Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 252

The BRI process uses a two-stage gasifier that raises the syngas temperature as high as 1,370 °C (2,500 °F) in the second stage to enable cracking of any high-boiling hydrocarbon derivatives to carbon monoxide and hydrogen, maximizing the ethanol yield, thus using a thermal cracking.

The hot producer gases are cooled to 37°C (98°F), and introduced into the biocatalytic reactor where ethanol is produced. Here, the modified bacteria culture Clostridium ljungdahlii is introduced and nutrients are added to provide for cell growth and automatic regeneration of the biocatalyst.

With a hydrogen/carbon monoxide ratio of 2, the reactions indicate that water and ethanol are the only products.

As the ethanol is toxic to the bacteria, there is a need to hold the ethanol concentrations below 3% in the reactor. A dilute, aqueous stream of ethanol is continuously removed through a membrane that retains cells for recycle to maximize reaction rates. Anhydrous ethanol is produced by conventional distillation followed by a molecular sieve, using the waste heat from the process. Water, with nutrients, is recycled from the distillation bottoms back to the biocatalytic reactor. With ambient temperature and pressures, a fermentation time of a few minutes has been achieved.