Shipboard trials of magnesium-based exhaust gas cleaning system

Ocean Engineering 128 (2016) 124–131

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Shipboard trials of magnesium-based exhaust gas cleaning system ⁎

Yimin Zhu , Xiaojia Tang, Tie Li, Yangyuan Ji, Quan Liu, Lin Guo, Jiao Zhao

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Institute of Environmental Remediation, Dalian Maritime University, Dalian, Liaoning 116026, China

A R T I C L E I N F O

A BS T RAC T

Keywords: Shipboard trials Magnesium-based Exhaust gas cleaning system Sulfur dioxide elimination

In this paper, the shipboard trials were conducted to investigate the efficacy of a magnesium-based exhaust gas cleaning system (Mg-EGCS) and the life cycle cost analysis method was utilized to evaluate the economic benefit of Mg-EGCS. The shipboard trials results indicated that the measured sulfur dioxide reduction was excellent, well within the IMO’s most stringent limits at any test loads. The discharge water was in compliance with IMO’s guidelines for exhaust gas scrubbers. Furthermore, the pressure drop was less than 400 Pa, which was far below a nominal scrubber pressure drop of 1500 Pa. The internal rate of return (IRR) value of Mg-EGCS implied that it had obvious economic advantage compared with the conventional closed loop, hybrid and dry system.

1. Introduction The SO2 emissions from marine diesel engines fueled with highsulfur fuel oils is one of the hottest environment issues concerned by all over the world. To limit the presence of such pollutant in the environment, the International Maritime Organization (IMO) recently introduced specific regulations to control sulfur content in fuel oils (IMO, 2008a). As an alternative for low-sulfur fuel, MARPOL Annex VI recognizes exhaust gas cleaning systems (EGCS) which provides reduces sulfur emissions as effective as that obtained by using lowsulfur fuel. The costs and benefits analysis of EGCS versus change of fuels have been studied (Wang et al., 2007; Caiazzo et al., 2012; Yang et al., 2012; Jiang et al., 2014; Ciatteo et al., 2014). The results encourage the ship owners to adopt the option of EGCS, mainly because of the rising price of fuel. By analyzing the research status quo of EGCS, there is variety of substances including seawater, sodium hydroxide+fresh water or dry substances. Accordingly, the EGCS is divided into four categories: open loop system, closed loop system, hybrid system (operated in both open loop and closed loop modes), and dry system. Up to now, over twenty companies have been committed to various EGCS development and promotion (Hombravella et al., 2011; Lloyd’s Register (LG), 2012; American Bureau of Shipping (ABS), 2013). Meanwhile, plenty of academic research on marine SO2 abatement technologies has been carried out, including seawater scrubber, fresh water scrubber, electrostatic water spraying scrubber, electrolyzing seawater scrubber and plasma method. (Sukheon and Osami, 2002; Andreasen and Mayer, 2007; Ariana et al., 2008; Mikko et al., 2011; Abbod et al., 2014; Jaworek et al., 2014).

⁎

Flue gas desulphurization (FGD) by magnesium oxide or magnesium hydroxide has been well developed for land application. Hereby, a novel magnesium-based EGCS (Mg-EGCS), which adopt magnesium oxide (MgO) or magnesium hydroxide (Mg(OH)2) and seawater as absorbent, have been reported in our previous studies. The pilot test results showed excellent desulphurization efficiency up to about 97% (Tang et al., 2012, 2014a; Li et al., 2014). In the current study, the shipboard trials of the project prototype of Mg-EGCS were conducted aboard the container ship Ling Yun He. Furthermore, the life cycle cost analysis result was also included in this paper. The efficacy and economic benefit of the full-scale Mg-EGCS was evaluated, and new option was provided for the ship owners. 2. Material and method 2.1. Vessel and Mg-EGCS details The Ling Yun He is a 1700 TEU container ship operated by China Ocean Shipping (Group) Company (COSCO). The type of main engine is B & W 6L70MCMK6 with rated power of 16,980 kW and rated rotating speed of 108 rpm. For saving oils and reducing carbon emissions, the vessel was sailed at the economical speed with output power of about 5000 kW and rotating speed of 68 rpm. In order to minimize the retrofit work, the Mg-EGCS was installed on the D deck as shown in Fig. 1. The rated exhaust gas treatment capacity of present Mg-EGCS is 50,000 Nm3/h. The schematic of the Mg-EGCS was shown in Fig. 2. By opening the bypass damper and shutting off the main damper, the hot exhaust gas would be forced into the bypass pipe. Before the gas was

Corresponding author. E-mail address: [email protected] (Y. Zhu).

http://dx.doi.org/10.1016/j.oceaneng.2016.10.004 Received 7 June 2016; Received in revised form 19 September 2016; Accepted 3 October 2016 Available online 24 October 2016 0029-8018/ © 2016 Elsevier Ltd. All rights reserved.

