2

/ / 2006-10- 

### Preface

This report has been writte n in cooperation between:

MARINTEK – Energysystems & Environment SINTEF - Water and Environment and NIVA – Norwegian Institute for Water Research

Some supporting dispertion calcula tions has been undertaken by CFD Norway A/S SINTEF Materials and Chemisty

Furthermore, information has been exchanged in common interest with Wärtsilä Finland Oy, VTT Technical research centr e of Finland and DNV.

The work has been sponsored jointly by Norweg ian shipowners and the Research Council of Norway as Work Package 3 of the MARULS project.3

/ / 2006-10- 

### Summary

Background Regulation 14(4)(b) of MARPOL A nnex VI requires ships to document that discharges from a possible exhaust gas-SOx cleaning systems (E GCS-SOx) have no adverse impact based upon criteria communicated by the authorities of the port State to the Organization.

IMO Guidelines for on-board exhaust gas-SO x cleaning systems (MEPC resolution 130.53) contain some information on discharges from th e EGCS-SOx. At MEPC 53, however, IMO is in the process of developing more specific recomm endations and criteria relevant to EGCS-SOx wash water discharges.

Taking advantage of data from trials using exha ust gas seawater scrubbe rs conducted in Norway in the early nineties as well as up to date toxc isity data and discharge modeling tools, a set of possible criteria have been developed and subm itted as a proposition IMO MEPC 55. This report provides background information regarding th e development of this proposition.

Outline of discharge criteria development The development of discharge criteria consists of three main steps;

.1 Identification of harmful compounds and effects. .2 Identification of the maximum permissible c oncentration that can be sustained over time for each of the compounds identified, the Pr edicted No Effect Concentration (PNEC). .3 Evaluation of the expected environmenta l concentration of eac h discharge compound, designated as Predicted Envir onmental Concentration (PEC).

A similar procedure is used to assess other possible effects of the discharge such as change in temperature, pH, Dissolved Oxygen (DO) , Chemical Oxygen Demand (COD) etc.

The PNEC-concentration is derived from scientific toxicology studies, either by use of species sensitivity distribution curves or by applying safety factors to realis tic worst case toxicity levels. These factors are very high when the amount of re levant studies is low and less conservative when the toxicity to several species is better known.

The PEC is usually derived from a study where di scharge measurement data and predictions is combined with distribution models.

A risk to the marine environment is indicated if the PEC is higher than the PNEC. However, according to international practice set out by UN, discharges resu lting in local concentrations that are higher than no-effects limits for long term (chronic) exposure can be acceptable in the immediate vicinity of the discharge point if the discharge is rapidly diluted.4

/ / 2006-10- The concentration of substances and variations in parameters in the di scharge water depends on the specific wash water rate, which may vary by a factor of 300 between EGCS-SOx principles. However, pollutant mass flow may be virtually the same. Hence concentration limits must be related to a nominal wash water rate.

Predicted No Effect Concentrations (PNECs) can be obtained from regulations (such as EU, USEPA, UK) or in scientific literature when standards are not available.

Differences in sensitivity to contaminants and other environmental stressors between freshwater and marine organisms are small, particularly when compared to the safety factors commonly used to derive PNEC values. For practical risk as sessment purposes one may regard freshwater, brackish water and marine species as equally se nsitive. PNEC values could thus be suitable world-wide with few exceptions. The principal di fference between locations would be the amount of discharge (i.e. traffic density) and how rapidly the water is exchanged.

Port States will have to consider both the extent of ship traffic, and natural dilution effects such as provided by wind, current and rivers when defining their local criteri a. To avoid proliferation of criteria it is proposed that IMO develops a set of default criteria that represent typical situations. (Level 1, 2 and 3) The Port State would then have the opportunity to choose one of the criteria on the list which would significantly ease verification of compliance.

Proposed criteria Waste water dispersion modelling show s that discharges are rapidly dilluted when the ships are in motion. The most critical situation is when the ship is at quay. In this case, it is likely that an average plume dilution of 1:150 may be obtained w ithin the near field (2 0 m) and within 6-7 minutes. Taking these dilution factors and the PN EC values for the actual scrubber components into account we have estimated the worst case discharge concentrations that may be allowed without the PEC/PNEC ratio exceedi ng 1 outside the near field.

In those cases where the scrubber discharge meas ured in trials was lower than the proposed criteria by a factor of ten, that particular substance was considered not to require a dischargecriteria. The modelling fu rther indicated that PNEC valu es can be obtained even with pH=0 and DO = O at outlet, indi cating that no regulation would ge nerally be needed for pH and COD.

As previously argued, to avoid proliferation of criteria it is advised that IMO develops a set of default criteria that represent typical situations. (Lev el 1, 2, 3, etc) The Port State would then have the opportunity to choose one of the predefined crit eria on the list which wo uld significantly ease verification of compliance and provide much needed design targets for EGCS-SOx manufacture. The resulting criteria proposition followi ng this logic is shown in Table 15

/ / 2006-10- Table 1 Proposed discharge water limits (μg/liter)

Criteria level* 1 2 3 “Safety Margin” 1 10 100 Nickel - 30 3 Vanadium - - 150 Copper - 40 4
Lead - - 12
THC 4500 (4.5 ppm) 450 (0.45 ppm) 45 (0.045 ppm) *At nominal wash water rate of 44 kg/kWh (repres entative of trials and dispersion models used)

These proposals are made based on results from two specific trials. They should be seen in conjunction with experiences from other trials, st udies as well as capabilities of water cleaning systems and means of verification. It is anticipa ted that some revision of the existing EGCS-SOx guideline, particularly chapter 7 (wash water mon itoring) and chapter 17 (wash water), could be appropriate when using this approach. An a dditional cosmetic criterion demanding no visible discharge and absolute limit values irrespective of wash water rate could also be considered.

Selection of predefined discha rge criteria by port States In order to select predefined discharge criteria, the port State would have to identify the rate of water exchange and the anticip ated discharge from scrubbers in the area in question. The concentration of contaminants in the area can then be calculated assuming different discharge levels and compared with PNECs as provided above or other as deemed necessary. The port state could then select the least stringent set of criteria which provide sufficient environmental protection.6

/ / 2006-10- 

### Table of Contents

1. Introduction

.............................................................................................................................. ........7

2. Exhaust Gas SOx Cleaning Systemes (EGCS-SOx) .........................................................................8

3. Principles for the development of EGCS-SOx discharge criteria ................................................10

4. Identification of harmful compounds in EGCS-SOx discharge water ........................................12 4.1 Harmful compounds from the exhaust gas .................................................................................12 4.1.1 Exhaust gas hydrocarbon compounds ................................................................................12 4.1.2 Exhaust gas Particulate Matter (PM) ..................................................................................13 4.2 Harmful compounds from the the sea wa ter used to clean the exhaust ......................................15 4.3 Harmful compounds and effect from the EGCS-SOx ................................................................15 4.4 Results of discharge water analysis from ECGS-SOx trials .......................................................16 4.4.1 Acidity

............................................................................................................................... .18 4.4.2 Oxygen demand ..................................................................................................................19 4.4.3 Particulate matter in untreated discharge water ..................................................................19 4.4.4 Metals in untreated discharge water ...................................................................................19 4.4.5 Hydrocarbons ......................................................................................................................20 4.5 General remark – concentrations vs flux ....................................................................................20

5. Toxicity of scrubber discharges and safe environmental levels ....................................................20 5.1 Risk assessment of discharge components - the PEC/PNEC approach ......................................20 5.2 PNEC derivation for relevant metals ..........................................................................................21 5.3 Compliance with other water regulation .....................................................................................22 5.4 PNEC derivation of organic compounds ....................................................................................23 5.5 PNEC derivation of other discharge compounds ........................................................................25

6. Prediction of environmental concentration ....................................................................................26 6.1 Modelling of discharge dilution from a single ship ....................................................................26 6.1.1 Dilution of discharges from a single ship in open sea ........................................................26 6.1.2 Dilution of discharges from a single ship at port operation ................................................28 6.1.3 Dilution of discharges from a single ship at quay side manoeuvring .................................28 6.1.4 Summary: Dilution of discharges from a single ship .........................................................28 6.2 Accumulation of discharges – local and regional effects ...........................................................29 6.2.1 The Oslo Fjord Case study – regional effects .....................................................................29

7. Current discharge criteria ................................................................................................................31

8. Proposed waste water discharge criteria for exhaust gas scrubbers ............................................31 8.1 Sensitivity of marine and brackish water organisms to contaminants ........................................31 8.2 Proposed waste water criteria for seawat er scrubber discharges from vessels at sea .................32 8.3 Proposed waste water criteria for seawat er scrubber discharges in closed waters .....................33

9. GLOSSARY

.............................................................................................................................. ......36

10. REFERENCES

............................................................................................................................... ...37

APPENDIX 1: Report CFD-Norway
APPENDIX 2: Memo Sintef Materials & Chemistry7

/ / 2006-10- 

### 1. Introduction

Emissions to air from international shipping ar e regulated by IMO in MARPOL Annex VI which entered into force on May 19 th 2005. Regulation 14 of MARPOL Annex VI limits sulphur emissions by placing a global limit on the sulphur content of marine fu els of 4.5% by mass. Regulation 14 further limits sulphur emissions in certain geographical areas, so called Sulphur Emission Control Areas (SECAs). In these areas, ships may only use fuels containing up to 1.5% sulphur or employ an exhaust gas SOx cleaning syst em (EGCS-SOx) that delivers an equivalent reduction in sulphur emissions. The SECA regulati ons will be effective for the Baltic Sea from May 2006 and for North Sea & English Channel from November 2007.

Discharges from exhaust gas SOx cleaning system are regulated in regula tion 14(4)(b) which inter alia reads: ... Waste streams from the use of such equipm ent shall not be discharged into enclosed ports, harbours and estuaries unless it can be thoroughly documented by the ship that such waste streams have no adverse impact on the ecosystems of such enclosed ports harbours and estuaries, based upon criteria communicated by the authoritie s of the port State to the Organization. The Organization shall circulate the criteri a to all parties to the Convention

...

No port State has, at the time of writing, communicated such criteria to the IMO.

Some guidance to the monitoring and handling of discharges are included as part pf the Guidelines for on-board exhaust gas-SOx cleaning systems adopted by IMO in resolution MEPC.130(53).

According to this guideline, the EGCS-SO x unit’s wash water systems should:

(a) eliminate, or reduce to a level at wh ich they are not harmful, hydrocarbons, carbon residue, ash, vanadium, other heavy metals , and other substances contained within EGCS-SO x unit’s wash water that may have an adverse impact on ecosystems if discharged overboard, (b) ensure that the approach adopted, to c ontrol wash water quality and residual waste is not achieved in a way that causes po llution in other areas or environmental media, (c) also taking into account guidelines to be developed by the Organization.

As of today, the guidelines referred to in bulle t (c) of the Guidelines for on-board exhaust gasSOx cleaning systems have not been developed. At its last meeting, the appropriate committee, MEPC 54, failed to make progress in the development of these guide lines, principally due to lack of information. MEPC 54 thus decided to extend its call for information on this matter.8

/ / 2006-10- The lack of IMO guidance and port State cr iteria makes the speci fication of EGCS-SO x unit’s difficult. Such criteria are thus urgently needed.

The work contained in this report has been done in an effort to contribute to the development of discharge criteria. The result of this work will be communicated to the Norwegian Maritime Directorate who in turn will submit results to the IMO as deemed appropriate.

EU regulations are not of primary in terest in this report which is written in the interest of the IMO process. It should, however, be mentioned that the European Comission has also implemented 1.5% sulphur SOx emission regulation for ship s in SECA area through Directive 2005/33/EC. The European Union basically impose the same require ments as IMO within SECA and the additional requirement that:

1. the same 1.5% sulphur limit applies to fuel s used by passenger vessels on regular services between EU ports from 19 May 2006; 2. fuel used by inland vessels and by seagoing ships at berth in EU ports is limited to 0.1 % sulphur, from 1 January 2010

Directive 2005/33/EC also opens for exhaust gas SOx cleaning as long as equivalent or higher reduction in sulphur emissions can be demonstrated with no adverse effect on the environment.



