U.S. patent application number 10/119844 was filed with the patent office on 2002-08-15 for chemical monitoring method and apparatus, and incinerator.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Hashimoto, Yuichiro, Kato, Yoshiaki, Mizumoto, Mamoru, Sakairi, Minoru, Suga, Masao, Tokita, Jiro.
Application Number | 20020110490 10/119844 |
Document ID | / |
Family ID | 18268775 |
Filed Date | 2002-08-15 |
United States Patent
Application |
20020110490 |
Kind Code |
A1 |
Sakairi, Minoru ; et
al. |
August 15, 2002 |
Chemical monitoring method and apparatus, and incinerator
Abstract
There was previously no monitoring method and monitoring
apparatus which could measure dioxins at ppt levels and dioxin
precursors at ppb levels with high sensitivity. According to this
invention, organic and inorganic compounds containing highly
electronegative elements are selectively ionized by atmospheric
pressure chemical ionization, the ions produced are detected by a
mass spectrometer, and their amount is measured. As a result,
interfering substances such as nitrogen, air, hydrocarbons and
carbon dioxide which are the main components of flue gas are
eliminated, and dioxins or organochlorine compounds such as dioxin
precursors can be selectively monitored.
Inventors: |
Sakairi, Minoru;
(Tokorozawa, JP) ; Kato, Yoshiaki; (Mito, JP)
; Mizumoto, Mamoru; (Hitachinaka, JP) ; Hashimoto,
Yuichiro; (Kokubunji, JP) ; Tokita, Jiro;
(Sagamihara, JP) ; Suga, Masao; (Hachioji,
JP) |
Correspondence
Address: |
MATTINGLY, STANGER & MALUR, P.C.
1800 DIAGONAL ROAD
SUITE 370
ALEXANDRIA
VA
22314
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
18268775 |
Appl. No.: |
10/119844 |
Filed: |
April 11, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10119844 |
Apr 11, 2002 |
|
|
|
09447577 |
Nov 23, 1999 |
|
|
|
Current U.S.
Class: |
422/68.1 |
Current CPC
Class: |
H01J 49/00 20130101;
Y10T 436/24 20150115; G01N 1/2258 20130101; G01N 33/0049 20130101;
Y10T 436/19 20150115; G01N 33/0047 20130101; Y10T 436/196666
20150115; G01N 33/0014 20130101 |
Class at
Publication: |
422/68.1 |
International
Class: |
G01N 033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 1998 |
JP |
10-333680 |
Claims
What is claimed is:
1. A monitoring apparatus comprising: a gas sampling unit for
sampling flue gas or atmospheric air; an ion source for ionizing
components present in very small amounts in said flue gas or
atmospheric air under atmospheric pressure or a pressure based
thereon; a mass analyzing unit, provided in a region evacuated to a
pressure lower than atmospheric, for mass analysis of ions
generated by said ion source and measuring their ion current
signals; and a data processor for processing the measured signals;
wherein at least one of dioxins, chlorobenzenes and chlorophenols
in said flue gas or atmospheric air is monitored.
2. A monitoring apparatus according to claim 1, wherein said ion
source is an atmospheric pressure chemical ion source operating in
a negative ion mode.
3. A monitoring apparatus according to claim 2, wherein said
analyzing part is an ion trap mass analyzing part.
4. A monitoring apparatus according to claim 3, wherein said
monitoring is performed by integrating ion currents derived from
isomers of dioxins, chlorobenzenes or chlorophenols.
5. A monitering apparatus according to claim 4, wherein said
monitored ion species of dioxins, chlorobenzenes or chlorophenols
comprises ions based on stable isotopes of the chlorine atom.
6. A monitoring apparatus according to claim 3, wherein said
monitored ion species are ions wherein a chlorine atom has been
removed from M.sup.+, (M-Cl+O) or orthoquinone ions in the case of
dioxins, M.sup.+ or (M-Cl).sup.- in the case of chlorobenzenes, and
M.sup.- or (M-H).sup.- in the case of chlorophenols.
7. A monitoring apparatus comprising: a gas sampling system for
sampling flue gas or atmospheric air; an ion source for ionizing
component present in very small amounts in said flue gas or
atmospheric air under atmospheric pressure or a pressure based
thereon; a mass analyzing part, provided in a region evacuated to a
pressure lower than atmospheric, for mass analysis of ions
generated by said ion source and measuring their ion current
signals; and a data processor for processing measured signals;
wherein at least one organic or inorganic compound containing at
least one element from Group VI or Group VII of the periodic table
such as oxygen, sulfur or halogen in the molecule of said
component, is monitored.
8. A monitoring apparatus according to claim 7, wherein said
organic compound is at least one of dioxins, chlorobenzenes or
chlorophenols.
9. A monitoring apparatus according to claim 8, wherein said
inorganic compound is at least one of nitrogen oxides (NO.sub.x),
sulfur oxides (SO.sub.x), hydrogen chloride (HCl), chlorine
(Cl.sub.2) or oxygen (O.sub.2).
10. A monitoring apparatus according to claim 9, wherein the
measurement of said inorganic compound and the measurement of said
organic compound are performed separately on a time sharing
basis.
11. An incinerator, wherein a sample gas is directly introduced to
an atmospheric pressure ion source via a pipe, and at least one
component of dioxins, chlorobenzenes or chlorophenols is monitored
by ionizing components present in very small amounts in said sample
gas and performing mass analysis.
12. A method of monitoring chemical substances comprising the steps
of: sampling a gas containing hydrocarbons; separating a sample gas
from said gas, a first introducing step for introducing said
separated sample gas to an ionizing unit; ionizing and producing
ionized substances by subjecting said introduced sample gas to a
discharge, a second introducing step for introducing said ionized
substances to an ion trap analyzing part; and detecting an ion
current of predetermined ionized substances.
13. A method of monitoring chemical substances comprising the steps
of: sampling a gas containing hydrocarbons; separating a sample gas
from said gas, a first introducing step for introducing said
separated sample gas to an ionizing unit; ionizing and producing
ionized substances by subjecting said introduced sample gas to a
discharge, a second introducing step for introducing said ionized
substances to an ion trap analyzing part; and detecting a mass of
predetermined ionized substances.
14. A method of monitoring chemical substances according to claim
12 or 13, wherein an ion trap mass spectrometer is used as said ion
trap analyzing part.
15. A method of monitoring chemical substances comprising the steps
of: sampling a gas comprising hydrocarbons; separating a sample gas
from said gas, a first introducing step for introducing said
separated sample gas to an ionizing unit; ionizing and producing
ionized substances by subjecting said introduced sample gas to a
discharge, a second introducing step for introducing said ionized
substances to an ion trap mass analyzing part; producing ion
substances wherein an atom is removed from the ionized substances
introduced in said second introducing step; and detecting an ion
current of said ion substances.
16. A method of monitoring chemical substances comprising the steps
of: sampling a gas comprising hydrocarbons; separating a sample gas
from said gas, a first introducing step for introducing said
separated sample gas to an ionizing unit; ionizing and producing
ionized substances by subjecting said introduced sample gas to a
discharge, a second introducing step for introducing said ionized
substances to an ion trap mass analyzing part; producing ion
substances wherein either an atom or molecule has been removed from
the ionized substances introduced in said second introducing step;
and detecting an ion mass of said ion substances.
17. A method of monitoring chemical substances comprising the steps
of: producing ion substances wherein a hydrogen atom has been
removed from dioxin precursors in flue gas; introducing said ion
substances to an ion trap mass spectrometer; producing negative
ions wherein a chlorine atom of the dioxin precursors is
selectively removed from said ionized substances; and measuring an
amount of the negative ions produced.
18. A monitoring apparatus comprising: a sampling pipe having a
sampling port for sampling a gas; a first filter for removing
impurities from said sampled gas; an ionizer for ionizing sample
gas which has passed through said filter by a discharge; a second
filter for removing microparticles from ionized substances; a mass
spectrometer which dissociates a chlorine atom from the ionized
substances which have passed through said second filter; and an
ion/charge converter for measuring the current of the remaining
ions.
19. An incinerator comprising: a garbage hopper; a furnace for
burning said garbage; a gas supply nozzle for supplying gas to the
interior of said furnace; a boiler for recovering heat from said
incinerator; a flue for discharging flue gas which has passed
through said boiler; a sampling port for sampling flue gas from
either or both of said gas supply nozzle or said boiler; an ion
source for ionizing gas from said sampling port by a discharge; a
measuring device for measuring a predetermined target substance
contained in said flue gas from the ionized substance from said ion
source; and a controller for controlling the temperature of said
incinerator by the measured results.
20. An incinerator comprising: a garbage hopper; a furnace for
burning said garbage; a gas supply nozzle for supplying gas to the
interior of said furnace; a boiler for recovering heat from said
incinerator and a flue for discharging flue gas which has passed
through said boiler; a sampling port for sampling flue gas from
either or both of said gas supply nozzle or said boiler; an ion
source for ionizing gas from said sampling port by a discharge; a
measuring apparatus for measuring a predetermined target substance
contained in said flue gas from the ionized substance from said ion
source; and a display device for displaying flue gas sampling
points of said incinerator, displaying measured results at said
sampling points, and outputting an alarm when said results exceed
predetermined values.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a monitoring apparatus which
measures the concentration of dioxins and related compounds such as
dioxin precursors in flue gas or the atmosphere by detecting
dioxins and related compounds present in combustion gases from
incineration of domestic waste and industrial waste, gases from
metal refineries, automobile exhaust or the atmosphere. It relates
also to a combustion controller which efficiently employs the
results of monitoring in combustion.
[0002] When waste is incinerated in a garbage incineration plant,
highly toxic dioxins are produced in the flue gas. This gives rise
to environmental pollution and is a serious social problem.