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the pH of the process and consequently the desulphurization efficiency (Tang et al., 2014b, 2015). In normal operation, a portion of spray liquid (named as wastewater) was extracted to the aeration tank. The wastewater flowed from the process tank to the aeration tank was controlled by EGCS automation based on the density setpoint. The aeration of the wastewater was done in the aeration tank to increase the oxygen content, thus the water-insoluble magnesium sulfite was oxidized into water-soluble magnesium sulfate. Accordingly, the chemical oxygen demand (COD) and turbidity were decreased. After the aeration processing finished, the wastewater was drained to a centrifugal separator, which was utilized to separate the liquid and sludge from the suspending liquid. The sludge was discharged to the sludge tank on regular intervals, and the treated wastewater would be discharged into sea after reaching the wastewater discharge criteria as detailed in MEPC. 184 (59) (IMO, 2009). Seawater was used as process water to maintain the liquid level of process tank, clean the demister, prepare the Mg(OH)2 slurry and adjust wastewater quality. 2.2. Parameters measurement 2.2.1. Raw exhaust gas measurement Because of the gas is exhausted with pulse form, it is difficult to measure accurately the exhaust gas volume flow rate. Thus the exhaust gas flow rate measurement was conducted using two different measurement methods. In accordance with the method set out in MEPC 177(58) (IMO, 2008b), the exhaust gas volume and mass flow rates were measured by Direct measurement method and Fuel flow and carbon balance method, respectively. Some necessary parameters such as sulfur content of fuel, fuel mass flow rate, exhaust gas temperature, and main engine power were measured as well.

Fig. 1. The stern of Ling Yun He.

driven into the scrubber, the gas temperature decreased sharply for the effect of the quench zone. One hundred and fifty spray nozzles were distributed uniformly inside the scrubber, which is a typical spray empty absorption tower. Scrubbing water was dispersed into microdiameter droplets with mean diameter of 850 µm through the spray nozzles. Thereby, SO2 could be captured efficiently. A chevron-type demister was employed to remove droplets from gas before the clean gas was discharged from the scrubber outlet. Then all droplets were precipitated at the bottom of the scrubber, and the liquid was returned into the process tank, from where the scrubbing water was circulated to the scrubber by the spray pump again. Mg(OH)2 slurry, which could be prepared by either mixing Mg(OH)2 powder with seawater or MgO hydration, was automatically added to the scrubbing water to maintain

2.2.2. SO2/CO2 measurement The SO2/CO2 ratio (S/C, ppm/%) was measured to monitor the exhaust gas emissions directly in order to verify the compliance with emissions limits (IMO, 2009). The SO2 and CO2 concentration in the clean gas was measured and recorded continuously by a continuous

Fig. 2. Schematic of Mg-EGCS.

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emission monitoring system (CEMS) (NSA 3080, Shimadzu, Japan, precision: ± 1% of full range (SO2: 0–200 ppm; CO2: 0–20%)). The principle of the CEMS was complied with the requirement by MEPC. 184(59). In order to improve the accuracy of SO2 concentration measurement, a precondition system (GASS6900, Perma Pure LLC, America) was applied to eliminate the gaseous water from the sampling pipe. The measured data was sent to the electronic logging system of the EGCS simultaneously. 2.2.3. Water quality measurement The water quality monitor is composed of a multi-parameter sensor probe (AP7000, Aquaread, UK, precision: ± 2% of reading) and a fluorescence probe (PAH064, Sea-Sun-Tech, Germany). Polycyclic aromatic hydrocarbons (PAHs), turbidity, temperature, oil and pH of the supplied seawater and discharged wastewater was measured and recorded online. Meanwhile, the water samples would be taken and tested by a third-party testing organization (Pony Testing International Group) in the laboratory for PAHs, turbidity, oil, nitrates and pH. 2.3. Shipboard trial process The shipboard trail was conducted when the vessel was sailing from Tianjin Port to Qinhuangdao Port, two important ports in China. All the ship parameters have been adjusted to suit the economical speed already, thus the testing load points were set below 68 rpm, and there are three other stable load points, 65 rpm, 52 rpm and 32 rpm. The exhaust gas volume and mass flow rate measurements of the four load points were conducted by the Pony Testing International Group before the EGCS running. After the gas flow rate measurements were done, the EGCS was started with the scrubbing water flow rate of 200 m3/h， and then the exhaust gas was driven to scrubber by switching the damper. The desulphurization effects of the Mg-EGCS at four load points (68 rpm, 65 rpm, 52 rpm and 32 rpm) were tested in turn. Proportion of Mg(OH)2 slurry used in the trial was 80 kg powder per 700 L seawater. In normal operation, alkali feeding and wastewater extraction were intermittently, which would affect the accuracy of the liquid flow meter. Therefore, the consumptions of Mg(OH)2 slurry and the drainage flow rate would be calculated based on changes of liquid level of the alkali tank and the process tank respectively. Other data including EGCS power consumption and the static pressure at the exhaust pipe (Fig. 2) were recorded as well.

