CA1088680A - Detection of impurities in fluid flowing in refinery pipeline or oil production operations using nuclear techniques - Google Patents
Detection of impurities in fluid flowing in refinery pipeline or oil production operations using nuclear techniquesInfo
- Publication number
- CA1088680A CA1088680A CA291,301A CA291301A CA1088680A CA 1088680 A CA1088680 A CA 1088680A CA 291301 A CA291301 A CA 291301A CA 1088680 A CA1088680 A CA 1088680A
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- Prior art keywords
- fluid
- chlorine
- concentration
- measure
- mev
- Prior art date
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
- G01N23/221—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material by activation analysis
- G01N23/222—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material by activation analysis using neutron activation analysis [NAA]
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2223/00—Investigating materials by wave or particle radiation
- G01N2223/07—Investigating materials by wave or particle radiation secondary emission
- G01N2223/074—Investigating materials by wave or particle radiation secondary emission activation analysis
- G01N2223/0745—Investigating materials by wave or particle radiation secondary emission activation analysis neutron-gamma activation analysis
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2223/00—Investigating materials by wave or particle radiation
- G01N2223/60—Specific applications or type of materials
- G01N2223/616—Specific applications or type of materials earth materials
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2223/00—Investigating materials by wave or particle radiation
- G01N2223/60—Specific applications or type of materials
- G01N2223/637—Specific applications or type of materials liquid
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2223/00—Investigating materials by wave or particle radiation
- G01N2223/60—Specific applications or type of materials
- G01N2223/652—Specific applications or type of materials impurities, foreign matter, trace amounts
Abstract
DETECTION OF IMPURITIES IN FLUID FLOWING
IN REFINERY PIPELINE OR OIL PRODUCTION
OPERATIONS USING NUCLEAR TECHNIQUES
(D#74,465-F) ABSTRACT OF THE DISCLOSURE:
Fluid in a pipeline or container at a refinery or at any of various petroleum producing operations is bombarded with neutrons and high energy gamma rays resulting from cap-ture of thermal neutrons are detected. The spectra of the detected gamma rays are then analyzed to determine the con-centration of the element chlorine, which gives an indica-tion of the presence and concentration of salt water in the fluid. The concentration of sulfur and the percentage gas in the fluid may be determined simultaneously with the con-centration of chlorine.
-I-
IN REFINERY PIPELINE OR OIL PRODUCTION
OPERATIONS USING NUCLEAR TECHNIQUES
(D#74,465-F) ABSTRACT OF THE DISCLOSURE:
Fluid in a pipeline or container at a refinery or at any of various petroleum producing operations is bombarded with neutrons and high energy gamma rays resulting from cap-ture of thermal neutrons are detected. The spectra of the detected gamma rays are then analyzed to determine the con-centration of the element chlorine, which gives an indica-tion of the presence and concentration of salt water in the fluid. The concentration of sulfur and the percentage gas in the fluid may be determined simultaneously with the con-centration of chlorine.
-I-
Description
~01~86t~
BACKGROUND OF THE INVENTION:
1. FIELD OF INVENTION:
The present invention relates to nuclear techniques for detecting impurities such as salt water and sulfur in petroleum refining and producing operations.
BACKGROUND OF THE INVENTION:
1. FIELD OF INVENTION:
The present invention relates to nuclear techniques for detecting impurities such as salt water and sulfur in petroleum refining and producing operations.
2. DESCRIPTION OF PRIOR ART:
Petroleum products often contain small concentra-tions of undesirable impurities, such as chlorine, sulfur and other elements. For example, even relatively small concentrations of salt water in crude oil can often cause major problems during refining operations. The amount of sulfur in petroleum or fuel oil must be closely monitored for processing and environmental reasons.
A recent article in Analytical Chemistry, Volume 46, Number 9, August, 1974, page 1223 and following, deals with determining the amount of sulfur in oil using neutron capture gamma ray spectroscopy. However, it has been found with the present invention that for crude oil of varying and unknown chlorine content, the sulfur readings are varied due to the varying chlorine content. The isotope 32S, upon cap-ture of thermal neutrons, emits relatively low intensity 8.64, 7.78, 7.42, 7.19, 6.64 and 5.97 MeV gamma radiation in addition to the relatively intense 5.43 MeV radiation.
The isotope 35Cl, upon capture of thermal neutrons, emits 7.79, 7.42, 6.64 and 6.11 MeV gamma radiation. The second and first escape peaks of the 6.64 and 6.kk MeV chlorine capture gamma radiation fall at energies 5.62 and 5.60 MeV, respectively. These escape peaks essentially overlap the primary sulfur capture peak at 5.43 MeV. Due to these overlapping energy peaks, unless the chlorine level in a .~ '.
36?~
sample were known and constant, sulfur readings obtained with this prior art technique were not accurate. However, the salt water (and thus chlorine) content of crude oil varies from well to well as well as during the production life of a well for a number of reasons. So far as is known, the only way prior to the present invention to determine chlorine content of crude oil was by chemical analysis.
SUMMARY OF THE INVENTION:
Briefly, the present invention relates to a new and improved method and apparatus for determining the presence of chlorine in a fluid conduit. The fluid may be crude oil at a wellhead, loading dock or other location, or refined product, feed stock or waste water to dispose of at a refinery.
The fluid is bombarded with fast neutrons from a neutron source which are slowed down and thereafter engage in thermal neutron capture reactions with materials in the fluid, giving rise to thermal neutron capture gamma rays. The energy spectra of the thermal neutron capture gamma rays are obtained, from which a measure of the concentration of chlorine in the fluid may be ascertained. If the salinity of the salt water is known, the concentration of salt water within the fluid is accordingly determined.
Alternatively, since substantially all the chlorine in fluids being sampled is present as sodium chloride, the measure of the relative presence of chlo-rine is in itself a measure of the presence of salt water. The concentration of sulfur is determined from the gamma ray spectra simultaneously with the concentration of chlorine.
Also, if the fluid contains -'' ~ ' , ''~ ':
g86~
a gas homogeneously mixed therein, the percentage of gas or gas oil ratio (GOR) may be determined according to the present invention.
~RIEF DESCRIPTION OF THE DRAWINGS:
Figs. 1 and 3 are schematic block diagrams of ap-paratus according to the present invention;
Fig. 2 is a graphical illustration of a typical thermal neutron capture gamma ray spectrum for crude oil;
Figs. 4 and 5 are graphical illustrations of the ratio of chlorine neutron capture gamma ray count to hydro-gen neutron capture gamma ray count in a fluid with the present invention;
Fig. 6 is a further graphical illustration of net counts of chlorine neutron capture gamma rays as a function of percent chlorine (chlorine concentration) in a fluid obtained with the present invention;
Fig. 7 is a graphical illustration of percent standard deviation of results of the present invention as a function of percent chlorine in a fluid; and Fig. 8 is a graph by which the chlorine and sulfur content of a fluid are simultaneously determined for a fluid as a function of the ratio of chlorine neutron capture gamma ray count and sulfur neutron capture gamma ray count, re-spectively, from the fluid to the hydrogen neutron capture gamma ray count from the fluid.
DESCRIPTION OF THE PREFERRED EMBODIMENT:
Relatively small concentrations of salt water in crude oil can often cause major problems in the crude oil refining process. The present invention relates to the detection in a flowing crude oil stream or other petroleum B
`` ~[)1~6.~?~
conduit of concentrations of chlorine as low as several parts per million with statistical accuracies of +15 percent or better. The present invention is based upon the bombardment or irradiation of a flowing stream of crude oil with neutrons and the detection of gamma radiation emitted by the element chlorine upon capture of thermal neutrons. For a given thermal neutron flux, the yield of chlorine capture radiation is proportional to the concentration of chlorine in the flowing stream of crude oil. If it is known or assumed that all chlorine is in the form of NaCl and if the water salinity is known, then the intensity of chlorine capture radiation is a direct indication of salt water concentration.
