I
CONSEIL INTERNATIONAL
DES MACHINES A COMBUSTION°141/
ON COMBUSTION ENGINES
20th INTERNATIONAL CONGRESS ON COMBUSTION ENGINES
P11 p 4,8 EIIIMEM111:11.11111HI-. 1,1 pr. :E:1111 111110i1I1+IIIWI,1 I 1111 EMI 11111,1EFFECTS OF LOW SULFUR FUEL OILS
ON COMBUSTION PERFORMANCE AND
ENVIRONMENT
byID? H Nomura, Mr T Oniata, Mr M Sekiriiiito and Mr. H Watanabe Nippon Oil Co
INTERNATIONAL COUNCIL
1LONDON 1993
CIMAC 1993D29i
Effects of Low Sulfur Fuel Oils
on Combustion Performance and Environment
Dr. H.Nomura
,Japan ,Manager,
Research and Development Depertment Nippon Oil Co.
Mr. T.Omata
,Japan
,Reseach Associate,
Mr. M.Sekimoto
,Japan, Senior Research Chemist,
Mr. H.Watanabe
,Japan
,Senior Reseach Engineer,
Central Technical Research Laboratory Nippon Oil Co.
Abstract
An effective method for reducing SO2 emissions from ships would be to reduce the sulfur content of the fuel. Marine diesel fuels mainly consist of residual components that have a high sulfur content. In order to reduce the sulfur content of the fuel, it is necessary to remove the
sulfur from these residual components by applying hydrodesulfurization. Residue desulfurization is carried out in a hightemperature highpressure hydrogen atmosphere. so the composition of the oil changes greatly during the desulfurization reaction. In this study. the effect of the composition change of the residual oil on engine combustion performance .
especially the exhaust gas, was analyzed using both raw and product oil from a commercial residue desulfurization unit. The results showed that the amount of asphaltenes. resins. and other heavy components in the residue decreased due to the hvdrodesulfurization. Conversely. the saturate content increased, resulting in a drop in the NOx and smoke emissions under low load conditions. However, this residue dcsulfurization process presents several problems. The
sulfur compounds contained in the residual oil arc very difficult to remove. Furthermore.
during the desulfurization process, vanadium and asphaltenes precipitate from the residue on
the catalyst and shorten the life of it. As a result, large amount of catalyst are required when operating in the hightemperature, highpressure conditions; this leads to much higher
construction and operating costs. The adoption of residue desulfurization unit for reducing the sulfur content of fuels should take into consideration a broad array of factors. including' the effect on fuel costs.
1
ABREGE
Un procede efficace pour reduire les emissions de SO2 des navires scrait de reduire la
teneur en soufrc du combustible. Les combustibles diesel pour la marine sont produits
principalcmcnt i partir de comosants residue's qui ont tine haute tencur en soufre. Afin dc recluire la teneur en soufrc du combustible, il est necessaire d'eliminer lc soufre de ccs
composants residue's en executant une hydrodesulfurization. Toutefois, In ciesulfuration des residus utilise un catalyseur ct a lieu clans un environnement d'hydrog'en it haute temperature et
sous haute prcssion, de sorte que la composition dc l'huile sc modifie fortemcnt pendant la
reaction de desulfuration. Dans la prescnte etude, l'effet de la modification de la composition dc l'huilc residulle sum
in performance de combustion du motcur, specialement des gaz
cl'echappement, a eta analyse tant avec de l'huile brute qu'avec dc l'huile trait6c provenant dune
installation effective de desulfuration de residus. Les resultas ont montr6 clue la quantit6
d'asphaltenes, de resins etd'autres
composants lourds dans le residu baissesuite 1
Phydrodesulfuration. Reciproyucmcnt, la tencur en composes satures augmentc, menant Ii unc haisse des emissions dc NOx et de furnees dans des conditions de charge faible. Toutefois, cc procede de desulfuration des residus prdscnte aussi diverses difficultes. Les composes sulfur6s contcnus dans l'huile residuelle sont fort difficiles a ciesulfurer. De surcoit, pendant lc processus de desulfuration, le vanadium et les asphaltenes precipitent a partir du rcsidu ct abregcnt la vie du catalyseur. Par consequent, de grandes guantites de catalyseur sont requiscs pour travailler dans les conditions de temperature elevee et de haute prcssion et ccci conduit a des depenses dc
construction et de fonctionnement beaucoup plus &levees. Lcchoix dun 6quipcmcnt de
desulfuration des residus pour recluire la teneur en soufre des combustibles dcvrait prendrc en consideration unc large variete de facteurs, notamment l'effect sur les coots des combustibles.
