About the Possibilities of the Heat Exchangers Network Retrofit for Post-Combustion CO₂ Capture Unit Without Stream Split

There is an increasing interest in post-combustion CO2 capture connected with climate change and further use of captured CO2 in enhanced oil and gas recovery and as a feed to produce such products as methanol, dimethylether and others, use in hot dry rock technologies etc. The currently used post-combustion method with monoethanolamine (MEA) absorption without stream split has two shortcomings: significant steam consumption to regenerate amine solution and relatively high cost of heat exchange equipment of absorption unit or Heat Exchange Network of Absorption Unit (HEN AU). The variation of temperature differences on rich/lean heat exchanger was considered and its influence on heat supply, cost of HEN AU and cold utility consumption was searched. The high effective plate heat exchangers are proposed as components of HEN AU to decrease its cost. The possibility of flue gas stream heat integration for heat supply to the desorber was searched too

Cost Effective Synthesis of Graphene Nanomaterials for Non-Enzymatic Electrochemical Sensors for Glucose: A Comprehensive Review

The high conductivity of graphene material (or its derivatives) and its very large surface area enhance the direct electron transfer, improving non-enzymatic electrochemical sensors sensitivity and its other characteristics. The offered large pores facilitate analyte transport enabling glucose detection even at very low concentration values. In the current review paper we classified the enzymeless graphene-based glucose electrocatalysts’ synthesis methods that have been followed into the last few years into four main categories: (i) direct growth of graphene (or oxides) on metallic substrates, (ii) in-situ growth of metallic nanoparticles into graphene (or oxides) matrix, (iii) laser-induced graphene electrodes and (iv) polymer functionalized graphene (or oxides) electrodes. The increment of the specific surface area and the high degree reduction of the electrode internal resistance were recognized as their common targets. Analyzing glucose electrooxidation mechanism over Cu-Co-and Ni-(oxide)/graphene (or derivative) electrocatalysts, we deduced that glucose electrochemical sensing properties, such as sensitivity, detection limit and linear detection limit, totally depend on the route of the mass and charge transport between metal(II)/metal(III); and so both (specific area and internal resistance) should have the optimum values. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.Asst. Prof. Brouzgou, A., thankfully acknowledges the Research, Innovation and Excellence Structure (DEKA) of the University of Thessaly for the funding of the research program entitled: ‘Electrochemical (bio)sensors: synthesis of novel carbon monolayer-based nanoelectrodes for biomolecules detection’ and Ms Balkourani, G. (PhD student) thankfully acknowledges the Hellenic Foundation for Research and Innovation (HFRI), the PhD Fellowship grant. 25, 6816

Carbon capture from natural gas combined cycle power plants: Solvent performance comparison at an industrial scale

Natural gas is an important source of energy. This article addresses the problem of integrating an existing natural gas combined cycle (NGCC) power plant with a carbon capture process using various solvents. The power plant and capture process have mutual interactions in terms of the flue gas flow rate and composition vs. the extracted steam required for solvent regeneration. Therefore, evaluating solvent performance at a single (nominal) operating point is not indicative and solvent performance should be considered subject to the overall process operability and over a wide range of operating conditions. In the present research, a novel optimization framework was developed in which design and operation of the capture process are optimized simultaneously and their interactions with the upstream power plant are fully captured. The developed framework was applied for solvent comparison which demonstrated that GCCmax, a newly developed solvent, features superior performances compared to the monoethanolamine baseline solvent

Βέλτιστος σχεδιασμός και λειτουργικότητα διεργασιών δέσμευσης CO2 καύσης με διαλύτες

