Radiant energy – Ionic separation or analysis – With sample supply means
Reexamination Certificate
2000-10-26
2003-06-03
Anderson, Bruce (Department: 2881)
Radiant energy
Ionic separation or analysis
With sample supply means
C250S287000, C250S282000
Reexamination Certificate
active
06573493
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and an apparatus for laser analysis of dioxins, adapted to analyze dioxins, which are contained in a gas such as an exhaust gas or water such as waste water, in real time. More specifically, the invention relates to a dioxins analyzer for directly analyzing dioxins in an exhaust gas, which is discharged from an incinerator, a thermal decomposition furnace, or a melting furnace, such as a municipal solid waste incinerator, an industrial waste incinerator, or a sludge incinerator, in real time without a time delay; a combustion control system for controlling combustion in the furnace based on the results of analysis by the analyzer; and a dioxins analysis method and a dioxins analyzer for measuring the concentration of a hazardous substance such as an organohalogen compound in seepage water from a dumping site or industrial waste water, and a waste water treatment system using the analysis method or analyzer.
2. Description of the Related Art
Dioxin has high toxicity in a tiny amount, and development of a high sensitivity method for its analysis is desired. Thus, the application of a laser analysis method capable of high sensitivity analysis has been worked out. In recent years, a proposal has been made that a combination of supersonic jet spectroscopy and resonance enhanced multiphoton ionization can measure the spectra of chlorine substituted compounds which belong to dioxins (C. Weickhardt, R. Zimmermann, U. Bosel, E. W. Schlag, Papid Commun, Mass Spectron, 7, 198(1993)).
However, the above proposal concerns a method for analyzing a gas, which ejects a gas sample as a jet in a vacuum and cools it instantaneously to a temperature close to absolute zero point, thereby simplifying its spectrum. The detection limit of this method for dioxin and its derivatives (hereinafter referred to as “dioxins”) is about ppb, and 5- to 6-digit concentration of the sample is necessary for the actual analysis of dioxin. As noted from this, the method takes a great deal of time and effort for detection.
The conventional manual analysis takes 1 to 2 months until the results of analysis are obtained. Thus, it is difficult to measure dioxins generated in the incinerator daily, and control combustion, as necessary, to perform an operation always fulfilling the proper regulatory value.
Furthermore, the above-mentioned method for analysis of dioxins uses laser light of a pulse width of the order of nanoseconds (10
−9
second) for selective ionization. As the number of the chlorine atoms increases, intersystem crossing into a triplet system occurs because of a so-called heavy atom effect, shortening the life of excitation. Consequently, no ion signals are observed.
A method for detecting sample molecules, which comprises irradiating sample molecules with laser light to ionize them selectively, was proposed (see Japanese Unexamined Patent Publication No. 222181/1996) . When the sample molecules are selectively ionized, only the targeted sample can be detected, and the current homologues of dioxins in the exhaust gas cannot be analyzed in real time. Moreover, nanosecond laser light with a satisfactory detection sensitivity is used in selective ionization. In this case, however, real-time analysis of dioxins is impossible, as stated earlier. According to the proposed method, only one particular isomer can be measured. When measuring other substances, wavelength scanning is necessary. In making measurements while scanning wavelengths, adjustment for varying wavelengths needs to be made for each measurement. The adjustment takes so much time that homologues of dioxins in the exhaust gas cannot be analyzed in real time. According to the proposal, moreover, selective ionization may result in the failure to show detection peaks, if the wavelength varies only by several picometers (pm). Thus, constant correction of wavelength is necessary. In detecting dioxins at a location adjacent to the incinerator in actual operation, extensive damping means is needed for preventing vibrations, and measurement of dioxins is interrupted at each wavelength correction.
It has also been proposed to estimate the concentration of dioxins by measuring the concentration of CO, and control combustion in an incinerator or the like based on the estimates. When the CO concentration is as high as 100 ppm, there confirms to be a correlation between the CO concentration and the dioxins concentration. As shown in
FIG. 14
, however, no correlation holds between the dioxins concentration and the CO concentration in a region in which the CO concentration is as low as 50 ppm or less. Thus, measurement of the CO concentration alone is not sufficient for effective control of combustion which can prevent the occurrence of dioxins. Recent years have seen the establishment of combustion control at low CO concentrations. Consequently, there is a demand for reliable prevention of dioxins occurrence by direct instantaneous measurement of dioxins.
Decomposition products of dioxins, such as chlorobenzene (CB) and dichlorobenzene (DCB), have been considered to be correlated to dioxins in terms of concentration. The measurement of these decomposition products or dioxins precursors is not direct measurement of dioxins, and cannot lead to strict evaluation of the state in the incinerator. Thus, real-time analysis of the exhaust gas is demanded, and the utilization of the results of analysis for combustion control is desired. In detail, it has been impossible to evaluate whether decreases in the decomposition products of dioxins mean that the occurrence of dioxins has been suppressed, or the decomposition of dioxins has been suppressed, although dioxins are occurring.
In measuring a substance whose concentration correlates to the concentration of dioxins, one particular substance is measured in selective ionization, as described previously. If dioxins cannot be detected, despite their actual occurrence, because of other factors, such as displacement of the optical axis of laser light and clogging of sampling piping, the concentration of dioxins cannot be measured properly. To dissolve this drawback, it is necessary to provide two measuring devices and conduct analysis while monitoring the data obtained. In this case, an extensive analyzer is required.
Conventionally, soil water, such as seepage water from a dumping site or industrial waste water, is placed in an adjustment tank, where its amount and pH are adjusted. Then, the adjusted soil water is rid of organic matter and nitrogen components in a bioremediation tank, and coagulated with the addition of a coagulant in a coagulation-sedimentation tank to separate heavy metals and suspended solids (SS). Then, the supernatant is subjected to accelerated oxidation to decompose difficultly decomposable organic substances contained therein, including dioxins. Then, the oxidized liquid is passed through a sand filtration tower and an activated carbon adsorption tower, and then discharged as treated water. A proposal for purification of water containing dioxins, the difficultly decomposable organic substances, is a method which comprises adding hydrogen peroxide to water containing organochlorine compounds, and applying ultraviolet radiation to decompose the compounds. A method for decomposing dioxins by introducing ozone instead of irradiation with ultraviolet radiation has also been proposed.
According to the conventional methods, analysis of dioxins has been carried out, with concentration from waste water being repeated with the use of an organic solvent. Usually, a long time of more than 70 hours has been taken, making rapid measurement difficult. To decrease the dioxins concentration in the waste water, application of ultraviolet rays or injection of much ozone, as described above, has been performed. Measurement responsive to the concentration of dioxins in waste water is still difficult, and decomposition of the dioxins in the presence of an excess of ultraviolet radiation or ozone is common practice. Thus, a dem
Futami Hiroshi
Takatsudo Yasuhiro
Anderson Bruce
Birch Stewart Kolasch & Birch, LLP.
Mitsubishi Heavy Industries Ltd.
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