[0003] Dioxins are toxic to humans in various ways. Not only do
they have acute toxicity, but they are also carcinogenic and
teratogenic, and recently, it has been shown that they act as
"environmental hormones", false hormones which disturb the internal
secretions of the body. Dioxins are also known to be discharged in
waste gases from metal refining, exhaust from automobiles, or lye
from bleaching processes.
[0004] The term "dioxins" is a general term referring to 75 isomers
of polychlorinated dibenzene paradioxin (PCDDs) and 135 isomers of
polychlorinated dibenzofuran (PCDFs), and in the wider sense
includes polybisphenyl chlorides (Coplanar PCBs). Hereafter, dioxin
and related compounds will be referred to simply by the general
term "dioxins".
[0005] Although a great deal is known about the mechanisms by which
dioxins are produced ("Bunseki", 1998, pp. 512-519), the conditions
under which this occurs vary widely depending on location and
mechanism, and are very complex. One of the leading factors is
considered to be reaction between carbon and chlorine (de novo or
new product synthesis) due to metal chlorides of cobalt, iron and
copper which are present in the ash of combustion processes under
the high temperature of incineration plants, and which act as
catalysts. In the basic reaction of this de novo synthesis, when
carbon atoms, chlorine atoms and oxygen atoms are present together
at high temperature, they produce many organochlorine compounds
such as dioxins, chlorobenzene and chlorophenol by radical
reactions. It is said that this chlorobenzene and chlorophenol are
themselves precursors of, and give rise to, dioxins. Formation of
dioxins in a waste incineration plant is said to mainly occur in
two places, i.e., a process which takes place during incomplete
combustion in an incinerator when the incineration temperature is
less than 800.degree. C., and in a de novo synthesis in a boiler or
dust filter at a temperature of 250.degree. C. to 550.degree.
C.
[0006] Various policies have been devised to reduce the formation
of highly toxic dioxins in an incinerator plant as much as
possible. To inhibit dioxin emission into the environment,
techniques have been devised to improve incineration conditions and
remove dioxin efficiently. However, much time and effort were
needed to develop this inhibition technology. Specifically, garbage
was incinerated under certain conditions, the concentration of
dioxins in flue gas or ash under these conditions was determined, a
correlation between combustion conditions and dioxin amount was
found, and optimum incinerator conditions or dioxin removal
conditions were then found from this correlation.
[0007] To make an accurate measurement of dioxin concentration,
reference must be made to the regulatory law concerning the assay
of dioxins. Generally, quantitative analysis of dioxins is carried
out by the technique shown on pp. 441-444 of Pharmacia Vol. 34, No.
5 (1998). This is done by complex pre-processing to separate only
desired components from a sample taken from an incinerator under
fixed conditions, and performing qualitative and quantitative
analysis using a costly, large-scale high resolution mass analyzing
device (having a mass resolution of 10000 or more) installed in
special equipment which does not release dioxins outside the
system.
[0008] At the same time, many observation monitors are installed in
various parts of an incinerator such as a garbage incinerator to
control its operation while it is running. These include monitors
for monitoring the temperature of various parts of the incinerator,
an oxygen concentration monitor, a carbon monoxide monitor, a
nitrogen oxide (NO.sub.x) monitor, a sulfur oxide (SO.sub.x)
monitor, etc. These monitors are used for monitoring and
controlling combustion, but they may also be used indirectly as
monitors for reducing dioxins as stated on pp. 89-92 of Waste
Incineration Technology (Ohm Co., 1995). Specifically, oxygen
monitors, carbon monoxide monitors and temperature monitors are
observed so that flue gases are completely burnt, and formation of
dioxins is inhibited as far as possible.
[0009] To monitor the operation of an incinerator, an alternative
method has been proposed wherein, instead of attempting to measure
the concentration of dioxins directly which may be present in only
very low concentrations, another substance present in relatively
high concentration is measured, and the concentration of dioxins is
estimated from the result. Examples of this technique and devices
employing it are given in Yokohama National University
Environmental Research Abstracts (Vol. 18, 1992), Japanese Patent
Laid-Open No. Hei 4-161849, Japanese Patent Laid-Open No. Hei
5-312796, Japanese Patent Laid-Open No. Hei 7-55731, Japanese
Patent Laid-Open No. Hei 9-015229, and Japanese Patent Laid-Open
No. Hei 9-243601.
[0010] In the technique disclosed by Yokohama National University
Research Abstracts (Vol. 18, 1992), Japanese Patent Laid-Open No.
Hei 4-161849, and Japanese Patent Laid-Open No. Hei 5-312796,
chlorobenzenes are measured by gas chromatography (GC), and are
used as indicator for dioxins. The dioxins are estimated from the
correlation between the two.
[0011] In the technique shown in Japanese Patent Laid-Open No. Hei
7-155731, dioxins in combustion ash are thermally decomposed by
heat treatment of the ash, and dioxins are thereby inhibited.
Chlorobenzenes or chlorophenols present in the ash before and after
heating are analyzed, and a dioxin elimination factor is estimated.
In this way, thermal decomposition conditions can be optimized.
[0012] In the technique shown in Japanese Patent Laid-Open No. Hei
9-015229, the concentrations of chlorobenzene and chlorophenol in
flue gas are measured, and the dioxin concentration is found from
this together with a dust concentration and flue gas retention time
which are measured separately.
[0013] In the technique shown in Japanese Patent Laid-Open No.
9-243601, chlorobenzenes and chlorophenols in flue gas are measured
in real time, and the dioxin concentration is measured
continuously. The concentrations of chlorobenzenes and
chlorophenols are found by leading flue gas into a laser ionization
mass spectrometer, ionizing the gas and performing a mass analysis.
As a result, the dioxin concentration is found indirectly.
[0014] It was hoped that the formation of dioxins and their
emission from garbage incineration plants would be reduced by these
attempts to improve combustion conditions or use of eliminating
techniques. However, it is necessary to measure, in real time, how
much dioxin has actually been reduced by adoption of these
curtailment policies. From this viewpoint, the following problems
are inherent in the conventional methods mentioned above.
[0015] Although precise analytical results for dioxins, including
types of isomers and their amount, can be obtained from the
mandatory methods for its assay, the analysis itself is extremely
complex. In addition, special equipment to avoid releasing dioxins
outside the system and a costly, bulky, high resolution magnetic
mass spectrometer are necessary, and skilled measurement techniques
are required. Consequently, the analysis of dioxins cannot be
conducted in the incineration plant "on site", which meant that ash
samples or gas samples had to be sent to an analysis center, the
analysis took almost a week, and the cost involved per sample was
of the order of several hundred thousand yen.
[0016] There is very little correlation between the numerical
values obtained by observation monitors currently employed to
control the operation of garbage incinerators, such as oxygen
monitors, carbon monoxide monitors, temperature monitors, nitrogen
oxide (NO.sub.x) monitors and sulfur oxide (SO.sub.x) monitors, and
the concentration of dioxins. Therefore, it was impossible to know
whether or not emission of dioxins was being suppressed, or how
much dioxins were being discharged, while an incinerator was
operating. Hence, from these indirect monitors, even an estimate of
dioxin concentration could not be obtained.
[0017] In the techniques indicated by Yokohama National University
Environmental Research Abstracts (Vol. 18, 1992), Japanese Patent
Laid-Open No. Hei 4-161849 and Japanese Patent Laid-Open No. Hei
5-312796, a minimum of 30 minutes to 1 hour is needed for
measurement apart from trapping and concentration time. Moreover,
it was difficult to selectively detect chlorobenzenes in the
organic compounds which are present in large quantities in flue
gas, and there was also a possibility of erroneous measurements due
to interfering substances.
[0018] In the technique disclosed by Japanese Patent Laid-Open No.
Hei 7-155731, specific techniques such as for as on-line sample
introduction and automatic measurement are not described, and the
measurement itself relied on conventional methods such as GC which
required about 20 or 30 minutes per sample apart from the
extraction operation.
[0019] In the technique disclosed by Japanese Patent Laid-Open No.
Hei 9-015229, a clear basis is not given for the relation between
dioxins, chlorophenols and chlorobenzenes which is assumed in the
invention, and the determination of chlorobenzenes and
chlorophenols was performed by the conventional methods which take
time such as gas chromatography.
[0020] The technique shown in Japanese Patent Laid-Open No. Hei
9-243601 discloses the possibility of real-time concentration
measurement of chlorobenzenes, but in this multiphoton ionization,
there is said to be a decrease of sensitivity of from {fraction
(1/7)} to {fraction (1/10)} for each additional chlorine atom
substituted in the benzene nucleus. Trichlorobenzene is ionized
with an efficiency of only about {fraction (1/100)} of that of
monochlorobenzene, i.e., it can be said that the sensitivity to
trichlorobenzene is only {fraction (1/100)} that of
monochlorobenzene. 2, 3, 7, 8 tetrachlorodibenzene-p-dioxin (2, 3,
7, 8-TCDD), which is known to be the most toxic dioxin, is a dioxin
wherein four hydrogens at positions 2, 3, 7 and 8 are replaced by
chlorine. Moreover, all other toxic dioxins are compounds
substituted by four or more chlorine atoms. If this highly toxic
dioxin is synthesized from chlorobenzenes and chlorophenols, a
chlorobenzene or chlorophenol with two, three or more chlorine
atoms must be the precursor material. However, in the multiphoton
ionization described in this publication, it is difficult to
efficiently ionize polysubstituted chlorine compounds. In other
words, it was extremely difficult to measure organochlorine
compounds such as chlorophenols at a concentration of 1000
ng/Nm.sup.3 which are said to be present in incinerator flue
gas.
