[Gasification] Gasification Air/Fuel Ratio

[Arnt Karlsen]

On Wed, 15 Nov 2006 08:25:09 -0000, Ken wrote in message 
<00ff01c7088f$90436570$0a00000a at KenLaptop>:

> Greg, Brennan and List,
> 
> If gasifiers can be considered as thermally driven matter
> transformers, especially when you detatch the oxidisation zone 

..bad move, you really want at least some combustion, to burn off 
all tar vapors before they enter the reduction zone.

> and supply heat from another source, would it be correct to assume
> that gas could be generated solely by passing hot nitrogen through the
> fuel,  assuming that the nitrogen was hot enough?  Whilst the drying
> and torrefaction of woody biomass will occur a temperatures below  300
> C,  some of the tar reduction and thermal cracking processes require
> higher temperatures.
> 
> However, in order to reach the high temperatures needed within the
> reduction zone  - say 1000 C, 

..me, I aim for 1050-1100C _exiting_ the gasifier.  Means 1200-1400C
entering the reduction zone, any higher means ash slag production. 

> it is much easier to achieve these
> temperatures by the sacrificial combustion of a layer of the biomass
> in an atmosphere that contains some oxygen.
> 
> Is oxygen liberated from the fuel in sufficient quantities to supply
> the combustion zone, or will oxygen always have to be supplied from
> atmospheric air?

..about 20% of the exhaust gas can be recycled back into the gasifier
into the tuyeres, supplying exhaust gas heat and O2 from the exhaust 
gas CO2 and exhaust gas water, lowering the combustion zone 
temperature, and saving about 20% of the fuel for the same power
production.

..now, piping these 20% should be done in a separate fuel hopper if at
all, as the cooled exhaust gas could easily find its way down thru the
combustion and reduction zones, greating tar vapor "tunnels".

..so, the heat recovery question becomes, heat up the fuel going
in, or heat up the air going into the gasifier.


-- 
..med vennlig hilsen = with Kind Regards from Arnt... ;o)
...with a number of polar bear hunters in his ancestry...
  Scenarios always come in sets of three: 
  best case, worst case, and just in case.