Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2 ~ 5 ~
INCLUSION OF 8ULFUR-CAPTURING
80R'8~NT8 INTO COAL AGGLONERaTE8
Bac~groun~ of the Invention
This invention relates to methods for
incorporating sulfur-capturing sorbents into agglomerates of
coal particles, and to the products so formed.
Agglomerates made of coal particles, using heavy
petroleum feedstock as a binding agent, are prepared
according to techniques well-known in the art.
Agglomeration techniques are disclosed, for example, in
"Review of Oil Agglomeration Techniques for Processing of
Fine Coals", Mehrotra, V.P., K.V.S. Sastry and B.W. Morey,
Intern~a~ g _ Mineral Processing, 11 (1983)
175-201; "Oil Agglomeration Process for the Treatment of
Fine Coal", Steedman and S.V. Krishnan, Fine Coal
Processina, (Editors S.K. Mishra and R.~. Klimpel), Noyes
Publications, N.J., U.S.A., (1987), Chapter 8; and Canadian
Patent No. 1,216,551 (Ignaslak), is~ued January 13, 1987.
The agglomerate~ are used as fuel. However, because of the
~ulfur content of most of the feedstoc~s employed, it is
usual that the sulfur content of the agglomerates is
sufficiently high that some method of controlling the sulfur
emissions during combustion of the agglomerates is needed.
Nethods of post-combustion scrubbing are known, but they are
often complex and expensive.
Techniques are known for incorporating calcium
(which can function as a sulfur-capturing sorbent) into
-- 1 --
2~0~6
coal. These include (1~ mixing ground limestone with coal
and subsequently injecting the mixed powder into the
combustor (Chang, K.K., R.C. Flagan, G.R. Gavalas and
P.K. Sharma, 1986, Fuel, 65, 75); (2) ion exchange
(Levendis, S.W., Nam. M. Lowenberg, R.C. Flagan and
G.R. Gavalas, 1989, Energy & Fuels, 3, 28);
(3) precipitating CaC03 (Sharma, P.K., G.R. Gavalas and
R.C. Flagan, 1987, Fuel, 66, 207; Chang, K.K., R.C. Flagan,
G.R. Gavalas and P.K. Sharma, presented at 1984 Annual
A.I.Ch.E. Meeting, San Francisco, November 25-30, 1984;
Porter, J.H., M.P. Manning, K.R. Benedek and P.K. Sharma,
Third Ouarterly Technical Proaress Report. Enerqy and
Environ~ental Enaineering Inc., Cambridge, Massachusetts,
September 1, 1983); and (4) impregnating the coal matrix
with calcium salts (Ohtsuka, Y. and A. Tomita, 1986, ~çl,
65, 1653).
It is also known to introduce calcium salt into
coal agglomerates by preparing the agglomerates in the
presence of a suspension of limestone in water ~Majid, A.,
V.P. Clancy and B.D. Sparks, 1988, Eneray & Fuels, ~, 651;
U.S. Patent No. 4,867,755, issued September 19, 1989, Majid
et al.). However, using this method, the calcium carbonate
is deposited in discrete particles and clusters of particles
on the surface of the agglomerates, rather than being
distributed in a finely divided state throuqhout the
agqlomerate.
It is accordingly an object of the invention to
provide methods of incorporating sulfur-capturing sorbents
into agglomerates. According to one aspect of the
invention, there is provided a method for incorporating
sulfur-capturing sorbents into agglomerates of finely
divided solid or semi-solid carbonaceous material, such as
coal particles, comprising the step of forming the
agglomerates using a liquid phase agglomeration process
wherein an aqueous slurry of finely divided coal particles
is first prepared using an aqueous solution of the sulfur-
capturing sorbent, such as a salt of calcium, magnesium,
barium or strontium.
According to another aspect of the invention,
there is provided a method for incorporating sulfur-
capturing sorbents into agglomerates of coal particles,
comprising the steps of (a) soaking agglomerates of coal
particles in an aqueous solution of a sulfur-capturing
sorbent, such as a calcium salt, and (b) drying the soaked
agglomerates to evaporate excess water.