A generalized framework for the optimal design of post-combustion CO2 capture processes is proposed. Structural blocks including the column section, heat transfer blocks as well as stream splitters and mixers enable the generation and evaluation of alternative flowsheet configurations within a non-linear optimization program. The proposed design framework is used for the optimal design of a number of alternative flowsheets for the separation of CO2 from an industrial flue gas stream using a variety of amine solvents. These flowsheets illustrate the various connection patterns between the process units and indicate suitable distribution of process driving forces through which the overall efficiency can be drastically enhanced. Interactions between the alternative solvents and process flowsheets are revealed during process operation and the performance of each candidate solvent/flowsheet pair is assessed using qualitative and quantitative considerations. Heat integration between the different processes within the CO2 capture plant as well as between the capture plant and the adjacent CO2 emitting plant are considered. Further, an integrated design and operability framework is also proposed. Within this framework the simultaneous assessment, rank ordering, and screening of various solvent, flowsheet configuration and control structure combinations is realized. The investigation of the steady state and dynamic effects that the process parameters and exogenous disturbances impose on the system for a given control structure is performed using steady state disturbance rejection analysis. Quantification of each system’s capabilities is performed with the aid of a controllability index. The diverse inherent system properties such as the structure of the selected flowsheet configuration of the nature of the employed solvent constitute additional design features that diversify the process response. The performed sensitivity analysis generates useful insights regarding the control structure selection and the range of parameter variations within which the candidate processes demonstrate optimum performance. Furthermore, it allows the adaptive modification of the process design characteristics in order to enhance process operability. Additionally, the evaluation of the system’s dynamic controllability results in a mapping of its open loop dynamic characteristics including the identification of operating regions of instability, oscillatory behavior or slow response.Στην παρούσα διατριβή προτείνεται ένα γενικευμένο πλαίσιο για το βέλτιστο σχεδιασμό διεργασιών δέσμευσης CO2 καύσης που βασίζεται σε ένα ευέλικτο μοντέλο ισορροπίας σε συνδυασμό με την τεχνική της ορθογώνιας ταξιθεσίας σε πεπερασμένα στοιχεία. Δομικές μονάδες όπως το τμήμα της στήλης διαχωρισμού, μονάδες μεταφοράς θερμότητας καθώς και διαχωριστές και αναμίκτες ρευμάτων επιτρέπουν τη δημιουργία και αξιολόγηση εναλλακτικών διαγραμμάτων ροής μέσα σε ένα μη-γραμμικό πρόγραμμα βελτιστοποίησης. Το προτεινόμενο πλαίσιο σχεδιασμού χρησιμοποιήθηκε για το βέλτιστο σχεδιασμό ενός αριθμού εναλλακτικών διαγραμμάτων ροής για τον διαχωρισμό του CO2 από ένα ρεύμα απαερίων. Αυτά τα διαγράμματα ροής απεικονίζουν τις διάφορες μορφές σύνδεσης μεταξύ των μονάδων επεξεργασίας και υποδεικνύουν κατάλληλη κατανομή των κινητήριων δυνάμεων με στόχο την ενίσχυση της απόδοσης της διεργασίας. Προσδιορίστηκαν οι αλληλεπιδράσεις μεταξύ των εναλλακτικών διαλυτών και διαγραμμάτων ροής και η απόδοση του κάθε υποψηφίου ζεύγους διαλύτη / διαγράμματος ροής αξιολογήθηκε με χρήση ποιοτικών και ποσοτικών δεικτών. Θεωρήθηκε ακόμα η ενεργειακή ολοκλήρωση μεταξύ των διαφόρων διεργασιών μέσα στη μονάδα δέσμευσης CO2, καθώς και μεταξύ της μονάδας δέσμευσης και της παρακείμενης μονάδας παραγωγής CO2. Επιπλέον, προτείνεται ένα ολοκληρωμένο πλαίσιο βέλτιστου σχεδιασμού και λειτουργικότητας. Μέσα σε αυτό πραγματοποιήθηκε η ταυτόχρονη αξιολόγηση και ιεράρχηση διάφορων συνδυασμών διαλυτών, διαγραμμάτων ροής και δομών ελέγχου. Η εξερεύνηση των χαρακτηριστικών σε μόνιμη κατάσταση και των δυναμικών αποκρίσεων σε εξωγενείς διαταραχές για μια δεδομένη δομή ελέγχου έγινε με τη χρήση μεθόδου αντιστάθμισης διαταραχών. Οι διαφορετικές εγγενείς ιδιότητες των συστημάτων, όπως η δομή του επιλεγμένης διαγράμματος ροής και η φύση του διαλύτη αποτελούν πρόσθετα χαρακτηριστικά σχεδιασμού που διαφοροποιούν την απόκριση της διεργασίας. Η ανάλυση ευαισθησίας παράγει χρήσιμες πληροφορίες σχετικά με την επιλογή της δομής ελέγχου και το εύρος των διακυμάνσεων των παραμέτρων εντός των οποίων οι υποψήφιες διεργασίες επιδεικνύουν τη βέλτιστη απόδοση. Επιπλέον, επιτρέπει την τροποποίηση των σχεδιαστικών χαρακτηριστικών της διεργασίας, προκειμένου να ενισχυθεί η λειτουργικότητα της. Ακόμα, καθίσταται δυνατή η αξιολόγηση της δυναμικής συμπεριφοράς των συστημάτων μέσω της χαρτογράφησης των δυναμικών χαρακτηριστικών ανοικτού βρόχου και του προσδιορισμού των περιοχών που σχετίζονται με αστάθεια, ταλαντωτική συμπεριφορά ή αργή απόκριση

