Adriano V. Ensinas

Multi-objective optimization of SNG production from microalgae through hydrothermal gasification

The conversion of microalgae biomass into biofuels is a quite well explored field of research. Due to high photosynthetic efficiency, microalgae are considered as a potential feedstock for next-generations biofuel conversion processes. This paper addresses the thermochemical conversion of highly diluted microalgae feedstock into synthetic natural gas (SNG) through supercritical hydrothermal gasification. The complete conversion chain is modeled including the cultivation phase, settling ponds, centrifuges, catalytic hydrothermal gasification with salt separation unit and SNG purification system. Thermodynamic, economic and environmental models are considered for each process step, in order to solve a Mixed Integer Non Linear Programming (MINLP) optimization problem. The problem is solved by applying a two steps decomposition approach, using Multi Objective Evolutionary Algorithm with Mixed Integer Linear Programming (MILP). It is finally demonstrated that coupling microalgae cultivation systems with hydrothermal gasification (HTG) and waste energy recovery utilities leads to high energy/exergy efficiencies, emissions reduction and globally better sustainable processes.

Dynamic Modeling of the Microalgae Cultivation Phase for Energy Production in Open Raceway Ponds and Flat Panel Photobioreactors

A dynamic model of microalgae cultivation phase is presented in this work. Two cultivation technologies are taken into account: the open raceway pond and the flat panel photobioreactor. For each technology, the model is able to evaluate the microalgae areal and volumetric productivity and the energy production and consumption. Differently from the most common existing models in literature, which deal with a specific part of the overall cultivation process, the model presented here includes all physical and chemical quantities that mostly affect microalgae growth: the equation of the specific growth rate for the microalgae is influenced by CO2 and nutrients concentration in the water, light intensity, temperature of the water in the reactor and by the microalgae species being considered. All these input parameters can be tuned to obtain reliable predictions. A comparison with experimental data taken from the literature shows that the predictions are consistent, slightly overestimating the productivity in case of closed photobioreactor. The results obtained by the simulation runs are consistent with those found in literature, being the areal productivity for the open raceway pond between 50 and 70 t/(ha*year) in Southern Spain (Sevilla) and Brazil (Petrolina) and between 250 and 350 t/(ha*year) for the flat panel photobioreactor in the same locations.

A New Proposal of Cellulosic Ethanol to Boost Sugarcane Biorefineries: Techno-Economic Evaluation

Commercial simulator Aspen Plus was used to simulate a biorefinery producing ethanol from sugarcane juice and second generation ethanol production using bagasse fine fraction composed of parenchyma cells (P-fraction). Liquid hot water and steam explosion pretreatment technologies were evaluated. The processes were thermal and water integrated and compared to a biorefinery producing ethanol from juice and sugarcane bagasse. The results indicated that after thermal and water integration, the evaluated processes were self-sufficient in energy demand, being able to sell the surplus electricity to the grid, and presented water intake inside the environmental limit for Sao Paulo State, Brazil. The processes that evaluated the use of the bagasse fine fraction presented higher economic results compared with the use of the entire bagasse. Even though, due to the high enzyme costs, the payback calculated for the biorefineries were higher than 8 years for all cases that considered second generation ethanol and the net present value for the investment was negative. The reduction on the enzyme load, in a way that the conversion rates could be maintained, is the limiting factor to make second generation ethanol competitive with the most immediate uses of bagasse: fuel for the cogeneration system to surplus electricity production.

Methodology for Minimising the Utility Consumption of a 2g Ethanol Process

The production of ethanol from lignocellulosic biomass has gained increased interest in recent years, notably in the context of valorising agricultural by-products and providing fuels from renewable sources In order to increase their competitiveness, the energy demand of such processes needs to be minimised. This issue procures two benefits : (1) reduce utility consumption and (2) increase cogeneration possibility. In the present article we investigate this problem for a study process: ethanol production from sugarcane bagasse by enzymatic hydrolysis and glucose fermentation. We therefore apply a rigorous optimisation methodology in which we control certain design parameters in order to maximize the net production of utility. As a result, we obtain a design for our process which (1) eliminates the need for an external hot utility, (2) minimizes the need for the cold utility and (3) maximises the cogeneration possibility.As a conclusion, the proposed methodology provides a strong tool for minimising the utility consumption for a 2G ethanol plant. Considering its key components, it can further be applied in the context of a multi-objective problem.

Optimal Design of Solar Assisted Hydrothermal Gasification for Microalgae to Synthetic Natural Gas Conversion

Catalytic hydrothermal gasification is a promising technology which allows the conversion of wet biomass into methane rich syngas. It consists of three major steps, in which thermal energy has to be supplied at different temperature levels, leading to multiple products, such as clean water, nutrients/salts and methane rich syngas. Microalgae have an important potential as a new source of biomass, principally due to the fact that they can grow much faster than others biomass feedstock available in nature. Considering the energy balance of the algae cultivation step, the gasification process and thecrude product upgrading step, part of the converted syngas has to be used to close the energy balance. In this context, solar heat can be considered as an alternative to replace the heat that has to be generated from product or crude product burning. This would lead to higher fuel production, higher carbon conversion efficiency and in general a better sustainable use of energy sources. In this paper, the goal is to show the integration potential of solar thermal energy use in the catalytic hydrothermal gasification of microalgae. In order to maximize the fuel production, thermal energy requirements of the gasification and SNG upgrading process can be generated in concentrating solar systems, coupled with thermal energy storage. This allows to continuously provide heat for the process at different temperature levels. A superstructure of design models will permit the estimation of the optimal size and integration of the solar utility for different process configurations. The optimal design configurations are evaluated by solving a multi objective optimization problem which aims at the maximization of conversion efficiency and the minimization of operating and total production costs. Copyright