According to a further aspect of the invention,
there is provided a method for incorporating sulfur-
capturing sorbents into agglomerates of coal particles,
comprising the steps of (a) soaking agglomerates of coal
particles under a pressure of between 0.101 to 5.6 MPa in
the presence of carbon dioxide in an aqueous solution of a
sulfur-capturing sorbent, such as a calcium salt, which is
capable of reacting with carbon dioxide to form calcium
carbonate, and (b) drying the soaked agglomerates to
evaporate excess water.
~ ~6`35~
According to a further aspect of the invention,
there is provided an agglomerate comprising finely divided
solid or semi-solid carbonaceous material, such as coal
particles, with oil or oil residue, sulfur and calcium, the
calcium being distributed throughout said agglomerate in a
finely divided and highly reactive form wherein it i8 very
effective for sulfur capture.
In the preferred embodiments of the invention, the
~ulfur-capturing sorbent employed is a calcium salt, such as
calcium nitrate, calcium formate or calcium acetate.
However, the salts of certain other Group IIA elements may
also be used, namely salts of magnesium, barium and
~trontium. Calcium salts are less expensive and are readily
available, and are therefore preferred. The Group IIA
elements beryllium and radium are not considered suitable by
reason of their radioactivity and the insolubility of their
salts.
The methods of the invention produce fuel with
lower sulfur emission. The examples detailed herein
employed coal particle~ as the finely divided carbonaceous
material, but other such high-sulfur materials, for example
coke, lignite, peat, and semi-solid petroleum fractions, can
also be employed in the present invention.
Brief De~cript~ the Drawing~
Embodiments of the invention will now be described
with reference to the accompanying drawings, of which:
2 ~
Figure 1 is a graph showing the sulfur capture
capacity versus Ca/S mole ratio for agglomerates prepared
according to a first embodiment of the invention;
Figure 2 is a graph showing the sulfur capture
capacity versus Ca/S mole ratio for agglomerates prepared
according to a second embodiment of the invention; and
Figure 3 is a graph showing the sulfur capture
capacity versus Ca/S mole ratio for agglomerates prepared
according to a third embodiment of the invention.
Detaile~ ~escription of the Preferred Embodiment~
The following examples illustrate aspects of the
invention. Agglomerate samples were prepared as follows.
Agglomerate sample #1 was prepared using
subbituminous Kemmerer coal with bitumen and diesel oil in
the ratio 4:1 as binding liquid (14.4-API; S, 3.67%). The
oil content in agglomerate sample #1 was 13.9 wt% ~MF). The
characteristics of one sample of Kemmerer coal are given in
Table 1.
TABLE 1 - Charaot~ristio~ of ~emmerer Coal
Proximate Analyses ~MF) Ultimate Analyses (MF)
W~% Wt%
Ash 6.6 C 69.5
Volatile Matter41.4 H 4.9
Fixed Carbon 52.0 N 1.52
S 0.37
Agglomerate sample #2 was prepared using the same
oil but with Kemmerer coal from a different seam (S content
1% (MF)). The oil content for this agglomerate was 13.4%
(MF). Agglomerate sample #3 was prepared using Kemmerer
coal from a different seam (S content 1.35% (MF)) and heavy
oil from Elk Point, Alberta (12.2-API; S, 4.1%). The oil
content for this agglomerate was 18.5% (MF). The standard
condition used for obtaining de-oiled agglomerates from the
original aqglomerates was by thQrmal treatment at 350 C
under a stream of nitrogen. The characteristics of the coal
and agglomerates are summarized in Table 2. The
agglomerates were in the size range 2-3 mm.