Fig. 3. The stabilization process of Mg-EGCS.

diesel engine is 1500 Pa. Therefore, booster fan or exhaust fan was unnecessary for the Mg-EGCS. Thus the equipment cost and power consumption was reduced greatly. 3.2. Stabilization process

3. Results and discussion

The period from the exhaust gas introduced into the scrubber until the SO2 emission meeting the standard was defined as stabilization process. For the first 14 min, no alkali was fed to the process tank in order to test the seawater desulphurization efficiency. It would take several minutes for the exhaust gas to form steady flow field inside the scrubber and then clean gas was sampled, dried and tested. As shown in Fig. 3, five minutes later, the CO2 concentration reached and maintained at 4.64%. And the value did not change whether the alkali was fed or not. For the conventional low alkali cleaning systems, no CO2 is absorbed during exhaust gas cleaning. During the seawater scrubbing process, there would be no CO2 release mainly because of the high CO2 partial pressure ( 4640 Pa) inside the scrubber. When the wastewater is open to the atmosphere, and the CO2 partial pressure is only 30 Pa, it will give rise to loss of CO2 from liquid to the atmosphere until the CO32−/HCO3− buffer system is re-established (Williams and le, 2010). Therefore, it could be concluded that the CO2 concentration before and after scrubbing remains approximately the same (maybe a slight decrease because of the scrubbing water evaporation). Thus, the CO2 concentration could be utilized as a criterion for determining whether the reading of CEMS was reliable. Based on the concentration variation law of CO2, the SO2 concentration after 5 min was considered to be reliable. The SO2 concentration increased from 32 ppm to 170 ppm in 2 min. And then, with the

3.1. Raw exhaust gas The static pressure (when Mg-EGCS running) at the exhaust pipe is mainly generated by the scrubber, meaning that the static pressure value is approximately equal to the pressure drop of the scrubber. As shown in Table 1, the pressure drop of the scrubber was less than 400 Pa. Commonly, the maximum allowable pressure drop of marine Table 1 Raw exhaust gas parameters. Item

Unit

68 rpm

65 rpm

52 rpm

32 rpm

Exhaust gas temperature Exhaust gas mass flow rate on wet basis Exhaust gas volume flow rate on dry basis Main engine power Fuel mass flow rate S content of fuel Static pressure (when Mg-EGCS running)

°C kg/h

264 41,929

219 35,702

189 30,304

128 23,661

Nm3/h

47,400

28,700

21,300

12,700

kW kg/h %m/m Pa

5234 921.0 1.75 330

4357 765.5 1.75 280

2064 475.3 1.75 270

850 197.0 1.75 120

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Fig. 4. SO2 and CO2 concentration in the outlet of scrubber (a) SO2 at different loads (b) CO2 at different loads (c) S/C at different loads.

holdup of Mg-EGCS was 0.7 m3 because of the cross-section area and the liquid level drop of process tank was 1.6 m2 and 0.45 m, respectively. In order to maintain the liquid level of process tank, seawater was supplied with flow rate of 3 m3/h until the liquid level reached 0.9 m.

fresh seawater supply, the SO2 concentration gradually decreased to a steady value, 150 ppm. In order to calculate the desulphurization efficiency of the EGCS, the SO2 concentration was converted to sulfur content of fuel according to standard data for lager two-stroke engines (Sher, 1998). Accordingly, the SO2 concentration of 150 ppm in the exhaust gas is equivalent to sulfur content of 0.75%m/m in the fuel. It indicated that the desulphurization efficiency was only 57% without alkali feeding. 14 min later, the feed pump was started and the Mg(OH)2 slurry was fed to process tank. Just as expected, the SO2 concentration decreased from 150 ppm to 20 ppm in 8 min. As the provision of MEPC. 184(59), the S/C of 4.3 ppm/% in the exhaust gas is equivalent to sulfur content of 0.1%m/m in the fuel. In other words, the SO2 concentration less than 20 ppm would be considered to be in compliance with the convention when CO2 concentration was 4.64%. The Mg-EGCS reached steady state at this moment. The pH of process decreased sharply, from 8.1 to 4.5 in 5 min, once the raw exhaust gas came into contact with the scrubbing water. Then the value increased to 5.4 slowly due to the fresh seawater supply and increased further to 7.5 until the alkali was fed to the process tank. Meanwhile, it indicated that the SO2 concentration decreased with the increasing of process pH sharply. However, there existed a 1 min lag between pH increasing and SO2 concentration decreasing. The scrubber and spray pipe interior would be filled with scrubbing water once the spray pump was started. The volume of this liquid was defined as dynamic liquid holdup, which resulted in the liquid level of the process tank dropping sharply. The calculated dynamic liquid

