Exhaust Gas Emission Improvements of Water/Bunker C Oil-Emulsified Fuel Applied to Marine Boiler

Journal of Marine Science and Engineering

Article Exhaust Gas Emission Improvements of Water/Bunker C Oil-Emulsiﬁed Fuel Applied to Marine Boiler

Tae-Ho Lee 1, Sang-Hyun Lee 2 and Jee-Keun Lee 3,*

1 Department of Power Plant, Korea Polytechnic College, Muan 58542, Korea; [email protected] 2 Greentech Co., Ltd., Jeongeup 56137, Korea; [email protected] 3 Department of Mechanical System Engineering, Jeonbuk National University, Jeonju 54896, Korea * Correspondence: [email protected]; Tel.: +82-63-270-2369

Abstract: In this study, emulsiﬁed fuels were prepared and produced by blending 0%, 5%, 15%, and 25% water with Bunker C oil to reduce the amount of air pollution emitted by ships and replace oil resources, and they were applied to an actual marine boiler to analyze the exhaust gas. The fuel

effects on the improvement in exhaust gas emissions were as follows: The oxygen (O2) concentration increased by up to 4.2%, and that of carbon dioxide decreased by approximately 2.1%. Under the

standard O2 concentration of 4%, the concentration of nitrogen oxides decreased by up to 31.41%, and that of sulfur oxides decreased by up to 37.47%. However, the exhaust gas temperature decreased by approximately 14.3%, and the combustion efficiency decreased by approximately 2.6%. Comparing the emission improvements, the combustion performance of the emulsified fuels was close to that of the conventional Bunker C fuel. These results indicate that the application of water-emulsified fuels to a marine boiler can reduce the amounts of certain air pollutants. Keywords: emulsified oil; marine boiler; Bunker C; exhaust emissions; International Maritime

Citation: Lee, T.-H.; Lee, S.-H.; Lee, Organization; nitric oxide; sulfur oxide; carbon dioxide J.-K. Exhaust Gas Emission Improvements of Water/Bunker C Oil-Emulsiﬁed Fuel Applied to Marine Boiler. J. Mar. Sci. Eng. 2021, 9, 1. Introduction 477. https://doi.org/10.3390/ Fossil fuels represent 80% of the global energy supply; however, discoverable oil jmse9050477 resources are expected to decrease. According to one report, global oil production is expected to reach its peak in 2020 and then rapidly decrease [1]. Figure1 displays the Academic Editor: Tie Li global oil production forecast based on the current scenario [2]. In addition, approximately 65% of global oil reserves are being produced in Middle Eastern countries [3], and this is Received: 22 March 2021 expected to accelerate the supply–demand imbalance of nonproducing countries, as they Accepted: 26 April 2021 Published: 29 April 2021 are highly dependent on oil imports. The consumption of alternative energy sources is expected to slowly increase due to

Publisher’s Note: MDPI stays neutral the depletion of oil resources. In addition to shortages of coal and oil resources, this is with regard to jurisdictional claims in because of serious environmental pollution caused by the exhaust gas from fossil energy published maps and institutional affil- use and the enforcement of strict emission regulations by various countries. iations. Exhaust gas emitted by ships in particular exhibits severe pollution levels. According to a report from the International Maritime Organization (IMO), nitrogen oxides (NOx), sulfur oxides (SOx), and carbon dioxide (CO2) emissions from ships account for 14%, 5%, and 2% of global emissions from transportation, respectively [4]. Therefore, the IMO requires the use of fuels with low sulfur contents or engines that Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. meet the allowed NOx emission threshold specified by the IMO to regulate ship exhaust This article is an open access article gas emissions [5]. distributed under the terms and To satisfy these emission regulations, after installing separate exhaust gas reduction conditions of the Creative Commons devices in existing combustion systems, the fuel is pretreated by applying alternative Attribution (CC BY) license (https:// energy sources. Regarding representative post-treatment systems, exhaust gas recirculation, creativecommons.org/licenses/by/ selective catalytic reduction, and diesel particulate filter methods are the most widely 4.0/). utilized exhaust gas reduction approaches [6].

J. Mar. Sci. Eng. 2021, 9, 477. https://doi.org/10.3390/jmse9050477 https://www.mdpi.com/journal/jmse J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW 2 of 11

J. Mar. Sci. Eng. 2021, 9, 477 2 of 11

selective catalytic reduction, and diesel particulate filter methods are the most widely utilized exhaust gas reduction approaches [6]. DespiteDespite the the continuous continuous efforts efforts required required for the for retrofitting the retrofitting of flue-gas of flue treatment-gas treatment plants, researchplants, research is trying is totrying offer to increasingly offer increasingly efficient efficient solutions solutions that are that adaptable are adaptable to stringent to strin- IMOgent requestsIMO requests and at and the a samet the timesame less time and less less and impactful less impactful from thefrom point the ofpoint view of of view costs of andcosts space and space required required for shipboard for shipboard installations installations [7–9]. [7–9].

FigureFigure 1.1.World World oil oil production production forecast forecast based based on on present present demand demand scenario. scenario.

