[Gasification] combustion gas analyzers, advice needed

[doug.williams]

Hi Jim, And Colleagues,

If I read your need correctly, you want to analyse the gas you make, rather 
than what is in the exhaust gas after you have burnt it.  The combustion gas 
analysers, are not suitable, and selective gas analysers expensive. (ours 
cost US40,000).
The real problem with these systems, is that they contaminate the sensor 
probes very easily, and  need recalibrating, always when things get 
exciting!!! (:-)

What I offer below applies to high temperature packed bed gasifiers using 
air as the oxidizer.

In the early days of our research, we used a German system, that used a 
liquid filled flask, to measure CO2 in flu gas. You just pumped about 10 
squeezes though it, and turned it upside down. The CO2 then gave a read out 
on the liquid level. I believe they are quite cheap now. While this is not 
laboratory measuring, it provides you with a good idea as to how the 
reduction zone is performing, with 7-16% CO2 within a ballpark range of 
acceptable CO2. As Nitrogen dilutes around 51%, the rest will be combustible 
gas.

If you then take this gas and cool it right down without condensing visible 
tar, this means the CH4 is  below 3%, and then you have mainly H2 and CO. 
Then to guess how much H2 is in this balance, test lighting the gas with a 
spark from a flint gun, (mixed with air of course). If you get instant 
ignition, a good guess is that the H2 will be around 15-18%. The 
flammability is always a good indicator of the H2 level. In an engine, this 
translates to easy starting, and fast response to load change.Gas of this 
quality has around 135-140 btu / Nft3.

All good quality producer gas (tar free) has a similar gas analysis, 
although it is possible to tweak things using mysterious black boxes, and 
cylinders that clank in the night ( I'm not kidding). For most of us mere 
mortals though, all the above applies, and if used intelligently, provides 
enough knowledge to get to the next stage of our interest. However, if you 
are going to get serious and  stating gas specifications, then you need to 
send samples for approved lab testing. Darren Schmidt can offer you these 
facilities over in Grand Forks, N.D.  dschmidt at undeerc.org

While many are obsessed with gas analysis, it hides a multitude of sins if 
taken at face value, and alone should not be taken to a prove a gas making 
process. It only records gas quality at one moment in time, at an output in 
that moment, no more.  Many factors affect the analysis, and that is why we 
see such big variations in the literature. The ultimate gas test, is an 
engine doing work, and if you can use it without killing it, you are on your 
way.

Hope this helps.
Doug Williams,
Fluidyne Gasification.