Gamma radiation resulting from thermal capture (n,y) reactions is "prompt" in the sense that it is emitted within microseconds after the capture event. This is in contrast to "delayed" gamma radiation resulting from "acti-vation" type reactions which is emitted from milliseconds to years after the reaction. Since thermal neutron capture radiation is almost instantaneous, the velocity and volume flow rate of the crude oil stream do not affect the measure-ment. Another advantage of the present invention is that since thermal neutrons are required, a chemical source rather than an evacuated envelope accelerator type neutron generator source can be used. Chemical sources are rela-tively inexpensive and, of course, require no associated electronics or maintenance.
THEORY AND SENSITIVITY CALCULATIONS
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The counts C recorded by a gamma ray detector during time T (seconds) is given by the equation C = E B N G ~ T (l) ~86~
where E = the efficiency of the detector B = the branching ratio of the counted gamma radiation N = the nuclear density o the isotope of interest = the capture cross section for the reaction of interest (cm2) = the thermal neutron flux (neutrons/cm - sec3 The detector efficiency term E can be expressed as E = K b ~ f (2) where K = a constant depending upon the source-detector geometry = total efficiency of the detector to the counted gamma radiation b = the fraction correction for the absorption of gamma radiation within the sample f = the peak to total ratio for the gamma radiation of interest For the C135(n,~) reaction, ~Cl = 33.6 barns. The nuclear density NCl is given by the equation Ncl (PCl ICl_35 Q)/(Acl lOO) = PCl Q 2 15 10 4 (3) where PCl = percent by weight of elemental chlorine in the fluid ICl 35 = isotopic fraction of C135=.755 Q = Avogadro's number Acl = atomic weight of Cl = 35 The gamma radiation of interest for chlorine are encompassed within Window 1 (Fig. 2) and their MeV levels along with their corresponding branching ratios B are ~ 86~
(MeV) Gamma ray energy B
7.79 0.078 7.42 0.140 6.64 0.144 6.11 0.214 ~ = 0.576 All of the above gamma radiations in Window 1 will be counted so that the sum of branching ratios . BCl = 0.576 (4) will be used in Equation (1) to compute Ccl.
For a 5" tdiameter) x 5" NaI(Tl) cylindrical crys-tal, the - 1.4 for counted gamma radiation in the 5.75- -8.0 MeV range and since this range contains not only photo but escape peaks, f ~ 0.8. Therefore ( f)Cl = 1.12 (5) Substituting Equations (2) through (5) into Equation (1) and :
subscripting C to designate the C135(n,y) reaction yields Ccl = (1.12 KClbcl)~0.576~(2.15~10 PCl Q)-33~6 ~cl T
= 0.466 PCl Q ~Cl TCl KCl bCl (6) The prior art article discussed above has measured sulfur content in crude oil using the S32(n,y) reaction.
For S (n,y) ~S = 0.51 barns. The nuclear density NS is given by the equation NS (PS IS-32 Q)/(AS 100) = PS Q 2.95 ! 10 4 (7) where PS = percent by weight of elemental sulfur within the oil IS 32 = isotopic fraction of S32 = 0 95 Q = Avogadro's number AS = atomic weight of S = 32 The predominant gamma radiation of interest from the S32 (n,~) reaction is 5.42 MeV with BS = 0.42 (8) For the technique used in this article using a 3"
x 3" NaI(Tl) detectox (~ f)S = 0 04 (9) Substituting Equations (2), t7), (8) and (9) into (1) and subscripting C to designate the S32(n,y) reaction yields CS = (-04 KSbs) 0.42 (2.95 10 4 PsQ) 0.51 ~S T
= 2.52 10 PSQ ~S TS KS bS (10) From Equations (6) and (10), we have C = 1 844 103 C PCl~ClTClKClbCl (11) If a geometry similar to that in Figure 1 of the prior art article were used to measure the chlorine content in crude oil, the geometric factors Xcl . bCl KS . bS (12) Also referring to the results of the prior art reference, for a controlled sample it was found that for PS = 1% and TS
= 2000 seconds (33.3 minutes), Cs = 763 counts using a Cf252 source emitting 5 105 neutrons per second. If the chlorine measurement is made using a source emitting 5 107 neutrons per second, ~Cl/~S = 102 (13) Substituting the above values from this article along with Equations (12) and (13) into Equation (11) yields Ccl = 7 03 x 10 PCl TCl (14) which relates the counts recorded in a 5.75-8.0 MeV window resulting from the C135(n,~) reaction to the percent (by weight) of elemental chlorine in the crude oil for a counting time TCl. In the prior art reference, it was estimated that ~86~
the CB, the background recorded in the energy window 5.75 to -~
8.0 MeV is approximately 37 counts per second.
Figure 1 shows an apparatus A according to the present invention with a neutron source S and a detector D
mounted in suitable sockets 10 and 12, respectively, of a counting chamber C mounted in a crude oil flow line 14. The detector D is preferably a 5" x 5" NaI(Tl) cylindrical cr~s-tal coupled to a photomultiplier tube T. The source S shown is a Cf252 neutron source emitting 5 x 107 neutrons per second, although it should be understood that a different source material, such as actinium-beryllium or americium-beryllium could be used, if desired.
The chamber C preferably should be constructed of some material which contains no elements producing appreci-able capture gamma radiation above 5.0 MeV. Aluminum or certain fiberglass-epoxy materials would be suitable, al-though iron, which produces 9.30 and 7.64 MeV gamma radiation through (n,y) reactions, should be avoided. It should be noted that the chamber C is designed such that the detector D and source S are physically isolated in the sockets 10 and 12 from the crude oil. This eliminates the possibility of contaminating the crude oil if the source S should leak and :
also permits the detector D and source S to be removed without interrupting the flow of crude oil.
The physical shape of the chamber C is not critical as long as the source S and detector D are surrounded by at least several inches of fluid. In certain situations it might be desirable to coat the inside of the chamber C with a material of high thermal neutron cross capture cross section, such as boron. This would reduce the thermal ~ 36~
, ~
neutron interactions with the walls of the chamber and also prevent the escape from the chamber of thermal neutrons that might react wlth elements outside the chamber producing additional "background" radiation. Boron (boron carbide mixed with epoxy resin) would be ideal for this application since it has a large thermal neutron capture cross section (~ = 775 barns) and a capture reaction which produces no radiation above 5.0 MeV.
The detector D produces scintillations or discrete flashes of light whenever gamma rays pass therethrough, while the photomultiplier tube T generates in response to each such scintillation a voltage pulse proportional to the intensity of the scintillation. A conventional preamplifier circuit 16 amplifies the pulses from the photomultiplier tube T and furnishes the amplifier pulses to a further amplifier stage 18. A B+ power supply 20 is provided for the preamplifier 16, and a high voltage power supply 22 is provided for the photomultiplier tube T.
The output pulses from amplifier 18 are fur-nished to a gain stabilizer circuit 24 which is calibrated to respond to the energy level of a selected reference peak in the gamma ray energy spectrum, such as the 2.23 MeV
energy peak of hydrogen in Window 2 (Fig. 2). It should be understood, however, that other gamma ray energy peaks may be used for gain stabiliation, if desired. The gain stabi-lizer circuit 24 is an automatic gain control circuit which responds to energy level of pulses at the calibrated peak level and adjusts the gain of all energy level pulses from the photomultiplier tube T to compensate for gain shift or variations in tube T and other circuitry of the apparatus of :
8~
the present invention due to power supply voltage fluctuations and/or temperature effects.
The output pulses from gain stabilizer circuit 24 are supplied to a pulse height or multi-channel analyzer 26.
The pulse height analyzer 26 may be of conventional design as known in the art and having, for example, four or more channels or energy divisions corresponding to quantizations or energy ranges of the pulse heights of the input pulses, if desired. The pulse height analyzer 26 functions to sort and accumulate a running total of the incoming pulses into a plurality of storage locations or channels based on the height of the incoming pulses which, it will be recalled, is directly related to the energy of the gamma rays causing the pulse. The output of the pulse height analyzer 26 in the case of the present invention consists of count pulses occurring in each of three energy ranges or windows as depicted in Fig. 2. It should also be understood the three appropriately biased single channel analyzers may be used in place of the multi-channel 26, if desired.
