MARINIZATION OF A TWO-STAGE MIXED STRUCTURED PACKING SCRUBBER FOR SOX ABATEMENT AND CO2 CAPTURE.

In this paper, a practical investigation to evaluate the impact of a two-stage mixed structured packing scrubber for SO x abatement and CO 2 capture using amine solutions is presented. The practical test consists to connect the two-stage packing column to the diesel engine (DE) exhaust outlet. The first stage of the scrubber, fed with a sodium hydroxide solution, served as a SO X absorber, where the liquid flow rate and the sodium concentration are the operating variables. Gasses are then transported from the first stage to the second stage, where they encounter an amine solution that can be recycled in a closed loop to absorb residual CO 2 streams. Tests are conducted with a 250kW diesel generator (DG) filled with a 0,5% Sulphur content fuel. Results revealed a significant decrease of SO by an of 89% CO 2 has shown a decrease by an amount of 49%. pressure was detected when DG operates at high loads due to the fouling structured packing. packed bed closed loop scrubber systems for sulfur abatement and CO2 capture was examined. For the evaluation of the efficiency of the system, a soda solution (NaOH) for sulfur abatement and monoethanolamine solution for CO2 capture were used. Tests are conducted using a 250KW diesel generator filled with a 0, 5% sulfur content fuel. The results showed the possibility to achieve valuable emission reduction percentage for the SO X and CO 2 by an average of 89% and 49%. However, the accumulation of the sodium sulfate (Na 2 SO 4 ) in the packed bed due to the chemical reaction between the SO x and the NaOH solution, served further to the pressure drop in the scrubber by an amount of 17%.

However, there are different feasible methods to meet Annex VI requirements. This can be accomplished by switching to a low-sulfur fuel or by applying exhaust after-treatment through absorption. As an alternative to lowsulfur fuel, MARPOL Annex VI recognizes exhaust gas cleaning systems (EGCS) that reduces sulfur emissions as efficiently as they do with low-sulfur fuel. The cost and benefit analysis of EGCS versus fuel changes was examined in [8][9][10][11][12]. Results have encouraged shipowners to choose primarily the EGCS option due to the ascending fuel price. 3,5% 0,1% 0,1% 0,1% 0,0015% 2020-(2025) ** 0,5% 0,1% 0,1% 0,1% 0,0015% 0, 5% * : Marine Gas Oil, or 0, 1% Marine Diesel Oil (2025) ** : Implementation of Oceans limit at 0, 5% Sulphur In the last decade, application of absorbers for Sulphur dioxide (SO 2 ) elimination has increased considerably in marine transport and they are generally called scrubbers [13]. Scrubbers are categorized as dry scrubbers, using dry lime and other calcium-based pH control minerals, or as wet scrubbers using an alkaline solution, figure 2 [14]. The open loop scrubber is the easiest system, where water is supplied from the sea, pumped, filtered and sprayed into the scrubber using nozzles that diffuse water into droplets. However, open loop scrubber is only profitable if the water is alkaline. This can be accomplished by adding an alkali chemistry or by using seawater with a natural alkalinity extracted from the bicarbonate ion (HCO 3 -) existing in the seawater [14]. The water is released back into the sea after particular matters are eliminated. Figure 3 illustrates a schematic of an open loop wet scrubber [15]. However, operation of the open loop scrubber system in fresh water can restrict scrubbing of SO X due to the weak alkalinity of the water [16]. into the sea [15].
For this, it is therefore more interesting to develop closed loop technology for shipowners sailing in fresh water such as the St. Lawrence River (Canada) and the Great Lakes (USA and Canada). Fresh water treated with an alkaline chemical like caustic soda is employed for neutralization in a closed loop scrubber system (including hybrid SO X scrubbers when operating in closed loop mode). Fresh water scrubbers are used when high efficiency cleaning is required or when the varying alkalinity associated with seawater prevents the use of marine scrubbers [16]. Nevertheless, closed loop fresh water scrubber systems have much smaller discharge rates than open loop sea scrubber systems by an amount approximately of 0,1 to 0,3 m 3 /MWh and occurs a smaller volume of effluent [17]. Moreover, closed loop fresh water scrubber system can periodically be operated in zero discharge mode without discharging any overboard wash water. Figure 3 shows the schematic for a closed loop fresh water scrubber system [15].   2 ) which react with sulfur oxides to form gypsum (CaSO 4 -2H 2 O). Contrary to wet SO X scrubbers, dry scrubbers do not require wash water treatment making them ideal for areas where there is an increased sensitivity to discharge to the sea. However, as with closed loop operation of a wet system, consumables need to be stored and handled. Granules used must also be stored offshore before disposal.
The objective of this paper is to evaluate the effect of a vertical two-stage mixed structured closed loop-packing scrubber using a sodium hydroxide solution for SO X abatement and CO 2 capture in aqueous Monoethanolamine (MEA) solutions. Indeed, the closed loop technology is much more interesting to develop for shipowners sailing in fresh waters and who have hybrid or closed loop with a 0,5% sulfur content fuel. Attention was given to the drop pressure in the scrubber column due to the fouling structured packing and on the level of SO X abatement and CO 2 capture.

