Journal of RadioarutO,tical Chemistry, Vol. 71, No. 1-2 (1982) 253-264
ON-LINE ANALYSIS OF COAL BY NEUTRON INDUCED GAMMA SPECTROMETRY* H. R. WILDE, W. HERZOG
Staatliches MaterialpriiJi4ngsamt NIr D~4600 Dortmund 41 (FRG) (Received July 7, 1981)
Thermal neutron prompt gamma activation analysis (PGNAA) has proven to be a useful tool for the multi-elemental characterization of cQal. The use of isotopic neutron sources allows the construction of relatively small irradiation facilities for the on.line analysis of large volume samples. As a first step to an on-line analysis system for process control in a coal blending plant we have developed a facility using a Cf-252 neutron source with an actual strength of 1 rag. This source, which is shielded by layers of high purity lead and paraffin, can be moved to the center of cylindrical sample holders containing up to 150 kg of coal. To avoid background radiation the sample holders are made from polyethylene. The prompt gamma rays emitted from the sample are measured with a 22% high purity germanium detector housed in a special horizontally extended cryostate assembly. The detector is positioned on top of the sample; it is surrounded by a multi-layer decreasing Z-absorber to reduce low energy gamma background. Paraffin loaded with 95% enriched lithium-6-carbonate is used between sample and detector as a gamma window with high absorption for thermal neutrons. Moreover the detector is shielded against background radiation by lead and natural lithiumcarbonate. The data processing system consists of high count-rate analogue electronics including pileup-suppression and a fast data acquisition system, which permits on-line analysis of the collected data. Analysis of several samples of simulated coals as well as Western Germany coals shows a good spectral response of our system for the elements H, C, AI, Si, S, C1, Ca, Ti and Fe, whereas the sensitivity for N, K and Na is somewhat lower. This means, that the quantitative determination of the above elements will be possible within 20 minutes. Optimization of the system is continued with a stress on analysis time and detection sensitivity,
Introduction
Due to the increasing generation
importance
of coal for electric power
as well as for gazification
and liquefaction
there
is a growing need for on-line analysis of coal composition quality in large process
streams,
and
since the efficiency of these
*Supported by Bundesministerium flit Forschung und Teehnologie D-5300 Bonn 1, Fed. Rep, of Germany.
J. Radioanal. Chem. 71 (1982)
253
H. R. WILDE, W. HERZOG: ON-LINE ANALYSIS OF COAL
combustion
or c o n v e r s i o n
by even small changes Several
methods
elements
processes
may be affected I) in coal composition
for m o n i t o r i n g
gross
coal c o m p o s i t i o n
in the coal have been reported
PNAA-method
(prompt neutron
seriously
activation
2,3,4).
or special
Among
analysis)
has proven
be the most p r o m i s i n g
tool
coal.
based upon the fact that the capture
This method
a neutron compound energy
is
by a nucleus
for the m u l t i - e l e m e n t
these the
leads
to the formation
nucleus which decays
istic of the e m i t t i n g
nucleus,
y-rays
the neutron
capture
a particular
energy
of the e m i t t i n g Cf-252
allows
facilities process
section.
directly
applications
of r e l a t i v e l y
or even complete or electric
elemental
experiments
of an on-line
to the abundance sources small
this means,
ash analysis, analysis
such as
irradiation samples.
For
that an upper
Possible
applications
sulfur d e t e r m i n a t i o n
for coal b l e n d i n g
This paper presents
of several p a r a m e t e r s
facilities
the results
done at the M a t e r i a l p r H f u n g s a m t
coal analysis
depends
flux and
time must be less than
should be achieved.
power plants.
to study the effect
the analysis
The
of y-rays with
of large volume
time of the coal;
BTU-determination,
laboratory
proportional
of
is character-
neutron
So the number
The use of isotopic
the c o n s t r u c t i o n
10 - 15 min~
(~I0-IOs)
the b o m b a r d i n g
for the rapid analysis
the t r a n s p o r t a t i o n
include
is
element.
control
limit of
cross
of y-rays.
and their p r o d u c t i o n - r a t e
on the n u m b e r of target nuclei,
of
of a highly excite(
by the emission
spectrum of these prompt
analysis
to
for optimal
of the
Dortmund performance
system.
