JP2002071585A - Method and device for measuring oil content in soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make measurable oil contents in soil with an apparatus. SOLUTION: A sample soil is irradiated with fast neutrons from a neutron source. The counted value of thermal neutrons in which the fast neutrons are scattered and decelerated is measured by a proportional counter tube. As guiding part of resonance microwaves inside a cavity resonator into the sample soil, the attenuation value of the resonance microwaves is measured. The sum content of moisture content and oil content in the sample soil is estimated from the measured value of the thermal neutrons, and the moisture content in the sample soil is estimated from the attenuation value of the microwaves. The oil content in the sample soil is estimated from both estimated contents in the method for measuring oil content in soil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for measuring oil content in soil.

[0002]

2. Description of the Related Art When assessing the environmental impact of soil contaminated with oils such as crude oil or heavy oil, and when purifying the contaminated soil, first, the degree of oil contamination and the state of distribution of the contamination. It is important to know It is also necessary to measure the residual oil content after decontamination even after the purification treatment.

[0003] A chemical analysis method and a physical analysis method are known for the analysis of soil oil content. Quantitative analysis of oil content by a usual chemical analysis method requires about one day for the analysis operation. Therefore, it takes a great deal of time and effort to obtain a large number of samples from a wide range of soils to determine the distribution of oil contamination, and when contamination occurs, take some action on the spot based on the analysis results. When it is necessary, it may take time and effort to perform the analysis, making it impossible to take appropriate measures.

On the other hand, as a physical method, an instrumental analysis method for measuring the fluorescence of oil generated by light irradiation is known. However, since the light transmission power into soil is small, only the surface of a soil sample is measured. You can only measure. For this reason, it is not possible to determine the total or average oil content of a bulk (volume) sample having a certain size, and it can hardly function as a means of measuring oil content in contaminated soil. .

[0005]

As described above, there is no appropriate method and apparatus for measuring oil content in soil quickly and sufficiently with good accuracy. Thus, contamination by crude oil or heavy oil has occurred. This was an obstacle to taking appropriate and necessary measures for the soil. An object of the present invention is to solve this problem, and an object of the present invention is to provide a method and an apparatus for measuring a soil oil content which enable real-time quantitative analysis of the soil oil content in situ.

[0006]

According to the present invention, sample soil is irradiated with fast neutrons from a neutron source, and the fast neutrons are scattered and decelerated, and the thermal neutron count is measured by a proportional counter. Measure the attenuation value of the resonant microwave while guiding a part of the resonant microwave in the resonator into the sample soil,
Estimate the total amount of water and oil in the sample soil from the former thermal neutron count, and estimate the amount of moisture in the soil sample from the microwave attenuation value of the latter, and estimate the oil content in the soil sample from both estimates. And a method for measuring oil content in soil.

Further, according to the present invention, there is provided an apparatus for measuring a soil oil content comprising a neutron hydrogen meter sensor section and a microwave moisture meter surrounding a tubular sample container as a center, wherein the neutron hydrogen A neutron source mounted near the outside of the sample container, a neutron reflector having a predetermined thickness disposed outside the sample container so as to enclose the neutron source, a neutron reflector disposed outside the sample container, It consists of a proportional counter arranged within the thickness of the neutron reflector, and the microwave moisture meter described above transmits a cavity resonator attached to the outer periphery of the sample container and a microwave of a predetermined frequency into the cavity resonator. A microwave antenna for guiding the antenna, a resonant waveguide for guiding the resonant microwave in the cavity into the sample container, and a detector for measuring the intensity of the microwave in the cavity. To provide a measuring device in the soil oil to butterflies.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An ordinary soil sample to be analyzed contains water in addition to oil. Therefore, simultaneous analysis of oil and moisture must be performed under these conditions. However, there is no suitable method or equipment to simultaneously analyze these two components in soil. That is, there is no suitable means for selectively analyzing only the oil content in soil. Therefore, the present invention is to simultaneously analyze the oil content and the water content in soil by combining two different kinds of physical means, and to determine the total amount of hydrogen in the sample by utilizing the neutron scattering slowdown. At the same time, the free water is selectively measured by the absorption attenuation of microwaves, and a subtraction operation (not just a subtraction) is performed from these two types of measurement results to determine the oil content.