3.3. SOx emissions compliance The SO2 and CO2 concentration at scrubber outlet with Mg-EGCS running steady was recorded. As shown in Fig. 4, the SO2 concentration decreased with the reduced main engine load. The mean values of SO2 concentration at four different loads were 14.5 ppm, 10.8 ppm, 3.3 ppm and 1.7 ppm, respectively (Fig. 4(a)). The scrubbing water flow rate was maintained at 200 m3/h, while the exhaust gas volume flow rate decreased with the reduced main engine loads. Accordingly, the liquid-to-gas ratio (L/G) increased from 4.2 L/Nm3 to 15.7 L/Nm3, which is considerably larger than the design value, 4 L/Nm3. Consequently, the SO2 concentration at low load points (52 rpm and 32 rpm) was much lower than 20 ppm. Considering the CO2 concentrations at the four load points were 4.64%, 4.51%, 3.12% and 1.22% (Fig. 4(b)), the S/C value should be always blew 4.3 ppm/%. Nevertheless, a transient peek S/C value of 17.3 ppm/% was observed at 32 rpm (Fig. 4(c)). The abnormal data were mainly caused by inverse-blow of CEMS. Usually, the CEMS is inherent with automatic inverse-blow and calibration cycle. The sampling pump would be shut down when inverse-blow or calibration procedure was executed. This 127

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evaporation rate testing period (h). Other liquid level drops, except the initial one which was caused by the dynamic liquid holdup as mentioned above, were accumulated for each load point. The drainage flow rate is obtained according to equation (2): n

Qd =

∑i =1 ((Lhi − Lli )⋅A − Δti⋅Qe ) td

(2) 3

where Qd is the drainage flow rate (m /h), i is the ith liquid level drop at a certain load point, n is the number of liquid level drop at a certain load point, Lhi is the initial liquid level of the ith liquid level drop (m), Lli is the final liquid level of the ith liquid level drop (m), Δti is the duration of ith liquid level drop (h), td is the duration of the certain load point (h). In order to better illustrate the relationship between the seawater consumption, main engine power and sulfur content of fuel, the Qe and Qd are converted to Q′e and Q′d according to Eqs. (3) and (4):

Qe′ = 1000⋅

Qe Mep

(3)

Qd′ = 1000⋅

Qd Mep⋅S

(4)

Fig. 5. Liquid level of process tank at different loads.

leaded directly to irregular drifting of measurement data. In the traditional control strategies, some operating parameters, such as the speed of spray pump and process pH, were adjusted automatically based on the S/C value at the scrubber outlet. In order to avoid overreacting, the automatic program of EGCS should have functionality particular for abnormal data identification and ignoring.

where Q′e is the Qe of unit power (L/MWh), Mep is the main engine power, Q′d is the Qd of unit power and sulfur content of fuel (L/MWh/ %), S is the sulfur content of fuel (%m/m). The calculated results were shown in Fig. 6. As a rule of thumb, the Q′e should not change with the main engine power. However, the data in Fig. 6(a) indicated that the Q′e increased with the decrease of main engine load. When the gas with droplets passed through the demister, the gas flow direction was forced to change quickly. Then the heavy droplets would be captured by the vane due to the inertia effect. Thus, there should be an optimal gas velocity for an established demister. The present demister was designed and arranged based on the rated exhaust gas treatment capacity of the present Mg-EGCS. So the exhaust gas volume flow rate should be about 50,000 Nm3/h to assure optimal efficiency of the demister. As shown in Table 1, only the exhaust gas volume flow rate of 68 rpm was close to 50,000 Nm3/h. As a result, a lager mount of droplets was expelled with the clean gas at other three load points. It will cause the Q′e increased with the reduced main engine load. As the seawater is salty, the increasing of Q′e resulted in an increment of scrubbing water density. In order to maintain the density, more wastewater needed to be replaced with fresh seawater, which resulted in an enhanced Q′d consequently, just as shown in Fig. 6(b). In the operational situations where the wastewater discharge needs to be avoided, the wastewater can be diverted to a holding tank for the

3.4. Material and power consumption The liquid level of process tank was maintained at about 0.9 m during normal operation as shown in Fig. 5. The variation of liquid level of process tank was caused by seawater supplement, scrubbing water evaporation and wastewater extraction. The level change caused by alkali feeding was slight, so that it was ignored in calculation. Within a certain time period (the dotted box), none seawater was supplied nor wastewater was extracted. The liquid level variation and the duration of the period were recorded, and the evaporation rate at each load point was obtained according to equation (1):

Qe =

(Lh − Ll )⋅A t

(1) 3

where Qe is the evaporation rate (m /h), Lh is the initial liquid level within the evaporation rate testing period (m), Ll is the final liquid level within the evaporation rate testing period (m), A is the cross-section area of the process tank (m2), 1.6 m2, t is the duration of the

Fig. 6. Seawater consumption at different load points (a) Evaporation flow rate (b) Drainage flow rate.