Experimental As a first.step a testing
analysis
system
for process
facility has been built up using a Cf-252
with an actual in the p l a n n i n g
254
to an on-line
strength of 1 mg.
There were
control
neutron
sourc(
four main consideratio~
of the experiments:
J. Radioanal. Chem. 71 (1982)
H. R. WILDE, W. HERZOG: ON-LINE ANALYSIS OF COAL
Detector with n-shield
I
i I Cc~l ~mple
~_~2Cf souro _
/
9
Lead
/
Boron-
/ potyetht.jtene
~///////j////////A=///
"H Screening container
~.~
t 10cm.. i Fig. 1. Schematic graph of the experimental setup
a) the
1 mg neutron
analysis,
size should be variable
c) the detector sensitivity
for c o n v e n t i o n a l
in the range
should have good energy against n e u t r o n
d) the arrangement
activation
should be d e s i g n e d
these design
resolution
50 - 150 kg, and low
irradiation,
and the shields
in order to optimize Following
installed
had to be used,
b) the sample
detector
source,
of neutron
flexibly
source,
sample and
to allow easy m o d i f i c a t i o n
the system. rules
it will be p o s s i b l e
to extrapolate
from the data of the laboratory
experiment
a prototype
graph of the e x p e r i m e n t a l
is shown
system.
in Fig.
A schematic
I. The sample
J. Radioanal.Chem. 71 (1982) 17
to the p a r a m e t e r s
and the d e t e c t o r
of
setup
have been installed
255
H. Ri WILDE, W. HERZOG: ON-LINE ANALYSIS OF COAL
on top of the s c r e e n i n g
container
for c o n v e n t i o n a l
s e p a r a t e d by layers of b o r a t e d p o l y e t h y l e n e
and lead to avoid
a c t i v a t i o n of the iron in the c o n t a i n e r walls. source
is
m o v e d up and down inside
m o t o r drive.
S h i e l d e d by two
The
cups of high p u r i t y
sample h o l d e r s
1 mg Cf-252
a zircaloy-tube
it can be m o v e d out of the s c r e e n i n g c o n t a i n e r the c y l i n d r i c a l
INAA analyses,
by a step
lead and paraff5
to the c e n t e r of
c o n t a i n i n g up to 150 kg of coal.
The source s t r e n g t h can be r e g u l a t e d w i t h i n a l i m i t e d range by l o w e r i n g the s o u r c e position. radiation
the sample h o l d e r s
To avoid b a c k g r o u n d
are made of p o l y e t h y l e n e .
They
may be r e m o v e d or i n s t a l l e d w i t h a small crane b o o m w i t h i n a few minutes.
The samples
ted p o l y e t h y l e n e
are s u r r o u n d e d by
- not shown in this
tron i n d u c e d b a c k g r o u n d
10 cm of bora-
figure - to reduce neu-
from the c o n c r e t e w a l l s
of our labora-
tory. The p r o m p t gamma rays e m i t t e d w i t h a 22 % h i g h p u r i t y special horizontally advantages tectors
extended
cryostate
of high p u r i t y d e t e c t o r s
are m e a s u r e d
and the a p p a r e n t l y
assembly.
de-
c o o l i n g only d u r i n g
lower s e n s i t i v i t y
The use of NaJ d e t e c t o r s
The m a i n
c o m p a r e d w i t h Ge(Li)
are the n e e d of liquid n i t r o g e n
operation damage.
from the sample
g e r m a n i u m d e t e c t o r h o u s e d in a
to n e u t r o n
i n s t e a d of g e r m a n i u m types
has n o t been taken into a c c o u n t b e c a u s e of their poor resolution.
The d e t e c t o r
in Fig.
