Seawater Scrubbing Research Articles

Modeling the Reduction of Ship Exhaust Emissions through CO2 Capture/Chemical Conversion and SO2 Seawater Scrubbing

Modeling the Reduction of Ship Exhaust Emissions through CO₂ Capture/Chemical Conversion and SO₂ Seawater Scrubbing

Mass transfer model of packed seawater scrubbers for marine exhaust gas cleaning

Stricter limits on marine sulfur dioxide emissions have led to a need for action for ship operators. Installation or retrofit with exhaust gas scrubbers along with the continued use of sulfur-rich fuels is commonly deemed an economically attractive compliance choice. The development of adequate mass transfer models is therefore crucial for efficient scrubber design. In this work, a concise modeling approach for sulfur dioxide absorption in seawater scrubbers is presented. The model combines calculation methods for sulfur dioxide equilibrium molality in seawater with mass transfer properties (kGa and kLa) of the investigated packings. Packing kGa and kLa values are determined experimentally with standardized methodology using absorption and desorption test systems. The packed section is discretized for segment-wise calculation of sulfur dioxide molar flux. A pseudo Henry coefficient is used to jointly describe equilibrium molality of sulfur dioxide and its dissociation reaction products. The presented model is verified experimentally for five different structured packings through absorption measurements of sulfur dioxide in synthetic seawater. Model predictions for sulfur dioxide removal efficiency and effluent scrubbing liquid pH are in good agreement with experimental results over a range of operating conditions, especially for high separation efficiencies.

Marine Exhaust Gas Treatment Systems for Compliance with the IMO 2020 Global Sulfur Cap and Tier III NOx Limits: A Review

In the present work, the contemporary exhaust gas treatment systems (EGTS) used for SOx, PM, and NOx emission mitigation from shipping are reviewed. Specifically, after-treatment technologies such as wet scrubbers with seawater and freshwater solution with NaOH, hybrid wet scrubbers, wet scrubbers integrated in exhaust gas recirculation (EGR) installations, dry scrubbers, inert gas wet scrubbers and selective catalytic reduction (SCR) systems are analyzed. The operational principles and the construction specifications, the performance characteristics and the investment and operation of the reviewed shipping EGTS are thoroughly elaborated. The SCR technology is comparatively evaluated with alternative techniques such as LNG, internal engine modifications (IEM), direct water injection (DWI) and humid air motor (HAM) to assess the individual NOx emission reduction potential of each technology. Detailed real data for the time several cargo vessels spent in shipyards for seawater scrubber installation, and actual data for the purchase cost and the installation cost of seawater scrubbers in shipyards are demonstrated. From the examination of the constructional, operational, environmental and economic parameters of the examined EGTS, it can be concluded that the most effective SOx emission abatement system is the closed-loop wet scrubbers with NaOH solution which can practically eliminate ship SOx emissions, whereas the most effective NOx emission mitigation system is the SCR which cannot only offer compliance of a vessel with the IMO Tier III limits but can also practically eliminate ship NOx emissions.

CFD MODEL TO ANALYZE SO2 ABSORPTION IN A SEAWATER DROPLET

In the recent years, seawater scrubbers have become an interesting option to reduce SO2 emissions in marine engines. In this regard, this paper proposes a numerical model to analyze SO2 absorption in seawater. A single seawater droplet was analyzed, and the developed model was used to predict the influence of several parameters on the desulphurization efficiency, such as the droplet diameter, SO2 concentration, alkalinity and temperature. It was found that a droplet of 200 μm initial diameter can absorb up to 1.77∙10-14 mol of S for the parameters analyzed, and this reduction improves when the alkalinity and SO2 concentration are increased and diameter, seawater temperature and gas temperature are reduced. Differences up to of 21.5%, 19.8%, 2.2% and 16.3% in the S reduction were obtaining varying the SO2 initial concentration, alkaline initial concentration, initial liquid temperature and initial gas temperature respectively.

