Energy Savings and Emission Reduction of Traditional Pollutants

ARTICLE pubs.acs.org/EF

Energy Savings and Emission Reduction of Traditional Pollutants, Particulate Matter, and Polycyclic Aromatic Hydrocarbon Using Solvent-Containing Water Emulsified Heavy Fuel Oil in Boilers Sheng-Lun Lin,*,†,‡ Wen-Jhy Lee,*,†,‡ Shun-Shiang Chang,†,‡ Chia-fon Lee,§ Lien-Fwu Lee,^ Chiao-Shang Lin,^ and Haiti Loong|| †

Department of Environmental Engineering, National Cheng Kung University, Tainan City 70101, Taiwan Sustainable Environment Research Center, National Cheng Kung University, Tainan City 70101, Taiwan § Department of Mechanical Science and Engineering, University of Illinois at Urbana
Champaign, Illinois 61801, United States ^ Everlight Chemical Industrial Corperation (Third Factory), Taoyuan County 32849, Taiwan Energy and Environment Research Laboratories, Industrial Technology Research Institute, Taiwan

)

‡

ABSTRACT: Heavy fuel oil is one of the most commonly used petroleum fuels in boilers, although it is associated with a high level of pollutants. Emulsification is a developing technique to enhance fuel efficiency and reduce regulated pollution emissions. In the current study, the water phase of emulsified heavy oil contained 1 vol % methanol, 4 vol % isopropyl alcohol (IPA), and 95 vol % water, representing actual industrial solvent-containing wastewater (SCW). The SCW fractions in emulsified fuel were optimized by thermal, centrifugal, and 14-day standing stability tests. The emulsion M1P4-10 with 10 vol % SCW showed no separation and contained the smallest and most homogeneous water-in-oil (W/O) droplets after stability tests. Four boilers, including three with 3.6 and one with 10 ton h
1 steam capacities, were employed to be operated for 30 h with a regular heavy fuel oil and M1P4-10. The microexplosion and tinder effects of solvent contents improved boiler efficiency by 10
33% and reduced fuel consumption by 5
31% using M1P4-10. The emulsion also reduced SOx by 3.3
7.1%, particulate matter (PM) by 41
85%, CO by 89
93%, HC by 91
60%, and NOx by 3.3
23%. With regard to inhibiting toxic air pollutants, the emission levels of total polycyclic aromatic hydrocarbons (PAHs) and total benzo[a]pyrene (BaPeq) were reduced by 37.7 and 61.8%, respectively using M1P4-10. The PM and NOx trade-off problem could be solved by lower temperature combustion of M1P4-10. Consequently, the solvent-containing wastewater emulsified heavy fuel oil could effectively promote boiler efficiency and reduce the pollutant emissions in a specific emulsifying ratio.

1. INTRODUCTION In some small countries, such as Taiwan, over 99% of the energy required is imported,1 since they lack natural energy resources. Reducing fossil fuel consumption is the most direct and effective way to deal with this problem, and thus, the development of sustainable alternative fuels is essential. There are over 6700 industrial boilers used as heating devices in Taiwan.2 The three major fuels for such boilers are coal, heavy fuel-oil (HFO), and natural gas, with HFO-fueled boilers accounting for almost 50% of the total. The annual HFO consumption in Taiwan was over 15 mega kiloliters (MkL) from 1991 to 2008. Moreover, the annual carbon dioxide (CO2) emissions from industrial boilers, the most significant green house gas (GHG), can be estimated as 44.3 mega metric tons (Mt) by multiplying the HFO consumption (kL) by CO2 emission factor of HFO (2.98 t kL
1 HFO).3 Additionally, the high viscosity and sulfur content of HFO results in incomplete combustion and leads to the emission of various pollutants, including sulfur dioxide (SO2), particulate matter (PM), carbon monoxide (CO), unburned hydrocarbon (HC), nitrogen oxide (NOx), and polycyclic aromatic hydrocarbon (PAHs).4
6 In other words, pollutant emissions are likely to be decreased if the combustion efficiency of such boilers can be improved. r 2011 American Chemical Society

