Felipe Fernando Furlan

Bioelectricity versus bioethanol from sugarcane bagasse: is it worth being flexible?

BackgroundSugarcane is the most efficient crop for production of (1G) ethanol. Additionally, sugarcane bagasse can be used to produce (2G) ethanol. However, the manufacture of 2G ethanol in large scale is not a consolidated process yet. Thus, a detailed economic analysis, based on consistent simulations of the process, is worthwhile. Moreover, both ethanol and electric energy markets have been extremely volatile in Brazil, which suggests that a flexible biorefinery, able to switch between 2G ethanol and electric energy production, could be an option to absorb fluctuations in relative prices. Simulations of three cases were run using the software EMSO: production of 1G ethanol + electric energy, of 1G + 2G ethanol and a flexible biorefinery. Bagasse for 2G ethanol was pretreated with a weak acid solution, followed by enzymatic hydrolysis, while 50% of sugarcane trash (mostly leaves) was used as surplus fuel.ResultsWith maximum diversion of bagasse to 2G ethanol (74% of the total), an increase of 25.8% in ethanol production (reaching 115.2 L/tonne of sugarcane) was achieved. An increase of 21.1% in the current ethanol price would be enough to make all three biorefineries economically viable (11.5% for the 1G + 2G dedicated biorefinery). For 2012 prices, the flexible biorefinery presented a lower Internal Rate of Return (IRR) than the 1G + 2G dedicated biorefinery. The impact of electric energy prices (auction and spot market) and of enzyme costs on the IRR was not as significant as it would be expected.ConclusionsFor current market prices in Brazil, not even production of 1G bioethanol is economically feasible. However, the 1G + 2G dedicated biorefinery is closer to feasibility than the conventional 1G + electric energy industrial plant. Besides, the IRR of the 1G + 2G biorefinery is more sensitive with respect to the price of ethanol, and an increase of 11.5% in this value would be enough to achieve feasibility. The ability of the flexible biorefinery to take advantage of seasonal fluctuations does not make up for its higher investment cost, in the present scenario.

Assessing the production of first and second generation bioethanol from sugarcane through the integration of global optimization and process detailed modeling

Abstract There is a worldwide effort to make economically feasible the use of lignocellulosic biomass for production of biofuels. In sugarcane industry, cane juice (sucrose) is fermented for bioethanol production. Sugarcane bagasse is used as fuel in cogeneration systems, to produce steam and electric power to the plant, and the surplus of electric power may be delivered to the grid. The hydrolysis of bagasse to produce second generation ethanol poses a challenge: how much bagasse can be diverted, since the process must continue energetically self-sufficient. This work presents a computational tool developed within an equation-oriented process simulator that couples the simulation of first and second generation bioethanol production with a global optimization algorithm. The tool was robust, optimizing the steady state process in any economic scenario and for different process configurations. Four case studies are presented, and their implications on process internal demands and on the surplus electrical power are discussed.

Modeling the Kinetics of Complex Systems: Enzymatic Hydrolysis of Lignocellulosic Substrates

Lignocellulosic biomass is mainly composed of cellulose, hemicellulose, and lignin. Fuzzy logic, in turn, is a branch of many-valued logic based on the paradigm of inference under vagueness. This paper presents a methodology, based on computational intelligence, for modeling the kinetics of a complex reactional system. The design of a fuzzy interpolator to model cellulose hydrolysis is reported, within the perspective of applying kinetic models in bioreactor engineering. Experimental data for various types of lignocellulosic materials were used to develop the interpolator. New experimental data from the enzymatic hydrolysis of a synthetic substrate, on the other hand, were used to validate the methodology. The accuracy of the results indicates that this is a promising approach to extend the application of models fitted for specific situations to different cases, thus enhancing their generality.

Integrated tool for simulation and optimization of a first and second generation ethanol-from-sugarcane production plant

Abstract An integrated first and second generation ethanol production plant was simulated and optimized in an equation-oriented process simulator. Two optimization methods were used: ipopt, a deterministic algorithm, and PSO, a stochastic one. The optimization of cash flow and of ethanol production was carried out for three different pretreatments. PSO was able to solve the optimization problems, while ipopt did not converge. The objective functions exhibited opposite behavior, i.e. ethanol maximization leaded to lower cash flows for the considered economic scenario.

Defining research & development process targets through retro-techno-economic analysis: The sugarcane biorefinery case

A new approach is reported for techno-economic analysis of lignocellulosic ethanol production. With this methodology, general targets for key process variables can be draw, a valuable feedback for Research & Development teams. An integrated first- and second-generation ethanol from sugarcane biorefinery is presented as a case study for the methodology, with the biomass pretreated by liquid hot water, followed by enzymatic hydrolysis of the cellulose fraction. The hemicellulose fraction may be either fermented or biodigested. The methodology was able to identify the main variables that affect the process global economic performance: enzyme load in the cellulose hydrolysis reactor, cellulose-to-glucose, and xylose-to-ethanol yields. Windows of feasible operation are the graphical output of the methodology, outlining regions to be further explored experimentally. One example of quantitative result is that the maximum feasible enzyme load was 11.3 FPU/gcellulose when xylose is fermented to ethanol and 7.7 FPU/gcellulose when xylose is biodigested.