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Fig. 7. Liquid level of alkali tank and pH at different loads. Fig. 8. Power consumption at different loads. Table 2 The Mg/S ratio of Mg-EGCS. Items

Units

Alkali volume flow rate Mg(OH)2 mass flow rate Mg(OH)2 mol flow rate Fuel mass flow rate S content of fuel SO2 mole flow rate Mg/S ratio

L/h kg/h Mol/h kg/h %m/m Mol/h Mol/mol

for SO2 elimination. Typically, the Na/S ratio for closed loop system is about 2 mol/mol, and the price of Mg(OH)2 is about half of NaOH. So the chemical cost of Mg-EGCS is one third of closed loop system, approximately. For most of the time, the power consumption of Mg-EGCS varied between 30 kW and 40 kW (Fig. 8). But because of large start current of the centrifugal separator, the power reached up to 58 kW and then fell back to normal level in 7 min. Meanwhile the power could fluctuate in a small range because of the start-stop of some low-power equipment. The main engine power was about 5.2 MW when the rotating speed was 68 rpm. So when ling yun he was sailed at economical speed, the additional fuel consumption of Mg-EGCS was 0.58–0.77%, which was close to that of a typical closed loop system, about 0.5%.(US EPA, 2011). But the additional fuel consumption at low points (52 rpm and 32 rpm) was unsatisfactory. The reason for this condition was that the scrubbing pump, the main contributor to power consumption, was set a constant power for any load points. However, it would be not enough to guarantee the minimum atomization pressure of the spray nozzle if the scrubbing pump power was turned down with the main engine load reduction. Further work will be conducted on the spray system improvement to balance the desulphurization efficiency with power consumption at low load. The similar issue is also worthy of attention of counterparts in this field.

Load points 68 rpm

65 rpm

52 rpm

32 rpm

244.01 27.89 480.86 921.04 1.75 503.70 0.95

206.06 23.55 406.03 765.49 1.75 418.63 0.97

107.05 12.23 210.86 475.30 1.75 259.93 0.81

52.22 5.97 102.89 197.00 1.75 107.73 0.95

subsequent scheduled and periodical discharge. Hereby, the volume of the holding tank is determined by the duration of the discharge avoiding situation and the drainage flow rate of the wastewater. The higher drainage flow rate means more occupied space, which is concerned by ship owner particularly. The Q′d of the Mg-EGCS was 95–230 L/MWh/% of fuel S. The Q′d is 50–100 L/MWh/% of fuel S for closed loop system and 13 t/M W h/% of fuel S for open loop system, based on data from Wärtsilä (Wärtsilä, 2014). Relatively, the Q′d of the Mg-EGCS was higher than that of closed loop system but much lower than that of open loop system. And one thing to be noted was that only seawater but no fresh water would be consumed by Mg-EGCS. As shown in Fig. 7, the process pH was maintained at 7.3. Meanwhile the Mg/S ratio could be calculated by the liquid level of alkali tank and fuel consumption, as shown in Table 2. The crosssection area of alkali tank is 0.785 m2. 175 L seawater and 20 kg Mg(OH)2 powder were added to the alkali tank in the later phase of 68 rpm. The calculation results indicated that the Mg/S ratios for all load points were close to, but less than 1 mol/mol. It could be concluded that, for Mg-EGCS, the seawater was a contributing factor

3.5. Water quality The results of water quality obtained by two methods were listed in Table 3 and Table 4. It indicated that the treated wastewater quality obtained by both methods were compliance with the criteria. However, two distinct values were got on the same test projects, especially for turbidity and PAHs. As the on-line probe for PAHs and turbidity detection was made based on optical principle, the performance of the probe would be interfered by the micro-bubble, which was generated

Table 3 Results of water quality monitoring.

