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NOX AND SOX EMISSION CONTROL
ABSTRACT
Ship’s SOX emissions forms 60% of total SOX Emissions.
We are polluting our environment by our choice of fuel.
Emission control in the angle of MARPOL and the technologies for reduction are taken into account.
POLLUTANTS
Air pollutants can also be of primary or secondary nature.
Primary is emitted directly to atmosphere. Secondary is formed by reactions between primary
pollutants. The major pollutants are
1. Oxides of nitrogen
2. Oxides of sulphur
3. Particulate matter
CHEMISTRY OF FORMATION
N2+O2 2NO
2NO+O2 2NO2
S+O2 SO2
SO2+NO2 NO+SO3
2NO+O2 2NO2
NO2+SUNLIGHT NO+O
O+O2 O3
HAZARDS
Corrosion Climate change Photochemical smog SO2 irritates the eyes, nose and lungs
SO2 causes acid rain
NO2 causes pulmonary edema
MARPOL LEGISLATION
Annex VI- Regulations for the prevention of air pollution from ships
Came to force on 19th May 2005 For every ship with 400 gross tonnage and
above and for fixed and floating drilling rig Certificate- “International air pollution
prevention certificate” Validity- period not exceeding five years
MAJOR REGULATIONS There are 19 Regulations but the following
Regulations impact Vessel operation :
Regulation 12 – Ozone Depleting Substances Regulation 13 – NOx emissions Regulation 14 – Sulphur Oxide emissions Regulation 15 – VOC emissions Regulation 16 – Shipboard Incinerators Regulation 18 – Fuel Oil Quality control
Emission standards are referred to a Tier I, II,III
Tier I came into force on 19th May 2005. The revised Annex VI enters into force on 1st
July 2010. Tier II,III are more stringent than Tier I . Tier II standards are expected to be met by
combustion process optimization. Tier III standards are expected to require
dedicated NOx emission control technologies.
REGULATION 13
Deals with control of NOX emissions. All engines with power more than 130KW and
built on or after 1/1/2000 Doesn’t apply to engines used in emergency. Emissions must be limited to, 17.0 g/kWh when n <130 rpm; 45.0 x n-0.2 g/kWh when n is 130 or more but
less than 2000 rpm; 9.8 g/kWh when n is 2000 rpm or more
SOX CONTROL
Sulphur content of fuel shall not exceed 4.5%. SOX emission ECA include Baltic and North sea
area. Sulphur content shall not exceed 1.5% in ECA. Total emission must be less than 6 g SOX/kWh
in ECA
FUEL OIL QUALITY
Fuel oil shall be free from inorganic acid. Bunker delivery note must be maintained. Bunker delivery note must kept for 3 years. Fuel oil sulphur content must never exceed
4.5%. Parties of 1997 protocol must maintain a
register of local suppliers of fuel oil.
EMISSION MEASUREMENT
For Attaining Interim Certificate of Compliance.
Engines combined into engine groups by manufacturer
Engine from this group selected for emission testing
EXHAUST GAS MONITORING TECHNIQUES
Exhaust Gas Monitoring Equipments
ExtractiveExtractive
Systems SystemsNon-Extractive Non-Extractive
SystemsSystems
UV UV AnalysersAnalysersChemi-
luminescence
Infrared Infrared
AnalysersAnalysers
Ultra-Violet Ultra-Violet
AnalysersAnalysers
Extractive Systems Permanently installed Requires additional equipment to process the
exhaust gas sample. Advantages Able to be remotely located in a controlled environment Easier to operate, calibrate and maintain. Can be set up to monitor exhaust gas emissions from more
than one engine.
Disadvantage High Cost
NON-EXTRACTIVE SYSTEMS
Predominately use infrared or ultra-violet techniques.
Measure the exhaust gas emissions without extracting the exhaust gas from the uptake system.
Advantages More portable Provides more rapid responses.
Disadvantages Difficult to calibrate.