### 2. Exhaust Gas SOx Cleaning Systemes (EGCS-SOx)

It is generally acknowledged that EGCS-SOx units, at least in the short term, will be based on the principle of sea water scrubbing wi th or without the use of a chemical additive. These units have the potential to remove a very high fraction of the SO 2 in the exhaust. The use of such equipment can thus permit much larger emission reductions than is achievable with low the use of sulphur residual fuels.

Exhaust gas scrubbing is a process where the exha ust gas is contacted with a liquid (most often seawater) for select ive absorption of SO 2 . Once the SO 2 is absorbed into the sea water, the SO 2 is converted by reaction with alkali ne material in the liquid to SO 3 and finally SO 4 . The conversion of the SO 2 helps the sulphur to stay in the water and allows more SO 2 to be absorbed. For this reason, the alkalinity of the water is important to the efficiency of the scrubber. The alkalinity in seawater is normally a function of salinity according to the relation

alkalinity (mmol/l) = 0.0697* salinity (psu) 1

1 PSU = Practical Salinity Unit, in practice the same as per mille9

/ / 2006-10- This relation m a y be m o dified a nd even reversed in areas of st rong freshw ater input to the sea where the alkalinity of the freshwater is high due to m i neral com position in the watershed. Rivers running trough a calcite area will ha ve increased alkalinity. In su ch situations the calculation above gives an underestim ate of the alkali nity, and hence represents a worst case.

Since the alkalin ity of s ea water is c o m p arative l y low, large quantity of sea water is n eeded. Even more scrubbing water w ould be needed in bracki s h water regions such as the Baltic Sea. The alkalinity of sea water can in certa in regions also vary significantly with tim e due to variab tions in winds, currents, m e lting of ice etc.

Different scrubber designs have been developed to obtain m a xim u m contact area between the sea water and exhaust gas. T h e exhaust gas m a y be si gnificantly cooled in the scrubber. To preven white sm oke and ensure a buyoyant exhaust, the exhaust m a y be reheated. One option is heat exchange between the hot exhaust from the engine and the cold exhaust leaving the scrubber. A principal arrangem e nt of a sea wate r scrubber is shown in Figure 1.

Figure 1 Principal arra ngemen t of seaw ater scrubber unit10

/ / 2006-10- The amount of water needed to clean the exha ust will depend on a number of factors including system design, fuel sulphur content, SOx emi ssion target, alkalinity of the water and use of chemicals. Some field testing experience indicat es that pure sea water consumption needed for near-complete (~ 90%) SOx removal will be in the range of 40-100 kg/kWh. This water requirement can be

• Approximately halved if the system is designed according to current minimum requirements (emission equivalent to 1.5% sulphur fuel)

• Significantly increased in fresh water and brackish water

• Very significantly reduced if alkaline chemicals are added to the sea water

Sea water scrubbing will also remove some of the particulate matter generated during combustion. Sea water scrubbing is also capable of removing some NO 2 from the exhaust. Since the fraction of NO 2 in NOx is usually about 5% (t he remainder being NO which is not appreciably affected), the potential for NOx removal is limited. (The use of chemical additives could potentially alter this)

The principal challenge with sea water scrubbing is not solely to reduce th e SOx emissions, but to do so while:

• maintaining a buoyant exhaust

• maintaining minimum consumption of space, weight and energy

• maintaining minimum pressure drop in the exhaust

• keeping discharge water emissions at a level where it is not harmful

• preventing corriosion

• prevent water droplets in exhaust

Discharge of wash water is regulated in ports, ha rbours and estuaries. In case of scrubbers using chemical additives, temporary storage may be po ssible; however in case of scrubbers relying on sea water only, storing used wash water on-board, even termporarily, will be difficult due to the large quantities needed and because the wash wate r will be corrosive. Hence the wash water will generally have to be cleaned (as necc esary) and discharged continuously.

As indicated in the introduction to this report , discharge criteria for EGCS-SOx wash water composition must be developed.



### 3. Principles for the development of EGCS-SO x 

### discharge criteria

Man-made impact on the marine ecosystem is expr essed at all levels of biological organisation, from sub-individual (biochemical and physiological effects), via individua l and population levels to the ecosystem level. Covering all these levels of effects in a risk assessment context is impractical and will not necessarily result in a better protection of marine resources.11

/ / 2006-10- GESAMP (the Joint Group of Experts on the Scie ntific Aspects of Marine Pollution in the UN system) has given the following definition of ma rine pollution: “Polluti on means the introduction by man, directly or indirectly, of substances or energy into the marine environment (including estuaries) resulting in such dele terious effects as harm to livi ng resources, hazards to human health, hindrance to marine activities including fish ing, impairment of quality for use of seawater and reduction of amenities” (GESAMP 1991).

Since man made effects on individual organism s not necessary results in effects on a higher ecological level, the definition limits pollution to those perturbations which have an impact on populations and/or ecosystems. This limitation is very important when assessing significant spatial end temporal impact s from scrubber discharges.

In practical terms, this means that discharges re sulting in local concentrati ons that are higher than no-effects limits for chronic exposure can be acceptabl e if the discharge is rapidly dilluted. Part of the challenge when defining discharge criteria is deciding how rapid the dilution must be or – in other words – how large water volume can be pe rmitted to be ‘affected’ without resulting in effects on any marine populations . Naturally, this may vary from one location to another. The following steps must generally be followed in order to develop such discharge criteria:

The first step in the process of the development of discharge criteria is the identification of harmful compounds that must be controlled.

The second step is identifying the maximum permi ssible concentration that can be sustained over time for each of the compounds identified. This leve l is often designated as PNEC (Predicted No Effect Concentration). The PNEC-concentration is derived from scientif ic toxicology studies, either by use of species sensitiv ity distribution curves or by applying safety factors to realistic worst case toxicity levels. These factors are very high when the am ount of relevant studies is low and less conservative when the toxicity to several species is better known.

The third step is to evaluate the expected environmental concentration of each discharge compound, often designated as PEC (Predicted Environmental Concentration). A risk to the marine environment is indicated if the PEC is higher than the PNEC. According to the GESAMP principle the risk will be accepta ble if PEC exceedes PNEC only in the immediate vincinity of the discharge point, which may result in effects on individuals but not on populations. However a PEC>PNEC value cannot be accepted for a larger area where the risk for population effects is present.

Port States will have to consider both the extent of ship traffic, and natural dillution effects such as provided by wind, current and ri vers when defining their local cr iteria. To avoid prolifieration of criteria it is advised that IMO develops a set of default criteria that represent typical situations. (Level 1, 2, 3, etc) The Port State would then ha ve the opportunity to choose one of the criteria on the list which would significantly ease verification of compliance.12

/ / 2006-10- 

### 4. Identification of harmfu l compounds in EGCS-SO x 

### discharge water

The discharge water from the EGCS-SO x unit contains material from three sources: 1. the exhaust gas exiting the engine (air, fuel, lubrican t and combustion products); 2. the sea water used to clean the exhaust 3. the scrubber itself (possible reaction pr oducts and possible chemical additives)

4.1 Harmful compounds from the exhaust gas The composition of the exhaust ga s will vary with engine type, engine age, operating conditions, fuel and lubricating oil compos ition. Table 1 indicates concen tration levels of the main constituents in the exhaust gas from 4 stroke diesel engines. The concentration can vary considerably for some of the constituents depending on engine load (fuel/air ratio) and fuel composition

Table 2 Typical exhaust gas concentration levels in exhaust gas from 4 stroke diesel engines.
Component Concentration level (Vol.-%) Nitrogen - N 2 75,6 (74,3-77) Oxygen - O 2 12,5 (11,25-15,5) Carbon dioxide - CO 2 6,2 (4,0-6,5) Water vapour - H 2 O 4,5 (4-8) Argon - Ar 0,9 Nitrogen oxides - NO x 0,15-0,20 Sulphur oxides - SO x 0,01-0,15 Hydrocarbon compounds HC, <0,03 CO, <0,03
Particulate matter 0.5-1.5 g/kWh on heavy fuel

All substances in Table 2 can be captured or to some extent entrained in the EGCS-SO x washwater. Of the elements on this list, however, it is mainly the particulate matter and hydrocarbons that is of interest as potentially harmful pollutants. Particulate matter is of concern primarily due to its content of potentially harmful contaminants (cf chapter 4.1.2.).

4.1.1 Exhaust gas hydrocarbon compounds The hydrocarbon compounds are principally derived from fuel that has not been burned or is only partly burned. Hydrocarbon compounds can also originate in lubri cating oil. Hydrocarbon compounds are generally biodegradable. Certain hydrocarbon compounds are more harmful than others. In particular, the polyaromatic co mpounds PAH. Some of the hydrocarbon compounds, and particularily the larger molecules such as P AHs, will contribute to the formation of particles13

/ / 2006-10- or associate strongly with soot particles. The i ssue of PAHs is discussed futher in conjunction with particulate matter.

4.1.2 Exhaust gas Particulate Matter (PM) Particulate matter is small, solid or liquid substan ces that can be collected on a filter in the exhaust stream. The formation of the particles is an ac cumulation process. The amount and size of the particles will depend upon where and how the pa rticulate matter is collected. There are two fundamentally different standard proc edures for the measurement of PM.

ISO 8178 – where particles are collected afte r dilution in air which promotes particle growth by condensation ISO 9096 – where particles are collected on a hot filter in order to avoid condensed

matter

The total amount of PM measured depends on the measurement method and fuel quality. An example is given in Table 3.

Table 3 Particulate mass PM in exhaust gas as a function of the fuel sulphur content.
Fuel sulphur content ISO 8178 ISO 9096
% g/kWh g/kWh
1.0 0.6 0.2
2.5 1.2 0.4

Particulate emissions are affected substansially by the ash and sulphur content of the fuel used. Particle size is variable, but of great importa nce because it affects dispersion and how harmful they are. Figure 2 illustrates classifi cation and variation in particle size.

The composition of particles of different sizes is di fferent. Generally, the sm allest particulates are condensed water, sulphuric acid and hydrocar bons. Intermediate particles contain more carbonaceous compounds, metal oxides, and ash. Larger particles contain relatively less carbonaceous compounds and are dominated by metal oxides and ash.

The particulate matter contains a variable mixture of compounds, most importantly

• Soot

• Ashes

• PAH and PAH-derivatives.

• Aldehydes, alkanes and alkenes

• Unburned fuel or incombustible elements in the fuel

• Metal salts like sulphates14

/ / 2006-10- Figure 2 Particu l ate s i ze and classification

Fi ne parti c l es PM 2, 5 Particulate matter PM 10

10μm 1 0,01 0, 2,5

100 10 1000 2500 10000

Many of the PAHs and PAH-derivatives, especia lly nitro-PAHs, have been found to be potent mutagens and carcinogens. Analysis data of partic les generated in a m e dium speed engine using residual fuel oil 380 cSt/50 o C at 100 % load is shown in Table 4. The analyses refer to dry particle s.

Table 4 Analysis of marine dies el particula t e matter

Metal oxides and sulfates 65 % Carbon (soot) 25 % Hydrocarbons (fuel and lube oils) 10 % including traces of
PAH 1 7 ppm Plychlorinated biphenyls (PCB) 17 ppm Chlorophenols 4 0 ppm Chlorobenzenes 4 4 ppm Polychlorinated dibenzodioxins (PC DD) 3,9 ppb Polychlorinated dibenzofurans (PCDF) 2,8 ppb

Table 5 gives an exam ple of a m easurem ent perform e d with the ISO 9096 m e thod of a W 6 L20

m e dium spe e d engine operating on high ash HFO (2.6 % S) and 100 % load, in %-m a ss. nm

Ultrafine p articles15

/ / 2006-10- Table 5 Elemental composition of particles of different size (%)
90 nm particles 8 micron particles
Silicon Si 0.5 0.3 Sulphur S 11.2 11.8 Nickel Ni 1.9 1.1 Sodium Na 3.5 0.8 Calcium Ca 0.3 0.1 Oxygen O 43.3 34.6 Carbon C 10.6 41.8
Iron Fe 0.4

- Vanadium V 28.2 9.6 TOTAL 100.0 100.0

Some fuel constituents are uncombustible. In general, these uncombustible compounds will be emitted from the engine as particulate matter. Therefore, some aspects of the paticle composition will mirror the fuel composition.