Water-in-oil (W/O) emulsification has been used as an alternative fuel technology to achieve more complete combustion and less pollutant emissions.7 Microexplosion (ME) phenomenon is the major mechanism at work in emulsified fuels. The water phase is first dispersed uniformly by external forces, such as mechanical stirring or ultrasonication. The specific surfactant is then added into the mixture during the emulsification process to stabilize the W/O droplets. In the beginning of the combustion process, the water droplets wrapped in oil are heated and transformed into water vapor. Furthermore, the vapor which has a volume about 1000 times that of the liquid water explodes through the surrounding oil and separates the W/ O droplets into much smaller droplets that increase the total contact area with the air. Thus, the combustion efficiency is improved, and CO, HC, and PM emissions are further reduced at the same time.8 In addition, the water vapor could react with CO by water-shift reaction (CO þ H2O f CO2 þ H2) to reduce the CO emissions and form hydrogen (H2). Nevertheless, using emulsified fuel also could decrease the temperature of metal units Received: January 16, 2011 Revised: February 21, 2011 Published: March 08, 2011 1537

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Figure 1. Emulsification and boiler systems.

and increase the thermal load of a device.9,10 The water emulsified heavy fuel-oil (WEHFO) technique thus requires further investigation with regard to use in industrial boilers. The stability and W/O droplet size of the emulsion affects the strength of the microexplosions. The fuel, water content, density, dispersed phase fraction, surfactant, and dispersion technique were all optimized for stable emulsion in previous studies;11 however, the high water fractions of WEHFO decreased the fuel economy in those earlier works, because the high latent heat of water consumed more enthalpy when the fuel droplet was heated at the beginning of combustion. Chen showed a breakthrough of 14% boiler efficiency improvement by using oily wastewater emulsified with heavy fuel-oil in 2008.12 Very few studies focus on the content and concentration of the dispersed phase of an emulsion. In Taiwan, not only oily but also high chemical-content wastewater, such as solvent-containing wastewater, lubricant wastewater, and cutting oil wastewater, causes significant environmental problems. Biodegradation and incineration are the most common treatment processes to deal with these specific wastewaters. However, those end-of-pipe (EOP) treatment processes have several disadvantages: (1) the high capital cost of treatment equipment; (2) extra energy and operating costs are required; and (3) the generation of secondary hazardous pollutants, such as active sludge waste and air pollutants. Gong indicated that the addition of more volatile components cam significantly shorten the ignition delay of emulsified oil.13 In other words, solvent-containing water might improve the ignitability of emulsified fuel. With reference to both Chen and Gong, replacing the dispersed phase of emulsified heavy fuel oil with solvent-containing wastewater might be a feasible way to deal with pollutants. In other words, the organics in the wastewater could be considered as “energy” and be “recovered” by being emulsified with HFO as a boiler fuel. In this study, methanol and isopropyl alcohol (IPA) were blended with water to simulate the specific solvent-containing wastewater. The wastewater emulsified heavy fuel-oil (WWEHFO) was produced by a mechanical stirring emulsification system. Furthermore, three 3.6 ton h
1 steam capacity boilers and one 10 ton h
1 boiler were tested by using both traditional HFO and WWEHFO. The goals of this study were as follows: (1) to produce a more stable emulsion by

narrowing the density gap between the dispersed and continuous phases; (2) to achieve better fuel economy by having more homogeneous emulsion and less latent heat of the water phase by lowering boiling point of the methanol content; and (3) reducing pollutant emissions by attaining more complete combustion. Consequently, WWEHFO is expected to improve the boiler efficiency, reduce pollution, as well as reuse the energy contained in industrial wastewater.

