Thermal integration and termoeconomic optimization applied to the industrial process of sugar and ethanol from surgacane

Orientadores: Silvia Azucena Nebra de Perez, Luis Maria Serra de RenobalesTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: A produção de açúcar e etanol a partir da cana-de-açúcar no Brasil compõe um dos setores mais importantes da economia nacional e tem se caracterizado, ao longo de sua história, pelo alto consumo de energia no processo industrial. O uso do bagaço de cana como combustível para o sistema de cogeração permite que as usinas sejam auto-suficientes em energia térmica e elétrica, ainda que utilizem sistemas de baixa eficiência. Uma nova realidade, que prevê a venda de eletricidade excedente nas usinas e o uso do bagaço como matéria prima para outros processos, tem levado o setor a investir em redução do consumo de energia no processo. Este estudo propõe um método de integração térmica para o produção de açúcar e etanol, visando obter uma redução da demanda de utilidades quentes e frias. Um procedimento de otimização termoeconômica foi também aplicado para avaliar a redução de custo no projeto de integração da planta, que inclui uma rede de trocadores de calor e um sistema de evaporação. As análises mostraram que a integração pode proporcionar aumentos significativos na produção de excedentes de eletricidade e/ou bagaço de cana, além de reduzir a demanda de água da usina. Uma análise exergética foi realizada, avaliando as melhorias obtidas com a integração, mostrando que a geração de irreversibilidade pode ser minimizada com a redução do consumo de energia no processo e aumento da eficiência do sistema de cogeraçãoAbstract: The sugar and ethanol production from sugarcane in Brazil constitutes one of the most import sectors of the national economy and has been characterized, during its history, by high energy consumption in the industrial process. The use of the bagasse as fuel for the cogeneration system permits mills to be self-sufficient in thermal and electric energy requirements, even using low efficient systems. A new reality, which foreseen sell of surplus electricity by the mills or the use of bagasse as raw material for other processes, has encouraged this sector to invest in process energy consumption reduction. This study proposes a method for thermal integration of sugar and ethanol process, aiming at the reduction of hot and cold utilities requirements. An thermoeconomic optimization procedure was also applied for the evaluation of cost reduction in the plant integration design, which includes the heat exchangers network and the evaporation system. The analysis showed that the process integration may promote a significant increase in the production of surplus of electricity and/or bagasse, reducing also the water demand of the mills. An exergetic analysis was performed, evaluating the improvements obtained with the thermal integration, showing that the irreversibility generation can be minimized with reduction of process energy consumption and increase of the cogeneration systems efficiencyDoutoradoTermica e FluidosDoutor em Engenharia Mecânic

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 and slightly overestimating the productivity in the 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 methodology for designing flexible multi-generation systems

An FMG (flexible multi-generation system) consists of integrated and flexibly operated facilities that provide multiple links between the various layers of the energy system. FMGs may facilitate integration and balancing of fluctuating renewable energy sources in the energy system in a cost- and energy efficient way, thereby playing an important part in smart energy systems. The development of efficient FMGs requires systematic optimization approaches. This study presents a novel, generic methodology for designing FMGs that facilitates quick and reliable pre-feasibility analyses. The methodology is based on consideration of the following points: Selection, location and dimensioning of processes; systematic heat and mass integration; flexible operation optimization with respect to both short-term market fluctuations and long-term energy system development; global sensitivity and uncertainty analysis; biomass supply chains; variable part-load performance; and multi-objective optimization considering economic and environmental performance. Tested in a case study, the methodology is proved effective in screening the solution space for efficient FMG designs, in assessing the importance of parameter uncertainties and in estimating the likely performance variability for promising designs. The results of the case study emphasize the importance of considering systematic process integration when developing smart energy systems. (C) 2016 Elsevier Ltd. All rights reserved

A method for aggregating external operating conditions in multi-generation system optimization models

This paper presents a novel, simple method for reducing external operating condition datasets to be used in multi-generation system optimization models. The method, called the Characteristic Operating Pattern (CHOP) method, is a visually-based aggregation method that clusters reference data based on parameter values rather than time of occurrence, thereby preserving important information on short-term relations between the relevant operating parameters. This is opposed to commonly used methods where data are averaged over chronological periods (months or years), and extreme conditions are hidden in the averaged values. The CHOP method is tested in a case study where the operation of a fictive Danish combined heat and power plant is optimized over a historical 5-year period. The optimization model is solved using the full external operating condition dataset, a reduced dataset obtained using the CHOP method, a monthly averaged dataset, a yearly-averaged dataset, and a seasonal peak/off-peak averaged dataset. The economic result obtained using the CHOP-reduced dataset is significantly more accurate than that obtained using any of the other reduced datasets, while the calculation time is similar to those obtained using the monthly averaged and seasonal peak/off-peak averaged datasets. The outcomes of the study suggest that the CHOP method is advantageous compared to chronology-averaging methods in reducing external operating condition datasets to be used in the design optimization models of flexible multi-generation systems. (C) 2015 Elsevier Ltd. All rights reserved