However,However, installing installing these these systems systems does does notnot addressaddress thethe problemproblem ofof fuelfuel consumption,consumption, andand itit isis difficultdifficult forfor thethe systemssystems toto improveimprove thethe maintenancemaintenance costcost problemproblem becausebecause thethe mechanicalmechanical systemsystem structurestructure mustmust bebe modified,modified, and and regular regular maintenance maintenance is is required required [ 3[3].]. VariousVarious studies studies have have beenbeen conductedconducted toto improveimprove thesethese mechanical mechanical technologies technologies and and developdevelop alternativealternative energy energy sources sources that that do do not not require require separate separate reduction reduction systems. systems. Repre- Rep- sentativeresentative research research fields fields include include the the biodiesel biodiesel field, field, in in which which bioresources bioresources are are applied applied to to dieseldiesel oil;oil;the the dimethyldimethylether etherfield; field; and and the the emulsion emulsion field, field, which which blends blends materials materials [ 10[10].]. TheseThese alternativealternative energyenergy sourcessources advantageouslyadvantageously produce produce outputs outputs similar similar to to those those of of conventionalconventional fuels fuels while while also also reducing reducing air air pollution, pollution, and and they they do do not not modify modify the the mechanical mechan- systemical system structure. structure. Various Various studies studies have h beenave been conducted conducted on emulsifiedon emulsified fuels, fuels, primarily primarily in advancedin advanced countries, countries, because because exhaust exhaust gashas gas been has improved been improved by physically by physically blinding blinding water andwater fuel and [11 fuel]. [11]. KimKim etet al.al. foundfound thatthat anan emulsifiedemulsified fuelfuel createdcreated byby blendingblending waterwater withwith dieseldiesel oiloil reducedreduced thethe NOx anandd soot soot in in a a2456 2456-cc-cc diesel diesel engine engine [12]. [12 Lim]. Lim et al. et researched al. researched the com- the combustionbustion characteristics characteristics of emulsified of emulsified fuels fuels in a ship in a shipdiesel diesel engine engine and reduced and reduced NOx NOemis-x emissionssions by approximately by approximately 30%, 30%, depending depending on on the the water water content content [13,14]. [13,14]. In In these studies,studies, fuelsfuels createdcreated byby blendingblending waterwater andand dieseldiesel oiloil werewere appliedapplied toto dieseldiesel engines,engines, andand otherother studiesstudies havehave beenbeen conductedconducted underunder similarsimilar conditions conditions [ 15[15,16].,16]. ParkPark etet al.al. simultaneouslysimultaneously injectedinjected waterwater andand dieseldiesel oiloil intointo aa hybridhybrid boilerboiler burnerburner toto compensate for water and diesel oil separation, demonstrating that NOx emissions can be compensate for water and diesel oil separation, demonstrating that NOx emissions can be reducedreduced byby upup toto 45.5%45.5% [[17].17]. SimilarSimilar toto ourour study,study, ChungChung appliedapplied aa mixturemixture ofof BunkerBunker CC oil, low-quality fuel, and livestock wastewater to a boiler and reported that the exhaust oil, low-quality fuel, and livestock wastewater to a boiler and reported that the exhaust gas temperature was reduced by approximately 100 ◦C, and certain air pollutants were gas temperature was reduced by approximately 100 °C, and certain air pollutants were reduced [18]. reduced [18]. In previous studies conducted by the authors of this study, emulsified fuel created In previous studies conducted by the authors of this study, emulsified fuel created by blending approximately 10.6% water with Bunker C oil was applied to a gun-type by blending approximately 10.6% water with Bunker C oil was applied to a gun-type in- industrial boiler burner, and NOx and SOx emissions were reduced by approximately dustrial boiler burner, and NOx and SOx emissions were reduced by approximately 30% 30% [19,20]. Therefore, in this study, emulsified fuels created by blending water with [19,20]. Therefore, in this study, emulsified fuels created by blending water with Bunker Bunker C oil were applied to an actual marine boiler to analyze their effects on NOx, SOx, C oil were applied to an actual marine boiler to analyze their effects on NOx, SOx, and CO2 and CO emissions, which are typical exhaust gas emissions. emissions,2 which are typical exhaust gas emissions. 2. Materials and Methods The emulsified fuels used in this study were produced using dedicated plant equipment capable of instantaneous automatic production, and the production process occurred in seven steps. Figure2 displays the plant equipment, and Figure3 illustrates the seven steps of the production process [21].

J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW 3 of 11 J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW 3 of 11

2. Materials and Methods 2. Materials and Methods The emulsified fuels used in this study were produced using dedicated plant equip- The emulsified fuels used in this study were produced using dedicated plant equipment capable of instantaneous automatic production, and the production process oc- J. Mar. Sci. Eng. 2021, 9, 477 ment capable of instantaneous automatic production, and the production process3 of oc- 11 curred in seven steps. Figure 2 displays the plant equipment, and Figure 3 illustrates the curred in seven steps. Figure 2 displays the plant equipment, and Figure 3 illustrates the seven steps of the production process [21]. seven steps of the production process [21].

Figure 2. Photograph of emulsification equipment [21]. FigureFigure 2.2. PhotographPhotograph ofof emulsiﬁcationemulsification equipmentequipment [[21].21].