AN OVERVIEW: ENVIRONMENTAL AND ECONOMIC STRATEGIES FOR IMPROVING QUALITY OF SHIPS EXHAUST GASES

In spite of the fact that most of different transport means have achieved a significant reduction of their emissions quantity during the last few years; maritime field still suffers from the steady increase in the quantity of exhaust gases emitted from ships. As a result, the International Maritime Organization was prompted to issue a set of regulations for facing the seriousness of those emissions. The present paper handles the different methods which can be used to reduce the environmental damage caused by ship emissions. Through the study of the advantages and disadvantages of ships, emission reduction strategies; use of natural gas, selective catalytic reduction and sea water scrubbing systems have appeared as the best ways that can be utilized to reduce the environmental harms caused by ship emissions. Applicability of these methods aboard ships could vary from ship to another. Two high-speed passenger ships of different age were studied to evaluate the importance of applying these strategies. The results showed the possibility to attain valuable emission reduction percentage by using of selective catalytic reduction and sea water scrubbing systems, but they will be of high initial cost and will increase operating cost of both ships. On the other hand using of LNG as alternative fuel will be more convenient from the point of view of environment and economic issues for the newer existing ship.

Simulation investigation on marine exhaust gas SO2 absorption by seawater scrubbing

Ships have become an important source of SO2 emission in coastal areas with the rapid development of maritime transport. It’s of great significance to develop marine scrubber for reducing SO2 emission of ships. In this study, numerical simulation of a full-scale marine spray scrubber is conducted to investigate two-phase flow pattern and SO2 absorption process in the scrubber. A desulfurization model based on seawater absorbent is couple into the simulation, which considers the mass transfer between phases and seawater aqueous phase chemistry simultaneously. Distribution ring is introduced in the scrubber to enhance the desulfurization performance of the scrubber. The result of simulation shows that the distribution ring can optimize effectively the distribution of gas-liquid phases and enhance the SO2 absorption. Under vertical condition, the desulfurization efficiency could be promoted approximate 6% after installing distribution ring. The inclined condition resulting from the ship swinging could lead to the uneven distribution of droplets and an obvious decrease (8.7%) of desulfurization efficiency, whereas the desulfurization performance of scrubber could be ensured with distribution ring installed even under inclined condition. Finally, a spray scrubber design scheme has been developed and successfully applied in EGCS of a container ship. Test result shows the outlet average value of SO2/CO2 can be reduced to 3.55. Meanwhile, the consistency of test data and calculation result indicates the applicability of the numerical model established for the simulation and optimization of the scrubber in industrial applications also. Exhaust gas cleaning system (EGCS) is an effective method to reduce SO2 emission of marine industry. However, different from land desulfurization tower, the application of spray scrubber in EGCS faces more problems due to the different application scenarios and complex sea conditions (inclined condition resulting from ships swinging and so on) during sailing. In this work, a numerical model capable of investigating physical and chemical phenomena in the scrubber simultaneously is established, which can produce great amount of data for the operation instruction of EGCS and the design and optimization of marine spray scrubber. The distribution ring is introduced in the marine spray scrubber to intensify the SO2 absorption and enhance the desulfurization performance of scrubber under different working conditions.

Effect of seawater alkalinity on the performances of a marine diesel engine desulphurization scrubber

Since the last fifteen years, Flue Gas Desulphurization (FGD) plants based on seawater scrubbing found an interesting application in the maritime transportation, as an answer to the stringent regulations imposed by International Maritime Organization (IMO) on sulphur emissions. This work reports the experimental results on desulphurization in a pilot seawater scrubber (DN 400) from a marine Diesel engine (80 kW) operated under different loads (10, 25 and 50%). The pilot scrubber was fed with a gas velocity 0.15 m/s and a liquid to gas mass ratio 1-3 kg/kg. The scrubbing liquid was available at different alkalinity and salinity levels representing the ion speciation of marine water in different geographic areas. The experiments evaluate the SO2 removal efficiency of the scrubber as a function of seawater alkalinity and pH. Finally, the paper reports a correlation to assess the seawater flow rate required to comply with the current IMO restrictions. This correlation allows tuning the seawater flow rate during the ship navigation based on the registered marine alkalinities and to the operating conditions of the engine. The model can be integrated in the scrubber control system to identify optimal operating conditions and reduce pumping costs, helping to reduce the EEDI and the SEEMP ships energy indexes.