4.2 Harmful compounds from the the sea water used to clean the exhaust Naturally, any harmful compounds entering the EGCS-SOx unit with the seawater used for scrubbing will be expected to come out as part of the wash water. This is, however, not an additional pollution, and the issue is not gene rally expected to be problematic, however background levels must be considered when de termining discharge limits and monitoring.

4.3 Harmful compounds and eff ect from the EGCS-SOx Harmful compounds can enter the washwater as resu lt of chemical reacti ons in the EGCS-SOx unit. The absorption of SOx will also cause th e seawater pH to drop and consume dissolved
oxygen.

Chemicals may be added to improve the SOx rem oval or reduce the water consumption needed to achieve a given SOx reduction rate. This is particulary attractive when the alkalinity of the sea water is low. The most common additives in land based plants are lime and sodium hydroxide.

Sodium hydroxide (NaOH) can be supplied either as granulate or as concentrated solutions (up to 40 %). Handling and dosing is more convenient in the liquid form. The use of NaOH does not result in increased precipitati on since sodium sulphate and sulphite are very soluble.

Neutralization with lime or Ca(OH) 2 results in the formation of large amounts of gypsum (CaSO 4 ). Although the product is considered harmless to the environment it could create a visible plume after the ship which may be unwanted. Aslo, the product is insoluble in water and tends to16

/ / 2006-10- settle in tanks and pipes, part icularily where the flow is slow . For practical reasons lime is generally considered unsuitable fo r use onboard a marine vessel.

Small amounts of wear metals fr om the scrubber may al so show up on analysis of scrubber water.

4.4 Results of discharge water anal ysis from ECGS-SOx trials MARINTEK has coordinated two ship trials of ECGS-SOx units. Both units were based on scrubbing exhaust with pure seawater , and neither used a ny after-treatment of the discharge water. Some key information from these two trials is shown in Table 6.

Table 6 Key information from ECGS-SOx trials coordinated by MARINTEK
Ship Kronprins Harald Fjordshell Propulsion Engines Wärtsilä Sulzer 12ZAV40 * 2, 6ZAL40 * 2 (4 stroke) Sulzer 6RND76, 10400 kW (2 stroke) Ship Owner Color Line Norske Shell Shipping
Test Year 1991 1993 Description Part flow prototype using spray, high swirl (cyclone) and packaged bed with counter current water flow. 1:10 scale prototype with inlet venturi/ spray and mist catchers based on inert gas generator. Combined with SCR Water consumption 64 m 3 /h at 8 bar ~ 50 kg/kWh at maximum load (constant water rate) Measured SO 2 reduction 57 % in port (from 70 to 30 ppm) 73% in transit (from 454-121 ppm) 90 % over a wide range

The scrubbers and analysis have been made at different operating conditions:

Transit: Loaded ship at service speed Port operation: Approaching por t at reduced speed (4 knots) Quay side maneuvering: (0 knots) , same power as port operation17

/ / 2006-10- Table 7 Discharge water analysis data
Washing

water characteristic Unit Intake/Outlet Fjordshell M/S Kronprins Harald

Transit Port operation Transit Port operation Salinity p.p.t 19,1 19,0 17,4 14,5
Intake 12,6 9,8 n.a. n.a. Temperature o C Outlet 23 17,2 n.a. n.a. Intake 2,71 2,76 1,4 1,18 SO 4 g/l
Outlet 2,91 2,82 1,83 1,46
Intake n.a n.a <0,5 <0,5 SO 2 mg/l
Outlet n.a n.a <0,5 57
Intake 8,01 7,96 8,11 7,95 pH
Outlet 2,95 3,76 3 2,7
Intake 2,1 n.a. n.a. n.a. TOC mg/l
Outlet 2,7 1,5 n.a. n.a. Intake n.a n.a. n.a. n.a. COD mg/l
Outlet 33,3 10 n.a. n.a. Intake 0,42 4,3 0,6 2,3 Particles and

soot mg/l
Outlet 0,68 0,88 14,7 14,7
Intake 0,031 0,053 <0,1 <0,1 Hydrocarbons mg/l
Outlet 0,081 0,045 1,0 1,7
Intake 62,5 43,9 17 38 AOX μ g/l Outlet 25,3 33,2 700 51
Intake <0,1 <0,1 n.a. n.a. PAH μ g/ Outlet <0,1 <0,1 n.a. n.a. Intake 59,8 n.a. n.a. n.a. PCDD pg/l
Outlet 13,7 n.a. n.a. n.a. Intake 50,3 n.a. n.a. n.a. PCDF pg/l
Outlet 291 n.a. n.a. n.a.

Table 8 Measurement principles used in trials – discharge water18

/ / 2006-10- Parameter Measurement principle Water sample particulate material weight Norwegian Standard NS 4733

Salinity Titration by silver pH Electrodes
SOx Gravimetry(BaSO 4 )
THC Gas Chromatography
PAH Gas Chromatography
AOX SCAN-W9-89 Cu, Pb, Cd, Ni, V Atomic absorption, NS 47771 As, Hg, Zn Atomic absorption – hydride method
Cl Titration by silver
Cr 6+ Photometric (diphenylcarbazid) PCDD (polychlorinated dibenzo-p-dioxines) Gas chromatography, Mass spectroscopy, conforming to EN-450001

PCDF (polychlorinated dibenzofurans) Gas chromatography, Mass spectroscopy, conforming to EN-450001

Temperature Chromel-Alumel thermocouple
Flow Electromagnetic flowmeter (Fisher&Porter ND100)

Table 9 Measurement principles used in trials – other parameters

Parameter Measurement principle Gas flow Pitot tube conforming to ISO 3966
CO NDIR, Rosemount Binos 100, calibrated at 804 ppm
CO 2 NDIR, Rosemount Binos 100, 0-20%, calibrated at 4,13%
O 2 Paramagnetism, Signal 8000, 0-25% , calibrated in air (20.95%)
NO x CLA, Signal 4000, Calibrated at 855 ppm
HC FID, IPM Ratfish calibrated at 84 ppm
SO 2 * Absorbtion(H 2 O 2 ), distillation and titration
Particulate material (exhaust) Collected in dillution tunnel (ISO 8178-1), Weighted in lab using Mettler Microweight AE163.
NH 3 * Absrorption (5% H 2 SO 4 ), distillation and titration
N 2 O * Absrorption (3M NaOH), drying (Mg(ClO 4 )) Noise Hand portable instrument * Analysed in laboratory

4.4.1 Acidity Sulphur dioxide and NO x are known as the main constituents of acid rain. In the scrubber a very small part of NO x (less than 5 %) will be absorbed, unless specific absorbents (e.g. ammonia) is19

/ / 2006-10- added to the water. Carbon dioxide does not cont ribute to the acidity. The acidity of the wash water is therefore mainly due to the sulphur co mpounds and especially sulphurous and sulphuric acids. Environmental aspects of low pH are discussed in chapter 5.5.

Example: Assuming a fuel with 4 % sulphur (m/m ) and a specific wash water consumption of 80 kg/kWh and 100 % absorption efficiency a su lphur concentration of 100 mg/l (3.125
. 10 -3 mol/l) can be expected. If sea water with salinity 35 PSU is used, the pH of the water before dilution can be calculated to about 3.25

4.4.2 Oxygen demand It is expected that the oxidation of sulphite (HSO 3 - ) to sulphate (SO 4 2- ) ion is the main contributor to the Chemical Oxygen Demand (COD) of the wash ing water. However, there may also be other components, e.g NO x , uncombusted fuel, VOC or others that contribute to the COD.

Example: Assuming the same condition as in the previous example (4 % S and 80 kg water/kWh ) and provided that 100 % of the sulphur is on the bisulphite form, it can be calculated that the COD resulting from sulphur alone will be 50 mg /l before dilution.

In the Fjordshell experiments the COD was found to be 33 mg/l under tr ansit operation and 10 mg/l under port operation. In the M/S Kronprins Ha rald experiments COD was not analysed, but under transit operation no SO 2 was detected and under port operation only a small part of the absorbed sulphur was detected as SO 2 . The concentration of SO 2 was found to be 57 mg/l, representing only 23 % of the total absorbed sulphur. This is equi valent to a COD of 14 mg/l.

The results so far indicate that a substantial part of the SO 2 is oxidized to sulphate during the combustion and/or scrubbing process.

4.4.3 Particulate matter in untreated discharge water The amount and composition of particles generated by marine diesel engines are influenced by the combustion process and the type of fuel used. Some of the particulate matter will be trapped in the scrubber water, resulting in particulate pollution of the discharge. Particle concentration in the wash water from two different scrubbers were fo und to vary from less than 1 to about 15 mg/l (Table 7).

Micropollutants are to a large extent associated with particles or suspended in the wash water. The composition of particles may be divided in the th ree main groups; 1) metal oxides and sulphates, 2) carbon (soot), and 3) ot her organic compounds.

4.4.4 Metals in untreated discharge water Table 10 gives examples of concentrations of sp ecific heavy metals found in wash water from scrubbers.20

/ / 2006-10- Table 10 Examples of heavy metal concentratio ns observed in scrubber discharge water.
Fjordshell Substance Unit

Transit load Port load Vanadium (V) mg/l 0.035 0.023 Nickel (Ni) μ g/l 32.8 10.4 Zinc (Zn) μ g/l 6 15 Chromium (Cr) μ g/l <1 <1 Lead (Pb) μ g/l 5 0.6 Copper (Cu) μ g/l 41.6 15.3 Mercury (Hg) μ g/l <0.1 <0.1 Arsene (As) μ g/l <0.1 <0.1 Cadmium (Cd) μ g/l 0.05 0.08 Specific water consumption kg/kWh ~ 50 ~ 150

Generally an increase in the content of h eavy metals across the scrubber is observed.

4.4.5 Hydrocarbons As shown in Table 7, the concentration of hydrocar bons in the wash water varies from 0.05 to 1.7 mg/l.

4.5 General remark – con centrations vs flux The concentration of pollutants in the discharge water will naturally be reduced when the amount of wash water is increased, and the pH reduction w ill be smaller. In this case, the water can be considered partly diluted before discharge. Ho wever, the mass flow of many pollutants may be virtually the same.

Especially for non-degradable const ituents the concentration at the discharge point is less relevant than the long term concentration in a larger area. For this purpose, it is the flux or mass flow of pollutants that is important, not the concentration.



### 5. Toxicity of scrubber discharges and safe environmental levels

5.1 Risk assessment of discharge components - the PEC/PNEC approach

In order to perform a risk assessment of scrubber water discharges to the sea it is necessary both to evaluate the expected environmental con centration of each discharge compound, the PEC (Predicted Environmental concentration) and the toxic properties of the same compound the21

/ / 2006-10- PNEC (Predicted No Effect Concentration). If the PEC/PNEC ratio is >1 then a risk to the marine environment is indicated. Usually, as a firs t approach both PEC and PNEC is estimated conservatively, meaning that realistic worst cas e assumptions are included in both PEC and PNEC derivation. Therefore if a PEC/ PNEC<1 the risk to marine li fe should be negligible. If a PEC/PNEC>1 is arrived at during the first appro ach one should investigate whether it is possible to refine the PEC and PNEC estimates and make th em more realistic for the actual situation. In this case refinement can be achieved by performing measurements either of actual releases in the case of PEC or performing chronic toxicity studies on relevant a quatic organisms in the case of PNEC. If the PEC/PNEC ratio is still >1 then risk reducti on measurements have to be implemented leading to reduction in releases. Su ch a reduction can either be achieved by treating the effluent or if this is not effective, prohibi ting the processes that give rise to the emissions.

