NOx Reduction Techniques

[tomatge]

I work for a stationary power plant that uses slow speed deisel (Sulzer RNF and RTA series) engines. At present in my location there is no specific environmental legislation in place in respect of emissions from the power plant, but this is currently under review.

Should legislation be introduced, the largest difficulty would probably be oxides of nitrogen (NOx). Nox levels, particularly from the RTA series engines, are very high in comparison with many "clean air" type legal requirements. Indeed, there is a visible orange/brown tinge in the exhaust (which if memory serves me correctly is NO2).

I have read technical papers about methods of NOx reduction from slow speed plant. Techniques like water/fuel emulsions, direct water injection, exhaust gas recirculation and selective catalytic reduction would appear to offer best methods of Nox reduction.

I wonder if any forum members have direct experience of such techniques on operational plant, with regard to cost, effectiveness, reliability etc.

Thanks in advance.

 

[DougMSOE]

About 10 -12 years ago I worked on some technology that since has been used in Japan and elsewhere. Recently in Business Week 4 Feb 04 it showed up again. The technology is called 'cold plasma' and it does work very well and not just on NOx but SOx and COx as well (diesel and coal fired as well). Most of the info has been found in the academic papers and I believe EPRI may be doing something as well.
A little known technology that does work!!

 

[1969grad]

On another forum page is a paper about air/fuel ratio. Perhaps that paper would give you some ideas.

How about a catalytic muffler?

Frankly all of the solutions you listed would fall into the "if nothing else works" category for me.

Final thought is have you contacted the engine manufacturer about possible fixes.

 

[tomatge]

You need to appreciate the characteristics of a slow speed diesel engine to understand the difficulties on this subject, which is why I posted in the Marine Engineering forum. The techniques I suggested are not actually "if all else fails" rather they are the very techniques that the major slow speed diesel manufacturers seem to be focussing on.

I understand that IMO directives have become increasingly stringent over the years, and new engines are likely to have NOx reduction measures fitted. I would be interested to hear of anyone who has operational experience.

 

[oxilume]

Tomatge,

In 2001 I was funded by US DOE to conduct a symposium on PhotoChemistry for the Chemical Industry (Gulf Coast US).

With my patented UV light, I demonstrated 18% NOx reduction from a tractor diesel engine. This was documented and verified by University of Louisiana at Lafayette, Louisiana Dept. of Natural Resources, and DOE.

Since then I have made dramatic improvements on the UV light system. I am currently in the development stages of a system that will reduce NOx to below detectable limits.

You must keep in mind why NOx regulations are in place. It is a precursor molecule for the formation of smog. However, smog is ground level ozone. NOx in combination with certain hydrocarbons acts as a photo-initiator for forming ozone. Also, NOx can form an acid gas, which is thus scrubbed from the air with rain to form acid rain.

 

[Xtrema]

If you choose exhaust gas recirculation, you are attempting to prevent NOx from forming in the cylinder. By transferring some of the combustion heat to inert recirculated exhaust gas, you keep the N2 and O2 from splitting into radicals that want to join each other. It is effective, but can create soot issues in the lubricating oil. A special engine oil must be used to withstand the EGR-induced soot. Modern over-the-road diesels have recently converted to EGR, and it took a lot of engineering.

You can easily make a diesel EGR valve. Contact me directly if you would like a sketch.

 

[jmw]

I think you may find that visiting the web pages for the large diesel engine manufacturers will provide the information you need plus a visit to the CIMAC webs site.
Past conference papers from CIMAC relate to this issue very well. An enquiry directed to them should provide you with copies.


JMW

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[taylorg]

Which part of the world are you in tomatge?
Several slow speed plants in the Caribbean have recently retro-fitted SCR systems to reduce NOx.
The cost of such a system is expensive, from both a capex and opex point of view. The effectiveness is extremely high and reliability isn't a problem.

 

[tomatge]

Taylorg

I'm in Europe, but am aware of Caribbean utilities that operate similar plant to ours. I would be interested to know how they are getting on.

 

[GreenRichie]

Tomatage

As you probably know MARPOL annex VI gives limits to diesel engine exhaust emissions. For a Diesel Engine operating at less than 130rpm this amounts to 17.0 g/kWh, 45n*10-0.2 g/kWh for 130 - 2000 (where n is engine speed) and 9.8 g/kwWh there after. There are various weighting factors to be applied to the test data dependant on what the engine is driving but I doubt that this will affect you as much as it does the marine industry. I have experience of DWI as installed from new and have found that unless you buy ultra low sulphur fuel (shouldn’t be a problem in the EU other than cost but hard to find globally) you will have problems with the piston crowns. Catalytic reduction SCR works but all of my experience is from the new building aspect and in the marine industry.

The only other thing is that as the legislation was brought in for the marine industry it was not applied retrospectively so if your plant is up an running there will be no legal, only a moral, obligation to reduce emissions. Sorry I can not be more help


Richie

 

[MSurfaceblow]

Tomatage

I am just starting an NOx reduction study for a major tanker operator and met yesterday with Wartsila/Sulzer. They reviewed some of the costs associated with installation and have a client list of installations for the technologies that you mention. Some of these clients may be able to help you, particularly with the RTA engine which is installed on many ships.