus for determining the total carbon content of aqueous systems
Teal et al. - January 1967 - 3296435
METHOD AND APPARATUS FOR DETERMINING THE OXYGEN DEMAND OF OXIDIZABLE MATERIALS
Stenger et al. - January 1969 - 3421856
OPTIMIZED BLOWING CONTROL FOR BASIC OXYGEN FURNACES
Blum et al. - September 1970 - 3528800
/3560156.html
Teal et al. - February 1971 - 3560156
/3567385.html
Van Hall - March 1971 - 3567385
Method and apparatus for determining the total carbon content of aqueous systems
Teal et al. - January 1967 - 3296435
METHOD AND APPARATUS FOR DETERMINING THE OXYGEN DEMAND OF OXIDIZABLE MATERIALS
Stenger et al. - January 1969 - 3421856
OPTIMIZED BLOWING CONTROL FOR BASIC OXYGEN FURNACES
Blum et al. - September 1970 - 3528800
/3560156.html
Teal et al. - February 1971 - 3560156
/3567385.html
Van Hall - March 1971 - 3567385
Inventors:
Csaky, Ernoe (Midland, MI)
Thompson, Hugh C. (Falls Church, VA)
Thompson, Hugh C. (Falls Church, VA)
Application Number:
05/278531
Publication Date:
12/17/1974
Filing Date:
08/07/1972
View Patent Images:
Export Citation:
Assignee:
The Dow Chemical Company (Midland, MI)
Primary Class:
Other Classes:
422/79, 436/159, 436/146, 436/160
International Classes:
G01N31/12; G01N33/18; G01N31/12
Field of Search:
23/23PC,253PC,232,254
US Patent References:
Primary Examiner:
Serwin R. E.
Attorney, Agent or Firm:
Hummer, Richard W.
Claims:
What is claimed is
1. A process for simultaneously measuring the total oxygen demand and total carbon of an aqueous dispersion of combustible material which comprises the steps of:
2. flowing a feed gas stream containing a relatively small amount of oxygen at a constant rate through a confined combustion zone heated at a combustion supporting temperature within the range from about 600° to about 1200°C. and, within the combustion zone, flowing the feed gas stream through a combustion supporting catalyst bed,
3. flowing the effluent gas from the combustion zone into a continuous analyzer for quantitatively indicating the carbon dioxide in the gaseous product,
4. flowing the effluent gas from the combustion zone after passing through the carbon dioxide detector of step (2) above, into a continuous quantitative detector for gaseous oxygen and while continuing to flow the feed gas stream, injecting a small amount of the aqueous dispersion of a combustible material into the combustion zone upstream from the catalyst bed, whereby electrical signals correlative with the carbon content of the aqueous sample and its total oxygen demand are produced by the carbon dioxide and oxygen detectors, respectively.
5. A method as in claim 1 including the additional step of calibrating each of the signals obtained from the carbon dioxide detector and oxygen detector to yield a measurement of carbon and total oxidizable material contained in the aqueous dispersion.
6. A method for determining the degree of oxidation change in a process stream which comprises generating signals proportional, respectively, to a ratio of the total oxygen demand and the total carbon in the influent stream to an oxidative reaction zone and in the effluent stream from said zone and combining said signals to generate a signal the value of which is an index of the degree of oxidation occurring in said zone.
7. A method according to claim 3 wherein the process stream is sewage and the derived value is a measure of the degree of nitrification occurring in the oxidative process.
1. A process for simultaneously measuring the total oxygen demand and total carbon of an aqueous dispersion of combustible material which comprises the steps of:
2. flowing a feed gas stream containing a relatively small amount of oxygen at a constant rate through a confined combustion zone heated at a combustion supporting temperature within the range from about 600° to about 1200°C. and, within the combustion zone, flowing the feed gas stream through a combustion supporting catalyst bed,
3. flowing the effluent gas from the combustion zone into a continuous analyzer for quantitatively indicating the carbon dioxide in the gaseous product,
4. flowing the effluent gas from the combustion zone after passing through the carbon dioxide detector of step (2) above, into a continuous quantitative detector for gaseous oxygen and while continuing to flow the feed gas stream, injecting a small amount of the aqueous dispersion of a combustible material into the combustion zone upstream from the catalyst bed, whereby electrical signals correlative with the carbon content of the aqueous sample and its total oxygen demand are produced by the carbon dioxide and oxygen detectors, respectively.