5.2 PNEC derivation for relevant metals

The following metals have been found relevant for risk assessment concerning release of Scrubber effluent; Nickel (Ni), Copper (Cu), Zinc (Zn), Qu icksilver (Hg), Lead (P b), Arsen (As), Cadmium (Cd), Chromium (Cr) and Vanadium (Va). Most of these metals have other release soursces and have therefore been evaluated w ith regard to aquatic toxicity both nationally and internationally. UK and USA have developed quality standards for several of these metal compounds and within the EU Directive for existing chemicals (Commission regulation No 1488/94), PNEC values have also been derived. As EU PNEC values may have limited international acceptance, national quality standards may have to be employed when these are lower than the EU PNEC values in order to ensure international acceptance of the risk assessment. Table 11 contains a summary of available PNEC values for metals which has und ergone evaluation within EU existing chemicals regulation. Notice that for some metals both a marine and freshw ater PNEC has been derived. Lack of a specific marine PNEC is mainly due to that one has not found scientific basis that indicate a significant difference in the toxicity between organisms in these two compartments. Therefore use of a freshwater PNEC should ad equately protect also marine organisms.

Table 11 Metals with PNECs suggested by EU risk assessment program for existing chemicals (regulation no 1488/94)

Metal PNEC consept HC5 AF PNEC(μg/l) Cd (fresh) SSD total 0.38 2 0.19 Cu (fresh) SSD total 8.2 1 8.2 Ni (fresh) SSD total 6.43 3 2.1 Pb (fresh) SSD total 14.5 1 14.5 Pb (marine) SSD total 8.3 1 8.3 Zn (fresh) SSD added 15.6 2 7.8 Zn (marine) SSD added 6.1 2 3.522

/ / 2006-10- For those metals not having been assessed in the EU risk assessment program for existing chemicals the data from Crommentuijen et al (1997) may be used. The Maximum Permissible Concentrations (MPC) derived by Crommentuijen et al (1997) are assessed according to the same methods as in the EU risk assessment program for existing chemicals. The MPC is similarly derived as HC5 in Table 1, but with addition of a mean background level in the environment. In order that these values should be equal to PNEC it is necessary to divide by an assessment factor (AF). It seems that an AF=2 most closely match current practice in EU as indicated in Table 1. Except for As, Cr and V where only freshwater MPCs are available, these estimates include marine tests.

Table 12 shows MPCs for some metals which have not been assessed in the EU risk assessment program for existing chemicals. The data is fr om Crommentuijen et al (1997). The PNEC is derived using an AF=2.

Table 12 MPCs for some metals not assessed in EU risk assessment program for existing chemicals.

Metall PNEC consept MPC (μg/l) PNEC (μg/l) As (fresh) SSD total 25 12.5 Cr (fresh) SSD total 8.7 4.3 Hg (fresh) SSD total 0.24 0.12 Hg (marine) SSD total 0.23 0.11 V (fresh) Lowest NOEC AF=1000 4.3 4.3

5.3 Compliance with other water regulation

In order that the PNECs used in the risk assessment are internationally accept ed they should also comply with national water quality standards. Both UK, EU (The EC Dangerous Substances Directive (76/464/EEC) and USA EPA have deve loped national standards for many compounds. These are shown in Table 13 for the relevant metals. The US EPA Water Quality Standards (WQS) are based on a scientific assessment of av ailable ecotoxicological information, and deviate in some cases significantly from the European PNEC values. For Hg, US EPA has taken into account also risk to humans via biomagnification in the food chain. The Environmental Quality Standards (EQS) of EU are esta blished through a similar proce dure as US EPA. There is good agreement in levels between these two standards, except again with respect to Hg were EU has a 10x higher value than US EPA.23

/ / 2006-10- Table 13 Relevant US EPA and UK Water Quality Standards.
compound US EPA WQS μg/l freshwater US EPA WQS μg/l seawater EQS (UK) μg/l seawater
Cd 0.66 8.8 2.5
Ni 56 7.1 30
Pb 1.3 5.6 25
Zn 180 58 40
As 190 36 25
Cr 11 50 15
Cu 6.5 2.9 (1 hr max) 5 Hg 0.012 0.024 0.3
V 100

The derived metal PNECs are all below the s hown aquatic WQSs, the only exception being the very low US WQS value for Hg. One should theref ore proceed with the risk assessment using the PNECs presented here. In addition Hg should be assessed also using th e US EPA derived WQS value of 0.024 μg/l for Hg in order to be able to conclude that also the human endpoint associated with the WQS value is assessed.

5.4 PNEC derivation of organic compounds The organic compounds that might be of concer n as identified in Chapter 4 are hydrocarbons (THC), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and dioxins (PCDD/PCDF). Except to some extent the THC, these compounds together with the metals are associated with the total partic ulate matter (PM) being trapped in the scrubber water (cf Chapter 4.1.2).

OSPAR (1996) developed Ecotoxico logical Assessment Criteria (EAC) for a large range of chemicals to facilitate evaluation of monito ring data on toxic substances in the marine environment. The EAC values were derived essentia lly in the same way as the PNEC values given above (based on available toxicity test data and us e of application factors) and should therefore in principle be applied as PNEC values. This is proposed in the present context. The OSPAR EAC values for the relevant compounds are given in Table 14. Later on OSPAR (2004) provided EAC values for groups of PAH compounds according to molecular size (Table 15). PNEC values for THC, total PAH or sumPAH 16 and for dioxins are not available from this source.

Most of these organic substances will be adsorbed to particles in the discharge and due to their strong particle association (especially to soot particles) they will to a large extent be particle bound also after discharge. An impact assessment should thus focus on their behaviour as part of the PM, e.g they might settle to the sediment with other PM over time. The EAC-sediment might therefore be the most relevant assessment criteria, but modelling of PM settling behaviour will be highly unreliable.24

/ / 2006-10- Table 14 Ecotoxicological Assessment Criteria (EAC) for PCBs and PAHs as proposed by OSPAR (1996).

Substance EAC-water (μg/l) EAC-sediment (mg/kg dw) PAHs Naphtalene 5 - 50 f 0,05 – 0,5 f
Phenanthrene 0,5 – 5 p 0,12 – 1 f
Anthracene 0,001 – 0,01 p 0,05 – 0,5 f
Fluoranthene 0,01 – 0,1 p 0,5 – 5 p Pyrene 0,05 – 0,5 p 0,05 – 0,5 p Benzo(a)anthracene n.d. 0,1 – 1 p Chrysene n.d. 0,1 – 1 p Benzo(a)pyrene 0,01 – 0,1 p 0,1 – 1 p sumPCB 7 n.r. 0,001 – 0,01 p f: firm p: provisional n.d.: no/insufficient data n.r.: not relevant vs OSPAR monitoring

Table 15. Ecotoxicological Assessment Criter ia (EAC) for PAH groups as proposed by OSPAR (2004).
PAH group EAC-water (μg/l) EAC-sediment (mg/kg ww) 2 rings: naphtalene 2,4 p 0,038 p* 3 rings: phenanthrene& anthracene 0,17 p 0,031 p* 4 rings: fluoranthene, pyrene, benzo(a)- anthracene, chrysene 0,69 p 0,141 p*

5 rings: benzo(k)fluoranthene, benzo(a)pyrene 0,03 p 0,021 p* 6 rings: benzo(ghi)perylene, indeno(123-cd)-
pyrene 0,016 p 0,0037 p*

p: provisional * sediment normalised to 1% organic carbon

Agreed PNEC values for THC have not been found in the available literature. A value of 40,4 μg/l has been proposed by Scholten et al 1993 for the ali phatic fraction of the oil (the aromatic fraction should be covered by the PAH criteria) and is adopted by the Norwegian Oil Operators Association (OLF) for risk assessment of offshore produced water (Johnsen et al 2000). The large wealth of toxicity data on oil hydrocarbons is difficult to condense due to variability in experimental conditions, analytical procedures and oil composition, but there appears to be consensus that chronic environmental impact of oil is observed when concentration of THC exceeds 50 μg/l, which is close to the aliphatic PN EC given above. We therefore propose that the PNEC for THC is set at 40 μg/l.25

/ / 2006-10- 5.5 PNEC derivation of other discharge compounds The other discharge components of concern woul d be pH, total particulate matter (PM), total organic carbon (TOC) and potential chemical oxygen demand (COD). The PM and TOC are both typical features of the seawater and vary consid erably in space and time. PM originates from a range of natural (e.g. river runoff, resuspen sion of bottom sediments, phytoplankton growth intensity) and manmade sources (e.g. industrial and sewa ge outfalls, land runoff, mining, dredging). PM levels may be extremely patchy in nearshore waters. We consider PNEC values for PM and TOC as of minor importance in the environmental risk assessment.

Review of the literature on pH tolerance indicates that there is little evid ence of harm to marine organisms from a decrease of 0.5 –1 pH units fr om ambient (Knutzen 1981). It is also suggested that marine organisms are more sensitive to a rise in pH than a decrease (Wolff et al 1988). Table 13 shows some national EQS (Environmental Quality Standards) values for pH. The strictest is given by the US EPA allowing not more than 0.2 pH unit deviation from what is the normal pH range of the ambient water. This implies a va riable PNEC depending on the natural pH-levels which normally range from 7.0 to 8.5 (partially correlated with primary production). Otherwise we would propose a PNEC for pH of 7.0 which according to the UK Water Research Centre should safeguard both fish and shellfish at chronic exposure.

Table 16 Examples of national environmenta l quality standards (EQS) for pH in marine waters (From Wolfe et al 1988).
EQS given by value
US EPA 6,5 – 8,5 1) Australia 6,5 – 8,5 China 7,5 – 8,3 Japan 7,8 – 8,3 UK Water Research Centre, prot ection of shellfish 7,0 – 8,5 UK Water Research Centre, protection of fish 6,0 – 8,5 1) but not more than 0,2 units outside normally occurring range

Although many countries have discharge limits for COD (typically 150 - 350 mg/l) there are no environmental standards. This is because COD will manifest itself through oxidation and hence by reducing the dissolved oxygen correspondingly. This process takes time which implies that there will be a gradual oxygen consumption taking place concurrent with dispersion and dilution. An assessment will therefore have to evaluate to what extent the COD will contribute to the risk of reduced dissolved oxygen in the rece iving waters. A worst (but not en tirely realistic) case is that the COD is oxidised immediately.

There is a wealth of literature showing that tolerance to redu ced dissolved oxygen in seawater varies considerably dependent on organism , life stage and environmental conditions. A concentration that should safeguard most marine temperate-coldwater organisms are proposed to26

/ / 2006-10- be 5 mgO 2 /l (Bakke et al. 2002). Fully saturated cold -temperate seawater contains about 9-10 mgO 2 /l.



### 6. Prediction of environmental concentration

The Predicted Environmental C oncentration (PEC) resulting fr om the operation of scrubbers depends on the dilution of the discharge water. Su ch dilution is difficult to measure in field; however it can be readily be modelled and numeric dillution models are commonly used to obtain a PEC.

6.1 Modelling of discharge dilution from a single ship The dillution of the discharge from a single ship has been numerically modelled by SINTEF Material and Chemistry (2006, 1994) and by CFD No rway as (2006). Reports on these studies are included as appendix 1 and 2 to this report. The overall dispersion has been modelled for different scenarios regarding ship size, washwater discha rge point and speed, however the results are in accordance and point towards the same general conclusion.

The dilution of the wastewater plume after disc harge during transit and port operations may be described as a combination of 3 main processes:

• Dilution of the waste water in the exit jet emerging from the outlet

• Turbulent mixing in the boundary layer along the hull

• Dispersion in the propeller and the turbulent wake left behind the vessel.