SUMMARY OF THE INVENTION
[0021] In order to solve the above-mentioned problems, this
invention provides a monitor equipped with a sampling system for
sampling flue gas and the atmosphere, an ion source for ionizing
trace compounds in the sample gas at atmospheric pressure or a
pressure close to atmospheric pressure, a mass analyzing part for
mass analysis of ions produced by this ion source and measuring its
ion current, and a data processor for processing measured signals.
As ions can be detected rapidly by mass analysis, monitoring can be
performed in real-time.
[0022] In this monitor, the tendency of dioxins, chlorobenzenes and
chlorophenols to form negative ions is fully exploited. First,
sample gas containing hydrocarbon molecules from the incinerator is
led to the ion source using a pipe which is heated to prevent
adhesion. In this ion source, trace compounds in the sample gas are
selectively ionized by a negative corona discharge under a
predetermined pressure to form negative ions. These negative ions
are analyzed by mass spectrometry, then a qualitative determination
of the sample gas is performed from the mass numbers of the
observed ions and a quantitative determination of the sample gas is
performed from the ion amount. In atmospheric pressure chemical
ionization, unlike the conventional laser ion method, the ionizing
efficiency does not depend much on the number of chlorine atoms, so
dioxins, or dioxin precursors (chlorobenzenes or chlorophenols)
with different numbers of chlorine atoms can be detected with high
sensitivity. This means that components such as dioxins or dioxin
precursors can be monitored. Further, a negative ion is formed by
deprotonation from the dioxin precursors in flue gas. This negative
ion is introduced to a three-dimensional quadruple mass
spectrometer to form a negative ion wherefrom one chlorine atom has
been eliminated. The method makes it possible to predict the dioxin
generation amount by selectively performing mass analysis on
particular decomposition products from dioxin precursors in the
negative ions which are produced.
[0023] Therefore, dioxins or dioxin precursors present at low
concentrations in flue gas can be detected with high sensitivity
and rapidity using an ion trap mass spectrometer which traps the
ions using a high frequency electric field, and then performs mass
analysis.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a diagram showing the construction of a flue,
monitor and combustion controller.
[0025] FIG. 2 is a diagram showing the construction of the flue and
monitor.
[0026] FIGS. 3A, 3B are diagrams showing the construction of a
filter.
[0027] FIG. 4 is a diagram showing the external appearance of the
monitor.
[0028] FIG. 5 is a diagram showing a typical construction of the
monitor interior.
[0029] FIG. 6 is a diagram showing another construction of the
monitor interior.
[0030] FIG. 7 is a diagram showing a typical construction of an ion
source.
[0031] FIG. 8 is a diagram showing another construction of the ion
source.
[0032] FIG. 9 is a diagram showing yet another construction of the
ion source.
[0033] FIG. 10 is a diagram showing a corona discharge ion
generation process.
[0034] FIG. 11 is a diagram showing the construction of an ion trap
mass analyzing part.
[0035] FIG. 12 is a diagram describing the construction of the ion
trap mass analyzing part.
[0036] FIGS. 13A, 13B are diagrams showing an ion generation
process.
[0037] FIGS. 14A, 14B are diagrams showing constructions of a dust
filter.
[0038] FIG. 15 is a diagram showing monitor observation points.
[0039] FIG. 16 is a diagram showing a typical arrangement of the
monitor.
[0040] FIG. 17 is a diagram showing another arrangement of the
monitor.
[0041] FIG. 18 and FIG. 19 are diagrams showing other arrangements
of the monitor.
[0042] FIG. 20 is a diagram showing a relation between gas
temperature and ion intensity in an atmospheric pressure ion
source.
[0043] FIG. 21 is a diagram showing a relation between gas
temperature and ion current in the atmospheric pressure ion
source.
[0044] FIG. 22 is a diagram showing a relation between pressure and
ion intensity in the atmospheric pressure ion source.
[0045] FIG. 23 is a diagram showing a relation between pressure and
ion current in the atmospheric pressure ion source.
[0046] FIG. 24 is a diagram showing a typical mass spectrum.
[0047] FIG. 25 is a diagram showing a typical mass spectrum of a
chlorobenzene.
[0048] FIG. 26 is a diagram showing a typical mass spectrum of a
dioxin.
[0049] FIG. 27 is a diagram showing an example of detection of
chlorophenols.
[0050] FIG. 28 is a diagram showing an example of measurement of a
sensitivity curve.
[0051] FIG. 29 is a diagram showing an example of measurement of a
calibration line.
[0052] FIG. 30 is a diagram showing the main components of flue
gas.
[0053] FIGS. 31A, 31B and 31C are respectively diagrams showing
detected ions.
[0054] FIG. 32 is a diagram showing an example of the operation of
a monitor.
[0055] FIG. 33 is a diagram showing an example of a measurement
sequence for dioxins.
[0056] FIG. 34 is a flowchart of a typical measurement
sequence.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0057] (Embodiment 1)
[0058] FIG. 1 is a diagram showing the construction of a monitoring
system according to one embodiment of this application. This system
basically comprises a gas sampling unit 88 (inside the dotted line
in FIG. 1) for sampling gas from a flue 1 which is to be measured,
a monitor 11 for detecting substances to be measured in the sample
gas, and a combustion controller 15 for utilizing the detection
results in combustion control.
[0059] The sampling unit 88 comprises a gas sampling probe 3,
sample gas pipe 4, change-over valve 6, filter 7, gas blow pump 8,
waste gas pipe 5, and waste gas probe 2. As a whole, the sample gas
introduction system has the function of sending sample gas to the
monitor regularly without loss of substances to be measured due to
adhesion and condensation, and at a fixed flowrate. For this
purpose, although not illustrated, the whole of the sampling unit
88 is heated to from 100 degrees C. to about 300 degrees C. by a
wire heater. This heating temperature varies with the substances to
be measured. To keep the sampling unit warm, it is effective to
surround the sample gas pipe 4, for example, with an insulating
material. In the monitor 11, the substances to be measured are
detected (monitored) by selectively and efficiently ionizing these
substances in the sample gas introduced, and performing mass
analysis of the ions produced in the mass analysis part.
[0060] The detected signal is sent to the data processing part
where it is converted to a concentration from a calibration curve,
and output to a CRT or printer as data. It is also sent to the
combustion controller 15 as data for combustion control of the
incineration plant via signal and control lines 14. Further, an
instrument part 13 is provided comprising observation monitors such
as an oxygen monitor, carbon monoxide monitor, temperature monitor,
nitrogen oxide (NO.sub.x) monitor, sulfur oxide (SOx) monitor and
hydrogen chloride monitor, and combustion is controlled by the
monitor 11 in view of the results obtained.
[0061] In FIGS. 2 and 3A, 3B, the gas sampling part 88 and monitor
11 are shown enlarged. When gas is sampled, the gas sampling probe
3 which has a sampling port 89 upstream of the flow of flue gas is
inserted in the flue 1. A change-over valve 6 is provided after the
gas sampling probe 3 to control the introduction of sample gas to
the monitor 11. The sample gas pipe 4 is used to transport the
sample gas, and this is heated to from 100 degrees C. to about 300
degrees C. by a wire heater, not shown, to prevent adsorption and
condensation of the substances to be measured on the pipe wall.
Temperature unevenness can be reduced by winding a heat insulating
material around the whole piping. The bore of the sample gas pipe 4
depends on the flowrate of sample gas to be passed through it, but
it is of the order of 1 mm to 100 mm.
[0062] The sample gas is introduced to the filter 7 where solid
impurities and ash in the sample gas are removed. FIG. 3 shows an
enlargement of the filter 7. The diagram shows a case where two
kinds of filter, i.e., a dust filter 20 and metal filter 23, are
provided midway along the sample gas pipe 4. In FIG. 3A, the dust
filter 20a comprises a dust filter inlet pipe 21, a dust filter
outlet pipe 22 and silica wool 19a packed in the dust filter. The
tip of the dust filter inlet pipe 21 is led close to the base of
the dust filter so that the sample gas is bound to come in contact
with the silica wool 19a packed therein by the time the gas leaves
the dust filter outlet pipe 22. The silica wool 19a is gradually
contaminated by the gas, and is replaced when necessary. Also, a
dust filter 20b filled with silica wool 19b may be arranged
horizontally as in FIG. 3B, and if the construction is such that
the interior may be observed, the state of contamination can be
easily determined and the time when the silica wool should be
replaced can be known.
[0063] To reduce adsorption of sample gas by the silica wool 19 in
the dust filter 20 which does not easily transmit temperature, the
wall surface temperature of the dust filter 20 must be raised above
the temperature of the sample gas pipe 4. For example, when
measuring dioxin precursors such as chlorobenzenes and
chlorophenols, and the sample gas pipe 4 is at about 120 degrees
C., it is effective to increase the temperature of the dust filter
20 to about 180 to 200 degrees C. Many solid impurities, ash, etc.
can be removed by the dust filter 20, but if a metal filter 23 is
provided thereafter, influx of still finer dust to the monitor 11
can be prevented. The size of the dust removed may be controlled by
the mesh of the metal filter, and is often of the order of several
micrometers. This part is also replaceable. Depending on the amount
of solid impurities or ash at the gas sampling points, two or three
of these filters may be combined. In such a case, prolonged
monitoring is possible if the mesh of the filters is arranged to be
progressively finer from upstream to downstream of the gas sampling
points in the pipe. To prevent corrosion by flue gas, it is
desirable that pipes and valves are made from stainless steel or
titanium which do not easily corrode. To prevent components present
in very small amounts from adsorbing to the wall surface of the
piping, it is desirable to use a polytetrachloroethylene lined pipe
or a glass lined pipe. Instead of a glass lined pipe, piping may be
packed with glass tubes or quartz tubes cut to short lengths. A
wide bore fused silica column used as a gas chromatography (GC)
column may also be employed.
