Preparation of composite fuels, with reduced sulfur emission characteristics, from oily and carbonaceous wastes

A method of preparing a sulfur-containing composite fuel is provided to utilize some high-sulfur content solid and semi-solid fuels such as tar sand coke and refinery tank sludges by reducing their sulfur emission on combustion. The method comprises the steps of making an aqueous slurry including a finely divided carbonaceous material, a comminuted sulfur capture agent and an oily agglomeration aid obtained from the refinery or tailing sludges and coagglomerating these components and an optional conditioning agent. The resulting agglomerated composite fuel has a reduced content of inorganic impurities and is suitable for fluidized-bed combustion.

The present invention relates to a process for treating oily refinery 
wastes with high sulfur content such as tank sludges etc., to produce a 
composite fuel with reduced sulfur emission during combustion or 
gasification or sulfur-containing fuels, and more particularly, to 
sulfur-containing carbonaceous composite fuels comprising a sulfur capture 
agent and to a method of preparing such fuels. 
BACKGROUND OF THE INVENTION 
Oily wastes or sludges are undesirable by-products of the separation or 
recovery of bitumen or heavy oils by surface mining or in situ techniques. 
Stricter environmental regulations have made the disposal of these wastes 
more difficult. The recovery operations themselves are energy intensive 
but in order to meet environmental constraints on sulfur emissions it has 
been necessary to use clean burning natural gas as the fuel. In the long 
term the cost of natural gas is expected to rise and ancillary fuels will 
need to be considered. Combustible wastes such as refinery coke or oily 
sludge offer a potential alternative to natural gas but their high sulfur 
content makes them unacceptable as a fuel due to the emission of gaseous 
sulfur compounds, mainly sulfur dioxide. The reduce such emissions, 
various methods of desulfurizing fuels have been devised to date in an 
attempt to capture sulfur at the source of combustion rather than to 
absorb the gaseous sulfur compounds from the flue gas. 
U.S. Pat. No. 4,111,755 to Ban et al. discloses a method of producing a 
pelletized fixed-sulfur coal or coke. A mixture of coal and a sulfur 
sorbent (limestone) is ground and blended and then balled or compacted to 
form pellets. The pellets are then subjected to pyrolysis whereby sulfur 
is fixed in a calcium compound which remains stable in the ash after the 
pellets are burned as a fuel. 
In a process disclosed in U.S. Pat. No. 4,148,613 to Myers, 
sulfur-containing solid fuel, e.g. coal, is pulverized and then mixed with 
a finely divided inorganic material by precipitating the inorganic 
material such as dolomite or hydroxide or carbonate of sodium, potassium, 
calcium or barium onto the pulverized fuel. The resulting mixture can be 
formed into pellets or briquettes by agglomeration using binders or 
adhesives such as coal tar pitch, petroleum pitch or lignin sulphates. The 
agglomeration step is provided to improve handling, transportation and 
storage of the fuel pellets. 
In Canadian Patent No. 1,200,778, a process was described in which refinery 
coke or other carbonaceous waste could be used to separate the 
hydrocarbons from tailings sludges or other oily wastes such as tank 
sludges. The result of this process was a solid coke-oil agglomerate and a 
clean aqueous slurry suitable for disposal. The coke-oil agglomerate has a 
high sulfur content and hence its use as an ancillary fuel is somewhat 
limited. If a sulfur capture agent could be incorporated into the 
agglomerate during the sludge cleaning step then a by-product of the 
process would be a useable fuel which would not require any additional 
desulfurization treatment, such as flue gas scrubbing, during combustion. 
The problem of desulfurizing potential ancillary fuels from a sludge 
cleaning process has been addressed in the present research. This work has 
concentrated on the tar sand bitumen and coke produced in the two oil sand 
plants operating in Alberta, Canada. The coke produced during the 
upgrading of Athabasca bitumen contains 6-8 % sulfur almost entirely in 
the form of organic sulfur compounds. The coke produced in these two 
plants can be referred to as Suncor delayed coke and Syncrude fluid coke. 