I; it is s u r r o u n d e d by a m u l t i l a y e r
a b s o r b e r to reduce Paraffin
low e n e r g y
loaded w i t h
used b e t w e e n
is p o s i t i o n e d
sample
above the sample as shown decreasing-Z
gamma background.
95 % e n r i c h e d
lithium-6-carbonate
and d e t e c t o r as a n e u t r o n
is
absorber with
good t r a n s m i s s i o n
for high e n e r g y gamma rays.
side the d e t e c t o r
is s h i e l d e d a g a i n s t t h e r m a l n e u t r o n s by
a thicker Whereas
256
layer of p a r a f f i n w i t h
the n e u t r o n
absorption
F r o m the back-
n a t u r a l l i t h i u m carbonate.
coefficients
of n a t u r a l b o r o n
J. Radioanal. Chem, 71 (1982)
H. R. WILDE, W. HERZOG: ON-LINE ANALYSIS OF COAL
H
106
511
8ock@roundradiQtion
~
Simulated COQI motrix =" 105
~10 4
C
2 Pb
u
.
103
1000
500
2O00 Channel number
1500
Fig. 2. Spectrum of the background radiation measured with a pure polystyrene sample to simulate the coal matrix
and e n r i c h e d
l i t h i u m are about
the same,
the use of l i t h i u m
is a d v a n t a g e o u s
because
ring a neutron.
In this w a y the total c o u n t r a t e
by about
it p r o d u c e s no gamma rays w h e n captu-
The data p r o c e s s i n g and a c o m p u t e r rate amounts
source,
fully;
e.g.
- though
system consists
the a n a l o g u e
a combination
system.
electronics
Since the count-
in the experiment.
analysis.
representation
all further e x p e r i m e n t a l time is
collects
of the results.
sample.
radiation measured
For this m e a s u r e m e n t
data p r e s e n t e d
and for
in this p a p e r the
4000 s. Only a few p h o t o peaks
J. Radioanal. Chem. 71 (1982) 17'
the s p e c t r a l
A graphic plotter enables
a s p e c t r u m of the b a c k g r o u n d
with a pure p o l y s t y r e n e
So it was useless
A 4096 channel pulse
to a m i n i c o m p u t e r
data and allows an o n - l i n e
and p i l e u p r e j e c t o r
in the test - c a u s e d uncon-
element determination.
height analyzer connected
the i m m e d i a t e
must be s e l e c t e d c a r e -
of main a m p l i f i e r
loss of c o u n t r a t e
for a q u a n t i t a t i v e
shows
of fast linear a m p l i f i e r s
a i d e d data a c q u i s i t i o n
s h o w i n g good p e r f o r m a n c e
trollable
collect
lowered
to 30 - 40 kcs due to the high s t r e n g t h of the
Cf-252
Fig. 2
is
10 %.
t o g e t h e r with
25 7
H. R. WILDE, W. HERZOG: ON-LINE ANALYSIS OF COAL
their e s c a p e peaks are to be seen:
carbon and h y d r o g e n
components
lead and b o r o n peaks
resulting
of the sample material;
f r o m the s h i e l d i n g of the source
respectively
only small c o n t r i b u t i o n s
(in the low e n e r g y come
results.
to iron and
not shown here)
this s p e c t r u m
the first
than
In this way
r e d u c e d by a factor of two,
1o kcs it amounts
the s t a t i s t i c a l is
the first q u a r t e r of the s p e c t r ~
in all m e a s u r e m e n t s .
the a n a l y z e r is
Since
contain
region is high and the s e n s i t i v i t y
low due to the high b a c k g r o u n d , is s u p p r e s s e d
shows that
1000 c h a n n e l s
far more than h a l f of the total countrate. in this
silicon
c e i l i n g and m u s t be s u b t r a c t e d
Moreover
due to the c o m p t o n b a c k g r o u n d
e r r o r of peaks
are
and the detector,
tail of the carbon peak,
from the close c o n c r e t e
from the a n a l y s i s
are
the dead time of at c o u n t r a t e s
less
to 10 - 15 %.