6.1.1 Dilution of discharges from a single ship in open sea SINTEF (2006) found that the dispersion in the wa ke behind the vessel wa s the dominant dilution process. Under the tran sit operation conditions of a discharg e of 440 m3/hour wastewater at 8 m depth 20 m ahead of the stern from a 163 m lengt h vessel at constant speed of 14,5 knot, the process water was diluted by a factor of 1:30 before the effluent passed the stern of the ship and by a factor 1:2000 at a distance 50 m behind the stern. (Appendix 2)

By use of a different numerical model, CFD No rway investigated the dilution of a discharge behind a large container ship. (Appendix 1) Ship particulars are given in Table 17. Discharge point was at the stern just in front of the propellers.27

/ / 2006-10- Table 17 Ship particulars
Ship length L=230 m Ship speed 24 knots Propeller (single screw) diam eter 7.9 m Thrust 2600 kN Shaft power 32 M W Washwater discharge rate 75 ton/MW (670 kg/s)

Figure 3 shows the dillution as m odelled. Som e maxim u m concentr ation s behind the s h ip in a r e given in Table 18.

Figure 3 Gr aphical illu strat i on of dillut i on of discharge28

/ / 2006-10- Table 18 Dilution of original discharge
Distance behind ship Maximum concentration x/L x [m] log 10 (c/c 0 ) )
max c/c 0 max

0.004 0.92 -0.37 0.43 0.035 8.05 -1.28 0.052 0.1 23 -1.59 0.026 0.25 57.5 -1.85 0.014 0.5 115 -2.05 0.009 1 230 -2.15 0.007 C = Concentration, C 0 = concentration at discharge point

This model estimated dilution by a factor of 1:70 at 57 m behind the stern. If one assumes an additional 1:30 times dilution for a side outlet as used by SINTEF the total dilution at 57 m behind the stern will be 1:2150, i.e. essentiall y the same as for th e SINTEF modelling.

6.1.2 Dilution of discharges from a single ship at port operation This scenario has only been modelled by SINTEF ( 2006) for the same vessel as above, but with a speed of 4 knots and a discharge of 130 m3/h. Un der such conditions the dilution factor at 50 m behind the stern was 1:1750, i.e. almost as large as during transit operation.

6.1.3 Dilution of discharges from a sing le ship at quay side manoeuvring During quay side manoeuvring the followi ng processes regulate dispersion:

• Dilution of the waste water in the exit jet emerging from the outlet

• Turbulent mixing during vertical tran sit of the plume to neutral buoyancy

• Ambient turbulence such as caused by currents, winds and ship movement.

Dillution at quay side will be strongly influen ced by local conditions. One scenario has been modelled by SINTEF (1994) using the same disc harge arrangement as for the port operation, speed 0 knots, temperature of the wastewater 7,5°C and ambient current speed of 5 cm/s. A dilution factor of 1:100 in the centre of the plume was reached at less than 20 m distance downstream from the outlet, corres ponding to an average dilution f actor of approximately 1:150.

6.1.4 Summary: Dilution of discharges from a single ship In summary, the discharges from a single ship are rapidly diluted when the ship is moving. A small area behind the ship will be affected, how ever. The dilution at quay side is strongly influenced by local conditions, but should be expected to be much sl ower than when the ship is in moving operation.29

/ / 2006-10- 6.2 Accumulation of discharges – local and regional effects The combined effect of the discharges from severa l ships must be considered in relation to the prevailing local conditions. The most important para meter is the exchange rate of the receiving surface water with ne ighbouring areas.

6.2.1 The Oslo Fjord Case study – regional effects In this project we have made an evaluation of the risk that the total ship traffic in the land-locked Inner Oslo Fjord including Oslo harbour would gradually reduce the buffering capacity and other aspects of water quality of the local water masse s if all ships were equipped with seawater scrubbers.

The exchange of water in the Inner Oslo Fjord is achieved by an outflow of brackish surface water compensated by an inflow of saline water beneath the surface layer. This exchange is driven by river runoff and winds, and is st rongest during periods with northerly wind. The annual mean water exchange of the surface layer (i.e. down to a depth of 10 m) is estimated to 900 m 3 /s.

Traffic data for Inner Oslo Fj ord are based on data from Oslo and Drammen harbours and is shown in Table 19.

Table 19 Marine vessels visiting Inner Oslo Fjord 2004.
Harbour and ship type Number of ships Total dead weight (1000 tonnes) Oslo international 3003 60775 Oslo domestic cargo 98 378 Oslo domestic tankers 38 95
Drammen international 938 5436
Total 4077 66684

Local ferries, fishing boats and other vessels smaller than ca 2500 tonnes are assumed to use distillate fuel and hence have no incentive to clean their exhaust.

Average tonnage of visiting ships included is 16.356 tonnes. It is assumed that these ships will have an average main engine power of 5200 kW.

We consider the two different cases 1) tran sit operation and 2) port operation. Under port operation an engine operation of 30 % is expected for a total operation time of 1 hour. Under transit operation an average speed of 14 knots and an engine load of 90 % is assumed. The Oslo Fjord is about 80 km long giving a total transit time of 6 hours.30

/ / 2006-10- For the calculation of the sulphur emission an average consumption of 0.2 kg fuel per kWh is used. The calculation is based on an average sulphur content of 2.7 % in the fuel. One hundred % of the sulphur is removed in the scrubber and discharged to the sea as sulphurous acid.

Estimated sulphur discharge:

Transit operation 4077 · 5200 · 6 · 0.9 · 0.2 · 0.027/1000 = 618 t/year

Port operation 4077 · 5200 · 1 · 0.3 · 0. 2 · 0.027/1000 = 34 t/year

Total discharge 652 t/year =74 kg/h

It is seen from this calculation that the port ope ration discharge will contribute to about 5,5 % of the total sulphur discharge. In addition comes discharge at berth which is not included here.

Neutralization proceeds according to the equation:

H 2 SO 3 + 2 HCO 3 - = SO 3 2- + 2 H 2 CO 3 Each mole of sulphur needs 2 mole s of bicarbonate to be neutralized. Provided that the incoming water has a salinity of 20 ‰ the alkalinity can be assessed to 1.394 mmol/l. The rate of water exchange necessary to provide enough alkalini ty for neutralization of the discharge is

Q = 74/32 · 2 · 1000/1.394 = 3.318 m 3 /h = 0.9 m 3 /s

This is about 0.1 % of the actual exchange, whic h suggests that the risk of gradual reduction in buffering capacity is negligible.

Based on the same water exchange regime as above for the Inner Oslo Fjord, the modelling of discharge dilution at port operation (chapter 6.1.2), and a traffi c load of 6000 visits/year, SINTEF (1994) calculated the risk of the wastewater chan ging the water quality in the local surface waters. The total waste water discharge from these ve ssels was estimated to roughly 4000 m3/day or 167 m3/hour. This amounts to 0.2 % of the annual mean freshwater input to the Inner Oslo Fjord of about 90.000 m3/hour, and 0.003 % of the total mean exchange of surface water between the fjord and the sea outside (6.4x10 6 m3/hour). These fluxes suggest that the overall equilibrium dilution of the total wastewater volume in the surface water of the Inner Os lo Fjord is in the range of 1:38000. This is way above the dilution necessary to reduce the PEC/PNEC ratio to less than 1 for all discharge components of concern, and shows clear ly that the risk of gradual deterioration of the water quality of the Inner Oslo Fjord if all vessels were equi pped with sea water scrubbers is negligible.

The methods used in the assessments above ought to be of general value. It must, however, be pointed out that such assessments depend entirely on site-specific data on water exchange rates,31

/ / 2006-10- traffic densities (i.e. discharge water volumes and fluxes) and specific knowledge of the acidity and contaminant content of the actual waste water effluents.



### 7. Current discharge criteria The content of petroleum hydrocar bons in discharges of bilgew ater from ships is limited by MARPOL Annex I to 15 ppm. This limit is much higher than what would be expected from a regular seawater scrubber. However, this li mit is not intended for regulation of scrubber discharges and the limit does not in intself im ply that hydrocarbon con centrations up to 15 ppm would be acceptable. In fact hydrocarbon concentr ations that are acutely lethal to marine organisms may be as low as 1 ppm.

An effort has been made to identify other discharg e standards, criteria or limits of relevance that may exist nationally or interna tionally. We have looked for st andards for the most relevant components such as dissolved oxygen (DO), chemical oxygen demand (COD), pH, total suspended solids (TSS), total organic carbon (TOC ), nickel, vanadium, zink, copper, lead, mercury, chromium, and total PAH/PAH 16
.

The conclusion from structured internet searches and contacts to the Norwegian Pollution Control Authority (SFT) and the Ministry of Envir onment is that there are few if any such criteria/standards of direct relevanc e to scrubber discharge from ships.



### 8. Proposed waste water discharge cr iteria for exhaust gas scrubbers

8.1 Sensitivity of marine a nd brackish water organisms to contaminants Available literature suggests th at there may be some systematic , compound-specific differences in sensitivity to contaminants and other environm ental stressors between freshwater and marine organisms (Wheeler et al 2002). Metals appear to be most toxic to fres hwater organisms while organic compounds seem more toxic to marine or ganisms. These differences are in general not large, and for all practical risk assessment purposes one may regard freshwater and marine species as equally sensitive. Brackish water species are in general more tolerant to natural large environmental fluctuation than their freshwater a nd marine counterparts, but there is no reason to assume that they also are more tolerant to toxi cants. Still it is reasonable to expect that toxicant sensitivity in brackish water organisms does not de viate systematically from that of freshwater and marine organisms. We therefore find no argu ments to develop ecosystem-specific waste water discharge criteria for scrubber components to safe guard the inherent organisms of marine and brackish water ecosystems, as long as agreed safe ty factors are applied to develop PNEC values.32

/ / 2006-10- 8.2 Proposed waste water criteria for seawater scrubber discharges from vessels at sea The waste water dispersion modelling shows that a gradual dilution of the plume in the surface water will occur and can be described. There appear s to be no discontinuity in this pattern that might serve as a definition of a near field impact area or volume in the wake of a ship. We will therefore rather arbitrarily define that a near field should be limited to 50 m behind the stern. Within this area or volume one must expect that organisms encountering the waste water will be affected, but this should be accepted on basis of the GESAMP principle since this area/volume in all aspects is small compared to the comple te water body the ship is moving through. The modelling in transit and port operation show s that a plume dilution of 1:2000 and 1:1700 respectively are achieved at this distance, a nd within less than 10 seconds. For quay side manoeuvring we have also arbitrarily defined a distance of 20 m from the outlet as the nearfield. It is likely that an averag e plume dilution of 1:150 may be obtaine d within the nearfield and within 6-7 minutes.

Taking these dilution factors a nd the PNEC values for the actual scrubber components into account we have estimated the worst case discharg e characteristics that may be allowed without the PEC/PNEC ratio exceeding 1 outside the near fi eld. This should then be proposed as the waste water discharge criteria values. These values are presented in Table 20 and Table 21.

Table 20 shows that even at quay side manoeuvr ing with the lowest estimated dilution, the wastewater may have metal, THC, and PAH conten t that is 1-3 orders of magnitude higher than those reported as typical for scrubber wastewater effluents, and still th e PEC/PNEC ratio would be <1 at the border of the near field. The component that comes closest to the proposed discharge criterion is THC, where the quay side criterion is only 3 times higher than the estimated typical discharge concentration, but still on the safe side.

For pH and dissolved oxygen (Table 21) the outlet concen trations would theoretically have to be negative to cause a PEC/PNEC=1 at the border of th e near fields. This implies that even with pH = 0 and no dissolved oxygen (DO) in the discharge, the PEC/PNEC ratio would be far below 1 at the border of the nearfield. For DO the table s hows that even a COD of 150-350 mg/l (a typical range for national discharge limits for COD) coul d have been realised within the near field without raising the PEC/PNEC ratio fo r DO above 1 outside this field.