Out let

Inlet Criteria

68 rpm 65 rpm 52 rpm 32 rpm

Temperature (°C)

pH

Oil (mg/L)

Turbidity (NTU)

PAHsμg/L

32 33.4 35.3 36.1 23.5 –

7.66 7.7 7.59 7.58 7.66 > 6.5

0 0 0 0 0 < 15 mg/L

134 56.8 0 9.4 111 < 25 NTU than inlet

236.85 228.48 222.27 219.79 79.75 < 2250 μg/L

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Table 4 Water quality data from laboratory testing. Inlet

pH Turbidity, NTU Oil, mg/L NO3−, mg/L NO2−, mg/L PAHs, μg/L

7.62 1 < 0.04 0.264 0.208 0.088 < 0.005 0.144 < 0.006 < 0.012 < 0.005 < 0.002 0.004 < 0.007 < 0.008 < 0.003 < 0.004 < 0.004 < 0.003 < 0.004 < 0.003 < 0.302

Naphthalene Acenaphthene Fluorene Acenaphtylen Phenanthrene Anthracene Fluoranthene Pyrene Benzo(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(k)fluoranthene Benzo(a)pyrene Dibenzo(a,h)anthracene Benzo(g,h, i)perylen Indeno(1,2,3-cd)pyrene

Total PAHs, μg/L

Outlet

Criteria

68 rpm

65 rpm

52 rpm

32 rpm

8.05 6 0.06 2.29 3.59 < 0.011 < 0.005 < 0.004 < 0.006 < 0.012 < 0.005 < 0.002 < 0.003 < 0.007 < 0.008 < 0.003 < 0.004 < 0.004 < 0.003 < 0.004 < 0.003 < 0.084

8.22 2 < 0.04 4.02 4.08 < 0.011 < 0.005 < 0.004 < 0.006 < 0.012 < 0.005 < 0.002 < 0.003 < 0.007 < 0.008 < 0.003 < 0.004 < 0.004 < 0.003 < 0.004 < 0.003 < 0.084

8 3 0.07 3.95 4.41 < 0.011 < 0.005 < 0.004 < 0.006 < 0.012 < 0.005 < 0.002 < 0.003 < 0.007 < 0.008 < 0.003 < 0.004 < 0.004 < 0.003 < 0.004 < 0.003 < 0.084

8.15 8 0.05 3.77 5.31 < 0.011 < 0.005 < 0.004 < 0.006 < 0.012 < 0.005 < 0.002 < 0.003 < 0.007 < 0.008 < 0.003 < 0.004 < 0.004 < 0.003 < 0.004 < 0.003 < 0.084

> 6.5 < 25 NTU than inlet < 15 mg/L < 2700 mg/l

< 2250 μg/L

Note: the PAHs were test by HPLC in the laboratory.

employed as a pre-condition unit for water quality monitor. The variation for pH value was mainly caused by the test temperature. When the actual pH value was higher than 7, the measured value would decease with the increased temperature. The temperature of

during the wastewater treatment process. The similar phenomenon was also reported by Wärtsilä, Alfa Laval and Hamworthy Krystallon (Wärtsilä, 2010; Holland America Line, Hamworthy-Krystallon, 2010; Alfa Laval, 2012). An efficient steam-water separator should be Table 5 Life cycle cost analysis of various EGCS. Scrubber type

Mg-EGCS

Open loop

Closed loop

Hybrid

Dry

Investment terms Life cycle Analysis date Scrubber installation date Discount rate

# of years Year Year %

10 2016 2016 10%

10 2016 2016 10%

10 2016 2016 10%

10 2016 2016 10%

10 2016 2016 10%

Capital expense for scrubber Equipment(today) Engineering/design Training/documents Install/commission

USD/one time % equip cost % equip cost % equip cost

5,000,000 9% 2% 65%

5,761,715 7% 2% 50%

7,037,036 9% 2% 65%

5,978,891 9% 2% 75%

5,643,791 11% 2% 85%

Operating expense- annual ECA fuel consumption Chemical consumption Additional fuel consumption Distillate calorie correction HFO process and heating Operating engineer (today) Operating engineer M & R equipment

MT/annual % of fuel cost % of fuel cost % of fuel cost % of fuel cost USD/annual % of position % equip cost/annual

9636 1.00% 1.00% 4.00% 0.80% 220,030 50% 4.00%

9636 0 2.00% 4.00% 0.80% 220,030 50% 4.00%

9636 3.00% 1.00% 4.00% 0.80% 220,030 50% 4.00%

9636 1.50% 1.50% 4.00% 0.80% 220,030 50% 4.00%

9636 3.00% 3.00% 4.00% 0.80% 220,030 50% 4.00%

Variables-uncertain Fuel differential(Today) Fuel/chemical escalation rate Personnel Inflation rate Equipment inflation rate

USD/MT % annual for op period % annual for op period % annual for op period

319 8.00% 3.00% 3.30%

319 8.00% 3.00% 3.30%

319 8.00% 3.00% 3.30%

319 8.00% 3.00% 3.30%

319 8.00% 3.00% 3.30%

Analysis results Capital cost Expenses - year One Fuel Savings - year One Net present value Internal rate of return

USD USD USD USD %

8,800,000 640,896 3,073,884 11,800,630 32.02%

9,052,530 621,594 3,073,884 12,137,872 31.95%

12,385,183 788,086 3,073,884 7,573,417 20.95%

11,487,722 721,006 3,073,884 8,976,233 23.65%

11,543,472 738,213 3,073,884 8,762,433 23.31%

-

year zero dollars year one dollars year one dollars present dollars

Note: the updated data was set in bold type.

