Measuring and testing – Instrument proving or calibrating – Gas or liquid analyzer
Reexamination Certificate
2000-02-04
2002-07-23
Raevis, Robert (Department: 2856)
Measuring and testing
Instrument proving or calibrating
Gas or liquid analyzer
Reexamination Certificate
active
06422056
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for correcting the effect of a coexistent gas in a gas analysis, and a gas analyzing apparatus using the method.
BACKGROUND OF THE INVENTION
In determining a particular gas component (measurement of an objective component or subjective component) having an absorption spectrum in the infrared region by NDIR (Non-Dispersive Infrared Detection) or FTIR (Fourier Transform Infrared Spectroscopy), there may be cases where the measurement amount (span sensitivity) is affected by the coexistent component which has likewise an absorption spectrum in the infrared region but is separated from the objective component or the coexistent component which does not have an absorption spectrum in the infrared region.
This is based on the premise that, notwithstanding the fact that there may be cases to cause differences in spectral intensity depending on the gas composition (coexistent components) with the same gas components and same gas concentrations, according to the conventional infrared absorption method, the interference between the components is attributed to the fact that a complete separation of an overlapping absorption spectra cannot be performed. In practice, it has been observed in the analysis of automobile gases that H
2
O and O
2
, which are the coexistent components to the span directives of CO and CO
2
which are the objective components and do not exhibit a constant concentration, are liable to give effects.
However, since O
2
does not absorb in the infrared spectrum and since it is difficult to calibrate the concentration of H
2
O, they are difficult to analyze under the infrared absorption method.
FIG.
6
(A) shows the relations between the coexistent H
2
O concentration and the error of the CO
2
indication value at the time when various concentrations of CO
2
are measured. As the H
2
O concentration increases, the error of the CO
2
indication value is shown largely to be positive. FIG.
6
(B) shows the relation between the coexistent O
2
concentration and the CO
2
indication value at the time when various concentrations of CO
2
are measured by using two gas analyzers. As the O
2
concentration increases, the error of the CO
2
indication value is shown largely to be negative. In other words, it can be seen that, because the sensitivity calibrations of these gas analyzers are carried out by a standard gas produced on the basis of N
2
gas, sensitivity change has been produced in the case where the mixed gas containing H
2
O and O
2
becomes the base gas.
Although a mechanism explaining the phenomena shown in FIGS.
6
(A) and (B) is not fully understood, in one factor it can be presumed that a quenching occurs from the mutual interactions of gas molecules.
FIGS. 7A and 7B
show a model where quenching may lead to a variation in the amount of infrared absorption.
The model demonstrates a supposition that the amount of variation in infrared absorption depends on the probability of collision between an objective component X and a coexistent component A along with the size of the reciprocal actions at the time of the collision. That is to say, FIG.
7
(A) shows a case where both the probability of collision of the coexistent component A with the objective component X and the reciprocal actions at the time of the collision are relatively small. Because the coexistent component A has little effect upon the equilibrium of the base condition or excitation condition of the objective component X, the concentration of the coexistent component A scarcely affects the amount of infrared absorption by the component X. On the other hand, FIG.
7
(B) shows the case where both the probability of collision of a coexistent component B with an objective component X and the reciprocal actions at the time of the collision are relatively large. Because the equilibrium of the objective component X is displaced to the base condition side, new light absorption becomes likely to occur. In other words, due to the presence of the coexistent component B, the absorption concentration of the objective component X becomes relatively large, and the objective component X shows a stronger absorption than the case where the base gas is of the coexistent component A and of the same concentration.
With respect to other mechanisms that can cause the above phenomenon, it is possible that a “collision spreading” mechanism broadens the width of the absorption line because the absorption wavelength is affected by the actions of the objective component itself and the coexistent component.
The phenomenon of “collision spreading” is a problematic matter even for the gas analysis of a fuel battery system which is regarded as a promising automobile power source for the next generation.
FIG. 8
shows schematically a general fuel battery system
40
having a methanol supply source
41
. CH
3
OH from the supply source
41
is supplied to a quality reformer
42
, where the CH
3
OH is reformed under an optional catalyst to generate a reformed gas. The reformed gas contains, besides H
2
gas, unreacted CH
3
OH, high concentrations of CO
2
and H
2
O as bicomponents, CO, CH
2
and the like as impurities. Accordingly, it is so constituted that the reformed gas, after removing the components (such as CO) which poison a fuel battery
44
at an impurity eliminating part
43
, is supplied to the fuel battery
44
.
Here, the concentration of the generated H
2
gas, CO
2
, H
2
O, etc. falls into the range of several % to several tens %, while the concentration of CO, CH
4
, etc. as impurities is significantly less in the order of ppm. However, in order to favorably operate the fuel battery
44
it is desirable to reduce the concentration of impurities such as CO or the like as much as possible, which requires an accurate measurement of the concentrations. In addition, in order to verify or control the efficiency of H
2
gas generation, the concentration of CH
3
OH or other hydrocarbons (HC) need to be measured.
Therefore, the above fuel battery system
40
, has, a sample gas flow route
46
connected to the gas flow route
45
immediately following the reformer
42
. The gas flow route
46
is provided with various gas analysis gauges
47
such as a Non-Dispersive Infrared Detection (NDIR) analyzer, magnetic oxygen meter, Flame Ionization Detector (FID), FTIR, etc. The fuel battery system
40
is configured such that the concentration of the impurities, such as CO, CO
2
, HC, etc. contained in the H
2
gas generated in the reformer
42
, are monitored at the output of the reformer
42
or immediately after the impurity eliminating part
43
. In the case of measuring the concentration immediately after the impurity eliminating part, a sample gas flow route
49
is connected to a gas flow route
48
which is immediate after the impurity eliminating part
43
. The sample gas flow route
49
is provided with a gas analyzer
50
similar to the above gas analyzer
47
, and the difference of the outputs of the gas analyzers
47
,
50
is taken to make it possible to grasp to what extent the above impurities have been removed in the impurity eliminating part
43
. Based on the data, the reformer
42
and impurity. eliminating part
43
are controlled to supply high quality H
2
gas to the fuel battery
44
.
However, when measuring CO by FTIR or NDIR, for example, there is a possibility for sustaining the effect of H
2
gas as the coexistent gas due to the mechanism of spectral intensity variation by the coexistent gas as described above. Furthermore, with respect to FID, the H
2
gas in the sample gas is apt to affect the sensitivity in the form of a collapse of balance between the fuel gas (H
2
gas) and the auxiliary combustion gas (Air) which are supplied to the detector. With respect to the O
2
gauge (gas analyzer for determining the oxygen concentration), the H
2
gas which is contained in only the sample gas and not in the calibration gas may affect the sensitivity.
FIG. 3
shows an effect of the H
2
gas concentration in the sample gas upon the span sensitivity. Cu
Inoue Kaori
Ishihara Masaaki
Miyai Masaru
Takeda Kenji
Horiba Ltd.
Oppenheimer Wolff & Donnelly LLP
Raevis Robert
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