I just come across this, we were talking bout this a little in the chat last night …
I thought this was pretty interesting , and may explain premature failure on some areas of a gasifier .
http://chimneysweeponline.com/homillends.htm
Another short interesting paper on the subject …
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&ved=0CFcQFjAF&url=http%3A%2F%2Finfo.ornl.gov%2Fsites%2Fpublications%2Ffiles%2FPub28998.docx&ei=xTXIUujbAoigkQezxYCgAQ&usg=AFQjCNFhSH01uh7Mg-tk6uGUdyl1SrqjCA&sig2=polU8LhQmgnjo0Ex0DvMWQ&bvm=bv.58187178,d.eW0