Multi-objective optimization of SNG production through hydrothermal gasification from microalgae

Abstract Microalgae cultivation for biofuel conversion is widely treated in literature as it could allow reducing fossil fuel consumptions. One of the challenges of this technology is related to the high power and cost requirements for the harvesting and dewatering steps. The influence of dewatering process can be substantially reduced when considering hydrothermal gasification (HTG). This technology, which have already been demonstrated and tested, allows treating feedstock with more than 80% moisture content and can lead to high SNG conversion efficiencies. The object of this paper is to show the combination of microalgae growing and processing coupled with the HTG and syngas purification for SNG grid quality production. The productivity potential for this given technology is evaluated considering global solar radiation data available and the cultivation technology, which can be characterized by photosynthesis conversion efficiency. Systematic system design methodology followed by multi-objective optimization technique using evolutionary algorithms are carried out to provide a set of candidate solutions considering different configurations and conflictive objectives such as efficiency, cost and environmental impact.

Energy Consumption Versus Antioxidant Activity of Pressurized Fluid Extracts from Pfaffia glomerata Roots

Conventional extraction techniques have been applied to obtain antioxidant extracts from Pfaffia glomerata roots, most of the times, using polar extracting solvents. Even if these techniques are able to provide extracts with antioxidant activities, more environmentally friendly techniques are nowadays preferred. Among them, supercritical fluid extraction (SFE) and pressurized liquid extraction (PLE) with green solvents have been widely applied to natural bioactive compounds extraction. The limitation of the use of pure supercritical CO2 for obtaining antioxidant extracts from Pfaffia glomerata roots was already demonstrated. When high amounts of modifier are added, the formation of a gas-expanded liquid is observed. This extracting solvent combines the advantages of the solvation properties of typical liquids and the transport properties of supercritical fluids, being an intermediate process between SFE and PLE, which can be called as pressurized fluid extraction (PFE). In this work, PFE of Brazilian ginseng (Pfaffia glomerata) roots were performed in order to obtain antioxidant extracts with potential applications in the pharmaceutical and food areas. Several CO2+ethanol mixtures (90:10 %, 50:50 % and 0:100 %, w/w) as extracting fluid were assayed. The effects of other two process parameters including pressure (10-20 MPa) and temperature (323-363 K) on the extraction yield, antioxidant activity and energy consumption per unit of manufactured product were investigated. PFE process was simulated using the SuperPro Designer simulation platform. The use of 10 % (w/w) of ethanol produced extracts with the highest antioxidant activity. On the other hand, higher temperature and ethanol percentage resulted in higher extraction yield and lower energy consumption per unit of manufactured product, while pressure did not affect any response variables. Copyright

Multi-objective optimization of utility systems and heat exchanger networks: method and application to the solar assisted hydrothermal gasification case

This work presents a novel framework for the multi-objective synthesis of utility systems and Heat Exchanger Networks (HEN) under single or multi-period operations. In order to solve the resulting Mixed Integer Non Linear (MINLP) programming problem, a bi-level approach is proposed to optimize process and utility systems design, utility scheduling, as well as Heat Exchanger Network Synthesis (HENS), including thermal storage. At the upper level the derivative free Queuing Multi Objective Optimization (QMOO) algorithm proposed by Molyneaux et al. (2001) is used to optimize process and utility design variables as well as Heat Exchanger Network design variables with respect to multiple competing objectives. At the lower level, first the process and utility systems are simulated with Belsim Vali, then the sequential algorithm proposed by Mian et al. (2016a), Mian et al. (2016b) is used to optimize the utility scheduling and the HEN configuration for multi-period operations. The proposed framework is applied to the Multi-objective synthesis of solar-assisted catalytic hydrothermal gasification problem. The plant consists of a catalytic hydrothermal gasification (CHTG) process including a thermal solar concentrator, a photovoltaic field and a high temperature thermal storage utility.

Techno-Economic and Environmental Optimization of Palm-based Biorefineries in the Brazilian Context, 27th European Symposium on Computer Aided Process Engineering

Abstract Due to the global increase in energy consumption, greenhouse gas emissions, and the depletion of fossil energy resources, the research presented here is focused on finding economically and environmentally competitive renewable energy resources. Fuel production from biomass is an attractive solution in this regard. Competing interests between food and energy have yielded increased interest in lignocellulosic biomass (LGB) as a feedstock. Processes such as biodiesel production from palm oil generate large volumes of LGB residues. Valorization of these residues through biorefineries may bring economic and environmental benefits through substitution of fossil fuels and such options must be studied in a systematic manner. The goal of this research is to propose a methodology for economic and environmental analysis of such biorefineries. A case study of a palm-based biorefinery in Brazil is used to illustrate this. Results indicate that multi-product processes can yield significant cost and environmental benefits.

Recent Trends in Integrated Biorefineries Development for Sustainable Production

1 School of Food Engineering (LASEFI/DEA/FEA), University of Campinas (UNICAMP), Cidade Universitaria “Zeferino Vaz,” Rua Monteiro Lobato, 80, 13083-862 Campinas, SP, Brazil 2 Industrial Process and Energy Systems Engineering (IPESE), Swiss Federal Institute of Technology Lausanne (EPFL), Station 9, 1015 Lausanne, Switzerland 3Department of Chemical Engineering, University of Arkansas, 3202 Bell Engineering Center, Fayetteville, AR 72701-1201, USA