[0009] The use of neutrons has the effect that the effect of slowing down the scattering by hydrogen nuclei is hardly affected by the state of chemical bonding of hydrogen, and therefore, irrespective of the oil and water contents, This is because a slow neutron count corresponding to the amount of hydrogen can be obtained. On the other hand, microwaves were selected because their frequencies can be selected and the use of the cavity resonance phenomenon enables selective high-sensitivity measurement of almost only free moisture.

As described above, according to the present invention, the oil content and the water content are obtained by the subtraction operation from the two types of measurement results of the neutron scattering moderation effect and the microwave absorption attenuation phenomenon, so that the final accuracy is guaranteed. It is important to ensure that the accuracy of the two measurements on which the measurement is based is sufficiently high, and it is also necessary to prevent errors from increasing in the calculation method.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a main part of a soil oil content measuring device according to the present invention. A neutron hydrogen meter sensor unit 2 is provided around a tubular sample container 1 so as to surround it.
And a simple structure in which a microwave moisture meter 3 is juxtaposed. In the illustrated example, the neutron hydrogen meter sensor unit 2 is arranged in the lower half of the sample container 1, and the microwave moisture meter 3 is arranged in the upper half. However, this arrangement may be reversed.

The sample container 1 is preferably made of resin. In the example shown in the figure, a polyvinyl chloride tube (length: 500 mm) having a bottom 4 and an open upper end is used.

The neutron hydrogen meter sensor section 2 includes a neutron source 5 mounted near the outside of the sample container 1 and a neutron reflector having a predetermined thickness disposed outside the sample container 1 so as to surround the neutron source 5. 6 and a He-3 (helium-3) proportional counter tube 7 arranged outside the sample container 1 in parallel with the sample container 1 and within the thickness of the neutron reflector 6. In the illustrated example, the neutron source 5 is 3.7
MBq of calcium-252 is used. The neutron reflector 6 has a height of 200 mm and a ring thickness of 6 mm.
A 0 mm cast iron boring cylinder (ring) is used. The sample container 1 is fitted into the center hole of the iron ring without leaving a gap. In the iron ring, nest holes for the neutron source 5 and holes for installing the He-3 proportional counter 7 are formed, and these holes are attached to these holes. He-
The free end 8 of the three-proportional counter tube 7 is exposed outside the iron reflector 6, and the free tube 8 is connected to a measuring instrument (not shown).

The microwave moisture meter 3 comprises a cavity resonator 9 mounted on the outer periphery of the sample container 1. This cavity resonator 9 is a double cylinder coaxial with the sample container 1 (the inner cylinder 10 and the outer cylinder 1).
1) and a hollow cylindrical cavity 14 surrounded by a lower plate 12 and an upper plate 13. The cavity 14 is formed of a metal plate, and the inner tube 10 is provided with a resonance waveguide port 15 for guiding a resonance microwave into the sample container 1. In the illustrated example, the resonance waveguide port 15 has a gap perpendicular to the axis which divides the inner cylinder 10 at a half distance (2 / L) of the distance from the lower plate 12 to the upper plate 13 (referred to as the axial length L). It is formed as A microwave oscillator 16 introduces a microwave whose frequency has been adjusted so that 2L becomes an integral multiple of the wavelength from the antenna 17 into the cavity 14. Reference numeral 18 denotes a detector, which detects the resonant microwave and measures its attenuation value.

The operation and effect of the neutron hydrogen meter sensor unit 2 and the microwave moisture meter 3 configured as described above will be described below.

In the neutron hydrogen meter sensor section 2, high-speed neutrons emitted from the neutron source 5 (3.7 MBq of Californium-252) are transferred to the soil sample 20 in the sample container 1.
Is irradiated. At this time, if hydrogen exists in the sample,
Neutrons collide with hydrogen nuclei and are elastically scattered, and the energy is reduced by half on average for each scattering.
Therefore, the average energy of fast neutrons, which was initially about 2 MeV, was scattered about 20 times, and almost all thermal neutrons (≒ 0.0
25 eV). The slow neutrons slowed down to near the thermal neutrons are detected and counted by the proportional counter 4 (slow neutron detector). Since this count value increases with the amount of hydrogen in the sample, the hydrogen content can be measured thereby.