2. EXPERIMENTAL SECTION 2.1. Preparation of Emulsified Heavy Fuel-oil. Heavy fuel-oil (HFO) produced by the Chinese Petroleum Corporation (CPC) was used in this study as a base fuel. The sulfur content, viscosity at 50 C, and pour point of the base fuel are 0.5 wt %, 110 cSt, and 15 C, respectively. The solvent-containing water (SCW) was prepared by blending 1 vol % methanol (M, purity >99.9%, LiChrosolv) and 4 vol % IPA (P, purity >99.5%, J.T. Baker) with 95 vol % tap water to simulate the compositions of a specific wastewater from chemical processes. A surfactant was added to form stable emulsions, M1P4-N (N = 10, 20, and 30 vol % water phases) to retard the flocculation, coalescence, and creaming.14 The surfactant used in the current study was composed of the chemicals that were used in Lin’s research15 and will not be described in this article. The emulsified heavy fuel oil was produced by employing a typical emulsion technology, as shown in Figure 1. First, HFO, surfactant, and SCW were added in specific fractions into a premixing tank under 180 rpm stirring velocity to make each content spread uniformly before emulsification. The tested SCW ratios in M1P4-N were 9, 19, and 29 vol % with 1 vol % surfactant and 90, 80, and 70 vol % HFO, respectively. The contents were then emulsified by an inline emulsifier (Tokoshu, Osaka, Japan) at 3600 rpm, resulting in small W/O droplets. The medium product was recycled to the premix tank until the fuel stability approached the acceptable level. A valve at the outlet of the homogenizer could provide a sample to check on fuel stability. Depending on the residence time and motor speed, this emulsification equipment could produce around 1
3 t h
1 stable emulsified fuel with six cycles per hour. 2.2. Fuel propertIes and Stability Tests. To optimize the feasible ratio of SCW in emulsions, centrifugal tests were conducted in three conditions to simulate the delivery temperature, preheated for petroleum gas ignition, and for electrode ignition as 25, 80, and 120 C, 1538

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respectively. Each emulsified fuel was centrifuged in a 15 mL tube at 5000 rpm for 15 min. The ratios of the unstable separate layers (water) in the centrifuged tubes were recorded to quantify the emulsion stability after centrifugation. The lower the volume of a separate layer in the tubes represents a more stable condition. Additionally, the following two methods were employed to characterize the stability of the emulsion: (1) a two-week (14-day) continuous record of fuel daily changes and (2) observation and analysis of W/O droplet sizes using an optical microscope (Olympus BX51TF, Tokyo, Japan) with 400 amplification and a charge-coupled device video camera (Olympus DP20). The count mean diameter (CMD), count median diameter (CMdD), and Sauter mean diameter (SMD) of the W/O droplets were calculated using Image-Pro Plus software version 5.0.2.9. After the stable blends were found, the viscosities were further measured using an analog rotary viscometer (NDJ-1) with the measurement range of around 0.1
10 000 cP and (5% error. The heating values of fuels were measured using a calorimeter (IKA C2000 basic) with a cooling water supplier (IKA KV600). 2.3. Boiler Test. Four boilers, A, B, C, and D with 3.6, 3.6, 3.6, and 10 ton h
1 steam capacities, respectively, were utilized to test M1P4-N. The boiler system used in this study is showed in Figure 1. The flow rates and temperatures of both fed fuel and flue gas were monitored by flow rate meters and thermometers. The boilers were equipped with pressure gauges and thermometers, which employed a control panel, to measure the steam produced. The operation steam pressure was controlled in the range of 6
7 kg cm
2. Both HFO and M1P4-10 could satisfy the steam demand and keep the downstream production operating well. For maintaining the fuel at the desired preheated temperature, a set of heating system was installed in the daily fuel storage tank, and the thermocouple was fixed at the fuel pipe just before the injector. Therefore, the injected fuel temperature could be well monitored and controlled. The boiler efficiencies (η) were defined as the ratio of output steam energy to input fuel energy as in the following equation which was also used in Chen’s research.12 η¼

Wðhv
hl Þ HB

ð1Þ

In eq 1, hv and hl are the enthalpy (kJ kg
1) of the steam produced and water fed, respectively, W is the mass of produced steam (kg), H is the calorific value of fed fuel (kJ kg
1), and B is the fuel consumption (kg). All the parameters were recorded once per 30 min and continuously operated for 30 h. The enthalpy of steam and heating value of fuel were calculated and illustrated as a regression line. The slope of the line is the estimated boiler thermal efficiency and would be further discussed. The gaseous pollutants in the exhaust were monitored by the standard methods of the National Institute of Environmental Analysis (NIEA). Specifically, carbon monoxide (CO) and carbon dioxide (CO2) were measured by a nondispersive infrared (NDIR) analyzer in the measurement range of 0
10 and 0
20 vol %, while nitrogen oxides (NOx) and sulfur dioxide (SO2) were measured using an electrochemical detector (ECD). An automatic stack sampler (AST) was used to collect the particulate matter (PM) on a silicon glass fiber filter. The PM mass on each filter was determined gravimetrically by an electronic analytical microbalance (Sartorius ME 5-F) with an accuracy of 0.01 mg. According to the regular standards of stationary source and sampling method released from Taiwan Environmental Protection Administration, the concentrations of the emissions in flue gas had to be calibrated by following equations because the water content in WEHFO might dilute the pollutant concentration.16 C¼

21
On Cs 21
Os

ð2Þ

Where, C represented the calibrated concentration; Ov was the reference oxygen level (6%) in stack; Os was the oxygen level in the flue gas; and Cs stood for the pollutant concentration collected by the regular method.