[0064] It is convenient if the aforesaid sample gas preprocessing
part is provided with plural lines which can be changed over. That
is, when one of the dust filters 20 is clogged with ash, etc., the
line can be changed over to another of the filters 20, and the
filter clogged with ash cleaned while measurements are
continued.
[0065] Sample gas is introduced into the monitor 11 by the gas blow
pump 8. The flowrate of sample gas introduced depends on the bore
and length of the sample gas pipe, and the blowing speed of the
pump 8, but it is of the order of 1-300 liter/minute. A mechanical
pump such as a diaphragm pump may be used for the pump 8, but it is
important to be able to heat the parts in contact with sample gas
to some extent to prevent adsorption of the sample in the pump
parts. Dioxin and its related compounds exist in flue gas only in
minute amounts. These compounds are easily adsorbed to the wall
surface of sampling systems such as pipes and filters, etc. To
prevent this adsorption as much as possible, therefore, the whole
sampling system is heated as mentioned above, or pipes are made of
materials with low adsorption. Adsorption can be reduced if the
amount of flue gas flowing in the piping is increased. That is, the
residence time of flue gas in the piping is shortened as much as
possible.
[0066] Moreover, when there is a difference in the sample gas
amount flowing through the pipe 4 and an optimum sample gas amount
which should flow into the monitor 11, a branch valve 9 may be
formed as shown in FIG. 1 to control the gas amount flowing into
the monitor 11.
[0067] Next, the sample gas is introduced into the monitor 11.
[0068] FIG. 4 and FIG. 5 respectively show the external appearance
of the monitor 11 and the detail of the interior of the monitor 11.
In order to install the analysis mainframe of the monitor 11
outdoors near the flue, it is placed in a well-sealed monitor rack
90 whereof temperature control is performed to some extent
(approximately 10 to 50 degrees C.). The monitor rack 90 is fixed
by a monitor support 28. An atmospheric pressure chemical
ionization ion source housing 26 for ionizing the sample gas is
installed in such a way that it can be easily dismantled to
facilitate periodic cleaning of the ion source. Also, as will be
described later, it is preferable to place a vacuum pump 12 which
radiates a large amount of heat outside the monitor rack 90, as
shown in FIG. 4. As mentioned above, the filter 7 is installed
midway along the sample gas pipe 4, but in view of fine dust which
has passed through it flowing into the interior of the mass
analysis part, it is preferable to provide a dust filter housing 27
in a vacuum tank. The data measured by the monitor 11 are
transmitted to the combustion controller 15 via the signal and
control line 14.
[0069] An arrangement may be made so that the results on the CRT or
printer may also be observed on the monitor 11 via an observation
window 18 of the monitor. Also, by providing a standard sample
generator 10, periodic inspection of monitor performance can be
made via a standard sample change-over valve 24 and a standard
sample pipe 25. That is, a standard gas is periodically introduced
instead of flue gas, and it is confirmed whether or not ions from
the standard gas are observed to be equal to or greater than a
fixed amount. If the ion intensity observed is below the fixed
amount, maintenance is performed.
[0070] The sample gas is then sent to a atmospheric pressure
chemical ionization ion source 30 shown in FIG. 5. FIG. 7 shows an
enlargement of the ion source 30. A high voltage (from about -3 kV
to -7 kV) is applied to a corona discharge needle electrode 57 in a
discharge counter electrode 58. The temperature of this area is
kept at approximately 50 to 300 degrees C. by a heater, not shown.
The distance between the corona discharge needle electrode 57 and
discharge counter electrode 58 is about 1 to 10 mm. Due to the
negative corona discharge at the tip of the needle electrode as a
result of applying the high voltage, ionization of dioxins and
dioxin precursors takes place. The details of this ionization due
to the negative corona discharge may be described as follows.
Dioxins and related substances have elements with high
electronegativity in the molecule, such as a large number of
chlorine atoms, oxygen atoms, etc., (Group VI and Group VII of
Periodic Table). That is, they are organochlorine compounds. A
toxic dioxin is a dioxin having from four to eight chlorine
substitutions. These compounds easily trap low energy
thermoelectrons to become negative ions. On the other hand, there
is no ionization process wherein hydrocarbons which occur in large
quantities in flue gas trap thermoelectrons to become negative
ions. Therefore, even if hydrocarbon molecules are present in large
quantities in sample gas, they do not become negative ions.
Thermoelectrons can be produced in large quantities by corona
discharge in the atmosphere, as shown in FIG. 10, and if a negative
high voltage (approximately -3 kV to -7 kV) is applied to the
needle-like corona discharge electrode 57, a corona discharge will
start at the tip of the corona discharge electrode 57.
Specifically, primary electrons due to this corona discharge are
emitted from the tip of the corona discharge electrode 57. These
primary electrons due to corona discharge are accelerated by the
high voltage applied to the discharge electrode, and collide with
surrounding atmospheric molecules (nitrogen and oxygen) to give
rise to large numbers of secondary and tertiary electrons. These
secondary, tertiary and quartenary electrons then suffer repeated
elastic collisions with neutral molecules, so their energy
gradually decreases, and they finally attain a resonance capture
energy (2 eV or less). Consequently, the thermoelectrons which are
produced in large amounts around the corona discharge electrode 57,
are selectively captured by organochlorine compounds, such as
dioxins, chlorobenzenes and chlorophenols. Oxygen captures a
thermoelectron to form a O.sub.2.sup.- ion. This ion collides with
a dioxin or related compound, supplies a charge to an
organochlorine compound which more easily becomes a negative ion,
or reacts with an organochlorine compound to form these negative
ions. Therefore, even if oxygen is present in flue gas or the
atmosphere to a concentration of 100 ppm or more, it does not
interfere with the formation of negative ions. In an atmospheric
pressure ionization process, water forms an OH.sup.- ion. This
OH.sup.- ion collides with a dioxin or an organochlorine compound,
and the negative charge is transferred to the dioxin or
organochlorine compound, or withdraws a proton (H.sup.+) from a
neutral molecule to form a negative ion. Hence, there is a
considerable advantage in using a negative corona discharge for
ionizing organochlorine compounds, such as dioxins, chlorobenzenes
and chlorophenols.
[0071] Water molecules which are present in large amounts in flue
gas collide with the negative ions produced, and plural water
molecules bond with the negative ions to form cluster ions. If the
mass of a naked ion is M, and if the number of added water
molecules is n, the mass of this cluster ion will be (M+18 n). 18
is the molecular weight of water. The formation of cluster ions not
only interferes with the analysis, but makes a high sensitivity
measurement impossible. The formation of these cluster ions is
promoted by cooling the molecules or ions, therefore an effective
means of suppressing cluster ions is to maintain the ion source 30
at from about 50 to 500 degrees C., and preferably in the range of
from about 100 to 300 degrees C. Heating may be performed by
providing a heater to each part, or by providing a sample gas
heater unit 62 and heating the sample gas directly by a heater 63
comprising multiple coils of metal wire wound therein, as shown in
FIG. 9. The importance of this may also be seen from the data shown
in FIGS. 20 and 21. FIG. 20 shows the relation of the temperature
of the sample gas to the ion intensity obtained when the gas is
heated by the sample gas heater unit 62. It is seen that when the
gas temperature rises, the ion intensity rises abruptly, the
variation above 100 degrees C. being particularly remarkable. FIG.
21 shows the difference of ion intensity obtained when the
temperature of the gaseous sample is (a) 150 degrees C. and (b) 30
degrees C. It is seen that when heating is performed, the current
increases by about 2.5 times compared to the case where heating is
not performed for the same corona discharge voltage (-2.5 kV).
Current stability is also much better when heating is performed. If
the sample gas is at high temperature, for example, if it has
reached 100 degrees C. or more, the moisture in the gaseous sample
introduced will also evaporate and ionization by corona discharge
will proceed efficiently and stably.
[0072] The details of the mass analysis part, etc., will now be
described using FIGS. 5 and 7. Mass spectrometers of various kinds
can be used in analyzing the ions which are produced, but below,
the case is described where an ion accumulating type ion trap mass
spectrometer is used. The situation is the same when a quadruple
mass spectrometer which performs a mass separation using the same
high frequency electric field, and a magnetic field type mass
spectrometer using mass variance in a magnetic field, are
employed.
[0073] The negative ions produced by the corona discharge at the
tip of the corona discharge needle electrode 57 pass through a
first aperture 59 (diameter approximately 0.3 mm, length
approximately 0.5 mm) in a first flange 31 of a differential
pumping region, a second aperture 60 (diameter approximately 0.3
mm, length approximately 0.5 mm) in a second flange 32 and a third
aperture 61 (diameter approximately 0.3 mm, length approximately
0.5 mm) in a third flange 33 which are heated by a heater, not
shown. These apertures are heated by the heater to about 100 to 200
degrees C. A voltage is applied between the first aperture 59 and
second aperture 60, and between the second aperture 60 and third
aperture 61, which increases ion transmission efficiency. At the
same time, cluster ions formed by adiabatic expansion are
declustered due to collision with remaining molecules so as to
produce ions of the sample molecules. The differential pumping
region is usually evacuated by a robust pump such as a rotary pump,
scroll pump or a mechanical booster pump. A turbomolecular pump may
also be used to evacuate this area. The pressure between the second
aperture 60 and the third aperture 61 is in the range of 0.1 to 10
Torr. It is also possible to construct the differential pumping
region using two apertures, i.e., the first aperture 59 and third
aperture 61, as shown in FIG. 8. However, as the gas amount flowing
in increases as compared with the above-mentioned case, the
evacuation rate of the vacuum pump used must be increased and the
distance between the holes must be increased. In this case also, it
is important to apply a voltage between the two apertures.