5. A method as in claim 1 including the additional step of calibrating each of the signals obtained from the carbon dioxide detector and oxygen detector to yield a measurement of carbon and total oxidizable material contained in the aqueous dispersion.
6. A method for determining the degree of oxidation change in a process stream which comprises generating signals proportional, respectively, to a ratio of the total oxygen demand and the total carbon in the influent stream to an oxidative reaction zone and in the effluent stream from said zone and combining said signals to generate a signal the value of which is an index of the degree of oxidation occurring in said zone.
7. A method according to claim 3 wherein the process stream is sewage and the derived value is a measure of the degree of nitrification occurring in the oxidative process.
Description:
BACKGROUND OF THE INVENTION
Instruments to measure TOD and TC individually have been developed and are now commercially available. The capability provided by these measurements has made the detection of pollution much simpler and less costly. At the same time, the instruments have afforded a technical basis for the control of remedial processes to alleviate pollution.
It is an object of the instant invention to provide improved instrumentation for making TOD and TC measurements.
It is a further object of the instant invention to provide instrumentation for achieving simultaneous TOD and TC measurements on a given sample of an aqueous dispersion.
A still further object is to provide the capability of measuring a nitrification parameter in the form of the difference of the measured TOD and the TOD calculated from the TC measured.
SUMMARY OF THE INVENTION
The foregoing objects, and other benefits as will become apparent hereinafter, are achieved in a process which comprises the steps of flowing a feed gas stream composed of an inert gas containing a minor proportion of oxygen into a heated combustion zone at a constant rate. Within the combustion zone, the feed gas is passed through a combustion supporting, porous catalyst bed. The combustion zone is heated at a combustion-supporting temperature within the range from about 600° up to about 1200°C., preferably within the range from about 800° to about 1000°C. From the heated combustion zone, the gas stream is fed into a detector train. First in this train is means for cooling the gas, which may be simply the gas conduit itself as cooled by the surrounding atmosphere, and means for separating any condensate that may be formed as a result of the intermittent introduction of combustion products. The feed gas stream is then passed through a detector for carbon dioxide. Subsequently, the gas stream is passed through a continuous, quantitative oxygen detector.
Once the feed gas stream containing a relatively small quantity of oxygen is established through the heated combustion zone, a small amount of an aqueous dispersion containing a combustible material is injected into the combustion zone upstream from the porous catalyst bed. This sample is vaporized and any combustibles contained therein are oxidized to produce carbon dioxide. In addition, nitrogenous compounds will be oxidized to some degree.
The carbon dioxide detector measures the amount of total carbon (TC) that was contained in the injected sample. Subsequently, within the oxygen detector, the total oxygen demand, which includes the oxygen used in forming the carbon dioxide and in oxidizing oxidizable nitrogen compounds, is measured in terms of the decrease in the amount of oxygen relative to the background oxygen content of the feed gas stream. This measurement yields what is termed herein the total oxygen demand (TOD) of the aqueous dispersion.
The difference between the measured TOD and the calculated TOD from the measured TC measurements yields an indication of the amount of oxidizable nitrogenous materials present in the sample analyzed. Thus, by introducing the carbon dioxide detecting capability into an instrument, otherwise especially adapted for the measurement of total oxygen demand, a triple capability is provided for the measurement of pollution parameters. The combined capabilities of the instrument provide means for determining an index of the degree of nitrification in certain waste treatment processes.
Details as to means for providing a feed gas stream, effecting combustion within the heated zone and measuring by detecting, recording and calibrating the recording results are further elaborated by the teachings of U.S. Pat. No. 3,560,156.
Means for conditioning the effluent gases from the combustion zone by cooling them and removing condensate prior to analysis of the carbon dioxide are shown by Teal et al. in U.S. Pat. No. 3,296,435.