Simultaneous deSOx and deNOx of marine vessels flue gas on ZnO-CuO/rGO: Photocatalytic oxidation kinetics

Marine Pollution Convention has been updated to prevent the excessive emissions from diesel machine. For high concentrated, large fluxed SO2 and NO photocatalytic oxidation, a novel dual stages oxidation-scrubbing process was proposed. The p–n junction ZnO-CuO/rGO ternary catalysts were prepared via the co-precipitation route and supported on reduced graphene oxide (rGO). The UV–vis spectra showed that the bandgap Eg of ZnO-CuO/rGO was notably narrowed to 2.3–2.6eV for facilitating electron transfer, and its flat band potential of was −0.54V versus Ag/AgCl. The PL spectra and photocurrent curves revealed that the formation of heterojunctions and the introduction of graphene promoted an efficient separation of the photo-induced charge carriers. The photocatalytic activity of the ZnO-CuO/rGO with 5wt% GO was evaluated for simultaneous DeSOx and DeNOx, and 97% desulfurization rate and 64% denitration rate could be reached under GHSV 2000h−1 for 270min. In seawater scrubber, ZnO-CuO/rGO(5%) addition made SO32− conversion was 80.72%. The radical scavenging experiments demonstrated that holes (h+) and superoxide radicals (•O2−) contributed most to SO32− photocatalytic oxidation. Kinetic studies showed that SO32− oxidation on ZnO-CuO/rGO fitted the L-H model. The mechanism of photocatalytic oxidation in gas and liquid phases were also proposed to address the reaction pathway.

Modification of Sea Water Scrubber System into Fresh Water of Inert Gas System on the Crude Oil Tanker 85,000 DWT

Each ship carrying a hydrocarbon must be equipped with an inert gas system. On tankers, the function of inert gas is to prevent fires or explosions caused by oxygen levels contained in cargo tanks. Inert gas is produced by cleaning the exhaust gas boiler using a sea water scrubber system. However, seawater has corrosive properties that cause the use of material in scrubber system components to be resistant to corrosion. Therefore, through this research a modification of the sea water scrubber system was made into a freshwater scrubber system. The advantages of a freshwater scrubber system include a low corrosive level that causes the use of inexpensive materials. Modification of seawater scrubber systems into fresh water causes additional components to be made, including adding NaOH tank, expansion tank of freshwater, seawater pumps, freshwater pumps, NaOH pumps, heat exchanger, and wash water treatment unit. Economic calculations are carried out to determine the installation costs and operational costs needed from this modification. Based on the technical and economical analysis, modification of the sea water scrubber system into fresh water inert gas system of Crude Oil Tanker 85,000 DWT can be done with an estimated installation cost of 1.5 Bill. Rupiahs.

Constraints on eruption processes and event masses for the 2016–2017 eruption of Bogoslof volcano, Alaska, through evaluation of IASI satellite SO2 masses and complementary datasets

Bogoslof volcano, Alaska, experienced at least 70 explosive eruptions between 12 December 2016 and 31 August 2017. Due to its remote location and limited local monitoring network, this eruption was monitored and characterized primarily using remote geophysical and satellite techniques. SO2 emissions from Bogoslof were persistently detected by the Infrared Atmospheric Sounding Interferometer (IASI) satellite sensors. Of Bogoslof’s 70 explosive events, 50% produced measurable SO2 masses ranging from 0.1 to 21.5 kt, with a median and standard deviation of 0.7 ± 4.0 kt SO2, respectively. Here, we compare IASI-derived SO2 masses from Bogoslof events to complementary geophysical datasets to provide insights into eruption source processes, namely the degree of seawater scrubbing of water-soluble SO2 and variations in magma flux. Correlations with the number of lightning strokes and infrasound energy are expected to indicate magma-flux as a controlling process, while correlations with infrasound frequency index are expected to indicate variations in vent-water content as a controlling factor. These comparisons suggest that the measured SO2 masses are primarily a function of eruption magnitude (degassed magma mass) and that scrubbing of SO2 emissions by vent seawater may have exerted a minor effect on the observed SO2 masses. SO2 masses were combined with petrologic constraints on melt inclusion and matrix glass S concentrations to calculate degassed magma masses and volumes. The cumulative SO2-derived degassed magma mass and estimated volume (dense-rock equivalent) for the full Bogoslof eruption were found to be 2.8 × 1010 kg and 9.3 × 106 m3, respectively. When individual event masses are compared against event masses calculated using an empirical plume-height method, a strong correlation is found (R2 = 0.83), with better than order-of-magnitude agreement in most cases. These estimates of eruption masses provide useful information on the magnitude, behavior, and associated hazards of the 2016–2017 eruption, and potentially future unrest at Bogoslof volcano.

