(616g) The Total Site Approach As a Synthesis Tool for the Selection of Valorization Paths in Lignocellulosic Biorefineries

Authors: 
Kokossis, A. C., National Technical University of Athens
Stefanakis, M. E., National Technical University of Athens
Pyrgakis, K. A., National Technical University of Athens
Mountraki, A. D., National Technical University of Athens, Greece



Since oil reserves are depleted, the production of fuels and chemicals from biomass resulted in the considerable need for the development of biorefineries. In this paper, it is proposed that a Process Integration procedure for under study biorefineries should be combined with a process synthesis tool, since possible chemical production paths constitute important degrees of freedom. The methodology is apparently applicable to any other biorefinery. A Process Integration procedure is significant to secure the feasible and sustainable margins for energy efficiency improvement of chemical processes. Total Site Analysis is a powerful tool of a Process Integration procedure able to consider and manage the complex energy interactions among plants. However, it has been exclusively used to address cases of known and installed plants and not to address cases of processes that are possible to enter in a total biorefinery. Pinch Analysis is also a useful Process Integration tool able to determine the minimum energy consumption and maximum energy recovery of a process.

This paper addresses the use of Total Site Analysis in a process synthesis approach for the valorization and selection of possible chemical paths composing an energy intensive biorefinery. So that, given a scheme of chemical production paths, there are processes that are possible to enter in a final biorefinery. The purpose of this methodology is to select the appropriate combination of processes that subject to minimum energy consumption and offer the highest energy savings using Total Site Analysis upgraded in a process synthesis approach. This purpose gives the guidelines for the development of clusters of processes – each of which represents a Total Site – that are integrated together and include all possible combinations depending on feed distribution and the number of the selected processes each time. Thus, a cluster is able to include as much as possible processes provided that they do not use the same feedstock.

The great advantage of process to process integration is that high available energy of a process is able to be used to cover energy duties of other incoming processes making them very promising. This energy benefit even augments as long as more processes are selected to get integrated together in a cluster. The proposed synthesis approach offers the answers about which processes seem to be the most promising and should be included in the final biorefinery.

The studied Lignocellulosic biorefinery consist of the main process, Organosolv, for the fractionation of biomass to its main components: C5 Sugars, C6 Sugars and Lignin. These intermediate products can be used as available feeds for a range of other chemical processes. Thus, a set of chemical paths, each of which constitutes an individual plant, are branched to convert these intermediates to the final products which are C5 Ethanol and Xylitol (biological and catalytic process) from C5 Sugars, Itaconic Acid and C6 Ethanol from C6 Sugars and PF Resins and PolyUrethanes from Lignin. As a result, there are eight processes that are possible to enter to the final lignocellulosic biorefinery. Energy consumption is targeted in Background Process Heat Exchangers, Evaporator Systems and Distillation Columns. The purpose of this process synthesis approach is to valorize and select the best combination of plants that subject to minimum energy consumption and offer the highest energy benefit.

For the studied chemical production paths, where four feeds are involved (Biomass, C5 Sugars,C6 Sugars and Lignin), there are detected four different types of clusters. Specifically, there are developed Types 1, 2, 3 and 4 including 1, 2, 3 and 4 processes, respectively. As a result, each process can be integrated individually (Type 1) or together with other processes (Types 2, 3 and 4) according to the number of processes selected to be involved in a cluster provided that they use different feedstocks.

Under these circumstances, there are calculated the energy savings of all combinatorial clusters of Types 1, 2, 3 and 4 that may be involved in the final solution. Specifically, there are detected energy savings in ranges of 15 - 87 % for Type 1, 18 - 82 % for Type 2, 22 - 83 % for Type 3 and 67 - 84 % for Type 4. The advantage of integrating more processes together is obviously shown by the increase of the lower limit of the energy benefit ranges proving that existence of available energy is able to be used to cover energy duties for other promising incoming processes. As a result, there are screened and previewed options for the construction of the final lignocellulosic biorefinery.

Therefore, developing this synthesis approach, the selected processes that offer the highest energy savings are Organosolv, BioXylitol, Itaconic Acid and PF Resins integrated in one Total Site (Type 4). The total energy consumption reduced from 226 and 229 MW to 38 and 36 MW of heating and cooling duties, respectively, offering energy savings of 83 % and 84 % for heating and cooling duties, respectively. Additionally, the highest energy savings in another case study where all processes are selected to be included in the final biorefinery resulted in the selection of Organosolv, BioXylitol, Itaconic Acid and PF Resins (Type 4) to be included in the first Total Site, C5 Ethanol, C6 Ethanol and PolyUrethanes (Type 3) to be included in the second Total Site and CatXylitol to be individually integrated (Type 1). Including all processes to the final biorefinery, the total energy consumption reduced from 280 and 282 MW to 79 and 76 MW of heating and cooling duties, respectively, offering energy savings of 72 % and 73 % for heating and cooling duties, respectively.