Figure 3. Seven-step production process. FigureFigure 3.3. Seven-stepSeven-step productionproduction process.process. Each storage tank was installed before the supply pipe of the plant equipment. Water, EachEach storagestorage tanktank waswas installedinstalled beforebefore thethe supplysupply pipepipe ofof the plant equipment. Water, Bunker C oil, and a small amount of emulsifier (less than 1%) were secured, and each fluid BunkerBunker CC oil,oil, andand aa smallsmall amountamount ofof emulsifieremulsifier (less(less thanthan 1%)1%) werewere secured,secured, andand eacheach fluidfluid was subjected to filtration as the first step. After the second step pretreatment process waswas subjectedsubjected toto filtrationfiltration asas thethe firstfirst step.step. AfterAfter thethe secondsecond stepstep pretreatmentpretreatment processprocess where water and emulsifier were blended, an emulsified aqueous solution was prepared wherewhere waterwater andand emulsifieremulsifier werewereblended, blended, anan emulsifiedemulsified aqueousaqueous solutionsolution waswas preparedprepared in the third step. The mixing ratio with Bunker C oil was then set via the fourth step mag- inin thethe third step. step. The The mixing mixing ratio ratio with with Bunker Bunker C oil C oilwas was then then set via set the via fourth the fourth step mag- step nification mixing process in which the producer set the water content of the emulsified magnificationnification mixing mixing process process in inwhich which the the producer producer set set the the water water content content of the emulsifiedemulsified aqueous solution between 0% and 25%. In the fifth step, the oil and water were preheated aqueousaqueous solutionsolution betweenbetween 0%0% andand 25%.25%. InIn thethe fifthfifth step,step, thethe oiloil andand waterwater werewere preheatedpreheated to approximately 60 °C, which is appropriate for mixing, to improve the mixing quality, toto approximatelyapproximately 6060 ◦°C,C, whichwhich isis appropriateappropriate forfor mixing,mixing, toto improveimprove thethe mixingmixing quality,quality, and homogenization and flash mixing were performed using ultra-high-speed rotation andand homogenizationhomogenization andand flashflash mixingmixing werewere performedperformed usingusing ultra-high-speedultra-high-speed rotationrotation between 10,000 rpm and 30,000 rpm. Afterward, the emulsion was stabilized using vacuum compression dispersion. Finally, in the seventh step ultrasonic process, various sludge lumps present in the Bunker C oil, which is a low-quality fuel, were finely crushed to improve the oil quality. In this study, four water contents were used for production. The set water contents were 0%, 5%, 15%, and 25%, and the names of the fuels were set to EM0, EM5, EM15, and EM25, respectively. Figure4 compares water-emulsified fuel samples produced using J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW 4 of 11

between 10,000 rpm and 30,000 rpm. Afterward, the emulsion was stabilized using vacuum compression dispersion. Finally, in the seventh step ultrasonic process, various sludge lumps present in the Bunker C oil, which is a low-quality fuel, were finely crushed J. Mar. Sci. Eng. 2021, 9, 477 to improve the oil quality. 4 of 11 In this study, four water contents were used for production. The set water contents were 0%, 5%, 15%, and 25%, and the names of the fuels were set to EM0, EM5, EM15, and EM25, respectively. Figure 4 compares water-emulsified fuel samples produced using variousvarious fuelfuel typestypes (marine(marine dieseldiesel oil,oil, marinemarine gasgas oil,oil, andand dieseldiesel oil).oil). TheThe otherother emulsiﬁedemulsified fuelfuel typestypes were were a a lighter lighter brown brown than than the the pure pure Bunker Bunker C oil C withoil with a water a water content content of 0%, of and0%, thereand there was nowas signiﬁcant no significant difference difference in color in betweencolor between the Bunker the Bunker C oils withC oils different with different water contentswater contents based onbased visual on inspection.visual inspection.

FigureFigure 4.4. ComparisonComparison ofof water-emulsiﬁedwater-emulsified oiloil samples.samples.

ToTo investigateinvestigate thethe componentcomponent characteristicscharacteristics ofof thethe producedproduced emulsiﬁedemulsified fuels,fuels, thethe fuelsfuels werewere analyzedanalyzed followingfollowing thethe InternationalInternational OrganizationOrganization forfor StandardizationStandardization (ISO)(ISO) 8217,8217, aa standardstandard test test method method for for ship ship fuel fuel oil. oil. Table Table1 lists 1 lists the the analysis analysis items items and and details details of theof the standard standard test test [3]. [3].

TableTable 1. 1.ISO ISO 8217 8217 fuel fuel component component analysis analysis methods. methods.

ListList Method UnitUnit WaterWater contentcontent KS KS M ISOISO 3733:20083733:2008 Vol,Vol, % % Sulfur contentcontent KS KS M ISOISO 2414:20112414:2011 m/m,m/m, %% ◦ Flash pointpoint KS KS M ISOISO 2592:20072592:2007 °CC Gravity API @ 60 ◦F KS M ISO 12185:2003 - GravityS.G @ API 15/4 @◦C- 60°F KS M ISO 12185:2003 - S.G @ 15/4 °C - The produced emulsified fuels were applied to the marine boiler VWH-600 [22], a deviceThe approved produced by theemulsified Korean fuels Register, were an applied approval to agencythe marine in South boiler Korea VWH [23-600]. [22], a deviceFigure approved5 displays by the the Korean boiler usedRegister, in the an actual approval experiment, agency in and South its detailedKorea [23 specifica-]. tionsFigure are listed 5 displays in Table the2. The boiler operation used in ofthe the actual boiler experiment, was applied and by its changing detailed onlyspecifica- the fueltions composition are listed in under Table the 2. The same operation conditions of asthe the boiler Bunker was C applied fuel. by changing only the fuel composition under the same conditions as the Bunker C fuel. Table 2. Marine boiler specifications.

