>AC> The furnace would not really rate as a pressure vessel, these
 >AC> plants were built to drive large stationary engines the same as
 >AC> used to ne fed by town gas. And the later automobile versions,
 >AC> simply breathed into the carby. The "safety valve" could be as
 >AC> simple as an open water column of say 1 meter height.
 > 
 > Pity our public transport people could not use this style of engine 
 > to generate electricity which could then run trams or trolley buses?
Jock,
 These wood-fired (or coal, whatever) 'producer gas' plants were very common 
during certain periods. The late 1800's/early 1900's saw a lot of them, 
furnishing what was called 'town gas' for lighting. WWII brought on portable 
gas generators, used to power automobiles and trucks.
The old Mother Earth News magazine had a couple of articles on these devices, 
including detailed plans for building them. I'd imagine a trip to a decent 
library would get one all the info needed to build one for yourself.
There's several good reasons why they fell from favor: the gas is 'dirty', 
which is especially bad for I.C. engines. They're not especially cheap to 
operate unless you have no alternative. And, the alternative is pretty 
inexpensive, all things considered.
--- FLAME v1.1
---------------