Experimental:-
The experimental setup is based on the absorption principle of contacting the gas phase with the liquid phase at room temperature and atmospheric pressure. A vertical two-stage gas-liquid counter-current packed bed (1) is used as absorbers and connected to the diesel engine exhaust outlet (Fig.4). The scrubber consists of an inox steel column (2), which is assembled up to a nominal height of 200cm around the 250kW diesel generator's main exhaust gas (3). The stainless steel fan (4), which is specifically designed to operate at high temperatures (up to 400ºC), is connected to the main exhaust of the diesel engine, the main purpose of which is to redirect the part of the gasses emitted to two heat exchangers (5), in order to reduce the temperature of the gasses below 115ºC, so that the amine solution can have an effect on the CO 2 capture. To adjust and control the amount of gas passing through the packaging column (10 l/min), a needle valve (6) with a rotameter (7) are used. Additionally, two pumps were used, the first (8) to feed the packing column with NaOH solution (0,1l/min) to capture the SO x , while the second (9) was used to feed the second packing column with a Monoethanolamine (MEA) solution (0,1l/min) to reduce CO 2 emissions. Finally, at the inlet and outlet of the column, gas sensors (10) are installed to assess the CO 2 and SO x levels before and after treatment with a differential pressure drop sensors (11).   The installation was conducted in a liquid phase recycling approach supplied and controlled by two peristaltic pumps. Two multipoint liquid distributors were used, consisting of 9 needle orifices with an internal diameter of 1mm for NaOH and MEA supply. The evolution of gas state for SO X and CO 2 as well pressure drops through the bed were measured in real time and transferred to the PC via a data acquisition system

Results and discussion:-
Evaluation of the SO X and CO 2 content at the outlet of the scrubber without the intervention of the NaOH and MEA solutions for different applied loads The main purpose of this section is to assess the amount of SO x in the inlet of scrubber as well as the CO 2 level after combustion at 30%, 50% and 85% of applied loads. A SO 2 -B4 sensor from alphasense air manufacturer was used for SO 2 detection, while a MH-410D sensor from winsensor manufacturer for CO2 detection was employed. Table 4 shows the SO X and CO 2 level at the outlet scrubber. In addition, photos were taken with a thermal camera to assess temperature variation in heat exchangers in order to ensure a reduction in exhaust gas temperature as shown in figure 5 (a), (b) and (c).