Table 1. Stabilities of Emulsified Heavy Fuel-oils after Centrifugal Tests with Various Temperaturesa separated layer, %

a

water fraction in emulsion, %

N = 10

N = 20

N = 30

25 C

0.00

0.11

2.13

80 C

0.00

0.58

5.76

120 C

0.00

0.89

8.47

N: percentages of water phase in volume.

Sampling and analysis of PAHs were conducted according to the NIEA A730.70C method promulgated by the Environmental Analysis Laboratory at the Environmental Protection Agency of Taiwan. This method quantifies both gaseous- and particulate-PAHs in the exhaust gas through a standard process, including flue gas collection, Soxhlet extraction, nitrogen purging concentration, cleanup, reconcentration, and gas chromatograph/mass spectrometer (GC/MS) quantification. The masses of primary and secondary PAH ions were determined by using the scan mode for pure PAH standards first. The PAHs were further quantified by using the selective ion monitoring (SIM) mode. The detection limit (DL) estimated by a serial diluted standard solution of 21 PAHs was 71
936 pg. The limit of quantification (LOQ) is defined as the DL divided by the sampling volume and was 0.118
1.56 ng m
3 for individual PAH compounds in the current study. Seven consecutive injections of a PAH standard yielded relative standard deviations (RSD) between 4.60 and 8.24% of the GC/MSD integration area. The R2 of calibration lines in the 21 PAH compounds ranged from 0.995 to 0.999. Additionally, the experimental results showed that the average recovery (n = 3) of individual PAHs by NIEA A730.70C was 83
112%. Analyses of field blanks, including glass-fiber filters and cartridges, indicated no significant PAH level (GC/MS integrated area less than DL). More experimental details can be obtained by referring to the NIEA method. According to the molecular weight, the 21 PAH homologues are divided into three categories: low molecular weights (LM-PAHs, containing two- and three-ring PAHs), middle molecular weights (MM-PAHs, containing four-ring PAHs), and high molecular weights (HM-PAHs, containing five-, six-, and seven-ring PAHs). The total-PAH level of the flue gas from the boiler is the summation of 21 individual PAHs. Additionally, the total equivalent toxicity of PAHs is defined as the total BaPeq, which is the summation of the products by multiplying the 21 individual PAHs toxic equivalency factors (TEFs) with their own emission concentrations.

3. RESULTS AND DISCUSSION 3.1. Fuel Stability. After the centrifugal test, the higher temperature induced significant separation (Table 1), because the increase in temperature effectively reduced the viscosity, and the water phase with higher density tends to separate from the emulsion. Table 1 also shows that the separate layer increased in volume with increasing SCW ratio. At 120 C, the separate layer increased significantly from 0 to 8.47 vol % with 10
30 vol % water phase. The emulsified fuel with 10 vol % water phase additive (M1P4-10) had almost no separate layer in all temperature conditions after centrifugation, which means 10 vol % water phase emulsion has the best stability among the three additive fractions. After a two-week (14-day) standing test, M1P4-30, which had the highest 30 vol % SCW addition, had the highest ratio in volume of separate layer, while M1P4-10 had no separate layer (Figure 2). Both M1P4-20 and M1P4-30 destabilized during the 1539

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Figure 2. Separate fractions of three emulsified fuels during the 14-day standing test.