It has been found that the coagglomeration of sulfurcontaining carbonaceous 
material with a sulfur capture agent can be combined with a sludge cleanup 
operation also resulting in a concomitant beneficiation of the 
carbonaceous material through the rejection of inorganic impurities. A 
composite agglomerated fuel may be obtained that offers a relatively high 
sulfur capture ability on combustion. 
Coal is an exemplary carbonaceous material. Where coal washing operations 
are conducted, waste coal slurry is usually present which is amenable to 
coagglomeration with oily sludge (waste) from oil refinery storage tanks 
to give a composite fuel particularly suitable for fluidized bed 
combustion. 
SUMMARY OF THE INVENTION 
The invention provides a composite fuel having reduced sulfur emission on 
combustion, the fuel comprising a finely divided sulfur-containing 
carbonaceous material, sulfur capture agent particles and an oily 
petroleum based agglomeration aid which is capable of wetting the surface 
of both the carbonaceous material and the sulfur capture agent. The 
invention also provides a method of preparing such composite fuel, 
comprising the steps of 
(a) providing an aqueous slurry including 
(i) a finely divided solid or semi-solid carbonaceous material, 
(ii) a finely divided solid sulfur capture agent and 
(iii) an oily agglomeration aid comprising a hydrocarbon fraction which is 
capable of wetting the surface of both the sulfur capture agent and the 
carbonaceous material; 
(b) agitating the slurry sufficiently to coagglomerate the carbonaceous 
material and the sulfur capture agent with the hydrocarbon fraction of the 
oily agglomeration aid while substantially excluding any hydrophilic 
inorganic impurities from the carbonaceous material, and 
(c) separating the agglomerates from the slurry. 
Limestone, lime and hydrated lime have been tested and found effective as 
sulfur capture agents in selected conditions as described hereinbelow. 
Although most oils will bind the carbonaceous particles together, only a 
few are suitable in the aqueous environment for conditioning the surface 
of the particles of the sulfur capture agent to render them hydrophobic 
and allow their coagglomeration with the carbonaceous material. This is 
due to their content of conditioning moieties, e.g. polar groups. 
As this invention is aimed at the utilization of oily wastes and sludges, a 
group of those substances has been investigated and found suitable as the 
agglomeration aids. The group consisted of refinery storage tank sludges, 
oil sands tailings, pond sludges, heavy oil emulsions from in situ 
recovery operations, crude oil contaminated drilling muds, and crude oil 
contaminated soil from refinery decommissioning. 
Another group of oily substances suitable as agglomeration media for the 
purpose of the invention are heavy oils or pitches including hydrocarbon 
residues, asphalts, petroleum asphalts, petroleum resins, tar sand 
bitumens and oils from the hot water processing of tar sands. Naturally, 
some of those substances require an elevated temperature during the 
coagglomeration procedure to decrease their viscosity. 
For the sake of clarity, oily wastes or sludges as referred to herein are 
substances containing a hydrocarbon fraction, hydrophilic solids such as 
clay or silica, and water. A substantial amount of the hydrophilic solids 
is excluded from the agglomerates due to the method of the invention. 
In order to ensure complete agglomeration it is advisable to precondition 
the sulfur sorbent before coagglomeration with the solid or semi-solid 
carbonaceous material. For sorbents such as limestone and freshly calcined 
lime this can be achieved simply by contacting the sorbent with the oily 
sludge before addition of the carbonaceous phase. In the absence of 
competition from the highly hydrophobic carbonaceous solid the sorbent has 
the opportunity to adsorb conditioning components from the oily phase 
(crude oil, heavy oil or bitumen) thereby rendering its surface 
hydrophobic. Conditioning occurs by interaction between a chemical entity, 
such as carboxylic acid, with the calcium atoms of the sorbent material. 
