GAS-L: Gas turbines

["Malcolm D. Lefcort" <mlefcort@compuserve.com>]

Joseph,

To fuel a gas turbine with a low calorific value producer gas made from
wood residue is generally quite complicated and very expensive.  The
producer gas has to be free of tar and particulate matter and it must be
pressurized to at least 10 atmospheres.  

In addition, its calorific value has to be constant.  Wet wood residue is
therefore almost always dried before it is gasified.  Small amounts of
natural gas can be used to maintain a constant calorific value of the
producer gas. 

A simpler approach in the 5 to 10 MWe power range is to indirectly fire a
gas turbine with the products of combustion of wood residue using a high
temperature, gas-to-air heat exchanger.  Most any gas turbine with an
external combustion chamber -  one whose combustion chamber axis  is at
right angles to the turbine axis - can be indirectly-fired.

However, in order for the "industrial" heat exchanger to have a life of 
100,000 hours - the industry standard - the turbine inlet temperature must
be de-rated to about 1550F (850C).  This reduces the power developed by,
for example, the GE/Nuovo Pignone PGT-5 , from 5 MWe to 3.5 MWe.   However
with 825F (440C) turbine exhaust and with the same temperature heat
exchanger exhaust, an additional 40 Million Btu/h (between 825F and 350F)
or 11.7 MWth  (between 440C and 177C) can be recovered for process heat -
or for additional power using a small condensing steam turbine generator.  
This application is well suited to the power and heat needs of large
sawmills out here in Western Canada. 

This approach is discussed in some detail in ASME paper 98-GT-62.  The
paper can be accessed from our web site:
http://www.heuristicengineering.com.  

The web site also describes our two-stage, wet wood residue, combustor, the
Heuristic  EnvirOcycler, and illustrates a number of its different
waste-disposal/ energy-recovery applications. 

Malcolm D. Lefcort
Heuristic Engineering Inc
Vancouver, BC, Canada
mlefcort@heuristicengineering.com 
The Gasification List is sponsored by
USDOE BioPower Program http://www.eren.doe.gov/biopower/
and PRM Energy Systems http://www.prmenergy.com

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