The heart of CHOREN’s technology is its patented Carbo-V Biomass-gasification process that converts biomass into ultra-clean tar-free synthetic gas.

The Carbo-V Process is a three-stage gasification process using:

• Low-temperature gasification. Biomass (with a water content of 15%–20%) is continually carbonized through partial oxidation (low-temperature pyrolysis) with air or oxygen at temperatures between 400º C and 500° C, i.e. it is broken down into a gas containing tar (volatile parts) and solid carbon (char).

• High-temperature gasification. The gas containing tar is post-oxidized using air and/or oxygen in a combustion chamber operating above the melting point of the fuel’s ash to turn it into a hot gasification medium.

• Endothermic entrained bed gasification. The char is ground down into pulverized fuel and is blown into the hot gasification medium. The pulverized fuel and the gasification medium react endothermically in the gasification reactor and are converted into a raw synthesis gas. Once this has been treated in the appropriate manner, it can be used as a combustible gas for generating electricity, steam and heat or as a syngas.

The syngas can then be converted into synthetic biofuels using the same Shell Middle Distillate Synthesis (SMDS) technology that Shell has developed for Gas-to-Liquids production (conversion of natural gas into synthetic oil products). Shell’s SMDS is a low-temperature, cobalt catalyst-based version of the Fischer-Tropsch GTL process.

The BTL fuels are identical in composition and properties to GTL fuels—and they have the added advantage of being based on renewable feedstocks.

BTL Fuel is as clear and virtually free of sulfur and aromatic substances. Its ignition qualities (as measured by a very high cetane number) are excellent, thereby reducing noise and resulting in cleaner combustion than with conventional diesel. Greenhouse gas emissions from BTL Fuel are less than 10% of those from fossil fuels. Moreover, BTL Fuel can either be used as a pure product or in a blend with conventional diesel fuel.

Unlike biodiesel production, BTL uses the entire plant, thus theoretically requiring less land use per unit of energy.

The combined process of energy conversion and Fischer-Tropsch synthesis, however, is energy intensive—and more so when using biomass as a feedstock than natural gas. On a Well-to-Wheels basis, BTL diesel is far better from a greenhouse gas emissions perspective than any other variant of synthetic or conventional petroleum fuel (except for DME from biomass) or conventional biofuel, but the worst in terms of energy requirement. (Earlier post.)

In the next two to three decades, liquid fuels will continue to dominate the market. Climate protection measures will mean that the share accounted for by biofuels is set to increase. We want to proactively participate in this shift as part of our commitment to the concept of sustainable mobility and maintain our leadership in formulating advanced fuels.

—Rob Routs, Executive Director Downstream, Shell

Volkswagen and DaimlerChrysler have been collaborating with Choren on the production SunDiesel since 2002 due to the cleaner-burning characteristics of the fuel. Tests have shown that Euro 3 engines can achieve Euro 4 level emissions when using SunDiesel.

Resources:

• CHOREN Process, Environmental Impact and Latest Developments, May 2005

• PriceWaterhouseCoopers Shell GTL Lifecycle Analysis

(A hat-tip to Bjorn!)