Additional of the carbonaceous phase then allows coagglomeration with the 
conditioned sorbent. For the case of slaked lime the sorbent surface is 
hydrated to such an extent that a more aggressive conditioner must be 
used. Fatty acids such as oleic or the soluble salt such as sodium oleate 
are suitable reagents for this purpose. A cheap, readily available source 
of fatty acids is crude tall oil, a byproduct of chemical paper pulp 
production. Again best results are obtained if the sorbent is 
preconditioned before mixing with the carbonaceous solid or semi-solid 
material. 
Although these investigations were carried out with tar sand cokes as 
carbonaceous materials, the method of the invention should be applicable 
to other types of high-sulfur fuels such as lignites, peats, coals, 
petroleum fractions, washery waste coals and some semi-solid petroleum 
fractions. 
Generally the amount of oil necessary to form suitable agglomerates, as 
related to the total weight of the carbonaceous material and the sulfur 
sorbent, was 10-25 w/w %. Particularly efficient agglomeration was 
achieved when the ratio was 15-20 w/w %. 
The retention of sulfur dioxide in the ash was found to be dependent on 
several factors including the calcium to sulfur mole ratio in the 
agglomerates. Good results were obtained with the ratio in the range from 
ca. 0.6 to 2.0, still depending on the combustion temperature, or ashing 
temperature of the composite fuel, the choice of sorbent, the use of 
conditioning agents and the partial pressure of oxygen on combustion. 
It has been found that limestone can be particularly effective as a sulfur 
capture agent when activated by certain conditioning agents in the aqueous 
slurry phase. The agents used successfully were sodium hydroxide, sodium 
oleate and a sodium salt of a petroleum sulfonate. Sulfur capture was 
improved by 15-30% over limestone alone when the abovementioned 
conditioning or activating agents, capable of reducing the surface tension 
in the slurry, were used. The effect was pronounced particularly when the 
Ca:S mole ratio was in the range 0.6-1.5. 
The method of the invention can produce wet agglomerates which are suitable 
for fluidized bed combustion after drying or without drying, when their 
water content is ca. 20-35%. 
The slurry may be defined as having a solids content of less than 40 wt. %, 
preferably 10-20% based on the total weight of the slurry. 
DETAILED DESCRIPTION OF THE INVENTION 
Suncor delayed coke and Syncrude fluid coke were used as carbonaceous 
material. The coke could be ground or used as in the case of fluid coke. 
Two different particle sizes, 75-150 .mu.m and 300-500 .mu.m, were tested 
in this research work. The size of the coke particles did not have any 
significant effect on its ability to agglomerate in the presence of 
limestone. Both sizes agglomerated well. The two materials were each 
coagglomerated with a sulfur dioxide capture agent, or sorbent, selected 
from line, hydrated lime and limestone. Suncor coker feed sand bitumen was 
used in most experiments as an agglomeration aid (bridging liquid). 
The composition of the coke samples is listed in Table I. 
TABLE 1 
______________________________________ 
Composition and physical data for cokes 
Ultimate analysis 
Suncor delayed 
Syncrude fluid 
(dry basis) coke coke 
______________________________________ 
Carbon 83.0 76.8 
Hydrogen 3.4 1.6 
Nitrogen 1.5 1.5 
Sulfur 5.9 6.9 
Oxygen 2.9 4.4 
Ash 3.4 8.0 
______________________________________ 
Lime was a laboratory grade CaO sample. The samples of slaked lime were 
prepared as shown in Table II&gt;The sample of limestone used was pulverized 
agricultural limestone (Domtar). It contained approximately 97% 
CaCO.sub.3. A partial size distribution of this sample is given in Table 
III. 
TABLE II 
______________________________________ 
Experimental conditions for 
various hydrated lime samples 
Sample 
# Experimental Conditions 
______________________________________ 
1. Laboratory grade CaO was mixed with distilled water 
in the ratio of 1:4 and then air dried at 90.degree. C. 
2. 20 g of CaO was mixed with 80 g of distilled water 
and 740 ml of isopropyl alcohol. The slurry was 
then dried at 90.degree. C. on a rotary evaporator under 
vacuum. 
