[Gasification] "Continuous analysis of elemental emissions from abiofuel gasifier"

[doug.williams]

Hi Philippe and Colleagues,

Thank you for drawing attention to this project.

>  http://biopact.com/2007/03/scientists-develop-analytical-system-to.html


> However, the behaviour of trace elements during gasification can be 
> problematic, with environmental concerns over toxic >components, and 
> process problems caused by alkali metal corrosion and fouling.

While it is appreciated that emissions need to be measured, combustion has a 
history of being the worst option for waste containing contamination. 
Because these compounds were found associated with gasification, it suggests 
that gasification is in itself responsible for the emission readings.

> David Poole and colleagues at the University of Sheffield and SPECTRO 
> Analytical Instruments, Germany have been >conducting experiments to 
> continuously monitor the concentration of various trace elements in the 
> raw gasification gas >from an experimental reactor (click to enlarge), in 
> an effort to determine which elements are volatilised. They published 
>  >their results in the Journal of Analytical Atomic Spectrometry [open 
> access article].


To embark on establishing a measuring standard for gasified emissions, the 
fact that a crude updraft gasifier (experimental) is even considered 
appropriate suggests a big gap in the credibility and value of such 
projects.


 > Results of initial tests indicate that the concentration of some elements 
in the gas phase are extremely high, far higher than >in combustion 
processes, and therefore are of significant concern.


The updraft gasifier drives all the very unstable distillation gases into 
the output gas, and provide a carrier for the toxic material. Combustion at 
least burns this gas close to the bed surface, and would fix a certain 
amount in the ash., so less contamination in the emission.


>Owing to problems with tar formation in the gasification process, the 
>analysis proved extremely challenging, and >further development of the 
>sampling and pre-treatment procedure would be required to obtain more 
>accurate, reliable, >and long-term continuous monitoring results.


What we see here is that emphasis is on trying to clean the tar out of the 
gas, not gasify the fuel in a way that does not make tar. If they used a 
downdraft, high temperature gasifier, that cracked the distillation gases, I 
doubt if they would find enough toxic emission to measure, as tar free 
producer gas can be extremely clean. Having said that, it does depend on 
what was being gasified, but in this case, the emission problem is created 
by the crude gasification process.

In New Zealand, we had expert advise back in the 1970's about contaminated 
wood, and our advise was that in the high temperature, oxygen deficient 
atmosphere of the reduction zone, the toxic molecules detach from their 
carrier molecules, and become fixed in the waste activated charcoal of the 
reduction zone. In more recent times, emission tests of contaminated waste, 
have shown that gasification is a reliable method of disposal, so long as 
the gasifier can handle the fuel.

These tests will be expensive, and could very well be insisted upon by 
authorities who do not understand the differing types of gasification. There 
is a need to keep a close eye on these types of academic studies, as it can 
be another created issue that if not challenged, be used to hold back 
implementation of start-up projects.


> 'Gasification is of growing interest as this can increase the energy 
> efficiency of biofuel use,' said Poole, 'but the >behaviour of trace 
> elements during gasification can be problematic, with environmental 
> concerns over toxic constituents >such as lead, cadmium and arsenic, and 
> process problems caused by others such as potassium and sodium.'


As they state biofuel specifically, and not MSW, I can only conclude that 
lead, cadmium, and arsenic, comes from demolition wood, but potassium and 
sodium is usually associated with young fresh wood like coppice willow, and 
poplar. In both cases, the correct gasification process can remove the 
problem.

> High concentrations of potassium and sodium were detected, which, 
> according to Poole, could result in fouling and >corrosion of gasification 
> plants.

This is the same for any combustion process that burns contaminated 
distillation gases, but is a non event if the gas making is correctly 
achieved, and the moisture stripped out before the gas is combusted.

>The heavy metals measured were not detected at significantly high 
>concentrations. The researchers will continue to >optimise and improve 
>their analytical system, and plan to develop more automated and robust 
>systems.

Heavy metals are not normally found in biomass, although they can be taken 
up in certain situations. Again high temperature tar cracking gasification 
fixes heavy metals in the waste activated carbon, and do not entrain with 
the gas.

I would appreciate comment or additional information on this subject, as 
there is a need to clarify emission issues as they appear.

Doug Williams,
Fluidyne Gasification.

> 
> "
>
>
>
>
> _______________________________________________
> Gasification mailing list
> Gasification at listserv.repp.org
> http://listserv.repp.org/mailman/listinfo/gasification_listserv.repp.org
> http://gasifiers.bioenergylists.org