The output from the pulse height analyzer 26 may be stored on a suitable memory device for subsequent proces-sing, or alternatively, is supplied directly over an appro-priate number of lines to a computer 28, which obtains from the number of chlorine counts, and the length of time for such count, a measure of the concentration of chlorine or salt water in the fluid in the line 14, in a manner to be set forth. Further, the computer 28 may also simultaneously determine from the output of analyzer 26 a measure of the concentration of sulfur in the fluid in line 14, and the percentage of gas in such fluid. The results of such 386~
computations may be stored or displayed, as desired with a recorder 30 or other suitable display device.
Fig. 2 shows a typical capture gamma ray spectrum 32 recorded using the equipment of Fig. 1 for a stream of crude oil containing small amounts of chlorine and sulfur.
The intense peak of 2.23 MeV results from the capture of thermal neutrons by hydrogen in the crude oil and is used, as set forth above, as an energy reference peak by the gain stabilizer circuit of Fig. 1. Fig. 2 also shows the energy settings of the multi-channel analyzer 26. The first set-ting, identified as "Window 1", extends from 5.75 to 8.0 MeV
and includes photoelectric and escape peaks from the 7.79, 7.42, 6.64 and 6.11 MeV radiation from the C135 (n,y) C136 reaction as well as the 7.78, 7.42, 7.19, 6.64 and 5.97 MeV
peaks from sulfur. The second setting, identified as Window 2, extends from 2.00 to 2.50 MeV and includes the 2.23 MeV hydrogen capture peak. The third setting, identified as Window 3, extends from 5.00 to 5.75 MeV and includes the 5.42 MeV sulfur capture peak.
DETERMINATION OF CHLORINE CONTENT
A. No Free Gas in the Crude Oil If it is assumed that there is no free gas in the flowing stream of crude oil, the counts recorded in window 1, Cl, for a count time T is given by the Equation Cl = CCl + Cl (17) where Ccl = counts due only to the C135(n,y)C136 reaction ClB = the background counts in Window 1 due to all gamma radiation other than that from the chlorine capture reaction Ccl can be expressed as Cl PClKcLT (18) --1 1-- :
36~1~
, where PCl = the percent (by weight) of elemental chlorine contained in the crude oil KCl = a calibration constant depending upon the source strength, source-detector spacing, de-tector efficiency, and geometry of the counting chamber T = the count time in seconds -Substituting Equation (18) into Equation (17) and solving for Pcl yields C C
P 1 = ( 1 ~ 1 )/K' (19) Theoretical Cl detection sensitivity of the appa-ratus A is summarized in Fig. 6 which shows a plt of C
versus PCl from Equation (14) using a count time T = 2000 seconds and KCl = 7.03 x 104. The grid at the top of the plot can be used to determine Ccl as a function of percent water cut and the salinity of the water in ppm NaCl. The use of Fig. 6 can best be illustrated by the following example:
Percent water in oil flow = 0.01%
Salinity of water = 50,000 ppm NaCl This concentration of water and salinity corresponds to a concentration (by weight) of 0.000303% elemental chlorine and will produce Ccl - 4.8 x 104 net counts for a count time T = 2000 seconds (33.3 minutes).
It is now of interest to determine the statistical accuracy to which chlorine concentration can be measured.
The percent standard deviation SD of the measured count C
is given by the equation.
SD = [(Ccl + [2 CB TCl]) / /Ccl] x 100 (20) where CB is the background count rate in the 5.75 to 8.0 MeV
window in counts per second. It was stated earlier that CB
was estimated to be 37 counts per second for a 3" x 3"
3B6~) NaI(Tl) detector and a Cf source emitting 5 x 10 neutrons/second. For a 5" x 5" NaI(Tl) detector, a 5 107 neutron/second source, and TCl = 2000 seconds, the quantity 2 CB TCl = 2 37 2000 (~5x5/ 3x3) = 2 37 2000 (1.4/0.4) 102 = 5.19 107 and Equation (20) reduces to SD - [(Ccl + 5.19 107)1/ /Ccl] x 100 (21) Fig. 7 shows a plot of SD from Equation (21) using Equation (14) to relate Ccl to PCl 1 with the percent water cut - salinity grid again included at the top of the plot.
Again using the example of 0.01% water cut at a salinity of 50,000 ppm NaCl, it can be seen from Fig. 7 that the chlorine concentration can be measured to a standard deviation of +15 percent.
B. Free Gas in the Flowing Stream of Crude Oil If a homogenous mixture of gas is present in the flowing stream of crude oil, Cl is now given by the Equation Cl = (CCl + Cl ) G(PG) (22) = (KclpclT + Cl ) G(pG) (22a) where G(PG) is a term dependent upon the hydrogen content of the crude oil-gas mixture which is, in turn, dependent upon PG, the percent gas content of the crude oil. Likewise, the total counts recorded in window 2, C2, is given by the Equa-tion C2 = tCH + C2 ) G(PG) (23) here CH = count rate in Window 2 due to H(n,y) H
activity C2B = the background counts in window 2 due to gamma radiation other than that resulting from neutron capture in hydrogen Solving Equations (22a) and (23) for PCl yields (the chlorine concentration) 1 LCl (C~+C2 ) ClB] (24) where Cl/C2 is the ratio of gross counts recorded in window 1 to window 2 during a count time T. The remaining terms on the right hand side of Equation (24) are determined when the system is calibrated. Specifically, ClB/T i5 determined by filling the chamber C with crude oil containing no free gas and no chlorine and recording the gross count in window 1 (estimated to be 37 counts per second, as set forth above) (CH+C2 )/T is also the gross count rate recorded in win-dow 2 with the counting chamber filled with crude oil containing no free gas and no chlor-lne K 1 is determined by (a) filling the count chamber C with crude oil containing no free gas and a known concentration PCl of chlorine, (b) re-cording C for a time T and (c~ solving equation ~19) for KCl using Cl as determined above.
It should be noted that Equation (24) does not contain the gas term G(PG) and is, therefore, independent of the amount of free gas in the fluid.
Subtracting Equation (22) from Equation (23) and -solving for G(PG) yields G(P ) = [C2-Cl] [(CH+c2 ) ~ (KClPCl 1 (25) here (C2-Cl) is the difference in gross counts recorded in windows 2 and 1, respectively, for time T
(CH+C2B) is predetermined in the calibration procedure above KCl and ClB are also predetermined in the calibration procedure above PCl (the chlorine concentration) is determined from equation (24) As mentioned earlier, G(PG) is indicative of the percentage gas content of the flowing stream of crude oil, if the free gas is homogeneously mixed in the fluid stream.
B
SIMULTANEOUS MEASUREMENT OF CHLORINE AND SULFUR CONTENT
With the present invention, it has also been found possible to determine the effects of variation in the fluid sulfur content upon the chlorine concentration measurement, and the precision to which sulfur concentration in the fluid can be measured. This determination of sulfur content is of particular importance in producing low sulfur fuels in refinery operations. A series of gamma ray spectra was measured after adding known incremental amounts of chlorine (as NaCQ) and sulfur (as H2SO4) to tap water in the counting chamber C
using a source-detector spacing of 8". The results are illustrated in Figs. 4 and 5 and summarized in Fig. 8. RcQ~
which is the ratio of counts in Window l to counts in Window 2, is plotted along the abcissa. Rs, the ratio of counts in Window
Petroleum products often contain small concentra-tions of undesirable impurities, such as chlorine, sulfur and other elements. For example, even relatively small concentrations of salt water in crude oil can often cause major problems during refining operations. The amount of sulfur in petroleum or fuel oil must be closely monitored for processing and environmental reasons.