[0074] After the ions so produced have passed through the third
aperture 61, they are focused by a focusing lens 34. An Einzel lens
comprising three electrodes is usually used for this focusing lens
34. The ions then pass through an electrode 35 with a slit. Due to
the focusing lens 34, the ion which have passed through the third
aperture 61 are focused on this slit. Dust which is not focused
collides with this slit part and seldom enters the mass analysis
part. After the ions have passed through the electrode 35 with the
slit, they pass through a gate valve 36, are again focused by a
double cylinder type focusing lens 91 comprising an inner
cylindrical electrode 37 and outer cylindrical electrode 38 having
a large number of openings, and are deflected by about 90 degrees
by a deflector 92 comprising deflector electrodes 40a, b, c, d (a
cylindrical electrode split into four parts) situated inside a
screening electrode 39 to eliminate the effect of external
voltages. In the double cylinder type focusing lens 91, the ions
are focused using the electric field of the outer cylindrical
electrode 38 which spreads out from the openings of the inner
cylindrical electrode 37. The reason why the ions are deflected at
about 90 degrees is so that only ions are introduced into the mass
analysis part, dust or other particles flowing into the vacuum from
the third aperture 61 being ejected straight ahead to accumulate in
a dust filter 43 in a vacuum tank. The dust filter 43 in the vacuum
chamber may be (a) a cylindrical type or (b) a 90.degree. curved
type as shown in FIGS. 14A, 14B. In the case of the curved type,
when dust accumulates at the bottom, cleaning may be easily
performed by removing the flange 71b.
[0075] After the ions which pass through the deflector 92 are
focused by a cylindrical electrode 44, they are introduced into an
ion trap mass analyzing part 93. FIG. 11 shows an enlargement of
the ion trap mass analyzing part 93 comprising a gate electrode 65,
endcap electrodes 45a, b, a ring electrode 46, collar electrodes
66a, b, insulating rings 68a, b, and an ion extracting lens 70. The
gate electrode 65 has the function of preventing ions outside from
entering the ion trap mass analyzing part 93 when ions trapped in
the mass analyzing part are removed from the system. As shown in
FIG. 12, ions introduced to the mass analyzing part 93 collide with
a buffer gas such as helium introduced into the mass analyzing part
93, and their orbit becomes small. They are then ejected from the
system, each mass number in turn, by scanning with a high frequency
voltage applied by a high frequency power supply 100 between the
endcap electrodes 45a, b and the ring electrode 46, and pass
through the ion extracting lens 70 to be detected by an ion
detector 94. The pressure in the mass analyzing part 93 when the
buffer gas is introduced is of the order of 10.sup.-3 to 10.sup.-4
Torr. The mass analyzing part 93 is controlled by a mass analyzing
part controller 51 (FIGS. 5 and 6). One of the advantages of an ion
trap mass spectrometer is that it has the ability to trap ions, and
it can therefore detect ions even at low sample concentrations if
the accumulating time is made longer. Therefore, even if the sample
concentration is low, ions can be concentrated by a high factor in
the mass analyzing part 93, and this very much simplifies sample
preprocessing, e.g. concentration.
[0076] If the magnitude of the high frequency voltage applied by
the high frequency power supply 100 between the endcap electrodes
45a, b and the ring electrodes 46 is set to a certain value while
introducing ions into the mass analyzing part 93, a cut-off (low
mass ion cutoff) of the ion mass numbers trapped between the endcap
electrodes 45a, b and the ring electrode 46 can be achieved. This
means that ions smaller than a certain mass are not trapped within
the electrodes. In the low mass number region below 100, there are
large numbers of ions derived from water, hydrogen chloride,
NO.sub.x, SO.sub.x, etc. If these ions are not trapped in the
endcap electrodes 45a, band the ring electrode 46, saturation of
ions in the electrodes can be prevented, and dioxins or
organochlorine compounds which have large mass numbers can be
efficiently trapped in the electrodes, as shown in FIGS. 31A to
31C. Further, unnecessary ions with large mass can be eliminated
from the electrode by controlling the frequency of an auxiliary
alternating voltage applied between the endcap electrodes 45a, b
from auxiliary alternating current power supplies 98a, 98b shown in
FIG. 12. In practice, a white noise auxiliary alternating current
which does not contain the resonant frequency of the ions to be
trapped by the mass analyzing part 93 is applied to the endcap
electrodes 45a, b. The mass analyzing part 93 traps and accumulates
only ions of target mass within the electrodes. Therefore, target
molecular ions and fragment ions are efficiently accumulated and
detected. In addition to the selectivity of the atmospheric
pressure chemical ionization method, the further improvement of
selectivity and sensitivity provided by the ion trap mass
spectrometer makes it possible to detect organochlorine compounds
including dioxins.
[0077] In the detection of ions extracted from the mass analyzing
part 93, the ions are converted to electrons by a conversion dynode
48, and these electrons are detected by a scintillation counter 49,
as shown in FIGS. 5 and 6. The signal obtained is amplified by an
amplifier 50, and sent to a data processor 47.
[0078] A chamber containing the focusing lens 34, the electrode
with a slit 35, the double cylinder type focusing lens 91, the
deflector 92, the cylindrical electrode 44, the mass analyzing part
93 and the ion detector 94 as shown in FIGS. 5 and 6, is evacuated
to approximately 10.sup.-4 to 10.sup.-6 Torr (at a rate of about 50
to 200 liter/second on the side of a second differential pumping
region evacuation pipe 55 and a rate of about 50 to 150
liter/second on the side of a third differential pumping region
evacuation pipe 56) by a split flow type turbomolecular pump
52.
[0079] In this regard, it is convenient to split the vacuum chamber
after the gate valve 36 into two parts at the deflector 92, and
evacuate the chamber split into two via the second differential
pumping region evacuation pipe 55 and third differential pumping
region evacuation pipe 56 using one split flow type turbomolecular
pump 52, as shown in FIG. 5. This is convenient for the following
reasons. Firstly, the mass analyzing part 93 is not easily
contaminated by dust, etc. In addition, when the gate valve 36 is
closed, the first to third apertures 61 are set at atmospheric
pressure and the ion source 30 and differential pumping region are
cleaned, the ion trap mass analyzing part 93 can be kept under
vacuum, so the monitor 11 can be rapidly reinstated within about 1
or 2 hours after cleaning. The auxiliary vacuum pump 12 must be
provided to the turbomolecular pump 52 on the back pressure side.
This may be used in conjunction with the pump used for the
differential pumping region, in which case a valve 53 is provided
midway in a first differential pumping region evacuation pipe 54.
In this embodiment, a scroll pump with a evacuation rate of
approximately 500 liter/minute is used as the auxiliary vacuum pump
12. Further, a robust vacuum pump connected to the first
differential pumping region evacuation pipe 54 can be made separate
from the auxiliary vacuum pump 12 of the turbomolecular pump 52 via
vacuum evacuation pipes 29a, b as shown in FIG. 6. In this case, a
pump with a small evacuation rate of approximately 100 liter/minute
may be used as the auxiliary vacuum pump 12 of the turbomolecular
pump 52. In both of the cases shown in FIGS. 5 and 6, the use of
this type of arrangement simplifies the vacuum pumping system of
the atmospheric pressure chemical ionization mass spectrometer
which tends to be very complex. In the examples of FIGS. 5 and 6,
the case was shown of three stage differential pumping region, but
if the gas flowrate in the first to third apertures 61 is
suppressed, a two stage differential pumping system may also be
used.
[0080] The detected ion current is sent to the data processor 47
via the amplifier 50, and a mass spectrum is thereby obtained. An
example of the mass spectrum obtained by the atmospheric pressure
chemical ionization method of the present application is shown in
FIG. 24 (NO.sub.2.sup.-, NO.sub.3.sup.-, etc.), FIG. 25 (case of 1,
2, 3-trichlorobenzene), and FIG. 26 (case of 1, 2,
3-trichlorodibenzo-para-dioxin). These spectra show ion currents (Y
axis) corresponding to the mass numbers (X axis) of ions of
components to be monitored. In the case of 1, 2,
3-trichlorobenzene, and 1, 2, 3-trichlorodibenzo-para-dioxin,
plural isotope peaks are observed in the molecular ion part. This
is due to the stable isotopes of the chlorine atom (.sup.35C and
.sup.37C, intensity ratio being 76:24). The measurement of the mass
spectrum is usually completed in a short time of about 1 second to
several tens of seconds. Mass spectrum measurements may also be
repeated, and an average of the spectra taken to improve the S/N
ratio.
[0081] From the ion current for the mass number due to the
substance to be measured, and a relation (calibration curve)
between the amount and ion current of a standard substance prepared
beforehand, the amount of a target substance can be calculated. For
example, in the case of 2, 3-dichlorophenol (molecular weight 162,
observed ion mass number 161), a variation of ion intensity
relative to concentration in the sample gas is measured as shown in
FIG. 28, and a calibration curve shown in FIG. 29 is drawn. Based
on this, concentration data in the sample gas at that time are
estimated from the observed ion intensity. The obtained data are
processed further, the concentration of the component is stored
together with other parameters, and is output to a CRT or printer
as necessary.
[0082] Chlorobenzenes which are precursors of dioxins capture one
electron to produce a molecular ion M.sup.-. Herein, a neutral
molecule is represented by M, and a molecule which has captured an
electron to become a negative ion is represented by M.sup.-.
