[Gasification] lighting

[doug.williams]

 Hi Toby,

When you do get a gasifier to ignite, you should be aware of a couple of 
points, and consider how best to apply them to the design of your choice.

>  I guess that I did not mention that as a cutting torch, oxygen is also 
> part of the cutting machinery, is mixed in the tip, has an anti blow back 
> device and can withstand a lot of air >without being blown out, positive 
> or negative pressure.

The problem with a cutting torch trying to burn in an ignition tube that is 
blocked at the end with a packed char bed, is the back pressure, not a 
blowback into the torch. In most cases the torch will not stay alight if 
pointed down a dead end tube, as it just fills with CO2.  ( I was for seven 
years the equipment repairs manager for New Zealand Industrial Gases, now 
BOC in Auckland so can appreciate their limitations).

If you just have a port hole in the side of the gasifier for ignition, it's 
position should be into the packed bed of charcoal (even with a wood 
gasifier). Even with a cutting torch, the bed will fail to ignite after 
turning on the air flow, unless the air is injected at the same point as the 
char is lit. In a sealed fuel hopper system, there is no air circulation to 
bring up the oxidation temperature in any other place exept at the point of 
air entry, although the oxidation can get going if in close proximity to the 
air. Open core gasifiers are easier, because they can just burn like a 
stove, so you need to be specific about the type of gasifier being lit, so 
comments can be correctly offered.

  >  And I do not suggest that one fill any device with LP then try to light 
it, with or without a blower or suction.

The point being made here is that you cannot use a gas ignition system 
without the source of air supply to the bed, because the CO2 produced from 
the gas flame in an enclosed space will put out your gas flame by back 
pressure.

>  I suggest however that because a cutting torch does have it's own oxygen, 
> it may not even be necessary to turn on a blower and create suction or 
> pressure prior to lighting and that the effect of that pressure could be 
> avoided by the cutting torch with both LP and oxygen and a simple lighting 
> port.  Fire up and then turn on the blower/suction.

In all the charcoal gasifiers I have seen, both in literature and with my 
own eyes, have been ignited down the singular air nozzle in the presence of 
suction air. Our own wood gasifiers have a ignition cap over the end of one 
nozzle, and the oxidation quickly moves across the air flooded bed, towards 
the air from the other nozzles.  The original Imbert gasifiers had an 
ignition port through the main air box that fed the separate nozzles, but 
only lit the bed through the one nozzle. The other aspect to consider in all 
this, is that to encourage the oxidation to originate in the char against 
the wall, through a port, can create a unnecessary hot spot against the 
sheet metal. It is easier to start a gasifier with air if you have it in the 
first place, and to light it right where the oxidation lobe is formed, 
because when a gasifier is difficult to light, and fails to make gas within 
a few minutes, you can only wonder why, if nobody has bothered to give you a 
few pointers.
Doug Williams.
Fluidyne Gasification.