A recent article in Analytical Chemistry, Volume 46, Number 9, August, 1974, page 1223 and following, deals with determining the amount of sulfur in oil using neutron capture gamma ray spectroscopy. However, it has been found with the present invention that for crude oil of varying and unknown chlorine content, the sulfur readings are varied due to the varying chlorine content. The isotope 32S, upon cap-ture of thermal neutrons, emits relatively low intensity 8.64, 7.78, 7.42, 7.19, 6.64 and 5.97 MeV gamma radiation in addition to the relatively intense 5.43 MeV radiation.
The isotope 35Cl, upon capture of thermal neutrons, emits 7.79, 7.42, 6.64 and 6.11 MeV gamma radiation. The second and first escape peaks of the 6.64 and 6.kk MeV chlorine capture gamma radiation fall at energies 5.62 and 5.60 MeV, respectively. These escape peaks essentially overlap the primary sulfur capture peak at 5.43 MeV. Due to these overlapping energy peaks, unless the chlorine level in a .~ '.
36?~
sample were known and constant, sulfur readings obtained with this prior art technique were not accurate. However, the salt water (and thus chlorine) content of crude oil varies from well to well as well as during the production life of a well for a number of reasons. So far as is known, the only way prior to the present invention to determine chlorine content of crude oil was by chemical analysis.
SUMMARY OF THE INVENTION:
Briefly, the present invention relates to a new and improved method and apparatus for determining the presence of chlorine in a fluid conduit. The fluid may be crude oil at a wellhead, loading dock or other location, or refined product, feed stock or waste water to dispose of at a refinery.
The fluid is bombarded with fast neutrons from a neutron source which are slowed down and thereafter engage in thermal neutron capture reactions with materials in the fluid, giving rise to thermal neutron capture gamma rays. The energy spectra of the thermal neutron capture gamma rays are obtained, from which a measure of the concentration of chlorine in the fluid may be ascertained. If the salinity of the salt water is known, the concentration of salt water within the fluid is accordingly determined.
Alternatively, since substantially all the chlorine in fluids being sampled is present as sodium chloride, the measure of the relative presence of chlo-rine is in itself a measure of the presence of salt water. The concentration of sulfur is determined from the gamma ray spectra simultaneously with the concentration of chlorine.
Also, if the fluid contains -'' ~ ' , ''~ ':
g86~
a gas homogeneously mixed therein, the percentage of gas or gas oil ratio (GOR) may be determined according to the present invention.
~RIEF DESCRIPTION OF THE DRAWINGS:
Figs. 1 and 3 are schematic block diagrams of ap-paratus according to the present invention;
Fig. 2 is a graphical illustration of a typical thermal neutron capture gamma ray spectrum for crude oil;
Figs. 4 and 5 are graphical illustrations of the ratio of chlorine neutron capture gamma ray count to hydro-gen neutron capture gamma ray count in a fluid with the present invention;
Fig. 6 is a further graphical illustration of net counts of chlorine neutron capture gamma rays as a function of percent chlorine (chlorine concentration) in a fluid obtained with the present invention;
Fig. 7 is a graphical illustration of percent standard deviation of results of the present invention as a function of percent chlorine in a fluid; and Fig. 8 is a graph by which the chlorine and sulfur content of a fluid are simultaneously determined for a fluid as a function of the ratio of chlorine neutron capture gamma ray count and sulfur neutron capture gamma ray count, re-spectively, from the fluid to the hydrogen neutron capture gamma ray count from the fluid.
DESCRIPTION OF THE PREFERRED EMBODIMENT:
Relatively small concentrations of salt water in crude oil can often cause major problems in the crude oil refining process. The present invention relates to the detection in a flowing crude oil stream or other petroleum B
`` ~[)1~6.~?~
conduit of concentrations of chlorine as low as several parts per million with statistical accuracies of +15 percent or better. The present invention is based upon the bombardment or irradiation of a flowing stream of crude oil with neutrons and the detection of gamma radiation emitted by the element chlorine upon capture of thermal neutrons. For a given thermal neutron flux, the yield of chlorine capture radiation is proportional to the concentration of chlorine in the flowing stream of crude oil. If it is known or assumed that all chlorine is in the form of NaCl and if the water salinity is known, then the intensity of chlorine capture radiation is a direct indication of salt water concentration.
Gamma radiation resulting from thermal capture (n,y) reactions is "prompt" in the sense that it is emitted within microseconds after the capture event. This is in contrast to "delayed" gamma radiation resulting from "acti-vation" type reactions which is emitted from milliseconds to years after the reaction. Since thermal neutron capture radiation is almost instantaneous, the velocity and volume flow rate of the crude oil stream do not affect the measure-ment. Another advantage of the present invention is that since thermal neutrons are required, a chemical source rather than an evacuated envelope accelerator type neutron generator source can be used. Chemical sources are rela-tively inexpensive and, of course, require no associated electronics or maintenance.
THEORY AND SENSITIVITY CALCULATIONS
:~
The counts C recorded by a gamma ray detector during time T (seconds) is given by the equation C = E B N G ~ T (l) ~86~
where E = the efficiency of the detector B = the branching ratio of the counted gamma radiation N = the nuclear density o the isotope of interest = the capture cross section for the reaction of interest (cm2) = the thermal neutron flux (neutrons/cm - sec3 The detector efficiency term E can be expressed as E = K b ~ f (2) where K = a constant depending upon the source-detector geometry = total efficiency of the detector to the counted gamma radiation b = the fraction correction for the absorption of gamma radiation within the sample f = the peak to total ratio for the gamma radiation of interest For the C135(n,~) reaction, ~Cl = 33.6 barns. The nuclear density NCl is given by the equation Ncl (PCl ICl_35 Q)/(Acl lOO) = PCl Q 2 15 10 4 (3) where PCl = percent by weight of elemental chlorine in the fluid ICl 35 = isotopic fraction of C135=.755 Q = Avogadro's number Acl = atomic weight of Cl = 35 The gamma radiation of interest for chlorine are encompassed within Window 1 (Fig. 2) and their MeV levels along with their corresponding branching ratios B are ~ 86~
(MeV) Gamma ray energy B
7.79 0.078 7.42 0.140 6.64 0.144 6.11 0.214 ~ = 0.576 All of the above gamma radiations in Window 1 will be counted so that the sum of branching ratios . BCl = 0.576 (4) will be used in Equation (1) to compute Ccl.
For a 5" tdiameter) x 5" NaI(Tl) cylindrical crys-tal, the - 1.4 for counted gamma radiation in the 5.75- -8.0 MeV range and since this range contains not only photo but escape peaks, f ~ 0.8. Therefore ( f)Cl = 1.12 (5) Substituting Equations (2) through (5) into Equation (1) and :
subscripting C to designate the C135(n,y) reaction yields Ccl = (1.12 KClbcl)~0.576~(2.15~10 PCl Q)-33~6 ~cl T
= 0.466 PCl Q ~Cl TCl KCl bCl (6) The prior art article discussed above has measured sulfur content in crude oil using the S32(n,y) reaction.