first 10 days and then separated into two stable phases between the 11th and 14th days. The final separate fractions of M1P4-10, M1P4-20, and M1P4-30 are 0.00, 0.12, and 2.21 vol %, respectively. The relatively lower separate fraction of M1P4-10 indicated its better stability, which supported the results of the centrifugal tests. Therefore, M1P4-10 is the most stable and feasible fuel among these emulsions and should be further tested in industrial boilers. The W/O size distribution can distinguish the homogeneities of different fuels, and a smaller droplet diameter leads to a greater reaction surface per volume of fuel, thus promoting more complete combustion.17,18 Figure 3a
c shows the droplet appearances, sizes, and homogeneities of the three different SCW emulsified fuels under a 400 optical microscope. Obviously, M1P4-10 had the smallest and most homogeneous droplet distribution. For the statistical analysis, Figure 4a and b shows the probability density function (PDF) and cumulative density function (CDF) of the W/O droplet sizes. The PDF curves indicate that different SCW-containing ratios lead to different peak diameters, which were in the order of M1P4-10, M1P4-20, and M1P4-30, from low to high. In the CDF illustrations, the sharpest slope existed in the diameter range from 0.5 to 1 μm, meaning the droplet sizes were highly precise and fine. Additionally, the CMDs of M1P4-10, M1P4-20, and M1P4-30 were 0.674, 0.684, and 0.730 μm, while the CMdDs were 0.589, 0.601, and 0.633 μm, respectively. The above results show that less SCW in the emulsified fuel lead to the formation of smaller W/O droplets, which could also support the PDF trends. Sauter mean diameter (SMD) can be defined as the diameter of a drop having the same volume/surface area ratio as the entire spray. The SMD of M1P4-10, M1P4-20, and M1P4-30 were 0.624, 0.656, and 0.677 μm, which had the same trend to the CMD and CMdD. These three kinds of diameters were very close and could support the high homogeneity of each kind of emulsion. In comparison, the droplet size of M1P4-10 was significantly smaller than that with oily wastewater and water emulsified heavy fuel-oil, which were between 2 and 3 μm when using a pilot-scale mechanical homogenizer in Chen’s research.12 Nevertheless, the W/O droplet size of M1P4-10 is close to that of the lab-impeller-produced emulsified diesel fuel, which has been shown to have a high stability.19 Another disadvantage of high water content in emulsified fuel was highlighted by Tarlet et al., who indicated that the ME delay increased along with the water content and that a 30% water phase increases the ME delay by nearly 100 ms,

Figure 3. W/O droplets of M1P4-10 (a), M1P4-20 (b), and M1P4-30 (c) under 400 microscope.

which inhibits the propagation reaction in emulsified fuel combustion.20 Consequently, the good physical stability and small droplet size of M1P4-10 could directly prove the good stability of M1P4-10 and lower tendency of destabilization, respectively. 3.2. Viscosities and Energy Performances. The thermal efficiencies of the four boilers by using HFO and M1P4-10 were shown as the slopes of regression lines in Figure 6. The R2 of regression lines were all over 0.97 which indicated that the 1540

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Figure 5. Kinematic viscosities of fuels at various temperatures.

Figure 4. Probability density functions of various W/O droplet diameters (a) and cumulative density fractions of various W/O droplet diameters (b).

operation of boilers were smooth enough to get the reliable thermal efficiency data. The efficiencies are enhanced 10.4, 11.7, 32.9, and 10.8% by using M1P4-10. At the same time, the equivalent HFO consumption is reduced by 12.3, 6.2, 31.2, and 5.0% in the four boilers, respectively. These improvements are due to several changes in the properties of emulsified fuel. Kinematic viscosity is the most effective factor with regard to spray combustion. The viscosities of emulsified heavy fuel oils have been reported as having higher values than that of regulated heavy fuel oil.7 No exception, the viscosities of the emulsified fuels in this study increased with increasing SCW fractions, and significantly decreased with increasing temperature (Figure 5). Generally, a more viscous fuel results in higher surface tension and harder nebulization, which further produces coarse droplets, incomplete combustion, and reduction of energy efficiency.7 However, the performances of the four boilers showed significant improvements when using more viscous M1P4-10 emulsion. This conflicting result is based on the effects of microexplosions. Ikegami et al. indicated that fuel would splash less but have a higher tendency to microexplode if it was heavier and more viscous.21 In comparison to the emulsified diesel tested in engines, the injector of diesel engine is much more precisely designed which provide a relatively better atomization. According to the