List Speciﬁcation Unit Model VWH-600 - Evaporation 600 kg/h Caloriﬁc Value 323,300 kcal/h Fuel consumption Max. 39.0 kg/h Steam pressure Max. 10.0 kg/cm2 Burner Pressure atomizing type - Electrical capacity Max. 6.8 kw Weight (dry) 2140 kg

J. Mar. Sci. Eng. 2021, 9, 477 5 of 11 J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW 5 of 11

FigureFigure 5.5. PhotographPhotograph ofof marinemarine boilerboiler assembly.assembly.

TableTESTO-340 2. Marine boiler was specifications. selected as the gas analyzer for the exhaust gas measurements [24]. The measurement items were the oxygen (O ) content, CO , NO , SO , and exhaust gas List Specification2 2 x x Unit temperature (◦C). The detailed specifications are listed in Table3. Model VWH-600 - NOx and SOx emissions were continuously measured for 5 min per the Korea National InstituteEvaporation of Environmental Research (NIER)600 air pollution process test standardskg/h [25] to obtain theirCalorific average Value values, and this procedure323,300 was repeated three timeskcal/h to determine the total averageFuel consumption values. For SOx, however,Max. only 39.0 sulfur dioxide (SO2) waskg/h measured based on the testSteam standard, pressure and the measurementMax. method 10.0 is presented in Tablekg/cm4. When2 the fuel was changed,Burner measurements werePressure performed atomizing after approximately type 1 h to ensure- sufficient replacementElectrical of thecapacity residual fuel and stabilizationMax. 6.8 of combustion. kw Weight (dry) 2140 kg Table 3. Gas analyzer specification [20]. TESTO-340 was selected as the gas analyzer for the exhaust gas measurements [24]. Parameter Range Unit Resolution The measurement items were the oxygen (O2) content, CO2, NOx, SOx, and exhaust gas temperatureO2 (°C ). The detailed0–25.0 specifications are listed Vol, in % Table 3. 0.01 CO2 0–15.8 Vol, % 0.1 NOx and SOx emissions were continuously measured for 5 min per the Korea Na- NOx 0–4000 ppm 1 tional InstituteSO2 of Environmental0–5000 Research (NIER) air ppmpollution process test standards 1 [25] to obtainTemperature their average values,−40–1200 and this procedure was◦ Crepeated three times 0.1to determine the total average values. For SOx, however, only sulfur dioxide (SO2) was measured based on the test standard, and the measurement method is presented in Table 4. When the fuel Tablewas changed, 4. NIER air measurements pollution process were test performed method [24 ].after approximately 1 h to ensure sufficient replacementParameter of the residual fuel Range and stabilization Unit of combustion. Method

NOx 0–1000 ppm Average value of three SOx 0–1000 ppm consecutive measurements (only SO2) every 5 min.

J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW 6 of 11

Table 3. Gas analyzer specification [20].

Parameter Range Unit Resolution O2 0–25.0 Vol, % 0.01 CO2 0–15.8 Vol, % 0.1 NOx 0–4000 ppm 1 SO2 0–5000 ppm 1 Temperature −40–1200 °C 0.1

Table 4. NIER air pollution process test method [24].

Parameter Range Unit Method NOx 0–1000 ppm Average value of three consecutive measure- J. Mar. Sci. Eng. 2021, 9, 477 6 of 11 SOx 0–1000 ppm ments every 5 min. (only SO2)

FigureFigure6 6 displays displays a a schematic schematic of of the the experiment experiment used used in in this this study. study. The The experimental experimental setupsetup consistedconsisted ofof twotwo separateseparate fuelfuel tanks,tanks, andand thethe replacementreplacement ofof thethe emulsiﬁedemulsified fuelfuel andand BunkerBunker CC oiloil cancan bebe freelyfreely changedchanged usingusing aa three-waythree-way valve.valve. TheyThey werewere suppliedsupplied toto thethe boilerboiler after preheating through through an an electricity electricity-powered-powered coil coil heater. heater. In Inaddition, addition, because because the theboiler boiler operation operation was wasautomatically automatically stopped stopped when when the boiler the boiler feed water feed water reached reached the evap- the evaporationoration pressure, pressure, the theopen open-loop-loop method method was was used used instead instead of of the the closed closed-loop-loop circulationcirculation methodmethod toto ensure ensure the the continuous continuous supply supply and and discharge discharge of feedof feed water, water, considering considering the naturethe na- ofture the of experiment, the experiment which, which requires requires long-term long- operation.term operation.

FigureFigure 6.6. SchematicSchematic ofof experimentalexperimental apparatus.apparatus.

3.3. ResultsResults andand DiscussionDiscussion 3.1.3.1. ComponentComponent CharacteristicsCharacteristics ofof EmulsifiedEmulsified FuelsFuels FigureFigure7 7illustrates illustrates the the component component characteristics characteristics of theof the water/Bunker water/Bunker C oil-emulsified C oil-emulsi- fuelsfied fuels produced produced for the for experiment the experiment in this in study. this study. The water contents were 25.0% for EM25, 15.0% for EM15, 5.0% for EM5, and ap- The water contents were 25.0% for EM25, 15.0% for EM15, 5.0% for EM5, and approx- proximately 0.6% for EM0, respectively. The sulfur content of the Bunker C oil selected imately 0.6% for EM0, respectively. The sulfur content of the Bunker C oil selected for the for the experiment was less than 0.3%, indicating that the oil was a low-sulfur fuel. The experiment was less than 0.3%, indicating that the oil was a low-sulfur fuel. The compo- component analysis results demonstrated that the sulfur content decreased from 0.28% to nent analysis results demonstrated that the sulfur content decreased from 0.28% to 0.20% 0.20% as the water content increased. This percentage reduction is due to the dilution by water per unit volume. The specific weight ranged from 0.9471 to 0.9382, and this can be considered the difference in the specific gravity of water due to the increase in water content. The flash point ranged from 172 ◦C to 101 ◦C. This result satisfies the minimum condition of 60 ◦C or higher for Bunker C oil; however, it is impossible to measure the flash point due to the boiling phenomenon in which the water contained in the fuel reaches 100 ◦C. Analytical laboratories typically suggested that the conditions were satisfied, and they predicted that the actual flash point exceeded 172 ◦C, which is that of EM0. J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW 7 of 11