TABLE 2 - Chara¢teristlcs of Coal and Agqlomerates
-
A~hX SX C~lciu~ X C~l. v~lw BET ~r~ Pore Vol. Avg. Por-
(~F) (~F) ~F) ~J/kg ~/9 c~P/9 R-d)u~, nm
K _ r~r co l 6.6 0.37 0.30 27.8 5.93 0.0189 6.4
15Agglomeratell 1 4.3 0.94 0.26 30.5 0.27 0.00093 6.9
De-oiled A~g. 1 4.6 O.ff 0.27 -30.5 0.50 0. W 353 14.1
Ag~lomærate~ 2 3.3 1.45 0.35 -30.5 --- --- ---
Agglomer~tes 3 3.0 2.02 0.2, 32.4 --- --- ---
D--o~l~d Agg. 3 3.5 1. ff 0.32 31.6 0.12 0.00048 8.0
2 0
~?1- 1
Agglomerates were prepared using aqueous solutions
of various calcium salts, as shown in Table 3. The method
described in Canadian Patent 1,216,551 (Ignasiak) was
employed, except that the slurries of finely divided coal
particles were formed using aqueous solutions of the calcium
salts rather than pure water. Kemmerer coal (S, 0.37% (MF))
was used with bitumen and diesel oil (4:1) to prepare the
2~0~6
agglomerates. The coal concentration was about 28% and oil
loading was about 18 to 24 wt% of dry coal content. The
process involved preparing an aqueous solution of the
selected calcium salt, of the selected concentration,
providing a ~lurry of coal particles using this solution,
adding the bitumen/diesel oil agglomeration agent, agitating
the m$xture to form agglomerates, and separating the
agglomerates from the slurry.
~x~mpl~ 2
Impregnation of agglomerates was done by soaking
for up to about 14 hours 20 g of agglomerates with 10 cc of
aqueous calcium ~alt solution, and drying in the oven at
110 C. In some cases, the agglomerates were not de-oiled
prior to soaking. The volume of aqueou~ solution of calcium
salt is preferably approximately the same as the pore volume
of the agglomerates used.
Bx~mple ~
~n situ impregnation was carried out by soaking
for up to about 2 hours 20 g of agglomerates in 40 cc of
aqueous calcium salt solution (eg. calcium formate or
calcium acetate) with 10 cc of concentrated ammonia solution
in a bomb pressurized to 5.6 MPa (800 psig) with C02 for a 2
hour period. The agglomerate~ were then taken out washed
and dried in the oven. In some runs, ammonia addition was
omitted. Pressures from about 101 KPa to 5.6 MPa were used~
In some cases, the agglomerates were not de-oiled prior to
2~605~
soaking. The reaction between Co2 and Ca-Salt
(eg. Ca-Acetate) is:
Ca-Acetate + C02 + H20 ~ CaC03 + Acetic Acid.
; This reaction results in the formation of fine CaC03 in situin the pores of the agglomerates. The reaction is favoured
in the alkaline pH, a pH of at least 9.0 being preferred.
The addition of ammonia serves this purpose.
In the above examples, residual salt adhering to
the ~urface of the dried agglomerates was cleaned by
physical scrubbing before testing for sulfur capture
capacity. The feedstock agglomerates, as well as calcium
treated agglomerates, were tested for sulfur capture
capacity based on the sulfur in the agglomerates and in the
ash (ashing done by ASTM method at 750 C). A summary of the
experiments performed is shown in Table 3.
The comparison of sulfur content in the coal and
in the agglomerates in Table 2 shows that preparation of
agglomerates results in an increase in the sulfur content
from 0.37% to a value as high as 2.0%. The tests on ~ulfur
capture capacity of these agglomerates show only 12-20%
sulfur capture.
Figure~ 1, 2 and 3 show the effect on ~ulfur
capture of different Ca/S mole ratios for agglomerates
prepared u~ing aqueous Ca salt solution (Fig. 1),
agglomerates impregnated with an aqueous Ca salt solution
(Fig. 2), and agglomerates impregnated by the in situ method
of Example 3 (Fig. 3). Percent sulfur capture increases
with the increase of Ca/S ratio in the agglomerates and i~
2~0~
independent of aqueous precursor or the nature of
agglomerate feedstock.