1. Introduction
In recent years, environmental problems related to atmospheric air pollution have
become more serious, and restrictions have begun to be applied not only to on-land sources of pollution but to pollutants emitted by ships at sea as well, On a global scale, emissions from
ships account for only-a few percents of all atmospheric pollutants, but in coastal regions
their effect is much greater.
In November 1990, the International Maritime Organization(IMO) proposed target
values for " Prevention of Air Pollution from Ships, Including Fuel Oil Quality ". These targets call for a 50% reduction in SO2 and a 30% reduction in NOx. While countermeasures such as after-treatment equipment on ships arc being considered for reducing NOx emissions, a strong candidate for reducing SO2 emissions is using hydrodesulfurization to reduce the sulfur content of the fuel itself.
This paper reports on how changes in
fuel compositionresulting from
hydrodesulfurization affect engine combustion performance, especially the NOx and smoke content of the exhaust gas. Problems with the manufacturing of low-sulfur fuel oils are
discussed as well.
2. Experimental Method
2.1 Test Engine and Conditions
The main specifications of the engine used in this test are shown in Table 1. The engine test conditions followed the propeller law for 100% load, 50% load, and 25% load.
The NOx content of the exhaust gas was calculated assuming an 02 content of 13% and
using the following formula['] for humidity compensation. The smoke was measured with a BOSCH type smoke meter..
1 N 0 Leon =NO X meas
1+a(H-10.34)+b(TA-25)+c(TaCaC-25).
PROPOSED COEFFICIENTS : a=-01.0120,b=-0.00275,c=0.00285
FORMULA :
H : abs humidity [g/kg dry air]
TA ambient temperature ['CI
Tacac: temperature after charge. air cooler rC
The combustion analysis was conducted by measuring the pressure in the cylinder, the fuel injection pressure, and the needle lift. The indicator analysis was then used to obtain the ignition delay, combustion duration, and other data.
Table 1 Engine Specifications
3
-
-UNIT
Engine Model NIIGATA-SEMT 4PA5L
Type 11 4-stroke, 1CT Bore mm I 255 Stroke mm 270 Number of Cylinder 4 Compression ratio 13. 1 B. M. E. P MPa 1.648 Engine Speed rpm 1000 Engine Power kW 757. 6 :
2.2 Test Fuels
Marine fuels are usually manufactured from a blend
of residual components and
distillate components. Table 2 shows the blend composition and the properties of the five types of fuel used in this experiment. The effect of sulfur content was studied by comparing Fuel 1-1(high sulfur content), Fuel M(medium sulfur content), and Fuel Ll(low sulfur content); the
residual components of these fuels were, respectively, the raw oil of our hydrodesulfurization unit(reaction temperature 400°C , reaction pressure 115 kgf/cm2), the product oil of the unit, and a 1:1 blend of the raw and product oil. We also compared three distillate components with low sulfur contents ; Fuel Ll,which was blended with 25% LCO(light catalytic cracked cycle oil); Fuel L2, which was blended with 25% LGO(light
straight gas oil); and Fuel L3, which was blended with 40% LCO.
Table 2 Test Fuel Properties
4
UNIT H M
Li
L2
L3
RAW OIL vol% 75 37.5
PRODUCT OIL vol% 37. 5 75 75 60
LCO
vol% 25 25 25 40LGO
vol% 25Density(15°C) kg/m3 955.9 944.6 931.3 923.9 920. 1
Viscosity (50°C) mm2/s 117. 8 75. 47 47. 14 60. 36 20. 90
(100°C) mm2/s 17.49 12. 88 9. 02 10.28 5.26
Lower Calorific Value kJ/kg 41000 41500 41730 41790 41710
Conradson Carbon wt% 10. 30 8. 23 5. 81 5. 61 4. 37 Asphal tens wt% 1. 8 1. 5 1. 2 0. 9 0. 9 Anilin Point °C 81.5 82.7 84.0 88.4 77.6 C wt% 86. 4 86. 9 87. 5 87. 0 87. 8 H wt% 11.2 11.4 11.7 12.0 11.6 N wt% O. 16 O. 15 O. 13 O. 13 O. 11 Sulfur wt% 2. 3 1. 5 0. 6 0. 9 0. 5 Nickel ppm 7.0 5.0 2.0 2.0 2.0 Vanadium ppm 19. 0 9. 0 3. 0 3. 0 2. 0
CCAI
831 825 819 808 8221 1.. 400 1. 200 1-1-1 1-C-3 L000.-U-1 CC CC 800 3. Results
3.1EffectofDifferences in Fuel on Exhaust Gas
Fig. 1 and Fig.2 show the NOx and smoke content, respectively, of the exhaust gas for various load conditions with Fuels H,M,andLl. As described above, these three fuels consist of different components with different sulfur contents
of residual oil by
means of thehydrodesulfuization. For all the fuels,the NOx tended to increase as the load conditions decreased. At the load conditions of 50% and 25%,the lower sulfur Fuels
M and Li had
slightly lower NOx concentrations in their exhaust than the high sulfur Fuel H. No differencein smoke emissions was observed among different loads and fuels when high load
conditions of 50% or higher were used.