3. Same as above, except the excess liquid was removed 
under atmospheric pressure at 90.degree. C. 
4. 10 g of CaO was mixed with 40 g of 0.5% aqueous 
solution of sodium sulfonate (Witco TRS-10-80) 
and 370 ml of isopropyl alcohol. Contents were 
mixed into a slurry and then dried on a rotary 
evaporator at 90.degree. C. under vacuum. 
5. Same as above, except the excess liquid was removed 
under atmospheric pressure at 90.degree. C. 
6. Same as sample 1 except that the sample was freeze 
dried. 
7. Same as sample 1 except that the sample was dried 
in a vacuum oven at 90.degree. C. 
______________________________________ 
TABLE III 
______________________________________ 
Size distribution of limestone sample 
Sieve Size Cumulative Weight Percent 
(um) Passing 
______________________________________ 
44 67.0 
53 74.7 
74 91.8 
______________________________________ 
Combustion of Coke-Oil Agglomerates 
Two procedures were used for the washing of dried coke-oil agglomerates. 
The first procedure involved weighting an agglomerate sample into a 
porcelain crucible, and placing it into a muffle furnace preset at the 
desired temperature. The second procedure involved burning a preweighed 
sample in a bench scale fluidized-bed reactor at 850.degree. C. For the 
latter procedure, the SO.sub.2 concentration in the combustion gases was 
measured using a Beckmann model 865 SO.sub.2 infrared analyzer. Blank 
experiments were also carried out in which coke-oil agglomerates prepared 
in the absence of limestone were burned under similar conditions. The 
results are discussed in the examples. 
Agglomeration Procedure 
20g of ground coke was mixed with corresponding amounts of ground sorbent 
depending on the desired Ca:S ratio, and the mixture was dispersed in 100 
ml of tap water contained in a Waring Blender. If required, an appropriate 
amount of a conditioning or activating agent was then added and the 
contents were agitated at 250 rps for 15 seconds. At this stage the 
blending speed was lowered to 120 rps. Bitumen was added slowly while 
continuing blending until discrete agglomerates or a unitary phase was 
obtained (5-15 minutes). Coke-oil agglomerates/oil phase were then 
separated from the aqueous phase by screening. A portion of the 
agglomerates was used for analysis of bitumen, coke and ash content. The 
rest was dried at 100.degree. C. to a constant weight. The coke-oil 
agglomerates before drying contained about 20-35% water. 
Sulfur analysis 
Sulfur contents of coke and coke agglomerates were determined by three 
methods for comparison: ASTM method D4239-83, Leco sulfur analyzer, and 
x-ray fluorescence spectrometry. The latter method gave values which were 
closest to the expected sulfur content. Hence, all the results discussed 
herein are based on the x-ray spectrometry method.

EXAMPLE 1 
100 g of a storage tank sludge from a heavy oil project (bitumen 
content.apprxeq.14%) was agitated with 50 g of Syncrude coke (ratio of 
coke to bitumen.apprxeq.3.5:1) to recover residual oil according to our 
Canadian patent No. 1,200,778. Coke-oil agglomerates thus obtained were 
divided into two portions. One portion was first dried at 100.degree. C. 
followed by ashing at 900.degree. C. in a muffle furnace. The other 
portion was reslurried and then coagglomerated with 15% Domtar 
agricultural limestone so as to give a Ca to sulfur ratio of 1.1:1. These 
agglomerates were fist dried and then ashed at 900.degree. C. as above. 
Total sulfur in both agglomerate samples and their ashed samples was 
determined using x-ray fluorescence spectroscopy. The results are shown in 
the Table IV below. 