CHEMILUMINESCENCE HCD (Heated Chemiluminescence Detector). Accepted standard for laboratory and test cell
measurement of NOx. Was the only available NOx detector available
during the development of the IMO Technical code.
Needs to have a continuous supply of clean dry air else damage to the analyser components will result.
NO determination with detection limits down to 1 ppb.
ULTRA-VIOLET ANALYSERS
Particularly useful for measuring SO2 .
Used in extractive and non-extractive systems. Not suitable for the measurement of NOx.
REDUCING SOX EMISSIONS
2 Possibilities :- Burning fuels with lower sulphur content Treating the engine exhaust gases
At Present limits on sulphur content of marine fuel
Globally – 4.5% SECA – 1% from 1st july,2010
SOX emission control areas (SECA) North Sea, English Channel and the Baltic Sea.
TECHNIQUES FOR REDUCING SOX EMISSIONS
3 possibilities to reduce SO2 emissions from combustion processes:
1) REMOVAL OF SULPHUR BEFORE COMBUSTION
2) REMOVAL OF SULPHUR DURING COMBUSTION
3) REMOVAL OF SOX AFTER COMBUSTION ( I.E. FLUE GAS DESULPHURISATION )
REMOVAL OF SULPHUR BEFORE COMBUSTION
Process used : Hydrotreating or Hydrodesulphurisation Treatment of the oil with hydrogen gas obtained e.g. during
catalytic reforming. Sulphur compounds are reduced by conversion to hydrogen
sulphide (H2S) in the presence of a catalyst.
H2S washed from the product gas stream by an amine wash H2S is recovered in highly concentrated form Converted to elemental sulphur via the Claus-Process Feedstock is mixed with hydrogen-rich make-up and recycled
gas and reacted at temperatures of 300 - 380 °C.
Removal of sulphur from heavier oils such as marine fuel oil often requires pressures of up to 200 bar.
Catalysts employed : cobalt, molybdenum or nickel finely distributed on alumina extrudates.
CLAUS PROCESS
Most significant Gas desulphurizing process Recovers elemental sulphur from gaseous
hydrogen sulphide The overall main reaction equation is:
2 H2S + O2 → S2 + 2 H2O
REMOVAL OF SULPHUR DURING COMBUSTION
Experimental Stage The combustible compound is mixed with an
admixture of water soluble and water insoluble sulphur sorbent.
Such admixtures, remarkably, produces a reduction in the SOX level far greater than would be expected based on the activity of each sorbent alone.
REMOVAL OF SOX AFTER COMBUSTION
THE THE SEAWATERSEAWATER SCRUBBER SCRUBBER
SPRAY SPRAY DRYDRY
SYSTEMSYSTEM
WELLMAN-LORD WELLMAN-LORD PROCESSPROCESS
LIMESTONELIMESTONE/GYPSUM /GYPSUM SYSTEMSYSTEM
FLUEFLUE GASGAS
DESULPHURISATION DESULPHURISATION (FGD)(FGD)
LIMESTONE/GYPSUM SYSTEM
Most widely used process Principle Suspension of crushed limestone in water is
sprayed into the flue gases. SO2 reacts with calcium ions to form calcium
sulphite slurry Aeration of the slurry with compressed air
oxidizes calcium sulphite to calcium sulphate After removal of the water, the calcium
sulphate can be disposed off
Advantage : SO2 reduction around 90 %
Disadvantages : limestone has to be stored onboard large quantities of gypsum waste is produced
SPRAY DRY SYSTEM A slurry of slaked lime is used as an alkaline
sorbent The slurry is injected into the flue gases in a
fine spray. The flue gases are simultaneously cooled by
the evaporation of water The SO2 present reacts with the drying sorbent
to form a solid reaction product, with no wastewater.