Chlorophenols lose one proton of a phenoxy group (--OH group) to
give the pseudomolecular ion (M-H). Dioxins give (M-C1).sup.- and
(M-C1+O).sup.- apart from the molecular ion M.sup.-, and they also
undergo fragmentation to give a 1, 2 orthoquinone type fragment
ion. If these characteristic peaks are selectively detected, a high
selectivity, high sensitivity measurement can be made.
[0083] The molecular weights and monitored ions of chlorobenzenes,
chlorophenols and dioxins are shown in FIGS. 31A to 31C. As the
natural isotopes of chlorine, 35 and 37, exist in the ratio of 3:1,
the number of chlorine atoms contained in an ion can be estimated
by observing this isotope pattern. Moreover, if plural isotope
peaks are monitored and integrated, high precision monitoring is
possible. For example, trichlorobenzene gives an isotope pattern of
27:27:9:1 to masses 180, 182, 184 and 186. If these ions are
integrated, a high S/N ratio will be obtained as compared with the
case when they are separate. In an actual measurement, all the ions
in these tables may be monitored and the dioxin concentration
estimated from their total amount, or only some of these ions may
be monitored. For example, if only the ions present in largest
amounts are monitored, simple, high sensitivity monitoring can be
performed. Alternatively, if ions with 2 to 4 chlorine
substitutions which contribute largely to the formation of dioxin
are selectively monitored, simple, high precision monitoring can be
performed.
[0084] In order to estimate the dioxin concentration from the
concentration of chlorobenzenes and chlorophenols, a correlation
between the two is used which is calculated beforehand. As the
correlation differs somewhat depending on the type and model of
incinerator, it is desirable to determine this correlation for
every incinerator where a monitor is installed.
[0085] As shown in FIGS. 1 and 2, flue gas which has passed through
the ion source 30 is passed through the waste gas pipe 5 by a waste
gas pump 95 (diaphragm pump), and is returned downstream of the gas
sampling probe 3 from the waste gas probe 2. This is so as not to
discharge noxious flue gas indoors during measurement. The gas
discharged by the vacuum pump 12 of the mass spectrometer is also
collected by a vacuum pump waste gas pipe 96 (FIG. 2), and returned
to the flue 1 together with flue gas which has passed through the
ion source 30. The sampling part 88 and ion source 30 are made
airtight to prevent leakage to the exterior, prevent entry of the
atmosphere, and prevent disturbances.
[0086] The flue gas contains water, hydrogen chloride, sulfur
oxides, high boiling components and tar, etc. in large amounts, and
if condensation, adsorption or corrosion due to these substances
has an adverse effect on measurements, it is effective to remove
them by an impinger inserted into the pipe system.
[0087] In the description given so far, when a sample gas was
introduced into the monitor 11, the gas blow pump 8 was provided
upstream. As shown in FIG. 17, the flowrate of sample gas
introduced into the ion source is determined to be from several
liters/minute to several tens of liters/minute by the blowing
capacity of the gas blow pump 8, the needle valves 79a, 79b and the
resistance of the branch pipe 80, and the pressure in the ion
source can be increased by controlling the needle valves 79a, b.
Normally, in an atmospheric pressure ion source which uses corona
discharge, excess gas which does not flow in from the holes which
take ions into the vacuum is expelled outside the ion source, so
the corona discharge area is effectively at atmospheric pressure
(approximately 760 Torr). Actually, the ionization efficiency
increases to the extent that the molecular density in the corona
discharge area is higher, and the optimum value of the pressure of
the corona discharge area is higher than the atmospheric pressure
of 760 Torr. However, if the pressure in the vicinity of the holes
which take ions into the vacuum is too high, too many molecules
will flow into the mass analysis part high vacuum through the
holes, and it is difficult to maintain the high vacuum in the mass
analysis part. FIG. 22 shows a relation between ion source pressure
and ion intensity. It is seen that in the maximum of ion intensity
occurs at a higher pressure than 760 Torr. FIG. 23 shows a
sensitivity comparison between the case when the measurement is
performed when the pressure of the corona discharge area is
increased (approximately 1.2 atmospheres), and the case when the
measurement is performed under effectively atmospheric pressure
(approximately 1 atmosphere). The sensitivity is approximately
three times higher in the former case than in the latter, showing
that it is effective to increase the pressure in the ion source 30.
To control the pressure inside the ion source, a pressure adjusting
part may also be provided before the needle valve 79a, and the
pressure of the corona discharge area of the ion source 30
controlled by this pressure adjusting part 97 while the pump 8 is
operating.
[0088] Alternatively, only a discharge pump 78 may be provided
after the monitor 11 as shown in FIG. 16 to control the flowrate of
sample gas entering the ion source 30 of the monitor 11 from
several liters/minute to several tens of liters/minute. In this
case, the flowrate is determined by the discharge rate of the pump
78, the needle valves 79a, b and the resistance of the branch pipe
80. It also possible to dispense with the branch pipe 80.
[0089] FIG. 33 shows a flowchart for the measurement of dioxins.
The gain of the detecting system is set to the highest sensitivity.
Moreover, the ion introduction time is made as long as possible
(from about several 100 msecs to several 10 secs). The ions derived
from dioxins shown in FIG. 31C are monitored one after another. It
is not necessary to monitor all the ions shown in FIG. 31C, and the
number monitored can be reduced. Ions from components having the
same number of chlorine atoms (e.g., m/z 320 and 322) are added to
realize even a small improvement of the S/N ratio. Further, the
currents of all the ions originating from dioxins are integrated
(sigmaIm) and taken as the total amount of dioxins. After one
dioxin ion monitoring cycle is complete, monitoring of dioxins is
repeated. The number of repeat measurements may be set by an
external device. Integration is performed as required starting from
one cycle to improve the S/N ratio. When measurement of dioxins is
complete, measurement of clorobenzenes begins. The sensitivity of
the detector is set to medium sensitivity, and the ion introduction
time is also set. The ions derived from chlorobenzene in FIG. 31A
are monitored one after another. The results are integrated for
monitored ions having the same number of chlorine atoms. In this
way, a component distribution for isomers of chlorobenzenes can be
calculated. All the ion amounts are also integrated (sigmaIm10) to
calculate the total amount of chlorobenzenes. After one measurement
cycle is complete, monitoring of chlorobenzenes is performed again
and the ion amount is integrated. The number of repeat measurements
may be one or more depending on the concentration. One cycle is
completed in about 1 second. When measurement of chlorobenzenes is
complete, monitoring of chlorophenols begins. For chlorophenols,
the ions shown in FIG. 31B are monitored. Monitoring is repeated as
in the case of chlorobenzenes, and the distribution of components
and total amount of chlorobenzenes are calculated. After
measurement of chlorobenzenes is complete, NO.sub.x, SO.sub.x,
hydrogen chloride and oxygen, etc., are monitored. After
measurements are complete, a comparison with previously measured
values and mass spectra is made to determine whether an abnormal
state exists. If an abnormal state exists, an alarm is output. This
monitoring is performed in an endless loop, and monitoring
conditions are changed by external devices as necessary.
[0090] Herein, measurements and embodiments were described
concerning mainly the dioxin and related compounds in flue gas
discharged from a garbage incineration plant. Measurements of
dioxins and related compounds in flue gas from a metal refining
process and the atmosphere can be made with the same equipment and
methods. This monitoring device makes it possible to directly know
how much dioxins are contained in flue gas, such as from an
incinerator, and how much fluctuation there is. It permits real
time dioxin monitoring and concentration measurement of dioxins in
many locations in an incinerator. After combustion starts in the
incinerator, the flue gas passes through a large number of
different areas at different temperatures until it is discharged
into the atmosphere from a flue, and many chemical reaction
processes occur in the flue gas before it is discharged. Using this
monitoring device, it is possible to follow dioxin formation and
decomposition in each of these complicated processes. It is of
course also possible to acquire information for changing and
optimizing process conditions aimed at cutting down dioxins.
[0091] In the above-mentioned example, the ions produced by the
negative corona discharge were introduced into the mass
spectrometer after deflection, although they may of course be
introduced into the mass analysis part without deflection.
[0092] Furthermore, although the case was described where an ion
trap mass spectrometer was used as the mass spectrometer, other
mass spectrometers, such as a quadruple mass spectrometer and a
compact magnetic field type mass spectrometer, may also be
used.
[0093] (Embodiment 2)
[0094] FIG. 30 shows the general abundance ratio of the main
components contained in flue gas from a garbage incineration plant.
The vertical axis shows abundance ratio. 1 represents 100%.
10.sup.-6 corresponds to ppm, 10.sup.-9 corresponds to ppb, and
10.sup.-12 corresponds to ppt. After oxygen, carbon dioxide and
water which are present at % levels, carbon monoxide and
hydrocarbons are present at a level of 1000 ppm. There are a large
number of components in hydrocarbons and their concentrations are
distributed over a wide range from 10 ppm to the 1 ppt level.
Hydrogen chloride (250 ppm to 1300 ppm), NO.sub.x (100 to 200 ppm)
and SO.sub.x (-100 ppm), etc., are present at a level of several
100 ppm. On the other hand, the concentration of chlorobenzenes and
chlorophenols which are said to be precursors of dioxin is of the
order of 1 ppb (1000 ng/Nm.sup.3). The concentration of dioxins is
below 10 ppt (10 ng/Nm.sup.3). Thus, to directly measure target
components such as dioxin precursors and dioxins in flue gas, high
selectivity is essential to detect only minute amounts of the
target components together with many interfering substances which
are present in large concentrations. For this reason, it is very
effective to use negative corona discharge and to use a mass
spectrometer for detection of the ions produced. There are some
cases when substances are present which are ionized by negative
corona discharge in the same way and generate ions of the same ion
mass number as the target components, and in these cases, detection
of the target components alone is very difficult with a mass
spectrometer using negative corona discharge.
