international congress of combustion engines ptnss kongres - 2007

© 2005 PRS S.A.

TECHNOLOGIES REDUCING EXHAUST GAS EMISSIONS

FROM LARGE MARINE DIESEL ENGINES

Andrzej ADAMKIEWICZ Szczecin Maritime Academy,

Technical Commitee of Polski Rejestr Statków

Krzysztof KOŁWZANStatutory Department of Polski Rejestr Statków S.A, Gdańsk

INTERNATIONAL CONGRESS OF COMBUSTION ENGINES PTNSS KONGRES - 2007

THE DEVELOPMENT OF COMBUSTION ENGINES KRAKOW 20- 23 MAY 2007

© 2005 PRS S.A.

TECHNOLOGIES REDUCING EXHAUST GAS EMISSIONS FROM LARGE MARINE DIESEL ENGINES

Presenter: Krzysztof Kołwzan

Polski Rejestr Statków S.A.Statutory Department

Gdańsk, POLAND

PTNSS KONGRES - 2007

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OVERVIEW EXHAUST GAS EMISSIONS FROM LARGE MARINE DIESEL ENGINES

MARPOL ANNEX VI REQUIREMENTS

METHODS OF LOWERING NOX IN EXHAUST GAS

CONCLUSIONS AND FINAL REMARKS

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EXHAUST GAS EMISSIONS FROM LARGE MARINE DIESEL ENGINES

Diesel engines manufactured today demonstrate impressive gains in engine fuel economy and reliability over engines produced a decade ago.

Better turbocharging and fuel injection have resulted in much higher thermal efficiencies, but in higher firing pressures and temperatures – and NOX emissions.

Various technologies are available for retrofit on existing engine installations and for new engines.

Diesel engines emit low amounts of carbon di-oxide (CO2), carbon monoxide (CO) and hydrocarbons (HC), but their emissions are high in nitrogen oxides (NOX).

Additionally marine engines use residual bunker fuels containing sulphur, asphaltenes and ash.

Thus exhaust emissions contain a lot of nitrogen and sulphur oxides and particulate matter.

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MARPOL ANNEX VI REQUIREMENTS

The International Maritime Organization’s (IMO) MARPOL 73/78 Annex VI agreement introduced, new marine NOX emission limits for the international shipping industry.

Protocol of 1997 Annex VI to MARPOL 73/78 Convention - Regulations for the Prevention of Air Pollution from Ships entered into force on the 19 May 2005.

MARPOL Annex VI sets limits on sulphur oxide and nitrogen oxide emissions from ship exhausts, prohibits deliberate emissions of ozone depleting substances and regulates emission of volatile organic compounds (VOCS).

The annex includes also a global cap of 4.5% m/m on the sulphur content of fuel oil and calls on IMO to monitor the worldwide average sulphur content of fuel.

The IMO NOX limits are applied to all new (or major retrofits) engines built after January 1, 2000, rated greater than 130 kW.

In anticipation of this, all marine engine makers have made internal modifications to their designs to meet the proposed limits.

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FOUR METHODS : 1. Pretreatment or conditioning of the fuel and/or the

combustion air,

2. Engine tuning or operational mode,

The first two methods can be adapted for existing installations with little or no limitations.

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3. Hardware design such as modifications and enhancements to the combustion chamber components, fuel system components, engine control system, etc.,

Third metod is suitable for new engines and most manufacturers are conducting extensive research with the intention of making them more eco-friendly without sacrificing fuel economy.

4. Conditioning the exhaust gas after the combustion process

The fourth approach involving the treatment of exhaust gas after the combustion entails installation for NOX

reduction – a Selective Catalytic Reactor (SCR) unit. Due to size and the prohibitive installation costs, this option is also generally considered for new projects.


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1. PRETREATMENT OR CONDITIONING OF THE FUEL

Fuel Conditioning - addition of water to the fuel to create a stable and homogeneous emulsion.

When this emulsified fuel is injected into the combustion chamber is achieved NOX reduction.

Fuel Pretreament - homogenization In the process of homogenization, the asphaltenes

in the fuel, are broken down to about 3-5 microns. This relates to better combustion and thus lessening the amount of deposits in the combustion chamber.

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1. PRETREATMENT OR CONDITIONING OF THE COMBUSTION AIR

Combustion Air PretreatmentInjecting water directly into the combustion air stream is another

method of lowering the peak temperatures of combustion.

There are several ways of injecting water depending on the engine type.

On 4 stroke trunk piston engines, water can be injected through a spray nozzle in the intake manifold.

As with the fuel/water emulsion the NOX reduction attainable is around

25-30%.

However, on 2 stroke engines (all large marine propulsion engines), there is a risk of engine damage if the injected water washes away the cylinder

lube oil film which may lead to excessive wear and/or seizure.

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2. ENGINE TUNING OR OPERATIONAL MODE

Engine Timing Engine manufacturers optimize this pre-ignition angle for fuel

economy and reliability of the engine components. Retarding the injection timing can lead to lower peak

temperatures in the combustion chamber and thus lower NOX emissions.

Operational Mode With the advent of electronically controlled engines where the

fuel injector is controlled by electronic means, fuel injection rate shaping is possible.

This shaping rate can be optimized for fuel economy or low NOX emissions and selecting between the two modes of operation is a control panel function and is done in service

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3. HARDWARE DESIGN MODIFICATIONS AND ENHANCEMENTS

Direct Water Injection (DWI) System

Continuous Water Injection to Charge Air - CWI System

Fuel-Water Emulsions (FWE) System

WACOREG: Water-cooled Residual Gas

Humid Air Motor (HAM) System

Exhaust Gas Recirculation (EGR) System

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The injection of a high-pressurized fine water mist into the combustion chamber.