WELLMAN-LORD PROCESS Hot flue gases are passed through a pre-scrubber Ash, hydrogen chloride, hydrogen fluoride and SO3 are
removed. the gases are then cooled and fed into an absorption tower SO2 reacts with a saturated sodium sulphite solution to form
sodium bisulphite. The sodium bisulphate is regenerated after a drying step to
sodium sulphite again. The released and clean SO2 - may then be liquefied or
converted to elemental sulphur or sulphuric acid. The sorbent is regenerated during the combustion process and
is continuously recycled, but the products (sulphur compounds) have to be stored.
THE SEAWATER THE SEAWATER SCRUBBER Krystallon Sea-Water Scrubber Removes 90-95 % of SO2 In addition removes 80 % of the particulates
and 10-20% of hydrocarbons. Advantages♦ no limestone has to be stored on board, ♦ no waste (gypsum) is produced, which has to
be deposited on land, ♦ the seawater already contains substantial
amounts of sulphate and nitrate ♦reduction of engine noise and a reduction of
the diesel smell. .
Uses Cyclone Technology The system needs only a little extra space Aeration of the effluent is necessary high degree of recirculation
FeaturesFeatures
WorkingWorking
Water in contact with hot exhaust gas Exhaust gas is channelled through a concentric
duct into a shallow water tank. Mixing baffles break up large gas flow into
smaller bubbles SOx in exhaust gas is dissolves in seawater Larger particles (greater than 2.5 micron)
captured in the water. Fine particles (smaller than 2.5 micron) may
pass through without capture.
Pumped through a set of large cyclones Designed to separate some of the heavy
particles, as well as light particles in a two-stage system.
Fed to a settling tank for collection of soot and oil.
Runs with no ongoing maintenance Cleaned recirculated water is maintained at
extremely low concentrations of hydrocarbons, making it safe for discharge to sea.
OPERATIONAL CONCERNS AROUND THE CHANGE TO
LOW SULPHUR FUELS REDUCED FUEL VISCOSITY FUEL ACIDITY IGNITION AND COMBUSTION QUALITY FUEL LUBRICITY
REDUCED FUEL VISCOSITY
MGO and MDO fuels have a lower inherent viscosity than heavy fuel oil which can :
Effect Diesel Engines Effect Steam Boilers
Effect On Diesel Engines
Changes in fuel atomisation Adversely affects power output and engine
starting performance. Solution Recommended : Use fuel coolers to
control fuel viscosity
Effect On Steam Boilers
Affects fuel flow setting (for a given pressure) at the burners
Can lead to “Over Firing” Increased risk of flame failures and flame
impingement on boiler tube plates. Solution Recommended : Change the nozzle Or the air/fuel ratio settings
FUEL ACIDITYFUEL ACIDITY Does not present a problem for steam boilers But has a significant effect on diesel engines Engine lube oils are formulated with alkaline
additives to neutralise the acidic, sulphur, by-products of combustion.
IF amount of sulphur in the fuel is reduced, THE amount of alkaline additives should be reduced.
Too much alkalinity causes build-up of deposits that will affect the lubricating film
Solution Recommended : Oil with a lower Base Number (BN).
IGNITION AND IGNITION AND COMBUSTION QUALITYCOMBUSTION QUALITY
Effect On Diesel Engines Effect On Steam Boilers
Effect On Diesel Engines
Poor combustion and ignition may lead to increased fouling of the engine
Fouling is so excessive that moving parts such as exhaust valves are inhibited by the soot, leading to broken/bent valves
Excessive fouling of the scavenge air receiver combined with late ignition or prolonged combustion may lead to a buildup of soot deposit and the risk of fire.
Effect On Steam Boilers
Leads to starting failures and more frequent flame failures
May lead to increased soot formation and consequent fouling of the boiler and exhaust system.
Solution Recomended: Follow detailed advice given by manufactures on procedures to follow when switching fuel qualities.
FUEL LUBRICITYFUEL LUBRICITY
Ultra Low Sulphur Diesel (ULSD) contains <15ppm sulphur.
Inherent lubricity of such diesel is reduced which in turn increases wear on fuel pumps and injectors.