Optimal design of biomass supply chains with integrated process design

The current work focuses on the optimal design of biomass supply chains, addressing the conversion of raw materials into useful services. The latter include not only heat and power but also synthetic bio-based fuels (e.g. bio-SNG). Optimally pre-designed processing units representing the conversion facilities responsible for the transformation of biomass are employed. This permits the use of standardized units that act as building blocks within a MILP optimization problem, significantly simplifying the formulation and solution of the problem. These building blocks encompass a variety of transformation options and carry specific information regarding their capacity, total processing cost, overall efficiency and energetic performance. Then, the supply chain design optimization problem aims not only to identify the most suitable conversion plant type but also to determine their location by minimizing the overall cost, expressed as the capital and operating expenses of the processing units as well as the transport costs between the points of operation. The above formulation is applied for the conversion of animal manure to different end products in the district of Brig in southern Switzerland. Results reveal the predominance of large centralized bio-SNG producing units as a consequence of their higher conversion efficiency

Thermochemical conversion of biomass to second generation biofuels through integrated process design--A review

The need for clean and environmental friendly fuels is leading the world to the production of biofuels and replacing conventional fuels by them. Second generation biofuels derived from lignocellulosic feedstocks tackle the drawbacks posed by the so-called first generation ones regarding feedstock availability and competition with the food industries. Thermochemical conversion of biomass to biofuels is a promising alternative route relying on well-established technologies including gasification and the Fischer-Tropsch synthesis. The conjunction of these processes creates a pathway through which the production of biofuels is sustainable. However, the multiple interactions between the processing steps greatly increase the difficulty in the accurate design of such processes. Detailed process modelling and optimization studies combined with process integration methods are necessary to demonstrate an effective way for the exploitation of these interactions. The aim of this work is to present and analyze the thermochemical conversion of biomass to second generation liquid biofuels as well as to indicate the emerging challenges and opportunities of the application of process integration on such processes towards innovative and sustainable solutions concerning climate concerns and energy security.Biomass Second generation biofuels Process integration Process design Modelling Optimization

Energetic assessment of a combined heat and power integrated biomass gasification-internal combustion engine system by using Aspen Plus®

This study aims at the assessment of a combined heat and power (CHP) biomass bubbling fluidized bed gasification unit coupled with an internal combustion engine (ICE) by using a comprehensive mathematical model based on the Aspen Plus® process simulator. The model is based on a combination of modules that Aspen Plus simulator provides representing the 3 steps of gasification process (drying, pyrolysis, and oxidation), gas cleaning and ICE. The model is based on mass and energy balances and reaction kinetics. The model was validated by using data obtained by operating a pilot atmospheric bubbling fluidized bed gasifier at Aristotle University of Thessaloniki, fed with olive kernel with a capacity of 1 kg/h and an energy output of 5 kW th, and has showed very good agreement. A sensitivity analysis was further conducted for the investigation of the system's behavior under different temperatures and air equivalence ratios. The proposed model is capable of dealing with a wide variety of biomasses (olive kernel, corn cob/stalks, rapeseed and sunflower stalks) using air as the fluidization agent and to predict the system's performance in terms of cold gas and thermal efficiency. © 2011 Elsevier B.V. All rights reserved

Dynamic Modeling and Control of a Coupled Reforming/Combustor System for the Production of H2 via Hydrocarbon-Based Fuels

The present work aims to provide insights into the dynamic operation of a coupled reformer/combustion unit that can utilize a variety of saturated hydrocarbons (HCs) with 1–4 C atoms towards H2 production (along with CO2). Within this concept, a preselected HC-based feedstock enters a steam reforming reactor for the production of H2 via a series of catalytic reactions, whereas a sequential postprocessing unit (water gas shift reactor) is then utilized to increase H2 purity and minimize CO. The core unit of the overall system is the combustor that is coupled with the reformer reactor and continuously provides heat (a) for sustaining the prevailing endothermic reforming reactions and (b) for the process feed streams. The dynamic model as it is initially developed, consists of ordinary differential equations that capture the main physicochemical phenomena taking place at each subsystem (energy and mass balances) and is compared against available thermodynamic data (temperature and concentration). Further on, a distributed control scheme based on PID (Proportional–Integral–Derivative) controllers (each one tuned via Ziegler–Nichols/Z-N methodology) is applied and a set of case studies is formulated. The aim of the control scheme is to maintain the selected process-controlled variables within their predefined set-points, despite the emergence of sudden disturbances. It was revealed that the accurately tuned controllers lead to (a) a quick start-up operation, (b) minimum overshoot (especially regarding the sensitive reactor temperature), (c) zero offset from the desired operating set-points, and (d) quick settling during disturbance emergence