O p t i m i z a t i o n o f the s e t u p - Test m e a s u r e m e n t s
The s e n s i t i v i t y
of this d e v i c e
m a n y parameters:
is a c o m p l i c a t e d
it is not simply d e t e r m i n e d
a c e r t a i n peak of the spectrum,
because
function of
by the y i e l d
the b a c k g r o u n d
the peak i n f l u e n c e s
the e x p e r i m e n t a l
area and b a c k g r o u n d
show a d i f f e r e n t e n e r g y d e p e n d e n c e .
optim~ization of such a s y s t e m must source,
sample and detector,
shields
and the source strength,
source position. a polystyrene or iron oxide.
These
the a r r a n g e m e n t of
s i m u l a t e d by v a r i a t i o n
of the
have been done w i t h
filled into p o l y e t h y l e n e equally
the e x p e r i m e n t a l
3400 k e V ~ E ( 8 O O O
258
So
of sulfur
In order to save time and recycle m a t e r i a l
3. It shows
and A1
Both peak net
and shape of the v a r i o u s
test m e a s u r e m e n t s
each and then d i s t r i b u t e d
Fig.
involve
material
too.
coal m a t r i x c o n t a i n i n g a few p e r c e n t
a d d e d e l e m e n t s were
of o p t i m i z i n g
error,
keV. W h e r e a s
(from the detector)
bottles
a m o n g the matrix.
arrangement
the high e n e r g y
in
under
the
of 100 g The result
is d e m o n s t r a t e d
in
region of two s p e c t r a w i t h
the b a c k g r o u n d peaks of Si,
are c l e a r l y
suppressed,
Fe
the s p e c t r a l
J. Radioanal. Chem. 71 (1982)
H. R. WILDE, W. HERZOG: ON-LINE ANALYSIS OF COAL
1/-(
~ ~
Improved experimental arrant::jemen ~,
c
s
70
8 ~o~ 35--
Pb
0 1700 A
2275
2850
c 260 - S, 195 ~
3~.25
Fe
1-000 DChonnel number
F,rst st~ experimentol arrangement
u Si/C " . ~ 1 ~ ~ ~ . , ~ . .
m 130-
~
,
65-
1700
2275
2850
3/-25
~000 Chonnel number
Fig. 3. Result of optimizing the experimental arrangement including sample and detector shields
c o n t r a s t of the e l e m e n t s
in the sample,
sulfur and carbon,
could
be i n c r e a s e d appreciably. Fig.
4 demonstrates
relative
the e f f e c t of c h a n g i n g the source p o s i t i o n
to the sample.
Here the net area of the iron d o u b l e t
7632 + 7646 keV and the b a c k g r o u n d r e s o l v e d peaks scale of this Whereas
are p l o t t e d figure
under these not c o m p l e t e l y
against
zero means
the source position.
In the
the h i g h e s t p o s s i b l e position.
the peak area does not change very much w i t h the source
position,
the r e l a t e d b a c k g r o u n d
area i n c r e a s e s
steeply
p o s i t i o n s > -16 cm, thus g i v i n g rise to a q u i c k l y m e n t a l error.
The peaks of other e l e m e n t s
the b e s t value Optimizing
tural coal.
the p e r f o r m a n c e
Fig.
rise d e p e n d s
slightly
A source p o s i t i o n of -14 cm has p r o v e n to be
for this e x p e r i m e n t a l
p o r t a n t parameter.
g r o w i n g experi-
show the same behaviour;
h o w e v e r the s t a r t i n g p o i n t of the b a c k g r o u n d on the peak energy.
for
setup.
the sample t h i c k n e s s
is a n o t h e r
im-
This test has been done w i t h a high ash na-
5 shows the b e h a v i o u r of three d i f f e r e n t peak
1 Radioanal. Chem. 71 (1982J
259
H. R. WILDE, W. HERZOG: ON-LINE ANALYSIS OF COAL
--52
26
" :J6
-;0
_,;o
CF-source position~cm Fig. 4. Net peak area and related background as a function of the source position ( ~ source strength)
Coal sample Ewald-1 o '~ 90 x
~
Averaged
60 --
~
l
m Peak area of: CI(66!1 keY)
30 n o,
o o
n Si(3539keY) 3
Fe(7632§ 015
t
20
I
o o
keY) I
,.