TABLE ~ - 8ummary of ~xperiments on Incorporating
Calcium into Aqalomerates
Agglomeration In situ Impreg.
with Aqueous Impregnation with with CO Pressure
Solution of Aqueous Solution above Aqueous
Ca Salts of Ca Salt Ca Salt Solution
(Example 1) (Example 2) (Example 3)
lM Ca-Acetate~a) lM Ca-A~etate(b) IM Ca-Acetate(b)
(oil 23.8%) (agg. 1) (agg. l)
lM Ca-Acetate lM Ca-Formate(b) lM Ca-Acetate(C)
(oil 17.8%) (agg. 1) (agg. 1)
lM Ca-Acetate lM Ca-Nitrate(b) 2M Ca-Acetate(b)
(oil 20.8%) (agg. 1) (agg. 1)
lM Ca-Formate(~) 2M Ca-Acetate lM Ca-Formate(b)
(oil 20.8~) (agg. 1) (agg. 1)
lM Ca-Nitrate(~) lM Ca-Acetate(b) lM Ca-Formate(C)
(oil 2~.8%) (agg. 2) (agg. 1)
Saturated CaC03 lM Ca-Acetate(d) lM Ca-Acetate
(agg. 2) (agg. 2)
IM Ca-Acetate
(de-oiled agg. 3)
lM Ca-Formate
(de-oiled agg. 3)
~a) runJ ~n duplicate ~b) run~ ~ith both original and db-oilod agglomerate~ ~c) runs ~ithout
~mmonla ddlt~on and ~d) runs ~ith d--olleci ~99 2 ~ 1~ Ca-Acetate)
The calcium loading is dependent on the method
used for incorporating calcium into the agglomerates. The
de-oiled agglomerates have a sulfur capture capacity of
21.7% which increased to 45.9~ when agglomerates were
blended with 20% CaCO3 and de-oiled. The effect of the
$
aqueous precursor on calcium loading and on the sulfur
capture capacity for the methods of Examples 1, 2 and 3 are
summarized in Table 4.
TABL~ffect of Agueou~ Precur~or on
% C~lcium Loadin~ and % ~ulfur Ca~ture
A~lcmer~te~Ca-Acetate Ca-Acetate Ca-Frrmate Ca-~itrate CI~CO3
D-t~21~ 1) t 11~ 111) Su~p
_
0 A~rlanerateg Pre~r~tion ~Exanole 1)
Agglarerat~ prep~red1 44P) ---- 1 61 1 31 1 05
u~1ng Aq Ca-Salts~70 5)(66 3)(C' (77 2) (57 8)
ImPre~nation of ~glomerates ~ExamDle 2)
A~g 1 0 520 38 1 60 1 89 ----
~42 5)(34 9) (58 5) (75 2)
De-oiled Ag~ 1 0 28 ---- 0 69 1 76 ----
(26 3)(51 2) ~78 3)
In situ ImDre~nation of A~lomerates ~Ex~le 3)
Ag~ 1 0 76'b' 0 79 0 86 -~
~56 2) ~55 3)~64 6)
A~ thout ~noni~ ) ---- ---- 0 73
~53 3)
D--o~l~d Ag9 1 0 58 0 55 1 22 ---- ----
~45 3) ~49 3)~63 9)
De-cilod Ag~ t ~1thrut 0 43 ---- ---- ---- ----
~non~a) ~37 5)
~a) sulfur content about 0 8 - O ff ~b) avera~e of t~o runs ~c) value in the p~rer~thesis refers
to X sulfur capture
The results in Table 4 show that calcium loading
for the de-oiled agglomerates made according to the methods
of Examples 2 and 3 is, in general, much lower than for the
original agglomerates. The surface area and pore volume for
the de-oiled agglomerates are higher than those of the
original agglomerates (see Table 1) and should permit higher
calcium loading. However, the surface of the de-oiled
agglomerates is hydrophobic due to the removal of oil and
water. The capacity moisture i8 also low. This results in
-- 10 --
low wetting of agglomerates by aqueous solutions of calcium
salts, which accounts for the low calcium loading and less
sulfur capture capacity.