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According to table 4, we can notice that the SOx and CO2 levels are lower when the charge increases. This can be explained by the fact that the combustion becomes better and the majority of the particles are burned under high loads.
Evaluation of the SOx content at the outlet of the scrubber with the intervention of the NaOH solution for different applied loads SO 2 associates with a salt in freshwater scrubbers and therefore does not react with the natural seawater bicarbonate. There are the coming reactions: A freshwater scrubber usually discharges 250 times less water than an open loop seawater scrubber. The bleed off is significantly smaller for fresh water units (0.1-0.3m 3 /MWh) and as a result, the concentration of pollutants is higher, making washwater cleaning easier [18]. Table 5 shows the results of the reduction, followed by a comparison before and after NaOH's intervention, see table 6 and figure 6. It should be noted that only 0.1 liters of NaOH solution has been injected into the packing column. In order to compare results, we calculated the average of SO X emissions before and after NaOH intervention and this for eight minutes of testing. Table 6 shows the average of SO x emissions, while figure 6 shows the comparison.  Figure 6:-Influence of the NaOH intervention on the SO X abatement with a 0,5% sulfur content fuel.
According to table 6 and figure 6, the reduction of the SO X emissions is 89% when the scrubber is fed with the NaOH solution. It can also be noted that due to better combustion in the piston chamber, the SO X emission rate is further reduced at high load. However, an increase in pressure drop in the packing column has been detected due to the fouling structured packing under a high load. Figure 7 shows the microscopic Sulphur particles stuck on the packed bed causing an increase in the pressure drop. Comparison of the SOx emissions before and after NaOH intervention Without NaOH With NaOH intervention 80

Pressure drop
The overall pressure drop consists of gas-liquid interactions and static head of the liquid phase in the packed beds with gas-liquid simultaneous flow. According to table 7, the pressure drop (inlet Vs outlet of the scrubber) increase by 9,93% after 3 minutes of operation between a low load (30%) and a medium load (50%), while it is 16,6% under a high load (85%). This can be explained by the increase in the flow and pressure of exhaust gasses when the load increase. Furthermore, the amount of the sodium sulfate (Na 2 SO 4 ) increases further due to the reaction causing the fouling of the packed beds in the column. Figure 8 shows the pressure drop across the different applied loads.  Carbon dioxide is considered as potential source for greenhouse gas (GHG) development. Different studies have evaluated that 3 to 4 percent of universal CO 2 emissions are attributable to marine vessels [19]. A 10 percent reduction in cruise speed is an effective operational methodology that offers a significant reduction in CO 2 and fuel consumption up to 20 percent over the same distance [20].
In this section, attention is given to reduce the carbon dioxide level at the exit of the scrubber by injecting a 0,1l/min of MEA solution. The following reversible reaction provides the basic reaction chemistry for an aqueous Monoethanolamine solution and CO 2 [21]: This is an exothermic reaction and per mole of CO 2 absorbed in MEA solution, 72KJ of thermal energy is released. Absorption normally occurs around 50ºC [21]. Table 8 shows the results of the reduction with a comparison before and after MEA solution intervention. It should be noted that only 0.1 liters of MEA solution has been injected into the packing column. Figure 9 illustrates the percentage reduction of the CO 2 after MEA solution intervention.  According to table 8 and figure 9, the CO2 rate has decreased by an average of 49%. However, CO2 level increased with the load. This can be explained by the fact that the turbo absorbs a larger amount of air when the load increases.

Conclusion:-
Ship emissions are one of the major issues affecting those interested in the maritime domain, as they have a negative impact on the marine environment. The present paper discussed the various wet scrubber technologies, which could carry out to reduce those emissions.
A two-stage packed bed closed loop scrubber systems for sulfur abatement and CO2 capture was examined. For the evaluation of the efficiency of the system, a soda solution (NaOH) for sulfur abatement and monoethanolamine solution for CO2 capture were used. Tests are conducted using a 250KW diesel generator filled with a 0, 5% sulfur content fuel. The results showed the possibility to achieve valuable emission reduction percentage for the SO X and CO 2 by an average of 89% and 49%. However, the accumulation of the sodium sulfate (Na 2 SO 4 ) in the packed bed due to the chemical reaction between the SO x and the NaOH solution, served further to the pressure drop in the scrubber by an amount of 17%. On the other hand, the application of this methodology by ship operators allows them to meet the requirements set by IMO established in 2015 and that is to burn fuel with a sulfur content of less than 0,1% percent in ECAs starting by January 2020.