Biochemical and thermochemical conversion technologies can be integrated into a large- scale biorefinery for additional efficiency, yield, and cost improvements. For example, an ad­vanced state-of-technology biorefinery optimized for maximum ethanol production could use an approach as follows: biochemical conversion extracts the carbohydrate portion of the feedstock and then converts it to fermentable sugars and, ultimately, ethanol. The remain­ing residue, primarily lignin, cannot be fermented, but it is a valuable organic feedstock. By directing this byproduct to a thermochemical process, it can be converted to syngas and, ultimately, ethanol. Integrating these technologies will improve the energy efficiency of the process, lower costs, and produce more ethanol than a standalone biochemical or thermochemical process.

Figure 2.13 depicts the advanced, integrated biochemical and thermochemical alcohol production scheme analyzed. Some of the lignin-rich residue is used to provide steam and electricity to the biochemical process, and the remainder is processed in the thermochem­ical process. The larger biochemical processes (8000-10 000 tonnes/day) expected in the 2020-2030 time frame will be needed to feed a reasonably sized gasification plant (1500­2000 tonnes/day) with only lignin-rich residues. The scale of the biochemical processing plant is five times larger than that targeted for near-term biorefineries, but the scale of the thermochemical conversion plant is the same.

This combined process can maximize feedstock handling efficiencies and heat and power integration. Integrated biorefineries can also process feedstocks with both high and low carbohydrate contents. A steady supply of low-carbohydrate feedstock could be fed directly into the thermochemical process, which allows increased size and some benefit to the capital cost. Integrated biochemical-thermochemical biorefineries also capitalize on the process improvements identified in the independent developments of the two technologies.