25 30 Samptethickness,cm
Fig. 5. Net area of three different peaks and average trend of their background as a function of sample thickness
260
J. Radioanal. Chem. 71 (1982)
H. R. WILDE, W. HERZOG: ON-LINE ANALYSIS OF COAL
areas
from all regions
of the s p e c t r u m and the a v e r a g e
of their r e l a t e d b a c k g r o u n d when the sample t h i c k n e s s the source h o u s i n g and the d e t e c t o r W i t h i n a few p e r c e n t
c l e a r l y w i t h r i s i n g sample
whereas
varied
between
(c.f. Fig.
I).
the peak areas may be r e g a r d e d as indepen-
dent from the sample thickness,
of the m e a s u r e m e n t
is
trend
whereas
thickness.
the b a c k g r o u n d
This means
decreases
that the a c c u r a c y
depends only s l i g h t l y on the sample thickness,
the e x p e r i m e n t a l
error is
a f f e c t e d a p p r e c i a b l y by this
parameter.
Results and discussion
Analysis
of several
G e r m a n y coals
shows
samples of s i m u l a t e d a good s p e c t r a l
the e l e m e n t s H, C, AI, sensitivity
Si,
6 presents
4000 s. All e l e m e n t s m e n t i o n e d
in this spectrum.
are not yet k n o w n - e x c e p t chemical
Fig.
analysis
Their absolute
is still under way.
to the coal sample.
A preliminary
are shown in Fig.
bottles.
Obviously
basic
calibration
The results
is
of these
7. Here the peak net areas
the a d d e d e l e m e n t content.
its single escape peaks
Content,
conventional
a d d i n g these e l e m e n t s
iron d o u b l e t and
shown w i t h d i f f e r e n t
the y i e l d is a linear
are
In the u p p e r p a r t of
the figure the peak area of the m o s t p r o m i n e n t
added.
above are to
The a d d e d m a t e r i a l was d i v i d e d into p o r t i o n s
of 100 g and p a c k e d in p o l y e t h y l e n e
plotted against
a spectrum
concentrations
sulfur and iron - b e c a u s e
for s u l f u r and iron has been done by s t e p w i s e
measurements
the
from the Ruhr d i s t r i c t w i t h about 20 % ash c o n t e n t
The c o l l e c t time is be seen c l e a r l y
of our s y s t e m for
S, CI, Ca, Ti and Fe, w h e r e a s
for N, K and Na is lower.
of a coal sample
coal as well as W e s t e r n
response
amounts of iron
f u n c t i o n of the total elemen
and thus e x t r a p o l a t i n g the two lines back leads to a
iron c o n t e n t of about
the three most p r o m i n e n t the 2379 k e V and the
3 %. A p p l y i n g
sulfur peaks
3221 keY lines.
leads to a sulfur c o n t e n t of about
J. Radioanal, Chem. 71 (1982)
the same p r o c e d u r e
shows good a g r e e m e n t Extrapolating
1.1
to
for
their yields
%. The results of this
261
H . R . W I L D E , W. H E R Z O G :
ON-LINE ANALYSIS
OF COAL
40 -- %%~ 1H
Coal sample
08 2o
~
u _
"~
Ewald-1
\
30
~
10
o]
,
,
I 1278
,
1022 ~,
~
,
I 1534
~
,
,
,
I 1790
,
,
,
I 2046
Channel number
SdC
I
~Sl
91~.~ l.
l -'~%~. I
"
31
J ..~
"~"r
~
20/.6
CI
S,/C CI
~lR
I
J
Ct
J
I
2,~I'I~ II ct ,
~
i
2302
I
K.Na
_JU sSl Fe I
1
I
%
J
II
I
i
2558
C,
T,
1
1
t
J
,
~
2814
3070 Channel number
3838
4094 Channel number
--
8.c u
6i --
Re
pbCl
|
T~
r: II,,,co IA ~,,,Cl ~c,
~a
~ AL Cl
i 4
%
_
o
3326
~70
Fig. 6. E n e r g y s p e c t r u m
3582
of a coal sample from the Ruhr district with about
20% ash content.
