José Luiz de Medeiros

A methodology for screening of microalgae as a decision making tool for energy and green chemical process applications

The increasing interest for biotechnological use of microalgae demands a methodology for selection of species suitable to support the development of technologies based on the use of such non-conventional renewable raw material, i.e., green industrial applications. The vast and expanding collection of experimental data on both cell growth and biomass composition available in the literature can be used to reduce the cost of the experimental investigations required to support process engineering and optimization. Selecting the appropriate organism requires extracting useful information from such data, a cumbersome task since various multidisciplinary factors must be considered. This paper presents a computer-aided methodology for selecting appropriate algal species given an energy or green chemical process application employing microalgae as a renewable raw material. The approach is “system oriented”, based on biomass composition and chemical processing of the biomass downstream of the CO2 biofixation and harvesting operations. Quantitative performance results are supported by professional process simulation. Besides comparison of a set of species performances, the proposed methodology also allows the discrimination among distinct algal compositions resulting from different growth conditions for a given species. Furthermore, three categories of screening metrics are proposed to be maximized by the decision making procedure in order to elicit the relevant information. To demonstrate the potential of the proposed methodology, a databank of both biochemical and elemental compositions of microalgal biomass was used in three green applications: Assessment of biomass heating value; production of syngas by gasification of the biomass; and production of Bio-H2. Within the accuracy of the databank employed to illustrate the procedure, the methodology selected Botryococcus braunii and Isochrysis galbana as potential promising candidates, for the three examined applications.

Effects of CO2 enrichment and nutrients supply intermittency on batch cultures of Isochrysis galbana.

Aiming at enhanced performance to increase economic feasibility of microalgae based processes, Isochrysis galbana was grown in three modes of cultivation: batch, intermittent fed batch and semi-continuous. The batch mode was conducted under two regimes of aeration: conventional aeration and CO2 enriched aeration (5% v/v in air). Increased biomass productivity without significant impact on lipid accumulation was observed for CO2 enriched aeration relatively to cultivation aerated with air only. The intermittent fed batch cultivation policy was proven to be useful for lipid accumulation, increasing the lipid content by 19.8%. However, the semi-continuous mode resulted in higher productivity due to increased biomass concentration; the biomass productivity reached 0.51 g/(Ld). Fluorescence measurements were performed; the calculated low electron transport rate showed the need to increase the irradiance. The results showed that I. galbana can be grown in semi-continuous condition at high levels of biomass productivity.

Cultivation of Spirulina maxima in medium supplemented with sugarcane vinasse

The feasibility of sugarcane vinasse as supplement in growth medium of Spirulina maxima was investigated. The cell was cultivated under autotrophic (no vinasse, 70 μmol photons m(-2) s(-1)), heterotrophic (no light, culture medium supplemented with vinasse at 0.1% v/v and 1.0% v/v) and mixotrophic conditions (70 μmol photons m(-2) s(-1), vinasse at 0.1% v/v and 1.0% v/v). These preliminary results suggested a cyclic two-stage cultivation - CTSC, with autotrophic condition during light phase of the photoperiod (12 h, 70-200 μmol photons m(-2) s(-1)) and heterotrophic condition during dark phase (12h, 3.0% v/v vinasse). The adopted CTSC strategy consisted in three cycles with 75% withdrawal of suspension and reposition of medium containing 3.0% v/v vinasse, separated by autotrophic rest periods of few days between cycles. Results show an increase of biomass concentration between 0.495 g L(-1) and 0.609 g L(-1) at the 7th day of each cycle and high protein content (between 74.3% and 77.3% w/w).

Optimal programming of ideal and extractive batch distillation: single vessel operations

Abstract This work addresses the problem of optimal programming of multi-component batch distillation columns with a single vessel (batch rectifier, batch stripper, middle vessel and extractive middle vessel) so as to maximize an annualized profit function. A smooth price function is formulated for product valuation, allowing to release traditional purity constraints. The solution is the optimal batch policy of top/bottom withdrawals. A simplified cascade model is developed for separation calculations, offering several operational patterns. Ideal and non-ideal mixtures can be handled with this model that is proposed as a substitute for traditionally used Fenske–Underwood–Gilliland cascades. Batch separations of ideal quaternary feeds are optimally programmed for the first three operations aforementioned. The extractive middle vessel column was optimally programmed for production of anhydrous ethanol from hydrated, nearly azeotropic, alcohol with ethylene–glycol as entrainer. All applications considered fixed number of stages, heat duty, and, in the extractive system, fixed pump-around rate of entrainer.

Global optimization of water distribution networks through a reduced space branch-and-bound search

A branch-and-bound approach to the problem of optimal design of water distribution networks is presented. Global optimum is reached through the generation of convergent sequences of upper and lower bounds. The relaxations responsible for the lower bounds correspond to linear programming problems formulated through the enlargement of the original feasible region by outer approximations of the constraints. Although formulated within an arc-based framework, the proposed scheme does not apply the branching process to all flow variables; by utilizing the mass conservation principle, only a reduced set of variables is assigned for branching. The algorithm was applied to three variants of a classical problem from the literature. Comparisons with previous results indicates a faster convergence to the optimum (fewer linear programming problems solved) in several situations.