TABLE IV 
______________________________________ 
SO.sub.2 Capture by Limestone 
SO.sub.2 Capture (As 
Run w/w % of w/w % of total 
# Sample Sulfur Sulfur in the feed) 
______________________________________ 
1 Coke-Oil Agglomerates 
3.62 -- 
2 Ash from Above 0.46 5.0 
3 Coke-oil-15% lime- 
3.33 -- 
stone Agglomerates 
4 Ash from Above 7.65 98.8 
______________________________________ 
The coagglomeration was carried out in two steps to facilitate the 
determination of CA:S ratio. Normally the sulfur adsorbent would be 
incorporated into the agglomerate during the oil collection stage. 
The agglomeration method as described above thus provides a means of 
cleaning waste sludges and tailings of oil while producing an oil enriched 
solid fuel with good sulfur capture efficiency. This whole process can be 
achieved in a series of simple mixing steps. The resulting oil-cokesorbent 
agglomerates can be used as an ancillary fuel for steam generation in 
conventional burners without modification for sulfur dioxide capture such 
as flue gas scrubbers. 
EXAMPLE 2 
Samples of Suncor and Syncrude coke oil agglomerates with and without the 
presence of Domtar limestone were prepared as described under 
"Agglomeration Procedure". These samples were burnt in a bench scale 
fluidized bed reactor of 850.degree. C. with air flow rate of 15 litres 
per minutes. Combustion tests were also carried out in a muffle furnace at 
900.degree. C. The results of these tests are listed in Table V. 
TABLE V 
______________________________________ 
SO.sub.2 Capture by Limestone - Muffle furnace 
vs. Fluidized-bed Combustion 
Percent, SO.sub.2 capture 
Syncrude coke 
Suncor coke 
Muffle Muffle 
Ca:S molar ratio 
furnace FB-reactor furnace 
FB-reactor 
______________________________________ 
0 5 -- 2 -- 
1 76 68 77 54 
______________________________________ 
Because of the considerably shorter retention time in a fluidized bed 
combustor compared with a muffle furnace, and the lack of recirculation 
capability, the results from the two systems are not directly comparable. 
This explains the lower sulfur capture in a fluidized bed combustor 
compared to that in a muffle furnace. However, combustion in a 
recirculating fluidized bed reactor is expected to give comparable results 
to those obtained from a muffle furnace. 
The difference in the extent of sulfur capture from the two cokes as noted 
from the fluidized bed combustion results, can be explained on the basis 
of the differences in the reactivities of the two cokes. On combustion, 
more reactive Suncor coke will release SO.sub.2 faster compared with the 
less reactive Syncrude coke. Thus the contact time of SO.sub.2 with the 
sorbent will be much shorter for Suncor coke than for Syncrude coke, 
resulting in a greater utilization of the sorbent for Syncrude coke than 
for Suncor coke. 
EXAMPLE 3 
Coke-oil agglomerates containing a quantity of Domtar limestone 
corresponding to Ca:S molar ratio of 1:1 were prepared according to the 
procedure described under "Agglomeration Procedure". Half of the samples 
were first dried in the oven and then burnt in a bench scale fluidized bed 
reactor at 850.degree. C. while maintaining the air flow at 15 litres per 
minute. The other half of the sample was burnt wet in the fluidized bed 
combustor under similar conditions. The results are given in the Table VI 
below. 
TABLE VI 
______________________________________ 
The effect of moisture on the capture of SO.sub.2 by limestone 
Sulfur Capture (As w/w % of total Sulfur) 
Description 
Syncrude Fluid Coke 
Suncor Delayed Coke 
______________________________________ 
1 mm Size dry 
67.6 54.4 
agglomerates 
1 mm Size wet.sup.1 
59.1 59.4 
agglomerates 
______________________________________ 
.sup.1 Water content: Suncor coke agglomerates, 35%; Syncrude coke 
agglomerates, 20%. 