However, if most of the fast neutrons are simply irradiated on the sample, the neutrons will go out of the sample only by causing a small number of scattering reactions in the sample, and the probability of becoming thermal neutrons is small. For this reason, in the present invention, a neutron reflector 6 made of iron is used.
And the thickness of the counter tube 7 is sufficient to reflect neutrons. Therefore, the neutrons directed to the outside of the sample container 1 are efficiently reflected by the reflector 6 and return to the sample many times. That is, neutrons pass through the sample a number of times due to the effect of multiple reflections by the reflector 6, and the probability of collision of neutrons with hydrogen increases, and the efficiency of thermal neutron generation also increases significantly. For this reason, the count value of thermal neutrons generated per unit hydrogen amount increases, and the sensitivity and stability of hydrogen measurement can be improved.

Further, since the sample container 1 is made of a plastic (polyvinyl chloride in the illustrated example) which is a hydrogen-containing compound, even if the hydrogen content in the sample is not so large, scattering and scattering at this portion are not possible. There is an effect that deceleration is promoted. The extent of this effect depends on the amount of the hydrogen-containing compound in container 1 and the relative proportions of the sample volume and the hydrogen content. If the relative proportions are appropriate, the promotion of neutron deceleration by plastic materials can be effectively used. can do.

Therefore, in the neutron hydrogen meter sensor unit 2 according to the present invention, due to the multiple reflection of neutrons by the reflector 6 and the action of accelerating the neutron deceleration by the plastic material, sufficient hydrogen measurement can be performed even when a relatively small amount of sample is used. Sensitivity is obtained.

The thermal neutron count value thus measured corresponds to the sum of the hydrogen content in the sample and the hydrogen content of the compound constituting the container. The hydrogen content in the sample is the sum of the hydrogen content of the compounds that make up the oils and the other hydrogen compounds (mostly water) in the sample, and the hydrogen content of the compounds that make up the container. Since is constant, if the amount of water in the sample is separately measured, the relative value of the hydrogen content of the compounds constituting the oils, and thus the oil content in the soil, can be detected.

The operation and effect of the microwave moisture meter 3 according to the present invention for measuring moisture in the soil will be described below. In the microwave moisture meter 3, the axial length L (17 in the illustrated example) is set.
A microwave having a frequency that resonates at the distance L is introduced into the hollow cylindrical cavity 14 (6 mm). Then, since the resonance waveguide 15 is provided at the resonance position, a part of the resonance microwave is sent from the resonance waveguide 15 into the sample container 1. At that time, when there is moisture in the soil sample 20, the resonant microwave sent into the sample container 1 is absorbed, and the degree of absorption increases as the amount of moisture increases. The effect of the absorption is the cavity resonator 9
Therefore, when the intensity of the resonant microwave is monitored by the detector 18, as the moisture content of the soil sample 20 increases, the degree of attenuation of the intensity increases. In other words, the degree of attenuation of the resonant microwave changes according to the amount of water, whereby the amount of water in the soil sample 20 is measured. The role of the cavity resonator 9 is to allow the microwave to pass multiple times through the sample by the action of the resonance phenomenon, and to increase the degree of absorption and attenuation of the microwave by several tens of times in the case of a single pass. Thereby, the sensitivity of the moisture measurement can be improved.

FIGS. 2 and 3 show the results of an experimental investigation of the basic characteristics of the apparatus shown in FIG. Sample 20
Is used as a mixture of river sand and distilled water, and the content of distilled water in the mixture is 2.5%, 5.0%, 7.5%, 10%.
%.

