On the Systematic Integration of Different Generation Biorefineries

As the world strives to create a more sustainable environment, the biorefinery community fights to minimize the environmental impact of bioprocesses and build a green economy. The use of biomass as raw material for production of energy carriers and chemicals has emerged as a promising alternative to fossil resources for mitigating climate change and enhancing energy security. Second generation biorefineries (2G) came up as the natural evolution of the first generation (1G) bioprocesses to preserve food resources, while, recently, seaweed and microalgae processes have also started to hatch as the third generation (3G) biorefieneries. As different generation biorefineries treat different feedstock, their integration can reduce energy consumption and result in a more economical design with lower environmental impacts than the stand-alone.

To date, first and second generation processes have been integrated by the adoption of grassroots design methodologies [1-4], while, in reality, their coupling is far more complex. The upgrade of first generation plants constitutes a retrofit problem, constrained to make the best use of the invested equipment of the existing plant. Second and third generation upgrades account for new technology and investment very flexible to adjust so that the upgrades are best, but the portfolios of products need also to be investigated. Apart from integrating energy, there is also significant potential to exchange (by-) products. For example, bagasse can be used as feedstock in the second generation process, and, similarly, lignin can be used as fuel for the co-generation unit, while wastewater could be used for algae cultivation. Moreover, the processes may share common sections, like the downstream processes. Finally, the co-generation (CHP) unit, after modifications, can support both plants. Thus, the integration of first and second generation biorefineries is a combined grassroots–retrofit design problem, much larger and complex than most conventional applications, that hides inner trade-offs and proves the deficiency of present-day practices in proposing realistic. The size and the complexity of the problem impose the need for a systematic approach in the form of mathematical models.

This work studies the different symbiotic options in the integration of different generation biorefineries, scoping for the development of a new systematic methodology, which can combine different process systems engineering tools for the integration of grassroots-retrofitted problems. Detailed designs for sugarcane (1G), bagasse (2G), and seaweed (3G) ethanol production are developed in Aspen Plus^®, validated by the industrial partner (CIMV Process^TM) and laboratory experiments, and the potential of cultivating microalgae in wastewater is also investigated. The detailed models feed the mathematical models, developed in GAMS^®. The processes are integrated following a mixed mathematical model. The model applies the methodology of retrofit integration on first generation [5] and grassroots integration on second and third generation technology [6, 7], following the transhipment analysis. Preliminary results indicate a significant potential in internal trade-offs savings, both in operating and capital cost.

Acknowledgment: The financial support from Marie Curie European Research Program, RENESENG (FP-607415) is gratefully acknowledged.

References

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