An age-structured population balance model for microbial dynamics

This work presents an age-structured population balance model (ASPBM) for a bioprocess in a continuous stirred-tank fermentor. It relates the macroscopic properties and dynamic behavior of biomass to the operational parameters and microscopic properties of cells. Population dynamics is governed by two time- and age-dependent density functions for living and dead cells, accounting for the influence of substrate and dissolved oxygen concentrations on cell division, aging and death processes. The ASPBM described biomass and substrate oscillations in aerobic continuous cultures as experimentally observed. It is noteworthy that a small data set consisting of nonsegregated measurements was sufficient to adjust a complex segregated mathematical model.

PARETO OPTIMIZATION OF AN INDUSTRIAL ECOSYSTEM: SUSTAINABILITY MAXIMIZATION

This work investigates a procedure to design an Industrial Ecosystem for sequestrating CO2 and consuming glycerol in a Chemical Complex with 15 integrated processes. The Complex is responsible for the production of methanol, ethylene oxide, ammonia, urea, dimethyl carbonate, ethylene glycol, glycerol carbonate, β-carotene, 1,2-propanediol and olefins, and is simulated using UNISIM Design (Honeywell). The process environmental impact (EI) is calculated using the Waste Reduction Algorithm, while Profit (P) is estimated using classic cost correlations. MATLAB (The Mathworks Inc) is connected to UNISIM to enable optimization. The objective is granting maximum process sustainability, which involves finding a compromise between high profitability and low environmental impact. Sustainability maximization is therefore understood as a multi-criteria optimization problem, addressed by means of the Pareto optimization methodology for trading off P vs. EI.

Exergy Analysis of Monoethylene Glycol (MEG) Recovery Systems

Abstract Hydrates are ice-like compounds comprised of water and light hydrocarbons whose formation in natural gas pipelines can lead to several problems such as pipeline blockage. To avoid these problems, the injection of Thermodynamic Hydrate Inhibitors (THI) in well-heads is widely employed. There are several options of THIs. In the present work, Monoethylene Glycol (MEG) was chosen due to its comparative advantages. As MEG can be reused, it must be re-concentrated and stripped of salts before recirculation through subsea pipelines. MEG Recovery Units (MRU) can be divided into three types: Traditional Process (TP), Full-Stream Process (FS) and Slip-Stream Process (SS). TP, FS and SS were discussed and compared via Energy and Exergy Analyses. The Exergy Analysis was based on two different approaches: firstly allocating the Reference Environmental Reservoir (RER) as the atmosphere at sea level; secondly allocating the RER as sea level atmospheric air saturated with water in equilibrium with liquid water containing MEG at infinite dilution. Those two approaches led to different results, but, in both cases TP shows the highest exergy efficiency and lowest energy consumption, while FS exhibits the lowest exergy efficiency and highest energy consumption. SS occupied an intermediate position.

A Comparative Economical Analysis of Technologies for CO2 Removal from Offshore Natural Gas

Abstract In the scenario of the Brazilian Pre-Salt fields, where associated Natural Gas (NG) shows high concentration of CO 2 , gas conditioning comes out as one of the main challenges. Among the possible capture technologies available, three alternatives stand out for CO 2 sequestration: (A) gas permeation through membranes, (B) absorption columns using aqueous blends of ethanolamines and (C) application of hybrid - membrane modules in series with amine absorption and regeneration columns. The main objective of this work is to investigate the technical and economical feasibility of applying these three separation processes on offshore platforms, given the stringent constraints on footprint and equipment weight, and for minimizing NG production and transportation costs. The methodology involves: (i) development of cases based on the Brazilian Pre-Salt gas composition. NG streams with CO 2 molar concentrations ranging from 8 to 18% are applied; (ii) Simulations of three process flowsheets, corresponding to each one of chosen technologies - A, B and C; (iii) Equipment sizing; and (iv) Analysis of economic performance through calculation of capital (CAPEX) and operational (OPEX) costs.

Detection, Localization and Quantification of Leaks in Pipeline Networks Using a Parameter Estimation Approach

This paper presents a pipe network monitoring system based on a parameter estimation approach. The initial step involves the calibration of a dynamic pipe network simulator to the analyzed network, using a parameter estimation procedure. After the calibration, the network can be monitored, through an online simulation employing updated input data. If a properly statistical criterion indicates a discrepancy between the predicted and measured output variables, a possible leak is detected. Then, automatically, a routine of leak localization and quantification starts. This routine consists of an estimation procedure where the network model includes two additional parameters: the leak diameter and location in a pipeline section. This procedure is applied for each pipeline section selected by the user to be investigated. The section with the best match between predicted and measured data corresponds to the leak information that must be checked by the operation staff.Copyright