as the water content increased. This percentage reduction is due to the dilution by water per unit volume. The specific weight ranged from 0.9471 to 0.9382, and this can be considered the difference in the specific gravity of water due to the increase in water content. The flash point ranged from 172 °C to 101 °C . This result satisfies the minimum condition of 60 °C or higher for Bunker C oil; however, it is impossible to measure the flash point due to the boiling phenomenon in which the water contained in the fuel reaches 100 °C . Analytical J. Mar. Sci. Eng. 2021, 9, 477 7 of 11 laboratories typically suggested that the conditions were satisfied, and they predicted that the actual flash point exceeded 172 °C, which is that of EM0.

(a)

(b)

(c)

FigureFigure 7. 7. FuelFuel composition composition comparison comparison of of emulsified emulsiﬁed oils: oils: (a (a) )water water content, content, ( (bb)) sulfur sulfur content content,, and and ((cc)) specific speciﬁc gravity. gravity.

3.2.3.2. Exhaust Exhaust G Gasas E Emissionmission C Characteristicsharacteristics FigureFigure 8 displays the characteristics of thethe exhaustexhaust gasgas emissionsemissions measuredmeasured during thethe combustion combustion process. process. The The O O2 2contcontentent was was 6.20% 6.20% for for EM0, EM0, which which is is the the pure pure Bunker Bunker C C oil, 7.51% for EM5, 8.82% for EM15, and 10.40% for EM25, increasing O2 content by up to 4.20%. This result appears to be due to the O2 dissolved in the water that was contained in the emulsiﬁed fuels and the unburned content of the air supplied to the boiler. The CO2 content (%) was 11.1% for EM0, 10.2% for EM5, 9.2% for EM15, and 8.0% for EM25, demonstrating a reduction in the CO2 content by up to 2.1% within the scope of this study. The NOx concentrations were 129.7 ppm for EM0 and 63.7 ppm for EM25, exhibiting a reduction of up to 50.9%. This appears to be because the NOx concentration increases in high-temperature areas of exhaust gas, and it was therefore affected by the reduction in the exhaust gas temperature caused by the latent evaporation heat of the water contained in the emulsion. J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW 8 of 11

oil, 7.51% for EM5, 8.82% for EM15, and 10.40% for EM25, increasing O2 content by up to 4.20%. This result appears to be due to the O2 dissolved in the water that was contained in the emulsified fuels and the unburned content of the air supplied to the boiler. The CO2 content (%) was 11.1% for EM0, 10.2% for EM5, 9.2% for EM15, and 8.0% for EM25, demonstrating a reduction in the CO2 content by up to 2.1% within the scope of this study. The NOx concentrations were 129.7 ppm for EM0 and 63.7 ppm for EM25, exhibiting a reduction of up to 50.9%. This appears to be because the NOx concentration increases in J. Mar. Sci. Eng. 2021, 9, 477 high-temperature areas of exhaust gas, and it was therefore affected by8 the of 11 reduction in the exhaust gas temperature caused by the latent evaporation heat of the water contained in the emulsion.

(a) (b)

Figure 8. Exhaust gas emissions comparison of emulsified oil: (a) O2, (b) CO2, (c) NOx, and (d) SO2. Figure 8. Exhaust gas emissions comparison of emulsiﬁed oil: (a)O2,(b) CO2,(c) NOx, and (d) SO2.

The SOx concentrationThe SO signiﬁcantlyx concentration decreased significantly by approximately decreased by 62.7% approximately from 113.2 62.7% ppm from 113.2 for EM0 to 50.5ppm ppm for for EM0 EM25. to 50.5 This ppm is because for EM25. the This sulfur is because content the per sulfur unit volumecontent per of theunit volume of fuel was reducedthe by fuel an was increased reduced water by an content increased [19]. water As the contentNOx and[19].SO Asx theconcentrations NOx and SOx concentrations were the actual measured values, and the O2 concentration varied, their reduction were the actual measured values, and the O2 concentration varied, their reduction effects effects were calculated by applying a 4% O2 concentration correction factor, which is the were calculated by applying a 4% O2 concentration correction factor, which is the standard standard O2 concentration. This is because the generated exhaust gas was diluted using O2 concentration. This is because the generated exhaust gas was diluted using different amounts of supplydifferent air, depending amounts of on supply the fuel. air, depending on the fuel. 푂2푟푒푓−푂2푠 푁푂푥[푝푝푚, 4%] = 푁푂푥푎 × (1) O2re f − O2s 푂2푟푒푓−푂2푎 NOx[ppm, 4%] = NOxa × (1) O2re f − O2a 푂2푟푒푓−푂2푠 푆푂푥[푝푝푚, 4%] = 푆푂푥푎 × (2) 푂2푟푒푓−푂2푎 O2re f − O2s Therefore,SO [theppm standard, 4%] = SOO2 concentration× of 4% can be applied to Equations(2) (1) and x xa − (2). Here, NOxa and SOxa are the measuredO2re f NOOx2 anda SOx data, respectively. O2ref is the O2