Apparatus for carrying out the foregoing process will be better understood by reference to the accompanying drawing. The depicted apparatus comprises a dilute oxygen feed stream supply means 2, which in this particular illustration is composed of an arrangement of an inert gas (for example, nitrogen) supply tank 3 and an oxygen supply tank 4 integrally feeding a feed gas line 6. Nitrogen and oxygen are metered into the feed gas line 6 through pressure and flow control valves 7 and 8. Any known means for producing a carrier gas stream containing a controlled amount of oxygen may be used in place of the particular means illustrated. Line 6 feeds the mixed gas stream into a confined combustion zone defined by that portion of the combustion tube 15 within the heating zone 13 of an electric furnace 9. Within the heated combustion zone is a gas permeable, catalyst bed 16 of an oxidation supporting catalyst material. The temperature of the heating zone 13 is controlled by a variable power control 10 feeding through the electrical input lines 11 and 12 which are connected to the terminals of a resistance heating coil 14.
Injection of the aqueous dispersion to be analyzed is accomplished by suitable injection means such as the illustrated syringe 17. Optionally, pneumatic automatic injection valves may be used. The trajectory for sample injection is such that the sample will be deposited within the heating zone 13 on the upstream side of the catalyst bed 16.
Gaseous products from the heated zone 13 of the combustion conduit 15 are passed through cooling means, which in the illustration is simply conduit 19 as cooled at ambient air conditions. The gas is passed through a water trap 54 which is vented as required through valve 52 to remove condensate. From the water trap 54, the gas is passed through conduit 33 into the carbon dioxide-sensitized, infrared analyzer 35 containing a detection cell 36. The variable voltage signal from the carbon dioxide detector is amplified by means of a low voltage amplifier 38 connected to said detector by electrical leads 63 and 64. The enhanced electrical signal is then fed through leads 61 and 62 into a continuous graphic recorder 39, which produces a curve 41 on a continuous strip of recording paper 42. The amplitude of, and the area under, the curve 41 are each a function of the carbon dioxide concentration continuously measured in the detection cell 36 of the infrared analyzer 35. The degree of amplification and the base line for the curve can be adjusted through controls 43 and 44.
After passing through the detection cell 36 the gaseous product is passed through conduit 37 into an oxygen detector 21 and from this detector exhausts into the atmosphere through vent 20. The oxygen detector 21 produces an electrical signal which is fed through electrical connections 23 to read out means 30, which is a graphic recorder 26.
The signal from the oxygen detector, which may be measured as voltage or current, is proportional to, and therefore correlative with, the oxygen content of the gaseous effluent. If desired, the recorded signal can be calibrated for direct reading of the signal as the oxygen content of the effluent gas stream.
The total oxygen demand (TOD) is defined according to the formula: ##SPC1##
wherein Q is a function of t, which is time, and Q 1 is the oxygen content of the feed gas stream, or in other terms the oxygen content of the effluent gas under steady state conditions. t 1 and t 2 are the times of sample injection and return of the oxygen content of the effluent gas to that of the feed gas stream, respectively. A graphic illustration of the value of the above equation solved for TOD is shown in the drawing by the shaded area 31 between the base line 29 representing the oxygen content of the feed gas stream and curve 27 plotted by the graphic recorder 26 between t 1 and t 2 .
Alternatively, variations in the oxygen content of the gaseous effluent from the combustion zone, as the result of oxygen used to oxidize combustible material present in the injected aqueous dispersion, are reflected in the amplitude or displacement of the curve 27 from the recorder base line 29. In fact, the displacement of the recorded curve 27 from the base line 29 is directly proportional to the amount of oxygen used in the combustion of the sample, i.e., the total oxygen demand of the aqueous dispersion.
In a further embodiment of the invention, the output results from recorders 26 and 39 can be tabulated in conventional fashion and stored in a computer for recombination in accordance with predetermined programs. Alternatively, the outputs from analyzer 35 and detector 21 are fed through suitable amplifiers, not shown, to an integrating calculator from which the results are stored in a computer by known methods. Such stored results are thus available for recombination by available programs to provide functions such as quotients (TC/TOD) and quotient differences ([TC 1 /TOD 1 ] - [TC 2 /TOD 2 ]).
