Germán Aroca: Process design and environmental impacts of biorefineries
The second presentation of the afternoon was held by Germán Aroca, who is a Professor at the School of Biochemical Engineering of the Pontificia Universidad Católica de Valparaíso (PUCV) in Chile.
Mr Aroca started with an introduction on the topic of global warming and the role that the “fossil age” played here. The increase of carbon in the atmosphere compared to the pre-industrial age amounts already to 250 Giga tonnes and would be a threat to the global climate. In his presentation Mr Aroca introduced the methodology of Life Cycle Analysis (LCA) and alternatives for the production of bioethanol in Chile. A LCA is a methodology that evaluates the environmental impacts of a determined product or service and it considers all steps of the aforementioned, from the extraction of the prime materials, the processing and use of the product until the treatment of the residues. Several systems can be described by a LCA, Well to Gate, Well to Tank, Well to Wheels, Tank to Wheels or the complete LCA, Cradle to Grave. Several LCA web applications are available on the market which facilitate the LCA. At PUCV Mr Aroca is using the Simapro application which relies on Ecoinvent databases and offers many different impact categories.
Next Mr Aroca reported the results of LCAs of different process alternatives for 2G bioethanol in Chile. Therefore he first drew the market scenario for Chile, where no mandate exists yet for the use of bioethanol as fuel. However, Chile imports Methyl tert-butyl ether (MBTE) as additive for premium gasoline. MBTE is considered a contaminant in some countries and is replaced by Ethyl tert-butyl ether (ETBE). The latter can be produced from bioethanol and isobutylene. For the substitution of MTBE in Chile, 140 Mio litres of bioethanol would be necessary to produce ETBE. The demand for bioethanol is thus given.
The technical and economic challenges of the bioethanol production include the process integration in order to minimize the demand for energy and for water treatment, the valorisation of the process residues and to secure the sustainability of the process (energy balance, GHG emissions). The production of bioethanol can be realised via many different ways, 128,520 as being precised by Mr Aroca.
Following Mr Aroca presented the outline of a plant using eucalyptus as lignocellulosic feedstock. Out of 1,100 ODMT (oven dried metric tonnes) per day of eucalyptus 118-160 million litres of bioethanol and 13-26 MW electrical energy can be generated (equals a capacity of 250-350 l/ton at production costs of 0.5-0.7 US$/litre). Purchase costs for the woody feedstock were given as 65-85 US$/ton.
Mr Aroca then showed four different process configurations which are all producing 99.5% pure bioethanol. A LCA was made for the four different scenarios which brought the result that the base case (refining at low consistency, separate fermentation of glucose, xylose left in liquor and pulp generate biogas) and case 4 (refining at low consistency and separated fermentation of xylose – LoCo-cSSF+C5F) are the most sustainable ones.
Concluding Mr Aroca stated that the process design can have a significant effect on the environmental impact of the process.