FISCHER-TROSPHE

 

 

The conversion of biomass into liquid transport fuels is frequently proposed as a substitute for fossil fuels. In some cases suggestions for micro scale plants do have potential, depending of course on the type of conversion process.

Where existing oil refineries can be utilised, the gasification of biomass using air as the oxidising medium offers interesting options.

As a feed stock, producer gas can be processed through a fairly simple Fischer-Trosphe system. The economics are of course driven by need, and when need is related to national wellbeing, things can happen with an acceptance of greater effort.

During the oil price crisis of the 1970s, New Zealand was caught without supplies of natural gas or oil from the reserves known to exist. The then Department of Scientific and Industrial Research (DSIR) conducted extensive investigation into biomass based fuels and their trials with oxygen blown gasification bought them to Fluidyne's workshop looking for assistance.

By choosing the oxygen blown gasification process, their first tests were very successful and it was thought the whole project would be completed in a couple of months. Then the accounts came in for the oxygen killing the trials stone dead as the gasifier wouldn't work with air.

Fluidyne's own development work was also in the early stages of evolving tar free gas, so we pooled our knowledge with the DSIR and facilitated each other to sort out some of the less understood phenomena.

Once the DSIR started to make air blown producer gas, they constructed a small plant to simulate the Fischer-Trospche process. Producer gas was compressed to 10 atmospheres and released through a column of volcanic iron sand that had diesel fuel as the saturating agent. Off the top came petroleum wax which then could be refined into diesel or petrol. At that time (1976), the economics required 2,000T/D to supply all of New Zealand's transport fuels. One million hectares of pinus radiata forest would have produced more wood energy than New Zealand's then current annual fossil fuel and electrical energy usage of about 330 x 1015 J/yr.

Producer gas can meet lower expectations of national need if that need exists. We cannot control the politics or the economics that surround the implementation of renewable energies, but we should continue to be responsible for their technical evolvement.

Irrespective of how we perceive producer gas and gasification as a technology, it is but a stepping stone into the next phase of technical evolution.

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A rare photo of Dr Jim Cousins on the right who was New Zealand's leading researcher into biomass energy in the 1970s. The gasifier is on the left end of the base, and the slightly modified standard air compressor for the gas compression is just visible at the rear. The only drawback to this process is the need for tar free gas.

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Basic layout of sawdust fed gasifier and simple Fischer-Trospche process.