Utilization of the components of the foregoing apparatus and variations therein are well described in the above patents incorporated herein by reference. It will be apparent from reading these teachings that numerous changes in equipment can be made without detracting from the benefit of achieving both TOD and TC measurements on a given aqueous sample plus the capability of differential measurement of oxidizable nitrogenous materials as will be described in detail below.
In various processes for treating sewage and other industrial and municipal wastes containing organic matter biological oxidation is employed to remove much of such organic matter. In such processes part of the carbon from the organic matter may be converted to carbon dioxide while a further part is incorporated into the biologically active organisms such as activated sludge. Thus, the determination of the TC of the effluent from such a process as compared to the TC of the influent provides an index of the efficiency of the process in eliminating oxidizable organic matter from the process stream. However, the TC determination provides no information on the fate of nitrogen compounds in the treated wastes. Nitrogen occurs in sewage predominantly in the reduced state, for example, in the form of ammonium, amino and amido nitrogen. Such reduced nitrogen moieties contribute to the TOD for a process stream but not to the TC. Thus, in a preferred embodiment, the present invention provides a method for determining the degree of oxidation occurring in a process stream such as, for example, the degree of nitrification occurring in the biooxidation of a waste stream.
In such operations, a sample from the influent stream to an oxidation process is analyzed in the combination TC-TOD apparatus and the results are stored in a computer. Then a sample from the effluent stream from the oxidation process is analyzed and the results stored in the same fashion. Since the oxidation of carbon and the loss of volatiles during the process will change the TC and TOD in substantially the same proportion while any oxidation of nitrogen will affect only the TOD, the computer is programmed to read out a function such as the ratio of TC to TOD of the influent minus the ratio of TC to TOD of the effluent and the values of this function serve as an index of the degree of nitrification occurring in the oxidative process. For additional precision, if desired, the apparatus is calibrated with samples of known composition and/or compared with analyses of like samples by standard methods of analysis.
In the light of modern instrumentation for electronic data processing, the foregoing method can be considered as comprising generating a first signal proportional to the TC and a second signal proportional to the TOD of an influent stream of a process and combining said first and second signals to generate a third signal proportional to a ratio of said first and second signals. Similar first, second and third signals are generated from a sample of the effluent stream from said process and the third signals from the influent and effluent streams are combined to generate a signal having a value which serves as an index of the degree of oxidation occurring in said process. Conventional electronic equipment is available for storing, reproducing and combining the above signals and for producing a read-out of the resultant index value either in numerical or graphical form.
Instruments to measure TOD and TC individually have been developed and are now commercially available. The capability provided by these measurements has made the detection of pollution much simpler and less costly. At the same time, the instruments have afforded a technical basis for the control of remedial processes to alleviate pollution.
It is an object of the instant invention to provide improved instrumentation for making TOD and TC measurements.
It is a further object of the instant invention to provide instrumentation for achieving simultaneous TOD and TC measurements on a given sample of an aqueous dispersion.
A still further object is to provide the capability of measuring a nitrification parameter in the form of the difference of the measured TOD and the TOD calculated from the TC measured.
SUMMARY OF THE INVENTION
The foregoing objects, and other benefits as will become apparent hereinafter, are achieved in a process which comprises the steps of flowing a feed gas stream composed of an inert gas containing a minor proportion of oxygen into a heated combustion zone at a constant rate. Within the combustion zone, the feed gas is passed through a combustion supporting, porous catalyst bed. The combustion zone is heated at a combustion-supporting temperature within the range from about 600° up to about 1200°C., preferably within the range from about 800° to about 1000°C. From the heated combustion zone, the gas stream is fed into a detector train. First in this train is means for cooling the gas, which may be simply the gas conduit itself as cooled by the surrounding atmosphere, and means for separating any condensate that may be formed as a result of the intermittent introduction of combustion products. The feed gas stream is then passed through a detector for carbon dioxide. Subsequently, the gas stream is passed through a continuous, quantitative oxygen detector.