For S (n,y) ~S = 0.51 barns. The nuclear density NS is given by the equation NS (PS IS-32 Q)/(AS 100) = PS Q 2.95 ! 10 4 (7) where PS = percent by weight of elemental sulfur within the oil IS 32 = isotopic fraction of S32 = 0 95 Q = Avogadro's number AS = atomic weight of S = 32 The predominant gamma radiation of interest from the S32 (n,~) reaction is 5.42 MeV with BS = 0.42 (8) For the technique used in this article using a 3"
x 3" NaI(Tl) detectox (~ f)S = 0 04 (9) Substituting Equations (2), t7), (8) and (9) into (1) and subscripting C to designate the S32(n,y) reaction yields CS = (-04 KSbs) 0.42 (2.95 10 4 PsQ) 0.51 ~S T
= 2.52 10 PSQ ~S TS KS bS (10) From Equations (6) and (10), we have C = 1 844 103 C PCl~ClTClKClbCl (11) If a geometry similar to that in Figure 1 of the prior art article were used to measure the chlorine content in crude oil, the geometric factors Xcl . bCl KS . bS (12) Also referring to the results of the prior art reference, for a controlled sample it was found that for PS = 1% and TS
= 2000 seconds (33.3 minutes), Cs = 763 counts using a Cf252 source emitting 5 105 neutrons per second. If the chlorine measurement is made using a source emitting 5 107 neutrons per second, ~Cl/~S = 102 (13) Substituting the above values from this article along with Equations (12) and (13) into Equation (11) yields Ccl = 7 03 x 10 PCl TCl (14) which relates the counts recorded in a 5.75-8.0 MeV window resulting from the C135(n,~) reaction to the percent (by weight) of elemental chlorine in the crude oil for a counting time TCl. In the prior art reference, it was estimated that ~86~
the CB, the background recorded in the energy window 5.75 to -~
8.0 MeV is approximately 37 counts per second.
Figure 1 shows an apparatus A according to the present invention with a neutron source S and a detector D
mounted in suitable sockets 10 and 12, respectively, of a counting chamber C mounted in a crude oil flow line 14. The detector D is preferably a 5" x 5" NaI(Tl) cylindrical cr~s-tal coupled to a photomultiplier tube T. The source S shown is a Cf252 neutron source emitting 5 x 107 neutrons per second, although it should be understood that a different source material, such as actinium-beryllium or americium-beryllium could be used, if desired.
The chamber C preferably should be constructed of some material which contains no elements producing appreci-able capture gamma radiation above 5.0 MeV. Aluminum or certain fiberglass-epoxy materials would be suitable, al-though iron, which produces 9.30 and 7.64 MeV gamma radiation through (n,y) reactions, should be avoided. It should be noted that the chamber C is designed such that the detector D and source S are physically isolated in the sockets 10 and 12 from the crude oil. This eliminates the possibility of contaminating the crude oil if the source S should leak and :
also permits the detector D and source S to be removed without interrupting the flow of crude oil.
The physical shape of the chamber C is not critical as long as the source S and detector D are surrounded by at least several inches of fluid. In certain situations it might be desirable to coat the inside of the chamber C with a material of high thermal neutron cross capture cross section, such as boron. This would reduce the thermal ~ 36~
, ~
neutron interactions with the walls of the chamber and also prevent the escape from the chamber of thermal neutrons that might react wlth elements outside the chamber producing additional "background" radiation. Boron (boron carbide mixed with epoxy resin) would be ideal for this application since it has a large thermal neutron capture cross section (~ = 775 barns) and a capture reaction which produces no radiation above 5.0 MeV.
The detector D produces scintillations or discrete flashes of light whenever gamma rays pass therethrough, while the photomultiplier tube T generates in response to each such scintillation a voltage pulse proportional to the intensity of the scintillation. A conventional preamplifier circuit 16 amplifies the pulses from the photomultiplier tube T and furnishes the amplifier pulses to a further amplifier stage 18. A B+ power supply 20 is provided for the preamplifier 16, and a high voltage power supply 22 is provided for the photomultiplier tube T.
The output pulses from amplifier 18 are fur-nished to a gain stabilizer circuit 24 which is calibrated to respond to the energy level of a selected reference peak in the gamma ray energy spectrum, such as the 2.23 MeV
energy peak of hydrogen in Window 2 (Fig. 2). It should be understood, however, that other gamma ray energy peaks may be used for gain stabiliation, if desired. The gain stabi-lizer circuit 24 is an automatic gain control circuit which responds to energy level of pulses at the calibrated peak level and adjusts the gain of all energy level pulses from the photomultiplier tube T to compensate for gain shift or variations in tube T and other circuitry of the apparatus of :
8~
the present invention due to power supply voltage fluctuations and/or temperature effects.
The output pulses from gain stabilizer circuit 24 are supplied to a pulse height or multi-channel analyzer 26.
The pulse height analyzer 26 may be of conventional design as known in the art and having, for example, four or more channels or energy divisions corresponding to quantizations or energy ranges of the pulse heights of the input pulses, if desired. The pulse height analyzer 26 functions to sort and accumulate a running total of the incoming pulses into a plurality of storage locations or channels based on the height of the incoming pulses which, it will be recalled, is directly related to the energy of the gamma rays causing the pulse. The output of the pulse height analyzer 26 in the case of the present invention consists of count pulses occurring in each of three energy ranges or windows as depicted in Fig. 2. It should also be understood the three appropriately biased single channel analyzers may be used in place of the multi-channel 26, if desired.
The output from the pulse height analyzer 26 may be stored on a suitable memory device for subsequent proces-sing, or alternatively, is supplied directly over an appro-priate number of lines to a computer 28, which obtains from the number of chlorine counts, and the length of time for such count, a measure of the concentration of chlorine or salt water in the fluid in the line 14, in a manner to be set forth. Further, the computer 28 may also simultaneously determine from the output of analyzer 26 a measure of the concentration of sulfur in the fluid in line 14, and the percentage of gas in such fluid. The results of such 386~
computations may be stored or displayed, as desired with a recorder 30 or other suitable display device.
Fig. 2 shows a typical capture gamma ray spectrum 32 recorded using the equipment of Fig. 1 for a stream of crude oil containing small amounts of chlorine and sulfur.
The intense peak of 2.23 MeV results from the capture of thermal neutrons by hydrogen in the crude oil and is used, as set forth above, as an energy reference peak by the gain stabilizer circuit of Fig. 1. Fig. 2 also shows the energy settings of the multi-channel analyzer 26. The first set-ting, identified as "Window 1", extends from 5.75 to 8.0 MeV
and includes photoelectric and escape peaks from the 7.79, 7.42, 6.64 and 6.11 MeV radiation from the C135 (n,y) C136 reaction as well as the 7.78, 7.42, 7.19, 6.64 and 5.97 MeV
peaks from sulfur. The second setting, identified as Window 2, extends from 2.00 to 2.50 MeV and includes the 2.23 MeV hydrogen capture peak. The third setting, identified as Window 3, extends from 5.00 to 5.75 MeV and includes the 5.42 MeV sulfur capture peak.
DETERMINATION OF CHLORINE CONTENT
A. No Free Gas in the Crude Oil If it is assumed that there is no free gas in the flowing stream of crude oil, the counts recorded in window 1, Cl, for a count time T is given by the Equation Cl = CCl + Cl (17) where Ccl = counts due only to the C135(n,y)C136 reaction ClB = the background counts in Window 1 due to all gamma radiation other than that from the chlorine capture reaction Ccl can be expressed as Cl PClKcLT (18) --1 1-- :
36~1~
, where PCl = the percent (by weight) of elemental chlorine contained in the crude oil KCl = a calibration constant depending upon the source strength, source-detector spacing, de-tector efficiency, and geometry of the counting chamber T = the count time in seconds -Substituting Equation (18) into Equation (17) and solving for Pcl yields C C
P 1 = ( 1 ~ 1 )/K' (19) Theoretical Cl detection sensitivity of the appa-ratus A is summarized in Fig. 6 which shows a plt of C
versus PCl from Equation (14) using a count time T = 2000 seconds and KCl = 7.03 x 104. The grid at the top of the plot can be used to determine Ccl as a function of percent water cut and the salinity of the water in ppm NaCl. The use of Fig. 6 can best be illustrated by the following example:
Percent water in oil flow = 0.01%
Salinity of water = 50,000 ppm NaCl This concentration of water and salinity corresponds to a concentration (by weight) of 0.000303% elemental chlorine and will produce Ccl - 4.8 x 104 net counts for a count time T = 2000 seconds (33.3 minutes).
It is now of interest to determine the statistical accuracy to which chlorine concentration can be measured.
The percent standard deviation SD of the measured count C
is given by the equation.