First, when a sample was loaded, a shock was applied to the upper and lower portions of the sample container by gravity to test the sample of each water content with the degree of sample filling considerably changed. As shown in FIG. 2, the thermal neutron count value (count / 2 minutes) by the proportional counter 7 is affected by the degree of filling, but when converted to the amount of water per unit volume (g / cm ³ ) A good correlation was observed between the water content and the neutron count, and a calibration curve for the neutron hydrogen meter was created. On the other hand, the detector 1 in the microwave moisture meter 3
The microwave attenuation value at 8 is significantly affected by the degree of filling, as seen in FIG. However, it was confirmed that a good reproducibility can be obtained if the filling degree is close to a certain degree of saturation and the change is reduced, and if the filling degree is controlled to be almost constant. The calibration curve in this case is shown by a solid line.

Therefore, using the same apparatus shown in FIG. 1, a river sand sample of 5% distilled water was used as a base, and 3% of heavy oil A was added thereto.
%, 5%, and 5%, and neutron counts and microwave attenuation values were measured in the same manner as in FIGS. The results are summarized in FIG. In each of the upper and lower diagrams of FIG. 4, the calibration curves of only the water obtained in FIGS. However, the horizontal axis shows the total g / cm ³ of water and oil. In addition, a plot group of 3%, a plot group of 4%, and a plot group of 5% are shown in the figure.

As is clear from the results shown in FIG. 4, the calibration curve gradient is not significantly different between oil and moisture in the neutron count value, whereas the change due to the oil content in the microwave attenuation value is larger than that in the moisture case. Unlikely, it has become very small. However, the effect of the sample filling degree was more pronounced in the microwave attenuation value when oil was present, so the degree of filling was determined by the distance of the sample level measured from the top of the container (the degree of sinking). They are shown separately (120 mm and 103 mm).

From the test results, as a practical method of obtaining the oil content, first, using only the water calibration curve, the total content of water and oil was obtained from the neutron count value, and obtained from the microwave attenuation value. It can be seen that “the first approximation of the oil content” is obtained by subtracting the water content. That is, the corresponding (moisture + oil) (g / cm ³ ) is obtained from the neutron count value of the sample to be measured using the moisture calibration curve in the upper part of FIG. 4, and the microwave attenuation value of the sample is used as shown in FIG. The first approximate value of the oil content can be obtained by obtaining the amount of water in the sample using the water calibration curve and subtracting the latter from the former. The first approximation of this oil content is slightly biased because the neutron count value is calculated using the calibration curve of moisture only (moisture + oil content). It is possible to calculate a more reliable oil content by making an appropriate correction to the oil content. The result of this correction is shown in FIG.

In the upper graph of FIG. 5, the horizontal axis represents the oil content (wt%) in the sample, and the vertical axis represents the deviation error from the true value of the first approximation value of the oil (oil component deviation error). It is shown. Because the first approximation value uses a moisture calibration curve, when the sample filling degree is 103 mm, an error occurs as shown in the upper line in the figure, and when the sample filling degree is 120 mm, an error appears as in the lower line. An error has occurred. Therefore, if an appropriate correction is applied to the first approximate value, a value close to the true value can be obtained.

The error when the correction is performed is shown in the lower graph of FIG. The correction equation is simply a coefficient (1-
α) (L ₁₂₀ / L ₁₀₃ ). _L120 and _L103 are the respective net heights of the sample, the value of α in this case being 0.0
6. After this correction, as shown in the lower graph of FIG. 5, even when the filling degree was 103 mm or 120 mm, the deviation error of the fixed amount of oil was within ± 0.1%. The unit of oil content (wt / wt ³ ) on the horizontal axis in FIG.
%) Can be divided by the bulk density determined from the net volume and weight of the sample.

As described above, according to the present invention, the amount of oil in a soil sample can be accurately measured. The neutron hydrogen meter sensor unit 2 and the microwave moisture meter 3 in the example shown in FIG.
It is not necessarily limited to this mode. For example, the cavity resonator 9 may be of a hollow cylindrical shape as shown in the figure, a surface-compatible type of a large object or an insertion type depending on the shape of the sample container. However, as long as performance, such as measurement sensitivity and accuracy, is not an issue in configuring the neutron hydrogen meter sensor section, high-speed neutron multiple reflection with a neutron reflector block such as iron (or graphite) and an appropriate amount of moderator are added. It is necessary to use scattering and deceleration in the mold.