Once the feed gas stream containing a relatively small quantity of oxygen is established through the heated combustion zone, a small amount of an aqueous dispersion containing a combustible material is injected into the combustion zone upstream from the porous catalyst bed. This sample is vaporized and any combustibles contained therein are oxidized to produce carbon dioxide. In addition, nitrogenous compounds will be oxidized to some degree.
The carbon dioxide detector measures the amount of total carbon (TC) that was contained in the injected sample. Subsequently, within the oxygen detector, the total oxygen demand, which includes the oxygen used in forming the carbon dioxide and in oxidizing oxidizable nitrogen compounds, is measured in terms of the decrease in the amount of oxygen relative to the background oxygen content of the feed gas stream. This measurement yields what is termed herein the total oxygen demand (TOD) of the aqueous dispersion.
The difference between the measured TOD and the calculated TOD from the measured TC measurements yields an indication of the amount of oxidizable nitrogenous materials present in the sample analyzed. Thus, by introducing the carbon dioxide detecting capability into an instrument, otherwise especially adapted for the measurement of total oxygen demand, a triple capability is provided for the measurement of pollution parameters. The combined capabilities of the instrument provide means for determining an index of the degree of nitrification in certain waste treatment processes.
Details as to means for providing a feed gas stream, effecting combustion within the heated zone and measuring by detecting, recording and calibrating the recording results are further elaborated by the teachings of U.S. Pat. No. 3,560,156.
Means for conditioning the effluent gases from the combustion zone by cooling them and removing condensate prior to analysis of the carbon dioxide are shown by Teal et al. in U.S. Pat. No. 3,296,435.
Apparatus for carrying out the foregoing process will be better understood by reference to the accompanying drawing. The depicted apparatus comprises a dilute oxygen feed stream supply means 2, which in this particular illustration is composed of an arrangement of an inert gas (for example, nitrogen) supply tank 3 and an oxygen supply tank 4 integrally feeding a feed gas line 6. Nitrogen and oxygen are metered into the feed gas line 6 through pressure and flow control valves 7 and 8. Any known means for producing a carrier gas stream containing a controlled amount of oxygen may be used in place of the particular means illustrated. Line 6 feeds the mixed gas stream into a confined combustion zone defined by that portion of the combustion tube 15 within the heating zone 13 of an electric furnace 9. Within the heated combustion zone is a gas permeable, catalyst bed 16 of an oxidation supporting catalyst material. The temperature of the heating zone 13 is controlled by a variable power control 10 feeding through the electrical input lines 11 and 12 which are connected to the terminals of a resistance heating coil 14.
Injection of the aqueous dispersion to be analyzed is accomplished by suitable injection means such as the illustrated syringe 17. Optionally, pneumatic automatic injection valves may be used. The trajectory for sample injection is such that the sample will be deposited within the heating zone 13 on the upstream side of the catalyst bed 16.
Gaseous products from the heated zone 13 of the combustion conduit 15 are passed through cooling means, which in the illustration is simply conduit 19 as cooled at ambient air conditions. The gas is passed through a water trap 54 which is vented as required through valve 52 to remove condensate. From the water trap 54, the gas is passed through conduit 33 into the carbon dioxide-sensitized, infrared analyzer 35 containing a detection cell 36. The variable voltage signal from the carbon dioxide detector is amplified by means of a low voltage amplifier 38 connected to said detector by electrical leads 63 and 64. The enhanced electrical signal is then fed through leads 61 and 62 into a continuous graphic recorder 39, which produces a curve 41 on a continuous strip of recording paper 42. The amplitude of, and the area under, the curve 41 are each a function of the carbon dioxide concentration continuously measured in the detection cell 36 of the infrared analyzer 35. The degree of amplification and the base line for the curve can be adjusted through controls 43 and 44.
After passing through the detection cell 36 the gaseous product is passed through conduit 37 into an oxygen detector 21 and from this detector exhausts into the atmosphere through vent 20. The oxygen detector 21 produces an electrical signal which is fed through electrical connections 23 to read out means 30, which is a graphic recorder 26.
The signal from the oxygen detector, which may be measured as voltage or current, is proportional to, and therefore correlative with, the oxygen content of the gaseous effluent. If desired, the recorded signal can be calibrated for direct reading of the signal as the oxygen content of the effluent gas stream.