At the lowload condition of 25% the smoke increased sharply and differences among the fuels slightly appeared; the smoke emissionswere lower for the low sulfur Fuels M and Li than for Fuel H.
SULFUR CONTENT 2.27 1. 51 0. 63
wt% 0
M L 1
SULFUR CONTENT 2.21 1. 51 0. 63
wt%
*
F4 2
Effect of Residual Conponents on Smoke25 50 73 100'
LOAD %
figil Effect of Residual Components on, NOX
50 LOAD 75 54/ 100 M
Fig.3 and Fig.4 show the NOx and smoke content, respectively,of the exhaust gas for Fuels
Li, L2, and L3, which contained various amounts of distillate components. The tendency
relative to the load conditions was the same as in the above case when the residual components
were varied. Similarly, the differences among the fuels were noticed at the lower load
conditions. Fuel L2, which was blended with 25% LCD, had a lower NOx content in its exhaust than Fuel Li, which was blended with 25% LCO. Fuel 13, which had a 40% blending ratio of LCO, produced more NOx. The smoke content was highest for Fuel Li, followed by
Fuel L2 and L3. 1.400 1. 200 1. 000 ] 800 .
Fig. 3
3. 0 Cl, c. 2. 0 -MI LU CD 1 0 Cl, ss Oz.; 0.0 25\
N, S.Li
L2 L3 LCO 25% LCD 25% LCO 40%,
....AS..,,
,
....l ,.... ....,
,
',.. ,... _Effect of Distillate Components on NOx
50
LOAD %
Fig.4 Effect of Distillate Components on Smoke
75 100
Li
LCO 25% L2 LGO 25% m L3 LCO 40% 25 50 75 100 LOAD %a
3.2 Relation Between Fuel Composition and NOx
As shown in Fig.1 and Fig.3, the residual and distillate components affected NOx
emissions differently. Fig.5 shows the combustion analysis results for the ignition delay time, which has been thought to correlate with N0x121. In this case, the lower the load conditions, the greater the ignition delay and the greater the differences among the fuels. For the residual components, the low sulfur Fuel Li had a shorter ignition delay than the high sulfur Fuel H.
For the distillate components, Fuel Li, which was blended with 25% LCO, had a shorter
ignition delay than Fuel L3, which was blended with 40% LCO, and the ignition delay was even shorter for Fuel L2, which was blended with 25% LOU.
These differences in ignition characteristics of the various fuels resemble the NOx characteristics shown in Fig.1 and Fig.3. In Fig.6, we summarize the relationship between the ignition delay time and NOx, taking into consideration the differences in both the load
conditions and the fuels.
1.400 1,300 1. 200 1, 100 -; 1,000 7 900 -.1 800 700 O. 5 7 25 50 75 100 LOAD %
Fig. 5 Effect of Different Fuels on Ignition Delay Time
1.0 1.5 2.0 2. 5
IGNITION DELAY TIME msec
Fig.6 Relationship between Ignition Delay and NOx
2.
2.
10. 5
Next, we analyzed the fuel compositions using silica gel chromatography to investigate in detail the relation between the composition and the ignition characteristics. The coposition of
each fuel are shown in Fig.7. For the residual components, the product oils of
hydrodesulfurizationunit had a smaller proportion
of polyaromatics(tri and higher
aromatics),resines and asphaltenes than the raw oil, and there were more saturates, which
provide good ignition performance. The reason for this is that the hightemperature, high
pressure conditions necessary for the desulfurization of residual oil also cause the hydrocrack-ing of polyaromatics and other heavy components while the sulfur compounds are behydrocrack-ing con-verted into hydrogen sulfide.
