Technology Evaluation of Process Configurations for Second Generation Bioethanol Production using Dynamic Model-based Simulations
نویسندگان
چکیده
An assessment of a number of different process flowsheets for bioethanol production was performed using dynamic model-based simulations. The evaluation employed diverse operational scenarios such as, fed-batch, continuous and continuous with recycle configurations. Each configuration was evaluated against the following benchmark criteria, yield (kg ethanol/kg dry-biomass), final product concentration and number of unit operations required in the different process configurations. The results has shown the process configuration for simultaneous saccharification and co-fermentation (SSCF) operating in continuous mode with a recycle of the SSCF reactor effluent, results in the best productivity of bioethanol among the proposed process configurations, with a yield of 0.18 kg ethanol /kg dry-biomass. INTRODUCTION Biofuels can potentially contribute to alleviate the current climate change and energy resource challenges, which today’s society is facing. Second generation (2G) bioethanol is one of the sustainable biofuels candidates that can potentially address this issue. However, the transfer of these conversion technologies from proof-of concepts to industrial scale has been done on an empirical basis (Aden et al., 2002; Larsen et al., 2008). Thus, this study has employed the Dynamic Lignocellulosic Bioethanol (DLB1.0) modelling platform (MoralesRodriguez et al., 2011a), which allowed the quantitative simulation and assessment of diverse process configurations for 2G bioethanol production, thereby providing a basis for evaluation of the most promising process flowsheets. The present work has taken a conventional process configuration as a base case (Margeot et al., 2009), which involves different sections such as, pre-treatment of the substrate, enzymatic hydrolysis of oligosaccharides, co-fermentation of sugars and downstream processes for purification and recovery of most value-added products (see Figure 1), using the dimensions and process conditions proposed by Aden et al. (2002) and Morales-Rodriguez et al. (2011a). Figure 1 Bioethanol production process from lignocelluloses. XXXII National Meeting and First International Congress AMIDIQ May, 3-6, 2011, Riviera Maya, Mexico ©2011 Academia Mexicana de Investigación y Docencia en Ingeniería Química AM IDIQ Each section is represented using dynamic mathematical models. The assessment has been carried out evaluating different process configurations and operational scenarios, such as, fed-batch, continuous and continuous with recycle, mainly found in the enzymatic hydrolysis and co-fermentation sections. Each configuration was evaluated against the following benchmark criteria, yield (kg ethanol/kg dry-biomass), final product concentration and number of unit operations required in the different process configurations. The evaluation has been performed using MatLab/Simulink as a modeling platform. MATHEMATICAL MODELS FOR THE DYNAMIC LIGNOCELLULOSIC BIOETHANOL (DLB1.0) MODELLING PLATFORM The implementation of the model-based simulation framework involved two main parts (Sin et al., 2010): 1) the collection, analysis and identification of the most promising mathematical models for pretreatment (Lavarack et al, 2002), enzymatic hydrolysis (Kadam et al, 2004) and co-fermentation (Krishnan et al., 1999), and, 2) the design, simulation and comparison of different integrated operational scenarios such as, fed-batch, continuous and continuous-recycle. The chosen configurations employ Separate Hydrolysis and Co-Fermentation (SHCF), where as the name implies the enzymatic hydrolysis as well as the fermentation of sugars have been performed in different unit operations. In addition, a model for the Simultaneous Saccharification and CoFermentation (SSCF) (Morales-Rodriguez et al., 2011b) process was also implemented and its configurations including SSCF reactors were simulated and compared with the results from the base case. Compilation and explanation of the the complete set of used mathematical models can be found in a recent publication (MoralesRodriguez et al., 2011a). PROCESS CONFIGURATIONS FOR 2G BIOETHANOL Technology evaluation was performed proposing twelve different process configurations employing SHCF and SSCF technologies, nine and three