[Gasification] Pyrolysing compost to make fuel

[CAVM at aol.com]

David, this is very interesting.  You say that the gas production from  mixed 
food waste is higher than for cattle dung.  Is it significantly  higher?
 
We generally recommend that dry material be processed dry and wet material  
be processed wet.  For example, dairy manure and hog manure are both  slurries 
of various densities.  We recommend anaerobic digestion as an  energy process 
for we slurries.  For beef manure, sawdust, and others, we  recommend 
combustion or gasification as an energy producing process.  
 
In this way we do not spend valuable energy drying wet inputs nor do  we risk 
water contamination by wetting dry inputs.  However, if we can  effectively 
and economically produce methane from cellulose materials we might  reap 
significant rewards.  
 
It is our opinion that the fermentation process of anaerobic digestion for  
the production of methane is potentially very economical, scalable, and  
effective in a wide variety of situations.  Most commercial digesters of  which we 
are aware are fairly costly to build, complicated to operate and  marginally 
effective given the energy value of the input material.  If used  for the 
production of electricity they must be offsetting an electrical cost of  at least 
$.075/kwh to be economical for power production alone.
 
Neal

Neal

Can I suggest you are wrong as far as anaerobic digestion  is concerned.

There are biogas digesters in Sri Lanka that use very  high total solid 
loadings of straw and these generate gas fairly  effectively. They are batch 
digesters, cylindrical tanks made from  ferrocement, which are packed full 
of straw and the lid is put on. Slurry  from another plant is poured in, but 
just enough to soak the straw  through. The TS value must be 80%. The gas 
production starts after a week  or so and follows a typical batch curve 
(increasing to a maximum and then  steadily dropping). When the lid is 
removed, when the gas production has  dropped to a low level, the lignin 
remains, but the cellulose in the straw  has been digested. The straw looks 
very similar to when it is put in, but  crumbles to a paste when it is 
disturbed. This was described at a  conference I went to in Sri Lanka 
several years ago, but I am not sure  where my references are to the papers 
in which it was described. We did  visit a working unit on a local farm and 
the owner seemed happy with the  gas produced.

On a more recent visit to Mumbai, I saw the Nisargruna  process that uses 
food residues for biogas generation. It is fed almost  entirely on 
cellulosic materials (poorer people in India are mainly  vegetarian) and 
gives a very good gas production, better than that from  cattle dung plants.

regards,

David  Fulford