Therefore, the standard O2 concentration of 4% can be applied to Equations (1) and (2). Here, NOxa and SOxa are the measured NOx and SOx data, respectively. O2ref is the O2 concentration of 21% in the atmosphere, O2s is the standard O2 concentration of 4%, and O2a is the actual measured O2 concentration. Figure9 displays the NOx and SOx results obtained by applying the standard O2 concentration. The NOx concentration decreased by up to 31.41% from 148.93 ppm for EM0 to 102.15 ppm for EM25, and the SOx concentration decreased by up to 37.47% from 130.0 ppm for EM0 to 81.3 ppm for EM25. J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW 9 of 11

J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW 9 of 11

concentration of 21% in the atmosphere, O2s is the standard O2 concentration of 4%, and O2a is the actual measured O2 concentration. concentration of 21% in the atmosphere, O2s is the standard O2 concentration of 4%, and Figure 9 displays the NOx and SOx results obtained by applying the standard O2 con- O2a is the actual measured O2 concentration. centration. The NOx concentration decreased by up to 31.41% from 148.93 ppm for EM0 J. Mar. Sci. Eng. 2021, 9, 477 Figure 9 displays the NOx and SOx results obtained by applying the standard O92 ofcon- 11 to 102.15 ppm for EM25, and the SOx concentration decreased by up to 37.47% from 130.0 centration. The NOx concentration decreased by up to 31.41% from 148.93 ppm for EM0 ppmto 102.15 for EM0 ppm to for81.3 E M25,ppm andfor EM25.the SO x concentration decreased by up to 37.47% from 130.0 ppm for EM0 to 81.3 ppm for EM25.

(a) (b) (a) (b) FigureFigure 9. 9.EmissionEmission comparison comparison of of emulsified emulsiﬁed oils when standardstandard O O24% 4% was was applied: applied: (a ()a NO) NOandx and (b ()b SO) SO. 2. Figure 9. Emission comparison of emulsified oils when standard O2 2 4% was applied: (a) NOxx and (b) SO22.

3.3.3.3.3.3. Exhaust ExhaustExhaust Gas GasGas Temperature TemperatureTemperature Characteristics Characteristics TheTheThe exhaust exhaustexhaust gas gasgas temperature temperaturetemperature decreased decreased asas thethe water waterwater content contentcontent increasedincreased increased inin in thethe the emulsi-emulsi- emulsi- fiedﬁedfied fuels. fuels.fuels. Fig FigureFigureure 10 1010 shows shows shows the thethe exhaustexhaust gasgasgas temperaturetemperature results. results.results. TheThe The exhaustexhaust exhaust temperaturetemperature temperature showedshowedshowed a aatendency tendencytendency to toto decrease decreasedecrease byby upupup tototo approximately approximately 14.3% 14.3%14.3% withinwithin within thethe theexperimental experimental experimental ◦ rangerangerange of ofof this thisthis study study,study, ,as asas it itit was waswas foundfound tototo bebebe 319.9 319.9319.9 °CC for forfor EM0, EM0,EM0, whichwhich which isis is purepure pure BunkerB unkerBunker CC oilCoil oil ◦ withoutwithoutwithout water, water,water, and andand 274.1 274.1274.1 °C °CC for for EM25.EM25. ThisThis appearsappears tototo be bebe due duedue toto to thethe the temperaturetemperature temperature reduc-reduc- reduc- tiontiontion caused causedcaused by byby the thethe latent latentlatent heat heatheat of of evaporationevaporation ofof thethethe water waterwater contained containedcontained inin in thethe the fuelfuel fuel andand and thethe the temperaturetemperaturetemperature reduction reductionreduction caused causedcaused by by thethe increase increaseincrease in in the the amount amountamount of of of excess excess excess air. air. air.

FigureFigure 10.10. ExhaustExhaust gasgas temperaturetemperature comparisoncomparison ofof emulsifiedemulsified oils.oils. Figure 10. Exhaust gas temperature comparison of emulsified oils. 3.4.3.4. CombustionCombustion EfficiencyEfficiency 3.4. CombustionTheThe combustioncombustion Efficiency efficiencyefficiency waswas calculatedcalculated byby applyingapplying thethe experimentalexperimental resultsresults ofof exhaustexhaustThe gascombustion gas emissions. emissions. efficiency The The formula formula was used calculatedused to calculateto calculate by theapplying combustionthe combustion the experimental efficiency efficiency is displayed results is dis- of exhaustinplayed Equation gasin Equation emissions. (3). qA is (3). the The qA combustion isformula the combustion used efficiency to efficiencycalculate (%), and (%),thef is thecombustionand specific f is the fuelspecific efficiency constant fuel isco for n-dis- heavy oils, such as Bunker C fuel. T is the exhaust gas temperature, and T is the playedstant forin Equationheavy oils (3)., such qA asis Bunthe kercombustion Cgas fuel. Tgas efficiency is the exhaust (%), andgas temperaturef is the specific, andamb fuel Tamb co is n- supply air temperature. These two temperature differences were divided by CO2 to obtain stant for heavy oils, such as Bunker C fuel. Tgas is the exhaust gas temperature, and Tamb is the combustion efficiency. f × Tgas − Tamb qA[%] = 100 × , (3) CO2 J. Mar. Sci. Eng. 2021, 9, x FOR PEER REVIEW 10 of 11

the supply air temperature. These two temperature differences were divided by CO2 to J. Mar. Sci. Eng. 2021, 9, 477 obtain the combustion efficiency. 10 of 11

