CA2026056A1

CA2026056A1 - Inclusion of sulphur-capturing sorbents into coal agglomerates

Info

Publication number: CA2026056A1
Application number: CA 2026056
Authority: CA
Inventors: Huseni Akberali Rangwala
Original assignee: Alberta Innovates
Current assignee: Alberta Innovates
Priority date: 1990-09-24
Filing date: 1990-09-24
Publication date: 1992-03-25

Abstract

ABSTRACT OF THE DISCLOSURE

A method is provided for incorporating a sulfur-capturing sorbent, such as calcium, into coal agglomerates, to reduce sulfur emission on combustion. In one variant of the method, the incorporation is carried out by preparing the agglomerates using an aqueous solution of a calcium salt. Other variants involve impregnating agglomerates with calcium salts either directly by soaking or via in situ precipitation of calcium salt in the agglomerates by reaction under pressure of carbon dioxide. The methods produce an agglomerate having the sulfur-capturing sorbent distributed throughout.

Description

2 ~ 5 ~

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 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 ~?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 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.

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 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

Claims

1. A method of preparing an agglomerated fuel containing sulfur-capturing sorbents comprising the steps of:
(a) providing an aqueous solution of a salt of an element selected from the group consisting of calcium, magnesium, barium and strontium;
(b) preparing a slurry of finely divided solid or semi-solid carbonaceous material in said solution:
(c) adding an agglomeration agent to said slurry;
(d) agitating the mixture of slurry and agglomeration agent to form agglomerates: and (e) separating said agglomerates from said slurry.

2. A method for incorporating sulfur-capturing sorbents into agglomerates of finely divided solid or semi-so1id carbonaceous material, comprising the step of forming the agglomerates using a liquid phase agglomeration process wherein an aqueous slurry of the finely divided material is first prepared using an aqueous solution of a salt of an element selected from the group consisting of calcium, magnesium, barium and strontium.

3. A method according to claim 2 wherein the finely divided carbonaceous material is coal particles.

- Page 1 of Claims -

4. A method for incorporating sulfur-capturing sorbents into agglomerates of finely-divided solid or semi-solid carbonaceous material, comprising the steps of:
(a) soaking agglomerates of the finely divided material in an aqueous solution of a salt of an element selected from the group consisting of calcium, magnesium, barium and strontium; and (b) drying the soaked agglomerates to evaporate excess water.

5. A method according to claim 4 wherein the finely divided carbonaceous material is coal particles.

6. A method according to claim 4 or 5 wherein the agglomerates are physically scrubbed to remove excess salt following drying of the agglomerates.

7. A method according to claim 4, 5 or 6 wherein the volume of aqueous solution of the salt is approximately the same as the pore volume of the agglomerates used.

8. A method according to claim 2, 3, 4 or 5 wherein the salt used is calcium nitrate, calcium formate, or calcium acetate.

9. A method according to claim 2, 3, 4 or 5 wherein the - Page 2 of Claims -agglomerates are soaked in the aqueous solution of the salt for up to approximately fourteen hours.

10. A method for incorporating sulfur-capturing sorbents into agglomerates of finely divided solid or semi-solid carbonaceous material, comprising the steps of:
(a) soaking agglomerates of the finely divided material under a pressure of between 0.101 and 5.6 MPa in the presence of carbon dioxide in an aqueous solution of a salt selected from the group consisting of calcium, magnesium, barium and strontium, said salt being capable of reacting with carbon dioxide to form the carbonate of the said element; and (b) drying the soaked agglomerates to evaporate excess water.

11. A method according to claim 10 wherein the finely divided carbonaceous material is coal particles.

12. A method according to claim 10 or 11 wherein the salt is a calcium salt.

13. A method according to claim 10 or 11 wherein a concentrated solution of ammonium hydroxide is added to the aqueous solution of the salt prior to soaking of the agglomerates in sufficient quantities such that the pH of the aqueous solution of the salt following the addition of - Page 3 of Claims -the ammonium hydroxide is at least 9Ø

14. A method according to claim 10, 11, 12 or 13 wherein the soaked agglomerates are washed prior to drying.

15. A method according to claim 10, 11, 12 or 13 wherein the soaking of the agglomerates continues for approximately 2 hours.

16. A method according to claim 12 wherein the calcium salt is calcium formate or calcium acetate.

17. A method according to claim 4, 5, 10, 11 or 12 wherein the agglomerates are not de-oiled prior to being soaked in the aqueous solution of the salt.

18. A method according to claim 8 wherein the aqueous solution of calcium salt has a concentration of approximately 1M.

19. A method according to claim 12 wherein the aqueous solution of calcium salt has a concentration of approximately 1M.

20. A method according to claim 2, 3, 4, 5, 8 or 9 wherein the agglomerates are dried in an oven at a maximum temperature of approximately 110°C.

- Page 4 of Claims -

21. An agglomerate comprising finely divided solid or semi-solid carbonaceous material, oil or oil residue, sulfur and an element selected from the group consisting of calcium, magnesium, barium and strontium, said element being finely distributed throughout said agglomerate.

22. An agglomerate according to claim 21 wherein said carbonaceous material is coal particles.

23. An agglomerate according to claim 21 or 22 wherein the element is calcium.

24. An agglomerate according to claim 23 wherein the mole ratio of calcium to sulfur on the outside surface of the agglomerate is in the range 0.71:1 to 9.16:1.

25. An agglomerate according to claim 23 wherein the mole ratio of calcium to sulfur on the inside of the agglomerate is in the range 0.26:1 to 0.51:1.

26. An agglomerate according to claim 23 wherein the mole ratio of calcium to sulfur in the agglomerate is in the range of about 0.2 to 2Ø

- Page 5 of Claims -