Direct water injection (DWI) Wartsilla technology can reduce NOX emissions from marine engines by 40 to 60%.

Direct Water Injection (DWI) System

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A fine, freshwater mist is injected directly into the hot compressed air of the turbocharger outlet.

Continuous water injection (CWI) to the charge air - method of reducing NOX by up to 30% and PM emissions by about 25%, without engine modifications.

Continuous Water Injection (CWI) System

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The resulting dispersion of microfine water droplets in fuel are injected into the engine cylinders.

The systems have only recently been commercialized as an option on new MAN B&W marine engines and are rarely used in retrofits.

Fuel-water emulsion (FWE) systems can reduce NOX formation in marine diesel engines by 30 to 60% by intimately mixing water into the fuel oil.

A significant benefit of FWE systems is a drastic reduction of PM emissions (smoke) and lower engine soot deposition.

Fuel-Water Emulsions (FWE) System

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EGR: Internal exhaust gas recirculation by reduced scavenging ports and smaller turbocharges

DWI – direct water injection to reduce comabustion chamber temperatures and NOx emissions

RTF – flex : Common rail technology and variable exhaust valve timing to adjust EGR level

NOx reduction: up to 70% = 5 g/kWh

Wartsila engines

WACOREG: WATER-COOLED RESIDUAL GAS Combining water injection with internal exhaust gas

recirculation

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HAM method is partly based on reducing the oxygen content of the cylinder charge and partly on increasing the heat capacity of the cylinder charge by the addition of water vapour.

The charge air is humidified by water vapour produced in a humidification vessel by evaporating freshwater or seawater directly into the charge air using the heat from the engine or its exhaust gases.

The system was developed by Munters AB of Sweden and is only available commercially on new Pielstick engines.

NOX emissions reductions of 60 to 80% have been achieved in demonstration tests

Humid Air Motor (HAM) System

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The EGR method is based on a reduction of the oxygen content in the cylinder charge.

In an EGR system, exhaust gases from the engine pass through the turbocharger, releasing energy to compress the incoming combustion air.

The temperature and pressure of the gases are reduced considerably.

A portion of the exhaust gases is recirculated back and is added to the compressed air before the cylinder.

Particulate filters are used to remove entrained solids prior to mixture with the combustion air. The lower temperature of the exhaust gases contributes to a cooler combustion. The increased mass flow increases the combustion pressure and dilutes the oxygen content.

EGR system achieving 50 % reduction of NOX

Exhaust gas recirculation (EGR) System

Schematic design of EGR and HAM systems application on the 4T50ME-X engine (MAN B&W)

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4. CONDITIONING THE EXHAUST GAS AFTER THE COMBUSTION PROCESS

SCR unit is an effective means of conditioning the exhaust gas after the combustion process for reducing NOX already formed in the combustion process.The process essentially involves injecting ammonia (urea solution) in the exhaust stream and in the presence of a catalyst the NOX reacts with the ammonia and forms water vapor and nitrogen.

SCR is capable of reducing NOX emissions by up to 99% by reacting NOX with ammonia (from a urea solution) over a catalyst in the hot exhaust gases of marine engines. Inert nitrogen and water are produced in the reaction. HC and CO are also reduced significantly, but PM and SOX are uncontrolled.

Selective Catalytic Reduction (SCR) Unit

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The available options are pre-treatment of the fuel and/or the combustion air.

Conditioning the fuel with water to produce a stable water emulsion is considered the most suitable option for large 2-stroke engines.

Conditioning the combustion air by water injection is not suitable for 2-stroke engines due to the risk of destruction of the cylinder lube oil film.

The high pressure homogenizer/emulsifier is considered the better alternative to the other designs.

The following conclusions were drawn from the analysis in this study

© 2005 PRS S.A.

CONCLUSIONS AND FINAL REMARKS– Direct Water Injection (DWI) technology appears to be

effective for medium levels of NOX reduction (40-60%), but may not be a practical technology for engine retrofits, due to its specific engine design requirements. It becomes much more cost effective on new engines.

– Continuous Water Injection (CWI) to the charge air appears to be most cost-effective system for low levels (10-30%) of NOX reductions, but the low level of operating experience makes further testing a necessity. It would be best used for trimming NOX emissions to meet minimum IMO limits.

– The Fuel-Water Emulsion (FWE) system appears to be a promising, medium-cost technology for achieving medium levels (30-50%) of NOX reduction. Since FWE is reasonably simple to retrofit onto existing ships without significant structural engine modifications, it appears to be a practical retrofit solution.

© 2005 PRS S.A.


– Humid Air Motor (HAM), despite high initial capital costs, appears to be a practical, cost-effective method of achieving medium to high levels (60-80%) of NOX reduction. Limited operating experience suggests that it can be retrofitted in the engine room without the need

for new water supply, and performs well. – The Selective Catalytic Reduction (SCR) system has the highest unit

cost of the five technologies analyzed, but can achieve almost complete NOX reduction. Installation costs are a significant issue if major retrofitting is required. This technology is best suited for vessels operating in regions having very stringent environmental control programs and financial incentives.

– Most engine manufacturers are now producing standard engines which comply with MARPOL Annex VI NOX emissions levels. This has been achieved by engine tuning measures, which commonly involve increased compression ratio, retarded injection timing, increased injection intensity and optimized spray patterns.

international congress of combustion engines ptnss kongres - 2007

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