The results in Table 4 also show that use of 2M
concentration is not as beneficial as lM in Examples 2 and
3. In Example 1, the use of Ca-Nitrate is the most
effective and Ca-Acetate and Ca-Formate give nearly
comparable results, whereas CaCO3 i8 least effective. In
Example 2, for lM concentration of the precursor, the order
of effectiveness for different precursors is Ca-Nitrate >
Ca-Formate > Ca-Acetate.
The use of Ca-Formate i~ more effective than
Ca-Acetate in Example 3. The dissociation constants for
nitrate is much larger than that for the formate which in
lS turn is about ten times larger than that for acetate. Th~s
results in larger concentrations of Ca~ ions in the aqueous
Ca-Nitrate than in Ca-Formate and least in Ca-Acetate, which
explains the above behaviour.
It has also been found that the incorporation of
calcium, although beneficial for sulfur capture, has a
detrimental effect on the resulting ash content, which
increases with calcium loading or with increase in % S
capture.
Inclusion of calcium during preparation of the
agglomerates (Example 1) results in the largest calcium
loading with high sulfur capture capacity but at the expense
of higher ash content. However, nearly the same sulfur
capture capacity can be obtained with the methods of
2~12&~35t~
Examples 2 and 3 at much lower level of calcium loading.
Thus, calcium is more effectively placed into the
agglomerate matrix by the methods of Examples 2 and 3.
Comparison of the results for Examples 2 and 3 in Table 4
shows that the latter is a superior method resulting in
larger and more effective calcium loading.
Scanning Electron Micro6cope (SEM) studies of the
selected samples were done to investigate the Ca/S loading
obtained by various techniques at the microscopic level.
The agglomerate particles were individually scanned as a
whole and split into half to scan the cross-section of the
particle. The Energy Dispersive X-Ray Analysis (EDXA) was
performed for different elements including Ca and S. A scan
of the cross-section of an agglomerate showed uniform
distribution of Ca/S in the interior with a higher value at
the surface. Table 5 summarizes the results of EDXA for
different agglomerates. The 'outside' and 'inside' Ca/S
area ratios were obtained by scanning the surface of a whole
particle and entire cross-section of a split agglomerate
particle respectively. The repeat analyses on different
particles are also given to show the variations from
particle to particle.
The Ca/S 'inside' represents a value proportional
to the Ca/S in bulk whereas the value Ca/S 'outside'
represents Ca/S on the surface. For agglomerates produced
according to the methods of Examples 1 and 2, the Ca/S
ratios 'inside' are very close to each other and are lower
than for Example 3, showing that in the latter case the
calcium is deposited well into the interior of the particle.
- 12 -
For agglomerates produced according to the method
of Example 2, the Ca/S ratio on the 'outside' is much larger
than Ca/S ratio 'inside', showing that impregnation is a
surface phenomena. In situ impregnation without ammonia
results in low Ca/S ratio on the 'inside' and 'outside'
compared to that in the presence of ammonia. This explains
the better results obtained with ammonia addition during
Impregnation. Also, higher loading on the surface in
Examples 2 and 3 results in more effective utilization of
calcium by making it more readily accessible to reaction
with sulfur.
TABLE 5 - EDXA Results For Diff~r~nt
Çalçium ~reated Agglomer~tes
~Ca/S~ outsido ~Ca/S) In~idk
Based on S-sed on
1 5 Aoglomer~e Detsilc Area Ratio ~ro- Ratio
~mol_ 1 0 26 0 39 0 27
A~g ppn uN'ng q Ca-Acet-te ~lM) 0 41 0 54
ExamDle 2 0 71 0 26
De-oilod 99 1 ~ Ca-Acetate ~1M)
ExamDle 3 9 16 7 93 0 51
D--oiled a~o 1 ~ C~-Acot-te ~1M~ 6 67 4 53
4 26
De-oiled a~o 1 ~ Ca-Acetate ~1M) O K 0 35
~1 thout amnon~- a Wition)
De~oil-d a9~ 1 ~ C--Formate ~1M) 1 57 0 50
- 1 3