CFD Model to Analyze SO2 Absorption in a Seawater Droplet

In the recent years, seawater scrubbers have become an interesting option to reduce SO2 emissions in marine engines. In this regard, this paper proposes a numerical model to analyze SO2 absorption in seawater. A single seawater droplet was analyzed, and the developed model was used to predict the influence of several parameters on the desulphurization efficiency, such as the droplet diameter, SO2 concentration, alkalinity and temperature. It was found that a droplet of 200 μm initial diameter can absorb up to 1.77∙10-14 mol of S for the parameters analyzed, and this reduction improves when the alkalinity and SO2 concentration are increased and diameter, seawater temperature and gas temperature are reduced. Differences up to of 21.5%, 19.8%, 2.2% and 16.3% in the S reduction were obtaining varying the SO2 initial concentration, alkaline initial concentration, initial liquid temperature and initial gas temperature respectively.

Effects of scrubber washwater discharge on microplankton in the Baltic Sea

In 2020, the global cap of maximum allowable sulphur content in marine fuel will be reduced from the current 3.5% to 0.5%. Another way to reduce the sulphur emissions is to install a seawater scrubber that cleans exhausts but instead release acidic water containing nutrients and contaminants back to the marine environment. In the current study, scrubber washwater was tested on a Baltic Sea microplankton community. A significant increase in chlorophyll a, particulate organic phosphorus (POP), carbon (POC) and nitrogen (PON) were observed when the community was exposed to 10% scrubber washwater for 13 days as compared to the control. A laboratory experiment with the filamentous cyanobacteria Nodularia spumigena and the chain-forming diatom Melosira cf. arctica showed negative responses in photosynthetic activity (EC10 = 8.6% for N. spumigena) and increased primary productivity (EC10 = 5.5% for M. cf. arctica), implying species-specific responses to scrubber washwater discharge.

Modeling and Simulations of NOx and SO2 Seawater Scrubbing in Packed-Bed Columns for Marine Applications

Seawater scrubbing of nitrogen oxides and sulfur oxide from marine emissions was simulated in packed-bed columns exposed to static inclination and heaving/oscillating motions. Fourth generation random packings (Raschig super-Rings) while providing much smaller pressure drop than traditional Pall-Rings ensure comparable absorption efficiency for the pollutants. Complete removal of SO2 was predicted over the tested pressure range with absorption efficiency indifferent to scrubber inclination or heaving/oscillating motions. In contrast, NOx and CO2 absorptions are negatively impacted for inclined seawater scrubbers. Removal efficiency is not lowered significantly owing to larger scrubber pressure and because diffusion of N2O4 into the liquid phase is associated with a rapid pseudo first-order reaction. The asymmetrical oscillating motion of the scrubber degrades the removal performance which exhibits wavy patterns close to the steady-state solution of the average inclination angle. NO and CO2 absorption performance waves are moving toward a steady-state solution of vertical scrubber when the asymmetry of the two inclined positions of the scrubber downgrades. Symmetric oscillation and heaving motion led to performance disturbance waves around a steady-state solution of the vertical scrubber which are determined by the parameters of angular/heaving motion.

