Gasification and Pyrolysis: Hot and Getting Hotter

Uhde's PRENFLO highly efficient gasification process is illustrated above. It will be utilised for the French Bio T fuel project. The gasifier operates above 2,000 degrees C and above 40 bar pressure (580 psi).

The PRENFLO Direct Quench (PDQ) process is an optimized design of Uhde’s PRENFLO PSG gasification process (steam generation) for chemical applications (e.g. ammonia, methanol, hydrogen, synthetic fuel) and IGCC plants with Carbon Capture and Storage (CCS), where hydrogen-rich syngases are required. It combines the technologically advanced dry feed system, multiple burners and membrane wall of the PRENFLO PSG process with a proprietary water quench system which saturates the raw syngas with water for subsequent gas treatment.

Capital-intensive systems, such as the waste heat boiler system, the dry fly ash removal system and the quench gas compressor, are therefore no longer required.

The PRENFLO PDQ gasifier operates at pressures of 40 bar (4 MPa, 580 psi) and higher and at temperatures above 2,000 °C. Gas temperature at the outlet of the gasifier/quench is 200-250 °C. Carbon conversion is greater than 99%, and typical composition of the raw syngas is more than 85 vol.% CO + H2, 6-8 vol.% CO2 and less than 0.1 vol.% CH4.

The PRENFLO PDQ process was selected for its suitability in processing a variety of feedstocks and in generating hydrogen-rich synthesis gases, such as for Fischer-Tropsch synthesis applications, by which diesel and kerosene can be produced. _GCC

On the pyrolysis front, a startup from U Mass, Amherst, Anellotech, aims to convert biomass into 5 hydrocarbon components of gasoline -- using "catalytic pyrolysis."

Anellotech's reactors perform a process called "catalytic pyrolysis," which converts three of the structural molecules found in plants--two forms of cellulose and the woody molecule lignin--into fuels. Ground-up biomass is fed into a high-temperature reactor and blended with a catalyst. The heat causes the cellulose, lignin, and other molecules in the biomass to chemically decompose through a process called pyrolysis; a catalyst helps control the chemical reactions, turning cellulose and lignin into a mix of carbon-ring-based molecules: benzene, toluene, and xylenes.

...Pyrolysis is also different from gasification, another process for using whole biomass. Gasification results in a mixture of carbon and hydrogen called syngas, which can then be used to make fuel. Pyrolysis, by contrast, turns biomass into liquid fuels in a single step. And while gasification can only be done economically at a very large scale, says Regalbuto, catalytic pyrolysis could be done at smaller refineries distributed near the supply of biomass. _TechnologyReview

It is the one-step promise of catalytic pyrolysis which may lead to an economic advantage for pyrolysis-based biomass-to-liquids processes over gasification.

In gasification, biomass is exposed to high heat, high pressure, and limited oxygen. The result is "syngas": a mixture of hydrogen, carbon monoxide, carbon dioxide, methane, and traces of larger hydrocarbons. This gas can then be refined to liquid fuels in a separate catalytic process.

Pyrolysis processes generally involve lower heat, less pressure, and no oxygen. The result is a liquid that can be refined to fuel, plus a solid carbon "biochar" (useful as a soil treatment) , and a small amount of gas. Again, in U Mass spinoff Anellotech's approach, the catalytic refining is combined with the pyrolytic transformation in "one step."

So there you have it: gasification vs. pyrolysis. Both are vying to be the first BTL approach to hit the big time. There will be plenty of biomass available for both or either, depending upon how the race ends.

Realistically: As long as cheap coal and cheap gas is available, either fossil fuel can be converted to liquid fuels more economically than biomass. Government mandates, tax breaks, and other incentives and regulations will have a lot to do with the near and intermediate term feedstocks for pyrolysis and gasification processes.

The advantage of BTL over CTL and GTL, is that you can grow biomass anywhere on Earth. Rich deposits of fossil fuels are not readily available everywhere on Earth. That fact may affect the pattern of BTL adoption across the third world.