The
c o l l e c t t i m e is 4 0 0 0 s
calibration in Tab. The
an i r o n
line
behaviour
is d u e
escape
may
to an
peak.
is s i m u l a t e d .
errors
262
compared
with
the w e t
chemical
analysis
results
I.
deviating
dashed
tent
are
occur
By
This
due
of the
5220
keY yield
interference this
effect
deviation
to u n d e t e c t e d
of t h i s
a much
shown sulfur
too high
is an e x a m p l e
what
interferences,if
J.
by
the
peak sulfur kind
with conof
detectors
Radioanal. Chem. 71 (1982)
H. R. WILDE, W. HERZOG: ON-LINE ANALYSIS OF COAL
A /
Iron calibration coa~ ,n somple Ewold -I o
700J--
I
o 525 --//~26~
k
35.0 ~ 1 " / .
-t.O
- 20
0
2.0
t.O
iron,% 5/.20keY .d %379 keY
Added Sulphur calibration cool 20.0
Sample Ewold-I
150-
~ lo.o~
~ s.~
1 MeV
s
s . SSS
.5.0
I
~s"
I - 2.0
- 1.0
1
1.0 20 Added sulphur, ~
Fig. 7. Calibration curves for the elements iron and sulfur, measured by stepwise adding these elements to a natural coal sample
Table 1 Comparison between chemical analysis and PNAA analysis results for sulfur and iron
Element
yield per % in 1OOO s ::)
S Fe
1 2 . 2 0 0 counts 9 . 1 0 0 counts
x) o n l y m a i n p e a k s
Z Radioanal. Chem. 71 [1982}
incl.
chemical analysis
PNAA analysis
1,35
%
1,1%
3,4
%
3,0 %
escapes
263
H. R. WILDE, W. HERZOG: ON-LINE ANALYSIS OF COAL
w i t h poor r e s o l u t i o n
are used;
to use high r e s o l u t i o n
it d e m o n s t r a t e s
detectors
the n e c e s s i t y
in this type of experiments.
C a l i b r a t i o n of the device will be c o n t i n u e d by using the m e t h o d d e s c r i b e d above as
w e l l as by a n a l y z i n g
determined elemental in Fig.
7 and Tab.
composition.
time.
Optimization
analysis
As to be seen from the yields
I the q u a n t i t a t i v e
w i t h good s p e c t r a l r e s p o n s e
samples w i t h chemically
determination
is now p o s s i b l e w i t h i n
of e l e m e n t s 10 - 15 minut
of the s y s t e m is c o n t i n u e d w i t h a stress on
time and d e t e c t i o n
sensitivity.
References 1. K. HEIN, J. Eng. Power, 99 (1977) 679. 2. B. D. SOWERBY, Nucl. Instr. Meth., 160 (1979) 173. 3; A. W. HALL, I. W. MARTIN, R. F. STEWART, A. M. POSTON, Precision Tests of Neutron Sulphur Meter in Coal Preparation Plant, Bureau of Mines Report no. 8038 (1975) p. 1. 4. T. GOZANI, The Development of Continous Nuclear Analyzer of Coal, ANS Trans. 28 (1978) 97. 5. C. L. HERZENBERG, N. M. O'FALLON, B. S. YARLAGADDA, R. W. DOERING, C. E. COHN, K. G. PORGES, Neutron-Induced Gamma Spectrometry for On-line Compositional Analysis in Coal Conversion and Fluidized-Bed Combustion Plants. Proc. Third Intern. Conf. on Nuclear Methods in Environmental and Energy research, Columbia, MO 1977.
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