Although the presence of moisture did not appear to affect the combustion 
efficiency of the agglomerates, it did interfere in the analysis of 
SO.sub.2 by the infrared analyzer. The difference in the sulfur capture 
results from the dry and wet agglomerates falls within 5-7% range for both 
cokes. Considering the analytical errors due to the presence of moisture it 
can be assumed that comparable levels of sulfur dioxide sorption are 
obtained from both wet and dry agglomerates. EXAMPLE 4 
Samples of coke-oil agglomerates containing varied proportions of Domtar 
limestone were prepared according to the procedure described under 
"Agglomeration Procedure". Combustion tests were carried out on the dried 
samples in the bench scale fluidized bed combustor at 850.degree. C. while 
maintaining the air flow at 15 litres per minute. The results of these 
tests are listed in Table VII below. 
TABLE VII 
______________________________________ 
The effect of increased quantities of limestone 
Percent, SO.sub.2 capture 
Ca:S Mole Ratio 
Syncrude Coke 
Suncor Coke 
______________________________________ 
0.85 58.6 -- 
0.89 -- 46.5 
1.00 67.6 54.4 
1.50 64.1 44.7 
2.00 68.1 54.4 
______________________________________ 
The results of Table VII demonstrate the effect of Ca to S mole ratio on 
the retention of sulfur by limestone. Contrary to our investigations in a 
muffle furnace and to the conventional fluidized bed combustion studies 
involving physical mixtures, increased quantities of limestone were not 
beneficial beyond the ratio of Ca:S of 1:1. Maximum limestone utilization 
was achieved for a limestone quantity corresponding to the Ca:S mole ratio 
of 1:1. Increasing the load of limestone beyond this amount resulted either 
in a decreased SO.sub.2 sorption or no further improvement. This can be 
explained on the basis of the dominance of calcination reaction with 
increasing amounts of limestone in the agglomerates. Increased CO.sub.2 
pressure from the calcination of limestone will result in the breakage of 
agglomerates and thus less contact time between SO.sub.2 and the sorbent. 
However, if this is true then the use of lime should give better results. 
EXAMPLE 5 
Samples of coke-oil agglomerates containing varying amounts of calcined 
limestone were prepared according to the Procedure described under 
"Agglomeration Procedure". Combustion tests were carried out on these 
samples in the fluidized bed reactor as described in Example 4. The 
results are listed in Table VIII. 
TABLE VIII 
______________________________________ 
The effect of increased quantities of lime 
in a fluidized-bed reactor 
Ca:S mole ratio 
Percent, SO.sub.2 capture 
______________________________________ 
0 -- 
0.5 55 
1.0 71 
1.5 75 
2.0 83 
______________________________________ 
The results in Table VIII demonstrate the effect of the increased amounts 
of lime on the reduction of SO.sub.2 emissions from the combustion of 
Syncrude coke. The degree of sulfur dioxide retention increases with 
increasing amounts of lime. These results are consistent with the above 
given explanation for the observed adverse effect of the increased amounts 
of limestone. 
Results and Discussion 
The SO.sub.2 capture rate was found to be dependent on the sorbent content 
for the static combustion tests (muffle furnace). Table IX shows, for 
Suncor coke and limestone, a decrease in sulfur dioxide emission with an 
increased limestone content of the agglomerates. The SO.sub.2 capture 
rate, however, becomes almost constant above Ca:S mole ratio of 1:1 at a 
temperature of 460.degree. C. At the higher ashing temperature 
(1000.degree. C.) and under higher partial pressures of CO.sub.2 (limited 
air), a higher percent of SO.sub.2 capture was found. 
TABLE IX 
______________________________________ 
Ca:S ratio effect on SO.sub.2 capture by limestone 
in the absence of a conditioning agent 
Percent, SO.sub.2 capture 
Ashing temp. 
Ashing temp. 
