RE: GAS-L: NOx and gasifiers

[Prof P P Parikh <parikh@me.iitb.ac.in>]

The point I would like to state is that low cal value fuel need not always
mean low temperatures! It is the cal value and stoichiomentric air-fuel
ratio together which define what can be called as mixture cal value! And
that is not much lower in case of producer-gas. It is better to measure
NOX in engine exhaust rather than go by assumptions.
Mrs Parikh
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Prof. (Mrs.) P.P.Parikh          Phone  Office : 5723496, 5767548 
Dept. of Mechanical Engg.                        5722545 Ext. 7548 / 8385 
I.I.T. Bombay				Home   : 5704646 	
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                    email : parikh@me.iitb.ac.in    			   
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On Tue, 25 Jun 2002, Mike Norris wrote:

> I don't believe there is much point in "cleaning" the wood gas as the
> original question focused on.  My simplified view of a gasifier for NOx
> formation is the fuel is burned very rich, where the low temperature and
> oxygen starved atmosphere suppress the formation of NOx. Any NOx that is
> formed is likely to be reduced to N2 as carbon and hydrogen radicals
> complete for the O atom within the gasifier.
> 
> Some of the nitrogen in the fuel or air will be reduced (as opposed to
> oxidized) to NH3 and HCN.  These species are less stable than N2 and more
> likely to form NOx, when the wood gas is burned with additional air in an
> engine.  I can not think of a good way to extract N2 from NH3 and HCN
> without oxidizing the whole mixture.  By the way, NH3 should make a dandy
> fuel as it has 40% of the heating value of kerosene. 
> 
> The main source of NOx in the exhaust of the engine is likely to be "Thermal
> NOx" resulting from relatively long residence times at high temperature in
> the presence of oxygen.  The thermal NOx is formed in the secondary
> combustion process, when the wood gas is burned with air.    I believe the
> Thermal NOx problem using woodgas
> is the same as with any other fuel.  Thermal NOx can be controlled by
> burning at a fairly cool temperature (Adiabatic flame temps < 1300 deg C).
> This can be accomplished by adding significant amounts of excess air or
> recycling significant amounts of exhaust gas.  Actually I would expect wood
> gas to burn at a fairly 
> low temperature due to the low energy density of the fuel.  
> 
> 
> Dr. Mike Norris
> Staff Scientist 
> DEKA Research and Development
> Manchester NH
> 
> > -----Original Message-----
> > From:	Claus Hindsgaul [SMTP:claush@et.dtu.dk]
> > Sent:	Tuesday, June 25, 2002 10:26 AM
> > To:	gasification
> > Subject:	Re: GAS-L: NOx and gasifiers
> > 
> > tir, 2002-06-25 kl. 14:05 skrev Tom Reed:
> > > First, there is very little "high temperature NOx"  -  probably less
> > than 1
> > > ppm - in wood gas because the flame temperature is lower than that of
> > > hydrocarbons.
> > 
> > I don't quite agree on that.
> > 
> > Our measurements of emissions from an IC engine[1] fueled by superficial
> > wood gas (mixed from flask without e.g. tars and NH3) showed NOx
> > emissions for lambda<1.5. Indeed they were lower than for natural gas
> > with this engine, but not negligible.
> > 
> > At the Biomass Conference in Amsterdam last week, a poster claimed that
> > 80-100% of NH3 was converted to NOx during flame(!) combustion.
> > 
> > At the same conference Markus Kleinhappl presented measurements of NH3
> > levels in the gas from their double fire gasifier in Graz in Austria to
> > 150-800 mg/Nm3. He claimed that a limit of <55 mg/Nm3 should be met for
> > engine operation.
> > 
> > Here at the DTU two-stage gasifier we also have massive amounts of NH3
> > in our gas condensate. We have not yet measured the NH3 concentration in
> > our gas. Tar is no longer an issue here, but it may be necessary to
> > remove some NH3 from the gas in order to meet NOx-regulations.
> > 
> > Fortunately NH3 is miscible in water so I expect it to be easy obtain
> > lower levels using water scrubbers. Only if there are tars in the gas,
> > the NH3 contaminated water needs special treatment. Otherwise it may be
> > processed at (Danish) biological surridge plants.
> > 
> > Can anybody elaborate on NH3 and NOx in wood gas and engine exhaust?
> > Measurements of either would be very interesting.
> > 
> > Claus Hindsgaul
> > 
> > 
> >     [1] Jesper Ahrenfeldt, Torben Kvist Jensen, Ulrik Henriksen and
> >     Jesper Schramm: "Experiments with Wood Gas Engines". SAE paper
> >     2001-01-3681, September 2001
> > 
> > 
> > -- 
> > Research Assistant M. Sc. Claus Hindsgaul
> > MEK, DTU, Building 120 - DK-2800 Lyngby, Denmark
> > Phone: (+45) 4525 4174 - FAX: (+45) 4593 5761
> > claush@mek.dtu.dk, http://www.et.dtu.dk/Halmfortet
> > 
> > 
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