Integration of Supercritical Water Gasification in Combined 1G/2G Ethanol Production

The present study investigates the potential conversion of sugarcane into ethanol and synthetic natural gas. The considered conversion path consists in combining ethanol first and second generation ethanol production plant with a catalytic supercritical water gasification system. The main steps of the ethanol conversion consider fermentation of sugars (1G) and enzymatic hydrolysis of bagasse (2G). Enzymatic hydrolysis is selected since it represents a promising alternative for 2nd generation biofuels due to its high conversion efficiency. Among streams that are leaving the ethanol production plant are some high watered streams, whose carbon/energy content is not negligible. These streams should be valorised in an efficient way in order to improve the energy conversion efficiency. In this context supercritical gasification process allows to valorise these flows leaving the ethanol plant. Using supercritical water gasification it is in fact possible to avoid the drying the ethanol production leftovers, thus performing a direct gasification. The conversion of ligno-cellulosic residues into synthetic natural gas is modelled considering a catalytic supercritical gasification plant. Since the goal is to achieve high energy and exergy conversion efficiencies, the potential use of an additional set of utilities, such as burners, steam injected gas turbines or steam networks, is added to the sizing problem. The mathematical nature of the optimal utility selection problem deals with mixed integer linear programming (MILP) model, in which the type and size of utilities represent the independent variables, having fixed the process size. The results of the integration are showed in terms of Composite and Grand Composite Curves, economic indicators and local CO2 balance. Finally, having identified the ratio of sugarcane that goes to second generation ethanol plant as key dependent variables, the results of a sensitivity analysis are presented. The sensitivity analysis results are shown accounting economics for the Brazilian market, energy conversion performance indicators and considering local carbon dioxide balance

Thermo-Economic Optimization of Integrated First and Second Generation Sugarcane Ethanol Plant

The sugarcane industry has been responsible in some countries for the production of most of the sugar and ethanol available in the world for internal and external markets. In this sector, ethanol can be produced by fermentation of sugars obtained directly from sugarcane biomass, commonly called 1st generation ethanol. New processes using the enzymatic hydrolysis technology of lignocellulosic residues like bagasse and sugarcane leaves as feedstock can increase the ethanol production in these plants, reducing the land requirements and the environmental of impact biofuels production in large scale. The lignocellulosic ethanol production using enzymatic hydrolysis technology is one of the most promising alternatives of 2nd generation biofuels, due to its high conversion efficiencies and low environment impact. Some problems like high water consumption and enzymes costs must be overcome in order to reach commercial scale. The process integration and thermo-economic optimization of the process can be important for the design of this process in a sugarcane autonomous distillery aiming at the cost and environmental impact reduction. In this paper a process integration of the sugarcane ethanol distillery model is carried out taking into account 1st and 2nd generation processes in the same site using sugars and bagasse as feedstock respectively. Conflictive objectives such as maximization of the electricity or ethanol production are adopted in a multi-objective optimization technique using evolutionary algorithms, in order to provide a set of candidate solutions considering different configurations of the ethanol production process design

Multi-objective Optimization of a Solar Assisted 1st and 2nd Generation Sugarcane Ethanol Production Plant

Ethanol production sites utilizing sugarcane as feedstock are usually located in regions with high land availability and decent solar radiation. This offers the opportunity to cover parts of the process energy demand with concentrated solar power (CSP) and thereby increase the fuel production and carbon conversion efficiency. A plant is examined that produces 1st and 2nd generation ethanol by fermentation of sugars (from sugarcane) and enzymatic hydrolysis of the lignocellulosic residues (bagasse), respectively. Enzymatic hydrolysis is a promising alternative for 2nd generation biofuels due to its high conversion efficiency and low environmental impact. In conventional ethanol production processes, electrical and thermal power is delivered to the system by burning parts of the feedstock to drive a steam based cogeneration cycle (between 400 and 800K). Introducing high temperature thermal power (at 800K) from a solar trough field coupled with sensible heat storage, for continuous operation, offers the opportunity to replace the heat generated from biomass burning, and thus increase the product yield. In this work, the potential for process integration of a solar trough field coupled with packed bed thermal storage to a 1st and 2nd generation ethanol production site is evaluated by means of pinch analysis. Decision parameters such as the solar fraction, the percentage of bagasse to 2nd generation, and the solar field size are optimized via multi- objective optimization based on evolutionary algorithms to maximize the carbon conversion efficiency and minimize the total annual cost for a plant located in Ribeirao Preto, Brazil