research of Ikegami, the much more viscous HFO has a higher tendency to microexplode. Thus, the atomization improvement of HFO would more significant than that of emulsified diesel fuel and further enhanced the thermal efficiency. Additionally, the solvent contents with lower boiling points and activation energies are first ignited and produce radicals as tinder in the initial combustion. Furthermore, the oil drops extract the heat, react with the radicals from precombusted solvents, and are then ignited. Thus, the chain-propagation combustion reactions are provoked more rapidly than with a traditional heavy fuel oil. The lower stack temperatures after using M1P4-10 also lead to the decrease in heat loss with the flue gas. Notably, the HFO based efficiency of boiler C was relatively lower than that of the other three boilers because of the lower preheating temperature and higher viscosity of fuel in the daily tank. However, the performance of boiler C was improved by nearly 30% after using M1P410. This result again supports the better ME hypothesis of Ikegami and explains why a slightly more viscous emulsified heavy fuel oil-leads to better nebulization and higher thermal efficiency. The preheating temperature was optimized by tuning 5 C down per test and checking if the circulated fuel pipe stayed in continuous flow. The preheating temperature is suggested to be set at 60 C, and this adjustment can provide both a suitable viscosity for nebulization and inhibit early evaporation of the water phase, which would break the fuel supply. Another reason that also provides this great improvement might be the different cleaning period of each boiler. Boilers A and B worked after a temporary cleaning process which leads to higher boiler efficiency and lower PM and CO emissions using based fuel. In the opposite condition, boiler C had relatively more coke which could reduce the thermal conductivity. Therefore, the use of M1P4-10 not only leads to a better atomization, but also had the cleaning effect of a long-term operating boiler. Consequently, the M1P4-10 with a suitable preheating temperature promotes microexplosions and combustion, even if the initial fuel droplets are coarser near the nozzle than those of HFO. With regard to the social effects of using M1P4-10 as an alternative heavy fuel-oil, the estimation could be based on the annual HFO consumption. The water to fuel volume ratio (W/ F) is a commonly used parameter to estimate the boiler efficiency in practical boiler operations. In the current study, M1P4-10 could reduce the “water to equivalent HFO ratio” (W/HFO) by 1541

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Figure 6. Thermal efficiencies (slope of regression line) of boilers A (a), B (b), C (c), and D (d) using HFO and M1P4-10.

11.2
16.5% in a 3.6 t steam h
1 boiler, as well as reduce W/ HFO by 6.1% in a 10 t steam h
1 boiler. According to the 15 MkL annual consumption of HFO in Taiwan, the 6.1
16.5% reduction in W/HFO can save 915
2475  103 kL HFO annually. Estimated using US$525 kL
1 HFO,22 the improvement in boiler efficiency might save US$48
129 million per year in Taiwan. In addition, the equivalent fuel consumption is directly related to the CO2 emissions, and the annual emissions in Taiwan could fall by 2726
7376 t, based on the CO2 emission factor of HFO (2.98 t kL
1 HFO). For the wastewater pretreatment point of view, the emulsification system is suggested to be setup in the factory that produces wastewater. The distillation tower might be originally installed and operated for solvent recovery in a chemical factory. Therefore, the overall extra energy consumption and cost are the electricity demand and capital cost of a homogenizer and a hydraulic pump in the emulsification system. 3.3. SO2 and PM Emissions. High sulfur content (∼5000 ppm) is one of the air pollution-inducing properties of HFO. By using M1P4-10, the SO2 concentration was reduced by 5.6, 7.9, 7.1, and 6.2% in four boiler flue gases (Table 3). These results can be simply described by the 10% reductions in sulfur content due to the 10% heavy oil altered by the water phase in emulsified fuel. Many researchers have focused on the emission of particulate matter, because of its harmful effects on the human respiratory system. This is also a major problem with boiler emissions due to incomplete combustion. The three main mechanisms of PM formation are the nucleation mode (10
100 nm), accumulation/condensation mode (0.1
1 μm), and coarsening mode (1
10 μm), with the condensation acting as the major path to increase the particle mass in combustion.23,24 In the four-boiler

test, the PM emissions were reduced by 55, 79, 85, and 41% by using M1P4-10 (Table 3). The above results indicate that microexplosions (ME) significantly improve the droplet nebulization. Thus, the emulsified fuel could react more completely with the oxidants and further decrease the nucleation process of soot. In addition, the presence of sulfur in fuel leads to the formation of sulfuric acid (H2SO4) in the stack flue gases at a lower temperature than that in the combustor. The lower temperature further promotes the condensation of sulfuric acid on the soot and metallic ash to increase the mass of PM in flue gases.25,26 Thus, the 10% lower sulfur content in M1P4-10 and the ME could reduce the level of PM emissions by inhibiting the condensation and nucleation pathways, respectively.27 From the same reason, 10% water alternative directly reduced the sediment and inert ashes in a regular HFO (