[0095] However, if an ion trap mass spectrometer is used, higher
selectivity can be obtained than in an ordinary mass spectrum by
dissociating the generated ions (removing certain component
elements or groups from the ions) to convert them to ions of
different mass number. This is the MS/MS method wherein, in
addition to the high frequency voltage applied to the ring
electrode 46 and endcap electrodes 45a, b from the high frequency
power supply 100, energy is given to the trapped molecular ions
from an auxiliary alternating current voltage applied to the endcap
electrodes 45a, b from an auxiliary alternating current power
supply 98, thereby causing the molecular ions to collide with the
buffer gas (e.g., He) in the electrodes so that they dissociate. In
practice, an alternating current voltage (amplitude less than V,
applied time of the order of several tens of ms, frequency of the
order of 50 to 500 kHz) having an identical or slightly different
characteristic frequency to that of the trapped ions is applied to
the endcap electrodes 45a, b. In the case of an organochlorine
compound, ions are observed by the MS/MS method from which one or
two chlorine atoms have been eliminated. For example, in the case
of 2, 4 dichlorophenol, as shown in FIGS. 31A and 31B, the negative
ion (M-H).sup.- (M: molecule, H: hydrogen) is produced by negative
corona discharge. If this negative ion is dissociated by the MS/MS
method, a negative ion is produced from which one chlorine atom has
been eliminated. Observing this negative ion means observing a
process wherein a negative ion is formed from which one chlorine
atom has been eliminated via (M-H).sup.- from M in dichlorophenol,
and very high selectivity can be obtained. Therefore,
dichlorophenol can be detected even if an interfering substance
which is ionized by a negative corona discharge and produces an ion
of the same mass number, exists. In this case, a chromatogram
(showing the variation of ion intensity with time) as shown in FIG.
27 is obtained, and if the amount of the negative ion from which
one chlorine atom was eliminated is measured from the intensity of
this peak, the amount of dichlorophenol in flue gas can be
estimated. When there are plural molecular species to be measured,
this measurement process may be repeated. In the case of dioxins, a
COCl desorption process is observed in addition to dechlorination.
Desorption of COCl is a process observed only in dioxins, and if
this process is observed, it can be said to prove that TCDD or
highly toxic dioxins are present. When there are plural molecular
species which are to be measured, measurement by the MS/MS method
may be repeated, but measurements may also be carried out
simultaneously as follows. Taking chlorophenols as an example, the
negative ions of di-, tri-, tetra- and pentachlorophenol produced
by corona discharge are selectively trapped in the mass analyzing
part. This is done by applying a white noise auxiliary alternating
current which does not contain the characteristic frequency of the
ion group to be trapped, to the endcap electrodes 45a and b, as
stated previously. Next, an auxiliary alternating current
comprising superimposed auxiliary alternating currents which are
identical to or slightly different from the characteristic
frequencies of the trapped ions, is applied to the endcap
electrodes 45a, b to supply energy to the trapped molecular ions,
and ions wherein a chlorine atom has been eliminated from the
above-mentioned negative ions of chlorophenol, are thereby
produced. The sum of the intensities of the ions corresponding to
mono-, di-, tri- and tetrachlorophenol corresponds to the total
amount of chlorophenols which is to be calculated.
[0096] In an actual incinerator, in the case of chlorophenols, di-,
tri- and tetrachlorophenols account for at least 50% of the total
amount of chlorophenols, therefore the amount of chlorophenols can
be represented by the amount of di-, tri- and tetrachlorophenols
instead of measuring all the chlorophenols. This reasoning can also
be applied to chlorobenzenes and dioxins.
[0097] (Embodiment 3)
[0098] Although measurements can be made continuously at one gas
sampling point in a garbage incineration plant for a long period of
time, combustion control conditions can be better grasped by
increasing the number of measurement points. FIG. 15 is a schematic
view of a garbage incineration plant. Garbage thrown into a hopper
72 is dried, thrown into a furnace 73 having a large number of
grates 74, and burnt by primary air supplied from underneath. The
combustion gases are mixed up in the furnace 73, and burn.
Secondary air is blown into the combustion gases from a secondary
air nozzle 75 to complete the combustion. Next, the hot combustion
gases are led to a boiler 76 where heat recovery is performed. Due
to the high temperature of the secondary combustion resulting from
supply of secondary air, most organic compounds and organochlorine
compounds are decomposed. However, although organochlorine
compounds decrease, more NO.sub.x, etc., is generated by the
secondary combustion. If the gas sampling points A and B of the
present application are provided in this area, the fluctuation in
the concentration of NO.sub.x, dioxins and organochlorine compounds
due to secondary air injection and combustion temperature can
effectively be monitored in real time. It is thus possible to
operate the incinerator so that the occurrence of NO.sub.x and
dioxins is inhibited. By monitoring a point B before the boiler 76
and a point C after it, information can be gained regarding the
generation and behavior of NO.sub.x and dioxins inside the boiler.
Further, if monitoring is performed before and after the
introduction of adsorbents such as active carbon and slaked lime,
the amount of these additions can be geared to higher efficiency,
the amounts added can be reduced, and cost reductions can be
achieved. When measurements are performed at a large number of
points by time sharing, the flowpath is changed over by a flowpath
change-over valve 81 as shown in FIG. 18. In FIG. 18, the case of
three measurement points is shown, but the number of measurement
points can be increased further. The operating state of an actual
monitor is shown in FIG. 32. If monitoring of plural points is
changed over by the flowpath change-over valve 81 with time
sharing, one monitoring device is sufficient. To sample at point A,
the flowpath is changed over to point A. Monitoring is completed in
about several seconds to several tens of seconds, but measurements
are repeated to improve the S/N ratio and smooth the signal. The
number of repeat measurements can be set freely as required. When
monitoring of point A is completed in several seconds to several
minutes, the flowpath change-over valve is changed over and
monitoring moves on to point B. If there are a larger number of
measurement points and the time for one measurement is about 30
seconds, even measurements at ten points can be performed in a
cycle of 5 minutes. Also, flue gas should be made to flow
continuously through the piping in the flowpath being measured, and
through piping in other flowpaths not being measured, to avoid
adsorption of components present in small amounts by the piping
system, temperature variations, and pressure variations.
[0099] (Embodiment 4)
[0100] In the case of dioxin measurements in the atmosphere, etc.,
the dioxin concentration is still less as compared with the flue
gas of a garbage incineration plant. It is therefore difficult to
detect dioxin even if a sample gas is directly introduced to the
ion source. In this case, a trap column 83 for trapping dioxin can
be inserted in the gas sampling path, as shown in FIG. 19. After
the dioxins have been adsorbed and concentrated, the flowpath is
changed over to desorb the dioxins which are then detected. In this
case, if high purity nitrogen gas or air in a cylinder 85 is used
as a carrier gas for desorption, moisture, carbon dioxide and
hydrocarbons, etc., in the gas can be eliminated. For monitoring
substances present in high concentration such as NO.sub.x and
SO.sub.x flue gas may be introduced to the ion source without
modification, adsorption and concentration being performed only for
components present in minute amounts like dioxins.
[0101] This will be described referring to FIG. 19. Sample gas is
extracted by the gas sampling probe 3 inserted in the flue 1, and
ash, etc., is removed by the dust filter 20 and the metal filter
23. Chlorobenzenes and chlorophenols, etc., which are present in
high concentration in the sample gas, pass through a three-way cock
82a, piping and a three-way cock 82b, and are sent directly to the
monitor part 11 where they are monitored. When dioxins are
monitored, the three-way cocks 82a, b are changed over. The sample
gas then passes through piping, a four-way cock 84, the trap column
83 and three-way cock 82b, and is led to the ion source 30. The
dioxins are adsorbed and concentrated by the trap column 83. When a
trap concentration time of about several minutes to several tens of
minutes has elapsed, the four-way cock 84 is changed over, and
nitrogen gas from the nitrogen cylinder 85 is passed through the
trap column 83. At the same time as the four-way cock 84 is changed
over, the trap column 83 is rapidly heated by energizing a column
heater 99 surrounding the trap column. Dioxins adsorbed by the trap
column 83 are then desorbed, and led to the ion source 30 where
they are ionized and monitored. For high concentration components,
the gas may be directly connected, whereas to monitor components
present in medium concentration or in very low amounts, plural trap
columns may be prepared and monitoring performed separately for
each component. For example, different trap times may be used,
e.g., 10 seconds for medium concentration components and 100
seconds for components present in very low amounts.
[0102] (Embodiment 5)
[0103] By using a calibration curve, the ion current measured by
the monitoring apparatus is converted into a concentration of a
dioxin or an organochlorine compound. For this purpose, the
change-over valve 24 for introducing a standard sample is
periodically changed over as required, or once a day, etc., to
introduce a fixed amount of a standard substance together with a
suitable gas from a chemical cylinder, not shown, or the standard
sample generator 10, and automatic calibration of the monitor is
performed. As the standard substance, a volatile organochlorine
compound such as a chlorobenzene or a chlorophenol may be used, or
NO.sub.x, SO.sub.x, etc., may be used. The signal obtained by
introducing the sample substance is compared with a value which was
previously input or a previously measured value, and if there is a
large deviation, an alarm is output and calibration is
performed.
[0104] (Embodiment 6)
[0105] During on-line measurement or whenever necessary, e.g., once
a day, a self-test is performed as to whether there are any
abnormalities in measured signals, the background, temperature of
the flue gas, pressure or flowrate, etc., and required operations,
such as automatic cleaning, automatic calibration, issue of device
fault alarms or device shutdown, are performed.