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Fund (for Collaborative Innovation Center) of Liaoning Province, China (20110216004). The authors sincerely appreciate China Ocean Shipping (Group) Company and the crew of Ling Yun He for their cooperation.

scrubbing water was 45 °C, and the value would drop to 35 °C after the wastewater treatment process, while the laboratory test was conducted at room temperature (25 °C). Even though the pH sensor has been qualified by the temperature compensation function, the calibration process was executed by standard solution but not the wastewater. Therefore, the reading of on-line pH sensor may not be completely dependable.

References Abbod, M., Beleca, R., Peirce, D., Ganippa, L., Manivannan, N., Balachandran, et W., 2014. Power controlled microwave reactor for the removal of NOx and SOx from the exhaust of marine diesel engine. Transp. Res. Arena 1, 1–9. Alfa Laval Aalborg A/S, 2012. Exhaust gas scrubber installed onboard MV Ficaria Seaways. Danish Ministry of the Environment EPA Environmental project NO. 1429. American Bureau of Shipping (ABS), 2013. . Exhaust gas scrubber systems advisory. Andreasen, A., Mayer, S., 2007. Use of seawater scrubbing for SO2 removal from marine engine exhaust gas. Energy Fuel 21, 3274–3279. Ariana, I.M., Fujita, H., Nishida, O., Harano, W., 2008. Using water-plate collector and water spray on ESP to reduce marine diesel exhaust emission. J. Mar. Environ. Eng. 9, 35–44. Caiazzo, G., Di Nardo, A., Langella, G., Scala, F., 2012. Seawater scrubbing desulfurization: a model for SO2 absorption in fall-down droplets. Environ. Prog. Sustain. Energy 31, 277–287. Ciatteo, V., Giacchetta, G., Marchetti, B., 2014. Dynamic model for the economical evaluation of different technical solutions for reducing naval emissions. Int. J. Prod. Qual. Manag. 14, 314–325. Holland America Line, Hamworthy-Krystallon, 2010. . Sea water scrubber technology demonstration projection on the ZAADAM. Holland America Line Sea Water Scrubber Technology Demonstration Project. Hombravella, A., Kılıçaslan, A., Péralès, J., Rüß, C., 2011. Study of exhaust gas cleaning systems for vessels to fulfill IMO III in 2016. Fachhochschule Kiel University of Applied Sciences and Caterpillar. IMO, 2008a. Revised MARPOL Annex VI: Regulations for the prevention of air pollution from ships and NOx technical code. IMO, 2008b. Amendments to the technical code on control of emission of nitrogen oxides from marine diesel engines. IMO, 2009. . Guidelines for exhaust gas cleaning systems. Jaworek, A., Szudyga, M., Krupa, A., Czech, T., Sobczyk, A.T., Marchewicz, A., Antes, T., Balachandran, W., Beleca, R., Di Natale, F., Lancia, A., Carotenuto, C., D’Addio, L., Gregory, D., Jackson, M., Kozak, S., Volpe, L., Charchalis, A., 2014. Technical issues of PM removal from ship diesel engines. Transp. Res. Arena, 2014, (Paris). Jiang, L.P., Kronbak, J., Christensen, L.P., 2014. The costs and benefits of sulphur reduction measures sulphur scrubbers versus marine gas oil. Transp. Res. D Transp. 28, 19–27. Li, T., Yu, H., Li, Y.Y., Liu, Q.,, Chen, Ch, Guo, L., Zhu, Y.M., 2014. Study on washwater effluent quality discharged by ship exhaust gas DeSO(x) system with magnesium and seawater desulphurisation method. Int. J. Environ. Pollut. 56, 1–10. Lloyd’s Register (LG), 2012. . Understanding Exhaust Gas Treatment Systems Guidance for Shipowners and Operators. Mikko, A., Risto, H., Seppo, T., 2011. . Method and an Equipment for Reducing the Sulphur Dioxide Emissions of a Marine Engine. United States Patent: 7976809. Reynolds, K.J., 2011. exhaust gas cleaning systems selection guide. Ship Operations Cooperative Program (SOCP). Sher, E., Ed., 1998. Handbook of Air Pollution from Internal Combustion Engines Pollutant Formation and Control. Academic Press, New York, pp. 477–534. Sukheon, A., Osami, N., 2002. Marine Air Pollution Control System Development Applying Seawater and Electrolyte. SAE Technical Papers. Report number: 2002-012295. Tang, X.J., Li, T., Yu, H., Zhu, Y.M., 2014a. Prediction model for desulphurization efficiency of onboard magnesium-base seawater scrubber. Ocean Eng. 76, 98–104. Tang, X.J., Li, T., Hao, Y., Wu, X.M., Zhu, Y.M., 2012. Removal efficiency of magnesiumbase seawater desulfurization for marine flue gas. J. B. Sci. Eng. 20, 1081–1087, (in Chinese). Tang, X.J., Guo, L., Chen, Ch, Liu, Q., Li, T., Zhu, Y.M., 2014b. The analysis of magnesium oxide hydration in three-phase reaction system. J. Solid State Chem. 213, 32–37. Tang, X.J., Guo, L., Liu, Q., Li, Y.Y., Li, T., Zhu, Y.M., 2015. Morphology analysis of magnesium hydroxide prepared by magnesium oxide hydration within seawater. Cryst. Res. Technol. 50, 203–209. US EPA, 2011. . Exhaust gas scrubber washwater effluent. Washington, EPA-800-R-11006. Wang, C.H.F., Corbett, J.J., Winebrake, J.J., 2007. Cost-effectiveness of reducing sulfur emissions from ships. Environ. Sci. Technol. 41, 8233–8239. Wärtsilä, 2010. . Exhaust gas scrubber installed onboard MT SUULA. Wärtsilä, 2014. . Wärtsilä scrubber product guide-ds. Williams, P.J., le, B., 2010. The natural oceanic carbon and sulfur cycles: implications for SO2 and CO2 emissions from marine shipping. Int. J. Soc. Underw. Technol. 29, 5–19. Yang, Z.L., Zhang, D., Caglayan, O., Jenkinson, I.D., Bonsall, S., Wang, J., Huang, M., Yan, X.P., 2012. Selection of techniques for reducing shipping NOx and SOx emissions. Transp. Res. D - Transp. 17, 478–486.