The total oxygen demand (TOD) is defined according to the formula: ##SPC1##
wherein Q is a function of t, which is time, and Q 1 is the oxygen content of the feed gas stream, or in other terms the oxygen content of the effluent gas under steady state conditions. t 1 and t 2 are the times of sample injection and return of the oxygen content of the effluent gas to that of the feed gas stream, respectively. A graphic illustration of the value of the above equation solved for TOD is shown in the drawing by the shaded area 31 between the base line 29 representing the oxygen content of the feed gas stream and curve 27 plotted by the graphic recorder 26 between t 1 and t 2 .
Alternatively, variations in the oxygen content of the gaseous effluent from the combustion zone, as the result of oxygen used to oxidize combustible material present in the injected aqueous dispersion, are reflected in the amplitude or displacement of the curve 27 from the recorder base line 29. In fact, the displacement of the recorded curve 27 from the base line 29 is directly proportional to the amount of oxygen used in the combustion of the sample, i.e., the total oxygen demand of the aqueous dispersion.
In a further embodiment of the invention, the output results from recorders 26 and 39 can be tabulated in conventional fashion and stored in a computer for recombination in accordance with predetermined programs. Alternatively, the outputs from analyzer 35 and detector 21 are fed through suitable amplifiers, not shown, to an integrating calculator from which the results are stored in a computer by known methods. Such stored results are thus available for recombination by available programs to provide functions such as quotients (TC/TOD) and quotient differences ([TC 1 /TOD 1 ] - [TC 2 /TOD 2 ]).
Utilization of the components of the foregoing apparatus and variations therein are well described in the above patents incorporated herein by reference. It will be apparent from reading these teachings that numerous changes in equipment can be made without detracting from the benefit of achieving both TOD and TC measurements on a given aqueous sample plus the capability of differential measurement of oxidizable nitrogenous materials as will be described in detail below.
In various processes for treating sewage and other industrial and municipal wastes containing organic matter biological oxidation is employed to remove much of such organic matter. In such processes part of the carbon from the organic matter may be converted to carbon dioxide while a further part is incorporated into the biologically active organisms such as activated sludge. Thus, the determination of the TC of the effluent from such a process as compared to the TC of the influent provides an index of the efficiency of the process in eliminating oxidizable organic matter from the process stream. However, the TC determination provides no information on the fate of nitrogen compounds in the treated wastes. Nitrogen occurs in sewage predominantly in the reduced state, for example, in the form of ammonium, amino and amido nitrogen. Such reduced nitrogen moieties contribute to the TOD for a process stream but not to the TC. Thus, in a preferred embodiment, the present invention provides a method for determining the degree of oxidation occurring in a process stream such as, for example, the degree of nitrification occurring in the biooxidation of a waste stream.
In such operations, a sample from the influent stream to an oxidation process is analyzed in the combination TC-TOD apparatus and the results are stored in a computer. Then a sample from the effluent stream from the oxidation process is analyzed and the results stored in the same fashion. Since the oxidation of carbon and the loss of volatiles during the process will change the TC and TOD in substantially the same proportion while any oxidation of nitrogen will affect only the TOD, the computer is programmed to read out a function such as the ratio of TC to TOD of the influent minus the ratio of TC to TOD of the effluent and the values of this function serve as an index of the degree of nitrification occurring in the oxidative process. For additional precision, if desired, the apparatus is calibrated with samples of known composition and/or compared with analyses of like samples by standard methods of analysis.
In the light of modern instrumentation for electronic data processing, the foregoing method can be considered as comprising generating a first signal proportional to the TC and a second signal proportional to the TOD of an influent stream of a process and combining said first and second signals to generate a third signal proportional to a ratio of said first and second signals. Similar first, second and third signals are generated from a sample of the effluent stream from said process and the third signals from the influent and effluent streams are combined to generate a signal having a value which serves as an index of the degree of oxidation occurring in said process. Conventional electronic equipment is available for storing, reproducing and combining the above signals and for producing a read-out of the resultant index value either in numerical or graphical form.