[0106] (Embodiment 7)
[0107] To detect short-term abnormalities, another process is
required. This constantly determines whether or not there are
faults, as shown in FIG. 34. The determination may be performed by
manually inputting an average value for the incinerator from an I/O
device beforehand, or by repeating measurements to automatically
calculate an average value. In FIG. 34, a method of automatically
calculating an average value is shown by a flowchart. After
sequentially determining dioxins, chlorobenzenes and chlorophenols,
the value of each component is compared with an average value. If
the deviation is greater than a predetermined value, an alarm is
output by an I/O device or alarm instrument, and measurement is
repeated. If the alarm is repeated, a higher level alarm is issued,
and self-diagnosis, calibration and monitoring apparatus shutdown
are performed.
[0108] The components causing the abnormal value are likely to be
contained in the flue gas, therefore, the trace component
monitoring apparatus shifts to a different determining mode from
ordinary monitoring. When there is a fault condition, the mass
spectrometer performs a mass scan to acquire mass spectra. These
are then filed and recorded together with other parameters, and
displayed on the I/O device. The blow volume of primary air or
secondary air supplied to the furnace is adjusted by the combustion
controller 15 while monitoring the situation, and emission of
dioxins, chlorobenzenes and chlorophenols is suppressed. This
determination also aids in identifying the cause of the abnormal
condition.
[0109] Mass spectra are obtained not only in abnormal conditions.
If a mass spectrum scan is included in the monitoring cycle for
dioxins, and mass spectra are constantly acquired as monitoring is
performed, the state of the furnace can be known at any time. For
example, if a large amount of garbage containing water is
incinerated, large peaks due to water ions appear in the mass
spectrum, and if a large amount of vinyl chloride is incinerated,
large peaks due to chlorine ions appear in the mass spectrum. If a
mass spectrum is periodically interspersed in the monitoring of
components present in very small amounts and this mass spectrum is
observed, an abnormal state can be detected. The measured mass
spectrum is compared with a previously measured mass spectrum
(comparison mass spectrum), and if a new mass peak appears or a
large mass peak disappears, it is determined that an abnormal state
exists. Specifically, the intensities of mass peaks having the same
mass/charge ratio (m/z) on the spectra to be compared are
subtracted from one another. If there is no peak on a mass
spectrum, the intensity is taken to be 0. If a large peak appears
on the difference spectrum, it signifies a component that has
suddenly appeared in the flue gas, so this is regarded as abnormal
and an alarm is output.
[0110] The measured data are processed by data processing, and
filed and stored together with set values or experimental values of
combustion conditions. If there are parts showing values exceeding
the reference values, they are color-coded, e.g., with red or pink,
and an alarm is immediately output to the operator. If necessary,
the data are output to a printer or CRT, and also sent to an
incineration surveillance and control system.
[0111] (Embodiment 8)
[0112] During measurements, flue gas is allowed to flow
continuously through the atmospheric pressure ion source and piping
to maintain an equilibrium in the exchange of gas and substances
adsorbed on the wall surface, and eliminate adsorption of
components present in very small amounts on the wall surface. When
the flow of flue gas is stopped during shutdown of the incinerator,
maintenance inspections or filter replacement in the sampling
system, high purity nitrogen gas is automatically circulated to
prevent soiling of the atmospheric pressure ion source or piping.
Also, depending on the state of soiling of the ion source or
piping, a purge gas such as a high purity gas is circulated, for
example once a week, to perform automatic cleaning of the ion
source and pipes. When the emission of the standard sample from the
standard sample generator 10 in the monitoring apparatus shown in
FIG. 1 is stopped, nitrogen gas from a nitrogen cylinder, not
shown, is passed through the valves, piping and the ion source 30
without modification to perform cleaning. The device is
periodically cleaned by allowing nitrogen gas to flow periodically
when the device is started or stopped, or during measurement. The
nitrogen gas may be introduced into the gas sampling unit 88
separately from the standard sample introduction system. If flue
gas is introduced and measurements are begun after passing pure
nitrogen through the system, the flue gas is allowed to flow for at
least 30 minutes to prevent adhesion to the pipe walls.
[0113] (Embodiment 9)
[0114] FIG. 30 shows abundance ratios for the main components
included in flue gas. The vertical axis shows the abundance ratio.
1 represents 100%. 10.sup.-6 represents ppm, 10.sup.-9 represents
ppb and 10.sup.-12 represents ppt. After nitrogen, oxygen, carbon
dioxide and water which are present at % levels, carbon monoxide
and hydrocarbons are present at a level of 1000 ppm. Hydrocarbons
contain many components, and their concentrations are distributed
over a wide range from 10 ppm to 1 ppt. Hydrogen chloride (250 to
1300 ppm), NO.sub.x (100 to 200 ppm) and SO.sub.x (.about.100 ppm)
are present to the extent of several hundred ppm. On the other
hand, the concentration of chlorobenzenes and chlorophenols which
are said to be dioxin precursors, is said to be of the order of 1
ppb (1000 ng/Nm.sup.3). The concentration of dioxins is below 10
ppt (10 ng/Nm.sup.3). Inorganic compounds containing highly
electronegative elements such as oxygen, sulfur and halogens (F,
Cl, Br and I) (nitrogen oxides (NO.sub.x), sulfur oxides
(SO.sub.x), chlorine (Cl.sub.2), hydrogen chloride (HCl)) are also
present in flue gas to the extent of several hundred ppm. These
substances are also noxious substances of which the discharge into
the atmosphere is regulated. Moreover, by using negative ion mode
atmospheric pressure chemical ionization, in addition to these
substances, oxygen and water can be ionized and measured in the
same way as dioxins and organochlorine compounds such as
chlorophenols and chlorobenzenes.
[0115] NO.sub.xand SO.sub.x are present in high concentrations 108
to 109 times greater than the concentration of dioxins. Therefore,
even if the ionizing efficiency is somewhat inferior, the amount of
such ions detected is far greater than that of dioxins, and
consequently, it is not the best policy to measure dioxins,
chlorophenol and chlorobenzene at the same time as NO.sub.x and
SO.sub.x. In this case, the mass spectrum of NO.sub.x and SO.sub.x
is obtained at low sensitivity in one mass analysis (one mass
scan), the mode is changed over to medium sensitivity and
measurement of chlorobenzenes and chlorophenols is performed, and
finally, the mode is changed over to high sensitivity and a mass
analysis of dioxins is performed.
[0116] There are several methods of changing over the sensitivity.
FIG. 33 shows the case where the mass spectrometer is an ion trap
mass spectrometer. By adjusting the time during which ions are
introduced to and accumulated in the ion trap mass analyzer from an
external device, a large dynamic range can be covered. When the ion
current is small, the ion accumulating time is lengthened.
Conversely, when there is a large ion current, the ion accumulating
time is shortened. After introducing and accumulating ions, a mass
scan is performed and a mass spectrum is obtained. The detector is
also synchronized, and is switched between low, medium and high
gain to perform measurements. If measurements are alternately
repeated while switching through the three sensitivities, dioxins,
chlorobenzenes, chlorophenols, NO.sub.x and SO.sub.x, etc. can
effectively be measured in real time. Dioxins are present only in
extremely low amounts as compared with chlorobenzenes and
chlorophenols, or NO.sub.x and SO.sub.x. For this reason, these
three groups of substances are not monitored equally, the number of
measurements in one cycle is increased in the case of dioxins which
are present in only very small amounts, and the data are smoothed.
The frequency of monitoring between the three groups may also be
varied.
[0117] (Embodiment 10)
[0118] In the above example, the case was mainly described where
negative ion atmospheric pressure chemical ionization is used.
Various components are present in flue gas, but for hydrocarbon
compounds, such as olefinic hydrocarbons or aromatic compounds
typified by benzene, etc., or compounds with low numbers of
chlorine atoms, measurements can also be made by positive ion mode
atmospheric pressure chemical ionization. For example, with benzene
and monochlorobenzene, the ion species M+ is generated by positive
ion atmospheric pressure chemical ionization. Other ion species
observed in positive ion mode are (M+H).sup.+, etc.
[0119] The ions derived from hydrocarbons obtained by the positive
ion mode represent the combustion state of the furnace, and may
also be used as an indicator of incomplete combustion like carbon
monoxide. Specifically, when ions derived from hydrocarbons with
high molecular weight are observed in large quantities, it can be
presumed that combustion is inadequate. Further, in actual sample
gas monitoring, it is also effective to increase the amount of
information during gas sampling by making measurements alternately
in the positive and negative ionization modes.
[0120] (Embodiment 11)
[0121] In the above-mentioned example, the description focused
mainly on removing solids, such as ash, from the dust filter part,
but filters may also be provided for removing gaseous components
present in large amounts such as hydrogen chloride. In an ordinary
incinerator, the composition of gas produced by burning garbage may
vary. In such a case, it is effective to provide a filter before
the monitor part 11 for removing large amounts of gaseous
components and suppressing large fluctuations of gas component
composition. For example, in the case of hydrogen chloride, if a
filter filled with calcium carbonate or slaked lime is provided,
the level of hydrogen chloride falls to several 100 ppm even if it
originally exceeded 1000 ppm, so interference with the ionization
of target substances by a large amount of hydrogen chloride gas is
mitigated, and monitoring is made easier.
[0122] Atmospheric pressure chemical ionization using a negative
corona discharge is a high sensitivity, high selectivity ionization
technique which can selectively ionize organochlorine compounds or
compounds containing highly electronegative elements in the
presence of large numbers of interfering substances. By combining
this with ion trap mass spectrometry, an even more highly sensitive
and selective monitoring method is obtained. Hence, this
application permits direct monitoring of dioxins, dioxin precursors
(chlorobenzenes and chlorophenols) and NO.sub.x, SO.sub.x in flue
gas by directly sampling gas from the flue.
* * * * *