Among the distillate components, LCO, which is a light cracked oil, contains a higher proportion of monoaromatics and diaromatics, while LGO, which is distilled from crude oil, has a higher proportion of saturates.
20
0
RAW OIL PRODUCT OIL LCO LGO
Fig.7 Comparison of Residual and Distillate Composition
Fig.8 shows the compositions of the fuels used in the experiment. If we look at the relationship between the saturate contents and the ignition delay times, we can SCC,C1S shown in Fig.9, that the fuels with the higher saturate contents had the shorter ignition delay at low load conditions except Fuel L3 which was blended with 40% LCD. Thus thc increase in the saturate concentrations that accompanies the hydrodesulfurization of the residual components can be expected to reduce the NOx emissions because of the improved ignition performance. If too
much LCO with a high ratio of monoaromatics and diaromatics is added as a mean of reducing the amount of sulfur,the NOx emissions will increase.
8
FiSATURATES
MONOAROMAT I CS
D I AROMAT I CS
POLYAROMAT I CS
IE LOW MOLECULAR RESINS PA HIGH MOLECULAR RESINS
ASPHALTENES
100
80
4-3
825 819 808 822
H M L1 L2 L3
FUELS
Fig.8 Comparison of Test Fuel Composition
SATURATES MONOAROMAT I CS
D I AROMAT I CS
POLYAROMAT I CS
LOW MOLECULAR RESINS HIGH MOLECULAR RESINS ASPHALTENES
0.0 = , . = 1
30 35 40 45
SATURATES CONTENT wt%
Fig. 9 Effect of Saturates Contents on Ignition Delay
Fig.10 summarizes the relation between the ignition performance and the commonly used CCAl(calculated carbon aromaticity index)131.141. We can use CCAI as the fuel parameter and apply multiple regression analysis to the following formulaI5I for estimating the ignition delay
timc(including data from past experiments) in order to obtain the various constants. Then we
can see from Fig. 11 that there is a good correlation between the actual values and the estimated values, including in the case of low sulfur fuel oil.
9 50 55 CD 831 2. 5 25% H 50% 100% A L1 L2 O.5
2. 5
0 0
COEFFICIENT OF CORRELAT I ON=O.959
PAST TEST DATA
LOW SULFUR MIDDLE SULFUR
HIGH SULFUR
AL
0 1 2
MEASURED IGNITION DELAY TIME msec
Correlation between Measured and Calculated Ignition Delay
10
800 810 820 830
C 'CA 1
Fig. 10 Effect of CCAI on Ignition Delay
= A P-nexp(D
T)
: Ignition Delay Time [msecJ
P : Pressure in Cylynder at Start of Injection [kg/cm 2]
T : Temperature in Cylynder at Start of Injection [KJ
A,
n,
D: constantD is given by D = aCCAl+b
A=110.08 n=1.1686 a=4.1535 b=-3462.3 fib ci& 25% 50% 100% 2.0 0 0.5 3 2 1'r
r
33.3 Relation Between Fuel Composition and Smoke
As shown in Fig.2 and Fig.4, the residual and distillate components affected smoke
emissions differently as well. FIg.12 shows the relation between the combustion duration and the smoke emissions at 25% load,where the difference among the various fuels was particu-larly large. Fuel Li, which used low sulfur residual components, had less smoke than Fuel if, which used high sulfur residual components, even though the combustion duration of Fuel Li was longer. In contrast, the combustion duration was short and the smoke emissions were low for Fuel L3, which contained 40% I.Ja) as its distillate component. In these OAT cases, the
tendencies differ depending on the fuel. Fig.13 summarizes the relation between the smoke and the fuel composition shown in Fig.8, indicating that there is no visible correlation between the smoke and the ratio of monoaromatics and diaromatics. However, the smoke does correlate
with the ratio of polyaromadcs and other relatively heavy components. This suggests that
Rid Li had less smoke than Fuel FT because of the decrease in polyaromadcs resulting from hydrodesulfurization. And ,
as shown in Fig.14, the qualitative change of the heavier
conponcnts in the residual oil may have been another factor that influenced the drop in smoke. The aromaticity of Da) was high but the ratio of polyaromatics was only about 10%,as
shown in Fig.7. When La) was blended at the ratio of 40% to give Fuel 13, the heavy
components of the residual oil were diluted, thus the smoke was reduced.
