Processes for production of fuel-ethanol from lignocellulosic materials involving micro-organisms and biomass are very complex. Therefore, it can be difficult to design a full-scale or even a pilot-plant facility based on lab-scale data only. One of the most efficient ways of assessing the technological and economic feasibility of such processes is through the use of techno-economic computer modelling. Since a biomass-to-ethanol process consists of several process steps, all strongly interdependent, it is extremely difficult to identify the relative merits of a change in

To distillation

Figure 9. Schematic flowsheet of evaporation with stripper incorporated.

one subprocess and its influence on the final production cost of ethanol. By computer simulations different process strategies can be evaluated and experiments in a bench — scale unit can serve as feed-back to the process simulations.

A bench-scale unit is due to its flexibility very well suited for studying various process configurations and also the recycling of process streams. In this chapter we have shown how the use of a bench-scale unit in combination with process simulations can be used to study process integration. In an environmentally sustainable process, waste water must be minimised. Several process configurations with recycling of process streams were investigated which will result in reduced waste water streams as well as reduced energy consumption. The experimental investigation in the bench-scale unit showed that recycling of non-volatile compounds had an inhibitory effect on the fermentation process. This suggests an incorporation of a multi-effect evaporation line in the process. If internal energy integration is employed, the demand for extra energy can be reduced. The data thus gathered will now be included in Aspen Plus to refine the models which will lead to new simulation results. The aim is to reach an optimal process for production of ethanol which is economic and environmentally feasible. Final process optimisation should preferably be performed on a pilot-scale, since it is difficult to study the whole effect of energy integration options in a bench-scale unit.

Acknowledgments

The Swedish National Board for Industrial and Technical Development is gratefully acknowledged for its financial support.