푓×(푇푔푎푠−푇푎푚푏) 푞퐴[%] = 100 × , (3) 퐶푂2 TheThe combustioncombustion efficiencyefficiencydecreased decreased as as thethe waterwater contentcontent increasedincreased inin thethe emulsifiedemulsified fuels.fuels. Fig Figureure 1111 presentspresents the the combustion combustion efficiency efficiency results. results. The The combustion combustion efficiency efficiency ex- exhibitedhibited a decreasing a decreasing tendency tendency by up by to up approximately to approximately 2.6% 2.6% within within the experimental the experimental range rangeof this of study this; study; it was it85.84% was 85.84% for EM0, for which EM0, whichis pure is Bunker pure Bunker C oil without C oil without water, and water, 83.24% and 83.24%for EM25. for EM25.

FigureFigure 11.11. CombustionCombustion efﬁciencyefficiency comparisoncomparison ofof emulsiﬁedemulsified oils.oils.

4.4. ConclusionsConclusions InIn thisthis study, study, the the emulsiﬁed emulsified fuels fuels produced produced by blendingby blending water water with with Bunker Bunker C oil wereC oil appliedwere applied to a marine to a marine boiler, boiler, and their and effectstheir effects on exhaust on exhaust gas emissions gas emissions were were analyzed. analyzed. The followingThe following conclusions conclusions can be can drawn: be drawn:

(1)(1) The O 2 concentrationconcentration was was 6. 6.2%2% for for EM0 EM0 and and 10.4% 10.4% for for EM25, EM25, demonstrating demonstrating an anin- increasecrease of of 4.2%. 4.2%. (2)(2) The CO2 concentration decreased by 2.1% 2.1%;; it was 11.1% for EM0 and 8.0% for EM25. (3)(3) The actual measuredmeasured NONOxx concentration decreased byby upup toto 50.9%,50.9%, andand itit decreaseddecreased by up to 31.41% when a standard OO22 concentration of 4% was applied. (4)(4) The SOx concentration decreased by up to 62.7%, and itit decreaseddecreased byby upup toto 37.47%37.47% when a standard O concentration of 4% was applied. when a standard O22 concentration of 4% was applied. (5)(5) The exhaustexhaust gasgas temperaturetemperature exhibited exhibited a a decreasing decreasing tendency tendency by by approximately approximately 14.3% 14.3% whenwhen the waterwater contentcontent waswas 25%,25%, whichwhich waswas thethe maximummaximum conditioncondition ofof thisthis study.study. (6)(6) The combustioncombustion efficiencyefficiency exhibitedexhibited aa decreasingdecreasing tendencytendency byby approximatelyapproximately 2.6%2.6% whenwhen the waterwater contentcontent waswas 25%,25%, whichwhich waswas thethe maximummaximum conditioncondition ofof thisthis study.study. Because the marine boiler applied in this study is a fixed operating condition where Because the marine boiler applied in this study is a fixed operating condition where proportional control of the supply air volume is not possible, the emission gas reduction proportional control of the supply air volume is not possible, the emission gas reduction effect can be further improved if applied to a boiler capable of proportional control. There- effect can be further improved if applied to a boiler capable of proportional control. There- fore, a future experimental study can apply emulsified fuel to a rotary-cup marine boiler fore, a future experimental study can apply emulsified fuel to a rotary-cup marine boiler that can automatically control the optimal combustion. that can automatically control the optimal combustion. Author Contributions: Conceptualization, T.-H.L.; Funding acquisition, S.-H.L.; Investigation, Author Contributions: Conceptualization, T.-h.L.; Funding acquisition, S.-h.L.; Investigation, S.- S.-H.L.; Methodology, T.-H.L.; Project administration, J.-K.L.; Resources, T.-H.L.; Supervision, J.-K.L.; h.L.; Methodology, T.-h.L.; Project administration, J.-k.L.; Resources, T.-h.L.; Supervision, J.-k.L.; Visualization, T.-H.L.; Writing—original draft, T.-H.L.; Writing—review & editing, T.-H.L. All authors Visualization, T.-h.L.; Writing—original draft, T.-h.L.; Writing—review & editing, T.-h.L. All au- have read and agreed to the published version of the manuscript. thors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable.