Solution : Lubricity additives are commonly added at source to such fuels to reduce these problems
ENGINE EXHAUST DEPENDS ENGINE EXHAUST DEPENDS UPONUPON
ENGINE TYPE ( i.e LOW,MEDIUM AND HIGH SPEED)
ENGINE SETTING ( i.e LOAD,SPEED AND FUEL INJECTION TIMING)
FUEL USED
FACTORS AFFECTING FACTORS AFFECTING NOx FORMATIONSNOx FORMATIONS
SPEED OF ENGINE MAXIMUM TEMPERATURE INSIDE CYLINDER COMPRESSION RATIO/PEAK PRESSURE AMOUNT OF SCAVENGE AIR
NOxNOx REDUCTIONREDUCTION TECHNIQUESTECHNIQUES
PRE-TREATMENT
INTERNAL MEASURE(PRIMARY
METHODS)
AFTER TREATMENT(SECONDARY METHODS)
NOxNOx REDUCTIONREDUCTION TECHNIQUESTECHNIQUES
PRE-TREATMENT
INTERNAL MEASURE(PRIMARY
METHODS)
AFTER TREATMENT(SECONDARY METHODS)
ALTERNATIVE FUELSALTERNATIVE FUELS
METHANOL LIQUIFIED PETROLEUM GAS
METHANOLMETHANOL
50% REDUCTION NO SULPHUR BAD IGNITION QUALITY CORROSIVE EXPENSIVE FUEL
LIQUIFIED PETROLEUM GASLIQUIFIED PETROLEUM GAS
BUTANE(C4H10)+PROPANE(C3H8)
LOW ENERGY DENSITY SO MORE FUEL CONSUMPTION
NON-CORROSIVE NON-TOXIC
WATER ADDITION TO FUELWATER ADDITION TO FUEL
UNDER RESEARCH WITH 30% OF WATER IN FUEL
30% REDUCTION IN NOx EMISSION EFFECT ON ENGINE COMPONENTS IS
NOT KNOWN DECREASE MAXIMUM TEMPERATURE
INSIDE CYLINDER HIGH SPECIFIC HEAT
NOxNOx REDUCTIONREDUCTION TECHNIQUESTECHNIQUES
PRE-TREATMENT
INTERNAL MEASURE(PRIMARY
METHODS)
AFTER TREATMENT(SECONDARY METHODS)
MODIFICATIONS IN MODIFICATIONS IN COMBUSTION PROCESSCOMBUSTION PROCESS
INJECTION TIMING RETARDATION INCREASE IN INJECTION PRESSURE OPTIMIZATION OF INDUCTION SWIRL MODIFICATION OF INJECTOR
SPECIFICATION CHANGE IN NUMBER OF INJECTORS
INJECTION TIMING INJECTION TIMING RETARDATIONRETARDATION
REDUCE MAXIMUM COMBUSTION TEMPERATURE & PRESSURE
REDUCTION UPTO 30% OF NOx EMISSION
INCREASE IN SFC BY 5% MORE EFFECTIVE FOR MEDIUM/HIGH
SPEED ENGINES
INCREASE IN INJECTION INCREASE IN INJECTION PRESSUREPRESSURE
COMBINED WITH OTHER TECHNIQUES PROVIDES BETTER ATOMIZATION
OPTIMIZATION OF OPTIMIZATION OF INDUCTION SWIRLINDUCTION SWIRL
COMBINED WITH OTHER NOx REDUCTION TECHNIQUES
HELPS IN GOOD COMBUSTION NO ADDITIONAL COST
INJECTOR SPECIFICATIONSINJECTOR SPECIFICATIONS
INJECTION PRESSURE NUMBER AND ANGLE OF HOLES SIZE OF HOLES
CHANGE IN NUMBER OF CHANGE IN NUMBER OF INJECTORINJECTOR
COMBUSTION PROCESS CAN BE CONTROLLED BETTER
REDUCE MAXIMUM COMBUSTION TEMPERATURE
ADDITIONAL COST OF FUEL INJECTOR AND PIPING
INCREASE IN MAINTENANCE COST 30% REDUCTION IS ACHIEVABLE
SCAVENGE/CHARGE AIR SCAVENGE/CHARGE AIR COOLINGCOOLING
14% REDUCTION IS POSSIBLE BY LOWERING CHARGE AIR TEMP. FROM 40oC to 25oC
REDUCE COMBUSTION TEMPERATURE SUITABLE FOR MEDIUM AND HIGH