Estudo da geração de biogas no aterro sanitario Delta em Campinas - SP

Orientador: Waldir Antonio BizzoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: A disposição final do lixo é um dos graves problemas ambientais enfrentados pelos grandes centros urbanos, particularmente no Brasil onde o uso de "lixões" ainda é muito comum. A emissão descontrolada do biogás produzido na decomposição anaeróbia da matéria orgânica pode ser uma ameaça ao ambiente local causando danos à vegetação, gerando odores desagradáveis, oferecendo ainda riscos de explosão em concentrações entre 5 e 15% no ar. O biogás pode ser também um problema global pois é formado por cerca de 50% de metano que é um gás causador do efeito estufa. O uso do biogás produzido nos aterros pode promover vários benefícios para os governos locais, estimulando a adoção de práticas de engenharia que maximizam a geração e a coleta do biogás, também reduzindo os riscos de contaminação do meio ambiente. Neste estudo desenvolveram-se testes no aterro sanitário Delta na cidade de Campinas, onde foram realizadas análises da composição e medições de vazão do biogás emitido no local para avaliar o potencial de geração de energia elétrica utilizando o biogás como combustível. Também foi calculada a partir dos resultados obtidos em campo, a produção futura para o aterro, com a adoção de uma metodologia teórica presente na literatura. Concluiu-se que o aterro atingirá seu potencial máximo (4 MW) um ano após o seu fechamento que deve ocorrer em junho de 2006. A produção de biogás tende a diminuir exponencialmente até o final do consumo da matéria orgânicaAbstract: Disposal of waste into landfills represents one of the most important problems in urban sites, particularly in Brazil where the use of "open dumps" is still very common. Uncontrolled emission of biogas produced by anaerobic decomposition of the organic matter can be a local environmental hazard causing vegetation damage, unpleasant odors and may form explosive mistures at concentrations from 5 to 15 per cent in air. Biogas can also be global problem, once it is constituted by at least 50% of methane, which is an aggressive greenhouse gas. The use of produced biogas can promote many benefits for the local govemments, extimulating the adoption of engineering practices that maximize the biogas generation and collection efficiency, also reducing the risks of environment contamination. This study comprises field testing in Delta landfill located in Campinas city where were there performed composition analysis and flow measurements of the biogas emitted from the site to evaluate the electric power generation potential using biogas as combustible. The future biogas production was also calculated for the landfill adopting a methodology presented in the literature, using measured data as initial input. It was concluded that the landfill will achieve it's maximum potential (4MW) one year after the closure of the site that is planed to happen in 2006. The production of biogas tends to decrease exponentially until the end of the organic matter consumptionMestradoTermica e FluidosMestre em Engenharia Mecânic

Thermo-economic and environmental model of microalgae-to-SNG conversion process through hydrothermal gasification

Due to its high photosynthesis conversion efficiency, microalgae are currently considered as a serious feedstock for next-generation biofuels production. One possible conversion process is the production of synthetic natural gas (SNG) through catalytic hydrothermal gasification which uses a supercritical water-processing for the gasification and has the advantage to avoid drying of the biomass. The whole system includes four steps of production: microalgae cultivation, dewatering, gasification and product separation. In this paper the SNG production from microalgae is analyzed considering algal biomass cultivation system with open-ponds technology. To do so, a mathematical model based on mass and energy balances has been developed in order to represent microalgae growth process, and regarding culture temperature, solar-radiation incidence, CO2 and nutrients supply. The complete physical model of the biomass conversion system is developed including the dewatering system with settling ponds and centrifuges, catalytic hydrothermal gasification with salt separation unit and the SNG separation and purification system. An economic model is carried out for investment and operation cost of the process, from the biomass cultivation to the final product, including possibilities of nutrients, CO2 and water recovery. Finally, the environmental impact regarding the CO2 emission of this process and the avoided emission from the replacement of fossil natural gas is estimated in a complete life cycle analysis. A multi-objective optimization methodology is used to find the trade-off between the total cost of the system and the environmental impact that can be linked with the equipment size and the energy conversion efficiency