[0030]

As described above, according to the present invention,
Conventionally, it is possible to easily and accurately measure the oil content in soil, which has been difficult to measure with an instrument. Therefore, for example, it is possible to quickly measure the residual oil content in soil during and after cleaning in a contaminated soil cleaning plant, optimize the operating conditions of the plant, and check and control the quality of treated soil. It will be easier. In addition, the extent and distribution of oil pollution can be quickly and widely known for sedimentary soil in the field, greatly contributing to soil treatment and environmental management.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a main part of a soil oil content measuring device according to the present invention.

2 is a diagram showing the relationship between the amount of water in the sample soil and the neutron count value when the sample soil is measured by the apparatus shown in FIG. 1 (calibration curve of a neutron hydrogen meter).

3 is a diagram showing the relationship between the amount of water in the sample soil and the microwave attenuation value when the sample soil is measured by the apparatus shown in FIG. 1 (calibration curve of a microwave moisture meter).

Fig. 4 shows the relationship between (moisture + oil content) and neutron counting neutrons (upper row) and the relationship between microwave attenuation values (lower row) for sample soil with changed oil content, for sample soil with only water. And FIG.

Fig. 5 shows the relationship between the oil content (wt%) in the sample and the deviation error of the oil content. The upper column shows the relationship between the first approximation of the oil component and the deviation error from the true value. FIG. 7 is a diagram showing the relationship between the correction and the bias error when the correction is performed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sample container 2 Neutron hydrogen meter sensor 3 Microwave moisture meter 5 Neutron source 7 Proportional counter tube (He-3) 9 Cavity resonator 14 Cavity 15 Resonant waveguide 16 Oscillator 17 Microwave antenna 18 Detector 20 Soil sample

 ──────────────────────────────────────────────────続 き Continuing from the front page (71) Applicant 500403918 Japan Special Measurement Instruments Co., Ltd. 5-33-7, Shiba, Minato-ku, Tokyo (72) Inventor Hiroshi Tominaga 172 (72) Inventor Michio Tsuchihiro Kashima Construction Co., Ltd. 1-2-7 Moto-Akasaka, Minato-ku, Tokyo Inventor Isamu Ishikawa 3607 Niibori, Narita-cho, Oarai-machi, Higashi-Ibaraki-gun DA01 GA01 HA01 KA01 LA03 MA04 NA01 NA19 SA04 SA12

Claims (4)

[Claims] 1. A sample soil is irradiated with fast neutrons from a neutron source, and the fast neutrons are scattered and decelerated and the thermal neutron count is measured by a proportional counter. On the other hand, a part of the resonant microwave in the cavity resonator is measured. The attenuation value of the resonant microwave is measured while the water is introduced into the sample soil, and the total amount of water and oil in the sample soil is determined from the former thermal neutron count value, and the moisture content in the soil sample is determined from the latter microwave attenuation value. A method for measuring the amount of oil in soil by estimating the amount of oil and estimating the amount of oil in a soil sample from both estimates. 2. An apparatus for measuring oil content in soil comprising a neutron hydrogen meter sensor section and a microwave moisture meter near a sample container, wherein the neutron hydrogen meter sensor section is mounted near the outside of the sample container. A neutron source, a neutron reflector having a predetermined thickness arranged outside the sample container so as to enclose the neutron source, and a proportional counter arranged outside the sample container and arranged within the thickness of the neutron reflector. A microwave resonator mounted on the outer periphery of the sample container, a microwave antenna for guiding microwaves of a predetermined frequency into the cavity, and a resonant microwave in the cavity resonator. An apparatus for measuring oil content in soil, comprising: a resonant waveguide for guiding a wave into a sample container; and a detector for measuring the intensity of microwaves in a cavity resonator. 3. An apparatus for measuring oil content in soil according to claim 2, wherein the sample container comprises a cylindrical container, and a neutron hydrogen meter sensor section and a microwave moisture meter are provided so as to surround the cylindrical container. 4. The apparatus according to claim 2, wherein the sample container is made of a resin.