NOx, SOx, PM, CH4 and NMVOC emission reduction options

Emission reduction options for NOx:-
       The formation of NOx is mainly dependent on the combustion temperature and the detention time at high temperature.Key strategies for reducing NOx in the engine involve reducing peak temperature, reducing the time for which gases are at high temperature and reducing the concentration of O2 in the charge air. all these can be achieved through:-

• Fuel modification include using a water fuel emulsion, the use of fuel that have a lower nitrogen content and and using fuels with different combustion properties that enable different optimization of the engine.
• Possible modification of the charge air includes its humidification and a reduction in oxygen content through (EGR) Exhaust gas re circulation or by use of air intake membrane to reduce the partial pressure of oxygen in the charge air.
• Modification of the combustion process include adjusting fuel injection rate, timing,compression ratio etc. to minimize the creation of NOx.
• Use of LNG as fuel can reduce NOx emission up to 90% in 4-stroke engines.
• Treating exhaust gas to reduce NOx by SCR to convert NOx into nitrogen can be used. Other post treatment technologies are NOx scrubbing and NOx adsorption.

Emission reduction options for SOx:-

      SOx emissions can be reduced by following:-

• Use of fuel with low sulfur content is the best option to reduce SOx.
• As an alternative, an exhaust gas scrubbing system can be employed to reduce the level of SOx. Two main principles exist--Open loop sea water scrubbers and closed loop scrubber. Both scrubber concept may also remove PM and limited amount of NOx

Emission reduction options for PM:-

     Unlike other emissions, which are chemically defined, Particulate matter is traditionally defined as the mass that is collected on the filter under specified conditions. PM consists of 

1. Organic Material (OM)
2. Elemental Carbon (EC)
3. Sulphate (SO4) and associated water
4. Ash

All the above can be reduced by following:-

• OM is related to the consumption of lube oil, which may potentially be reduced by change in lube oil additives. 
• EC are related to soots that is formed during combustion, some of which may be removed. OM and EC are thus independent of fuel.
• Sulphates, associated water and ash are mainly determined by the fuel.Some PM emissions from high sulfur fuels can be reduced by scrubbing. With low sulfur fuels, PM emissions can be further reduced by optimizing combustion for increased oxidation of soot and of PM, minimizing the consumption of lube oil additives. Using fuel water emulsions instead of pure fuel can also reduce PM emission to a certain extent.

Emission reduction option for CH4 and NMVOC :-

      These can be reduced by following:-

• These emissions are comparatively low. Some reduction may be achieved by optimizing the combustion process. NMVOC may also be oxidized with a catalyst. Oxygen can be used in conjunction with SCR installation
• Emission of CH4 from gas fueled engines are due to unburnt methane from the premixed combustion process.The level of CH4 emission depends on the lay out of the combustion chamber.By careful design to avoid crevices, emissions can be significantly reduced.
• CH4 emissions from a gas fueled engines can be virtually eliminated by replacing the lean premix combustion concept with high pressure gas injection. This concept is believed to be beneficial for 2-Stroke engines.