One should point out that these di scharge criteria are very conser vative since the PNEC values chosen cover impact during chronic exposure, wher eas the anticipated expos ure time in the near fields is only 10 seconds during transit and port load and 6-7 mi nutes at quay side manoeuvring. Also the calculation is based on the strictest PN EC values where alternative values are given by different authorities (cf chapter 6).33

/ / 2006-10- Table 20: Proposed discharge criteria (WDC) for scrubber waste water compounds that are elevated in the waste water (μ g/liter). These criteria will ensure that the PEC/PNEC ratio does not exceed 1 at the border of the nearfields in the transit load, port load, and quay side manoeuvring scenarios.
Compound Most conservative PNEC Ambient WDC transit load WDC port load WDC quay side manoeuvring Waste water concentration

Nickel 2,1 0,1 4000 3400 300 32,8 Vanadium 100 2 196000 166600 14700 35 Copper 2,9 0,3 5200 4420 390 41,6
Lead 8,3 0,05 16500 14025 1238 5 Mercury 0,024 0,001 46 39 3 <0,1 Cadmium 2,5 0,03 4940 4199 371 0,08
THC 40 10 60000 51000 4500 1700
PAH 3,3 0,1-0,2 6212 5280 466 0,25

Table 21: Proposed discharge criteria (WDC) for scrubber waste water compounds that are elevated in the waste water. These criteria will ensure that the PEC/PNEC ratio does not exceed 1 at the border of the nearfields in the transit load, port load, and quay side manoeuvring scenarios.
Compound Most conservative PNEC Ambient WDC transit load WDC port load WDC quay side manoeuvring pH 6,8 7,0 -392 -92 -38 DO mg/l 5 8-10 -9990 -8190 -755 *NOTE: Negative WDC values indicates that PNEC values can be obtained even with pH=0 and DO = O at outlet, indicating that no regulation would generally be needed for pH and COD.

The large safety margin between the trial result s and the indicated criteria, and considering the conservative approach used in defining them, indi cates that there is no ap parent need for scrubber wastewater criteria in the ope n sea. This is in good harmony with MARPOL Regulation 14 which places no restrictions on discharges outside enclosed ports, harbours and estuaries.

8.3 Proposed waste water criteria for seawater scrubber discharges in closed waters To protect the water quality, the port State needs to limit the total discharges of pollutants within the area of concern. The total di scharge of pollutants depend both on the amount of exhaust that is being scrubbed and the discharge criteria.

Even though the Inner Oslo Fjord case conclude d that there is no apparent risk for gradual deterioration of the water quality even if all present vessel traffic uses seawater scrubbing of their34

/ / 2006-10- exhaust, this may not be the case for other enclosed water bodies w ith high ship traffic. As said earlier each site and situation is uni que and has to be evaluated separately to generate site specific waste water discharge criteria, however, the risk procedure used in the Oslo Fjord case is applicable to other enclosed ship traffic areas as well.

As previously argued, to avoid pr olifieration of criteria it is advised that IMO develops a set of default criteria that represent typical situations. (Lev el 1, 2, 3, etc) The Port State would then have the opportunity to choose one of the predefined crit eria on the list which wo uld significantly ease verification of compliance and provide much needed design targets for EGCS-SOx manufacture.

Table 22 Comparison of Possible discharge water li mits and worst case trial results (μg/liter)

Criteria level 1 2 3 “Safety Margin” 1 10 100 Trial worst case
Nickel 300 30 3 32.8 Vanadium 15000 1500 150 35 Copper 400 40 4 41.6
Lead 1200 120 12 5 Mercury 3 0.3 0.03 <0.1 Cadmium 350 35 4 0.08
THC 4500 450 45 1700
PAH 450 45 5 0.25

As seen in Table 22, there is a considerable di fference between the worst case results observed in the trials and proposed criteria in many cases. It is suggested that a limit value is not needed when the worst case observed in the trial is about one order of magnitude or more below the proposed criteria. The resulting criteria proposition following this logic is shown in Table 23.

Table 23 Proposed discharg e water limits (μg/liter)

Criteria level* 1 2 3 “Safety Margin” 1 10 100 Nickel - 30 3 Vanadium - - 150 Copper - 40 4
Lead - - 12
THC 4500 (4.5 ppm) 450 (0.45 ppm) 45 (0.045 ppm) *At nominal wash water rate of 44 kg/kWh (repres entative of trials and dispersion models used)

The safety margin indicates how much more discharge an area can sustain compared to the unregulated situation, all other aspects being equal.35

/ / 2006-10- These proposals are made based on results from two specific trials. They should be seen in conjunction with experiences from other trials, st udies as well as capabilities of water cleaning systems and means of verification. An addi tional cosmetic criterion demanding no visible discharge and absolute limit values irrespective of wash water rate could also be considered.

In order to select predefined discharge criteria, the port State would have to identify the rate of water exchange and the anticip ated discharge from scrubbers in the area in question. The concentration of contaminants in the area can then be calculated assuming different discharge levels and compared with PNECs as provided above or other as deemed necessary. The port state could then select the least stringent set of criteria which provide sufficient environmental protection.36

/ / 2006-10- 

### 9. GLOSSARY

COD chemical oxygen demand
AOX absorbate organic chloride
PAH polyaromatic hydrocarbons
PCDD polychlorinated dibenzo-p-dioxines
PCDF polychlorinated dibenzofurans
PEC predicted environmental concentration
PNEC predicted no-e ffect concentration
THC Total Hydrocarbon
HC Hydrocarbon
WDC water discharge criteria
DO dissolved oxygen EQS environmental quality standard
TSS total suspended solids
TOC total organic carbon
SPM suspended particular matter
PCB polychlorinated biphenyls
EAC Ecotoxicological Assessment Criteria37

/ / 2006-10- 

### 10. REFERENCES

Bakke T, B Braaten, J Molvær and MT Scaanning, 2002 . Seawater flue gas desulfurization FGD may require new regulations on ambient dissolved oxygen . Paper no 71226 at the 14 th Conference of the Electric Power Supply Industry (CEPSI), Fukuoka Japan. 7p.

Crommentuijn, T., Polder, M.D. & van de Plasse, E.J. (1997). Maximum permissible concentrations and neglible c oncentrations for metals, taki ng background concentrations into account. RIVM report No. 601501 001.

IMO resolution MEPC.130(53) Guidelines for on-board exhaust gas SOx cleaning systems

MARPOL 73/78 Annex VI – Regulations for the prevention of air emissions from ships. IMO Publication – Sales number I664E

EU directive 2005/33/EC

MARINTEK div. Machinery, MT 22-F93-0220: Exhaust gas seawat er scrubbing, ‘SSN Project’

Ives R,, SN Klokk, 1993. Exhaust gas sulphur removal by sea water washing, marine diesel engines. 20th international congress on combustion engines, (CIMAC) London 1993

Johansen, Ø, 1993: Exhaust Gas Sea Water Wash ing System – Dispersion of Process Water. OCEANOR Report OCN R-93069, 38 pp.

Johansen, Ø, K. Tangen, and F. Moy, 1994: Exhaust Gas Sea Water Washing System – Environmental Impact Assessment . OCEANOR Report OCN R-94003, 71 pp.

Johnsen et. al. (2000) Johnsen S, Frost TK, Hjelsvold M, Statoil, and Utvik, TR. 2000. The environmental impact factor - a proposed tool for produc tion water impact reduction, management, and regulation . SPE 61178. Society of Petroleum Engineers.

Knutzen (1981) Effects of decreased pH on marine organisms . Mar.Poll.Bull., 12, 25-29.38

/ / 2006-10- Wolff et. al (1988) Wolff EW. et al 1988. Proposed environmental quality standards for List II substances in water. pH . WRC Technical Report TR 259. Water Research Centre UK. 66pp.

Wheeler et al 2002 Wheeler JR, Grist EPM, Leung KMY, Morrit D and Crane M. 2002. Species sensitivity distributions : data and model choice. Mar. Poll. Bull., 45, 192-202.39

/ / 2006-10- APPENDIX 1 Report CFD-Norway

APPENDIX 2 Memo Sintef Materials & Chemistry

# CFD Analysis of Process Water Dispersion from KRISO Container Ship (KCS)

Ivar Øye

June 2006 CFDn Report 325:2006 Preliminary, 12.06.2006-1



# CFD norway asCFD norway as

CFDn report 325:2006 i 

## REPORT DOCUMENTATION PAGE

Principal: MARINTEK Classification: Konfidensiell

Address of principal: Norsk Marinteknisk Forskningsinstitutt A/S Otto Nielsens vei 10 Postboks 4125 Valentinlyst 7450 Trondheim Local co-ordinator: Øyvind Buhaug

Title: CFD Analysis of Process Water Dispersion from KRISO Container Ship (KCS) Author(s): Ivar Øye

Abstract:

By applying a CFD code for computing viscous, incompressible flows, the dispersion of process water from a container ship of length 230 meters and of speed 24 knots was analysed. The results should be regarded as a first assessment.

The computational results show a rapid dispersion of the wastewater concentrations. At 1 m aft of aft perpendicular (just behind the propeller) the maximum concentration had dropped to 43% of its initial value, at 8 meters the corresponding value was 5.2%. Due to the swirl in the propeller slip stream the concentration iso-lines became rapidly asymmetric. At distances of 0.5 L and above, the wastewater concentrations are confined to a 30-50 cm thick layer near the surface. Approved by:

Keywords: Ship hydrodynamics, CFD, Pollutant, Dispersion CFD norway as

Report number:
325:2006CFD norway as

CFDn report 325:2006 ii 

## Table of Contents

Table of Contents ........................................................................................................ii

1 Introduction............................................................................................................1

2 Numerical Modelling.............................................................................................2
2.1 Grid Generation ........................................................................................2 2.2 Propeller Model.........................................................................................2

3 Discussion of Results...........................................................................................3

4 Conclusions...........................................................................................................4

List of Figures..............................................................................................................5

Figures........................................................................................................................ ..6

A Description of the Numerical Method Used.....................................................16

A. Bibliography..........................................................................................................16CFD norway as

CFDn report 325:2006 1 

## 1 Introduction

By injecting water spray into the exhaust stack some pollutants may be washed out from the gas and hence resulting in cleaner air. However, the dispersion of the pollutants now contained in the wastewater and their impact on the environment must be investigated.
The objective of this study was to predict the dispersion of process water from a representative ship type to make first assessments of its decay and spreading rates. The actual ship was the Kriso Container Ship (KCS) of length 230 m which has been widely used as a reference test case for CFD codes in hydrodynamics, with supplementary experimental data 1 . The dispersion of pollutants is well modelled in the atmosphere, but more complicated in the wake of a ship including the swirling propeller slip stream. Computations were performed at a ship speed of 24 knots, at an estimated power requirement of 32 MW.

The computations were carried out with a Finite-Volume RANS code solving the incompressible Navier-Stokes equation coupled with a k-epsilon turbulence model. The code utilises structured multi-block grids well adopted for high Reynolds number flows about complex geometric shapes.
In the next sections we present the ship model and grid generation, followed by a discussion of the results. Finally, we arrive at some concluding remarks.

1 See http://hyperteam.kriso.re.kr for test case definition and data.CFD norway as

CFDn report 325:2006 2 

## 2 Numerical Modelling

2.1 Grid Generation

The CFD grid was constructed by using a total of 1.44 million grid points shared among 14 blocks, of which 9,200 was located on the hull surface, as observed in Figure 1. The surface grid was projected onto the NURBS patches from the supplied CAD geometry file.
Since the low-Reynolds number version of the k-epsilon model requires integration of the turbulence quantities in the inner layer of the boundary layer, the grid is highly clustered in the wall proximity, with a wall normal distance of y+ equal to 1 in the first cell layer. The far field boundaries were located at a distance of 5 ship lengths away.