SD = [(Ccl + [2 CB TCl]) / /Ccl] x 100 (20) where CB is the background count rate in the 5.75 to 8.0 MeV
window in counts per second. It was stated earlier that CB
was estimated to be 37 counts per second for a 3" x 3"
3B6~) NaI(Tl) detector and a Cf source emitting 5 x 10 neutrons/second. For a 5" x 5" NaI(Tl) detector, a 5 107 neutron/second source, and TCl = 2000 seconds, the quantity 2 CB TCl = 2 37 2000 (~5x5/ 3x3) = 2 37 2000 (1.4/0.4) 102 = 5.19 107 and Equation (20) reduces to SD - [(Ccl + 5.19 107)1/ /Ccl] x 100 (21) Fig. 7 shows a plot of SD from Equation (21) using Equation (14) to relate Ccl to PCl 1 with the percent water cut - salinity grid again included at the top of the plot.
Again using the example of 0.01% water cut at a salinity of 50,000 ppm NaCl, it can be seen from Fig. 7 that the chlorine concentration can be measured to a standard deviation of +15 percent.
B. Free Gas in the Flowing Stream of Crude Oil If a homogenous mixture of gas is present in the flowing stream of crude oil, Cl is now given by the Equation Cl = (CCl + Cl ) G(PG) (22) = (KclpclT + Cl ) G(pG) (22a) where G(PG) is a term dependent upon the hydrogen content of the crude oil-gas mixture which is, in turn, dependent upon PG, the percent gas content of the crude oil. Likewise, the total counts recorded in window 2, C2, is given by the Equa-tion C2 = tCH + C2 ) G(PG) (23) here CH = count rate in Window 2 due to H(n,y) H
activity C2B = the background counts in window 2 due to gamma radiation other than that resulting from neutron capture in hydrogen Solving Equations (22a) and (23) for PCl yields (the chlorine concentration) 1 LCl (C~+C2 ) ClB] (24) where Cl/C2 is the ratio of gross counts recorded in window 1 to window 2 during a count time T. The remaining terms on the right hand side of Equation (24) are determined when the system is calibrated. Specifically, ClB/T i5 determined by filling the chamber C with crude oil containing no free gas and no chlorine and recording the gross count in window 1 (estimated to be 37 counts per second, as set forth above) (CH+C2 )/T is also the gross count rate recorded in win-dow 2 with the counting chamber filled with crude oil containing no free gas and no chlor-lne K 1 is determined by (a) filling the count chamber C with crude oil containing no free gas and a known concentration PCl of chlorine, (b) re-cording C for a time T and (c~ solving equation ~19) for KCl using Cl as determined above.
It should be noted that Equation (24) does not contain the gas term G(PG) and is, therefore, independent of the amount of free gas in the fluid.
Subtracting Equation (22) from Equation (23) and -solving for G(PG) yields G(P ) = [C2-Cl] [(CH+c2 ) ~ (KClPCl 1 (25) here (C2-Cl) is the difference in gross counts recorded in windows 2 and 1, respectively, for time T
(CH+C2B) is predetermined in the calibration procedure above KCl and ClB are also predetermined in the calibration procedure above PCl (the chlorine concentration) is determined from equation (24) As mentioned earlier, G(PG) is indicative of the percentage gas content of the flowing stream of crude oil, if the free gas is homogeneously mixed in the fluid stream.
B
SIMULTANEOUS MEASUREMENT OF CHLORINE AND SULFUR CONTENT
With the present invention, it has also been found possible to determine the effects of variation in the fluid sulfur content upon the chlorine concentration measurement, and the precision to which sulfur concentration in the fluid can be measured. This determination of sulfur content is of particular importance in producing low sulfur fuels in refinery operations. A series of gamma ray spectra was measured after adding known incremental amounts of chlorine (as NaCQ) and sulfur (as H2SO4) to tap water in the counting chamber C
using a source-detector spacing of 8". The results are illustrated in Figs. 4 and 5 and summarized in Fig. 8. RcQ~
which is the ratio of counts in Window l to counts in Window 2, is plotted along the abcissa. Rs, the ratio of counts in Window
3 from 5.000 to 5.75 MeV (which includes the 5.42 MeV radiation from thermal neutron capture in sulfur) to the counts in Window 2, is plotted along the ordinate. Data points are denoted by (i, j) where i and j are the grams of chlorine and sulfur, respectively, added to the fluid. Adjacent to each data point is the quantity (McQ~ Ms) where McQ and MS
are the masses (in grams) of chlorine and sulfur, respectively, added to the fluid. The grid is constructed by least-squares fitting straight lines through the data and is labeled in grams and ppm or percent of the element added.
The concentrations of chlorine and sulfur are also shown in parts per million and percent, respectively. Typical observed standard deviations are shown for RcQ and RS for a 20 minute count. For this count time, the sulfur concen-tration can be determined to +0.08 percent. Results similar to those shown in Fig. 8 can be expected using oil as a base fluid since oil and water have similar neutron moderation properties. Once the RS versus RcQ grid has been constructed for a given counting `
36~
chamber, the chlorine and sulfur content of an unknown fluid can be obtained from the measurement of RS and RcQ.
It can be seen that RcQ is affected to some extent by the sulfur content of the fluid. This is a result of the low intensity, high energy capture radiation from sulfur whose primary and escape peaks fall within the "chlorine"
Window 1 (Fig. 2). Likewise, it can be seen that RS is also affected by the chlorine content of the fluid. This results from the escape peaks of the 6.64 and 6.11 MeV
chlorine capture radiation that fall within the "sulfur"
Window 3. It is apparent, however, that sulfur and chlorine concentrations can be determined uniquely by recording RS
and RcQ simultaneously and using the grid of Fig. 8.
Thus, with the present invention, it is possible to obtain simultaneous measurements of chlorine and sulfur in a flowing stream of crude oil (or waste water), provided three energy windows of interest in the measured gamma ray spectrum are obtained. As set forth above, they are:
Window 1 5.75 MeV to 8.00 MeV
Window 2 2.00 MeV to 2.50 MeV
Window 3 5.00 MeV to 5.75 MeV
As described above, the ratio of counts recorded in Window 1 to the counts recorded in Window 2, RcQ~ increases linearly for a given sulfur concentration and (for concentrations of the subject element less than a few percent) with the chlo-rine content of the fluid and is independent of the hydrogen index or density of the fluid. The ratio of counts recorded in Window 3 to Window 2, Rs, also increases linearly (again, for a given chlorine content for concentrations of the subject element less than a few percent) with the sulfur 86~1~
content of the fluid. This is shown in Figure 4. It is possible, therefore, to measure RcQand RS simultaneously and obtain elemental concentrations of both chlorine and sulfur from a plot RS versus RcQ such as that of Fig. 8.
It should be understood that the techniques des-cribed above are not necessarily confined to a counting chamber geometry. In the event that the subject measurement must be made in a flow line without cutting the pipr or without diverting a portion of the stream to a counting chamber as described above, it would still be possible to make an estimation of the chlorine content (albeit not as precise) by locating the source S and detector D against the pipe 14 on opposite sides of it.
The neutron souce S and detector D are mounted on the outside of the existing flow line 14 by means of a suit-able clamp device C, or other suitable pipe attachment means, as shown in Fig. 3. The remainder of the apparatus of Fig. 3 corresponds to that of Fig. 1 and thus is not shown. However, this apparatus is connected to the preamp-lifier 16 and photomultiplier tube T in the manner set forth above for Fig. 1. Measurements have been made indicating that ppm concentrations of chlorine and 0.1 percent concen-trations of sulfur can be detected using this "through-pipe"
technique of Fig. 3; however, for a given count time, the precision to which the through-pipe measurements can be made is not as good as that obtained using a counting chamber.
From the foregoing, it can be seen that the pre-sent invention provides for the simultaneous measurement of chlorine and sulfur and can be used in various producing operations such as B
(1) Monitoring chlorine and sulfur content at a well head. The chlorine measurement could be used to monitor the water cut of the produced fluid if the salinity of the produced water is known.
(2) Monitor chlorine and sulfur at a loading dock.
(3) Monitor the chlorine and sulfur content of water prior to disposal.
