[Gasification] Myanmar: Engineering society preparing code for gasifier standards
tmiles at trmiles.com
Mon Mar 19 12:14:11 CDT 2012
Cristobalite silica is a fact of life with some rice husk gasifiers. You are bound to get over 800C with some reactors like updrafts. In the US where more than 30,000 tons of rice husk ash are produced from gasification cristobalite can exceed the hazardous classification, which I believe is 10%. So the bags are appropriately labeled and the material, which is mostly used in the steel industry. Is handled accordingly. Cristobalite has also been found in rice husk biochar from updraft gasifiers in Australia.
The concern in Mynmar is likely the water pollution from simple scrubbers that was identified by Robert. You will remember the Alaska Village Energy Project by Marenco in the 1980s. At the time a long list of toxics were identified in the scrubber water by Gas Technology Institute. The test facility later became a superfund site.
While testing an Indian gasifier some years ago we found that the water scrubbing system is very good at removing benzene, cresols, etc. The discharge from the system contained about five times the concentration of benzene allowable by EPA. The hazards are clearly there. EERC has tested and documented these. They have worked on various ways to handle tars.
The best solution is to consume the tars in the oxidation process, regardless of reactor type. We find that in the simple downdraft designs that are often used air penetration is insufficient (which cals to mind your six particle theory) so as you increase the diameter of the reactor you wind up with a cold (<500C) core through which a lot of tars pass and are created without being oxidized. Open core designs also suffer from good air-fuel mixing.
Even with hot dry fuel and good mixing residual tars in the condensate will have to be incinerated for zero discharge, which clearly costs more than $100. In a small scale demonstration in Cambodia one of my clients filtered the effluent and stabilized it with lime.
You will also remember the effort by Mrs. Parikh to develop gasifier standards in India in the 1980s. I don’t know if those standards addressed effluents.
A useful reference is the EU Gasification Guide: “Guideline for Safe and Eco-friendly Biomass Gasification” by the European Commission.
From: gasification-bounces at lists.bioenergylists.org [mailto:gasification-bounces at lists.bioenergylists.org] On Behalf Of Thomas Reed
Sent: Monday, March 19, 2012 6:09 AM
To: Discussion of biomass pyrolysis and gasification
Subject: Re: [Gasification] Myanmar: Engineering society preparing code for gasifier standards
If there is anything I can do to advise these people day to day on the realities of gasification, I'd be happy to help.
Ali Kaupp wrote his thesis at UCDavis on rice hull gasifiers.
Here's a question for you. If you pyrolyse hulls at <700C, the resulting silica ash is quartz. If the temperature goes over 800C it comes out cristobalite, which is carcinogenic I believe.
Thomas B Reed
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