### 2.2 Propeller Model

The propeller slipstream was computed with a simplified propeller model implemented as an actuator disc model for the thrust including the effect of swirl. The actuator disc model is a widely used simplification of rotor-stator configurations. By assuming a constant velocity in circumferential direction, the necessity of resolving the flow about each blade is avoided. Instead, momentum theory is applied which yield the relationship between total thrust T [N], the pressure jump ∆ p over the propeller disc, the ship speed V s , and the induced velocities u C in the propeller plane.

) ( 2
, C S C u V u p pA T + = ∆ ∆ = ρ

In the present computations the tangential velocity component (swirl) was given by propeller data. The propeller main dimensions were a diameter of 7.9 m, net thrust of 2,622 kN and a power consumption of 32 MW.CFD norway as

CFDn report 325:2006 3 

## 3 Discussion of Results

A finite-volume method for solving the Navier-Stokes (RANS) equations was applied to for computing the dispersion of wastewater from a container ship. A detail on the numerical method is found in Appendix A.
The mass flow rate of wastewater from the process was specified at 75 tons/MWh, or 667 kg/s for the current case. The wastewater was released at a depth of 8 meters, just ahead of the propeller. Due to the coarseness of the grid, the exact position of the outlet should be regarded as approximate. A sensitivity analysis of the location of the outlet was not a part of this study.

The results are presented as concentrations of wastewater at cross sections through the wake. The cross sections are defined at distances aft of the aft perpendicular as listed in Table 1.

Table 1. Distance to specified cross section for visualisation of wastewater concentrations, and the computed maximum value in each section.

x/L x [m] log 10 (c/c 0 ) max c/c 0 max 0.004 0.92 -0.37 0.43 0.035 8.05 -1.28 0.052 0.1 23 -1.59 0.026 0.25 57.5 -1.85 0.014

0.5 115 -2.05 0.009

1 230 -2.15 0.007

The dispersion of the wastewater is visualised by concentration plots, its development in the wake is shown in Figure 3. Note the logarithmic scale. At 1/250 of the initial concentration the logarithmic value is -2.4. Investigating the individual cross section in Figure 4 - 9, we find the maximum values of the normalised concentrations presented in Table 1. At a distance of 0.25 L and less the pollutant distribution has a shape of a round plume with swirl, see Figure 10. However, at further distance the maximum concentrations are located in a 30-50 cm thick layer near the surface. In the real situation encountering wind-induced waves, the wave-induced velocities will most likely increase the effective dispersion of the wastewater both in horizontal and vertical direction.
The results should be regarded as a first assessment, and further studies should emphasis on grid sensitivity and turbulence model sensitivity on the diffusion rate. Also, to make the validity of the results more general, computations should be carried out for several ship sizes and types, with various types of propulsion systems.CFD norway as

CFDn report 325:2006 4 

## 4 Conclusions

By applying a CFD code for computing viscous, incompressible flows, the dispersion of process water from a container ship of length 230 meters and of speed 24 knots was analysed. The results should be regarded as a first assessment.

The computational results show a rapid dispersion of the wastewater concentrations. At 1 m aft of aft perpendicular (just behind the propeller) the maximum concentration had dropped to 43% of its initial value, at 8 meters the corresponding value was 5.2%. Due to the swirl in the propeller slip stream the concentration iso-lines became rapidly asymmetric. At distances of 0.5 L and above, the wastewater concentrations are confined to a 30-50 cm thick layer near the surface.CFD norway as

CFDn report 325:2006 5 

## List of Figures

Figure 1 Wetted part of ship hull visualised by the CFD surface mesh.................................. 6
Figure 2 Definition of cross sections for plotting of results at (from left) 0.004 L, 0.035 L, 0.1L, 0.25 L, 0.5 L, and 1.0 L aft of aft perpendicular. .............................................. 7

Figure 3 Plot of wastewater concentration, log 10 (c/c 0 ), at cross sections defined in Figure 2.7
Figure 4 Computed normalized wastewater concentration at cross section 0.004 L aft of vessel. Grid size equals 2 by 2 metres. ........................................................... 8
Figure 5 Computed normalized wastewater concentration at cross section 0.035 L aft of vessel. Grid size equals 2 by 2 metres. ........................................................... 9

Figure 6 Computed normalized wastewater concentration at cross section 0.1 L aft of vessel. Grid size equals 2 by 2 metres. ..................................................................... 10

Figure 7 Computed normalized wastewater concentration at cross section 0.25 L aft of vessel. Grid size equals 2 by 2 metres. ......................................................... 11
Figure 8 Computed normalized wastewater concentration at cross section 0.5 L aft of vessel. Grid size equals 2 by 2 metres. ..................................................................... 12
Figure 9 Computed normalized wastewater concentration at cross section 1.0 L aft of vessel. Grid size equals 2 by 2 metres. ..................................................................... 13
Figure 10 Computed normalized wastewater concentration at cross sections (from top) 0.035 L, 0.1 L, 0.25 L , and 0.5 L. Grid size equals 2 by 2 metres........................... 14CFD norway as

CFDn report 325:2006 6 

## Figures

Figure 1 Wetted part of ship hull visualised by the CFD surface mesh.CFD norway as

CFDn report 325:2006 7 Figure 2 Definition of cross sections for plotting of results at (from left) 0.004 L, 0.035 L, 0.1L, 0.25 L, 0.5 L, and 1.0 L aft of aft perpendicular.

Figure 3 Plot of wastewater concentration, log 10 (c/c 0 ), at cross sections defined in Figure 2.CFD norway as

CFDn report 325:2006 8 Figure 4 Computed normalized wastewater concentration at cross section 0.004 L aft of vessel. Grid size equals 2 by 2 metres.CFD norway as

CFDn report 325:2006 9 Figure 5 Computed normalized wastewater concentration at cross section 0.035 L aft of vessel. Grid size equals 2 by 2 metres.CFD norway as

CFDn report 325:2006 10 Figure 6 Computed normalized wastewater concentration at cross section 0.1 L aft of vessel. Grid size equals 2 by 2 metres.CFD norway as

CFDn report 325:2006 11 Figure 7 Computed normalized wastewater concentration at cross section 0.25 L aft of vessel. Grid size equals 2 by 2 metres.CFD norway as

CFDn report 325:2006 12 Figure 8 Computed normalized wastewater concentration at cross section 0.5 L aft of vessel. Grid size equals 2 by 2 metres.CFD norway as

CFDn report 325:2006 13 Figure 9 Computed normalized wastewater concentration at cross section 1.0 L aft of vessel. Grid size equals 2 by 2 metres.CFD norway as

CFDn report 325:2006 14 Figure 10 Computed normalized wastewater concentration at cross sections (from top) 0.035 L, 0.1 L, 0.25 L , and 0.5 L. Grid size equals 2 by 2 metres.CFD norway as

CFDn report 325:2006 15CFD norway as

CFDn report 325:2006 16 

## A Description of the Numerical Method Used

The method used for the solution of the compressible or incompressible Reynolds-averaged Navier-Stokes (RANS) equations is a finite volume method based on central differences in space co-ordinates and an explicit Runge-Kutta method for the integration in time [A.1-3]. The method starts from an initial field which is marched in time until a stationary condition is reached. At this stationary condition is the conservation equations for mass and momentum satisfied. The time step is calculated locally in each control volume to increase the rate of convergence. The k-epsilon model was applied for the generation of turbulence [A.4].
The flow solver facilitates multi-block grids with a general and flexible specification of boundary conditions. The cell centred finite volume discretisation stems from the integral form of the Navier-Stokes equations which describes conservation of mass and momentum when viscous forces is neglected. On a finite control volume Ω this reads

0 = ⋅ + Ω ∂ ∂ 

# ∫ ∫

Ω dS d U t S n F a)

where the vector U contains the variables 

# [ ] w v u c p U T

, , , 2
= , b)

where p is static pressure and c is an artificial speed of sound. The variables u , v , and w are the Cartesian velocity components in x -, y -, and z -direction respectively. The variables are assumed to be averaged over each control volume. In Eq. a), F refer to the common flux vector for non-viscous transport terms while the vector n is the outward unit normal of the surface with

area S

. 

### A. Bibliography

[A.1] Jameson, A., Schmidt, W., Turkel, E., “Numerical Solutions of the Euler Equations Using Runge-Kutta Time-stepping Schemes,” AIAA Paper 81-1259, 1981.

[A.2] Eriksson, L.-E., "A finite volume solution technique for the Navier-Stokes equations governing viscous compressible flow,'' HOG Report 1987:102(A), Division of Hydro- and Gas Dynamics, The Norwegian Institute of Technology, Trondheim, 1987.

[A.3] Øye, I.J., “On the Aerothermodynamic Effects on Space Vehicles,” dr.ing. thesis, MTFrapport 1996:140 (D), NTNU, Trondheim 1996.
[A.4] Øye, I.J., “Evaluation of Turbulence Models for Flow about Wings and Bodies”, in: Haase, W., Chaput, E., Elsholz, E., Leschiner, M.A., Müller, D. (Eds.), “ECARP – European Computational Aerodynamics Research Project: Validation of CFD Codes and Assessment of Turbulence Models”, Notes on Numerical Fluid Mechanics, Volume 58., Vieweg Verlag, 1997.

# MEMO

MEMO CONCERNS Marine Use of Low Sulphur Heavy Fuel Oil, WP3 Wastew ater Criteri, Dispersion ModellingFOR YOUR ATTENTIONCOMMENTS ARE INVITEDFOR YOUR INFORMATIONAS AGREED

DI STRI BUTI O N SINTEF Mate rials and Ch emistr y

Address: NO-7465 T r ondh eim, NORWA Y Location: Brattørkaia 17B, 4. etg. Telephone: +47 4000 3730 Fax: +47 930 70730

Enterprise No.: N O 948 0 07 029 MVA

FI LE CODE CLASSIFICAT I ON R e s t r i c t e d

ELECTRONIC FIL E CODE

Disper sion mo del memo.doc Harald Fløgstad, SINTEF Byggforsk AS Henrik Rye, SINTEF Materialer og kjem i x

x

PROJECT NO

. DATE PERSON RESPON S IBLE / AUTHOR NUMBER OF PAG ES 8 0 4 0 1 8 2 7 2 0 0 6

- 0 5

- 2 9 Øistein J o h a n s e n 8



### 1 BACKGROUND
This m e mo contain s a b r ief desc ription of a computer m o del for dispersion of aqueous effluents from vessels in the open sea. The m odel was developed as a part of a study conducted by MARINTEK in the 1990’ies on a scrubber system fo r re moval of sulphur and particulate m a tter from exhaust gas em itted from vessel engines. The system was based on a scrubber where sea
water was u s ed to absor b the conta m inants before the exh a ust is r e le as ed to the a t mosphere. The washing water should be discharged to the sea through outlet ports below the water line. The dispersion model was developed at OCEANOR and presented in two repor ts. T h e f i rst is a description of the m ode l concept, refe rred to la ter in this m e mo as the Model Report (Johansen 1993). The second contains m odel applications in the context of environmental im pact

assessm ents, late r ref e r r e d to as th e EIA Report (Johansen 1994). The exhaust gas washing concept has gained renewed interest recently due to forthcom ing regulations of per m itted sulphur co ntent of fuel oils us ed by vessels s a iling in th e North Sea region. On this background, an extensive resear ch programm e has been in itiated (MAROFF), with contributions from SI NTEF Byggforsk, MA RINTEK and others. As dispersion m o del developm ents and applications have so far not been included in the programm e , SINTEF Byggforsk has asked SINTEF Materials and Chem istry to give a brie f description of the dispersion model developed in the before-m entione d project, and to indicate possible scaling laws that could be applied to m a ke use of m odel results from the previous study. The description of the model is g i v e n in Chap te r 2 of th is m e m o , while the discu ssio n of scaling laws is give n in Chapter 3.