In refining operations, the proposed technique can be used to (1) Monitor sulfur and chlorine in a feed stock.
(2) Monitor sulfur and/or chlorine content of re-fined products.
Among the primary advantages of the present inven-tion are:
1. Concentrations of chlorine as small as 0.0001 percent (by weight) can be detected in a flow-ing stream of crude oil.
2. The chlorine concentration measurement is inde-pendent of the linear flow velocity or the volume flow rate of the crude oil.
3. The technique is ideally suited for remote, continuous monitoring in the sense that the system requires minimal maintenance and rela-tively simple electronic equipment.
are the masses (in grams) of chlorine and sulfur, respectively, added to the fluid. The grid is constructed by least-squares fitting straight lines through the data and is labeled in grams and ppm or percent of the element added.
The concentrations of chlorine and sulfur are also shown in parts per million and percent, respectively. Typical observed standard deviations are shown for RcQ and RS for a 20 minute count. For this count time, the sulfur concen-tration can be determined to +0.08 percent. Results similar to those shown in Fig. 8 can be expected using oil as a base fluid since oil and water have similar neutron moderation properties. Once the RS versus RcQ grid has been constructed for a given counting `
36~
chamber, the chlorine and sulfur content of an unknown fluid can be obtained from the measurement of RS and RcQ.
It can be seen that RcQ is affected to some extent by the sulfur content of the fluid. This is a result of the low intensity, high energy capture radiation from sulfur whose primary and escape peaks fall within the "chlorine"
Window 1 (Fig. 2). Likewise, it can be seen that RS is also affected by the chlorine content of the fluid. This results from the escape peaks of the 6.64 and 6.11 MeV
chlorine capture radiation that fall within the "sulfur"
Window 3. It is apparent, however, that sulfur and chlorine concentrations can be determined uniquely by recording RS
and RcQ simultaneously and using the grid of Fig. 8.
Thus, with the present invention, it is possible to obtain simultaneous measurements of chlorine and sulfur in a flowing stream of crude oil (or waste water), provided three energy windows of interest in the measured gamma ray spectrum are obtained. As set forth above, they are:
Window 1 5.75 MeV to 8.00 MeV
Window 2 2.00 MeV to 2.50 MeV
Window 3 5.00 MeV to 5.75 MeV
As described above, the ratio of counts recorded in Window 1 to the counts recorded in Window 2, RcQ~ increases linearly for a given sulfur concentration and (for concentrations of the subject element less than a few percent) with the chlo-rine content of the fluid and is independent of the hydrogen index or density of the fluid. The ratio of counts recorded in Window 3 to Window 2, Rs, also increases linearly (again, for a given chlorine content for concentrations of the subject element less than a few percent) with the sulfur 86~1~
content of the fluid. This is shown in Figure 4. It is possible, therefore, to measure RcQand RS simultaneously and obtain elemental concentrations of both chlorine and sulfur from a plot RS versus RcQ such as that of Fig. 8.
It should be understood that the techniques des-cribed above are not necessarily confined to a counting chamber geometry. In the event that the subject measurement must be made in a flow line without cutting the pipr or without diverting a portion of the stream to a counting chamber as described above, it would still be possible to make an estimation of the chlorine content (albeit not as precise) by locating the source S and detector D against the pipe 14 on opposite sides of it.
The neutron souce S and detector D are mounted on the outside of the existing flow line 14 by means of a suit-able clamp device C, or other suitable pipe attachment means, as shown in Fig. 3. The remainder of the apparatus of Fig. 3 corresponds to that of Fig. 1 and thus is not shown. However, this apparatus is connected to the preamp-lifier 16 and photomultiplier tube T in the manner set forth above for Fig. 1. Measurements have been made indicating that ppm concentrations of chlorine and 0.1 percent concen-trations of sulfur can be detected using this "through-pipe"
technique of Fig. 3; however, for a given count time, the precision to which the through-pipe measurements can be made is not as good as that obtained using a counting chamber.
From the foregoing, it can be seen that the pre-sent invention provides for the simultaneous measurement of chlorine and sulfur and can be used in various producing operations such as B
(1) Monitoring chlorine and sulfur content at a well head. The chlorine measurement could be used to monitor the water cut of the produced fluid if the salinity of the produced water is known.
(2) Monitor chlorine and sulfur at a loading dock.
(3) Monitor the chlorine and sulfur content of water prior to disposal.
In refining operations, the proposed technique can be used to (1) Monitor sulfur and chlorine in a feed stock.
(2) Monitor sulfur and/or chlorine content of re-fined products.
Among the primary advantages of the present inven-tion are:
1. Concentrations of chlorine as small as 0.0001 percent (by weight) can be detected in a flow-ing stream of crude oil.
2. The chlorine concentration measurement is inde-pendent of the linear flow velocity or the volume flow rate of the crude oil.
3. The technique is ideally suited for remote, continuous monitoring in the sense that the system requires minimal maintenance and rela-tively simple electronic equipment.
4. By stabilizing the gain of the gamma ray de-tector automatically on a suitable peak with gain stabilizer 24, the system will require minimal adjustment and can be operated by un-skilled personnel. -`
86~
86~
5. The system can also give a quantitative in-dication of the free gas content of the crude oil, (a) if the free gas/liquid mixture is homogeneous and (b) if the linear flow velocities of the liquid and gas phases are the same.
The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction may be made witho~t departing fro= the spirit of the invention.
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The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction may be made witho~t departing fro= the spirit of the invention.
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Claims (24)
1. A method for analysis of a fluid flowing in a conduit to determine the presence of low concentrations of salt water in the fluid, comprising the steps of:
(a) bombarding the fluid with fast neutrons, which are slowed down and thereafter engage in thermal neu-tron capture reactions with materials in the fluid;
(b) obtaining gamma ray energy spectra of the materials in response to the capture of thermal neutrons by the materials in the fluid;
(c) obtaining a measure of the concentration of chlorine in the fluid from the gamma ray energy spectra;
(d) obtaining from the measure of the concen-tration of chlorine a measure of the concentration of salt water in the fluid; and (e) obtaining a measure of the concentration of sulfur in the fluid from the gamma ray spectra simultaneously with said step of obtaining a measure of the concentration of chlorine.
(a) bombarding the fluid with fast neutrons, which are slowed down and thereafter engage in thermal neu-tron capture reactions with materials in the fluid;
(b) obtaining gamma ray energy spectra of the materials in response to the capture of thermal neutrons by the materials in the fluid;
(c) obtaining a measure of the concentration of chlorine in the fluid from the gamma ray energy spectra;
(d) obtaining from the measure of the concen-tration of chlorine a measure of the concentration of salt water in the fluid; and (e) obtaining a measure of the concentration of sulfur in the fluid from the gamma ray spectra simultaneously with said step of obtaining a measure of the concentration of chlorine.
2. The method of Claim 1, wherein the fluid is feed stock in a petroleum refining conduit.
3. The method of Claim 1, wherein the fluid is refined product in a petroleum refining conduit.
4. The method of Claim 1, wherein the fluid is crude oil in a well head conduit at an oil well.
5. The method of Claim 1, wherein the fluid is crude oil at a loading dock.
6. The method of Claim 1, wherein the fluid is waste water which is to be disposed.
7. The method of Claim 1, wherein substantially all the chlorine in the fluid is present as sodium chloride, and wherein the measure of the concentration of salt water is obtained from the measure of the concentration of chlorine.
8. The method of Claim 1, wherein gas is present in the fluid in the conduit and further including the step of:
obtaining from the measure of the concentra-tion of chlorine a measure of the percent gas content of the fluid.
obtaining from the measure of the concentra-tion of chlorine a measure of the percent gas content of the fluid.
9. The method of Claim 1, wherein said step of obtaining gamma ray energy spectra comprises:
obtaining gamma ray energy spectra in the range of from 5.0 MeV to 8.0 MeV.
obtaining gamma ray energy spectra in the range of from 5.0 MeV to 8.0 MeV.