SPEED ENGINES COOLING AIR TOO MUCH COULD LEND
TO COMBUSTION PROBLEMS
WATER INJECTIONWATER INJECTION
DURING COMBUSTION THROUGH SPECIAL INJECTOR
REDUCES THE BULK TEMPERATURE OF COMBUSTION
40% REDUCTION IN NOx EMISSION IS ACHIEVED
WATER INJECTION WATER INJECTION LIMITATIONSLIMITATIONS
NEED OF SEPARATE PUMP FOR FUEL AND WATER
COST FACTOR CORROSION
NOxNOx REDUCTIONREDUCTION TECHNIQUESTECHNIQUES
PRE-TREATMENT
INTERNAL MEASURE(PRIMARY
METHODS)
AFTER TREATMENT(SECONDARY METHODS)
WHAT IS SCR?WHAT IS SCR?
SELECTIVE CATALYST REDUCTION IS THE PROCESS OF REDUCING NOx COMPOUNDS WITH AMMONIA INTO NITROGEN AND WATER VAPOURS IN PRESENCE OF CATALYST.
SCR SYSTEM COMPONENTSSCR SYSTEM COMPONENTS
REDUCTANT STORAGE TANK PUMP VAPORIZER (NOT IN CASE OF
ANHYDROUS AMMONIA) MIXER INJECTION NOZZELS CATALYST CHAMBER
WORKING OF SCR SYSTEMWORKING OF SCR SYSTEM
AFTER TREATMENT TECHNIQUE REDUCTANT(AMMONIA) IS INJECTED
AND MIXED INTO EXHAUST PASS THIS MIXTURE THROUGH
CATALYST CHAMBER TEMPERATURE OF CATALYST
CHAMBER SHOULD BE 450K-720K
REACTIONS INVOLVEDREACTIONS INVOLVED
REDUCTANTS USEDREDUCTANTS USED
ANHYDROUS AMMONIA AQUEOUS AMMONIA UREA
CATALYST USEDCATALYST USED
BASE METAL OXIDES SUCH AS (VANADIUM AND TUNGSTEN)
TITANIUM OXIDE ZEOLITE (HIGH TEMPERATURE
DURABILITY)
EXHAUST GAS EXHAUST GAS RECIRCULATIONRECIRCULATION
REDUCES LOCAL COMBUSTION TEMPERATURE.
HIGH SPECIFIC HEAT OF EXHAUST GAS AND WATER VAPOUR.
DECREASES OXYGEN CONCENTRATION.
BUBBLE BATH SCRUBBERBUBBLE BATH SCRUBBER
EMISSION TRADE
Credit based system This system was proposed by the swedish ship
owners association. Large combustion installations are capped by
their maximum annual emissions. Installation that emits less than its allocated
credits can trade the difference in theemissions market.
HOW IT WORKS? Emission reductions become a tradable
commodity, which can be bought and sold like any other product in the market.
Each ship will be allocated points depending on its yearly emissions in tons.
Trading can be made anonymously through an emissions market.
CONCLUSION
Emission control is a necessity to make shipping transport viable.
CSR and Green marketing are the new buzz words.
One time investment and high returns. Decrease in peak temperature can limit NOX
emission. Limit SOX by removing sulphur prior
combustion.
REFERENCES
Reduction of NOx and SOx in an emission a snapshot of prospects and benefits for ships in the northern European SECA area.
www.imo.org MARPOL consolidated edition 2006 Exhaust emissions from ship engines - significance,
regulations, control technologies by Laurie Goldsworthy www.dieselnet.com
THANK YOUTHANK YOU