6 50 g 40 c, 5 30 ig 20 h3 10
LATER COMBUSTION DURATION
20 30 40 50 60 70
CONTENT
Fig. 13 Effect of Fuel Composition on Smoke
11
Fig. 12 Comparison of Combustion Duration and
Smoke at 25% Load 3 0 2.5 CO 20 uJ 1.5 1. 0 A 0 MONOARCMATICS--ASPHALTENES DIAROMATICS--ASPHALTENES POLYAROMATICS--ASPHALTENES Li L2 L3 FUEL 0 0 A H'
1( % High Molecular Resins 3. 1 Asphalt ens 15.4
Raw Oil Product Oil
Fig. 14 Qualitative Change of Aspha 'I' tens and Resins
during Desuul fur i zat i on Reaction
4. Effect of the Desulfurization of Residual Oil on Cost
As shown above, hydrodesulfurization residual oil does not have a particularly bad effect On combustion performance. In fact, under low load conditions it can have a positive effect. The problem, however, is the increase in manufacturing costs.
A simplified flow scheme of a desulfurization unit is shown in Fig.15. The residual oil
that is the raw material for the process is introduced together with hydrogen under high temperature and pressure into the reactor, which has been filled with a catalyst(usually
CoMo/alumina or NiMo/alumina). Here the sulfur compounds react with the hydrogen to
become hydrogen sulfide, which is then separated and recovered.
The problem with this method for desulfurizing residual oil is that the sulfur contained in residual oil is more difficult to remove than the sulfur contained in gas oil or other distillates. Furthermore, the desulfurization causes the precipitation of vanadium andasphaltenes from the residual oil; because these components shorten the life of the catalyst, large amounts of catalyst are needed to handle the high reaction temperature and pressure161.m. As a result, the large construction and operating cost must be required to remove the sulfur from the residual
oil.
The actual cost will varyclepending on the properties of the feed oil, the process conditions, and the sulfur level of the finished products. According to one trial calculation that has been reported, the cost will climb by $55 per kiloliter if the sulfur content is lowered from 3% to 1.5%.
12
13. 9
Hydrogen Feed Oil Reactor Hot HP Separator 13 Recycle Gas crubbing Cold Hp Separator
HIGH REACTION TEMPERATURE HIGH REACTION PRESSURE HIGH CATALYST VOLUME
---H2s
COST UP
Product Oil
Separator
Fig. 15 Residual Oil Desulfurizer - Simplified Flow Scheme
4.Conclusion
When residual components were hydrodesulfurized in order to reduce the sulfur
content of marine fuels, the
saturate content increased and improved ignitionperformance under lowload conditions tended to reduce the NOx emissionsslightly.
Similarly, a slight reduction in smoke was observed at low load conditions when residual components were hydrodesulfurized. This is believed to have resulted from the
decrease in polyaromatics and other heavier components due to hydrocracking
accompanied the desulfurization process.
When the blending ratio was increased too much for LCO with a high ratio of monoaromatics and diaromatics as a mean of reducing a sulfur content, the smoke declined but the NOx increased.
As described above, generally good results can be expected for engine combustion performance as a result of the reduction in the sulfur content of marine fuels, which is being considered as a method for reducing SO, emissions. In addition, the reduction in the content of asphaltenes and vanadium can be expected to improve engine durability. However, the introduction of desulfurization unit to reduce the sulfur content of residual oil will lead to large increases in manufacturing costs. Indepth studies arc needed in
order to decide how to balance this increase in costs against the overall effect on the
environment.
REFERENCES
"Exaust Emissions Measurement", CIMAC(1991), PAGE 72
T.NAGAI, M.KAWAKAMI, "Reduction of NOx Emission from Medium Speed Diesel Engines", Journal of the M.E.S.J., Vol. 25 (1990), PAGE 4
A.P.ZEELENBERG, H.J.FUN van DRAAT, H.L.BARKER, "The Ignition Per formance of Fuel Oils in Marine Diesel Engines", CIMAC 1983, Paper 66
H.Nomura, E.YOSHIDA, "Indices for Estimating the Ignition and Combustion Properties of Marine Diesel Fuels", CIMAC 1987, Paper 59
J.B.HEYWOOD. "Internal Combustion Engine Fundamental", (1988), PAGE 543 R.L.HOWELL, C.HUNG, "Catalyst Selection Important for Residuum Hydro processing", Oil Gas J, July 29 (1985)
J.F.HOHNHOLT, C.Y.FAUSTO, "Upgrading Residual Oil by Fixed Bed Hydro processing", Chem.Eng.Progress, Vol.81 (1985), PAGE 6
14 [1], [3] '[411 161 1[7]