Meeting future emission regulation at sea by combining low-pressure EGR and seawater scrubbing

In the current study, the environmental performance of the first full-scale combined low-pressure exhaust gas recirculation (EGR) and seawater scrubbing system was investigated thoroughly onboard an LPG carrier operated on high-sulfur HFO. Results clearly show that the chosen approach allows around 70% $$\hbox {NO}_x$$ reduction and simultaneous elimination (98% reduction) of $$\hbox {SO}_x$$ emissions. This would allow compliance both with $$\hbox {NO}_x$$ Tier III and future ECA sulfur regulations, although it would result in minor fuel penalty due to slightly deteriorated combustion (effect of EGR) and increased backpressure (effect of scrubber). The performed chemical analysis of the water samples revealed a fairly good performance of the wash water treatment plant with water samples identified as a good-quality water almost against all measured compounds. The values for pH, turbidity and nitrates were also far below the IMO requirements. However, in terms of certain metals (vanadium, nickel and zinc) and PAHs (fluoranthene and pyrene), the quality of discharge water was somewhat poorer. These compounds also appear to be the main drivers of risk of the environmental damage as was determined by the PEC/PNEC analysis. Here, the sufficient dilution with ambient seawater is essential to bring down the corresponding concentrations to the acceptable levels, although the measured excessive pollution of ambient water in terms of arsenic, copper and molybdenum should be kept in mind. Finally, different sampling procedures (IMO MARPOL and US EPA VGP rules) were practically evaluated providing some ideas for their further improvement, as with wrong sampling the obtained results can be very misleading.

Modeling of SO2 seawater scrubbing in countercurrent packed-bed columns with high performance packings

Packed-bed columns with fourth generation random packings offer an attractive way to implement SO2 seawater scrubbing on-board large marine ships because of small two-phase pressure drop, high capacity and high SO2 removal efficiency. SO2 seawater scrubbing was investigated via an Eulerian 3-D model based on the macroscopic volume-averaged continuity, momentum, energy and species balance equations in the liquid and gas phases. The performance of SO2 seawater absorption process in packed-bed column reactors with fourth generation random packings can be enhanced by the increase of liquid flow rate and the decrease of liquid temperature. Consequently, SO2 seawater scrubbing on-board large marine ships improves significantly in the temperate oceans with an average temperatures between 10 and 20 °C. The increase of pressure improves the driving force of gas-liquid mass transfer and subsequently SO2 removal process which becomes completely at lower values of liquid-to-gas ratio. SO2 seawater scrubbing at higher pressure increases the capital cost and energy requirement but offers major improvements such as total removal of SO2 at large sulfur content of fuel and prevention of losing of engine power because of the large counter pressure to the incoming exhaust. The operation with extra packed bed height allows to amplify the gas–liquid contact time and consequently the absorption process performance.

Experimental investigation of seawater scrubbing of SO₂ in turbulent contact absorbers and spray absorbers

Experimental investigation of seawater scrubbing of SO₂ in turbulent contact absorbers and spray absorbers

Utilization of alumina-supported K2CO3 as CO2-selective sorbent: A promising strategy to mitigate the carbon footprint of the maritime sector

This paper investigates the application of K2CO3 supported onto porous alumina, as sorbent for selective CO2 capture in marine applications. Alumina-functionalized sorbents were prepared by incipient wetness impregnation achieving K2CO3 loadings from 3.6 to 14.1% wt. Carbonation tests were performed in a fixed-bed column at temperatures between 60 and 105 °C, as those typically occurring at the outlet of a scrubber and/or a waste heat recovery unit, with a model diesel engine exhaust (5% vol. CO2, 5% vol. H2O, balance N2). According to the carbonate loading, the sorbents may reach conversion degrees of carbonate up to 90% and overall capture capacity up to 0.66 mol kg−1 sorbent. Experimental data showed higher conversion degree and capture capacity compared with unsupported K2CO3, which is affected by significant intraparticle diffusion limitations. Steam regeneration tests performed in a fixed-bed column on the sorbent with 3.6% wt K2CO3 loading revealed that a temperature of 120 °C assures almost complete recovery of captured CO2 while preserving the sorbent carbonation degree for 10 consecutive carbonation/regeneration cycles. The preliminary design of a temperature swing carbonation/regeneration unit for on-board ship installation was performed for the reference case study of a passenger ship equipped with a 4.35 MW marine engine fueled with marine gas oil and with a commercial seawater scrubber for SO2 removal. The proposed unit appeared able to cut up to 30% carbon dioxide emission by using the sorbent containing 3.6% wt K2CO3 and operating the carbonation and regeneration stage at 60 and 120 °C, respectively.