respectively (see Table 1). The distinctions among the process configurations refer to various combinations of fed-batch (FB), continuous (C) and continuous-recycle (C_RECY) operations. Table 1. Process configurations proposed for the analysis of the most promising flowsheet. Operational Scenario Acronyms SHCF H: Fed-batch –CF: Fed-batch FB-FB H: Fed-batch – CF: Continuous FB-C H: Fed-batch – CF: Continuous-Recycle FB-C_RECY H: Continuous – CF: Fed-batch C-FB H: Continuous – CF: Continuous C-C H: Continuous – CF: Continuous-Recycle C-C_RECY H: Continuous-Recycle – CF: Fed-batch C_RECY-FB H: Continuous-Recycle – CF: Continuous C_RECY-C H: Continuous-Recycle – CF: Continuous-Recycle C_RECY-C_RECY SSCF Fed-batch SSCF-FB Continuous SSCF-C Continuous-recycle SSCF-C_RECY H: Enzymatic hydrolysis, CF: Co-Fermentation Process configuration for FB-FB, C-FB, C_RECY-C_RECY and SSCF-C_RECY are illustrated in Figure 2, more details about the rest of the process configurations can be analyzed in material published by MoralesRodriguez et al. (2011a). For FB-FB process configuration (see Figure 2.a), the feedstock is treated in the pretreatment section (using diluted acid pretreatment), and the product from this operation is passed to the enzymatic hydrolysis unit to perform the conversion of cellulose biomass to glucose. Afterwards, the effluent leaving the enzymatic hydrolysis unit passes through the solid-liquid separator where a percentage of solids is sent to the power generation section (not shown in Figure 2.a), while the liquor stream is sent to the fermentation XXXII National Meeting and First International Congress AMIDIQ May, 3-6, 2011, Riviera Maya, Mexico ©2011 Academia Mexicana de Investigación y Docencia en Ingeniería Química AM IDIQ to ferment the glucose into ethanol. The output stream from the fermentation unit is then transferred to the downstream operations to separate the most valuable products (ethanol) and recover those compounds that can be reused in the upstream sections especially water. Figure 2 Bioethanol process configurations: a) FB-FB, b) C-FB, c) C_RECY-C_RECY, b) SSCF-C_RECY With enzymatic hydrolysis in fed-batch mode as a reference, continuous operation requires less unit operations to handle the biomass flow rate from the pretreatment section in order to fulfill the necessary residence time in the hydrolysis reactors (see figure 2.b). Co-fermentation reactors are operated in the same manner as described above. However, some differences are found in other parts of the process flowsheet. For example, in the cofermentation reactors operating in fed-batch mode (Fig. 1.d), the liquor generated by the solid-liquid separator is fed to the co-fermentation reactors until reaching their maximum capacity while the remaining amount is stored in the buffer tank. Another process configuration in the enzymatic hydrolysis section is based on the recycle of the insoluble solids stream from the solid-liquid separator (see Figure 2.c). This recycle stream is then mixed with the effluent generated in the pretreatment section before entering the hydrolysis reactor. After solid-liquid separation, liquid stream is conveyed directly to the co-fermentation section where the conversion of sugars into ethanol is accomplished. The settler tank separates the solids from the liquids in the effluent of the fermentor by gravity XXXII National Meeting and First International Congress AMIDIQ May, 3-6, 2011, Riviera Maya, Mexico ©2011 Academia Mexicana de Investigación y Docencia en Ingeniería Química AM IDIQ settling and recycles the solids back to the mixer unit which also contains the yeast. This recycling ensures that a high concentration of solids and yeast is maintained in the co-fermentation reactors. In the SSCF configuration operating in continuous with solid recycle in the output stream (see Figure 2.d), the solid content is mixed with the stream from the pretreatment unit. This action aims to produce the highest possible yield of ethanol per amount of processed raw biomass material, thereby reducing the waste of raw materials in the biofuel production plant. OPERATION POLICIES FOR THE PROCESS CONFIGURATIONS FOR 2G BIOETHANOL When fed-batch processes are used, it is assumed that parallel fed-batch reactors are operated following a batch scheduling scheme consisting of a sequence of different operational phases – for example