Ca:S mole 460.degree., excess air, 
1000.degree., limited air 
ratio muffle furnace 
muffle furnace 
______________________________________ 
0.5 26 50 
1.0 53 68 
1.5 57 75 
2.0 58 80 
2.5 58 79 
______________________________________ 
The effect of Ca:S mole ratio on the retention of sulfur dioxide by lime is 
illustrated in Table X. These tests were carried out by preparing the 
samples in the presence of 0.25% sodium oleate and burning the samples in 
a muffle furnace. It is evident that the degree of sulfur dioxide 
retention increases with increasing amounts of lime in the agglomerates up 
to about 90% at a calcium to sulfur mole ratio of about 2:1. Maximum sulfur 
dioxide retention was obtained new 750.degree. C. in contrast to a value of 
1000.degree. C. for limestone. This is consistent with other published data 
regarding optimum sulfation temperature. 
TABLE X 
______________________________________ 
Ca:S mole ratio effect on the retention 
of SO.sub.2 by Suncor coke samples containing lime 
Ca:S mole ratio 
Percent, SO.sub.2 capture 
______________________________________ 
0 2 
1.0 72 
2.0 87 
3.0 90 
4.0 89 
______________________________________ 
Table XI shows the effect of Ca:S mole ratio on the SO.sub.2 retention by 
samples containing hydrated lime and Suncor coke. Sample preparation and 
combustion procedure was similar to that described above. 
TABLE XI 
______________________________________ 
Calcium to sulfur ratio effect on SO.sub.2 
capture by hydrated lime 
Ca:S mole ratio 
Percent, SO.sub.2 capture 
______________________________________ 
0 2 
0.5 38 
1.0 70 
1.5 99 
2.0 -- 
______________________________________ 
TABLE XII 
______________________________________ 
SO.sub.2 Capture Efficiencies of Limestone 
vs Lime for Syncrude Coke 
Percent, SO.sub.2 capture 
Ca:S mole ratio Limestone Lime 
______________________________________ 
0 5 5 
0.5 50 30 
1.0 94 70 
1.5 95 86 
2.0 95 87 
______________________________________ 
Coke to bitumen ratio did not appear to affect the reactivity or capacity 
of hydrated lime for SO.sub.2 capture. This suggests that hydrated lime is 
an effective sorbent for sulfur dioxide for bitumen as well as from coke. 
Contrary to the findings noted for CaO and limestone, the presence of 
excess air does not have any significant effect on the overall retention 
of sulfur dioxide by hydrated lime. 
In order to assess the efficiency of this process for controlling sulfur 
dioxide emissions from the combustion of various types of cokes, 
coagglomeration of Syncrude fluid coke with lime or limestone was also 
attempted. The results were essentially identical to those observed for 
Suncor coke. The efficiencies of sulfur dioxide retention from the 
combustion (muffle furnace) of Syncrude coke by limestone and lime can be 
compared with the results presented in Table XII. Although both curves 
follow essentially the same trend, it is obvious from the results that 
limestone is a more efficient sorbent, compared with lime, over the entire 
range of calcium to sulfur ratios. This could be attributed to the higher 
porosity and reactivity produced by the in situ calcination reaction. The 
effect of the pore size is known to be significant in determining the rate 
as well as the extent of reaction between SO.sub.2 and CaO. It has been 
found that small pores in the calcines resulted in high rates of reactions 
and low overall conversions due to pore plugging, while large pores caused 
lower rates of reaction with higher conversions. It is probable that the 
freshly calcined limestone particles have bigger pores than the CaO used. 
This is a very important result as the ability to use a cheap and readily 
available material in its natural form has a considerable economic 
significance. The cost ratio of lime to limestone on a molar basis may 
vary from 2 to 4 depending on the transportation distance. Even the costs 
for transportation and handling of limestone tend to be lower than for 
lime since it can be transported in open trucks. 
The effect of some conditioning or activating agents on sulfur dioxide 
capture by limestone-containing agglomerates was investigated. The agents 
tested were sodium hydroxide, sodium oleate and Witco TRS 10/80, a sodium 
salt of a petroleum sulfonate (Table XIII). The addition of all three 
agents in the slurry stage of the agglomeration procedure improved the 
coagglomeration of the components, resulting in enhanced and more 
reproducible desulfurization, especially at higher Ca:S mole ratios. This 
could have been due to the improved wettability of the components towards 
the bridging oil as a result of the use of surfactants or by in situ 
formation of surfactants. It appears that the three additives all have the 
ability to distribute limestone uniformly within the agglomerates. 