Experimental and modelling analysis of seawater scrubbers for sulphur dioxide removal from flue-gas

Scrubbing with seawater is a reliable technology for flue-gas desulfurization in coal-fired power plants or in marine applications. The introduction of new regulations for emission control in Europe and the due increment of operational efficiency are pushing forward the optimization of scrubber’s design, for which packing columns may be a better solution compared to spray columns. The design of a seawater scrubber mainly relies on a correct assessment of the equilibrium conditions and of the mass transfer coefficients in the absorber. In this work, experiments are performed on a model flue-gas (32 m3·h−1) having a SO2 concentration in the range 500–2000 ppmv, treated in a packed column filled with a structured packing (Mellapak 250X®) at 1 atm and 25 °C, with liquid-to-gas ratio between 1.06 and 3.44 kg·kg−1. Three different absorbing solutions are investigated: (a) a seawater; (b) a basic solution obtained by adding 200 mg·L−1 NaOH solution to the seawater and (c) distilled water, used as benchmark. In order to analyze the packed column tests, SO2 equilibrium absorption tests at low concentrations (100–2000 ppmv) are carried out in a feed-batch reactor, using the same absorbing solutions tested in column tests. The experimental tests in packed column indicate that, for SO2 concentration as low as 500 ppm, an absorption efficiency above 98% can be achieved by using liquid-to-gas mass ratio about to 2.91 kg·kg−1. In this condition, few differences appear among solutions (a) and (b). For the highest SO2 concentration (i.e. 2000 ppmv), a maximum of 85% efficiency is observed for liquid-to-gas mass ratio of 3.44 kg·kg−1. Modeling of both the equilibrium and the dynamic data are implemented in Aspen Plus® V 8.6. However, while modeling assures a very good prediction of the equilibrium data, it is not able to properly describe the dynamic test results, with a systematic underestimation for tests having a removal efficiency higher than 85%.

Combined poisoning effect of K+ and its counter-ion (Cl− or NO3−) on MnOx/TiO2 catalyst during the low temperature NH3-SCR of NO

Heterogeneous catalysts for the low temperature NH3-SCR of NOx can be strongly deactivated due to the accumulation of specific compounds deriving from an upstream desulphurization unit, such as a Sea Water Scrubber. In this work, we set out to investigate the specific role of K+ and of its counter-ion (Cl− or NO3−) on the combined poisoning effect induced on the catalytic features of a MnOx/TiO2 system. Poisoning of the catalyst was performed ex situ by impregnation with two target loadings of each K salt, followed by a mild thermal treatment at 250°C, corresponding to the maximum operating temperature of the SCR system. Fresh and poisoned catalysts were characterized by means of ICP-MS, BET, H2-TPR, NH3-Adsorption, NH3-Temperature Programmed Desorption-Reaction and in situ DRIFT and the impact of poisoning was assessed and compared for the NH3-SCR of NO as well as for the NH3-SCO (Selective Catalytic Oxidation) reaction.

Eco-environmental analysis of ship emission control methods: Case study RO-RO cargo vessel

Air pollution from ships mainly comes from using heavy fuel oils for power generation. Although, these fuels are economical, they produce significant amounts of pollutant emissions. Two methods can be considered to cope with the International Maritime Organization's new emission regulations, either by using diesel fuel or marine gas oil with exhaust gas reduction measures, or by using alternative fuels like Liquefied Natural Gas (LNG). The aim of the current research is to compare between these two methods from environmental and economic points of view. As a case study, medium speed RO-RO cargo vessel operating in the Red Sea area has been investigated. Results show specific environmental benefits of selective catalytic reduction method for reducing NOx emissions by 90% with cost effectiveness of 873.5 $/ton and SOx emissions by 98% with 3115 $/ton in case of using seawater scrubbing. On the other hand, LNG appears the optimum proposed solution from environmental and economic points of view. It reduces NOx, SOx and CO2 emissions by about 77.6%, 92.5% and 14.5% with cost effectiveness of 1486 $/ton, 4084 $/ton and 160.8 $/ton, respectively.