3.6. Life cycle cost analysis The life cycle cost analysis was conducted according to the methodology provided by Reynolds, 2011. The equipment costs and operating engineer wages were updated to current values based on the base values and inflation rates listed in the original literatures. Fuel differential between HFO and MGO in this study is 319 USD/MT according to the average fuel price of Shanghai port, June, 2016. Constituent and complexity of Mg-EGCS were similar to that of closed loop system, thus the same percentage of design, training and installation was adopted in this study. Based on the above results, additional fuel consumption of Mg-EGCS was close to that of closed loop system and the chemical consumption of Mg-EGCS was a third of closed loop system. Compared with closed loop system, freshwater supply equipment, scrubbing water cooling equipment and exhaust fan were unnecessary for Mg-EGCS. So the equipment cost of Mg-EGCS was estimated at 5 million USD. The internal rate of return (IRR) was adopted to evaluate the economy of various EGCS. The analysis results listed in Table 5 indicated the IRR value of Mg-EGCS and open loop system were approximate, and were lager than that of other three systems. It implied that the Mg-EGCS has the obviously economic advantage compared with closed loop, hybrid and dry system. 4. Conclusions The shipboard trials of full scale Mg-EGCS are demonstrated for the first time. Tests were carried out at four load points (main engine rotating speed of 68 rpm, 65 rpm, 52 rpm and 32 rpm) with the sulfur content of fuel as 1.75% m/m. The important performance parameters such as pressure drop of the scrubber, SO2/CO2 ratio at outlet of the scrubber, material and power consumption and wastewater quality were investigated. In addition, the life cycle cost of the Mg-EGCS was analyzed. The results indicated that resistance of scrubber is pretty low with pressure drop of less than 400 Pa. The SO2/CO2 value at the outlet of scrubber was less than 4.3 ppm/% when the sulfur content of fuel was 1.75%m/m and main engine power was below 5.2 MW. The discharge water was in compliance with IMO’s guidelines for exhaust gas scrubbers. The wastewater was drained at a flow of 95–230 L/MWh/ % of fuel S, which is a bit higher than typical closed loop system but much lower than open loop system. Meanwhile the additional fuel consumption and chemical cost are both about 1% of fuel cost. The results of life cycle cost analysis indicated that the Mg-EGCS could be an economical approach for fulfilling the convention. Further research is needed in order to reduce the power consumption at low engine load. Also the abnormal data caused by the exhaust gas and wastewater quality monitors should be treated properly. The experiences and problems emerged during the trial have important reference value for design and operation of EGCS. Acknowledgement This research was funded by the Marine High-tech Research Project of Chinese Ministry for Industry and Information Technology ([2012] 541), the Fundamental Research Funds for the Central Universities (3132016326 and 3132016058) and Higher Education Development

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