Overall sulfur capture by limestone was independent of the concentration of 
these conditioning agents. This is consistent with the presumed catalytic 
nature of these additives. 
TABLE XIII 
______________________________________ 
Effect of various conditioning agents on the 
retention of SO.sub.2 by limestone 
Percent, SO.sub.2 capture 
Ca:S mole ratio 
Blank NaOH Sodium oleate 
TRS 10/80 
______________________________________ 
0 2 2 2 2 
0.5 48 48 50 50 
1.0 65 80 78 78 
______________________________________ 
Sodium oleate was found to be beneficial in the agglomeration of laboratory 
prepared samples of hydrated lime, but none of the other agents affected 
either the retention of SO.sub.2 or agglomeration in the presence of 
reagent grade Ca(OH).sub.2. 
It has been established that all the three sorbents investigated: lime, 
hydrated lime and limestone, particularly in the presence of conditioning 
agents, are efficient in their capacity to retain SO.sub.2 on combustion 
of the agglomerates. Comparative tests were conducted for Suncor 
coke-based agglomerates, wherein limestone, lime and hydrated lime were 
conditioned as discussed above. SO.sub.2 capture efficiencies of ca. 
80-90% were obtained (Tables XIV and XV), but activated limestone was 
still found to be the most efficient. This is of considerable significance 
since limestone is less expensive than the other sorbents. 
TABLE XIV 
______________________________________ 
Comparative SO.sub.2 capture efficiencies of 
various sorbents with Suncor coke 
Percent, SO.sub.2 Capture 
Ca:S mole ratio 
Lime Limestone Hydrated Lime 
______________________________________ 
0 2 2 2 
0.5 41 47 37 
1.0 71 77 71 
1.5 87 90 90 
2.0 95 -- -- 
______________________________________ 
Lime and hydrated lime both have comparable efficiencies for low calcium to 
sulfur ratio (up to.apprxeq.1:1). However, in the range of Ca to S ratios 
beyond 1:1, hydrated lime appears to be more efficient than lime, 
approaching in efficiency that observed for activated limestone. 
TABLE XV 
______________________________________ 
Efficiency of SO.sub.2 Capture, 
Suncor coke vs Syncrude coke 
Percent, SO.sub.2 capture 
Ca:S mole ratio 
Suncor coke 
Syncrude coke 
______________________________________ 
0 2 5 
0.5 45 60 
1.0 77 84 
1.5 &gt;90 &gt;90 
2.0 -- -- 
______________________________________ 
A comparison of the efficiency of this process in terms of sulfur retention 
by the ash has been made for the two cokes investigated. It is obvious that 
although this process is effective for both cokes it is slightly more 
efficient of Syncrude coke especially at higher calcium to sulfur ratios. 
Thus, at a calcium to sulfur mole ratio of about 1;1, over 90% sulfur 
retention can be achieved for Syncrude coke compared with over 80% sulfur 
retention for Suncor coke. This difference may be due to the reportedly 
higher bulk gasification reactivity of Syncrude fluid coking coke compared 
with that of Suncor delayed coking coke. Higher reactivity of fluid coke, 
compared with delayed coke, is surprising as the former was subjected to 
more severe treatment in the coking process. However, no reason for this 
reactivity difference has be suggested. 
This size of agglomerates can be controlled to suit the particular 
application of the composite fuel. For fluidized bed combustion, the size 
of agglomerates should be in the range 0.5 to 3 mm; for bubbling bed, 
about 4 to 5 mm, while for combustion in a nozzle burner, their size 
should not exceed 0.5 mm. 
The size of agglomerates is in direct proportion to the oil content. The 
size also increases with longer agitation periods, while the degree of 
agitation has a reverse effect, i.e. the agglomerates tend to decrease in 
size when the agitation is more vigorous.