The plant will be the first of its kind at pre-commercial scale and will be based on the innovative PROESA® technology, developed by Biochemtex and successfully demonstrated at the Crescentino plant, that is operational since 2013 with a capacity of 40.000 tons per year of bioethanol.
The Crescentino plant was designed with some operative margins, in order to allow for the further optimization and improvement of processes and layout. Relying on this technology validation phase, the COMETHA plant will then implement these improvements and will then represent an important milestone towards the real commercialization of cellulosic ethanol.
COMETHA will demonstrate that it is possible to integrate second generation processes into a full industrial-scale biorefinery that will include key innovative elements such as:
• a proprietary biomass pre-treatment unit;
• SSCF technology for the simultaneous saccharification of cellulose and hemicellulose and co-fermentation of glucose and pentose, with the use of novel high-performance enzymes;
• a high-efficiency integrated distillation and dehydration system;
• the valorisation of secondary streams and process integration.
While implementing the industrial technology component, COMETHA will address the development of a sustainable biomass supply chain for the provision of lignocellulosic biomass, that will be necessary to fulfill the plant’s annual feedstock demand.
The feedstock will be mainly constituted by dedicated perennial crops (Arundo donax) and agricultural residues.
In parallel to the technological and feedstock supply component, COMETHA will develop a detailed life cycle assessment of the bioethanol flagship plant in order to demonstrate the actual GHG emission savings of second generation ethanol and the overall sustainability of the Biochemtex PROESAⓇ technology.
The goal of the pre-treatment step is to modify the structure of the lignocellulosic material in order to make the sugar fractions more easily hydrolysable. During the pretreatment step it is important to limit the degradation or loss of carbohydrates and to reduce the formation of by-products inhibitory for the subsequent hydrolysis and fermentation processes. The main advantages of the pretreatment technology demonstrated in the Crescentino plant are:
• Minimum request of feedstock size reduction and high flexibility
• No chemical addition
• High C5 sugars recovery with low inhibitors production
• Accessibility of pretreated material to enzymatic hydrolysis
• Limited formation of fermentation inhibitor compounds and degradation products
• Possibility to reduce energy consumption
In the COMETHA project, design improvements will be evaluated and adopted since the engineering phase in order to enable the scale-up of the pre-treatment technology in the flagship plant.
In order to achieve high process efficiency with low capital investment, hydrolysis and fermentation steps should be considered as an integrated single process. The major advantages of the viscosity reduction/enzymatic hydrolysis process demonstrated at the Crescentino plant are:
• Easily scalable design;
• Fast liquefaction of the biomass even at low enzymes load and with high dry matter content;
• Very low energy consumption for mixing;
• Pumpable outlet stream liquid that can be easily sent to the fermentation section
• Adjustable degree of hydrolysis according to different requirements from other types of fermentation (i.e. sugars route to biochemical other than ethanol).
In COMETHA, further research will be carried out in order to achieve high performances of enzymatic hydrolysis and mass transfer.
The enzymatic hydrolysis is a key step to make the feedstock available for an efficient fermentation of the lignocellulosic materials cellulose and hemicellulose. To develop a successful commercial process, all of the process steps of 2G technology need to be integrated as there is a complex interplay between them.
The aim of the partnership between Biochemtex and Novozymes in the COMETHA project is to develop, produce and utilize an enzyme mix with superior performance which will efficiently convert both cellulose and hemicellulose into C5 and C6 sugars.
In particular the main objectives of the COMETHA project for the biochemical conversion phase are:
• Development of an optimal enzyme mix for the selected process to enable efficient hydrolysis of the pre-treated feedstock;
• Reduction in the enzyme dose achieved by:
– synergistic effect of all the activities required for the section
– use of more efficient enzymes
– optimization of pretreatment conditions for enzyme hydrolysis
Several fermentation processes exist for the efficient production of ethanol at high concentration and productivity. Among these, Simultaneous Saccharification and Cofermentation (SSCF) was selected by Biochemtex as key process for ethanol production. In this process, product streams from the pre-treatment stage are not separated but sent directly to the hydrolyzer/fermenter reactor. The challenge consists in fermenting both hexoses and pentoses in a bioreactor using a single microorganism. The separation of the unreacted solid is carried out at the exit of the reactor. This integrated system can convert more than 50% of all sugars that are potentially available in the original biomass feedstock.
In terms of design, this configuration allows to use a small reaction volume with a low residence time, consequently the capital investment and production costs will be improved.
The large amount of energy required for the distillation of ethanol from the fermentation broth is a significant element affecting the final production costs. Therefore improvements in this specific aspect would greatly benefit the overall process energy demand and economics.
In the COMETHA project the process design of these steps will be focused on:
• Energy integration and optimization to reduce steam consumption;
• Improvement in column design to reduce fouling due to solids
• Modeling of distillation configurations.
The results of the Crescentino plant performance in the distillation phase will constitute the basis for improvement or process adjustment in COMETHA. This optimization will be mainly focused on the energy integration of the process by means of a proper managing of recycles and heat waste in the flagship plant.
An industrial scale second generation biorefinery will require the establishment of an agricultural supply chain capable of providing an amount of lignocellulosic biomass in the range of hundreds of tons of dry matter every year in an environmentally and socio-economically sustainable way.
The plant will require continuous feeding with stable quantities and composition of the raw material. The agricultural supply chain will provide the plant with lignocellulosic biomass from both dedicated energy crops and agricultural residues.
The combined use of different biomass sources with non-contemporary harvesting times, will be indispensable in order to provide uniformity of supply and the regular functioning of the plant.
The biorefinery will be fed with fresh biomass from Arundo donax and agricultural residues in the seasons when they will be readily available from the fields.
Sufficient stocks will be kept in form of Arundo straw and agricultural residue bales in order to guarantee the constant supply to the plant even in the autumn/winter period when rain or snow are likely to occur.
For the supply of Arundo donax, two types of harvest are expected:
• direct supply to the plant “on demand” of wet shredded biomass
• indirect supply to the plant of dried, baled and stored biomass
For agricultural residues it is expected to use indirect supply to the plant of dried and baled biomass for storage.