fill, react, draw, idle – that are repeated over time. The schedule for fed-batch operation (see Figure 3) describing the operation of the hydrolysis and cofermentation units (used in the configuration in Figure 2.a) can be understood as follows: for reactor number one a cycle of operation lasts 60 hours. It starts with the loading, an operation that takes 12 hours, and is followed by 36 hours of reaction time. Finally it ends with 12 hours of drawing/emptying the reactor contents. Upon the completion of the first cycle, the next cycle starts again by repeating the same schedule. The first fermentation reactor therefore starts after 48 hours then following the 12, 36 and 12 hours scheduling (Figure 3). Figure 3 Scheduling for FB operation in the hydrolysis and fermentation sections. Regarding the co-fermentation unit, the loading period is assumed to start simultaneously with the drawing of the contents from the hydrolysis unit, thus assuming that an ideal solid-liquid separation operating in steady state is present between hydrolysis and co-fermentation. It is important to remark that a buffer tank is needed after the hydrolysis units (operating in continuous) to buffer the continuous flow before it is fed to the fed-batch operated fermentors (see figure 2.b). BENCHMARK CRITERIA FOR COMPARISON OF THE DLB1.0 SIMULATION OF THE CONFIGURATIONS The comparison of the performance of the different process flowsheets has been performed by using as evaluation criteria: the ethanol/dry-biomass ratio, the fraction of unreacted raw material and the final ethanol concentration. The ethanol/dry-biomass ratio has been calculated on the basis of the total amount of ethanol that is transferred to the downstream processing section as follows:
منابع مشابه
A Switchgrass-based Bioethanol Supply Chain Network Design Model under Auto-Regressive Moving Average Demand
Switchgrass is known as one of the best second-generation lignocellulosic biomasses for bioethanol production. Designing efficient switchgrass-based bioethanol supply chain (SBSC) is an essential requirement for commercializing the bioethanol production from switchgrass. This paper presents a mixed integer linear programming (MILP) model to design SBSC in which bioethanol demand is under auto-r...
متن کاملPerformance Evaluation of Magnetorheological Damper Valve Configurations Using Finite Element Method
The main purpose of this paper is to study various configurations of a magnetorheological (MR) damper valve and to evaluate their performance indices typically dynamic range, valve ratio, inductive time constant and pressure drop. It is known that these performance indices (PI) of the damper depend upon the magnetic circuit design of the valve. Hence, nine valve configurations are considered fo...
متن کاملEnhanced Bioethanol Production in Batch Fermentation by Pervaporation Using a PDMS Membrane Bioreactor
The integration of batch fermentation and membrane-based pervaporation process in a membrane bioreactor (MBR) was studied to enhance bioethanol production compared to conventional batch fermentation operated at optimum condition. For this purpose, a laboratory-scale MBR system was designed and fabricated. Dense hydrophobic Polydimethylsiloxane (PDMS) membrane was used for pervaporation. For fer...
متن کاملTechno-economic evaluation of 2nd generation bioethanol production from sugar cane bagasse and leaves integrated with the sugar-based ethanol process
BACKGROUND Bioethanol produced from the lignocellulosic fractions of sugar cane (bagasse and leaves), i.e. second generation (2G) bioethanol, has a promising market potential as an automotive fuel; however, the process is still under investigation on pilot/demonstration scale. From a process perspective, improvements in plant design can lower the production cost, providing better profitability ...
متن کاملComposite Multi Wall Carbon Nano Tube Polydimethylsiloxane Membrane Bioreactor for Enhanced Bioethanol Production from Broomcorn Seeds
Broomcorn seed (Sorghum vulgare) was used as raw material for bioethanol production. Optimum conditions were obtained from response surface method. Broomcorn seed flour (45 g/l) was treated by alkaline treatment and dual enzymatic hydrolysis (0.7 g/l of α- amylase and 0.42 g/l of amyloglucosidase). The hydrolyzed total sugar of 25.5 g/L was used in conventional bioethanol production (8.1 g/l) u...
متن کامل