10. The method of Claim 1, further including the steps of:
(a) obtaining gamma ray energy spectra in the range of approximately 2.0 MeV to 2.50 MeV to include the 2.23 MeV capture reaction of hydrogen; and (b) using the energy spectra of the 2.23 MeV
hydrogen capture reaction as a reference reading for gain stabilization.
(a) obtaining gamma ray energy spectra in the range of approximately 2.0 MeV to 2.50 MeV to include the 2.23 MeV capture reaction of hydrogen; and (b) using the energy spectra of the 2.23 MeV
hydrogen capture reaction as a reference reading for gain stabilization.
11. The method of Claim 1, wherein said fast neu-trons are emitted from a neutron source and further including the step of:
attaching said neutron source to the conduit prior to said step of bombarding.
attaching said neutron source to the conduit prior to said step of bombarding.
12. The method of Claim 1, wherein said fast neu-trons are emitted from a neutron source and further including the step of:
inserting said neutron source into the con-duit prior to said step of bombarding.
inserting said neutron source into the con-duit prior to said step of bombarding.
13. An apparatus for analysis of a fluid flowing in a conduit to determine the presence of low concentrations of salt water in the fluid, comprising:
(a) means for bombarding the fluid with fast neutrons, which are slowed down and thereafter engage in thermal neutron capture reactions with the materials in the fluid;
(b) means for obtaining gamma ray energy spectra of the materials in response to the capture of thermal neutrons by the materials in the fluid;
(c) means for obtaining a measure of the concentration of chlorine in the fluid from the gamma ray energy spectra;
(d) means for obtaining from the measure of the concentration of chlorine a measure of the concentration of salt water in the fluid; and (e) means for obtaining a measure of the concentration of sulfur in the fluid from the gamma ray spectra, simultaneously with a measurement of the concentration of chlorine.
(a) means for bombarding the fluid with fast neutrons, which are slowed down and thereafter engage in thermal neutron capture reactions with the materials in the fluid;
(b) means for obtaining gamma ray energy spectra of the materials in response to the capture of thermal neutrons by the materials in the fluid;
(c) means for obtaining a measure of the concentration of chlorine in the fluid from the gamma ray energy spectra;
(d) means for obtaining from the measure of the concentration of chlorine a measure of the concentration of salt water in the fluid; and (e) means for obtaining a measure of the concentration of sulfur in the fluid from the gamma ray spectra, simultaneously with a measurement of the concentration of chlorine.
14. The apparatus of Claim 13, wherein said means for bombarding is mounted adjacent a petroleum refining con-duit to bombard refinery feed stock and sense the concentra-tion of salt water in feed stock in said conduit.
15. The apparatus of Claim 13, wherein said means for bombarding is mounted adjacent a petroleum refining conduit to bombard refinery refined product and sense the concentration of salt water in refined product in said conduit.
16. The apparatus of Claim 13, wherein said means for bombarding is mounted adjacent a well head conduit at an oil well to bombard crude oil with neutrons to sense the con-centration of salt water in crude oil.
17. The apparatus of Claim 13, wherein said means for bombarding is mounted adjacent a conduit at a loading dock to bombard crude oil with neutrons to sense the concen-tration of salt water in crude oil.
18. The apparatus of Claim 13, wherein said means for bombarding is mounted adjacent a conduit to bombard with neutrons waste water to be disposed to sense the concentra-tion of salt water therein.
19. The apparatus of Claim 13, wherein substanti-ally all the chlorine in the fluid is present as sodium chloride, and wherein the measure of the concentration of salt water is obtained from the measure of the concentration of chlorine.
20. The apparatus of Claim 13, wherein gas is present in the fluid in the conduit and further including:
means for obtaining from the measure of the concentration of chlorine a measure of the percent gas content of the fluid.
means for obtaining from the measure of the concentration of chlorine a measure of the percent gas content of the fluid.
21. The apparatus of Claim 13, wherein said means for obtaining comprises:
means for obtaining gamma ray energy spectra in the range of from 5.0 MeV to 8.0 MeV.
means for obtaining gamma ray energy spectra in the range of from 5.0 MeV to 8.0 MeV.
22. The apparatus of Claim 13, further including:
(a) means for obtaining gamma ray energy spectra in the range of approximately 2.0 MeV to 2.50 MeV to include the 2.23 MeV capture reaction of hydrogen; and (b) means for using the energy spectra of the 2.23 MeV hydrogen capture reaction as a reference read-ing for gain stabilization.
(a) means for obtaining gamma ray energy spectra in the range of approximately 2.0 MeV to 2.50 MeV to include the 2.23 MeV capture reaction of hydrogen; and (b) means for using the energy spectra of the 2.23 MeV hydrogen capture reaction as a reference read-ing for gain stabilization.
23. The apparatus of Claim 13, wherein said means for bombarding is attached to the exterior of said conduit.
24. The apparatus of Claim 13, wherein said means for bombarding is inserted into the exterior of said conduit.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US74807276A | 1976-12-06 | 1976-12-06 | |
| US748,072 | 1976-12-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088680A true CA1088680A (en) | 1980-10-28 |
Family
ID=25007876
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA291,301A Expired CA1088680A (en) | 1976-12-06 | 1977-11-21 | Detection of impurities in fluid flowing in refinery pipeline or oil production operations using nuclear techniques |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS53105290A (en) |
| CA (1) | CA1088680A (en) |
| DE (1) | DE2754143A1 (en) |
| FR (1) | FR2373055A1 (en) |
| GB (1) | GB1585305A (en) |
| IT (1) | IT1113805B (en) |
| NL (1) | NL7713414A (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4200789A (en) * | 1978-06-29 | 1980-04-29 | Texaco Inc. | Measuring oil and water cuts in a multiphase flowstream with elimination of the effects of gas in determining the liquid cuts |
| US4190768A (en) * | 1978-06-29 | 1980-02-26 | Texaco Inc. | Determining the water cut and water salinity in an oil-water flow stream by measuring the sulfur content of the produced oil |
| EP0007759A1 (en) * | 1978-07-21 | 1980-02-06 | United Kingdom Atomic Energy Authority | Method of and apparatus for measuring the water content of crude oil |
| US4365154A (en) * | 1980-03-06 | 1982-12-21 | Texaco Inc. | Detection of impurities in a fluid containing free gas using nuclear techniques |
| CN107796861B (en) * | 2016-09-05 | 2021-01-01 | 中国石油化工股份有限公司 | Method for detecting content of organic chlorine in crude oil containing free water |
| CN116341764B (en) * | 2023-05-24 | 2023-09-26 | 中国石油大学(华东) | Method and system for predicting mixed oil concentration distribution of finished oil pipeline based on historical data |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2744199A (en) * | 1952-11-28 | 1956-05-01 | Exxon Research Engineering Co | Determination of halogen in oil streams |
| US2983817A (en) * | 1956-07-23 | 1961-05-09 | Gulf Research Development Co | Neutron-capture, gamma-ray prospecting method |
-
1977
- 1977-11-18 GB GB4804377A patent/GB1585305A/en not_active Expired
- 1977-11-21 CA CA291,301A patent/CA1088680A/en not_active Expired
- 1977-12-05 IT IT3038777A patent/IT1113805B/en active
- 1977-12-05 NL NL7713414A patent/NL7713414A/en not_active Application Discontinuation
- 1977-12-05 DE DE19772754143 patent/DE2754143A1/en not_active Ceased
- 1977-12-06 FR FR7736642A patent/FR2373055A1/en active Granted
- 1977-12-06 JP JP14650777A patent/JPS53105290A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE2754143A1 (en) | 1978-06-08 |
| FR2373055A1 (en) | 1978-06-30 |
| IT1113805B (en) | 1986-01-27 |
| JPS53105290A (en) | 1978-09-13 |
| NL7713414A (en) | 1978-06-08 |
| GB1585305A (en) | 1981-02-25 |
| FR2373055B1 (en) | 1983-04-29 |
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