A simple approach to improve the robustness of equation-oriented simulators: Multilinear look-up table interpolators

Abstract Equation-oriented simulators have some advantages over the modular sequential ones, but improvements are still necessary to deal with nonlinearities, while preserving the robustness of the solver. Linear approximations and/or surrogate models can be used in place of nonlinear models, but the loss of predictive accuracy may be a drawback. An alternative to circumvent this problem is the use of grid-based look-up tables for interpolating responses from rigorous models. This methodology was integrated in an equation-oriented simulator (EMSO). A case study involving the production of bioethanol from sugarcane is used to demonstrate the robustness of this approach. Look-up tables replaced the models of two distillation column trains and of the cellulose hydrolysis reactor. These models were included into the global process and an optimization problem aiming at the maximum production of ethanol was successfully solved by a PSO algorithm varying the solid mass fraction in the hydrolysis reactor.

Integrated Production of 1G–2G Bioethanol and Bioelectricity from Sugarcane: Impact of Bagasse Pretreatment Processes

The industrial plant for production of second-generation (2G) ethanol from sugarcane bagasse will most probably be integrated to the already existing facilities for first-generation (1G) ethanol from sugarcane juice. This will allow lower investment costs, since the former would be able to take advantage of the existing infrastructure, setup for the later. Nevertheless, the exploitation of sugarcane bagasse as raw material must take into account that this biomass is also used as boiler fuel in order to produce steam to meet process demands. Additionally, steam demand is highly dependent on the pretreatment used. In this context, five pretreatments were chosen and an ethanol production process was proposed for each of them. Steam demand was calculated and used to determine the maximal bagasse that could be diverted from steam production. Among the pretreatments considered, the alkaline one presented the higher increase in ethanol production (5.7 L/tonne of sugarcane). This was due the almost complete cellulose hydrolysis and the lower steam demand of this process. On the other hand, pretreatment and hydrolysis reactor volumes were first and second higher, respectively, for this pretreatment. This suggests that, from an economic perspective, steam explosion (with a 2G ethanol production of 2.8 L/tonne of sugarcane) might be a better option.

Retro-Techno-Economic-Environmental Analysis (RTEEA) from the cradle: a new approach for process development

Abstract The chance of a successful industrial implementation of innovative or unconventional processes can be greatly enhanced if the analysis of economic feasibility and environmental impacts is performed from the beginning. In this study, Retro-Techno-Economic Analysis was expanded into Retro-Techno-Economic-Environmental Analysis (RTEEA), combining Life Cycle Analysis (LCA) metrics with economic ones, in order to define regions of feasible operation for the process. In addition, the selection of key process variables was done through global sensitivity analysis (GSA). RTEEA was applied to the case study, the production of succinic acid (SAc) from sugarcane sucrose. Greenhouse gases emissions (GHG, in kg CO 2 eq./kg SAc) and the process Net Present Value (NPV) were chosen as performance metrics. For mapping the GSA response surface, Latin hypercube sampling was used. Sensitivity analysis pointed out that GHG is only influenced by yeast selectivity while NPV was more sensitive to concentration, productivity and yeast selectivity (99.6% of explained variance). The feasible region is bounded by the limits in yeast selectivity and by the infinite productivity curve (obtained assuming instantaneous reaction). The methodology was able to identify the main process variables that influence the process economic and environmental performance, derive their threshold values, and make explicit their relations.

A Kriging-based approach for conjugating specific dynamic models into whole plant stationary simulations

Abstract Steady-state simulators are usually applied for design, techno-economic analysis and optimization of industrial processes. However, sometimes dynamic systems are important parts of the process, which cannot be disregarded. Coupling a dynamic model within a full-plant for steady-state simulation is a challenging task, whatever might be the simulator concept, either sequential or equation-oriented. An alternative to solve this problem is the use of surrogate models to substitute specific dynamic models, by taking the variable time as an extra input of the meta-model. This methodology was applied in an equation-oriented simulator (EMSO) by the use of Kriging meta-models. A case study involving the production of bioethanol from sugarcane was used to demonstrate the capability of this approach. A Kriging meta-model used to substitute the kinetic model of an enzymatic hydrolysis reactor was conjugated into the global plant simulation and an optimization problem was successfully solved.

Process Alternatives for Second Generation Ethanol Production from Sugarcane Bagasse

Abstract In ethanol production from sugarcane juice, sugarcane bagasse is used as fuel for the boiler, to meet the steam and electric energy demand of the process. However, a surplus of bagasse is common, which can be used either to increase electric energy or ethanol production. While the first option uses already established processes, there are still many uncertainties about the techno-economic feasibility of the second option. In this study, some key parameters of the second generation ethanol production process were analyzed and their influence in the process feasibility assessed. The simulated process includes the enzymatic hydrolysis of sugarcane bagasse pretreated with liquid hot water, and the analyzed parameters were the solid consistency in the hydrolysis and pretreatment reactors and the hydrolysis reaction time. The solid consistency in the hydrolysis reactor had the highest influence on the economic feasibility of the process. For the economic scenario considered in this study, using bagasse to increase ethanol production yielded higher ethanol production costs compared to using bagasse for electric energy production, showing that further improvements in the process are still necessary.