Measuring and testing – Gas analysis – Solid content of gas
Reexamination Certificate
2000-12-05
2003-02-11
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
Solid content of gas
C073S028010, C436S155000, C436S157000, C436S160000
Reexamination Certificate
active
06516654
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and method for analyzing particulate matter (hereinafter referred to as PM) contained in a gas discharged, for example, from diesel engine. The present. invention further relates to a carbon differentiating and analyzing apparatus and method capable of differentiating and analyzing organic carbon and elemental carbon contained in a sample.
DESCRIPTION OF THE PRIOR ART
As a procedure for determining PM contained in an emission of diesel engine, there is known in general a filter weighing method for quantitative analysis based on the weight difference from the filter before capturing PM which comprises diluting a high temperature emission discharged from the diesel engine with clean air, capturing PM with a filter by inhaling the diluted emission by a fixed capacity, and weighing the filter with a precision balance or the like.
However, in the above filter weighing method, the large effect of water content absorbed by the filter leads to measurement error. Constant temperature and constant moisture processing is required to maintain the water content at a constant in the filter before and after capture. Furthermore, in determining the emission of low concentration PM, it is necessary to weigh accurately PM of 0.1 mg captured on a filter of for example 200 mg. Thus, there is a problem such that the measurement error of the weight of the filter itself gives a significant effect on the measurement error of the PM weight.
Against the above, as shown in U.S. Pat. Nos. 5,110,747, 5,196,170, 5,279,970, and 5,401,468 publications, there is a procedure of heating a filter which has captured PM in a heating furnace by elevating the temperature stepwise, oxidizing PM, and determining PM with a gas analyzer.
However, the majority of PM is constituted by the inorganic carbon called dry soot (hereinafter, to be dry soot), hydrocarbon called SOF (soluble organic fraction) (hereinafter, to be SOF), and sulfuric acid hydrate called sulfate (hereinafter, to be sulfate), and depending on the procedure described in the above publication, separation of high boiling SOF and reduction of sulfate in an oxidation atmosphere are difficult. Accordingly, it has been difficult to measure individually the concentration or weight of the dry soot, SOF and sulfate by separating them which occupy the majority part in PM.
The present invention has been made in consideration of the matters described above, and its object is to provide a method for analyzing simply and with high precision the particulate matter in an engine emission and an apparatus therefor by which dry soot, SOF and sulfate in PM contained in an engine emission can be fractionated individually even when in a minute amount.
Further, elemental carbon, which is one of the carbon components contained in TSP (total suspended particulate matter) in atmospheric air, is involved in the oxidation of SO
2
into SO
4
2−
, and may cause climatic change depending on its concentration. One technique for analyzing the elemental carbon is to thermally separate between elemental carbon and organic carbon, which is the other carbon component contained in TSP.
FIG. 11
is a schematic view showing a construction of a conventional carbon differentiating and analyzing apparatus. Referring to
FIG. 11
, a thermal decomposition tube
61
includes, on one end, a sample entrance
62
having a lid freely openable and closable for inserting a sample S, and on the other end, a gas exit
63
. The thermal decomposition tube
61
further includes, on the sample entrance
62
side thereof (hereafter to be referred to as upstream side), an inlet
64
of carrier gas CG. A heater
65
is wound around the outer circumference of the thermal decomposition tube
61
on the downstream side of the carrier gas inlet
64
, and the temperature of the heater
65
can be set to both a low temperature and a high temperature. A CO
2
analyzer
66
is connected to the gas exit
63
via a suitable passageway (not illustrated). Further, the sample S is mounted on a sample boat
67
.
Operation of the carbon differentiating and analyzing apparatus having the aforesaid construction will be described. First, a sample boat
67
having a sample S mounted thereon is set at a predetermined position in the thermal decomposition tube
61
. In this state, the heater
65
is set at a low temperature (for example, about 400° C.) to heat the sample S, whereby the organic carbon contained in the sample S is evaporated to become CO
2
and then carried to the CO
2
analyzer
66
by the carrier gas CG to be measured for CO
2
concentration. Next, the heater
65
is set at a high temperature (for example, about 1000° C.) to further heat the sample S, whereby the elemental carbon contained in the sample S is thermally decomposed to become CO
2
and then carried to the CO
2
analyzer
66
by the carrier gas CG to be measured for CO
2
concentration. Based on the CO
2
concentration obtained in each of the aforesaid measurements, the amount of the organic carbon and the amount of the elemental carbon in the sample S can be determined.
However, in the case of the aforesaid conventional carbon differentiating and analyzing apparatus, only a single heater
65
is used. Thus, it takes time to set the heater
65
from a low temperature to a high temperature, and further time is needed to set the heater
65
from a high temperature to a low temperature. Moreover, since it is difficult to detect the HC component evaporating at a low temperature with the use of the CO
2
analyzer, a HC gas sensor is further needed. Also, CO is generated to cause errors if the oxidation does not sufficiently takes place because of insufficient temperature.
The present invention has been made in order to take the above-mentioned matters into account. An object thereof is to provide a carbon differentiating and analyzing apparatus capable of differentiating and analyzing, with precision, the organic carbon and the elemental carbon contained in a sample, and capable of performing a predetermined analysis with high precision in a short time by reducing the period of time required for analysis.
SUMMARY OF THE INVENTION
In order to attain the above object, the method for analyzing PM in gas of the present invention comprises providing a filter which has caught PM contained in engine emission in a heating furnace, firstly heating the filter at a predetermined temperature while passing an inert gas into a heating furnace to evaporate the SOF and sulfate. contained in PM, oxidizing the evaporated SOF into CO
2
and reducing the evaporated sulfate into SO
2
, analyzing the CO
2
and SO
2
with a gas analyzer unit, and thereafter, heating the filter while passing oxygen into the heating furnace to oxidize the PM remaining on said filter to have it generate CO
2
, and analyzing the CO
2
with the gas analyzer unit.
As a concrete apparatus for executing the above analyzing method, there is used in the present invention an apparatus comprising a gas feeder for selectively feeding an inert gas or oxygen to a heating furnace, a heating furnace for heating at a predetermined temperature a filter which has captured the PM contained in the engine emission in a condition where the inert gas or oxygen is fed, an oxidation reduction processor for oxidizing or reducing the gas generated by heating, and a gas analyzer unit for determining the concentrations of CO and SO under supply of a gas from the oxidation reduction processor.
According to the method for analyzing particulate matter in gas of the present invention, a filter is installed in a flow passage in which an emission from an engine is passed. The emission is passed at a predetermined flow amount and the PM in the emission is captured by a filter. The filter is provided in a heating furnace which is maintained for example at 1000° C. Firstly, the filter is heated while an inert gas such as nitrogen gas is passed into the heating furnace to gasify SOF and sulfate in PM, and the evaporated SOF is oxidized into CO
2
and the evaporated
Adachi Masayuki
Asano Ichiro
Bando Atsushi
Fukushima Hirokazu
Ikeda Masahiko
Cygan Michael
Horiba Ltd.
Oppenheimer Wolff & Donnelly LLP
Swienton Brian F.
Williams Hezron
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