Data Availability Statement: Not applicable. Conﬂicts of Interest: The authors declare no conﬂict of interest. J. Mar. Sci. Eng. 2021, 9, 477 11 of 11

References 1. Demirbas, A. Biodiesel: A Realistic Fuel Alternative for Diesel Engines; Springer: London, UK, 2008. 2. Mohd, N.C.W.; Noor, M.M.; Mamat, R. Biodiesel as alternative fuel for marine diesel engine applications: A review. Renew. Sustain. Energy Rev. 2018, 94, 127–142. [CrossRef] 3. Lee, T.H. A Study on the Characteristics of Exhaust Emissions in a Marine Boiler Using Emulsified Bunker-C Oil; Jeonbuk National University: Jeonju, Korea, 2020. 4. Force, C.A.T. Prevention of Air Pollution from Ships: Reducing Shipping Emissions of Air Pollution-Feasible and Cost-Effective Options Submitted by Friends of the Earth International to the Marine Environment Protection Committee; International Maritime Organization: London, UK, 2005. 5. Choi, J.S.; Han, S.G.; Choi, J.H.; Park, S.K.; Park, R.S.; Kim, D.H. A Study on Characteristics of Exhaust Gas Emissions of Water-Bunker Oil Mixed by Homogenizer. J. Korean Soc. Mar. Environ. Saf. 2013, 19, 518–524. [CrossRef] 6. Son, J.H.; Kim, J.H.; Jung, S.W.; Yoo, H.M.; Hong, H.K.; Mun, S.H.; Choi, K.H.; Lee, J.T.; Kim, J.S. Characteristics of Air Pollutants Emission from Medium-duty Trucks Equipped EGR and SCR in Korea. J. ILASS-Korea 2016, 21, 130–136. [CrossRef] 7. Flagiello, D.; Parisi, A.; Lancia, A.; Carotenuto, C.; Erto, A.; Di Natale, F. Seawater desulphurization scrubbing in spray and packed columns for a 4.35 MW marine diesel engine. Chem. Eng. Res. Des. 2019, 148, 56–67. [CrossRef] 8. Flagiello, D.; Di Natale, F.; Carotenuto, C.; Erto, A.; Lancia, A. Seawater Desulphurization of Simulated Flue Gas in Spray and Packed Columns: An Experimental and Modelling Comparison. Chem. Eng. Trans. 2018, 69, 799–804. [CrossRef] 9. Flagiello, D.; Di Natale, F.; Erto, A.; Lancia, A. Wet oxidation scrubbing (WOS) for flue-gas desulphurization using sodium chlorite seawater solutions. Fuel 2020, 277, 118055. [CrossRef] 10. Yoon, J.H.; Yeom, J.K. Numerical Analysis on Behavior Characteristics of Evaporative Spray of Emulsified Fuel Impinging on a Heated Flat Plate. Trans. KSME-B 2019, 43, 471–477. [CrossRef] 11. No, J.M. Combustion Characteristics of Steam Boiler Using Heavy Oil/Emulsified Fuel; Ajou University: Suwon, Korea, 2008. 12. Kim, M.C.; Lee, C.S. It’s effects for engine emission of water/oil emulsified fuel. Anal. Sci. Technol. 2008, 21, 156–166. 13. Lim, J.K.; Cho, S.G.; Hwang, S.J.; Yoo, D.H. Effect on Characteristics of Exhaust Emissions by Using Emulsified Fuel in Diesel Engine. J. Korean Soc. Mar. Eng. 2007, 31, 44–50. [CrossRef] 14. Lim, J.K.; Cho, S.G.; Hwang, S.J.; Yoo, D.H. Effects on Characteristics of Combustion by Using Emulsified Fuel in Diesel Engine. J. Korean Soc. Mar. Eng. 2007, 31, 51–55. 15. Lim, H.K.; Lee, M.J.; Chi, G.Y.; Lim, J.C. Emission Evaluation of Emulsified fuel Prepared from Bunker C Oil. Appl. Chem. Eng. 2017, 28, 186–192. [CrossRef] 16. Gollahalli, S.R.; Nasrullah, M.K.; Bhashi, J.H. Combustion and Emission Characteristics of Burning Sprays of a Residual Oil and Its Emulsion with Water. Combust. Flame 1984, 55, 93–103. [CrossRef] 17. Park, K.H.; Kim, D.K.; Kim, C.J. Burner Combustion Characteristics of Hybrid Type Water Mixing Emulsified fuel. J. Korean Soc. Mar. Eng. 2013, 37, 308–315. [CrossRef] 18. Chung, J.D. An Experimental Study on the Combustion Characteristics of Wastewater-Emulsified fuel. J. Energy Eng. 2003, 12, 267–273. 19. Lee, T.H.; Lee, J.K. An Experimental Study on the SO2 Reduction of Water 10% Mixed Emulsified Oil Applied to Boiler-Burner Using Bunker-C Oil. J. Fish. Mar. Sci. Educ. 2019, 31, 1801–1807. [CrossRef] 20. Lee, T.H.; Lee, J.K. An Experimental Study on the NOx Reduction of Emulsified Oil Applied to Boiler-Burner Using Bunker C Oil. J. Korean Soc. Mech. Technol. 2019, 21, 1071–1076. [CrossRef] 21. Lee, T.H.; Lee, J.K. Manufacturing and Component Characteristics of Emulsified Fuel Oil by Mixing Water-Heavy Oil. J. Korean Soc. Mech. Technol. 2020, 22, 884–890. [CrossRef] 22. MIURA. Z-Boiler Operating Instructions for Marine Use Model VWH; Miura Co. Ltd.: Matsuyama, Japan, 1992. 23. Korea Register (KR). Korean Register of Shipping Certificate Report; No. 294-738-92; Korean Register of Shipping: Busan, Korea, 1992. 24. TESTO. Flue Gas Analyzer Instruction Manual on Testo-340; Testo Co. Ltd.: West Chester, PA, USA, 2016. 25. National Institute of Environmental Research (NIER). Air Pollution Process Test Standard No. 2017-51; National Institute of Environmental Research: Incheon, Korea, 2018.