This memo co ntain s p r oje c t informatio n and preliminary r e sul t s a s a ba si s fo r fi nal r epor t(s). SIN T EF a ccep t s n o re spon sibili ty of thi s memo and no par t o f it may be copie d

.2



### 2 DISPERSION M O DEL CONCEPTS This chapter contains a brief description of the concepts u s ed in the d i spers i on model that was developed at OCEANOR in conjun ction with the previous exhaus t gas w a shing system study. The model was developed as a particle s

- fluid-m odel, where th e release of pro cess water is represen ted by m odel pa rticles that are subjec t to advection and turbulent di ffusion. The subsequent dilution of

the proce ss water wa s dete rm ined f r om the concentr ation of m odel particle s in v a rious cross

sections downstream of the vessel.
The m odel took into account three different m echanism s for turbulent diffusion, i.e. :

 dilution of process water in the ex it jet em erging f r om the outlet po rt

 turbulent m i xing in the b oundary layer along the hull

 dispersion in the turbulent wake left behind the vessel The influences of the exit jet and the boundary laye r on the advection of th e process water in the vicin ity of the outle t por t were also included in the m odel.
The sub-m o del for the exit jet was based on well known sem i -e m p irical relations for m o mentum jets in cross-flow (Briggs for m ula). The sub-m o de l f o r the v e locity and turbulenc e pr of iles in th e boundary layer was derived from c l assical theo ry of boundary layer flow. A s ub-m odel for turbulent m i xing behind the stern of vessel was de veloped on the basis of the theory for wakes behind self-propelled bodies, assum i ng stationary flow (the vessel is m o ving at con s tant ve locity ). Figure 2.1 shows the results in no rmaliz ed f o rm

.

B

U'

K

0.001

0.01

0.1

1 10

0.1 1 10 100 1000
Normal iz e d distance, X = x / b 0Normalized wake variables,B,U', K

Figure 2.1. Normalized turbulent dispersion par ameters for a wake behind a self propelled body. X=x/b 0 is the normalized downstream distance, scaled with the initial wa ke radius b 0 =0.5 R, where R is the half width ( r adius) of the hull. B=b/b 0 , U’=u’/U and K=D/(U b 0 ) are normalized wake variables repres enting the wake radius b, turbulent veloc ity fluc t uations u ’ a nd turbulen t diffus i v ity D as a function of th e no rmalized downstream distance.3

One important aspect of this sub-model is that for a given vessel geometry (hull radius), the dilution of the effluent at a given downstream distance x will be independent of the vessel speed.
It should also be noted that this model was f ound to produce significantly less dilution at a given downstream distance than a more conventional model for dispersion in a momentum wake, i.e. a wake formed behind an obstacle in a stationa ry flow. The momentum wake model might be relevant during manoeuvring and acceleration from rest, but the self propelled body model seems to be most appropriate for trans port conditions (constant velocity). Simulations with different vessel speeds indicated that turbulent mixing in the exit jet dominated the dilution of the process water along the hull of the vessel at lo w vessel speeds, while turbulent mixing in the boundary layer dominated at high vessel speeds. In the former case, dilution tends to increase with increasing discharge rate and decrease with increasing vessel speed at a given down stream distance from the exit port. In the latter case, dilution tends to decrease with increasing discharge rate, and increase with increasing vessel speed. In general, however, turbulent dispersion occurring in the wake behind the vessel will be the dominant process governing the dilution of the process water. Example calculations in the environmental impact assessment report (see Figur e 2.2) showed that the process water was diluted by a factor of 1:30 before the effluent pa ssed the stern of the vess el, while dilution ratios of 1:2000 were found in the wake at a distance of 50 meters behind the stern of the vessel. This seems to imply that, as a first order estimate, one might neglect the initial dilution due to (a) turbulent entrainment in the ex it jet and (b) turbulent dispersi on in the boundary layer along the hull, and make dilution estimates entirely on turb ulent dispersion in the wake. These observations will have certain implications on the possible scaling of the results to other discharge conditions and vessel speeds. This will be the main issue in the next chapter. However, the model results will also to a certain extent be sensitive to the discharge arrangement, particularly the location of the di scharge port. In the simulations presented in the EIA-report, the discharge port was located 8 m below the water, 20 m ahead of the stern of the vessel. As the example taken from the Model Report indicates (Figure 2.2), this arrangement implies that the plume of diluted process enters into the periphery of the wake as it passes the stern of the vessel. A discharge port located in the stern of the vessel would bring the plume directly into the central parts of the wake, where the turbulent mixing would be st ronger. Obviously, simplified approaches based on scaling laws ca n not account for such effects.
It should also be noted that the dominant role of the turbulent mixing in the wake is limited to the cases where the vessel is moving at a presumed c onstant velocity, i.e. the for the port load and transport load cases defined in the previous st udy. For the quay side manoeuvring case, where the vessel was supposed to be almost at rest, turbul ent entrainment in the exit jet will be the main cause of the dilution of the process water.4

Figure 2.2. Example of results from the proces s water dispersion model for the transport load case (discharge rate 440 m 3 /h, vessel speed 14.5 knots) . Solid lines indica te vess e l hu ll with elliptic a l cross s ection, thin line s s how the extent o f

the wake. Open markers represent model particles. Reproduction of Figure 9 in the Model Report.5



### 3 SCALING LAWS The environmental impact assessment (EIA) that was made in the previous study on exhaust gas sea water washing systems was partly based on results from the dispersion model we have described briefly in the previous chapter. The case s that were considered were defined as follows: Table 3.1. Vessel dimensions and location of outlet port
Vessel dimensions: Length of vessel 163 m Vessel width 26 m Vessel draft 11.4 Outlet port: Distance ahead of vessel stern 20 m Depth below sea level 8.2 m Diameter of outlet 332 mm

Table 3.2. Description of discharges

Case Quay side manoeuvring Port load Transport load Discharge rate 130 m 3 /h 130 m 3 /h 440 m 3 /h Vessel speed 0 knots 4 knots 14.5 knots

As a starting point for the present discussion on scaling laws, we have re produced the results for the port load and transport load in Table 3.3. Table 3.3. Results from dispersion calculations of process water for the port load and transport load cases. Maximum concentrations are gi ven as parts per thousand (ppt) of process water as a function of distance from the st ern of the vessel. Th e corresponding transit times are computed from the distance from the discharge point and the given vessel speed.
Distance 50 m 100 m 200 m 500 m 1000 m Case: Port load (4 knots) Max. conc. (ppt) 0.570 0.300 0.170 0.110 0.090 Transit time 34 sec 60 sec 110 sec 250 sec 500 sec Case: Transport load (14.5 knots) Max. conc. (ppt) 0.450 0.290 0.200 0.090 0.075 Transit time 10 sec 16 sec 30 sec 70 sec 140 sec

As pointed out in the EIA-repor t, it was found that the computed concentrations at a given distance from the stern of the vessel were striki ngly similar for the two cases. By inspecting the discharge conditions for the port load and the trans port load (Table 3.2), one will also find that the ratio q = Q/U is almost equal for the two cases, i.e. about 18 L/m for port load vs. 16 L/m for transport load. This significance of the ratio q can be explained by the following deduction:

 The volume of process water V discharged in a given time period t is V = Q t , where Q is the discharge rate.6

 The trans it tim e to a certain downstream distance x is t = x / U , where U is the vesse l sp eed.

 Hence, the v o lum e of process water cont ain e d within a certain downstream distance x is given by V = Q x/U = q x , where q is the volum e of process water contained per unit downstream distan ce.
This im plies that f o r a n arbitrary discharg e ra te Q and vessel speed U , we m a y estim ate th e

m a xi m u m c oncentrations of process water at a given downstream distance x by scaling the concentratio n values with a factor ref q q q r / = , where q ref is the ratio Q/U for the reference c a se. If
the vessel dim e nsions (vessel width and draft) also differ for the two cases, the downstream distan ces x must be scaled with the radius R of the hull by a multiplica tio n f actor . The

exam ple described in Table 3.4 is chosen to illustrate the m e thod. R R r ref x /

=

Figure 3.1 shows the results of the proposed scali ng procedure (new case co m p ared with reference case). The concentration values are shifted upwards for the new case due to the larger discharge
rate -to

- vesse l speed ra tio ( q = Q/U ), and the dow nstream distances are sh if ted to th e le f t due to the larger width of the hull (36 m v.s. 26 m ) . In tota l, we find that the concen trations are increas ed by

a m u ltiplication factor of about 1. 7 at a g i ve n downstream distance due to th e changes in discharge conditions and vessel dim e nsions.

0.01

0. 1

1 10

10 1 0 0 100 0 1 00 00
Distan c e d o w ns trea m, mMax. concentration, ppt T r anspor t load - ref e rence case

T r anspor t load - new case

Figure 3.1. Example of application of the scal ing method described above. See Table 3.4 for description of the two cases.
Table 3.4. Example used to illustrate the use of the scaling laws for di spersion in the wake.

C a s e D i s c h a r g e r a t e , Q Vessel speed, U q = Q/U Hull width Reference case 440 m 3 /h 14.5 knot 16.4 L/m 26 m New case 800 m 3 /h 12.5 knot 34.6 L/m 36 m7

However, as mentioned in the previous chapter, the model results are also to a certain extent sensitive to the discharge arrangement, particularly the location of the discharge port. As noted, a discharge port located in the stern of the vessel rather than in the side of the hull would imply stronger turbulent mixing and enhanced dilution of the plume of produced water. Obviously, the scaling laws presented above can not account for such effects. Finally, it should be noted that for other treatment systems than the one presumed in the EIF Report, the recalculated concentration values must be compared with the actual acidity or toxicity corresponding to different dilution ratios of the effluent. To illu strate the problem, we will use data reported for the treatment system considered in the EIF Report as an example: For transport load conditions in seawater the initial pH of the effluent was measured as low as 2.9. This value will be raised as a result of diluti on with seawater, but the environmentally acceptable dilution ratio will depend on the established “no-eff ect” pH value. In the EIF Report, it is assumed that a reduction of 1 pH unit from the average pH of 8 in seawater can be considered acceptable. However, it is also mentioned that EPA has r ecommended a stronger criter ion, implying that the pH should be reduced not more than 0.2 units below the normal pH in seawater. For the transport load case (133 mg SO 2 /L seawater with 34 ppt salin ity), it was found that pH could be raised from the initial value of 2.9 to 7 by a dilution of one part of the effluent with 22 parts of seawater. An increase in pH to 7.8 would on the other ha nd require a dilution ratio of 300. The EIF Report concluded that these “critical” dilution ratios were well below the ratios obtained at downstream distances more than 50 meters behi nd the vessel stern. It should be kept in mind that these numbers depend on the makeup of the di scharge, and that changes in the treatment system might change the picture due to changes in the make up of the effluent. The following points may serve as a conclusion:

 For transport load and port load cases (vesse l moving with constant velocity), where the dilution process is dominated by turbulent dispersion in the wake behind the vessel, simple scaling laws may be used to make estimate s of concentrations dow nstream of the vessel (recalculations based on pr evious model results).

 These scaling laws are not applicable for quay side manoeuvring (stagnant vessel), where the dilution process is dominated by turbulen t dispersion in the exit plume model.

 The results from such recalculations must be asse ssed against expected acid ities of the effluent at given dilution ratios, and accepted no-effect values of pH.

 If such assessments show small margins relative to no-effect values, actual dispersion model calculations will be required. If the margins are large, recalculated values may be sufficient. Finally, we should add that the EIA Report also included possible regional effects of discharges of process water. The possible effects were assessed on the basis of water exchange values for a specific region (the Inner Oslo Fj ord), and the expected vessel tra ffic density in the same area. The method used in the assessment might be of genera l value, but it must be pointed out that such assessments depends on site-specific water exch ange data, traffic densities, and specific knowledge of the acidity of the actual e ffluent at various dilution ratios.8



### 4 REFERENCES Johansen, Ø, 1993: Exhaust Gas Sea Water Washing Syst em – Dispersion of Process Water

. OCEANOR Report OCN R-93069, 38 pp. Johansen, Ø, K. Tangen, and F. Moy, 1994: Exhaust Gas Sea Water Washing System – Environmental Impact Assessment . OCEANOR Report OCN R-94003, 71 pp.